Strongly Absorbing Nanoscale Infrared Domains within Graphene Bubbles

TL;DR

This study demonstrates that nanoscale strain variations within graphene bubbles significantly influence infrared absorption, revealing potential pathways for strain-engineered IR devices using 2D materials.

Contribution

The paper introduces a nanoscale IR response measurement of graphene bubbles, linking strain configurations to IR absorption domains, advancing strain-based optoelectronic device design.

Findings

Distinct IR absorption domains correlate with strain variations.

Bubbles induce bi- or uniaxial strain configurations.

Ridges in bubbles coincide with domain boundaries.

Abstract

Graphene has shown great potential for modulating infrared (IR) light in devices as small as 350 nm. At these length scales, nanoscale features of devices, and their interaction with light, can be expected to play a significant role in device performance. Bubbles in van der Waals heterostructures are one such feature, which have recently attracted considerable attention thanks to their ability to modify the optoelectronic properties of 2D materials through strain. Here we use scattering-type scanning near-field optical microscopy (sSNOM) to measure the nanoscale IR response from a network of variously shaped bubbles in hexagonal boron nitride (hBN)-encapsulated graphene. We show that within individual bubbles there are distinct domains with strongly enhanced IR absorption. We correlate this with strain in the graphene, found with confocal Raman microscopy and vector decomposition analysis. This reveals intricate and varied strain configurations, in which bubbles of different shape induce more bi- or uniaxial strain configurations. Ridges in the bubbles, seen by atomic force microscopy (AFM), coincide with the domain boundaries, which leads us to attribute the domains to nanoscale strain differences in the graphene. This reveals pathways towards future strain-based graphene IR devices.