Anisotropic optical response of the diamond (111)-2x1 surface

The optical properties of the 2$\times$1 reconstruction of the diamond (111) surface are investigated. The electronic structure and optical properties of the surface are studied using a microscopic tight-binding approach. We calculate the dielectric response describing the surface region and investigate the origin of the electronic transitions involving surface and bulk states. A large anisotropy in the surface dielectric response appears as a consequence of the asymmetric reconstruction on the surface plane, which gives rise to the zigzag Pandey chains. The results are presented in terms of the reflectance anisotropy and electron energy loss spectra. While our results are in good agreement with available experimental data, additional experiments are proposed in order to unambiguously determine the surface electronic structure of this interesting surface.Comment: REVTEX manuscript with 6 postscript figures, all included in uu file. Also available at http://www.phy.ohiou.edu/~ulloa/ulloa.html Submitted to Phys. Rev.

THE SILICON/GERMANIUM (111) INTERFACE : THE ONSET OF EPITAXY

No abstract availabl

Carbon 1 s studies of diamond(111): Surface shifts, hydrogenation, and electron escape lenaths

As probed by photoemission, the valence band emission spectra of diamond(lll) undergo reversible changes due to cycles of hydrogen adsorption and desorption. We report here carbon Is spectra from diamond(111) as a function of hydrogen exposure-annealing cycles and as a function of photon energy. We find an additional shoulder to lower binding energy in the C Is spectra of the hydrogen-free reconstructed 2 X 2/2 X1 surface and interpret this result as due to a chemical shift (0.95 \uc2\ub10.1 eV) of the surface atoms. We analyze the data in terms of models for reconstruction and also derive the inelastic scattering length (escape length) of electrons in diamond over the kinetic energy range 25\ue2\u80\u931000 eV

Surface Segregation And Surface Electronic Interactions In Ptcu

Photoemission and Auger electron spectroscopy on Pt0.98Cu0.02 show that the (110) face has over twice as much Cu surface segregation as the (111) face. The Cu 3d-derived surface "density of states" differ strikingly in peak shape and in width (by 0.5 eV). The centroids, compared with bulk Cu d states, are shifted by more than 0.3 eV towards the Fermi level. This is the first experimental correlation between surface segregation and surface bonding. © 1982.1151L86L91Williams, Nason, (1974) Surface Sci., 45, p. 377Donnelly, King, (1978) Surface Sci., 74, p. 89Kerker, Moran-Lopez, Bennemann, (1977) Phys. Rev., 15 B, p. 638Shek, Stefan, Weissman-Wenocur, Pate, Lindau, Spicer, (1981) Journal of Vacuum Science and Technology, 18, p. 533Lindau, Spicer, Miller, Ling, Pianetta, Chye, Garner, (1977) Physica Scripta, 16, p. 388The Pt emission is relatively flat and is spread over a larger width in energy. That the Pt emission does not contribute to the structure assigned as Cu 3d states in the hv=150 eV data, can be seen from the photon energy dependence of the valence band spectra. We have taken data (unpublished) at hv=80, 110 and 130 eV as well. The strengths of the Cu-derived features increase with respect to the rest of the valence band, in accordance with the photon energy dependence of the Pt 5d and Cu 3d photoionization cross-sectionsStohr, Feely, Apai, Wehner, Shirley, (1976) Physical Review B, 14 B, p. 4431By “binding energy” we mean the energy difference between the Fermi level EF and the average energy of the d band as seen in photoemissionThe depth which is sampled is the electron escape depth multiplied by cos 42°The relative strengths of Cu 3d and Pt 5d emissions are estimated as follows. For the (111) alloy sample, the peak area under the difference spectrum PtCu(111)-Pt(111) [i.e. fig. lb] is divided by the area under the pure Pt(111) valence band spectrum (with the inelastic background subtrated). For the (110) alloy sample, the Pt contribution is assumed to be similar to the Pt(111) valence emission. The use of Pt(110) as reference for the PtCu(110) sample would be unlikely to lead to significantly different results at hv = 150eV. Moreover, the emissions integrated over the Pt bandwidths (about 7 eV) should be rather insensitive to the shape of the Pt valence electronic density of statesBrongersma, Sparnaay, Buck, (1978) Surface Sci., 71, p. 657Kelly, Swatzfager, Sundaram, (1979) Journal of Vacuum Science and Technology, 16, p. 664Ng, McLane, Jr., Tsong, (1980) Journal of Vacuum Science and Technology, 17, p. 154Brundle, Wandelt, (1981) Journal of Vacuum Science and Technology, 18, p. 537Kleiman, Sundaram, Barreto, Rogers, (1979) Solid State Commun., 32, p. 919. , Unfortunately, it is beyond the scope of this letter to compare and contrast the present results with these authors' X-ray photoemission results on polycrystalline PtCu foilsMiedema, (1978) Z. Metallk., 69, p. 45

Banksia species (Proteaceae) from severely phosphorus-impoverished soils exhibit extremem efficiency in the use and re-mobilization of phosphorus

Banksia species (Proteaceae) occur on some of the most phosphorus (P)-impoverished soils in the world. We hypothesized that Banksia spp. maximize P-use efficiency through high photosynthetic P-use efficiency, long leaf lifespan (P residence time), effective P re-mobilization from senescing leaves, and maximizing seed P concentration. Field and glasshouse experiments were conducted to quantify P-use efficiency in nine Banksia species. Leaf P concentrations for all species were extremely low (0.14–0.32 mg P g−1 DM) compared with leaf P in other species reported and low relative to other plant nutrients in Banksia spp.; however, moderately high rates of photosynthesis (13.8–21.7 µmol CO2 m−2 s−1), were measured. Some of the Banksia spp. had greater P proficiency (i.e. final P concentration in senesced leaves after re-mobilization; range: 27–196 µg P g−1 DM) than values reported for any other species in the literature. Seeds exhibited significantly higher P concentrations (6.6–12.2 mg P g−1 DM) than leaves, and species that sprout after fire (‘re-sprouters’) had significantly greater seed mass and P content than species that are killed by fire and regenerate from seed (‘seeders’). Seeds contained only small amounts of polyphosphate (between 1.3 and 6 µg g−1 DM), and this was not correlated with P concentration or fire response. Based on the evidence in the present study, we conclude that Banksia species are highly efficient in their use of P, explaining, in part, their success on P-impoverished soils, with little variation between species.Matthew D. Denton, Erik J. Veneklaas, Florian M. Freimoser and Hans Lamber