Surface-enhanced Raman Scattering Effect From The Charge Transfer In Metal Nanoparticle Array

The assembly of the nanosized metal nanoparticles with functionalized molecules have received considerable attention and shown extensive application in various fields. It has been demonstrated that the properties of the individual particles can be considerably modified by interactions with the substrate and with other particles. One of the most important properties of the metal nanoparticls in the nanodevices is the charge transfer at the interface between the metal nanoparticls and absorbed functionalized molecules. The effect of the substrates on the interfacial charge transfer of the assembled metal nanoparticls, however, has scarcely been studied. It has been well known that the charge transfer (CT) at the molecules/metal interface has contributions to the Surface-enhanced Raman scattering (SERS) of the molecules absorbed on the metal nanoparticles. Besides providing the spectral information associated the interfacial charge transfer, the SERS spectroscopy in fact has proved to be very useful tool to study the molecule/metal nanoparticle systems, due to its richness of molecular structure information, high sensitivity and surface selectivity. In general, the SERS enhancement can be attribute to electromagnetic (EM) and"chemical"mechanism. The EM mechanism is based on that nanoparticles of coinage metal, such as gold and silver, exhibit surface plasmon resonance (SPR) in the UV-visible region due to the collective oscillations of the free electrons inside the particles. Under the SPR conditions, the electric fields near the metal particles can be greatly amplified. The molecules near the surface of the particles consequently undergo an electric field greater than the incident field. The"chemical"mechanism is related to photon-driven charge transfer process which involves dynamic charge transfer between the energy levels of the molecules and the Fermi levels of the metals. In most of the SERS studies, the CT mechanism is normally inextricably linked with the EM mechanism. Nevertheless, it is possible to relatively amplify the SERS spectral features related to the interfacial charge transfer process of the metal nanoparticls by properly controlling the experimental conditions, because the EM mechanism is dependent to the SPR of the metal nanoparticles.In this thesis, the main research works and the conclusions are as follows:1. Stable and uniform-sized silver colloid has been prepared and formed two-dimensional assembly on glass substrate. Absorption spectra of the assemblies demonstrate that interaction between silver nanoparticles result in large shifts of dipolar...