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

Walter Giurlani,Enrico Berretti,Massimo Innocenti,Alessandro Lavacchi

doi:10.3390/coatings9020079

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.

Highlights

Thickness determination of metallic and ceramic coatings is often performed by X-ray Fluorescence (XRF), a widespread, non-destructive technique applied in the industry as a tool for Quality Assurance (QA) and Materials Science R&D [1,2,3,4,5]
The applicability of the proposed method is strongly connected to the ability of the simulation software to provide good results; for this reason, we evaluated the accuracy and the reproducibility of XMI-MSIM
1 μm of gold software to provide good results; for this reason, we evaluated the accuracy and the reproducibility coating on brass was performed using values from 1 to 10 as the number of interactions; the PR of of each element for all the spectra was compared to the simulation with the highest number of parameter that affects of the simulations is the number of interactions per trajectory: interactions permitted, and the the accuracy relative deviation was calculated

Summary

Introduction

Thickness is a crucial parameter in coatings technology and affects material functionality. Thickness determination of metallic and ceramic coatings is often performed by X-ray Fluorescence (XRF), a widespread, non-destructive technique applied in the industry as a tool for Quality Assurance (QA) and Materials Science R&D [1,2,3,4,5]. The variability of thickness, layer composition, multilayer architectures, and substrate chemical nature create difficulties in producing certified standards. This issue is critical in industrial applications; among them, the determination of precious metal coatings in the fashion industry is a major one, as production employs a large number of coatings and substrates, with extreme variability in the system. The most common approach is the use of the fundamental parameter (FP) method [6,7,8,9]

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Results

Conclusion