Sb Adatoms Research Articles

Electrocatalysis by ad-atoms: Part XVII. Electronegativity effect on oxygen donation by oxygen-adsorbing ad-atoms and steric hindrance by alkyl groups in Shole control in aldehyde oxidation

The oxidation of propionaldehyde was examined on electrodes modified by Ru, Ag, Hg, Ge, Sn, As, Sb, Bi, S, Se and Te ad-atoms. The feature of the enhancement of propionaldehyde oxidation by ad-atoms was found to be quite similar to that of formaldehyde and acetaldehyde oxidation. The oxidation was found to be enhanced strikingly by oxygen donation by oxygen-adsorbing ad-atoms as well as by the inhibition of poison formation by S hole control by non-oxygen-adsorbing ad-atoms, but to a lesser extent. In the enhancement by S hole control, steric hindrance by alkyl groups is observed. In the enhancement by oxygen-adsorbing ad-atoms, the difficulty in oxygen donation from ad-atoms to aldehyde molecules depends on the size of the alkyl group: the smaller the electronegativity of the oxygen-adsorbing ad-atoms, the more difficult is this donation. The donation is discouraged by the orientation of aldehyde molecules caused by the induced negative charge of adsorbed oxygen atoms.

The interaction of Sb 4 molecular beams with Si(100) surfaces: Modulated-beam mass spectrometry and thermally stimulated desorption studies

Modulated-beam mass spectrometry and thermally-stimulated desorption measurements were used to show that Sb 4 is dissociatively chemisorbed on clean Si(100) at all temperatures investigated, from 100 to 1025°C. For Si substrate temperatures T s less than 600°C, desorption was only observed from precursor states corresponding to Sb 4 molecules adsorbed on top of a dissociatively chemisorbed Sb layer. The Sb 4 sticking probability s was nearly unity and independent of θ Sb for θ Sb ≲ 0.7 monolayers (ML) but decreased rapidly with increasing θ Sb above 0.7 ML to reach s = 0 at a saturation coverage of θ Sb = 1.0 ML (referenced to the surface site density of unreconstructed Si(100), 6.8 × 10 14 cm −2). Above 600°C, the desorbing Sb 4 flux decreased rapidly as the saturation coverage decreased and an increasing fraction of the impinging Sb 4 flux was desorbed from dissociatively chemisorbed states as Sb monomers. Sb 1 was the only desorbing species detected at T s ≳ 800°C. The activation energy for Sb 1 desorption was 2.40 ± 0.1 eV for θ Sb ≲ 0.5 ML and 2.33 ± 0.1 eV for θ Sb ≳ 0.5 ML as determined by thermally stimulated desorption, surface lifetime, and saturation coverage measurements. A simple model for Sb 4/Si(100) interactions involving a mobile Sb 4 precursor state and repulsive lateral interactions between chemisorbed Sb adatoms was used to calculate desorption rate kinetics and found to provide excellent agreement with the measured data.

Secondary implantation of Sb into Si molecular beam epitaxy layers

We report on the influence of low-energy Si+ ions on the incorporation of Sb adatoms existing on growing (100) Si molecular beam epitaxy layers. At a growth temperature of 650 °C employed for these experiments an increase of incorporation of about three orders of magnitude compared to the spontaneous incorporation is obtained at ion flux densities of typically 1012 cm−2 s−1. Dopant activation coefficients of almost unity are established up to 1019 cm−3. The number of incorporated adatoms is found to increase proportionally with preadjusted adatom density as well as with Si+ ion dose. At an ion energy of 500 eV the constant of proportionality is estimated to be σI =(5±2)×10−16 cm2.

Electron states of an Sb-ordered overlayer on GaAs(110)

The electronic properties of an Sb overlayer deposited onto a GaAs(110) surface have been calculated using a self-consistent-pseudopotential approach and assuming the ordered-overlayer geometry proposed in recent low-energy electron diffraction studies. The results show that Sb adatoms are bound by strong covalent bonds to the substrate and that various overlayer or chemisorption-induced states appear throughout the valence band. Comparison with photoemission data allows us to assign a major Sb-induced structure appearing in the energy distribution curves.