POTENTIOMETRY FOR THIN-FILM STRUCTURES USING ATOMIC FORCE MICROSCOPY

The compliance of the tip-sample contact region in a scanning tunneling/atomic force microscope (STM/AFM) is found to increase from — 1 N/m to more than 200 N/m with decreasing tip-to-surface distance in a distance interval of — 200 nm. When a tungsten tip and a metal sample are used, this interval includes the distance at which a tunneling current is measurable. An STM/AFM was operated at this tip-to-surface distance in the constant-compliance mode. Since a tunneling contact to the tip is established at conducting sections of the sample, the electrical potential can be measured there. An array of interconnected niobium squares and an array of metal strips alternately connected to two electrodes of different voltage were examined using this method. Both structures were fabricated by electron beam lithography from Nb films on oxidized Si substrates. The topography and the value of the electrical potential were recorded. A potential resolution of the order of 1 mV was achieved. © 1990, American Vacuum Society. All rights reserved.