Optical control of size, shape, or orientation of a metal nanoparticle is important for development of nanoscale optical devices and elements of photonic circuits. Thus far, however, independent control of two or more parameters has not yet been achieved. Here we place a simple spherical Ag nanoparticle on TiO(2) with high refractive index and separate a plasmon mode localized at the Ag-TiO(2) interface from the other mode distributed over the nanoparticle. Selective excitation of each mode gives rise to a corresponding morphological change and selective suppression of the plasmon mode, resulting in multicolor changes of scattering light from orange to red, green, or a dark color.

Plasmon-induced charge separation (PICS) at the interface between a plasmonic nanoparticle and semiconductor is now widely used for photovoltaics and photocatalysis. Here we take advantage of PICS for site-selective nanoetching of silver nanocubes on TiO beyond the diffraction limit. A silver nanocube exhibits two resonance modes localized at the top and bottom of the nanocube (distal and proximal modes, respectively) when it is placed on TiO. We achieved selective etching at the top and the bottom of the nanocubes by PICS based on the distal and proximal modes, respectively. The site-selective nanophotonic etching reveals that the anodic reaction involved in PICS is induced by the plasmonic near field, which causes an external photoelectric effect. In particular, the distal mode etching at the top edges is explained in terms of ejection of energetic electrons (or hot electrons) from the distal site to TiO across the nanocube.

Step, ridge, and crack submicro/nanostructures of epitaxial graphene on 4H-SiC (0001̅ ) were characterized using tip-enhanced Raman scattering (TERS) spectroscopy. The nanostructures were created during graphene synthesis due to a difference in the thermal expansion coefficient of graphene and SiC. These structures are a distinctive property of epitaxial graphene, together with other desirable properties, such as large graphene sheet and minimal defects. The results of this study illustrate that the exceptional spatial resolution of TERS allows spectroscopic measurements of individual nanostructures, a feat which normal Raman spectroscopy is not capable of. By analyzing TERS spectra, the change of local strain on the nanoridge and decreased graphene content in the submicrometer crack were detected. Using G′ band positions in the TERS spectra, the strain difference between the ridge center and flat area was calculated to be 1.6 × 10 −3 and 5.8 × 10 −4 for uniaxial and biaxial strain, respectively. This confirms the proposed mechanism in previous researches that nanoridges on epitaxial graphene form as a relief against compressive strain. With this study, we demonstrate that TERS is a powerful technique for the characterization of individual local nanostructures on epitaxial graphene.

A novel “turn-off” SERS strategy for the detection of metal ions was demonstrated based on the optical and catalytic properties of semiconductor materials.