Study of surface plasmon excitation of nanometer size metallic particles in the STEM

Abstract

The study of small particles or microclusters has been very active in recent years. When the particle size becomes smaller, its electronic properties deviate from those of bulk material and become size dependent. This phenomenon is referred to as the quantum size effect. In order to study the electronic states of small particles, the excitation energies of the surface plasmon (SP) have been measured by optical absorption spectroscopy and by broad beam angular resolved electron energy loss spectroscopy (EELS). Changes in the SP excitation energy were observed when the particle diameters were smaller than 40 Å.With the high spatial resolution of the scanning transmission electron microscope (STEM), we hope to overcome the difficulties associated with effects of particle size distribution encountered in previous broad beam measurements. For particles with diameters ranging from 100 Å to 200 Å, the SP energy was found decreasing with decrease of the particle size.