JP2008032458A - Hydrogen gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen gas sensor excellent in sensitivity and response, capable of rapidly detecting even a very small amount of a hydrogen gas and developing sufficient durability. <P>SOLUTION: The hydrogen gas sensor is equipped with a meso-porous body 11 with a center pore diameter of 1.5-5.0 nm, the metal components 12 having a hydrogen occluding capacity arranged in the pores of the meso-porous body 11 and the electrode 13 electrically connected to the metal components 12. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a hydrogen gas sensor.

  Recently, various technologies have been developed for practical use of clean energy, and hydrogen gas having a low environmental load has been attracting attention. However, such hydrogen gas is highly explosive and dangerous. Therefore, various hydrogen gas sensors have been studied in order to use hydrogen gas safely.

For example, as such a hydrogen gas sensor, a sensor using a SnO ₂ film (a commercially available product such as “TGS 821” manufactured by Figaro) is known. However, in such a hydrogen gas sensor using a SnO ₂ film, it is necessary to use a sensitive film with a large area in order to increase the sensitivity of hydrogen gas. In order to avoid this, there is a problem that energization heating is required, and standby power consumption increases.

As such a hydrogen gas sensor, a hydrogen gas sensor using a hydrogen storage alloy such as Pd is also known. For example, a hydrogen gas sensor of a type that utilizes bimetallic mechanical deformation utilizing expansion and contraction of a hydrogen storage alloy (such as the hydrogen gas sensor described in Japanese Patent Laid-Open No. 2001-296238 (Patent Document 1)) or a thin film multilayer structure is used. Hydrogen gas sensors of the type that detect tunnel current (Okuyama S, Usami H, Okuyama K, Yamada H, Matsushita K., “Improved response time of Al-Al ₂ O ₃ -Pd tunnel diode AP PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 36 (11), 1997, 6905-69 Page 08, NO.V (see Non-Patent Document 1) is known. However, in the conventional hydrogen gas sensor using the hydrogen storage alloy as described in Patent Document 1 and Non-Patent Document 1, it takes several minutes to detect the hydrogen gas concentration, and the response is not sufficient. It was. Further, in such a conventional hydrogen gas sensor, it is necessary to perform an initialization process for expelling all the stored hydrogen from the hydrogen storage alloy, and it is necessary to perform high-temperature heating (about 400 ° C.) before use.

In addition, hydrogen gas sensors using hydrogen storage alloys such as Pd as nanodots have been studied (Walter EC, Penner RM, Liu H, Ng KH, Zach MP, Fabier F., “Sensors from electrodeposited metal Nanowires”, SURFACE TERFACE. ANALYSIS 34 (1), August 2002, pp. 409-412 (Non-Patent Document 2), and Favier F, Walter EC, Zach MP, Benther T, Penner RM., “Hydrogen sensors and switches flemtrodetromicrodetroelectronics. mesoire arrays ", SCIENCE 293 (5538) .2 Issued on September 21, 001, pages 2227-2231 (non-patent document 3)). A hydrogen gas sensor using such a hydrogen storage alloy as nanodots has a response speed of several seconds and exhibits a sufficient response. However, in the conventional hydrogen gas sensors as described in Non-Patent Documents 2 to 3, performance deterioration due to the collapse phenomenon of dot particles occurs, and there is a problem in durability when repeatedly used.
JP 2001-296238 A Okuyama S, Usami H, Okuyama K, Yamada H, Matsushita K. et al. , "Improved response time of Al-Al2O3-Pd tunnel diode gas sensor, pp. 8-9, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULA PAPERS SH36 V Walter EC, Penner RM, Liu H, Ng KH, Zach MP, Fabier F. , “Sensors from electrodeposited metal Nanowires”, SURFACE AND INTERFACE ANALYSIS 34 (1), August 2002, pp. 409-412 Fabier F, Walter EC, Zach MP, Bender T, Penner RM. , "Hydrogen sensors and switches from electrodeposited palladium mesh arrays", SCIENCE 293 (5538). Published September 21, 2001, pp. 2227-2231

  The present invention has been made in view of the above-described problems of the prior art, is excellent in sensitivity and responsiveness, can be detected quickly even with a small amount of hydrogen gas, and exhibits sufficient durability. An object of the present invention is to provide a hydrogen gas sensor that can be used.

  As a result of intensive studies to achieve the above object, the inventors of the present invention have a mesoporous material having a central pore diameter of 1.5 to 5.0 nm and are arranged in the pores of the mesoporous material. By providing a metal having hydrogen storage capacity and an electrode electrically connected to the metal, it has excellent sensitivity and responsiveness, and can detect even a small amount of hydrogen gas quickly. The inventors have found that a hydrogen gas sensor capable of exhibiting sufficient durability can be obtained, and have completed the present invention.

  That is, the hydrogen gas sensor of the present invention includes a mesoporous material having a central pore diameter of 1.5 to 5.0 nm, a metal having a hydrogen storage capacity arranged in the pores of the mesoporous material, and the metal And an electrode electrically connected to the electrode.

  In the hydrogen gas sensor according to the present invention, it is preferable that the metal has a quantum dot array structure in which the metal is arrayed at the same period as the periodic structure of the pores of the mesoporous material.

  In addition, the hydrogen gas sensor according to the present invention preferably detects hydrogen gas from the magnitude of the tunnel current, since the electrical characteristics change due to expansion of the metal due to hydrogen storage.

In the hydrogen gas sensor according to the present invention, the metal preferably has a lattice constant that changes by 1 to 50% due to hydrogen storage,
Moreover, as a hydrogen gas sensor concerning the said invention, it is preferable that the said metal can occlude 1-5 mass% hydrogen.

  The reason why the hydrogen gas sensor of the present invention has excellent sensitivity and responsiveness, can detect even a small amount of hydrogen gas quickly, and can exhibit sufficient durability. Although not necessarily certain, the present inventors infer as follows. That is, first, in the hydrogen gas sensor of the present invention, a mesoporous material is used as a base, a metal having a hydrogen storage capacity is introduced into the pores of the mesoporous material, and metal particles (quantum dots) are introduced into the pores. Array. Therefore, in the present invention, quantum dots having a diameter of several nanometers are regularly arranged in the same period as the periodic structure of the pores in the pores of the mesoporous material having a central pore diameter of 1.5 to 5.0 nm. A quantum dot array structure is formed. When such a hydrogen gas sensor is placed in the presence of hydrogen gas, hydrogen storage of a metal (quantum dot) having a hydrogen storage capacity occurs, and the diameter of the quantum dot increases. Further, when the diameter of the quantum dot increases, the distance between adjacent quantum dots is reduced, and a tunnel current flows between the quantum dots. Such a tunnel current changes sensitively depending on the distance between quantum dots. Therefore, in the hydrogen gas sensor of the present invention, even if the amount of hydrogen gas is very small, an increase in current depending on the concentration is observed, so that the hydrogen gas can be detected with high sensitivity. As described above, in the present invention, hydrogen gas can be detected based on the magnitude of the measured tunnel current. In addition, since the hydrogen gas sensor of the present invention can detect hydrogen gas by a change in tunneling current due to a hydrogen occlusion phenomenon, the hydrogen gas is present in a plurality of types of gases (such as in the atmosphere). It is also possible to selectively detect hydrogen gas.

  In the hydrogen gas sensor of the present invention, since the metal is arranged in the pores of the mesoporous material, the size of the quantum dot is small. Therefore, in the presence of hydrogen gas, the hydrogen gas itself is taken in and out at high speed. Therefore, in the present invention, hydrogen gas can be detected at a sufficient response speed.

  Furthermore, the hydrogen gas sensor of the present invention has improved durability compared to conventional hydrogen gas sensors (Non-Patent Documents 2 to 3 and the like). The reason why the durability is improved in this way is presumed as follows. That is, in a conventional hydrogen gas sensor using a hydrogen storage alloy as nanodots, the nanodots are formed by vapor deposition and have a diameter of about 100 nm. However, nanodots with such diameters store and desorb hydrogen. Along with this, expansion and contraction occurred, and the particles were broken into smaller particles by the generated stress. Therefore, in the conventional hydrogen gas sensor, the performance of the sensor deteriorates and sufficient durability cannot be obtained. On the other hand, in the hydrogen gas sensor of the present invention, the quantum dot formed by the metal has a small diameter of 5 nm or less and a small volume change amount, and the quantum dot is confined in the silica pore. It is sufficiently suppressed that the dots collapse due to stress or the like. Therefore, in the present invention, it is presumed that performance is hardly deteriorated and sufficient durability can be exhibited.

  In the hydrogen gas sensor of the present invention, the performance of the sensor can be easily fine-tuned by adjusting the diameter of the quantum dots and the wall thickness of the mesoporous material used. For example, under conditions where there is no hydrogen gas, the hydrogen gas sensor can be in an insulated state or a state close thereto, and standby power consumption can be sufficiently reduced. Further, in the conventional hydrogen gas sensor using a metal having hydrogen storage ability, since the metal having hydrogen storage ability has a slight catalytic action, malfunction due to autocatalytic action on carbohydrate-based gas and water vapor has occurred. However, in the present invention, the diameter of the quantum dots and the wall thickness of the mesoporous material to be used can be easily adjusted, so that such a malfunction can be sufficiently suppressed.

  According to the present invention, it is possible to provide a hydrogen gas sensor that has excellent sensitivity and responsiveness, can detect even a small amount of hydrogen gas quickly, and can exhibit sufficient durability. It becomes.

  And the hydrogen gas sensor of the present invention can easily fine-tune its performance by adjusting the diameter of the quantum dots and the wall thickness of the mesoporous material, so that standby power consumption can be made sufficiently small. In addition, the malfunction can be sufficiently suppressed.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

  The hydrogen gas sensor of the present invention includes a mesoporous material having a central pore diameter of 1.5 to 5.0 nm, a metal having hydrogen storage ability arranged in the pores of the mesoporous material, and an electric current connected to the metal. It is characterized by providing the electrode connected electrically.

(Mesoporous material)
The mesoporous material used in the present invention is a porous material having pores (also referred to as mesopores) having a central pore diameter of 1.5 to 5.0 nm (more preferably 2.5 to 3.5 nm). Therefore, any porous material having such mesopores can be used. If the center pore diameter of such a mesoporous material is less than 1.5 nm, the crystal growth of the metal cannot be performed inside the mesopore. On the other hand, if it exceeds 5.0 nm, the periodicity of the mesopore deteriorates and the quantum The barrier between dots is not constant and the sensor does not operate.

  Further, as such a mesoporous material, 60% or more of the total pore volume is included in the diameter range of ± 40% of the pore diameter (center pore diameter) showing the maximum peak in the pore diameter distribution curve. It is preferable to use a mesoporous material. The pore diameter distribution curve of the mesoporous material refers to a curve obtained by plotting the value (dV / dD) obtained by differentiating the pore volume (V) by the pore diameter (D) against the pore diameter (D). The pore size distribution curve is created, for example, by the gas adsorption method shown below. The most commonly used gas in this method is nitrogen. First, nitrogen gas is introduced into a sample as an adsorbent at a liquid nitrogen temperature (−196 ° C.), and the amount of adsorption is determined by a constant volume method or a weight method. An adsorption isotherm is created by gradually increasing the pressure of the introduced nitrogen gas and plotting the amount of nitrogen gas adsorbed against each equilibrium pressure. From the adsorption isotherm, the pore size distribution is obtained by using, for example, a Cranston-Inklay method or a Polimore-Heal method.

  The mesoporous material used in the present invention has one or more peaks at a diffraction angle corresponding to a d value of 1 nm or more (more preferably 2.0 to 5.0 nm) in the X-ray diffraction pattern. Is preferred. The X-ray diffraction peak means that a periodic structure having a d value corresponding to the peak angle is present in the sample. The X-ray diffraction pattern reflects a structure in which pores having a diameter of 1.5 to 5.0 nm are regularly arranged at intervals of 1 nm or more. That is, it can be said that the mesoporous material having such a diffraction pattern has a uniform pore diameter due to the regularity of the structure indicated by the diffraction pattern. When such a d value is less than the lower limit, the thickness of the barrier layer between the quantum dots in the obtained hydrogen gas sensor becomes small, so that it cannot be in an insulating state during standby, and standby power consumption tends to increase. On the other hand, if the upper limit is exceeded, even if the metal expands due to the occlusion of hydrogen, the thickness between the barriers is large and the tunnel current hardly flows, so the performance of the obtained hydrogen gas sensor tends to deteriorate.

  Furthermore, the shape of the pores of the mesoporous material used in the present invention is preferably a three-dimensionally bonded box-shaped pore. By using a mesoporous material having such a pore shape, quantum dots can be formed in the pores, thereby obtaining a hydrogen gas sensor with higher performance.

  Moreover, the arrangement state (pore arrangement structure) of the pores in the mesoporous material used in the present invention is not particularly limited, and has, for example, a hexagonal pore arrangement structure such as 2D-hexagonal or 3D-hexagonal. Alternatively, it may have a cubic or disordered pore arrangement structure. Here, that the silica-based mesoporous material has a hexagonal pore arrangement structure means that the arrangement of the pores of the silica-based mesoporous material is a hexagonal structure (S. Inagaki et al., J. Chem. Soc., Chem. Commun., 680, 1993; see S. Inagaki et al., Bull. Chem. Soc. Jpn., 69, 1449, 1996; ).

  In addition, that the mesoporous material has a cubic pore arrangement structure means that the arrangement of the pores in the mesoporous material is a cubic structure (JC Vartuli et al., Chem. Mater.,). 6, 2317, 1994; see Q. Huo et al., Nature, 368, 317, 1994). When the mesoporous material has a disordered pore arrangement structure, it means that the arrangement of the pores is irregular (P. T. Tanev et al., Science, 267, 865, 1995; S A. Bagshaw et al., Science, 269, 1242, 1995; R. Ryoo et al., J. Phys. Chem., 100, 17718, 1996).

  When the mesoporous material has a regular pore arrangement structure such as hexagonal or cubic, all of the pores do not have to have these regular pore arrangement structures. That is, the mesoporous material may have both a regular pore arrangement structure such as hexagonal and cubic and a disordered irregular pore arrangement structure. However, it is preferable that 80% or more of all the pores have a regular pore arrangement structure such as hexagonal or cubic.

  In addition, as such a mesoporous material, a silica-based mesoporous material is preferable from the viewpoint of high electrical insulation. In addition to silica, the composition of such a mesoporous material includes silica-aluminum (Al), titanium (Ti), magnesium (Mg), zirconium (Zr), molybdenum (Mo), cobalt (Co), nickel (Ni), gallium (Ga), beryllium (Be), yttrium (Y), lanthanum (La), tin (Sn), lead (Pb), vanadium (V), boron (B), etc. Good.

  The shape of such a mesoporous material is not particularly limited, but it is preferable to use a membranous material. Below, the suitable manufacturing method for manufacturing such a membranous mesoporous material will be described.

  As a suitable manufacturing method for manufacturing such a membranous mesoporous material, for example, a method of manufacturing a mesoporous material using alkoxysilane can be mentioned. As a method using such an alkoxysilane, there is a method in which a composite liquid of an alkoxysilane and a surfactant is coated on a substrate and solidified to form a mesoporous material precursor, which is then fired.

  As such an alkoxysilane, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, alkylalkoxysilane such as methyltrimethoxysilane, or the like is used. One type or a combination of two or more types can be used.

As the surfactant, a compound having an alkyl group and a hydrophilic group is used. As the alkyl group, those having 2 to 18 carbon atoms are preferable. Examples of the hydrophilic group include N ⁺ , NH ₂ , NO, OH, and COOH. Specifically, as the surfactant, the following general formula (1)
C _n H _{2n + 1} N (CH ₃ ) ₃ X (1)
(In the formula, n is an integer of 2 to 18, and X represents a halide ion such as chloride ion or bromide ion, or an organic anion such as HSO ₄ or acetate ion.)
There are alkyltrimethylammonium, alkylalcohol, fatty acid and the like represented by

  The method for preparing the composite liquid is not particularly limited. First, a small amount of water (0.5 to 10 mol of water relative to 1 mol of Si) is added to the alkoxysilane, and then at room temperature for several minutes to about 3 hours. It is preferable to employ a preparation method in which a surfactant is added after stirring. At this time, it is preferable to add a small amount of acid as a pH adjuster. Thus, by adding an acid, each component melt | dissolves and it exists in the tendency which can prepare a uniform solution. Moreover, it is preferable to adjust pH of the said complex liquid in the range of 1-4. Further, dilute hydrochloric acid (for example, 2N) can be suitably used as the acid, but other acids such as nitric acid and sulfuric acid may be used. The surfactant may be added as a powder, but may be added after being dissolved in a small amount of water.

Further, it is preferable that _H 2 O / Si molar ratio in the composite liquid is 1 to 10. Here, the “H ₂ O / Si molar ratio in the raw material” indicates the ratio of the Si raw material to the total amount of water added to the composite liquid. When the H ₂ O / Si molar ratio in the composite liquid exceeds 10, for example, a gap between metal oxide fine particles generated by hydrolysis and condensation of silane alkoxide becomes large, and as a result, On the other hand, when the ratio is less than 1, the silane alkoxide is not hydrolyzed, and as a result, the mesoporous material tends not to be obtained.

  Furthermore, the addition amount of the surfactant is preferably 1 to 10 mol with respect to 1 mol of Si in the composite liquid. When the amount of the surfactant added exceeds the upper limit, surplus surfactant that does not contribute to the formation of the mesoporous material tends to be mixed in the sample. On the other hand, when the amount is less than the lower limit, it does not contribute to the formation of the mesoporous material. Excess Si is mixed, and the silica layer becomes thick and the pore volume tends to decrease. The solution prepared as described above is coated on a substrate, and when left standing, the whole is gradually solidified and a mesoporous material precursor is obtained.

  A method for coating such a composite liquid on the substrate is not particularly limited, and a known method can be appropriately employed, and a spin coating method, a casting method, a dip coating method, or the like can be employed.

  In addition, the surfactant can be removed by firing the obtained mesoporous precursor. In such a firing method, the mesoporous material precursor is heated in the range of 300 ° C to 1000 ° C, preferably in the range of 400 to 700 ° C. The heating time may be 30 minutes or longer, but it is preferable to heat for 1 hour or longer to completely remove the organic components. In addition, air may be circulated in the heating atmosphere, but since a large amount of combustion gas is generated, an inert gas such as nitrogen may be circulated in the early stage of combustion.

  Moreover, as another suitable manufacturing method for manufacturing the membranous mesoporous material as described above, a method of synthesizing a mesoporous material using a layered silicate can be mentioned.

  In such a synthesis method, first, a layered silicate is dispersed in a solvent in which a surfactant is dissolved to obtain a dispersion solution.

As such a layered silicate, for example, kanemite (NaHSi ₂ O ₅ .3H ₂ O) is preferable. Other layered silicates include sodium disilicate crystals (α, β, γ, δ-Na ₂ Si ₂ O ₅ ), macatite (Na ₂ Si ₄ O _9).
5H ₂ O), ialite (Na ₂ Si ₈ O ₁₇ · xH ₂ O), magadiite (Na ₂ Si ₁₄ O ₂₉ · xH ₂ O), kenyaite (Na ₂ Si ₂₀ O ₄₁ · xH ₂ O), etc. Representative. As another layered silicate, for example, a layered silicate obtained by treating a clay mineral such as sepiolite with an acid aqueous solution to remove elements other than silicon dioxide can be used. Typical clay minerals in this case include montmorillonite, vermiculite, mica, kaolinite, and smectite in addition to sepiolite, but these can be used without limitation. In the method for synthesizing the mesoporous material from the layered silicate, water glass, sodium silicate, Si alkoxide, silica, or the like may be used instead of the layered silicate.

  Examples of the surfactant include chlorides, bromides, iodides and hydroxides of alkyltrimethylammonium, dimethylalkylammonium, alkylammonium and benzylammonium. Further, water is preferable as the solvent, but a water-alcohol mixed solvent and other solvents can also be used. The concentration of the surfactant in such a solvent is preferably 0.05 mol / L to 1 mol / L.

  Further, the content of the layered silicate in such a solvent varies depending on the type of the layered silicate used. For example, when kanemite is used, the amount of the aqueous solution of the 0.1 mol / L surfactant is 1000 ml. The amount is preferably 5 to 200 g.

  Next, the obtained dispersion solution is coated on a substrate and heated and dried at 30 to 150 ° C., and then baked at a temperature of 550 ° C. or higher, or treated with a hydrochloric acid / ethanol mixed solution to form crystals. The incorporated surfactant is removed, and a mesoporous material is generated on the substrate. As a method for coating on the substrate, a method similar to the method described in the above-described method using alkoxysilane can be employed.

  The heating time for drying is preferably about 1 to 24 hours. In such heating, it is preferable to stir the dispersion while heating. In such heat drying, it is preferable to adjust the pH of the dispersion solution to 10 or more for 1 to 5 hours from the start of heating, and to adjust the pH of the dispersion solution to 10 or less for the remaining heating time. . When adjusting the pH, for example, when kanemite is used as the layered silicate, the kanemite is alkaline, so the pH of the dispersion solution is 10 or more without any action, but other layered silicates other than kanemite may be used. When the pH does not become 10 or higher, an alkali such as sodium hydroxide can be added to adjust the pH to 10 or higher. By controlling the pH as described above, a highly crystalline mesoporous material can be obtained.

  Furthermore, the firing is preferably performed for 1 hour or longer in an atmosphere of air, oxygen, nitrogen or the like. Moreover, the above-mentioned hydrochloric acid / ethanol mixed solution in the above step is merely an example, and a mixed solution of an acid and an organic solvent other than this combination can be used as long as it is a mixed solution of an acid / organic solvent combination.

  In the method for producing a mesoporous material as described above, the length of the hydrophobic portion including the alkyl chain of the surfactant is changed by changing the type of the surfactant used. It is possible to control the pore diameter of the mesoporous material to be produced, and thereby the mesoporous material having a central pore diameter of 1.5 to 5.0 nm used in the present invention can be produced.

(Metal with hydrogen storage capacity)
In the present invention, the metal arranged in the pores of the mesoporous material has hydrogen storage capacity. Such a metal is not particularly limited as long as it has hydrogen storage capacity, and may be composed of a single metal element or an alloy. Examples of such a metal, e.g., palladium, vanadium, other such as magnesium, titanium-based alloy (Ti-Fe-based alloy, Ti-Ni based alloys, Ti-V alloys, etc.), Mg-based alloys _(Mg 2 -Ni And rare earth-based AB ₅ type alloys (LaNi ₅ alloy and the like). Among these metals, Pd, LaNi ₅ , TiVCr, and TiVMn are preferable, and Pd and LaNi ₅ are particularly preferable from the viewpoint of chemical stability and selectivity from other types of gases.

  Moreover, as such a metal which has hydrogen storage ability, it is preferable that a lattice constant changes 1 to 50% by hydrogen storage, and it is more preferable that it changes 5 to 20%. If the amount of change in the lattice constant is less than the lower limit, the metal does not deform much (e.g., expands) when occluded hydrogen, so it tends to be difficult to recognize the magnitude of the tunnel current with high sensitivity. On the other hand, if the upper limit is exceeded, the metal itself tends to be easily broken by stress.

  Furthermore, although it does not restrict | limit especially as a metal which has such a hydrogen occlusion ability, It is preferable that it is a metal which can occlude 1-5 mass% (more preferably 1-3 mass%) hydrogen. If the ratio of the amount of hydrogen that can be stored in the metal is less than the lower limit, the hydrogen gas detection sensitivity tends to be outside the practical range.On the other hand, if the upper limit is exceeded, the metal particles collapse and long-term stability can be maintained. It tends to disappear.

(electrode)
The electrode according to the present invention is electrically connected to the metal. The shape of the electrode is not particularly limited, and an electrode appropriately manufactured by a known method can be used. Further, the material of such an electrode is not particularly limited, and a known material capable of constituting the electrode can be appropriately used. For example, aluminum, aluminum silicon alloy, aluminum silicon copper alloy, titanium, nickel, cobalt Platinum, gold, etc. can be used.

(Hydrogen gas sensor)
The hydrogen gas sensor of the present invention includes the mesoporous material, the metal, and an electrode that is electrically connected to the metal.

  In the hydrogen gas sensor of the present invention, the mesoporous material is used as a base, metal particles are generated in the pores of the mesoporous material, and metal (quantum dots) are arranged in the pores. It has a unique arrangement structure depending on the periodic structure of the pores of the mesoporous material, and the electrical characteristics change due to the expansion of the metal due to hydrogen absorption, and it becomes possible to detect hydrogen gas. And as such a hydrogen gas sensor, it is preferable that an electrical characteristic changes with expansion | swelling by the hydrogen occlusion of the said metal, and can detect hydrogen gas from the magnitude of a tunnel current. Thus, by detecting the hydrogen gas based on the magnitude of the tunnel current resulting from the hydrogen storage of the metal, the hydrogen gas can be detected with excellent sensitivity and sufficient response speed. Gas can be selectively detected. In addition, the apparatus, method, etc. which detect the above-mentioned change etc. of an electric current are not restrict | limited in particular, A well-known apparatus and method can be employ | adopted suitably.

  Moreover, as such a hydrogen gas sensor, it is preferable that the quantum dot formed with the said metal forms the quantum dot arrangement | sequence structure arranged with the period similar to the periodic structure of the pore of the said mesoporous body. Thus, when a quantum dot array structure arranged in a mesoporous material is formed, a higher quantum effect can be obtained, and thus hydrogen gas tends to be detected with higher sensitivity.

  Hereinafter, preferred embodiments of the hydrogen gas sensor of the present invention as described above will be described in detail with reference to the drawings. In the following description and drawings, the same or corresponding elements are denoted by the same reference numerals, and duplicate descriptions are omitted.

  FIG. 1 is a schematic longitudinal sectional view showing the structure of a preferred embodiment of the hydrogen gas sensor of the present invention. The hydrogen gas sensor 1 shown in FIG. 1 basically includes a mesoporous material 11, a metal 12, an electrode 13, a substrate 20, and a thin film 21a. Further, in the hydrogen gas sensor 1 shown in FIG. 1, the mesoporous material 11 is disposed on the thin film 21 a formed on the substrate 20, and the metal 12 is arranged in the pores of the mesoporous material 11. Yes. Furthermore, in the hydrogen gas sensor 1 shown in FIG. 1, the quantum dots formed by the metal 12 are arranged with the same period as the periodic structure of the pores of the mesoporous body 11 to form a quantum dot array structure. In the hydrogen gas sensor 1 shown in FIG. 1, the mesoporous material 11 is disposed so as to be sandwiched between two electrodes 13, and the metal 12 and the electrode 13 are electrically connected.

  As the mesoporous material 11, the metal 12, and the electrode 13, the aforementioned mesoporous material, metal, and electrode are used, respectively. Furthermore, it does not restrict | limit especially as the board | substrate 20, The well-known board | substrate used for such a hydrogen gas sensor can be used suitably.

  The thin film 21a is not particularly limited, and for example, a thin film (for example, USG film, SiN film, etc.) formed of a known material as a material used for a surface protection film of a hydrogen gas sensor can be appropriately used. . In addition, the thin film 21a is preferably a non-porous film in which when the mesoporous material 12 is covered with this, the outside and the pores of the mesoporous material cannot be communicated with each other. Moreover, as such a thin film, a film | membrane with high adhesiveness with a mesoporous body is preferable.

  Further, the thickness of the film formed of the mesoporous material 11 is preferably about 50 to 300 nm, although it varies depending on the structure of the sensor to be manufactured. If the thickness of such a film is less than the lower limit, a continuous film is not formed, so that elements cannot be formed, and the yield of the sensor tends to decrease. On the other hand, if the upper limit is exceeded, cracks are likely to occur in the film due to stress. There is a tendency.

  The thickness of the thin film 21a varies depending on the structure of the sensor to be manufactured, but is preferably about 300 to 600 nm. If the thickness of the film is less than the lower limit, background noise due to charging of the substrate tends to increase. On the other hand, if the thickness exceeds the upper limit, a strain force tends to be easily applied to the element portion due to the stress of the film. .

  Next, a preferred method for producing the hydrogen gas sensor of the present invention will be described with reference to the drawings.

  First, the thin film 21a is formed on a predetermined substrate (not shown), the film of the mesoporous material 11 is formed on the thin film 21a, and the laminated body in which the mesoporous material is laminated on the thin film shown in FIG. 2 is formed. Let me. The method for forming such a thin film 21a is not particularly limited, and a known method can be adopted as appropriate, and a method for forming a dense film by an SOG method or a CVD method having a high leveling effect can be preferably used. it can. Moreover, as a formation method of the mesoporous body 11, a suitable manufacturing method for manufacturing the above-described mesoporous body can be employed.

  Next, the thin film 21b is formed on the surface of the mesoporous material 11 obtained in this way, and the surface layer-formed wafer shown in FIG. 3 is obtained. Such a thin film 21b is the same as the above-mentioned thin film 21a. Thus, by covering the porous body with the thin film 21a and the thin film 21b, the pores of the porous body cannot communicate with the outside. In addition, the method similar to the formation method of the above-mentioned thin film 21a is employable as the method of forming such a thin film 21b.

  Next, the thin film 21b on the surface and the mesoporous material 11 are etched to form contact holes that allow communication between the outside and the pores of the mesoporous material, thereby obtaining a contact hole-formed wafer shown in FIG.

In such etching, it is possible to employ a method of forming a predetermined pattern using a predetermined stepper and then performing etching using this as a mask. Moreover, it does not restrict | limit especially as an etching method, A well-known method can be employ | adopted suitably, for example, reactive ion etching can be employ | adopted. When such reactive ion etching is employed, for example, CF ₄ , CHF ₃ , CCl ₄ or the like can be employed as an etching gas.

  In the case of using such an ion etching method, various conditions such as the magnitude of electric power to be input, the gas pressure during the reaction, and the gas flow rate of the reaction gas depend on the type of apparatus used and the state of the thin film to be etched. . Under the optimum conditions such as gas pressure, the shape of the contact hole has good verticality with almost vertical walls. In the final step of the etching process, the 02 ashing process is performed to remove precipitates protecting the etching wall, so that the deposits attached to the side walls can be removed and the inner surface of the pores can be modified. Can do. In such processing, it is possible to modify the contact hole to a certain distance by taking a specific processing time.

  The diameter of the contact hole formed in this way is not particularly limited, and the diameter is preferably about 10 to 50000 nm. If the diameter of the contact hole is less than the lower limit, it is difficult to supply a sufficient amount when supplying a raw material solution described later.

  Next, using the contact hole formed in the wafer as a raw material compound supply port, the raw material compound is introduced from the contact hole into the pores of the mesoporous material 11 to generate metal in the pores.

  Although it does not restrict | limit especially as such a raw material compound, For example, the metal salt (for example, palladium chloride) or complex salt (for example, diethyl palladium, dimethyl palladium) containing the above-mentioned metal can be used conveniently.

  Moreover, such a raw material compound is preferably dissolved in water or an organic solvent and introduced into the pores as a raw material solution. As such an organic solvent, for example, ethanol, methanol, dioxane and the like can be used.

  Further, when the raw material compound is introduced into the pores of the mesoporous material 11, the raw material solution is injected into the contact hole. By injecting the raw material solution into the contact hole in this manner, the raw material solution is diffused into the pores of the mesoporous material by the capillary phenomenon to the nanopores.

  The capillary phenomenon is a phenomenon in which the water surface rises or falls in the liquid when a capillary is erected in the liquid. By utilizing this phenomenon in the present invention, the raw material solution is densely contained in the pores of the mesoporous material. Can be introduced.

Further, when introducing such a raw material solution, it is preferable to evacuate. By evacuating in this way, adsorbates such as water components, various gases, and organic components adsorbed in the pores can be removed, and the raw material solution can be diffused more efficiently into the pores. Tend to be possible. Furthermore, the pressure during the evacuation is not particularly limited, but is preferably 10 ⁻² torr or less.

  After introducing the raw material solution into the pores of the porous body in this way, metal particles are generated in the pores by treatment using heat, light, γ rays, or the like. In the present invention, the method and conditions for producing a metal from a raw material compound are appropriately selected according to the type of the raw material compound, but when employing a method of treating a raw material solution with heat, for example, air, nitrogen, A method of treating by heating at 200 to 600 ° C. for 1 to 5 hours in an air stream such as hydrogen or in a vacuum can be employed.

  In addition, when adopting a method of processing a raw material solution using light, for example, a method of performing light irradiation for 10 minutes to 3 hours using a high-pressure mercury lamp or the like while cooling after vacuum degassing is adopted. it can. In such light irradiation, it is preferable to introduce alcohol vapor such as 2-propanol, water vapor, carbon monoxide (CO), or the like as a reducing gas. By introducing such a reducing gas, the reducing gas diffuses anisotropically, so that crystal growth in a certain direction tends to be more reliably performed. Furthermore, when adopting a method of performing treatment using γ-rays, it is preferable to perform γ-ray irradiation for 1 to 100 hours after vacuum degassing. In addition, carbon monoxide is introduced during the γ-ray irradiation. It is preferable.

Furthermore, among the methods of treating a raw material solution using such heat, light, γ-rays, etc., using a method of treating using a light allows a metal to be formed more uniformly and at a high density. Particularly preferred. Moreover, in the method of processing using such light, the light applied to the mesoporous material is preferably ultraviolet light, more preferably 140 to 360 nm, and 200 to 300 nm. It is particularly preferred. As a light source for irradiating such light, a UV lamp or a laser can be used in addition to the above-mentioned light source. Further, as the light intensity of the irradiated light is preferably 1~200mW / cm ^2, more preferably 5~20mW / cm ^2. By irradiating with light, active H radicals can be generated, and the metal ions in the raw material solution introduced into the pores are reduced to zero-valent metal by the strong reducing action of the H radicals, Metals can be generated within the pores.

  Next, the electrode 13 is formed on the wafer in which metal is generated in the pores of the mesoporous material (FIG. 5). A method for forming such an electrode 13 is not particularly limited, and a known method for forming an electrode can be appropriately employed. For example, the electrode material as described above is deposited on the wafer to form an electrode material. After forming this film, after forming a predetermined pattern using a predetermined stepper, a method of forming an electrode by performing a reactive ion etching process can be employed.

  And after forming an electrode in this way, the hydrogen gas sensor of a structure as shown in FIG. 1 can be obtained by removing the thin film 21b of the exposed part. The method for removing the thin film 21b is not particularly limited, and a known method capable of removing the formed thin film 21 (for example, a method employing a reactive ion etching process) can be appropriately employed. .

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

(Example 1)
First, a p-type silicon wafer having 100 Ω · cm conductivity was used as a substrate, and a USG (Undoped Silica Glass) film having a thickness of 1 μm was formed on the substrate by a CVD method.

Next, a composite liquid of tetramethoxysilane (TMOS), a surfactant used as a template for forming nanopores and water is uniformly applied on the USG film by a dip coating method, and this is applied at a temperature condition of 100 ° C. Then, a mesoporous film was formed on the USG film by drying for 24 hours at 500 ° C. for 2 hours. As such a surfactant, alkyltrimethylammonium chloride (C18-TMACl) having a linear alkyl group having 18 carbon atoms was used. In the composite liquid, the amount of tetramethoxysilane added is such that the molar ratio of all Si and H ₂ O contained in the composite liquid (Si: H ₂ O) is 1: 2. The surfactant was prepared so that the amount of the surfactant added was 0.1 mol of the surfactant relative to 1 mol of Si contained in the composite liquid. The mesoporous film thus obtained was a mesoporous film having a cubic structure and a pore having a central pore diameter of 3.2 nm.

  Next, a surface USG film (thickness: 200 nm) having no nanopores was formed on the mesoporous film by a CVD method to obtain a wafer. In this way, access to the pores of the mesoporous material from the outside was made impossible.

Next, after forming a pattern on the wafer using a stepper, reactive ion etching (RIE) is performed to simultaneously etch the surface USG film of the wafer and the mesoporous film, and the raw material is formed on the wafer. A contact hole capable of supplying the solution was formed. For such pattern formation, a positive resist used in a normal silicon semiconductor process was used as a mask, and an I-line stepper (FPA 2500 manufactured by Canon) was used as the stepper. In the reactive ion etching, CF ₄ gas was used as an etching gas. In the final step of such etching, 02 ashing was performed in order to remove precipitates protecting the etching wall.

Next, a raw material solution (10 mass% palladium chloride solution) was injected into the contact hole formed in the wafer, and the palladium chloride solution was introduced into the pores of the mesoporous material in the wafer by capillary action. In addition, before injecting such a raw material solution, in order to remove moisture in the pores, a vacuum was drawn (1 × 10 ⁻² Torr) for one day and the palladium chloride solution was introduced. Maintained a vacuum state (1 × 10 ⁻² Torr). Further, after the palladium chloride solution was introduced into the pores of the mesoporous material in this way, the surface was washed with methanol to hold the raw material solution in the pores.

  Next, in a state in which the raw material solution was introduced into the pores of the mesoporous material, vacuum was further applied for 24 hours, methanol was introduced into the pores as a reducing gas, and UV lamp light (263 nm) was applied to the entire wafer. ), Crystal growth was performed in the pores to generate Pd metal particles, and a wafer on which Pd quantum dots were formed was manufactured. The thickness of the barrier layer (insulating layer) formed by the mesoporous material between the Pd quantum dots was 2.5 nm.

  Next, metal aluminum was vapor-deposited on the wafer on which the Pd quantum dots had been formed to a thickness of 400 nm to form a positive resist pattern, and then an RIE process was performed by a dry process to place electrodes. Thereafter, the exposed USG film on the surface was removed by RIE, and a hydrogen gas sensor having a joining surface of Al / Pd / Al was obtained by making the inside and outside of the mesoporous body accessible.

<Confirmation of hydrogen gas sensor structure>
In order to confirm the structure of the hydrogen gas sensor obtained as described above, the wafer at the stage where Pd metal was produced was observed with a transmission electron microscope. The obtained transmission electron microscope image is shown in FIG. As is clear from the transmission electron microscope image shown in FIG. 6, it was confirmed that nano-sized Pd metal particles were generated.

<Characteristic test 1 of hydrogen gas sensor>
In order to confirm the characteristics of the hydrogen gas sensor obtained in Example 1, the current change was made by changing the concentration of hydrogen gas in the atmosphere from 0 to 2000 ppm with a constant voltage of 200 mV applied to both ends of the electrode of the hydrogen gas sensor. Was measured. A graph of the change in current obtained is shown in FIG.

  As a result of such measurement, when the hydrogen gas concentration is in the range of 0 to 1000 ppm, an increase in current proportional to the hydrogen gas concentration is observed, and in the range exceeding about 1000 ppm, the current is saturated and remains saturated. It was. From these results, it was confirmed that the hydrogen gas sensor of the present invention can detect hydrogen gas by a change in tunnel current. Moreover, in the hydrogen gas sensor of this invention, even if hydrogen gas was trace amount (for example, 0-1000 ppm), since the change of an electric current was detectable, it was confirmed that hydrogen gas can be detected with sufficient sensitivity.

<Characteristic test 2 of hydrogen gas sensor>
In order to confirm the characteristics of the hydrogen gas sensor obtained in Example 1, first, in a state where a constant voltage of 200 mV was applied to both ends of the electrode of the hydrogen gas sensor, a gas not containing hydrogen gas was charged for 15 seconds and the hydrogen gas was set to 0. The gas containing 1% by volume was alternately flowed at intervals of 15 seconds, the supply of hydrogen gas was turned on and off, and the change in current was measured. The graph of the change of the obtained electric current is shown in FIG.

  As is clear from the results shown in FIG. 8, it was confirmed that the hydrogen gas sensor of the present invention can detect hydrogen gas with sufficient sensitivity from the change in current. Further, since hydrogen gas was detected at a response speed of about 1 second, it was confirmed that the hydrogen gas sensor of the present invention was excellent in responsiveness.

  As described above, according to the present invention, the hydrogen gas sensor is excellent in sensitivity and responsiveness, can be detected quickly even with a small amount of hydrogen gas, and can exhibit sufficient durability. Can be provided.

  Therefore, since the hydrogen gas sensor of the present invention is excellent in sensitivity and responsiveness, it is particularly useful as a sensor that detects leakage of hydrogen gas from, for example, an energy system using a fuel cell as a power source.

It is a schematic longitudinal cross-sectional view which shows the structure of suitable one Embodiment of the hydrogen gas sensor of this invention. It is a schematic longitudinal cross-sectional view which shows the structure of suitable one Embodiment of the laminated body which laminated | stacked the mesoporous body on the thin film. It is a schematic longitudinal cross-sectional view which shows the structure of suitable one Embodiment of the wafer in which the surface layer was formed. It is a schematic longitudinal cross-sectional view which shows the structure of suitable one Embodiment of the wafer in which the contact hole was formed. It is a schematic longitudinal cross-sectional view which shows the structure of suitable one Embodiment of the wafer in which the electrode was formed. It is a transmission electron micrograph of the wafer of the stage which produced | generated Pd metal. It is a graph which shows the relationship between the electric current which flows into the hydrogen gas sensor of this invention, and the density | concentration of hydrogen gas in atmosphere. It is a graph which shows the change of the electric current when supply of hydrogen gas is turned on and off to the hydrogen gas sensor of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Hydrogen gas sensor, 11 ... Mesoporous body, 12 ... Metal (quantum dot), 13 ... Electrode, 20 ... Substrate, 21a ... Thin film, 21b ... Thin film

Claims (5)

  A mesoporous material having a central pore diameter of 1.5 to 5.0 nm, a metal having a hydrogen storage capacity arranged in the pores of the mesoporous material, and an electrode electrically connected to the metal A hydrogen gas sensor comprising:   2. The hydrogen gas sensor according to claim 1, wherein the metal forms a quantum dot array structure in which the metal is arrayed at a period similar to the periodic structure of the pores of the mesoporous material.   3. The hydrogen gas sensor according to claim 1, wherein electrical characteristics change due to expansion of the metal due to hydrogen absorption, and hydrogen gas is detected from the magnitude of a tunnel current. 4.   The hydrogen gas sensor according to any one of claims 1 to 3, wherein the metal has a lattice constant that is changed by 1 to 50% by hydrogen storage.   The hydrogen gas sensor according to any one of claims 1 to 3, wherein the metal can occlude 1 to 5 mass% of hydrogen.