Investigation of localized surface plasmons with the photon scanning tunneling microscope

A Photon Scanning Tunneling Microscope (PSTM) with probe-sample distance control by electron tunneling is used to probe the localized surface-plasmon fields of individual nanometric silver particles. As samples, conventional island films produced by thermal evaporation and regular particle arrays produced by an electron-beam-lithography-based technique, respectively, are used. In either case the strength and spatial localization of the surface-plasmon fields strongly depend on the excitation wavelength. The results are interpreted as different resonance frequencies of individual particles or of different sample areas. On regular arrays consisting of particles with a smallest diameter of 40 nm, the PSTM maps represent the plasmon field strength spatially resolved for individual particles.