Density functional theory based study of graphene and dielectric oxide interfaces

TL;DR

This study uses density functional theory to analyze how crystalline dielectric oxides like SiO2 and Al2O3 affect the electronic band structure of graphene, highlighting the importance of atomic relaxations and surface terminations.

Contribution

It provides a first-principles analysis of crystalline oxide-graphene interfaces, emphasizing the role of atomic relaxations over dangling bonds in band structure perturbations.

Findings

Atomic relaxations significantly influence graphene's band structure.

Adding layers can restore the Dirac cone in certain oxide interfaces.

Crystalline oxides offer promising options for graphene electronics.

Abstract

We study the effects of insulating oxides in their crystalline forms on the energy band structure of monolayer and bilayer graphene using a \textit{first principles} density functional theory based electronic structure method and a local density approximation. We consider the dielectric oxides, SiO$_{2}$ ($\alpha$-quartz) and Al$_{2}$O$_{3}$ (alumina or $\alpha$-sapphire) each with two surface terminations. Our study suggests that atomic relaxations and resulting equilibrium separations play a critical role in perturbing the linear band structure of graphene in contrast to the less critical role played by dangling bonds that result from cleaving the crystal in a particular direction. We also see that with the addition of a second graphene layer, the Dirac cone is restored for the quartz surface terminations. Alumina needs more than two graphene layers to preserve the Dirac cone. Our results are at best semi-quantitative for the common amorphous forms of the oxides considered. However, crystalline oxides for which our results are quantitative provide an interesting option for graphene based electronics, particularly in light of recent experiments on graphene with crystalline dielectrics (hexagonal BN) that find considerable improvements in transport properties as compared to the those with amorphous dielectrics.