REACTION OF I-2 WITH THE (001) SURFACES OF GAAS, INAS, AND INSB .2. ORDERING OF THE IODINE OVERLAYER

The overlayer formed by the reaction of molecular iodine (I-2) with Ga As(001), InAs(001), and InSb(001) is investigated with synchrotron sof t x-ray photoelectron spectroscopy (SXPS) and scanning tunneling micro scopy (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 satu rates, however, the two components have equal intensities. In contrast to GaAs and InAs, exposure of InSb(001)-c(8x2) to additional I-2 resu lts in a further increase of the relative intensity of the low-BE comp onent. STM images of I-2 covered InSb(001)-c(8x2) directly reveal the ordering in the overlayer. Islands are visible for submonolayer covera ges, suggesting that adsorption occurs via a mobile precursor state. S TM images feature occupies a 1x1 unit cell with the same spacing as bu lk-terminated InSb(001). The other feature has a coverage of similar t o 1/3 ML and is arranged in pairs oriented along the [110] azimuth.