Density functional theory based study of graphene and dielectric oxide interfaces

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Graphene's unique electronic properties stem from its linear energy band structure near the Dirac points.
• Interactions with dielectric substrates can significantly modify graphene's electronic behavior.
• Understanding these substrate effects is crucial for designing graphene-based electronic devices.

Purpose of the Study:

• To investigate the impact of crystalline insulating oxides on the electronic band structure of monolayer and bilayer graphene.
• To compare the influence of different oxide materials (SiO2 and Al2O3) and their surface terminations.
• To elucidate the role of atomic relaxations versus dangling bonds in substrate-induced perturbations.

Main Methods:

• Employed first-principles density functional theory (DFT) for electronic structure calculations.
• Utilized the local density approximation (LDA) for exchange-correlation interactions.
• Simulated graphene interacting with crystalline SiO2 (α-quartz) and Al2O3 (α-sapphire) with specific surface terminations.

Main Results:

• Atomic relaxations and equilibrium separation distances were found to be critical in altering graphene's band structure.
• The influence of dangling bonds was less significant compared to atomic relaxations.
• A Si-terminated quartz substrate retained the Dirac cone in monolayer graphene; O-terminated quartz restored it in bilayer graphene. Alumina required more than two graphene layers to preserve the Dirac cone.

Conclusions:

• The dielectric environment and interfacial atomic arrangement profoundly influence graphene's electronic properties.
• Careful selection of oxide substrates and layer configurations is necessary to maintain graphene's desirable electronic characteristics.
• Results provide semi-quantitative insights for crystalline oxides, with potential implications for amorphous forms.