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

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 PL [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.
The present work describes a gap-less TEPL study 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 could 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.