JP5499406B2 - Method for producing silicon nanowire - Google Patents

Description

  The present invention relates to a method for producing silicon nanowires. More specifically, the present invention relates to a method for producing silicon nanowires that are useful for photovoltaic power elements for solar cells, negative electrode materials for lithium batteries, and the like. In particular, silicon nanowires are expected to be used as a negative electrode material for lithium batteries because they are difficult to be powdered even when subjected to repeated expansion and contraction due to charge and discharge.

  Known methods for producing silicon nanowires include a melting method (for example, see Patent Document 1), an evaporation method (for example, see Patent Document 2), a catalyst method (for example, see Patent Document 3), and the like. As a method for eliminating the disadvantages of these silicon nanowire production methods and producing high-purity silicon nanowires at a low temperature, a mixed gas of silicon tetrachloride gas and an inert gas or silicon tetrachloride gas is used in an amount of 700 to 1000. A silicon nanowire that passes through a high temperature region of ° C and flows to a region having a lower temperature than the high temperature region, supplies aluminum to the high temperature region, and deposits silicon nanowires in a region having a lower temperature than the high temperature region. A manufacturing method has been proposed (see, for example, Patent Document 4).

  According to the manufacturing method of the silicon nanowire, since the temperature in the high temperature region is 700 to 1100 ° C., there is an advantage that the silicon nanowire can be manufactured at a temperature lower than the conventional heating temperature (1300 ° C.). However, it is hard to say that the temperature range when manufacturing silicon nanowires is the high temperature range, and it is difficult to say that the temperature range is low. From the viewpoint of significantly improving energy efficiency, silicon nanowires are manufactured at a much lower temperature. The development of a method that can do this is awaited.

  In addition, since the silicon nanowire manufacturing method requires aluminum, and aluminum has a good affinity with silicon, aluminum is mixed as an impurity in the silicon during the production of silicon nanowires. It is difficult to produce silicon nanowires.

JP 2003-142680 A JP 2004-296750 A JP 2006-117475 A JP 2009-161404 A

  This invention is made | formed in view of the said prior art, The method which can manufacture the silicon nanowire which has the high purity which does not mix aluminum in a low-temperature area | region further than the manufacturing method of the said silicon nanowire. The issue is to provide.

The present invention
(1) A method for producing silicon nanowires, comprising heating silicon tetrachloride to a temperature of 450 to 600 ° C. in the presence of zinc in an inert gas atmosphere,
(2) The method for producing silicon nanowires according to (1), wherein a mixture of silicon tetrachloride and zinc is used,
(3) The method for producing silicon nanowires according to (1) or (2), wherein the amount of zinc per mole of silicon tetrachloride is 2 to 5 moles,
(4) Heating silicon tetrachloride in the presence of at least one catalyst selected from the group consisting of gold, silver, copper, platinum, palladium, nickel, iron, aluminum, gallium, indium, germanium, tin and lead. The method for producing a silicon nanowire according to any one of (1) to (3),
(5) The method for producing silicon nanowires according to any one of (1) to (4) above, wherein silicon tetrachloride is heated in the presence of silicon pieces, and (6) silicon tetrachloride is heated in a closed system. It is related with the manufacturing method of the silicon nanowire in any one of said (1)-(5).

  According to the method for producing silicon nanowires of the present invention, there is an excellent effect that silicon nanowires having high purity can be produced at a low temperature without mixing aluminum.

In the silicon nanowire obtained in Example 1, (a) is an optical photograph of the lower part of the glass tube before heating, and (b) is an optical photograph of the lower part of the glass tube after heating. 2 is a powder X-ray diffraction diagram of powder after heating silicon nanowires obtained in Example 1. FIG. In Example 1, it is a scanning electron microscope (SEM) photograph of the silicon nanowire obtained at the lower part of the glass tube. In Example 1, it is the optical photograph in the area | region from the center part of the glass tube after a heating to the bottom part (right direction toward the paper surface). 2 is a Raman spectrum of silicon nanowires obtained in Example 1. In Example 1, it is a scanning electron microscope (SEM) photograph of the silicon nanowire obtained in the center part of the glass tube. It is a figure which shows the EDX spectrum of the nanowire obtained in Example 1. FIG. 2 is a field emission scanning electron microscope (FE-SEM) photograph of the nanowire obtained in Example 1. FIG. In Example 4, it is a scanning electron microscope (SEM) photograph of the silicon nanowire obtained inside the glass tube. It is a figure which shows the EDX spectrum of the nanowire obtained in Example 4. (A) is a scanning electron microscope (SEM) photograph of a nanowire existing at the end of a silicon wafer piece, and (b) is a scanning electron microscope of a nanowire existing at the center of the silicon wafer piece ( SEM).

  As described above, the method for producing silicon nanowires of the present invention is characterized by heating silicon tetrachloride at a temperature of 450 to 600 ° C. in the presence of zinc in an inert gas atmosphere.

  The present invention has one major feature in that silicon tetrachloride is heated in the presence of zinc. According to the present invention, since the operation of heating silicon tetrachloride in the presence of zinc is taken in this way, the heating temperature (Japanese Patent Application Laid-Open No. 2009-161404) in the conventional method for producing silicon nanowire ( In contrast to (700 to 1100 ° C.), the heating temperature can be greatly reduced to produce silicon nanowires. Therefore, the manufacturing method of the silicon nanowire of the present invention has an advantage that energy efficiency can be remarkably improved as compared with the conventional method.

  In addition, since the conventional silicon nanowire manufacturing method requires aluminum, aluminum is mixed as an impurity in the obtained silicon nanowire, so that there is a drawback that the purity of the silicon nanowire is lowered. On the other hand, in the manufacturing method of the silicon nanowire of this invention, since aluminum is not required, it can prevent that aluminum mixes in the silicon nanowire obtained. Furthermore, in the method for producing silicon nanowires of the present invention, zinc is used instead of aluminum used in the conventional method. However, since the zinc has a very low affinity for silicon, the silicon nanowires obtained can be obtained. Since it is hard to mix in as an impurity to a wire, the silicon nanowire which has high purity can be manufactured easily.

  Furthermore, since zinc chloride by-produced by the reaction between the raw material silicon tetrachloride and zinc is easily vaporized and removed by heating, it can be prevented from being taken into silicon nanowires.

  Therefore, according to the method for producing silicon nanowires of the present invention, since there is no mixing of aluminum and silicon nanowires having high purity can be produced at a low temperature, the method for producing silicon nanowires of the present invention is, for example, It can be suitably used when producing silicon nanowires useful for photovoltaic power elements for solar cells, negative electrode materials for lithium batteries, and the like.

  Hereinafter, one embodiment of the method for producing silicon nanowires of the present invention will be described in detail. However, the present invention is not limited to such an embodiment.

  In the present invention, zinc and silicon tetrachloride are used as raw materials for silicon nanowires.

  Zinc is preferably as pure as possible from the viewpoint of increasing the purity of the resulting silicon nanowires. The purity of zinc is preferably 99.9% by weight or more from the viewpoint of producing high-purity silicon nanowires.

  The shape of zinc is not particularly limited because it has a melting point of 420 ° C. and melts during heating, but is preferably in the form of particles from the viewpoint of handleability.

  Silicon tetrachloride having high purity can be easily obtained commercially at a low price. Silicon tetrachloride is preferably as high in purity as possible from the viewpoint of increasing the purity of the resulting silicon nanowires. The purity of silicon tetrachloride is preferably 99.9% by weight or more from the viewpoint of producing high-purity silicon nanowires.

  The amount of zinc per mole of silicon tetrachloride is preferably 2 moles or more, more preferably 2.5 moles or more from the viewpoint of efficiently producing silicon nanowires. Since not only improvement of the production efficiency of nanowire cannot be expected, but also the economic efficiency is lowered, it is preferably 5 mol or less, more preferably 4.5 mol or less.

  According to the method for producing silicon nanowires of the present invention, silicon nanowires can be efficiently produced even in the absence of a catalyst, but a catalyst may be used when producing silicon nanowires. .

  When silicon nanowires are manufactured without using a catalyst, amorphous silicon nanowires having a diameter of about 300 nm or less can be obtained. However, when a catalyst is used, the diameter is further reduced. The diameter of the silicon nanowire can be controlled and the production efficiency of the silicon nanowire can be increased.

  Examples of the catalyst include gold, silver, copper, platinum, palladium, nickel, iron, aluminum, gallium, indium, germanium, tin, lead and the like, but the present invention is not limited to such examples. Absent. These catalysts may be used alone or in combination of two or more. Among these catalysts, gold is preferable from the viewpoint of easily controlling the diameter of the obtained silicon nanowire and crystallizing the silicon nanowire. When gold is used as the catalyst, ultrafine crystalline silicon nanowires having a diameter of 20 nm or less can be produced.

  In addition, when aluminum is used as the catalyst, as described above, there is a possibility that it is mixed as an impurity in the obtained silicon nanowire, but there is no problem as long as a minute amount is used as the catalyst at a low temperature as in the present invention.

  The size (maximum diameter) of the catalyst is not particularly limited, but is preferably about the same as the diameter of the target silicon nanowire from the viewpoint of efficient production while controlling the diameter of the silicon nanowire. For example, when it is desired to produce silicon nanowires having a diameter of 50 nm, the size of the catalyst is preferably 30 to 70 nm, more preferably 40 to 60 nm.

  The amount of the catalyst is preferably 0.03 parts by weight or more, more preferably 0.3 parts by weight or more from the viewpoint of sufficiently expressing the catalytic effect per 100 parts by weight of the total amount of silicon tetrachloride and zinc. Even if it is used in a large amount, not only the improvement of the catalytic effect cannot be expected, but also the economy is lowered. Therefore, it is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, and further preferably 3 parts by weight. Less than parts by weight. The catalyst can usually be used by vapor deposition or coating on the surface inside the reaction vessel and / or on a surface such as a piece of silicon.

  In the present invention, silicon tetrachloride may be heated in the presence of silicon pieces. Since silicon pieces are made of silicon like silicon nanowires, both have the same quality and are excellent in affinity. Therefore, silicon nanowires can be efficiently generated on the surface of the silicon pieces. it can.

  Since the size and shape of the silicon piece are different depending on the production scale of the silicon nanowire and cannot be determined unconditionally, the silicon piece is not particularly limited. As an example, the length is 50 to 200 mm, the width is 5 to 50 mm, the thickness is Examples thereof include a plate having a rectangular shape of about 0.5 to 5 mm. The purity of silicon used for the silicon piece is preferably as high as possible from the viewpoint of efficiently generating silicon nanowires on the surface of the silicon piece.

  After introducing silicon tetrachloride and zinc and optionally a catalyst into the reaction vessel, the resulting mixture is heated in an inert gas atmosphere.

  The inert gas means a gas that is inert with respect to silicon tetrachloride and zinc, which are raw materials for silicon nanowires. Examples of the inert gas include nitrogen gas, helium gas, and argon gas, but the present invention is not limited to such examples. These inert gases may be used alone or in combination of two or more. Of these inert gases, nitrogen gas and argon gas are preferred.

  Silicon tetrachloride and zinc may be heated in a closed system or may be heated in an open system, but it is preferable to heat in a closed system from the viewpoint of efficiently producing silicon nanowires.

  When silicon tetrachloride and zinc are heated in an open system, in an inert gas atmosphere, for example, silicon tetrachloride, zinc and, if necessary, a catalyst is placed in a heat resistant container, and the heat resistant container is moved by a conveyor or the like. Since it can heat, there exists an advantage that a silicon nanowire can be manufactured continuously and efficiently.

  Examples of the material constituting the heat-resistant container include heat-resistant glass, carbon, silicon carbide, silicon nitride, aluminum nitride, alumina, and the like, but the present invention is not limited to such examples. Examples of the heat resistant container include a reaction tube, a tube, a boat, a dish, and the like, but the present invention is not limited to such an example.

  On the other hand, when silicon tetrachloride and zinc are heated in a closed system, silicon tetrachloride, zinc and, if necessary, a catalyst are placed in a heat-resistant container such as a heat-resistant glass tube whose internal atmosphere is an inert gas, and the opening is opened. Since the heat-resistant container can be heated after sealing, the gas in the heat-resistant container can be prevented from leaking to the outside, so that silicon nanowires can be produced with high yield. There are advantages.

  The heating temperature when heating the silicon tetrachloride, zinc and, if necessary, the catalyst is 450 ° C. or higher from the viewpoint of efficiently producing silicon nanowires, and 600 ° C. or lower from the viewpoint of increasing energy efficiency. In addition, the time required to heat the silicon tetrachloride, zinc and, if necessary, the catalyst varies depending on the heating temperature, and thus cannot be determined unconditionally. Usually, however, the time required to generate silicon nanowires, for example, , 30 minutes to 100 hours.

  After heating the silicon tetrachloride, zinc, and if necessary, the catalyst may be allowed to cool to room temperature, but may be rapidly cooled if necessary.

  Although silicon nanowires are obtained as described above, the obtained silicon nanowires may be washed with, for example, purified water, lower alcohol such as ethanol, and dried, if necessary.

  Silicon nanowires obtained by the production method of the present invention can be suitably used for, for example, photovoltaic power elements for solar cells, negative electrode materials for lithium batteries, and the like.

  Next, the present invention will be described in more detail based on examples. However, the present invention is not limited to such examples.

Example 1
In a glove box filled with high-purity argon gas, liquid silicon tetrachloride [Wako Pure Chemical Industries] is placed in a Pyrex (registered trademark) glass tube (diameter: 10 mm, length: 100 mm) sealed at one end. Yakuhin Kogyo Co., Ltd., purity: 99.9%] 0.2 mL and zinc powder [Wako Pure Chemical Industries, Ltd., purity: 99.9%, particle size: 75-150 μm] 0.4 g were added. .

  Next, after the opening of the glass tube was sealed with a gas burner, it was placed in an electric furnace, the heating temperature was adjusted to 500 ° C. and held for 48 hours. After completion of heating, the glass tube was allowed to cool to room temperature, the upper end of the glass tube was opened, and the powdered product adhering to the inner wall of the glass tube was recovered. The collected powder was washed with distilled water and further washed with ethanol. Subsequently, the powder was dried with warm air, and then the physical properties were examined by the following method.

[X-ray diffraction]
Using a powder X-ray diffractometer (manufactured by Rigaku Corporation, product number: Ultima IV), X-ray diffraction was performed on the obtained powder by irradiating with CuKα rays at a current of 40 mA and a voltage of 40 keV.

[Structural analysis]
The obtained powder was observed with a scanning electron microscope [manufactured by Hitachi, Ltd., product number: S-2600H]. In addition, the obtained powder was identified using an energy dispersive X-ray analyzer [manufactured by Horiba, Ltd., trade name: EMAX ENERGY EX-200].

[Raman spectrum]
The obtained powder is not exposed to the atmosphere, and a micro-Raman spectrum measurement apparatus (manufactured by HORIBA Jobin Yvon Inc., product using He-Ne laser (wavelength: 632.8 nm)) Name: Labram 010], the Raman spectrum of the powder was measured.

  First, the optical photograph of the glass tube before and after heating to 500 degreeC is shown in FIG. In FIG. 1, (a) is an optical photograph of the lower part of the glass tube before heating, and (b) is an optical photograph of the lower part of the glass tube after heating. In the optical photograph (b) at the bottom of the glass tube after heating, liquid silicon tetrachloride and solid zinc powder were changed to black or dark brown powder by heating, but the literature [AT Heitsch, DD Fanfair, H. Tuan and BA Korgel, J. Am. Chem. Soc., 130, 5436 (2008)], since the silicon nanowires are dark brown, the powder may be silicon nanowires. Inferred.

  Further, when the powder X-ray diffraction of the heated powder obtained above was examined, the X-ray diffraction diagram shown in FIG. 2 was obtained. From the result of this X-ray diffraction pattern, it was identified that the powder was a mixture of crystalline silicon and unreacted zinc. From this, it was confirmed that the silicon nanowire was produced | generated by the said heating.

  Next, FIG. 3 shows a scanning electron micrograph of silicon nanowires obtained at the bottom of the glass tube. The powder photographed in this scanning electron micrograph is mainly powder collected from the bottom of the glass tube. As shown in the photograph, the obtained powder includes aggregated particles. It can be seen that nanowire fragments exist. Moreover, it was confirmed from the analysis result by an energy dispersive X-ray analyzer that both the particles and the nanowire are made of silicon.

  Moreover, the optical photograph from the center part of the glass tube after a heating to the bottom part (right direction toward the paper surface) is shown in FIG. From this photograph, it was confirmed that a dark brown powder was formed not only at the bottom but also at the center, and the literature [AT Heitsch, DD Fanfair, H. Tuan and BA Korgel, J. Am. Chem. Soc ., 130, 5436 (2008)], since the nanowires of silicon were dark brown, it was inferred that the powder was silicon nanowires.

When the Raman spectrum of the powder was examined without contacting the powder in the center of the heated glass tube with the atmosphere, the Raman spectrum shown in FIG. 5 was obtained. From this Raman spectrum, an acute peak was observed at a wave number of 518 cm ⁻¹ . It is described in the literature [ID Wolf, Semicond. Sci. Technol., 11, 139 (1996)] that crystalline silicon has a sharp peak when the wave number is about 520 cm ⁻¹ . It was confirmed that the peak was attributed to optical phonons.

  From the above, it was confirmed that crystalline silicon was also generated in the central portion in the longitudinal direction of the glass tube.

  Next, the silicon formed at the center in the longitudinal direction of the glass tube was observed with a scanning electron microscope. The result is shown in FIG. The results show that this silicon is a number of relatively uniform nanowires, unlike the silicon formed at the bottom of the glass tube.

  Further, the EDX spectrum of the nanowire obtained above was examined using an energy dispersive X-ray analyzer. The result is shown in FIG. From the EDX spectrum, it was confirmed that the obtained nanowire was composed of silicon. From this, it can be seen that a large number of silicon nanowires are formed at the center in the longitudinal direction of the glass tube.

  The EDX spectrum shows the presence of zinc and chlorine, which are considered to be by-products generated from zinc chloride.

  Next, the surface state of the silicon nanowire obtained above was observed with a field emission scanning electron microscope (FE-SEM) at a high magnification. The field emission scanning electron micrograph is shown in FIG. As shown in FIG. 8, it can be seen that the silicon nanowire has a diameter of about 300 nm.

Example 2
In Example 1, the same operation as in Example 1 was performed, except that the heating temperature was changed from 500 ° C to 480 ° C. As a result, it was confirmed that silicon nanowires were obtained as in Example 1.

Example 3
In Example 1, the same operation as in Example 1 was performed, except that the heating temperature was changed from 500 ° C to 580 ° C. As a result, it was confirmed that silicon nanowires were obtained as in Example 1.

Example 4
First, 0.004 g of a gold powder (manufactured by Sumitomo Electric Co., Ltd., particle diameter: 20 to 30 nm) was applied inside a glass tube (diameter: 10 mm, length: 100 mm) made of Pyrex (registered trademark) glass. Next, in a glove box filled with high-purity argon gas, 0.2 mL of liquid silicon tetrachloride [manufactured by Wako Pure Chemical Industries, Ltd., purity: 99.9%], zinc powder [Wako Pure Chemical Industries ( Co., Ltd., purity: 99.9%, particle size: 75-150 μm] 0.4 g was added.

  Next, this glass tube was sealed with a gas burner, placed in an electric furnace, and held at 500 ° C. for 48 hours. After completion of heating, the glass tube is allowed to cool to room temperature, the upper end of the glass tube is opened, the powdery substance adhering to the inner wall of the glass tube is recovered, and the recovered powder is washed with distilled water, Washed with ethanol. The powder was dried with warm air, and the physical properties were examined in the same manner as in Example 1.

  The obtained powder was colored brown. This powder was observed with a scanning electron microscope, and a scanning electron microscope (SEM) photograph thereof is shown in FIG. From this result, it was confirmed that this powder was a nanowire having a diameter of 100 nm or less. From this, when silicon nanowires are manufactured in the presence of gold, the diameter is smaller than when silicon nanowires are manufactured in the absence of gold. It can be seen that the diameter of the silicon nanowire can be controlled.

  Moreover, the EDX spectrum was investigated about the obtained nanowire edge part. The result is shown in FIG. From the results shown in FIG. 10, it was confirmed that gold was present at the end.

Example 5
A single crystal silicon wafer [manufactured by Shin Nippon Steel Co., Ltd.] was cut with a diamond cutter, and the obtained single crystal silicon wafer piece (length: 50 mm, width: 5 mm, thickness: 1 mm) was washed with ethanol.

  In a glove box filled with high-purity argon gas, liquid silicon tetrachloride [manufactured by Wako Pure Chemical Industries, Ltd.] is placed in a glass tube (diameter: 10 mm, length: 100 mm) made of Pyrex (registered trademark) glass. , Purity: 99.9%] 0.2 mL, zinc powder [manufactured by Wako Pure Chemical Industries, Ltd., purity: 99.9%, particle size: 75 to 150 μm] 0.4 g and the above-mentioned single crystal silicon wafer piece I put it in.

  Next, this glass tube was sealed with a gas burner, placed in an electric furnace, and held at 500 ° C. for 48 hours. After the heating, the glass tube was allowed to cool to room temperature, the upper end of the glass tube was opened, and the powdery substance adhering to the silicon wafer piece was recovered. The recovered powder was washed with distilled water and then with ethanol, and the powder was dried with warm air.

  Scanning electron microscope (SEM) photographs of nanowires present at the end and center of the silicon wafer piece are shown in FIGS. 11 (a) and 11 (b), respectively. From these photographs, it can be seen that the nanowire generated at the end of the silicon wafer piece has a smaller diameter than the nanowire generated at the center. This is considered due to the fact that the surface of the end portion of the silicon wafer piece is rougher than the center portion of the silicon wafer piece.

  From the above results, high-purity silicon nanowires free from aluminum contamination are produced at low temperatures by heating silicon tetrachloride to a temperature of 450 to 600 ° C. in the presence of zinc in an inert gas atmosphere. You can see that

Claims (6)

  A method for producing silicon nanowires, wherein silicon tetrachloride is heated to a temperature of 450 to 600 ° C in the presence of zinc in an inert gas atmosphere.   The method for producing silicon nanowires according to claim 1, wherein a mixture of silicon tetrachloride and zinc is used.   The method for producing silicon nanowires according to claim 1 or 2, wherein the amount of zinc per mole of silicon tetrachloride is 2 to 5 moles.   The silicon tetrachloride is heated in the presence of at least one catalyst selected from the group consisting of gold, silver, copper, platinum, palladium, nickel, iron, aluminum, gallium, indium, germanium, tin and lead. The manufacturing method of the silicon nanowire in any one of 1-3.   The manufacturing method of the silicon nanowire in any one of Claims 1-4 which heat a silicon tetrachloride in presence of a silicon piece.   The method for producing silicon nanowires according to any one of claims 1 to 5, wherein silicon tetrachloride is heated in a closed system.