Kelvin Probe Force Microscopy on MgO(001) Surfaces and Supported Pd Nanoclusters

Kelvin probe force microscopy measurements of the clean (001) surface of UHV cleaved MgO and of the same surface with supported palladium nanoclusters are presented. Kelvin images of the clean surface show a bright contrast at steps, pits, and fragments of MgO. The bright contrast is due to negatively charged defects, which deliver the surface a net negative charge. Kelvin images of supported Pd nanoclusters exhibit a mean voltage difference of 2.4 V between Pd clusters and the MgO(001) surface. It is shown that the voltage difference equals the work function difference between MgO(001)/Mo and Pd, which was found by recent MIES and UPS measurements.