Atomic scale structure of InAs(001)-(2×4) steady-state surfaces determined by scanning tunneling microscopy and density functional theory

The structure of InAs(0 0 1)-(2×4) surfaces equilibrated under typical MBE conditions is studied by scanning tunneling microscopy (STM). Depending on the magnitude of the As flux, typical surfaces are found to contain a mixture of α2(2×4) and β2(2×4) reconstructions. The relative populations of the α2 and β2 reconstructions are found to depend on substrate temperature and the magnitude of the As flux. The atomic-scale details of the reconstructed units on these mixed-phase surfaces are definitively determined by comparing atomic-resolution dual-bias STM images to first-principles calculations. The imaging mechanism for revealing atomic-scale details, particularly the trench dimer, is found to be qualitatively similar to that for GaAs, although the effect is less pronounced. Additionally, a significant population of ad-atom related structures are observed on quenched surfaces, apparently unrelated to any equilibrium ad-atom population.