Contrast inversion in dynamic force microscopy on silicon(111) 7 X 7 and gold(111) 23 X root 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 re solution on Si(111)7 x 7 in force gradient images-using either slow AFM fee dback via FM frequency shift (Delta f) detection, or slow STM feedback. Dep ending on the feedback parameters selected, it is possible to cause a contr ast inversion of the atomic resolution image. AFM experiments in non-contac t mode on Au(111) in UHV showed monoatomic steps and the 23 x root 3 surfac e reconstruction. Enhanced corrugation of step edges and a variation of dam ping could be observed, which could indicate a reduced local conductivity. Contrast inversion could also be obtained. (C) 1999 Elsevier Science B.V. A ll rights reserved.