Atomic Structure of the GaAs(001)-(2×4) Surface Resolved Using Scanning Tunneling Microscopy and First-Principles Theory

The atomic arrangement of the technologically important As-rich GaAs(001)-(2×4) reconstructed surface is determined using bias-dependent scanning tunneling microscopy (STM) and first-principles electronic structure calculations. The STM images reveal the relative position and depth of the atomic-scale features within the trenches between the top-layer As dimers, which are in agreement with the β2(2×4) structural model. The bias-dependent simulated STM images reveal that a retraction of the topmost dangling bond orbitals is the novel electronic mechanism that enables the STM tip to image the trench structure.