Gate-Voltage Control of Chemical Potential and Weak Anti-localization in Bismuth Selenide

We report that Bi$_2$Se$_3$ thin films can be epitaxially grown on SrTiO$_{3}$ substrates, which allow for very large tunablity in carrier density with a back-gate. The observed low field magnetoconductivity due to weak anti-localization (WAL) has a very weak gate-voltage dependence unless the electron density is reduced to very low values. Such a transition in WAL is correlated with unusual changes in longitudinal and Hall resistivities. Our results suggest much suppressed bulk conductivity at large negative gate-voltages and a possible role of surface states in the WAL phenomena. This work may pave a way for realizing three-dimensional topological insulators at ambient conditions.Comment: 5 pages, 4 figures

Low Temperature Precursor Route for Highly Efficient Spherically Shaped LED-Phosphors M2Si5N8:Eu2+ (M = Eu, Sr, Ba)

The highly efficient nitridosilicate phosphors M2Si5N8 (M = Sr, Ba, Eu) for phosphor-converted pc-LEDs were synthesized at low temperatures using a novel precursor route involving metal amides M(NH2)2. These precursors have been synthesized by dissolution of the respective metals in supercritical ammonia at 150°C and 300 bar. The thermal behavior and decomposition process of the amides were investigated with temperature programmed powder X-ray diffractometry and thermoanalytical measurements (DTA/TG). These investigations rendered the amides as suitable intermediates for reaction with silicon diimide (Si(NH)2). Thus, the desired nitridosilicate phosphors were obtained at relatively low temperatures around 1150−1400°C which is approximately 300°C lower compared to common synthetic approaches starting from metals or oxides. The influence of the thermal treatment on the phosphor morphology has been studied extensively. The accessibility of spherical phosphor particles represents another striking feature of this route since it improves light extraction from the crystallites due to decreasing light guiding and decreasing re-absorption inside the phosphor particle. The synthesized luminescent materials M2Si5N8:Eu2+ (M = Sr, Ba) exhibit quantum efficiencies and emission band widths (FWHM 70−90 nm) comparable to standard phosphor powders. Employment of Eu(NH2)2 as dopant reagent for synthesis of Ba2Si5N8:Eu2+ proved favorable for the formation of spherical crystallites compared to doping with Eu metal, halides, or oxide

Critical Behavior of a Three-State Potts Model on a Voronoi Lattice

We use the single-histogram technique to study the critical behavior of the three-state Potts model on a (random) Voronoi-Delaunay lattice with size ranging from 250 to 8000 sites. We consider the effect of an exponential decay of the interactions with the distance,$J(r)=J_0\exp(-ar)$, with $a>0$, and observe that this system seems to have critical exponents $\gamma$ and $\nu$ which are different from the respective exponents of the three-state Potts model on a regular square lattice. However, the ratio $\gamma/\nu$ remains essentially the same. We find numerical evidences (although not conclusive, due to the small range of system size) that the specific heat on this random system behaves as a power-law for $a=0$ and as a logarithmic divergence for $a=0.5$ and $a=1.0$Comment: 3 pages, 5 figure

Efficient integrated module of gravity driven membrane filtration, solar aeration and GAC adsorption for pretreatment of shale gas wastewater

Low-cost and efficient treatment processes are urgently needed to manage highly decentralized shale gas wastewater, which seriously threatens the environment if not properly treated. We propose a simple integrated pretreatment process for on-site treatment, whereby gravity driven membrane filtration is combined with granular activated carbon (GAC) adsorption and solar aeration. The rationale of exploitment of sustainable solar energy is that most shale gas production areas are decentralized and located in desert/rural areas characterized by relatively scarce transportation and power facilities but also by abundant sunshine. In this study, GAC and aeration significantly increased the stable flux (170%) and improved effluent quality. Specifically, the dissolved organic carbon removal rate of the integrated system was 44.9%. The high stable flux was attributed to a reduction of extracellular polymeric substances accumulated on the membrane, as well as to the more porous and heterogeneous biofilm formed by eukaryotes with stronger active predation behavior. The prevailing strains, Gammaproteobacteria (35.5%) and Alphaproteobacteria (56.5%), played an important active role in organic carbon removal. The integrated system has great potential as pretreatment for shale gas wastewater due to its low energy consumption, low operational costs, high productivity, and effluent quality

Superlattices of Bi2Se3/In2Se3: Growth Characteristics and Structural Properties

Superlattices (SLs) consisted of alternating Bi2Se3 and In2Se3 layers are grown on Si(111) by molecular-beam epitaxy. Bi2Se3, a three-dimensional topological insulator (TI), showed good chemical and structural compatibility with In2Se3, a normal band insulator with large energy bandgap. The individual layers in the SLs are very uniform and the hetero-interfaces are sharp. Therefore, such SL structures are potential candidates for explorations of the quantum size effects of TIs

Enhancement of the performance of covalently immobilized lipase using alcohol quenching technology

In order to modulate the microenvironment for enzyme covalently attached on support and improve the covalent immobilization of lipase, alcohol molecules were used to quench the excessive activated functional group on support surface. Effects of kind and content of alcohol molecules on the relative activity of the immobilized enzyme and the characteristics of the immobilized enzyme were examined carefully. The maximum relative activities of the immobilized lipase quenched with methanol and npropanol, were 224.3 and 224.5%, respectively, both 1.96 fold of the just immobilized lipase which was not quenched with alcohol. Residual activity of the immobilized lipase using methanol to quench the excessive activated groups on support surface was 65.9% after heating at 50°C for 60 h, 1.29 folds higher than that of the ordinarily immobilized lipase (with no blockage). Alcohol molecules could alter the physical and chemical properties to modulate the microenvironment on support surface bychanging the hydrophobicity. Suitable microenvironment, resulted from the methanol quenching the excessive active groups, would further favor the activity and the stability of lipase at higher temperature