Effect of bromine depletion and oxidization on magnetic, mechanical, and optical properties of CrSBr semiconductor

Abstract

Variations in the physical properties of 2D semiconductors due to differing growth conditions present challenges for the reliable design of nanodevices. In this study, we analyzed the chemical composition and physical properties of several commercially grown CrSBr samples and observed that detailed characterization can reveal differences in magnetic and optical properties, which can be explained by crystal heterogeneity. A reduction in bromine content was clearly detected in bulk material through magnetic studies, although it was not always identified by Raman scattering. The samples exhibited variations in chemical composition due to bromine depletion in one of them. This depletion led to a shift in the critical temperature for a paramagnetic-to-metamagnetic transition from 132 K to 120 K in the non-stoichiometric sample. The critical temperature of 120 K, along with XRD spectra, aligns well with those typical of the Cr₂S₃ phase. Bromine depletion promotes the nucleation of the Cr₂S₃ phase, which coexists with the primary CrSBr phase. Mechanical exfoliation of bromine-depleted CrSBr crystals produced single flakes with characteristic CrSBr spectra, along with a small number of additional flakes exhibiting different compositions. We further investigated the mechanical properties of CrSBr bulk material. In the surface layer (up to 0.5 μm deep), we observed deviations in nanohardness relative to the bulk material. Nanoindentation measurements revealed a hardness of 3 GPa and a Young's modulus of 45 GPa at deeper indentation into the bulk.