Electronic transport for impurity-doped armchair-edge graphene nanoribbons

We investigate the electronic transport for an impurity-doped armchair-edge graphene nanoribbon (AGNR), with 7 or 8 dimer lines along zigzag direction, sandwiched between two normal leads. By using the standard nonequilibrium Green’s function technique, it is demonstrated that, the impurity influence on the transport properties for system with semiconducting 7-AGNR system is more sensitive than that for one with metallic 8-AGNR system in the vicinity of the impurity energy level. In particular, in the absence of impurity the density of states (DOS) and linear conductance G possess a small zero value interval for 7-AGNR system and a large nonzero plateau for 8-AGNR one, respectively. Interestingly, as impurity included the DOS and G show a single sharp resonant peak around the impurity energy level for 7-AGNR system due to resonant tunneling, while a small dip appears in the same position for 8-AGNR system due to the antiresonance states. Moreover, we have also inspected the behavior of the differential conductance upon varying the impurity concentration for the systems. The findings here may suggest it is more favorable to fabricate an electric switch with high on-off ratio by using an impurity-assisted semiconducting AGNR.     

First-principles study of the electronic and magnetic properties of a Nickel-Zinc ferrite: ZnxNi1−xFe2O4

Using first-principles density functional theory within the generalized gradient approximation method, the effect of Zn doping on electronic and magnetic properties of NiFe₂O₄ ferrite spinel has been studied. The crystal structure of the compounds is assigned to a pseudocubic structure and the lattice constant increases as the Zn concentration increases. Our spin-polarized calculations give a half-metallic state for NiFe₂O₄ and a normal metal state for Zn_xNi_1−xFe₂O₄ (0<x≤0.5). Based on the magnetic properties calculations, it is found that the saturation magnetic moment enhances linearly with increase in the Zn content in NiFe₂O₄. The Zn doping in NiFe₂O₄ also induces strong ferrimagnetism since it decreases the magnetic moment of A-sites.     

Strong Fermat Rules for Constrained Set-Valued Optimization Problems on Banach Spaces

In this paper, we propose two kinds of optimality concepts, called the sharp minima and the weak sharp minima, for a constrained set-valued optimization problem. Subsequently, we extend the Fermat rules for the local minima of the constrained set-valued optimization problem to the sharp minima and the weak sharp minima in Banach spaces or Asplund spaces, by means of the Mordukhovich generalized differentiation and the normal cone. As applications, we investigate the generalized inequality systems with constraints, and get some characterizations of error bounds for the constrained generalized inequality systems in convex and nonconvex cases.     

Adaptive synchronization of weighted complex dynamical networks through pinning

This paper considers the problem of controlling weighted complex dynamical networks by applying adaptive control to a fraction of network nodes. We investigate the local and global synchronization of the controlled dynamical network through the construction of a master stability function and a Lyapunov function. Analytical results show that a certain number of nodes can be controlled by using adaptive pinning to ensure the synchronization of the entire network. We present numerical simulations to verify the effectiveness of the proposed scheme. In comparison with feedback pinning, the proposed pinning control scheme is robust when tested by noise, different weighting and coupling structures, and time delays.     

Electron dynamics in modulation p-doped InGaAs/GaAs quantum dots

We investigate the electron dynamics of p-type modulation doped and undoped InGaAs/GaAs quantum dots using up-conversion photoluminescence at low temperature and room temperature. The rise time of the p-doped sample is significantly shorter than that of the undoped at low temperature. With increasing to room temperature the undoped sample exhibits a decreased rise time whilst that of the doped sample does not change. A relaxation mechanism of electron-hole scattering is proposed in which the doped quantum dots exhibit an enhanced and temperature independent relaxation due to excess built-in holes in the valence band of the quantum dots. In contrast, the rise time of the undoped quantum dots decreases significantly at room temperature due to the large availability of holes in the ground state of the valence band. Furthermore, modulation p-doping results in a shorter lifetime due to the presence of excess defects.     

Explicit and approximate theories of photothermal deformation in surface thermal lens technique

An explicit thermoelastic model is developed to describe the photothermal deformation of a coated sample excited by a cw modulated laser beam with a top-hat profile. The surface displacement obtained with this explicit model is compared to that obtained by an approximate model developed by Reichling and Gr?nbeck (J. Appl. Phys. 75, 1914 (1994)). Both thermoelastic models are then applied in a Fresnel diffraction based surface thermal lens (STL) theory. Numerical calculations are performed to investigate the differences between the explicit and approximate models in both surface displacement and STL signal. The simulation results show that the approximate model over-estimates the surface displacement and the corresponding STL signal amplitude. A decrease in the thermal diffusion length reduces the differences between the results obtained with the two thermoelastic models.