LIBS Protocol for the Assessment of Depth Profile, Homogeneity, and Quantification of Fe/Co - based Bilayer Ribbon

Abstract

The present work explores the applicability of a single spectroscopic technique, Laser-induced breakdown spectroscopy (LIBS), for the rapid quality assessment and quantification of individual layers of an amorphous bilayer ribbon (thickness ~ 35 μm). This kind of materials (ribbon) offer a convolution of the two sets of unique properties of individual layer, in a single ribbon, in contrast to the layered systems prepared by thin film technologies, and are useful and applicable for sensing and actuating in different experimental conditions. The sample was prepared by rapid quenching using the modified double-nozzle technique. One side of the ribbon is a layer of iron (Fe) - silicon (Si) - boron (B) and other side of the ribbon consists of cobalt (Co) - silicon (Si) - boron (B). Owing to its versatility and advantages, LIBS has been used for assessing the elemental distribution on the surface of the investigated matrices and across the layer interface. After optimizing the experimental parameters, the LIBS measurements have been performed using a Q-switched Nd:YAG laser working at its second harmonic wavelength (532 nm) with the 30 mJ/pulse energy under ambient air and atmospheric pressure conditions. Following the LIBS spectral analysis, a chemometric approach, principal component analysis (PCA), has been used for the visualization of the spectra from the two layers and to observe dominant spectral lines responsible for the discrimination of both layers. The depth profile analysis of the layers has been carried out using LIBS and the number of pulses corresponding to the individual layers have been correlated with the depth of the ablation craters obtained using the 3D-optical profilometry in order to estimate the thickness of the individual layers and the ablation rates. Furthermore, the homogeneity of the sample has been examined by measuring the intensity of selected spectral lines corresponding to the composition of the sample. Calibration-free (CF) - LIBS analysis has been performed for the compositional quantification of both layers of the sample and found in a good agreement with the production ratio. This work paves the way towards the investigation and control of the properties of such intelligent materials.