Reaction of I2 with the (001) surfaces of GaAs, InAs, and InSb. II. Ordering of the iodine overlayer.

The overlayer formed by the reaction of molecular iodine (${\mathit{I}}_{2}$) with GaAs(001), InAs(001), and InSb(001) is investigated with synchrotron soft x-ray photoelectron spectroscopy (SXPS) and scanning tunneling microscopy (STM). Two components, separated by about 0.5 eV, are present in all of the I 4d SXPS spectra. At very low iodine coverages, the high binding energy (BE) component dominates. When the iodine coverage saturates, however, the two components have nearly equal intensities. In contrast to GaAs and InAs, exposure of InSb(001)-c(8\ifmmode\times\else\texttimes\fi{}2) to additional ${\mathrm{I}}_{2}$ results in a further increase of the relative intensity of the low-BE component. STM images of ${\mathrm{I}}_{2}$-covered InSb(001)-c(8\ifmmode\times\else\texttimes\fi{}2) directly reveal the ordering in the overlayer. Islands are visible for submonolayer coverages, suggesting that adsorption occurs via a mobile precursor state. STM images collected from fully covered surfaces display two distinct types of atomiclike features. The predominant feature occupies a 1\ifmmode\times\else\texttimes\fi{}1 unit cell with the same spacing as bulk-terminated InSb(001). The other feature has a coverage of \ensuremath{\sim}1/3 ML and is arranged in pairs oriented along the [110] azimuth. \textcopyright{} 1996 The American Physical Society.