Optically Triggered Emergent Mesostructures in Monolayer WS2.
Young-Chul Leem1, Zhenyao Fang2, Yun-Kyung Lee3
1Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia 19104, Pennsylvania, United States.
Nano Letters
|April 24, 2024
Summary
Two-dimensional materials like WS₂ exhibit photostrictive behavior, forming mechanical protrusions upon optical excitation. This opto-mechanical coupling opens new avenues for ultrathin microactuators.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Nanotechnology
Background:
- Two-dimensional (2D) materials possess ultrahigh surface areas enabling unique multimodal coupling.
- Coupling between optical, electrical, and mechanical properties leads to emergent dynamical responses.
- Such responses are not achievable in traditional three-dimensional systems.
Purpose of the Study:
- To investigate the photostrictive behavior in WS₂ monolayers.
- To explore the underlying mechanisms of optical excitation-induced mechanical changes.
- To understand the opto-electrical-mechanical coupling in 2D materials.
Main Methods:
- Optical excitation of WS₂ monolayer above exciton energy.
- Laser intensity and wavelength control of mechanical protrusions.
- Scanning Kelvin probe force microscopy (SKPFM) for charge transport analysis.
- Density functional theory (DFT) calculations for mechanistic insights.
Main Results:
- Observed symmetrically patterned mechanical protrusions induced by optical excitation.
- Attributed photostriction to lattice expansion from polaron formation.
- Revealed unconventional n- to p-type conversion dependent on spatial location and optical intensity.
- Identified formation of effective p-n junctions due to defect density variations.
Conclusions:
- Strong opto-electrical-mechanical coupling exists in WS₂ monolayers.
- This coupling leads to previously unexplored properties.
- Potential applications include optically driven ultrathin microactuators.
