Atomic structure determination for GaAs(001)-(6×6) by STM

We present a model structure for the GaAs(001)-(6×6) reconstructed surface based on high-resolution scanning tunneling microscopy images. This surface has previously also been referred to as (1×6), (2×6), (3×6) and (2×6)/(3×6) mixed, and contributes to the “4×6” mixed surface. Phase coexistence with the Ga-rich c(8×2) is used to determine the basic structure. Chemically selective halogen (Cl2) adsorption is used to distinguish Ga atoms from As atoms and to extract structural details that are not visible in scanning tunneling microscopy images of the clean surface. The structure is consistent with the electron-counting rule. Partial disorder appears in the structure. While some of the disorder is due to kinetic barriers to equilibrium, some is intrinsic to the structure.