Contrast inversion in dynamic force microscopy on silicon 111/ 7=7 and gold 111/ 23=(3

The combination of atomic force microscopy AFM.in contact and non-contact mode with scanning tunnelling microscopy STM.in ultra-high vacuum UHV.was used to experimentally separate the different interactions between tip and sample surface such as repulsive or attractive van der Waals forces or electrostatic forces. Simultaneous STM and AFM measurements showed atomic resolution on Si 111.7=7 in force gradient images using either slow AFM feedback via FM frequency shift D f.detection, or slow STM feedback. Depending on the feedback parameters selected, it is possible to cause a contrast inversion of the atomic resolution image. AFM experiments in non-contact mode on Au 111.in UHV showed monoatomic steps and the 23=ʹ3 surface reconstruction. Enhanced corrugation of step edges and a variation of damping could be observed, which could indicate a reduced local conductivity. Contrast inversion could also be obtained. q1999 Elsevier Science B.V. All rights reserved