Visualization of Band Shifting and Interlayer Coupling in WxMo1-xS2 Alloys using Near-Field Broadband Absorption Microscopy

TL;DR

This paper demonstrates a novel near-field broadband absorption microscopy technique to visualize and analyze the spatially-varying band structures and interlayer coupling in WxMo1-xS2 alloys, revealing detailed optoelectronic properties.

Contribution

It introduces a new microscopy method for directly imaging band shifts and interlayer interactions in 2D alloy materials at sub-diffraction resolution.

Findings

Visualized excitonic band shifts due to composition and interlayer effects

Identified the top layer as pure WS2 in bilayer alloys

Demarcated boundaries of alloyed and pure TMD regions

Abstract

Beyond-diffraction-limit optical absorption spectroscopy provides profound information on the graded band structures of composition-spread and stacked two-dimensional materials, in which direct/indirect bandgap, interlayer coupling, sliding, and possible defects significantly modify their optoelectronic functionalities such as photoluminescence efficiency. We here visualize the spatially-varying band structure of monolayer and bilayer transition metal dichalcogenide alloys for the first time by using near-field broadband absorption microscopy. The near-field-spectral and -spatial diagrams manifest the excitonic band shift that results from the interplay of composition spreading and interlayer coupling. These results enable us to identify the top layer of the bilayer alloy as pure WS2. We also use the aberration-free near-field transmittance images to demarcate the exact boundaries of alloyed and pure transition metal dichalcogenides. This technology can offer new insights on various layered structures in the era of stacking science in quest of novel quantum optoelectronic devices.