Mixed ab initio quantum mechanical and Monte Carlo calculations of secondary emission from SiO2 nanoclusters

A mixed quantum mechanical and Monte Carlo method for calculating Auger spectra from nanoclusters is presented. The approach, based on a cluster method, consists of two steps. Ab initio quantum mechanical calculations are first performed to obtain accurate energy and probability distributions of the generated Auger electrons. In a second step, using the calculated line shape as electron source, the Monte Carlo method is used to simulate the effect of inelastic losses on the original Auger line shape. The resulting spectrum can be directly compared to 'as-acquired' experimental spectra, thus avoiding background subtraction or deconvolution procedures. As a case study, the O K-LL spectrum from solid SiO2 is considered. Spectra computed before or after the electron has traveled through the solid, i.e., unaffected or affected by extrinsic energy losses, are compared to the pertinent experimental spectra measured within our group. Both transition energies and relative intensities are well reproduced.Comment: 9 pageg, 5 figure

On the use of elastic peak electron spectroscopy (EPES) tomeasure the H content of hydrogenated amorphous carbon films

Quasi-elastic scattering of 1–2 keV electrons is consideredwith respect to measuring theHcontent in hydrogenated amorphous carbon (a-C :H)materials. Interest in the technique lies in the fact that H cannot be typically detected by electron spectroscopic means (AES or XPS for instance). The feasibility of the approach is demonstrated and a quantification procedure is proposed. At the same time however, limitations of the technique (electron stimulated H desorption, low intensity of the H related signal and its spectral interference with the π-plasmon peak) are discussed

Characterization of Pristine and Functionalized Graphene on Metal Surfaces by Electron Spectroscopy

Graphene is a candidate material to replace silicon for the development of electronic devices with unsurpassed characteristics and of new carbon-based technologies. The success of graphene in this regard depends critically on three factors: first, a better understanding of the growth dynamics on substrate surfaces, notably metals, intended to achieve high-quality large grain size; second, functionalization or doping intended to open a tunable band gap in the otherwise zero-gap pristine graphene; and third, accurate monitoring of optical and electronic properties by spectroscopic investigation. Concerning the aforementioned interconnected aspects, this chapter focuses on current theoretical and experimental advances on the dynamics of graphene growth, and on the chemistry and morphology of functionalized graphene sheets. In particular, electron spectroscopy measurements (time-dependent x-ray photoelectron spectroscopy, angle-resolved photoemission spectroscopy, near-edge x-ray absorption fine structure) and ab initio calculations are used: (i) to follow graphene growth on metals starting from atomic and molecular scale to nanoscale; (ii) to study the interaction mechanisms between the growing graphene layer and the substrate; (iii) to investigate the effect of doping elements and adsorbates on the electronic structure of graphene. The last point represents a means (alternative to the use of graphene nanoribbons) to control the band gap, essential for the development of graphene- based electronics

Computational and experimental study of pi and pi + sigma plasmon loss spectra for low energy (<1000 eV) electrons impinging on highly oriented pyrolitic graphite (HOPG)

A Monte Carlo simulation is described and used to calculate the energy distribution spectra of low primary energy E0 (lower than 1000 eV) electrons impinging on HOPG. The simulated spectra are compared with experimental electron energy loss (EEL) spectra. Similarities and differences between experimental and simulated data are discussed. Copyright 2006 Elsevier B.V. All rights reserved

The graphite Valence Band electronic structure: a combined Core-Valence-Valence Auger and Valence Band Photoemission study

The Valence Band (VB) electronic str5ucture of grphite is investigated via two VB probes, namely Core-Valence-Valence (CVV) Auger emission and VB photoemission, both induced by X-Ray (hv=1486.6eV) irradiation. The associated spectral structure is resolved by taking either the spectrum second derivative or the spectrum difference with respect to a smooth curve. Comparison between the two derived curves shows that both probes reproduce the VB Density Of States (DOS) in the upper VB region, while many body effects (Coulomb interaction between two final state holes of s-character) distort the CVV spectrum in the lower VB regio

Comparison between Monte Carlo and experimental aluminum and silicon electron energy loss spectra

A Monte Carlo (MC) simulation is described and used to calculate the energy distribution spectra of backscattered electrons from Al and Si. For the simulations, elastic scattering cross sections are calculated by numerically solving the Dirac equation in a central field. Inelastic scattering cross sections are computed within the dielectric response theory developed by Ritchie, and by Tung et al. Extension from the optical case to non-zero momentum transfer is done according to Ritchie and Howie. To evaluate surface and bulk contributions to the spectra, the Monte Carlo model treats the surface excitations according to the Werner differential surface and volume excitation probability theory. The Monte Carlo calculations are compared with the experimental reflection electron energy loss (REEL) spectra acquired in our laboratory

Energy loss of electrons backscattered from solids: measured and calculated spectra for Al and Si

Electron energy loss distributions relative to Al and Si are calculated for primary electron energies ranging from 500 eV to 2000 eV under the assumption that experimental spectra arise from electrons undergoing a single large-angle elastic scattering event (so-called V-type trajectories). The method used to calculate the spectra is based on the combination of the Chen and Kwei dielectric formalism with the V-type trajectory modeling. Good agreement is found between calculated and measured spectra