Imaging Nanoscale Inhomogeneities and Edge Delamination in As-Grown MoS2 Using Tip-Enhanced Photoluminescence

TL;DR

This study demonstrates nanoscale imaging of inhomogeneities and edge delamination in as-grown MoS2 using tip-enhanced photoluminescence without pretreatment, revealing defect-related PL behavior and differences from exfoliated flakes.

Contribution

First gap-less TEPL imaging on as-grown MoS2 without plasmonic substrates, providing high-resolution insights into inhomogeneities and delamination.

Findings

Homogeneous layer interiors distinguished from defective edges.

Defects and lack of substrate doping influence PL behavior.

Exfoliated flakes show topography- and contamination-related heterogeneities.

Abstract

Methods for nanoscale material characterization are in ever-increasing demand, especially those that can provide a broader range of information at once. Near-field techniques based on combinations of scanning probe microscopy (SPM) and Raman or photoluminescence (PL) spectroscopy (tip-enhanced Raman spectroscopy [TERS] and/or tip-enhanced photoluminescence [TEPL]) are, thanks to their capabilities and fast development, strong candidates for becoming widespread across the scientific community as SPM and Raman microscopy did only a decade or two ago. Herein, a gap-less TEPL study is performed directly on as-grown MoS2 monolayer samples without any pretreatment or transfer, i.e., without the utilization of plasmonic substrate. Thanks to a mapping resolution as low as a few tens of nanometers, homogeneous layer interiors from defective edge fronts in the grown monolayers can be distinguished. With the aid of additional high-resolution SPM modes, like local surface potential and capacitance measurements, together with nanomechanical mapping, a combination of defects and a lack of substrate doping is suggested as being responsible for the observed PL behavior in the partially delaminated MoS2 layers. In contrast, mechanically exfoliated flakes show topography- and contamination-related heterogeneities in the whole flake area.