Characteristic Energy Loss Spectra Research Articles

Comparative Investigation of XPS Spectra of Oxidated Carbon Nanotubes and Graphene

X-ray photoelectron emission spectra of thermally reduced graphene oxide samples and carbon nanotubes (CNTs) with various oxidation degrees are presented in this paper. A method for the reconstruction of differential electron inelastic scattering cross sections from the energy loss spectra of photoelectrons is described and discussed. The analysis of the part of the characteristic photoelectron energy loss spectrum adjacent to the C1 peak indicated a considerable influence of the thermal reduction of graphene oxide on the electron properties of the samples obtained. On the contrary, the oxidation of CNTs by refluxing in a concentrated HNO3 solution does not change the free electron excitation spectrum.

Annealing Effect on the Composition and Electrophysical Properties of N-Type Silicon Surface

During low-temperature annealing, the segregation of the alloying element leads to a strong enrichment of the surface layer, causing a rearrangement of the surface electron structure. This change in the electron structure is manifested in the characteristic energy loss spectra. Annealing of single crystals at 400–500 K leads to an increase in the density of surface electron states. As shown by the calculations of the surface potential using experimental data on the temperature dependence of the surface concentration, dopant segregation causes a linear increase in the surface potential.

Direct numerical reconstruction of inelastic cross sections from REELS and ISS spectra

The reconstruction of inelastic scattering cross sections faces two problems: the measured signal (energy spectrum) is a multiple scattering signal; the inelastic energy loss is nonuniform over the target depth. In this paper, we present a method for numerical reconstruction of cross sections from characteristic energy loss spectra, which efficiently solves both problems within a multilayer model. It is shown that the inverse problem of cross section extraction in the three-layer model is ill-conditioned, and the method is practically inapplicable to the three-layer model. The direct numerical reconstruction method yields a strongly “noised” result and can be applied only to obtain a priori information on the inelastic cross section form for further fitting. Using a combination of two methods, inelastic scattering cross sections were reconstructed for aluminum from characteristic energy loss spectra at probe beam energies of 5 and 40 keV. It is shown that ionization in solids should be described as a local process and as a collective one using the dispersion formula similarly to the case of excitation plasmons.

Low energy electron induced characteristic losses in the Fe 73.6Cu 1Nb 2.4Si 15.8B 7.2 (FINEMET) alloy surface

Electron Energy Loss Spectroscopy has been employed for investigation of the electronic states of amorphous and crystalline Fe 73.6Cu 1Nb 2.4Si 15.8B 7.2 (FINEMET) alloy surface and alloy components. Electron energy losses have been measured for primary electron beam energies E 0 from 150 to 650 eV. The characteristic energy loss spectra were composed of main peaks which we have interpreted due to surface and bulk plasmons, a combination of surface and bulk losses, high harmonics of plasma losses, inter-band transitions and ionization of core levels. The measured energies for the plasmon excitations were found not to agree with calculated values according to the classical theory for the collective oscillations in solids. Changes in the intensity lines of the surface and bulk plasmons were observed for all specimens depending on primary electron energy E 0. The present results are compared with characteristic energy loss data reported in the literature.

Spectra of fundamental optical functions of BeSe

Spectra of sets of fundamental optical functions of BeSe were derived for the range of 0–25 eV. Calculations were performed using an experimental ɛ2(E) spectrum and integral Kramers-Kronig relations. Using combined Agrand diagrams, the spectra of permittivity and characteristic energy losses of electrons were decomposed into elementary transverse and longitudinal components. The main parameters of these components were determined. The results obtained were compared with theoretical spectra of optical functions calculated using the OPW and APW methods and with the energy bands obtained in an ab initio GW approximation.

Optical properties of imperfect In2Se3

Spectra of complete sets of optical functions for α-and β-In2Se3 in the range of 0–20 eV were calculated using experimental reflection spectra and the Kramers-Kronig relation. Special features in the spectra of optical functions for both In2Se3 phases were analyzed. The spectra of both permittivity and characteristic electron energy losses were decomposed into elementary transverse and longitudinal components using the combined Argand diagrams. The main parameters of the electron transitions for these components were determined. The structure of the components was compared with the structure of the expected spectrum of interband transitions.

The comparative investigation of spectra of characteristic energy losses of electrons reflected from the surface of semiconductors and their alloys

The spectra of electrons backscattered from the surfaces of semiconductors (Si,Ge) and their alloys (Si+Ge) were studied using the reflected electron energy loss spectroscopy (REELS) at 500–2000 eV primary beam energies. Seven peaks corresponding to different energy losses have been revealed in the spectra. Based on an analysis of the experimental data on the REEL spectra measured for different primary energies and angles of incidence of the electron beam as well as on Brillouin zone diagrams and electron density distributions in both the valent band and the conduction band the following features have been established. In addition to two peaks resulting from the surface — and bulk plasmon oscillations of valent electrons there are four peaks from the interband electron transitions and one (sometimes two) connected with the electron polarisation of the ion cores. An oscillator model of a the dielectric function of a solid taking into account the weight of the functions of bulk — and surface energy losses has been proposed to account for the REEL spectra. The model takes into consideration the fact that the energy losses of primary electrons are connected not only with excitation of plasmons but also with electron transitions from the valent band to the conduction band. For the calculation of the REEL spectra in terms of the model we used information on the band structure of the solid under investigation. It has been shown that the REEL spectra calculated with the proposed model agree with the experimental ones.

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 neff(E) and ɛeff(E) are calculated. The energies of volume and surface plasmons are established.

The energy loss spectroscopy of ABO3 ferroelectrics

Optical spectroscopy methods were used to study the spectra of characteristic energy losses of some ABO 3 (oxygen-octahedral) ferroelectrics. The dominant role of the BO 6 octahedra in the formation of the energy spectra of oxygen octahedral ferroelectrics was demonstrated. Anomalous behaviour was exhibited by the function representing the characteristic energy losses in the region of the phase transitions (PT) of some crystals.

Monte Carlo simulation of 0.1–100 keV electron and positron transport in solids using optical data and partial wave methods

A new Monte Carlo code for the detailed simulation of the transport of low-energy electrons and positrons in solids is presented, including a critical discussion of concepts and approximations in the scattering model. Inelastic scattering is calculated using a Bethe surface model based on optical and photoelectric data for the solid, making possible a good accuracy at low energies, and a high resolution (∼1 eV) in simulated energy loss spectra. Exchange corrections for electrons and relativistic corrections for energies up to ∼100 keV are included. Elastic scattering is calculated by means of a differential cross section obtained by relativistic partial wave analysis for an exchange corrected muffin-tin Dirac-Hartree-Slater atomic potential. In the simulation, no adjustments of parameters to empirical scattering data are made. For comparison, measurements have been made of the characteristic low energy loss spectrum of 100 keV electrons through a thin silicon film. Simulated results for electrons and positrons are also compared with other available experimental data, in particular at low (a few keV) energies. In general, very good agreement is obtained.

Location of adatoms on Si(100) surface using the electron channeling effect on Auger electron emission

Atomic-site location by channeling enhanced microanalysis (ALCHEMI) is a powerful technique for identifying both the atomic number and the location of impurity atoms in crystals. The principle of the technique is simple: electron intensities on particular crystallographic sites within unit cell oscillate with variation of the incident beam direction. The corresponding characteristic emission spectra from atoms at those atomic sites follow these oscillations if the inelastic scattering events are localized. By careful analyzing the spectra of the impurity species and those of the reference atoms on known sites at various tilting angles, the location of the impurity atoms can be obtained. However, most applications of this technique have used the channeling effect on characteristic x-ray emission or energy loss spectra for location of impurity atoms in bulk crystals Here we study the possibility of applying this technique for locating adatom positions on a crystal surface, using the channeling effect on characteristic Auger emissions.

Irreversible energy transfer in ionization of physisorbed adsorbates: II. Inelastic energy spectra of temporarily ionized adatoms

We have studied inelastic processes following core ionization of a physisorbed adsorbate by an external probe (electron impact or photon absorption), which typically occur in the intermediate, temporary ionized adatom states of electron (ESD) or photon (PSD) stimulated desorption and XPS of adsorbates. In the ionization process the adsorbate makes a diabatic or Franck-Condon transition from the neutral state potential V (0) (r) to the ionic potential V (+) (r) in which the charge of the moving ion is cou the charge density fluctuations of the substrate. This suddenly switched on dynamical interaction gives rise to inelastic energy transfer from the probe and the ionized adsorbate to the substrate degrees of freedom (heat bath). In order to qualitatively assess such dissipative processes we have calculated the characteristic energy loss spectrum of the adatom, the spectrum of energy absorbed by the heat bath and the characteristic energy spectrum of the whole system. From these spectral functions and their characteristics (e.g. the Debye-Waller factor, the shape of the inelastic side-band, mean energy loss, etc.) we can obtain information on the dynamics of each constituent of the system in the presence of dissipative coupling between the ionized adatom and the substrate heat bath. This enables us to discuss the role which inelastic effects may play in recently studied cases of stimulated desorption of neutral Ar atoms from metal surfaces.

Microscopic analysis of the characteristic energy loss spectra of 3d-and 4d-transition metal carbides and nitrides

Microscopic studies of the electron-energy-loss-spectra (EELS) of the nitrides and carbides of the transition metals Ti, V, Zr, Nb in the energy range to about 35 eV have been done using the linear-muffin-tin-orbital (LMTO) method for solving the band structure problem. Special attention has been paid to the low energy region where for some of these compounds there is an interesting feature in the EELS. Good agreement between the calculations and experiment was obtained. The similarities and differences of these compounds are discussed in terms of their electronic structure.

Reciprocity in electron energy-loss spectra from non-centrosymmetric crystals

The energy losses of fast electrons propagating through a thin crystal show a strong effect associated with the interference term between Bloch-wave eigenstates. Reversing the direction of the electrons gives the same spectrum, and reciprocity is observed in the interference term between eigenstates in inelastic electron scattering. The reciprocity principle may be used to advantage to observe for GaAs a very large difference in the characteristic energy-loss spectra for pairs of experimental arrangements related by a mirror operation around the polar (111) planes. This provides a sensitive way of determining the polarity of a crystal based on simple two-beam arguments, and may also be used to obtain direct structure-factor phase information.

Auger electron and characteristic energy loss spectra for electro-deposited americium-241

Auger electron energy spectra for electro-deposited americium-241 on platinum substrate were obtained using a cylindrical mirror analyzer. Characteristic energy loss spectra for this sample were also obtained at primary electron beam energies of 990 and 390 eV. From these measurements PI, PII, and PIII energy levels for americium-241 are determined. Auger electron energies are compared with theoretically calculated values. Minimum detectability under the present condition of sample preparation and equipment was estimated at approximately 1.2×10−8 g/cm2 or 3.9×10−8 Ci/cm2. Minimum detectability for plutonium-239 under similar conditions was estimated at about 7.2×10−10 Ci/cm2.

Studies of the methanation catalysts ThNi 5 and ZrNi 5 by Auger and Characteristic Energy Loss Spectra

ThNi 5 and ZrNi 5 (fresh, used, and H 2S poisoned) have been examined by Auger spectroscopy (AES) and Characteristic Energy Loss Spectroscopy (CELS) to elucidate the strikingly different behavior of these materials as methanation catalysts. With use ZrNi 5 is transformed into Ni supported on ZrO 2 and ThNi 5 into Ni supported on ThO 2. AES indicates that the Ni on ZrO 2 is heavily overlaid with graphite. This does not occur with Ni and ThO 2, accounting for the exceptional activity of this catalyst compared to Ni on ZrO 2. Plasmon excitation energy determined from CELS are consistent with this picture. The large amount of surface Ni for the transformed ThNi 5 catalyst accounts for its high resistance to H 2S poisoning compared to that of ZrNi 5. A strong CELS peak is observed at 6.5 eV in ZrNi 5 and ThNi 5 as well as in elemental Ni, suggesting a very similar band structure for these materials. In this respect Ni and the Ni intermetallics are similar to Co and Co intermetallics as deduced from photoemission studies and recent APW band calculations.

Electron scattering from pentacene and coronene polycrystals

The energy distribution curves of secondary electrons and scattered electrons with the characteristic energy loss from pentacene and coronene polycrystals have been measured. Fine structures were observed in the secondary electron spectra for both materials. The origins of the fine structures are discussed in connection with the characteristic energy loss spectra and the photoelectron spectra.

Solid State Broadening in the Auger Spectra of Rare Gases

AbstractThe L23MM Auger spectrum of solid argon, the M45NN Auger spectrum of solid krypton, and the M45N45N45 Auger spectrum of solid xenon have been measured at high resolution. The data has been compared with a computer simulation in which solid data is represented by the gas phase data with broadened lines. The solid phase breadths are 3.6, 4.6, and 2.9 eV, respectively. Characteristic energy loss spectra of the three solids are also reported.

Study of surface dissociation in KCl and LiF by observation of plasmon losses associated with K and Li

Peaks in the characteristic energy loss spectra of KCl and LiF obtained with an incident electron beam of 500 eV, have been associated with plasmon excitations in the alkali metal layer formed on the surface of these crystals by electron irradiation stimulated dissociation. The irradiation time and temperature dependence of these peaks seem to confirm this interpretation. Auger electron spectroscopy gives good qualitative agreement with previous results.

Luminescence of NaOH, KBr:OH−, and KBr:Tl+ under slow electron impact

Under low-energy electron impact the principal luminescence band of thin-film NaOH at 420 nm resembles that of KBr:OH− at 410 nm, both at ∼ 300 °K. The lowest energy luminescence excitation peaks occur at 4.5 and 6.5 eV for NaOH and at 4.9 and 6.0 eV for KBr:OH−, all below the first optical excitons at 7.7 and 6.7 eV, respectively. The excitations of the 320 and 360 nm bands of KBr:Tl+ are very similar to those for KBr:OH−. Electron characteristic energy loss spectra for the three systems correlate with luminescence excitation spectra. Host sensitization of 3.0 eV emission of the OH− activator cannot involve the self-trapped exciton of KBr which emits at 2.3 eV. Neither can the emissions of thallium-doped KBr at 3.4 and 3.8 eV be so accounted for. Direct excitation of the activators by electron impact is very improbable and host sensitization is assumed. In doped KBr, unrelaxed excitons at ∼4.9 eV may undergo cubic relaxation and diffuse by hopping to the activator site where they are trapped and emit (360 nm, KBr:Tl+) or transfer (320 nm, KBr:Tl+ and 420 nm, KBr:OH−).