High-resolution Core-level Photoelectron Spectroscopy Research Articles

Conversion between two binding states of benzene on Si(001)

The adsorption and reaction of benzene $({\mathrm{C}}_{6}{\mathrm{H}}_{6})$ on the Si(001) surface are investigated by first-principles density-functional calculations within the generalized gradient approximation. We find that the ``tight-bridge'' configuration in which ${\mathrm{C}}_{6}{\mathrm{H}}_{6}$ bonds across two adjacent Si dimers is more stable than the ``butterfly'' configuration in which ${\mathrm{C}}_{6}{\mathrm{H}}_{6}$ bonds on top of a single Si dimer. Upon ${\mathrm{C}}_{6}{\mathrm{H}}_{6}$ adsorption the latter configuration is initially formed but is converted to the former one with an energy barrier of 0.87 eV. As the coverage increases, such a conversion will be blocked if the butterfly configuration is formed at a single Si dimer site between two tight-bridge benzenes. Therefore we suggest that both the butterfly and tight-bridge configurations could coexist at saturation coverage, providing an explanation for recent high-resolution core-level photoelectron spectroscopy data.

Coverage-dependent adsorption behavior of benzene on Si(100): A high-resolution photoemission study

The adsorption of benzene molecules on Si(100) is investigated by high-resolution core-level photoelectron spectroscopy using synchrotron radiation as well as ultraviolet photoelectron spectroscopy (UPS) for valence bands. The C $1s$ photoelectron spectra of benzene adsorbates are found to consist of two different components, which represent carbon atoms with or without a direct $\mathrm{Si}\ensuremath{-}\mathrm{C}$ bond. The population ratio of these two components exhibits a drastic change upon increasing the molecular coverage. This is explained by the coverage-dependent change of the adsorbate structure, which is corroborated by the noticeable variation of the molecular orbitals in the valence bands as observed by UPS. From these results, it is deduced that the population of the di-$\ensuremath{\sigma}$ structure increases significantly at a high coverage over the tetra-$\ensuremath{\sigma}$ structure which is energetically favored at a low coverage. This indicates the importance of the interaction between the adsorbate molecules at a high coverage.

Growth of anα-Sn film on an InSb(111)A−(2×2)surface

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.

Atomic and electronic structure of the Si(0 0 1)2 × 1–Li chemisorption system at 1.0 monolayer coverage

Ab initio plane-wave pseudopotential density functional theory (DFT) calculations have been performed to determine the atomic and electronic structure of the Si(0 0 1)2 × 1–Li adsorption system at 1.0 monolayer (ML) coverage. Chemisorption of the lithium atoms is found to result in a minimum energy configuration characterized by symmetric Si dimers in agreement with the results of high-resolution core-level photoelectron spectroscopy. The transition from the asymmetric Si dimers of the clean Si(0 0 1) surface to the symmetric dimers of the Li chemisorbed surface is due to charge transfer from the Li adatoms to the substrate. The dispersion of the occupied electronic surface state bands is found to be in good agreement with the angle-resolved photoemission data. The nature of the lowest energy unoccupied surface state band suggests that silicide formation may occur at coverages greater than 1.0 ML.

Photoelectron spectroscopy of atomic core levels on the silicon surface: A review

Recent studies of the atomic structure of the single-crystal silicon surface (both clean and covered by adsorbates) that are performed by high-resolution core-level photoelectron spectroscopy using synchrotron radiation are reviewed. The physical principles of the method, experimental techniques, the spectrum processing procedure, and the procedure of determining the energy shifts of the core levels in the subsurface layer are outlined. Emphasis is placed on the surface modes of silicon 2p spectra, which are observed for the main types of silicon surface reconstruction (Si(111)-7×7 and Si(100)-2×1), and on a correlation between these modes and the atomic structure of the (111) and (100) surfaces. Also, particular attention is given to the studies of the Ge/Si system, which is viewed as a promising material of nanoelectronics, as well as to those concerned with metal and gas adsorption on basic (low-index) silicon faces. These studies clearly demonstrate that core-level photoelectron spectroscopy provides extremely detailed information on the structure of adsorbed layers and on the adsorption-stimulated reconstruction of the substrate surface.

Effects of annealing on the structure of the Au/Si(111)–H interface

The interaction between the hydrogenated silicon surface and gold, has been investigated as a function of temperature by means of high resolution core-level photoelectron spectroscopy (PES) and scanning photoelectron microscopy (SPEM). We have studied the effect of the annealing on a sample obtained by deposition of 1.5 ML of gold on an in-situ hydrogenated Si(1 1 1)-7 × 7 substrate. In order to characterize the substrate as well as the adsorbate, both Si 2p and Au 4f core-levels have been analysed. Our results show that, after annealing at 550 °C, bidimensional (2D) and tridimensional (3D) phases coexist. The two phases have been spectroscopically characterized. On the 3D phase (micrometer sized islands) a bulk-Au component is present in the Au 4f 7/2 spectrum. We argue that the presence of the hydrogen layer promoted the formation of the islands. We propose a model for the temperature evolution of this interface.

Structural Investigation of the So-Called Ca/Si(111)-(5×1) Surface

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.

High-resolution Si 2p core-level and low-energy electron diffraction studies of the Ca/Si(1 1 1)-(3 × 2) 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 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 Si 2p 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.

High-resolution core-level study of the Ca/Si(1 1 1)-(2×1) surface

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 π-bonded Seiwatz Si chains with a Ca coverage of 0.5 ML.

Structural investigation of Ca/Si(111) surfaces

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 ...

Surface chemistry of TiCl 4 on clean and hydrogen modified W( [formula omitted]): identification of surface intermediates

The adsorption and decomposition of titanium tetrachloride (TiCl 4) on W(1 1 0) were studied with high-resolution core level photoelectron spectroscopy. At least two stable intermediates are formed along the pathway to TiCl 4 decomposition: TiCl 4(a), which is stable up to 300 K, and TiCl 3(a), which is stable up to 500 K. Successive adsorption at 80 K shows that the TiCl 4(a) species forms in the presence of dissociated TiCl 4 or hydrogen. This indicates that dissociative sites must be blocked before TiCl 4 can adsorb intact.

HIGH-RESOLUTION Si2p CORE-LEVEL STUDY OF THE K/Si(111)-(3 × 1) SURFACE

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.

Identification of the basic structure of the Ag/Si(111)-(6×1)surface: Observation of a low-temperaturec(12×2)phase

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 ...

Spectroscopic characterization of catalytically active surface sites of a metallic oxide

High-resolution core-level photoelectron spectroscopy in combination with density functional theory calculations was used to identify the spectroscopic signatures of the catalytically active sites on the RuO 2(1 1 0) surface, i.e., the coordinatively unsaturated Ru sites (cus-Ru) and the bridging oxygen atoms. These assignments provide the necessary spectroscopic information for in situ studies of catalytical reactions over the RuO 2(1 1 0) surface.

Electron-Spectroscopy Study of Amorphous CN:Ti Films

Amorphous CN:Ti films deposited by using the reactive magnetron sputtering method were annealed in vacuum under 200 to 600° C. Incorporation of Ti (less than 3 at.%) has brought some new perspectives to the material. Electron-energy-loss spectrum indicates improved conductivity in CN:Ti films as in the insulating CN films. The high-resolution core-level x-ray photoelectron spectroscopy (XPS) studies show that most carbon atoms form homeopolar bonding in as-deposited CN:Ti film. While the N 1s line always shrinks with increasing annealing temperature, the total full width at half maximum of C 1s line decreases only at annealing temperature over 300° C when the broadening due to heterobonding formation is outdone by the effect of increasing order. An enhanced π-band feature in the valence-XPS spectra at high annealing temperatures confirms the graphitisation tendency of this material.

Surface reconstructions of 3C-SiC(001) studied by high-resolution core-level photoemission

The different surface reconstructions of the 3C-SiC(001) surface have been systematically studied by high-resolution core-level photoelectron spectroscopy. For the Si-rich 3×2 surface, three different Si 2p surface components are clearly identified supporting the structure model with 2 3 ML of Si ad-dimers. It is confirmed that the c(2×2) and 2×1 surfaces are respectively C- and Si-terminated by observing a single dominant surface component in the C 1s or Si 2p spectra with binding energy shifts of 1.04 eV and −0.50 eV respectively relative to the bulk component. The atomic origins of these surface core levels are assigned and the core-level shifts are compared with previous measurements and recent theoretical calculations.

Alkyl-terminated Si(111) surfaces: A high-resolution, core level photoelectron spectroscopy study

The bonding of alkyl monolayers to Si(111) surfaces has been studied with high-resolution core level photoelectron spectroscopy (PES). Two very different wet-chemical methods have been used to prepare the alkyl monolayers: (i) Olefin insertion into the H–Si bond of the H–Si(111) surface, and (ii) replacement of Cl on the Cl–Si(111) surface by an alkyl group from an alkyllithium reagent. In both cases, PES has revealed a C 1s component shifted to lower binding energy and a Si 2p component shifted to higher binding energy. Both components are attributed to the presence of a C–Si bond at the interface. Along with photoelectron diffraction data [Appl. Phys. Lett. 71, 1056, (1997)], these data are used to show that these two synthetic methods can be used to functionalize the Si(111) surface.

The surface core-level shift of the Nb(110) surface

The surface core-level shift (SCLS) of the Nb(110) surface has been determined by means of high-resolution core-level photoelectron spectroscopy of the Nb 3d5/2 core level. A SCLS of 180 +- 15 meV towards higher binding energy with respect to the bulk component was estimated by curve fitting the Nb 3d5/2 core-level spectra taken using several photon energies. The sign of the SCLS agrees with recent ab initio calculations including both initial- and finalstate effects, but the shift is significantly smaller than predicted in these calculations.

Huge charge transfer from potassium on H:Si(111)-(1×1)

Potassium adsorption on the hydrogen-terminated H:Si(111)-(1×1) surface is studied by high-resolution core-level and valence-band photoelectron spectroscopy. New light is shed on the interpretation of core-level spectra at the K/Si(111) interface. Low potassium coverages induce a large downward band bending. The Fermi level moves ∼0.26 eV above the conduction band minimum, which is explained by a huge charge transfer from the adsorbate to the semiconductor bulk. For room-temperature saturation coverage, the Fermi level drops back into the semiconductor band gap. This leads to a vanishing n-type Schottky barrier height Φ (n)=0.02±0.03 eV in agreement with theoretical results.

Au/H:Si(111)−(1×1)interface versusAu/Si(111)−(7×7)

The room-temperature growth of gold on Si(111) surfaces has been directly compared for nonreconstructed hydrogen-terminated surfaces and the bare $7\ifmmode\times\else\texttimes\fi{}7$-reconstructed surface by means of high-resolution core-level and valence-band photoelectron spectroscopy and Auger spectroscopy. The growth modes show strong differences with gold island formation on the passivated $\mathrm{H}:\mathrm{S}\mathrm{i}(111)\ensuremath{-}(1\ifmmode\times\else\texttimes\fi{}1)$ surface. Silicon segregated on top of the deposited gold film is seen for both interfaces. The Schottky barrier is only weakly affected by the hydrogen termination.