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 (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.

References in corpus (8)

• Valley polarization in MoS2 monolayers by optical pumping
• Strained bubbles in van der Waals heterostructures as local emitters of photoluminescence with adjustable wavelength
• Optical response of monolayer, few-layer and bulk tungsten disulfide
• Second order resonant Raman scattering in single layer tungsten disulfide (WS${}_2$)
• Understanding Variations in Circularly Polarized Photoluminescence in Monolayer Transition Metal Dichalcogenides
• The edge delamination of monolayer transition metal dichalcogenides
• Exciton-to-trion conversion as a control mechanism for valley polarization in room-temperature monolayer WS${}_{\text{2}}$
• Valley Depolarization in Monolayer Transition-Metal Dichalcogenides with Zone-Corner Acoustic Phonons