Structure of the In-rich InAs (001) surface

Using scanning tunneling microscopy, frequency-modulated scanning atomic-force microscopy, electron diffraction, and density functional theory calculations we investigate a structure of the InAs (001) surface displaying c(8 × 2)/(4 × 2) reconstruction at room temperature. It is found that the room temperature data are satisfactorily interpreted based on the model proposed by Kumpf et al. [Phys. Rev. Lett. 86, 3586 (2001)], however, at cryogenic temperatures the model fails since a different structure, characterized by fourfold period along [110] crystallographic direction, partial disorder and instability, is observed. By the present study we find that the structure is described by corrected Kumpf et al. model where most of atomic rows are left as in the original model and only the dominant indium atom rows running along [110] are changed. At room temperature the dominant rows are disordered and rapidly fluctuate thermally while at cryogenic temperatures they convert to chains of indium aggregates and acquire fourfold period. Moreover, frequently observed incomplete occupancy of the dominant indium rows leads to many different local surface structures, reflected by characteristic “features” in scanning tunneling microscopy patterns. We have classified and explained most of these structures.