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M. Weiss, H. Riedl, P.H. Mayrhofer, A. Limbeck:
"Determination of the stochiometric composition of ternary boride thin films via LA-ICP-MS and LIBS";
Talk: ANAKON 2019, Münster, Germany; 2019-03-25 - 2019-03-28; in: "Programm", (2019), 100.

Hard coatings are widely used to enhance the surface of material and protect them from abrasion, corrosion and fatigue. Today the most common coatings are based on nitrides and carbides. Beside them, boride based thin films gain interest through their superior chemical and physical resistance, including the combination of hardness and ductility, corrosion resistance and good tribological behavior. These properties are retained even at elevated temperatures. The use of physical vapor (PVD) deposition allows to alloy different metal borides in arbitrary combination to fine tune the properties for the specific application. To understand these materials and to control the production process it is necessary to know the stochiometric composition of the film, which is influenced by elemental fractionation effects and the inclusion of vacancies during the PVD process.
Borides pose to be challenging to elemental characterization, the low number of electrons of boron makes X-Ray based methods, like X-Ray diffraction and X-Ray fluorescence, hard to apply. Other solid sampling techniques require the use of matrix matched standards or certified reference materials for quantitative analysis, which are often not available, especially for a new class of materials like borides. Another option is to use liquid measurements, for which the solid material has to be brought into liquid form, e.g. by acid digestion. These methods are reported in literature and well understood, but the time-consuming sample handling inhibits a high throughput and spatial information is lost during the digestion process.
In this work two laser-based methods, based on laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and laser induced breakdown spectroscopy (LIBS), are presented to characterize the stoichiometry, but also the homogeneity of ternary boride thin films. The used samples were micrometer thick ternary boride thin films based on tungsten diboride, which was alloyed with aluminum, tantalum, titanium, vanadium and zirconium, produced by PVD. The quantification was done using selfaliquoting microgrooves, which are an improvement of the "dried droplet" approach. This allows the use of widely available liquid standard solution, which can be mixed in arbitrary combinations to meet the requirements of the experiment, so that the use of matrix matched solid standards can be circumvented. The results of the LA-ICP-MS and LIBS data were verified by wet digestions of the samples, which confirmed the accuracy and applicability of the used methods.

LA-ICP-MS, LIBS, stoichiometry analysis, ternary boride thin films