We have performed frequency-modulated scanning atomic-force (FM-AFM) microscopy
on the c(2x8)/(2x4) GaAs (001) surface. Highly resolved interaction patterns reflect prevailing surface dimer pairs consistent with a so called beta2 structure, but more rare motifs characteristic of alpha2 and beta structures are also seen. Atoms of the dimers interact with the AFM tip repulsively and appear as sharp features on a smooth background when imaged in constant height mode. An analysis of the interaction decay length and lateral size of the atomic features indicates that the surface atoms are visualised through a core-core repulsion mechanism. In this imaging mode the FM-AFM may be regarded as a true surface structure tool, since the observed features can directly be associated with surface atoms.