STM observations of GaAs(110) showing the top and bottom zig-zag rows of the surface

We present an unusual image form of the GaAs(110) surface observed in cross-sectional scanning tunneling microscopy in UHV. It clearly shows the zig-zag row formed between the cations and anions in the top row of the GaAs(110) surface, as well as traces of the bottom row that lies between the top rows. It thereby closely resembles the true atomic lattice usually depicted by ball-and-stick models. We interpret the occurrence of this image form in terms of a chemical bond that forms between the apex of the tip and the nearest Ga atom in the top row of the sample surface. The formation of such a bond has recently been predicted theoretically. The results thus show that the tip-sample interaction, when it becomes significant, can give rise to entirely different and interesting image forms.