Internal charge distribution of iodine adatoms on silicon and silicon oxide investigated with alkali ion scattering

Time-of-flight spectra were collected for low energy ⁷Li⁺ and ²³Na⁺ ions backscattered from Si(1 1 1) surfaces covered with sub-monolayers of iodine. Li ions singly scattered from the iodine adatoms have consistently larger neutralization probabilities than those scattered from the silicon substrate, and the neutralization decreases with off-normal emission. This indicates that the internal charge distribution of the iodine adatoms is not uniform, presumably due to attraction of electron density to the positively charged bonding Si atom. Photoelectron spectroscopy shows that iodine adsorbed on pre-oxidized Si bonds through the oxygen atom, forming hypoiodite (-OI) moieties. The neutralization of ²³Na⁺ backscattered from such iodine adatoms is independent of the emission angle, indicating that there is less charge rearrangement than for iodine bonded directly to Si.