Spatially resolved measurements of the capacitance by scanning tunneling microscope combined with a capacitance bridge

We have measured spatially resolved capacitance between a metal surface and the tip of a scanning tunneling microscope (STM) by using a capacitance br idge combined with STM. The spatial variation of the capacitance can be cor related with the topographic image for the carbon grating and the gold film with a capacitance resolution of about 10 aF (1 aF = 10(-18) F). The obser ved spatial resolution is about 50 nm along the surface as well as normal t o the surface. The spatial resolution of this method is discussed in relati on to the STM-tip radius and the corrugation of the sample. The resolution estimated by theoretical calculations is consistent with the experimental r esults. (C) 2001 American Vacuum Society.