Progress in the Characterization of Layered Structures by X-Ray Microanalysis

Rickerby, D. G.

doi:10.1051/mmm:1995152

Cited by 4 publications

(2 citation statements)

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“…The actual value, 1435 cm 2 g À1 , is close to that of 1457 cm 2 g À1 for the L mass absorption coef®-cient determined from WDS measurements on a GaAs standard. The experimentally measured effective mass absorption coef®cient for Ti L, 9311 cm 2 g À1 , is lower than the value of 12680 cm 2 g À1 [2], which was found to give improved analysis results for a thin Ti layer deposited on Si. This may be due to the relative insensitivity of measurements on thin layers to differences in the mass absorption coef®cient, or to the contribution of O K radiation emitted from the surface oxide layer on the standard to the apparent Ti L intensity at low accelerating voltages.…”

Section: Resultsmentioning

confidence: 63%

“…In the ®rst, the L intensity is estimated by multiplying the total intensity of the Lshell radiation by a relative intensity factor, a L , corresponding to the ratio of the L intensity to that emitted by the entire L-shell. In the second, the entire L-shell emission is considered [10] and the use of an effective L-shell mass absorption coef®cient is necessary [2]. Values of a L have been determined experimentally [11,12] and, provided that the mass absorption coef®cients of L and L radiation are similar, should be relatively independent of the accelerating voltage.…”

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confidence: 99%

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Effective L-Series Mass Absorption Coefficients for EDS

Rickerby

Wächter

2000

Mikrochim Acta

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Energy dispersive X-ray spectroscopy has insuf®cient resolution to separate the individual lines of low energy L-series peaks. However, the mass absorption coef®cients for L and L radiation differ signi®cantly for elements with atomic numbers between 21 and 32. Effective mass absorption coef®-cients for the entire L-shell emission were determined by measuring the variation of the X-ray intensities emitted from pure element standards, as a function of the accelerating voltage, and ®tting the experimental data with a theoretical curve using the XMAC software. These experimentally determined mass absorption coef®cients were compared with average values calculated on the basis of the theoretical line intensities, taking into account the primary vacancy generation and the radiationless Coster-Kronig transitions.The component lines of the L-series are not completely resolvable by energy dispersive spectrometry for X-ray energies less than approximately 3 keV. This results in the L and L peaks appearing as a single peak with an energy shift $ 10 eV with respect to the exact L line position. Use of the undeconvoluted L peak for quantitative analysis may therefore lead to large errors in cases where mass absorption differs signi®cantly for the individual lines [1±3]. The elements principally affected are those lying between atomic numbers 21 (scandium) and 32 (germanium), for which the energy of the L line is slightly greater than the ionization energy of the L 3 subshell. Due to the proximity of the absorption edge the mass absorption coef®cients for L radiation in these elements are up to a factor of six higher than for L.An additional source of error in analysis constitutes the uncertainty in the reported values of the mass absorption coef®cients for the L lines of the elements from Ti to Zn [4 ± 6]. The self absorption coef®cient for atoms bonded with atoms of other elements can furthermore vary noticeably from that in the pure element because the electron transition probabilities and X-ray absorption properties are in¯uenced by modi®cations in the structure of the valence band caused by alloying. The 3d transition elements, in which the valence band is incompletely ®lled, are most strongly affected and the self absorption of Ni L in alloys such as Ni-Al or Ni-Zn, for example, is consequently weaker than in the pure metal [7,8].Because of the uncertainties in analysis using soft X-rays, a method has been developed to determine precise values for mass absorption coef®cients by measuring the variation of the emitted line intensity with accelerating voltage. The experimentally measured values of the X-ray emission rate per unit beam current are compared to a theoretical curve computed by the XMAC software [8,9], which is based on the XPP model of X-ray generation. Using an iterative procedure to optimize the ®t a value for the mass absorption coef®cient can be obtained.Two alternative approaches may be used to perform quantitative energy dispersive analysis using compound L-series peaks. In the ®rst, the L intensity is e...

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Section: Resultsmentioning

confidence: 63%

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confidence: 99%