Polarized light enhanced gas sensor based on two-dimensional R-TiO2

Abstract

The invention discloses a polarized light enhanced gas sensor based on two-dimensional R-TiO2, which is prepared by the following steps: firstly, preparing two-dimensional rutile phase titanium oxide on a SiO2 / Si substrate, and then preparing the gas sensor by a micro-nano processing technology; the gas-sensitive sensing performance of the gas-sensitive sensor can be improved under the auxiliary action of polarized light. Specifically, when the gas sensitive sensor is used, incident light is converted into linearly polarized light through a linear polarizer to irradiate and excite the sensor. The method for preparing the two-dimensional rutile phase titanium oxide on the SiO2 / Si substrate comprises the following steps: S1, depositing a pure Ti metal layer on the SiO2 / Si substrate through electron beam evaporation; s2, rutile phase titanium oxide is prepared on the SiO2 / Si substrate through a self-limiting gas-solid interface oxidation method; and S3, stripping the rutile phase titanium oxide on the SiO2 / Si substrate into a few-layer two-dimensional nanosheet by adopting a mechanical stripping method. According to the invention, polarized light is applied as exciting light, so that the photon-generated carrier concentration of the 2D R-TiO2 sensor is increased, and the gas-sensitive sensing performance of the 2D R-TiO2 sensor is further improved.

Description

Technical Field

[0001] The invention relates to the technical field of gas sensors, in particular to a polarized light enhanced gas sensitive sensor based on two-dimensional R-TiO2. Background Art

[0002] Semiconductor metal oxide (SMO) gas sensors have broad application prospects. TiO2 is non-toxic, biocompatible, photocorrosion-resistant, low-cost, rich in raw materials, and simple in preparation process. Nano-TiO2 has high chemical stability, thermal stability, surface activity, and corrosion resistance. It is an important inorganic nanostructured material with a large specific surface area, unique physical and chemical properties, and catalytic properties. TiO2 is sensitive to a variety of gases, such as H2, O2, NO2, ethanol vapor, etc. It is an ideal material for the preparation of SMO gas sensors.

[0003] However, TiO2-based gas sensors also have shortcomings such as low sensitivity, slow response and recovery rate, etc. In order to obtain fast-response, high-sensitivity, and long-term stable gas sensors, researchers have improved the overall performance of gas sensor devices by constructing heterojunctions, doping modifications, and precious metal modifications. Summary of the invention

[0004] In view of the shortcomings of TiO2-based gas sensors such as low sensitivity, slow response and recovery rate, the present invention provides a polarization light enhanced gas sensor based on two-dimensional R-TiO2.

[0005] The polarized light enhanced gas sensor based on two-dimensional R-TiO2 provided by the present invention is prepared by preparing two-dimensional rutile phase titanium oxide (R-TiO2) on a SiO2 / Si substrate and then combining it with micro-nano processing technology. The gas sensor can improve the gas sensing performance under the auxiliary effect of polarized light.

[0006] Specifically, when the gas sensor is used, the incident light is converted into linearly polarized light through a linear polarizer to illuminate and excite the sensor, so as to improve the gas sensing performance.

[0007] The method for preparing two-dimensional rutile phase titanium oxide on SiO2 / Si substrate is as follows:

[0008] S1, depositing a pure Ti metal layer on a SiO2 / Si substrate by electron beam evaporation;

[0009] S2, placing a SiO2 / Si substrate with a Ti metal layer deposited thereon in a tube furnace, evacuating the tube to a vacuum level below 0.01 MPa, and then filling the tube with argon gas to normal pressure, and then heating the tube to 873-1073 K at a heating rate of 12 K / min, and keeping the temperature for 4-8 h to form rutile phase titanium oxide two-dimensional nanosheets on the SiO2 / Si substrate;

[0010] S3. Use mechanical exfoliation to exfoliate the rutile phase titanium oxide on the SiO2 / Si substrate into a few-layer two-dimensional nanosheets.

[0011] Preferably, in step S2, after evacuating to less than 0.01 MPa, the chamber is filled with argon gas to normal pressure and this process is repeated three times to strictly control the oxygen concentration in the chamber.

[0012] The micro-nano processing technology includes the steps of spin coating photoresist, heating and curing, exposure, development, evaporation, degumming, etc. The Au electrode is made on the two-dimensional rutile phase titanium oxide by micro-nano processing technology to form a gas sensor.

[0013] Compared with the prior art, the present invention is beneficial in that:

[0014] (1) The present invention synthesizes and exfoliates single-crystalline rutile phase two-dimensional titanium oxide through a self-limiting gas-solid interface method, thereby increasing the specific surface area of ​​the material and improving the gas sensitive sensing performance.

[0015] (2) The present invention uses polarized light as an aid to increase the photogenerated carrier concentration of the 2D R-TiO2 sensor, thereby further improving the gas sensing performance. By changing the polarization angle of the applied light, the performance of the sensor is improved by about 7.5 times, and the response becomes faster, with the response time reduced by 50%.

[0016] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 AFM image of R-TiO2 nanosheets.

[0018] Figure 2 This is the XRD pattern of R-TiO2 nanosheets.

[0019] Figure 3 This is the EDS image of R-TiO2 nanosheets.

[0020] Figure 4 This is the XPD diagram of R-TiO2 nanosheets.

[0021] Figure 5 TEM image of R-TiO2 nanosheets.

[0022] Figure 6 Two-dimensional R-TiO2 nanosheets and their crystal orientation.

[0023] Figure 7Process flow chart for making two-dimensional R-TiO2 gas sensor.

[0024] Figure 8 This is the response of the R-TiO2 Ns-based gas sensor to 10 ppm NO2 at room temperature without light excitation.

[0025] Fig. 9 The response change diagram of the R-TiO2 Ns-based gas sensor to 10ppm NO2 under light excitation. (a) is the response change of the sensor to 10ppm NO2 polarization angle with a step of 30° under 405nm light excitation; (b) is the polar coordinate diagram of the corresponding figure (a).

[0026] Fig.10 The dynamic response and stability of R-TiO2 Ns-based gas sensor to NO2 under 405nm light excitation along the y-axis at room temperature, where (a) is the dynamic response to NO2; (b) is the stability to 10ppm NO2. DETAILED DESCRIPTION

[0027] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0028] Example 1

[0029] A method for preparing rutile phase titanium oxide (R-TiO2) two-dimensional nanosheets on a SiO2 / Si substrate:

[0030] First, 30g of 99.9% Ti metal target was placed in a crucible, and a 300nm thick pure Ti metal layer was deposited on a 1x1 cm SiO2 / Si substrate by electron beam evaporation, and then cooled to room temperature to obtain a Ti / SiO2 / Si sample. The SiO2 / Si substrate is a silicon plate with a surface layer of silicon dioxide purchased on the market. The Ti / SiO2 / Si sample was placed in a tubular furnace, and the entire cavity was confirmed to be well sealed. After evacuating to less than 0.01Mpa, it was filled with argon to normal pressure and this process was repeated three times to strictly control the concentration of oxygen in the cavity. Then annealing was performed, and the annealing parameters were as follows: heating temperature was 950K, heating rate was 12K / min, and holding time was 6h, and rutile phase titanium oxide (R-TiO2) was prepared on the SiO2 / Si substrate. Furthermore, another clean SiO2 / Si substrate is used to cover the prepared rutile titanium oxide surface, and is slightly pressed to allow a layer of rutile titanium oxide to adhere to the surface of the clean SiO2 / Si substrate, thereby forming a few layers of rutile titanium oxide two-dimensional nanosheets on the SiO2 / Si substrate.

[0031] The thickness of the two-dimensional R-TiO2 nanosheets was characterized by atomic force microscopy (AFM). The crystal structure of the material was characterized by X-ray diffraction. The elements of the material were qualitatively and quantitatively analyzed by energy dispersive spectroscopy (EDS). The binding energy and valence state of Ti and O elements were characterized by X-ray photoelectron spectroscopy (XPS). The crystal structure of the two-dimensional R-TiO2 nanosheets was characterized by transmission electron microscopy (TEM).

[0032] Figure 1 This is an AFM image of R-TiO2 nanosheets. It can be seen from the image that the thickness of the two-dimensional R-TiO2 nanosheets is about 13.1nm, the lateral size is 10-30um, and it has excellent surface flatness.

[0033] Figure 2 This is the XRD pattern of R-TiO2 nanosheets. The XRD spectrum has a clear peak at 36°, which belongs to the rutile phase (110) plane (JCPDS card 21-1276, Diffraction of α=β=γ=90°).

[0034] Figure 3 is the EDS image of R-TiO2 nanosheets, which shows the distribution of elements Ti and O, proving the presence of these elements and showing the uniform distribution of Ti and O atoms in Ns.

[0035] Figure 4 The XPS spectrum of R-TiO2 nanosheets verifies the chemical valence state of R-TiO2 Ns. The XPS results of Ti 2p at binding energies of 463.8 and 458.1 eV are assigned to 2p 1 / 2 and 2p 3 / 2 energy state, indicating the tetravalent state of Ti; the deconvoluted peak of 41O 1s is located at 533.0 eV, proving to be a Ti-O bond.

[0036] To further confirm the exposure plane, high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) were performed, and the results are shown in Figure 5 . (a) is the HRTEM image, and (b) is the SAED image. The lattice fringes shown in the figure indicate a d spacing of 0.32 nm, corresponding to the (110) plane. In addition, the SAED image results show clear diffraction spots from the (110) and (001) planes.

[0037] Figure 6 are two-dimensional R-TiO2 nanosheets and their crystal orientation.

[0038] The SiO2 / Si substrate with a few layers of rutile phase titanium oxide two-dimensional nanosheets attached to the surface obtained in Example 1 is combined with micro-nano processing technology to make Au electrodes on the two-dimensional rutile phase titanium oxide to form a gas sensor. Micro-nano processing technology is as follows Figure 7 The process includes the steps of spin coating photoresist, heating and curing, exposure, development, evaporation, and degumming. The gas sensing performance of the two-dimensional R-TiO2 nanosheets was tested using a gas sensing test platform.

[0039] Figure 8 This is the response change diagram of the gas sensor to 10ppm NO2 at room temperature without light excitation. As can be seen from the figure, the sensor is about 2.6 (R g / R o ), the response time and recovery time are 271s and 287s respectively.

[0040] The incident light was converted into linearly polarized light as excitation light by a linear polarizer, and the corresponding gas-sensing properties were studied. Fig. 9 The following is a graph showing the response of the gas sensor to 10ppm NO2 under light excitation at room temperature. Figure (a) shows the response of the sensor to 10ppm NO2 polarization angle with a step length of 30° under 405nm light excitation; (b) is the polar coordinate graph of the corresponding figure (a). It can be seen that the NO2 gas sensitive response rate shows an obvious periodic change with the change of polarization angle. The responsiveness reaches a maximum value of 19.8 (R g / R o ), decays to a minimum value of 2.9 (R g / R o To further analyze the results, Fig. 9 The polar coordinate diagram (b) is extracted from (a), and the polar coordinate diagram shows a double leaf shape. This periodic change determines that the polarized light-assisted two-dimensional R-TiO2 gas sensor mainly relies on charge transfer to enhance gas sensing. As the number of photoexcited carriers increases, the charge transfer between R-TiO2 and NO2 increases significantly, which is manifested as a significant increase in the response resistance.

[0041] Fig.10 The dynamic response and stability of the sensor to NO2 under 405nm light excitation along the y-axis. (a) is the dynamic response of NO2; (b) is the stability to 10ppm NO2. It can be seen that the dynamic response of the gas sensor to NO2 under 405nm light excitation along the y-axis at room temperature has a linear function relationship with the NO2 concentration. And under this condition, the gas sensor has achieved a significant improvement in the response rate to 10ppmNO2, and the response has become faster, with the response time increased to 126s.

[0042] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A polarization-enhanced gas sensor based on two-dimensional R-TiO2, characterized in that: Firstly, two-dimensional rutile titanium oxide is prepared on a SiO2 / Si substrate, and then a gas sensor is made through micro-nano processing technology; the gas sensor can improve the gas sensing performance with the assistance of polarized light.

2. The polarization-enhanced gas sensor based on two-dimensional R-TiO2 according to claim 1, characterized in that: When the gas sensor is in use, the incident light is converted into linearly polarized light through a linear polarizer to illuminate and excite the sensor, so as to improve the gas sensing performance.

3. The polarization-enhanced gas sensor based on two-dimensional R-TiO2 as claimed in claim 1, characterized in that: The method for preparing two-dimensional rutile phase titanium oxide on SiO2 / Si substrate is as follows; S1, depositing a pure Ti metal layer on a SiO2 / Si substrate by electron beam evaporation; S2, placing a SiO2 / Si substrate with a Ti metal layer deposited thereon in a tube furnace, evacuating the tube to a vacuum level below 0.01 MPa, and then filling the tube with argon gas to normal pressure, and then heating the tube to 873-1073 K, and keeping the temperature for 4-8 hours to form rutile phase titanium oxide two-dimensional nanosheets on the SiO2 / Si substrate; S3. Use mechanical exfoliation to exfoliate the two-dimensional nanosheets on the SiO2 / Si substrate into two-dimensional nanosheets with a few layers.

4. The polarization-enhanced gas sensor based on two-dimensional R-TiO2 as claimed in claim 3, characterized in that: In step S2, after evacuating to less than 0.01 MPa, the chamber is filled with argon gas to normal pressure and this process is repeated three times to strictly control the concentration of oxygen in the chamber.

5. The polarization-enhanced gas sensor based on two-dimensional R-TiO2 as claimed in claim 3, characterized in that: In step S2, the heating rate is 12K / min.

6. The polarization-enhanced gas sensor based on two-dimensional R-TiO2 as claimed in claim 1, characterized in that: The micro-nano processing technology includes a spin coating photoresist step, a heating and curing step, an exposure step, a development step, a vapor deposition step, and a degumming step which are performed in sequence.

7. The polarization-enhanced gas sensor based on two-dimensional R-TiO2 as claimed in claim 6, characterized in that: Au electrodes are made on two-dimensional rutile phase titanium oxide through micro-nano processing technology to form a gas sensor.

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