A method for manufacturing a high-moisture-resistance gas sensor based on a hetero film

Abstract

The application discloses a kind of high humidity resistance gas sensor manufacturing method based on hetero film, comprising the following steps: 1) ZnO nanorod is grown on the surface of Si substrate;2) MoS2 nanosheet is grown on the outer surface of ZnO nanorod, and MoS2 nanosheet is wrapped around ZnO nanorod;3) ZnO / MoS2 film is scraped from Si substrate;4) ZnO / MoS2 film is dissolved, to obtain ZnO / MoS2 dissolving solution;5) ZnO / MoS2 dissolving solution is cast on ceramic substrate with interdigital electrode, to obtain gas sensor with ZnO / MoS2 hetero film layer.The application synthesizes sensor with ZnO / MoS2 hetero film layer by chemical vapor deposition method, and the sensor has very high sensitivity to NO2 gas, and compared with traditional sensor, the sensor prepared by the application is more resistant to high humidity environment.

Description

Technical Field

[0001] This invention relates to the field of gas sensor fabrication, specifically a method for fabricating a highly moisture-resistant gas sensor based on a heterogeneous film. Background Technology

[0002] Zinc oxide (ZnO) possesses good stability and high sensitivity, and has been widely used in gas sensors. However, its high detection limit (LoD) and humidity-dependent response are two significant drawbacks affecting its sensing performance.

[0003] When the ambient RH is sufficiently high, polarization often occurs due to the presence of strongly bound chemisorption or physisorption of water molecules. Water molecules interact with hydroxyl groups or oxygen on the zinc oxide surface via H+ ions. Since the adsorbed H2O can act as both a proton acceptor and a proton donor, this interaction leads to a reduction in the number of active sites.

[0004] To reduce the humidity-dependent response of MOS-based sensors, researchers have employed various strategies, including AC testing, doping, surface loading, and heterostructure reconstruction. While these measures effectively reduce the impact of humidity on gas-sensing properties, unavoidable phenomena such as resistance changes, selectivity alterations, and response degradation still frequently occur.

[0005] Some scholars have proposed coating the MOS sensing layer with hydrophobic materials. However, the adsorption or reaction of gas molecules with the sensing material is usually hindered by the hydrophobic layer, which impedes the surface activity of the MOS and leads to a decrease in the performance of the gas sensor. Summary of the Invention

[0006] The purpose of this invention is to provide a method for fabricating a highly moisture-resistant gas sensor based on a heterogeneous film, comprising the following steps:

[0007] 1) ZnO nanorods are grown on the surface of a Si substrate;

[0008] 2) MoS2 nanosheets are grown on the outer surface of ZnO nanorods, so that the MoS2 nanosheets encapsulate the ZnO nanorods;

[0009] 3) Scrape ZnO / MoS2 thin films from Si substrates;

[0010] 4) Dissolve the ZnO / MoS2 film to obtain a ZnO / MoS2 solution;

[0011] 5) The ZnO / MoS2 solution is poured onto a ceramic substrate with interdigitated electrodes to obtain a gas sensor with a ZnO / MoS2 heterostructure film.

[0012] Furthermore, in step 1), the steps for preparing ZnO nanorods include:

[0013] 1.1) Mix ZnO powder and carbon powder to obtain a first mixed powder; then, place the first mixed powder into a quartz boat in a chemical vapor deposition furnace, and place the Si substrate with the SiO2 layer facing the mixed powder.

[0014] 1.2) Heat the chemical vapor deposition furnace. When the temperature reaches T1℃, inject argon gas into the chemical vapor deposition furnace for a duration of t1.

[0015] 1.3) Continue heating the chemical vapor deposition furnace. When the temperature reaches T2℃, inject oxygen into the chemical vapor deposition furnace for a duration of t2.

[0016] 1.4) Annealing to obtain ZnO nanorods grown on the surface of a Si substrate.

[0017] Furthermore, in step 1.1), the mass ratio of ZnO powder to carbon powder is 3:1.

[0018] Further, in step 2), the step of growing MoS2 nanosheets on the outer surface of the ZnO nanorods includes:

[0019] 2.1) MoO3 powder, NaCl powder and S powder are mixed to obtain a second mixed powder; then, the second mixed powder is placed in a quartz boat of a chemical vapor deposition furnace;

[0020] 2.2) Invert the ZnO nanorods on top of the second mixed powder;

[0021] 2.3) Heat the chemical vapor deposition furnace. When the temperature reaches T3℃, inject argon gas into the chemical vapor deposition furnace to grow MoS2 nanosheets.

[0022] 2.4) Annealing to obtain MoS2 nanosheets encapsulating ZnO nanorods.

[0023] Furthermore, the mass ratio of MoO3 powder, NaCl powder, and S powder is 15:3:5.

[0024] Further, in step 4), the step of dissolving the ZnO / MoS2 film includes: placing the ZnO / MoS2 film in ethanol and then performing ultrasonic dissolution.

[0025] Furthermore, in step 5), the interdigitated electrodes are manufactured using screen printing technology.

[0026] The technical effects of this invention are undeniable. This invention synthesizes a sensor with a ZnO / MoS2 heterostructure film layer by chemical vapor deposition. This sensor has extremely high sensitivity to NO2 gas. Compared with traditional sensors, the sensor produced by this invention is more resistant to high humidity environments. Attached Figure Description

[0027] Figure 1 (A) is a SEM image of ZnO nanorods; Figure 1 (B) is a SEM image of the ZnO / MoS2 heterostructure; Figure 1 (C) and Figure 1 (D) SEM images of individual ZnO nanorods of different diameters coated with MoS2 nanosheets;

[0028] Figure 2 (A) Figure 2 (B) Raman spectra of ZnO nanorods and ZnO / MoS2 heterostructures, respectively; Figure 2 (C) Figure 2 (D) are the XRD patterns of ZnO nanorods and ZnO / MoS2 heterostructures, respectively;

[0029] Figure 3 (A) is a sensor prototype; Figure 3 (B) is the schematic diagram of the dual-probe measurement circuit; Figure 3 (C) is the schematic diagram of the four-probe measurement circuit;

[0030] Figure 4 (A) Comparison of the responses of sensors based on ZnO nanorods and ZnO / MoS2 heterostructures to 100 ppm NO2 and NH3 at different temperatures;

[0031] Figure 4 (B) is a schematic diagram of the band gap of the ZnO / MoS2 heterostructure;

[0032] Figure 4 (C) is the response of a sensor based on a ZnO / MoS2 heterostructure to different gases with a concentration of 100 ppm at 50 °C.

[0033] Figure 5 (A) Figure 5 (B) Comparison of real-time responses of sensors based on ZnO nanorods and ZnO / MoS2 heterostructures to 100ppm NO2 under room temperature conditions and without ultraviolet irradiation.

[0034] Figure 5 (C) Figure 5 (D) Comparison of real-time responses of sensors based on ZnO nanorods and ZnO / MoS2 heterostructures to 100ppm NO2 under ultraviolet irradiation at room temperature;

[0035] Figure 6 (A) is the energy band diagram of the ZnO / MoS2 heterostructure sensor exposed to NO2 gas molecules under ultraviolet light irradiation; Figure 6(B) shows the response behavior of the ZnO / MoS2 heterostructure sensor to different concentrations of NO2; Figure 6 (C) is the response curve and the corresponding NO2 concentration curve. Figure 6 (D) is a log-scale fit plot of the response versus NO2 concentration;

[0036] Figure 7 (A) and (C) show the dynamic response curves of ZnO nanorods and ZnO / MoS2 heterostructure sensors at 150℃ using the dual-probe measurement method for 100ppm NO2 under different RH conditions.

[0037] Figure 7 (B) and (D) are the dynamic response curves of ZnO nanorods and ZnO / MoS2 heterostructure sensors at 150℃ using the four-probe measurement method for 100ppm NO2 under different RH conditions.

[0038] Figure 8 This is a schematic diagram of the sensor manufacturing process.

[0039] Figure 9 (A) Figure 9 (B) EDS images and spectra of the ZnO / MoS2 heterostructure, respectively; Figure 9 (C) Figure 9 (D) Figure 9 (E) Figure 9 (F) SEM and EDS images of the four elements S, Mo, O and Zn, respectively;

[0040] Figure 10 The noise in the response of the ZnO / MoS2 heterostructure to NO2 gas molecules under ultraviolet light irradiation;

[0041] Figure 11 Real-time response of ZnO / MoS2 sensor to 100ppm NO2 under different RH levels and experimental conditions: (A) at RT and in darkness, (B) at RT and under UV illumination, (C) at 150°C and in darkness;

[0042] Figure 12 To measure the real-time response of the ZnO / MoS2 sensor to 100ppm NO2 when measuring different RH levels under AC power;

[0043] Figure 13 Real-time response of nO / MoS2 sensor to 100ppm NO2 at different RH levels (A) RT and (B) 150℃;

[0044] Figure 14 (A) Figure 14 (B) is a SEM image of the ZnO / MoS2 heterostructure; Figure 14 (C) Figure 14 (D) shows the SEM image and spectrum of the ZnO / MoS2 heterostructure; Figure 14 (E) Figure 14 (F) Figure 14 (G) Figure 14 (H) is the EDS image of S, Mo, O and Zn elements, with a CVD growth time of 40 minutes for the sample;

[0045] Figure 15 The response values ​​of sensors prepared at different CVD growth times to 100ppm NO2 gas at 0% RH and 95% RH levels are given. Detailed Implementation

[0046] The present invention will be further described below with reference to embodiments, but it should not be construed that the scope of the present invention is limited to the following embodiments. Various substitutions and modifications made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention should be included within the scope of protection of the present invention.

[0047] Example 1:

[0048] See Figures 1 to 15 A method for fabricating a highly moisture-resistant gas sensor based on a heterogeneous membrane includes the following steps:

[0049] 1) Growing ZnO (zinc oxide) nanorods on the surface of a Si (silicon) substrate;

[0050] 2) MoS2 (molybdenum disulfide) nanosheets are grown on the outer surface of ZnO nanorods, so that the MoS2 nanosheets encapsulate the ZnO nanorods;

[0051] 3) Scrape ZnO / MoS2 thin films from Si substrates;

[0052] 4) Dissolve the ZnO / MoS2 film to obtain a ZnO / MoS2 solution;

[0053] 5) The ZnO / MoS2 solution was poured onto a ceramic substrate with Pt (platinum) interdigitated electrodes to obtain a gas sensor with a ZnO / MoS2 heterostructure film.

[0054] Step 1) includes the following steps for preparing ZnO nanorods:

[0055] 1.1) Mix ZnO powder and carbon powder to obtain a first mixed powder; then, place the first mixed powder into a quartz boat in a chemical vapor deposition furnace, and place the Si substrate with the SiO2 layer facing the mixed powder.

[0056] 1.2) Heat the chemical vapor deposition furnace. When the temperature reaches T1℃, inject argon gas into the chemical vapor deposition furnace for a duration of t1.

[0057] 1.3) Continue heating the chemical vapor deposition furnace. When the temperature reaches T2℃, inject oxygen into the chemical vapor deposition furnace for a duration of t2.

[0058] 1.4) Annealing to obtain ZnO nanorods grown on the surface of a Si substrate.

[0059] In step 1.1), the mass ratio of ZnO powder to carbon powder is 3:1.

[0060] Step 2), the step of growing MoS2 nanosheets on the outer surface of ZnO nanorods, includes:

[0061] 2.1) MoO3 (molybdenum trioxide) powder, NaCl (sodium chloride) powder and S (sulfur) powder are mixed to obtain a second mixed powder; then, the second mixed powder is placed in a quartz boat of a chemical vapor deposition furnace;

[0062] 2.2) Invert the ZnO nanorods on top of the second mixed powder;

[0063] 2.3) Heat the chemical vapor deposition furnace. When the temperature reaches T3℃, inject argon gas into the chemical vapor deposition furnace to grow MoS2 nanosheets.

[0064] 2.4) Annealing to obtain MoS2 nanosheets encapsulating ZnO nanorods.

[0065] The mass ratio of MoO3 powder, NaCl powder, and S powder is 15:3:5.

[0066] In step 4), the step of dissolving the ZnO / MoS2 film includes: placing the ZnO / MoS2 film in ethanol and then dissolving it by ultrasonication.

[0067] In step 5), the Pt interdigitated electrodes are manufactured using screen printing technology.

[0068] Example 2:

[0069] See Figures 1 to 15 A method for fabricating a highly moisture-resistant gas sensor based on a heterogeneous membrane includes the following steps:

[0070] I) Preparation of ZnO nanorods

[0071] First, ZnO powder and carbon powder were mixed at a weight ratio of 3:1 and placed in a quartz boat at the center of a chemical vapor deposition (CVD) quartz tube. A Si substrate with a SiO2 layer was then placed with the powder mixture facing upwards. When the furnace was heated to 450°C, argon gas was injected at a flow rate of 120 sccm for 10 minutes. When the temperature rose to 600°C, oxygen was also introduced into the CVD tube. During the experiment, the pressure inside the tube was maintained at 35 kPa, the temperature at 950°C, and the reaction time at 40 minutes. After the experiment, the tube was allowed to cool naturally under an argon atmosphere.

[0072] The reactions during the growth of ZnO nanostructures are shown in equations (1) and (2):

[0073] ZnO + C → CO2 (1)

[0074] Zn + O2 → ZnO (2)

[0075] II) MoS2 nanosheets coated on ZnO nanorods

[0076] A mixture of MoO3 powder (1.5 g), NaCl powder (0.3 g) (weight ratio 5:1), and S powder (0.5 g) was placed in a quartz boat for growing MoS2 samples. NaCl powder was used to lower the melting point of the MoO3 powder, thus increasing the reaction rate. A prepared ZnO sample was then inverted on top of the powder mixture. When the furnace was heated to 700 °C, argon gas was introduced into the quartz tube as a carrier gas at a rate of 70 sccm to grow the MoS2 material. After growth, the sample was annealed in argon gas at 700 °C for 3 hours.

[0077] III) Sensor Manufacturing

[0078] After surface characterization, a ZnO / MoS2 thin film was scraped from the Si substrate and ultrasonically dissolved in ethanol for 30 minutes. The dissolved liquid was then poured onto a ceramic substrate with Pt interdigitated electrodes (IDs), which were fabricated using screen printing. The sensor prototype was then dried in an oven at 75°C for 20 minutes. A schematic diagram of the manufacturing process is shown below. Figure 8 As shown.

[0079] After the gas sensor was fabricated, it was tested as follows:

[0080] 1) Material property determination

[0081] The surface morphology and nanostructure of the samples were determined by scanning electron microscopy (SEM), while the chemical composition was determined by energy dispersive spectroscopy (EDS). Raman spectroscopy was performed on the materials using a 514 nm laser wavelength Raman spectroscopy system (LabRAM HR Evolution, Horiba), and finally, the crystal structure was characterized by X-ray diffraction (XRD).

[0082] 2) Sensing Measurement

[0083] The sensor sample was placed in a stainless steel test chamber, and the concentration of the test gas was controlled by adjusting the flow rates of the test gas and the carrier gas (dry air). To improve the sensor's sensing performance, an ultraviolet light source with a wavelength of 254 nm was used for illumination, and the sensor's gas response behavior was tested under different gas types, concentrations, illumination conditions, and operating temperatures.

[0084] The sensing characteristics of a sensor include selectivity, sensitivity, reproducibility, LoD (LoD), humidity tolerance, and the static and dynamic response behavior of the sensor device. This study investigated the sensor's humidity tolerance by introducing water vapor to adjust the humidity (RH) level in the test chamber. The sensor's response behavior was compared and studied by adjusting humidity, operating temperature, lighting conditions, DC or AC power supply, and dual-probe or quad-probe measurements.

[0085] Figure 1 SEM images of ZnO nanorods and ZnO / MoS2 heterostructures are shown. Figure 1 As shown in (A), the top view of the ZnO sample shows the vertical growth structure of ZnO nanorods uniformly distributed on a Si substrate. Figure 1 The SEM images of the ZnO / MoS2 sample in (B) show that the nanorods with the MoS2 coating have a large and dense microstructure. The SEM images of the sensors formed by coating MoS2 nanosheets on ZnO nanorods of different diameters are shown below. Figure 1 As shown in (C) and (D), the corresponding EDS images of the ZnO / MoS2 heterostructure confirm the presence of Zn, O, Mo, and S elements in the sample, as shown in (C) and (D). Figure 9 As shown in the figure. The results show that the atomic ratio in the ZnO / MoS2 heterostructure sample is Zn:O = 1:1 and Mo:S = 3:1.

[0086] Figure 2 The Raman spectra and XRD patterns of ZnO nanorods and ZnO / MoS2 heterostructures are shown in the figure. All ZnO peaks are highlighted with circles, while MoS2 peaks are marked with asterisks. Figure 2 As shown in (A), the two typical Raman spectra of ZnO are located at 323.3 cm⁻¹. -1 and 363.75cm -1 At these locations, the E2(high)-E2(low) and Al(TO) modes of wurtzite ZnO are respectively denoted, while 432.3 cm -1 The peak value corresponds to the E2 (high) mode. Figure 2In (B), the ZnO / MoS2 heterostructure exhibits two MoS2-related peaks, located at 379.3 cm⁻¹. -1 and 403.9cm -1 At this point, the two new peaks correspond to E in MoS2. 2g (1) and A 1g Pattern. E 2g (1) and A 1g The gap between the peaks is approximately 24 cm. -1 This demonstrates the multilayered nature of MoS2 nanosheets, as evidenced by the SEM images. 2g (1) / A 1g The intensity ratio is 0.56, which indicates that there are a large number of exposed edge sites in the MoS2 nanosheets. At the same time, due to the high adsorption energy, the material exhibits a relatively sensitive characteristic to NO2. Figure 2 The XRD diffraction pattern in (C) shows the region located at 31.8 cm⁻¹. -1 34.5cm -1 and 36.3cm -1 The three peaks at the position correspond to the (002), (100), and (101) modes of ZnO, indicating that ZnO is essentially a polycrystalline structure. After MoS2 is coated on the surface of ZnO nanorods, two more peaks with asterisks associated with MoS2 appear, such as... Figure 2 As shown in (D), the 2H phase of MoS2 is demonstrated.

[0087] After characterization, prototype sensor devices based on ZnO nanorods and ZnO / MoS2 heterostructures were fabricated. Figure 3 Images of two prototype gas sensing devices, along with schematic diagrams of the electrodes and test circuitry, are shown. Figure 3 As shown in (A), the sensor electrode consists of two external electrodes (labeled 3 and 4) connected to the ID electrode and two internal electrodes (labeled 1 and 2). This structure allows the sensor to perform two different measurement methods: dual-probe measurement and four-probe measurement. For the dual-probe measurement method, the two internal electrodes are connected in series with a DC power supply and a reference resistor (Rp) to form a sensing measurement circuit, as shown... Figure 3 As shown in (B). A schematic diagram of the four-probe measurement is shown below. Figure 3 As shown in (C), in this measurement method, the sample is connected to an external circuit via electrodes 3 and 4. This method can detect only the portion of the gas sensing material between internal electrodes 1 and 2. In a high RH environment, the H2O molecules absorbed on the surface of the sensing material generate H2O. + Ions can induce the aggregation of hydrogen ions around a metal probe, causing a polarization effect. However, by detecting changes in the electrical properties between the two internal electrodes, the polarization effect can be avoided because there is no carrier aggregation between the internal electrodes.

[0088] Figure 4 (A) shows the response curves of sensors based on ZnO nanorods and ZnO / MoS2 heterostructures to 100ppm NO2 and NH3 in the temperature range of 25 to 250℃, respectively. The sensor response value estimation formula is shown in Equation (3):

[0089]

[0090] Where R g and R a The figures represent the resistance values ​​measured by the sensor for the test gas and the pure air mixture, respectively. As can be observed from the figures, the sensor based on the ZnO / MoS2 heterostructure exhibits better sensing performance than the sensor based on pure ZnO. Both sensors show similar response behavior under different gas environments, with an optimal operating temperature of approximately 150℃. Theoretically, gas reaction processes generally involve three steps: absorption, diffusion, and adsorption. With temperature changes, different equilibria are reached between absorption and adsorption, thus affecting the sensor's gas response behavior.

[0091] The main reason why coating ZnO with MoS2 can improve sensing performance is that the construction of the ZnO / MoS2 heterostructure leads to a lattice mismatch between MoS2 and ZnO, resulting in a large number of defects and interface states. Furthermore, it introduces abundant S and Mo dangling bonds, creating more adsorption sites for gas molecules. The indirect band gap and high carrier mobility of multilayer MoS2 also provide significant sensing potential. Another reason is the increased electron concentration at the ZnO / MoS2 interface. A schematic diagram of the band gap structure of the ZnO / MoS2 heterostructure is shown below. Figure 4 As shown in (B), when the material forms a ZnO / MoS2 heterojunction, electrons transfer from the low work function MoS2 (4.6 eV) to the high work function ZnO (5.2 eV), thereby generating a carrier depletion layer on the n-type MoS2 at the heterojunction interface. Conversely, n-type ZnO can achieve a higher electron concentration near the heterojunction. The increased electron density at the ZnO / MoS2 interface can enhance oxygen adsorption capacity, thereby improving the gas response of the sensor.

[0092] To evaluate the selectivity of the ZnO / MoS2 heterojunction sensor, we investigated the sensor's response to gases such as NH3, CH4, H2O (95% RH), CO, CO2, O2, and CH3OH. Figure 4(C) shows the response values ​​of the ZnO / MoS2 heterostructure-based sensor to gases above 100 ppm at 50 °C. It can be seen that the ZnO / MoS2 heterostructure sensor has the highest response value to NO2, at 112.1%, indicating that the ZnO / MoS2 sensor has high sensitivity to NO2 gas. This high sensitivity mainly originates from the large charge transfer value between the MoS2 material and NO2 molecules and its high adsorption energy for NO2 molecules. It can be considered that the ZnO / MoS2 heterostructure-based sensor has the best sensing performance for NO2, and we will focus on its gas-sensing characteristics below.

[0093] Figure 5 The response curves of two sensors to a NO2 concentration of 100 ppm are shown in room temperature environments under darkness and ultraviolet light irradiation. Figure 5 As shown in (A), the ZnO nanorod-based sensor exhibits a very weak response to NO2 in the dark, indicating that the sensor hardly reacts with NO2 gas molecules at room temperature. In contrast, the ZnO / MoS2 heterostructure-based sensor shows a response of approximately 101% at room temperature, but its recovery ability weakens after each exposure to NO2, as shown in (A). Figure 5 (B) shows this. This is because MoS2 material has a high adsorption energy for oxidizing gases, a characteristic that benefits high responsivity but also reduces the sensor's recovery capability. Studies suggest that ultraviolet light irradiation can effectively improve the material's response to gases and aid in recovery. Figure 5 The experimental results in (C) and (D) verify this. At room temperature and under ultraviolet irradiation, the response values ​​of the two sensors to 100 ppm NO2 gas were 21% and 396%, respectively, which showed an increase in responsivity compared to the condition without ultraviolet light, and the recovery ability was also improved.

[0094] like Figure 6 As shown in (A), the ZnO / MoS2 heterostructure sensor generates a large number of photoexcited electron-hole pairs (eps) under ultraviolet light irradiation, thus increasing the number of charge carriers by several orders of magnitude. Furthermore, the light-induced photoenhancing effect generates positive charges and causes a Fermi level shift in the conduction band, further increasing the number of free electrons. Meanwhile, the absorption of reduced NO2 molecules by the sensing material traps free electrons, leading to an increase in the resistance of the ZnO / MoS2 heterojunction. Figure 6 (B) shows the real-time response behavior of the sensor to NO2 concentrations from 10 ppm to 20 ppb under ultraviolet light irradiation. The sensor exhibits good recovery characteristics to NO2 gas, and the response baseline decreases as the NO2 concentration decreases, with an extremely low detection limit (LoD) of less than 20 ppb.

[0095] The sensor's responses to linear and logarithmic scales of NO2 gas concentration functions are as follows: Figure 6 As shown in (C) and (D). Figure 6 The slope of the linear fit plot of the curve in (D) is defined as: sensitivity Under ultraviolet light irradiation, the sensor's sensitivity to NO2 is estimated to be: The theoretical LoD of the sensor can be calculated using equations (4) and (5):

[0096]

[0097]

[0098] Among them RMS noise R i and Represents the noise level, the arbitrary response value of the sensor before exposure to the test gas, and R, respectively. i The average value. In this study, RMS noise The noise level of NO2 gas molecules in the ZnO / MoS2 heterostructure under ultraviolet irradiation was estimated (see [reference]). Figure 10 The calculated value was 2.98%. The final theoretical LoD value of the sensor was 7.1 ppb.

[0099] Figure 7 The dynamic response curves of the two sensors for measuring 100ppm NO2 gas at 150℃ and different RH levels are shown using two probe and four probe methods. Figure 7 As shown in (A) and (C), when using dual-probe measurements, the responses of both sensors exhibit response degradation in environments with progressively increasing RH. This is due to the decrease in the number of holes, the migration of free electrons from H2O molecules to the valence band, thus increasing the gap between the valence band and the Fermi level, and reducing the resistance of the n-type semiconductor. When the RH level increases from 0% to 95%, the response of the ZnO sensor decreases by 28.6%, while the response of the ZnO / MoS2 sensor decreases by only 18.8%, indicating that the MoS2 coating on ZnO can improve its moisture resistance by partially isolating the ZnO sensing layer from the H2O molecules.

[0100] To investigate moisture resistance, this study tested the effect of varying RH levels under different temperature and light conditions on the response of a ZnO / MoS2 sensor to measure 100 ppm NO2 gas. Figure 11 As shown, it can be concluded that ultraviolet light has only a weak effect, while temperature has a significant impact on the sensor's moisture resistance. Figure 12 and Figure 13This demonstrates the real-time response behavior of the ZnO / MoS2 sensor to 100ppm NO2 under different RH levels when measured using dual or quad probes in combination with AC or DC power. Comparative studies show that an effective method to avoid the influence of humidity on the sensing performance of the ZnO / MoS2 sensor is to increase the experimental temperature to 150℃ and simultaneously perform four-probe measurement on the sample under high RH conditions for sensing characterization. Figure 7 The sensor response in (B) shows that when using dual-probe measurements and humidity changes, the baseline drift reaches 23.4%. However, when using the four-probe method, even with humidity levels varying over a wide range from 0% to 90%, the resistance baseline of the ZnO / MoS2 sensor is almost unaffected. Figure 7 As shown in (D).

[0101] The growth time of MoS2 is also crucial. If the growth time is too short, the MoS2 nanosheets will not adequately cover the surface of the ZnO nanorods; however, excessively thick MoS2 nanosheets can lead to complete isolation between ZnO and NO2 molecules. Therefore, this study prepared ZnO sensor samples coated with MoS2 at different growth times and investigated the responses of the samples to NO2 gas under different humidity levels to evaluate the impact of MoS2 growth time on moisture resistance. Figure 14 SEM and EDS images of a sample with MoS2 deposition time of 1 hour are shown, revealing dense MoS2 nanosheets encapsulating the surface of ZnO nanorods. We measured the sensing response of this sample to 100 ppm NO2 at 0% RH and 95% RH levels and presented the results. Figure 15 In the 0% RH condition, as the MoS2 growth time increased from 10 minutes to 30 minutes, the sample response gradually increased and then decreased slightly, with no significant change after 1 hour. However, when the RH level was increased to 95%, the response showed a significant increasing trend due to the partial encapsulation of the MoS2 material. But with further increases in MoS2 growth time, a slight deterioration in the response was observed, because the complete coverage of MoS2 prevented the reaction between NO2 molecules and the ZnO sensing material.

[0102] This embodiment synthesized pure ZnO nanorods and a ZnO / MoS2 heterostructure sensor via chemical vapor deposition (CVD). The sensor's sensing characteristics were systematically characterized, including selectivity, response, sensitivity, optimal operating temperature, LoD, and humidity resistance. The ZnO / MoS2 heterostructure-based sensor achieved extremely high sensitivity for NO2 gas at 1.26% / ppb and a theoretical LoD of 7.1 ppb. The enhanced gas sensing performance of the ZnO / MoS2 sensor is attributed to the formation of its heterojunction and unique hierarchical structure. The response baseline of the ZnO / MoS2 sensor can be stabilized by increasing the temperature to 150°C or applying ultraviolet illumination. To eliminate the influence of humidity on the sensor, this study explored several methods, including using a MoS2 coating, ultraviolet irradiation, increasing the temperature, using AC power, and four-probe measurement. The study demonstrated that combining a hydrophobic MoS2 nanosheet coating with sensor heating and four-probe measurement strategies can effectively enable the ZnO sensor to withstand high humidity environments.

[0103] Example 3:

[0104] A method for fabricating a highly moisture-resistant gas sensor based on a heterogeneous membrane includes the following steps:

[0105] 1) ZnO nanorods are grown on the surface of a Si substrate;

[0106] 2) MoS2 nanosheets are grown on the outer surface of ZnO nanorods, so that the MoS2 nanosheets encapsulate the ZnO nanorods;

[0107] 3) Scrape ZnO / MoS2 thin films from Si substrates;

[0108] 4) Dissolve the ZnO / MoS2 film to obtain a ZnO / MoS2 solution;

[0109] 5) The ZnO / MoS2 solution is poured onto a ceramic substrate with interdigitated electrodes to obtain a gas sensor with a ZnO / MoS2 heterostructure film.

[0110] Example 4:

[0111] A method for fabricating a highly moisture-resistant gas sensor based on a heterostructure film is described in Example 3. Step 1), specifically the preparation of ZnO nanorods, includes:

[0112] 1.1) Mix ZnO powder and carbon powder to obtain a first mixed powder; then, place the first mixed powder into a quartz boat in a chemical vapor deposition furnace, and place the Si substrate with the SiO2 layer facing the mixed powder.

[0113] 1.2) Heat the chemical vapor deposition furnace. When the temperature reaches T1℃, inject argon gas into the chemical vapor deposition furnace for a duration of t1.

[0114] 1.3) Continue heating the chemical vapor deposition furnace. When the temperature reaches T2℃, inject oxygen into the chemical vapor deposition furnace for a duration of t2.

[0115] 1.4) Annealing to obtain ZnO nanorods grown on the surface of a Si substrate.

[0116] Example 5:

[0117] A method for fabricating a highly moisture-resistant gas sensor based on a heterogeneous membrane is described in Example 3, wherein in step 1.1), the mass ratio of ZnO powder to carbon powder is 3:1.

[0118] Example 6:

[0119] A method for fabricating a highly moisture-resistant gas sensor based on a heterostructure film is described in Example 3. Step 2), which involves growing MoS2 nanosheets on the outer surface of ZnO nanorods, includes:

[0120] 2.1) MoO3 powder, NaCl powder and S powder are mixed to obtain a second mixed powder; then, the second mixed powder is placed in a quartz boat of a chemical vapor deposition furnace;

[0121] 2.2) Invert the ZnO nanorods on top of the second mixed powder;

[0122] 2.3) Heat the chemical vapor deposition furnace. When the temperature reaches T3℃, inject argon gas into the chemical vapor deposition furnace to grow MoS2 nanosheets.

[0123] 2.4) Annealing to obtain MoS2 nanosheets encapsulating ZnO nanorods.

[0124] Example 7:

[0125] A method for fabricating a highly moisture-resistant gas sensor based on a heterogeneous membrane is described in Example 3, wherein the mass ratio of MoO3 powder, NaCl powder, and S powder is 15:3:5.

[0126] Example 8:

[0127] A method for fabricating a highly moisture-resistant gas sensor based on a heterogeneous film is described in Example 3. In step 4), the step of dissolving the ZnO / MoS2 film includes: placing the ZnO / MoS2 film in ethanol and then performing ultrasonic dissolution.

[0128] Example 9:

[0129] A method for fabricating a highly moisture-resistant gas sensor based on a heterogeneous film is described in Example 3, wherein, in step 5), the interdigitated electrodes are fabricated using screen printing technology.

Claims

1. A method for fabricating a highly moisture-resistant gas sensor based on a heterogeneous membrane, characterized in that, Includes the following steps: 1) ZnO nanorods are grown on the surface of a Si substrate; 2) MoS2 nanosheets are grown on the outer surface of ZnO nanorods, so that the MoS2 nanosheets encapsulate the ZnO nanorods; 3) Scrape ZnO / MoS2 thin films from Si substrates; 4) Dissolve the ZnO / MoS2 film to obtain a ZnO / MoS2 solution; 5) The ZnO / MoS2 solution was poured onto a ceramic substrate with interdigitated electrodes to obtain a gas sensor with a ZnO / MoS2 heterostructure film. Step 2), the step of growing MoS2 nanosheets on the outer surface of ZnO nanorods, includes: 2.1) MoO3 powder, NaCl powder and S powder are mixed to obtain a second mixed powder; then, the second mixed powder is placed in a quartz boat of a chemical vapor deposition furnace; 2.2) Invert the ZnO nanorods on top of the second mixed powder; 2.3) Heat the chemical vapor deposition furnace. When the temperature reaches T3℃, inject argon gas into the chemical vapor deposition furnace to grow MoS2 nanosheets. 2.4) Annealing to obtain MoS2 nanosheets encapsulating ZnO nanorods; In step 4), the step of dissolving the ZnO / MoS2 film includes: placing the ZnO / MoS2 film in ethanol and then dissolving it by ultrasonication.

2. The method for fabricating a highly moisture-resistant gas sensor based on a heterogeneous membrane according to claim 1, characterized in that, Step 1) includes the following steps for preparing ZnO nanorods: 1.1) Mix ZnO powder and carbon powder to obtain a first mixed powder; then, place the first mixed powder into a quartz boat in a chemical vapor deposition furnace, and place the Si substrate with the SiO2 layer facing the mixed powder. 1.2) Heat the chemical vapor deposition furnace. When the temperature reaches T1℃, inject argon gas into the chemical vapor deposition furnace for a duration of t1. 1.3) Continue heating the chemical vapor deposition furnace. When the temperature reaches T2℃, inject oxygen into the chemical vapor deposition furnace for a duration of t2. 1.4) Annealing to obtain ZnO nanorods grown on the surface of a Si substrate.

3. The method for fabricating a highly moisture-resistant gas sensor based on a heterogeneous membrane according to claim 1, characterized in that, In step 1.1), the mass ratio of ZnO powder to carbon powder is 3:

1.

4. The method for fabricating a highly moisture-resistant gas sensor based on a heterogeneous membrane according to claim 1, characterized in that, The mass ratio of MoO3 powder, NaCl powder, and S powder is 15:3:

5.

5. The method for fabricating a highly moisture-resistant gas sensor based on a heterogeneous membrane according to claim 1, characterized in that, In step 5), the interdigitated electrodes are manufactured using screen printing technology.

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