High precision elemental analysis of rock samples and archaeological artifacts by X-Ray photoelectron spectroscopy

Abstract

Introduction. Despite a fairly wide range of methods currently used for the chemical and elemental analysis of rocks and archaeological artifacts, many questions regarding the qualitative and quantitative accuracy of the analysis and the distribution of elements over the surface and volume of the sample with a high degree of locality remain open. In this regard, to solve these issues, in this work, for the first time, the method of X-ray photoelectron spectroscopy (XPS) was proposed and tested, which allows unambiguous and high-precision chemical identification of an object and the construction of its elemental map of the surface and volume. Materials and methods. The physical principles of the XPS method operation, which determine its record high qualitative and quantitative accuracy, are considered, a description of one of the most highly efficient X-ray photoelectron spectrometers Escalab 250 Xi, features of its operation and methods of adaptation for the study of rocks and archaeological artifacts are given. A special methodological advantage is the possibility of sample preparation and research under ultrapure conditions of ultrahigh vacuum. Results. XPS spectra were obtained in a wide range of photoelectron binding energies, which makes it possible to cover a fairly wide range of chemical elements that make up rocks and archaeological artifacts. With a high degree of spatial locality – at the level of 30 μm – elemental maps of the objects under study were built. Using the additional advantage of the method, based on the analysis of the energy position and the shape of the photoelectron spectral line, the chemical states of the elements that make up the samples were determined. Discussion. The obtained results of high-precision chemical analysis, combining both the general composition of the elements of the test sample as a whole and their spatial distribution with a high degree of locality, make it possible to achieve greater unambiguity in the identification of the objects under study compared to currently used analysis methods. Such high accuracy makes it possible to establish a correspondence between the composition of the rock and the archaeological artifact from the same area. The non-destructive nature of the XPS method, combined with ultrapure analysis conditions, makes it possible to ensure the safety of often unique objects. Conclusion. As a result of the study, it was shown that the XPS method can be quite effectively used for high-precision qualitative and quantitative analysis of rocks and archaeological artifacts, which is achieved both by the features of the method itself and by sample preparation and study of materials in ultrapure conditions of ultrahigh vacuum. The advantage of the method is the combination of a number of possibilities, such as not only the elemental, but also the chemical composition of objects, as well as the possibility of chemical mapping of the surface and analysis of the depth of the object with high spatial resolution. The research results can be used in solving a wide range of problems – from archeology to the development of mountainous areas, in particular, solving environmental problems by developing a scientific reserve for creating effective geochemical barriers. Further research should be focused on the development of techniques for adapting the XPS method to obtain three-dimensional tomographic models of the studied objects, which will improve the quality of their identification, in particular, from the point of view of geology and archeology.