Forming Weakly Interacting Multi Layers of Graphene by using Atomic Force Microscope Tip Scanning and Evidence of Competition Between Inner and Outer Raman Scattering Processes Piloted by Structural Defects

TL;DR

This paper presents a novel AFM-based method to create weakly interacting multi-layer graphene from single layers, analyzing the structural and Raman spectral changes to understand defect roles and scattering processes.

Contribution

It introduces an AFM nanomechanical folding technique to produce multi-layer graphene and investigates the interplay of structural defects with Raman scattering processes.

Findings

AFM tip induces folding of single-layer graphene into multi-layer structures.

Folding maintains in-plane properties with limited defects.

Structural defects influence inner and outer Raman scattering processes.

Abstract

We report on an alternative route based on nanomechanical folding induced by AFM tip to obtain weakly interacting multi-layer graphene (wi-MLG) from a chemical vapor deposition (CVD) grown single-layer graphene (SLG). The tip first cuts, then pushes and folds graphene during zigzag movements. The pushed graphene has been analyzed using various Raman microscopy plots: $A_D /A_G \times E_L{}^4$ vs $\Gamma_G$, $\omega_{2D}$ vs $\Gamma_{2D}$, $\Gamma_{2D}$ vs $\Gamma_G$, $\omega_{2D+/-}$ vs $\Gamma_{2D+/-}$, and $A_{2D-}/A_{2D+}$ vs $A_{2D}/A_G$. We show that the SLG in plane properties are maintained under the folding process and that a few tens of graphene layers are stacked, with a limited amount of structural defects. A blue shift of about 20 cm-1 of the 2D band is observed. The relative intensity of the 2D$_-$ and 2D$_+$ bands have been related to structural defects, giving evidence of their role in the inner and outer processes at play close to the Dirac cone.