Abstract
The present case study critically assesses the efficacy of a previously proposed segmentation methodology as a means to discriminate phases via post-processing the image of an elemental map. In the Bi2Te2.5S0.5 multiphase compound, the reference spectra of the Bi2Te3 and Bi2Te2S phases are distinct enough to effectively distinguish two phases during map acquisition. Since the counts of the sulphur-K peak in the X-ray emission data are significantly higher for Bi2Te2S compared to Bi2Te3, the segmentation methodology exploits this variation and enables successful phase discrimination via post-processing the image of the elemental map.
Highlights
Over the last decade, bismuth telluride based alloys have been investigated due to their exceptional performance as room temperature thermoelectric coolers and generators
Comparing the phase maps obtained a er map acquisition and segmentation on a per-pixel basis shows that when the segmentation parameters are optimised, the absolute error in phase discrimination via segmentation is $5%
Since this study aims to assess the efficacy of segmentation, various combinations of neighbourhood matrix size, neighbourhood density threshold and dilation kernel size were applied (Table 1) to the absolute error in the phase map from segmentation (Table 1) was determined by calculating the absolute difference between this segmented map and the reference phase map obtained by combined energy dispersive X-ray spectroscopy (EDS) + EBSD (Fig. 1d) on a per-pixel basis using the ‘Image Calculator’ function in ImageJ
Summary
Bismuth telluride based alloys have been investigated due to their exceptional performance as room temperature thermoelectric coolers and generators. The above close correspondence in the crystal structure and lattice parameters of Bi2Te3 and Bi2Te2S renders phase discrimination via electron back-scattering diffraction patterns impossible.† In this regard, energy dispersive X-ray spectroscopy (EDS) coupled with EBSD provides the appropriate solution. Other thermoelectric systems such as multiphase quaternary lead chalcogenides and other novel bismuth telluride alloys could require phase segmentation via the proposed segmentation methodology.[12,13,14,15,16] In this case, phase segmentation of Bi2Te2.5S0.5 is presented due to its promising thermoelectric properties.[17] The counts of the sulphur-K peak in the X-ray emission data (similar to carbon, sulphur is a low density element at 2.067 gm cmÀ3) are signi cantly higher for Bi2Te2S compared to Bi2Te3. Comparing the phase maps obtained a er map acquisition and segmentation on a per-pixel basis shows that when the segmentation parameters are optimised, the absolute error in phase discrimination via segmentation is $5%
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