STM observation of Ga-dimers on a GaAs(001)-c(8 × 2)-Ga surface

Abstract

Using in situ scanning tunneling microscopy (STM) we have obtained high-resolution empty-state images exhibiting triple-protrusion rows on GaAs(001)-c(8 × 2)-Ga surface. We assign the middle protrusion rows to the surface Ga dimers in the ξ model proposed by Lee et al. [Phys. Rev. Lett. 85, 3890 (2000)]. The surface Ga dimers, which are responsible for the c(8 × 2) periodicity, are the key feature of the ξ structure and have never been imaged in previous STM studies. The current study provides direct evidence for the ξ model, while all other existing models can be readily excluded from our STM images.