X-ray microanalysis of thin specimens in the transmission electron microscope at voltages up to 1000 Kv.

Abstract

In a specimen which is transmission thin to 100 kV electrons - a sample in which X-ray absorption is so insignificant that it can be neglected and where fluorescence effects can generally be ignored (1,2) - a ratio of characteristic X-ray intensities, I1/I2 can be converted into a weight fraction ratio, C1/C2, using the equationwhere k12 is, at a given voltage, a constant independent of composition or thickness, k12 values can be determined experimentally from thin standards (3) or calculated (4,6). Both experimental and calculated k12 values have been obtained for K(11<Z>19),kα(Z>19) and some Lα radiation (3,6) at 100 kV. The object of the present series of experiments was to experimentally determine k12 values at voltages between 200 and 1000 kV and to compare these with calculated values.The experiments were carried out on an AEI-EM7 HVEM fitted with an energy dispersive X-ray detector.

Multiscale analysis of grain boundary microstructure in high strength 7xxx Al alloys

“…To analyse the smaller η-phase GB precipitates formed during ageing, particles were selected on HAGBs from PFIB-prepared and electropolished samples that had no visual signs of chemical attack and analysed following the same procedure described above as close to their centre as possible. At least 12 A-GBPs were again measured for each material and the data plotted against Al content, to deconvolute the background matrix signal following the method of Cliff et al [56]. This allowed their average Al concentration to be determined by extrapolation of the fitted data to the assumed ideal Mg stoichiometry of 33 at.%.…”

“…Due to the relatively small size of the A-GBPs, the Cliff-Lorimer extrapolation procedure [56] was employed to deconvolute their Al content from the surrounding matrix. Typical STEM-EDS chemical maps from the A-GBPs are shown in Figure 9, which again indicate they have relatively uniform compositions.…”

Theoretical and Experimental X-Ray Peak/Background Ratios and Implications for Energy-Dispersive Spectrometry in the Next-Generation Analytical Electron Microscope

“…In the absence of absorption, fluorescence, and electron channeling effects (Goldstein, 1979; Zaluzec, 1979; D’Alfonso et al, 2010; Allen et al, 2015), the characteristic α th-shell X-ray emission from a thin solid film of atomic number Z and thickness t , is essentially isotropic, and can be written approximately aswhere I α is the measured X-ray intensity (counts) per unit area, σ α ( E o , Z ) the α th-shell ionization cross-section (Inokuti, 1971, 1978; Zaluzec, 1984) excited by electrons of incident energy ( E o ), ω α the α th-shell fluorescence yield, Γ α the α th-shell radiative partition function, W Z and C Z the atomic weight composition (in at%) of the element Z , N o Avogadro’s number, ρ the local specimen density, ξ o = η o × τ the incident electron flux, ε α the detector efficiency, and Ω α the detector collection solid angle. As there is no angular dependence in this equation, the emission can be described as spherically uniform over 4 π steradians, a plane section through the specimen and incident beam results in an angularly symmetric and circular intensity profile as illustrated in Figure 1.

Figure 1Illustration of the angular distribution of characteristic and bremsstrahlung radiation relative to the incident electron beam from a thin specimen.

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“…Since the initial inception of interfacing an X-ray energydispersive spectrometer (XEDS) to the column of a scanning/transmission or analytical electron microscope (AEM), numerous predictions have been made concerning the optimum configuration of the detector/specimen relative to the incident electron beam (Cliff et al, 1978;Zaluzec, 1978). There are four criteria, which can be considered to be major parameters, that contribute to this optimum:…”