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Register a new userStructure and Dynamics of Boron Nitride Nanoscrolls
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Carbon nanoscrolls (CNSs) are structures formed by rolling up graphene layers into a papyruslike shape. CNNs have been experimentally produced by different groups. Boron nitride nanoscrolls (BNNSs) are similar structures using boron nitride instead of graphene layers. In this work we report molecular mechanics and molecular dynamics results for the structural and dynamical aspects of BNNS formation. Similarly to CNS, BNNS formation is dominated by two major energy contributions, the increase in the elastic energy and the energetic gain due to van der Waals interactions of the overlapping surface of the rolled layers. The armchair scrolls are the most stable configuration while zigzag scrolls are metastable structures which can be thermally converted to armchair. Chiral scrolls are unstable and tend to evolve to zigzag or armchair configurations depending on their initial geometries. The possible experimental routes to produce BNNSs are also addressed.
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Imaging and spectroscopy performed in a low-voltage scanning transmission electron microscope (LV-STEM) are used to characterize the structure and chemical properties of boron-terminated tetravacancies in hexagonal boron nitride (h-BN). We confirm earlier theoretical predictions about the structure of these defects and identify new features in the electron energy-loss spectra (EELS) of B atoms using high resolution chemical maps, highlighting differences between these areas and pristine sample regions. We correlate our experimental data with calculations which help explain our observations.
High pressure Raman experiments on Boron Nitride multi-walled nanotubes show that the intensity of the vibrational mode at ~ 1367 cm-1 vanishes at ~ 12 GPa and it does not recover under decompression. In comparison, the high pressure Raman experiments on hexagonal Boron Nitride show a clear signature of a phase transition from hexagonal to wurtzite at ~ 13 GPa which is reversible on decompression. These results are contrasted with the pressure behavior of carbon nanotubes and graphite.
In this work, we report our results on the geometric and electronic properties of hybrid graphite-like structure made up of silicene and boron nitride (BN) layers. We predict from our calculations that this hybrid bulk system, with alternate layers of honeycomb silicene and BN, possesses physical properties similar to those of bulk graphite. We observe that there exists a weak van der Waals interaction between the layers of this hybrid system in contrast to the strong inter-layer covalent bonds present in multi-layers of silicene. Furthermore, our results for the electronic band structure and the density of states show that it is a semi-metal and the dispersion around the Fermi level (E_F) is parabolic in nature and thus the charge carriers in this system behave as textit{Nearly-Free Particle-Like}. These results indicate that the electronic properties of the hybrid bulk system resemble closely those of bulk graphite. Around E_F the electronic band structures have contributions only from silicene layers and the BN layer act only as a buffer layer in this hybrid system since it does not contribute to the electronic properties near E_F. In case of bi-layers of silicene with a single BN layer kept in between, we observe a linear dispersion around E_F similar to that of graphene. However, the characteristic linear dispersion become parabola-like when the system is subjected to a compression along the transverse direction. Our present calculations show that the hybrid system based on silicon and BN can be a possible candidate for two dimensional layered system akin to graphite and multi-layers of graphene.
In this study we present a theoretical investigation of structural, electronic and mechanical properties of pentagonal monolayers of carbon (p-graphene), boron nitride (p-B$_{2}$N$_{4}$ and p-B$_{4}$N$_{2}$) and silver azide (p-AgN$_{3}$) by performing state-of-the-art first principles calculations. Our total energy calculations suggest feasible formation of monolayer crystal structures composed entirely of pentagons. In addition, electronic band dispersion calculations indicate that while p-graphene and p-AgN$_{3}$ are semiconductors with indirect bandgaps, p-BN structures display metallic behavior. We also investigate the mechanical properties (in-plane stiffness and the Poissons ratio) of four different pentagonal structures under uniaxial strain. p-graphene is found to have the highest stiffness value and the corresponding Poissons ratio is found to be negative. Similarly, p-B$_{2}$N$_{4}$ and p-B$_{4}$N$_{2}$ have negative Poissons ratio values. On the other hand, the p-AgN$_{3}$ has a large and positive Poissons ratio. In dynamical stability tests based on calculated phonon spectra of these pentagonal monolayers, we find that only p-graphene and p-B$_{2}$N$_{4}$ are stable, but p-AgN$_{3}$ and p-B$_{4}$N$_{2}$ are vulnerable against vibrational excitations.
Recently hybridized monolayers consisting of hexagonal boron nitride (h-BN) phases inside graphene layer have been synthesized and shown to be an effective way of opening band gap in graphene monolayers [1]. In this letter, we report an ab initio density functional theory (DFT)- based study of h-BN domain size effect on the elastic properties of graphene/boron nitride hybrid monolayers (h-BNC). We found both inplane stiffness and longitudinal sound velocity of h-BNC linearly decrease with h-BN concentration.
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