Thermoelectric properties of the bismuth telluride nanowires in the constant-relaxation-time approximation

Electronic structure of bismuth telluride nanowires with the growth directions [110] and [015] is studied in the framework of anisotropic effective mass method using the parabolic band approximation. The components of the electron and hole effective mass tensor for six valleys are calculated for both growth directions. For a square nanowire, in the temperature range from 77 K to 500 K, the dependence of the Seebeck coefficient, the electron thermal and electrical conductivity as well as the figure of merit ZT on the nanowire thickness and on the excess hole concentration are investigated in the constant-relaxation-time approximation. The carrier confinement is shown to play essential role for square nanowires with thickness less than 30 nm. The confinement decreases both the carrier concentration and the thermal conductivity but increases the maximum value of Seebeck coefficient in contrast to the excess holes (impurities). The confinement effect is stronger for the direction [015] than for the direction [110] due to the carrier mass difference for these directions. The carrier confinement increases maximum value of ZT and shifts it towards high temperatures. For the p-type bismuth telluride nanowires with growth direction [110], the maximum value of the figure of merit is equal to 1.3, 1.6, and 2.8, correspondingly, at temperatures 310 K, 390 K, 480 K and the nanowire thicknesses 30 nm, 15 nm, and 7 nm. At the room temperature, the figure of merit equals 1.2, 1.3, and 1.7, respectively.Comment: 13 pages, 7 figures, 2 tables, typos added, added references for sections 2-

Three-dimensional lanthanide-organic frameworks based on di-, tetra-, and hexameric clusters

Three-dimensional lanthanide-organic frameworks formulated as (CH3)2NH2[Ln(pydc)2] · 1/2H2O [Ln3+ ) Eu3+ (1a) or Er3+ (1b); pydc2- corresponds to the diprotonated residue of 2,5-pyridinedicarboxylic acid (H2pydc)], [Er4(OH)4(pydc)4(H2O)3] ·H2O (2), and [PrIII 2PrIV 1.25O(OH)3(pydc)3] (3) have been isolated from typical solvothermal (1a and 1b in N,N-dimethylformamide - DMF) and hydrothermal (2 and 3) syntheses. Materials were characterized in the solid state using single-crystal X-ray diffraction, thermogravimetric analysis, vibrational spectroscopy (FT-IR and FT-Raman), electron microscopy, and CHN elemental analysis. While synthesis in DMF promotes the formation of centrosymmetric dimeric units, which act as building blocks in the construction of anionic ∞ 3{[Ln(pydc)2]-} frameworks having the channels filled by the charge-balancing (CH3)2NH2 + cations generated in situ by the solvolysis of DMF, the use of water as the solvent medium promotes clustering of the lanthanide centers: structures of 2 and 3 contain instead tetrameric [Er4(μ3-OH)4]8+ and hexameric |Pr6(μ3-O)2(μ3-OH)6| clusters which act as the building blocks of the networks, and are bridged by the H2-xpydcx- residues. It is demonstrated that this modular approach is reflected in the topological nature of the materials inducing 4-, 8-, and 14-connected uninodal networks (the nodes being the centers of gravity of the clusters) with topologies identical to those of diamond (family 1), and framework types bct (for 2) and bcu-x (for 3), respectively. The thermogravimetric studies of compound 3 further reveal a significant weight increase between ambient temperature and 450 °C with this being correlated with the uptake of oxygen from the surrounding environment by the praseodymium oxide inorganic core

Micrometre-long covalent organic fibres by photoinitiated chain-growth radical polymerization on an alkali-halide surface

On-surface polymerization is a promising technique to prepare organic functional nanomaterials that are challenging to synthesize in solution, but it is typically used on metal substrates, which play a catalytic role. Previous examples on insulating surfaces have involved intermediate self-assembled structures, which face high barriers to diffusion, or annealing to higher temperatures, which generally causes rapid dewetting and desorption of the monomers. Here we report the photoinitiated radical polymerization, initiated from a two-dimensional gas phase, of a dimaleimide monomer on an insulating KCl surface. Polymer fibres up to 1 μm long are formed through chain-like rather than step-like growth. Interactions between potassium cations and the dimaleimide’s oxygen atoms facilitate the propagation of the polymer fibres along a preferred axis of the substrate over long distances. Density functional theory calculations, non-contact atomic force microscopy imaging and manipulations at room temperature were used to explore the initiation and propagation processes, as well as the structure and stability of the resulting one-dimensional polymer fibres

New loci required for Streptomyces coelicolor morphological and physiological differentiation.

Streptomyces coelicolor colonies differentiate both morphologically, producing aerial spore chains, and physiologically, producing antibiotics as secondary metabolites. Single mutations, which block both aspects of differentiation, define bld (bald colony) genes. To identify new bld genes, mutagenized colonies were screened for blocks in the earliest stage of sporulation, the formation of aerial mycelia, and blocks in antibiotic synthesis. The mutations in 12 mutants were mapped; in each strain, the pleiotropic phenotype was due to a single mutation. Seven of the strains contained mutations in known bld loci, bldA and bldB. Three strains contained mutations in a new locus, bldG, and two contained mutations in another new locus, bldH. Like the previously defined bldA mutants, the bldG and bldH mutants were developmentally blocked on glucose. On a variety of carbon sources whose utilization was subject to glucose repression, the developmental blocks were partially relieved for bldG (and bldA) mutants and fully relieved for bldH mutants. These results are compatible with an hypothesis which suggests that there are two alternative controls on S. coelicolor differentiation, one of which is glucose repressible

CCDC 790708: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures