JP7029126B2 - Nanocrystal manufacturing method and semiconductor device manufacturing method - Google Patents

Description

The present invention relates to a method for producing nanocrystals and a method for producing a semiconductor device.

In recent years, nanomaterials with properties different from bulk materials have been attracting attention. Nanomaterials are being applied in the field of engineering devices. Examples of nanomaterials include nanocrystals made of oxides such as copper oxide, iron oxide, tungsten oxide, tin oxide, nickel oxide, titanium oxide, zinc oxide, and zirconium oxide. The oxides have long been applied to dyes, pigments, catalysts, magnetic materials, positive electrode materials for secondary batteries, abrasives, conductive materials, fillers, bonding materials, sintering aids and the like. The oxide also has the characteristics of a semiconductor. Nanocrystals having the characteristics of semiconductors are being applied to devices such as photocatalytic materials, light emitting materials, solar cells, quantum computers, and biosensors.

As a method for obtaining nanocrystals composed of the above oxides, the following Patent Documents 1 to 6 disclose a hydrothermal synthesis method, a coprecipitation method, a laser irradiation method, or a chemical vapor deposition method (CVD method).

The semiconductor may be used as a p-type semiconductor or an n-type semiconductor by introducing an impurity element into the semiconductor or causing a defect. In a p-type semiconductor, the carrier carrying an electric charge is a hole. In an n-type semiconductor, the carrier carrying an electric charge is a free electron. A structure in which a p-type semiconductor and an n-type semiconductor are in contact with each other is called a pn junction. The pn junction exhibits rectifying action, light emission, photoelectric effect and the like. The pn junction is applied to semiconductor devices such as diodes, transistors, and solar cells.

For example, Non-Patent Document 1 below discloses the use of nanostructures having a pn junction. In the method described in Non-Patent Document 1, first, nanowires made of copper (II) oxide are formed by thermal oxidation of Cu foil or Cu mesh. Copper (II) oxide is a p-type semiconductor. Next, nanocrystals of zinc oxide (II) are formed into branches on the nanowires by a hydrothermal synthesis method. Zinc oxide (II) is an n-type semiconductor. The result is a nanostructure with a pn junction.

Special Publication No. 43-12435 Japanese Unexamined Patent Publication No. 54-151598 Japanese Unexamined Patent Publication No. 62-41722 Japanese Unexamined Patent Publication No. 62-22307 Japanese Unexamined Patent Publication No. 2009-57568 Japanese Unexamined Patent Publication No. 63-181305

A. Kargar et al. , "ZnO / CuO Heterojunction Branched Nanowires for Photoelectrochemical Hydrogen Generation", ACS Nano. , Vol. 7, no. 12, pp. 1112-111120, 2013.

In the hydrothermal synthesis methods described in Patent Documents 1 to 4, a compound having a desired composition can be formed while being controlled to a size on the order of nanometers. However, the process is multi-step and very complex and requires a process at high temperature and high pressure (eg 150 ° C., 10 atmospheres). Further, when a highly alkaline aqueous solution is used, in addition to requiring precise control of pH, there are problems in terms of environmental load and manufacturing cost.

The laser irradiation method described in Patent Document 5 and the CVD method described in Patent Document 6 are not suitable for industrial mass production of nanocrystals from the viewpoint of the size of the manufacturing apparatus and the manufacturing cost.

Further, the method described in Non-Patent Document 1 can obtain a pn junction having good characteristics and is expected to be applied to a semiconductor device for the purpose of water splitting. However, a hydrothermal synthesis method is part of the process. Therefore, it is necessary to solve the process and cost issues mentioned above.

The present invention has been made in view of the above circumstances, and a method for producing nanocrystals capable of easily forming nanocrystals containing at least one of oxides and hydroxides, and a method for producing the nanocrystals. It is an object of the present invention to provide a manufacturing method of a used semiconductor device.

The method for producing a nanocrystal according to one aspect of the present invention comprises a light irradiation step of irradiating the surface of a metal member immersed in water with light to form nanocrystals on the surface of the metal member, and the metal member comprises a light irradiation step. It has a first member containing a first metal and a second member containing a second metal, the standard electrode potential of the first metal is higher than -2.00 V, and the standard electrode potential of the second metal is-. Higher than 2.00 V, the first member and the second member are electrically connected, the nanocrystal contains at least one of an oxide and a hydroxide, and the oxide is the first. It is an oxide of at least one of a metal and a second metal, and the hydroxide is a hydroxide of at least one of the first metal and the second metal.

In the method for producing nanocrystals according to one aspect of the present invention, the metal member may contain an alloy.

In the method for producing nanocrystals according to one aspect of the present invention, the content of the first metal in the first member may be 10.0 to 100.0% by mass based on the total mass of the first member. , The content of the second metal in the second member may be 10.0 to 100.0% by mass with respect to the total mass of the second member.

The method for producing nanocrystals according to one aspect of the present invention may further include a surface roughening step of roughening the surface of the metal member before the light irradiation step.

In the method for producing nanocrystals according to one aspect of the present invention, the surface roughening step may be performed by machining, chemical treatment, or subliquid discharge treatment.

In the method for producing nanocrystals according to one aspect of the present invention, the first member and the second member may be in direct contact with each other.

In the method for producing nanocrystals according to one aspect of the present invention, the first member and the second member may be welded together.

In the method for producing nanocrystals according to one aspect of the present invention, the metal member may further have a conductive material, and the first member and the second member may be connected via the conductive material.

In the method for producing nanocrystals according to one aspect of the present invention, the conductive material is a group consisting of a wiring material containing copper, silver, gold, platinum, aluminum, chromium, nickel, iron, tin, or lead, and a brazing material. It may be at least one more selected.

In the method for producing nanocrystals according to one aspect of the present invention, the light may be sunlight or pseudo-sunlight.

In the method for producing nanocrystals according to one aspect of the present invention, the wavelength having the maximum intensity in the spectrum of light may be 360 nm or more and less than 620 nm.

In the method for producing nanocrystals according to one aspect of the present invention, water is pure water, ion-exchanged water, rainwater, tap water, river water, well water, filtered water, distilled water, back-penetration water, spring water, spring water, and the like. It may be at least one selected from the group consisting of dam water and seawater.

In the method for producing nanocrystals according to one aspect of the present invention, the pH of water may be 5.00 to 10.0.

In the method for producing nanocrystals according to one aspect of the present invention, the electrical conductivity of water may be 0.05 to 1.0 μS / cm.

In the method for producing nanocrystals according to one aspect of the present invention, the shape of the nanocrystals can be changed from needle-like, columnar, rod-like, tube-like, flaky, lump-like, flower-like, starfish-like, branch-like and convex-like. It may be at least one selected from the group.

In the method for producing nanocrystals according to one aspect of the present invention, a gas containing hydrogen may be generated in the light irradiation step.

In the method for producing nanocrystals according to one aspect of the present invention, the number of moles of oxygen in the gas may be 0 times or more and less than 1/2 times the number of moles of hydrogen.

The method for producing nanocrystals according to one aspect of the present invention may further include a step of removing and recovering the nanocrystals from the surface of the metal member.

In the method for producing nanocrystals according to one aspect of the present invention, the standard electrode potential of the second metal may be higher than the standard electrode potential of the first metal.

In the method for producing nanocrystals according to one aspect of the present invention, hydroxocomplex ions of the first metal may be generated from the surface of the first member in water.

In the method for producing nanocrystals according to one aspect of the present invention, at least one of oxides and hydroxides may be a semiconductor.

In the method for producing nanocrystals according to one aspect of the present invention, the semiconductor may include nanocrystals.

In the method for producing nanocrystals according to one aspect of the present invention, the semiconductor may include at least one of a p-type semiconductor and an n-type semiconductor.

In the method for producing nanocrystals according to one aspect of the present invention, the n-type semiconductor may be an oxide containing a first metal, and the p-type semiconductor may be an oxide containing a second metal.

In the method for producing nanocrystals according to one aspect of the present invention, the p-type semiconductor is copper (I) oxide, copper (II) oxide, silver (I) oxide, nickel (II) oxide, iron (III) oxide, and the like. It may be at least one selected from the group consisting of tungsten oxide (VI) and tin (II) oxide.

In the method for producing nanocrystals according to one aspect of the present invention, the n-type semiconductor is iron (III) oxide, indium (III) oxide, tungsten oxide (VI), lead (II) oxide, vanadium (V) oxide, and the like. It may be at least one selected from the group consisting of niobium oxide (III), titanium oxide (IV), zinc oxide (II), tin oxide (IV), aluminum oxide (III) and zirconium oxide (IV).

The method for manufacturing a semiconductor device according to one aspect of the present invention is a method for manufacturing a semiconductor device using the above-mentioned method for manufacturing nanocrystals, in which a p-type layer containing a p-type semiconductor is formed on the surface of a second member. Further, by forming an n-type layer containing an n-type semiconductor on the surface of the p-type layer, a pn junction layer including the p-type layer and the n-type layer is obtained.

In the method for manufacturing a semiconductor device according to one aspect of the present invention, the p-type semiconductor may be at least one of copper (I) oxide and copper (II) oxide, and the n-type semiconductor may be zinc oxide ( II) may be.

In the method for manufacturing a semiconductor device according to one aspect of the present invention, a photovoltaic power may be generated by irradiating the pn junction layer with light.

INDUSTRIAL APPLICABILITY According to the present invention, there is provided a method for producing nanocrystals capable of easily forming nanocrystals containing at least one of oxides and hydroxides, and a method for producing semiconductor devices using the method for producing nanocrystals. can do.

FIG. 1 is a schematic diagram showing a method for producing nanocrystals according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a method for producing nanocrystals according to an embodiment of the present invention. FIG. 3 is a schematic view showing a metal member according to an embodiment of the present invention. FIG. 4 is a schematic view showing a metal member according to an embodiment of the present invention. FIG. 5 is a schematic view showing a metal member according to an embodiment of the present invention. FIG. 6 is a schematic view showing a metal member according to an embodiment of the present invention. FIG. 7 is a schematic view showing a metal member according to an embodiment of the present invention. FIG. 8 is a schematic diagram showing the relationship between the band gap (energy difference between the lower end of the conduction band and the upper end of the valence band) of a typical metal oxide semiconductor and the redox potential of water. FIG. 9 is a schematic diagram showing a change in the energy band of the n-type semiconductor due to contact between the n-type semiconductor and water. FIG. 10 is a schematic diagram showing a change in the energy band of the p-type semiconductor due to contact between the p-type semiconductor and water. FIG. 11 is a schematic diagram showing the energy band structures of the n-type semiconductor and the p-type semiconductor electrically connected in water, and the flow of electrons when the n-type semiconductor and the p-type semiconductor are irradiated with light. FIG. 12 is a schematic view showing changes in the energy bands of the p-type semiconductor (Cu _2O ) and the n-type semiconductor (ZnO) with the formation of the pn junction layer. FIG. 13 is a schematic view showing changes in the energy bands of the p-type semiconductor (CuO) and the n-type semiconductor (ZnO) with the formation of the pn junction layer. FIG. 14 is an image showing an example of rod-shaped nanocrystals taken with a scanning electron microscope (SEM). FIG. 15 is an image showing an example of rod-shaped nanocrystals taken with a scanning electron microscope (SEM).

Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the present specification, the term "process" is included in this term not only as an independent process but also as long as the purpose of the process is achieved even if it cannot be clearly distinguished from other processes. In the present specification, the numerical range indicated by using "-" indicates a range including the numerical values before and after "-" as the minimum value and the maximum value, respectively. In the present specification, the content of each component in the composition refers to the content of each component in the composition when a plurality of substances corresponding to each component are present in the composition, unless otherwise specified. Means the total amount. In the drawings, equivalent components are designated by the same reference numerals.

(Outline of manufacturing method of nanocrystals)
The method for producing nanocrystals according to the present embodiment includes a light irradiation step. As shown in FIG. 1, in the light irradiation step, the surface of the metal member 100 immersed in water 2 is irradiated with light L to form nanocrystals on the surface of the metal member 100. The metal member 100 has a first member and a second member. The light L may irradiate both the first member and the second member. The first member contains a first metal. The second member contains a second metal. The first metal is a metal different from the second metal. The standard electrode potential of the first metal is different from the standard electrode potential of the second metal. The standard electrode potential of the first metal is higher than -2.00V. The standard electrode potential of the second metal is higher than -2.00V. The first member and the second member are electrically connected to each other. The nanocrystals contain at least one of oxides and hydroxides. The oxide is an oxide of at least one of a first metal and a second metal. The hydroxide is a hydroxide of at least one of a first metal and a second metal. The method for producing nanocrystals according to the present embodiment may further include a step of removing and recovering the nanocrystals from the surface of the metal member 100.

In the light irradiation step, nanocrystals may be generated on the surfaces of the first member and the second member. The nanocrystals formed on the surface of the first member may contain at least one of an oxide of the first metal and a hydroxide of the first metal. The nanocrystals formed on the surface of the second member may contain at least one of the oxide of the second metal and the hydroxide of the second metal. Hereinafter, nanocrystals containing at least one of an oxide of the first metal and a hydroxide of the first metal are also referred to as first nanocrystals. A nanocrystal containing at least one of an oxide of a second metal and a hydroxide of a second metal is also referred to as a second nanocrystal. Further, on the surface of the second member, first nanocrystals may be formed in addition to the second nanocrystals. As described above, in the light irradiation step, the first nanocrystals may be preferentially (selectively) produced. One of the reasons why the first nanocrystals are preferentially generated is that galvanic corrosion occurs due to the electrical connection between the first member and the second member. Another reason is that an oxide film containing an n-type semiconductor is formed on the surface of the first member, and an oxide film containing a p-type semiconductor is formed on the surface of the second member. Further, a pn junction layer may be formed by forming an n-type semiconductor (first nanocrystal) on a p-type semiconductor (oxide film or second nanocrystal) formed on the surface of the second member. .. This pn junction layer may promote the formation of first nanocrystals on the surface of the first member. In the following, first, the mechanism by which the first nanocrystals are formed on the surface of the first member and the mechanism by which the second nanocrystals are formed on the surface of the second member will be described. Next, the mechanism by which the first nanocrystals are preferentially produced will be described. The mechanism by which nanocrystals are formed in this embodiment is not limited to the above mechanism.

(Mechanism of forming nanocrystals on the first and second members)
In the light irradiation step, underwater crystal photosynthesis (SPSC: Submerged Photosynthesis of Crystallites) occurs on the surfaces of each of the first member and the second member. In general, SPSC is a method of irradiating the surface of a metal member immersed in water with light to form nanocrystals on the surface of the metal member. In this embodiment, SPSC produces first nanocrystals on the surface of the first member. In addition, SPSC produces second nanocrystals on the surface of the second member. The mechanism of SPSC in the first member is common to the mechanism of SPSC in the second member. Hereinafter, the SPSC in the first member will be described. In the light irradiation step, the surface of the first member immersed in water is irradiated with light to generate first nanocrystals on the surface of the first member.

In the light irradiation step, a gas containing hydrogen may be generated. For example, in the light irradiation step, a gas containing hydrogen may be generated from the vicinity of the surface of the first member by irradiating the surface of the first member immersed in water with light. In the light irradiation step, a gas containing hydrogen may be generated from the vicinity of the surface of the second member by irradiating the surface of the second member immersed in water with light. The mechanism by which hydrogen is generated from the vicinity of the surface of the first member is common to the mechanism by which hydrogen is generated from the vicinity of the surface of the second member. Hereinafter, the mechanism by which hydrogen is generated near the surface of the first member will be described. The term "near the surface of the first member" implies at least one of the surface of the first member, the oxide formed on the first member, and the hydroxide. For example, in the process of converting a hydroxide into an oxide, at least one of water molecules and hydrogen gas may be generated from the hydroxide.

When the first member containing the first metal (M) is immersed in water, the reaction in which the first metal is corroded proceeds. That is, in water, the first metal is ionized to generate ions (M ^{n +} ) of the first metal as shown in the following reaction formula (1). In general, the corrosion reaction of a metal is a reaction in which an anodic reaction in which a metal is dissolved as a metal ion and a cathode reaction in which an oxidant in water is reduced are combined. The reaction shown in the following reaction formula (1) is an anodic reaction. The reaction shown in the following reaction formula (2) and the reaction shown in the following reaction formula (3) are both cathode reactions. The reaction shown in the following reaction formula (2) occurs when water is acidic. The reaction represented by the following reaction formula (3) occurs when the water is neutral or alkaline, or when the water contains dissolved oxygen. Here, when the standard electrode potential of the metal is positive, it is generally considered that the anodic reaction represented by the following reaction formula (1) does not occur. However, depending on the concentration of hydrogen ions (H ⁺ ) or dissolved oxygen in water, the metal is ionized and ^{Mn +} is generated as shown in the following reaction formula (4). ^{Mn +} dissolved in water by the reaction shown in the following reaction formula (1) or the reaction shown in the following reaction formula (4) is generated by the reaction shown in the following reaction formula (3), for example, in water containing dissolved oxygen. Reacts with hydroxide ion (OH- ⁾ . As a result, a hydroxide (M (OH) _n ) is produced as shown in the following reaction formula (5). After that, the water molecules are separated from the hydroxide to generate an oxide (MO _x ) as shown in the following reaction formula (6). However, it is difficult to produce highly crystalline hydroxides and oxides in the above-mentioned general corrosion reaction of metals. That is, the hydroxides and oxides produced by the general corrosion reaction of metals are inferior in crystallinity to the nanocrystals obtained by SPSC according to the present embodiment. Further, in a general metal corrosion reaction, hydrogen gas (H ₂ ) is not generated when water is neutral or alkaline. Further, when water is acidic, hydrogen gas is generated by the reaction represented by the following reaction formula (2), but the corrosion reaction of the metal is stopped in a short time, so that the amount of hydrogen gas generated is small.
M → M ^{n +} + ne- ⁽ 1)
2H ⁺ + ^2e- → H ₂ (2)
O ₂ + 2H ₂ O + ^4e- → ^4OH- (3)
2M + O ₂ + 2nH ⁺ → 2M ^{n +} + 2H _2O (4)
M ^{n +} + ^noh- → M (OH) _n (5)
M (OH) _n → MO _x + (n−x) H ₂ O (6)

It is considered that the hydroxide ion is generated in a reaction other than the reaction shown in the above reaction formula (3). For example, there are cases where hydroxide ions are present due to dissociation of water molecules, and cases where hydroxide ions are present due to the use of alkaline water. However, the reaction in which these hydroxide ions produce hydroxide (M (OH) _n ) and oxide (MO _x ) is the above-mentioned general metal corrosion reaction. Therefore, in this case, nanocrystals as obtained by the SPSC according to the present embodiment are not formed.

In contrast to the general metal corrosion reaction, in the method of producing nanocrystals using SPSC, the surface of the first member is irradiated with light to generate the first nanocrystals on the surface of the first member. , Hydrogen gas is generated from the vicinity of the surface of the first member. The present inventors speculate that the mechanism of nanocrystal formation by SPSC is as follows. In the present embodiment, first, the reactions represented by the above reaction formulas (1) to (5) occur. After that, in the light irradiation step of the present embodiment, nanocrystals containing the oxide of the first metal (MO _x ) grow from the hydroxide of the first metal (M (OH) _n ) on the surface of the first member. At the same time, not only water molecules but also hydrogen gas (H ₂ ) is produced as a by-product. For example, the generated hydroxide of the first metal reacts with the hydroxide ion (OH ⁻ ) in water to form the hydroxo complex ion ([M (OH) _x ] ^y −) of the first metal. , Dissolve again in water. The higher the pH of water, the easier it is to generate hydroxocomplex ions. Then, at least a part of the hydroxocomplex ion is changed into nanocrystals. Nanocrystals contain at least one of a hydroxide and an oxide. For example, when the metal (M) is zinc (Zn), tetrahydroxozinc (II) acid ion ([Zn (OH) ₄ ] ^2- ) is formed by the reaction represented by the following reaction formula (7). Then, the ZnO nanocrystals are produced by the reaction represented by the following reaction formula (8). When the metal (M) is not the first metal but the second metal copper (Cu), the reaction represented by the following reaction formula (9) causes a tetrahydroxocopper (II) acid ion ([Cu (OH). ) ₄ ] ^2- ) is formed. Then, nanocrystals of CuO are produced by the reaction represented by the following reaction formula (10). With the formation and growth of the above nanocrystals, water molecules and hydrogen gas are generated. For example, in the process of converting a hydroxide into an oxide, at least one of water molecules and hydrogen gas may be generated from the hydroxide. Here, the nanocrystals may be formed, for example, by photo-induced tip growth. Photoinduced tip growth means that the tip growth of crystals is promoted in a columnar or needle shape by light irradiation. The mechanism by which nanocrystals are formed is not limited to the above reaction mechanism.
Zn (OH) ₂ + ^2OH- → [Zn (OH) ₄ ] ^2- (7)
[Zn (OH) ₄ ] ^2- → ZnO + ^2OH- + H _2O (8)
Cu (OH) ₂ + ^2OH- → [Cu (OH) ₄ ] ^2- (9)
[Cu (OH) ₄ ] ^2- → CuO + ^2OH- + H ₂ O (10)

In the light irradiation step, when the water in which the metal member is immersed is irradiated with light, radiolysis of the water may occur. Hydrogen radicals (H.), hydroxyl radicals ( ^.OH ), and hydrated electrons (e _aq- ) are generated as the decomposition species. Of these, hydroxide ions are immediately generated by the reaction of hydroxyl radicals and hydrated electrons. In the light irradiation step, the reaction between the hydroxyl radical and the hydrated electron may promote the production of hydroxide ions, the production of nanocrystals, and the production of hydrogen gas. That is, in the light irradiation step, a photochemical reaction accompanied by the generation of radicals may occur.

In the reaction mechanism in which the above nanocrystals are generated, it is difficult to generate oxygen gas (O ₂ ), unlike the photodecomposition of water by the photocatalytic reaction described later. In the case of photolysis of water, the ratio of the number of moles of hydrogen gas produced to the number of moles of oxygen gas produced is 2: 1. That is, based on stoichiometry, the number of moles of oxygen gas produced is half the number of moles of hydrogen gas produced. On the other hand, in the above method for producing nanocrystals using SPSC, the number of moles of oxygen in the gas generated in the light irradiation step is 0 times or more and less than 1/2 times, and 0 times or more and 1/5 of the number of moles of hydrogen. It may be double or less, or 0 times or more and 1/10 times or less. The concentration of hydrogen in the produced gas may be larger than 66.7% by volume, 80.0 to 100% by volume, or 90.0 to 100% by volume, based on the total volume of the gas. The concentration of hydrogen in the produced gas may be greater than 66.7 mol%, 80.0 to 100 mol%, or 90.0 to 100 mol, based on the total number of moles of all components contained in the gas. May be%. In the method for producing nanocrystals according to the present embodiment, hydrogen gas having high purity may be obtained together with the nanocrystals.

The concentration of hydrogen in the produced gas may be measured by gas chromatography-mass spectrometry. The device used for the measurement may be a general gas chromatograph. As the gas chromatograph, for example, GC-14B manufactured by Shimadzu Corporation may be used. The measurement using a gas chromatograph may be carried out by placing argon, which is a carrier gas, and a sample in a syringe.

In gas chromatography-mass spectrometry, it is preferable to correct the concentration of hydrogen gas in consideration of air contamination. When nitrogen (N) is not contained in the metal member and water, and nitrogen gas (N ₂ ) is contained in the analyzed gas, the measurement by gas chromatography-mass spectrometry is performed. It is probable that air was mixed in the syringe. The volume of the generated hydrogen gas can be obtained by subtracting the total of the volume of the nitrogen gas and the volume of the component (for example, oxygen gas) excluding the nitrogen gas from the mixed air from the total volume of the analyzed gas. can.

For example, as a result of measurement by a gas chromatograph, the type and volume ratio of the gas contained in the analyzed gas are hydrogen gas (H ₂ ): oxygen gas (O ₂ ): nitrogen gas (N ₂ ) = A: B: C. Suppose that it was. When the metal member and the water do not contain nitrogen, the generated gas can be considered to be only hydrogen gas and oxygen gas. At this time, it is assumed that the analytical value of air measured by using the gas chromatograph is oxygen gas (O ₂ ): nitrogen gas (N ₂ ) = b: c. The ratio of the gas after deducting the air content is hydrogen gas (H ₂ ): oxygen gas (O ₂ ) = A: {B- (C × b ÷ c)}. Using this ratio, the concentration of the generated hydrogen gas can be calculated.

The above-mentioned method for producing nanocrystals using SPSC can easily form nanocrystals containing at least one of oxides and hydroxides as compared with the conventional method for producing nanocrystals. That is, the above-mentioned method for producing nanocrystals using SPSC does not require a heating step, a vacuum process, or the like, and can form nanocrystals at room temperature and atmospheric pressure. Further, in the above method for producing nanocrystals using SPSC, if the formed nanocrystals are recovered from the surface of the metal member, the surface of the metal member is exposed again. Then, the surface of the exposed metal member can be reused for forming nanocrystals. Further, in the above-mentioned method for producing nanocrystals using SPSC, nanocrystals can be formed without using a high-temperature process such as a hydrothermal synthesis reaction or using strongly alkaline water. From the above, in the above-mentioned nanocrystal manufacturing method using SPSC, the manufacturing cost of nanocrystals can be reduced, and the environmental load associated with the manufacturing of nanocrystals can be reduced.

The above-mentioned SPSC also holds when the metal (M) is the second metal. That is, SPSC also proceeds in the second member containing the second metal.

(Mechanism of preferential production of first nanocrystals)
(1) Galvanic corrosion The mechanism by which first nanocrystals are preferentially generated due to galvanic corrosion will be described below.

The standard electrode potential of the first metal contained in the first member is higher than -2.00V. The standard electrode potential of the second metal contained in the second member is higher than -2.00V. The standard electrode potential is a potential generated during the exchange of electrons in a redox reaction system in a liquid. Tables 1 and 2 show the electrode reaction of each element in water and the standard electrode potential of each element. The standard electrode potential is also used as a measure of the susceptibility of metal to corrosion. The standard electrode potential of a metal that is easily dissolved in water and easily ionized is low. In this embodiment, by using the first metal and the second metal whose standard electrode potential is higher than -2.00 V, an excessive reaction between the first metal and the second metal and water (with the first metal and the second metal). (Direct reaction with water) is suppressed. As a result, nanocrystals and high-purity hydrogen gas can be effectively produced by SPSC.

Galvanic corrosion occurs when two metals with different standard electrode potentials are brought into contact with each other in water. Of the two types of metals, the metal with the lower standard electrode potential is called the "base metal". Of the two types of metals, the metal with the higher standard electrode potential is called the "precious metal". The rate of corrosion of a base metal immersed in water with a noble metal is greater than the rate of corrosion of a base metal when only the base metal is immersed in water. The corrosion rate of a noble metal immersed in water with a lowly metal is lower than the corrosion rate of a noble metal when only the noble metal is immersed in water. In this embodiment, the standard electrode potential of the second metal may be higher than the standard electrode potential of the first metal. That is, the first metal may be a low-key metal and the second metal may be a noble metal. When the first metal is a base metal and the second metal is a noble metal, galvanic corrosion preferentially corrodes the first member containing the base first metal, and the first metal becomes the second metal. Priority is given to elution in water. That is, when the metal M is a base first metal, the reaction rate shown in the above reaction formula (1) increases due to galvanic corrosion. As a result, the formation of the hydroxide of the first metal represented by the reaction formula (5), the subsequent formation of the first nanocrystals by SPSC, and the production of hydrogen gas are promoted. On the other hand, galvanic corrosion suppresses the corrosion reaction of the second metal. That is, when the metal M is a noble second metal, the reaction rate shown in the above reaction formula (1) decreases. As a result, the formation of the hydroxide of the second metal represented by the reaction formula (5), the subsequent formation of the second nanocrystal by SPSC, and the generation of hydrogen gas are suppressed. Therefore, the first nanocrystals are preferentially generated on the surface of the first member. The following embodiments assume that the standard electrode potential of the second metal is higher than the standard electrode potential of the first metal.

The absolute value of the difference between the standard electrode potential of the first metal and the standard electrode potential of the second metal (the value obtained by subtracting the standard electrode potential of the base metal from the standard electrode potential of the noble metal) is 0.10 to 3. It is preferably 00V, more preferably 0.15 to 2.80V, and even more preferably 0.20 to 2.50V. The larger the absolute value of the difference between the standard electrode potential of the first metal and the standard electrode potential of the second metal, the more likely it is that the formation of the first nanocrystal and the generation of hydrogen gas in the first member will occur preferentially.

The standard electrode potential of the first metal is preferably −2.00 to 1.20 V from the viewpoint of the reactivity between the first metal and water and the solubility of the ions of the first metal in water. It is more preferably 1.80 to 1.00V, and even more preferably -1.70 to 0.90V.

The standard electrode potential of the second metal is preferably −2.00 to 1.20 V from the viewpoint of the reactivity between the second metal and water and the solubility of the second metal ion in water. It is more preferably 1.80 to 1.00V, and even more preferably -1.70 to 0.90V.

The first metal is, for example, gold, platinum, iridium, palladium, silver, rhodium, copper, bismuth, tungsten, lead, tin, molybdenum, nickel, cobalt, indium, cadmium, iron, zinc, chromium, itterbium, niobium, vanadium. , Manganese, zirconium, titanium, aluminum, thorium, beryllium, iridium and the like.

As the second metal, a metal different from the first metal is selected. The second metal is, for example, gold, platinum, iridium, palladium, silver, rhodium, copper, bismuth, tungsten, lead, tin, molybdenum, nickel, cobalt, indium, cadmium, iron, zinc, chromium, itterbium, niobium, vanadium. , Manganese, zirconium, titanium, aluminum, thorium, beryllium, iridium and the like.

The combination of the first metal and the second metal is not particularly limited as long as the standard electrode potential of the second metal is higher than the standard electrode potential of the first metal. The combination of the first metal and the second metal may be, for example, the first metal being zinc and the second metal being copper. The first metal may be zinc and the second metal may be tungsten. The first metal may be zinc and the second metal may be nickel. The first metal may be titanium and the second metal may be tungsten.

(2) Electron transfer from the p-type semiconductor on the second member to the n-type semiconductor on the first member In the light irradiation step, an oxide film containing the n-type semiconductor may be formed on the surface of the first member, and An oxide film containing a p-type semiconductor may be formed on the surface of the second member. The formation of an oxide film containing an n-type semiconductor is formed on the surface of the first member, and the oxide film containing a p-type semiconductor is formed on the surface of the second member, whereby the formation of first nanocrystals is promoted. The reason will be explained below.

Due to the above-mentioned galvanic corrosion, the corrosion reaction of the first member is promoted, and the corrosion reaction of the second member is suppressed. However, the corrosion reaction of the second member is not completely prevented, and the corrosion reaction of the second member also occurs. As a result, an oxide film containing the first metal is formed on the surface of the first member, and an oxide film containing the second metal is formed on the surface of the second member. The oxide film may contain at least one of a hydroxide and an oxide. The hydroxide contained in the oxide film is generated by the reaction represented by the above reaction formula (5). The oxide contained in the oxide film is generated by the reaction represented by the above reaction formula (6). The formation of the oxide film (corrosion reaction) described above occurs even when no light is irradiated, and does not depend on SPSC. The hydroxides and oxides contained in the oxide film do not have to be nanocrystals as obtained by SPSC. It is considered that the oxide film uniformly covers the surfaces of the first member and the second member.

At least one of the hydroxide and the oxide contained in the oxide film may be a semiconductor. The semiconductor may include at least one of a p-type semiconductor and an n-type semiconductor. The n-type semiconductor may be an oxide containing a first metal or a hydroxide. The oxide film formed on the surface of the first member may be an n-type semiconductor containing the first metal. The p-type semiconductor may be an oxide containing a second metal or a hydroxide. The oxide film formed on the surface of the second member may be a p-type semiconductor containing a second metal. Hereinafter, a case where an oxide film containing an n-type semiconductor is formed on the surface of the first member and an oxide film containing a p-type semiconductor is formed on the surface of the second member will be described as an example.

FIG. 9A shows the energy band of the n-type semiconductor at the moment when the n-type semiconductor (oxide film of the first member) comes into contact with water. FIG. 9B shows the energy band of the n-type semiconductor in an equilibrium state after contact between the n-type semiconductor (oxide film of the first member) and water. In FIG. 9, the moment of contact means the moment when the n-type semiconductor is formed in water. After equilibrium means after the n-type semiconductor is formed in water and the energy band of the n-type semiconductor is in an equilibrium state. E _redox is the redox potential of water. When water is acidic, E _redox corresponds to the potential at which the reaction represented by the above reaction formula (2) occurs. E _redox corresponds to the potential at which the reaction represented by the above reaction formula (3) occurs when the water is neutral or alkaline, or when the water contains dissolved oxygen. _EF represents the Fermi level. The Fermi level means an energy level when the probability of existence of an electron in a semiconductor becomes 50%. As shown in FIG. 9B, when the n-type semiconductor and water come into contact with each other, EF and _{E redox} become equal. That is, the energy level of the n-type semiconductor moves downward, and the energy level of water moves upward. As a result, the energy band of the n-type semiconductor bends upward near the interface between the n-type semiconductor and water. Bending an energy band is called band bending.

FIG. 10A shows the energy band of the p-type semiconductor at the moment when the p-type semiconductor (oxide film of the second member) comes into contact with water. FIG. 10B shows the energy band of the p-type semiconductor in an equilibrium state after contact between the p-type semiconductor (oxide film of the second member) and water. As shown in FIG. 10 (b), when the p-type semiconductor and water come into contact with each other, EF and _{E redox} become equal. That is, the energy level of the p-type semiconductor moves up, and the energy level of water moves down. As a result, the energy band of the p-type semiconductor bends downward near the interface between the p-type semiconductor and water.

As a result of the above-mentioned energy band bending, an energy barrier is generated at the interface between the n-type semiconductor (oxide film of the first member) and water, and the interface between the p-type semiconductor (oxide film of the second member) and water. Due to this energy barrier, charge separation occurs as follows. As shown in FIG. 8, various oxide semiconductors have their own band gaps. When the oxide semiconductor absorbs light having an energy larger than the band gap, the electrons in the valence band are excited in the conduction band, and holes are formed in the valence band. At this time, charge separation occurs due to the presence of an energy barrier at the interface between the oxide semiconductor and water. Specifically, in the case of the n-type semiconductor (oxide film of the first member) shown in FIG. 9, electrons generated by light irradiation move from the interface between the n-type semiconductor and water to the n-type semiconductor bulk. On the other hand, the holes generated by light irradiation move to the interface between the n-type semiconductor and water. In contrast, in the case of the p-type semiconductor (oxide film of the second member) shown in FIG. 10, the electrons generated by light irradiation move to the interface between the p-type semiconductor and water. Further, the holes generated by light irradiation move from the interface between the p-type semiconductor and water to the p-type semiconductor bulk.

When the above-mentioned charge separation occurs, electron movement occurs as shown in FIG. That is, the electrons excited in the conduction band in the p-type semiconductor (oxide film of the second member) move to the interface between the p-type semiconductor and water by band bending. Then, at least a part of the electrons transferred to the interface between the p-type semiconductor (oxide film of the second member) and water is an n-type semiconductor because the first member and the second member are electrically connected. Move to (oxide film of the first member). On the other hand, holes generated in the valence band of the n-type semiconductor (oxide film of the first member) move to the interface between the n-type semiconductor and water by band bending. The holes that have moved to the interface between the n-type semiconductor (oxide film of the first member) and water may corrode the n-type semiconductor by the reaction represented by the following reaction formula (11). M in the following reaction formula (11) means the first metal.
MO _x + nh ⁺ + xH ₂ O → M ^{n +} + noh ⁻ (11)

After that, the electrons transferred to the n-type semiconductor (oxide film of the first member) generate hydroxide ions (OH ⁻ ) as shown in the above reaction formula (3). As described above, the reaction represented by the reaction formula (3), the reaction represented by the reaction formula (11), and the like increase the amount of hydroxide ion produced in the vicinity of the surface of the first member. When the amount of hydroxide ion produced increases, the production of the first metal hydroxide (M (OH) _n ) represented by the above reaction formula (5) is promoted, and the hydroxo complex ion ([M (OH)) by SPSC is promoted. _x ] The formation of ^y− ) is promoted. Here, M is the first metal. As a result, nanocrystals (first nanocrystals) containing at least one of the hydroxide of the first metal and the oxide of the first metal are generated from the hydroxo complex ion, and from the vicinity of the surface of the first member. Hydrogen gas is preferentially generated. Therefore, the first nanocrystal can be selectively and efficiently produced. Further, hydrogen gas can be preferentially and efficiently produced from the vicinity of the surface of the first member.

The above phenomenon is effective when the bandgap of the n-type semiconductor is large for the following reasons. When the first member and the second member are not electrically connected and the n-type semiconductor (oxide film of the first member) is present alone in water, the reaction shown in the above reaction formula (3) can be obtained. The required electrons must be generated only by the photocatalytic reaction of the n-type semiconductor itself. Here, when the bandgap of the n-type semiconductor (oxide film of the first member) is large, light having a short wavelength is required for the excitation of electrons by the photocatalytic reaction. Therefore, when using sunlight, only a part of the sunlight can be used. Therefore, when the n-type semiconductor (oxide film of the first member) is present alone in water, the production efficiency of hydrogen gas and nanocrystals by SPSC is low. On the other hand, when the first member and the second member are electrically connected in water, as described above, the p-type semiconductor (the oxide film of the second member) is connected to the n-type semiconductor (the oxide film of the first member). Electrons are supplied from. Therefore, even when the band gap of the n-type semiconductor itself is large, the hydroxide ion (OH ⁻ ) can be efficiently generated by the reaction represented by the reaction formula (3). As a result, the efficiency of producing hydrogen gas and nanocrystals by SPSC is improved.

In the present embodiment, a natural oxide film may be formed in advance on the surface of the metal member. That is, the oxide film (n-type semiconductor) of the first member may be a natural oxide film. The oxide film (p-type semiconductor) of the second member may be a natural oxide film. Oxides contained in natural oxide films may exhibit semiconductor properties. However, since the natural oxide film is sufficiently thin, it is considered that the natural oxide film is dissolved when the metal member is immersed in water, and the metal surface of the metal member is exposed.

(3) Formation of a pn junction layer on the surface of the second member In the light irradiation step, a pn junction layer may be formed on the surface of the second member with the generation of hydrogen gas. That is, the p-type layer containing the p-type semiconductor is formed on the surface of the second member, and subsequently, the n-type layer containing the n-type semiconductor is formed on the surface of the p-type layer, whereby the p-type layer and the p-type layer and A pn junction layer containing an n-type layer may be obtained. The size of the pn junction layer may be based on the size of the nanocrystals. The n-type layer may contain first nanocrystals. The n-type layer may consist of only the first nanocrystals. The p-type layer may contain second nanocrystals. The p-type layer may consist only of the second nanocrystal. In the following, first, the mechanism by which the pn junction layer is formed will be described. Next, the mechanism by which the pn junction layer promotes the formation of first nanocrystals will be described. The formation mechanism of the pn junction layer is premised on an oxide film (n-type semiconductor) formed on the surface of the first member and an oxide film (p-type semiconductor) formed on the surface of the second member.

As described above, the transfer of electrons from the p-type semiconductor on the surface of the second member to the n-type semiconductor on the surface of the first member causes hydroxocomplex ions ([M (OH) _x ]] on the surface of the first member. The formation of ^y- ) is promoted. Here, M is the first metal. A part of the hydroxocomplex ion of the first metal dissolves into water from the surface of the first member and moves to the vicinity of the surface of the second member. For example, the hydroxocomplex ion of the first metal is an oxide film (p-type semiconductor) formed on the surface of the second member by a corrosion reaction, and a second nanocrystal (p-type semiconductor) formed on the surface of the second member by SPSC. Move to the vicinity of. Then, when the p-type semiconductor (p-type layer) covering the surface of the second member comes into contact with the hydroxocomplex ion of the first metal in water, the hydroxocomplex ion of the first metal is transferred to the surface of the p-type layer by SPSC. 1 Metal is changed to hydroxide or oxide (first nanocrystal), and hydrogen gas is generated. When the hydroxide or oxide of the first metal is an n-type semiconductor, the surface of the p-type layer is covered with the n-type semiconductor. That is, an n-type layer is formed on the surface of the p-type layer. By the above mechanism, the pn junction layer is formed on the surface of the second member.

When the first metal M is aluminum (Al), the hydroxocomplex ion ([M (OH) _x ] ^y− ) generated from the first member is a tetrahydroxoaluminate ion ([Al (OH) ₄ ] ⁻ ). May be. When the first metal M is zinc (Zn), the hydroxocomplex ion generated from the first member may be tetrahydroxozinc (II) acid ion ([Zn (OH) ₄ ] ^2- ). When the first metal M is copper (Cu), the hydroxocomplex ion generated from the first member may be tetrahydroxocopper (II) acid ion ([Cu (OH) ₄ ] ^2- ). When the first metal M is tin (Sn), the hydroxocomplex ion generated from the first member may be a tetrahydroxotin (IV) acid ion ([Sn (OH) ₆ ] ^2- ). When the first metal M is lead (Pb), the hydroxocomplex ion generated from the first member may be tetrahydroxolead (II) acid ion [Pb (OH) ₄ ] ^2- ).

Whether or not hydroxocomplex ions are present in water can be confirmed by whether or not precipitation occurs when hydrochloric acid is added to water. For example, in the case of tetrahydroxozinc (II) acid ion ([Zn (OH) ₄ ] ^2- ), when hydrochloric acid is added to water, the reaction shown in the following reaction formula (12) causes a hydroxide (Zn (OH)). ₂ ) White precipitate is formed.
[Zn (OH) ₄ ] ^2- + 2H ⁺ → Zn (OH) ₂ + H ₂ O (12)

The pn junction layer may have a structure in which oxide nanocrystals containing an n-type semiconductor are formed on an oxide film containing a p-type semiconductor. The pn junction layer may have a structure in which an oxide nanocrystal containing an n-type semiconductor is formed on an oxide nanocrystal containing a p-type semiconductor. The pn junction layer may have a structure in which oxide nanocrystals containing a p-type semiconductor are formed on an oxide film containing an n-type semiconductor. The pn junction layer may have a structure in which an oxide nanocrystal containing a p-type semiconductor is formed on an oxide nanocrystal containing an n-type semiconductor.

Hereinafter, the mechanism of forming the pn junction layer will be described by taking the case where the first metal is zinc (Zn) and the second metal is copper (Cu) as an example. Zinc, the first metal, is a lowly metal, and copper, the second metal, is a noble metal. Due to the above-mentioned galvanic corrosion, copper is less likely to be corroded, but an oxide film having a certain thickness is formed on the surface of the second member containing copper. The composition of the oxide film formed on the surface of the second member depends on the pH of water or the ionic species dissolved in water. The oxide film formed on the surface of the second member contains at least one of Cu ₂ O and Cu O. Both Cu ₂ O and Cu O are p-type semiconductors. On the other hand, in the first member containing zinc, the zinc corrosion reaction proceeds. An oxide film is formed on the surface of the first member by the corrosion reaction. The oxide film formed on the surface of the first member contains zinc oxide (ZnO). ZnO is an n-type semiconductor.

As described above, in the p-type semiconductor on the surface of the second member, at least a part of the electrons generated by light irradiation moves to the n-type semiconductor on the surface of the first member. Therefore, in the vicinity of the interface between the p-type semiconductor and water on the surface of the second member, electrons are insufficient, and the production of hydroxide ion (OH ⁻ ) represented by the reaction formula (3) is also reduced. In addition, galvanic corrosion reduces the amount of Cu ions (Cu ⁺ or Cu ²⁺ ) dissolved. As a result, in the vicinity of the surface of the second member, copper hydroxide (Cu (OH) ₂ ) is produced, followed by SPSC to produce nanocrystals containing copper oxide (Cu ₂ O or Cu O) and hydrogen gas. Generation is less likely to occur.

On the other hand, in the vicinity of the surface of the n-type semiconductor on the surface of the first member, the amount of hydroxide ion (OH ⁻ ) generated increases due to the supply of electrons from the p-type semiconductor on the surface of the second member. Zinc ion generated by galvanic corrosion reacts with hydroxide ion to increase the amount of zinc hydroxide (Zn (OH) ₂ ) produced. The reaction between zinc hydroxide and hydroxide ion (OH ⁻ ) increases the amount of tetrahydroxozinc (II) acid ion ([Zn (OH) ₄ ] ^2- ) produced. SPSC produces nanocrystals of zinc oxide (ZnO) from tetrahydroxozinc (II) acid ions and hydrogen gas. As a result, the amount of hydrogen gas produced and the amount of nanocrystals produced increase. Here, a part of the tetrahydroxozinc (II) acid ion ([Zn (OH) ₄ ] ^2- ) dissolved in water is formed by the p-type semiconductor contained in the oxide film on the surface of the second member and SPSC. It moves to the vicinity of the p-type semiconductor (second nanocrystal) formed on the surface of the second member. As a result, on the p-type semiconductor on the surface of the second member, the tetrahydroxozinc (II) acid ion is changed into a nanocrystal (first nanocrystal) by SPSC, and hydrogen gas is generated. The nanocrystals formed on the p-type semiconductor contain zinc hydroxide (Zn (OH) ₂ ) and zinc oxide (ZnO). Zinc oxide (ZnO) is an n-type semiconductor. That is, the nanocrystal formed on the p-type semiconductor includes an n-type semiconductor. Therefore, the pn junction layer is obtained by forming the n-type semiconductor on the p-type semiconductor on the surface of the second member.

FIG. 12A shows the energy bands of the p-type semiconductor (Cu _2O ) and the n-type semiconductor (ZnO) before the pn junction layer is formed. FIG. 12B shows the energy bands of the p-type semiconductor (Cu _2O ) and the n-type semiconductor (ZnO) after the pn junction layer is formed. As shown in FIG. 12 (b), when the _pn junction layer is formed, the Fermi level EF of the p-type semiconductor (Cu ₂ O) and the Fermi level EF of the n-type semiconductor ( _Zn O) become equal. .. That is, the energy level of the p-type semiconductor (Cu ₂ O) moves upward, and the energy level of the n-type semiconductor (Zn O) moves downward. As a result, band bending occurs near the interface between the p-type semiconductor (Cu ₂ O) and the n-type semiconductor (Zn O).

FIG. 13A shows the energy bands of the p-type semiconductor (CuO) and the n-type semiconductor (ZnO) before the pn junction layer is formed. FIG. 13B shows the energy bands of the p-type semiconductor (CuO) and the n-type semiconductor (ZnO) after the pn junction layer is formed. As shown in FIG. _13B , when the pn junction layer is formed, the Fermi level EF of the p-type semiconductor ( _CuO ) and the Fermi level EF of the n-type semiconductor (ZnO) become equal. That is, the energy level of the p-type semiconductor (CuO) moves up, and the energy level of the n-type semiconductor (ZnO) moves down. As a result, band bending occurs near the interface between the p-type semiconductor (CuO) and the n-type semiconductor (ZnO).

After the pn junction layer is formed in the light irradiation step, the pn junction layer is also irradiated with light. When the pn junction layer is irradiated with light, electrons are excited in the p-type semiconductor and the n-type semiconductor contained in the pn junction layer. The pn junction layer efficiently moves electrons to the interface between the n-type semiconductor and water of the pn junction layer while suppressing the recombination of electrons and holes excited by light irradiation. Then, at least a part of the electrons transferred to the interface between the n-type semiconductor of the pn junction layer and water is n of the surface of the first member because the first member and the second member are electrically connected. Move to a type semiconductor (oxide film or nanocrystal). After that, the electrons transferred to the n-type semiconductor on the surface of the first member generate hydroxide ions (OH ⁻ ) as shown in the above reaction formula (3). As described above, the reaction represented by the reaction formula (3) increases the amount of hydroxide ion produced in the vicinity of the surface of the first member. When the amount of hydroxide ion produced increases, the production of the first metal hydroxide (M (OH) _n ) represented by the above reaction formula (5) is promoted, and the hydroxo complex ion ([M (OH)) by SPSC is promoted. _x ] The formation of ^y− ) is promoted. Here, M is the first metal. As a result, the first nanocrystal is generated from the hydroxocomplex ion, and hydrogen gas is preferentially generated from the vicinity of the surface of the first member. By the above mechanism, the pn junction layer promotes the formation of first nanocrystals.

The pn junction layer exhibits properties such as rectification, electroluminescence, and a photovoltaic effect. The pn junction layer formed in the light irradiation step can be applied to miniaturization and high performance of semiconductor devices utilizing the above properties. The semiconductor device provided with the pn junction layer may be, for example, a photocathode for hydrogen production, a diode, a transistor, or the like.

The photocathode for hydrogen production may include, for example, a Cu plate, a p-type layer formed on the surface of the Cu plate, and an n-type layer formed on the surface of the p-type layer. The p-type layer contains a p-type semiconductor. The n-type layer includes an n-type semiconductor. The p-type semiconductor may consist of, for example, Cu ₂ O or Cu O. The n-type semiconductor may consist of ZnO nanocrystals. The photocathode for hydrogen production may be used as an operating electrode. Further, a wiring material such as a copper wire may be connected to the Cu plate of the photocathode for hydrogen production. Further, the hydrogen production apparatus provided with the photocathode for hydrogen production may include a reference electrode for controlling the potential of the operating electrode, a constant potential electrolyzer, and the like. The photoelectric cathode for hydrogen production efficiently moves electrons to the interface between the n-type semiconductor and water while suppressing the recombination of electrons and holes excited by the p-type semiconductor and the n-type semiconductor by light irradiation. As a result, electron transfer occurs at the interface between the n-type semiconductor and water. For example, when water is acidic, hydrogen gas can be generated by the reaction represented by the above reaction formula (2).

Another example of a semiconductor device using the pn junction layer is a solar cell element. The solar cell element may include, for example, a Cu plate, a p-type layer formed on the surface of the Cu plate, and an n-type layer formed on the surface of the p-type layer. The p-type semiconductor may consist of, for example, Cu ₂ O or Cu O. The n-type semiconductor may consist of ZnO nanocrystals. A conductive layer may be formed on the surface of the n-type layer, and the pn junction layer may be sealed with a glass substrate or the like. The material of the conductive layer may be ITO (indium-tin oxide), FTO (fluorinated tin oxide) or the like. By electrically connecting the Cu plate and the conductive layer and irradiating the pn junction layer with light while controlling the voltage, electrical energy is suppressed while suppressing the recombination of carriers generated in the p-type semiconductor and the n-type semiconductor. Can be taken out.

The method for manufacturing a semiconductor device according to the present embodiment is a manufacturing method for manufacturing a semiconductor device using the method for manufacturing a nanocrystal according to the present embodiment, in which a p-type layer containing a p-type semiconductor is formed on the surface of a second member. By forming an n-type layer formed on the surface and containing an n-type semiconductor on the surface of the p-type layer, a pn junction layer including a p-type layer and an n-type layer is obtained. The method for manufacturing a semiconductor device may involve the generation of opto-electrical energy. That is, a photovoltaic power may be generated by irradiating the pn junction layer obtained in the light irradiation step with light. In this case, a bias may be applied between the first member and the second member, and electrons directed from the p-type semiconductor to the n-type semiconductor may be extracted as a photocurrent.

The n-type semiconductor included in the n-type layer may be any one of the above-mentioned oxide semiconductors. The p-type semiconductor included in the p-type layer may be any one of the above-mentioned oxide semiconductors. The combination of the n-type semiconductor and the p-type semiconductor is not particularly limited. From the viewpoint of the bandgap of the semiconductor (p-type semiconductor) on the electron supply side and the progress of corrosion due to holes generated in galvanic corrosion and photocatalytic reaction, the p-type semiconductor is copper (I) oxide and copper oxide (II). ), And the n-type semiconductor is preferably zinc oxide (II).

(Composition of metal members)
The metal member has a first member and a second member. The first member may be any member as long as it contains the first metal, and is not particularly limited. The first member may be composed of only the first metal. The first member may contain an oxide of the first metal in addition to the first metal (elementary substance). However, the member made of only the oxide of the first metal does not correspond to the first member according to the present embodiment. The content of the first metal in the first member is 10.0 to 100.0% by mass based on the total mass of the first member from the viewpoint of the productivity of nanocrystals and the promotion of hydrogen gas production. It is preferably 15.0 to 100.0% by mass, more preferably 20.0 to 100.0% by mass, and even more preferably 20.0 to 100.0% by mass. The higher the content of the first metal in the first member, the more easily hydrogen gas is generated, the oxide or hydroxide is easily generated, and the composition of the oxide or hydroxide is easily controlled.

The second member may be any member as long as it contains the second metal, and is not particularly limited. The second member may be composed of only the second metal. The second member may contain an oxide of the second metal in addition to the second metal (elementary substance). However, the member made of only the oxide of the second metal does not correspond to the second member according to the present embodiment. The content of the second metal in the second member is 10.0 to 100.0% by mass based on the total mass of the second member from the viewpoint of promoting the production of hydrogen gas and the productivity of nanocrystals. It is preferably 15.0 to 100.0% by mass, more preferably 20.0 to 100.0% by mass, and even more preferably 20.0 to 100.0% by mass. The higher the content of the second metal in the second member, the easier it is for oxides or hydroxides to be generated, the easier it is for the composition of the oxides or hydroxides to be controlled, and the easier it is for hydrogen gas to be generated.

The metal member may contain an alloy. The first member may contain an alloy of the first metal, or may be composed of only the alloy of the first metal. The composition of the alloy of the first metal may be any composition as long as it contains the first metal, and is not particularly limited. The alloy of the first metal may be, for example, an iron alloy, a copper alloy, a zinc alloy, or the like. The second member may contain an alloy of the second metal, or may be composed of only the alloy of the second metal. The composition of the alloy of the second metal may be any composition as long as it contains the second metal, and is not particularly limited. The alloy of the second metal may be, for example, an iron alloy, a copper alloy, a zinc alloy, or the like. When the first metal is an alloy, the standard electrode potential of the first metal may be the standard electrode potential of the alloy. When the second metal is an alloy, the standard electrode potential of the second metal may be the standard electrode potential of the alloy.

Examples of the iron alloy include Fe—C alloys, Fe—Au alloys, Fe—Al alloys, Fe—B alloys, Fe—Ce alloys, Fe—Cr alloys, and Fe—Cr—Ni alloys. , Fe—Cr—Mo alloy, Fe—Cr—Al alloy, Fe—Cr—Cu alloy, Fe—Cr—Ti alloy, Fe—Cr—Ni—Mn alloy, Fe—Cu alloy, Fe -Ga-based alloys, Fe-Ge-based alloys, Fe-Mg-based alloys, Fe-Mn-based alloys, Fe-Mo-based alloys, Fe-N-based alloys, Fe-Nb-based alloys, Fe-Ni-based alloys, Fe-P. Based alloys, Fe—S based alloys, Fe—Si based alloys, Fe—Si—Ag based alloys, Fe—Si—Mg based alloys, Fe—Ti based alloys, Fe—U based alloys, Fe—V based alloys, Fe -W-based alloys, Fe-Zn-based alloys and the like can be mentioned.

Examples of the copper alloy include Cu—Sn based alloys, Cu—Ni based alloys, Cu—Zn based alloys, Cu—P based alloys, Cu—Sn—P based alloys, Cu—Al based alloys, and Cu—Zn—Sn. Based alloys, Cu—Zn—Mn based alloys, Cu—Zn—Si based alloys, Cu—Zn—Ni based alloys, Cu—Mn based alloys, Cu—Be based alloys, Cu—Ag based alloys, Cu—Zr based alloys And so on.

Examples of the zinc alloy include Zn—Ni based alloys, Zn—Sb based alloys, Zn—Cu based alloys, Zn—Al based alloys, Zn—Mg based alloys and the like.

The content of the first metal in the alloy of the first metal is preferably 10.0 to 99.8% by mass, preferably 15.0 to 99.8% by mass, from the viewpoint of promoting the productivity of nanocrystals and the production of hydrogen gas. It is more preferably 99.5% by mass, further preferably 20.0 to 99.9% by mass. The content of the second metal in the alloy of the second metal is preferably 10.0 to 99.8% by mass, preferably 15.0 to 99.8% by mass, from the viewpoint of promoting the production of hydrogen gas and the productivity of nanocrystals. It is more preferably 99.5% by mass, further preferably 20.0 to 99.9% by mass.

The first member may further contain other atoms that are inevitably mixed. The content of other atoms inevitably mixed may be, for example, 3% by mass or less based on the total mass of the first member. The content of the atom contained in the first member is preferably 1% by mass or less from the viewpoint of the productivity of nanocrystals and the promotion of hydrogen gas production. The second member may further contain other atoms that are inevitably mixed. The content of other atoms inevitably mixed may be, for example, 3% by mass or less based on the total mass of the second member. The content of the atom contained in the second member is preferably 1% by mass or less from the viewpoint of the productivity of nanocrystals and the promotion of hydrogen gas production.

The shape of the first member is not particularly limited. Examples of the shape of the first member include a plate shape, a block shape, a ribbon shape, a round wire shape, a sheet shape, a mesh shape, or a shape obtained by combining these. The shape of the first member is preferably plate-shaped, block-shaped, or sheet-shaped from the viewpoint of recoverability of nanocrystals and hydrogen gas and workability of immersion in water. The shape of the second member may be the same as or different from the shape of the first member.

(Electrical connection method between the first member and the second member)
The method of electrically connecting the first member and the second member is not particularly limited. For example, the first member and the second member may be in direct contact with each other. The first member and the second member may be welded together. The metal member may further have a conductive material. The first member and the second member may be electrically connected via the conductive material. The electrical connection between the first member and the second member does not mean an electrical connection via water.

The arrangement of the first member and the second member in the metal member is not particularly limited. The arrangement shown in FIGS. 3 to 7 is preferable from the viewpoints of workability when assembling the metal member, recoverability of nanocrystals, selectivity of composition of nanocrystals, recoverability of hydrogen gas, and the like.

3 to 5 are schematic views of a metal member in which the first member and the second member are in direct contact with each other. For example, as in the metal member 100 shown in FIG. 3, the first member 22a and the second member 24 may be arranged side by side, and the side surface of the first member 22a and the side surface of the second member 24 may be in direct contact with each other. The first member 22a and the second member 24 may be fixed by winding the connecting material 26 around the entire first member 22a and the second member 24. The position around which the connecting material 26 is wound and the number of connecting materials 26 are not particularly limited. Further, as in the metal member 110 shown in FIG. 4, the entire first member 22b may be directly overlapped on the surface of the second member 24. The area of the surface of the first member 22b may be smaller than the area of the surface of the second member 24. One of the surfaces of the first member 22b may be covered with the surface of the second member. Further, as in the metal member 120 shown in FIG. 5, the first member 22a and the second member 24 may be directly overlapped with each other. The entire first member 22a and the second member 24 may have a cross shape. That is, the first member 22a may intersect the second member 24 substantially perpendicularly.

The connecting material 26 is not particularly limited as long as it does not dissolve or deteriorate in water and can firmly fix the first member and the second member. The connecting material 26 may be a conductive material or a non-conductive material. Even if the metal member is immersed in water, the connecting material 26 does not have to have conductivity as long as the first member and the second member are in direct contact with each other as shown in FIGS. 3 to 5. The conductive material may be the same as the conductive material 28 below. The non-conductive material may be, for example, cotton octopus yarn.

6 and 7 are schematic views of a metal member in which the first member and the second member are electrically connected via a conductive material. In the metal members of FIGS. 6 and 7, the first member and the second member are not in direct contact with each other. For example, as in the metal member 130 shown in FIG. 6, the first member 22a and the second member 24 may be electrically connected via the conductive material 28. In the case of FIG. 6, one end of the conductive material 28 is wound around the first member 22a, and the other end of the conductive material 28 is wound around the second member 24. Further, as in the metal member 140 shown in FIG. 7, the conductive material 28 may be composed of a metal wire 30 and a brazing material 32 connected to both ends of the metal wire 30. The brazing filler metal 32 may be solder. In the case of FIG. 7, one end of the metal wire 30 and the first member 22a are connected via the brazing material 32, and the other end of the metal wire 30 and the second member 24 form another brazing material 32. Connecting via. Further, the conductive material 28 may be arranged between the first member 22a and the second member 24, and the first member 22a and the second member 24 may be bonded to each other via the conductive material 28.

The conductive material 28 may be at least one selected from the group consisting of, for example, a wiring material containing copper, silver, gold, platinum, aluminum, chromium, nickel, iron, tin, or lead, and a brazing material.

The connection using the brazing filler metal 32 is effective when electrical conductivity is required. When at least one of the first member and the second member is thin and it is difficult to weld the first member and the second member, the connection using the brazing material 32 is particularly effective. As the brazing filler metal 32, one having a known composition can be preferably used. The brazing material 32 may be, for example, silver brazing (Ag—Cu—An alloy), brass brazing (Cu—Zn based alloy), phosphor copper brazing (Cu—P based alloy), aluminum brazing (Al—Si based alloy) or the like. May be.

The solder may be Sn—Pb-based solder, Sn-Pb-Ag-based solder, Sn-Ag—Cu-based solder, or the like. Considering the influence on the environment, the solder is preferably Sn-Ag-Cu based solder containing substantially no lead. When making an electrical connection using solder, the solder may be heated to a temperature above its melting point. Specifically, when the solder is a Sn—Pb-based solder, the solder may be heated to a temperature range of 230 to 300 ° C. to melt the solder.

(About light irradiation method)
As shown in FIG. 1, the water 2 and the metal member 100 may be housed in the container 6a. The container 6a may include a container body 8a for accommodating the water 2 and the metal member 100, and a lid 10a. The container 6a does not have to include the lid 10a. The container 6a preferably includes a lid 10a from the viewpoint of collecting hydrogen gas. The lid body 10a may seal the container body 8a. The lamp (light source) 12 may be used to irradiate the light L. By using the lamp 12, the surface of the metal member 100 can be irradiated with light of a certain intensity. The position of the lamp 12 may be appropriately adjusted so that nanocrystals or hydrogen gas are effectively generated. When irradiating sunlight, the lamp 12 may not be used. When irradiating sunlight, the position and orientation of the container 6a may be appropriately adjusted so that the surface of the metal member 100 is irradiated with sunlight.

As shown in FIG. 1, the metal member 100 may have a surface irradiated with light standing vertically, or the surface irradiated with light may be horizontal as shown in FIG.

The distance from the water surface to the light irradiation surface of the metal member 100 can be appropriately set according to the type of the metal member and the water, and is not particularly limited. The distance may be, for example, 5 mm to 10 m. The distance is preferably 5 mm to 8 m, more preferably 5 mm to 5 m, from the viewpoint of suppressing the decrease in the effect due to light scattering, recovering nanocrystals, and promoting the generation of hydrogen gas.

The shape of the container body 8a is not particularly limited. The shape of the container body 8a may be rectangular parallelepiped as in the container body 8a shown in FIG. 6, or may be columnar as in the container body 8b included in the container 6b shown in FIG. The shape of the container body 8a may be appropriately selected so that light can effectively irradiate the surface of the metal member 100.

The shape of the lid 10a is not particularly limited. The shape of the lid 10a may be a rectangular parallelepiped like the lid 10a shown in FIG. 1, or may be a columnar shape like the lid 10b shown in FIG. As the shape of the lid 10a, one that can effectively irradiate the surface of the metal member 100 with light may be used as appropriate.

The material of the container 6a (container body 8a and lid 10a) is not particularly limited as long as it does not block the surface of the metal member 100 from being irradiated with light. The material of the container body 8a and the lid 10a is preferably one that does not react with water. The material of the container body 8a and the lid 10a may be, for example, glass, plastic, or the like. From the viewpoint of collecting hydrogen gas, the material of the container body 8a and the lid 10a is preferably glass.

(About the wavelength of light)
The wavelength of light used in the light irradiation step is not particularly limited. The wavelength of the light may be shorter than the wavelength of the infrared lamp. For example, the wavelength of light may be 1000 nm or less. In the spectrum of light used in the light irradiation step, the wavelength having the maximum intensity may be 360 nm or more and less than 620 nm. The spectrum of light may be paraphrased as the spectral irradiance distribution of light, and the intensity may be paraphrased as the spectral irradiance or the spectral irradiance. That is, in the present embodiment, in the spectral radiation distribution (spectrum) of the light used in the light irradiation step, the wavelength of the light having the maximum spectral irradiance (intensity) may be 360 nm or more and less than 620 nm. The unit of the spectral irradiance (intensity) of light may be, for example, Wm- ^2.m - ¹ . By adjusting the wavelength of the light irradiating the metal member in the wavelength region of 360 nm or more and less than 620 nm, it is easy to control the composition of the oxide and the hydroxide generated from the metal member and water. Therefore, nanocrystals with high crystallinity can be obtained, and hydrogen gas with high purity can be easily obtained. The crystallinity (crystallinity) of nanocrystals can be confirmed by, for example, X-ray diffraction (XRD) analysis. The composition of oxides and hydroxides can be confirmed, for example, by point analysis by energy dispersive X-ray analysis (EDX). When the wavelength is 620 nm or more, it is difficult to obtain nanocrystals and it is difficult to generate hydrogen gas. When the wavelength is less than 360 nm, the nanocrystals are easily decomposed, the shape of the nanocrystals is easily deformed, and it is difficult to obtain high-purity hydrogen. The present inventors presume that the reason why nanocrystals are easily decomposed when the wavelength is less than 360 nm is as follows.

When the wavelength is less than 360 nm, if the nanocrystal is a semiconductor, the nanocrystal may act as a photocatalyst when irradiated with light. When nanocrystals act as a photocatalyst, as will be described later, photodecomposition of water occurs, and not only hydrogen gas but also oxygen gas is generated. As a result, the formed oxide returns to the hydroxide, the nanocrystals are decomposed, and the purity of the obtained hydrogen gas becomes low. Further, when the wavelength is less than 360 nm, energy is easily converted into heat, so that energy efficiency is liable to decrease and the metal member is liable to be damaged by heat. From the viewpoint that the above effect can be easily obtained by the above wavelength, the wavelength having the maximum intensity in the spectrum of light used in the light irradiation step is preferably 380 to 600 nm, and more preferably 400 to 580 nm. From the viewpoint of the efficiency of radiolysis of water, equipment restrictions, band gaps of oxides and hydroxides, and prevention of heat energy generation (heat generation) when excited electrons are relaxed, the above wavelengths are in the above range. It may be adjusted as appropriate within.

The light source of the light to irradiate the metal member is not particularly limited as long as it can irradiate the above-mentioned light. The light source may be, for example, the sun, an LED, a xenon lamp, a mercury lamp, a fluorescent lamp, or the like. The light irradiating the metal member may be, for example, sunlight or pseudo-sunlight. Sunlight can be suitably used from the viewpoint that it can be used as a renewable energy that does not emit warming gas or the like by inexhaustibly falling on the earth. Pseudo-sunlight means light that does not use the sun as a light source and whose spectrum of light matches the spectrum of sunlight. Pseudo-sunlight can be emitted by, for example, a solar simulator using a metal halide lamp, a halogen lamp or a xenon lamp. Pseudo-sunlight is generally used for the purpose of evaluating the strength of a material against ultraviolet rays, evaluating a solar cell, or evaluating weather resistance. Also in this embodiment, pseudo-sunlight can be preferably used.

In the light irradiation step, light may be irradiated to the interface where the surface of the metal member and water are in contact with each other. The interface is obtained, for example, by immersing the metal member in water, circulating water through a part or all of the metal member, and the like. In the light irradiation step, it is preferable to immerse the metal member under the water surface from the viewpoint of recovering the nanocrystals.

(Details of nanocrystals)
The nanocrystals formed on the surface of the first member include at least one of a first metal and a second metal. The nanocrystals formed on the surface of the first member include at least one of an oxide and a hydroxide. The nanocrystals formed on the surface of the first member may be composed of an oxide and a hydroxide, may be composed of only an oxide, or may be composed of only a hydroxide. The nanocrystals formed on the surface of the second member include at least one of a first metal and a second metal. The nanocrystals formed on the surface of the second member include at least one of an oxide and a hydroxide. The nanocrystals formed on the surface of the second member may be composed of an oxide and a hydroxide, may be composed of only an oxide, or may be composed of only a hydroxide.

It is preferable that at least one of the oxide and the hydroxide is a semiconductor. That is, the nanocrystals preferably contain semiconductors. Nanocrystals may consist only of semiconductors. When nanocrystals contain semiconductors, nanocrystals can be applied to semiconductor devices such as photocatalytic materials, light emitting materials, solar cells, quantum computers, and biosensors. FIG. 8 is a schematic diagram showing the relationship between the band gap (energy difference between the lower end of the conduction band and the upper end of the valence band) of a typical metal oxide semiconductor and the redox potential of water. A metal oxide semiconductor having various band gaps as shown in FIG. 8 may be produced by the method for producing nanocrystals according to the present embodiment.

The semiconductor may include at least one of a p-type semiconductor and an n-type semiconductor. That is, the nanocrystal may contain at least one of a p-type semiconductor and an n-type semiconductor. When the nanocrystal contains at least one of a p-type semiconductor and an n-type semiconductor, the conductivity of the nanocrystal (semiconductor) is improved, and the range of application of the nanocrystal to the semiconductor device is widened. Further, in this case, since the above-mentioned pn junction layer can be easily formed, the manufacturing cost of the semiconductor device using nanocrystals can be suppressed.

Oxide semiconductors (MO _x ) may become p-type semiconductors or n-type semiconductors when the oxide semiconductor is doped with an impurity element or the ratio of metal to oxygen deviates from the chemical quantitative composition. .. When the ratio of metal and oxygen deviates from the chemical quantitative composition, oxygen in the oxide semiconductor is lost, the composition of the oxide semiconductor becomes MO _xn , and the electrons of the metal that do not contribute to the bond are left over. As a result, the oxide semiconductor becomes n-type. Further, when the oxide semiconductor takes in excess oxygen, the composition of the oxide semiconductor becomes MO _{x + n} , and the defective portion of the metal atom acts as a hole. As a result, the oxide semiconductor becomes p-type.

The p-type semiconductors include copper (I) oxide (Cu ₂ O), copper (II) oxide (Cu O), silver (I) oxide (Ag ₂ O), nickel oxide (II) (NiO), and iron (III) oxide. It may be at least one selected from the group consisting of (Fe ₂ O ₃ ), tungsten oxide (VI) (WO ₃ ) and tin (II) oxide (SnO).

The n-type semiconductors include iron (III) oxide (Fe ₂ O ₃ ), indium oxide (III) (In ₂ O ₃ ), tungsten oxide (VI) (WO ₃ ), lead (II) oxide (PbO), and vanadium oxide. (V) (V ₂ O ₅ ), Niobide Oxide (III) (Nb ₂ O ₃ ), Tungsten Oxide (IV) (TIO ₂ ), Zinc Oxide (II) (ZnO), Tin Oxide (IV) (SnO ₂ ) , Aluminum (III) Oxide (Al ₂ O ₃ ) and Zinc Oxide (IV) (ZrO ₂ ) may be at least one selected from the group.

Some of the above oxides can be both p-type semiconductors and n-type semiconductors. For example, iron (III) oxide (Fe ₂ O ₃ ) usually behaves as an n-type semiconductor because oxygen is easily deficient. However, when iron (III) is doped with nitrogen (N), iron (III) oxide may be p-typed. In tungsten oxide (VI) (WO ₃ ), either the metal (W) or oxygen may be deficient. When the metal (W) is missing, the tungsten oxide (VI) is a p-type semiconductor. When oxygen is deficient, tungsten oxide (VI) is an n-type semiconductor.

The shape of the nanocrystals may be at least one selected from the group consisting of needle-like, columnar, rod-like, tubular, flint-like, lump-like, flower-like, starfish-like, branch-like and convex-like. The flower shape means a shape in which a plurality of columnar crystals radiate from the center of the crystal. The starfish shape means a shape in which a plurality of columnar crystals extend at substantially equal intervals in the same plane from the center of the crystal.

The maximum width (eg, length) of the nanocrystals may be 2 nm to 10 μm, or 2 nm to 1000 nm. The maximum width of nanocrystals implies the maximum width of an aggregate of a plurality of nanocrystals. The height of the nanocrystals from the surface of the metal member is not particularly limited. The nanocrystals may have a solid structure or a hollow structure.

(About the surface roughening process)
The method for producing nanocrystals according to the present embodiment may further include a surface roughening step of roughening the surface of the metal member before the light irradiation step. That is, in the light irradiation step, the surface of the roughened metal member may be irradiated with light. By performing the surface roughening step, irregularities are formed on the surface of the metal member, the growth rate of nanocrystals is likely to be improved, and the generation of hydrogen gas is also likely to be promoted. When irregularities are formed on the surface of the metal member, the electron density at the tip of the nanocrystal tends to increase. It is presumed that this causes a large amount of hydrated electrons to be generated at the tip of the nanocrystal, which promotes the formation of the above-mentioned hydroxide ion, the subsequent formation of the nanocrystal, and the generation of hydrogen gas.

The size of the unevenness on the surface of the metal member formed by the surface roughening step is not particularly limited. From the viewpoint of promoting the photochemical reaction, promoting the growth of nanocrystals, and promoting the generation of hydrogen gas, the average value of the size of the base of the convex portion is preferably 10 nm or more and 500 nm or less, and adjacent to each other. The average value of the spacing between the matching convex portions is preferably 2 nm or more and 200 nm or less. The average value of the size of the bottom of the convex portion is more preferably 15 nm or more and 300 nm or less, and the average value of the distance between the adjacent convex portions is more preferably 5 nm or more and 150 nm or less. It is more preferable that the average value of the size of the bottom of the convex portion is 20 nm or more and 100 nm or less, and the average value of the distance between the adjacent convex portions is 10 nm or more and 100 nm or less. The size of the base of the convex portion means the maximum width of the convex portion in the direction perpendicular to the height direction of the convex portion.

The surface roughening step may be performed, for example, by machining, chemical treatment, or liquid discharge treatment (discharge treatment in a liquid) on the surface of the metal member. The liquid discharge process means a process of discharging in a conductive liquid. Examples of machining include grinding using abrasive paper, buffs, or grindstones, blasting, and processing using sandpaper. Examples of the chemical treatment include etching with an acid or an alkali. As the submerged discharge treatment, for example, as described in International Publication No. 2008/099618, a voltage is applied to a counter electrode composed of an anode and a cathode arranged in a conductive liquid, and the vicinity of the cathode is applied. This may be done by generating plasma in the water and locally melting the cathode. In the liquid discharge treatment, by using a metal member for the cathode, unevenness can be formed on the surface of the metal member.

The liquid discharge treatment may be performed using, for example, the following device. The device that performs the submerged discharge treatment includes a cell that houses a conductive liquid, a pair of electrodes that are not in contact with each other arranged in the cell, and a DC power supply that applies a voltage to the pair of electrodes. The electrode pair is a cathode and an anode. A metal member is used for the cathode. The material of the anode is not particularly limited as long as it is stable in a conductive liquid without being energized. The material of the anode may be, for example, platinum or the like. The surface area of the anode may be larger than the surface area of the cathode. The liquid having conductivity may be, for example, an aqueous solution of potassium carbonate (K ₂ CO ₃ ) or the like.

The surface of the metal member after the surface roughening step may be exposed to the outside or may be covered with a natural oxide film.

(About water)
The water in which the metal parts are immersed is selected from the group consisting of pure water, ion-exchanged water, rainwater, tap water, river water, well water, filtered water, distilled water, back-penetration water, spring water, spring water, dam water and seawater. It may be at least one kind. As the water, pure water, ion-exchanged water, and tap water are preferable from the viewpoint of promoting the production of hydrogen gas, controlling the composition of nanocrystals, and productivity. However, as naturally derived water, river water, well water, dam water, seawater and the like can also be preferably used.

The pH of the water may be 5.00 to 10.0. By setting the pH to 5.00 or higher, the formation of nanocrystals under light irradiation can be promoted and the production of hydrogen gas can be promoted. Further, by setting the pH to 10.0 or less, the workability when recovering the nanocrystals from the surface of the metal member and the workability when recovering the hydrogen gas are improved. The pH of water is preferably 5.5 to 9.5, more preferably 6.0 to 9.0, from the viewpoint of controlling the composition of nanocrystals. The pH of the water may be 5.5 to 8.2, or 5.5 to 7.5.

The pH of water may be measured by, for example, a pH meter (LAQUAact, portable pH meter / water quality meter) manufactured by HORIBA, Ltd.

The electrical conductivity of water may be 80,000 μS / cm or less. The electrical conductivity of water is preferably 10,000 μS / cm or less, more preferably 5000 μS / cm or less, and 1.0 μS / cm, from the viewpoint of enhancing the crystallinity of nanocrystals and promoting the generation of hydrogen gas. It is more preferably cm or less. The lower limit of the electrical conductivity of water may be, for example, 0.05 μS / cm.

The electrical conductivity of water may be measured, for example, with a pH meter (LAQUAact, portable pH meter / water quality meter) manufactured by HORIBA, Ltd.

The purity of water is not particularly limited. The purity of water means the ratio of the mass of water molecules contained in water. The purity of water may be, for example, 80.0% by mass or more based on the total mass of water. By setting the purity of water to 80.0% by mass or more, the influence of impurities under light irradiation can be suppressed. The effects of impurities include, for example, salt precipitation and formation of a passivation film. The purity of water is preferably 85.0% by mass or more, more preferably 90.0% by mass or more, from the viewpoint of controlling the composition of nanocrystals and promoting the production of hydrogen gas. The upper limit of the purity of water may be, for example, 100.0% by mass.

The purity of water may be controlled by electrical conductivity. For example, when the type of solute (impurity) dissolved in water is specified and the purity of water is within the above range, the concentration of the solute and the electrical conductivity are often in a proportional relationship. On the other hand, in water containing a plurality of solutes (impurities), it is difficult to grasp the purity of water from the value even if the electrical conductivity is measured. The purity of water is preferably controlled by the electrical conductivity of water.

The concentration of dissolved oxygen in water is not particularly limited. The concentration of dissolved oxygen in water is preferably 15 mg / L or less, preferably 12 mg / L, based on, for example, the total volume of water, from the viewpoint of promoting the growth reaction of nanocrystals by light irradiation and promoting the production of hydrogen gas. The following is more preferable, and 10 mg / L or less is further preferable. The lower limit of the concentration of dissolved oxygen in water may be, for example, 8.0 mg / L.

The concentration of dissolved oxygen in water may be measured, for example, with a pH meter (LAQUAact, portable pH meter / water quality meter) manufactured by HORIBA, Ltd.

The temperature of water is not particularly limited. The temperature of water is preferably, for example, 0 to 80 ° C, more preferably 2 to 75 ° C, still more preferably 5 to 70 ° C, from the viewpoint of preventing solidification and evaporation of water and corrosion of metal materials.

(Supplementary information on hydrogen gas generation mechanism)
In this embodiment, the mechanism of the reaction in which hydrogen is generated with nanocrystals (oxide or hydroxide) has not always been elucidated. The present inventors consider that one of the hydrogen production reaction mechanisms is a photocatalytic reaction in which the nanocrystal itself functions as a photocatalyst. However, in the present embodiment, the photocatalytic reaction by nanocrystals is not a dominant reaction, but as described above, the reaction in which water and hydrogen are generated with the formation of hydroxides and oxides is the dominant reaction. The present inventors think. In the following, a photocatalytic reaction whose reaction mechanism is relatively known will be described. In the following, the photocatalytic reaction when the oxide is an iron oxide and the hydroxide is an iron hydroxide will be described. However, the photocatalytic reaction described below is also established when the oxide is not an iron oxide and the hydroxide is not an iron hydroxide.

In the present embodiment, the reaction in which hydrogen gas is generated together with nanocrystals is different from the photodecomposition reaction of water using a photocatalyst such as titanium dioxide (TiO ₂ ). The reaction that hydrogen gas is generated in the photocatalytic reaction with titanium dioxide is as follows. The bandgap Eg of titanium dioxide is 3.2 eV. Therefore, by irradiating the titanium dioxide immersed in water with light having an energy corresponding to the band gap of titanium dioxide and having a wavelength of 380 nm or less, the titanium dioxide absorbs the light. As a result, electrons and holes are excited. The holes oxidize water to produce oxygen gas as shown in the reaction equation (13) below. The electrons reduce hydrogen ions (H ⁺ ) to generate hydrogen gas as shown in the following reaction formula (14). In the photocatalytic reaction, not only hydrogen gas but also oxygen gas is generated by photodecomposition of water.
H ₂ O + 2h ⁺ → 0.5O ₂ + 2H ⁺ (13)
2H ⁺ + ^2e- → H ₂ (14)

In the above photocatalytic reaction with titanium dioxide, the energy level of the conduction band of titanium dioxide is negative when the hydrogen generation potential is used as a reference (zero), and hydrogen is hydrogen at a molar ratio of 2: 1 (chemical quantity theory ratio). Gas and oxygen gas are generated. In contrast, in photocatalytic reactions with nanocrystals (iron oxides or iron hydroxides), the energy level of the conduction band of the nanocrystals is positive, and the molar ratio of hydrogen and oxygen in the generated gas is not necessarily the chemical amount. I'm not satisfied with the argument. The present inventors speculate that the mechanism of the reaction in which hydrogen gas is generated in the photocatalytic reaction using the nanocrystals is as follows.

By irradiating the nanocrystals with light having an energy corresponding to the band gap of iron oxide or iron hydroxide, the iron oxide or iron hydroxide absorbs the light. For example, when the iron oxide is iron oxide (Fe ₂ O ₃ ), the bandgap Eg is 2.2 eV, and the wavelength of light having energy corresponding to the bandgap is 563 nm or less. When iron oxide or iron hydroxide absorbs light, electrons and holes are excited. The holes oxidize water to produce oxygen gas, as shown in reaction equation (13) above. The electrons reduce hydrogen ions to generate hydrogen gas as shown in the above reaction formula (14).

Here, in the photocatalytic reaction, in order for a reaction in which hydrogen ions are reduced by electrons to generate hydrogen gas, the band gap of the photocatalyst is large and the conduction band of the photocatalyst is taken as a reference (zero). It is necessary to satisfy the condition that the energy level of is negative. Although titanium dioxide satisfies this condition, the energy level of the conduction band of titanium dioxide is close to the hydrogen generation potential. In addition, titanium dioxide has low catalytic activity for hydrogen generation. Therefore, in order to actually use titanium dioxide as a photocatalyst for water splitting, a platinum (Pt) electrode is provided at the counter electrode of titanium dioxide, and a negative bias voltage (for example, about -0.5 V) is applied to the titanium dioxide side. It may have to be applied.

On the other hand, for example, the bandgap of nanocrystals made of iron oxide (Fe ₂ O ₃ ) is narrower than the bandgap of titanium dioxide. The reaction proceeds. However, the energy level of the conduction band of iron oxide is positive with respect to the hydrogen generation potential. Generally, when the energy level of the conduction band of the photocatalyst is positive, it is considered that hydrogen is not produced without the bias voltage. However, we speculate that in the photocatalytic reaction with nanocrystals, hydrogen is produced by chemical bias even without a bias voltage, as described below. As described above, the growth of nanocrystals occurs through the reaction of hydroxide ions generated by the radiolysis of water or the reaction of water with holes with Fe ³⁺ . Therefore, the pH of water is locally shifted to the alkaline side, especially at the tip of the nanocrystal. As a result, this becomes a chemical bias, and charge separation between electrons and holes proceeds efficiently, hydrogen ions are reduced by electrons, and a reaction that produces hydrogen gas is promoted.

The photocatalytic reaction using the nanocrystals does not require the application of a bias voltage, and hydrogen gas can be produced by photodecomposition of water while forming nanocrystals using visible light. In addition, the photocatalytic reaction using nanocrystals described above does not require the use of two types of electrodes, a positive electrode and a negative electrode, and it is possible to generate hydrogen gas using visible light. Industrially superior to reaction.

In general water photolysis, oxygen gas is also produced in addition to hydrogen gas, but most of the gas produced in the photocatalytic reaction by nanocrystals may be hydrogen gas. In other words, the concentration of hydrogen in the produced gas may be higher than the concentration of hydrogen stoichiometrically calculated from the molecular formula ( _H2O ) of water. That is, the concentration of hydrogen in the generated gas may be larger than 66.7% by volume based on the total volume of the gas. The concentration of hydrogen in the produced gas may be greater than 66.7 mol% based on the total number of moles of all the components contained in the gas. The present inventors speculate that the mechanism for obtaining high-purity hydrogen gas in a photocatalytic reaction using nanocrystals is as follows. In the photocatalytic reaction using nanocrystals, as described above, oxygen gas is generated by the reaction between water and holes, but even if oxygen gas is generated, oxygen gas and iron ions (Fe ²⁺ or Fe ³⁺ ) ionized in water are generated. ) Reacts directly. As a result, the growth of iron oxides (nanocrystals) is promoted, the concentration of oxygen in the gas becomes low, and the concentration of hydrogen becomes high. Further, since the solubility of oxygen gas in water is higher than that of hydrogen gas, the concentration of hydrogen gas in the generated gas is high.

Although the preferred embodiment of the present invention has been described above, the present invention is not necessarily limited to the above-described embodiment. Various modifications of the present invention can be made without departing from the spirit of the present invention, and examples of these modifications are also included in the present invention. For example, the metal member may have a first member containing the first metal, a second member containing the second metal, and a third member containing the third metal. That is, the metal member may include three or more types of members (three or more types of metal).

Hereinafter, the contents of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

<Example 1>
In Example 1, a metal member was prepared by the method shown below, and a surface roughening step and a light irradiation step were performed.

(1st member and 2nd member)
Zinc having a purity of 99.8% by mass was rolled to form a plate-shaped first member. The standard electrode potential of zinc (first metal) was higher than -2.00V. The dimensions of the first member were 50 mm × 10 mm × 0.5 mm. Copper having a purity of 99.9% by mass was rolled to form a plate-shaped second member. The standard electrode potential of copper (second metal) was higher than -2.00V. The dimensions of the second member were 50 mm × 10 mm × 0.5 mm.

(Surface roughening process)
Next, a liquid discharge treatment was performed on the surface of the first member by the method shown below. In a glass container, 300 mL of an aqueous potassium carbonate solution having a concentration of potassium carbonate (K ₂ CO ₃ ) of 0.1 mol / L was contained. The cathode and anode were placed in an aqueous potassium carbonate solution at a depth within 100 mm from the liquid surface. The distance between the cathode and the anode was 50 mm. As the cathode, the above-mentioned first member was used. A net-like platinum electrode was used as the anode. The dimensions of the platinum electrode were 40 mm × 550 mm. The line width of the platinum electrode was 0.5 mm. The length of the platinum wire in the electrode area of the platinum electrode was 600 mm. Then, the liquid discharge treatment was performed with the cell voltage set to 120 V and the discharge time set to 10 minutes.
The surface roughening steps of Examples 2 to 6, 8 to 15 and all the comparative examples described later are the same as the surface roughening steps of Example 1.

The surface of the first member after the surface roughening step was observed using a scanning electron microscope. As the scanning electron microscope, JSM-7001F manufactured by JEOL Ltd. was used. As a result, a large number of irregularities were formed on the surface of the first member. The size of the base of the convex portion was 5 nm on average.

A liquid discharge treatment was performed on the surface of the second member by the same method as described above. The surface of the second member after the surface roughening step was observed using the scanning electron microscope. As a result, a large number of irregularities were formed on the surface of the second member. The size of the base of the convex portion was 5 nm on average.

(Metal member)
A metal member was produced by electrically connecting the first member after the surface roughening step and the second member after the surface roughening step by the method shown below. As shown in FIG. 5, the first member and the second member were arranged in a cross shape and brought into direct contact with each other. A copper wire was wound around the contact portion between the first member and the second member to fix the first member and the second member. The purity of the copper wire was 99.9% by mass. The diameter of the copper wire was 0.5 mm.

(Light irradiation process)
Then, the light irradiation step was performed by the method shown below. Pure water was put into a glass container, and the metal member was immersed in pure water. The pH and electrical conductivity of pure water were measured with a pH meter. As the pH meter, LAQUAact (portable pH meter / water quality meter) manufactured by HORIBA, Ltd. was used. The pH of pure water was 7.0, and the electrical conductivity of pure water was 1.0 μS / cm or less. The container was sealed with a plastic lid.

As shown in FIG. 1, a metal member, a container and a light source were arranged, and the surface of the metal member in water was irradiated with light. That is, the surface of the metal member was irradiated with light from the direction perpendicular to the surface of the metal member. A xenon lamp was used as the light source. As the xenon lamp, a spot light source (LightningCureLC8) manufactured by Hamamatsu Photonics Co., Ltd. was used. A special optical filter was attached to the xenon lamp to set the wavelength range of light to 400 to 600 nm. The surface of the metal member was irradiated with light for 48 hours. The light output was 280 W. The spectral spectrum of light was measured with a spectroradiometer. As the spectroradiometer, SOLO 2 manufactured by Gentec-EO was used. As a result, in the spectrum of the light emitted from the xenon lamp, the wavelength having the maximum intensity was 360 nm or more and less than 620 nm. In the spectrum of light emitted from a xenon lamp, the wavelength with the highest intensity was about 493 nm. The light intensity at the light irradiation position 5 cm away from the light source was 3025 Wm ^-2 . The light irradiation position may be rephrased as the position on the surface of the metal member.

<Example 2>
In Example 2, the same metal member as in Example 1 was prepared. Then, the light irradiation step was performed in the same manner as in Example 1 except for the following points. In the light irradiation step of Example 2, the light irradiation time was set to 72 hours.

<Example 3>
In Example 3, the same metal member as in Example 2 was prepared. Next, the light irradiation step was performed in the same manner as in Example 2 except for the following points.

In the light irradiation step of Example 3, pseudo-sunlight was irradiated on the surface of the metal member without using a xenon lamp as a light source. As a light source of pseudo-sunlight, a solar simulator (HAL-320) manufactured by Asahi Spectroscopy Co., Ltd. was used. The solar simulator uses a xenon lamp. The wavelength range of pseudo-sunlight emitted by the solar simulator is 350 to 1100 nm. Further, as shown in FIG. 2, a metal member, a container and a light source were arranged. That is, the surface of the metal member was irradiated with light from the direction perpendicular to the surface of the metal member. The light output was 300 W. The spectral spectrum of light was measured with the above spectroradiometer. As a result, in the spectrum of pseudo-sunlight, the wavelength having the maximum intensity was 360 nm or more and less than 620 nm. In the spectrum of pseudo-sunlight, the wavelength with the highest intensity was about 460 nm. The light intensity at the light irradiation position 60 cm away from the light source was 1000 W / m ² .

<Example 4>
In Example 4, the same metal member as in Example 2 was prepared. Next, the light irradiation step was performed in the same manner as in Example 2 except for the following points.

In the light irradiation step of Example 4, sunlight was irradiated to the surface of the metal member without using a xenon lamp as a light source. The wavelength range of sunlight is approximately 300-3000 nm. The sunlight was irradiated from 9:00 am to 3:00 pm in the area of 43 degrees north latitude under fine weather conditions in June until the total time of light irradiation was 72 hours. The spectral spectrum of light was measured with the above spectroradiometer. As a result, in the sunlight spectrum, the wavelength having the maximum intensity was 360 nm or more and less than 620 nm. In the spectrum of sunlight, the wavelength with the highest intensity was about 520 nm. The light intensity at the light irradiation position was 750 W / m ² on average.

<Example 5>
In Example 5, the same metal member as in Example 3 was prepared. Next, the light irradiation step was performed in the same manner as in Example 3 except for the following points.

In the light irradiation step of Example 5, river water was used instead of pure water. The pH and electrical conductivity of river water were measured with the above pH meter. As a result, the pH of the river water was 7.5, and the electric conductivity of the river water was 350 μS / cm.

<Example 6>
In Example 6, the same metal member as in Example 3 was prepared. Next, the light irradiation step was performed in the same manner as in Example 3 except for the following points.

In the light irradiation step of Example 6, seawater was used instead of pure water. The pH and electrical conductivity of seawater were measured with the above pH meter. As a result, the pH of the seawater was 8.2, and the electrical conductivity of the seawater was 55,000 μS / cm.

<Example 7>
In Example 7, the same first member as in Example 3 and the same second member as in Example 3 were prepared. Then, the following surface roughening step was performed. Next, a metal member was prepared in the same manner as in Example 3. Then, the light irradiation step was performed in the same manner as in Example 3.

(Surface roughening process)
The surface of the first member was polished with abrasive paper by the method shown below. First, the surface of the first member immersed in water was polished with # 400 water-resistant abrasive paper, and then the surface of the first member was polished with # 800 water-resistant abrasive paper. As the water-resistant polishing paper, a polishing paper manufactured by Fujimoto Kagaku Co., Ltd. was used. The surface of the first member after the surface roughening step was observed using the scanning electron microscope. As a result, a large number of irregularities were formed on the surface of the first member. The distance between adjacent convex portions was 13 μm on average.

The surface of the second member was polished with abrasive paper by the same method as described above. The surface of the second member after the surface roughening step was observed using the scanning electron microscope. As a result, a large number of irregularities were formed on the surface of the second member. The distance between adjacent convex portions was 13 μm on average.

<Example 8>
In Example 8, the same first member as in Example 3 and the same second member as in Example 3 were prepared. Then, the surface roughening step was performed in the same manner as in Example 3. Next, the following metal members were prepared. Then, the light irradiation step was performed in the same manner as in Example 3.

(Metal member)
A metal member was produced by electrically connecting the first member after the surface roughening step and the second member after the surface roughening step by the method shown below. As shown in FIG. 5, the first member and the second member were arranged in a cross shape and brought into direct contact with each other. An octopus thread was wound around the contact portion between the first member and the second member to fix the first member and the second member. The octopus thread was a non-conductive cotton thread. The diameter of the octopus thread was 0.5 mm.

<Example 9>
In Example 9, the same first member as in Example 3 and the same second member as in Example 3 were prepared. Then, the surface roughening step was performed in the same manner as in Example 3. Next, the following metal members were prepared. Then, the light irradiation step was performed in the same manner as in Example 3.

(Metal member)
A metal member was produced by electrically connecting the first member after the surface roughening step and the second member after the surface roughening step by the method shown below. As shown in FIG. 3, the first member and the second member are arranged side by side and brought into direct contact with each other. Copper wires were wound around the upper part and the lower part of the whole of the first member and the second member to fix the first member and the second member. The purity of the copper wire was 99.9% by mass. The diameter of the copper wire was 0.025 mm.

<Example 10>
In Example 10, the same first member as in Example 3 and the same second member as in Example 3 were prepared. Then, the surface roughening step was performed in the same manner as in Example 3. Next, the following metal members were prepared. Then, the light irradiation step was performed in the same manner as in Example 3.

(Metal member)
A metal member was produced by electrically connecting the first member after the surface roughening step and the second member after the surface roughening step via a copper wire by the method shown below. As shown in FIG. 7, one end of the copper wire and the first member were connected via solder. Further, the other end of the copper wire and the second member were connected via solder. During the above connection, the solder was melted at a temperature of 280 ° C. The solder was a Sn-Ag-Cu-based rod solder containing 96.5% by mass of Sn, 3.0% by mass of Ag, and 0.5% by mass of Cu. The purity of the copper wire was 99.9% by mass. The diameter of the copper wire was 0.5 mm.

<Example 11>
In Example 11, the following first member and second member were prepared. Then, the surface roughening step was performed in the same manner as in Example 3. Next, a metal member was prepared in the same manner as in Example 3. Then, the light irradiation step was performed in the same manner as in Example 3.

(1st member and 2nd member)
Zinc having a purity of 99.8% by mass was rolled to form a plate-shaped first member. The dimensions of the first member were 50 mm × 10 mm × 0.5 mm. Tungsten having a purity of 99.9% by mass was processed to form a plate-shaped second member. The standard electrode potential of tungsten (second metal) was higher than -2.00V. Tungsten was processed by electric discharge machining. The dimensions of the second member were 50 mm × 10 mm × 0.5 mm.

<Example 12>
In Example 12, the following first member and second member were prepared. Then, the surface roughening step was performed in the same manner as in Example 3. Next, a metal member was prepared in the same manner as in Example 3. Then, the light irradiation step was performed in the same manner as in Example 3.

(1st member and 2nd member)
Zinc having a purity of 99.8% by mass was rolled to form a plate-shaped first member. The dimensions of the first member were 50 mm × 10 mm × 0.5 mm. Nickel having a purity of 99.5% by mass was rolled to form a plate-shaped second member. The standard electrode potential of nickel (second metal) was higher than -2.00V. The dimensions of the second member were 50 mm × 10 mm × 0.5 mm.

<Example 13>
In Example 13, the following first member and second member were prepared. Then, the surface roughening step was performed in the same manner as in Example 3. Next, a metal member was prepared in the same manner as in Example 3.

(1st member and 2nd member)
Titanium having a purity of 99.5% by mass was processed to form a plate-shaped first member. Titanium was processed by electric discharge machining. The standard electrode potential of titanium (first metal) was higher than -2.00V. The dimensions of the first member were 50 mm × 10 mm × 0.5 mm. Tungsten having a purity of 99.9% by mass was processed to form a plate-shaped second member. Tungsten was processed by electric discharge machining. The dimensions of the second member were 50 mm × 10 mm × 0.5 mm.

Next, the light irradiation step was performed in the same manner as in Example 3 except for the following points. In the light irradiation step of Example 13, tap water was used instead of pure water. The pH and electrical conductivity of tap water were measured with the above pH meter. As a result, the pH of tap water was 8.2, and the electrical conductivity of tap water was 150 μS / cm.

<Example 14>
In Example 14, the same first member as in Example 2 and the same second member as in Example 2 were prepared. Then, the surface roughening step was performed in the same manner as in Example 2. Next, the following metal members were prepared. Then, the light irradiation step was performed in the same manner as in Example 2.

(Metal member)
By the method shown below, the first member after the surface roughening step and the second member after the surface roughening step were electrically connected via a brazing material to prepare a metal member. As shown in FIG. 5, the first member and the second member are arranged in a cross shape. Phosphor bronze brazing was placed between the first member and the second member. Phosphor bronze wax contained 93% by weight of copper and 7% by weight of phosphorus. The first member, the second member, and the entire phosphor bronze wax were heated in a vacuum furnace at 750 ° C. to completely melt the brazing material, and the first member and the second member were fixed.

<Example 15>
In Example 15, the following first member and second member were prepared. Then, the surface roughening step was performed in the same manner as in Example 3. Next, a metal member was prepared in the same manner as in Example 3. Then, the light irradiation step was performed in the same manner as in Example 3.

(1st member and 2nd member)
Zinc having a purity of 99.8% by mass was rolled to form a plate-shaped first member. The dimensions of the first member were 50 mm × 10 mm × 0.5 mm. A copper-nickel alloy was rolled to form a plate-shaped second member. The copper-nickel alloy contained 75.0% by weight of copper and 25.0% by weight of nickel. The standard electrode potential _VA of the copper-nickel alloy (first metal) is obtained by the following formula (A). In the following formula (A), V _Cu is the standard electrode potential of copper. C _Cu is the mass ratio of copper contained in the alloy. V _Ni is the standard electrode potential of nickel. C _Ni is the mass ratio of nickel contained in the alloy. The VA obtained by the following formula ( _A ) was 0.325V, which was higher than -2.00V. The dimensions of the second member were 50 mm × 10 mm × 0.5 mm.
V _A = (V _Cu x C _Cu ) + (V _Ni x C _Ni ) (A)

<Comparative Example 1>
In Comparative Example 1, the same metal member as in Example 1 was prepared. Next, pure water was put into a glass container, and the metal member was immersed in pure water. The pH and electrical conductivity of pure water were measured with the above pH meter. As a result, the pH of pure water was 7.0, and the electrical conductivity of pure water was 1.0 μS / cm or less. The container was covered with a plastic lid, the container was sealed, and the container was held for 48 hours. In Comparative Example 1, the light irradiation step was not performed.

<Comparative Example 2>
In Comparative Example 2, the same metal member as in Example 3 was prepared. Next, the light irradiation step was performed in the same manner as in Example 3 except for the following points.

In the light irradiation step of Comparative Example 2, acetone was used instead of pure water. As acetone, acetone (purity 99.5% by mass) manufactured by Wako Pure Chemical Industries, Ltd. was used.

<Comparative Example 3>
In Comparative Example 3, a first member similar to that of Example 3 and a second member similar to that of Example 3 were prepared. Then, the surface roughening step was performed in the same manner as in Example 3. Next, the light irradiation step was performed in the same manner as in Example 3 except for the following points.

In the light irradiation step of Comparative Example 3, the first member after the surface roughening step and the second member after the surface roughening step were not electrically connected and were immersed in pure water in an isolated state.

<Comparative Example 4>
In Comparative Example 4, the following first member and second member were prepared. Then, the surface roughening step was performed in the same manner as in Example 3. Next, a metal member was prepared in the same manner as in Example 3. Then, the light irradiation step was performed in the same manner as in Example 3.

(1st member and 2nd member)
Magnesium having a purity of 99.5% by mass was rolled to form a plate-shaped first member. The dimensions of the first member were 50 mm × 10 mm × 0.5 mm. The standard electrode potential of magnesium (first metal) was lower than -2.00V. Zinc having a purity of 99.8% by mass was rolled to form a plate-shaped second member. The dimensions of the second member were 50 mm × 10 mm × 0.5 mm.

Table 3 shows the first member, the second member, the connecting material, the arrangement of the first member and the second member, the water, and the light irradiation conditions of Examples 1 to 15 and Comparative Examples 1 to 4.

<Evaluation>
(Crystal phase)
The surface of the first member after each of the light irradiation steps of Examples 1 to 15 and Comparative Examples 2 to 4 was individually analyzed by the X-ray diffraction (XRD) method, and the main crystal phase generated on the surface of the first member. Was identified. In Comparative Example 1, after holding the metal member in water for the time shown in Table 3, the surface of the first member was analyzed by an X-ray diffraction (XRD) method, and the main crystal phase formed on the surface of the first member was formed. Was identified. In the XRD analysis, the surface of the first member was irradiated with Cu—Kα rays using an X-ray diffractometer. The measurement conditions for the XRD analysis were as follows. As the X-ray diffractometer, ATG-G (powder X-ray diffraction) manufactured by Rigaku Co., Ltd. was used. By the same method as above, the main crystal layer formed on the surface of the second member was identified. The main crystal phases detected are shown in Table 4.
Output: 50kV-300mA
Scan speed: 4.0 ° / min Measurement mode: θ-2θ
Diffraction angle: 10-60 °

(Presence / absence and shape of nanocrystals)
The surfaces of the metal members after the light irradiation steps of Examples 1 to 15 and Comparative Examples 2 to 4 were individually observed with the scanning electron microscope to check for the presence or absence of nanocrystals. In Comparative Example 1, after holding the metal member in water for the time shown in Table 3, the surface of the metal member was observed with the scanning electron microscope to check for the presence or absence of nanocrystals. When nanocrystals were formed, the shape of the nanocrystals was evaluated. Furthermore, elemental analysis of the microstructure generated on the surface of the metal member was performed by point analysis by energy dispersive X-ray analysis (EDX) attached to the scanning electron microscope.

Many rod-shaped nanocrystals as shown in FIGS. 14 and 15 were observed on the surfaces of the metal members of Examples 1 to 15. In Examples 1-10, 14 and 15, the first member was zinc and the second member was copper or a copper alloy. As a result, many Zn (OH) ₂ nanocrystals were generated on the surface of the first member, and many ZnO nanocrystals were generated on the surface of the second member. Further, although ZnO was generated on the surface of the first member, the amount thereof was small. In Examples 1 to 10, 14 and 15, ZnO is generated on the surface of the first member by normal corrosion or SPSC, and then ZnO is converted to Zn by corrosion by light irradiation (reaction shown in the above reaction formula (11)). It is probable that the ions (Zn ²⁺ ) have melted out. On the other hand, the present inventors consider that the reason why many ZnO nanocrystals are generated on the surface of the second member is as follows. Zn ²⁺ melted from ZnO generated on the surface of the first member reaches the second member. Further, [Zn (OH) ₄ ] ^2- generated by the reaction between Zn (OH) ₂ generated on the surface of the first member and hydroxide ion also reaches the second member. As a result, Zn (OH) ₂ is generated again on the surface of the second member. After that, it is considered that Zn (OH) ₂ formed on the surface of the second member was changed to ZnO (nanocrystals) by SPSC, and ZnO grew. Also in Examples 11 and 12, a large amount of ZnO was generated on the surface of the second member. It is considered that the same reaction as described above occurred in Examples 11 and 12. Further, in Example 13, a large amount of TiO ₂ was generated on the surface of the second member. Even when the first member is titanium, it is considered that a large amount of TiO ₂ is generated on the surface of the second member by the same mechanism as when the first member is zinc.

From the observation of the microstructure generated on the surface of the metal member and the EDX analysis, the following was found. The ZnO (n-type layer) formed on the surface of the second member of Examples 1 to 10 and 14 was in contact with at least one of Cu ₂ O and Cu O (p-type layer). The ZnO (n-type layer) generated on the surface of the second member of Example 11 was in contact with WO ₃ (p-type layer). The ZnO (n-type layer) formed on the surface of the second member of Example 12 was in contact with the NiO (p-type layer). The TiO ₂ generated on the surface of the second member of Example 13 was in contact with WO ₃ . The ZnO (n-type layer) formed on the surface of the second member of Example 15 was in contact with at least one of Cu _2O , CuO and NiO (p-type layer). That is, in Examples 1 to 15, nanocrystals were formed and a pn junction layer was formed.

No nanocrystals were formed on the surfaces of the metal members of Comparative Examples 1 and 2. In Comparative Examples 1 and 2, the oxide or hydroxide shown in Table 4 uniformly covered the surface of the metal member.

In Comparative Example 3, a large amount of Zn (OH) ₂ oxide film was formed on the surface of the first member, and a large amount of Cu (OH) ₂ oxide film was formed on the surface of the second member. In addition, almost no ZnO nanocrystals were confirmed on the surface of the metal member. In Comparative Example 3, since the first member and the second member are not electrically connected, the reaction based on SPSC was individually performed in the vicinity of the surface of each of the first member and the second member. However, galvanic corrosion and electron transfer due to electrical connection between the p-type semiconductor and the n-type semiconductor did not occur. As a result, it is considered that the dissolution of Zn from the first member and the production of hydroxide ion (OH ⁻ ) were reduced, and almost no nanocrystals were produced.

In Comparative Example 4, a large amount of non-nanocrystal Mg (OH) ₂ was formed on the surface of the first member, and a large amount of an oxide film of Zn (OH) ₂ was formed on the surface of the second member. In addition, almost no ZnO nanocrystals were confirmed on the surface of the metal member. The standard electrode potential of magnesium is lower than -2.00V. Since the first member was magnesium, the direct reaction between magnesium and water proceeded. As a result, it is considered that the production of Mg (OH) ₂ has progressed in the first member. On the surface of the first member, a small amount of MgO was thermodynamically generated. However, the band gap of MgO is 7.8 eV, which is high. Therefore, MgO can be regarded as an insulator. Therefore, even though the first member and the second member were electrically connected, the movement of electrons did not substantially occur. As a result, it is considered that ZnO nanocrystals were hardly generated as in Comparative Example 3 because the SPSC-based reactions were individually performed in the vicinity of the surfaces of the first member and the second member.

(Analysis of gas)
Whether or not gas was generated inside the container in each of the light irradiation steps of Examples 1 to 15 and Comparative Examples 2 to 4 was visually confirmed individually. That is, it was individually visually confirmed whether or not air bubbles were accumulated in the upper part of the container after the light irradiation steps of Examples 1 to 15 and Comparative Examples 2 to 4. In Comparative Example 1, after holding the metal member in water for the time shown in Table 3, it was visually confirmed whether or not gas was generated inside the container. When gas was generated inside the container, the volume of the generated gas was visually measured. In addition, the type and concentration of the components contained in the produced gas were measured by gas chromatography-mass spectrometry (GC-MS). In gas chromatography-mass spectrometry, a gas chromatograph was used to measure argon as a carrier gas and a sample in a syringe. As the gas chromatograph, GC-14B manufactured by Shimadzu Corporation was used. As the volume of the generated gas, a value (unit: cc / cm ² ) per light irradiation area on the surface of the metal member was calculated. If the metal member and water before use do not contain nitrogen and the analyzed gas contains nitrogen gas, the volume of nitrogen and oxygen derived from air can be increased by the above method. The concentration of the produced hydrogen gas was corrected so that it was excluded from the total volume of the produced gas.

In Examples 1 to 15 and Comparative Examples 3 and 4, it was visually confirmed that gas was accumulated in the container after the light irradiation step. Table 4 shows the volumes of the produced gases of Examples 1 to 15 and Comparative Examples 3 and 4. On the other hand, in Comparative Examples 1 and 2, no gas was generated. As a result of gas chromatography-mass spectrometry, hydrogen gas (H ₂ ), nitrogen gas (N ₂ ), and oxygen gas (O ₂ ) were detected from the gases of Examples 1 to 15 and Comparative Examples 3 and 4, respectively. Further, it was found that hydrogen gas (H2) is dominant in _each of the gases of Examples 1 to 15 and Comparative Examples 3 and 4.

The gas produced in the light irradiation step of Example 2 was analyzed by gas chromatography-mass spectrometry. In the produced gas of Example 2, the volume ratio of hydrogen gas (H ₂ ): oxygen gas (O ₂ ): nitrogen gas (N ₂ ) was 52: 1: 3. In Example 2, nitrogen was not contained in the metal member and water before use. Therefore, it is considered that the nitrogen gas detected by gas chromatography-mass spectrometry is due to the mixing of air during the analysis. When only air was analyzed by gas chromatography-mass spectrometry, the volume ratio of oxygen gas: nitrogen gas was 2: 7 in air. Based on this result, the corrected hydrogen gas concentration (unit: volume%) was calculated by the above-mentioned method. The concentration of hydrogen gas in Example 2 was 99.7% by volume. In Examples 1 and 3 to 15 and Comparative Examples 3 and 4, the corrected hydrogen gas concentration was calculated in the same manner as in Example 2. Table 4 shows the concentrations of hydrogen gas in Examples 1 to 15 and Comparative Examples 3 and 4.

As shown in Table 4, in Examples 1 to 15, it was found that the volume of the produced gas per light irradiation area exceeded 1 cc / cm ² , and high-concentration hydrogen gas was produced. Further, as shown in Table 4, there was a tendency for the volume of the produced gas to differ depending on the composition of the first member, the composition of the second member, the pH of water or the electrical conductivity. Here, it was found that the volume of the gas produced in Example 3 was larger than the volume of the gas produced in Example 7. The third and seventh embodiments differ only in the method of the surface roughening step for the surface of the first member and the surface of the second member. The present inventors consider that the reason why the volume of the produced gas of Example 3 is larger than the volume of the produced gas of Example 7 is as follows. The unevenness of the surface of the first member formed by the submerged discharge treatment of Example 3 is finer than the unevenness of the surface of the first member formed by the polishing of Example 7. Further, the unevenness of the surface of the second member formed by the submerged discharge treatment of Example 3 is finer than the unevenness of the surface of the second member formed by the polishing of Example 7. Therefore, the electron density at the tip of the nanocrystal generated on the surface of the metal member of Example 3 becomes high, and a large amount of hydrated electrons are generated at the tip of the nanocrystal. As a result, the production of hydroxide ions, the formation of subsequent nanocrystals, and the production of hydrogen gas are further promoted.

In Comparative Example 1, no gas was generated. Further, in Comparative Example 1, as described above, nanocrystals were not formed on the surface of the metal member. From the above, it is considered that no gas was generated in the light irradiation step because hydroxides were predominantly formed on the surface of the metal member of Comparative Example 1 due to the rusting of the metal member in water. ..

In Comparative Example 2, since the metal member was immersed in acetone instead of water, hydroxide ions did not exist and nanocrystals were not formed. As a result, it is considered that gas was not generated in the light irradiation step. With acetone, no radiolysis of water occurs even when irradiated with light, and there are no dissociated hydroxide ions.

The concentration of hydrogen gas in Comparative Example 3 was high. However, the volume of the produced gas of Comparative Example 3 was significantly smaller than the volume of the produced gas of Examples 1 to 15. In Comparative Example 3, since the first member and the second member are not electrically connected, it is considered that galvanic corrosion does not occur and the leaching of the ions of the first metal from the first member is suppressed. Further, in Comparative Example 3, a ZnO oxide semiconductor was slightly formed on the surface of the first member. However, since the band gap of ZnO is large, the amount of electrons obtained by the photocatalytic reaction is small. As a result, it is considered that the amount of hydroxide ion (OH ⁻ ) produced in the above reaction formula (3) was reduced, and the production of nanocrystals by SPSC and the subsequent production of hydrogen gas were significantly suppressed.

The volume of the produced gas of Comparative Example 4 was larger than the volume of the produced gas of Examples 1 to 15. In Comparative Example 4, since the standard electrode potential of magnesium, which is the first member, was too low, magnesium and water reacted directly. As a result, magnesium hydroxide was produced, and at the same time, hydrogen gas was generated as a by-product, so that it is considered that the volume of the produced gas was large. However, the concentration of hydrogen gas in Comparative Example 4 was 90.0% by volume, which was lower than the concentration of hydrogen gas in Examples 1 to 15. The present inventors consider that the reason why the concentration of hydrogen gas in Comparative Example 4 is low is as follows. The reaction between magnesium and water to produce hydrogen gas does not depend on light irradiation. That is, hydrogen gas is generated immediately after the metal member of Comparative Example 4 is immersed in water. Therefore, after immersing the metal member in water, it is difficult to seal the container while filling it with water, and air tends to be mixed when the container is covered. Mixing air into the container can be a major problem, especially when an acidic aqueous solution having a low pH is used and when an industrially large area metal member is used. Further, in Comparative Example 4, hydrogen continued to be generated for about 5 hours from the start of light irradiation. However, after 5 hours, no hydrogen was generated. In Comparative Example 4, magnesium hydroxide produced by the reaction of magnesium and water acted as a passivation film, and the subsequent generation of hydrogen gas was substantially stopped. Therefore, in Comparative Example 4, it is considered that the time during which hydrogen gas was generated was short. When a passivation film such as magnesium hydroxide is formed on the surface of the metal member, it is difficult to continue the purification and recovery of hydrogen gas for an industrially desired time.

INDUSTRIAL APPLICABILITY According to the present invention, there is provided a method for producing nanocrystals capable of easily forming nanocrystals containing at least one of oxides and hydroxides, and a method for producing semiconductor devices using the method for producing nanocrystals. can do.

2 ... water, 6a, 6b ... container, 8a, 8b ... container body, 10a, 10b ... lid, 12 ... lamp (light source), 22a, 22b ... first member, 24 ... second member, 26 ... connection material, 28 ... Conductive material, 30 ... Metal wire, 32 ... Wax material, 100, 110, 120, 130, 140 ... Metal member, L ... Light.

Claims (29)

A light irradiation step of irradiating the surface of a metal member immersed in water with light to form nanocrystals on the surface of the metal member is provided.
The metal member
The first member containing the first metal and
The second member containing the second metal and
Have,
The first metal is a metal different from the second metal,
The standard electrode potential of the first metal is higher than -2.00V,
The standard electrode potential of the second metal is higher than -2.00V,
The first member and the second member are electrically connected to each other.
The nanocrystals contain at least one of oxides and hydroxides.
The oxide is an oxide of at least one of the first metal and the second metal.
The hydroxide is a hydroxide of at least one of the first metal and the second metal.
Manufacturing method of nanocrystals. The metal member contains an alloy,
The method for producing nanocrystals according to claim 1. The content of the first metal in the first member is 10.0 to 100.0% by mass with respect to the total mass of the first member.
The content of the second metal in the second member is 10.0 to 100.0% by mass with respect to the total mass of the second member.
The method for producing nanocrystals according to claim 1 or 2. Prior to the light irradiation step, a surface roughening step of roughening the surface of the metal member is further provided.
The method for producing nanocrystals according to any one of claims 1 to 3. The surface roughening step is performed by machining, chemical treatment, or submerged discharge treatment.
The method for producing nanocrystals according to claim 4. The first member and the second member are in direct contact with each other.
The method for producing nanocrystals according to any one of claims 1 to 5. The first member and the second member are welded to each other.
The method for producing nanocrystals according to any one of claims 1 to 6. The metal member further has a conductive material and
The first member and the second member are connected via the conductive material.
The method for producing nanocrystals according to any one of claims 1 to 7. The conductive material is at least one selected from the group consisting of wiring materials containing copper, silver, gold, platinum, aluminum, chromium, nickel, iron, tin, or lead, and brazing materials.
The method for producing nanocrystals according to claim 8. The light is sunlight or pseudo-sunlight.
The method for producing nanocrystals according to any one of claims 1 to 9. In the spectrum of light, the wavelength having the maximum intensity is 360 nm or more and less than 620 nm.
The method for producing nanocrystals according to any one of claims 1 to 10. The water is at least one selected from the group consisting of pure water, ion-exchanged water, rainwater, tap water, river water, well water, filtered water, distilled water, back-penetration water, spring water, spring water, dam water and seawater. be,
The method for producing nanocrystals according to any one of claims 1 to 11. The pH of the water is 5.00 to 10.0.
The method for producing nanocrystals according to any one of claims 1 to 12. The electric conductivity of the water is 0.05 to 1.0 μS / cm.
The method for producing nanocrystals according to any one of claims 1 to 13. The shape of the nanocrystal is at least one selected from the group consisting of needle-like, columnar, rod-like, tube-like, lint-like, lump-like, flower-like, starfish-like, branch-like and convex-like.
The method for producing nanocrystals according to any one of claims 1 to 14. In the light irradiation step, a gas containing hydrogen is generated.
The method for producing nanocrystals according to any one of claims 1 to 15. The number of moles of oxygen in the gas is 0 times or more and less than 1/2 times the number of moles of hydrogen.
The method for producing nanocrystals according to claim 16. Further comprising a step of removing and recovering the nanocrystals from the surface of the metal member.
The method for producing nanocrystals according to any one of claims 1 to 17. The standard electrode potential of the second metal is higher than the standard electrode potential of the first metal.
The method for producing nanocrystals according to any one of claims 1 to 18. Hydroxocomplex ions of the first metal are generated from the surface of the first member in the water.
The method for producing nanocrystals according to claim 19. At least one of the oxide and the hydroxide is a semiconductor.
The method for producing nanocrystals according to any one of claims 1 to 20. The semiconductor contains the nanocrystals.
The method for producing nanocrystals according to claim 21. The semiconductor includes at least one of a p-type semiconductor and an n-type semiconductor.
The method for producing nanocrystals according to claim 21 or 22. The n-type semiconductor is an oxide containing the first metal.
The p-type semiconductor is an oxide containing the second metal.
The method for producing nanocrystals according to claim 23. The p-type semiconductor is a group consisting of copper (I) oxide, copper (II) oxide, silver (I) oxide, nickel (II) oxide, iron (III) oxide, tungsten oxide (VI) and tin (II) oxide. At least one of the more selected,
The method for producing nanocrystals according to claim 23 or 24. The n-type semiconductor includes iron (III) oxide, indium (III) oxide, tungsten oxide (VI), lead (II) oxide, vanadium (V) oxide, niobium (III) oxide, titanium (IV) oxide, and zinc oxide. (II), at least one selected from the group consisting of tin oxide (IV), aluminum oxide (III) and zirconium oxide (IV).
The method for producing nanocrystals according to any one of claims 23 to 25. A method for manufacturing a semiconductor device by using the method for manufacturing nanocrystals according to any one of claims 23 to 26.
By forming the p-type layer containing the p-type semiconductor on the surface of the second member and forming the n-type layer containing the n-type semiconductor on the surface of the p-type layer, the p-type layer and A pn junction layer containing the n-type layer is obtained.
Manufacturing method of semiconductor device. The p-type semiconductor is at least one of copper (I) oxide and copper (II) oxide.
The n-type semiconductor is zinc oxide (II).
The method for manufacturing a semiconductor device according to claim 27. By irradiating the pn junction layer with the light, a photovoltaic power is generated.
The method for manufacturing a semiconductor device according to claim 27 or 28.

Images