Tip–sample distance dependency of non-contact atomic force microscopy images on a GaAs(110) surface

Tip–sample interactions are at the origin of atomic resolution in non-contact atomic force microscopy (NC-AFM) but also make it difficult to understand the meaning of atomic features observed as NC-AFM images. (110) surfaces of III–V semiconductors such as GaAs or InP have relaxed (1 × 1) surfaces with both anions and cations of different dangling bond states. Since these atoms are located at the surface where an atom attached to the tip apex can reach to interact with them and show significant relaxation via tip–sample interaction, NC-AFM images of the surface are expected to strongly depend upon the atomic species or the electronic state of the topmost atom at the tip apex. We have taken a number of NC-AFM images of GaAs(110) surfaces with a Si tip by means of room-temperature ultra-high vacuum NC-AFM and categorized them into two types of image which have different tip–sample distance dependencies. In comparison with a theoretical prediction of tip–surface interaction on the GaAs(110) surface, we have found that one of these images is due to a Si atom attached to the apex which reveals the tip–sample interaction with As and Ga surface atoms as individual peaks in the NC-AFM image.