Tip-induced nano-engineering of strain, bandgap, and exciton dynamics in 2D semiconductors

TL;DR

This paper demonstrates real-time, reversible nano-mechanical strain engineering of WSe2 monolayer wrinkles, enabling tunable exciton dynamics and emission properties with high spatial resolution using hyperspectral tip-enhanced PL spectroscopy.

Contribution

It introduces a dynamic nano-mechanical strain-engineering method on naturally-formed wrinkles in 2D semiconductors with real-time spectroscopic characterization, advancing nanoscale optoelectronic control.

Findings

Nanoscale wrinkles show modified excitonic properties under tensile strain.

Strain tuning affects PL energy, quantum yield, and spectral symmetry.

Reversible control of emission properties enables tunable nano-optical sources.

Abstract

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.