Initial-state and scattering-factor effects in photoelectron holography

Angular anisotropies in the source wave and scattering factor are shown to cause artifacts in the images reconstructed from multiple-energy photoelectron holograms. A variable-axis small-angular-cone method is introduced to eliminate such anisotropies. We show that within the small angular cone, the anisotropy of the source wave towards an atom is canceled by that towards the detector. Also, the cone only samples the flat part of the slope of the scattering factor’s phase. The remaining shift in the image position can be quantitatively corrected for the near-neighbor atoms.published_or_final_versio

Angle-resolved x-ray circular and magnetic circular dichroisms: Definitions and applications

We introduce definitions of angle-resolved x-ray circular dichroism (ARXCD) and magnetic x-ray circular dichroism (ARMXCD). As defined, the much larger effect of circular dichroism (ARXCD) is separated from the smaller magnetic (ARMXCD) effect. In all materials, ARXCD is zero along mirror planes while nonzero elsewhere. ARMXCD is nonzero only in magnetic materials. The measurement and analysis of ARMXCD allow element specific surface magnetism and surface structure as well as their inter-relationship to be studied as functions of the outgoing electron's directionpublished_or_final_versio

Direct observation of ordered trimers on Si(111)√3×√3 R30°-Au by scanned-energy glancing-angle Kikuchi electron wave-front reconstruction

We report the first atomically resolved images of ordered Au trimers on Si(111)√3×√3R30°-Au using wave-front reconstruction of scanned-energy glancing-angle Kikuchi electron spectra. Each Au image has a resolution (full width at half magnitude) of less than 1 Å . The images indicate that Au trimers are ordered and nonrotated within the surface plane and with respect to the second-layer Si plane providing direct evidence of the conjugate honeycomb-chained-trimer model for the Au-√3 system. © 1996 The American Physical Society.published_or_final_versio

Multilayer structural determination of the GaAs(1¯1¯1¯)2×2 reconstruction by automated tensor LEED

The multilayer atomic coordinates for the GaAs(1¯ 1¯ 1¯)(2×2) surface have been determined using automated tensor low-energy electron diffraction. The results confirm the As adatom trimer model found by total-energy calculations and scanning tunneling microscopy studies although details of the displacements are different. The low-energy electron diffraction analysis, being sensitive to multilayer spacings in the surface region, shows that substantial subsurface relaxations are present.published_or_final_versio

Thermodynamics of carrier distribution within localized electronic states with a broad Gaussian energy distribution and its effect on luminescence behavior of localized states

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Surface structure of epitaxial Gd(0001) films on W(110) studied by quantitative LEED analysis

The surface structure of thick (400 Å) Gd(0001) films, epitaxially grown on W(110), is investigated by low-energy electron-diffraction (LEED) IV measurements in combination with dynamical LEED calculations. A first-layer contraction of 2.4% and a second-layer spacing expansion of 1% is found. These findings are in good agreement with literature values determined for the (0001) surface of bulk Gd crystals. No significant difference in the LEED IV data is found between films grown at room temperature and films grown at elevated temperatures.published_or_final_versio

GaN thin films on SiC substrates studied using variable energy positron annihilation spectroscopy

A variety of GaN epilayers, grown on 6H-SiC substrates using different growth conditions, have been studied using variable energy positron annihilation spectroscopy. In the S-E plots, a peak structure in the S-parameter is seen which is related to the GaN/substrate heterojunction. The position of the peak is found to be much closer to the sample surface than expected from simple mean implantation depth arguments. This anomaly is attributed to the fact that there is a rectifying potential step that prevents diffusing positrons in the GaN from entering the SiC substrate. This effect has been successfully mimicked by inserting an artificial electric field into the thin interfacial region in the VEPFIT analysis.link_to_subscribed_fulltex