. Associated with electron oscillation, polarization of surface charges also occurs on the metal surface when excited by light. Unlike bulk metals, the induced charges of a nanocrystal cannot propagate as a wave along the flat surface but are confined to and concentrated on the particle surface, in which case it is called localized surface plasmon resonance (LSPR). LSPR creates intense local electric fields within a few nanometers of the particle surface. As a direct application of LSPR, this near-field effect enhances the Raman scattering cross-sections of molecules adsorbed on a nanocrystal surface, providing a “fingerprint” spectrum rich with chemical information. The ultimate goal of this research is to manipulate the LSPR properties of metal nanocrystals. Specifically, we will use a series of physical tools to understand the intrinsic features of LSPR, such as ultrafast spectroscopy and tip-enhanced Raman spectroscopy (TERS).