GaAs(001) (2 x 4) to c(4 x 4) transformation observed in situ by STM during As flux irradiation

Atomic resolution scanning tunnelling microscopy (STM) has been used to study in situ the As-terminated ;reconstructions formed on GaAs(0 0 1) surfaces in the presence of an AS(4) flux. The relationship between the As-rich (2 x 4) and c(4 x 4) surfaces is observed throughout the gradual evolution of the reconstruction transformation. The results suggest that during the initial stage of the transformation, Ga-rich As-terminated variations of the c(4 x 4) form in order to accommodate excess mobile Ga produced by pit formation. These transient structures later planarize, as excess Ga is incorporated at step/island edges. Successive imaging of the same sample area during As-4 irradiation allows point-by-point adatom binding to be analysed in a way inaccessible to MBE-STM systems relying on sample quenching and transfer. (C) 2009 Elsevier B.V. All rights reserved.