Highly anisotropic and ultra-diffusive vacancies in α-antimonene.

α-Antimonene has recently been successfully fabricated in experiment; hence, it is timely to examine how various types of point defects in α-antimonene can affect its novel electronic properties. Herein, we present a comprehensive investigation of a total of nine possible types of point defects in α-antimonene via first-principles calculations. Particular attention is placed on the structural stability of the point defects and the effects of point defects on the electronic properties of α-antimonene. Compared with its structural analogs, such as phosphorene, graphene, and silicene, we find that most defects in α-antimonene can be more easily generated, and that among the nine types of point defects, the single vacancy SV-(5|9) is likely the most stable one while its presence can be orders of magnitude higher in concentration than that in phosphorene. Moreover, we find that the vacancy exhibits anisotropic and low diffusion barriers, of merely 0.10/0.30 eV in the zigzag/armchair direction. Notably, at room temperature, the migration of SV-(5|9) in the zigzag direction of α-antimonene is estimated to be three orders faster than that along the armchair direction, and also three orders faster than that of phosphorene in the same direction. Overall, the point defects in α-antimonene can significantly affect the electronic properties of the host two-dimensional (2D) semiconductor and thus the light absorption capability. The anisotropic, ultra-diffusive, and charge tunable single vacancies, along with the high oxidation resistance, render the α-antimonene sheet a unique 2D semiconductor (beyond the phosphorene) for developing vacancy-enabled nanoelectronics.

Ultrahigh Lithium Storage Capacity of Al2C Monolayer in a Restricted Multilayered Growth Mechanism.

Designing anode materials with high lithium specific capacity is crucial to the development of high energy density lithium (ion) batteries. Herein, a distinctive lithium growth mechanism, namely, the restricted multilayered growth for lithium, and a strategy for lithium storage are proposed to achieve a balance between ultrahigh specific capacity and the need to avert uncontrolled dendritic growth of lithium. In particular, based on first-principles computation, we show that the Al2C monolayer with a planar tetracoordinate carbon structure can be an ideal platform for realizing the restricted multilayered growth mechanism as a two-dimensional (2D) anode material. Furthermore, the Al2C monolayer exhibits the ultrahigh specific capacity of lithium of 4059 mAh/g, yet with a low diffusion barrier of 0.039-0.17 eV and low open circuit voltage in the range of 0.002-0.34 V. These novel properties render the Al2C monolayer a promising anode material for future lithium (ion) batteries. Our study also offers a design of promising 2D anode materials with a high specific capacity, fast lithium-ion diffusion, and safe lithium storage.