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

The atomic arrangement of the technologically important As-rich $\mathrm{GaAs}\left(001\right)-(2\times 4)$ 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 $\beta 2(2\times 4)$ 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.