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 scanning probe microscopes. The instrument is specially designed to provide quantitative information on the nature of the tip-surface interaction. Forces are applied directly to magnetic material deposited behind the AFM tip via a current carrying coil. Oscillating the applied force and measuring the resulting displacement amplitude gives a continuous measurement of the absolute force gradient or contact stiffness. From this measurement the contact area or effective interaction area can be calculated for clean surfaces, thus eliminating the problems of unknown resolution and also facilitating the study of conduction and mechanical properties of small volumes. (C) 1996 American Institute of Physics.