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  • 1. Demers, LM
    et al.
    Östblom, Mattias
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics .
    Zhang, Hanmin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Jang, NH
    Liedberg, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics .
    Mirkin, CA
    Thermal desorption behavior and binding properties of DNA bases and nucleosides on gold2002In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 124, no 38, p. 11248-11249Article in journal (Refereed)
  • 2. Jemander, S.T.
    et al.
    Lin, N.
    Kern Department, Max-Planck-Institute FKF, 70569, Stuttgart, Germany.
    Zhang, Hanmin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Uhrberg, Roger
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Hansson, Göran
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    STM study of the surface defects of the (v3×v3)-Sn/Si(1 1 1) surface2001In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 475, no 1-3, p. 181-193Article in journal (Refereed)
    Abstract [en]

    The (v3×v3)-Sn/Si(1 1 1) surface has been studied with scanning tunneling microscopy (STM) and Auger electron spectroscopy, and it is found that it contains basically five different types of defects originating from substitutional atoms and vacancies. The influence the defects have on their immediate neighbourhood is investigated and found to extend to the third nearest (v3×v3) adatom neighbour. Close to some defect constellations, a very local (3×3) periodicity in the apparent height in the STM images is found. This periodicity is shown to be a linear superposition of the perturbations generated by the individual defects in the constellations. The superposition of the height modulation is accurate and linear for a wide range of tip biases, as for combinations of different types of defects. Its linearity is explained in terms of small perturbations in the surface electronic structure. We also provide an explanation why the linearity breaks down when large perturbations are probed with small tip biases.

  • 3.
    Jemander, S.T.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Zhang, Hanmin
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Hansson, Göran
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    STM study of the C-induced Si(100)-c(4×4) reconstruction2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, no 11, p. 115321-Article in journal (Refereed)
    Abstract [en]

    We report a direct and reliable way to produce the Si(100)-c(4×4) reconstruction by submonolayer deposition from a SiC source and subsequent annealing. Auger electron spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy (STM) investigations reveal that a C amount equivalent to 0.07 monolayers (ML’s) is sufficient to obtain full coverage of the c(4×4) reconstruction. A deposition of 0.035 ML’s C produces a c(4×4) coverage of only 19%, indicating that C is not only present in the c(4×4) areas, but also in the 2×1 areas. There is not enough C to make it a regular part of the c(4×4) reconstruction and we therefore conclude that the c(4×4) reconstruction is strain induced. We find that a combination of the mixed ad-dimer and buckled ad-dimer models explains all main features observed in the STM images. Images of freshly prepared c(4×4) surfaces exhibit a decoration of approximately 50% of the unit cells, which is attributed to perpendicular ad-dimers. Long exposures (>20 h) to the UHV background gas quench these features and the c(4×4) reconstruction appears as if more homogeneous.

  • 4. Jemander, S.T.
    et al.
    Zhang, Hanmin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Uhrberg, Roger
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Hansson, Göran
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Surface structure of Si(100) with submonolayer coverages of C2002Conference paper (Refereed)
    Abstract [en]

    We report a combined STM, LEED and AES study of Si(100) surfaces prepared by coevaporation from two MBE-sources with Si and SiC, respectively. The flux from the SiC source contains 10% C, enabling studies of deposited layers with C-concentrations in the range 0-10%. After room temperature deposition, the structures have been annealed at 600 °C to generate a c(4 × 4) reconstruction. This has previously been reported to contain from 0.0 to 0.5 monolayers (ML) of C. Annealing at 800 °C irreversibly transforms the c(4 × 4) surface to a 2 × 1-reconstructed surface that contains precipitates of SiC. Since only 0.07 ML of C is needed to have 98% of the surface covered with the c(4 × 4) reconstruction, we conclude that the c(4 × 4) reconstruction is impurity-induced rather than having C-atoms in well defined positions within each unit cell. The c(4 × 4) reconstruction is attributed to a basic structure containing buckled parallel ad-dimers, which in approximately 50% of the reconstructed unit cells is decorated with perpendicular dimers. © 2002 Elsevier Science B.V. All rights reserved.

  • 5.
    Razado Colambo, Ivy
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Zhang, Hanmin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Electronic structure of H/Ge(111)1×1 studied by angle-resolved photoelectron spectroscopy2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, no 19, p. 193403-Article in journal (Refereed)
    Abstract [en]

    The electronic structure of H/Ge(111)1×1 was investigated using angle-resolved photoelectron spectroscopy. Spectra were measured along the high-symmetry lines of the 1×1 surface Brillouin zone. In the Γ̅ −K̅ −M̅ direction, two surface states, labeled a and a, were found in the lower and upper band-gap pockets. The a and a surface states are associated with the Ge-H bonds and the Ge-Ge backbonds, respectively. In the Γ̅ −M̅ direction, only the Ge-H surface state, a, can be identified. It is found in the band-gap pocket around the M̅ point. The two hydrogen-induced surface states on H/Ge(111)1×1 show strong similarities with the corresponding surface states on H/Si(111)1×1. Results from H/Ge(111)1×1 and H/Si(111)1×1 are compared in this Brief Report.

  • 6.
    Razado, Ivy
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    He, Jiangping
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Zhang, Hanmin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Hansson, Göran
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Uhrberg, Roger
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Electronic structure of Ge(111)c(2x8): STM, angle-resolved photoemission, and theory2009In: PHYSICAL REVIEW B, ISSN 1098-0121, Vol. 79, no 20, p. 205410-Article in journal (Refereed)
    Abstract [en]

    The surface electronic structure of Ge(111)c(2x8) was studied by experimental techniques [low-energy electron diffraction, scanning tunneling microscopy (STM), and angle-resolved photoelectron spectroscopy (ARPES)] and theoretical band-structure calculations. Bias-dependent STM images exhibit two different types of adatoms (A(T),A(R)) and rest atoms (R-T,R-R) confirming the presence of asymmetries within the c(2x8) cell. The ARPES study resulted in a more detailed picture of the surface electronic structure of the Ge(111)c(2x8) surface compared to earlier studies. The energy dispersion curves showed the presence of seven surface bands labeled A1, A2, A2(), A3, A4, A4(), and A5. The experimental surface bands were compared to the calculated band structure of the full c(2x8) unit cell. The most important results are (i) we have identified a split surface-state band in the photoemission data that matches a split between R-T and R-R derived rest atom bands in the calculated surface band structure. This allows us to identify the upper A2 band with the R-R and the lower A2() band with the R-T rest atoms. (ii) The uppermost highly dispersive band (A1) originates from states below the adatom and rest atom layers and should not be confused with rest atom bands A2 and A2(). (iii) The bias-dependent changes in the adatom/rest atom contrast in the experimental STM images were closely reproduced by simulated STM images generated from the calculated electronic structure. (iv) A split was observed in the back-bond derived surface band at higher emission angles (A4 and A4()).

  • 7.
    Razado-Colambo, Ivy
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Zhang, Hanmin M.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Hansson, Göran
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Uhrberg, Roger
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Hydrogen-induced metallization on Ge(1 1 1) c(2 × 8)2006In: Applied Surface Science, ISSN 0169-4332, Vol. 252, no 15, p. 5300-5303Article in journal (Refereed)
    Abstract [en]

    We have studied hydrogen adsorption on the Ge(1 1 1) c(2 × 8) surface using scanning tunneling microscopy (STM) and angle-resolved photoelectron spectroscopy (ARPES). We find that atomic hydrogen preferentially adsorbs on rest atom sites. The neighbouring adatoms appear higher in STM images, which clearly indicates a charge transfer from the rest atom states to the adatom states. The surface states near the Fermi-level have been followed by ARPES as function of H exposure. Initially, there is strong emission from the rest atom states but no emission at the Fermi-level which confirms the semiconducting character of the c(2 × 8) surface. With increasing H exposure a structure develops in the close vicinity of the Fermi-level. The energy position clearly indicates a metallic character of the H-adsorbed surface. Since the only change in the STM images is the increased brightness of the adatoms neighbouring a H-terminated rest atom, we identify the emission at the Fermi-level with these adatom states.

  • 8.
    Razado-Colambo, Ivy
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Zhang, Hanmin M.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Uhrberg, Roger
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Electronic structure of H/Ge(111)1x1 studied by angle-resolved photoelectron spectroscopyManuscript (Other academic)
    Abstract [en]

    The electronic structure of H/Ge(111)1x1 was investigated using angleresolved photoelectron spectroscopy (ARPES). Spectra were measured along the high symmetry lines of the 1x1 surface Brillouin zone (SBZ). In the Γ − Κ −M direction, two surface states, labelled a and a’, were found in the lower and upper band gap pockets. The a and a’ surface states are associated with the Ge-H bonds and the Ge- Ge backbonds, respectively. In the Γ − Μ direction, only the Ge-H surface state, a, can be identified. It is found in the band gap pocket around the Μ -point. The two hydrogen induced surface states on H/Ge(111)1x1 show strong similarities with the corresponding surface states on H/Si(111)1x1. Results from H/Ge(111)1x1 and H/Si(111)1x1 are compared in the paper.

  • 9.
    Razado-Colambo, Ivy
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Zhang, Hanmin M.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Uhrberg, Roger I. G.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Hansson, Göran V.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    STM study of site selective hydrogen adsorption on Si(111) 7×72005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 71, no 23, p. 235411-Article in journal (Refereed)
    Abstract [en]

    Adsorption of atomic hydrogen has been studied by scanning tunneling microscopy (STM) and photoelectron spectroscopy with a focus on the different adsorption sites provided by the Si(111) 7×7 surface. At low temperature, the hydrogen atoms adsorb preferentially on adatoms while at elevated temperatures the rest atoms are the first to become hydrogen terminated. The hydrogen-terminated rest atoms are no longer visible in the STM images and the surrounding adatoms appear brighter compared to the clean 7×7 surface. This indicates that there is a local charge transfer back to the adatoms from the rest atoms. Three kinds of modified triangular subunit cells of the 7×7 reconstruction have been identified corresponding to one, two, and three hydrogen-terminated rest atoms, respectively. A detailed study of the apparent height using STM line profiles through the adatom and rest atom positions on the surface is presented. These line profiles show a characteristic and reproducible variation of the apparent heights of the adatoms for the different kinds of triangular subunit cells and the changes are interpreted in terms of charge transfer. The very local nature of the charge transfer is concluded from the fact that only the hydrogen termination of neighboring rest atoms is significantly affecting the apparent height of an adatom.

  • 10.
    Sakamoto, K.
    et al.
    Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522, Japan.
    Takeyama, W.
    Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.
    Zhang, Hanmin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Uhrberg, Roger
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    High-resolution core-level study of the Ca/Si(1 1 1)-(2×1) surface2003In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 428, no 1-2, p. 115-118Article in journal (Refereed)
    Abstract [en]

    We have investigated the geometric structure of the Ca/Si(1 1 1)-(2×1) surface using low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. A clear (2×1) periodicity was observed in LEED after annealing the (7×1) phase formed at room temperature in LEED. In the Si 2p core-level spectra, three surface components were observed. By considering the energy shift and intensity of each surface component and the Ca 3p core-levels of the two phases, we regard the (2×1) phase to be formed by p-bonded Seiwatz Si chains with a Ca coverage of 0.5 ML. © 2002 Elsevier Science B.V. All rights reserved.

  • 11.
    Sakamoto, K.
    et al.
    Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522, Japen.
    Takeyama, W.
    Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.
    Zhang, Hanmin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Uhrberg, Roger
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    High-resolution Si2p core-level and low-energy electron diffraction studies of the Ca/Si(1 1 1)-(3 × 2) surface2003In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 532-535, p. 628-632Article in journal (Refereed)
    Abstract [en]

    We have investigated the surface structure of the Ca/Si(1 1 1)-(3 × 2) surface using low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. Weak ×2 streaks were observed in LEED at 300 K. After cooling the sample to 100 K, ×2 spots, which originate from both (3 × 2) and c(6 × 2) periodicities, appeared. By considering the energy shift and intensity of each surface component observed in the Si2p core-level spectra, we conclude that the structure of the (3 × 2) surface is basically the same as that of the honeycomb-chain-channel model with a Ca coverage of 1/6 ML. Further, we propose that the weak ×2 streaks at 300 K result from thermally induced disorder. © 2003 Elsevier Science B.V. All rights reserved.

  • 12. Sakamoto, K.
    et al.
    Zhang, Hanmin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Uhrberg, Roger
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    High-resolution Si 2p core-level study of the K/Si(111)-(3×1) surface2002Conference paper (Refereed)
    Abstract [en]

    The structure of the K/Si(111)-(3 × 1) surface was studied by high-resolution core-level photoelectron spectroscopy. Five surface components were observed in the Si 2p core-level spectra. Compared to the bulk component, three components are shifted to lower and two to higher binding energies. The two components with the lowest binding energies are assigned to the top-layer Si atoms bonded to the K atoms with different configurations. The component with highest binding energy has a contribution from the p-bonded Si atoms of the top layer. The two other components originate from the Si atoms of the second and third layers.

  • 13.
    Sakamoto, K.
    et al.
    Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.
    Zhang, Hanmin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Uhrberg, Roger
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Initial oxidation process of an Si(111)-(7 × 7) surface studied by photoelectron spectroscopy2004In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 464-465, p. 10-13Article in journal (Refereed)
    Abstract [en]

    We have investigated the initial oxidation stage of an Si(111)-(7 × 7) surface using valence-band photoemission measurements. As the oxygen exposure increases, the intensities of the dangling bond states of adatoms (S 1) and rest atoms (S2) decrease. Among the four oxygen-induced states, three originate from the orbitals of adsorbed oxygen species, and one originates from the dangling bonds of adatoms with more than one oxygen atom adsorbed into its back-bond. Taking the dosage-dependent intensity of this modified dangling bond state into account, we conclude that the first adsorption site of oxygen is the back-bond of an adatom. © 2004 Elsevier B.V. All rights reserved.

  • 14.
    Sakamoto, Kazuyuki
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ashima, Hidenori
    Department of Physics, Graduate School of Science, Tohoku University, Japan .
    Zhang, Hanmin
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Identification of the basic structure of the Ag/Si(111)-(6×1) surface: Observation of a low-temperature c(12×2) phase2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, no 4, p. 045305-Article in journal (Refereed)
    Abstract [en]

    The surface structure of the so-called Ag/Si(111)-(6×1) surface is studied by low-energy electron diffraction (LEED), high-resolution core-level photoelectron spectroscopy, and angle-resolved photoelectron spectroscopy. A c(12×2) phase is observed in LEED after cooling the room-temperature (6×1) phase to 100 K. In the Si 2p core-level spectra, no significant difference is observed between the two surfaces. In the valence-band spectra, five surface states are observed on both the (6×1) and c(12×2) surfaces. None of these surface states crosses the Fermi level. The binding energies and dispersions of the surface states observed on the (6×1) surface are quite similar to those of the c(12×2) surface. These results indicate that the basic structure of this Ag/Si(111) surface has a c(12×2) periodicity, and that the (6×1) structure results from thermal vibrations of the surface atoms. Moreover, we assign two of the surface states to bonding states between Ag and Si atoms, and one of them to a π-bond state.

  • 15.
    Sakamoto, Kazuyuki
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Matsui, Fumihiko
    Graduate School of Material Science, Nara Institute of Science and Technology, Japan.
    Hirano, Masumi
    Department of Physics, Graduate School of Science, Tohoku University, Japan.
    Yeom, Han Woong
    Atomic-Scale Surface Science Research Center and Institute of Physics and Applied Physics, Yonsei University, Seoul, Korea.
    Zhang, Hanmin
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Determination of the bonding configuration of the metastable molecular oxygen adsorbed on a Si(111)-(7×7) surface2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, no 20Article in journal (Refereed)
    Abstract [en]

    The initial adsorption stage of oxygen on a Si(111)-(7×7) surface has been investigated using real time high-resolution core-level measurements at 100 K. Among the six O 1s components observed on an O2 exposed Si(111) surface, the three components, whose intensities saturate at the same dosage, have the same lifetime. These results lead to a conclusion that three oxygen atoms with different chemical environments compose the metastable species. Based on a comparison with our calculated O 1s binding energies, we have determined the bonding configuration of the metastable oxygen.

  • 16.
    Sakamoto, Kazuyuki
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Takeyama, Wakabe
    Department of Physics, Graduate School of Science, Tohoku University, Japan.
    Zhang, Hanmin
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Structural investigation of Ca/Si(111) surfaces2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 16Article in journal (Refereed)
    Abstract [en]

    The surface structures of different Ca/Si(111) surfaces were studied by low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. Five different phases were observed in LEED depending on the Ca coverage. The lowest coverage phase has both (3×2) and c(6×2) periodicities, and the highest coverage phase has a (2×1) periodicity. The LEED patterns of the three intermediate phases were (5×2), (7×1), and (9×1). In the Si 2p core-level spectra, three surface components were observed in both the lowest and highest coverage phases. These three surface components were also observed in each intermediate phase together with two other components. The presence of the two extra components indicates that the intermediate phases are not completely described by simple combinations of the two end phases as suggested in the literature. By considering the energy shift and intensity of each surface component, we conclude that the structure of the (3×2) phase is basically the same as that of the honeycomb-chain-channel model with a Ca coverage of 1/6 ML, and the (2×1) phase is formed by π-bonded Seiwatz Si chains with a coverage of 0.5 ML. Moreover, taking the energy shifts and intensities of the extra surface components into account, we propose a structural model of the (5×2) phase, whose Ca coverage is 0.3 ML.

  • 17.
    Sakamoto, Kazuyuki
    et al.
    Department of Physics, Graduate School of Science, Tohoku University, Japan.
    Zhang, Hanmin
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Adsorption and reaction processes of physisorbed molecular oxygen on Si(111)-(7×7)2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 7, p. 075346-Article in journal (Refereed)
    Abstract [en]

    The adsorption and reaction processes of physisorbed oxygen molecules on a Si(111)-(7×7) surface have been investigated using time-resolved O 1s core-level photoemission measurements at 45 K. Physisorbed oxygen molecules are only observed at 45 K and lower temperatures on a Si(111)-(7×7) surface. At the dosage when the dangling bonds are saturated by chemisorbed oxygen, the coverage of the physisorbed species increases drastically. This result indicates that oxygen species, which are chemisorbed on top of adatoms, modifies the potential energy curve for an oxygen molecule approaching the surface such that physisorbed oxygen molecules are stabilized. Further, the longer lifetime at a higher dosage indicates that an intermolecular force plays a role for the stabilization of this species. Taking these results into account, an oxidation stage-dependent gas-surface interaction for an oxygen molecule approaching the Si(111) surface is suggested.

  • 18.
    Sakamoto, Kazuyuki
    et al.
    Graduate School of Advanced Integration Science, Chiba University, Japan.
    Zhang, Hanmin
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Band structure of the Ca/Si(111)-(2×1) surface2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, no 24, p. 245316-Article in journal (Refereed)
    Abstract [en]

    We have investigated the electronic structure of the Ca/Si(111)-(2×1) surface using angle-resolved photoelectron spectroscopy. Two semiconducting surface states were clearly observed in the bulk band gap, and one was found in a pocket of the bulk band projection. Qualitatively, the dispersions of the two surface states observed in the band gap agree well with theoretical dispersions for a clean Si(111)-(2×1) surface with the Seiwatz structure. Taking this result into account, we conclude that the two surface states in the band gap originate from orbitals of Si atoms that form a Seiwatz structure, and that two electrons are donated from Ca to Si per (2×1) unit cell. This conclusion supports the structure of the Ca/Si(111)-(2×1) surface proposed in the literature.

  • 19.
    Sakamoto, Kazuyuki
    et al.
    Department of Physics, Graduate School of Science, Tohoku University, Japan.
    Zhang, Hanmin
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Electronic structure of the Ca/Si(111)-(3×2) surface2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, no 12, p. 1253211-1253217Article in journal (Refereed)
    Abstract [en]

    The electronic structure of the Ca/Si(111)-(3×2) surface has been investigated by angle-resolved photoelectron spectroscopy. Five surface states, none of which crosses the Fermi level, were observed in the bulk band gap, and one surface state was observed in a bulk band pocket. The dispersion features of three of the surface states in the band gap agree well with results from monovalent atom adsorbed Si(111)-(3×1) surfaces along the chain direction. The close resemblance indicates that the origins of the surface states are the same as or quite similar to those of the (3×1) surface. The two other states observed in the band gap have not been reported in the literature, and they are interpreted as surface states that occur on Ca/Si(111)-(3×2) due to the lower coverage (1/6 monolayer of Ca). Further, based on the finite surface state dispersion in the direction perpendicular to the Ca chains, we conclude that the electronic character of this surface is not completely one dimensional.

  • 20.
    Sakamoto, Kazuyuki
    et al.
    Graduate School of Advanced Integration Science, Chiba University, Japan.
    Zhang, Hanmin
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Observation of two metastable oxygen species adsorbed on a Si(111)-(7×7) surface: Reinterpretation of the initial oxidation process2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, no 7, p. 075302-Article in journal (Refereed)
    Abstract [en]

    Using high-resolution core-level photoemission measurements, we show that two different metastable species exist on a Si(111)-(7×7) surface, instead of only one as suggested in the literature. One metastable species has a finite lifetime and is composed of both molecular and atomic oxygen. The other one, which is formed by atomic oxygen only, is stable in terms of time at 300 and 100 K but disappears after annealing at 600 K. The present study reconciles the inconsistent former results and provides a detailed atomic-level understanding of the complex initial oxidation process of this surface.

  • 21.
    Sakamoto, Kazuyuki
    et al.
    Department of Physics, Graduate School of Science, Tohoku University, Japan.
    Zhang, Hanmin
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Photoemission study of metastable oxygen adsorbed on a Si(111)-(7×7) surface2004In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 70, no 3, p. 035301-Article in journal (Refereed)
    Abstract [en]

    We have investigated the metastable oxygen species adsorbed on a Si(111)-(7×7) surface at room temperature using real time valence-band and core-level photoemission measurements. The dosage- and time-dependent changes in the intensity of the metastable 3.8 eV peak observed in the valence-band spectra were different from those of the metastable O 1s components. Further, although no metastable O 1s components were observed in the core-level measurement after annealing the sample at 600 K, the 3.8 eV peak was still observed. These results indicate that both the stable and the metastable oxygen species produce the 3.8 eV valence-band peak, and we therefore conclude that the contradicting lifetimes reported in the literature result from a misinterpretation of the 3.8 eV peak.

  • 22.
    Takeyama, W
    et al.
    Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.
    Sakamoto, K
    Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522, Japan.
    Zhang, Hanmin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Uhrberg, Roger
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Structural investigation of the so-called Ca/Si(111)-(5 x 1) surface2003In: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 42, no 7B, p. 4663-4666Article in journal (Refereed)
    Abstract [en]

    We have investigated the geometric, structure of the so-called Ca/Si(111)-(5 x 1) surface using low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. In LEED, dim extra spots besides the x 5 spots were observed after cooling the sample to 100 K. The positions of these dim spots reveal that this phase has a x 2 periodicity along its one-dimensional (ID) chains. In Si 2p core-level spectra, we observed five surface components. By considering the energy shift and intensity of each surface component and the 0.3ML Ca coverage, we propose a structural model of this surface.

  • 23.
    Uhrberg, Roger
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Zhang, Hanmin
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    High-resolution photoemission studies of adsorbates and overlayers on semiconductor surfaces2004In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 137, p. 205-210Article in journal (Refereed)
    Abstract [en]

    High-resolution photoemission provides important information about the electronic and atomic structure of surfaces. To make full use of the high-energy resolution that is available at many synchrotron radiation facilities, it is important to lower the phonon induced broadening by reducing the sample temperature. Another equally important factor is the sample quality. Sample inhomogeneities may have a significant detrimental effect on the line widths of the core-levels masking essential information. The surfaces discussed in this paper include Si(111)7 x 7, Si(111)1 x 1:As and Si(111)root3 x root3:Ag. The Si(111)root3 x root3:Ag surface is a good example of the importance of the sample preparation and characterization. A tiny amount of additional Ag atoms on top of the root3 x root3 layer leads to a significant broadening of the apparent core-level widths. (C) 2004 Elsevier B.V. All rights reserved.

  • 24.
    Uhrberg, Roger
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Zhang, Hanmin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Balasubramanian, T.
    Maxlab, Lund University, Box 118, S-221 00 Lund, Sweden.
    Determination of the Sn 4d line shape of the Sn/Ge(111) v3 × v3 and 3 × 3 surfaces2000In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 85, no 5, p. 1036-1039Article in journal (Refereed)
    Abstract [en]

    In this study, low energy electron diffraction (LEED), valence band, and core-level photoemission were used to establish the correct Sn 4d line shape of both the v3 × v3 and 3 × 3 phases of Sn/Ge(111). It was found that the Sn 4d and valence band spectra of these phases are similar.

  • 25.
    Uhrberg, Roger
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Zhang, Hanmin
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Balasubramanian, T.
    Maxlab, Lund University, Lund, Sweden.
    Jemander, S.T.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Lin, N.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Hansson, Göran
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Electronic structure of Sn/Si(111) √3×√3: Indications of a low-temperature phase2000In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 62, no 12, p. 8082-8086Article in journal (Refereed)
    Abstract [en]

    The Sn/Si(111) √3×√3 surface has been studied by photoelectron spectroscopy, low-energy electron diffraction (LEED), and scanning tunneling microscopy. Unlike Sn/Ge(111), the Sn/Si(111) surface shows a √3×√3 LEED pattern at low temperature also (70 K). The electronic structure, however, is inconsistent with a pure √3×√3 phase. Sn 4d spectra exhibit two major components and the valence band shows two surface bands. These features have been associated with the low-temperature 3×3 phase in the case of Sn/Ge(111). The similarity in the electronic structure points to stabilization of a low-temperature phase for Sn/Si(111) also, but at a significantly lower temperature (<70 K).

  • 26.
    Uhrberg, Roger
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Zhang, Hanmin
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Balasubramanian, T
    MAX-Lab, Lund University, Sweden.
    Landemark, E
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Yeom, HW
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Photoelectron spectroscopy study of Ag/Si(111)√3×√3 and the effect of additional Ag adatoms2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, no 8, p. 081305(R)-Article in journal (Refereed)
    Abstract [en]

    High-resolution core-level spectroscopy has been applied to the Ag/Si(111)√3×√3 surface. The Si 2p line shape is found to depend critically on the presence of additional Ag adatoms on the surface. A significant broadening caused by the surplus of Ag atoms could be eliminated by careful annealing. The resulting Si 2p spectra are significantly sharper than any published data for this or other Si based surface systems. Two major surface components are identified for the √3×√3 surface, which find a natural explanation in terms of the honeycomb-chained-trimer model. A small but characteristic contribution to the Si 2p spectrum of the Ag/√3×√3 surface is tentatively assigned to defects.

  • 27.
    Yeom, H. W.
    et al.
    Atomic-scale Surface Science Research Center and Institute of Physics and Applied Physics, Yonsei University, bKorea.
    Horikoshi, K
    Department of Physics, The University of Tokyo, Japan.
    Zhang, Hanmin
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ono, K
    Department of Applied Chemistry, The University of Tokyo, Japan .
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Nature of the broken-symmetry phase of the one-dimensional metallic In/Si(111) surface2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, no 24Article in journal (Refereed)
    Abstract [en]

    The phase transition of a metallic In chain structure on Si(111) was investigated by high-resolution photoemission. Core-level spectra clearly elucidate that the symmetry breaking at low temperature occurs only within the inner parts of the In chains. In the valence bands, the transition is accompanied by the formation of pseudogaps of 80–150 meV and the band backfolding with only marginal changes of the band dispersion. No sign of Luttinger liquid behavior is observed in the spectral function near the Fermi level. This result is generally consistent with the idea of a fluctuating one-dimensional charge-density wave state but conflicting with the present structure model for the low-temperature phase.

  • 28.
    Zhang, Hanmin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Balasubramanian, T
    MAX-lab, Lund University, Sweden.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Core-level photoelectron spectroscopy study of the Au/Si(111) 5×2, α-√3×√3, β-√3×√3, and 6×6 surfaces2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, no 3Article in journal (Refereed)
    Abstract [en]

    Submonolayer coverages of Au on Si(111), known as the 5×2, α-√3×√3, β-√3×√3, 2√21×2√21, and 6×6 surfaces, have been investigated by low-energy electron diffraction and photoelectron spectroscopy. Three Si 2p surface components on the 5×2 surface, and four surface components on the α-√3×√3, quenched β-√3×√3, and 6×6 surfaces have been identified by surface sensitive high resolution core-level spectroscopy. The photoemission data of the α-√3×√3, the 6×6 and the quenched β-√3×√3 phases are discussed in terms of extra Au adatoms on the √3×√3 surface described by the ideal 1 ML conjugate honeycomb chained trimer model. The similarity between the 6×6 and the quenched β-√3×√3 surface is obvious from the decomposition of the Si 2p spectra, suggesting an order-disorder relation.

  • 29.
    Zhang, Hanmin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Balasubramanian, T
    Max-lab, Lund University, Lund, Sweden.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Metal to semiconductor transition on Ag/Ge(111): Surface electronic structure of the √3×√3, √39×√39, and 6×6 surfaces2001In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 63, no 19, p. 195402-Article in journal (Refereed)
    Abstract [en]

    The √3×√3, √39×√39, and 6×6 phases of Ag/Ge(111) have been studied by angle-resolved photoemission and low-energy electron diffraction. The √3×√3 surface, formed at a one-monolayer (ML) Ag coverage, shows a metallic behavior with two partially occupied surface bands resulting from a tiny amount of extra Ag atoms on the surface. The √3×√3 surface transforms into a √39×√39 periodicity, below ∼250 K, when a small amount of Ag is added to the surface. The presence of the additional Ag atoms leads to an increased filling of two partially occupied surface bands. By depositing ∼0.2 ML of Ag on the √3×√3 surface, it transforms into a 6×6 periodicity. We observe an interesting transition from the metallic √3×√3 and √39×√39 phases to a semiconducting phase for the 6×6 surface, with a gap of around 0.2 eV with respect to the Fermi level. On the 6×6 surface, the lower band of the partially occupied surface bands is pulled down entirely below the Fermi level while the upper band is missing in the photoemission spectra. These changes result in the observed band gap.

  • 30.
    Zhang, Hanmin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Balasubramanian, T
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Univ Lund, Max Lab, S-22100 Lund, Sweden.
    Uhrberg, Roger
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Surface electronic structure of the root 3x root 3, root 39x root 39 and 6x6 surfaces of Ag/Ge(111): observation of a metal to semiconductor transition2001In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 175, p. 237-242Article in journal (Refereed)
    Abstract [en]

    Deposition of 1 monolayer (ML) of Ag on the clean Ge(1 1 1) surface, followed by annealing at 300 degreesC for 2 min, results in a sharp root3 x root3 low-energy electron diffraction (LEED) pattern. This surface transforms into a root 39 x root 39 surface, as observed by LEED, due to a tiny amount of additional Ag atoms when the temperature is below approximately -20 degreesC. The presence of the additional Ag leads to an increased filling of two partially occupied surface bands. By depositing approximately 0.2 ML of Ag on the root3 x root3 surface, it transforms into a 6 x 6 periodicity. The addition of Ag leads to an interesting transition from the metallic surfaces (root3 x root3 and root 39 x root 39) to the semiconducting 6 x 6 surface with a gap of around 0.2 eV with respect to the Fermi-level. On the 6 x 6 phase, the lower one of the partially occupied surface bands of the root3 x root3 and root 39 x root 39 surfaces seems to be entirely pulled down below the Fermi-level, while the upper one is missing. The electronic structures of the different Ag/Ge(111) surfaces an also discussed in comparison with the Ag/Si(111) surfaces. (C) 2001 Elsevier Science B.V. All rights reserved.

  • 31.
    Zhang, Hanmin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Balasubramanian, T
    MAX-lab, Lund University, Sweden.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Surface electronic structure study of Au/Si(111) reconstructions: Observation of a crystal-to-glass transition2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 16Article in journal (Refereed)
    Abstract [en]

    The α-√3×√3, β-√3×√3, and 6×6 surfaces of Au/Si(111) have been studied by angle-resolved photoelectron spectroscopy (ARPES). The α-√3×√3 surface shows four surface state bands, one of which is a dispersing metallic band. Except for one nondispersing band near the Fermi level, the β-√3×√3 surface shows surface bands that are similar to those of α-√3×√3. Eight surface state bands have been found on the 6×6 surface instead of two as reported in the literature. Seven of these surface states are broadened into three, when the 6×6 phase is transformed into the quenched β-√3×√3 phase just by annealing followed by quick cooling. The transition between the 6×6 and quenched β-√3×√3 phases is consistent with a crystal-glass transition.

  • 32.
    Zhang, Hanmin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Jemander, S.T.
    Lin, N.
    Hansson, Göran
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Uhrberg, Roger
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Origin of 3 × 3 diffraction on the Sn1-xSix/Si(1 1 1) v3 × v3 surface2003In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 531, no 1, p. 21-28Article in journal (Refereed)
    Abstract [en]

    An evolution of an apparent 3 × 3 low-energy electron diffraction (LEED) pattern has been observed for the Sn1-xSix/Si(1 1 1) v3 × v3 surface alloy. The origin of this additional diffraction has been investigated in detail by scanning tunneling microscopy (STM). The 3 × 3 diffraction, which appears after annealing, is associated with the arrangement of the Sn and substitutional Si atoms in the surface layer, forming many local structures such as honeycombs, hexagons, and atomic lines. As revealed by Fourier-transforms of the STM-images, these local structures are the origins of the 3 × 3 diffraction and a weak 23×3 streaky background superposed on the 3 × 3 LEED pattern. © 2003 Elsevier Science B.V. All rights reserved.

  • 33.
    Zhang, Hanmin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Sakamoto, K.
    Graduate School of Advanced Integration Science, Chiba University, Japan.
    Hansson, Göran
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    High-temperature annealing and surface photovoltage shifts on Si(111)7×72008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 3, p. 035318-Article in journal (Refereed)
    Abstract [en]

    The relation between annealing temperature and surface photovoltage (SPV) shifts on the Si(111)7×7 surface of lightly n-doped substrates has been studied by core-level and valence-band photoelectron spectroscopies at 100 K. The SPV shift was found to depend strongly on the annealing temperature and the photon flux. Between 900 and 1150 °C the magnitude of the SPV shift shows a general decrease with annealing temperature. After a narrow plateau, the SPV shift becomes positive for annealings at 1250 and 1270 °C. As a consequence, the adatom surface state of the 7×7 surface appears above the Fermi level. The unexpected SPV shift can be explained by the formation of a p-type layer during high-temperature annealing of the Si sample. The role of boron and carbon contaminations has been discussed in this context in the literature. By correlating the SPV shifts with the C 1s and B 1s core-level signals, we conclude that carbon, but not boron, is involved in the formation of the p-type layer. Further, our results show that the annealing temperature plays a crucial role when binding energies are determined from photoemission spectra at low temperature. The effect is of particular importance in the study of surface band-gap openings related to phase transitions at low temperature.

  • 34.
    Zhang, Hanmin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Sakamoto, K
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Semiconductor-metal-semiconductor transition: valence band photoemission study of Ag/Si(111) surfaces2002In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 190, no 1-4, p. 103-107Article in journal (Refereed)
    Abstract [en]

    The root3 x root3, root21 x root21 and 6 x 6 phases of Ag/Si(111) have been studied by angle-resolved photoemission and low-energy electron diffraction. The Ag/Si(111) root3 x root3 surface has an intrinsic semiconducting character with two fully occupied, dispersing surface state bands. We find that only one of the additional surface bands on the root21 x root21 surface is metallic in contrast to the two metallic bands discussed in the literature. On the 6 x 6 surface, the partially occupied surface band of the root21 x root21 surface seems to be absent, resulting in a gap of about 0.2 eV with respect to the Fermi-level. (C) 2002 Elsevier Science B.V. All rights reserved.

  • 35.
    Zhang, Hanmin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Sakamoto, K.
    Graduate School of Advanced Integration Science, Chiba University, Chiba 266-8522, Japan.
    Uhrberg, Roger
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Surface electronic structures of Au-induced reconstructions on the Ag/Ge(1 1 1) v3 × v3 surface2003In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 532-535, p. 934-939Article in journal (Refereed)
    Abstract [en]

    A small amount of Au atoms deposited at room temperature transforms the Ag/Ge(1 1 1)v3 × v3 surface into a v 39 × v39 surface. The presence of the Au atoms leads to downward shifts and modifications of the surface state bands compared to the initial v3 × v3 surface. Further deposition of Au on the v39 × v39 surface changes it into a 6 × 6 periodicity. At the same time the surface electronic structure changes from a metallic to a semiconducting phase with a gap of around 0.2 eV with respect to the Fermi-level. Finally, the 6 × 6 phase transforms into a new 2v3 × 2v3 phase when more Au is added, and the surface switches back to a metallic state. © 2003 Elsevier Science B.V. All rights reserved.

  • 36.
    Zhang, Hanmin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Sakamoto, Kazuyuki
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Comprehensive study of the metal/semiconductor character of adatom-induced Ag/Si(111) reconstructions2001In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 64, no 24Article in journal (Refereed)
    Abstract [en]

    A √21×√21 reconstruction can be formed by either Ag or Au adsorption on the Ag/Si(111) √3×√3 surface. The electronic structures determined by angle-resolved photoemission from these two √21×√21 surfaces show clear similarities. The presence of the extra Ag or Au adatoms results in a metallic surface with two surface state bands near the Fermi level. Only one of these bands crosses the Fermi level instead of two as reported in the literature. A tiny amount of Ag deposited onto the √21×√21-Ag surface below 100 K transforms it into a 6×6 periodicity. The additional Ag leads to an interesting transition from the metallic √21×√21 surface to a semiconducting 6×6 surface with a gap of about 0.2 eV with respect to the Fermi level.

  • 37.
    Zhang, Hanmin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Sakamoto, Kazuyuki
    Department of Physics, Graduate School of Science, Tohoku University, Japan.
    Uhrberg, Roger I.G.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Surface electronic structure of K- and Cs-induced √21×√21 phases on Ag∕Si(111)√3×√32004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 24, p. 245301-Article in journal (Refereed)
    Abstract [en]

    A √21×√21 reconstruction has been formed by adding either K or Cs atoms on the Ag∕Si(111)√3×√3 surface at 120 K. The electronic structures of these surfaces have been studied by angle-resolved valence band and core-level spectroscopy. In similarity with Ag or Au adatoms, the presence of K or Cs adatoms on Ag∕Si(111)√3×√3 results in a metallic √21×√21 surface. The formation of two surface bands near the Fermi level can be explained by band folding of a partially occupied surface band originating from the underlying Ag∕Si(111)√3×√3 surface. A detailed analysis of the Si 2p core-level spectra of the above surfaces is presented and compared to the Ag∕Si(111)√3×√3 surface. In the case of Ag∕Si(111)√3×√3, we find that the metallic tail of the Si 2p spectra is related to extra Ag. Both the valence band and the Si 2p spectra of the Ag∕Si(111)√3×√3 surface show that the surface is semiconducting after annealing at ∼600°C.

  • 38.
    Zhang, Hanmin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Ag∕Si(111)√3×√3: Surface band splitting and the inequivalent triangle model2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 19, p. 195329-Article in journal (Refereed)
    Abstract [en]

    The atomic and electronic structures of the Ag∕Si(111)√3×√3 surface are currently under debate. By employing angle-resolved valence-band spectroscopy, the surface band dispersions around the K̅ point of the Ag∕Si(111)√3×√3 surface have been investigated in detail. Contrary to a recent study, we conclude that the S2 and S3 surface state bands do not show any detectable split at 100 K. Thus, photoemission spectra at both room temperature and 100 K show only a single peak at the K̅ point without any direct evidence of a split. Calculated band structures for the inequivalent triangle (IET) model show a gap at the K̅ point in contrast to the honeycomb-chain-trimer (HCT) model. We find, however, that there is no real contradiction between our photoemission data and the IET model provided the energy gap of the latter model is small as indicated by a recent calculation [ Phys. Rev. B 70 245431 (2004)].

  • 39.
    Zhang, Hanmin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Uhrberg, Roger
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Atomic structures of Ag/Ge(1 1 1) v39 × v39 and 6 × 6 surfaces studied by STM: Observations of bias dependent reconstruction transformations2003In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 212-213, no SPEC., p. 353-359Article in journal (Refereed)
    Abstract [en]

    The 6 × 6 and v39 × v39 phases on Ag/Ge(1 1 1) have been studied by scanning tunneling microscopy (STM). Four types of 6 × 6 configurations are found which all consist of a v3 × v3 layer with six extra Ag adatoms per 6 × 6 unit cell. These reconstructions show either mirrored or complementary relations. We observe interesting transitions between the different 6 × 6 reconstructions. The v39 × v39 surface appears to have five extra Ag atoms per unit cell. By using various tip biases, we show that the v39 × v39 domain orientation can be changed. Surface structure models of the v39 × v39 and 6 × 6 phases are proposed based on the HCT structure of the underlying v3 × v3 surface. © 2003 Elsevier Science B.V. All rights reserved.

  • 40.
    Zhang, Hanmin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Uhrberg, Roger
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics.
    Scanning tunneling microscopy study of Ag/Ge(1 1 1): Observation of surface reconstruction transformations2003In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 546, no 2-3, p. L789-L796Article in journal (Refereed)
    Abstract [en]

    The 6×6 and v39×v39 phases of Ag/Ge(1 1 1) have been studied by scanning tunneling microscopy (STM). Surface atomic structures of the 6×6 and the v39×v39 phase are proposed in terms of additional Ag adatoms on top of a v3×v3 layer described by the honeycomb-chain-trimer (HCT) model. By varying the STM tip bias, the reconstruction can be changed reversibly between the v39×v39 and the 6×6 phase. Besides the switching between two different phases, it is also possible to flip the domain orientation of the v39×v39 phase. The mechanisms of the reconstruction transformation have been discussed in terms of the role of the STM tip. © 2003 Elsevier B.V. All rights reserved.

1 - 40 of 40
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