Strain effects on stability, electronic and optical properties of two-dimensional C4X2 (X = F, Cl, Br)

Abstract

Employing first-principles calculations, the stabilities, electronic and optical properties of halogenated diamane (C₄X₂; X = F, Cl, Br) are systematically investigated. In particular, strain effects on these properties are carefully checked. The energetic, dynamical, and thermal stabilities of these structures are first confirmed by binding energies, phonon spectra, and molecular dynamics simulations, respectively. The C₄F₂ and C₄Cl₂ are predicted to have wide direct bandgaps using the GW method, while the C₄Br₂ is a metal. Also, the bandgap in the C₄F₂ and C₄Cl₂ can be modulated widely by applying in-plane biaxial strains. More interestingly, the calculated optical spectra clearly show that the C₄F₂ (C₄Cl₂) has significant absorption for the near-ultraviolet light (visible and near-ultraviolet lights). Once applying biaxial strains on the C₄F₂ and C₄Cl₂, they can lead to the red/blue-shift of optical spectra and enhancement of optical absorption. These suggest that the C₄F₂ and C₄Cl₂ have promising applications in electronic and optoelectronic devices such as ultraviolet photodetectors and sensors.