  The tunability of the bandgap, absorption and emission energies,
photoluminescence (PL) quantum yield, exciton transport, and energy transfer in
transition metal dichalcogenide (TMD) monolayers provides a new class of
functions for a wide range of ultrathin photonic devices. Recent
strain-engineering approaches have enabled us to tune some of these properties,
yet dynamic control at the nanoscale with real-time and -space
characterizations remains a challenge. Here, we demonstrate a dynamic
nano-mechanical strain-engineering of naturally-formed wrinkles in a WSe2
monolayer, with real-time investigation of nano-spectroscopic properties using
hyperspectral adaptive tip-enhanced PL (a-TEPL) spectroscopy. First, we
characterize nanoscale wrinkles through hyperspectral a-TEPL nano-imaging with
<15 nm spatial resolution which reveals the modified nano-excitonic properties
by the induced tensile strain at the wrinkle apex, e.g., an increase in the
quantum yield due to the exciton funneling, decrease in PL energy up to ~10
meV, and a symmetry change in the TEPL spectra caused by the reconfigured
electronic bandstructure. We then dynamically engineer the local strain by
pressing and releasing the wrinkle apex through an atomic force tip control.
This nano-mechanical strain-engineering allows us to tune the exciton dynamics
and emission properties at the nanoscale in a reversible fashion. In addition,
we demonstrate a systematic switching and modulation platform of the wrinkle
emission, which provides a new strategy for robust, tunable, and ultracompact
nano-optical sources in atomically thin semiconductors.
