Configurational entropy in action

Post date: Oct 11, 2016 2:23:12 PM

New insights into the atomic structure of the GaAs(001)-c(4x4) surface

The atomic structure of the c(4x4) reconstruction, formed on the GaAs(001) surface under high arsenic overpressure, has recently been attracting renewed interest. This has lead to a revision of the commonly accepted c(4x4) structural model but a definitive understanding of the driving force for the newly proposed structure was lacking. Targeting the later problem, in a recent Letter [Phys. Rev. Lett. 93, 146102 (2004)] we have presented a state-of-the-art theoretical study of the GaAs(001)-c(4x4) surface employing ab initio atomistic thermodynamics based on density-functional theory calculations. We have demonstrated that in a range of stoichiometries, between those of the conventional three As-dimer and the new three Ga-As dimer model, there exists a diversity of atomic structures featuring Ga-As heterodimers, driven by surface configurational entropy. These results fully explain the experimental scanning tunneling microscopy images and are likely to be relevant also to the c(4x4)-reconstructed (001) surfaces of other III-V semiconductors.