Hydrogen gas sensor and method of manufacturing the same

Abstract

To provide a hydrogen gas sensor equipped with a small-sized hydrogen gas sensor element operated at room temperature and having high sensitivity, and its manufacturing method.SOLUTION: The hydrogen gas sensor includes a graphene element 30 including a graphene thin film 13 terminated with zigzag ends and having palladium nanoparticles 21 vapor-deposited on a surface thereof, a vacuum container in which the graphene element 30 is installed, a hydrogen gas introduction unit that selectively introduces hydrogen gas into the evacuated vacuum container, an electrical resistance measurement unit that measures an electrical resistance of the graphene element 30, and a hydrogen gas detection unit that detects the hydrogen gas introduced into the vacuum container by the hydrogen gas introduction unit based on the electrical resistance.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a hydrogen gas sensor and a manufacturing method thereof, and more particularly to a hydrogen gas sensor using a nanoscale graphene element and a manufacturing method thereof. [Background technology]

[0002] Hydrogen is attracting attention as a next-generation energy source that will be essential for realizing a carbon-neutral society. Hydrogen gas is also thought to be useful in medical treatment and disease diagnosis.

[0003] On the other hand, hydrogen has the disadvantages of exploding over a wide range of atmospheric concentrations, from 4 to 75%, and of deteriorating steel due to its high permeability to materials. However, it is colorless, tasteless, and odorless, making it imperceptible to humans.

[0004] Therefore, it is important to check for hydrogen leaks and measure hydrogen concentration at each stage of hydrogen generation, storage, transportation, and use.

[0005] Conventionally, hydrogen gas sensors that can perform precise concentration measurements have used mass spectrometry techniques, but these have the problem of being large in size.

[0006] On the other hand, smaller sensors primarily intended for leak detection include those that detect changes in the electrical resistance of metal oxide semiconductors due to oxidation-reduction reactions with hydrogen, those that detect changes in the electrical resistance of platinum wires due to the combustion of hydrogen gas, and those that detect changes in the thermal conductivity of gas.However, all of these operate at high temperatures of several hundred degrees Celsius, which means that not only does power consumption increase, but there is also the risk of explosion depending on the hydrogen gas concentration.

[0007] Therefore, there is a need for the development of a small, low-power hydrogen gas sensor element that can operate at room temperature.

[0008] For example, Non-Patent Document 1 discloses a hydrogen gas sensor element using graphene with palladium (Pd) nanoparticles vapor-deposited on the surface. Pd is known as a metal that absorbs hydrogen. This hydrogen gas sensor element can be used at room temperature because the changes in the physical properties of Pd due to its reaction with hydrogen can be detected through the graphene. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] Rakesh Kumar, Shweta Malik, BR Mehta, "Interface induced hydrogen sensing in Pd nanoparticle / graphene composite layers," Sensors and Actuators B: Chemical Volume 209 , 31 March 2015, Pages 919-926. Summary of the Invention [Problem to be solved by the invention]

[0010] However, conventional hydrogen gas sensor elements such as those disclosed in Non-Patent Document 1 can only detect hydrogen concentrations down to a few tens of ppm, and have the problem of being unable to perform the highly sensitive hydrogen gas detection that has been demanded in recent years.

[0011] The present invention has been made to solve these conventional problems, and aims to provide a hydrogen gas sensor equipped with a small, highly sensitive hydrogen gas sensor element that operates at room temperature, and a method for manufacturing the same. [Means for solving the problem]

[0012] In order to solve the above problems, the hydrogen gas sensor of the present invention is a hydrogen gas sensor (50) for detecting hydrogen gas, and is configured to include a graphene element (30) having a graphene thin film (13) terminated with zigzag ends and having palladium nanoparticles (21) vapor-deposited on its surface, a vacuum container (56) in which the graphene element is installed, hydrogen gas inlet units (51, 52, 53, 54) that selectively introduce the hydrogen gas into the vacuum container that has been evacuated, an electrical resistance measuring unit (61) that measures the electrical resistance of the graphene element, and a hydrogen gas detection unit (62) that detects the hydrogen gas introduced into the vacuum container by the hydrogen gas inlet unit based on the electrical resistance.

[0013] With this configuration, the hydrogen gas sensor according to the present invention can detect hydrogen gas with high sensitivity approaching 1 ppm using a small graphene element that operates at room temperature.

[0014] Furthermore, the hydrogen gas sensor according to the present invention may be configured so that, when the difference between the electrical resistance of the graphene element in a vacuum and the electrical resistance of the graphene element when the hydrogen gas is introduced into the vacuum container by the hydrogen gas introduction part exceeds a predetermined threshold, the hydrogen gas detection part determines that a concentration of hydrogen gas higher than a concentration corresponding to the predetermined threshold has been detected.

[0015] With this configuration, the hydrogen gas sensor according to the present invention can detect hydrogen gas at a concentration higher than a predetermined concentration based on the difference between the electrical resistance of the graphene element in a vacuum and the electrical resistance of the graphene element when hydrogen gas is introduced into the vacuum container.

[0016] In addition, the hydrogen gas sensor according to the present invention may be configured such that the graphene element further includes a conductive substrate (12) and an oxide film (11) formed on the surface of the conductive substrate, the graphene thin film is formed on the surface of the oxide film, and the hydrogen gas detection unit changes the concentration according to the predetermined threshold by changing the gate voltage applied to the conductive substrate.

[0017] With this configuration, the hydrogen gas sensor according to the present invention can change its sensitivity in detecting the presence or absence of hydrogen gas by changing the gate voltage applied to the conductive substrate of the graphene element.

[0018] Furthermore, the hydrogen gas sensor according to the present invention may be configured such that the hydrogen gas detection unit calculates the rate of change of the electrical resistance according to the concentration of the hydrogen gas, and estimates the concentration of the hydrogen gas based on the rate of change.

[0019] With this configuration, the hydrogen gas sensor according to the present invention can estimate the concentration of hydrogen gas based on the rate of change in the electrical resistance of the graphene element relative to a change in the concentration of hydrogen gas in the vacuum vessel.

[0020] A manufacturing method according to the present invention is a method for manufacturing any of the hydrogen gas sensors described above, in which the zigzag edges of the graphene element are formed by hydrogen plasma etching.

[0021] With this configuration, the manufacturing method of the present invention can manufacture a hydrogen gas sensor that can detect hydrogen gas at room temperature with high sensitivity approaching 1 ppm by forming zigzag edges of the graphene element by hydrogen plasma etching. [Effects of the Invention]

[0022] The present invention provides a hydrogen gas sensor having a small, highly sensitive hydrogen gas sensor element that operates at room temperature, and a method for manufacturing the same. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram illustrating the edge structure of graphene. [Figure 2] (a) is a schematic diagram showing the gate voltage dependence of the Dirac cone and electrical resistivity of graphene, and (b) is a graph showing the electronic density of states of graphene near the zigzag edge and bulk graphene. [Figure 3] Figure 1 shows examples of nanoscale graphene element structures terminated with zigzag edges: (a) an array of zigzag graphene nanoribbons, (b) a zigzag graphene nanomesh, and (c) a zigzag graphene nanosnake. [Figure 4] 1A to 1C are diagrams (part 1) illustrating a method for producing a Pd-modified graphene element included in a hydrogen gas sensor according to an embodiment of the present invention. [Figure 5] FIG. 2 is a diagram (part 2) illustrating a method for producing a Pd-modified graphene element included in a hydrogen gas sensor according to an embodiment of the present invention. [Figure 6] 1A and 1B are diagrams illustrating a Pd-modified graphene element included in a hydrogen gas sensor according to an embodiment of the present invention. [Figure 7] 10 is a graph showing the results of measuring the electrical resistance of a Pd-modified graphene element while changing the concentration of hydrogen gas. [Figure 8] 10 is a graph showing the results of measuring the gate voltage dependence of the electrical resistance of a Pd-modified graphene element in vacuum and in hydrogen gas with a concentration of 18 ppm. [Figure 9] 1 is a schematic diagram illustrating a configuration of a hydrogen gas sensor according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of a hydrogen gas sensor and a method for manufacturing the same according to the present invention will be described with reference to the accompanying drawings.

[0025] The hydrogen gas sensor of this embodiment detects hydrogen gas by using a nanoscale graphene element (hereinafter also referred to as a "Pd-modified graphene element") on which palladium (Pd) nanoparticles are vapor-deposited as a hydrogen gas sensor element.

[0026] Figure 1 is a diagram illustrating the edge structure of graphene. Reflecting its honeycomb structure, graphene has edge structures such as zigzag edges (left side of Figure 1), armchair edges (right side of Figure 1), or a regular or random mixture of these. The properties of graphene are influenced by this edge structure. This effect is particularly pronounced when the edge structure accounts for a large proportion of the total, as in the case of nanoribbons.

[0027] As shown in Figure 2(a), graphene has a linear energy dispersion (Dirac cone) that intersects at a charge neutral point called the Dirac point. The Fermi energy (E F ) can be controlled to a large extent. At the Dirac point, the density of electronic states becomes zero, so E F When is near the Dirac point, the electrical resistance becomes large.

[0028] At the armchair edge, the symmetry of the two equivalent sublattices, A and B, that make up the honeycomb lattice is preserved, whereas near the zigzag edge, the symmetry is broken. As a result, an electronic state essentially equivalent to that of bulk graphene appears at the armchair edge, whereas an electronic state localized at the edge (zigzag edge state) appears at the zigzag edge.

[0029] Figure 2(b) shows the electronic density of states near the zigzag edge of graphene and in bulk graphene (partially modified from Figure 6b in Tomohiro Matsui, Hideki Sato, Kazuma Kita, Andre EB Amend, and Hiroshi Fukuyama, "Hexagonal Nanopits with the Zigzag Edge State on Graphite Surfaces Synthesized by Hydrogen-Plasma Etching," The Journal of Physical Chemistry C 2019, Volume 123, Issue 36 Pages 22665-22673). Near the zigzag edge, EF A peak structure clearly indicating the zigzag edge state appears around 0 meV, which corresponds to

[0030] 3(a) to 3(c) are diagrams showing examples of the structure of nanoscale graphene elements terminated with zigzag edges.

[0031] The left image in Figure 3(a) shows an array of zigzag graphene nanoribbons (zGNRs), which are nanoscale ribbons of graphene with zigzag edges. The center image in Figure 3(a) shows that approximately 10 nm-sized Pd nanoparticles are attached to the entire surface of the zGNRA. The right image in Figure 3(a) is an enlarged view of the boxed area in the center image, showing that the Pd nanoparticles are selectively attached to the zigzag edges.

[0032] Figure 3(b) shows the zigzag graphene nanomesh (zGNM), a network structure of zGNRs, and Figure 3(c) shows the zigzag graphene nanosnake (zGNS), a meandering structure of zGNRs.

[0033] Hereinafter, with reference to FIGS. 4 to 6, a method for manufacturing the Pd-modified graphene element 30 included in the hydrogen gas sensor of this embodiment will be described, taking a Pd-modified zGNRA element having zGNRA as an example.

[0034] First, a graphene thin film 13 having an arbitrary thickness is formed on a conductive substrate 12 having an oxide film 11 formed on its surface (step i).

[0035] Here, the conductive substrate 12 is a semiconductor such as silicon (Si) or a metal. The oxide film 11 is an oxide film of the semiconductor (e.g., SiO2) or an oxide film of the metal. The graphene thin film 13 can be, for example, cleaved graphene.

[0036] Next, a resist film 15a is applied onto the oxide film 11 including the graphene thin film 13 (step ii).

[0037] Next, linear slits 14 are formed at desired positions in the resist film 15a, and a resist mask 15 is formed on the graphene thin film 13 (step iii).

[0038] More specifically, the side of the conductive substrate 12 on which the resist film 15a is applied is irradiated with light or an electron beam to expose the resist film 15a, thereby forming linear slits 14. The resist film 15a with the slits 14 formed therein becomes the resist mask 15. The length and width of the slits 14 can be adjusted as appropriate according to the specifications (length, width) of the GNRA to be manufactured.

[0039] Next, the graphene thin film 13 to the oxide film 11 are etched in the depth direction through the slits 14 in the resist mask 15 (step iv).

[0040] This etching is performed by CHF3 plasma etching. After etching, grooves 16 are formed in the oxide film 11 in the depth direction. The depth of the grooves 16 is arbitrary. In FIG. 4, the depth of the grooves 16 reaches about the middle of the thickness of the oxide film 11, but they may also reach the conductive substrate 12.

[0041] Next, the resist mask 15 is stripped (step v).

[0042] Next, the graphene thin film 13 is etched in the surface direction of the conductive substrate 12 (anisotropic etching) using the grooves 16 as nuclei (step vi).

[0043] This etching is performed by hydrogen plasma etching, and the graphene thin film 13 is etched into an equiangular hexagonal shape with the grooves 16 as nuclei.

[0044] The graphene thin film 13 between the etched equiangular hexagons becomes GNRs, so the etching is stopped when the graphene thin film 13 between the equiangular hexagons reaches the desired width. GNRs formed by such hydrogen plasma etching have a structure terminated with zigzag edges.

[0045] Next, the graphene thin film 13 is completely removed by etching, leaving only the GNRs in an arbitrary portion (step vii). After step vii is completed, zGNRA20 is completed.

[0046] Next, as shown in FIG. 6, electrodes 22 and 23 are formed on both ends of the zGNRA20.

[0047] Next, a Pd film with a thickness of approximately 1 nm is vacuum-deposited on the zGNRA20. -4 The pressure starts at 10 Pa or less. As a result, as shown schematically in Figure 6, Pd nanoparticles 21 with a size of just over 10 nm are attached onto the zGNRA 20, completing the Pd-modified zGNRA element.

[0048] In the above description, the electrodes 22 and 23 are formed on both ends of the zGNRA20, and then the Pd film is vacuum-deposited on the zGNRA20. However, this order may be reversed. That is, after step vii is completed, the Pd film may be vacuum-deposited on the zGNRA20, and then the electrodes 22 and 23 may be formed on both ends of the zGNRA20.

[0049] When fabricating a Pd-modified graphene element 30 having, for example, a zGNM or zGNS structure, in step iii, round holes or alternating parallel slits may be formed in the resist film 15a instead of the linear slits 14.

[0050] 6, the Pd-modified graphene device 30 includes a conductive substrate 12, an oxide film 11 formed on the surface of the conductive substrate 12, a graphene thin film 13 formed on the surface of the oxide film 11 and terminated with zigzag edges, and Pd nanoparticles 21 deposited on the surface of the graphene thin film 13. A gate voltage Vg is applied to the conductive substrate 12 as needed.

[0051] FIG. 7 is a graph showing the results of measuring the electrical resistance of the Pd-modified graphene device 30 placed inside a vacuum chamber that has been evacuated, while changing the concentration of hydrogen gas introduced into the vacuum chamber.

[0052] The electrical resistance measurement was performed between the electrodes 22 and 23 using a measurement system as shown in Figure 6, with the gate voltage Vg set to 0 V. The Pd-modified graphene element 30 used in the measurement was a Pd-modified zGNRA element made of two- or three-layer graphene, with 12 ribbons of approximately 240 nm width arranged in parallel.

[0053] This measurement was performed by repeatedly introducing hydrogen gas into a vacuum chamber containing the Pd-modified graphene element 30 and then evacuating the hydrogen gas from the vacuum chamber. Specifically, approximately 18 ppm of hydrogen gas was introduced into the vacuum chamber for 300 seconds from 0 to 300 seconds, approximately 10 ppm of hydrogen gas for 300 seconds from 500 to 800 seconds, and approximately 2 ppm of hydrogen gas for 300 seconds from 1000 to 1300 seconds. Note that in this specification, hydrogen concentration (ppm) is based on atmospheric pressure.

[0054] The graph in Figure 7 shows the rate of change in the electrical resistance R of the Pd-modified graphene element 30 {(R-Rs) / Rs} x 100 (%), based on the electrical resistance Rs of the Pd-modified graphene element 30 at the start times of three hydrogen gas introductions (0 seconds, 500 seconds, and 1000 seconds).

[0055] From these measurement results, it was found that the electrical resistance R of the Pd-modified graphene element 30 decreased when the Pd-modified graphene element 30 was exposed to hydrogen gas. This is the opposite behavior to that of the hydrogen gas sensor element disclosed in Non-Patent Document 1, in which the electrical resistance increases due to hydrogen gas. Note that the hydrogen gas sensor element in Non-Patent Document 1 was measured at atmospheric pressure, whereas the Pd-modified graphene element 30 of this embodiment was measured in a vacuum. Therefore, this difference in behavior is thought to be due to the fact that gases other than hydrogen, such as oxygen and nitrogen, are present at atmospheric pressure, while only hydrogen gas is present in a vacuum.

[0056] It was also found that the rate of change in the electrical resistance R of the Pd-modified graphene element 30 was in a linear relationship with the hydrogen concentration when the time for which the Pd-modified graphene element 30 was exposed to hydrogen gas was constant.

[0057] Furthermore, while conventional hydrogen gas sensor elements such as those disclosed in Non-Patent Document 1 can only detect hydrogen concentrations down to about several hundred ppm, the Pd-modified graphene element 30 of this embodiment can detect hydrogen concentrations approaching 1 ppm when measured in a vacuum as described above.

[0058] 8 is a graph showing the results of measuring the gate voltage dependence of the electrical resistance of the Pd-modified graphene device 30, similar to that used in the measurement shown in FIG. 7, in vacuum and in hydrogen gas with a concentration of 18 ppm. -3 It is Pa.

[0059] 8, the gate voltage giving the peak value of the electrical resistance in 18 ppm hydrogen gas is higher than the gate voltage giving the peak value of the electrical resistance in vacuum, which indicates that the graphene thin film 13 of the Pd-modified graphene element 30 is hole-doped by hydrogen gas. This behavior is different from that of the hydrogen gas sensor element of Non-Patent Document 1, in which it is believed that electrons are doped into graphene by hydrogen gas.

[0060] Furthermore, the peak value of the electrical resistance in 18 ppm hydrogen gas is lower than the peak value of the gate voltage dependence of the electrical resistance in vacuum.

[0061] That is, when the Pd-modified graphene element 30 is exposed to hydrogen gas, the graphene thin film 13 is hole-doped and the peak value of the gate voltage dependence of the electrical resistance decreases, so that the electrical resistance becomes lower than in a vacuum.

[0062] Furthermore, the gate voltage applied to the conductive substrate 12 may be changed. For example, when the gate voltage is 20 V, the difference in electrical resistance of the Pd-modified graphene element 30 between in a vacuum and in 18 ppm hydrogen gas is approximately 0.015 kΩ. On the other hand, when the gate voltage is 0 V, the difference in electrical resistance of the Pd-modified graphene element 30 between in a vacuum and in 18 ppm hydrogen gas is approximately 0.03 kΩ.

[0063] Therefore, in the gate voltage range of 0 to 25 V, it is desirable to set the gate voltage to 0 V, at which point the difference in electrical resistance becomes large, in terms of the accuracy of the electrical resistance measurement, and the accuracy of the electrical resistance measurement may be further improved by setting the gate voltage to a negative value.

[0064] Furthermore, by changing the gate voltage, it is possible to change the sensitivity when detecting the presence or absence of hydrogen gas.

[0065] For example, when the threshold value for the difference in electrical resistance is 0.015 kΩ, the following applies: When the gate voltage is 20 V and the difference in electrical resistance is 0.015 kΩ or greater, the presence or absence of hydrogen gas with a concentration of 18 ppm or greater can be detected; when the gate voltage is lower than 20 V and the difference in electrical resistance is 0.015 kΩ or greater, the presence or absence of hydrogen gas with a predetermined concentration lower than 18 ppm can be detected; and conversely, when the gate voltage is higher than 20 V and the difference in electrical resistance is 0.015 kΩ or greater, the presence or absence of hydrogen gas with a predetermined concentration higher than 18 ppm can be detected.

[0066] An example of a specific configuration of the hydrogen gas sensor 50 of this embodiment will now be described.

[0067] As shown in FIG. 9, the hydrogen gas sensor 50 mainly includes, for example, a variable leak valve V1, a first vacuum pump 52, a second vacuum pump 53, a vacuum container 56 in which the Pd-modified graphene element 30 is installed, an operation unit 57, a display unit 58, and a control unit 60.

[0068] The vacuum vessel 56 is connected to the first vacuum pump 52 via a valve V2 and a second vacuum pump 53.

[0069] The first vacuum pump 52 is connected to the exhaust port side of the second vacuum pump 53. The first vacuum pump 52 is, for example, a dry pump, a rotary pump, or a membrane pump. The second vacuum pump 53 is, for example, a turbomolecular pump.

[0070] The variable leak valve V1 is attached to the intake port side of the vacuum vessel 56. A test gas that may contain hydrogen gas is drawn into the vacuum vessel 56 through the variable leak valve V1. The test gas may be, for example, a gas present in any piping or vessel, or the outside air.

[0071] Furthermore, the vacuum vessel 56 is provided with a vent valve V3, so that nitrogen gas or the like can be introduced into the vacuum vessel 56 via the vent valve V3 as necessary when hydrogen gas detection is completed.

[0072] In addition, the first vacuum pump 52 is provided with a vent valve V4, so that air, nitrogen gas, etc. can be introduced into the first vacuum pump 52 through the vent valve V4 when the operation of the first vacuum pump 52 is finished.

[0073] The open / closed states of the valves V1 to V4 are controlled by the control unit 60 in response to a user's operation input to the operation unit 57. The number of vacuum pumps and valves is not limited to that shown in Fig. 9 and can be changed as appropriate depending on the device configuration.

[0074] The control unit 60 includes an electrical resistance measuring unit 61 and a hydrogen gas detecting unit 62 .

[0075] The electrical resistance measuring unit 61 is configured to measure the electrical resistance of the Pd-modified graphene device 30. For example, as shown in FIG. 6 , the electrical resistance measuring unit 61 is configured to measure the DC electrical resistance between the electrodes 22 and 23 in a state where a predetermined gate voltage is applied to the conductive substrate 12.

[0076] An example of a procedure for detecting hydrogen gas using the hydrogen gas sensor 50 of this embodiment will now be described.

[0077] First, the variable leak valve V1 and vent valves V3 and V4 are closed, and valve V2 is opened, and the inside of the vacuum vessel 56 is evacuated to a predetermined pressure or less by the serial configuration of the second vacuum pump 53 and the first vacuum pump 52. Here, the "predetermined pressure" is preferably, for example, 0.01 Pa or less, which is lower than the partial pressure of hydrogen in the atmosphere.

[0078] Next, the electrical resistance measuring unit 61 measures the electrical resistance Rv of the Pd-modified graphene device 30 in vacuum.

[0079] Next, the variable leak valve V1 is opened to draw a predetermined amount of test gas into the vacuum vessel 56, and hydrogen gas detection is started by the Pd-modified graphene element 30 in the vacuum vessel 56. At this time, the degree of opening of the variable leak valve V1 may be automatically adjusted according to the pressure of the vacuum gauge P attached to the vacuum vessel 56.

[0080] That is, the variable leak valve V1, the first vacuum pump 52, and the second vacuum pump 53 constitute a hydrogen gas introduction section that selectively introduces hydrogen gas into the vacuum vessel 56 that has been evacuated.

[0081] Next, the hydrogen gas detection unit 62 detects the hydrogen gas introduced into the vacuum vessel 56 by the hydrogen gas introduction unit based on the electrical resistance R of the Pd-modified graphene element 30 measured by the electrical resistance measurement unit 61 .

[0082] That is, the electrical resistance measuring unit 61 is configured to measure, for example, the electrical resistance Rv of the Pd-modified graphene element 30 in a vacuum below a predetermined pressure, and the electrical resistance R of the Pd-modified graphene element 30 when hydrogen gas is introduced by the hydrogen gas introduction unit into the vacuum container 56 that has been evacuated to below the predetermined pressure.

[0083] For example, when the difference between the electrical resistance Rv and the electrical resistance R exceeds a predetermined threshold, the hydrogen gas detection unit 62 determines that it has detected a hydrogen gas concentration higher than the concentration corresponding to the predetermined threshold. As already described, the hydrogen gas detection unit 62 can change the concentration corresponding to the predetermined threshold by changing the gate voltage applied to the conductive substrate 12.

[0084] As already mentioned, the rate of change in the electrical resistance of the Pd-modified graphene element 30 has a linear relationship with the concentration of hydrogen gas. Therefore, the hydrogen gas detection unit 62 may calculate the rate of change in the electrical resistance R based on the electrical resistance Rv, {(R-Rv) / Rv}×100(%), and estimate the hydrogen concentration according to the calculated rate of change in the electrical resistance.

[0085] The display unit 58 displays the detection result by the hydrogen gas detection unit 62, that is, the presence or absence of hydrogen gas at a concentration higher than a predetermined concentration, or an estimated value of the hydrogen concentration.

[0086] As described above, the hydrogen gas sensor 50 according to this embodiment is configured such that the Pd-modified graphene element 30, which is terminated with a zigzag end and has a graphene thin film 13 on the surface of which Pd nanoparticles 21 are vapor-deposited, is placed inside a vacuum container 56 that has been evacuated.

[0087] As a result, the hydrogen gas sensor 50 according to this embodiment can detect hydrogen gas with high sensitivity approaching 1 ppm using the Pd-modified graphene element 30, which is small and operates at room temperature.

[0088] Furthermore, the hydrogen gas sensor 50 according to this embodiment can detect hydrogen gas at a concentration higher than a predetermined concentration based on the difference between the electrical resistance Rv of the Pd-modified graphene element 30 in a vacuum and the electrical resistance R of the Pd-modified graphene element 30 when hydrogen gas is introduced into the vacuum vessel 56.

[0089] Furthermore, the hydrogen gas sensor 50 according to this embodiment can change its sensitivity in detecting the presence or absence of hydrogen gas by changing the gate voltage applied to the conductive substrate 12 of the Pd-modified graphene element 30.

[0090] Furthermore, the hydrogen gas sensor 50 according to this embodiment can estimate the concentration of hydrogen gas based on the rate of change in the electrical resistance R of the Pd-modified graphene element 30 relative to the change in the concentration of hydrogen gas in the vacuum vessel 56.

[0091] Furthermore, the manufacturing method according to this embodiment can manufacture a hydrogen gas sensor 50 capable of detecting hydrogen gas at room temperature with high sensitivity approaching 1 ppm by forming zigzag edges of the Pd-modified graphene element 30 by hydrogen plasma etching. [Explanation of symbols]

[0092] 11 Oxide film 12 Conductive substrate 13 Graphene thin film 20zGNRA 21 Nanoparticles 22,23 electrode 30 Pd-modified graphene element (graphene element) 50 Hydrogen gas sensor 52 No. 1 vacuum pump 53 Second vacuum pump 56 Vacuum container 57 Operation section 58 Display section 60 Control Unit 61 Electrical resistance measurement section 62 Hydrogen gas detector V1 Variable Leak Valve

Claims

1. A hydrogen gas sensor (50) for detecting hydrogen gas, comprising: a graphene element (30) comprising a graphene thin film (13) terminated with zigzag edges and having palladium nanoparticles (21) deposited on its surface; a vacuum vessel (56) in which the graphene element is placed; a hydrogen gas inlet (51, 52, 53, 54) for selectively introducing the hydrogen gas into the vacuum vessel; An electrical resistance measuring unit (61) that measures the electrical resistance of the graphene element; a hydrogen gas detection section (62) that detects the hydrogen gas introduced into the vacuum vessel by the hydrogen gas introduction section based on the electrical resistance.

2. 2. The hydrogen gas sensor according to claim 1, wherein the hydrogen gas detection unit determines that a concentration of hydrogen gas higher than a concentration corresponding to a predetermined threshold has been detected when a difference between the electrical resistance of the graphene element in a vacuum and the electrical resistance of the graphene element when the hydrogen gas is introduced into the vacuum container by the hydrogen gas introduction unit exceeds a predetermined threshold.

3. The graphene device further includes a conductive substrate (12) and an oxide film (11) formed on a surface of the conductive substrate, the graphene thin film being formed on the surface of the oxide film; 3. The hydrogen gas sensor according to claim 2, wherein the hydrogen gas detection unit changes the concentration according to the predetermined threshold value by changing a gate voltage applied to the conductive substrate.

4. 2. The hydrogen gas sensor according to claim 1, wherein the hydrogen gas detection unit calculates a rate of change of the electrical resistance depending on the concentration of the hydrogen gas, and estimates the concentration of the hydrogen gas based on the rate of change.

5. A method for manufacturing the hydrogen gas sensor according to any one of claims 1 to 4, comprising the steps of: The method of manufacturing the graphene element, wherein the zigzag edges are formed by hydrogen plasma etching.

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