STM light emission from Si(1 1 1)-(7 7) surface using a silver tip

Scanning tunneling microscope-light emission (STM-LE) from the Si(1 1 1)-(7 7) surface has been measured using silver tips. For silver tips photon emission was enhanced by more than 100 times as compared with that for tungsten or platinum± iridium alloy tips. A broad spectrum with a single peak at 2.25 eV was observed. The spectrum obtained can be reproduced by a theory based on the macroscopic dielectric response of the tip-sample system, indicating that the observed emission arises from the localized plasmons on the silver tip excited by tunneling electrons. Spatial variations in the emission intensity at the atomic scale was observed even under low bias voltage (2 V) and low tunneling current (1 nA) conditions. # 2001 Elsevier Science B.V. All rights reserved