Using high-resolution x-ray standing waves and low-energy electron diffraction, the structure of Te adsorbed on Ge͑001͒ was studied. A coverage-dependent structural rearrangement was observed between Te coverages of 1 and 0.5 monolayer ͑ML͒. At Te coverages near 1 ML, Te was found to adsorb in a bridge site, as expected. However, at Te coverages near 0.5 ML, a structure unanticipated for Group VI/Group IV adsorption was discovered. Te-Ge heterodimers were formed with an average valency of 5, allowing them to satisfy all surface dangling bonds. The results help explain the efficacy of Te as a surfactant in epitaxial growth of Ge/Si͑001͒.

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An x-ray-diffraction method that directly senses the phase of the structure factor is demonstrated and used for determining the local polarity of thin ferroelectric films. This method is based on the excitation of an x-ray standing-wave field inside the film as a result of the interference between the strong incident x-ray wave and the weak kinematically Bragg-diffracted x-ray wave from the film. The method is used to sense the displacements of the Pb and Ti sublattices in single-crystal c-domain PbTiO 3 thin films grown by metal-organic chemical-vapor deposition on SrTiO 3 ͑001͒ substrates. RAPID COMMUNICATIONS

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