Strain superlattices and macroscale suspension of Graphene induced by corrugated substrates

TL;DR

This study explores how the geometry of corrugated substrates influences the formation of strain, ripples, and suspension in large-area graphene sheets, revealing controllable strain domains and potential for nanomechanical applications.

Contribution

It introduces a comprehensive experimental and theoretical analysis of how substrate geometry controls graphene's morphology and strain, enabling tailored stress engineering.

Findings

Graphene conformally coats, partially collapses, or suspends depending on substrate geometry.

Ripples transition from random pleats to organized domains with increased pillar density.

Uniaxial strain domains are induced and controlled by substrate geometry.

Abstract

We investigate the organized formation of strain, ripples and suspended features in macroscopic CVD-prepared graphene sheets transferred onto a corrugated substrate made of an ordered arrays of silica pillars of variable geometries. Depending on the aspect ratio and sharpness of the corrugated array, graphene can conformally coat the surface, partially collapse, or lay, fakir-like, fully suspended between pillars over tens of micrometers. Upon increase of pillar density, ripples in collapsed films display a transition from random oriented pleats emerging from pillars to ripples linking nearest neighboring pillars organized in domains of given orientation. Spatially-resolved Raman spectroscopy, atomic force microscopy and electronic microscopy reveal uniaxial strain domains in the transferred graphene, which are induced and controlled by the geometry. We propose a simple theoretical model to explain the transition between suspended and collapsed graphene. For the arrays with high aspect ratio pillars, graphene membranes stays suspended over macroscopic distances with minimal interaction with pillars tip apex. It offers a platform to tailor stress in graphene layers and open perspectives for electron transport and nanomechanical applications.