|M.Sc Student||Raya Goldberg|
|Subject||Vapor Phase Synthesis of ZnO and Si Nanowires|
|Department||Department of Materials Science and Engineering||Supervisors||Professor Emeritus Lifshitz Yeshayahu|
|Ms. Tamir Shoshana|
|Full Thesis text|
One-dimensional semiconducting nanostructures are considered as candidate materials for future electronic devices. This requires their controlled growth which is difficult in currently available systems. The present work studies the effects of growth parameters on the nanowires (NWs) evolution in two systems (thermal evaporation chemical vapor deposition (TCVD) and laser ablation chemical vapor deposition (LACVD)) and two different materials (Si and ZnO).
Three research channels are included: (1) A calculational and experimental study of the distribution of species in the growth tube under different parameters and its significance for NWs growth; (2) Growth of ZnO NWs from a ZnO:C mixture (TCVD) and a ZnO target (LACVD); (3) TCVD growth of Si NWs from SiO.
ZnO and Si NWs were grown onto various pristine and Au deposited substrates at different distances from the heated source in both downstream and upstream directions of the carrier gas admitted. The distribution of growth species at different locations under various growth conditions was evaluated by handwaving calculations and numerical simulations (applying COMSOL). The morphology and structure of the NWs grown at different locations under a variety of flow, pressure and temperature conditions were studied by a host of techniques.
The main findings are:
1. The distribution of growth species is in the TCVD system is dictated by the balance between diffusion and convection. ZnO and Si NWs were grown in both downstream and upstream directions, in accord with the simulations, depending on the parameters applied. The simulations provide information on the distribution and time dependence of the growth species concentration highlighting conditions for steady growth. The distribution of growth species in LACVD was found to be strongly affected by the laser induced shock wave which pushes the growth species upstream so that convection by the carrier gas flow and diffusion are much less effective.
2. ZnO NWs growth on a variety of pristine and Au deposited substrates with different Au thickness values was characterized. The size of the Au crystallites formed upon annealing to the growth temperature depends on the initial Au thickness and affects the grown ZnO NWs.
3. Si NWs TCVD growth from SiO was observed on catalyst deposited substrates only. The morphologies obtained (tunable by the source and substrate temperatures) include single-crystalline Si NWs embedded in a SiO2 sheath, and nanochains of Si nanospheres embedded in SiO2. SiNWs synthesis by a pure (metal catalyst free) oxide assisted growth was not observed.