Controlled Growth of Metal and Semiconductor Nanomaterials in Vapor-Deposition Processes

• Main Authors: Yung-Jung Hsu, 徐雍鎣
• Other Authors: Shih-Yuan Lu
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/08084393871943952240

博士 === 國立清華大學 === 化學工程學系 === 94 === The present research focuses on the synthesis of semiconductor and metal nanomaterials in a variety of structures via the gas-phase based deposition processes. These materials included (CdS)ZnS core-shell particle films, CdS nanowires, coaxial core-shell CdS-ZnS nanowires, ternary Cd1-xZnxS alloy nanowires, Sn nanowires, Sn nanosquares, Sn nanodisks, and Sn nanoparticles. The relevant properties of the synthesized nano-sized materials with different structures and compositions were also investigated and discussed. By using two co-fed single source precursors of sufficient reactivity difference, we successfully prepared the core-shell (CdS)ZnS particle films with a one-step MOCVD process. The photoluminescence (PL) quantum yield enhancement achieved by the effective passivation of CdS core by ZnS shell was observed. An additive, silver nitrate (AgNO3), was used to prepare nanostructured films of CdS via a MOCVD process. The effect of AgNO3 addition in enhancing the deposition rate and PL efficiency of CdS deposit was demonstrated. It was also observed that morphology change can be induced through additive addition. We successfully developed a low-temperature VLS process for preparation of one-dimensional (1-D) nanostructure of CdS. The PL quantum yield of CdS nanowires was found to decrease with increasing wire length, but to increase with decreasing wire diameter. Besides, a narrow PL emission peak resulting from the formation of CdS-catalyst metal solid solution at the tip region of CdS nanostructures was observed. By co-feeding two single source precursors of sufficient reactivity difference, we successfully prepared coaxial CdS-ZnS nanowires with a one-step MOCVD process through the VLS growth mechanism. The PL quantum yield enhancement achieved by the effective passivation of CdS by ZnS was also observed in 1-D coaxial nanostructures. By appropriately adjusting the reaction conditions in the one-step MOCVD process, ternary Cd1-xZnxS alloy nanowires were successfully synthesized. Different optical properties from those of CdS and ZnS were observed in Cd1-xZnxS nanowires. A non-catalytic and template-free vapor transport process was developed to prepare various nanostructures of Sn, including nanowires, nanosquares, and nanodisks, and nanoparticles, in a single run of operation. The three anisotropically shaped nanostructures (nanowires, nanosquares, and nanodisks) showed a significant enhancement in working magnetic field ranges for superconductivity as compared to those of bulk Sn and the Sn nanoparticles. The formation of such a rich morphology may be attributed to the competition in growth rate among different crystallographic planes of Sn.