The electron energy loss spectrum of EuO(100)

Energy losses of 200 eV to 2 keV electrons reflected from a disordered EuO(100) crystal show a bulk plasmon loss consistent with just less than six “quasi free” electrons per EuO unit, and 5p → nd resonance losses above the 5p threshold. The ratio of intensity of the 4d¹⁰ 4fⁿ⁰ → 4d⁹ 4fⁿ⁺¹ “giant resonance” loss at 142 eV to the corresponding direct recombination feature varies with energy, while the direct recombination and related Auger channels show similar energy dependence.     

The effect of inhomogeneous dopant profiles on the electron energy loss spectra of Si(100)

Surface Plasmon excitations are measured by high resolution electron energy loss spectroscopy (HREELS) on highyln-doped, clean Si(100) wafers. After different annealing cycles at 900°C the plasmon loss shifts to lower loss energy. This effect can be quantitatively described by out-diffusion of the phosphorus dopant. The assumption of diffusion profiles and fits of calculated loss spectra to the experimental data allow a determination of the diffusion constant of phosphorus in silicon.     

Leed,auger, and electron energy loss studies of Ni epitaxially grown on Cu(100)

Nickel was epitaxially deposited onto a clean, flat Cu(100) surface. Low energy electron diffraction I(E) curves were recorded for 0.6, 1.1, and 2.7 monolayer (ML) Ni coverage. Multilayer relaxation was considered in theoretical calculations, which were compared with experiment by means of the R|ΔE| factor. The estimated relaxations of the first and second interlayer spacings are estimated to be − 2% and + 1.5% for clean Cu(100), − 2% and − 1.5% for 1 ML Ni coverage, relative to the bulk Cu interlayer spacing of 1.81 Å, and −1% and 0% for 3 ML Ni coverage, relative to the bulk Ni spacing of 1.76 Å. Decreasing the surface Debye temperature of the Ni layer to 268 K from the bulk value of 440 K improves the agreement between theory and experiment. The optimum inner potential values are − 9 and − 10 eV for clean Cu(100) and Ni on Cu(100), respectively. Auger electron spectroscopy was used to determine the thickness of the Ni films, and LEED indicates layer-by-layer growth until about 4 layers, when the LEED spots begin to spread, indicating island formation. Electron energy loss spectra were obtained with primary electron energies of 150 and 300 eV. The 3p core ionization transition was clearly observed after 0.5 ML Ni coverage. Peaks at 3.8 and 7.5 eV for clean Cu are ascribed to interband transitions, and shift to higher energy with Ni coverage. Peaks at 10 and 16 eV for clean Cu (ascribed to an interband transition and a surface plasmon, respectively) disappear with Ni coverage. Bulk plasmon peaks at 19 and 27 eV remain unshifted with Ni coverage. The effect of 0.9 and 1.3 ML Ni coverage of Cu(100) on the chemisorption of Co and oxygen was also studied. The behavior of the surface towards oxygen chemisorption was similar to that of the pure Ni surface. For a large exposure of oxygen (50 L and more) the EEL and Auger spectra are very similar to those observed for NiO. In the case of CO, for submonolayer Ni coverage, the surface shows a more Cu-like behavior, while for larger Ni coverage (a monolayer and more) there is a great similarity with the behavior of the pure Ni(100) surface.     

Characteristic energy loss and Auger electron spectra of GaP (110)

The characteristic energy loss and Auger electron spectra of clean GaP (110) have been measured with a four grid retarding field analyser. A peak in the loss spectrum has been found at 11.2 eV which is probably due to a surface plasma loss. The remaining structure has been assigned to direct interband transitions, to single and double bulk plasma losses and to d-band transitions by analogy with previous optical and electron transmission studies. Suggestions are made as to the origin of the peaks in the Auger spectrum and changes in the spectrum in the presence of oxygen are discussed.     

The electron energy loss spectrum of Br on Au (100)

The electron energy loss spectrum of Br on Au (100) shows a sharp loss at 2.5 eV accompanied by a weaker broader feature at 5.5 eV and a broad enhancement centred at 16 eV. It is suggested that an adsorbate resonance lies above the top of the d-band allowing adsorbate → free metal state transitions without appreciable coupling to or competition from metal excitations.     

Characteristic electron energy loss spectra for diamond

The complete set of optical fundamental functions is determined for diamond in the range from 4 to 32 eV. The features of the bulk and surface characteristic energy loss spectra are elucidated and the functions n _eff(E) and ?_eff(E) are calculated. The energies of volume and surface plasmons are established.     

Hydrogen chemisorption on Ni(110) by high-resolution electron energy loss spectroscopy

High-resolution electron energy loss spectra of hydrogen-covered Ni(110) surfaces both at 100 and 300 K are presented. The adsorbed sites of hydrogen atoms are discussed.High-resolution electron energy loss spectra of hydrogen covered Ni(110) surfaces have been studied. Tentative models for the adsorbed sites of hydrogen atoms are as follows: (1) For the (2 × 1)-H surface, hydrogen is adsorbed in the three-coordinated sites of the rudimentary (111) face of the unreconstructed Ni(110) substrate. (2) For the low-temperature (1 × 2)-H surface, hydrogen is adsorbed in the three-coordinated sites and, probably, in the two-fold hollow sites of the distorted Ni(110) substrate. (3) For the room-temperature (1 × 2)-H surface, hydrogen is disorderedly adsorbed in the three-coordinated, two-fold hollow and short-bridge sites and, possibly, in the octahedral sites of the distorted Ni(110) substrate. Some of the unresolved problems in the above assignments are summarized: (1) Strictly, the three-coordinated sites above are somewhat different from those discussed in the molecular-beam diffraction study [5]. (2) For the low-temperature (1 × 2)-H surface, the loss associated with hydrogen in the two-fold hollow sites is apparently not observed. (3) Intensity changes of the three losses for the room-temperature (1 × 2)-H surface with increasing hydrogen pressure (Fig. 2) are not well understood.     

Simple algorithm for quantitative analysis of reflection electron energy loss spectra (REELS)

A detailed comparison of two different physical approaches for quantitative analysis of reflection electron energy loss spectra (REELS) is presented. The Tougaard–Chorkendorff (TC) algorithm [S. Tougaard, I. Chorkendorff, Phys. Rev. B35 (1987) 6570] is analyzed theoretically and applied to experimental spectra of four elemental solids (Si, Cu, Ag, and Au). A closed expression is derived for the quantity retrieved by the TC-algorithm, the so-called “effective” cross section, which was originally only given as a recursive procedure. Single scattering loss distributions are derived from the experimental spectra using the bivariate reversal method [W.S.M. Werner, Phys. Rev. B74 (2006) 075421]. The latter agree satisfactorily with density functional theory (DFT) calculations and other data found in the literature. Using these single scattering loss distributions, the TC “effective” cross section can be perfectly reproduced if the fact is taken into account that the effective cross section is not a single scattering loss distribution and is governed to a significant extent by elastic scattering. On the basis of the above results, a dramatically simplified deconvolution scheme for quantitative analysis of REELS is developed.     

Characteristics electron energy loss studies of molecular halogens adsorbed on Fe(100)

The electron energy loss spectra for several molecular Br₂ monolayers adsorbed on a chemisorbed bromine overlayer on Fe(1 0 0) show a sharp loss at about 3.0 to 3.8 eV. For one or more molecular layers of I₂ adsorbed on a chemisorbed iodine overlayer on Fe (1 0 0), a sharp electron loss feature is observed at 4.4 ± 0.2 eV. It is suggested that the electron energy losses for condensed Br₂ at 3.0 eV and for condensed I₂ at 4.4 eV are a result of a 1π_g to 2σ_u electron excitation.     

Electron energy loss and Auger study of epitaxially grown Cu on Ni(100)

Auger and electron energy loss spectra have been measured on films of Cu epitaxially grown on Ni(100). The films were prepared under UHV conditions using a quartz crystal for monitoring the deposition rate. LEED measurements were taken to determine the orientation of the films. The presence of a monolayer of Cu on Ni(100) is enough to suppress the 3p-3d transition on the surface of the sample. The electron energy loss spectra were studied as a function of the primary electron energy (50 to 300 eV). The experimental results were qualitatively analyzed using recent theoretical calculations of Cooper and co-workers. The effect of a small Cu coverage on Ni(100) on the chemisorption of CO and O₂ was also studied. A strong suppression of CO chemisorption at room temperature was observed. In the case of O₂, large exposures are necessary in order to observe a significant amount of oxygen on the surface. The absence of any appreciable chemisorption on the surface of the metal is attributed to the lack of empty d-surface states.     

Auger electron spectroscopy and electron energy loss spectroscopy studies on carbonization of Si(100) and (111) surfaces with ethylene

The reactions of Si(100) and Si(111) surfaces at 700 °C (973 K) with ethylene (C₂H₄) at a pressure of 1.3×10⁻⁴ Pa for various periods of time were studied by using Auger electron spectroscopy (AES) and electron energy loss spectroscopy (ELS). For a C₂H₄ exposure level, the amount of C on the (111) surface was larger than that on the (100) surface. The formation of β-SiC grain was deduced by comparing the C_KLL spectra from the sample subjected to various C₂H₄ exposure levels, and from β-SiC crystal.     

Observation of interband transitions in polarized electron energy loss spectra of Gd(0001)

We have detected the 4f ⁷(5d6s)³→4f ⁸(5d6s)² interband transition in an angular-resolved, inelastic scattering experiment with spin-polarized, low-energy electrons from ferromagnetic Gd(0001). The spectrum of the inelastic scattering asymmetry clearly reveals the dominant spin-dependent energy loss mechanism involved. Furthermore its comparison with elastic scattering data allows a characterization of the combined role of diffraction and energy loss processes in inelastic electron scattering.     

Direct transitions in isochromat spectra from Ni(100)

Bremsstrahlung isochromat spectra at $\text{h}\text{?}\text{ω = 9.7 eV}$ were recorded from well characterized samples of polycrystalline nickel and Ni(100). Differences between spectra from the two samples are attributed to direct optical interband-transitions. Predictions from theoretical band structure calculations are in accord with observed features.     

Auger electron and characteristic energy loss spectra of plutonium

The Auger electron and characteristic loss spectra of plutonium have been obtained for the first time using a four grid retarding potential analyzer. The surface of this reactive metal was prepared by scribing in situ in good vacuum with a titanium carbide blade. Oxygen and carbon impurities were still present after scribing. The origin of the Auger electron and loss peaks is suggested, and a correlation is made with the peaks observed for uranium dioxide by Ellis and Campbell.     

Computing electron energy loss spectra with the Discontinuous Galerkin Time-Domain method

In this work, we demonstrate how to extract electron energy loss spectra of metallic nano-particles from time-domain computations. Specifically, we employ the Discontinuous Galerkin Time-Domain (DGTD) method in order to model the excitation of individual metallic nano-spheres and dimers of spheres by a tightly focussed electron beam. The resulting electromagnetic fields that emanate from the particles act back on the electrons and the accumulated effect determines the electrons’ total energy loss. We validate this approach by comparing with analytical results for single spheres. For dimers, we find that the electron beam allows for an efficient excitation of dark modes that are inaccessible for optical spectroscopy. In addition, our time-domain approach provides a basis for dealing with materials that exhibit a significant nonlinear response.     

Low temperature electron energy loss spectra of acetylene chemisorbed on metal single-crystal surfaces; Cu(111), Ni(110) and Pd(110)

Vibrational spectra of acetylene chemisorbed on Cu(111), Ni(110) and Pd(110) at 110–120 K were measured using electron energy loss spectroscopy. Loss peaks were assigned to vibrational modes of the non-dissociatively adsorbed molecules with the aid of the corresponding C₂D₂ spectra. The spectra show that the molecules undergo significant rehybridisation on adsorption. Comparisons are made with the spectra of acetylene adsorbed on a range of other transition metal surfaces at low temperature. Taking into account these and earlier literature results, two distinct patterns of spectra are observed (Type A and Type B) for specular spectra. The Cu(111) spectrum is classified as Type A while the Ni(110) and Pd(110) spectra are classified as Type B. Suggestions are made for the structures of the surface species corresponding to the two spectral types.     

Multiquantum scattering processes and transmission electron energy loss spectra

Microscopic many-body theory for electronic properties of solid states is developed with an emphasis on the role of correlation memory effects. Heisenberg equation of motion, fluctuation-dissipation theorem and operators of commutation have been used to calculate multiplasmon transmission electron energy loss spectra. Multiquantum integral kinetic equation for the longitudinal complex dielectric function is derived. Strong interaction between high-energy probe beam electrons penetrating the solid state and plasma of valence electrons is taken into account. It is shown that average number of high-frequency plasmons generated in every collision process is more than one for typical values of metal parameters. It is obtained that excitation of a good few plasmons is simultaneous event. Calculated multiplasmon structure of electron energy loss spectra coincides with experimental.     

Vibrational spectra of coadsorbed CO and H on Ni(100) and Ni(111)

High resolution electron energy loss spectra are reported for coadsorbed hydrogen and carbon monoxide on Ni(100) and Ni(111). On neither surface was there any evidence for either C-H or O-H bonds. On Ni(111) one CO stretching frequency is observed and it does not change significantly in the presence of coadsorbed hydrogen. This is consistent with segregation of CO and H into islands. On Ni(100) the situation is much different; one frequency is observed in the absence of H(a) while three CO stretching frequencies are observed for the coadsorbed layers. These are attributed to on-top, two-fold bridged and four-fold binding of CO to the Ni(100) surface. These results demonstrate significant structure sensitivity for the organization of these coadsorbed species.     

Infrared-visible sum-frequency generation spectra of CO on Ni(100)

Infrared-visible sum-frequency generation (SFG) spectra of the stretching region of carbon monoxide adsorbed on Ni(100) are measured as a function of overlayer coverage and substrate temperature. The frequency and linewidth of the CO vibrational resonance in SFG have a similar dependence on coverage and temperature to that observed in linear absorption and emission spectroscopies. The lineshape of the SFG resonance, however, is influenced by the nonlinear response of the underlying metal surface. A simple model indicates that the nonresonant response of the substrate is out of phase with respect to that of the resonant CO response.     

Analysis of reflection electron energy loss spectra (REELS) for determination of the dielectric function of solids: Fe, Co, Ni

A simple procedure is developed to simultaneously eliminate multiple scattering contributions from two reflection electron energy-loss spectra (REELS) measured at different energies or for different experimental geometrical configurations. The procedure provides the differential inverse inelastic mean free path (DIIMFP) and the differential surface excitation probability (DSEP). The only required input parameters are the differential cross section for elastic scattering and a reasonable estimate for the inelastic mean free path (IMFP). No prior information on surface excitations is required for the deconvolution. The retrieved DIIMFP and DSEP can be used to determine the dielectric function of a solid by fitting the DSEP and DIIMFP to theory. Eventually, the optical data can be used to calculate the (differential and total) inelastic mean free path and the surface excitation probability. The procedure is applied to Fe, Co and Ni and the retrieved optical data as well as the inelastic mean free paths and surface excitation parameters derived from it are compared to values reported earlier in the literature. In all cases, reasonable agreement is found between the present data and the earlier results, supporting the validity of the procedure.