P-type ZnO by Sb doping for PN-junction photodetectors

ABSTRACT Sb-doped p-type ZnO films were grown on n-Si (100) by electron cyclotron resonance (ECR)-assisted molecular-beam epitaxy (MBE). Room temperature Hall effect measurements reveal that a heavily Sb-doped ZnO sample exhibits a low resistivity of 0.2 cm, high hole concentration of 1.7×10 18 cm -3 , and high mobility of 20.0 cm 2 /V s. Low-temperature photoluminescence (PL) measurements show an Sb-associated acceptor-bound exciton (AºX) emission exists at 3.358 eV at 8.5 K. The acceptor energy level of the Sb dopant is estimated to be 0.14 eV above the valence band. Based on these electrical and optical properties, p-n hetero-and homojunction photodetectors employing Sb-doped p-type ZnO films were designed and fabricated. The heterojunction photodiode consists of Sb-doped p-type ZnO grown on n-Si (100) substrate. An Sb-doped p-type ZnO layer with an n-type Ga-doped ZnO layer was grown on a p-Si (111) substrate to form the homojunction. Current-Voltage (I-V) characterizations reveal rectifying characteristics. Good photoresponse to UV light has been demonstrated for both hetero and homojunction photodetectors

A refined invariant subspace method and applications to evolution equations

The invariant subspace method is refined to present more unity and more diversity of exact solutions to evolution equations. The key idea is to take subspaces of solutions to linear ordinary differential equations as invariant subspaces that evolution equations admit. A two-component nonlinear system of dissipative equations was analyzed to shed light on the resulting theory, and two concrete examples are given to find invariant subspaces associated with 2nd-order and 3rd-order linear ordinary differential equations and their corresponding exact solutions with generalized separated variables.Comment: 16 page

Ultra-low carrier concentration and surface dominant transport in Sb-doped Bi2Se3 topological insulator nanoribbons

A topological insulator is a new state of matter, possessing gapless spin-locking surface states across the bulk band gap which has created new opportunities from novel electronics to energy conversion. However, the large concentration of bulk residual carriers has been a major challenge for revealing the property of the topological surface state via electron transport measurement. Here we report surface state dominated transport in Sb-doped Bi2Se3 nanoribbons with very low bulk electron concentrations. In the nanoribbons with sub-10nm thickness protected by a ZnO layer, we demonstrate complete control of their top and bottom surfaces near the Dirac point, achieving the lowest carrier concentration of 2x10^11/cm2 reported in three-dimensional (3D) topological insulators. The Sb-doped Bi2Se3 nanostructures provide an attractive materials platform to study fundamental physics in topological insulators, as well as future applications.Comment: 5 pages, 4 figures, 1 tabl

A low-cost linkage-spring-sendon-integrated compliant anthropomorphic robotic hand : MCR-Hand III

This paper presents the design, analysis and development of an anthropomorphic robotic hand, i.e. MCR-Hand III. Based on the investigation of human hand anatomical structure and the related existing robotic hands, mechanical design of the MCR-Hand III is presented. Then, a detailed introduction for mechanical compliance of the hand is provided, which is achieved through the combinations of springs with four-bar 4R linkages and tendons. Using D-H convention, kinematics and force analysis of the hand are formulated and illustrated with numerical simulations, laying background for comparison and evaluation. Subsequently, a prototype of the proposed robotic hand is developed, and fingertip force calibration and validation are conducted. Further, a three-stage algorithm for object stiffness identification and adaptive grasping is proposed and evaluated, and grasping evaluation based on the Cutkosky taxonomy with additional deformable object lifting operation and piano manipulation is carried out. The proposed MCR-Hand III costs less than $800 and is hence affordable for wider applications. The experimental results indicate that the proposed hands are capable of implementing the grasp and manipulation for most of the objects used in daily life

Two-dimensional universal conductance fluctuations and the electron-phonon interaction of topological surface states in Bi2Te2Se nanoribbons

The universal conductance fluctuations (UCFs), one of the most important manifestations of mesoscopic electronic interference, have not yet been demonstrated for the two-dimensional surface state of topological insulators (TIs). Even if one delicately suppresses the bulk conductance by improving the quality of TI crystals, the fluctuation of the bulk conductance still keeps competitive and difficult to be separated from the desired UCFs of surface carriers. Here we report on the experimental evidence of the UCFs of the two-dimensional surface state in the bulk insulating Bi2Te2Se nanoribbons. The solely-B\perp-dependent UCF is achieved and its temperature dependence is investigated. The surface transport is further revealed by weak antilocalizations. Such survived UCFs of the topological surface states result from the limited dephasing length of the bulk carriers in ternary crystals. The electron-phonon interaction is addressed as a secondary source of the surface state dephasing based on the temperature-dependent scaling behavior

High-quality Bi2Te3 thin films grown on mica substrates for potential optoelectronic applications

We report high-quality topological insulator Bi2Te3 thin films grown on muscovite mica substrates by molecular beam epitaxy. The topographic and structural analysis revealed that the Bi2Te 3 thin films exhibited atomically smooth terraces over a large area and a high crystalline quality. Both weak antilocalization effect and quantum oscillations were observed in the magnetotransport of the relatively thin samples. A phase coherence length of 277 nm for a 6 nm thin film and a high surface mobility of 0.58 m2 V-1 s-1 for a 4 nm thin film were achieved. These results confirm that the thin films grown on mica are of high quality

Multifunctional Products of Isoprene Oxidation in Polluted Atmosphere and Their Contribution to SOA

Isoprene (2-methyl-1, 3-butadiene) is a nonmethane volatile organic compound (VOC) with the largest global emission and high reactivity. The oxidation of isoprene is crucial to atmospheric photochemistry and contributes significantly to the global formation of secondary organic aerosol. Here, we conducted comprehensive observations in polluted megacities of Nanjing and Shanghai during summer of 2018. We identified multiple functionalized isoprene oxidation products, of which 72% and 88% of the total mole concentration were nitrogen-containing species with the dominant compound being C5 dihydroxyl dinitrate (C5H10N2O8). We calculated the volatility using the group-contribution method and estimated the particle-phase concentration by equilibrium gas/particle partitioning. The results showed that the multifunctional products derived from isoprene oxidation can contribute to 2.6% of the total organic aerosol mass (0.28 +/- 0.27 mu g/m(3)), highlighting the potential importance of isoprene oxidation in polluted regions.Peer reviewe

Gaugino Condensation with S-Duality and Field-Theoretical Threshold Corrections

We study gaugino condensation in the presence of an intermediate mass scale in the hidden sector. S-duality is imposed as an approximate symmetry of the effective supergravity theory. Furthermore, we include in the K\"ahler potential the renormalization of the gauge coupling and the one-loop threshold corrections at the intermediate scale. It is shown that confinement is indeed achieved. Furthermore, a new running behaviour of the dilaton arises which we attribute to S-duality. We also discuss the effects of the intermediate scale, and possible phenomenological implications of this model.Comment: 19 pages, LaTeX, 3 postscript figures include