Chong Li

Magnetism of zigzag edge phosphorene nanoribbons

We have investigated, by means of ab initio calculations, the electronic and magnetic structures of zigzag edge phosphorene nanoribbons (ZPNRs) with various widths. The stable magnetic state was found in pristine ZPNRs by allowing the systems to be spin-polarized. The ground state of pristine ZPNRs prefers ferromagnetic order in the same edge but antiferromagnetic order between two opposite edges. The magnetism arises from the dangling bond states as well as edge localized π-orbital states. The presence of a dangling bond is crucial to the formation of the magnetism of ZPNRs. The hydrogenated ZPNRs get nonmagnetic semiconductors with a direct band gap. While, the O-saturated ZPNRs show magnetic ground states due to the weak P-O bond in the ribbon plane between the pz-orbitals of the edge O and P atoms.

Anomalous doping effect in black phosphorene using first-principles calculations

Using first-principles density functional theory calculations, we investigate the geometries, electronic structures, and thermodynamic stabilities of substitutionally doped phosphorene sheets with group III, IV, V, and VI elements. We find that the electronic properties of phosphorene are drastically modified by the number of valence electrons in dopant atoms. The dopants with an even number of valence electrons enable the doped phosphorenes to have a metallic feature, while the dopants with an odd number of valence electrons retain a semiconducting feature. This even-odd oscillating behavior is attributed to the peculiar bonding characteristics of phosphorene and the strong hybridization of sp orbitals between dopants and phosphorene. Furthermore, the calculated formation energies of various substitutional dopants in phosphorene show that such doped systems can be thermodynamically stable. These results propose an intriguing route to tune the transport properties of electronic and photoelectronic devices based on phosphorene.

Dilute Magnetic Semiconductor and Half-Metal Behaviors in 3d Transition-Metal Doped Black and Blue Phosphorenes: A First-Principles Study.

AbstractWe present first-principles density-functional calculations for the structural, electronic, and magnetic properties of substitutional 3d transition metal (TM) impurities in two-dimensional black and blue phosphorenes. We find that the magnetic properties of such substitutional impurities can be understood in terms of a simple model based on the Hund’s rule. The TM-doped black phosphorenes with Ti, V, Cr, Mn, Fe, and Ni impurities show dilute magnetic semiconductor (DMS) properties while those with Sc and Co impurities show nonmagnetic properties. On the other hand, the TM-doped blue phosphorenes with V, Cr, Mn, and Fe impurities show DMS properties, with Ni impurity showing half-metal properties, whereas Sc- and Co-doped systems show nonmagnetic properties. We identify two different regimes depending on the occupation of the hybridized electronic states of TM and phosphorous atoms: (i) bonding states are completely empty or filled for Sc- and Co-doped black and blue phosphorenes, leading to nonmagnetic; (ii) non-bonding d states are partially occupied for Ti-, V-, Cr-, Mn-, Fe- and Ni-doped black and blue phosphorenes, giving rise to large and localized spin moments. These results provide a new route for the potential applications of dilute magnetic semiconductor and half-metal in spintronic devices by employing black and blue phosphorenes.n PACS numbers: 73.22.-f, 75.50.Pp, 75.75. + a

First-principles investigation of mechanical and electronic properties of MNNi3 (M=Zn, Mg, or Cd)

Mechanical and electronic properties of an antiperovskite-type superconductor ZnNNi3 as well as its isostructural and isovalent counterparts MgNNi3 and CdNNi3 have been studied by using the first-principles calculations. Lattice constant a, bulk modulus B, elastic constants of cubic lattice (C11, C12, and C44), compressibility K, shear modulus G, tetragonal shear modulus G′, effective charges, as well as electronic structures of the three compounds have been calculated. The results show that the lattice constants of the three compounds have a relationship a(ZnNNi3)<a(MgNNi3)<a(CdNNi3), while on the contrary, the order of the bulk modulus is B(CdNNi3)<B(MgNNi3)<B(ZnNNi3), consisting with the tetragonal shear modulus G′. The neighboring Ni and N atoms are prone to form covalent bonds, while the M-Ni/N (M=Zn, Mg, or Cd) favor ionic nature. For the electronic structures, Ni 3d and the hybridization between Ni 3d and N 2p have the most contributions to the total density of states at the Fermi level [N(EF)] for...

Electronic and optical properties of quaternary alloy GaAsBiN lattice-matched to GaAs

Employing first-principles combined with hybrid functional calculations, the electronic and optical properties of GaAs alloyed with isovalent impurities Bi and N are investigated. As GaAsBiN alloy is a quaternary alloy, the band gap and the lattice constant of the alloy can be individually tuned. Both impurities are important to the valence band and conduction band of the alloy, with the band gap of the alloy being dramatically reduced by Bi 6p states and N localized 2s states. Interestingly, the calculated optical properties of the quaternary alloy are similar to those of undoped GaAs except that the absorption edge has a redshift toward lower energy. These results suggest potential interest in the long-wavelength applications of GaAsBiN alloy.

Intrinsic spin dependent and ferromagnetic stability on edge saturated zigzag graphene-like carbon-nitride nanoribbons

Using first-principles calculations, we have investigated the electronic and magnetic properties of zigzag graphene-like carbon-nitride nanoribbons (Zg-CNNRs) with mono- and dihydrogen-terminated edges asymmetrically. The results demonstrate that spin-down channel completely dominates the states adjacent Fermi level, which is an intrinsic feature and can be accounted for the valence band maximum derived from the nonbonding N-(px,py) orbitals, instead of the bonding C/N-pz π state. Importantly, ferromagnetic ordering is found to be preferred and the magnetism is entirely localized on the N sites of saturated edge due to its stronger electronegativity. Additionally, various edge saturations are further proposed to try to enhance the ferromagnetic ordering and to manipulate the magnetism distributions of Zg-CNNRs.

Imaging by the Veselago lens based upon a two-dimensional photonic crystal with a triangular lattice

The construction of the multifocal Veselago lens predicted earlier [Appl. Opt. 42, 5701 (2003)] is proposed on the basis of a uniaxial photonic crystal consisting of cylindrical air holes in silicon that make a triangular lattice in a plane perpendicular to the axis of the crystal. The object and images are in air. The period of the crystal should be 0.44 μm to work at the wavelength 1.5 μm. The lens does not provide superlensing, but the halfwidth of the image is 0.5 λ. The lens is shown to have wave-guiding properties, depending on the substrate material.

Magnetic evolution and anomalous Wilson transition in diagonal phosphorene nanoribbons driven by strain.

Inducing magnetism in phosphorene nanoribbons (PNRs) is critical for practical applications. However, edge reconstruction and Peierls distortion prevent PNRs from becoming highly magnetized. Using first-principles calculations, we find that relaxed oxygen-saturated diagonal-PNRs (O-d-PNRs) realize stable spin-polarized antiferromagnetic (AFM) coupling, and the magnetism is entirely localized at the saturated edges. The AFM state is quite stable under expansive and limited compressive strain. More importantly, not only does the irreversible Wilson transition occur when applying strain, but the nonmagnetic (NM) metal phase (a new ground state) becomes more stable than the AFM state when the compressive strain exceeds -4%. The related stability and transition mechanism are demonstrated by dual tuning of the geometric and electronic structures, which manifests as a geometric deviation from a honeycomb to an orthorhombic-like structure and formation of P-py bonding (P-pz nonbonding) from P-pz nonbonding (P-py antibonding) because of the increase of the proportion of the P-py (P-pz) orbital.

Catalytic activities of noble metal atoms on WO3 (001): nitric oxide adsorption

Using first-principles density functional theory calculations within the generalized gradient approximation, we investigate the adsorption of NO molecule on a clean WO3(001) surface as well as on the noble metal atom (Cu, Ag, and Au)-deposited WO3(001) surfaces. We find that on a clean WO3 (001) surface, the NO molecule binds to the W atom with an adsorption energy (Eads) of −0.48xa0eV. On the Cu- and Ag-deposited WO3(001) surface where such noble metal atoms prefer to adsorb on the hollow site, the NO molecule also binds to the W atom with Eadsu2009=u2009−1.69 and −1.41xa0eV, respectively. This relatively stronger bonding of NO to the W atom is found to be associated with the larger charge transfer of 0.43 e (Cu) and 0.33 e (Ag) from the surface to adsorbed NO. However, unlike the cases of Cu-WO3(001) and Ag-WO3(001), Au atoms prefer to adsorb on the top of W atom. On such an Au-WO3(001) complex, the NO molecule is found to form a bond to the Au atom with Eadsu2009=u2009−1.32xa0eV. Because of a large electronegativity of Au atom, the adsorbed NO molecule captures the less electrons (0.04 e) from the surface compared to the Cu and Ag catalysts. Our findings not only provide useful information about the NO adsorption on a clean WO3(001) surface as well as on the noble metal atoms deposited WO3(001) surfaces but also shed light on a higher sensitive WO3 sensor for NO detection employing noble metal catalysts.

Tuning the Nanofriction Between Two Graphene Layers by External Electric Fields: A Density Functional Theory Study

AbstractnUnderstanding and controlling nanofriction are important in practical applications of nanotechnology. Our first-principles calculations reveal that interlayer nanofriction between two graphene layers can be tuned by applying an external electric field; the tuned magnitude of the coefficient of friction ranges from −30 to 30xa0%, which is attributed to the increased disparity of electronic structures between AA and AB stackings. This effect is significantly observed in boron- or nitrogen-doped systems compared with a pristine graphene system. Our findings present a feasible and precise strategy to tune the frictional properties of graphene systems.