Electron energy loss study of TiC [111]

The electron energy loss (EEL) spectra of TiC (111) were measured over a wide range of electron primary energies. The electron energy losses below 16 eV were analyzed using the theoretical band calculations of Price and Cooper [11]. The volume and surface plasma excitations were identified from their electron primary energy dependence. Energy losses due to core electrons autoinization effects were identified above 35 eV. We observed a difference in the electronic structure of the surface vs the bulk of TiC. The temperature dependence of the EEL spectra was studied between 300 to 1250 K. The reaction of the TiC surface with ethylene and oxygen was also investigated. The ethylene bonding to the TiC surface was found to be very weak. There is evidence of the formation of surface defects on the TiC (111) surface at high temperatures.     

Electron energy loss spectroscopy of TiC,ZrC and HfC

The dielectric properties of commercial TiC, ZrC and HfC powders were determined by analyzing the low loss region of the EELS spectrum in a transmission electron microscope. From these data, the optical joint density of states (OJDS) were obtained by Kramers–Kronig analysis. As maxima observed in the OJDS spectra are assigned to interband transitions across the energy gap, these spectra can be interpreted on the basis of existing energy-band calculations. Comparison between experimental results and theory shows good agreement.     

Electron energy loss spectra of dye vapors

Electron energy loss studies of POPOP andp-terphenyl in the vapor phase at an incident electron energy of 25 eV have been performed. The spectra covering an energy loss between 0 and 9 eV revealed a considerable initial triplet population under electron impact excitation. The implications for electron-beam pumped vapor phase dye lasers are discussed.     

Electron energy loss spectra and optical constants of Bismuth

Energy losses of fast electrons through thin films are used to compute the energy loss function, the complex dielectric constant and the optical absorption coefficient in the spectral region 2–150 eV. The existence and the origin of all the previously observed features are discussed.     

X-ray emission spectra and chemical bonding in TiC,TiN and TiO

The experimental X-ray emission spectra of titanium carbide, nitride and oxide have been obtained. Quantum-chemical calculations of the electronic structure of clusters in TiC, TiN and TiO have been carried out by the semiempirical Mulliken-Wolfsberg-Helmholtz method with self-consistency on charges and configurations. The results of these calculations are in good agreement with the X-ray spectroscopy data and offer a reasonable explanation of the experimental spectra. Chemical bonding and electronic structure of the compounds are discussed. Ionicity is shown to increase from TiC to TiO according to the electronegativity principle, the calculated charges on the metal ions being close to experimental estimates. The role of metal-metal and metal-nonmetal interactions in the chemical bonding is analysed. Vacancy models for TiO and their effect on the X-ray emission spectra are investigated. By the CNDO method with configurational interactions the optical spectrum of titanium carbide has been calculated. It is shown that this spectrum may be interpreted from the results for the [TiC₆] cluster, without introducing the Lye-Logothetis band scheme with negative charge on the metal ion.     

Electron energy loss spectra of a Pd(110) clean surface

Electron energy loss spectra of a Pd(110) clean surface have been measured at primary energies of 40–100 eV. The observed peaks are at the loss energies of ∼ 3, 4.3, 7.5, 11.5, 16, 21.3, 26.5 and 33.8 eV. The 7.5, 26.5, and 33.8 eV peaks are attributed mainly to the bulk plasmon excitations associated with 5s electrons, coupled 5s and a limited number of 4d electrons, and total (4d+5s) electrons, respectively. The rest of the peaks are ascribed mainly to one-electron excitations.     

Electron energy loss spectra of the system Cu(311)/CO,Xe

The electron energy loss spectrum of a clean Cu(311) surface has been studied by reflected electrons using primary energies between 30 and 300 eV. The losses obtained are compared with literature values. Loss spectra with adsorbed CO and Xe are also reported. Some assignments of the loss mechanisms have been attempted.     

Electron characteristic loss spectra of molybdenum dichalcogenides

The complete sets of the fundamental optical functions of molybdenum dichalcogenides have been considered for the first time. The energies of their bulk and surface plasmons of two types are determined. It is found that the energies of long-wavelength plasmons correlate with the energies of the deep minima in the reflectivity and ?₂ E ² spectra and the maxima in the reflectivity phase spectra.     

First-principles calculation of the electronic structure and energy loss near edge spectra of chiral carbon nanotubes

We present first principles calculations of the electronic structure of small carbon nanotubes with different chiral angles theta and different diameters (d<1 nm). Results are obtained with a full potential method based on the density functional theory (DFT), with the local density approximation (LDA). We compare the band structure and density of states (DOS) of chiral nanotubes with those of zigzag and armchair tubes with similar diameters. The carbon K-edge energy loss near edge structures (ELNES) have been studied and pi* and sigma* contributions have been evaluated. These contributions give information on the degree of hybridization for the small chiral nanotubes.     

Electron energy loss spectra of microscopy regions of quasicrystalline and crystalline Al86Mn14 alloys

Quasicrystalline specimens of Al₈₆Mn₁₄ alloys have been examined in a scanning transmission electron microscope. Microdiffraction data and electron energy loss spectra from microscopic regions (0.5 nm radius) have been obtained. The relative intensities of the Mn L₃ and L₃ EELS peaks provide information on the local coordination of manganese in the alloys.     

Electron emission spectra in low energy positron-atom collisions

Energy spectra of electrons ejected from an Ar target, in the forward direction, by a low energy positron beam have been measured and compared with theory. Structures are present in these spectra at energies compatible with electron capture to continuum states of the scattered positron (ECC) and with binary collisions.     

Electron energy loss near edge structure (ELNES) spectra of AlN and AlGaN: a theoretical study using the Wien2k and Telnes programs

Several aspects of the modelling of the energy loss near edge structure (ELNES) using the Wien2k code and the Telnes program are discussed in this paper. A case study with ground state, partial and full core-hole calculations of wurtzite AlN was performed and the results were compared with experimental transmission electron microscopy data. The best agreement with the experimental observations was obtained for the full core-hole case. Changes in the ELNES spectra for various core-hole charges are explained by investigating the site and symmetry projected density of states. Directionally resolved N K-edge ELNES of AlN are discussed and the magic angle beta approximately 2.5mrad is identified which is in a good agreement with other theoretical predictions. Finally, preliminary results on a compositional study of Al(x)Ga(1-x)N are explored.     

Electron energy loss and secondary emission mechanisms in BaO

Electron Loss Spectroscopy (ELS), X-ray Photoemission (XPS), Secondary Emission Energy Distribution, and Secondary Electron yield data have been obtained on both evaporated films and sprayed-on coatings of BaO. Using the ELS correlated with the XPS data, bulk and surface plasmon losses as well as excitonic and interband transition electron loss mechanisms have been identified. It was found that at low primary beam energies (<100 eV), structure in the secondary emission energy distribution could be correlated with a conduction band energy structure. This structure was consistent with the model used to explain the loss transitions. The structure in the energy distribution curves shows little, if any, correlation with plasmon decay mechanisms and other two-step electron emission processes. On the contrary, for the case of BaO (at least at low primary energies), the energy distribution data and structure in the secondary yield vs. primary beam energy data indicate that most secondaries are produced by direct excitation of secondaries by the primary electrons.     

Electron energy loss processes in X-ray photoelectron spectroscopy

A technique is established in X-ray photoelectron spectroscopy (XPS), using spectra emitted from successively evaporated metallic films, to distinguish between electron energy loss mechanisms identified as, respectively, extrinsic and intrinsic to the photoelectron excitation process. It is demonstrated that tailing on the high kinetic energy side of many XPS peaks is due to intrinsic processes, while the background emission at energies generally some 30 eV below the peaks arises from extrinsic processes. Plasmon energy-loss peaks are believed to contain contributions from both intrinsic and extrinsic processes.     

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.     

Electron energy loss spectra and X-ray photoelectron spectra of Ca2V2O7

We have measured the electron energy loss spectra of Ca₂V₂O₇ in the reflexion mode, at incident energies between 200 and 2400 eV, and the X-ray photoelectron spectra excited by Al K α radiation. The abundant loss structures observed can be correlated with the possible interband transitions, collective oscillations, and excitation of O2s and V3p electrons within the V₂O₇^4- ion. The gap width and molecular orbital (MO) spread (or splitting) is about l eV larger in the V₂O₇^4- ion than in its component VO₄^3- ion. Excitation of O2s states, which may occur together with some MO over-gap transitions, displaces the collective oscillations about 7 eV towards lower energies. Deeper V3p electrons are excited with a maximum energy loss some 7 eV above their binding energy. Cross transitions from Ca3p levels into some empty states of the V₂O₇^4- ion, or direct transitions to available states of the Ca²⁺ ion could not be unambiguously identified. The energy dependence of the excitation cross section and of the electron penetration depth results in a significant variation of the relative intensity of various losses over the investigated energy range.     

Electron energy spectra in an elliptic quantum wire and elliptic nanotube

In the effective mass approximation, the electron spectra in an elliptic quantum wire and elliptic semiconductor nanotube are investigated. An exact electron energy spectrum in the GaAs elliptic quantum wire and elliptic semiconductor nanotube with impenetrable walls is obtained and an approximate solution of the Schrödinger equation is derived for a finite potential barrier height in the GaAs/Al _x Ga _1?x As elliptic quantum wire. It is demonstrated that the ellipticity of the quantum wire and nanotube results in removal of degeneration of the quasiparticle energy spectrum. Dependences of energies of even and odd states on the ratio of the ellipse semiaxes are nonmonotonic in character. In the limiting case of degeneration of elliptic quantum wires and nanotubes into circular ones, the quasi-particle energy spectrum coincides with the corresponding spectrum in cylindrical nanosystems.