Materials, electrical, and sensing properties of ZnO nanowires
ZnO is an interesting and versatile material due to its ample material properties and diverse applications. ZnO is an n-type direct and wide band gap semiconductor with band gap of 3.35eV, it has excellent chemical and thermal stability, photonic properties, with strong piezoelectric effect, and it is sensitive to some volatile organic compounds (VOCs) and can be fabricated in diverse morphologies. Additionally, improvement of electronic properties and enhancement of selectivity towards VOCs can be achieved with selective doping. This opens up the possibility of multiple gaseous analyte sensing with real time detection by using ZnO nanostructures as the sensing element. Important parameters to consider are the geometry of the nanostructures, for example nanowires vs. nanoparticles, the dimensions of the nanostructures such the diameter of the wires, the material quality (i.e. crystallinity), and the selection and quantity of the dopant material. In this work we have explored an electrosynthesis approach towards fabricating ZnO nanowires and investigated optimal deposition parameters such as solution composition, applied voltage and temperature. We have been able to obtain a voltage deposition window spanning from -0.6 to -1.0 V vs. Ag/AgCl where ZnO nanowires can be fabricated which allows for further implementation of simultaneous electrodeposition of dopants with ZnO. Deposition temperature analysis demonstrated that amorphous nanowires can be obtained at 25°C while single crystal nanowires can be acquired at 70°C. Furthermore, the diameter of the nanowires can be manipulated by controlling the pore size of the polycarbonate membrane used as the deposition templates. The resultant ZnO nanowires were electrophoretically aligned onto prefabricated micro electrodes and gas sensing performance as a function of crystallinity and nanowires diameter were investigated.
