Synthesis Of Zn₂GeO₄ Nanowires/MXene Composites And The Photoelectric Performance Of Deep Ultraviolet Light

With a bandgap of about 4.69 eV,Zn2GeO4 is considered as an ideal material for making deep ultraviolet(DUV)semiconductor detectors.Its dispersed energy level structure makes high mobility of free electrons in the conduction band.Previous studies have confirmed that the DUV detection of Zn2GeO4 nanowires(NWs)was fast response and high efficiency.Besides,conductive two-dimensional materials are beneficial for improving the photoelectric performances of one-dimensional materials,which is mainly attributed to the synergistic effect.When a large number of electrons are generated inside the composite,electrons directionally migrate from one-dimensional nanowires with higher conduction band to two-dimensional materials with lower Fermi energy level,thus increasing the conductivity.MXene,as a serial of new 2-d early transition metal carbon/nitride materials,have excellent electrical properties and customizability,which makes them suitable for matching with other materials and further increasing their chemical/physical properties.Therefore,this paper proposes that MXene can enhance the photoelectric performances of the Zn2GeO4 nanowire network in deep ultraviolet band In this paper,Ti3C2Tx from the MXene family was selected as the conductive two-dimensional material and was synthesized by etching MAX phase with hydrofluoric acid.Zn2GeO4 nanowire network was prepared by high temperature chemical vapor deposition with SiO2 as the substrates.The optimal Zn2GeO4 nanowire/MXene composite with the best DUV photoelectric performances was obtained by adjusting the content of MXene in the anhydrous ethanol solution.Photoelectric properties and the durability of composite is tested.The thesis is including the following two partsIn the first part,the Zn2GeO4 nanowire network was prepared by using high temperature chemical vapor deposition method with SiO2 as the substrate.High-purity ZnO powder,GeO2 powder and nano-diamond particles were as the reaction sources.The Zn2GeO4 nanowires with a diameter of about 500nm and a length of about 3?m were obtained.These Zn2GeO4 nanowires only absorbed ultraviolet light with the highest absorption peak at 245nm and the absorption sideband at 275nm.Photoluminescent peaks at 384nm(violet)and 469nm(green)appeared in the PL spectrum of the nanowieres.Pure MXene powder with 1-3?m edge length and 1.0nm thickness of each layer was synthesized by etching the MAX phase with concentrated hydrofluoric acid(49%in concentration).In the second part,MXene was dispersed into anhydrous ethanol and formed solutions with mass ratio of 0.005%,0.01%,0.02%,0.03%and 0.04%.Droplets in various concentrations were coated on the Zn2GeO4 nanowire network respectively to produce the Zn2GeO4/MXene-DUV photodetectors.The physical characterizations of the composite were tested by high-resolution field-emission scanning electron microscopy,X-ray diffractometer and UV-visible absorption spectrometer.The photoelectric performances were characterized by the electrochemical workstation.The photoresponsivity,external quantum efficiency and response time of Zn2GeO4/MXene composite were measured with a 254nm DUV radiation at 6V bias.The best photoelectric performance was provided by the composite with an MXene mass ratio of 0.03%.The responsiveness was 20.43mA/W,the external quantum efficiency was 9.9%and the response time is 1.16/0.39 sec.The performance was significantly improved compared with Zn2GeO4 without MXene,which was a responsiveness of 8.1 mA/W,external quantum efficiency of 3.9%and the response time of 3.397/1.05s.The excellent optical performance is from the synergistic effect of MXene and Zn2GeO4 nanowires.The metallic property of MXene provides a fast electron transport for Zn2GeO4/MXene,which leads to a larger photocurrent and a fast photoresponse.The construction of unique semiconductive-conductive networks and large interfaces of Zn2GeO4 NWs,MXene layers,and the interfaces between them also promotes photoinduced electron—hole separation in the sample.Durability of the photoelectric performances was verified at the end of the thesis.