g-B3N3C: a novel two-dimensional graphite-like material

A novel crystalline structure of hybrid monolayer hexagonal boron nitride (BN) and graphene is predicted by means of the first-principles calculations. This material can be derived via boron or nitrogen atoms substituted by carbon atoms evenly in the graphitic BN with vacancies. The corresponding structure is constructed from a BN hexagonal ring linking an additional carbon atom. The unit cell is composed of 7 atoms, 3 of which are boron atoms, 3 are nitrogen atoms, and one is carbon atom. It behaves a similar space structure as graphene, which is thus coined as g-B3N3C. Two stable topological types associated with the carbon bonds formation, i.e., C-N or C-B bonds, are identified. Interestingly, distinct ground states of each type, depending on C-N or C-B bonds, and electronic band gap as well as magnetic properties within this material have been studied systematically. Our work demonstrates practical and efficient access to electronic properties of two-dimensional nanostructures providing an approach to tackling open fundamental questions in bandgap-engineered devices and spintronics.Comment: 15 pages, 6 figure

Quantum confined peptide assemblies with tunable visible to near-infrared spectral range

Quantum confined materials have been extensively studied for photoluminescent applications. Due to intrinsic limitations of low biocompatibility and challenging modulation, the utilization of conventional inorganic quantum confined photoluminescent materials in bio-imaging and bio-machine interface faces critical restrictions. Here, we present aromatic cyclo-dipeptides that dimerize into quantum dots, which serve as building blocks to further self-assemble into quantum confined supramolecular structures with diverse morphologies and photoluminescence properties. Especially, the emission can be tuned from the visible region to the near-infrared region (420 nm to 820 nm) by modulating the self-assembly process. Moreover, no obvious cytotoxic effect is observed for these nanostructures, and their utilization for in vivo imaging and as phosphors for light-emitting diodes is demonstrated. The data reveal that the morphologies and optical properties of the aromatic cyclo-dipeptide self-assemblies can be tuned, making them potential candidates for supramolecular quantum confined materials providing biocompatible alternatives for broad biomedical and opto-electric applications

A large enhancement of magnetism in zigzag Janus MoSSe nanoribbons: First-principles calculations

In this letter, we demonstrate a large enhancement of the magnetic moment in zigzag Janus MoSSe nanoribbons arising from the out-of-plane mirror symmetry breaking. Owing to the broken mirror symmetry, the $d^{\uparrow}_{z^{2}}$ orbital of the edge Mo atom is tilted and largely overlaps the $d^{\uparrow}_{yz}$ orbital. As a result, a new band which is nearly completely occupied near the Fermi level emerges, leading to a large spin splitting and so a large magnetic moment in zigzag Janus MoSSe nanoribbons. The results shed new light on the understanding of magnetism correlated to the space symmetry breaking in low-dimensional materials

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Strain engineering of Dirac cones in graphyne

6,6,12-graphyne, one of the two-dimensional carbon allotropes with the rectangular lattice structure, has two kinds of non-equivalent anisotropic Dirac cones in the first Brillouin zone. We show that Dirac cones can be tuned independently by the uniaxial compressive strain applied to graphyne, which induces n-type and p-type self-doping effect, by shifting the energy of the Dirac cones in the opposite directions. On the other hand, application of the tensile strain results into a transition from gapless to finite gap system for the monolayer. For the AB-stacked bilayer, the results predict tunability of Dirac-cones by in-plane strains as well as the strain applied perpendicular to the plane. The group velocities of the Dirac cones show enhancement in the resistance anisotropy for bilayer relative to the case of monolayer. Such tunable and direction-dependent electronic properties predicted for 6,6,12-graphyne make it to be competitive for the next-generation electronic devices at nanoscale. © 2014 AIP Publishing LLC

d0 ferromagnetism in undoped sphalerite ZnS nanoparticles

We report the sulfur vacancies-related d ferromagnetism in undoped sphalerite ZnS nanoparticles. Systematically tune of sulfur deficiency in ZnS nanoparticles was done by selecting different synthesized temperatures and varying the ratio of hydrogen and argon in post-annealing processes. Our study suggests that such sulfur vacancies can induce the room temperature ferromagnetism. Importantly, the ferromagnetism can be modulated by changing the concentration of sulfur vacancies in the samples. This finding should be the focus of future electronic and spintronic devices

Origin of the unexpected room temperature ferromagnetism: formation of artificial defects on the surface in NaCl particles

The unexpected room temperature ferromagnetism in pure sodium chloride (NaCl) particles with different crystal size synthesized by breaking at different times is attributed to surface defects, which provides a novel opportunity to further understand the origin of ferromagnetism in the traditional "nonmagnetic" inorganic non-metallic materials. The results of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy suggest that breaking progress does not change the samples' body, but drastically reduces the size of the samples, what's more, it is found to enhance the strength of the ferromagnetic component with decreasing the samples' size through magnetism measure; the first-principle calculation results confirm the experimental conclusion. Ferromagnetism originates from surface effect, probably the long range ferromagnetic interactions between the surface Cl vacancies