2D V-V Binary Materials: Status and Challenges

2D Antimony-Arsenic Alloys

Alloying in group V 2D materials and heterostructures is an effective degree of freedom to tailor and enhance their physical properties. Up to date, black arsenic-phosphorus is the only 2D group V alloy that has been experimentally achieved by exfoliation, leaving all other possible alloys in the realm of theoretical predictions. Herein, the existence of an additional alloy consisting of 2D antimony arsenide (2D-As_x Sb_{1- x} ) grown by molecular beam epitaxy on group IV semiconductor substrates and graphene is demonstrated. The atomic mixing of As and Sb in the lattice of the grown 2D layers is confirmed by low-energy electron diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. The As content in 2D-As_x Sb_{1- x} is shown to depend linearly on the As₄ /Sb₄ deposition rate ratio and As concentrations up to 15 at% are reached. The grown 2D alloys are found to be stable in ambient conditions in a timescale of weeks but to oxidize after longer exposure to air. This study lays the groundwork for a better control of the growth and alloying of group V 2D materials, which is critical to study their basic physical properties and integrate them in novel applications.

Tunable anisotropic behaviors in phosphorene under periodic potentials in arbitrary directions

We investigate theoretically the anisotropic electronic and optical behaviors of a monolayer black phosphorus (phosphorene) modulated by periodic potential superlattices in arbitrary directions. We demonstrate that different strength and orientation of the phosphorene potential superlattice can give rise to distinct energy spectra, i.e. tuning the intrinsic electronic anisotropy. Accordingly, the anisotropic effective mass, and optical absorption modulated by superlattice strength and orientation are addressed systematically. This feature enables tuning capability more than one order of magnitude in the optical absorption spectrum. Our findings should be useful in building phosphorene optical and (opto)electronic devices by applying external potential superlattice.

Density functional study of Li/Na adsorption properties of single-layer and double-layer antimonenes

β-Antimonene, a stable two-dimensional material, has been successfully prepared recently. Experiments have demonstrated β-antimonene's excellent Li storage properties. Based on first-principles density functional theory (DFT), the adsorption properties of Li/Na atoms on single-layer antimonene (SL-Sb) and double-layer antimonene (DL-Sb) have been studied. The optimal adsorption position of Li/Na atoms on SL-Sb is the V site with an adsorption energy of 1.91/1.46 eV. With the increase of Li adsorption density, the crystal structure of the antimonene changes significantly. The optimal adsorption position of Li on DL-Sb is the V2 site in the interlayer with an adsorption energy of 2.71 eV, and that of Na is the V1 site outside the surface with an adsorption energy of 1.72 eV. With the increase of the adsorption density of Li, the antimonene presented a trend of forming an alloy. Whereas with the increase of Na adsorption density, the antimonene retains its original structure. The diffusion barrier of Li/Na atoms on the SL-Sb surface is 0.22/0.13 eV, and outside the DL-Sb surface is 0.25/0.15 eV. In short, DL-Sb can maintain a stable structure with a large Li/Na storage density; the diffusion barriers of Li/Na atoms on antimonene are relatively low, which is beneficial to the rapid insertion/extraction.

β-Antimonene, a stable two-dimensional material, has been successfully prepared recently.