STM light emission from Si(111)-(7 x 7) surface using a silver tip

Scanning tunneling microscope-light emission (STM-LE) from the Si(1 1 1)-(7 x 7) surface has been measured using silver tips. For silver tips photon e mission was enhanced by more than 100 times as compared with that for tungs ten or platinum-iridium alloy tips. A broad spectrum with a single peak at similar to2.25 eV was observed. The spectrum obtained can be reproduced by a theory based on the macroscopic dielectric response of the tip-sample sys tem, indicating that the observed emission arises from the localized plasmo ns 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. (C) 2001 Elsevi er Science B.V. All rights reserved.