Super-resolution imaging of nanoscale inhomogeneities in hBN-covered and encapsulated few-layer graphene

TL;DR

This study demonstrates super-resolution imaging of nanoscale inhomogeneities in hBN-encapsulated graphene using hyperlensing effects mediated by phonon and plasmon polaritons, revealing stacking-dependent features.

Contribution

It introduces a hyperlensing-based near-field imaging method to visualize subdiffractional inhomogeneities in encapsulated graphene, advancing nanoscale characterization techniques.

Findings

Hyperlensing enables magnified imaging of nanoscale inhomogeneities.

Coupling between hBN phonon polaritons and graphene plasmon polaritons is stacking-dependent.

The method reveals inhomogeneities that are otherwise below the diffraction limit.

Abstract

Encapsulating few-layer graphene (FLG) in hexagonal boron nitride (hBN) can cause nanoscale inhomogeneities in the FLG, including changes in stacking domains and topographic defects. Due to the diffraction limit, characterizing these inhomogeneities is challenging. Recently, the visualization of stacking domains in encapsulated four-layer graphene (4LG) has been demonstrated with phonon polariton (PhP)-assisted near-field imaging. However, the underlying coupling mechanism and ability to image subdiffractional-sized inhomogeneities remain unknown. Here, we retrieve direct replicas and magnified images of subdiffractional-sized inhomogeneities in hBN-covered trilayer graphene (TLG) and encapsulated 4LG, enabled by the hyperlensing effect. This hyperlensing effect is mediated by hBN's hyperbolic PhP that couple to the FLG's plasmon polaritons. Using near-field microscopy, we identify the coupling by determining the polariton dispersion in hBN-covered TLG to be stacking-dependent. Our work demonstrates super-resolution and magnified imaging of inhomogeneities, paving the way for the realization of homogeneous encapsulated FLG transport samples to study correlated physics.