Unconventional lattice dynamics in few-layer h-BN and indium iodide crystals

Unusual quadratic dispersion of flexural vibrational mode and red-shift of Raman shift of in-plane mode with increas- ing layer-number are quite common and interesting in low-dimensional materials, but their physical origins still remain open questions. Combining ab initio density functional theory calculations with the empirical force-constant model, we study the lattice dynamics of two typical two-dimensional （2D） systems, few-layer h-BN and indium iodide （InI）. We found that the unusual quadratic dispersion of flexural mode frequency on wave vector may be comprehended based on the com- petition between atomic interactions of different neighbors. Long-range interaction plays an essential role in determining the dynamic stability of the 2D systems. The frequency red-shift of in-plane Raman-active mode from monolayer to bulk arises mainly from the reduced long-range interaction due to the increasing screening effect.

Tailoring electronic properties of two-dimensional antimonene with isoelectronic counterparts

Using ab initio density functional theory calculations, we explore the three most stable structural phases, namely, α,β, and cubic(c) phases, of two-dimensional(2D) antimonene, as well as its isoelectronic counterparts SnTe and InI. We find that the band gap increases monotonically from Sb to SnTe to InI along with an increase in ionicity, independent of the structural phases. The band gaps of this material family cover the entire visible-light energy spectrum, ranging from 0.26 eV to 3.37 eV, rendering them promising candidates for optoelectronic applications. Meanwhile, band-edge positions of these materials are explored and all three types of band alignments can be achieved through properly combining antimonene with its isoelectronic counterparts to form heterostructures. The richness in electronic properties for this isoelectronic material family sheds light on possibilities to tailor the fundamental band gap of antimonene via lateral alloying or forming vertical heterostructures.

Electronic and magnetic properties of CrI3 nanoribbons and nanotubes

CrI3 in two-dimensional(2D) forms has been attracting much attention lately due to its novel magnetic properties at atomic large scale.The size and edge tuning of electronic and magnetic properties for 2D materials has been a promising way to broaden or even enhance their utility, as the case with nanoribbons/nanotubes in graphene, black phosphorus, and transition metal dichalcogenides.Here we studied the CrI3 nanoribbon(NR) and nanotube(NT) systematically to seek the possible size and edge control of the electronic and magnetic properties.We find that ferromagnetic ordering is stable in all the NR and NT structures of interest.An enhancement of the Curie temperature TC can be expected when the structure goes to NR or NT from its 2D counterpart.The energy difference between the FM and AFM states can be even improved by up to 3–4 times in a zigzag nanoribbon(ZZNR), largely because of the electronic instability arising from a large density of states of iodine-5p orbitals at EF.In NT structures, shrinking the tube size harvests an enhancement of spin moment by up to 4%, due to the reduced crystal-field gap and the re-balance between the spin majority and minority populations.