Symmetric domain segmentation in WS₂ flakes: correlating spatially resolved photoluminescence, conductance with valley polarization

Abstract

The incidence of intra-flake heterogeneity of spectroscopic and electrical properties in chemical vapour deposited (CVD) WS2 flakes is explored in a multi-physics investigation, via spatially resolved spectroscopic maps correlated with electrical, electronic and mechanical properties. The investigation demonstrates that the three-fold symmetric segregation of spectroscopic response, in topographically uniform WS2 flakes are accompanied by commensurate segmentation of electronic properties e.g. local carrier density and the differences in the mechanics of tip-sample interactions, evidenced via scanning probe microscopy phase maps. Overall, the differences are understood to originate from point defects, namely sulphur vacancies within the flake along with a dominant role played by the substrate. While evolution of the multi-physics maps upon sulphur annealing elucidates the role played by S-vacancy, substrate-induced effects are investigated by contrasting data from WS2 flake on Si and Au surfaces. Local charge depletion induced by the nature of the sample-substrate junction in case of WS2 on Au is seen to invert the electrical response with comprehensible effects on their spectroscopic properties. Finally, the role of these optoelectronic properties in preserving valley polarization, affecting valleytronic applications, in WS2 flakes is investigated via circular polarisation discriminated photoluminescence experiments. The study provides a thorough understanding of spatial heterogeneity in optoelectronic properties of WS2 and other two-dimensional transition metal chalcogenides, which are critical for device fabrication and potential applications.

Recent Strategies for the Synthesis of Phase-Pure Ultrathin 1T/1T′ Transition Metal Dichalcogenide Nanosheets

“…As soon as the Joule-heating-induced breakdown occurred in the FET device at a high applied bias, a Raman peak appeared at 125 cm –1 , which indicated the semiconducting 1H MoTe 2 phase transformed to the metallic 1T′ phase . In fact, more than the discussion above can Raman spectroscopy do when working together with other tools, such as PL and TEM, − enabling Raman a basic choice in the structure characterizations.…”