The Effect of Interfacial Structure on The Photo-induced Melting of Gold Nanorod in Gold Nanorod@non-uniform Silica Core-Shell Nanosystem

• Main Authors: Wu, CHIH-TING, 吳致廷
• Other Authors: Wang, Churng-Ren Chris
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/98334055868339668115

碩士 === 國立中正大學 === 化學暨生物化學研究所 === 104 === This thesis focuses on the effect of the interfacial structure between gold nanorod（AuNR）and silica in the photo-induced melting of the AuNR core. We synthesized silica coated gold nanorod with non-uniform thickness in major and minor axes（AuNR-nu-SiO2）as a basic nanosystem. The particle side-thickness（ST）and end-thickness（ET） are well controlled with the typical values of ca. 12 nm for ST and ca. 1 nm for ET. There are two kinds of interfacial structures between AuNR and silica we proposed herein, one is chemical bonding and the other one is physical adsorption. The former is Au-S covalent bonding, symbolized as AuNR-SH-nu-SiO2, and the latter is physical adsorption of CTAB on the AuNR surface, symbolized as AuNR-CTAB-nu-SiO2. The chemical bonding of the interfacial structure was introduced into the nanosystem by choosing the precursor of the sol-gel process as (3-mercaptopropyl)trimethoxysilane (MPS) for the silica coating The physisorption of the interfacial structure in the other nanosystem was accomplished by the use of tetraethyl orthosilicate (TEOS) as the precursor of the sol-gel process while the CTAB remain intact to the AuNR surface. Two nanosystems with different interfacial structures were designed to demonstrate a clear difference for the heat conductivity along the AuNR side to the silica and were expected that we should be able to observe different photo-induced melting products. It is well-known that AuNR will efficiently transform photon energy by light absorption to heat at its surface plasma resonance (SPR). Also, the transportation rate of heat flux is influenced by the porosity of the coated silica. In order to extract a clear evidence regarding the interfacial structure effect on the photo-induced melting process, we need to confirm that the porosity of the coated silica in both nanosystems are similar to begin with. The porosities were confirmed by examining the extent of the SPR spectral shift and also data collected from the surface area and porosimetry analyzer. The results of our photo-induced melting measurements clearly indicate that the melting process in AuNR-SH-nu-SiO2 system follows the conventional melting after absorbing single pulsed photon energy, AuNR melts to give sphere or shorter rod. A high yield of ca. 70% for such melting products was observed without any indication for the spilt-melting products. However, in AuNR-CTAB-nu-SiO2 nanosystem, after laser irradiation the split-melting products was clearly observed to give ca. 40% yield while the yield of the melting products is about 20%. We rationalized the split-melting result compared to the conventional melting process by the only reason that the temperature difference between the central region of AuNR and its ends is greatly enhanced in the AuNR-CTAB-nu-SiO2 nanosystem. The enhanced temperature gradient are attributed to the poorer thermal conductivity through its interface with weaker interaction. This less efficient thermal conductivity then results in higher temperature retained in the central region of the AuNR. Additionally, we also increased the both directions of side and end thickness of AuNR-CTAB-nu-SiO2. In those cases, we observed that increased percentage of the AuNRs melting particles via conventional pathway as we increased the thickness. It can be contributed by that the heat flux becomes more and more isotropic. Keywords：Gold nanorod, photo-induced