| 1. |
- Annese, Emilia, et al.
(author)
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Nonvortical Rashba Spin Structure on a Surface with C1h Symmetry
- 2016
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In: Physical Review Letters. - 0031-9007. ; 117:1
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Journal article (peer-reviewed)abstract
- A totally anisotropic peculiar Rashba-Bychkov (RB) splitting of electronic bands was found on the Tl/Si(110)-(1×1) surface with C1h symmetry by angle- and spin-resolved photoelectron spectroscopy and first-principles theoretical calculation. The constant energy contour of the upper branch of the RB split band has a warped elliptical shape centered at a k point located between Γ and the edge of the surface Brillouin zone, i.e., at a point without time-reversal symmetry. The spin-polarization vector of this state is in-plane and points almost the same direction along the whole elliptic contour. This novel nonvortical RB spin structure is confirmed as a general phenomenon originating from the C1h symmetry of the surface.
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| 2. |
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| 3. |
- Eriksson, Johan, et al.
(author)
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Atomic and electronic structures of the ordered 2√3 × 2√3 andthe molten 1×1 phase on the Si(111):Sn surface
- 2010
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:23, s. 235410-
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Journal article (peer-reviewed)abstract
- The Si(111) surface with an average coverage of slightly more than one monolayer of Sn, exhibits a 2√3 × 2√3 reconstruction below 463 K. In the literature, atomic structure models with 13 or 14 Sn atoms in the unit cell have been proposed based on scanning tunneling microscopy (STM) results, even though only four Sn atoms could be resolved in the unit cell. This paper deals with two issues regarding this surface. First, high resolution angle resolved photoelectron spectroscopy (ARPES) and STM are used to test theoretically derived results from an atomic structure model comprised of 14 Sn atoms, ten in an under layer and four in a top layer [Törnevik, et al., PRB 44, 13144 (1991)]. Low temperature ARPES reveals six occupied surface states. The calculated surface band structure only reproduces some of these surface states. However, simulated STM images show that certain properties of the four atoms that are visible in STM are reproduced by the model. The electronic structure of the Sn atoms in the under layer of the model does not correspond to any features seen in the ARPES results. New STM images are presented which indicate the presence of a different under layer consisting of eight Sn atoms, that is not compatible with the model. These results indicate that a revised model is called for. The second issue is the reversible transition from a 2√3 × 2√3 phase below 463 K to a 1×1 phase corresponding to a molten Sn layer, above that temperature. It is found that the surface band structure just below the transition temperature is quite similar to that at 100 K. The surface band structure undergoes a dramatic change at the transition. A strong surface state, showing a 1×1 periodicity, can be detected above the transition temperature. This state resembles parts of two surface states which, already before the transition temperature is reached, has begun a transformation and lost much of their 2√3×2√3 periodicities. Calculated surface band structures obtained from 1×1 models with 1 ML of Sn are compared with ARPES and STM results. It is found that the strong surface state present above the transition temperature shows a dispersion similar to that of a calculated surface band originating from the Sn-Si interface with the Sn atoms in T1 sites.
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| 4. |
- Eriksson, Johan, 1979-, et al.
(author)
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Electronic structure of the thallium induced 2×1 reconstruction on Si(001)
-
Other publication (other academic/artistic)abstract
- With a Tl coverage of one monolayer, a 2×1 reconstruction is formed on the Si(001) surfaceat room temperature. In this study, low temperature angle resolved photoelectron spectroscopy(ARPES) data reveal four surface state bands associated with this Tl induced reconstruction.Calculated surface state dispersions, obtained using the “pedestal + valley-bridge” model, are foundto be similar to those obtained using ARPES. Inclusion of spin-orbit coupling in the calculations isfound to be important to arrive at these results. A known effect of the strong spin-orbit coupling isthe reluctance of the Tl 6s2 electrons to participate in the bonding, i.e., the inert pair effect. In thecalculations, inclusion of spin-orbit coupling results in a ~5 eV downshift of the Tl 6s2 electrons.
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| 5. |
- Eriksson, Johan, et al.
(author)
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Electronic structure of the thallium-induced 2x1 reconstruction on Si(001)
- 2010
-
In: PHYSICAL REVIEW B. - : American Physical Society. - 1098-0121. ; 81:20, s. 205422-
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Journal article (peer-reviewed)abstract
- With a Tl coverage of one monolayer, a 2 x 1 reconstruction is formed on the Si (001) surface at room temperature. In this study, low-temperature angle-resolved photoelectron spectroscopy (ARPES) data reveal four surface state bands associated with this Tl induced reconstruction. Calculated surface state dispersions, obtained using the "pedestal + valley-bridge" model, are found to be similar to those obtained using ARPES. Inclusion of spin-orbit coupling in the calculations is found to be important to arrive at these results. A known effect of the strong spin-orbit coupling is the reluctance of the Tl 6s(2) electrons to participate in the bonding, i.e., the inert pair effect. In the calculations, inclusion of spin-orbit coupling results in a similar to 5 eV downshift of the Tl 6s(2) electrons.
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| 6. |
- Eriksson, Johan, 1979-, et al.
(author)
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Lithium-induced dimer reconstructions on Si(001) studied by photoelectron spectroscopy and band-structure calculations
- 2007
-
In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 75:20, s. 205416-
-
Journal article (peer-reviewed)abstract
- The electronic and atomic structure of Si(001) with 0.5 and 1 ML of lithium have been studied experimentally using angle resolved ultraviolet photoelectron spectroscopy, Si 2p core level spectroscopy, and low energy electron diffraction. Experimental surface state dispersions are compared with recent theoretical results in the literature and with results from additional density functional theory calculations. Four adsorption configurations for the 0.5 ML 2×2 surface and three configurations for the 1 ML 2×1 surface are compared. Fittings of Si 2p core level data support the alternation of strongly and weakly buckled Si dimers of the 2×2 models and symmetric Si dimers of the 2×1 models based on the relative intensities of the surface components. As a tool to differentiate between the different 2×2 and 2×1 models surface state dispersions are used since they are sensitive to the positions of the Li adatoms.
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| 7. |
- Eriksson, Johan, 1979-, et al.
(author)
-
Origin of a surface state above the Fermi level on Ge(001) and Si(001) studied by temperature-dependent ARPES and LEED
- 2008
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 77:L8, s. 085406-1-085406-5
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Journal article (peer-reviewed)abstract
- Variable temperature photoemission studies in the literature have revealed the presence of a surface state above the Fermi level on clean Ge(001). We present photoemission and low energy electron diffraction results from Ge(001) obtained between 185 and 760 K. Our measurements show a peak above the Fermi level with a maximum intensity at a sample temperature of around 625 K. At higher temperatures, we observe a gradual decrease in the intensity. Angle resolved spectra show that the surface state has a k̅ ∥ dependence and is therefore not attributed to defects. Very similar results were obtained on both an intrinsic (30 Ω cm) and a 10 m Ω cm n-type sample. The overall appearance of the spectral feature is found to be quite insensitive to sample preparation. Low energy electron diffraction investigations show how the sharp c(4×2) pattern becomes streaky and finally turns into a 2×1 pattern. The onset of the structure above the Fermi level takes place just before all c(4×2) streaks have disappeared which corresponds to a temperature of around 470 K. On Si(001), we also observe photoemission intensity above the Fermi level. It is weaker than on Ge(001) and appears at higher temperature. We find that the emission above the Fermi level can be explained by thermal occupation of the π* band derived from a 2×1 ordering of asymmetric dimers on the surface.
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| 8. |
- Inagaki, Shunsuke, et al.
(author)
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Effects of adsorbed molecular ordering to the superconductivity of a two-dimensional atomic layer crystal
- 2023
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In: Physical Review Materials. - : American Physical Society. - 2475-9953. ; 7:2
-
Journal article (peer-reviewed)abstract
- The effect of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) adsorption on the physical properties of the two-dimensional (2D) atomic layer superconductor (ALSC) In/Si(111)-(7×3) has been studied by angle-resolved photoelectron spectroscopy, transport measurements, and scanning tunneling microscopy. Hole doping from the adsorbed molecules has been reported to increase the superconducting transition temperature Tc of this ALSC, and the molecular spin tends to decrease it. Owing to its large electron affinity and its nonexistent spin state, the adsorption of PTCDA was expected to increase Tc. However, the PTCDA adsorption dopes only a small number of holes in the In layers and causes a suppression of Tc with a sharp increase in the normal-state sheet resistance followed by an insulating transition. Taking the disordering of the arrangement of PTCDA into account, we conclude that the increase in resistance is due to the localization effect originating from the random potential that is induced by the disordered PTCDA molecules. The present result also indicates the importance of the crystallinity of a 2D molecular film adsorbed on ALSCs.
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| 9. |
- Kobayashi, Takahiro, et al.
(author)
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Revealing the Hidden Spin-Polarized Bands in a Superconducting Tl Bilayer Crystal
- 2023
-
In: Nano Letters. - 1530-6992 .- 1530-6984. ; 23:16, s. 7675-7682
-
Journal article (peer-reviewed)abstract
- The interplay of spin-orbit coupling and crystal symmetry can generate spin-polarized bands in materials only a few atomic layers thick, potentially leading to unprecedented physical properties. In the case of bilayer materials with global inversion symmetry, locally broken inversion symmetry can generate degenerate spin-polarized bands, in which the spins in each layer are oppositely polarized. Here, we demonstrate that the hidden spins in a Tl bilayer crystal are revealed by growing it on Ag(111) of sizable lattice mismatch, together with the appearance of a remarkable phenomenon unique to centrosymmetric hidden-spin bilayer crystals: a novel band splitting in both spin and space. The key to success in observing this novel splitting is that the interaction at the interface has just the right strength: it does not destroy the original wave functions of the Tl bilayer but is strong enough to induce an energy separation.
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| 10. |
- Ohsuna, Tetsu, et al.
(author)
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TEM image simulation of mesoporous crystals for structure type identification
- 2011
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In: Solid State Sciences. - : Elsevier BV. - 1293-2558 .- 1873-3085. ; 13:4, s. 736-744
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Journal article (peer-reviewed)abstract
- Software, MesoPoreImage, for transmission electron microscope (TEM) image simulation of mesoporous crystals was developed. MesoPoreImage provides two-dimensional (2D) projected potential distributions along any directions as well as corresponding 2D TEM images calculated from a three-dimensional (3D) density distribution of an ideal mesoporous structure. In order to adjust the contrast of simulated TEM images to that observed, a parameter representing surface roughness on the pore surface is introduced. Simulated TEM images of four typical silica mesoporous crystals, MCM-48, AMS-10, SBA-16 and SBA-6 are shown and compared with observed ones, which shows the usefulness of the software for identification of the mesoporous structure type. A procedure for the identification of structure types of mesoporous crystals by using TEM and the simulation software is fully described.
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| 11. |
- Sakamoto, Kazuyuki, et al.
(author)
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Abrupt Rotation of the Rashba Spin to the Direction Perpendicular to the Surface
- 2009
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:9, s. 096805-
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Journal article (peer-reviewed)abstract
- The polarization vector of the Rashba spin, which must be parallel to the two-dimensional (2D) plane in an ideal system, is found to change abruptly and definitely to the direction perpendicular to the surface at the K̅ point of the Brillouin zone of a real hexagonal system, the Tl/Si(111)-(1×1) surface. This finding obtained experimentally by angle-resolved and spin-resolved photoemission measurements is fully confirmed by a first-principles theoretical calculation. We found that the abrupt rotation of the Rashba spin is simply understood by the 2D symmetry of the hexagonal structure.
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| 12. |
- Sakamoto, Kazuyuki, et al.
(author)
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Adsorption and reaction processes of physisorbed molecular oxygen on Si(111)-(7×7)
- 2005
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In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 72:7, s. 075346-
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Journal article (peer-reviewed)abstract
- 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.
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| 13. |
- Sakamoto, Kazuyuki, et al.
(author)
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Band structure of the Ca/Si(111)-(2×1) surface
- 2003
-
In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 68:24, s. 245316-
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Journal article (peer-reviewed)abstract
- 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.
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| 14. |
- Sakamoto, Kazuyuki, et al.
(author)
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Bias-dependent scanning tunneling microscopy study of the oxygen-adsorbed Si(111)-(7×7) surface : Observation of metastable molecular oxygen
- 2002
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 65:15, s. 155305-
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Journal article (peer-reviewed)abstract
- We have observed the initial stage of oxygen adsorption on a Si(111)-(7×7) surface using scanning tunneling microscopy. Among the bright sites observed after exposing the surface to oxygen in occupied state images, there are differences in the bias dependence of the brightness. Taking into account the local density of states of the oxygen-adsorbed Si(111)-(7×7) surface, we conclude that the sites appearing brightly only with a tip bias of >~+2.1 V are the molecular oxygen. The preferred adsorption site of this molecular species is a corner adatom, which has an oxygen atom adsorbed into its backbond, of the faulted half of the (7×7) unit cell.
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| 15. |
- Sakamoto, Kazuyuki, et al.
(author)
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Core-level photoemission study of thallium adsorbed on a Si(111)-(7×7) surface : Valence state of thallium and the charge state of surface Si atoms
- 2006
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:7, s. 075335-
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Journal article (peer-reviewed)abstract
- The coverage-dependent valence state of Tl adsorbed on a Si(111)-(7×7) surface and the coverage dependence of the charge states of surface Si atoms have been investigated by high-resolution core-level photoelectron spectroscopy. Although two different reconstructions were observed in low-energy electron diffraction at different coverages, a (1×1) pattern at a Tl coverage of 1 monolayer (ML) and a (√3×√3) pattern at a coverage of 1∕3 ML, the binding energy of the Tl 5d core-level was the same at Tl coverages up to 1 ML. Taking the valence state on a (1×1) surface reported in the literature into account, we conclude that the valence state of Tl is 1+, and that the 6s2 electrons of Tl are inactive as an inert pair in the Tl-Si bonding on a Si(111) surface at a coverage of 1 ML and below. In the Si 2p core-level spectra, one surface component was observed on the (1×1) surface, and three surface components were observed on the (√3×√3) surface. The binding energies and intensities of the Si 2p surface components indicate that the charge state of the surface Si atoms on Tl∕Si(111)-(1×1) is the same as that of the (√3×√3) surfaces induced by the other group III metals, but they are different on the Tl∕Si(111)-(√3×√3) surface.
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| 16. |
- Sakamoto, Kazuyuki, et al.
(author)
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Determination of the bonding configuration of the metastable molecular oxygen adsorbed on a Si(111)-(7×7) surface
- 2002
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In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 65:20
-
Journal article (peer-reviewed)abstract
- 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.
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| 17. |
- Sakamoto, Kazuyuki, et al.
(author)
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Electronic structure of the Ca/Si(111)-(3×2) surface
- 2004
-
In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 69:12, s. 1253211-1253217
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Journal article (peer-reviewed)abstract
- 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.
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| 18. |
- Sakamoto, Kazuyuki, et al.
(author)
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Electronic structure of the Si(110)-(16×2) surface : High-resolution ARPES and STM investigation
- 2009
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:4, s. 045304-
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Journal article (peer-reviewed)abstract
- The electronic structure of a single domain Si(110)-(16×2) surface has been investigated by high-resolution angle-resolved photoelectron spectroscopy and scanning tunneling microscopy (STM). Four semiconducting surface states with flat dispersions, whose binding energies are 0.2, 0.4, 0.75, and 1.0 eV, were observed in the bulk band gap and more than six states were observed within the projected bulk band at binding energies less than 5.2 eV. The origins of the four surface states and of one state at a binding energy of approximately 1.5 eV at the Γ̅ point are discussed based on the local density of states mappings obtained by STM. Further, a structural model that can explain all these five states is proposed.
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| 19. |
- Sakamoto, Kazuyuki, et al.
(author)
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Identification of the basic structure of the Ag/Si(111)-(6×1) surface : Observation of a low-temperature c(12×2) phase
- 2002
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In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 65:4, s. 045305-
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Journal article (peer-reviewed)abstract
- 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.
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| 20. |
- Sakamoto, Kazuyuki, et al.
(author)
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Observation of two metastable oxygen species adsorbed on a Si(111)-(7×7) surface : Reinterpretation of the initial oxidation process
- 2003
-
In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 68:7, s. 075302-
-
Journal article (peer-reviewed)abstract
- 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.
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| 21. |
- Sakamoto, Kazuyuki, et al.
(author)
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Photoemission study of metastable oxygen adsorbed on a Si(111)-(7×7) surface
- 2004
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In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 70:3, s. 035301-
-
Journal article (peer-reviewed)abstract
- 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.
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| 22. |
- Sakamoto, Kazuyuki, et al.
(author)
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Photoemission study of the thallium induced Si(111)-´`3x´`3 surface
- 2007
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In: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 601:22, s. 5258-5261
-
Journal article (peer-reviewed)abstract
- We have investigated the surface electronic structure of the Tl induced Si (1 1 1) - (sqrt(3) × sqrt(3)) surface by using angle-resolved photoelectron spectroscopy. Three semiconducting surface states were observed in the gap of the bulk band projection. Of these three states, the one, whose binding energy is approximately 0.3 eV, hardly disperses. Regarding the two other states, we discuss their properties by comparing their dispersion behaviors with those of the surface states of the other group III metal (Al, Ga and In) induced (sqrt(3) × sqrt(3)) reconstructions. The split observed at the over(G, -) point and the smaller dispersion widths of these two states indicate that the origins of the surface states of the Tl induced (sqrt(3) × sqrt(3)) reconstruction are not the same as those of the Al, Ga and In induced (sqrt(3) × sqrt(3)) reconstructions. These results support the idea that the atomic structure of the Tl / Si (1 1 1) - (sqrt(3) × sqrt(3)) surface is different from that of the (sqrt(3) × sqrt(3)) reconstructions induced by other group III metals, which was proposed in the literature.
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| 23. |
- Sakamoto, Kazuyuki, et al.
(author)
-
Structural investigation of Ca/Si(111) surfaces
- 2002
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:16
-
Journal article (peer-reviewed)abstract
- 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.
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| 24. |
- Sakamoto, Kazuyuki, et al.
(author)
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Structural investigation of the quasi-one-dimensional reconstructions induced by Eu adsorption on a Si(111) surface
- 2005
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In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 72:19, s. 195342-
-
Journal article (peer-reviewed)abstract
- 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 (3×2) periodicity, and the highest coverage phase has a (2×1) one. Of the intermediate phases, the LEED pattern of the so-called (5×1) surface indicates that this surface has actually a (5×4) periodicity. The Eu 4f core-level spectra show that the Eu coverages of the (3×2), (5×4), and (2×1) phases are 1∕6 monolayer (ML), 0.3 ML, 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 (3×2) phase is basically the same as that of the honeycomb-chain-channel model, and that the (2×1) phase is formed by π-bonded Seiwatz Si chains. Regarding the (5×4) 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 (5×4) phase.
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| 25. |
- Sakamoto, Kazuyuki, et al.
(author)
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Surface electronic structures of the Eu- and Ca-induced so-called Si(111)-(5×1) reconstructions
- 2006
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:23, s. 235311-
-
Journal article (peer-reviewed)abstract
- We have investigated the electronic structures of the so-called Eu- and Ca-induced Si(111)-(5×1) 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 (5×4). In the ARPES study, seven surface states were observed on each (5×4) reconstruction. Of these surface states, the dispersions of five of them show good agreement with those of the Eu- and Ca-induced (3×2) honeycomb-chain-channel (HCC) surfaces and the dispersions of the two other states agree well with those of the Eu- and Ca-induced (2×1) Seiwatz surfaces along the [1̅ 10] 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)-(5×1) reconstructions based on their electronic structures.
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| 26. |
- Sakamoto, Kazuyuki, et al.
(author)
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Symmetry induced peculiar Rashba effect on thallium adsorbed Si(111) surfaces
- 2015
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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier. - 0368-2048 .- 1873-2526. ; 201, s. 88-91
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Journal article (peer-reviewed)abstract
- The geometric symmetry of the surface plays an important role for the spin-orbit-induced spin texture of two-dimensional electronic states. This article reviews the peculiar Rashba spins induced by a C-3 symmetry, including the completely spin polarized surface states with the polarization vector oriented perpendicular to the surface, i.e. a direction that is not expected in a typical Rashba system. This review also describes that this peculiar Rashba situation has possibility to suppress backscattering and therefore to greatly improve the efficiency of spin transport, which is an essential issue in the development of high-performance semiconductor spintronic devices. (C) 2014 Elsevier B.V. All rights reserved.
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| 27. |
- Sakamoto, Kazuyuki, et al.
(author)
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Valley spin polarization by using the extraordinary Rashba effect on silicon
- 2013
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In: Nature Communications. - : Nature Publishing Group: Nature Communications. - 2041-1723. ; 4:2073
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Journal article (peer-reviewed)abstract
- The addition of the valley degree of freedom to a two-dimensional spin-polarized electronic system provides the opportunity to multiply the functionality of next-generation devices. So far, however, such devices have not been realized due to the difficulty to polarize the valleys, which is an indispensable step to activate this degree of freedom. Here we show the formation of 100% spin-polarized valleys by a simple and easy way using the Rashba effect on a system with C-3 symmetry. This polarization, which is much higher than those in ordinary Rashba systems, results in the valleys acting as filters that can suppress the backscattering of spin-charge. The present system is formed on a silicon substrate, and therefore opens a new avenue towards the realization of silicon spintronic devices with high efficiency.
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| 28. |
- Sakamoto, Shigeru, et al.
(author)
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Formation of Two- and Three-Dimensional Hybrid Mesostructures from Branched Siloxane Molecules
- 2009
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 131:28, s. 9634-9635
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Journal article (peer-reviewed)abstract
- We report the design of a new precursor having three branching disiloxane units capable of forming 3D mesostructures with a cubic Pm-3n and its orthorhombic and tetragonal variants Cmmm and P42/mnm, in addition to a conventional 2D hexagonal (p6mm) mesostructure, thus creating a novel research area of mesostructural design in silica-organic nanohybrid materials.
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| 29. |
- Suga, Mitsuo, et al.
(author)
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Recent progress in scanning electron microscopy for the characterization of fine structural details of nano materials
- 2014
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In: Progress in Solid State Chemistry. - : Elsevier BV. - 0079-6786 .- 1873-1643. ; 42:1-2, s. 1-21
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Research review (peer-reviewed)abstract
- Research concerning nano-materials (metal-organic frameworks (MOFs), zeolites, mesoporous silicas, etc.) and the nano-scale, including potential barriers for the particulates to diffusion to/from is of increasing importance to the understanding of the catalytic utility. of porous materials when combined with any potential super structures (such as hierarchically porous materials). However, it is difficult to characterize the structure of for example MOFs via X-ray powder diffraction because of the serious overlapping of reflections caused by their large unit cells, and it is also difficult to directly observe the opening of surface pores using ordinary methods. Electron-microscopic methods including high-resolution scanning electron microscopy (HRSEM) have therefore become imperative for the above challenges. Here, we present the theory and practical application of recent advances such as through-the-lens detection systems, which permit a reduced landing energy and the selection of high-resolution, topographically specific emitted electrons, even from electrically insulating nano-materials.
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| 30. |
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| 31. |
- Zhang, Hanmin, et al.
(author)
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Comprehensive study of the metal/semiconductor character of adatom-induced Ag/Si(111) reconstructions
- 2001
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In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 64:24
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Journal article (peer-reviewed)abstract
- 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.
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| 32. |
- Zhang, Hanmin, et al.
(author)
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Surface electronic structure of K- and Cs-induced √21×√21 phases on Ag∕Si(111)√3×√3
- 2004
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70:24, s. 245301-
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Journal article (peer-reviewed)abstract
- 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.
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