EPMA Measurements of Diffusion Profiles at the Submicrometre Scale

Abstract

International audienceConcentration profiles due to (inter)diffusion in materials may require high spatial resolution. These profiles may be measured by electron probe microanalysis, which allows one to determine the elemental composition with a good accuracy provided measurement ‘artefacts' can be accounted for. Standard phenomena are usually corrected by commercial softwares that assume a homogeneous elemental composition in the analysed area. However, in the case of a diffusion process on a small scale, the composition is no longer homogeneous and the effect of the hemispherical volume of the Xray emission on the spatial resolution of the concentration profiles, and consequently on the diffusion coefficients, has to be considered. Moreover, (secondary) fluorescence across interfaces or interphases has to be evaluated. A radial X-ray distribution associated with the characteristic depth distribution allows for the definition of a 2D X-ray emission function that enables the computation of the entire process for a given concentration profile

Specific effects and deconvolution in submicrometre EPMA: application to binary diffusion

“…3 This study completes the effect of the fluorescence radiations on the apparent concentration profiles that has been carried out elsewhere. 8 Some general deconvolution algorithms for close atomic number materials have been proposed and evaluated. They allow us to improve the EPMA resolution by a factor 5 if the B-radiations are only considered.…”

“…(33). The computation of the A-radiations 8 can be used to check the quality of the deconvolution. Note that the deconvolution is more accurate if the A-radiations are considered too as they give extra information without any additional unknowns since W A 1 W B and…”

“…28,29 Note that the previous derivation is exact for a perfect interface even for strong concentrationdependent coefficients if δ π 2. The above results can be used to identify σ from EPMA measurements 26,8 as described by Eq. (20) in Section 2.…”

“…Another important effect is the fluorescence that can be due to the X-ray continuum that can excite both A and B-atoms and the characteristic B-radiations that travel in the specimen and can excite A-atoms at any point M (since Z B Z A ) leading to fluorescent X-ray emission (noted I f A ) that is measured and modifies the analyzed spectra. 8 The volume concerned by this effect is much larger than that of the primary radiation and can be predominant over a longer range 6 especially for the characteristic fluorescence. Classical correction methods take this effect into account for a homogeneous volume but not when different phases or multilayered materials are concerned.…”

Wettability of Solid Metals by Molten MnO-SiO2 Slag

“…[9] Points taken near the interface will show false emissions of X-rays from the secondary phase. [6] The anomaly is greatest for elements of lower atomic weight. [10] Borom and Pask [7] noted that this effect was significant in studying the interface of iron with sodium disilicate.…”