Band-reject-filtering X-ray spectra by mosaic structures of pyrolytic graphite

The possibility of effective band-reject filtration of intense spectral lines in X-ray spectra and the creation of deep spectral valleys in the continuous spectrum by diffraction extinction was shown. Optimum material for band-reject filters in the energy range E > 6 keV is highly oriented pyrolytic graphite (HOPG). The filtering scheme in the form of an echelon arrangement of HOPG films is proposed, which suppresses the negative effect of multiple reflections due to diffraction extinction. The full width at half minimum of the spectral valleys can vary from tens of electronvolt to several kiloelectron volt depending on the HOPG mosaic spread, HOPG filters arrangement, and rejected energy region. At the energy range E of ~10 keV, the spectral density attenuation value may be of order 10⁻³ and lower. The obtained results can be used in various fields of X-ray spectrometry, as well as in static energy dispersive diffractometry and reflectometry.     

Effects of band structure on the X-ray spectra of metals

Using the change-of-mean-field model, the X-ray absorption, emission, and photoemission spectra of electrons in a one-dimensional nearest-neighbor tight-binding crystal are calculated and compared with the spectra of a corresponding free-electron model. Multi-electron recoil, and shake-off and replacement transitions, are included. The effects of band structure on the spectra are discussed.     

Energy band structure and X-ray emission spectra of ZrC and ZrN

Self-consistent augmented plane wave calculations are performed for ZrC and ZrN. The charge distributions resulting from valence bands in different regions of the unit cell are discussed and compared with related compounds, where the transition metal is varied between a 3d and 4d element of group IV and V. The limitations of the rigid band model are illustrated and general trends in the chemical bonding are discussed. In connection with X-ray emission spectra (XES) matrix element effects are shown for the three spectra Zr-L_III,-M_III, and-N_III. Further, comparison between theoretical and experimental XES is made with all data available for both ZrC and ZrN.     

Determining misorientation of graphite grains from the angular dependence of X-ray emission spectra

Angular-resolved X-ray absorption spectra were measured for pyrolytic graphite samples of various quality. A new approach to determining the misorientation of graphite grains in polycrystalline samples is proposed, which is based on calculations of the angular dependence of the relative intensity of a peak corresponding to the π* state for a normal distribution of grains. The experimental values are used to construct theoretical angular dependences using partial densities of the π* and σ* states determined from the nonempirical calculations for graphite.     

Modification of X-ray excited photoelectron and C KVV Auger spectra during radiative carbonization of poly(vinylidene fluoride)

Modifications of the photoelectron and C KVV Auger spectra during the long-term surface degradation of partially crystalline PVDF under simultaneous soft X-ray and electron followed by ion irradiation are reported. Deep radiative carbonization brings about the formation of carbynoid structures (chain-like carbon) in the surface, while the number of interchain cross-links is insignificant. As a result, the shape of the electron emission spectra of carbon in the carbonized sample essentially differs from that of graphite and PVDF. The ion bombardment of the carbonized sample destroys one-dimensional structure due to the formation of cross-links. Thus, carbon atoms transit into sp²-hybrid state and, therefore, the photoelectron and Auger spectra show features characteristic for microcrystalline graphite.     

Electron beam-induced decomposition of graphite fluoride

Irradiation of graphite fluoride with electron beams has been carried out on a electron probe microanalyzer. Radiation-induced decomposition took place predominantly instead of thermal decomposition. The decomposition tended to occur in the following order: powdery (CF)_n, white flaky (CF)_n, and (CF₂F)_n. The kinetics of the decomposition reaction induced by electron beams was evaluated by the ZAF correction of the measured intensities of F K- and C K-emission bands. It was found that the kinetic of the decomposition of graphite fluoride was of Avrami-Erofejev type; the rate equations were $\text{-}\text{ln}\text{(1?α)=kt}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for (CF)_n and -ln(1?α)=kt² for (C₂F)_n. An application to the electron microbeam processing of graphite fluoride was suggested in relation to its unique physicochemical properties.     

Electronic structure of LiMnO : X-ray emission and photoelectron spectra and band structure calculations

The electronic structure of LiMnO₂ and Li₂MnO₃ was studied by means of X-ray photoelectron and soft X-ray emission spectroscopy. For LiMnO₂, LSDA and LSDA+U calculations were carried out. The LSDA+U calculations are in rather good agreement with the measured valence-band structure as well as with the magnetic and electrical properties of LiMnO₂. It is shown that the band gap in LiMnO₂ is determined by the charge-transfer effect. Received 15 March 1999 and Received in final form 14 July 1999     

Energy band structure of cadmium fluoride

The electronic band structure of cadmium fluoride is calculated by a combined tight binding and pseudopotential method. The band structure is found to be rather similar in shape with that of CaF₂. In particular it is shown that the occupied cationic d⁺ bands do not perturb significantly the upper valence band predominantly composed of the F^-p-orbital. This explains the great similarity of the low energy part of the reflection spectra of CaF₂ and CdF₂.     

Backscattered electron spectra from graphite

The backscattered electron spectra from graphite sample were studied both experimentally and theoretically at impact energies between 500 and 5000 eV. The angle of the incident electron beam was 50° and the detection angle was 0° with respect to the surface normal, respectively. Monte Carlo (MC) simulations were performed based on the Classical Transport Theory (CTT) model to mimic the experimental spectra. In our simulations, both elastic and inelastic scattering of primary electrons and secondary electron emission from graphite are taken into account. There is found satisfactory agreement between measured and calculated electron spectra.     

X-ray band spectra and electronic structure of carbides and nitrides of zirconium,niobium and molybdenium

The L- and M-emission spectra of Zr, Mb and Mo carbides and nitrides have been studied. The spectra were excited by primary techniques, it is concluded that the valence bands of these carbides and nitrides consist of two sub-bands: a sub-band of states which participate in covalent bonds and a sub-band of states which share in the formation of metallic bonding and account for the metallic properties of these phases.     

Magnetic susceptibility effects on 13C MAS NMR spectra of carbon materials and graphite

13C high-resolution solid-state nuclear magnetic resonance (NMR) was employed to study carbon materials prepared through the thermal decomposition of four different organic precursors (rice hulls, endocarp of babassu coconut, peat, and PVC). For heat treatment temperatures (HTTs) above about 600 C, all materials presented 13C NMR spectra composed of a unique resonance line associated with carbon atoms in aromatic planes. With increasing HTT a continuous broadening of this resonance and a diamagnetic shift in its central frequency were verified for all samples. The evolution of the magnitude and anisotropy of the magnetic susceptibility of the heat-treated carbon samples with HTT explains well these findings. It is shown that these results are better understood when a comparison is made with the features of the 13C NMR spectrum of polycrystalline graphite, for which the magnetic susceptibility effect is also present and is much more pronounced.     

Electronic structure and X-ray photoelectron spectra of TiC and ZrC: Cluster and band structure approaches

The electronic structure for titanium and zirconium monocarbides have been calculated with the SCF MS X_α-cluster method. The results are compared with the experimental X-ray photoelectron spectra and augmented plane wave (APW) calculations.     

X-ray characterization of graphite intercalation compounds

The understanding of electronic and lattice properties of graphite intercalation compounds depends critically on the model describing the structural properties. We report here results showing that well-staged as-grown samples do not exhibit the expected in-plane intercalant density, and that careful analysis of the 00? x-ray diffractograms reveals important information on the in-plane occupation probability.     

B and C band excitation and emission spectra in KI:T1

Abstract

We present the excitation spectra of KI:T1 measured in the region of the B and C absorption bands at several emission wavelengths and at 20 K, 80 K and 300 K. An accurate analysis of these spectra shows new properties of the excitation spectra, that we relate to the non radiative relaxation of the excited electrons towards the luminescent states.     

Fermi surface parameters of graphite by band calculations

Energy bands near the Fermi surface of graphite are calculated by a new method suitable for layer-type crystals. Theoretical values for the band parameters in the Slonczewski-Weiss band model are obtained, and they are in good agreement with experimental ones.     

等离子体X射线吸收谱及发射谱研究

 报道计算高温高密等离子体吸收谱和发射谱（光学薄）的理论方法；该方法基于相对论原子理论，可以计算任何单元素以及多元素等离子体的谱分辨X射线吸收谱和发射谱（光学薄）；应用了量子亏损理论，可以减少计算量。利用该方法计算金等离子体LTE吸收谱，计算结果与实验符合良好。本文还对金等离子体LTE的光学薄发射谱进行了研究, 这将有利于对实验进行进一步的诊断分析。该理论计算方法还可提供等离子体内各电离度能级布居等重要物理参数。因此经“标准实验”检验的该理论计算方法将是提供ICF“精密”物理辐射参数的重要基础。     

等离子体X射线吸收谱及发射谱研究

报道计算高温高密等离子体吸收谱和发射谱（光学薄）的理论方法;该方法基于相对论原子理论,可以计算任何单元素以及多元素等离子体的谱分辨X射线吸收谱和发射谱（光学薄）;应用了量子亏损理论,可以减少计算量。利用该方法计算金等离子体LTE吸收谱,计算结果与实验符合良好。本文还对金等离子体LTE的光学薄发射谱进行了研究, 这将有利于对实验进行进一步的诊断分析。该理论计算方法还可提供等离子体内各电离度能级布居等重要物理参数。因此经“标准实验”检验的该理论计算方法将是提供ICF“精密”物理辐射参数的重要基础。     

X-ray determination of thermal expansion of cadmium fluoride and lead fluoride

The lattice parameters of CdF₂ andβ-PbF₂ have been determined over the temperature range 300–670 K. The coefficient of expansion at room temperature is 21·3 × 10⁻⁶ K⁻¹ and 25·4 × 10⁻⁶ K⁻¹ for CdF₂ and PbF₂ respectively and it increases linearly with temperature over the range of temperature covered. The Grüneisen parameter decreases with temperature in both the crystals.     

Absolute band gaps in two-dimensional graphite photonic crystal

The off-plane propagation of electromagnetic (EM) waves in a two-dimensional (2D) graphite photonic crystal structure was studied using transfer matrix method. Transmission spectra calculations indicate that such a 2D structure has a common band gap from 0.202 to 0.2035 c/a for both H and E polarizations and for all off-plane angles form 0° up to 90°. The presence of such an absolute band gap implies that 2D graphite photonic crystal, which is much easier and more feasible to fabricate, can exhibit some properties of a three-dimensional (3D) photonic crystal.