Kelvin probe force microscopy in ultra high vacuum using amplitude modulation detection of the electrostatic forces

We present a detailed study of contact potential difference measurements in ultra high vacuum using Kelvin probe force microscopy. A dependence of the contact potential difference on the tip-sample distance was measured and i s explained by an inhomogeneous work function of the highly doped silicon c antilever. On semiconducting samples the measured contact potential differe nce additionally depends on the AC sample voltage. By investigating this ef fect for different AC voltages and tip-sample distances, we can conclude th at bias-induced bandbending has to be considered in a quantitative analysis of the contact potential difference on semiconductors. Using amplitude mod ulation detection of the electrostatic forces at the second resonance frequ ency, a high sensitivity can be achieved at low AC voltages. Spatially reso lved contact potential difference measurements on submonolayer fullerene is lands grown on graphite were used to determine the lateral resolution of ap proximately 20 nm. (C) 2000 Elsevier Science B.V. All rights reserved.