Excitation‐energy‐dependent resonances in x‐ray emissions under near‐threshold electron excitation of the Ce 3d and 4d levels

1975 ◽  
Vol 12 (5) ◽  
pp. 1047-1051 ◽  
Author(s):  
M. B. Chamberlain ◽  
W. L. Baun
Keyword(s):  
Excitation Energy ◽  
Electron Excitation ◽  
X Ray ◽  
Energy Dependent ◽  
Near Threshold

Electron-excitation energy-dependent features in theM-series x-ray spectrum of lanthanum

1974 ◽  
Vol 9 (1) ◽  
pp. 316-322 ◽  
Author(s):  
Robert J. Liefeld ◽  
Alex F. Burr ◽  
Merrill B. Chamberlain
Keyword(s):  
Excitation Energy ◽  
Electron Excitation ◽  
X Ray ◽  
Electron Excitation Energy ◽  
Energy Dependent

Excitation-Energy-Dependent Resonances in Soft X-Ray Appearance Potential Spectra of the Cerium 4d- and 3d-Electron Levels

1974 ◽  
Vol 18 ◽  
pp. 415-424
Author(s):  
M. B. Chamberlain ◽  
W. L. Baun
Keyword(s):  
Excitation Energy ◽  
Exchange Interactions ◽  
Electron Excitation ◽  
X Rays ◽  
Core Electron ◽  
X Ray ◽  
Appearance Potential ◽  
Relaxation Effects ◽  
Many Core ◽  
Energy Dependent

AbstractWhen the excitation energy lies near the ionization potential of many core electrons, core-hole relaxation effects strongly affect x-ray emissions. Under near-threshold electron excitation of the cerium 4d subshell both the incident electron and a 4d-core electron are promoted into 4f-orbital excitation states which exist only during the life of and are bound to the 4d vacancy. The exchange interaction between the 4d hole and the excited electrons in the unfilled 4f subshe11 spreads the energies of the discrete excitation states over a 20eV range sending some levels well below the 4d threshold and others into the continuum. Exchange interactions and potential barrier effects have a dominant influence upon the cerium 4d and 3d soft x-ray appearance potential spectra reported in this paper. We observe sub-threshold x rays extending to 8.6eV below the binding energy of the 4d level as well as a maximum in the yield at 12eV above the 4d onset. As the electron excitation energy is swept through the thresholds of the two 3d levels we observe resonant x-ray emissions, while at 28eV above these levels we see plasmon loss structures.

Influence of X-Ray Induced Fluorescence on Energy Dispersive X-Ray Analysis of Thin Foils

1977 ◽  
Vol 35 ◽  
pp. 328-329
Author(s):  
E. A. Kenik ◽  
J. Bentley
Keyword(s):  
Thin Foil ◽  
Electron Excitation ◽  
Simple Approach ◽  
Foil Thickness ◽  
X Rays ◽  
X Ray ◽  
Hole Spectrum ◽  
Illumination System ◽  
Thin Foils ◽  
Intensity Ratios

Cliff and Lorimer (1) have proposed a simple approach to thin foil x-ray analy sis based on the ratio of x-ray peak intensities. However, there are several experimental pitfalls which must be recognized in obtaining the desired x-ray intensities. Undesirable x-ray induced fluorescence of the specimen can result from various mechanisms and leads to x-ray intensities not characteristic of electron excitation and further results in incorrect intensity ratios.In measuring the x-ray intensity ratio for NiAl as a function of foil thickness, Zaluzec and Fraser (2) found the ratio was not constant for thicknesses where absorption could be neglected. They demonstrated that this effect originated from x-ray induced fluorescence by blocking the beam with lead foil. The primary x-rays arise in the illumination system and result in varying intensity ratios and a finite x-ray spectrum even when the specimen is not intercepting the electron beam, an ‘in-hole’ spectrum. We have developed a second technique for detecting x-ray induced fluorescence based on the magnitude of the ‘in-hole’ spectrum with different filament emission currents and condenser apertures.

SIGMAL: A Program for Calculating L-Shell lonization Cross-Sections

1981 ◽  
Vol 39 ◽  
pp. 198-199 ◽  
Author(s):  
R.F. Egerton
Keyword(s):  
Cross Sections ◽  
Fortran Program ◽  
Absorption Data ◽  
X Ray ◽  
Atomic Electrons ◽  
Energy Dependent ◽  
Hydrogenic Model ◽  
Electron Energy Loss ◽  
X Ray Absorption ◽  
Shell Ionization

SIGMAL is a short (∼ 100-line) Fortran program designed to rapidly compute cross-sections for L-shell ionization, particularly the partial crosssections required in quantitative electron energy-loss microanalysis. The program is based on a hydrogenic model, the L1 and L23 subshells being represented by scaled Coulombic wave functions, which allows the generalized oscillator strength (GOS) to be expressed analytically. In this basic form, the model predicts too large a cross-section at energies near to the ionization edge (see Fig. 1), due mainly to the fact that the screening effect of the atomic electrons is assumed constant over the L-shell region. This can be remedied by applying an energy-dependent correction to the GOS or to the effective nuclear charge, resulting in much closer agreement with experimental X-ray absorption data and with more sophisticated calculations (see Fig. 1 ).

EXELFS Studies of Carbon Fibers

1990 ◽  
Vol 48 (2) ◽  
pp. 72-73
Author(s):  
V. Serin ◽  
K. Hssein ◽  
G. Zanchi ◽  
J. Sévely
Keyword(s):  
Carbon Fibers ◽  
Energy Analysis ◽  
Electron Excitation ◽  
Complex Structures ◽  
High Modulus ◽  
Promising Technique ◽  
X Ray ◽  
Fine Structures ◽  
X Ray Absorption

The present developments of electron energy analysis in the microscopes by E.E.L.S. allow an accurate recording of the spectra and of their different complex structures associated with the inner shell electron excitation by the incident electrons (1). Among these structures, the Extended Energy Loss Fine Structures (EXELFS) are of particular interest. They are equivalent to the well known EXAFS oscillations in X-ray absorption spectroscopy. Due to the EELS characteristic, the Fourier analysis of EXELFS oscillations appears as a promising technique for the characterization of composite materials, the major constituents of which are low Z elements. Using EXELFS, we have developed a microstructural study of carbon fibers. This analysis concerns the carbon K edge, which appears in the spectra at 285 eV. The purpose of the paper is to compare the local short range order, determined by this way in the case of Courtauld HTS and P100 ex-polyacrylonitrile carbon fibers, which are high tensile strength (HTS) and high modulus (HM) fibers respectively.

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