Speaker
Description
Transition metal borides (TMBs) are a class of compounds known for their exceptional mechanical strength, thermal stability, and chemical inertness. These compounds, formed by strong covalent bonding between transition metals and boron, are widely studied for applications in cutting tools, coatings, and high-temperature environments such as thermal fusion reactors and aerospace components [1]. Among the TMBs, tungsten borides (WxBy) stand out due to their remarkable hardness and oxidation resistance. The mechanical performance of tungsten boride strongly depends on its stoichiometry; studies indicate that stoichiometric phases such as WB5 exhibit greater hardness up to a Vickers hardness of 45 GPa due to their dense covalent B–B and W–B networks, which provide high hardness combined with good thermal and chemical stability [2].
Accurate stoichiometric quantification of such borides poses a major analytical challenge. Techniques like EDS, WDS, and XPS often fail to provide reliable boron quantification because of its low atomic number. One of the solutions is Laser-Induced Breakdown Spectroscopy (LIBS), which is a well-established technique for on-site stoichiometric analysis of the materials. However, conventional LIBS operated in the standard UV – NIR range (220-900 nm) is not effective for B detection as only one B I doublet @ 249.7 nm can be observed. Our experimental setup included a picosecond laser with a pulse width of 250 ps, a repetition rate of 100 Hz, λ=1064nm, an echelle-type spectrometer for the UV-NIR range, and a Seiya-Namioki operating in the VUV range. The electronic temperature (Te) varied between 0.65 - 0.80 eV at the considered gate delay and the Ar gas pressure.
By extending the measurements of LIBS spectra into the vacuum ultraviolet (VUV) region, more B lines could be observed. After extending the measurement to the VUV range, the upper-level energy of B I lines ranges between 4.96-9.54 eV, enabling the evaluation of Tₑ using the Boltzmann plot (BP) from both W and B lines rather than solely depending on W. This enables a more accurate elemental quantification using the calibration-free (CF) approach. An earlier study on quantifying lighter elements, including B, has been carried out by our group [3]. Additionally, the texture of the sample coating will be measured using the texture measurement using XRD.
[1] M. Magnuson et al., 196 (2022) p.110567, Elsevier Ltd.
[2] A. G. Kvashnin et al., J Phys Chem Lett, 9 (2018) p. 3470.
[3] P. Veis, et al, Plasma Sources Sci Technol, 27 (2018) p. 095001.