Nano-optical imaging of monolayer MoSe2-WSe2 lateral heterostructure with subwavelength domains

Abstract

Near-field optical microscopy can be used as a viable route to understand the nanoscale material properties below the diffraction limit. On the other hand, atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDs) are the materials of recent interest to study the spatial confinement of charge carriers, photon, and phonons. Heterostructures based on Mo or W based monolayer TMDs form type-II band alignment, and hence the optically excited carriers can be easily separated for applications pertaining to photonics and electronics. Mapping these spatially confined carriers or photons in a heterostructure with nanoscale resolution as well as their recombination behavior at the interfaces are necessary for the effective use of these materials in future high performance optoelectronics. We performed tip-enhanced photoluminescence (TEPL) imaging to increase the spatial resolution on multi-junction monolayer MoSe2-WSe2 lateral heterostructures grown by chemical vapor deposition (CVD) method. The near-field nano-PL emission map was used to distinguish the presence of distinct crystalline boundaries and the heterogeneities across the interfaces. This method significantly improves the nanoscale resolution of 2D materials, especially for understanding the PL emission properties at the vicinity of hetero-interfaces.

Exciton–Photonics: From Fundamental Science to Applications

“…This 2D structure allows it to maintain uniformly confined plasmonic gap modes throughout the entire flake. Within 2D materials, excitonic TMDCs have inspired increased interest in the near-field spectroscopy studies due to their distinct optical properties and emergence of locking in spin and valley degrees of freedom, , presence of spatial heterogeneity, − strain engineering, and in-plane epitaxial heterolayer structures. − …”

Multimodal Nanoscopic Study of Atomic Diffusion and Related Localized Optoelectronic Response of WS2/MoS2 Lateral Heterojunctions

“…Sahoo et al used TEPL to study the transition region width, alloying effect, and aging properties of MoSe 2 /WSe 2 HJs . Xue et al studied the exciton distribution of MoSe 2 /WSe 2 /MoSe 2 periodic HJs using TEPL . These studies provided preliminary information on the electronic and excitonic properties of HJs in a geometric scale (∼40 nm) far below the optical diffraction limitation. − However, the nanoscale localized optoelectronic behaviors caused by the diffusion-induced alloying effect and their correlations with the local crystal structure are still unknown.…”

Nano-spectroscopy of excitons in atomically thin transition metal dichalcogenides

“…A variety of scanning probe optical methods are in general suitable for the nanoscale characterization of the excitonic properties. Specifically, tip-enhanced photoluminescence (TEPL) studies have uncovered aspects of nanoscale excited state recombination in TMDs [10][11][12][13][14][15][16][17][18][19] . Complementary to the TEPL, absorption spectra encode not only the exciton resonance energy but also the oscillator strength and damping rate, offering additional detailed inquiry into the excitonic response.…”