Coating Thickness Determination Using X-ray Fluorescence Spectroscopy: Monte Carlo Simulations as an Alternative to the Use of Standards

Abstract

X-ray fluorescence is often employed in the measurement of the thickness of coatings. Despite its widespread nature, the task is not straightforward because of the complex physics involved, which results in high dependence on matrix effects. Thickness quantification is accomplished using the Fundamental Parameters approach, adjusted with empirical measurements of standards with known composition and thickness. This approach has two major drawbacks: (i) there are no standards for any possible coating and coating architecture and (ii) even relying on standards, the quantification of unknown samples requires the precise knowledge of the matrix nature (e.g., in the case of multilayer coatings the thickness and composition of each underlayer). In this work, we describe a semiquantitative approach to coating thickness measurement based on the construction of calibration curves through simulated XRF spectra built with Monte Carlo simulations. Simulations have been performed with the freeware software XMI-MSIM. We have assessed the accuracy of the methods by comparing the results with those obtained by (i) XRF thickness determination with standards and (ii) FIB-SEM cross-sectioning. Then we evaluated which parameters are critical in this kind of indirect thickness measurement.

Underpotential‐Assisted Electrodeposition of Highly Crystalline and Smooth Thin Film of Bismuth

“…The thickness of the sample A was evaluated as (55±6) nm from the measured SEM‐EDS spectra, assuming the surface as flat, through Monte Carlo simulations . This result is coherent with the order of magnitude of the peak‐to valley values given by the AFM analysis.…”

Measuring the Thickness of Metal Films: A Selection Guide to the Most Suitable Technique

“…The lateral resolution of XRF is very low, and spot size commonly ranges from 0.1 to 15 mm. The relative intensity (normalized respect to the bulk element) emitted from a film follows an exponential trend [18], but could be approximated to a second-order curve for small films far from the saturation thickness [7]. The emission of a gold film on Cu substrate, as a function of the thickness, is reported in Figure 9 using a log-log scale.…”

“…Besides the comparative method, MC simulation can be also employed to obtain a calibration curve based on a simulated standard. XMI-MSIM has been successfully used for this purpose for electroplated samples, normalizing the result with respect to a semi-infinite bulk element, with even better results than with the FP semi-empirical method [7]. A similar approach was used by Pessanha [8] for cultural heritage gildings on Pb using the PENELOPE code, exploiting the ratio between two lines of the same element for normalization, as if it were an internal standard.…”

“…In addition to that, with XRF, practically all the elements of the periodic table can be analyzed, except for the lighter ones (if not with some precautions), whether conductive or not. The thickness can be extrapolated from XRF data by means of standards [5], using the analytical equations of the fundamental parameter method (FP) [6] or through Monte Carlo (MC) simulations [7,8]. Other non-destructive techniques, more commonly used for research purposes, are ellipsometry [9], which however is rarely applicable to metallic coatings are generally not optically transparent, and X-ray reflectivity (XRR) [10,11] that can detect thicknesses from tens of nanometres to some micrometres.…”

Радиоактивационный контроль плотности износостойких покрытий AlN и CrN на кремнии

“…В [3] для нахождения массовых толщин покрытий, осажденных на подложки, использован метод РФА, основанный на детектировании кремниевым дрейфовым детектором (silicon drift detector, SSD) характеристического излучения как элементов покрытия, так и подложки под разными углами обзора, что в принципе не требует использования образцов сравнения. В работе [4] была сделана попытка обойти проблему использования в методе РФА сертифицированных образцов сравнения при применении для расчетов моделирования методом Монте-Карло. В целом рассмотренные выше подходы [2][3][4] к определению толщин покрытий без использования образцов сравнения выглядят ненадежными и неоправданными, поскольку выбор или изготовление тонких образцов сравнения материалов с известной массовой толщиной определяемых элементов не представляет серьезной проблемы.…”