Cross-Sections for K-Shell Excitation by Fast Electrons

1977 ◽  
Vol 35 ◽  
pp. 252-253
Author(s):  
R. F. Egerton ◽  
D. C. Joy
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Unit Volume ◽  
Direct Method ◽  
Specimen Thickness ◽  
Thin Specimen ◽  
Auger Electrons ◽  
Fast Electrons ◽  
X Ray ◽  
Image Position

The cross-section for excitation of an electron from the innermost shell of a given atom can be determined directly by measuring the proportion of fast incident electrons which have suffered an appropriate energy loss, or (if the X-ray or Auger yields are known) from the number of X-ray quanta or Auger electrons emitted as a result of de-excitation.In the direct method, this cross-section is obtained as a function of α, the maximum scattering angle allowed into the detector, and for a thin specimen it is given by:where n is the number of atoms per unit volume of specimen, t is the specimen thickness, Ik(α) represents the number of K-loss electrons reaching the detector and It represents the total number of fast electrons entering the detector,1 for the same value of α. Equation (1) can also be used12 for microanalysis of low-atomic-number elements in order to measure n or nt if σK(α) is known.

scholarly journals VUV and Soft X-ray Spectroscopy of Actinides

2003 ◽  
Vol 802 ◽  
Author(s):  
Clifford G. Olson ◽  
John J. Joyce ◽  
Tomasz Durakiewicz ◽  
Elzbieta Guziewicz ◽  
Martin Butterfield
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Spectral Characteristics ◽  
Electronic States ◽  
Momentum Dependence ◽  
Auger Electrons ◽  
X Ray ◽  
Relative Cross Section ◽  
Initial States ◽  
Valence Bands

ABSTRACTOptical and photoelectron spectroscopies using VUV and Soft X-ray photons are powerful tools for studies of elemental and compound actinides. Large changes in the relative atomic cross sections of the 5f, 6d and sp electrons allow decomposition of the character of the valence bands using photoemission. Resonant enhancement of photoelectrons and Auger electrons at the 5d core threshold further aids the decomposition and gives a measure of elemental specificity. Angle-resolved photoemission can be used to map the momentum dependence of the electronic states. The large changes in relative cross section with photon energy yields further details when the mapping is done at equivalent points in multiple zones. Spectra for well understood rare earth materials will be presented to establish spectral characteristics for known atomic character initial states. These signatures will be applied to the case of USb to investigate f-d hybridization near the Fermi level.

Absolute inner-shell cross section determination for EELS analysis

1988 ◽  
Vol 46 ◽  
pp. 534-535
Author(s):  
P.A. Crozier
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Absolute Cross Section ◽  
Specimen Thickness ◽  
Mass Thickness ◽  
Scattering Cross ◽  
Before And After ◽  
Estimated Error ◽  
Scattering Cross Sections ◽  
Electron Microscopist

Absolute inelastic scattering cross sections or mean free paths are often used in EELS analysis for determining elemental concentrations and specimen thickness. In most instances, theoretical values must be used because there have been few attempts to determine experimental scattering cross sections from solids under the conditions of interest to electron microscopist. In addition to providing data for spectral quantitation, absolute cross section measurements yields useful information on many of the approximations which are frequently involved in EELS analysis procedures. In this paper, experimental cross sections are presented for some inner-shell edges of Al, Cu, Ag and Au.Uniform thin films of the previously mentioned materials were prepared by vacuum evaporation onto microscope cover slips. The cover slips were weighed before and after evaporation to determine the mass thickness of the films. The estimated error in this method of determining mass thickness was ±7 x 107g/cm2. The films were floated off in water and mounted on Cu grids.

scholarly journals Chemical Quantification of Atomic-Scale EDS Maps under Thin Specimen Conditions

2014 ◽  
Vol 20 (6) ◽  
pp. 1782-1790 ◽  
Author(s):  
Ping Lu ◽  
Eric Romero ◽  
Shinbuhm Lee ◽  
Judith L. MacManus-Driscoll ◽  
Quanxi Jia
Keyword(s):  
Atomic Scale ◽  
Specimen Thickness ◽  
Peak Width ◽  
Thin Specimen ◽  
Gaussian Peak ◽  
X Ray ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
The Relationship ◽  
Chemical Quantification

AbstractWe report our effort to quantify atomic-scale chemical maps obtained by collecting energy-dispersive X-ray spectra (EDS) using scanning transmission electron microscopy (STEM) (STEM-EDS). With thin specimen conditions and localized EDS scattering potential, the X-ray counts from atomic columns can be properly counted by fitting Gaussian peaks at the atomic columns, and can then be used for site-by-site chemical quantification. The effects of specimen thickness and X-ray energy on the Gaussian peak width are investigated using SrTiO3 (STO) as a model specimen. The relationship between the peak width and spatial resolution of an EDS map is also studied. Furthermore, the method developed by this work is applied to study cation occupancy in a Sm-doped STO thin film and antiphase boundaries (APBs) present within the STO film. We find that Sm atoms occupy both Sr and Ti sites but preferably the Sr sites, and Sm atoms are relatively depleted at the APBs likely owing to the effect of strain.

scholarly journals Pore shape and sorption behaviour in mesoporous ordered silica films

2016 ◽  
Vol 49 (5) ◽  
pp. 1713-1720 ◽  
Author(s):  
Gerhard Fritz-Popovski ◽  
Roland Morak ◽  
Parvin Sharifi ◽  
Heinz Amenitsch ◽  
Oskar Paris
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Grazing Incidence ◽  
Dip Coating ◽  
Silica Films ◽  
Elliptical Cross ◽  
Sorption Behaviour ◽  
X Ray ◽  
Pluronic P123 ◽  
X Ray Scattering

Mesoporous silica films templated by pluronic P123 were prepared using spin and dip coating. The ordered cylindrical structure within the films deforms due to shrinkage during calcination. Grazing-incidence small-angle X-ray scattering (GISAXS) measurements reveal that both the unit cell and the cross section of the pores decrease in size, mainly normal to the surface of the substrate, leading to elliptical cross sections of the pores with axis ratios of about 1:2. Water take-up by the pores upon changing the relative humidity can be monitored quantitatively by the shift in the critical angle of X-ray reflection as seen by the Yoneda peak.

FiXR: a framework to reconstruct fiber cross-sections from X-ray fiber diffraction experiments

2020 ◽  
Vol 76 (2) ◽  
pp. 102-117
Author(s):  
Biel Roig-Solvas ◽  
Dana H. Brooks ◽  
Lee Makowski
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Amyloid Β ◽  
Diffraction Theory ◽  
Saxs Data ◽  
Molecular Conformations ◽  
X Ray ◽  
X Ray Scattering ◽  
Reconstruction Methods ◽  
Optimization Heuristics

Ab initio reconstruction methods have revolutionized the capabilities of small-angle X-ray scattering (SAXS), allowing the data-driven discovery of previously unknown molecular conformations, exploiting optimization heuristics and assumptions behind the composition of globular molecules. While these methods have been successful for the analysis of small particles, their impact on fibrillar assemblies has been more limited. The micrometre-range size of these assemblies and the complex interaction of their periodicities in their scattering profiles indicate that the discovery of fibril structures from SAXS measurements requires novel approaches beyond extending existing tools for molecular discovery. In this work, it is proposed to use SAXS measurements, together with diffraction theory, to infer the electron distribution of the average cross-section of a fiber. This cross-section is modeled as a discrete electron density with continuous support, allowing representations beyond binary distributions. Additional constraints, such as non-negativity or smoothness/connectedness, can also be added to the framework. The proposed approach is tested using simulated SAXS data from amyloid β fibril models and using measured data of Tobacco mosaic virus from SAXS experiments, recovering the geometry and density of the cross-sections in all cases. The approach is further tested by analyzing SAXS data from different amyloid β fibril assemblies, with results that are in agreement with previously proposed models from cryo-EM measurements. The limitations of the proposed method, together with an analysis of the robustness of the method and the combination with different experimental sources, are also discussed.

scholarly journals Cosmic Ray Antiprotons 5–12 GeV

1981 ◽  
Vol 94 ◽  
pp. 257-258 ◽  
Author(s):  
T. K. Gaisser ◽  
A. J. Owens ◽  
Gary Steigman
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Production Cross Section ◽  
Production Cross ◽  
Cosmic Ray ◽  
Image Position ◽  
Energy Dependent ◽  
Complex Nuclei

Secondary antiprotons are a potentially interesting probe of cosmic ray propagation because their production cross section is strongly energy-dependent, increasing by more than two orders of magnitude between 10 and 1000 GeV/c. This is quite unlike the case for fragmentation cross sections of complex nuclei, which are virtually constant with energy. Moreover, the flux depends primarily on the environment seen by protons which need not be identical to that probed by other nuclei.

Sputter-Deposited Films as Standards for Tem X-Ray Analysis

1980 ◽  
Vol 38 ◽  
pp. 134-135
Author(s):  
A. F. Marshall ◽  
C. Zercher
Keyword(s):  
Thin Film ◽  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Specimen Thickness ◽  
Detector Efficiency ◽  
X Ray ◽  
Transmission Electron ◽  
Sputter Deposited ◽  
Image Position ◽  
Deposited Films

Quantitative energy dispersive x-ray analysis in the transmission electron microscope is generally obtained in the form of relative concentrations using the equation: where CA, CB are the concentrations and IA, IB are the peak intensities of elements A and B, and kAB is a constant which is independent of specimen composition and specimen thickness, assuming the thin film criterion is satisfied. kAB may be determined experimentally from standards (Cliff-Lorimer technique1), or may be calculated from considerations of x-ray generation and detector efficiency for the elements being analyzed2. Due to differences in detector parameters, kAB may vary from instrument to instrument.

Plasmon Satellites in Auger Spectra

1974 ◽  
Vol 52 (7) ◽  
pp. 624-638 ◽  
Author(s):  
T. McMullen ◽  
B. Bergersen
Keyword(s):  
Perturbation Expansion ◽  
Core Hole ◽  
Auger Electrons ◽  
Fast Electrons ◽  
X Ray ◽  
Soluble Model ◽  
Bulk Plasmon ◽  
Initial Excitation ◽  
Auger Spectra ◽  
Limiting Case

A theory of Auger spectra in light metals, in which a nonequilibrium formalism is used to handle the aspects of the problem associated with energy loss of the fast electrons and decay of the excited core hole, is presented. The Auger electrons are assumed to reach the surface a time τ after the initial excitation. This time is determined by the decay characteristics of the initial core hole, the geometry, and the velocity of the Auger electrons. After τ, it is assumed that no interactions occur. Electron gas correlations are approximated by a bulk plasmon model. The initial excitation may be due to either X-ray or electron bombardment, although we concentrate on the former. Plasmon production by the primary ejected electrons and the suddenly created core hole is considered. The formalism is based on a perturbation expansion in the electron–plasmon interaction after extraction of the energy shifts, and this procedure is justified by comparison with a simple soluble model. It is applied to third-row (K; LL) Auger transitions. The plasmon gain satellite is compared to the main line, and the entire spectrum is computed in detail for the limiting case of a long lived core hole.

scholarly journals Three-Body Scattering and Hail Size

2010 ◽  
Vol 49 (4) ◽  
pp. 687-700 ◽  
Author(s):  
D. S. Zrnic ◽  
G. Zhang ◽  
V. Melnikov ◽  
J. Andric
Keyword(s):  
Size Distribution ◽  
Multiple Scattering ◽  
Cross Section ◽  
Cross Sections ◽  
Unit Volume ◽  
Wave Component ◽  
Coherent Wave ◽  
Storm Cells ◽  
Three Body ◽  
Radar Equation

Abstract The three-body scattering signature is an appendage seen on weather radar displays of reflectivity behind strong storm cells. It is caused by multiple scattering between hydrometeors and the ground. The radar equation for this phenomenon is reexamined and corrected to include the coherent wave component producing 3 dB more power than previously reported. Furthermore, the possibility to gauge hail size causing this phenomenon is explored. A model of forward scattering by spherical hail and accepted values of ground backscattering cross sections are used in an attempt to reconcile the reflectivity in this signature with observations. This work demonstrates that the signature can be caused by small- (<10 mm) to moderate- (20 mm) sized hail. An effort to gauge hail size by comparing the direct return from hail with the three-body scattered return is made. The theory indicates fundamental ambiguities in size retrieval resulting from resonant effects. Although theory eliminates the number of hailstones per unit volume, the shape of hail size distribution and the cross section of ground contribute additional uncertainty to the retrieval.

Quantitative elemental analysis by transmission electron spectroscopy

1978 ◽  
Vol 36 (1) ◽  
pp. 528-529
Author(s):  
David Joy ◽  
Dennis Maher ◽  
Peggy Mochel
Keyword(s):  
Cross Section ◽  
Electron Spectroscopy ◽  
Acceptance Angle ◽  
Ionization Cross ◽  
X Ray ◽  
Transmission Electron ◽  
Efficiency Factors ◽  
Image Position ◽  
Integrated Intensities ◽  
Fundamental Formula

In transmission electron spectroscopy the fundamental formula for elemental quantitation using inner-shell excitations gives the number n of atoms per cm2 contributing to the K-edge aswhere Ik and Io are the integrated intensities in the K-edge and zero-loss peak, respectively. Both of these integrals are measured for a spectrometer acceptance angle 2α and an energy interval ΔE. The parameter αk(α,ΔE) is the ionization cross-section for the same angular and energy parameters. The variation of αk with α and ΔE is a function of the generalized oscillator strength and little detailed information on this quantity is available. Therefore it is necessary to proceed empirically and the simplest assumption is thatwhere σk is a saturation (x-ray) cross-section and ηα,ηΔEcan be identified with efficiency factors.The accuracy of Equation (1) for K-edges from light elements (Li ≤ Z ≤ Al) is being tested by computer curve fitting and background stripping (see Fig. 1).

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