Mechanical, Optical And Electrical Coupling Performance Of Quasi One Dimensional ZnO Nanomaterial

Due to its peculiar piezoelectric property and semiconductor property, ZnO nanomaterials have been applied in many fields, such as photodetector, strain sensor, nanogenerator. To optimize performance of designed devices, it is important to investigate mechnical electrical and optical couplied performance of ZnO nanomaterials.In this thesis, ZnO nanowires and nanotetrapods were fabricated by a thermal evaporation method. Morphologies, structures of the obtained nanomaterials have been characterized by FESEM, XRD, TEM and PL, etc. The size effects of modulus, surface potential, carrier concentration, and fracture strength of ZnO nanomaterials was investigated by home-made electrical, mechanical and opticl coupling scan probe microscopy. The performance of fabricated Schottky UV detector was modulated by strain. Morover, UV irradiation was introduced to tune the performance of strain sensor.A size dependence of surface potential and carrier concentration was observed by Kelvin probe force microscopy (KPFM). When the diameter of ZnO nanowire was smaller than400nm, surface potential increase linearly with increasing diameter. The surface potential keep stable, while the diameter bigger than400nm. The contact potential difference of ZnO-PtIr tip increases with UV irradiation time and reach to saturation (5.37leV) after40min UV illumination. The carrier concentration of ZnO nanowire increase to saturation of2.68x1017after60min UV irradiation.UV detector was fabricated by ZnO nano/microwire and Pt electrode on the flexible substrate. Under UV irradiation with365nm and0.5mW/cm2power density, on/off ratio is5.34, and response time and recovery time of the detector under4V bias is3.7s and6.0s, respectively.A strain sensor was fabricated on flexible substrate based on single ZnO nano/microwire. Forward current increase linearly with increasing loading force without UV irradiation. The current through the device rise exponentially rather than linearly under UV illumination. It is verified that UV irradiation could tune the performance of strain sensor based on ZnO nanomaterial.A strain sensor was aslo fabricated based on a ZnO nanotetrapod. Tuning Schottky barrier height by UV iradiation leads to the increasing sensitivity of sensor from0.17A/N to2.05A/N under forward bias. A self-powered strain sensor based on ZnO/PEDOT.PSS hybrid structure on a flexible polystyrene substrate was realized by using of mechnical electrical and optical coupling effect. The sensor could work under solar light without battery. The sensitivity of the fabricated device is enhanced to1×104under solar light due to the piezo-phototronic effect of ZnO.The Young’s modulus of ZnO nanowires with different diameters were measured by AFM. The modulus of ZnO nanowireS decrease from73.9GPa to2.3GPa as the diameter decline from418nm to62.4nm. The loading force which the nanowire begin to elastic strain increase from53uN to113μN, as diameters of ZnO nanowire increased from259nm to446nm. The fracture force of nanowire increased from92μN to148μN. By force curves of ZnO nanowire was obtained by AFM at fixed positon, a new technology of fabricate one-dimensional nanomaterial with desired morphologies can be realized.