Symmetric Domain Segmentation in WS2 Flakes: Correlating spatially resolved photoluminescence, conductance with valley polarization

TL;DR

This study investigates the spatial heterogeneity of spectroscopic, electrical, and mechanical properties in WS2 flakes, revealing how defects and substrate interactions influence valley polarization and optoelectronic behavior relevant for device applications.

Contribution

It provides a comprehensive multi-physics analysis linking defect-induced heterogeneity, substrate effects, and valley polarization in WS2 flakes, advancing understanding for 2D material device engineering.

Findings

Symmetric segmentation of spectroscopic response correlates with electronic property variations.

Sulfur vacancies and substrate interactions significantly influence local optoelectronic properties.

Valley polarization is affected by spatial heterogeneity and defect distribution.

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 (photoluminescence and Raman (spectral and intensity)), 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.