Fabrication and Characterization of Zinc Oxide Nanostructures for Piezoelectric, Mechanical and Electrical Applications

Sammanfattning: Nanotechnology, the science of manipulating materials on an atomic or molecular scale is one of the fastest growing areas of research and technology. Nanotechnology has a vast range of applications in medicine, electronics, biomaterials and energy production. New developments in nanotechnology are growing all the time. In the near future, nanotechnology is expected to be a mature industry, with countless mainstream products.Zinc Oxide (ZnO) is an important and optimal material in electronic and photonic applications due to its important properties like direct band gap (3.3 eV) semiconductor with large exciton binding energy (60 meV) which can provide more efficient excitonic emission even at room temperature. Beside that noncentrosymmetric property of ZnO makes it an ideal piezoelectric material. Various onedimensional ZnO nanostructures appear as an interesting material for a variety of mechanical, piezoelectric, optical, and electrical applications. ZnO nanostructures used in study were grown by the lower temperature aqueous chemical growth (ACG) on a variety of substrates.The main objective of this research studies is to investigate the piezoelectric, mechanical and electrical phenomenon of ZnO nanostructured based nanodevices on cheap, disposable and flexible substrate like paper, plastic. As low cost fabrication of nanodevices is very crucial and best choice for the upcoming years. We have successfully demonstrated that paper substrates can be used for the growth of ZnO nanostructures.In the first part, piezoelectric power nanogenerators based on ZnO NRs / NWs on flexible paper substrates were demonstrated and output piezopotential was investigated using atomic force microscopy (AFM). Different p-type polymers like poly (3-hexylthiophene) P3HT, poly(3,4-ethylenedioxythiophene-Tosylate (PEDOT-Tos) were coated around the ZnO NRs / NWs in order to minimize the screening effect and increase the output piezopotential and it was found that by introducing a layer of p-type polymer we get more piezopotential compared to non-coated ZnO NRs / NWs. We also demonstrated the direct and converse piezoelectric response from ZnO NWs grown on lighter, flexible paper substrate for the first time by using nanoindentation technique.In the second part, the mechanical properties like elastic modulus and hardness of ZnO NRs / NWs and NTs were investigated by using nanoindenter. Elastic modulus of a single ZnO horizontal NR was demonstrated by nanoindentation technique based on three point bending configuration.  Buckling phenomena of ZnO NRs and NTs was investigated by nanoindenter and various parameters like buckling energy, elastic modulus, critical stress, and critical strain calculated under different end conditions.In the third part of thesis fabrication of Au/n-ZnO Schottky devices were fabricated and their electrical and optical properties were investigated by current voltage (I-V), electroluminescence (EL) and impedance spectroscopy. We investigated interface trap states of Au/n-ZnO nanorods interface by temperature dependence I-V parameters. That study reveals that the ideality factor decreases, while the barrier height increases with increase of temperature. Detailed and systematic analysis of the frequency-dependent capacitance and conductance measurements were performed to extract the information about the interface trap states. The energy of the interface states with respect to the valence band at the ZnO NR surface was also calculated. It was found that recombination-generation in the interface states are responsible for capacitance and conductance.The effect of the post-growth annealing of Au/n-ZnO NWs Schottky diodes were examined and it was shown that light from the LEDs can be tuned from cold white light to warm white light by post growth annealing in different ambient.