CN117030802A - Ammonia gas sensor based on thermal reduction graphene oxide and preparation method thereof - Google Patents
Ammonia gas sensor based on thermal reduction graphene oxide and preparation method thereof Download PDFInfo
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
- G01N27/122—Circuits particularly adapted therefor, e.g. linearising circuits
- G01N27/123—Circuits particularly adapted therefor, e.g. linearising circuits for controlling the temperature
- G01N27/124—Circuits particularly adapted therefor, e.g. linearising circuits for controlling the temperature varying the temperature, e.g. in a cyclic manner
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
Abstract
The invention belongs to the technical field of semiconductor gas sensors, and discloses an ammonia gas sensor based on thermal reduction graphene oxide and a preparation method thereof, wherein the ammonia gas sensor comprises a substrate supporting layer, an insulating medium layer, an electrode layer and a gas-sensitive sensing layer; wherein the gas-sensitive sensing layer is a thermal reduction graphene oxide film; the preparation process comprises spin coating graphene oxide solution on a substrate; then forming a graphene oxide film in a channel region by using the graphene oxide solution through a graphical micro-nano process; and finally, carrying out thermal reduction on the graphene oxide film on the substrate. The ammonia gas sensor with short response time and low detection lower limit can be obtained, has excellent long-term stability and selectivity, is simple and convenient in preparation process, and can be practically applied in the fields of industry, environmental monitoring, medical treatment and the like.
Description
Technical Field
The invention belongs to the technical field of semiconductor gas sensors, and particularly relates to a gas sensor for detecting ammonia gas and a preparation method thereof.
Background
Ammonia (NH) 3 ) Is a colorless and irritant poisonous inflammable gasCommon air pollutants are extremely prone to irritation and injury to human eyes and respiratory mucosa. In the fields of environmental monitoring, automobile industry, chemical industry, medical health and the like, the detection of ammonia gas is particularly critical: in haze treatment, it is necessary to detect ammonia concentration in the atmosphere to reduce the formation of secondary particulate matter; in the automobile industry, an air conditioning system needs to detect the ammonia concentration in the automobile to optimize the air quality, and an exhaust system also needs to detect and control the ammonia injection amount to perform selective catalytic reduction on the tail gas; almost all of the pure ammonia used in chemical fertilizer plants and refrigeration industry is ammonia gas, and whether the ammonia gas leaks or not must be monitored in real time so as to ensure the life safety of workers; in the medical field, the association diagnosis of the ammonia concentration in human exhaled air and kidney lesions is realized by non-invasive detection of the ammonia concentration in human exhaled air. Therefore, the high-performance ammonia sensor is indispensable, and simultaneously, higher requirements are put on the performances such as miniaturization and light weight, energy consumption, responsiveness, sensitivity, durability and the like of the ammonia sensor. Currently, widely studied ammonia gas-sensitive materials are mainly metal oxide semiconductors, but they all basically need to operate at high temperatures (150-300 ℃). The service life of the sensor can be shortened due to the influence on the service life of the device, the power consumption and the cost of the device can be greatly increased due to the generation of the high temperature, and the application range of the sensor is greatly limited due to the use limitation in the flammable and explosive gas environment.
Graphene has excellent room temperature conductivity and a very large specific surface area (2630 m 2 g -1 ) The advantages of low electronic noise and the like are paid attention as gas sensitive materials in recent years, and the method provides great possibility for reducing the working temperature of the semiconductor gas sensor. Due to the dirac cone-shaped energy band structure, even if a small amount of charge is transferred with graphene after gas adsorption, the conductivity can be changed obviously. And graphene is used as a two-dimensional material, is compatible with a modern planar micro-nano processing technology, can be used for preparing a high-density gas sensor array, can achieve a result of multiple measurements through single measurement, greatly improves the sensing efficiency, and saves the testing time. The array device is less influenced by uncertain factors and has good performanceStability. The epitaxial graphene is obtained on a SiC substrate under the high-temperature condition of more than 1000 ℃, and the requirements on growth equipment and the substrate are very high, so that the preparation cost of the graphene is definitely increased, the defect content is low, and a large number of high-energy sites for gas molecule adsorption are difficult to provide. In the process of preparing the graphene by a Chemical Vapor Deposition (CVD), the impurity pollution introduced in the transfer process is difficult to avoid, the impurities can seriously affect the electronic property of the graphene and cover the gas adsorption sites on the surface of the graphene, and the defects remain in the application of the sensor.
Compared with intrinsic graphene, the Reduced Graphene Oxide (RGO) is a gas-sensitive material with great potential because of the defects, oxygen-containing functional groups and the like contained in the Reduced Graphene Oxide (RGO) can be used as high-energy sites for gas molecular adsorption; and the raw materials are economical, the preparation is simple and easy, and the large-scale production can be realized. Since the RGO surface carries a plurality of oxygen-containing groups, the RGO provides great possibility for improving the sensitivity performance by adjusting the types and the quantity of the surface groups. Meanwhile, RGO can be dispersed in a solvent, so that functional modification can be conveniently carried out on the surface of the RGO.
The existing ammonia gas sensor based on RGO materials has the defects of long response and recovery time, poor long-term stability and higher detection lower limit. Some ammonia gas sensors using RGO modified by noble metal nanoparticles as a gas-sensitive material have the defects that the modification process is complex and time-consuming, and high response is difficult to realize at room temperature.
Disclosure of Invention
The invention aims to solve the common problem of the ammonia gas sensor at the present stage, and provides an ammonia gas sensor based on thermal reduction graphene oxide and a preparation method thereof, which can obtain the ammonia gas sensor with short response time and low detection lower limit, has excellent long-term stability and selectivity, has simple preparation process, and can be practically applied in the fields of industry, environmental monitoring, medical treatment and the like.
In order to solve the technical problems, the invention is realized by the following technical scheme:
according to one aspect of the present invention, there is provided an ammonia gas sensor based on thermally reduced graphene oxide, comprising a substrate support layer, an insulating medium layer, an electrode layer and a gas-sensitive sensing layer; the gas-sensitive sensing layer is a thermal reduction graphene oxide film; the gas-sensitive sensing layer is connected with the electrode layer in a direct stacking contact mode; the electrode layer is connected to the testing device through a metal lead, and the testing device detects the concentration of ammonia through measuring resistance signals.
Further, the surface of the thermally reduced graphene oxide film still contains oxygen-containing functional groups after being partially reduced.
Further, the thermally reduced graphene oxide film is distributed flatly, and the surface of the thermally reduced graphene oxide film is wrinkle-free.
Further, the thermally reduced graphene oxide film is in a non-agglomerated form.
Further, the thickness of the thermally reduced graphene oxide film is 1-10 nanometers.
Preferably, the electrode layer is prepared by patterning by a lithographic apparatus followed by deposition of a metal electrode using a thin film deposition apparatus.
Wherein, the photoetching equipment can adopt a laser direct writing instrument; the thin film deposition apparatus may employ an electron beam evaporation apparatus; the metal electrode comprises a source electrode, a drain electrode and a grid electrode with a certain interval, and the material can be Cr/Au.
Preferably, the insulating medium layer is alumina.
Preferably, the substrate supporting layer is a silicon wafer with an oxide layer.
According to another aspect of the present invention, there is provided a method for preparing the ammonia gas sensor based on thermally reduced graphene oxide, comprising the following steps:
(1) Spin-coating graphene oxide solution on a substrate;
(2) Forming a graphene oxide film in a channel region by the graphene oxide solution through a graphical micro-nano process;
(3) And carrying out thermal reduction on the graphene oxide film on the substrate.
Further, the concentration of the graphene oxide solution in the step (1) is 0.1-1mg/ml.
Further, the length of the thermally reduced graphene oxide film is 3-60 micrometers, so that the width of the channel region in the step (2) is 5-50 micrometers, and the channel region is matched with the size of the material.
Further, the temperature of the heating reduction in the step (3) is 100-350 ℃, and the heating time is 1-2 hours; the gas environment is one of argon, nitrogen and vacuum.
In order to create an environment with high oxygen isolation to prevent defects caused by carbon atom loss in the thermal reduction process, vacuum pre-pumping and argon flushing processes are required for the heating environment.
The beneficial effects of the invention are as follows:
according to the invention, the thermal reduction graphene oxide is used as a gas-sensitive material, and is distributed on the substrate smoothly, the surface is free from folds, and the non-agglomerated form is favorable for the diffusion of gas molecules. In the ammonia gas sensing process, residual oxygen-containing functional groups in RGO are fully utilized as adsorption sites of ammonia gas molecules. Compared with the traditional metal oxide gas sensor, the sensor has the advantages of no need of an additional heater, lower power consumption and convenient use in flammable and explosive gas environments. The ammonia sensor has short response time, low detection lower limit and good long-term stability.
The ammonia gas sensor provided by the invention has the advantages that the sensing film is attached to the substrate by adopting a mode of spin-coating graphene oxide dilute solution, the operation is simple, the processability is good, the processing on electrodes with different shapes is facilitated, and the problems that the traditional gas sensor needs high-temperature sintering and is complex in processing are solved.
After ammonia gas is adsorbed, the resistance of the sensor can be restored to the initial value without any additional treatment methods such as high-temperature heating, ultraviolet irradiation and the like, the restoring period is short, and the long-term repeated operation of the ammonia gas sensor in practical application is facilitated.
The preparation process is simple and convenient, and the graphene is clean and free from the pollution of photoresist. The product has strong reliability, is easy to realize industrial production, and can realize the rapid and reliable monitoring of ammonia in the fields of industry, agriculture, production, life and the like.
Drawings
Fig. 1 is a schematic structural diagram of an ammonia sensor based on a field effect transistor structure of thermal reduction graphene oxide provided by the invention;
FIG. 2 is a graph showing the repetitive response of the ammonia sensor of the thermal reduction graphene oxide-based FET structure prepared in example 1 to 100ppm ammonia;
FIG. 3 is a single cycle dynamic response curve of the thermal reduction graphene oxide based FET structured ammonia sensor prepared in example 1 for 100ppm ammonia;
FIG. 4 is a dynamic response curve of the thermal reduction graphene oxide based FET structured ammonia sensor prepared in example 2 to 5-200ppm ammonia;
FIG. 5 is a linear fit curve of responsivity versus ammonia concentration for the thermal reduction graphene oxide based field effect transistor structure ammonia sensor prepared in example 2;
fig. 6 is a long-term stability curve of the thermal reduction graphene oxide-based fet structured ammonia sensor prepared in example 2.
Detailed Description
The present invention is described in further detail below by way of specific examples, which will enable those skilled in the art to more fully understand the invention, but are not limited in any way.
Example 1
An ammonia gas sensor based on thermal reduction graphene oxide is prepared, and the structural schematic diagram of the ammonia gas sensor is shown in figure 1, and the ammonia gas sensor comprises a substrate supporting layer, an insulating medium layer, an electrode layer and a gas-sensitive sensing layer; the preparation method mainly comprises the following steps:
(1) Graphene oxide solutions were prepared using a modified Hummers method;
(2) A (gate) electrode pattern was constructed on a silicon wafer with an oxide layer 285nm thick using photolithographic techniques. Then, a chromium-gold electrode layer was deposited on the silicon substrate using an electron beam evaporation method, wherein the chromium thickness was 10nm and the gold thickness was 20nm. Then preparing a silicon wafer with a gate electrode through a stripping process;
(3) Growing alumina with a thickness of 25nm by using an atomic layer deposition technology;
(4) Constructing an interdigital source-drain electrode pattern by using a photoetching alignment technology, wherein the channel width is 10 mu m; then, a chromium-gold electrode layer was deposited using an electron beam evaporation method, wherein the chromium thickness was 10nm and the gold thickness was 20nm. And then preparing a source electrode and a drain electrode through a stripping process.
(5) Defining a patterned channel region by using a photoetching alignment technology, wherein the total channel region is 210 mu m wide and 300 mu m long;
(6) Spin coating graphene oxide solution between electrode channels: preparing a graphene oxide solution with the concentration of 0.3mg/ml, and spin-coating the graphene oxide solution on a substrate; then obtaining a sensing device with graphene oxide in a channel region through a stripping process;
(7) Thermally reducing graphene oxide: the device is placed in an annealing furnace which is independently designed and built in a laboratory, and is thermally reduced for 2 hours at 250 ℃ in an argon atmosphere.
(8) And connecting the device electrode with an aluminum wire by using silver colloid, and connecting the other end of the aluminum wire on a pin of a test base through the silver colloid to obtain the complete thermal reduction graphene oxide based field effect tube type ammonia gas sensor.
Example 2
An ammonia gas sensor based on thermally reduced graphene oxide was prepared using the method of example 1, differing only in: the thermal reduction temperature in step (7) was 100 ℃.
Example 3
An ammonia gas sensor based on thermally reduced graphene oxide was prepared using the method of example 1, differing only in: the thermal reduction temperature in step (7) was 350 ℃.
Example 4
An ammonia gas sensor based on thermally reduced graphene oxide was prepared using the method of example 1, differing only in: the thermal reduction time in step (7) was 1 hour.
Example 5
An ammonia gas sensor based on thermally reduced graphene oxide was prepared using the method of example 1, differing only in: the thermal reduction time in step (7) was 1.5 hours.
Example 6
An ammonia gas sensor based on thermally reduced graphene oxide was prepared using the method of example 1, differing only in: the concentration of the graphene oxide solution in the step (6) is 0.1mg/ml.
Example 7
An ammonia gas sensor based on thermally reduced graphene oxide was prepared using the method of example 1, differing only in: the concentration of the graphene oxide solution in the step (6) is 1mg/ml.
Example 8
An ammonia gas sensor based on thermally reduced graphene oxide was prepared using the method of example 1, differing only in: the channel width in step (4) was 5 μm.
Example 9
An ammonia gas sensor based on thermally reduced graphene oxide was prepared using the method of example 1, differing only in: the channel width in step (4) was 50 μm.
Fig. 2 and 3 are a repetitive response curve and a single-cycle dynamic response curve of the sensor prepared in example 1 with respect to 100ppm ammonia, respectively, and it can be seen that the resistance of the sensor is rapidly decreased after introducing ammonia, and the resistance is gradually recovered after flushing with nitrogen. This is because ammonia molecules act as electron donors to transfer electrons into the N-type RGO, increasing its multi-electron (electron) concentration, resulting in a decrease in its electrical resistance. And the response time is as short as 11s, and the sensor has good restorability and reversibility. Likewise, sensory tests were performed on examples 2-9 above to compare the performance impact of different manufacturing processes on thermally reduced graphene oxide based ammonia sensors.
(one) the effect of different thermal reduction temperatures on the performance of a thermal reduction graphene oxide based ammonia sensor at 100ppm ammonia, see Table 1.
TABLE 1
As can be seen from Table 1, the graphene oxide-based ammonia was thermally reduced at 100, 250 and 350℃for two hoursThe gas sensor showed a significant response to 100ppm ammonia gas, with a response time of within 40 seconds. Wherein the response time of the sensor obtained in example 1 was 11 seconds and the sensor obtained in example 2 had a responsivity of 1.97%. The sensing tests of ammonia gas with different concentrations were performed in example 2, and the results are shown in FIG. 4, and according to the fitting result of the responsivity-ammonia gas concentration in FIG. 5, the sensitivity of the sensor is 0.02%/ppm, and the following formula is obtaineda i And a is the selected responsivity baseline data point and the average value of the points respectively, N is the number of the data points), 10 data points (the values are-0.00664, 0.001659, 0, 0.001659, 0, 0.005806, 0.004147, 0.01327, 0.000829 and-0.00746 respectively) of the responsivity baseline of the sensor before ammonia is introduced are selected, and the noise level RMS is obtained noise 0.005919, and then according to the formula (lower detection limit=3×rms noise Sensitivity) gives a theoretical detection limit for this sensor as low as 0.9ppm. The long-term stability of example 2 was also monitored, and as shown in fig. 6, the responsiveness to 100ppm ammonia gas after natural standing in the atmosphere for 50, 79 and 89 days was maintained at 92.45%, 81.62%, 74.23% of the initial responsiveness, and the response times were 123%, 138% and 117% of the original responsiveness, respectively. This shows a weaker tendency to decay in sensing performance over time, and this sensor has better long-term stability.
(II) the effect of different thermal reduction times on the performance of a thermal reduction graphene oxide based ammonia sensor at 100ppm ammonia, see Table 2.
TABLE 2
As is clear from Table 2, the responsiveness of the thermal reduction graphene oxide-based ammonia sensor obtained by thermal reduction at 250℃for 1, 1.5 and 2 hours to 100ppm ammonia was about 2%, and the response time was within 40 seconds.
(III) the effect of different graphene oxide solution concentrations on the performance of a thermal reduction graphene oxide based ammonia sensor at 100ppm ammonia, see Table 3.
TABLE 3 Table 3
As can be seen from Table 3, the thermal reduction graphene oxide based ammonia sensor prepared from graphene oxide solutions with concentrations of 0.1, 0.3 and 1mg/ml has obvious response to 100ppm ammonia, the responsivity is between 12 percent, and the response time is within 25.
(IV) the effect of different channel widths on the performance of a thermal reduction graphene oxide based ammonia sensor at 100ppm ammonia, see Table 4.
TABLE 4 Table 4
From table 4, it is clear that the channel width has no significant effect on the performance of the thermally reduced graphene oxide based ammonia sensor.
In conclusion, the thermal reduction graphene oxide based ammonia gas sensor prepared by the method provided by the invention has the advantages of short response time, low detection lower limit and good long-term stability. The rapid and repeatable detection of ammonia gas at normal temperature can be realized without heating or ultraviolet assistance. And the preparation process is simple and convenient to operate, the raw material cost is low, and the industrial production is expected to be realized.
Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments, which are merely illustrative, not restrictive, and many changes may be made by those having ordinary skill in the art without departing from the spirit of the present invention and the scope of the appended claims, which are to be construed as falling within the scope of the present invention.
Claims (10)
1. An ammonia gas sensor based on thermal reduction graphene oxide comprises a substrate supporting layer, an insulating medium layer, an electrode layer and a gas-sensitive sensing layer; the gas-sensitive sensing layer is a thermal reduction graphene oxide film; the gas-sensitive sensing layer is connected with the electrode layer in a direct stacking contact mode; the electrode layer is connected to a testing device, and the testing device detects the concentration of ammonia through measuring resistance signals.
2. An ammonia sensor based on thermally reduced graphene oxide according to claim 1, wherein the partially reduced graphene oxide film has oxygen-containing functional groups on its surface.
3. An ammonia sensor based on thermally reduced graphene oxide according to claim 1, wherein the thermally reduced graphene oxide film is evenly distributed and has no surface wrinkles.
4. An ammonia sensor based on thermally reduced graphene oxide according to claim 1, wherein the thermally reduced graphene oxide film is in a non-agglomerated form.
5. An ammonia sensor based on thermally reduced graphene oxide according to claim 1, wherein the thermally reduced graphene oxide film has a thickness of 1-10 nm.
6. A method for manufacturing an ammonia gas sensor based on thermally reduced graphene oxide as claimed in any one of claims 1 to 5, comprising the following steps:
(1) Spin-coating graphene oxide solution on a substrate;
(2) Forming a graphene oxide film in a channel region by the graphene oxide solution through a graphical micro-nano process;
(3) And carrying out thermal reduction on the graphene oxide film on the substrate.
7. The method for producing an ammonia gas sensor based on thermally reduced graphene oxide according to claim 5, wherein the concentration of the graphene oxide solution in step (1) is 0.1-1mg/ml.
8. The method for manufacturing an ammonia sensor based on thermally reduced graphene oxide of claim 5, wherein the channel region width in step (2) is 5-50 microns.
9. The method for preparing an ammonia sensor based on thermally reduced graphene oxide according to claim 5, wherein the temperature of the heating reduction in the step (3) is 100-350 ℃ and the heating time is 1-2 hours; the gas environment is one of argon, nitrogen and vacuum.
10. The method for preparing an ammonia sensor based on thermally reduced graphene oxide according to claim 5, wherein the heating environment is pre-evacuated in vacuum and flushed with argon gas before the step (3).
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