Distorted iron films on GaAs(001)-(4x6)

Polarized K-edge x-ray absorption fine structure spectroscopy (XAFS) studie s were performed both in and ex situ on iron films deposited on GaAs substr ates. Samples with 5 and 10 ML (monolayers) of iron deposited on sulfur-pas sivated and (4x6)-reconstructed GaAs(001) surfaces, respectively, were stud ied ex situ (capped with 20 ML of gold) and compared with 9.3 ML on GaAs(00 1)-(4x6) measured in situ. Analysis of XAFS spectra for both samples on (4x 6)-GaAs reveals a tetragonal distortion of the iron film relative to bulk b ody-centered-cubic iron. The distortion involves an in-plane contraction an d an expansion perpendicular to the GaAs surface to give a c/a ratio of 1.0 3(1), with a comparable to half the bulk lattice constant of GaAs. The samp le on sulfur-passivated GaAs did not exhibit this distortion.