Molecular Dynamics Simulations of Dynamic Force Microscopy: Applications to the Si(111)-7x7 Surface

Molecular dynamics simulations have been performed to understand true atomic resolution, which has been observed on the Si(111)-7$\times$7 surface by dynamic force microscopy in ultra high vacuum(UHV). Stable atomic-scale contrast is reproduced in simulations at constant mean height above a critical tip-sample separation when monitoring the interaction force between tip and sample. Missing or additional adatoms can be recognized in such scans, although they are less well resolved than native adatoms. The resonance frequency shift, as well as arbitrary scans, e.g. at constant force can be computed from a series of force-distance characteristics. By means of dynamic simulations we show how energy losses induced by interaction with an oscillating tip can be monitored and that they occur even in the non-contact range.Comment: 5 pages, 5 figures, accepted publication in Applied Surface Scienc

Advances in atomic force microscopy

This article reviews the progress of atomic force microscopy (AFM) in ultra-high vacuum, starting with its invention and covering most of the recent developments. Today, dynamic force microscopy allows to image surfaces of conductors \emph{and} insulators in vacuum with atomic resolution. The mostly used technique for atomic resolution AFM in vacuum is frequency modulation AFM (FM-AFM). This technique, as well as other dynamic AFM methods, are explained in detail in this article. In the last few years many groups have expanded the empirical knowledge and deepened the theoretical understanding of FM-AFM. Consequently, the spatial resolution and ease of use have been increased dramatically. Vacuum AFM opens up new classes of experiments, ranging from imaging of insulators with true atomic resolution to the measurement of forces between individual atoms.Comment: In press (Reviews of Modern Physics, scheduled for July 2003), 86 pages, 44 figure

Separation of interactions by noncontact force microscopy

Quantitative measurements of frequency shift vs distance curves of ultrahigh-vacuum force microscopy in a noncontact mode are presented. Different contributions from electrostatic, van der Waals, and chemical interactions are determined by a systematic procedure. First, long-range electrostatic interactions are eliminated by compensating for the contact potential difference between the probing tip and the sample. Second, the long-range van der Waals contribution is determined by fitting the data for distances between 1 and 6 nm. Third, the van der Waals part is subtracted from the interaction curves. The remaining part corresponds to the shea-range chemical interaction, and is found to decrease exponentially. A Morse potential is used to fit these data. The determined parameters indicate that the interaction potential between single atoms can be measured by force microscopy in a noncontact mode