Study of enhanced Raman scattering through an isolating layer depositing on silver nanoparticles

• Main Authors: Lo, Chia-Ling, 羅嘉翎
• Other Authors: Tsai, Ming-Shang
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/28037673498526020711

碩士 === 國立嘉義大學 === 光電暨固態電子研究所 === 98 === 　　This thesis is mainly study surface enhanced Raman scattering (SERS) through an isolating layer depositing on silver nanoparticles. Generally speaking, SERS has two explanations: One is Physical Enhancement (Electromagnetic Enhancement), and the other is Chemical Enhancement (Charge Transfer). When the silver nanoparticles receive optics electric field, the free electrons of silver surface will induce a large quantity of vibration and get enhanced resonance. This is called localized surface plasmons (LSPs). The purpose of this work is emphatic to study the Physical Enhancement that is the influences on SERS of varied isolating layers deposit on silver nanoparticles. There are two kinds of materials, one is gold of conductors, and another one is SiOx of insulators: In experiment, Raman signals will be intercepted when gold as isolating layer, we deemed that was resulted from the localized electron field (LEF) decreased by the metal shield effect. The material changed from gold to SiOx, and an interesting phenomenon presents: Raman signals of dye molecules will be enhanced according to the different thickness to maximum, and then gradually decay. When the thickness of SiOx layer reaches to 20nm, Raman signals raised to maximum, in comparison with silver nanoparticles without SiOx, the intensity increased 40% or so; when the thickness of SiOx was 40nm, Raman signal declined; this trend kept until 60nm, but the intensity was still larger than the sample without SiOx one. Finally, Raman signal disappeared when it was 70nm thick. Those results show that Raman scattering signals were enhanced even though the SiOx isolating layer is an insulator and there was no contact between silver nanoparticles and dye molecules. By using scanning electron microscopy (SEM), we can observe that the sizes and shapes of silver nanoparticles became homogeneous after passing through evaporated SiOx isolating layer. The behavior of SiOx molecules were self-assembly-like nucleated by silver nanoparticles but not distributed even on the surface of samples. Therefore it can be reasoned that used SiOx as isolating layer, the shapes of silver nanoparticles will be modified and construct a lot of grooves among the silver nanoparticles because of volume grew, it made the dye molecules sink and adhere more easily. The shape after modifying can also make the localized electric field much larger and homogeneous. Hence, behind the thinner SiOx isolating layer of evaporation cause Raman signals of dye molecules will enhance. On the other hand, the surface tension of silver nanoparticles after being evaporated SiOx become evidently smaller to dye fluid. That brought about dye molecules were easy to adhere on them. Thus, I conjecture that made one reason of Raman scattering enhancement.