Tuning flexoelectricty and electronic properties of zig-zag graphene nanoribbons by functionalization

TL;DR

This study demonstrates how functionalization with hydrogen and fluorine significantly enhances the flexoelectric and electronic properties of zig-zag graphene nanoribbons, enabling improved flexible electronic device performance.

Contribution

The paper introduces a first-principles approach to tuning flexoelectricity and electronic properties of graphene nanoribbons through specific chemical functionalization.

Findings

Hydrogen and fluorine functionalization increases flexoelectric response by over two orders of magnitude.

Fluorine functionalization induces a large out-of-plane flexoelectric effect due to charge symmetry breaking.

Bending controls charge localization, tuning band gaps and hole effective masses.

Abstract

The flexoelectric and electronic properties of zig-zag graphene nanoribbons are explored under mechanical bending using state of the art first principles calculations. A linear dependence of the bending induced out of plane polarization on the applied strain gradient is found. The inferior flexoelectric properties of graphene nanoribbons can be improved by more than two orders of magnitude by hydrogen and fluorine functionalization (CH and CF nanoribbons). A large out of plane flexoelectric effect is predicted for CF nanoribbons. The origin of this enhancement lies in the electro-negativity difference between carbon and fluorine atoms, which breaks the out of plane charge symmetry even for a small strain gradient. The flexoelectric effect can be further improved by co-functionalization with hydrogen and fluorine (CHF Janus-type nanoribbon), where a spontaneous out of plane dipole moment is formed even for flat nanoribbons. We also find that bending can control the charge localization of valence band maxima and therefore enables the tuning of the hole effective masses and band gaps. These results present an important advance towards the understanding of flexoelectric and electronic properties of hydrogen and fluorine functionalized graphene nanoribbons, which can have important implications for flexible electronic applications.