True atomic resolution in non-contact atomic force microscopy in ultra high vacuum on Si(111)7 x 7

The subject of this paper is some methodical aspects of the application of Non-Contact AFM technique with true atomic resolution concerning simultaneo us usage of STM and AFM and application of external bias to compensate the long-range forces and therefore to provide the single tip-sample interactio n. It was found that variations of the built-in charge across the scanned a rea can cause variations in the total long-range interaction forces, and th erefore adjustment of the applied bias in necessary. On the other hand, the above effect, being an artifact for atomic resolution, could be used as a special kind of Electric Force Microscopy with very high resolution allowin g in potential to observe local built-in charge variations on the near-atom ic scale. The prospects for application of the NC AFM to investigation of n on-conductive materials (amorphous semiconductors, glasses, etc.) are discu ssed.