[Show abstract][Hide abstract] ABSTRACT: Optical anisotropy of graphene/graphane superlattices with zigzag interface and its dependence on the size of the superlattices are investigated with first-principles density functional calculations. Our results indicate that all of the superlattices show optical anisotropy and the degree of the anisotropy is dependent on the width of graphene segment rather than the composition. Using a unit photon energy as the incident light we find that all the superlattices have low reflectivity and high transmissivity, however, they show high reflective polarization. This kind of superlattices are hoping to be excellent polarized ultraweak photon emission source.
Solid State Sciences 01/2015; 40. · 1.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effect of H/F chemical decoration on the spin switch of a single 3d transition-metal (TM = Mn, Fe, Co) doped boron nitride (BN) sheet is systematically studied using density functional theory plus Hubbard U (DFT+U). It is found that the ground spin state of a TM embedded in a BN sheet is sensitive to the value of the on-site Coulomb energy. Interestingly, we find that the spin of the Fe–BN system is switched from “spin ON (S = 5/2)” to “spin OFF (S = 0)” for H decoration and from “spin high (S = 2)” to “spin low (S = 1/2)” for H-decorated Mn–BN and F-decorated Co–BN systems. Such spin state switching can open a new route to realize the applications of TM-doped BN for spintronics and quantum information.
The Journal of Physical Chemistry C 04/2014; 118(17):8899–8906. · 4.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The transport properties of graphene/metal (Cu(111), Al(111), Ag(111), and Au(111)) planar junction are investigated using the first-principles nonequilibrium Green's function method. The planar junction induce second transmission minimum (TM2) below the Fermi level due to the existence of the Dirac point of clamped graphene. Interestingly, no matter the graphene is p- or n-type doped by the metal substrate, the TM2 always locates below the Fermi level. We find that the position of the TM2 is not only determined by the doping effect of metal lead on the graphene, but also influenced by the electrostatic potential of the metal substrate and the work function difference between the clamped and suspended graphene.
[Show abstract][Hide abstract] ABSTRACT: Applying two-dimensional monolayer materials in nanoelectronics and spintronics is hindered by a lack of ordered and separately distributed spin structures. We investigate the electronic and magnetic properties of one-dimensional zigzag and armchair 3d transition metal (TM) nanowires on graphyne (GY), using density functional theory plus Hubbard U (DFT + U). The 3d TM nanowires are formed on graphyne (GY) surfaces. TM atoms separately and regularly embed within GY, achieving long-range magnetic spin ordering. TM exchange coupling of the zigzag and armchair nanowires is mediated by sp-hybridized carbon, and results in long-range magnetic order and magnetic anisotropy. The magnetic coupling mechanism is explained by competition between through-bond and through-space interactions derived from superexchange. These results aid the realization of GY in spintronics.
[Show abstract][Hide abstract] ABSTRACT: Using first-principles calculations within the framework of density-functional theory, we systematically study the modulation effect of chemical decoration including hydrogenation, fluorination, and oxidization on the surface work function of graphene. The chemical decoration is effective approach to modulate the surface work function, which expands the space to design diverse nano-devices based on graphene. Moreover, we also find some un-expectation chemically decorated cases which do not follow the traditional rule of “electronegative (electropositive) adsorbates, which increase (decrease) the work function of the surface”. Such a phenomenon is mainly derived from the charge redistribution induced by the bonding process between adsorbates and carbon atoms along with the chemical decoration.
Physics Letters A 10/2013; 377(s 28–30):1760–1765. · 1.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We propose a concept of half-semiconductor antiferromagnets in which both
spin-polarized valence and conduction bands belong to the same spin channel
with completely compensated spontaneous magnetization. Using density functional
theory plus Hubbard U (DFT+U) methods, we find a viable approach to achieve the
half-semiconductor antiferromagnets through the transition metal (TM) Fe and Cr
codoped boron nitride(BN) sheet. Moreover, spin gapless semiconductor
antiferromagnets with zero magnetic moment are also achieved in such systems.
[Show abstract][Hide abstract] ABSTRACT: We propose a promising two-dimensional nano-sheet of SiC2 (SiC2-pentagon)
consisting of tetrahedral silicon atoms and triple-linked carbon atoms in a
fully-pentagon network. The SiC2-pentagon with buckled configuration is more
favorable than its planar counterpart and previously proposed SiC2-silagraphene
with tetra-coordinate silicon atoms; and its dynamical stability is confirmed
through phonon analyzing. Buckled SiC2-pentagon is an indirect-band-gap
semiconductor with a gap of 1.388 eV. However, its one-dimensional nanoribbons
can be metals or semiconductors depending on the edge type, shape, and
decoration. Finally, we propose a method to produce the buckled SiC2-pentagon
through chemical exfoliation on the beta-SiC(001)-c(2*2) SDB surface.
[Show abstract][Hide abstract] ABSTRACT: Using density functional theory plus Hubbard-U (DFT+U) approach, we find that
quasi one-dementation(1D) 3d transition metal(TM) zigzag nanowire can be
constructed by TM adsorbed on the surface of graphyne sheet. The results show
that the TM exchange coupling of the zigzag nanowire mediated by sp hybridized
carbon atoms gives rise to long range ferromagnetic order except for Cr with
anti-ferromagnetic order. The magnetic exchange interaction of TM chains
follows like-Zener's p_z-d exchange mechanism: the coexistence of out-of plane
p_z-d and in-plane p_x-y-d exchange. Finally, by including spin-orbit
interactions within spin-DFT, we calculate the magnetic anisotropy energy of
the TM chain on graphyne. We find that the Fe and Co chains show considerable
magnetic anisotropy energy (MAE) and orbital magnetic moment. The easy axis of
V, Cr, Mn and Fe chains is perpendicular to the surface, whereas the easy axis
of Co lies in the surface. Moreover, only V chain shows relatively larger
in-plane anisotropy. Our results open a new route to realize the applications
of graphyne in spintronics.
[Show abstract][Hide abstract] ABSTRACT: Using first-principles calculations within the framework of density-functional theory, we studied the modulation effect of hydrogen/fluorine chemical decoration on the surface work function of BN sheets. We found that the difference in the work function (ΔWBN) between two surfaces of the chair structure varies with the different decoration. Geometric distortion and chemical effects cause opposite modulation effects, and the chemical effect plays a leading role by inducing charge redistribution in the system.
[Show abstract][Hide abstract] ABSTRACT: We propose a new allotrope of graphane, named as tricycle graphane,with a
4up/2down UUUDUD hydrogenation in each hexagonal carbon ring,which is different
from previously proposed allotropes with UUDUUD(boat-1) and UUUUDD (boat-2)
types of hydrogenation. Its stability and electronic structures are
systematically studied using first-principles method. We find that the tricycle
graphane is a stable phase in between the previously proposed chair and stirrup
allotropes. Its electronic properties are very similar to those of chair,
stirrup, boat-1, boat-2, and twist-boat allotropes. The negative Gibbs free
energy of tricycle graphane is -91 meV/atom, which very close to that of the
most stable chair one (-103 meV/atom). Thus, this new two-dimensional
hydrocarbon may be produced in the process of graphene hydrogenation with a
relative high probability compared to other conformers.
physica status solidi (RRL) - Rapid Research Letters 04/2012; 6(11). · 2.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The structures and surface work functions of graphanes with five fundamental configurations are systematically studied with the density functional theory. We find that, from the point of view of energy, hydrogenated graphene prefer forming the chair graphane than the other ones. The work function and layer thickness of the five structures vary with the hydrogenation, providing important theoretical data for experimental identifying the configurations of graphanes by STM and AFM.
Numerical Simulation of Optoelectronic Devices (NUSOD), 2012 12th International Conference on; 01/2012