Enhanced Difluoromethane Gas Sensing Performance of Au/ZnO Nanotree Arrays under Visible Light Pulse Excitement AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY24030020

Chinese Library Classification Number:TN304

Citation Information:

With the development of modern industry and the rise of Internet of Things （IoT） technology，gas sensors are widely employed in many fields，such as industrial production，environmental monitoring，food safety，and healthcare devices，playing important role in promoting industrial intelligence and ensuring human health. Among various types of sensors，resistive chemical sensors based on metal oxide semiconductors （MOS） have been considered be ideal gas sensors due to their low cost，mature technology，and good repeatability. However，some issues such as low sensitivity，long response/recovery time，and poor selectivity still impede further development of gas sensors. According to previous study，increasing specific surface area of sensing material and adding noble metal component were advisable strategies to enhance sensingperformance. Besides，interestingly，hot electrons could be generated through the surface plasmon resonance （SPR） effected of plasmonic materials （such as gold nanoparticles，Au NPs） under visible light illumination. They exhibited the potential to modulate carrier concentration and conductivity properties of the adjacent semiconductor material for further promoting sensingperformance. Motivated by these inspirations，in this study，the Au/ZnO nanotree arrays were prepared on silicon wafer and interdigital electrode substrate by a simple hydrothermal method，and used to detect difluoromethane （R32） gas with an optical enhancement working scheme. By using a variety of characterization methods like scanning electron microscopy （SEM），transmission electron microscopy （TEM），X-ray diffraction （XRD），X-ray photoelectron spectroscopy （XPS），ultraviolet and visible spectrophotometer （UV-vis），fluorescence spectrometer （FS），and atomic force microscope （AFM），the morphological structure，element composition and valence state，photoelectric properties and other concerning physical and chemical properties of the sample were systematically investigated and analyzed. In detail，the results showed that ZnO nanotree arrays grew closely perpendicular to the substrate. The diameter of the stem and branches were about 400 and 60 nm，respectively. Au NPs in an average particle size about 10 nm were uniformly distributed on the surface of ZnO. Energy dispersive spectroscopy （EDS） elemental mapping images confirmed that Zn，O，and Au elements were evenly distributed on ZnO surface. The lattice spacing of 0.26 and 0.24 nm observed by high-resolution TEM correspond to （002） crystal plane of ZnO and （111） crystal plane of Au，respectively. The bright diffraction spots on selected area electron diffraction （SAED） pattern were ascribed to （002） crystal plane of ZnO. XRD pattern showed the as-prepared ZnO and Au NPs match well with hexagonal wurtzite ZnO （JCPDS No. 36-1451） and cubic Au （JCPDS No. 04-0784），respectively. The diffraction peaks at 31.72°，34.42°，36.25°，47.53°，and 56.6° were assigned to （100）， （002）， （101）， （102），and （110） planes of ZnO，respectively. The diffraction peak at 36.61° was assigned to （111） plane of Au. XPS spectra affirmed the chemical valence state of Zn，O and Au elements. The doublet peaks at 1022.3 and 1045.3eV corresponded to Zn²⁺ species. The doublet peaks at 530.5 and 532.3 eV corresponded to the lattice oxygen （O_lat） and defect oxygen （O_v） of ZnO，respectively. The doublet peaks at 83.5 and 87.4 eV proved that Au elements exist in the form of metallic Au⁰. UV-vis spectrashowedthe light absorption of ZnO nanotree array modified by Au NPs was significantly enhanced in the wavelength range of 500~600 nm due to SPR effected of Au NPs. The band gaps of pure ZnO nanotree array and Au/ZnO nanotree array were accordingly calculated to be 3.17 and 3.09 eV through Tauc formula. The band gap of sample was reduced after modified with Au NPs owing to the regulation of the electron transfer characteristics. The fluorescence spectra showed the photoluminescence （PL） intensity of Au/ZnO nanotree array was decreased in 350~550 nm region compared with pure ZnO nanotree array，indicating that the photogenerated charges of Au/ZnO nanotree array possessed high the separation and transfer efficiency. AFM probe platform was used to image hot electron current that induced by SPR effect of Au NPs. The photocurrent imaging results showed that no obvious currents were detected for pure ZnO nanotree array with or without light irradiation. For Au/ZnO nanotree array，the current value increased by about 1 nA under light irradiation than that of in dark conditions，verifying that Au NPs could induce a large number of hot electrons under light irradiation. The influence of visible light on the resistance values of Au/ZnO nanotree array was also investigated on mini multi-functional probe station. It was found that Au/ZnO nanotree array exhibited outstanding sensitivity and stability to visible light，and short response and recovery time within 2 s. By utilizing the modulation function of hot electrons in the visible light pulse working mode，as well as the contribution from the unique structural merits of nanotree array，Au/ZnO nanotree array-based gas sensor showed a high response value of 6.9，fast response/recovery speed，and excellent selectivity in terms of detecting 1000×10^-6 R32. The research results could provide useful theoretical and practical guidance for the design and exploitation of enhanced functional nanostructures and optimized integration of high-performance gas sensors.