Raman spectroscopic study of artificially twisted and non-twisted trilayer graphene

Abstract

Twisted van der Waals systems have been receiving recent attention due to their potential for moiré-induced band modulation and corresponding exotic correlated phases. Here, we present a Raman spectroscopic study of artificial trilayer graphene (3LG), represented by monolayer graphene (1LG) on top of Bernal-stacked bilayer graphene (2LG), as a function of the twist angle (θt) with respect to each other. The artificially twisted 3LG with θt >5° shows a distinctive 2D peak, which is literally composed of the typical 2D peak of 1LG and that of 2LG, without signatures of strong coupling between the 1LG and the 2LG. The overall trends of the relative Raman shift and the full width at half maxima of the 2D peak are also provided as a function of θt ranging from 0° to 30°. In particular, non-twisted 3LG shows 2D peak characteristics very similar to those of natural Bernal-stacked 3LG, revealing that the top 1LG and the bottom 2LG are translationally rearranged to be the most thermodynamically stable state. We also realized slightly twisted 3LG with a finite θt <1°, which presents the signature of coexisting Bernal-stacked (ABA) and rhombohedral (ABC) 3LG domains.