Method for improving sensitivity and stability of semiconductor type methane sensor
阅读说明：本技术 一种提高半导体式甲烷传感器灵敏度和稳定性的方法 (Method for improving sensitivity and stability of semiconductor type methane sensor ) 是由 许令顺 周斯琛 赵小龙 付明 梁光华 于 2021-01-06 设计创作，主要内容包括：本发明属于催化材料制备领域,具体提供一种提高现有半导体式甲烷气体传感器检测灵敏度和稳定性的方法。半导体式甲烷传感器探头采用具氧缺陷的Pt/FeO复合体表面,该复合体表面的制备包括Pt样品除杂、蒸镀、生成氧化物、制备氧缺陷步骤。本发明通过在金属氧化物表面掺杂过渡金属,甲烷易在过渡金属表面吸附,然后通过“溢流”现象将吸附在过渡金属表面的甲烷分子转移到氧化物表面,增加氧化物甲烷检测的灵敏度；同时通过控制氧缺陷浓度的量,使氧缺陷维持在一定的平衡浓度,避免氧缺陷在使用过程中被空气中的氧气和水蒸汽氧化而发生变化。在增加半导体传感器灵敏度的同时,增加了传感器的使用稳定性。(The invention belongs to the field of catalytic material preparation, and particularly provides a method for improving the detection sensitivity and stability of an existing semiconductor type methane gas sensor. The probe of the semiconductor methane sensor adopts the surface of a Pt/FeO composite body with oxygen defects, and the preparation of the surface of the composite body comprises the steps of removing impurities from a Pt sample, evaporating, generating an oxide and preparing the oxygen defects. According to the invention, the transition metal is doped on the surface of the metal oxide, methane is easily adsorbed on the surface of the transition metal, and then methane molecules adsorbed on the surface of the transition metal are transferred to the surface of the oxide through an overflow phenomenon, so that the sensitivity of detecting the oxide methane is increased; meanwhile, the oxygen defect concentration is controlled to maintain a certain equilibrium concentration, so that the oxygen defect is prevented from being oxidized by oxygen and water vapor in the air to change in the using process. The sensitivity of the semiconductor sensor is increased, and meanwhile, the use stability of the sensor is increased.)
1. A method for improving the sensitivity and stability of a semiconductor methane sensor is characterized in that the probe of the semiconductor methane sensor adopts the surface of a Pt/FeO composite body with oxygen defect;
the preparation method of the Pt/FeO composite body surface with the oxygen defect comprises the following steps:
s1, removing impurities from a Pt sample, etching the Pt sample for 30min by using Ar plasma at room temperature, and annealing the etched Pt sample for 30min at the temperature of 1000K; the etching and annealing treatment is circulated until the surface of the Pt sample can not detect C atoms and O atoms;
s2, evaporation, fixing the Fe sample in an evaporation source at room temperature, heating the Fe sample by electron beam bombardment, and evaporating and covering the Fe on the surface of the Pt sample after impurity removal;
s3, generating oxide, and placing the Pt sample covered with Fe in high pressure O2Oxidizing at high temperature for 5-30min under the atmosphere to obtain a Pt/FeO complex containing a nano FeO particle film; continuously placing the Pt/FeO complex body in high pressure O2Waiting for cooling to room temperature under the atmosphere;
and S4, preparing oxygen defects, introducing atomic H into the cooled Pt/FeO complex under the vacuum condition, and heating to raise the temperature to obtain the Pt/FeO complex with the oxygen defects on the surface.
2. The method for improving the sensitivity and stability of the semiconductor methane sensor according to claim 1, wherein in S1, the Pt sample is first etched at 750K, 5 x 10 before Ar plasma etching-8O of torr2Keeping the temperature for more than 10min under the atmosphere condition.
3. The method for improving the sensitivity and stability of the semiconductor-type methane sensor according to claim 1, wherein in S1, the atomic H is H2When passing through the tungsten tube, the electron beam bombards and heats the tungsten tube to ensure that H is2Cleavage occurs.
4. The method for improving the sensitivity and stability of the semiconductor-type methane sensor according to claim 3, wherein the H is2Base pressure of 5X 10-9-5×10-8And the gas outlet end of the tungsten tube is 8mm away from the surface of the Pt sample.
5. The method for improving the sensitivity and stability of the semiconductor-type methane sensor according to claim 1, wherein in S3, the high pressure O is2The pressure of the atmosphere is 1X 10-6mbar。
6. The method for improving the sensitivity and stability of the semiconductor type methane sensor according to claim 1, wherein in S3, the high temperature oxidation temperature is 870-1000K.
Technical Field
The invention belongs to the field of catalytic material preparation, and particularly provides a method for improving the detection sensitivity and stability of an existing semiconductor type methane gas sensor.
Background
Types of sensors used for methane detection include semiconductor, catalytic combustion, infrared absorption, and optical interference. The semiconductor type is a type in which a gas is adsorbed on a semiconductor surface and then reacts with the semiconductor to generate electric charges, thereby changing the carrier density of the semiconductor and detecting the conductivity of the semiconductor to detect the concentration of the gas. The semiconductor type sensor has obvious advantages in the aspects of quick response time, low cost, simple manufacturing process and the like and is applied to the methane gas sensor. Semiconductor type is currently the most widely used gas sensor. However, semiconductor type sensors have certain disadvantages compared to other types of sensors, such as low sensitivity and poor stability compared to optical type sensors. In the practical application process, for example, leakage monitoring for an underground natural gas pipeline network, the service life and stability of the sensor are greatly influenced due to the complex underground space environment, high humidity and a large amount of various corrosive gases. Some sensors monitor the phenomenon that the concentration value gradually drifts in the using process, interference is generated on alarm judgment, and a large amount of manpower and material resources are consumed to judge the correctness of the monitoring value. Therefore, the development of a high-stability, high-sensitivity and low-cost methane gas sensor is of great significance to the aspects of ensuring urban safety, saving energy and the like.
The existing methane sensor is based on semiconductor materials such as ZnO, SnO2 and the like, and utilizes the fact that the conductivity of the semiconductor materials is changed after methane is adsorbed, and the concentration of methane gas is measured by using the relation that the change rate and the methane adsorption rate are in a certain proportion. Because the semiconductor material is generally exposed to oxygen atoms on the surface, the oxygen atoms have electron-withdrawing property, and the chemical adsorption of methane gas also needs substrate atoms to give electrons, the probability of methane adsorption is low, so that the sensitivity of the existing material to methane concentration detection is low.
A silicon-sulfur poisoning resistant hot-wire methane sensor is provided in application No. 201510750344.9 entitled "silicon-sulfur poisoning resistant Hot-wire methane sensor" and includes a catalytic element and a reference element arranged in a hot-wire configuration, the catalytic element including activated carbon particlesCarrier and SnO immobilized on said activated carbon particle carrier2Gas-sensitive layer, Pt/Pd catalyst and Al2O3/SiO2A separation layer, wherein the reference element comprises alumina pellets and SnO doped with conductive carbon black and supported on the alumina pellets2-C/TiO2-C gas-sensitive layer, Au/CuO catalyst, Al2O3/SiO2And (5) separating the layers. The patent realizes the sulfur poisoning resistance of the sensor through structures such as noble metal oxides. However, there is no technical content for improving the sensitivity and stability against water vapor and the like.
Disclosure of Invention
In order to solve the technical problem, the invention provides a method for improving the sensitivity and stability of a semiconductor type methane sensor.
In order to realize the purpose of the invention, the invention adopts the following technical scheme:
a method for improving the sensitivity and stability of a semiconductor methane sensor, wherein a probe of the semiconductor methane sensor adopts a Pt/FeO composite surface with oxygen defects;
the preparation method of the Pt/FeO composite body surface with the oxygen defect comprises the following steps:
s1, removing impurities from a Pt sample, etching the Pt sample for 30min by using Ar plasma at room temperature, and annealing the etched Pt sample for 30min at the temperature of 1000K; the etching and annealing treatment is circulated until the surface of the Pt sample can not detect C atoms and O atoms;
s2, evaporation, fixing the Fe sample in an evaporation source at room temperature, heating the Fe sample by electron beam bombardment, and evaporating and covering the Fe on the surface of the Pt sample after impurity removal;
s3, generating oxide, and placing the Pt sample covered with Fe in high pressure O2Oxidizing at high temperature for 5-30min under the atmosphere to obtain a Pt/FeO complex containing an FeO film; continuously placing the Pt/FeO complex body in high pressure O2Waiting for cooling to room temperature under the atmosphere;
and S4, preparing oxygen defects, introducing atomic H into the cooled Pt/FeO complex under the vacuum condition, and heating to raise the temperature to obtain the Pt/FeO complex with the oxygen defects on the surface.
Preferably, in S1, the Pt sample is first etched at 750K, 5 × 10, before Ar plasma etching-8O of torr2Keeping the temperature for more than 10min under the atmosphere condition.
Preferably, in S1, the atom H is H2When passing through the tungsten tube, the electron beam bombards and heats the tungsten tube to ensure that H is2Cleavage occurs.
Preferably, said H2Base pressure of 5X 10-9-5×10-8And the gas outlet end of the tungsten tube is 8mm away from the surface of the Pt sample.
Preferably, in S3, the high pressure O2The pressure of the atmosphere is 1X 10-6mbar。
Preferably, in S3, the high-temperature oxidation temperature is 870-1000K.
The invention has the beneficial effects that:
(1) the invention changes the traditional loading model that the catalyst carrier is oxide, adopts Pt/FeO reversed loading model, grows oxide on the metal single crystal by a certain means, can conveniently regulate and control the thickness and coverage rate of the oxide, and adapts to different researches and requirements.
(2) The invention utilizes atomic H to prepare the oxygen defect concentration on the surface of the semiconductor, gas-phase atomic H reduces FeO at room temperature, and H can generate OH on the surface of FeO-Heating to a certain temperature OH-Reaction to form H2O and H2By repeated O at high temperature2The diffusion of Fe between the Pt (111) surface and a bulk phase can be controlled by atmospheric oxidation and H atom reduction, the Pt/FeO surface with periodic oxygen defects can be prepared by oxidation at different temperatures, and the FeO surface can be reduced to O losing 1/4 monolayers at most.
(3) According to the invention, transition metal is doped on the surface of metal oxide, methane is easily adsorbed on the surface of the transition metal, and then methane molecules adsorbed on the surface of the transition metal are transferred to the surface of the oxide through an overflow phenomenon, so that the sensitivity of detecting the oxide methane is increased; meanwhile, the oxygen defect concentration is controlled to maintain a certain equilibrium concentration, so that the oxygen defect is prevented from being oxidized by oxygen and water vapor in the air to change in the using process. The sensitivity of the semiconductor sensor is increased, and meanwhile, the use stability of the sensor is increased.
Drawings
FIG. 1 shows the preparation process of FeO (111) on the surface of Pt (111) according to the present application;
FIG. 2 is an LEED graph of four different ferrite specific surfaces obtained by oxidizing FeO for 5min, 10min, 15min and 30 min;
FIG. 3 is an O1S XPS spectrum obtained by reducing FeO at room temperature with atomic H;
FIG. 4 is a schematic of a gas sensing system used in performing gas sensing performance tests;
FIG. 5 shows the results of the sensitivity test of Pt/FeO complex sensors with different oxygen defect concentrations to methane;
FIG. 6 is a graph comparing the stability of methane detection between a sensor doped with a transition element and having an increased oxygen defect concentration and an untreated sensor;
FIG. 7 is a graph comparing the results of methane detection sensitivity between a sensor doped with a transition element and increased oxygen defect concentration and an untreated sensor.
Detailed Description
The technical scheme of the invention is more specifically explained by combining the following embodiments:
example 1
Preparation of Pt/FeO composite body surface with oxygen defect
Taking a clean Pt sample, because the Pt sample is exposed in the air, the surface of the Pt sample can be covered with a large amount of different C atoms and O atoms, firstly removing impurities from the Pt sample: pt samples were first tested at 750K, 5X 10-8O of torr2Keeping the temperature for more than 10min under the atmosphere condition. Then, etching the Pt sample by Ar plasma for 30min at room temperature, and annealing the etched Pt sample at 1000K for 30 min; the etching and annealing treatments were cycled until the C and O atom signals on the Pt sample surface were not detectable by XPS and the Low Energy Electron Diffraction (LEED) results showed a clearer diffraction spot of Pt (111).
Fixing the Fe sample on a crucible in an evaporation source at room temperature, heating the Fe sample by electron beam bombardment, and evaporating the FeCovering the surface of the Pt sample after impurity removal; the Fe-coated Pt sample was placed at 1X 10-6O of mbar high pressure2Oxidizing at 870 ℃ and 1000K for 5min, 10min, 15min and 30min under the atmosphere to respectively obtain a monolayer FeO0.58、FeO0.82、FeO0.92Pt/FeO composite of FeO thin films, as shown in FIG. 2; continuously placing the Pt/FeO complex body in high pressure O2And (5) waiting to cool to room temperature under the atmosphere. And introducing atomic H into the cooled Pt/FeO composite body under the vacuum condition, and heating to raise the temperature to obtain the Pt/FeO composite body with the surface having oxygen defects.
The atom H is2When passing through the tungsten tube, the electron beam bombards and heats the tungsten tube to ensure that H is2Generated by pyrolysis at 1000 ℃ of H2Base pressure of 5X 10-9-5×10-8torr, the gas outlet end of the tungsten tube was 8mm from the surface of the Pt sample.
The H atom generates OH on the surface of FeO-Heating to a certain temperature OH-Reaction to form H2O and H2The FeO surface can be reduced to O losing 1/4 monolayer at most, as shown in FIG. 3, the O1S XPS spectrum obtained by reducing FeO at room temperature with atomic H, and it can be seen from the graph that the adsorption of atomic H can reduce the O part in FeO to OH-After heating to 500K, the surface O is reduced, and the final O amount stays at 0.67ML along with the increase of the exposure amount of the atomic H, which shows that certain oxygen defects can be produced on the Pt/FeO surface by utilizing H atomic reduction.
Example 2
Methane sensor sensitivity detection on surface of Pt/FeO composite body with oxygen defect
A sensitivity test was conducted on the surface of a Pt/FeO composite body having oxygen defects prepared in the methane sensor in the same manner as in example 1.
The gas-sensitive system shown in fig. 4 is used for gas-sensitive performance test, all the gases used in the experiment are standard gases, Mass Flow Controllers (MFCs) are used for controlling the flow rates of different gases to obtain the required gases with different concentrations, and the total flow rate of the gases is set to be 100 mL/min.
The surface temperature of the sensor is controlled by a digital voltage-stabilizing direct-current power supply and is subjected to infrared thermal imagingAnd (6) calibrating the instrument. The sensitivity is reacted using a catalytic efficiency of methane (CH)4) The gas consumption accounts for the percentage of the total amount of methane gas, and the sensor test circuit converts the gas-sensitive response signal into a voltage signal by using a Wheatstone bridge.
Catalytic efficiency is methane gas consumption/total methane gas amount × 100%
Voltage signal calculation: assuming that the resistance increment of the sensor is Δ Rb, the circuit outputs a voltage amount:
Uo＝EΔRb/2Rb
wherein, UO: outputting the voltage; rb: resistance values before conversion; Δ Rb: the resistance value variation; e: a supply voltage; ro: and a circuit protection resistor.
The Pt/FeO complex sensor containing 10 oxygen defect concentrations of 2.5%, 5%, 7.5%, 10% … 20%, 22.5% and 25% is prepared by placing FeO in a dosage ratio in an H atmosphere, controlling heating and annealing, and sequentially placing the Pt/FeO complex sensor in a methane gas concentration of 2 v% at room temperature, as shown in FIG. 5, the detection sensitivity of the sensor to methane tends to increase and decrease with the increase of the oxygen defect concentration, because the O defect causes the exposure of surface Fe atoms, the Fe atoms have high activity, and methane molecules adsorbed on the Pt surface are transferred to the FeO surface, so the detection sensitivity of the FeO to methane is increased with the increase of the oxygen defect concentration at the early stage, and when the oxygen defect concentration is about 15%, the sensitivity increase times are the highest.
As shown in FIGS. 6-7, the Pt/FeO complex sensor with 15% oxygen defect concentration was exposed to room temperature, and the concentration of methane gas was gradually increased, and the sensitivity curve of the Pt/FeO complex sensor treated with oxygen defects maintained a good linear relationship with time. The sensitivity of the oxygen defect treated Pt/FeO complex sensor increases along with the increase of the methane gas concentration, and no saturation phenomenon occurs in the concentration range of 0-35%. The sensor which is not doped with transition metal and treated by oxygen defects can not linearly reflect the concentration change of methane, and the detection result is in step jump due to insufficient precision.
The detection time is prolonged, the methane gas concentration rises within the range of 1.9% -2.3% along with the extension of time, the sensitivity curve of the Pt/FeO composite sensor subjected to oxygen defect treatment still keeps good linear relation and reaction sensitivity, and the sensor not subjected to transition metal doping and oxygen defect treatment cannot be used due to insufficient sensitivity or supersaturation when the methane concentration exceeds the range of 1.95-2.05%.
The above embodiments are only used to illustrate the technical solutions of the present invention, and do not limit the present invention; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those skilled in the art that: any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
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