IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Wednesday Sessions
       Session SS1-WeA

Paper SS1-WeA9
Progress in Dynamic Force Microscopy: From High-Resolution Imaging of Insulators to the Measurement of Dissipative Interaction Forces

Wednesday, October 31, 2001, 4:40 pm, Room 120

Session: New Opportunities in Surface Microscopy
Presenter: U.D. Schwarz, University of Hamburg, Germany
Authors: U.D. Schwarz, University of Hamburg, Germany
H. Hölscher, University of Hamburg, Germany
W. Allers, University of Hamburg, Germany
S. Langkat, University of Hamburg, Germany
B. Gotsmann, University of Münster, Germany
H. Fuchs, University of Münster, Germany
R. Wiesendanger, University of Hamburg, Germany
Correspondent: Click to Email
Recent progress in dynamic force microscopy (DFM) operated in ultrahigh vacuum, often also called non-contact atomic force microscopy (NC-AFM), enabled the imaging of the atomic structure of surfaces including the observation of point defects independent from the sample's conductivity. However, only few results on insulators have been published so far, possibly due to difficulties in preparing suitable sample surfaces for NC-AFM, e.g., electrostatic charging of the surfaces in vacuum. In order to illustrate the high-resolution capabilities of DFM on insulators, we present the first part of our talk results obtained on NiO(001) at low temperatures. Transition metal oxides are a class of magnetic insulators, which have been of great interest for several decades due to their electronic and magnetic properties. On this material, monatomic defects and atomic resolution across step edges could be observed, achieving a vertical resolution of 1.5 pm. In a second part, the spectroscopic potential of DFM based on a self-driven oscillator set-up is analysed. Introducing a very general tip-sample force law, we show that one of the two quantities measured, the frequency shift, is determined by the mean tip-sample force, while the other quantity, the gain factor (or excitation amplitude), is directly related to dissipative processes like hysteresis or viscous damping. This insight into the measurement principle can be used to examine the contrast mechanism in more detail. The application to non-reactive surfaces like graphite(0001) and xenon(111) allows us to simulate complete DFM images. A comparison between experiment and simulation shows that on xenon, atoms are imaged as maxima, whereas on graphite, the atomic positions of carbon atoms appear as minima and the hollow sites as maxima, in contrast to a simple interpretation of the experimental images.