Determination of effective ionization cross-sections for quantitative surface chemical microanalysis using REELS

1993 ◽  
Vol 48 (4) ◽  
pp. 465-473 ◽  
Author(s):  
Z.L. Wang ◽  
J. Bentley
Keyword(s):  
Cross Sections ◽  
Surface Chemical ◽  
Ionization Cross ◽  
Ionization Cross Sections ◽  
Effective Ionization

Teoretical Tools for Practical ALCHEMI

2001 ◽  
Vol 7 (S2) ◽  
pp. 348-349
Author(s):  
L. J. Allen ◽  
M. P. Oxley
Keyword(s):  
Ionization Potential ◽  
Cross Sections ◽  
First Principles Calculations ◽  
Ionization Cross ◽  
Precise Shape ◽  
Atomic Scattering ◽  
Computationally Intensive ◽  
Ionization Cross Sections ◽  
Shell Ionization ◽  
Effective Ionization

Precisely known atomic scattering factors are essential for accurate atom location by channelling enhanced microanalysis (ALCHEMI) based on inner-shell ionization.1 For ALCHEMI using energy dispersive x-ray analysis (EDX), first principles calculations of ionization cross sections, realistically modeling the “delocalization” of the ionization interaction, give excellent agreement with experiment.2 Such calculations are complex and computationally intensive. Hence, simple analytic forms are often assumed to describe the ionization potential. However such analytic forms require prior knowledge of the “delocalization” of the effective ionization interaction. Such an approach assumes that the precise shape of the ionization potential is not important but that at least the half width at half maximum (HWHM) should be accurately estimated, for example using estimates of the HWHM from root-mean-square impact parameters for ionization. However this is generally not a good approximation3 and we have provided more realistic estimates (Fig. 1).

scholarly journals Laboratory Determination of the Luminous Efficiency of Meteor Constituents

1971 ◽  
Vol 13 ◽  
pp. 83-87 ◽  
Author(s):  
Howard F. Savage ◽  
Charles A. Boitnott
Keyword(s):  
Cross Sections ◽  
Luminous Efficiency ◽  
Visible Spectral Range ◽  
Molecular Flow ◽  
Spectral Features ◽  
Velocity Range ◽  
Flow Conditions ◽  
Ionization Cross ◽  
Ionization Cross Sections

A crossed beam apparatus has been used to measure the emission and ionization cross sections for the prominent spectral features of Na, Ca, Mg, and Fe in collisions with N2 and O2 over the velocity range of 30 to 120 km/s. From the emission and ionization cross sections, the absolute luminous efficiencies in air were determined over the range of meteor velocities. The maximum luminous efficiencies for the brightest features were: greater than 1 percent for the Na D-lines, 0.2 percent for the CaI(2) singlet, 0.06 percent for the MgI(2) and MgI(3) triplets, and O.4 percent for Fe over the visible spectral range. These luminous efficiencies are valid for free molecular flow conditions for velocities above about 30 km/s and are directly applicable to spectroscopic observations of faint meteors. The luminous efficiency of a typical stone will be presented and compared with the efficiencies determined by other investigators. In contrast to previous work, the luminous efficiency found for stone in the present investigation decreases with velocity above about 50 km/s.

EELS of Niobium and Stoichiometric Niobium-Oxide Phases—Part II: Quantification

2009 ◽  
Vol 15 (6) ◽  
pp. 524-538 ◽  
Author(s):  
David Bach ◽  
Reinhard Schneider ◽  
Dagmar Gerthsen
Keyword(s):  
Cross Sections ◽  
Background Subtraction ◽  
Niobium Oxide ◽  
Nominal Composition ◽  
Atomic Concentration ◽  
Ionization Cross ◽  
Oxide Phases ◽  
Ionization Cross Sections ◽  
Electron Energy Loss

AbstractA comprehensive electron energy-loss spectroscopy (EELS) study of niobium (Nb) and stable Nb-oxide phases (NbO, NbO2, Nb2O5) was carried out. Part II of this work is devoted to quantitative EELS by means of experimental k-factors derived from the intensity ratio of the O-K edge and the Nb-M4,5 or Nb-M2,3 edges for all three stable Nb-oxides. The precision and accuracy of the quantification are investigated with respect to the influence of intensity-measurement energy windows, background subtraction, and sample thickness. Integration-window widths allowing optimum accuracy are determined. Owing to background-subtraction errors, the Nb-M4,5 edges rather than Nb-M2,3 are preferred for quantification. Different approaches are applied to improve the precision with regard to thickness-related errors. Thus, a precision up to ±1.5% is achieved by averaging spectra from all three reference oxides to determine a k-factor using Nb-M4,5. Using the experimental k-factor, the determination of atomic concentration ratios CNb/CO in the range of 0.4 (Nb2O5) to 1 (NbO) was found to be possible with an accuracy of 0.6% (relative deviation between measured and nominal composition), whereas ratios of calculated partial ionization cross sections lead to less accurate results.

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