Structural, Thermal, and Electronic Properties of Two-Dimensional Gallium Oxide (ß-Ga2 O3 ) from First-Principles Design.

Two-dimensional (2D) materials with exotic electronic, optical and mechanical properties have attracted tremendous attention in the last two decades, due to their potential applications in electronics, energy storage and conversion technologies. However, only a few dozen 2D materials have been successfully synthesized or exfoliated. Motivated by the recent discovery of 2D gallenene, we have explored new 2D allotropes of ß-Ga2 O3 , an emerging wide-band gap transparent conductive oxide (TCO) with a wide range of semiconducting applications. All the possible 2D allotropes of ß-Ga2 O3 with high energetic stability have been predicted using particle swarm optimization, combined with density functional theory calculations. The structural and dynamical stability of the predicted 2D allotropes has been analyzed. Although ß-Ga2 O3 is not a van der Waals material, results predict that one or two allotropes of ß-Ga2 O3 are stable. In addition, the accurate band structures of these 2D semiconducting oxides have been calculated using both the GGA and LDA-1/2 approach. Remarkably, monolayer Ga2 O3 (100) has a larger indirect band gap of 4 eV, demonstrating a new avenue for the discovery of 2D ß-Ga2 O3 based nano-devices with enhanced electronic properties.

Two-dimensional aluminium, gallium, and indium metallic crystals by first-principles design.

Rapidly emerging two-dimensional (2D) atomic layer crystals exhibit diverse, tunable electronic properties. They appear to be more flexible than 3D crystals with greater versatility and improved functionality in a wide range of potential applications. Among these 2D materials, metallic crystals are relatively unexplored although two allotropes of gallenene (2D gallium) have been synthesized on a range of substrates. Based on these experimental findings, we investigate systematically the group 13 metals using first-principles density functional theory calculations and an unbiased structural search. In this study, the electronic structure, bonding characteristics, and phonon properties of predicted 2D allotropes of group 13 metals are calculated, including the expected effects of strain induced by substrates on the dynamical stability. Theoretical results predict that most group 13 elements have one or more stable 2D allotropes with the preferred allotrope depending on the cell shape relaxation and strain, indicating that the substrate will determine the overall allotrope preferred. This demonstrates a new avenue for the discovery of thermodynamically stable 2D metallic layers, with properties potentially suitable for electronic and optoelectronic applications.