Full text
| |
| Author(s): |
Douglas Soares de Oliveira
Total Authors: 1
|
| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin |
| Defense date: | 2016-02-26 |
| Examining board members: |
Mônica Alonso Cotta;
Antonio Riul Júnior;
Odilon Divino Damasceno Couto Junior;
Thalita Chiaramonte;
Daniel Lorscheitter Baptista
|
| Advisor: | Mônica Alonso Cotta |
| Abstract | |
In this thesis we report results on three different subjects ¿ largely unexplored in literature ¿ related to the synthesis of III-V semiconductor nanowires using the vapor-liquid-solid method. In search for new catalysts to replace Au, we investigated the growth of silver-catalyzed InP nanowires. We show that the vapor-liquid-solid method can indeed be achieved with Ag nanoparticles, and established the growth conditions under which InP nanowires present pure wurtzite crystal structure and high aspect ratios. Additionally, a second synthesis process is reported, in which a blunt structure is formed at the nanowire apex. Finally, we compared the formation of spontaneous diameter oscillations in InP catalyzed by these two metal nanoparticles. We propose that the lower growth rate for silver catalyzed nanowires could be related to their higher average pitch between diameter oscillations. Looking for new strategies to integrate nanowires into planar devices, as a second subject of investigation, we studied the synthesis of gold catalyzed, planar InP nanowires grown through vapor-liquid-solid method. First we addressed the role of surface energies and catalyst composition in determining the nanowire configuration type, planar or vertical, on the substrate. We show that increasing the difference between solid-liquid and solid-vapor interfacial energy per unit area favors the formation of planar nanowires, while a decrease in this difference leads to the formation of vertical nanowires. We also observe that a thick oxide layer between nanowire and substrate induces a non-directional growth. Thin layers, on the other hand, promote directional growth. As the third and final subject of this thesis, we present an extensive study of the structural and morphological properties of core-shell [211]-oriented InGaP nanowires. We show that crystalline defects parallel to the nanowire axis are necessary in order to obtain long and stable [211]-oriented III-V nanowires. Those defects, however, will generate two <111> facets with different polarities. We also show that stacking fault formation in the crystal region corresponding to the {111}A facet termination balances the growth rates for these different facets and induces stable growth. Finally, we discuss how these results and the spontaneously-formed, non-concentric core-shell structure are related to the nanowire surface polarity (AU) | |
| FAPESP's process: | 11/22876-0 - Semiconductor nanowires: investigation of formation processes and applications in thermoelectric systems |
| Grantee: | Douglas Soares de Oliveira |
| Support Opportunities: | Scholarships in Brazil - Doctorate |