CN113740389A - Zinc oxide nanorod-based field emission hydrogen sensor and preparation method and application thereof - Google Patents
Zinc oxide nanorod-based field emission hydrogen sensor and preparation method and application thereof Download PDFInfo
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- CN113740389A CN113740389A CN202110983328.XA CN202110983328A CN113740389A CN 113740389 A CN113740389 A CN 113740389A CN 202110983328 A CN202110983328 A CN 202110983328A CN 113740389 A CN113740389 A CN 113740389A
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- 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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- G01N27/127—Composition of the body, e.g. the composition of its sensitive layer comprising nanoparticles
Abstract
The invention discloses a field emission hydrogen sensor based on zinc oxide nano-rod and a preparation method and application thereof, and the technical scheme is that the field emission hydrogen sensor comprises a field emission cathode and a field emission anode, wherein the field emission cathode comprises a substrate, a ZnO seed crystal layer arranged on the substrate in a spin coating manner, and a ZnO nano-rod array growing on the ZnO seed crystal layer on the substrate, and the field emission cathode is 10 times of that of the field emission cathode‑7‑10‑3The absorption of hydrogen on the surface of the field emission cathode under the Pa hydrogen partial pressure can lead to the enhancement of emission current under the same field intensity, thereby having the hydrogen sensing characteristic. The invention has the advantages that: the method has the advantages of stability, micro size, simple structure, quick recovery and the like, and in addition, compared with the traditional carbon nanotube preparation technology (chemical vapor deposition method), the zinc oxide nanorod is prepared by a hydrothermal method, does not need to use a transition metal catalyst, has lower temperature (70-95 ℃), has lower cost and can grow in a large area.
Description
Technical Field
The invention relates to a hydrogen sensor, in particular to a zinc oxide nanorod-based field emission hydrogen sensor and a preparation method and application thereof.
Background
Zinc oxide is a semiconductor material with wide forbidden band (3.37 eV), and the zinc oxide nano material can be widely applied to the fields of gas sensing, energy, piezoelectricity, field emission and the like. The zinc oxide nano material has obvious sensing performance on various gases, and in addition, the zinc oxide has simple growth conditions, is easy to prepare, is non-toxic and harmless, and is an environment-friendly material. By detecting the change in resistance, the zinc oxide sensor can be used to detect various gases such as methane, acetylene, ammonia gas, nitrogen dioxide, and the like.
Hydrogen sensing plays an important role in many scientific and industrial fields, and at present, research and development based on hydrogen sensing technology is mainly focused on normal pressure environment, however, low-pressure hydrogen detection also plays an important role in many fields including oil and gas transmission, space missions, low-emission fuel cells, high-vacuum processing equipment, vacuum electronic devices and the like. The hydrogen sensor based on the nano mechanical resonance technology and the metal substrate direct growth carbon nanotube technology can be applied to 10-5The Torr or above gas atmosphere is a low-pressure hydrogen sensing technology of a few kinds. However, no low-pressure hydrogen detection sensing technology related to the zinc oxide nano-rod is reported yet.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a field emission hydrogen sensor based on a zinc oxide nanorod and a preparation method and application thereof. The field emission hydrogen sensor based on the zinc oxide nanorod detects the hydrogen partial pressure in the low-pressure environment by detecting the change of the field emission current of the ZnO nanorod array.
In order to achieve the above object, a first aspect of the present invention provides a zinc oxide nanorod based field emission hydrogen sensor, comprising a field emission cathode and a field emission anode, wherein the field emission cathode comprises a substrate, a ZnO seed layer spin-coated on the substrate, and a ZnO nanorod array grown on the ZnO seed layer on the substrate by a hydrothermal method, and the field emission cathode has a hydrogen partial pressure of 10%-7-10-3And under Pa, the absorption of hydrogen on the surface of the field emission cathode can enhance the emission current under the same field intensity, thereby having the hydrogen sensing characteristic.
It is further provided that said field emission anode is planar or tip shaped.
The substrate is a silicon chip substrate or a metal substrate or conductive glass, the metal substrate is made of stainless steel, alloy, nickel sheets and the like, and the conductive glass is made of ITO, FTO and the like.
In addition, the invention also provides a field emission cathode of the field emission hydrogen sensor based on the zinc oxide nano rod, and the field emission cathode comprises a substrate, a ZnO seed crystal layer arranged on the substrate in a spin coating mode, and a ZnO nano rod array grown on the ZnO seed crystal layer on the substrate through a hydrothermal method.
The invention provides a method for detecting hydrogen by a field emission hydrogen sensor in a low-pressure hydrogen environment, which comprises the following steps:
(1) determining hydrogen sensing current and pressure curves:
under hydrogen partial pressure 10-7-10-3Under Pa, the concrete steps are as follows:
i) at each measurement point, the intrinsic emission I of the field emission cathode is measured by Joule heating degassing with an increased emission current0；
ii) applying a field emission voltage V and obtaining an initial emission current I0And detecting the change of the current within the time t;
iii) dividing the t time into N equal intervals as required, recording the current I at the end of each intervaliI ═ 0, …, N); vi) applying a current I per end of intervaliAccumulating, and averaging to obtain a current I which is used as the gas-sensitive sensing current of the measuring point;
v) after the measurement is finished, the sensor is subjected to pulse transmission for one to several times under a higher current, so that the purposes of cleaning the surface and recovering the detection function of the sensor are achieved;
drawing a hydrogen sensing current and pressure curve after multipoint testing according to the gas-sensitive sensing current of the measuring point and the hydrogen partial pressure of the corresponding test;
(2) and detecting gas-sensitive sensing current under the hydrogen partial pressure environment to be detected, and determining the hydrogen partial pressure value according to the hydrogen sensing current and pressure curve.
The invention has the advantages that: the method has the advantages of stability, micro size, simple structure, quick recovery and the like, and in addition, compared with the traditional carbon nanotube preparation technology (chemical vapor deposition method), the zinc oxide nanorod is prepared by a hydrothermal method, does not need to use a transition metal catalyst, has lower temperature (70-95 ℃), has lower cost and can grow in a large area.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is within the scope of the present invention for those skilled in the art to obtain other drawings based on the drawings without inventive exercise.
FIG. 1 is a zinc oxide nanorod cathode material, (a) SEM photograph, and (b) TEM photograph;
FIG. 2 is a field emission curve of zinc oxide nanorods, (a) J-E, and (b) F-N;
FIG. 3 is a test chart of zinc oxide (annealing at 400 ℃) with gradually increasing small current emission along with time and stronger effect along with pressure increase under different hydrogen pressure environments;
figure 4 shows a novel low pressure hydrogen sensing characteristic curve based on the zinc oxide nanorods (400 ℃ anneal) field emission principle.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings.
As shown in fig. 1 to 4, in the embodiment of the present invention, the ZnO nanorod array is prepared by a two-step method, in which a ZnO seed layer is spin-coated on a substrate, and then the ZnO nanorod array is obtained on the substrate by a hydrothermal method. The ZnO nanorod array can also grow by a chemical vapor deposition method, the sensor adopts a dipolar structure, and the working principle is field electron emission. The cathode A is a ZnO nanorod array, and the anode B can be a plane, a tip or other shapes. At low pressure (pressure less than or equal to 10)-2Pa), applying a specific cathode voltage V to the anode1High voltage V2When acting as a cathodeSurface electric field intensity E1After reaching a certain value, the ZnO surface emits electrons, and the current I generated by the electrons is measured1And obtaining a field emission current-voltage curve. For a field emission cathode of a ZnO nano rod with hydrogen sensing characteristics, the adsorption of hydrogen on the surface of the nano cathode can affect the field emission performance, wherein one effect is that the emission current is enhanced under the same field intensity; and, different hydrogen partial pressures have different effects on field emission performance, for example, the higher the hydrogen partial pressure, the more significant the field emission enhancement effect. When hydrogen sensing measurement is carried out, the change of field electron emission current is measured under a certain fixed electric field intensity, the measurement time can be different according to different sensors and measurement environments, and before field emission current measurement, Joule heat generated by large-current field emission can be used for cleaning and degassing the surface of the zinc oxide nano rod. In order to enhance the sensing effect and improve the sensing performances such as measurement stability and reliability, the improved test method can be properly adjusted on the premise of ensuring the time required by the sensing test: 1) in the measurement of the current variation along with time, parameters such as sensitivity, response time and the like can be integrated, and the measurement time can be properly adjusted; 2) repeated and multi-point measurements may be used. The repeated measurement is carried out for multiple times under the same field emission voltage; the multipoint measurement is to select different voltages and measure the field emission current. The repeated and multiple point measurements can be used individually or in combination, with the data weighted averaged using appropriate mathematical methods.
In the embodiment, a zinc oxide nanorod (shown in figure 1) is grown on a silicon wafer substrate by adopting a two-step method, and a field emission test is carried out on the zinc oxide nanorod, so that the field emission current enhancement effect is obvious under the conditions of a low-pressure hydrogen environment and a small current; at the same time at 10-7-10-3Under Pa, the higher the hydrogen partial pressure is, the more obvious the field emission enhancement effect is. Based on this, the inventors developed a hydrogen sensor based on the field emission of ZnO nanorods. The current-voltage curve of the field emission of fig. 2, along with the corresponding F-N curve, in the field emission test, shows that the electron emission deviates from the intrinsic emission characteristic of Fowler-Nordheim theory in the low current emission regime. Further experiments prove that: the deviation is caused by the field emission auxiliary emission effect of hydrogen molecules, and the hydrogen-sensitive field emission sensor is establishedThe technical basis of (1). Compared with the carbon nanotube preparation technology (chemical vapor deposition method), the zinc oxide nanorod is prepared by a hydrothermal method, does not need a transition metal catalyst, is low in temperature (70-95 ℃), is low in cost, and can grow in a large area. Compared with the carbon nanotube hydrogen sensitive field emission sensing technology, the zinc oxide nanorod hydrogen sensitive field emission current is related to the concentration of oxygen defects in the zinc oxide nanorod hydrogen sensitive field emission current, and the higher the concentration of oxygen defects is, the higher the field emission current is. The mechanism is mainly that after hydrogen molecules or hydrogen atoms are adsorbed to the surface of the zinc oxide nano rod, the hydrogen molecules or the hydrogen atoms interact with oxygen defects in the zinc oxide to cause the change of the work function of the zinc oxide, thereby initiating the change of field emission current. In addition, compared with the carbon nano tube, the zinc oxide has better emission stability under the condition of small current emission. FIG. 3 shows that the emission current is gradually increased at different hydrogen partial pressures in a hydrogen atmosphere when the field emission starting current is about 1 μ A. Based on this, the inventors tested the hydrogen partial pressure (10) at different values-7-10-3Pa) low current field emission characteristics. And an accumulation method is adopted for data acquisition, and the method comprises the following specific steps: i) at each measurement point, the intrinsic emission (or near intrinsic emission) I of the zinc oxide cathode is measured by Joule heating degassing with an increased emission current0(ii) a ii) applying a field emission voltage V and obtaining an initial emission current I0And detecting the change of the current within the time t; iii) dividing the t time into N equal intervals as required, recording the current I at the end of each intervali. (i ═ 0, …, N); vi) applying a current I per end of intervaliAccumulating, and averaging to obtain a current I which is used as the gas-sensitive sensing current of the measuring point; v) after the measurement is finished, the sensor can be subjected to pulse transmission for one to several times under a higher current, so that the purposes of cleaning the surface and recovering the detection function of the sensor are achieved.
The method has the advantages of stability, micro size, simple structure, quick recovery and the like.
The above disclosure is only for the purpose of illustrating the preferred embodiments of the present invention, and it is therefore to be understood that the invention is not limited by the scope of the appended claims.
Claims (6)
1. A zinc oxide nanorod-based field emission hydrogen sensor is characterized by comprising a field emission cathode and a field emission anode, wherein the field emission cathode comprises a substrate, a ZnO seed crystal layer arranged on the substrate in a spin coating mode, and a ZnO nanorod array growing on the ZnO seed crystal layer on the substrate, and the field emission cathode is under the partial pressure of hydrogen of 10 DEG C-7-10-3And under Pa, the absorption of hydrogen on the surface of the field emission cathode can enhance the emission current under the same field intensity, thereby having the hydrogen sensing characteristic.
2. The zinc oxide nanorod-based field emission hydrogen sensor of claim 1, wherein: the field emission anode is in a plane or tip shape.
3. The zinc oxide nanorod-based field emission hydrogen sensor of claim 1, wherein: the substrate is a silicon chip substrate or a metal substrate or conductive glass.
4. A field emission cathode of a field emission hydrogen sensor based on a zinc oxide nanorod is characterized in that: the field emission cathode comprises a substrate, a ZnO seed crystal layer arranged on the substrate in a spin coating mode, and a ZnO nano-rod array grown on the ZnO seed crystal layer on the substrate through a hydrothermal method.
5. A method of making a field emission cathode according to claim 4, wherein: firstly, a ZnO seed crystal layer is coated on a substrate in a spin mode, then a ZnO nanorod array is obtained on the substrate by adopting a hydrothermal method, the temperature of the hydrothermal method is 70-95 ℃, and a transition metal catalyst is not needed.
6. A method for detecting hydrogen in a low pressure hydrogen environment by a field emission hydrogen sensor as claimed in claim 1, comprising:
(1) determining hydrogen sensing current and pressure curves:
under hydrogen partial pressure 10-7-10-3Under Pa, the concrete steps are as follows:
i) at each measurement point, the intrinsic emission I of the field emission cathode is measured by Joule heating degassing with an increased emission current0；
ii) applying a field emission voltage V and obtaining an initial emission current I0And detecting the change of the current within the time t;
iii) dividing the t time into N equal intervals as required, recording the current I at the end of each intervaliI ═ 0, …, N); vi) applying a current I per end of intervaliAccumulating, and averaging to obtain a current I which is used as the gas-sensitive sensing current of the measuring point;
v) after the measurement is finished, the sensor is subjected to pulse transmission for one to several times under a higher current, so that the purposes of cleaning the surface and recovering the detection function of the sensor are achieved;
drawing a hydrogen sensing current and pressure curve after multipoint testing according to the gas-sensitive sensing current of the measuring point and the hydrogen partial pressure of the corresponding test;
(2) and detecting gas-sensitive sensing current under the hydrogen partial pressure environment to be detected, and determining the hydrogen partial pressure value according to the hydrogen sensing current and pressure curve.
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