The surface As/Ga atoms 3d core-level spectra of the atomically clean GaAs(1 1 1)A-2 x 2, GaAs(0 0 1)-2 x 4, and GaAs(0 0 1)-4 x 6 surfaces were firstly presented using high-resolution synchrotron radiation photoemission as a probe. The technique clearly explicates behaviors of the As atoms in different surface reconstruction. For GaAs(1 1 1) A-2 x 2, the surface As sits in the same plane as the Ga atoms. As to the GaAs(0 0 1)-2 x 4 surface, the As-As dimers dominate the surface layer, while for GaAs(001)-4 x 6, the As existed in two forms, the As in the As-Ga dimer and the 3-fold coordinated As. Next, we present a microscopic view of in situ atomic layer deposition (ALD) of Al2O3 on GaAs taking the two (0 0 1) surfaces as examples. The precursors were trimethylaluminum (TMA) and water. TMA could exist in either a chemisorbed or physisorbed form, depending on the charge environment of the associated surface atoms. The subsequent water purge resulted in both adsorbed forms being etched off or transformed the physisorbed TMA into the As-O-Al(CH3)(2) configuration. We found that the ALD process rendered the precursors partially and selectively in forming bonds with the surface atoms without disturbing the atoms in the subsurface layer. Upon annealing, the interfacial bonding was dominated with the As-Al as well as Ga-O bonds. (C) 2013 Elsevier B. V. All rights reserved.