arXiv subjects

Jin-Cheng Zheng

Publications and source records attributed to Jin-Cheng Zheng.

23 records · Page 2Linked to original sources

arXiv2006

Electronic Structure of ZnO nanowire

This paper presents two first-principles calculations on the lattice- and electronic- structures of a small-diameter infinite and truncated ZnO nanowire. The two calculations show excellent agreement with each other. For the small diameter nanowire, the lattice and electronic properties are determined by the relaxed surface. We find a similarity between the nanowire surface and the surface of the bulk material, and discuss the assignment of the rotational quantum number m to the bands.

cond-mat.mtrl-sci↗

arXiv2005

Inversion of two-band superconductivity at the critical electron doping of (Mg,Al)B$_2$

Electron energy-loss spectroscopy (EELS) was combined with heat capacity measurements to follow the change of superconductivity with systematic Al doping of MgB$_2$. By using x-ray diffraction and Vegard's law to assess the actual Al content in the samples, changes in behavior were found to be much more in agreement with theoretical predictions than in earlier studies. EELS data show that $σ$-band hole states disappear above 33% Al, approximately the composition at which the $σ$ band Fermi surface is predicted to lose its cylindrical shape in reciprocal space and break apart into ellipsoidal pockets. At this composition, the $σ$ gap obtained from the heat capacity data falls to the level of the $π$ gap, implying that band filling results in the loss of strong superconductivity on the $σ$ band. However, superconductivity is not quenched completely, but persists with $T_c < 7$ K up to about 55% Al, the Al concentration at which the entire $σ$ band is predicted to fall below the Fermi surface. Since, in the region $0.33 \alt x \alt 0.55$, only the $π$ band has appreciable density of states, it becomes the stronger of the 2 bands, thus inverting the 2-band hierarchy of MgB$_2$.

cond-mat.supr-con↗

arXiv2002

Possible complete miscibility of $(BN)_x(C_2)_{1-x}$ alloys

The stabilities of $(BN)_x(C_2)_{1-x}$ alloys and related superlattices are investigated by ab initio pseudopotential calculations. We find that the $(BN)_1/(C_2)_1$ superlattices in (111) orientations have the lowest formation energy among many short-range ordered $BNC_2$ structures due to the smallest number of B-C and C-N bonds. Based on the calculated formation energies at several compositions and for various ordered structures and assuming thermodynamic equilibrium, the solid solution phase diagram of $(BN)_x(C_2)_{1-x}$ alloys is constructed. We find that the complete miscibility of $(BN)_x(C_2)_{1-x}$ alloys is possible, which is in contrast with previous theoretical predictions but in agreement with experimental reports.

cond-mat.mtrl-sci↗

arXiv2002

Structural and electronic properties of Al nanowires: an ab initio pseudopotential study

The stability and electronic structure of a single monatomic Al wire has been studied using the ab initio pseudopotential method. The Al wire undergoes two structural rearrangements under compression, i.e., zigzag configurations at angles of $140^o$ and $60^o$. The evolution of electronic structures of the Al chain as a function of structural phase transition has been investigated. The relationship between electronic structure and geometric stability is also discussed. The 2p bands in the Al nanowire are shown to play a critical role in its stability. The effects of density functionals (GGA and LDA) on cohesive energy and bond length of Al nanostructures (dimmer, chains, and monolayers) are also examined. The link between low dimensional 0D structure (dimmer) to high dimensional 3D bulk Al is estimated. An example of optimized tip-suspended finite atomic chain is presented to bridge the gap between hypothetical infinite chains and experimental finite chains.

cond-mat.mtrl-sci↗

arXiv2002

Trends in bonding configuration at SiC/III-V semiconductor interfaces

The structural and electronic properties of interfaces between beta-SiC and III-V semiconductors are studied by first-principles calculations. Favorable bonding configurations are found to form between Si-V and C-III (model A) for BN, AlN, AlP, AlAs, GaN, GaP, GaAs, InN, InP, InAs and InSb, and Si-III and C-V (model B) for BP, BAs, BSb, AlSb and GaSb. The relationship between formation energy difference and lattice constant difference as well as charge distribution for these two models is found. The origin of bonding configurations can be explained in terms of the ionicity of III-V semiconductors, electrostatic effect, charge distribution and band-structure component.

cond-mat.mtrl-sci↗