Initial stages of the autocatalytic oxidation of the InAs(001)-(4 x 2)/c(8 x 2) surface by molecular oxygen

The initial stages of oxidation of the In-rich InAs(001)-(4 x 2)/c(8 x 2) surface by molecular oxygen (O-2) were studied using scanning tunneling microscopy (STM) and density functional theory (DFT). It was shown that the O-2 dissociatively chemisorbs along the rows in the [110] direction on the InAs surface either by displacing the row-edge As atoms or by inserting between In atoms on the rows. The dissociative chemisorption is consistent with being autocatalytic: there is a high tendency to form oxygen chemisorption sites which grow in length along the rows in the [110] direction at preexisting oxygen chemisorption sites. The most common site size is about 21-24 angstrom in length at similar to 25% ML coverage, representing 2-3 unit cell lengths in the [110] direction (the length of similar to 5-6 In atoms on the TOW). The autocatalysis was confirmed by modeling the site distribution as non-Poisson. The autocatalysis and the low sticking probability (similar to 10(-4)) of O-2 on the InAs(001)-(4 x 2)/c(8 x 2) are consistent with activated dissociative chemisorption. The results show that is it critical to protect the InAs surface from oxygen during subsequent atomic layer deposition (ALD) or molecular beam epitaxy (MBE) oxide growth since oxygen will displace As atoms. (c) 2009 Elsevier B.V. All rights reserved.