Measurement of layer thickness and fingerprint analysis using the X-ray fluorescence technique

Abstract

X-Ray Fluorescence (XRF) is a powerful technique of elemental quali-quantitative chemical analysis, non-destructive, fast, which does not require sample preparation and can be used in the simultaneous identification of chemical elements from Sodium (Na) to Uranium (U), being possible to quantify from sub parts per million (ppm) to concentrations of 100% with good precision (<5%). XRF can also be used to measure the thickness of overlay layers, and in this regard, in the case of multiple overlay layers, the XRF is unbeatable when compared to traditional techniques for thickness measurements, such as: a) magnetic induction method; b) eddy current method sensitive to phase or amplitude; c) magnetic method; d) microresistance method; e) coulometric method and STEP method (Simultaneous Thickness and Electrochemical Potential determination); f) titration method, among others. For each type of overlay layer and substrate involved in the measurement, in the case of using traditional techniques, there is a need for prior knowledge of the overlay layers to be measured and the substrate, as the materials involved will dictate which is the best technique or equipment to be used, often more than one technique or equipment is required to achieve the desired result, which requires complicated calibrations and very well-trained operators. Within this context, XRF has been replacing traditional layer thickness measurement techniques, since it can be used to obtain the thickness of layers of surfaces covered by one or more layers of various types of chemical elements, such as: Zn, Fe, Al, Sn, Ni, Ta, Cu, Ti, Pt, Ag, Au, among others, in a huge variety of substrates. XRF, in addition to providing the thickness of the multi-layer coatings, is able to measure thicknesses on the order of nanometers, while providing the elemental chemical composition of the layers. In the case of fingerprint analysis, we use XRF to analyze the conformity between different materials or to identify counterfeits, a technique that is very important for the pharmaceutical industry. The objective of this work is to implement a new line of research with the group that I coordinate at the University of Sorocaba, in the line of thickness measurement of covering layers and studies of conformity and forgeries using XRF, since there is an industry demand for developments in this area, there is a lack of trained personnel to implement them and there are challenges to be overcome. For example, in the area of layer measurement in the pharmaceutical sciences, this technique could be used to measure the thickness of the coating layers of solid pharmaceutical forms, where this technique is little used or unknown. Another area that could benefit from the technique is the covering of layers with non-metallic products, as in the thickness of the layer of cataphoretic varnish used as a protector by the ironmongery industry, among others. Therefore, we are requesting to FAPESP aid for the acquisition of two software modules, marketed by the company Malvern Panalytical (Stratos and Fingerprint modules), which will create the minimum conditions necessary to start a new branch of research, in the area of measurement of layer thickness and studies of conformity, since we already have equipment to do this, the Epsilon-1, purchased from the company Marlvern Panalytical, under Fapesp grant Nº 2018/06801-9. The lack of these modules, however, prevents us from proceeding with our current research. The installation of Stratos and Fingerprint will effectively complement the capacity and function of Epsilon-1 in a most essential way, allowing us to move forward with our studies. (AU)