Line Shape of the Raman 2D Peak of Graphene in Van Der Waals Heterostructures

TL;DR

This study investigates the detailed shape of the Raman 2D peak in graphene within van der Waals heterostructures, revealing lower peak splitting than previously reported, indicating high electronic quality and homogeneous strain.

Contribution

It provides systematic analysis of the 2D peak asymmetries in encapsulated graphene, showing reduced peak splitting compared to suspended graphene, and highlights the high quality of heterostructure samples.

Findings

Low doping and homogeneous strain in encapsulated graphene

Reduced 2D peak splitting compared to suspended graphene

High electronic quality of heterostructure samples

Abstract

The Raman 2D line of graphene is widely used for device characterization and during device fabrication as it contains valuable information on e.g. the direction and magnitude of mechanical strain and doping. Here we present systematic asymmetries in the 2D line shape of exfoliated graphene and graphene grown by chemical vapor deposition. Both graphene crystals are fully encapsulated in van der Waals heterostructures, where hexagonal boron nitride and tungsten diselenide are used as substrate materials. In both material stacks, we find very low doping values and extremely homogeneous strain distributions in the graphene crystal, which is a hall mark of the outstanding electronic quality of these samples. By fitting double Lorentzian functions to the spectra to account for the contributions of inner and outer processes to the 2D peak, we find that the splitting of the sub-peaks, $6.6 \pm 0.5$ cm$^{-1}$(hBN-Gr-WSe2) and $8.9 \pm 1.0$ cm$^{-1}$ (hBN-Gr-hBN), is significantly lower than the values reported in previous studies on suspended graphene.