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Hydrogen-induced reconstruction of stepped W(001) surfaces studied with LEED and EELS

Description: Low energy electron diffraction patterns show that the W(001) surface reconstructs at room temperature when exposed to hydrogen with a (..sqrt..2x..sqrt..2)R45/sup 0/ structure having a c2mm symmetry. Vibrational EELS data indicate that the tungsten atoms move together to form dimers which must be aligned in <10> directions to satisfy the symmetry requirements. The two possible dimer orientations define two orthogonal, degenerate domains. It has been shown that steps on a surface may limit the growth of the reconstruction domains and may also influence the relative abundance of the domain orientations. We report here an extension of previous work on step effects involving the relationship of step orientation to domain growth and selection. 7 refs., 2 figs.
Date: November 1, 1984
Creator: Wendelken, J. F. & Wang, G. C.
Partner: UNT Libraries Government Documents Department

Defect and impurity effects on the initial growth of Ag on Si(111)

Description: Step and impurity effects on the initial growth of a thin film have been demonstrated in the ({radical}3 {times} {radical}3)R30{degree} domain growth of Ag on Si(111) using high angular resolution LEED. Anisotropy in the {radical}3 domain shape and growth during deposition are found on the stepped Si(111) with the preferential growth along the step edge direction. The {radical}3 superlattice grows with coverage principally by domain coalescence at the temperature T {approximately} 450{degree}C and is self-similar at different coverages (scaling) as observed on a flat Si(111). The size distribution is shown to follow a Gamma distribution by a simple model calculation. A dramatic change in the growth mechanism is observed when oxygen impurities ({le}0.02 ML) appear. The {radical}3 domains in the presence of impurities grow with coverage more randomly and isotropically in contrast with the step edge effects and coalescence is inhibited. As a result, the {radical}3 superlattice stays in a microdomain morphology without long range order. 17 refs., 6 figs.
Date: October 1, 1990
Creator: Zuo, J.K. & Wendelken, J.F.
Partner: UNT Libraries Government Documents Department

Laser desorption from and reconstruction on Si(100) surfaces studied by scanning tunneling microscopy

Description: Laser irradiated Si(100) surfaces were studied with an ultrahigh-vacuum scanning tunneling microscopy (STM) system. Our observations indicate that only the dimerized outermost atomic layer is removed if the laser fluence is below the melting threshold with a photon energy larger than the band gap. The newly exposed layer, surprisingly, did not have a dimerized atomic structure, but rather, resembled that of a bulk-terminated structure. The uncovered layer remained atomically smooth (no vacancies) even after 90% of the outermost layer was removed. A possible explanation of these observations is that atom removal occurs by a preferential breakage of the atomic bonds in defect sites. When the laser fluence was increased to levels above the melting threshold, extensive surface roughening occurs.
Date: July 1, 1995
Creator: Xu, Jun; Overbury, S.H. & Wendelken, J.F.
Partner: UNT Libraries Government Documents Department