  Single-layer heterostructures exhibit striking quasiparticle properties and
many-body interaction effects that hold promise for a range of applications.
However, their properties can be altered by intrinsic and extrinsic defects,
thus diminishing their applicability. Therefore, it is of paramount importance
to identify defects and understand 2D materials' degradation over time using
advanced multimodal imaging techniques as well as stabilize degradation via
built-in interface protection. Here we implemented a liquid-phase precursor
approach to synthesize 2D in-plane MoS2-WS2 heterostructures exhibiting
nanoscale alloyed interfaces and map exotic interface effects during
photo-degradation using a novel combination of hyperspectral tip-enhanced
photoluminescence, Raman and near-field nanoscopy. Surprisingly, 2D alloyed
regions exhibit remarkable thermal and photo-degradation stability providing
protection against oxidation. Coupled with surface and interface strain, 2D
alloy regions create localized potential wells that concentrate excitonic
species via a charge carrier funneling effect. These results provide a clear
understanding of the importance of 2D alloys as systems able to withstand
degradation effects over time, and could be now used to stabilize
optoelectronic devices based on 2D materials.
