Atomic force microscopy (AFM) is a mechanical profiling technique that allows
to image surfaces with atomic resolution. Recent progress in reducing the noise
of this technique has led to a resolution level where previously undetectable
symmetries of the images of single atoms are observed. These symmetries are
related to the nature of the interatomic forces. The Si(111)-(7x7) surface is
studied by AFM with various tips and AFM images are simulated with chemical and
electrostatic model forces. The calculation of images from the tip-sample
forces is explained in detail and the implications of the imaging parameters
are discussed. Because the structure of the Si(111)-(7x7) surface is known very
well, the shape of the adatom images is used to determine the tip structure.
The observability of atomic orbitals by AFM and scanning tunneling microscopy
is discussed.Comment: 21 pages, 17 figure