High-resolution Core-level Photoemission Spectroscopy Research Articles

Three-dimensional angle-resolved photoemission study of bulk SiGe single crystals

The composition- and structure-dependent electronic band structure of SiGe alloys facilitates a rich variety of its application in various fields. In this study, we performed high-resolution core-level and angle-resolved photoemission spectroscopy (ARPES) of unstrained SiGe single crystals with the (001) surface. Thermally cleaned surfaces of the single crystals of SiGe alloys exhibited double domain (2 × 1) reconstruction, wherein the asymmetric dimer was composed of Ge atoms, and Si atoms were located below the subsurface region. The compositional dependence of three valence bands and their constant energy contours were clearly resolved by three-dimensional ARPES measurements using the high-intensity synchrotron radiation. The valence bands of unstrained SiGe alloys could be well described by the composition-based interpolation of the band parameters of pristine Si and Ge crystals.

Multiple phosphorus chemical sites in heavily phosphorus-doped diamond

We have performed high-resolution core level photoemission spectroscopy on a heavily phosphorus (P)-doped diamond film in order to elucidate the chemical sites of doped-phosphorus atoms in diamond. P 2p core level study shows two bulk components, providing spectroscopic evidence for multiple chemical sites of doped-phosphorus atoms. This indicates that only a part of doped-phosphorus atoms contribute to the formation of carriers. From a comparison with band calculations, possible origins for the chemical sites are discussed.

Adsorption Configuration for Cysteine on Ge(100): Coverage-Dependent Surface Reorientation

The adsorption structure and surface reorientation of cysteine molecules on a Ge(100) surface were studied using high-resolution core-level photoemission spectroscopy and low-energy electron diffraction (LEED) to track the variation in adsorption structure as a function of cysteine coverage. Analysis of the S 2p, C 1s, N 1s, and O 1s core-level spectra revealed quite different adsorption behaviors as a function of cysteine coverage. At 0.4 ML (below half a monolayer), a single S 2p peak and a single N 1s peak were observed, consistent with an adsorption structure that contained one type of thiol conformation and a neutrally charged amino moiety. At 0.60 ML (over half a monolayer), two S 2p peaks emerged with a binding energy difference of 0.91 eV, indicative of two types of thiols, and two N 1s peaks were observed, which were consistent with the presence of both neutrally charged NH2 and positively charged NH2+ moieties. The relative populations of the two thiols induced a structural change in the orderin...

Hydrogen-Promoted Chlorination of RuO2(110)

High-resolution core-level photoemission spectroscopy and temperature-programmed reaction experiments together with density functional theory calculations were used to elucidate on the atomic scale the chlorination mechanism of ruthenium dioxide RuO2(110) by hydrogen chloride exposure. The surface-selective chlorination accounts for the extraordinary stability of the RuO2 catalyst in the Sumitomo process-the heterogeneously catalyzed oxidation of hydrogen chloride by oxygen. The selective replacement of bridging oxygen atoms by chlorine atoms depends on the formation of water molecules serving as leaving groups. Water is produced by the chlorine-assisted recombination of two neighboring surface hydroxyl groups at around 450 K, a temperature where water instantaneously leaves the surface. Finally, the bridging vacancy is rapidly filled in by chlorine atoms, thereby forming bridging chlorine atoms. Preadsorbed hydrogen has shown to facilitate the chlorination process for stoichiometry reasons. The general strategy of transforming bridging O atoms into a good leaving group has been corroborated by the chlorination of RuO2(110) via CO pretreatment with CO2 as the leaving group and subsequent Cl-2 exposure. (Less)

The Adsorption Configuration of Valine on Ge(100)

The Adsorption Configuration of Valine on Ge(100)

Coverage Dependence of the Adsorption Structure of Alanine on Ge(100)

The variations with coverage and annealing temperature in the adsorption structure of alanine on Ge(100) have been investigated using high-resolution core-level photoemission spectroscopy (HRCLPES). The C 1s, N 1s, and O 1s core-level spectra at a low initial coverage show that both the carboxyl and amine groups of the alanine molecules participate in bonding with the Ge(100) surface in an "intrarow O-H dissociated and N dative bonded structure". However, at higher coverage we found that in addition to this structure an "O-H dissociation structure" is present. Moreover, we systematically monitored the variation of the bonding features of alanine adsorbed on Ge(100) with annealing temperature and thus were able to track the desorption processes. By analyzing the C 1s, N 1s, and O 1s spectra at 420 K, we conclude that the principal adsorption structure at this temperature is the "O-H dissociation structure" because of the disconnection of Ge-N dative bonding. At higher temperatures, the "O-H dissociation structure" is converted into various fragments such as Ge oxide (or Ge-CO), Ge nitride (Ge cyanide), and Ge carbide.

Intrarow Adsorption Structure of Glycine on Ge(100)

The adsorption structure of glycine on Ge(100) was investigated using scanning tunneling microscopy (STM), density functional theory (DFT) calculations, and high-resolution core-level photoemission spectroscopy (HRCLPES). We found a major adsorption feature of glycine on Ge(100) in the STM images. This feature appeared as a bright protrusion between two dimer rows with a dark adjacent dimer. The position of the bright protrusion located in the middle of the two dimer rows indicates a multibonding adsorption structure. The results of the theoretical calculations confirm that the adsorption structure of glycine on Ge(100) (between two possible multibonding adsorption structures) is an "intrarow O-H dissociated and N dative bonded structure". In the HRCLPES experiments, we found an N 1s peak (at 399.5 eV) and two O 1s peaks (at 531.1 and 532.0 eV), which represent strong evidence that the adsorption configuration of glycine on Ge(100) is composed of both O-H dissociation and N dative bonding. All our STM, DFT, and HRCLPES results suggest that the adsorption structure of glycine molecules on Ge(100) is an "intrarow O-H dissociated and N dative bonded structure".

Irreversible structural transformation of Si(1 1 4)-2 × 1 induced by subsurface carbon

Using scanning tunneling microscopy (STM), it has been found that the reconstruction of Si(1 1 4) is transformed irreversibly from a 2 × 1 structure composed of dimer (D), rebonded atom (R), and tetramer (T) rows (phase A) to a different kind of 2 × 1 structure composed of D, T, and T rows (phase B) by C incorporation. It has been confirmed by high-resolution synchrotron core-level photoemission spectroscopy (PES) that such an irreversible structural transformation is due to stable subsurface C atoms. They induce anisotropic compressive stress on the surface, which results in insertion of Si dimers to an R row to form a T row.

Cycloaddition on Ge(100) of the Lewis Acid AlCl3

The adsorption and decomposition of AlCl3 on Ge(100) was studied using scanning tunneling microscopy (STM) and high-resolution core-level photoemission spectroscopy (HRCLPES). Through the analysis of the STM image and Ge 3d and Cl 2p core-level spectra of AlCl3 on Ge(100), we found that an AlCl3 molecule reacts with two Ge atoms via a cycloaddition reaction, which forms Cl−Ge and AlCl2−Ge without breaking AlCl3. Additionally, by considering valence shell electron pair repulsion (VSEPR) arguments, the effect of molecular structure on the surface chemistry was explained. To our knowledge, the adsorption of Lewis acid molecules on a semiconductor surface has not been studied in detail. These are the first results for the adsorption structures of Lewis acid molecule on Ge(100).

Correlation of reaction sites during the chlorine extraction by hydrogen atom from Cl∕Si(100)-2×1

The Cl abstraction by gas-phase H atoms from a Cl-terminated Si(100) surface was investigated by scanning tunneling microscopy (STM), high-resolution core level photoemission spectroscopy, and computer simulation. The core level measurements indicate that some additional reactions occur besides the removal of Cl. The STM images show that the Cl-extracted sites disperse randomly in the initial phase of the reaction, but form small clusters as more Cl is removed, indicating a correlation between Cl-extracted sites. These results suggest that the hot-atom process may occur during the atom-adatom collision.

Synthesis and characterizations of Al-doped Zn 0.95Ni 0.05O nanocrystals

Nanocrystalline Zn0.95-xNi0.05AlxO (x = 0.01, 0.02, 0.05 and 0.10) diluted magnetic semiconductors have been synthesized by an autocombustion method. X-ray absorption spectroscopy, high-resolution transmission electron microscopy, energy-dispersive spectrometry and Ni 2p core-level photoemission spectroscopy analyses revealed that some of the nickel ions were substituted for Zn2+ into the ZnO matrix while others gave birth to NiO nanoclusters embedded in the ZnO particles. The Zn0.95Ni0.05O sample showed no enhancement of room-temperature ferromagnetism after Al doping. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Bond Character of Thiophene on Ge(100): Effects of Coverage and Temperature

We have studied the adsorption and decomposition of thiophene (C4H4S) on Ge(100) using scanning tunneling microscopy (STM), high-resolution core-level photoemission spectroscopy (HRPES), and density functional theory (DFT) calculation. Analysis of S 2p core-level spectra reveals three adsorption geometries, which we assign to a Ge-S dative bonding state, a [4 + 2] cycloaddition bonding state, and a decomposed bonding state (desulfurization reaction product). Furthermore, we found that the number ratio of the three adsorption geometries depended on the molecular coverage and the annealing temperature. At low coverages, the kinetically favorable dative bonding state is initially formed at room temperature. As the molecular coverage increases, thermodynamically stable [4 + 2] cycloaddition reaction products are additionally produced. In addition, we found that as the surface temperature increased, the [4 + 2] cycloaddition reaction product either possibly desorbed as molecular thiophene or decomposed to form a metallocycle-like species (C4H4Ge2) and a sulfide (Ge2S). We systematically elucidate the changes in the bonding states of adsorbed thiophene on Ge(100) according to the thiophene coverage and annealing temperature.

Self-Induced 1-D Molecular Chain Growth of Thiophene on Ge(100)

The adsorption of thiophene on Ge(100) has been studied using scanning tunneling microscopy (STM), high-resolution core-level photoemission spectroscopy (HRPES), and density functional theory (DFT) calculations. Until now, thiophene is known to react with the Ge(100) dimer through a [4 + 2] cycloaddition reaction at room temperature, similar to the case of thiophene on Si(100). However, we found that thiophene has two adsorption geometries on Ge(100) at room temperature, such as a kinetically favorable Ge-S dative bonding configuration and a thermodynamically stable [4 + 2] cycloaddition adduct. Moreover, our STM results show that under 0.25 ML thiophene molecules preferentially produce one-dimensional molecular chain structures on Ge(100) via the Ge-S dative bonding configuration.

Interfacial reaction in ZrO2/Si gate-stack structure probed by photoemission spectroscopy combined with combinatorial annealing system

We have investigated the mechanism of Zr silicidation from ZrO2/Si gate-stack structure in ultralarge-scaled-integration devices by high-resolution core-level photoemission spectroscopy with annealing-temperature controlling. We have found that the interfacial SiO2 layer thickness is tunable by controlling the annealing temperature and the silicidation occurs in the narrow annealing-temperature ranges. New method by combinatorial annealing system enables to control the narrow-range annealing temperature for the observation of the silicidation processes and to discuss the silicidation chemical reaction thermodynamically based on the annealing-temperature dependence in core-level photoemission spectra. [DOI: 10.1380/ejssnt.2006.263]

Annealing-temperature dependence: Mechanism of Hf silicidation in HfO2 gate insulators on Si by core-level photoemission spectroscopy

We have investigated the mechanism of Hf silicidation from HfO2 gate insulators on Si by high-resolution core-level photoemission spectroscopy with detailed annealing-temperature controlling. We have found that the silicidation temperature depends on the difference of the chemical states at the interfacial layer. The Hf-silicate layer which is more stable than the SiO2 layer prevents the silicidation. In addition, silicidation processes also promote the formation of SiO2. Chemical shifts in core-level photoemission spectra depend on the interfacial-layer thickness and SiO2 concentration in the HfO2 top layer, which are tunable by detailed annealing temperature.

Chemical analysis of Hf-silicide clusters studied by photoemission spectroscopy

High-resolution core-level photoemission spectroscopy has been performed on the nanoscaled Hf-silicide clusters, which were formed by the annealing at 1000 °C in ultra-high vacuum of HfO 2 films on Si(0 0 1) substrate utilized as ultra-large-scaled-integrated (ULSI) transistors. Angular dependence in Si 2p and Hf 4f core-level spectra revealed the chemical states in the metallic clusters. We compared two HfO 2 samples with and without Hf-metal predeposition on Si substrate before the HfO 2 deposition, which results in the different cluster size due to the different Hf concentration.

Photoemission and core-level absorption spectroscopy of Fe xNbS 2

High-resolution core-level photoemission and core-level absorption spectroscopy of a series of Fe intercalates, Fe x NbS 2 ( x = 0, ∼1/4 and ∼1/3) has been performed to investigate changes in the electronic structures induced by the intercalation. From the evolution of spectral line shapes from the host material, we obtained important information on the electronic and geometric structures specific to particular atomic sites upon intercalation with Fe. The spectra of Fe core-levels also show x dependence, suggesting appreciable mixing of orbitals between Fe and NbS 2.

Experimental and theoretical surface core-level shifts of aluminum (100) and (111)

The surface core-level shifts of Al(111) and Al(100) have been measured using high-resolution core-level photoemission spectroscopy and calculated using density functional theory (DFT). For Al(100), the 2p core-level shift of the first (second) layer was determined to be –75 meV (+20 meV) from experiment and –71 meV (+20 meV) from the DFT calculations. For Al(111), the corresponding values are –27 meV (0 meV) from experiment and –14 meV (–) from the DFT calculations. Core-level splittings caused by the low-symmetry crystal fields at the (111) and (100) surfaces have also been studied. These splittings turn out to be much smaller than previously reported provided proper care is taken of the influence of the core hole screening and of core–valence exchange beyond the DFT level. Finally, the experimental Al 2p line shape was found to contain structure caused by a sharp no-phonon line and a broad and weak phonon replica. (Less)

Carbon-Terminated 3C-SiC(100) Surface Oxidation Studied by High-Resolution Core Level Photoemission Spectroscopy using Synchrotron Radiation

Carbon-Terminated 3C-SiC(100) Surface Oxidation Studied by High-Resolution Core Level Photoemission Spectroscopy using Synchrotron Radiation

First-principles study ofNH3decomposition on the Si(001) surface

We present first-principles density-functional calculations for ${\text{NH}}_{3}$ decomposition on the Si(001) surface. Our calculations show that the dissociated NH (or N) species inserted into the dimer bond is thermodynamically favored over that inserted into the back bond of the Si dimer. However, $\mathrm{N}$ interdiffusion from the former configuration to a recently observed ${\text{Si}}_{3}\ensuremath{\equiv}\mathrm{N}$ configuration (where the $\mathrm{N}$ atom is incorporated at an interstitial site around the third layer) is kinetically prohibited because of the existence of a high activation barrier. On the other hand, there is a relatively lower-energy barrier from the latter configuration, leading to formation of the ${\text{Si}}_{3}\ensuremath{\equiv}\mathrm{N}$ configuration. This kinetics of $\mathrm{N}$ interdiffusion is consistent with the proposed reaction path from a recent high-resolution core-level photoemission spectroscopy data.