Low-energy Electron Energy-loss Spectra Research Articles

Synthesis and Characterization of Single-Phase TiC Nanotubes, TiC Nanowires, and Carbon Nanotubes Equipped with TiC Nanoparticles

Single-phase TiC nanotubes were successfully synthesized for the first time, by the reaction of carbon nanotubes (CNTs) with Ti powder at 1300 °C for 30 h. CNTs equipped with TiC nanoparticles and TiC nanowires were synthesized along with these single-phase TiC nanotubes, and the number ratio of single-phase TiC nanotubes to these other products was very small. According to the core and low-energy electron energy loss spectra taken from CNTs and the CNTs reacted with Ti powder, the ratio of Ti to C in TiC nanowire was higher than that in TiC nanotubes and the ratio in CNT equipped with TiC nanoparticles was the lowest. Three different types of TiC nanomaterials, TiC nanowires, TiC nanotubes, and CNTs equipped with TiC nanoparticles, as well as unreacted CNTs, were observed in this study, possibly because the concentration of Ti vapor decreased with increase in depth from the surface of CNT aggregates. A partly single-crystalline TiC nanotube was also observed.

On a dielectric approach to understand Electron Energy Loss Spectra from carbon materials

A phenomenological approach to understand the low energy Electron Energy Loss Spectra (EELS) from carbon materials is proposed. Within certain approximations, expressions relating the π and π + σ plasmon energy to the material mass density and sp 2 fraction are derived. The characteristic excitation energies of π and σ electrons as well as the screening of π electrons by the σ electron polarizability are shown to be crucial factors needed to reproduce the experimental dependence of plasmon energies on mass density. A comparison with earlier results shows the more general character of the present ones and allows a better understanding of previous proposals to characterize amorphous carbon by low energy EELS.

Low-energy electron energy loss spectroscopy of rutile and anatase TiO2 films in the core electron excitation regions

Abstract Low-energy electron energy loss spectra in the core electron excitation regions were successfully measured for TiO2 thin-films with rutile or anatase structure. Noticeable differences in the excitation spectra of both Ti 2p and O 1s core electrons were observed between rutile and anatase TiO2 films, which may be due to the difference in the local symmetry of conduction band states between these polymorphs. The present technique was applied to characterize the crystal structure of the TiO2/SnO2 stacked-layers in the near-surface region, which is important for the application of these layers to a novel multifunctional glazing with both photocatalytic and heat-insulating properties.

Growth mechanism for epitaxial cubic boron nitride films on diamond substrates by ion beam assisted deposition

Cubic boron nitride (c-BN) films were grown on highly (001)-oriented chemical vapour deposited diamond films at various substrate temperatures ( T s) ranging from 420 to 1000 °C by using ion beam assisted deposition (IBAD). The resulting c-BN films were characterized by Fourier transformed infrared spectroscopy, high-resolution transmission electron microscopy, Rutherford backscattering spectroscopy as well as X-ray diffraction. The results demonstrate that the epitaxial growth of c-BN films on diamond can be realized only at high values of T s (approx. 900 °C), while at, e.g. 420 °C, an intermediate hexagonal BN layer is formed between the substrate and the c-BN film as it is usually observed for c-BN growth on top of Si. This may be due to the amorphization or graphitization (radiation damage) of the diamond surface at low T s under the assisting ion bombardment during c-BN nucleation. The plasmon energies of the diamond substrates that were held at various temperatures and bombarded by a mixture of argon and nitrogen ions were determined from in situ low-energy electron energy loss spectra. The results indicate that at higher T s values radiation damage can be annealed out thereby maintaining an ordered substrate surface, hence allowing epitaxial growth of c-BN.

R-matrix approach to low-energy electron energy-loss spectroscopy from NiO

Low-energy electron energy-loss spectra from NiO have been calculated using R-matrix methods to describe the excitation of $3d\ensuremath{-}3d$ transitions on the Ni ions. The effect of the crystal field is fully included, though only single scattering is considered at this stage. The total scattering cross sections demonstrate the importance of exchange-scattering processes in addition to direct scattering, even at higher energies of the scattering electron. The differential cross sections allow the investigation of angular, spin, and symmetry dependence for comparison with experiment. For certain transitions the angular dependence shows zeros associated with the point group symmetry of the Ni ion, and these are discussed. The ratio of spin-flip to non-spin-flip contributions is calculated exactly for multiplicity-changing transitions, and is shown to be independent of scattering geometry and energy of the incident electron.

Low-Energy Electron Energy Loss Spectra of Gd-Chloride

Low-Energy Electron Energy Loss Spectra of Gd-Chloride

Low-Energy Electron Energy Loss Spectra of Transition Metal Halides

Low-energy electron energy loss spectra of transition metal halides MnBr 2 , MnF 2 and FeF 3 are measured for primary energies 20 to 400 V. For Mn halides, there are loss peaks which are thought to be due to the forbidden d-d transitions in Mn ++ ions. The intensities of these loss peaks are primary energy dependent and decrease with the increase of the incident energy. As to FeF 3 , intensities of loss peaks are also incident energy dependent, but the dependence is different among each loss peak. As to the origin of the primary energy dependent losses, it is thought that the mixing of ligand halide p-orbitals with the d-orbitals of central metal ions is essential.

Low-Energy Electron Energy-Loss Peak Due to Excitation of the Surface State Associated with Dangling Bonds on Si(001)-2×1 Surface

Low-energy electron energy-loss spectra (LEELS) from the Si(001)–2×1 surface were measured for some surface wave resonance (SWR) conditions: (1) The electron beam forms some surface waves associated with the fundamental lattice points (SWRb), and (2) the electron beam forms some surface waves with the 1/2-order superlattice rods (SWRs). In the LEELS for SWRb, the peak heights at 5, 8 and 11 eV in energy-loss value, ΔE, become slightly large. On the other hand, for SWRs, the peak heights at ΔE=1.5 and 8–9 eV are enhanced. The difference of LEELS for both SWR conditions reflects the difference in the thickness of the layers in which the electron beam propagates. It is discussed that the peak at ΔE=8–9 eV is due to excitation of a collective motion for the electrons in the dangling bonds out of the first plane of the surface atoms.

Electron Affinities of Polystyrene and Poly(2-vinylpyridine) by Low-Energy Electron Inelastic Scattering

Low-energy electron energy loss spectra including secondary electron bands and low-energy electron transmission spectra were measured for polystyrene and poly(2-vinylpyridine) thin films deposited on metal substrates. Almost all the features of these spectra could be explained as the result of electronic excitations localized in pendant molecules. The electron affinities of polystyrene and poly(2-vinylpyridine) were estimated as 0.4±0.1 eV and 0.3±0.1 eV, respectively, based on the one-to-one correspondence of the spectral features of these two types of spectra.

Angle-resolved electron energy-loss spectra from Si(111)−7 × 7 surface under surface wave resonance condition for low-energy electrons

Low-energy electron energy-loss spectra (LEELS) from Si(111)−7 × 7 surface were measured under surface wave resonance (SWR) conditions, under which (1) the electron beam forms a surface wave of the 1 7 -order superlattice reflections (SWR s), and (2) the beam forms the surface wave and another surface wave of fundamental lattice reflections (SWR b) simultaneously. The peak heights at 5, 7.5 and 15 eV in energy-loss value, Δ E, which are associated with a bulk band state and two surface states due to backbonds respectively, became slightly large under the SWR b condition. On the other hand, in the LEELS under the SWR s condition, the peak height at ΔE = 1–2 and 8–9 eV was enhanced. Since the peak at 1–2 eV is known to be associated with the surface state due to dangling-bonds, it is considered that LEELS measurement under the SWR s condition reflects some information on electronic structure of Si(111)−7 × 7 surface. Then it is also discussed that the peak at ΔE = 8–9 eV under the SWR s condition is due to excitation of a collective motion for electrons in the dangling-bonds out of the first plane of surface atoms.

Core electron excitation spectra of diamond, graphite, and glassy carbon

Low-energy electron energy loss spectra in theC(1s) core electron excitation region have been measured in diamond, graphite and glassy carbon in the non-differentiated form. The background subtractedN(E) spectrum has been proved to reflect the density-of-states (DOS) of the conduction band well, and the conduction band structures of these materials have been elucidated. The energy positions of the symmetry points in their conduction bands have been determined from the second-derivative spectra, which were obtained by numerical differentiation of the measuredN(E) spectra.

The sodium tungsten bronzes: a study of the changes in electronic structure with composition using high-resolution electron spectroscopy

The variation with composition of the electronic structure of polycrystalline sodium tungsten bronzes NaxWO3(0<x<1) has been studied using a combination of high-resolution electron spectroscopic techniques. Samples on either side of the metal-nonmetal transition (x approximately 0.25 from conductivity data) were used. Low-energy electron energy-loss spectra (LEELS) agree well with those predicted in previous optical studies. In particular the effective electron mass (m*) shows the expected variation with bulk composition. Ultraviolet photoelectron spectroscopy (UPS) has been used to study the valence and conduction bands. Measurements of work function ( phi ); density of states at the Fermi level (g(EF)); and effective electron mass at the Fermi level (mEF*) all show linear variations with bulk composition, in agreement with the findings of magnetic susceptibility and low-temperature specific heat capacity studies. A linear variation of the ratio of the intensities of the conduction and valence bands with bulk composition is also observed across the whole composition range. The variation in shape of the conduction band with composition is consistent with the formation of an impurity band which overlaps a nearly-free-electron-like conduction band that narrows with increasing sodium content. The data obtained in this study are consistent with a mechanism for the metal-nonmetal transition involving the formation of localised small polarons when the electron concentration falls below a critical value.

Surface wave resonance effect in low-energy electron energy-loss spectra from MgO(001)

The study the influence of inelastic diffraction on low-energy electron energy-loss spectra (LEELS), the LEELS from an air-cleaved (001) face of MgO were observed for various values of energy and angle of incidence of primary electrons, scattering angle and azimuthai angle. It has been confirmed that the LEELS consist of two kinds of loss peaks: those associated with an energy loss after the elastic diffraction and those associated with an energy loss before the elastic diffraction (Kikuchi line). The latter is observable only when inelastically scattered electrons are diffracted under the surface wave resonance (SWR) conditions. It has also been found that the Kikuchi Une splits into two with an intensity dip at the centre under one of the SWR conditions.

Surface wave resonance effect in low-energy electron energy-loss spectra from MgO(001)

Surface wave resonance effect in low-energy electron energy-loss spectra from MgO(001)

Surface wave resonance effect in low-energy electron energy-loss spectra from MgO(001)

The study the influence of inelastic diffraction on low-energy electron energy-loss spectra (LEELS), the LEELS from an air-cleaved (001) face of MgO were observed for various values of energy and angle of incidence of primary electrons, scattering angle and azimuthal angle. It has been confirmed that the LEELS consist of two kinds of loss peaks: those associated with an energy loss after the elastic diffraction and those associated with an energy loss before the elastic diffraction (Kikuchi line). The latter is observable only when inelastically scattered electrons are diffracted under the surface wave resonance (SWR) conditions. It has also been found that the Kikuchi line splits into two with an intensity dip at the centre under one of the SWR conditions.

Surfaces of Vacuum-Deposited Silicon Oxide Films Studied by Auger Electron Spectroscopy

Silicon oxide films were deposited at a rate of 10–20 Å/min by heating commercial SiO powder in vacuums of 10-5 and 10-7 Torr and were analyzed by Auger electron spectroscopy (AES). To assign the Auger spectra with the energy range 50–100 eV from the film surfaces, AES was carried out on air-fractured and electron-irradiated surfaces of quartz. The spectra are attributed to a three-dimensional network of Si(–O–)4 tetrahedra; no spectra due to networks of Si(–Si–)4 tetrahedra were observed. These results were supported by low-energy electron energy-loss spectra observations. The Auger spectrum associated with oxygen vacancies was also observed, the intensity of this being higher for the films prepared in the higher vacuum. Thus the silicon oxide film surfaces are presumed to consist of a three-dimensional network of Si(–O–)4 tetrahedra with some oxygen vacancies.