SI traceable characterisation of nanomaterials by X-ray spectrometry

Abstract

The development of new materials and the assessment of nanomaterials require the correlation of the materials’ functionality or toxicity with their chemical and physical properties. To probe these properties, analytical methods that are both sensitive and selective at the nano-and microscales are required. The reliability of most analytical methods is based on the availability of reference materials or calibration samples, the spatial elemental compositions of which have to be as similar as possible to the matrix of the specimens of interest. However, there is a drastic lack of reference materials in particular at the nanoscale. Physikalisch-Technische Bundesanstalt (PTB) addresses this challenge by means of a bottom-up X-ray analytical method where all instrumental and experimental parameters are determined with known contributions to the uncertainty of the analytical results. This first-principle (FP) based approach does not require any reference materials but a complete characterisation of the analytical instruments’ characteristics and, in addition, knowledge on the X-ray fundamental parameters related to the elements composing the sample. In order to reveal more reliable FP data in line with recent FP roadmap recommendations, PTB has been developing and using calibrated instrumentation, both energy- and wavelength-dispersive X-ray spectrometers, in conjunction with well-known synchrotron radiation (SR) of high spectral purity. Examples of recent PTB works on different FP determinations mostly of technologically relevant elements are given. SR based X-ray spectrometric methods allow for the variation of the analytical sensitivity, selectivity, and information depth needed to effectively reveal the spatial, elemental, and chemical specimen parameters of interest. Examples of particle characterisation, interfacial speciation, elemental depth profiling, as well as layer composition and thickness characterisations in advanced materials and nanostructures as well as for in-situ conditions are given.