Direction-Controlled Chemical Doping for Reversible G-Phonon Mixing in ABC Trilayer Graphene

TL;DR

This study demonstrates reversible, direction-controlled chemical doping in ABC trilayer graphene that modulates its inversion symmetry, leading to controllable G phonon mixing and potential applications in tuning material properties.

Contribution

It introduces a novel reversible doping method that selectively breaks and restores inversion symmetry in graphene, enabling control over phonon modes.

Findings

Reversible symmetry breaking and restoration in graphene via chemical doping.

Observation of G phonon mode splitting and mixing due to symmetry changes.

Chemical doping can be used to tune vibrational and electronic properties of 2D materials.

Abstract

Not only the apparent atomic arrangement but the charge distribution also defines the crystalline symmetry that dictates the electronic and vibrational structures. In this work, we report reversible and direction-controlled chemical doping that modifies the inversion symmetry of AB-bilayer and ABCtrilayer graphene. For the top-down and bottom-up hole injection into graphene sheets, we employed molecular adsorption of electronegative I2 and annealing-induced interfacial hole doping, respectively. The chemical breakdown of the inversion symmetry led to the mixing of the G phonons, Raman active Eg and Raman-inactive Eu modes, which was manifested as the two split G peaks, G- and G+. The broken inversion symmetry could be recovered by removing the hole dopants by simple rinsing or interfacial molecular replacement. Alternatively, the symmetry could be regained by double-side charge injection, which eliminated G- and formed an additional peak, Go, originating from the barely doped interior layer. Chemical modification of crystalline symmetry as demonstrated in the current study can be applied to other low dimensional crystals in tuning their various material properties.