Extraordinary Thermoelectric Properties of Topological Surface States in Quantum-Confined Cd3As2 Thin Films.

Topological insulators and semimetals have been shown to possess intriguing thermoelectric properties promising for energy harvesting and cooling applications. However, thermoelectric transport associated with the Fermi arc topological surface states on topological Dirac semimetals remains less explored. This work systematically examines thermoelectric transport in a series of topological Dirac semimetal Cd3As2 thin films grown by molecular beam epitaxy. Surprisingly, significantly enhanced Seebeck effect and anomalous Nernst effect are found at cryogenic temperatures when the Cd3As2 layer is thin. In particular, a peak Seebeck coefficient of nearly 500 µV K-1 and a corresponding thermoelectric power factor over 30 mW K-2 m-1 are observed at 5 K in a 25-nm-thick sample. Combining angle-dependent quantum oscillation analysis, magnetothermoelectric measurement, transport modeling, and first-principles simulation, the contributions from bulk and surface conducting channels are isolated and the unusual thermoelectric properties are attributed to the topological surface states. The analysis showcases the rich thermoelectric transport physics in quantum-confined topological Dirac semimetal thin films and suggests new routes to achieving high thermoelectric performance at cryogenic temperatures.

Lowered Cd toxicity, uptake and expression of metal transporter genes in maize plant by ACC deaminase-producing bacteria Achromobacter sp.

In this study, an ACC deaminase-producing bacterial strain Achromobacter sp. A1 was isolated from maize rhizosphere soil, characterized and evaluated for the effects on cadmium (Cd) immobilization in solution/rhizosphere, physiological characteristics and the tissue Cd contents in maize and the molecular mechanisms involved by hydroponic and pot experiments. ACC deaminase activity of strain A1 was significantly enhanced by Cd addition and Cd concentration decreased (55.54-63.62%) in solution supplemented with various Cd concentrations. Strain A1 significantly increased the maize dry weights (30.77-105%) and chlorophyll content (7.46-14.46%), decreased MDA content (25.16-36.87%) and ethylene production (20.93-35.86%) in hydroponic experiment. Strain A1 significantly reduced the above-ground tissue Cd uptake by 12.64-33.68% and 42-48% in hydroponic and pot experiments, reduced the DTPA-extractable Cd content and elevated invertase, urease and catalase activity in rhizosphere soils. In addition, the expression levels of Cd transporter genes HMA3 and Nramp5 were significantly reduced in root and shoot after strain A1 inoculation. These results indicate that strain A1 has great potential for application as a novel and environmentally friendly inoculant to immobilize Cd and reduce maize Cd uptake in Cd-contaminated environments, and will improve the understanding of the relative molecular mechanisms underlying the response to strain A1 in maize plant.

Paenibacillus zeisoli sp. nov., isolated from maize-cultivated soil artificially contaminated with cadmium.

A Gram-stain-negative, rod-shaped, motile bacterial strain, designated 3-5-3T, was isolated from maize-cultivated soil artificially contaminated with cadmium, in Nanyang, Henan Province, China. Strain 3-5-3T was oxidase- and catalase-positive. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain 3-5-3T was affiliated with the genus Paenibacillus and most closely related to Paenibacillus anaericanus MH2T (96.5 % similarity). The average nucleotide identity and digital DNA-DNA hybridization values between 3-5-3T and the closely related species ranged 69.4-84.5 % and 18.1-18.4 %. The genomic G+C content was 53.8 mol%. Anteiso-C15 : 0 was the major fatty acid and MK-7 was the only menaquinone. The diamino acid in the cell-wall peptidoglycan contains meso-diaminopimelic acid. The polar lipid profile contained diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylmethylethanolamine, two unidentified glycolipids, two unidentified aminolipids, one unidentified phospholipid, one unidentified phosphoaminolipid and six unidentified lipids. On the basis of the results obtained in this study, strain 3-5-3T is considered to represent a novel species of the genus Paenibacillus, for which the name Paenibacilluszei soli sp. nov. is proposed. The type strain is 3-5-3T (=CGMCC 1.13686T=KCTC 33998T).

Bacillus acidinfaciens sp. nov., isolated from farmland soil.

A Gram-stain-positive, rod-shaped, motile bacterial strain, designated 3-2-2T, was isolated from field topsoil collected from a western suburb of Nanyang city, Henan province, China. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain 3-2-2T was a member of the genus Bacillus and most closely related to Bacillus fortis R-6514T (98.9 % similarity), Bacillus terrae RA9T (98.0 %) and Bacillus fordii R-7190T (97.7 %). A draft genome sequence determined for strain 3-2-2T revealed a DNA G+C content of 42.2 mol%. The average nucleotide identity and digital DNA-DNA hybridization values between 3-2-2T and the closely related Bacillus species ranged 79.4-84.2 % and 23.4-24.6 %. The major fatty acids of strain 3-2-2T were iso-C15 : 0, anteiso-C15 : 0, iso-C14 : 0 and iso-C16 : 0. The major isoprenoid quinone was MK-7. meso-Diaminopimelic acid was detected in the peptidoglycan. The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, an unidentified phospholipid and an unidentified lipid. The results of phylogenetic analyses, in silico genomic comparisons, and chemotaxonomic and phenotypic analyses clearly indicated that strain 3-2-2T represents a novel species within the genus Bacillus, for which the name Bacillus acidinfaciens sp. nov. is proposed. The type strain is 3-2-2T (=CGMCC 1.13685T=LMG 30839T).

Twin Defect Derived Growth of Atomically Thin MoS2 Dendrites.

Morphology management for tailoring the properties of monolayer transition-metal dichalcogenides (TMDCs), that is, molybdenum disulfide (MoS2), has attracted great interest for promising applications such as in electrocatalysis and optoelectronics. Nevertheless, little progress has been made in engineering the shape of MoS2. Herein, we introduce a modified chemical vapor deposition method to grow monolayer MoS2 dendrites by pretreating substrates with adhesive tapes. The as-grown MoS2 crystals are featured with hexagonal backbones with fractal shapes and tunable degrees. By characterizing the atomic structure, it is found that these morphologies are mainly initiated from the twin defect derived growth and controlled by the S:Mo vapor ratio. Due to the accumulated sulfur vacancies in the cyclic twin regions, strong enhancement of photoluminescence emission is localized, which determines the shape dependency of optical property. This work not only enriches the understanding of the twin defects derived crystal growth mechanism and extends its applications from nanomaterials to two-dimensional crystals, but also offers a robust and controllable protocol for shape-engineered monolayer TMDCs in electrochemical and optoelectronic applications.

Shape-Dependent Defect Structures of Monolayer MoS2 Crystals Grown by Chemical Vapor Deposition.

Monolayer MoS2 crystals with tailored morphologies have been shown to exhibit shape-dependent properties and thus have potential applications in building nanodevices. However, a deep understanding of the relationship between the shape and defect structures in monolayer MoS2 is yet elusive. Monolayer MoS2 crystals in polygonal shapes, including triangle, tetragon, pentagon, and hexagon, are grown using the chemical vapor deposition technique. Compared with other shapes, the hexagon MoS2 crystal contains more electron-donor defects that are mainly due to sulfur vacancies. In the triangular shapes, the defects are mainly distributed at the vertices of the shapes while they are located at the center of hexagonal shapes. On the basis of the Coulomb interaction of exciton and trion, quantitative calculations demonstrate a high electron density (∼1012/cm2) and high Fermi level (EC - EF = 15 meV) for hexagonal shape at room temperature, compared to triangular shapes (∼1011/cm2, EC - EF ≈ 30 meV). These findings verify that a much higher number of donor-like sulfur vacancies are formed in hexagonal MoS2 shapes. This property allows more electrons or trions to localize in such sites through the physical/chemical adsorption of O2/H2O, which results in a strong enhancement of the light emission efficiency in the hexagonal crystal. The findings provide a better understanding of the formation of shape-dependent defect structures of monolayer MoS2 crystals and are inspiring for applications in fabricating nanoelectronic and optoelectronic devices through defect engineering.