A hydrogen sensor with palladium nanostructure modified high square resistance two-dimensional transition metal chalcogenide and preparation thereof

Abstract

The application belongs to the field of gas sensors, and discloses a hydrogen sensor with palladium nanostructure modified high-resistance two-dimensional transition metal dichalcogenide (TMDCs) and a preparation method thereof. The gas sensor is provided with palladium nanoparticles as a hydrogen sensitive layer and TMDCs as a conductive channel. The palladium nanostructure is in the form of discontinuous particles and is distributed on the surface of the TMDCs. When hydrogen gas molecules are adsorbed on the palladium and react with the palladium, the work function of the palladium nanostructure changes, the Fermi level balance between the palladium nanostructure and the TMDCs is broken, charge transfer occurs, and the carrier concentration in the high-resistance TMDCs material changes. At the same time, after the palladium nanoparticles react with hydrogen to form hydride, the scattering effect of the surface palladium nanoparticles on the carriers in the TMDCs weakens, and the carrier mobility in the TMDCs increases. The increase in the carrier concentration and the improvement in the carrier mobility jointly cause the resistance of the device to decrease, thereby realizing the sensing of hydrogen.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of gas sensors, and discloses a hydrogen sensor with high-resistance two-dimensional transition metal dichalcogenide (TMDC) modified by palladium nanostructures and a preparation method thereof. BACKGROUND

[0002] A gas sensor is a device or instrument that can sense a certain gas and its concentration in the environment, and can convert information related to the type and concentration of the gas into an electric, optical, or acoustic signal that can be directly read, quantified, and detected, monitored, analyzed, and alarmed. Hydrogen is a high-energy-density energy source, and as an important chemical raw material and industrial gas, it has been widely used in people's production and life. As a renewable clean energy, hydrogen is a hot topic in the field of new energy technology with the development of hydrogen fuel cell technology. However, hydrogen molecules are small and easy to leak into the interatomic gap of pipeline materials during production, transportation, and storage, and the leakage will increase the defects of the pipeline materials, reduce the hardness, and aggravate the leakage, forming a vicious cycle. In addition, hydrogen is colorless and odorless and is easy to burn. When the hydrogen content in the air reaches 4%, it will explode when encountering a fire, posing a great threat to people's life and property safety. Therefore, it is necessary to develop a hydrogen sensor with high sensitivity and safety and stability to monitor its leakage.

[0003] Metal oxide hydrogen sensors with high sensitivity suitable for low concentration detection usually need to work at high temperature (> 300℃) to improve the response, which has certain safety hazards for sensing flammable gases such as hydrogen. In addition, traditional metal oxide hydrogen sensors are based on oxide ceramic materials, which have large size and preparation process incompatible with semiconductor process, and also have the disadvantages of poor selectivity, high power consumption, large size, and difficulty in miniaturization, which do not meet the development trend of sensor integration and intelligentization. Therefore, developing a hydrogen sensor with good selectivity, high sensitivity, low working temperature, low power consumption, small size, and easy integration on a semiconductor chip is still an important direction in the field of sensor research.

[0004] Developing a new generation of hydrogen sensors based on new materials and new technologies is one of the key development directions in the field of sensors. Generally speaking, the sensitivity of the gas-sensitive material itself and the noise of the device are the two main factors that determine the detection limit of semiconductor gas sensors. The sensitivity of a gas sensor usually refers to the change in resistance of the sensor before and after exposure to a specific concentration of the gas to be detected. It is related to the specific surface area, carrier concentration and carrier mobility of the gas-sensitive material. Two-dimensional TMDCs are easily affected by the adsorption of gas molecules due to their molecular-level thickness and large specific surface area, which makes gas sensors based on TMDCs have high sensitivity. In particular, molybdenum disulfide (MoS2), tungsten disulfide (WS2), molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2) are four semiconductor TMDCs with high carrier mobility, high mechanical strength, good chemical stability and thermal stability, and thus have broad application prospects in the field of gas sensors. However, the selectivity of TMDCs to hydrogen is poor.

[0005] Among the many hydrogen-sensitive materials, catalytic noble metal palladium (Pd) has a large adsorption and dissociation coefficient for hydrogen, and high selectivity and sensitivity to hydrogen, making it an ideal hydrogen-sensitive material. However, these existing technologies often only use charge transfer to change the resistance of the material for gas sensing, resulting in low sensitivity. For example, a previously reported hydrogen sensor based on Pd-modified TMDCs prepared by chemical dispersion. In this device, the TMDCs layers are combined together in a random stack, and the Pd nanoparticles are randomly embedded in the interior and surface of the randomly stacked TMDCs layers. Due to the influence of interlayer carrier transport, the carrier mobility is low, and only charge transfer can be used to change the resistance of the material for gas sensing, which cannot take advantage of the high carrier mobility of TMDCs. At the same time, the above chemical preparation method inevitably introduces doping into the TMDCs, increasing the background carrier concentration and reducing the sensitivity of the sensor. SUMMARY

[0006] In view of the above shortcomings or improvement needs of the prior art, the present application aims to provide a hydrogen sensor with palladium nanostructures modifying high square resistance two-dimensional transition metal dichalcogenides (TMDCs), the palladium nanostructures being distributed in discontinuous particle form only on the surface of the TMDCs material and directly contacting the TMDCs; there is interaction between the palladium nanostructures and the TMDCs, and changes in the chemical composition and work function of the palladium nanostructures will cause changes in the carrier concentration and carrier mobility in the TMDCs. The gas sensor uses the palladium nanostructures as a hydrogen sensitive layer, and when the hydrogen sensor is exposed to a hydrogen-containing atmosphere, the palladium nanostructures absorb hydrogen to form hydride (PdHx), breaking the Fermi level balance between the palladium nanostructures and the two-dimensional TMDCs, resulting in charge transfer, which increases the carrier concentration in the high square resistance two-dimensional TMDCs material, which on the one hand reduces the resistance of the conductive channel of the TMDCs, and on the other hand reduces the contact resistance between the TMDCs and the metal electrode, so that the total resistance of the device is reduced. At the same time, after the palladium nanoparticles react with hydrogen to form hydride, the scattering effect of the surface palladium nanoparticles on the carriers in the TMDCs is weakened, and the carrier mobility in the TMDCs is improved. The increase in carrier concentration and the improvement in carrier mobility together cause the device resistance to decrease, realizing the sensing of hydrogen. At the same time, with the high square resistance TMDCs material, the high square resistance state ensures that the TMDCs have very low background carrier concentration, so a small amount of charge transfer can cause a significant change in the resistance of the two-dimensional TMDCs material. The device of the present application can effectively optimize the hydrogen detection limit, which is at least 2 orders of magnitude lower than the hydrogen sensor based on TMDCs reported in the prior art.

[0007] To achieve the above-mentioned object, according to one aspect of the present application, a hydrogen sensor with palladium nanostructures modifying high square resistance two-dimensional transition metal dichalcogenides (TMDCs) is provided, characterized in that the device uses two-dimensional transition metal dichalcogenides TMDCs as a conductive channel, the TMDCs being arranged on an insulating substrate and connected to a first electrode and a second electrode at both ends; and the TMDCs have a high square resistance, and the square resistance thereof at room temperature is not less than 1×10 8 Ω / square; the palladium nanostructures are distributed in discontinuous particle form only on the surface of the TMDCs and directly contact the TMDCs, serving as a hydrogen sensitive layer; when the device encounters hydrogen, the carrier mobility and concentration in the TMDCs will change, causing the resistance between the first electrode and the second electrode to change, thereby realizing the sensing of hydrogen.

[0008] As a further preferred embodiment of the present application, the palladium nanostructures are discontinuous nanoparticles; any one nanoparticle structure has a height of 1-5 nm and a projection size of 1-100 nm in the plane of the TMDCs.

[0009] As a further preferred embodiment of the present application, the first electrode and the second electrode are both N-type contact electrodes; preferably, the TMDCs are connected to the N-type contact electrodes through an N-type interface layer.

[0010] As a further preferred embodiment of the present application, the insulating substrate is additionally provided with a heating electrode.

[0011] According to another aspect of the present application, the present application provides a method for preparing the hydrogen sensor with high sheet resistance two-dimensional transition metal dichalcogenide (TMDCs) modified by palladium nanostructure, characterized in that, the method comprises the following steps:

[0012] (1) preparing an insulating substrate, and forming a high sheet resistance two-dimensional transition metal dichalcogenide (TMDCs) thin film layer on the insulating substrate;

[0013] (2) performing a photolithography process on the TMDCs thin film layer to form a window exposing part of the TMDCs thin film;

[0014] (3) using photoresist as a mask to deposit a metal electrode material, and forming a first electrode and a second electrode in the window area;

[0015] (4) performing a photolithography process to leave part of the window in the middle of the channel of the TMDCs thin film, and depositing a palladium nanostructure as a hydrogen sensitive layer.

[0016] As a further preferred embodiment of the present application, in the step (1), the insulating substrate is any one of glass, quartz, ceramic and sapphire or a composite structure composed of them, or a semiconductor substrate containing an insulating layer;

[0017] In the semiconductor substrate containing an insulating layer, the semiconductor substrate is specifically one of elemental semiconductors Si and Ge, and compound semiconductors GaAs and InP, or any one of alloys composed of two or more of them; the insulating layer is any one of SiO2, Al2O3, HfO2 and AlN, or any one of compounds or laminates composed of two or more of them, and the thickness of the insulating layer is 10-1000 nm;

[0018] In the step (1), the two-dimensional transition metal dichalcogenide (TMDCs) thin film layer is directly grown or transferred onto the insulating substrate;

[0019] In the step (1), the two-dimensional transition metal dichalcogenide (TMDCs) thin film layer is one of WSe2, MoSe2, MoS2 and WS2 or any one of compounds thereof, and the thickness of the two-dimensional transition metal dichalcogenide (TMDCs) thin film layer is 0.7-100 nm.

[0020] In step (3), before depositing the metal with the photoresist as a mask, an N-type interface layer is formed on the surface of the window area TMDCs with the photoresist as a mask to realize local N-type doping; preferably, the N-type interface layer is formed by physical deposition or chemical deposition, or is formed by surface treatment methods such as plasma process to cause physical or chemical changes of the window area TMDCs, and the thickness of the N-type interface layer is 1-50 nm;

[0021] In step (3), for any one of the first electrode and the second electrode, the metal electrode material is one of Ni, Ti, Cr, Al, Ag, Mo, W or any one of their alloys or laminates; the thickness of the first electrode and the second electrode is 5-200 nm;

[0022] In step (4), the palladium nanostructure is prepared by physical vapor deposition, chemical vapor deposition or spin coating method; preferably, it is prepared by an electron beam evaporation method.

[0023] As a further preferred embodiment of the present application, in step (1), the insulating substrate additionally has a heating electrode.

[0024] Compared with the prior art, the above technical scheme of the present application designs a two-dimensional TMDCs hydrogen sensor modified by a palladium nanostructure, which is a hydrogen sensor with a discontinuous palladium nano-particle film as a hydrogen sensitive layer and a two-dimensional transition metal chalcogenide with high sheet resistance as a conductive channel. The palladium nanostructure is only distributed in the form of discontinuous particles on the surface of the TMDCs and directly contacts the TMDCs. This not only takes advantage of the sensitivity of the palladium nano-particles to hydrogen, but also increases the effective contact area of palladium and hydrogen due to the discontinuous particle structure. In addition, the combination of the large surface area, good stability, low background carrier concentration, high carrier mobility and easy influence of surface modification of the two-dimensional transition metal chalcogenide with high sheet resistance helps to further improve the sensitivity and responsiveness of hydrogen.

[0025] Specifically, the present application is to utilize the interaction between palladium nanostructure and TMDCs, the change of chemical composition and work function of palladium nanostructure will cause the change of carrier concentration and carrier mobility in TMDCs. When hydrogen gas molecules act on the palladium nanostructure, the change of chemical composition and work function of palladium nanostructure will break the Fermi level balance between palladium nanostructure and two-dimensional TMDCs, resulting in charge transfer, which will increase the carrier concentration in the high square resistance two-dimensional TMDCs material, which will reduce the resistance of the TMDCs conductive channel on the one hand, and will also reduce the contact resistance between TMDCs and metal electrode, so that the total resistance of the device is reduced. At the same time, after the palladium nanoparticles react with hydrogen to form hydride (PdHx), the scattering effect of the surface palladium nanoparticles on the carriers in TMDCs is weakened, and the carrier mobility in TMDCs is improved. The increase of carrier concentration and the improvement of carrier mobility together cause the decrease of device resistance, realizing the sensing of hydrogen. When the sensor is exposed to air again, as the hydrogen concentration decreases, PdHx decomposes, and hydrogen atoms diffuse out of palladium, the carrier concentration and carrier mobility in TMDCs return to the level before exposure to hydrogen, so that the resistance of the sensor returns to the original state. The high square resistance state of TMDCs ensures that the background carrier concentration in TMDCs is very low, so a small amount of charge transfer can cause a significant change in the resistance of two-dimensional TMDCs material, further improving the sensitivity and responsiveness of the hydrogen sensor, and realizing the detection of lower concentration of hydrogen.

[0026] The TMDCs material itself has poor selectivity to hydrogen, and the present application utilizes the large surface area of TMDCs to attach palladium nanostructure, which can effectively realize high sensitivity and high selectivity hydrogen sensing. In the present application, the palladium nanostructure exists in the form of discontinuous nanoparticles, which has a large specific surface area. Such nanostructure can increase the effective contact area with hydrogen, while avoiding the short circuit problem caused by continuous palladium film, thereby realizing higher response and effective recovery of hydrogen.

[0027] The sensing mechanism of the device utilizes the change of carrier mobility in addition to the common charge transfer (i.e., carrier concentration change), so the total resistance change of the device as a whole will correspond to the charge transfer plus the change of carrier mobility, and the mobility change mechanism is not reported in the literature related to TMDCs hydrogen sensors. Palladium nanoparticles serve as a hydrogen sensitive layer, and hydrogen gas molecules act on the palladium nanostructure, causing changes in the chemical composition and work function of the palladium nanostructure. The difference in work function between the palladium nanostructure and the TMDCs will cause charge transfer; in addition to the common charge transfer mechanism, the palladium nanoparticles act as scattering centers to affect the mobility of carriers in the TMDCs in the present application. The gas sensor uses palladium nanostructures as a hydrogen sensitive layer, and when it is exposed to a hydrogen-containing atmosphere, the palladium nanostructure absorbs hydrogen to form hydride, causing the work function of the palladium nanostructure to change, breaking the Fermi level balance between the palladium nanostructure and the two-dimensional TMDCs, resulting in charge transfer, which increases the carrier concentration in the high square resistance two-dimensional TMDCs material; at the same time, after the palladium nanoparticles react with hydrogen to form hydride, the scattering effect of the surface palladium nanoparticles on the carriers in the TMDCs is weakened, and the mobility of the carriers in the TMDCs is improved; the increase in carrier concentration and the increase in carrier mobility work together to reduce the resistance of the device, realizing the sensing of hydrogen. The device can effectively optimize the hydrogen detection limit, and the hydrogen detection limit is at least 2 orders of magnitude lower than the hydrogen sensors based on TMDCs reported in the existing literature.Taking the device obtained by the examples in the following of the present application as an example, the detection limit of the device to H2 can be as low as 0.01 ppm; while the detection limit of the hydrogen sensor based on palladium modified TMDCs reported in the prior art is often in the order of 10 ppm~100 ppm (for example, see [1] Baek, Dae-Hyun, Kim, et al. MoS2 gas sensor functionalized by Pd for the detection of hydrogen [J]. Sensors and Actuators, B. Chemical, 2017, 250: 686-691.; [2] Sandeep Reddy Gottam, et al. Highly sensitive hydrogen gas sensor based on a MoS2-Pd nanoparticle composite [J]. Applied Surface Science, 506 (2020) 144981; [3] Zhang D, Sun Y, Jiang C, et al. Room temperature hydrogen gas sensor based on palladium decorated tin oxide / molybdenum disulfide ternary hybrid via hydrothermal route [J]. Sensors & Actuators B Chemical, 2017, 242: 15-24).

[0028] Meanwhile, the working temperature of the sensor of the present application is RT~100℃, compared with the metal oxide hydrogen sensor, the working temperature is lower, the power consumption is small, and the safety is also better.

[0029] The palladium nanostructure in the application is discontinuously distributed in the form of particles on the surface of the TMDCs, and can be prepared by controlling the deposition of palladium, for example, in the case of physical vapor deposition and chemical vapor deposition, the deposition is terminated at the island nucleation stage (for example, in the case of electron beam evaporation coating method, the thickness of the deposited palladium material can be set to 0.5-2 nm; since this thickness parameter corresponds to the ideal flat growth, the actual nucleation points only occur randomly on the substrate, and the palladium nanostructure obtained in this way will form a discontinuous particle structure, and the height of any palladium nanostructure is 1-5 nm, and the diameter is 1-100 nm); for example, in the case of spin coating, a solution containing palladium nanoparticles can be used for spin coating, and the density and size of the nanoparticles obtained by spin coating can be controlled by controlling the solution concentration and spin coating speed. The two-dimensional TMDCs used in the application are in a high sheet resistance state, and the sheet resistance at room temperature is not less than 1*10 8 Ω / square, which can be prepared by referring to the related methods of the prior art (for example, by preparing intrinsic materials, or preparing materials in a state close to intrinsic state with a small amount of defects and impurities, or by compensation doping; either directly grown on the surface of the insulating substrate by chemical vapor deposition method, or separately prepared and then transferred to the insulating substrate). The application can be compatible with standard photolithography process, and the size can be in the order of chip size, which is very convenient for chip compatibility.

[0030] In summary, the hydrogen sensor of the application not only has greatly improved sensitivity and selectivity of the device, but also reduces the working temperature, and the sensor working temperature can be room temperature to 100 DEG C, and is easy to integrate into mature semiconductor-based chips, which also conforms to the development trend of miniaturization, portability and intelligence of gas sensors. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 A structure schematic diagram of a hydrogen sensor of a high sheet resistance two-dimensional transition metal chalcogenide modified by a palladium nanostructure provided by the application; wherein, Figure 1 (a) in the above is a front view, Figure 1 (b) in the above is a plan view.

[0032] Figure 2 A flowchart schematic diagram of a preparation method of a hydrogen sensor of a high sheet resistance two-dimensional transition metal chalcogenide modified by a palladium nanostructure provided by the application.

[0033] Figure 3 An atomic force microscope diagram of the palladium nanostructure prepared in Example 1 of the application.

[0034] Figure 4The current change diagram corresponding to the repeated detection of the hydrogen gas sensor with high square resistance two-dimensional transition metal chalcogenide modified by palladium nanostructure obtained in Embodiment 1 on the environment with a hydrogen gas concentration of 0.01 ppm.

[0035] The meanings of the reference signs in the drawings are as follows:

[0036] 101 insulating layer

[0037] 201 two-dimensional transition metal chalcogenide TMDCs layer

[0038] 301 metal electrode layer

[0039] 401 palladium nanostructure layer

[0040] 501 heating electrode layer DETAILED DESCRIPTION

[0041] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0042] Embodiment 1

[0043] Figure 1 The present application provides a structure diagram of a high square resistance two-dimensional transition metal chalcogenide hydrogen gas sensor modified by palladium nanostructure, and the specific preparation method flow is as shown in Figure 2 It should be noted that the diagrams provided in the present embodiment only illustrate the basic concept of the present application in a schematic manner, and only show the components related to the present application in the diagrams, not the number, shape and size of the components actually implemented. The type, number and proportion of each component can be changed in actual implementation, and the layout type of the components can also be more complex.

[0044] As shown in Figure 1 The high square resistance two-dimensional transition metal chalcogenide hydrogen gas sensor modified by palladium nanostructure of the present embodiment at least includes: an insulating substrate 101; a two-dimensional transition metal chalcogenide layer 201 forming a conductive channel; a metal electrode layer 301; a palladium nanoparticle layer 401 as a hydrogen sensitive layer; and a heating electrode layer 501 (the heating electrode layer 501 is mainly used to provide a temperature environment required for detection. Since the device of the present application can be detected at room temperature, the heating electrode layer 501 is optional).

[0045] As shown in Figure 2As shown, the preparation method of the high-resistance two-dimensional transition metal dichalcogenide hydrogen sensor modified by palladium nanostructures in the embodiment at least includes:

[0046] In step S1, an insulating substrate 101 with a heating electrode layer 501 is provided, and the insulating substrate 101 has a two-dimensional transition metal dichalcogenide film layer 201 thereon, specifically:

[0047] The two-dimensional TMDCs layer film is directly grown or transferred to the surface of the insulating substrate, for example, a two-dimensional TMDCs film is directly formed on the surface of the insulating substrate by using a chemical vapor deposition, an atomic layer deposition, a dry transfer method, etc.

[0048] The insulating substrate 101 is any one of glass, quartz, ceramic, sapphire, etc. or a composite structure composed of them.

[0049] Optionally, the insulating substrate 101 can also be a semiconductor wafer containing an insulating layer.

[0050] The semiconductor wafer is any one of elemental semiconductors Si, Ge, and compound semiconductors GaAs, InP, etc. or any one of binary and binary or more alloys thereof.

[0051] The insulating layer is any one of SiO2, Al2O3, HfO2, AlN, etc. and any one of binary and binary or more compounds or laminates thereof.

[0052] The two-dimensional TMDCs film layer 201 is any one of MoS2, WS2, MoSe2, WSe2 or any one of alloys thereof.

[0053] In the embodiment, the insulating substrate 101 uses p-type resistive silicon with a resistivity of 0.001 Ωcm as a semiconductor wafer substrate, and SiO2 as an insulating layer. A multilayer WSe2 film (30 layers in the embodiment) is prepared on the insulating substrate by a mechanical exfoliation method, as a two-dimensional TMDCs film layer. The sheet resistance of the multilayer WSe2 film at room temperature is 1×10 8 Ω / square.

[0054] In step S2, a photolithography process is used to perform a patterning treatment on the TMDCs film to form a window exposing the TMDCs film. Specifically:

[0055] A photoresist is formed on the surface of the two-dimensional TMDCs layer, a photo mask with a predetermined layout is used to expose the photoresist layer, and then the photoresist is developed to pattern the photoresist;

[0056] In the embodiment, specifically:

[0057] Step S201, spin-coating PMMA photoresist on the surface of WSe2, first 1000 rpm for 5 s, then 2000 rpm for 40 s to form a photoresist film layer with a thickness of about 500 nm, and then baking at 170°C for 90 s;

[0058] Step S202, photoetching, exposing the photoresist through a photo mask with a predetermined layout, exposure dose 400 uc / cm 2 , developing for 60 s and then fixing in isopropyl alcohol to form a pattern structure on the photoresist;

[0059] Step S3, depositing metal with the photoresist as a mask to form N-type contact electrodes (i.e., the first electrode and the second electrode respectively located at both ends of the TMDCs) in the window area. Considering that in some cases it is difficult to obtain low-resistance ohmic contact by directly contacting the metal with the high-square-resistance two-dimensional TMDCs, thereby affecting the performance of the device, in this embodiment, an N-type interface layer is first formed on the surface of the TMDCs in the window area with the photoresist as a mask before the metal electrode is formed, to achieve local N-type doping, and then the metal is deposited to form the N-type contact electrode. The Fermi level position of the N-type interface layer is higher than that of the high-square-resistance two-dimensional TMDCs, to facilitate the transfer of electrons from the N-type interface layer to the TMDCs, achieve local electron doping of the TMDCs, and reduce the contact resistance. Specifically:

[0060] The N-type interface layer can be a TMDCs with high electron doping concentration or other conductive material with high doping concentration, as long as it can form an N-type contact with the TMDCs; the Fermi level position of the N-type interface layer is higher than that of the TMDCs, to facilitate the transfer of electrons from the N-type interface layer to the TMDCs, achieve local electron doping of the TMDCs.

[0061] The N-type interface layer can be a TMDCs with high electron doping concentration or other conductive material with high doping concentration, as long as it can form an N-type contact with the TMDCs; the Fermi level position of the N-type interface layer is higher than that of the TMDCs, to facilitate the transfer of electrons from the N-type interface layer to the TMDCs, achieve local electron doping of the TMDCs.

[0062] In this embodiment, Ar plasma treatment is used to artificially generate a large number of chalcogen vacancies in the surface layer of the TMDCs crystal, forming an interface layer rich in chalcogen vacancies. The high-concentration electrons introduced by the chalcogen vacancies doped in the interface layer result in N-type heavy doping, which serves as an N-type interface layer. Through charge transfer, the TMDCs in contact with the N-type interface layer are doped to become an N-type doped TMDCs region, reducing the contact resistance of the device.

[0063] In the Ar plasma treatment, the parameters can be set as follows: Ar flow rate 80 sccm, power 200 W, and treatment time 10 s.

[0064] The metal electrode layer is formed by taking the patterned photoresist as a mask, depositing metal by physical vapor deposition, and then removing the photoresist;

[0065] The N-type contact electrode layer 301 is a low work function metal such as one of Ni, Ti, Cr, Al, Ag, Mo, W, or any of their alloys or laminates;

[0066] In this embodiment, a 15-nm Ti and 35-nm Au laminate is selected for electron beam evaporation, and then the photoresist is removed to form the N-type contact electrode layer 301.

[0067] In step S4, a photoetching process is used to leave a portion of the window in the middle of the channel of the two-dimensional TMDCs film, and palladium nanoparticles 401 are deposited as a hydrogen-sensitive layer; specifically:

[0068] A photoresist is formed on the surface of the two-dimensional TMDCs layer, the photoresist layer is exposed by a photo mask with a predetermined layout, then developed, the photoresist is patterned, a palladium layer is deposited, and the photoresist is removed to form a hydrogen-sensitive layer;

[0069] In this embodiment, specifically:

[0070] In step S401, PMMA photoresist is spin-coated, first at 1000 rpm for 5 s, then at 2000 rpm for 40 s to form a photoresist film layer about 500 nm thick, and then baked at 170°C for 90 s;

[0071] In step S402, photoetching is performed by exposing the photoresist to a pre-drawn layout with an exposure dose of 400 uc / cm 2 , and developing for 60 s and then fixing in a large amount of isopropyl alcohol to form a window on the photoresist;

[0072] In step S403, the sample is placed in an electron beam evaporation film plating machine and vacuumed, and 1 nm of palladium is artificially deposited (this thickness corresponds to the island nucleation stage; this thickness parameter corresponds to ideal flat growth, and since the actual nucleation points occur randomly on the substrate, the palladium nanostructure obtained will form a discontinuous granular structure; of course, in addition to the deposition thickness of 1 nm, the deposition thickness can also be other values less than or equal to 2 nm, which all correspond to island nucleation, and the corresponding palladium nanostructure, the height of the single nanoparticle structure is 1-5 nm, and the projection size on the TMDCs plane is 1-100 nm, which also helps to increase the effective contact area with hydrogen in the test stage); the atomic force microscope image of the palladium nanostructure obtained in this embodiment is shown in Figure 3 ;

[0073] At step S404, the TMDCs film 201 is removed by a removing solution 1165 to form a palladium nanostructure layer to cover part of the conductive channel of the TMDCs film 201 as a hydrogen sensitive layer.

[0074] The prepared hydrogen sensor is subjected to H2 sensing test. Specifically, lead wires are first made for the hydrogen sensor to lead out the first electrode and the second electrode. Then, the device is placed in a sealed test chamber. The test chamber has two air flow pipes connected with a H2 gas cylinder and an air cylinder respectively. The flow of each air flow pipe is controlled by a flow meter. Under the condition that the device is heated to 70°C, the flow of H2 and air is controlled so that the concentration of H2 is 0.01ppm. At this time, the current of the device gradually increases. After 10 minutes, the valve of the H2 pipe is closed and the test chamber is opened so that the concentration of H2 rapidly decreases. The above process is repeated four times. The current change curve of the device is shown in FIG. 6. As can be seen from FIG. 6, the device of the present application can detect H2 with a concentration as low as 0.01ppm. Figure 4

[0075] It is to be understood by those skilled in the art that the above description is only the preferred embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.​

Claims

1. A hydrogen sensor with palladium nanostructures modified high square resistance two-dimensional transition metal dichalcogenides (TMDCs) characterized in that, The hydrogen sensor is provided with a two-dimensional transition metal dichalcogenide (TMDC) as a conductive channel, the TMDC is arranged on an insulating substrate and connected with a first electrode and a second electrode at two ends; and the TMDC has a high square resistance, and a square resistance thereof at normal temperature is not less than 1*10 8 Ω / square; a palladium nanostructure is distributed in a discontinuous particle form only on a surface of the TMDC and directly contacts the TMDC to serve as a hydrogen sensitive layer; when the hydrogen sensor encounters hydrogen, a mobility and a concentration of carriers in the TMDC will change, so that a resistance between the first electrode and the second electrode changes, thereby realizing sensing of the hydrogen.

2. The hydrogen sensor of claim 1, which uses palladium nanostructures to modify high sheet resistance two-dimensional transition metal chalcogenides (TMDCs), is characterized in that... The palladium nanostructure is discontinuous and nanoparticle-like; any one nanoparticle-like structure has a height of 1-5 nm and a projected size of 1-100 nm on the plane of the TMDCs.

3. The hydrogen sensor of claim 1, which uses palladium nanostructures to modify high sheet resistance two-dimensional transition metal chalcogenides (TMDCs), is characterized in that... The first electrode and the second electrode are both N-type contact electrodes; the TMDCs are connected to the N-type contact electrodes through an N-type interface layer.

4. The hydrogen sensor of claim 1, wherein the palladium nanostructure is modified to high square resistance two-dimensional transition metal dichalcogenide (TMDCs). The insulating substrate additionally has a heating electrode.

5. A method of fabricating a hydrogen sensor with high sheet resistance two-dimensional transition metal dichalcogenide (TMDCs) modified with palladium nanostructures as claimed in any one of claims 1 to 4, characterized in that, The method comprises the following steps: (1) preparing an insulating substrate and forming a high-square-resistance two-dimensional transition metal dichalcogenide (TMDCs) film layer on the insulating substrate; (2) performing a photolithography process on the TMDCs film layer to form a window exposing part of the TMDCs film; (3) depositing a metal electrode material using the photoresist as a mask to form a first electrode and a second electrode in the window area; (4) performing a photolithography process to leave part of the window in the middle of the channel of the TMDCs film, and depositing a palladium nanostructure as a hydrogen-sensitive layer.

6. The preparation method according to claim 5, characterized in that, In step (1), the insulating substrate is any one of glass, quartz, ceramic, sapphire or a composite structure formed by the above materials, or a semiconductor substrate containing an insulating layer; For the semiconductor substrate containing an insulating layer, the semiconductor substrate is specifically one of elemental semiconductors Si and Ge, and one of compound semiconductors GaAs and InP, or an alloy formed by two or more of the above semiconductors; the insulating layer is any one of SiO2, Al2O3, HfO2 and AlN, or a compound or a stack formed by two or more of the above insulating layers, and the thickness of the insulating layer is 10-1000 nm; In step (1), the two-dimensional transition metal dichalcogenide (TMDCs) film layer is directly grown or transferred onto the insulating substrate; In step (1), the two-dimensional transition metal dichalcogenide (TMDCs) film layer is one of WSe2, MoSe2, MoS2 and WS2, or any one of a compound of the above materials, and the thickness of the two-dimensional transition metal dichalcogenide (TMDCs) film layer is 0.7-100 nm; In step (3), before depositing the metal electrode material using the photoresist as a mask, an N-type interface layer is first formed on the surface of the TMDCs in the window area to achieve local N-type doping; the N-type interface layer is formed by physical deposition or chemical deposition, or by a plasma process surface treatment method to cause physical or chemical changes in the TMDCs in the window area, and the thickness of the N-type interface layer is 1-50 nm; In step (3), for any one of the first electrode and the second electrode, the metal electrode material is one of Ni, Ti, Cr, Al, Ag, Mo and W, or any one of an alloy or a stack of the above materials; the thickness of the first electrode and the second electrode is 5-200 nm; In step (4), the palladium nanostructure is prepared by physical vapor deposition, chemical vapor deposition or spin coating.

7. The preparation method according to claim 6, characterized in that, In the step (4), the palladium nanostructure is prepared by an electron beam evaporation method.

8. The preparation method according to claim 5, characterized in that, In the step (1), the insulating substrate additionally has a heating electrode.

Images