Contrast inversion in dynamic force microscopy on silicon(111) 7 X 7 and gold(111) 23 X √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 atrractive van der Weals forces or electrostatic forces Simultaneous STM and AFM measurements showed atomic resolution on Si(111)7 x 7 in force gradient images-using either slow AFM feedback via FM frequency shift (Delta 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 x root 3 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. (C) 1999 Elsevier Science B.V. All rights reserved.