Te Core Research Articles

Exploring the Te(II)/Te(IV) Redox Couple of a Tellurorosamine Chromophore: Photophysical, Photochemical, and Electrochemical Studies.

A tellurorosamine dye [Te(II)] undergoes aerobic photooxidation. Although Te(IV) species have been used in a number of oxidations, key Te(IV)-oxo and Te(IV)-bis(hydroxy) intermediates are challenging to study. Under aerobic irradiation with visible light, Te(II) (λmax = 600 nm) transforms into a Te(IV) species (λmax = 669 nm). The resultant Te(IV) species is not stable in the dark or at -20 °C, decomposing back to Te(II) and other byproducts over many hours. To eliminate the structural ambiguity of the Te(IV) photoproduct, we used spectroelectrochemistry, wherein the bis(hydroxy) Te(IV)-(OH)2 was electrochemically generated under anaerobic conditions. The absorption of Te(IV)-(OH)2 matches that of the Te(IV) photoproduct. Because isosbestic points are maintained both photochemically and electrochemically, the oxo core formed photochemically must rapidly equilibrate with Te(IV)-(OH)2. Calculations on the bis(hydroxy) versus oxo species further corroborate that the equilibration is rapid and the spectra of the two species are similar. To further explore Te(IV) cores, two novel compounds, Te(IV)-Cl2 and Te(IV)-Br2, were synthesized. Characterization of Te(IV)-X2 was simplified because these cores have no analogue to the Te(IV)-(O)/Te(IV)-(OH)2 equilibrium. This work provides insights into the photophysical and electrochemical behavior of Te analogues of chalcogenoxanthylium dyes, which are relevant for a broad range of photochemical applications.

Phase Change Ge-Rich Ge-Sb-Te/Sb2Te3 Core-Shell Nanowires by Metal Organic Chemical Vapor Deposition.

Ge-rich Ge–Sb–Te compounds are attractive materials for future phase change memories due to their greater crystallization temperature as it provides a wide range of applications. Herein, we report the self-assembled Ge-rich Ge–Sb–Te/Sb2Te3 core-shell nanowires grown by metal-organic chemical vapor deposition. The core Ge-rich Ge–Sb–Te nanowires were self-assembled through the vapor–liquid–solid mechanism, catalyzed by Au nanoparticles on Si (100) and SiO2/Si substrates; conformal overgrowth of the Sb2Te3 shell was subsequently performed at room temperature to realize the core-shell heterostructures. Both Ge-rich Ge–Sb–Te core and Ge-rich Ge–Sb–Te/Sb2Te3 core-shell nanowires were extensively characterized by means of scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction, Raman microspectroscopy, and electron energy loss spectroscopy to analyze the surface morphology, crystalline structure, vibrational properties, and elemental composition.

Multifunctional single‐crystal tellurium core multimaterial fiber via thermal drawing and laser recrystallization

AbstractIn the field of multimaterial optical fibers, the demand for high‐performance single‐crystal core glass‐clad multimaterial optical fibers is increasing. However, the applications of single‐crystal fibers are restricted by the complex fabrication processes and the slow growth of single‐crystal materials. Here, a two‐step method is demonstrated to achieve single‐crystal tellurium (Te) core fibers with high crystal quality over the length of the fiber. This method starts with the thermal drawing of a fiber preform into polycrystalline Te core multimaterial fibers (precursor fibers) that are long and mechanically stable. A 532‐nm continuous laser is then employed to recrystallize the Te core in the precursor fiber into a single crystal state along the entire length of the fiber. Experimental studies of these single‐crystal fibers demonstrate that the single‐crystal Te core fibers possess high transmittance (>90% at 2–10 μm) and high thermoelectric performance (ZT values from 0.03 to 0.13 at 300 K temperature). They are superior to previous reports and our previous work. This method works for fabricating various single‐crystal fibers and has important applications in the field of optical fibers, functional fibers, and their integrated devices.

Oxidation of MBE-Grown ZnTe and ZnTe/Zn Nanowires and Their Structural Properties.

Results of comparative structural characterization of bare and Zn-covered ZnTe nanowires (NWs) before and after thermal oxidation at 300 °C are presented. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, and Raman scattering not only unambiguously confirm the conversion of the outer layer of the NWs into ZnO, but also demonstrate the influence of the oxidation process on the structure of the inner part of the NWs. Our study shows that the morphology of the resulting ZnO can be improved by the deposition of thin Zn shells on the bare ZnTe NWs prior to the oxidation. The oxidation of bare ZnTe NWs results in the formation of separated ZnO nanocrystals which decorate crystalline Te cores of the NWs. In the case of Zn-covered NWs, uniform ZnO shells are formed, however they are of a fine-crystalline structure or partially amorphous. Our study provides an important insight into the details of the oxidation processes of ZnTe nanostructures, which could be of importance for the preparation and performance of ZnTe based nano-devices operating under normal atmospheric conditions and at elevated temperatures.

Single crystal tellurium semiconductor core optical fibers

Tellurium (Te) semiconductor core optical fibers with silicate glass cladding were drawn by the molten core method. The as-drawn precursor fiber has a large core diameter of about 123 µm, which was found to be polycrystalline. What is more, a Bridgman-type fiber postprocessing technique was constructed and used for the first time to anneal the polycrystalline Te semiconductor core optical fibers. The Te core in precursor fiber was melted and recrystallized to single crystal Te with c-axis orientation parallel to fiber axis, which was confirmed by X-ray diffraction, single crystal X-ray diffraction, micro-Raman spectra, and transmission electron microscope measurement results. Enhanced conductivities were observed in single crystal Te semiconductor core optical fibers under illuminated and stress states, respectively. This work demonstrates that the Bridgman-type fiber postprocessing technique could be an effective way to fabricate single crystal semiconductor core optical fibers with large core diameters (∼ 100 µm) and long lengths (a few centimeters).

Controlled Synthesis of Ag2 Te@Ag2 S Core-Shell Quantum Dots with Enhanced and Tunable Fluorescence in the Second Near-Infrared Window.

Fluorescence in the second near-infrared window (NIR-II, 900-1700 nm) has drawn great interest for bioimaging, owing to its high tissue penetration depth and high spatiotemporal resolution. NIR-II fluorophores with high photoluminescence quantum yield (PLQY) and stability along with high biocompatibility are urgently pursued. In this work, a Ag-rich Ag2 Te quantum dots (QDs) surface with sulfur source is successfully engineered to prepare a larger bandgap of Ag2 S shell to passivate the Ag2 Te core via a facile colloidal route, which greatly enhances the PLQY of Ag2 Te QDs and significantly improves the stability of Ag2 Te QDs. This strategy works well with different sized core Ag2 Te QDs so that the NIR-II PL can be tuned in a wide range. In vivo imaging using the as-prepared Ag2 Te@Ag2 S QDs presents much higher spatial resolution images of organs and vascular structures as compared with the same dose of Ag2 Te nanoprobes administrated, suggesting the success of the core-shell synthetic strategy and the potential biomedical applications of core-shell NIR-II nanoprobes.

Comparative genomics applied to Mucor species with different lifestyles

BackgroundDespite a growing number of investigations on early diverging fungi, the corresponding lineages have not been as extensively characterized as Ascomycota or Basidiomycota ones. The Mucor genus, pertaining to one of these lineages is not an exception. To this date, a restricted number of Mucor annotated genomes is publicly available and mainly correspond to the reference species, Mucor circinelloides, and to medically relevant species. However, the Mucor genus is composed of a large number of ubiquitous species as well as few species that have been reported to specifically occur in certain habitats. The present study aimed to expand the range of Mucor genomes available and identify potential genomic imprints of adaptation to different environments and lifestyles in the Mucor genus.ResultsIn this study, we report four newly sequenced genomes of Mucor isolates collected from non-clinical environments pertaining to species with contrasted lifestyles, namely Mucor fuscus and Mucor lanceolatus, two species used in cheese production (during ripening), Mucor racemosus, a recurrent cheese spoiler sometimes described as an opportunistic animal and human pathogen, and Mucor endophyticus, a plant endophyte. Comparison of these new genomes with those previously available for six Mucor and two Rhizopus (formerly identified as M. racemosus) isolates allowed global structural and functional description such as their TE content, core and species-specific genes and specialized genes. We proposed gene candidates involved in iron metabolism; some of these genes being known to be involved in pathogenicity; and described patterns such as a reduced number of CAZymes in the species used for cheese ripening as well as in the endophytic isolate that might be related to adaptation to different environments and lifestyles within the Mucor genus.ConclusionsThis study extended the descriptive data set for Mucor genomes, pointed out the complexity of obtaining a robust phylogeny even with multiple genes families and allowed identifying contrasting potentially lifestyle-associated gene repertoires. The obtained data will allow investigating further the link between genetic and its biological data, especially in terms of adaptation to a given habitat.

Carbon@Tellurium Nanostructures Anchored to a Si Nanowire Scaffold with an Unprecedented Liquid-Junction Solar Cell Performance.

Silicon nanowire (SiNW) arrays offer a range of exciting opportunities, from maximizing solar spectrum utilization for high-performance liquid-junction solar cells (LJSCs) to functioning as potential micro-supercapacitors in the near future. This work, contrasting strongly with the previously reported studies on SiNW-based LJSCs where electron-conducting nanoparticles of Pt or Au were employed to achieve high efficiencies, aims at tethering relatively inexpensive, hole-conducting, and photoresponsive carbon-coated tellurium nanorods (C@TeNRs) to SiNWs in the quest to achieve an outstanding solar cell performance. A SiNW LJSC (control cell) with a SiNWs/Br-, Br2/carbon-fabric architecture delivers a power conversion efficiency (PCE) of 4.8%. Further, by anchoring C@TeNRs, along the lengths of SiNWs via electrophoresis, a PCE of ∼11.6% is attained for a C@TeNRs@SiNWs/Br-, Br2/carbon-fabric-based LJSC. The multifunctionality of C@Te comes to the fore in this cell where (1) the p-type (hole) conducting nature of C@Te ensures efficient charge separation by rapidly collecting holes from SiNWs (and suppresses recombination), (2) the C@TeNRs are also photoresponsive and increase light-harvesting, and (3) the C coating restricts the chemical corrosion and photo-oxidation of SiNWs and the Te core by the acidic electrolyte, thereby improving the cell's operational lifetime. This LJSC also serves as an effective stand-alone energy-storage device giving an improved areal specific capacitance of 1605 μF cm-2 (at 1 mA cm-2). This study unravels the pivotal role played by C@TeNRs in controlling the performance of SiNW-based LJSCs.

Engineering Lateral Heterojunction of Selenium-Coated Tellurium Nanomaterials toward Highly Efficient Solar Desalination.

Herein, a core–shell tellurium–selenium (Te–Se) nanomaterial with polymer‐tailed and lateral heterojunction structures is developed as a photothermal absorber in a bionic solar‐evaporation system. It is further revealed that the amorphous Se shell surrounds the crystalline Te core, which not only protects the Te phase from oxidation but also serves as a natural barrier to life entities. The core (Te)–shell (Se) configuration thus exhibits robust stability enhanced by 0.05 eV per Se atom and excellent biocompatibility. Furthermore, high energy efficiencies of 90.71 ± 0.37% and 86.14 ± 1.02% and evaporation rates of 12.88 ± 0.052 and 1.323 ± 0.015 kg m−2 h−1 are obtained under 10 and 1 sun for simulated seawater, respectively. Importantly, no salting out is observed in salt solutions, and the collected water under natural light irradiation possesses extremely low ion concentrations of Na+, K+, Ca2+, and Mg2+ relative to real seawater. Considering the tunable electronic structures, biocompatibilities, and modifiable broadband absorption of the solar spectrum of lateral heterojunction nanomaterials of Te–Se, the way is paved to engineering 2D semiconductor materials with supporting 3D porous hydrophilic materials for application in solar desalination, wastewater treatment, and biomedical ventures.

Hacia un modelo de análisis del clientelismo político: el caso de México

The article describes patron—client relationships as te core of political groups in Mexico. Those kind of political formations begins in a local context but it raises regional and national levels, becoming the principal components in the struggle of power. On this basis the text is a formulation of a model for anthropological political analysis in countries like Mexico and similars.

Synthesis of Te-Bi core-shell nanowires by two-step electrodeposition in ionic liquids

Te-Bi core-shell nanowires were synthesized by electrochemical deposition in ionic liquids without using a template. The nanowires were synthesized in two steps: self-standing single crystal Te nanowires with a diameter of 76.2±28.4nm and a length of a few microns were electrodeposited first, taking advantage of the templating properties of the mixture of ionic liquids EOPipTFSI:EOPipBr 95:5 mole%. The Bi shell was then deposited on the Te core in EOPipTFSI. The influence of various experimental parameters on Bi shell deposition was studied. Thanks to the higher viscosity of the electrolyte compared to an aqueous medium, a lower growth rate is observed, leading to a thin layer of bismuth. In addition, High Resolution Transmission Electronic Microscopy shows that under optimal conditions the Te nanowires are entirely covered by a homogeneous, compact and polycrystalline Bi shell and that the core/shell interface is smooth.

Biomimetic Hierarchical Assembly of Helical Supraparticles from Chiral Nanoparticles

Chiroptical materials found in butterflies, beetles, stomatopod crustaceans, and other creatures are attributed to biocomposites with helical motifs and multiscale hierarchical organization. These structurally sophisticated materials self-assemble from primitive nanoscale building blocks, a process that is simpler and more energy efficient than many top-down methods currently used to produce similarly sized three-dimensional materials. Here, we report that molecular-scale chirality of a CdTe nanoparticle surface can be translated to nanoscale helical assemblies, leading to chiroptical activity in the visible electromagnetic range. Chiral CdTe nanoparticles coated with cysteine self-organize around Te cores to produce helical supraparticles. D-/L-Form of the amino acid determines the dominant left/right helicity of the supraparticles. Coarse-grained molecular dynamics simulations with a helical pair-potential confirm the assembly mechanism and the origin of its enantioselectivity, providing a framework for engineering three-dimensional chiral materials by self-assembly. The helical supraparticles further self-organize into lamellar crystals with liquid crystalline order, demonstrating the possibility of hierarchical organization and with multiple structural motifs and length scales determined by molecular-scale asymmetry of nanoparticle interactions.

Phosphate glass-clad tellurium semiconductor core optical fibers

For the first time to the best of our knowledge phosphate glass-clad optical fibers comprising tellurium (Te) semiconductor core have been fabricated using a molten core approach. The cores were found to be highly crystalline and phase-pure as evidenced by X-ray diffraction (XRD) and corroborated by Micro-Raman spectrum. Elemental analysis across the core/clad interface suggests that there is some diffusion of oxygen and phosphorus into the core region and, conversely, diffusion of Te into the cladding region. Unfortunately, the propagation loss of the Te core fibers was too high to measure due to the significant scattering from the grain boundaries, oxygen and phosphor precipitates. However, the larger Raman gain, infrared and terahertz transparency of tellurium over silicon and germanium should make these fibers of significant value for fiber-based mid- to long-wave infrared, terahertz waveguides and Raman-shifted infrared light sources.

HgTe/CdS/ZnS多壳层量子点的制备与表征

采用一种简单的方法合成HgTe/CdS/ZnS多壳层量子点。首先,以1-硫代甘油为稳定剂,在水相溶液中制备出HgTe核量子点;然后,采用外延生长法依次在HgTe核量子点表面包覆CdS和ZnS壳层,合成出最终具有稳定近红外发光的HgTe/CdS/ZnS多壳层量子点。该合成方法仅需3个步骤,具有操作简单、成本低廉的优点。实验结果显示,当反应温度为90℃、反应溶液pH为11.0、反应加热回流时间为4 min时,HgTe/CdS/ZnS多壳层量子点具有最高荧光量子产率36%。

Rational design, high-yield synthesis, and low thermal conductivity of Te/Bi2Te3 core/shell heterostructure nanotube composites

Te/Bi2Te3 core/shell heterostructure nanotube (NT) composites with rough serrated interfaces, and hollow structures were designed and synthesized to enhance phonon scattering. A conventional two-step solution phase method was used to synthesize the mass products in high-yield. The external diameter and wall thickness of the NTs measured approximately 250nm and 60nm, and their lengths ranged from 7μm to 9μm. The hexagonal phase Te core, rhombohedral phase Bi2Te3 shell, hollow structure, and saw-toothed interface were accurately determined through X-ray diffraction, scanning electron microscopy and transmission emission microscopy. Relatively stable and low thermal conductivities (from 0.43Wm−1K−1 to 0.46Wm−1K−1) were obtained when the temperatures increased from 300K to 400K (near room temperatures). Finally, this research systematically examined the formation mechanisms based on the in situ growth method and the phonon scattering occurring in both the hollow structures and on the saw-toothed interface.

Spectroscopic characterization of high-purity polycrystalline Bi–Te films grown by thermal evaporation

Thin films of BixTey with various compositions have been grown on Si(100) substrates by thermal evaporation with the use of a Molecular Beam Epitaxy (MBE) system. The growth was performed in the co-deposition mode. The effect of stoichiometry and growth conditions on the structural and electronic properties of the films was studied. Films with compositions corresponding to the compound Bi2Te3 and with compositions rich in Te and Bi were studied. Two different phases which crystallized in the hexagonal family were recognized: trigonal Bi2Te3 with the lattice parameters of a=4.44Å and c=30.47Å and hexagonal BiTe with the lattice parameters of a=4.39Å and c=24.02Å. The analysis of photoemission from the Bi and Te core levels confirmed the structural studies. The layered structure of BixTey films caused that the found crystal phases are accompanied by layers of pure elements Te or Bi depending on the stoichiometry. Angle dependent photoelectron spectroscopy studies showed the tendency of segregation direction – towards the surface for Te layers and opposite one for metallic Bi.

Synthesis and chemical etching of Te/C nanocables

In this paper, Te/C nanocables were fabricated by a hydrothermal method in the presence of cetyltrimethylammonium bromide (CTAB). The products were characterized in detail by multiform techniques: transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray analysis and Fourier transform infrared (FTIR) spectroscopy. The results showed that the products were nanocables with lengths of several microns, core about 20 nm in diameter, and a surrounding sheath of about 60–80 nm in thickness. Te/C nanocables were tailored freely by chemical etching. Carbonaceous nanotubes and Te/C nanocables with fragmentary Te core were obtained by adjusting time of chemical etching.

Synthesis of water-dispersible one-dimensional Te@ZnTe core–shell nanoparticles

One-dimensional (1D) Te nanostructures are a recent focus in various 1D materials due to their interesting properties of photoconductivity, thermoelectric, catalytic activity and strong piezoelectric effect. In this work, we report a new synthesis method for water-dispersible 1D Te@ZnTe core–shell nanoparticles by using ZnTe nanoparticles as precursors. The as-prepared 1D nanoparticles have a crystalline Te core and an amorphous ZnTe shell, which are believed to be available as the cathode for dye-sensitized nanocrystal solar cells and as nanocables in the interconnection of nanodevices. Moreover, the good water dispersibility of the as-prepared 1D nanoparticles facilitated the fabrication of nanodevices via the surface functional groups of the as-prepared 1D nanoparticles.

Understanding the Epitaxial Growth of SexTey@Te Core−Shell Nanorods and the Generation of Periodic Defects

This study demonstrates solution-processed epitaxial growth of Te on Se(x)Te(y) nanorods and the generation of periodic defects in the core. We investigated Se(x)Te(y)@Te core-shell nanorods with a diameter of 40-50 nm and a length of 600-700 nm. In spite of a large lattice mismatch between the Se(x)Te(y) core and the Te shell, the soft character of the core and the shell at a high reaction temperature allowed epitaxial growth of Te on the Se(x)Te(y) nanorods. During the cooling process to room temperature (below the glass transition temperatures), the lattice mismatch between the core and the shell led to homogeneous stress along the epitaxial interface so that periodic defects were generated in the core.

Synthesis and characterization of the tellurium/calcium silicate nanocomposite

A novel tellurium/calcium silicate nanocomposite with tellurium nanorods homogeneously dispersed in the calcium silicate matrix has been successfully synthesized using corresponding tellurium nanorods, Ca(NO 3) 2·4H 2O, and Na 2SiO 3·9H 2O in ethanol/water mixed solvents at room temperature for 48 h. The new material consists of a single crystalline Te core and an amorphous calcium silicate shell. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and energy-dispersive X-ray spectroscopy (EDS). The method is simple and does not need any surfactant or template or base. Cytotoxicity experiments indicated that the tellurium/calcium silicate nanocomposites with a low concentration had good biocompatibility. This nanocomposite is a very promising candidate for the application as bioactive materials.