A NEW FORCE CONTROLLED ATOMIC-FORCE MICROSCOPE FOR USE IN ULTRAHIGH-VACUUM

We introduce a magnetic force controlled atomic force microscope (AFM) and point contact probe for use in ultrahigh vacuum and describe how our technique can significantly enhance the current capabilities of sc anning probe microscopes. The instrument is specially designed to prov ide quantitative information on the nature of the tip-surface interact ion. Forces are applied directly to magnetic material deposited behind the AFM tip via a current carrying coil. Oscillating the applied forc e and measuring the resulting displacement amplitude gives a continuou s measurement of the absolute force gradient or contact stiffness. Fro m this measurement the contact area or effective interaction area can be calculated for clean surfaces, thus eliminating the problems of unk nown resolution and also facilitating the study of conduction and mech anical properties of small volumes. (C) 1996 American Institute of Phy sics.