K-shell Electron Excitation Research Articles

Excitación de electrones K del Li a baja transferencia de momento por dispersión inelástica de rayos X en LiH

Excitación de electrones K del Li a baja transferencia de momento por dispersión inelástica de rayos X en LiH

Excitation of K-shell electrons into ns states by the impact of charged particles

We have investigated the excitation process of hydrogen-like multicharged ions by the impact of different charged projectiles such as electrons, positrons, protons and antiprotons. The universal scaling behaviour for the differential and total cross sections is deduced within the framework of the non-relativistic perturbation theory, taking into account the one-photon exchange diagrams. Special emphasis is laid on the description of the reaction in the near-threshold energy domain, which requires the accurate account for interactions between all particles in the colliding system.

Excitation of K-shell electrons by electron impact

The universal scaling behavior for the electron-impact excitation cross sections of the 2s states of hydrogen- and helium-like multicharged ions is deduced. The study is performed within the framework of non-relativistic perturbation theory, taking into account the one-photon exchange diagrams. Special emphasis is laid on the near-threshold energy domain. The parametrical relationship between the cross sections for excitation of multicharged ions with different number of electrons is established.

Electronic structure analyses of BN network materials using high energy‐resolution spectroscopy methods based on transmission electron microscopy

Electronic structures of boron-nitride (BN) nanotubes and a BN cone-structure material were studied by using a high energy-resolution electron energy-loss spectroscopy (EELS) microscope. A trial of the whole electronic structure study of hexagonal BN (h-BN), which consists of flat BN honeycomb layers, was conducted by a combination of EELS and X-ray emission spectroscopy (XES) based on transmission electron microscopy (TEM) (TEM-EELS/XES). The pi and pi+sigma plasmon energies of BN nanotubes (BNT) were smaller than those of h-BN. The pi+sigma energy was explained by the surface plasmon excitation. The spectrum of a two-wall BNT of 2.7 nm in diameter showed a new spectral onset at 4 eV. The valence electron excitation spectra obtained from the tip region of the BN cone with an apex angle of 20 degrees showed similar intensity distribution with those of BNTs. The B K-shell electron excitation spectra obtained from the bottom edge region of the BN cone showed additional peak intensity when compared with those of h-BN and BNT. The B K-shell electron excitation spectra and B K-emission spectra of h-BN were compared with a result of a LDA band calculation. It showed that high symmetry points in the band diagram appear as peak and/or shoulder structures in the EELS and XES spectra. Interband transitions appeared in the imaginary part of the dielectric function of h-BN experimentally obtained were assigned in the band diagram. The analysis also presented that the LDA calculation estimated the bandgap energy smaller than the real material by an amount of 2 eV. Those results of TEM-EELS/XES analysis presented that high energy-resolution spectroscopy methods combined with TEM is a promising method to analyze whole electronic structures of nanometer scale materials.

X-ray Emission Measurement from Organic and Insulating Materials with Low Energy Ga Ion Beams

We observed a phenomenon of X-ray emission from various types of organic and insulating materials under irradiation of a low energy (30 kV) gallium ion beam. Energy dispersive X-ray spectrometer combined with a focused ion beam instrument could detect light elements with low K-shell electron excitation energy such as carbon, oxygen, fluorine, sodium and silicon. Effect of the current intensity of gallium ion beam on the normalized X-ray yield was investigated. It was found that a strong irradiation beam current could effectively enhance the normalized X-ray yield. [DOI: 10.1380/ejssnt.2006.365]

Internal conversion to bound final states in [formula omitted]Te

Theoretical results are presented for rate of decay of the 3/2+ isomeric nuclear state of 125Te by excitation of atomic electrons to bound states in the ions Te45+ and Te46+. In these ions the nuclear transition energy lies just below the threshold for emission of a K-shell electron to the continuum with the result that normal K-shell internal conversion is energetically forbidden. However recent experimental results indicate that excitation of K-shell electrons is still significant in these ions. The theoretical results presented here for internal conversion to bound final states are in quantitative agreement with experiment and thereby confirm the contribution of near-resonant electron–nucleus transitions involving a bound final state.

Saturation Effect of Projectile Excitation in Ion–Atom Collisions

Calculations of projectile K-shell electron excitation cross sections for He-like ions during ion-atom collisions have been performed in the distortion approximation by the use of Herman-Skillman wave functions. The calculated results are compared with the experimental data for several targets. The excitation cross sections deviate from the first-Born approximation and show the saturation effect as a function of target atomic number. This effect can be explained as the distortion of the projectile electronic states by the target nucleus.

Inner-shell resonances in elastic scattering of electrons from N 2 and CH 4

Resonances associated with excitation of K-shell electrons in N 2 and CH 4 are observed for the first time in the elastic scattering channel. In

Scattering-angle dependence of signal/background ratio of inner-shell electron excitation loss in EELS

EELS allows us to make analysis of light elements such as hydrogen to heavy elements of microareas on the specimen. In energy loss spectra, however, elemental signals ride on a high background; therefore, the signal/background (S/B) ratio is very low in EELS. A technique which collects the center beam axial-symmetrically in the scattering angle is generally used to obtain high total intensity. However, the technique collects high background intensity together with elemental signals; therefore, the technique does not improve the S/B ratio. This report presents the experimental results of the S/B ratio measured as a function of the scattering angle and shows the possibility of the S/B ratio being improved in the high scattering angle range.Energy loss spectra have been measured using a JEM-200CX TEM with an energy analyzer ASEA3 at 200 kV.Fig.l shows a typical K-shell electron excitation edge riding on background in an energy loss spectrum.

Scattering angle dependence of signal/background ratio of inner-shell electron excitation loss in eels

Scattering angle dependence of the signal/background ratio of Si K-shell and A1 K-shell electron excitation losses has been measured for single crystals and evaporated films. The ratio changed periodically with the scattering angle, and maxima were found to be located between Bragg reflections including the center beam. Thus the ratio is improved between the Bragg reflections and just outside the incident beam, which is very important as a practical technique for elemental analysis in the higher energy loss region in EELS.

The influence of finite lifetime of electronic states on the vibrational structure of molecular electronic spectra

A general theory describing the effect of finite lifetime of electronic states on the vibrational structure of electronic spectra is developed. A proper description of the decay of the excited state involved in the transition is achieved by summing the perturbation series for the T matrix to infinite order in the interaction responsible for the decay. An effective non-hermitian hamiltonian is obtained which describes the vibrational motion in the short-lived electronic state. The finite lifetime influences the spectra in a different way, depending whether the shoft-lived state is the final or the initial state of the electronic transition. In the former case the spectrum is given by an incoherent superposition to lorentzian lines, while in the latter case there are interferences between the vibrational levels of the short-lived electronic state which modify the vibrational structure is a characteristic manner. The theory is applied to various spectra of CO and N 2 involving the excitation of K-shell electrons. Interferences effects are predicted and identified in the experimental spectra.

The electron energy loss spectrum and band structure of diamond

Abstract The electronic properties of diamond were investigated by energy analysis of a 80 keV beam of transmitted electrons. Plasmon resonance of the valence electrons occurs at 33·3 eV (width ∼ 13 eV), with evidence of interband transitions centred around 10 ev. Peaks were also observed at energy losses of 294, 299 and 306 eV, due to the excitation of K-shell electrons. After corrections for instrumental broadening and plural scattering, the K-excitation spectrum correlates well with densities-of-states calculations of Keown (1966) and Painter, Ellis and Lubinsky (1971).

K-Shell Ionization of Beryllium by Proton and Heavy Ions

Experimental cross sections are presented for the ionization of K-shells of beryllium in collision with heavy ions and proton; C + , N + , O + , Ne + and Ar + for bombarding energy ranging from 0.3 to 30 keV per amu, while that for protons is 10 to 200 keV per amu. Proton data show good agreement with the prediction for Coulomb excitation of K-shell electrons. The date for heavy ions are several orders of magnitude larger than that for proton. These results are understood in terms of pseudomolecule formation and crossings of molecular orbitals during the collisions. Heavy ion cross sections show the trend to converge to the theoretical Coulomb excitation cross sections in high energies above about 10 keV per amu.

Excitation of K-Shell Electrons in Be by Soft X Rays and 20-keV Electrons*

The soft x-ray absorption spectra of Be and BeO were measured near the K edge using the NBS 180 MeV synchrotron as a background continuum source. The energy-loss spectrum of 20-keV electrons transmitted through thin Be films at zero scattering angle was measured in the corresponding 100–170 eV energy-loss range. The K edges of Be and BeO measured by x-ray absorption were at 112.1±0.2 eV and 118.4±0.2 eV, respectively. The Be K edge in the electron-energy-loss spectrum was at 111.7±0.4 eV. The positions of maxima in the absorption fine structure determined by the two techniques were also in good agreement.