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Title: Surface electronic structures of the Eu- and Ca-induced so-called Si(111)-(5x1) reconstructions

Abstract

We have investigated the electronic structures of the so-called Eu- and Ca-induced Si(111)-(5x1) surfaces by using angle-resolved photoelectron spectroscopy (ARPES) and low-energy electron diffraction (LEED). The LEED patterns of these surfaces indicate that the periodicities of both surfaces are actually (5x4). In the ARPES study, seven surface states were observed on each (5x4) reconstruction. Of these surface states, the dispersions of five of them show good agreement with those of the Eu- and Ca-induced (3x2) honeycomb-chain-channel (HCC) surfaces and the dispersions of the two other states agree well with those of the Eu- and Ca-induced (2x1) Seiwatz surfaces along the [110] direction--i.e., the direction parallel to the adsorbate chain. Taking the dispersion behavior of these surface states into account, we conclude that the interaction between the nearest-neighbor HCC chain and Seiwatz chain is quite small and that the electronic structure of one chain hardly affects the electronic structure of its neighboring chain. We also discuss the atomic structure of the Eu- and Ca-induced Si(111)-(5x1) reconstructions based on their electronic structures.

Authors:
;  [1]; ; ;  [2]
  1. Graduate School of Science and Technology, Chiba University, Chiba 263-8522 (Japan)
  2. Department of Physics, Chemistry and Biology, Linkoeping University, S-581 83 Linkoeping (Sweden)
Publication Date:
OSTI Identifier:
20853974
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 74; Journal Issue: 23; Other Information: DOI: 10.1103/PhysRevB.74.235311; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CALCIUM; ELECTRON DIFFRACTION; ELECTRONIC STRUCTURE; EUROPIUM; PERIODICITY; PHOTOELECTRON SPECTROSCOPY; SEMICONDUCTOR MATERIALS; SILICON; SURFACES

Citation Formats

Sakamoto, Kazuyuki, Ueno, Nobuo, Eriksson, P. E. J., Pick, A., and Uhrberg, R. I. G.. Surface electronic structures of the Eu- and Ca-induced so-called Si(111)-(5x1) reconstructions. United States: N. p., 2006. Web. doi:10.1103/PHYSREVB.74.235311.
Sakamoto, Kazuyuki, Ueno, Nobuo, Eriksson, P. E. J., Pick, A., & Uhrberg, R. I. G.. Surface electronic structures of the Eu- and Ca-induced so-called Si(111)-(5x1) reconstructions. United States. doi:10.1103/PHYSREVB.74.235311.
Sakamoto, Kazuyuki, Ueno, Nobuo, Eriksson, P. E. J., Pick, A., and Uhrberg, R. I. G.. Fri . "Surface electronic structures of the Eu- and Ca-induced so-called Si(111)-(5x1) reconstructions". United States. doi:10.1103/PHYSREVB.74.235311.
@article{osti_20853974,
title = {Surface electronic structures of the Eu- and Ca-induced so-called Si(111)-(5x1) reconstructions},
author = {Sakamoto, Kazuyuki and Ueno, Nobuo and Eriksson, P. E. J. and Pick, A. and Uhrberg, R. I. G.},
abstractNote = {We have investigated the electronic structures of the so-called Eu- and Ca-induced Si(111)-(5x1) surfaces by using angle-resolved photoelectron spectroscopy (ARPES) and low-energy electron diffraction (LEED). The LEED patterns of these surfaces indicate that the periodicities of both surfaces are actually (5x4). In the ARPES study, seven surface states were observed on each (5x4) reconstruction. Of these surface states, the dispersions of five of them show good agreement with those of the Eu- and Ca-induced (3x2) honeycomb-chain-channel (HCC) surfaces and the dispersions of the two other states agree well with those of the Eu- and Ca-induced (2x1) Seiwatz surfaces along the [110] direction--i.e., the direction parallel to the adsorbate chain. Taking the dispersion behavior of these surface states into account, we conclude that the interaction between the nearest-neighbor HCC chain and Seiwatz chain is quite small and that the electronic structure of one chain hardly affects the electronic structure of its neighboring chain. We also discuss the atomic structure of the Eu- and Ca-induced Si(111)-(5x1) reconstructions based on their electronic structures.},
doi = {10.1103/PHYSREVB.74.235311},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 23,
volume = 74,
place = {United States},
year = {Fri Dec 15 00:00:00 EST 2006},
month = {Fri Dec 15 00:00:00 EST 2006}
}
  • The electronic structures of the Eu/Si(111)-(3x2) and (2x1) surfaces have been investigated by angle-resolved photoelectron spectroscopy. On the (3x2) surface, we identify six surface states in the gap and a pocket of the bulk band projection. Among the five surface states observed in the bulk band gap, the dispersions of three of them agree well with those of the surface states of monovalent atom adsorbed Si(111)-(3x1) surfaces. The dispersions of the two other surface states observed in the band gap agree well with those observed on the Ca/Si(111)-(3x2) surface, which has basically the same structure as that of monovalent atommore » adsorbed Si(111)-(3x1) surfaces. Taking these results into account, we conclude that the five surface states observed in the band gap originate from the orbitals of Si atoms that form a honeycomb-chain-channel structure. In the case of the (2x1) surface, two semiconducting states are observed in the bulk band gap. The difference in binding energy of these two states at the {gamma} point agrees well with that of the surface states obtained theoretically for a clean Si(111)-(2x1) surface with a Seiwatz structure, and the dispersion of the upper state shows good agreement with the corresponding theoretical surface state. These observations indicate that the two surface states in the band gap originate from Si atoms that form a Seiwatz chain. The present results support the structures of the Eu/Si(111)-(3x2) and (2x1) surfaces proposed in the literature.« less
  • The surface structures of the (quasi-)one-dimensional reconstructions induced by the adsorption of Eu on Si(111) have been investigated by low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. Different phases were observed in LEED depending on the Eu coverage. The lowest coverage phase has a (3x2) periodicity, and the highest coverage phase has a (2x1) one. Of the intermediate phases, the LEED pattern of the so-called (5x1) surface indicates that this surface has actually a (5x4) periodicity. The Eu 4f core-level spectra show that the Eu coverages of the (3x2) (5x4), and (2x1) phases are 1/6 monolayer (ML), 0.3 ML,more » and 0.5 ML, respectively, and that the valence state of the adsorbate is 2+ in all these three phases. In the Si 2p core-level spectra, three surface components were observed in both the lowest and highest coverage phases. By considering the energy shift and intensity of each surface component, we conclude that the structure of the (3x2) phase is basically the same as that of the honeycomb-chain-channel model, and that the (2x1) phase is formed by {pi}-bonded Seiwatz Si chains. Regarding the (5x4) phase, two extra Si 2p surface components were observed together with the three components observed in the two end phases. Taking the energy shifts and intensities of the extra surface components into account, we propose a structural model of the (5x4) phase.« less
  • Eu-induced Si(111)3x2, 5x1, and 7x1 reconstructions have been investigated by low-energy electron diffraction (LEED) and high-resolution photoelectron spectroscopy using synchrotron radiation. According to LEED, the 3x2, 5x1, and 7x1 phases can be produced on the dominating area of the Si substrate at the 0.20, 0.40, and 0.45 monolayer (ML), respectively, and no contributions from other phases are found in the LEED patterns at these coverages. The Eu 4f spectra show that the 3x2, 5x1, and 7x1 surfaces are semiconducting, and that the Eu atoms are completely divalent in these reconstructions. Si 2p core-level spectroscopy measurements performed at various photon energiesmore » and emission angles reveal three surface-related components with core-level shifts of -0.51, -0.20, and +0.17 eV with respect to the bulk component for the 3x2 surface. In addition to these components, two other components with shifts of -0.78 eV and +0.28 eV are found for the 5x1 and 7x1 surfaces. These results are discussed in the context of previous studies and structural models reported in the literature. It is shown that the present photoemission data obtained for the 3x2 surface are well consistent with the honeycomb-chain-channel (HCC) model with an adsorbate coverage of 1/6 ML. For the 5x1 and 7x1 surfaces, we propose atomic models which include combinations of honeycomb and {pi}-bonded Seiwatz chains, with adsorbate coverages of 2/5 and 3/7 ML, respectively. Based on the LEED and Si 2p core-level results, a local x2 periodicity is expected for the 5x1 and 7x1 reconstructions, which is in good agreement with the nonmetallic electronic structure of these phases.« less
  • We have used the technique of impact collision ion scattering spectrometry (ICISS) to study the in-plane geometry of both the 7/8 {times} 7/8 and 4{times}1 reconstructions of indium on Si(111). For the 7/8 {times} 7/8 reconstruction the In adatoms are generally thought to lie on either threefold hollow ({ital H}{sub 3}) sites or on fourfold atop ({ital T}{sub 4}) sites. Our ICISS polar-angle scans agree with computer simulations of the {ital T}{sub 4} model. Separations of the In and Si layers have also been determined from our experimental data, in agreement with predictions from total energy calculations. The 4{times}1 reconstructionmore » is known to consist of double rows of adatoms running in {l angle}{bar 1}10{r angle} directions, from scanning tunneling microscopy images. Assuming the top layer adatoms to be indium, we perform ICISS polar-angle scans to determine whether the adatom positions lie in {ital H}{sub 3} or {ital T}{sub 4} sites. Our results show general agreement with the simulations for the {ital H}{sub 3} sites in the 4{times}1 geometry.« less
  • The crystal structure, electronic structure, and photoluminescence properties of Eu{sub x}Si{sub 6-z}Al{sub z-x}O{sub z+x}N{sub 8-z-x} (x=0-0.1, 0<z<1) and Eu{sub x}M{sub y}Si{sub 6-z}Al{sub z-x-y}O{sub z+x+y}N{sub 8-z-x-y} (M=2Li, Mg, Ca, Sr, Ba) have been studied. Single-phase Eu{sub x}Si{sub 6-z}Al{sub z-x}O{sub z+x}N{sub 8-z-x} can be obtained in very narrow ranges of x{<=}0.06 (z=0.15) and z<0.5 (x=0.3), indicating that limited Eu{sup 2+} ions can be incorporated into nitrogen-rich Si{sub 6-z}Al{sub z}O{sub z}N{sub 8-z}. The Eu{sup 2+} ion is found to occupy the 2b site in a hexagonal unit cell (P6{sub 3}/m) and directly connected by six adjacent nitrogen/oxygen atoms ranging 2.4850-2.5089 A. The calculatedmore » host band gaps by the relativistic DV-X{alpha} method are about 5.55 and 5.45 eV (without Eu{sup 2+} 4f5d levels) for x=0 and 0.013 in Eu{sub x}Si{sub 6-z}Al{sub z-x}O{sub z+x}N{sub 8-z-x} (z=0.15), in which the top of the 5d orbitals overlap with the Si-3s3p and N-2p orbitals within the bottom of the conduction band of the host. Eu{sub x}Si{sub 6-z}Al{sub z-x}O{sub z+x}N{sub 8-z-x} shows a strong green emission with a broad Eu{sup 2+} band centered at about 530 nm under UV to near-UV excitation range. The excitation and emission spectra are hardly modified by Eu concentration and dual-doping ions of Li and other alkaline-earth ions with Eu. Higher Eu concentrations can significantly quench the luminescence of Eu{sup 2+} and decrease the thermal quenching temperature. In addition, the emission spectrum can only be slightly tuned to the longer wavelengths ({approx}529-545 nm) by increasing z within the solid solution range of z<0.5. Furthermore, the luminescence intensity of Eu{sub x}Si{sub 6-z}Al{sub z-x}O{sub z+x}N{sub 8-z-x} can be improved by increasing z and the dual-doping of Li and Ba. - Graphical abstract: Excitation and emission spectra of Eu{sub x}Si{sub 6-z}Al{sub z-x}O{sub z+x}N{sub 8-z-x} with the project of a 2x2x2 supercell crystal structure viewed along (001), in which red spheres are the Eu atoms.« less