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He, Xue Du, chunmei Li & nanpu cheng ✉ The current work investigates a novel three-dimensional boron nitride called bulk B 4 n 4 and its corresponding two-dimensional monolayer B 4 n 4 based on the first-principles of density functional theory. The phonon spectra prove that bulk B 4 n 4 and monolayer B 4 n 4 are dynamically stable. The molecular dynamics simulations verify that bulk B 4 n 4 and monolayer B 4 n 4 have excellent thermal stability of withstanding temperature up to 1000 K. The calculated elastic constants state that bulk B 4 n 4 and monolayer B 4 n 4 are mechanically stable, and bulk B 4 n 4 has strong anisotropy. the theoretically obtained electronic structures reveal that bulk B 4 n 4 is an indirect band-gap semiconductor with a band gap of 5.4 eV, while monolayer B 4 n 4 has a direct band gap of 6.1 eV. The valence band maximum is mainly contributed from B-2p and N-2p orbits, and the conduction band minimum mainly derives from B-2p orbits. The electron transitions from occupied N-2p states to empty B-2p states play important roles in the dielectric functions of bulk B 4 n 4 and monolayer B 4 n 4. The newly proposed monolayer B 4 n 4 is a potential candidate for designing optoelectronic devices such as transparent electrodes due to its high transmissivity. In recent years, the physicochemical properties of boron nitrides in different crystal structures are widely studied 1. Besides the work on the four common boron nitrides, namely hexagonal boron nitride (h-BN) 2 , rhombohedral boron nitride (r-BN) 3 , cubic boron nitride (c-BN) 4 and wurtzite boron nitride (w-BN) 5 , researchers have also devoted themselves to the preparations and properties of BN nanosheets 6. Low dimensional BN nanomaterials, such as h-BN, are famous for their excellent chemical inertness and thermal stability 7. L. Li et al. studied the effect of thicknesses of h-BN on the electric field screening by electrostatic force microscopy (EFM) and theoretical calculations, and found that h-BN is excellent dielectric substrate to support two-dimensional (2D) nanomaterials such as graphene, and MoS 2 8

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CuInTe 2 chalcopyrite compound is widely used in the fields of optoelectronics and pyroelectricity, and doping atoms can further improve the physical properties of the CuInTe 2 compound. For all we know, this is the first time that the elastic behaviors and lattice dynamical properties of Ag-doped CuInTe 2 compounds with the tetragonal system are determined theoretically. The elastic, lattice dynamical and thermal properties of Cu 1−x Ag x InTe 2 (x=0, 0.25, 0.5, 0.75 and 1) compounds have been investigated by using density functional theory. The obtained elastic constants of Cu 1−x Ag x InTe 2 compounds indicate that these compounds are mechanically stable and elastic anisotropic. The anisotropy of the {001} plane is more obvious than those of the {100} and {010} planes. Additionally, with increasing Ag doping concentrations, the bulk and shear moduli of Cu 1−x Ag x InTe 2 compounds decrease and their toughness improves. The phonon spectra and density of states reveal that Cu (or Ag) atoms in Cu 1−x Ag x InTe 2 compounds form chemical bonds with Te atoms, and Cu-Te bonds are gradually replaced by Ag-Te bonds with increasing Ag doping concentration. Vibration modes of Cu 1−x Ag x InTe 2 compounds at the G point in the Brillouin zone show that each Cu 1−x Ag x InTe 2 (x=0 and 1) crystal includes five irreducible representations (A 1 , A 2 , B 1 , B 2 and E). As for Cu 1−x Ag x InTe 2 (x=0.25, 0.5 and 0.75) compounds, each crystal has three irreducible representations (A, B and E). The atomic displacements of several typical phonon modes in CuInTe 2 crystals have been analyzed to deepen the understanding of lattice vibrations in Cu 1−x Ag x InTe 2 compounds. With increasing Ag doping concentration, the Debye temperatures of Cu 1−x Ag x InTe 2 compounds decrease, while their heat capacities increase.

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