We have studied the interaction of ${\mathrm{N}}_{2}$O with GaAs(110) at 25 K as a function of photon beam exposure, using photoemission to detect and characterize reactions. The results show that x rays (h\ensuremath{\nu}=1486 and 1253 eV, photon flux 6.8\ifmmode\times\else\texttimes\fi{}${10}^{9}$ and 2.3\ifmmode\times\else\texttimes\fi{}${10}^{9}$ photons ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ ${\mathrm{sec}}^{\mathrm{\ensuremath{-}}1}$) induce ${\mathrm{N}}_{2}$O dissociation and surface oxidation while ultraviolet photons do not within our detectability limit (h\ensuremath{\nu}=21.2 and 40.8 eV). The primary dissociation process for physisorbed ${\mathrm{N}}_{2}$O involves the attachment of low-energy secondary electrons created by photoillumination. Following electron capture, ${\mathrm{N}}_{2}$O dissociation produces ${\mathrm{O}}^{\mathrm{\ensuremath{-}}}$ ions that react with GaAs to yield surface Ga and As oxides. Dissociation also produces ${\mathrm{N}}_{2}$ molecules that desorb without reacting but can be kinetically trapped at low temperature. The As oxides exhibit ${\mathrm{As}}_{2}$${\mathrm{O}}_{5}$-like, ${\mathrm{As}}_{2}$${\mathrm{O}}_{3}$-like, and intermediate ${\mathrm{AsO}}_{\mathit{x}}$-like bonding configurations in relative amounts determined by kinetic constraints and oxygen availability. The photon-enhanced formation of a thick oxide at low temperature is limited by diffusion through the oxide layer, and the formation of ${\mathrm{O}}_{2}$ molecules is observed. Warming to 300 K enhances ${\mathrm{Ga}}_{2}$${\mathrm{O}}_{3}$ growth at the expense of As-O configurations.
Synchrotron radiation photoemission results for Sm/GaAs(110) interfaces formed and studied at 20 and 300 K show temperature dependencies that can be related to differences in surface growth structures and kinetic constraints. Submonolayer growth at 300 K produces two distinct ordered Sm chain configurations, as shown by scanning tunneling microscopy, and the photoemission results demonstrate that Sm atoms in these chains are divalent. These low‐surface‐density divalent configurations are precursors to surface disruption that, with additional Sm deposition, produce reacted clusters in which the Sm atoms are trivalent. Ultimately, Sm metal nucleation occurs on the reacted region and the overlayer thickens, with Ga and As atoms segregating to the surface region. For 20‐K growth, the valence‐band results show much slower conversion from divalent to trivalent Sm bonding, despite evidence that the amount of disruption is equivalent at 20 and 300 K. We attribute these differences, and those in the Ga and As core levels, to the freezing‐in of an amorphous Sm–Ga–As mixture at 20 K. Hence, kinetic factors curtail atom rearrangements that occur readily at 300 K. Annealing of thin overlayers to 300 K removes kinetic constraints and produces Ga, As, and Sm bonding that is spectroscopically equivalent to that observed for 300‐K growth. Sm/GaAs(110) interfaces formed by cluster assembly are shown to be unstable. Together, these results demonstrate that high‐atom‐density Sm contacts to GaAs are thermodynamically very unfavorable and that the instability generated by increasing the surface coverage provides the driving force for disruption.
Initial stages of antimony (Sb) adsorption on the $\mathrm{Si}(5\phantom{\rule{0.3em}{0ex}}5\phantom{\rule{0.3em}{0ex}}12)\text{\ensuremath{-}}2\ifmmode\times\else\texttimes\fi{}1$ surface have been studied by scanning tunneling microscopy in order to understand interfacial reaction between adsorbed Sb atoms and the Si template with one-dimensional (1D) symmetry. It has been found that there are two distinct steps, Sb indiffusion and preferential adsorption, at the initial Sb adsorption on $\mathrm{Si}(5\phantom{\rule{0.3em}{0ex}}5\phantom{\rule{0.3em}{0ex}}12)\text{\ensuremath{-}}2\ifmmode\times\else\texttimes\fi{}1$ held at $600\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. Initially, deposited Sb atoms diffuse into the subsurface, cause indirect Si deposition, and result in surface reconstruction from a (5 5 12) terrace to (337) terraces with (113) steps. As soon as the subsurface Sb sites are saturated by indiffused Sb atoms, additionally deposited Sb atoms are preferentially adsorbed along the upper (113)-step edges and form 1D Sb wires with a spacing of about $10\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, which corresponds to two periodic lengths of the original (5 5 12) surface. Once Sb-adsorption sites, (113) steps, are saturated, deposited Sb atoms cluster for themselves and do not contribute to nanowire fabrication. From the present studies, it has been found that both Sb indiffusion and preferential adsorption stabilize the high-index surface through relieving surface strain by way of either inserting or attaching Sb atoms, but once such surface strain is relieved, the 1D growth mode also terminates.
The electronic band structure of InSb(111) along the direction was determined using angle-resolved photoemission spectroscopy for the photon energy between 9 and 39 eV via synchrotron radiation. The bulk band dispersion is in agreement with earlier theoretical calculations. The In- (group III-) terminated InSb(111) surface shows surface Umklapp transitions and reflection of the bulk density of states. We found two nondispersive features which were not reported before. They are related to the surface state and the resonance process of the InSb(111) - .
We have investigated Sb interface on the single-domain vicinal Si(001) surface inclined by 4° toward [110] direction using scanning tunneling microscopy and high-resolution synchrotron photoelectron spectroscopy. This vicinal Si(100)-4° off surface is reconstructed to form nine-dimer-wide single-domain (001)-p(2×2) terraces separated by rebonded DB double-layer steps, when the Si-dimer rows perpendicular to the steps. By 2ML Sb-deposition at RT and subsequent postannealing at 500°C, the Si surface has been covered by Sb-dimer rows whose direction is parallel to the steps composed of SA and SB (Sb rebounded atom) steps. And all the Si 2p components related to the clean surface have disappeared, while the Sb-Si interfacial component has been identified. Such a component is mainly due to charge transfer between Si and Sb atoms at the top layer. Based on these results, it has been concluded that Sb atoms passivate the vicinal Si(001)-4° off surface through forming 1ML Sb layers composed of Sb dimers and Sb rebonded atoms.
We grow a $\mathrm{Mn}{\mathrm{Pt}}_{3}$-type trilayer ordered surface alloy on Pt(001), $c(2\ifmmode\times\else\texttimes\fi{}2)$ $\mathrm{Mn}\text{\ensuremath{-}}\mathrm{Pt}∕1\mathrm{ML}$ $\mathrm{Pt}∕c(2\ifmmode\times\else\texttimes\fi{}2)$ $\mathrm{Mn}\ensuremath{-}\mathrm{Pt}∕\mathrm{Pt}(001)$, of which atomic structure is investigated by dynamic low energy electron diffraction analysis. Magneto-optic Kerr effect measurements of the surface alloy at $45\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ show no hysteresis, although bulk $\mathrm{Mn}{\mathrm{Pt}}_{3}$ ordered alloy is ferromagnetic. Ab initio total energy calculations based on density functional theory, rather, predict that ferromagnetic order is not the ground state for the surface alloy. We propose that the nonferromagnetic order of the surface alloy originates mainly from surface effects in regards to nonferromagnetic ground state also found for the near-surface layers of the bulk-terminated $\mathrm{Mn}{\mathrm{Pt}}_{3}(001)$.
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