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The thickness-dependent electronic structures of Dy silicide films grown on a Si(1 1 1) surface have been investigated by angle-resolved photoelectron spectroscopy. Two ( 1 × 1 ) periodic bands, both of them cross the Fermi level, have been observed in the silicide films formed by Dy coverages of 1.0 monolayer and below, and more than five ( 3 × 3 ) periodic bands have been observed in thicker films. Taking the ( 2 3 × 2 3 ) periodic structure of Dy atoms in the submonolayer silicide film into account, the periodicity of the two metallic bands indicate that they mainly originate from the orbitals of Si atoms, which form a ( 1 × 1 ) structure. Of the ( 3 × 3 ) periodic bands observed in thick films, four of them are well explained by the folding of the ( 1 × 1 ) bands into a ( 3 × 3 ) periodicity. Regarding the other band, the three ( 3 × 3 ) periodic bands would originate from the electronic states related to the inner Si layers that form a ( 3 × 3 ) structure, and the one observed in the 3.0 ML film only might originate from the electron located at the interface between bulk Si and the Dy silicide film.

This article describes the origins of the width of the highest occupied molecular orbital (HOMO) state observed in the ultraviolet photoemission spectra (UPS) of thin organic semiconductor films. Although much research has been performed on the electrical properties of organic devices, a lot of crucial problems still remain. Among these problems, the charge mobility in organic semiconductor systems is one the most important subjects to be elucidated. In order to discuss the mobility, it is essential to understand both the intermolecular interaction and the electron-molecular vibration coupling. Experimental measurements of the energy band dispersion give information about the intermolecular interaction, and experimental detection of the HOMO hole-vibration coupling is indispensable to comprehend impacts of the electron-vibration coupling on the hole transport. Since most of the information is hidden behind the finite bandwidth of the HOMO, only careful UPS measurements can provide information on these important phenomena related to charge carrier dynamics. In this article, we summarize our recent challenges on UPS measurements of organic thin films, which give the band dispersion of the HOMO and the HOMO hole-vibration coupling, and discuss the origins of the UPS bandwidth that relates to the charge carrier dynamics.

A totally anisotropic peculiar Rashba-Bychkov (RB) splitting of electronic bands was found on the Tl/Si(110)-(1×1) surface with C_{1h} 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[over ¯] 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 C_{1h} symmetry of the surface.

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 sta ...

We have investigated the electronic structure of the Yb/Si(1 1 1)-(3 × 2) surface using angle-resolved photoelectron spectroscopy. Five surface states have been identified in the gap of the bulk band projection. Among these five surface state, the dispersions of three of them agree well with those of the surface states of monovalent atom adsorbed Si(1 1 1)-(3 × 1) surfaces. The dispersions of the two other surface states agree well with those observed on the Ca/Si(1 1 1)-(3 × 2) surface, whose basic structure is the same as that of monovalent atom adsorbed Si(1 1 1)-(3 × 1) surfaces. Taking these results into account, we conclude that the five surface states observed in the band gap originate from the orbitals of Si atoms that form a honeycomb-chain-channel structure.

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.

In this review, we present a series of photoemission studies performed on the so-called metal induced Si(111)-(3×1) surface, which is one of the most well known 1D structure formed on a Si(111) surface. Three different kinds of metals have been used as adsorbate, K, Ca, and Ag.On the K/Si(111)-(3×1) surface, five surface components were observed in the Si 2p core-level spectra. The energy shift and intensity of each surface component indicates that this surface has the honeycomb-chain-channel (HCC) structure with a K coverage of 1⁄3 ML. The extra spots observed in the LEED pattern of the so-called Ca/Si(111)-(3×1) surface suggest that this surface has a (3×2) periodicity instead of the (3×1) periodicity reported in the literature. By considering the energy shift and intensity of each Si 2p surface component, we conclude that the structure of the (3×2) phase is basically the same as that of the HCC model, but with a Ca coverage of 1⁄6 ML. Regarding the valence-band, five surface states, none of which crosses the Fermi level, were observed in the bulk band gap. The dispersion features of three of them agree well with those of monovalent atom adsorbed Si(111)-(3×1) surfaces along the chain direction. The two other states observed in the band gap have not been reported in the literature, and they are interpreted as surface states that are peculiar to the Ca/Si(111)-(3×2) surface due to the 1⁄6 ML coverage. Regarding the Ag/Si(111) surface, a new c(12×2) phase is observed in LEED after cooling the room temperature (6×1) phase to 70 K. In the Si 2p core-level spectra and in the valence band spectra, no significant difference is observed between the two surfaces. Further, the origins of the Si 2p surface components and the surface states of these surfaces are well explained using the HCC model. These results indicate that the basic structure of this Ag/Si(111) surface is quite similar with the HCC model but with a c(12×2) periodicity, and that the (6×1) structure results from thermal vibrations of the surface atoms. [DOI: 10.1380/ejssnt.2004.210]

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

Surface electronic structures of Au-induced reconstructions on the Ag/Ge(111)sqrt3xsqrt3 surface

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 streak ...

The 3 × 3 , 21 × 21 and 6×6 phases of Ag/Si(1 1 1) have been studied by angle-resolved photoemission and low-energy electron diffraction. The Ag/Si(1 1 1) 3 × 3 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 21 × 21 surface is metallic in contrast to the two metallic bands discussed in the literature. On the 6×6 surface, the partially occupied surface band of the 21 × 21 surface seems to be absent, resulting in a gap of about 0.2 eV with respect to the Fermi-level.

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 π-bonded Si atoms of the top layer. The two other components originate from the Si atoms of the second and third layers.

We have measured the valence spectra of K-doped C 60 monolayer films adsorbed on Si(0 0 1)-(2×1) and Si(1 1 1)-(7×7) surfaces. No density of states is observed at the Fermi level for the undoped C 60 monolayer films on both Si surfaces. After a small K doping, a density of states is clearly observed at the Fermi level on a Si(0 0 1)-(2×1) surface. On the other hand, no density of states is observed at the Fermi level at any amount of K doping on a Si(1 1 1)-(7×7) surface. The difference observed on both Si surfaces indicates that the symmetry of C 60 molecules is almost the same as that in solid phase on a Si(0 0 1)-(2×1) surface, and is broken due to a stronger C 60 -substrate and/or C 60 –C 60 interaction on the Si(1 1 1)-(7×7) one.

We have investigated the interaction between metastable molecular oxygen and the adatom dangling bonds modified by the adsorption of atomic oxygen into the back-bonds of a Si(111)-(7×7) surface. Ultraviolet photoelectron spectroscopy shows that the metastable states increase in intensity faster but with a decrease in its saturated intensity as the coverage of atomic oxygen increases. This result suggests that the number of modified dangling bonds is not the only important factor for the adsorption process of metastable oxygen. Taking into account the observation of modified dangling bonds with different density of states in scanning tunneling microscopy, we conclude that the adsorption of the metastable oxygen species correlates closely with the density of states of the dangling bond.

We report here the temperature-dependent measurements of the valence spectra, and the C Is and the Si 2p core-level spectra of the C 60 adsorbed Si(111)-(7 × 7) surface, using photoelectron spectroscopy. At 300 K the valence spectra show the physisorption of most C 60 molecules for a one monolayer C 60 film. After annealing the sample at 1120 K the molecular orbitals disappear due to the breakdown of the C 60 cage. The C Is and Si 2p core-level spectra obtained at the same temperature indicate the progress of SiC formation at the interface between C 60 and the Si(111) surface. After annealing at 1170 K, the formation of SiC islands is confirmed by the binding energies of the peaks observed in the valence and C Is core-level spectra.

We report here measurements of the valence band spectra, the C 1s core level spectra and the vibrational excitation spectra of a C60 monolayer (ML) film on Si(111)7×7 and Si(100)2×1 surfaces, using photoelectron spectroscopy and high-resolution electron energy loss spectroscopy (HREELS) in combination with scanning tunneling microscopy. 1 ML films are formed after annealing the 5 ML films at 670 K. The bonding states between C60 molecules and Si substrates are clearly observed at 2.1 eV on both surfaces in the valence band spectra. The shift of binding energies of the molecular orbitals and the C 1s core level spectra indicate the charge transfer. The softening of several vibrational modes is observed on the Si(111)7×7 and Si(100)2×1 surfaces with HREELS. The charge transfer scheme explains the softening well. We discuss the bonding nature in terms of hybridization of C60 molecular orbitals with the surface states.

We have investigated the electronic structures of C60 molecules adsorbed on the Si(111)-(7×7) and Si(001)-(2×1) surfaces using photoelectron spectroscopy. The coverage-dependent valence band spectra show that the highest occupied molecular orbital (HOMO) of a C60 molecule splits into two peaks on both surfaces at a coverage of less than 0.25 monolayer. These split peaks are assigned to be the shifted HOMO and the bonding state with the polarization-dependent measurements. The binding energies of the molecular orbitals and the C 1s core level show a small shift on the Si(001)-(2×1) surface and no shift on the Si(111)-(7×7) surface with decreasing the coverage. These results indicate that the strong interaction between C60 molecules and the surfaces have a covalent character on the Si(111)-(7×7) surface, and both covalent and ionic characters on the Si(001)-(2×1) surface. We attribute the difference in the charge states of C60 molecules to the different surface structures.

We report here the temperature-dependent measurements of the valence spectra, the C 1s and the Si 2p core level spectra of the one monolayer ${\mathrm{C}}_{60}$ film adsorbed on Si(001)-$(2\ifmmode\times\else\texttimes\fi{}1)$ and Si(111)-$(7\ifmmode\times\else\texttimes\fi{}7)$ surfaces, using photoelectron spectroscopy. At 300 K, most ${\mathrm{C}}_{60}$ molecules are physisorbed with the coexistence of minority chemisorbed species on both Si(001)-$(2\ifmmode\times\else\texttimes\fi{}1)$ and Si(111)-$(7\ifmmode\times\else\texttimes\fi{}7)$ surfaces. After annealing the samples at 670 K, ${\mathrm{C}}_{60}$ molecules change the bonding nature to a chemisorption that has both covalent and ionic characters. The covalent bonding orbital is observed at a binding energy of 2.10 eV on both Si surfaces. The amount of charge transfer is estimated to be 0.19 electrons per ${\mathrm{C}}_{60}$ molecule on the Si(001) surface, and to be 0.21 electrons per molecule on the Si(111) surface. We consider the origin of the change in bonding nature to the different distance between two dangling bonds that results from the rearrangement of the surface Si atoms. After annealing at 1070 K, ${\mathrm{C}}_{60}$ molecules decompose and the SiC formation takes progress at the interface. On the Si(001) surface, the molecular orbitals (MO's) disappear at 1120 K and the binding energies of peaks observed in the valence spectra indicate the formation of SiC islands at this temperature. On the Si(111) surface, the disappearance of MO's and the formation of SiC islands are verified at 1170 K. The difference in formation temperature is attributed to the different surface structure.

We report here the measurements of vibrational excitation spectra, valence band spectra and C Is core level spectra of C 60 molecules adsorbed on Si(111)7 × 7 and Si(100)2 × 1 surfaces, using high-resolution electron energy loss spectroscopy (HREELS) and photoelectron spectroscopy (PES). At a coverage between 1 and 0.25 ML, HREELS and PES measurements show that the interaction is as weak as the van der Waals interaction on both surfaces. At a coverage lower than 0.25 ML, some contradictory results are obtained by HREELS and PES. With HREELS, the softening of several vibrational modes is observed on the Si(111)7 × 7 surface, but no indication of softening is observed on the Si(100)2 × 1 surface. The charge transfer scheme explains the softening well. These results by HREELS indicate that the nature of the bonding is ionic on the Si( 111)7 x 7 surface and of the van der Waals type on the Si(100)2 × 1 surface. In contrast, the bonding states between C 60 molecules and Si substrates are clearly observed at 2.4 eV on both surfaces with PES. The PES measurements indicate that the interaction has a covalent character on the Si(111)7 × 7 surface, and that it is in between covalent and ionic, i.e. not purely ionic or at the covalent limit, on the Si(100)2 x 1 surface. We will discuss the nature of the interaction manifested by HREELS and PES measurements in comparison with the spectra of C 60 molecules adsorbed on metal surfaces.

We have investigated the coverage-dependent electronic structures of C60 molecules adsorbed on the Si (111) -(7×7) and Si (001) -(2×1) surfaces using photoelectron spectroscopy. The valence band spectra show that the highest occupied molecular orbital (HOMO) of a C60 molecule splits into two peaks on both surfaces at a coverage lower than 0.25 monolayer. These split peaks are assigned to be the shifted HOMO and the bonding state, with the polarization-dependent measurements and the Si 2p core level spectra. The binding energies of the molecular orbitals and the C 1s core level show a small shift on the Si (001) -(2×1) surface, and no shift on the Si (111) -(7×7) surface with decreasing the coverage. These results indicate that the strong interaction between C60 molecules and the surfaces has a covalent character on the Si (111) -(7×7) surface, and both covalent and ionic characters on the Si (001) -(2×1) surface. We attribute the difference in the charge states of C60 molecules to the different surface structures.

We report here the measurements of the valence spectra, the C $1s$ and the Si $2p$ core-level spectra of ${\mathrm{C}}_{60}$ molecules adsorbed on a $\mathrm{Si}(111)\ensuremath{-}(7\ifmmode\times\else\texttimes\fi{}7)$ surface, using photoelectron spectroscopy. In the valence spectra, the highest occupied molecular orbital (HOMO) of a ${\mathrm{C}}_{60}$ splits into two peaks at a coverage lower than 0.25 ML. The binding energies of the split peaks are 1.8 and 2.4 eV. Taking into account the polarization-dependence of the valence spectra and the binding energy of the C $1s$ core-level spectra, it is found that the 2.4-eV peak observed in the valence spectra is the covalent bonding state between a ${\mathrm{C}}_{60}$ molecule and the Si substrate, and that the 1.8-eV peak is the shifted HOMO. The Si $2p$ core-level spectra suggest that the bonding site is localized at the interface. We also present the energy-level scheme of the bonding state in terms of the symmetry of the HOMO.

A (–Cu–O–) string on a Ag(110) surface defined by scanning tunneling microscopy (STM) was studied using the x-ray photoelectron spectroscopy (XPS), high resolution electron energy loss spectroscopy (HREELS). These data give the information about bonding properties which cannot be derived from the STM images. The combinative studies could show the structure as well as the growth mechanism of (–Cu–O–) strings on the Ag(110) surface. Deposition of Cu atoms on a p(2×1)-O Ag(110) surface resulted in a new O(1s) peak at 529.9 eV in the XPS and a new electron energy loss peak at 35 meV in the HREELS. These new peaks are assignable to the (Cu–O) bonding state on Ag(110), which is corresponding to the growth of new (–Cu–O–) strings in the [110] direction shown by the STM. These results suggest a stoichiometric reaction producing (–Cu–O–) strings according to an equation of (–Ag–O–)+Cu→(–Cu–O–)+Ag on the Ag(110) surface. The fact that the Ag atoms released by the chemical reaction make layered Ag islands and the (...

The initial stages of Ag growth on a single domain (SD) Si(001)2 × 1 surface have been studied by LEED, XPS and X-ray photoelectron diffraction (XPD). It is observed that at room temperature (RT) Ag grows in the Stranski-Krastanov mode with the first layer of ∼ 1 monolayer coverage, with a SD 2 × 1 periodicity but the 1 2 order spots partially elongated. Annealing the RT deposited film to ∼ 80°C results in an intermediate layer with a well-ordered SD c(6 × 2) periodicity. The presence of c(6 × 2) phase has never been reported previously for Ag Si (001) . Depositing Ag onto the substrate at ∼ 80°C results in an intermediate layer with a SD 2 × 3 periodicity. The Ag coverages for the SD c(6 × 2) and SD 2 × 3 phases are determined to be the same. XPD shows that the local atomic arrangements of the two SD phases are different in spite of the proximity in coverage and temperature of formation. Annealing the two SD phases to ∼ 300°C results in a transformation into a double domain (DD) 2 × 3 phase with LEED spots partially streaked along the “2 ×” direction. XPS shows no change in Ag coverage for the transformation. Depositing Ag onto substrates at temperatures greater than ∼ 160°C results in the DD 2 × 3 phase.

Initial stage growth of In and A1 on a wide-terrace single-domain Si(001)2 × 1 surface has been studied by low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy. Several submonolayer phases that were not reported on double-domain Si(001)2 × 1 substrates are observed, in addition to those already reported. The resulting sequences of two-dimensional (2D) phases for In and A1 coverages of ≤ 0.5 ML can be interpreted based on an order-disorder transition of arrays of 1D metal-dimer chains. The results show close resemblance to the initial growth of Ga on Si(001) and thus indicate that there is a general mode of growth for the Group-III metals on a Si(001)2 × 1 surface below 0.5 ML. Growth for coverages greater than 0.5 ML and the onset of 3D growth are also discussed.

A well-ordered single-domain Si(001)2 × 3-In surface as well as a 2 × 2-In surface were made on a single-domain Si(001)2 × 1 substrate. Azimuthal X-ray photoelectron diffraction patterns of In 3d levels have been measured for the two surfaces and single-scattering cluster analyses have been made. It is clearly found that both surfaces are composed of basically similar overlayers of In dimers whose orientations are parallel to that of Si dimers of substrate.

Using angle-resolved photoelectron spectroscopy we investigate the surface electronic structure of the three-dimensional topological insulator (TI) Sb${}_{2}$Te${}_{3}$(0001). Our data show the presence of a topological surface state in the bulk energy gap with the Dirac point located above the Fermi level. The adsorption of Cs atoms on Sb${}_{2}$Te${}_{3}$(0001) gives rise to a downward energy shift of the electronic valence band states which saturates at a value of $\ensuremath{\sim}$200 meV. For the saturation coverage the Dirac point of the linearly dispersive surface state resides in close proximity to the Fermi level. The electronic structure of the Cs/Sb${}_{2}$Te${}_{3}$ interface therefore considerably deviates from previously studied metal-TI interfaces based on the isostructural compound Bi${}_{2}$Se${}_{3}$ which points to the importance of atomic composition in these hetero systems.

The electronic structures of a single-domain Si(001)2 × 1-Na surface at a saturation coverage have been studied by angle-resolved photoelectron spectroscopy (ARPES) with linearly polarized synchrotron radiation (SR). To determine the dispersion of surface states in detail, the ARPES spectra have been measured along several symmetry axes of the 2 × 1 surface Brillouin zone. The result revealed a new assignment of surface-state dispersions. Symmetry properties of upper surface-state bands are determined using a linearly polarized character of SR. It has been found that the upper two surface states have the same symmetries as the dangling bond of the clean Si(001)2 × 1 dimer surface. The electronic structure of the Si(001)2 × 1-Na surface determined here is very similar to that of the Si(001)2 × 1-K surface [Surf. Sci. 261 (1992) 217] and is consistent with that expected for an alkali double-layer model.

The electronic structures of a single-domain Si(001)2 × 1-K surface at saturation coverage have been studied by synchrotron radiation (SR) angle resolved photoelectron spectroscopy (ARPES). The ARPES spectra have been measured along several symmetry axes of the 2 × 1 surface Brillouin zone and surface state dispersions are depicted. Symmetry properties of upper surface-state bands are determined using the linearly polarized character of SR. The symmetries and dispersions of the upper surface states determined here are consistent with those expected for a K double-layer model.

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.

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 diffract ...

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-le ...

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.

The electronic structures of the Eu∕Si(111)-(3×2) and (2×1) surfaces have been investigated by angle-resolved photoelectron spectroscopy. On the (3×2) surface, we identify six surface states in the ...

We have investigated the initial growth process of $\ensuremath{\alpha}$-Sn films on the In-terminated InSb(111)A-$(2\ifmmode\times\else\texttimes\fi{}2)$ surface using low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. Taking the LEED observation and the Sn coverage-dependent integrated intensities of the In $4d$, Sb $4d$, and Sn $4d$ core-level spectra into account, we conclude that the $\ensuremath{\alpha}$-Sn film grows epitaxially by a bilayer mode and that there is no interdiffusion of the substrate atoms as suggested in the literature. Furthermore, the coverage-dependent In $4d$ and Sn $4d$ core levels indicate that the In vacancy site of InSb(111)A-$(2\ifmmode\times\else\texttimes\fi{}2)$ surface is not the preferable Sn absorption site.

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.

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.

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.

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 photo ...

Undoped and slightly Eu-doped SmB6 show the opening of a gap with decreasing temperature below ~150 K. The spectral shapes near the Fermi level (EF) at 15 K have shown strong increase in intensity of a peak at a binding energy (EB) of around 12 meV with decreasing the photon energy (hn) from 17 eV down to 7 eV. Angle resolved spectra of SmB6 measured at hn = 35 eV just after the in-situ cleavage showed clear dispersions of several bands in the EB region from EF to 4 eV. Spin-polarized photoelectron spectra were then measured at 12 K and light incidence angle of ~50 deg. In contrast to the lack of spin polarization for the linearly polarized light excitation, clear spin polarization was observed in the case of circularly polarized light excitation. The two prominent peaks at EB~12 and ~150 meV have shown opposite signs of spin polarization which are reversed when the helicity of the light is reversed. The sign and the magnitude of spin- polarization are consistent with a theoretical prediction for the 6H5/2 and 6H7/2 states., Comment: all correspondence should be addressed to ssmsuga@gmail.com

We have investigated the growth mechanism of SiC film by the thermal reaction of C60 molecules adsorbed on a Si(111)-(7×7) surface using photoelectron spectroscopy. The growth of SiC film, performed by repeating the sample annealing at 1370 K following the adsorption of C60 molecules, is confirmed by the profile of the valence spectrum. The bonding nature between C60 molecules and the SiC surface is considered to have a covalent character at 300 and 670 K, and both covalent and ionic characters at 870 K by the thermal-dependent valence and C 1s core level spectra of a 1 monolayer C60 film adsorbed on SiC. Furthermore, we determined that the breaking of the C60 cage and the formation of SiC occurred at 1070 K, i.e. at a temperature 100 K lower than that on a Si(111) surface.

We report here the temperature-dependent electronic structure of C60 molecules adsorbed on a Si(001)-(2×1) surface, measured by photoelectron spectroscopy. At room temperature, the valence spectra reveal that the interaction between a 1 monolayer (ML) C60 film and a Si(001)-(2×1) surface is mainly a physisorption. After annealing the 1 ML C60 film adsorbed on a Si(001)-(2×1) surface at 500 K, in the valence spectra the highest occupied molecular orbital (HOMO) of a C60 molecule splits into two peaks. The binding energies of the two peaks are 1.6 and 2.1 eV. We assign the 1.6-eV peak to the shifted HOMO and the 2.1-eV peak to the bonding state between C60 molecules and a Si(001)-(2×1) surface from the polarization-dependent measurement and the Si 2p core level spectrum. Moreover, the molecular orbitals and the C 1s core level of a C60 molecule shift to the lower binding energy side. These results indicate that the interaction between C60 molecules and the Si(001)-(2×1) surface changes from physisorption to chemisorption, which has both covalent and ionic characters, at 500 K.