Graphene gas sensor based on edge structure regulation and preparation method thereof

Abstract

The application relates to a graphene gas sensor based on edge structure regulation and a preparation method thereof. The graphene gas sensor comprises a gas-sensitive material and electrodes arranged at two ends of the gas-sensitive material, and the gas-sensitive material is a graphene strip with a specific edge structure, and the specific edge structure comprises ZZ edge structure or AC edge structure formed by directional processing along ZZ crystal orientation or AC crystal orientation. The preparation method comprises the following steps: forming single-layer graphene on a silicon substrate through a chemical vapor deposition method, and then performing characterization on the lattice structure of the graphene, determining the AC direction and the ZZ direction in the graphene lattice, and determining the crystal orientation; based on the determined crystal orientation, directional processing is performed along the specific crystal orientation to form the target specific edge structure, so that the graphene strip with the specific edge structure is obtained; and the graphene strip with the specific edge structure is used as the gas-sensitive material, electrodes are deposited at two ends of the graphene strip, ohmic contact is formed, and the device preparation of the graphene gas sensor is completed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas sensors, and in particular to a graphene gas sensor based on edge structure regulation and a preparation method thereof. BACKGROUND

[0002] In the field of gas sensors, traditional gas sensors (such as electrochemical oxygen sensors, optical oxygen sensors, and metal oxide semiconductors) generally have poor stability, are easily disturbed by the environment, are high in cost, and have single selectivity, which makes it difficult to meet the demand for high-precision detection. For example, metal oxide sensors have a significant decrease in sensitivity in a high-humidity environment due to surface adsorption of water, and the complex optical path design of optical oxygen sensors increases the system cost and volume.

[0003] Graphene has become an ideal sensor channel material due to its excellent electrical properties and tunable band gap of the edge structure. For example, CN109374688A discloses a graphene-based gas detection method, device, and graphene gas sensor. The method includes: a graphene gas sensor detects a to-be-measured gas in an environment in which the graphene gas sensor is located and outputs an electrical signal for representing a concentration of the to-be-measured gas; and a microprocessor converts an electrical signal value corresponding to the electrical signal for representing the concentration of the to-be-measured gas into a concentration value of the to-be-measured gas based on a corresponding relationship between the gas concentration value and the electrical signal value. For another example, CN114778618A discloses a preparation process of a graphene / tungsten disulfide gas sensor, which includes: depositing an insulating layer on the upper surface of a substrate; ultrasonic cleaning the substrate and depositing a thickness-controllable spline electrode on the surface of the insulating layer; using a wet transfer method to transfer a graphene layer to the surface of the spline electrode; preparing a 10 mg / ml tungsten disulfide suspension, dropping 1-2 drops of the suspension onto the surface of the graphene layer using a pipette, and drying at room temperature and at 60°C to obtain the graphene / tungsten disulfide gas sensor.

[0004] However, existing research is insufficient in exploring the differences in electrical properties and chemical activity of two typical edge structures of graphene, Zigzag edge (ZZ edge) and Armchair edge (AC edge), and their influence on the response of gas sensors. For example, existing graphene sensors mostly use planar graphene structures, and the effective active site density of gas adsorption is low (only 1-3×10 12 cm -2 ), which results in a response sensitivity (ΔR / R0) to target gases (such as O2) generally lower than 5%.

[0005] Furthermore, on the one hand, there are differences in understanding among those skilled in the art; on the other hand, the applicant studied a large number of documents and patents when making this invention, but due to space limitations, not all details and contents were listed in detail. However, this does not mean that the present invention does not possess the features of these prior art. On the contrary, the present invention already possesses all the features of the prior art, and the applicant reserves the right to add relevant prior art to the background art. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to provide a graphene gas sensor based on edge structure modulation and its preparation method. By modulating the edge structure of graphene, the sensor's response sensitivity, response speed, recovery speed, repeatability, and stability to target gases are improved, thus solving at least some of the aforementioned technical problems. O2 adsorption molecules alter the local carrier concentration in graphene, thereby changing its conductivity. Specifically, when O2 molecules attach to the graphene film, they act as p-type dopants, adsorbing electrons through electronegativity (forming epoxides or carboxyl groups), prompting more holes to enter the conduction band, thereby increasing the hole concentration in the conduction band. This process not only enhances the hole conduction ability but also leads to a significant change in the gas sensor's response and sensitivity. The advantage of the ZZ edge sensor stems from the unpaired π electrons (spin polarization > 90%) of the edge carbon atoms, resulting in a higher chemisorption energy (-0.8 eV) for O2 molecules compared to the AC edge (-0.5 eV), and an increase in charge transfer of 0.2 e, leading to an improvement in ΔR / R0. O2 molecules are primarily adsorbed at defect sites or step edges on the graphene plane. Compared to the original graphene gas sensor, sensors with AC edges and ZZ edges have abundant edge defect sites for adsorbing active gases, thus enabling them to adsorb more O2 molecules and increase sensor sensitivity. In contrast, ZZ edge sensors exhibit relatively higher sensitivity than AC edge sensors, mainly due to the higher reactivity of their edge structure, providing more adsorption active sites than AC edges, making it easier to adsorb or adsorb more O2 molecules.

[0007] This invention discloses a graphene gas sensor based on edge structure modulation, which includes a gas-sensitive material and electrodes disposed at both ends of the gas-sensitive material. The gas-sensitive material is a graphene strip with a specific edge structure, which includes a ZZ edge structure or an AC edge structure formed by orientation processing along a ZZ crystal orientation or an AC crystal orientation.

[0008] According to a preferred embodiment, the method for regulating specific edge structures includes, but is not limited to, mechanical scratching, plasma etching, chemical trimming, or template-assisted growth. The above-mentioned regulation methods are used to oriented the graphene strips along the ZZ crystal orientation or AC crystal orientation to form the target specific edge structure.

[0009] According to a preferred embodiment, the graphene strip is a monolayer graphene formed on a silicon substrate by chemical vapor deposition. The AC and ZZ directions in the graphene lattice are determined by characterizing the lattice structure of the monolayer graphene, thereby clarifying the AC crystal orientation and the ZZ crystal orientation.

[0010] According to a preferred embodiment, the electrode material includes silver, gold, platinum or their alloys, with a thickness of 200-400 nm, and is deposited on both ends of a graphene strip by vapor deposition, sputtering or electron beam evaporation processes to form an ohmic contact.

[0011] This invention also discloses a method for fabricating a graphene gas sensor based on edge structure modulation, which includes the following steps:

[0012] S1. A single layer of graphene is formed on a silicon substrate by chemical vapor deposition, and its lattice structure is characterized to determine the AC and ZZ directions in the graphene lattice and clarify the crystal orientation.

[0013] S2. Based on the determined crystal orientation, directional processing is carried out along the specific crystal orientation to form the specific edge structure of the target, thereby obtaining graphene strips with specific edge structures;

[0014] S3. Using graphene strips with specific edge structures as gas-sensitive materials, electrodes are deposited at both ends to form ohmic contacts, thereby completing the fabrication of the graphene gas sensor device.

[0015] According to a preferred embodiment, monolayer graphene is deposited on a silicon substrate with an oxide layer. During the chemical vapor deposition process, the reaction chamber temperature, methane flow rate, hydrogen flow rate, growth time, and cooling rate are controlled to ensure that the monolayer coverage of the graphene film is not less than 95%. The number of layers and crystal quality are confirmed by optical microscopy and Raman spectroscopy analysis.

[0016] According to a preferred embodiment, the method for regulating specific edge structures includes, but is not limited to, mechanical scratching, plasma etching, chemical trimming, or template-assisted growth. The above-mentioned regulation methods are used to oriented the graphene strips along the ZZ crystal orientation or AC crystal orientation to form the target specific edge structure.

[0017] According to a preferred embodiment, mechanical scratching is performed using a friction and wear testing machine, with the scratch direction along the calibrated ZZ crystal orientation or AC crystal orientation. After scratching, the graphene strip is sequentially subjected to ultrasonic cleaning, deionized water rinsing, and high-purity nitrogen purging to remove surface contaminants and maintain interface cleanliness.

[0018] According to a preferred embodiment, the electrode material includes silver, gold, platinum or their alloys, with a thickness of 200-400 nm, and is deposited on both ends of a graphene strip by vapor deposition, sputtering or electron beam evaporation processes to form an ohmic contact.

[0019] According to a preferred embodiment, the edge structure of the graphene strip is characterized by conductive atomic force microscopy and Raman spectroscopy to confirm that its edge orientation is ZZ or AC, and to verify the edge defect density and dangling bond distribution.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0021] (1) This invention prepares graphene strips with specific edge structures (ZZ edge and AC edge) as gas-sensitive materials. Compared with the original planar graphene, it increases the effective area and active sites for gas adsorption, and significantly improves the response sensitivity (ΔR / R0) of the gas sensor to the target gas (such as O2). The sensitivity of the ZZ edge sensor is twice that of the AC edge sensor and about four times that of the original planar sensor.

[0022] (2) Graphene strip sensors with specific edge structures provide more adsorption sites and improve the reactivity with gas molecules, resulting in a significant improvement in the response and recovery speed of the sensor compared to the original planar graphene sensor.

[0023] (3) Through repeatability testing of the sensor, the results show that the graphene sensor of the present invention has a highly consistent response to the target analytical gas in multiple cycles of testing without any additional light or heat treatment, demonstrating excellent repeatability and stability, and is suitable for gas detection in various environments. Attached Figure Description

[0024] Figure 1 An optical microscope image of CVD graphene;

[0025] Figure 2 CAFM lattice characterization image of the surface smooth region of CVD graphene;

[0026] Figure 3 Raman image of CVD graphene;

[0027] Figure 4 The image is obtained by Fourier transform processing of the CAFM lattice characterization image of CVD graphene;

[0028] Figure 5 The fabrication design diagram for ZZ edge structure graphene strips;

[0029] Figure 6 An optical microscope image of ZZ edge-structured graphene strips;

[0030] Figure 7 CAFM atomic lattice structure characterization image of ZZ edge structure graphene strips;

[0031] Figure 8 Raman characterization image of ZZ edge structure graphene strips;

[0032] Figure 9 A schematic diagram of a graphene sensor fabricated using graphene strips with ZZ and AC edge structures and unprocessed pristine graphene planes as gas-sensitive materials.

[0033] Figure 10 The graph shows the IV curve test results of the basic resistance measurement of three graphene gas sensors.

[0034] Figure 11 The graph shows the Rt curve test results of the basic resistance measurement of three graphene gas sensors.

[0035] Figure 12 The graph shows the test results of the response characteristics of three graphene gas sensors to O2.

[0036] Figure 13 The graph shows the sensitivity test results of three graphene gas sensors.

[0037] Figure 14 The graph shows the test results of response time and recovery time of a graphene gas sensor with an original planar structure.

[0038] Figure 15 The graph shows the test results of the response time and recovery time of the graphene gas sensor with AC edge structure.

[0039] Figure 16 The graph shows the test results of the response time and recovery time of the graphene gas sensor with ZZ edge structure.

[0040] Figure 17 The figure shows the repeatability and stability verification test results of a graphene gas sensor with an original planar structure.

[0041] Figure 18 The figure shows the repeatability and stability verification test results of a graphene gas sensor with an AC edge structure.

[0042] Figure 19 Figure showing the repeatability and stability verification test results of a graphene gas sensor with a ZZ edge structure;

[0043] Figure 20A fabrication design diagram for AC edge-structured graphene strips;

[0044] Figure 21 Optical microscope image of graphene strips with AC edge structure;

[0045] Figure 22 Image representing the CAFM atomic lattice structure of AC edge-structured graphene strips;

[0046] Figure 23 Raman characterization image of AC edge structure graphene strips. Detailed Implementation

[0047] The following is a detailed explanation with reference to the accompanying drawings.

[0048] This invention discloses a graphene gas sensor based on edge structure modulation and its fabrication method. The graphene gas sensor includes a gas-sensitive material and electrodes. The gas-sensitive material is a graphene strip with a specific edge structure, namely a Zigzag edge (ZZ edge) or an Armchair edge (AC edge). The electrodes are disposed at both ends of the gas-sensitive material. The electrode material includes silver, gold, platinum, or their alloys, with a thickness of 200-400 nm, and can be deposited by vapor deposition, sputtering, or electron beam evaporation. More preferably, the electrodes can be silver electrodes deposited by vapor deposition with a thickness of 300 nm. However, the following metallic materials and alloys are all suitable and can achieve equivalent or better electrical contact performance: Gold (Au) electrodes can be selected with a thickness of 200~400 nm (preferably 300 nm), with a contact resistance 15% lower than silver (Ag) electrodes (≤80 Ω), suitable for high-temperature environments (temperature resistance >300℃); Platinum (Pt) electrodes can be selected with a thickness of 250~350 nm, with better corrosion resistance than Ag electrodes, and 30% improved electrode stability in high humidity (>90% RH) environments, suitable for marine or chemical applications; Alloy electrodes (such as Ag-Au alloys) also possess high conductivity (conductivity ≥4×10⁻⁶). 7 The electrode exhibits improved S / m (solar flux ratio) and oxidation resistance, resulting in a lifespan twice that of pure Ag electrodes. Electrode thickness can be adjusted between 200 and 400 nm. Increasing thickness reduces contact resistance (e.g., a 10% reduction in resistance at 400 nm compared to 300 nm), but thicknesses exceeding 400 nm may introduce edge warping (warping > 5% affects performance). Besides vapor deposition, magnetron sputtering (100 W sputtering power, 0.5 Pa pressure, 2 nm / s deposition rate) or electron beam evaporation (10 kV accelerating voltage, 1.5 nm / s evaporation rate) can also achieve uniform electrode thickness (deviation ≤ 5%).

[0049] Preferably, graphene strips with specific edge structures can be prepared in the following manner:

[0050] S1. A single layer of graphene is formed on a silicon substrate by chemical vapor deposition, and its lattice structure is characterized to determine the AC and ZZ directions in the graphene lattice and clarify the crystal orientation.

[0051] S2. Based on the determined crystal orientation, directional processing is carried out along a specific crystal orientation to form a specific edge structure of the target, thereby obtaining graphene strips with a specific edge structure.

[0052] Preferably, in step S1, a silicon substrate with a smooth surface, good thermal stability, and a 300 nm thick oxide layer can be selected first, and the surface roughness of the oxide layer should not exceed 0.2 nm to ensure high-quality transfer and interface stability of the subsequent graphene material. On such a substrate, a single-layer graphene film with a size of 10 cm × 10 cm is formed by chemical vapor deposition (CVD). During the deposition process, the reaction chamber temperature is precisely controlled at 1000 ± 10 °C, the flow rate of methane (CH4) is 20 sccm, the flow rate of hydrogen (H2) is 50 sccm, the growth time is set to 30 minutes, and then the temperature is reduced to room temperature at a cooling rate of 50 °C / min, finally obtaining high-quality CVD graphene with a single-layer coverage of not less than 95%. To confirm its crystal quality and layer number, the uniformity of graphene coverage can be initially observed using an optical microscope, and then combined with Raman spectroscopy analysis of its G peak (approximately 1580 cm⁻¹). -1 ) and 2D peak (approximately 2680 cm) -1 Based on the intensity ratio and full width at half maximum (FWHM), it was determined to be a typical monolayer. Simultaneously, conductivity imaging and morphology scanning of the local area using conductive atomic force microscopy (CAFM) further verified its low surface defect density, uniform conductivity distribution, and the absence of obvious multilayer or wrinkled structures. Building upon this, atomic-resolution images obtained from CAFM were processed using Fourier transform to identify the AC and ZZ directions in the graphene lattice, clarifying the crystal orientation and providing precise guidance for subsequent anisotropic edge processing. The crystal orientation includes armchair-shaped crystal orientation (i.e., AC crystal orientation) and serrated crystal orientation (i.e., ZZ crystal orientation).

[0053] Preferably, after determining the planar lattice structure (i.e., crystal orientation) in step S1, step S2 can be performed to control the edge structure. Using a tribological testing machine (UMT) equipped with 6 mm diameter silica spheres, directional scratching is performed on the graphene surface with calibrated AC and ZZ crystal orientations. The normal load is set to 100 mN, the scratching speed to 0.5 mm / s, and 10 reciprocating scratches are performed along both the ZZ and AC crystal orientations, forming graphene strip structures with a width of approximately 0.5 mm. This mechanical scratching process induces carbon atom bond breakage through localized stress, preferentially cleaving along specific crystal orientations, thereby controllably exposing edge structures dominated by ZZ or AC. After scratching, the sample is immersed in anhydrous ethanol and ultrasonically cleaned at 40 kHz for 5 minutes (power density ≤100 mW / cm²). 2 The cavitation effect was used to effectively remove micron-sized particulate contaminants generated during the scratching process. The surface was then rinsed three times with high-purity deionized water (resistivity ≤18.2 MΩ·cm), 30 seconds each time, to remove residual ethanol and soluble ionic impurities. Finally, high-purity nitrogen (≥99.999%) was used to purge the surface at a 45° angle for approximately 2 minutes to ensure the sample surface was completely dry and free of droplets. To verify the crystal orientation of the prepared edges, CAFM was used again to characterize the area near the scratch edges at the nanoscale: a flat area was first selected within a 30 μm × 30 μm range, then the area was reduced to 3 nm × 3 nm for high-resolution scanning. Fourier transform analysis was used to analyze the crystal orientation of the planar lattice and graphene strip edges, confirming that the strip edges were aligned along the ZZ or AC directions, respectively. Simultaneously, the D peak (approximately 1350 cm⁻¹) in the Raman spectrum was used to further analyze the crystal orientation. -1 Using spatial imaging characteristics, the edge structure of graphene strips was tested. It was found that the D peak signal was significantly enhanced at the AC edge, indicating that there is a high density of defect states and dangling bonds at the edge. The D peak intensity near the ZZ edge was relatively weak, reflecting that the edge structure was more ordered, but still had abundant unsaturated carbon atom active sites. Together, they constitute different types of edge chemical active centers.

[0054] Preferably, in addition to the scratch method using a friction and wear testing machine, the edge structure control of the present invention can also be achieved through the following equivalent technical solutions, all of which can achieve the technical effect of directional control of the ZZ / AC edge ratio: plasma etching directional processing method; chemical trimming method; template-assisted growth method.

[0055] Preferably, the graphene strips with specific edge structures (ZZ edges and AC edges) prepared based on the above method are used as gas-sensitive materials, and a graphene gas sensor is prepared in the following manner:

[0056] S3. Using graphene strips with specific edge structures as gas-sensitive materials, electrodes are deposited at both ends to form ohmic contacts, thereby completing the fabrication of the graphene gas sensor device.

[0057] Preferably, in step S3, an electron beam evaporation deposition technique can be used to deposit a silver (Ag) electrode, with the vacuum level maintained at ≤10 during the deposition process. -4 At a deposition rate of 1 nm / s, an electrode structure with a thickness of 300 nm and a width of not less than 3 mm was formed, with an overlap length of ≥3 mm between the electrode and the graphene strip to ensure good ohmic contact. For example, an electron beam evaporation deposition system (E-Beam Evaporator, JSD500, Anhui Jiashuo Vacuum Technology Co., Ltd, China) was used. After deposition, the contact properties between the electrode and graphene were verified by current-voltage (IV) characteristic testing. The results showed that all three curves exhibited a good linear relationship, indicating the formation of a stable ohmic contact, which is beneficial for efficient carrier injection and transport.

[0058] Preferably, after the device fabrication is completed, a systematic gas-sensing performance test can be conducted. Using unscratched raw graphene planar strips as the gas-sensing material, electrodes of the same material and thickness are deposited at both ends of the gas-sensing material using the same evaporation method with an electron beam evaporation deposition machine, thereby preparing a raw planar graphene gas sensor (i.e., the original device) for reference. Before testing, the entire testing system undergoes rigorous purification: high-purity nitrogen (N2) is used as the carrier gas and purging gas to continuously purge the test chamber and pre- and post-conduction pipelines for 60 minutes to thoroughly remove residual water vapor, oxygen, and other interfering gases from the environment. The graphene gas sensor is placed in an optoelectronic integrated test platform (CGS-MT, Ailite Technology Co., Ltd, China), and after its resistance in air stabilizes, a sealed gas hood is applied. To further remove impurities such as organic matter and moisture adsorbed on the graphene surface, the temperature control module was activated to heat the platform to 100 ℃ and maintain this temperature for 60 minutes, allowing the sample to undergo surface desorption under an N2 atmosphere. Subsequently, the water circulation cooling system was activated for 30 minutes to cool the sample back to room temperature (25 ℃), and N2 was continuously introduced under constant temperature conditions until the resistance stabilized again, serving as the baseline for subsequent testing. During the test, a digital dynamic gas mixing system (DGD-II, Ailite Technology Co., Ltd, China) precisely prepared O2 / N2 mixed gases of different concentrations (total flow rate 500 sccm), which were sequentially introduced into the test chamber. A smart gas-sensitive analysis system (CGS-8, Ailite Technology Co., Ltd, China) was used to collect real-time data on the sensor resistance changes over time. The change in relative conductivity was defined as the response value, and the calculation formula was ΔR / R0(%)=(R-R0) / R0×100%, where R0 is the stable resistance of the sensor in a pure N2 environment, and R is the real-time resistance after exposure to the target gas. The tests included: response amplitude at different O2 concentrations, response time (time required for the response to reach 90% of its maximum value from gas introduction), recovery time (time required for the response to recover to below 10% from gas supply cessation), repeatability (response consistency in five consecutive cycles at the same concentration), and long-term stability (performance degradation after 72 hours of continuous operation). Experimental results showed that, compared to the original planar graphene gas sensor, sensors with AC-edge and ZZ-edge structures exhibited significantly enhanced gas-sensing responses.

[0059] The common technical features of equivalent technical solutions of this invention are specifically reflected in the following aspects: On the one hand, it has controllable edge structure, that is, through conventional technical means such as physical etching, chemical trimming or template growth, the construction of graphene ZZ (zigzag) edge or AC (armchair) edge can be accurately realized, and the edge defect density can be effectively controlled. According to the actual application requirements, the number and distribution of defects in the edge region can be controlled, laying the foundation for the subsequent performance optimization of graphene gas sensors; on the other hand, it has consistent performance improvement. Regardless of the edge control technology used, or the combination with different types of electrode materials such as metal electrodes, alloy electrodes, and conductive compound electrodes, the prepared graphene gas sensor can achieve a sensitivity improvement of ≥2 times in terms of relative resistance change ΔR / R0 compared with the original planar graphene sensor without edge structure, and the response time reduction is ≤50%. This fully demonstrates the stability and universality of edge structure control in improving sensor performance, and is not significantly affected by changes in non-core technical parameters. All technical alternatives that follow the core inventive concept of "improving the sensitivity and response speed of gas sensors by controllably constructing graphene edge structures" and possess the common technical features of consistent edge structure controllability and performance improvement are within the scope of protection of this patent.

[0060] Example 1

[0061] This embodiment describes the process of preparing a graphene gas sensor with ZZ edges based on the above preparation method.

[0062] A silicon substrate with a 300 nm thick oxide layer was selected, on which a 10 cm × 10 cm monolayer chemical vapor deposition graphene film was deposited. The presence of graphene could be discerned by optical microscopy. Figure 1 As shown. Further Raman spectroscopy analysis was performed on it, and the result was observed at approximately 1580 cm⁻¹. -1 A distinct G peak appears at approximately 2700 cm. -1 It exhibits a sharp and symmetrical 2D peak at approximately 1350 cm⁻¹, with an intensity higher than the G peak. -1 No significant D-peak signal was detected nearby, indicating that the graphene sample has a low in-plane defect density and is confirmed as a monolayer structure. Figure 3 As shown. Subsequently, lattice orientation calibration was performed under environmental conditions using a conductive atomic force microscope. First, a large area of ​​30 μm × 30 μm was scanned to locate flat areas on the surface (such as…). Figure 2 (As shown), the scanning scale is then gradually reduced to 20 nm × 20 nm, and high-resolution imaging is performed with a normal load of approximately 100 nN in a contact mode with applied bias. Finally, the scanning area is refined to 3 nm × 3 nm. Combined with the image obtained through Fourier transform processing, it is clear that in Figure 4The graphene lattice has an AC crystal orientation in the horizontal direction and a ZZ crystal orientation in the vertical direction, providing a directional reference for subsequent anisotropic edge processing.

[0063] Based on this, a tribological testing machine equipped with 6 mm diameter silica spheres was used to perform directional scratching along the calibrated ZZ crystal direction. Mechanical stress induced the graphene to fracture along a specific crystal orientation, forming a nanoribbon structure dominated by ZZ edges, such as... Figure 5 and Figure 6 As shown, where, Figure 5 This is a schematic diagram of the graphene lattice and the direction of the scratches. The arrows indicate that the scratches are carried out along the serrated crystal orientation related to ZZ. Figure 6 This is a strip image under an optical microscope, showing a clear ZZ edge region.

[0064] After scratching, the sample was sequentially subjected to ultrasonic cleaning with anhydrous ethanol, rinsing with deionized water, and drying with high-purity nitrogen at an angle to remove surface contaminants and ensure interface cleanliness. The edge regions of the resulting stripes were locally characterized using a conductive atomic force microscope (AFM). The analysis was performed by comparing the frictional force image with lattice-resolved images (such as...). Figure 7 As shown in the diagram (where the AC crystal direction and ZZ crystal direction are clearly marked), analysis confirms that the edge orientation is mainly arranged along the ZZ direction. Figure 8 As shown, by combining Raman spectroscopy and spatial imaging techniques, a relatively weak but still identifiable D peak signal was detected in the edge region, indicating that although there are a certain number of defect states at the edge, the overall structure is relatively ordered, mainly exhibiting ZZ crystal orientation characteristics, and there may be a small number of composite edge structures in some areas.

[0065] Using the ZZ edge graphene strip as the gas-sensitive functional material, silver electrodes were deposited at both ends using a vapor deposition method to form metal contacts with a thickness of 300 nm, thus constructing a complete sensor device structure, as shown in the figure. Figure 9 As shown.

[0066] Example 2

[0067] This embodiment describes the process of preparing a graphene gas sensor with AC edges based on the above preparation method.

[0068] The CVD graphene material used in this embodiment and its initial lattice characterization process are the same as in Example 1, i.e., it is also confirmed to be high-quality monolayer graphene using optical microscopy, Raman spectroscopy, and conductive atomic force microscopy, and the AC and ZZ crystal orientations are precisely determined. The difference lies in that, during the nanostructure processing stage, a tribological testing machine is used to perform scratch treatment along the AC crystal orientation, causing the graphene to preferentially break along the AC crystal orientation under mechanical action, thereby obtaining a strip structure dominated by the AC edge, such as... Figure 20 and Figure 21As shown, where, Figure 20 This is a schematic diagram of the graphene lattice and the direction of the scratches. The arrows indicate that the scratches are carried out along the armchair-shaped crystal orientation associated with AC. Figure 21 The image shows a stripe pattern under an optical microscope, revealing a clear AC edge region; subsequent cleaning processes are the same as described above, ensuring no residual particles or organic contaminants remain on the surface. Figure 22 As shown, the AC edge strip was characterized by conductive atomic force microscopy, and lattice image analysis confirmed that its edge orientation mainly extends along the AC direction. Figure 23 As shown, Raman spectroscopy tests revealed a significant enhancement of the D-peak signal in the edge region. Furthermore, spatial imaging of the D-peak showed a strong and concentrated signal distribution, indicating that the AC edge has a higher defect density and abundant dangling bond structure, which is conducive to the chemisorption of gas molecules. This verifies that its main characteristic is the orientation of AC crystals.

[0069] Using these AC-edge graphene strips as gas-sensitive materials, silver electrodes of the same thickness are deposited at both ends to fabricate a graphene gas sensor with AC edges. The device structure is as follows: Figure 9 As shown.

[0070] Example 3

[0071] This embodiment describes the process of preparing a raw planar graphene gas sensor by using an unscratched raw graphene planar strip as the gas-sensitive material and depositing electrodes of the same material and thickness at both ends of the gas-sensitive material using an electron beam evaporation deposition machine with the same evaporation method as described above.

[0072] This embodiment does not perform any mechanical scratch treatment, directly using pristine, unstructured monolayer CVD graphene as the gas-sensitive material. This material is also deposited on a silicon substrate with a 300 nm oxide layer, and its continuous, uniform, low-defect monolayer structure was confirmed by optical microscopy and Raman spectroscopy before fabrication. Figure 1 As shown. This pristine graphene film was directly used for device fabrication, with 300 nm thick silver electrodes symmetrically deposited at both ends to form a pristine planar graphene gas sensor. The electrode structure, contact method, and overall configuration of this device are consistent with those of Examples 1 and 2, with only the edge structure of the gas-sensitive material differing, thus forming a control experimental group used as a reference. The device structure is shown below. Figure 9 As shown.

[0073] Example 4

[0074] This embodiment compares the performance of graphene gas sensors with ZZ edges, graphene gas sensors with AC edges, and the original planar graphene gas sensor prepared in Examples 1-3, respectively.

[0075] Preferably, the above three devices undergo basic electrical performance tests, including original basic resistance measurement, current-voltage characteristic curve testing, and resistance-time response curve testing, to ensure that these devices have stable ohmic contacts. The test results are as follows: Figure 10 and Figure 11 As shown. Based on the test results, Figure 10 In the current-voltage (IV) characteristic curves, the graphene gas sensors with the original planar shape, ZZ edge, and AC edge all exhibit good linearity, indicating that all three devices possess stable ohmic contacts. Calculations of the curve slopes show that the resistance of the original planar graphene is approximately 970 Ω, while the resistances of the graphene with ZZ and AC edges are approximately 735 Ω and 719 Ω, respectively, demonstrating that the introduction of the graphene edge structure significantly reduces its resistance. Furthermore, Figure 11 The resistance-time (Rt) response curves show that the resistance of all three devices remained stable during the 250-second test period. The resistance of the original planar graphene stabilized at approximately 978 Ω, while the resistances of the ZZ-edge and AC-edge graphene stabilized at approximately 724 Ω and 709 Ω, respectively. This further verifies that these devices not only have stable ohmic contacts but also good electrical stability. Furthermore, the graphene gas sensor with edge structures exhibits lower resistance and better stability.

[0076] Preferably, under room temperature conditions, a constant bias voltage of 1000 mV is applied and zero gate voltage is maintained. Using a dynamic resistance monitoring method, the sensor is exposed to a mixture of oxygen and nitrogen with a concentration of 1% to 5%, and its resistance change is recorded in real time. The corresponding sensitivity, response time, and recovery time are calculated. The test results are as follows: Figures 12-16 As shown. From Figure 12 As can be seen from the real-time resistance change curve, as the oxygen concentration increases from 1% to 5%, the resistance fluctuation amplitude of the graphene gas sensor with ZZ edge and AC edge is significantly greater than that of the original planar graphene, reflecting that the edge structure can enhance the response to changes in oxygen concentration. Figure 13 In the sensitivity curves using relative resistance change (ΔR / R0) as an indicator, the original planar graphene has the lowest sensitivity (slope of only 0.24), the ZZ edge graphene has improved sensitivity (slope of 0.52), and the AC edge graphene has the highest sensitivity (slope of 1.02). Moreover, the ΔR / R0 of all three has a good linear relationship with oxygen concentration, indicating that the graphene edge structure (especially the AC edge) can significantly improve the sensing sensitivity of oxygen and has reliable quantitative detection potential. Figures 14-16The dynamic response characteristics under 1% oxygen concentration were further presented: the response time of the original planar graphene was 501s and the recovery time was 483s, while the response time of the graphene with AC edges was shortened to 388s and the recovery time was 249s, and the response time of the graphene with ZZ edges was 405s and the recovery time was 342s. This shows that the introduction of edge structures can accelerate the adsorption and desorption process of oxygen by the sensor and improve the dynamic response performance. Among them, the AC edge showed better performance in response speed and the ZZ edge showed better performance in recovery speed.

[0077] Preferably, four consecutive gas adsorption-desorption cycle tests were performed at a 2% oxygen concentration to verify the repeatability and stability of these devices. The test results are as follows: Figures 17-19 As shown in the results, in four consecutive adsorption-desorption cycles at a 2% oxygen concentration, the resistance change (ΔR) of the original planar graphene gas sensor was small and the fluctuation was gradual. Figure 17 The response to oxygen cycling is not significant; although the graphene gas sensor with AC edge can generate a resistance response, the repeatability and stability of the response are poor. Figure 18 ); while the graphene gas sensor with ZZ edges exhibits a large resistance variation and displays more regular and stable fluctuation characteristics in four cycles ( ); Figure 19 This indicates that the graphene gas sensor with ZZ edge structure exhibits better repeatability and stability in the adsorption-desorption process of oxygen at a 2% oxygen concentration, enabling more reliable cyclic detection. In contrast, sensors with the original planar structure and AC edge structure are relatively inferior in terms of the stability or amplitude of the cyclic response.

[0078] It should be noted that the specific embodiments described above are exemplary. Those skilled in the art can devise various solutions inspired by the disclosure of this invention, and these solutions all fall within the scope of this invention and its protection. Those skilled in the art should understand that this specification and its accompanying drawings are illustrative and do not constitute a limitation on the claims. The scope of protection of this invention is defined by the claims and their equivalents. This specification contains multiple inventive concepts; phrases such as "preferred" or "according to a preferred embodiment" indicate that the corresponding paragraph discloses an independent concept. The applicant reserves the right to file divisional applications based on each inventive concept. Throughout the text, the feature introduced by "preferred" is only an optional mode and should not be construed as mandatory. Therefore, the applicant reserves the right to abandon or delete relevant preferred features at any time.

Claims

1. A method for fabricating a graphene gas sensor based on edge structure modulation, characterized in that, It includes the following steps: S1. A single layer of graphene is formed on a silicon substrate by chemical vapor deposition, and its lattice structure is characterized to determine the AC and ZZ directions in the graphene lattice and clarify the crystal orientation. S2. Based on the determined crystal orientation, directional processing is carried out along the specific crystal orientation to form the specific edge structure of the target, thereby obtaining graphene strips with specific edge structures; S3. Using graphene strips with specific edge structures as gas-sensitive materials, electrodes are deposited at both ends to form ohmic contacts, thereby completing the fabrication of graphene gas sensor devices. The method for regulating the specific edge structure is mechanical scratching. The above-mentioned regulation method is used to process the graphene strip along the ZZ crystal orientation or AC crystal orientation to form the target specific edge structure. The monolayer graphene is deposited on a silicon substrate with an oxide layer. During the chemical vapor deposition process, the reaction chamber temperature, methane flow rate, hydrogen flow rate, growth time, and cooling rate are controlled to ensure that the monolayer coverage of the graphene film is not less than 95%. The number of layers and crystal quality are confirmed by optical microscopy and Raman spectroscopy analysis. The mechanical scratches are performed using a friction and wear testing machine, with the scratch direction along the calibrated ZZ crystal orientation or AC crystal orientation. After the scratches are applied, the graphene strips are sequentially subjected to ultrasonic cleaning, deionized water rinsing, and high-purity nitrogen purging to remove surface contaminants and maintain interface cleanliness.

2. The preparation method according to claim 1, characterized in that, The electrode material includes silver, gold, platinum or their alloys, with a thickness of 200~400 nm, and is deposited on both ends of the graphene strip by vapor deposition, sputtering or electron beam evaporation processes to form ohmic contacts.

3. The preparation method according to claim 2, characterized in that, The edge structure of the graphene strips was characterized by conductive atomic force microscopy and Raman spectroscopy, confirming that the edge orientation was ZZ or AC, and verifying the edge defect density and dangling bond distribution.

4. A graphene gas sensor based on edge structure modulation prepared by any one of claims 1 to 3, comprising a gas-sensitive material and electrodes disposed at both ends of the gas-sensitive material, wherein the gas-sensitive material is a graphene strip with a specific edge structure, the specific edge structure including a ZZ edge structure or an AC edge structure formed by orientation processing along a ZZ crystal orientation or an AC crystal orientation.

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