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Direct Observation of Incommensurate-Commensurate Transition in Graphene-hBN Heterostructures via Optical Second
E A Stepanov1,2, S V Semin3, C R Woods4,5
1Institute of Theoretical Physics, Department of Physics, University of Hamburg, Jungiusstrasse 9, Hamburg 20355, Germany.
ACS Applied Materials & Interfaces
|May 23, 2020
Summary
Optical second harmonic generation detects structural changes in layered materials. This nonlinear optical technique probes alignment in graphene/hexagonal boron nitride heterostructures, observing phase transitions via signal modification.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Nanotechnology
Background:
- Commensurability effects in layered heterostructures significantly influence electronic properties.
- Moiré superlattices in twisted bilayer graphene exhibit intriguing phenomena like superconductivity and metal-insulator transitions.
- Efficient experimental methods are needed to determine the alignment of layered materials.
Purpose of the Study:
- To investigate the alignment of graphene/hexagonal boron nitride heterostructures.
- To explore the potential of optical second harmonic generation (SHG) for probing structural changes in layered systems.
- To establish a straightforward and efficient technique for detecting material alignment.
Main Methods:
- Utilizing optical second harmonic generation (SHG), a nonlinear optical technique sensitive to inversion symmetry breaking.
- Inducing a commensurate-incommensurate phase transition in graphene/hexagonal boron nitride heterostructures via thermal annealing.
- Monitoring changes in the nonlinear optical signal to correlate with structural modifications.
Main Results:
- A strong modification of the nonlinear optical signal was observed, directly correlating with the structural phase transition.
- Second harmonic generation (SHG) proved sensitive to the alignment and structural changes in the heterostructure.
- The technique successfully detected the transition between commensurate and incommensurate phases.
Conclusions:
- Optical second harmonic generation (SHG) is a viable and efficient method for probing structural changes and alignment in layered materials.
- The observed signal modification provides a direct readout of structural transitions in moiré superlattices.
- This nonlinear optical approach offers a powerful tool for characterizing novel layered heterostructures.
