Te Rods Research Articles

Mechanistic consideration of ZnTe microspheres formation in a PVP-contained polyol system via hot injection method

Zinc telluride (ZnTe) microspheres have been synthesized in a polyol system with adding various amount of poly(N-vinyl-2-pyrrolidone) (PVP, K-90) at 200 °C via a hot injection method. The smallest sized ZnTe microspheres obtained in this study had an average size of 634 nm through reaction for 48 h using 518 mg of PVP. A retrospective study was conducted to evaluate the formation process of ZnTe microspheres by conducting experiments from 0.2 h to 48 h. Nucleation and growth of ZnTe at the tips of Te rods in a PVP-contained polyol system were observed in sample reacted less than 1 h. More ZnTe microspheres and less Te rods were observed when the reaction was proceeded for longer time, suggesting that Te rods were the sacrificial template for the growth of ZnTe. Amount of PVP is the key factor of controlling dimensions of Te rods formed at the initial stage as well as the sizes of ZnTe microspheres by influencing the nucleation and growth rate of ZnTe. The obtained ZnTe microspheres at 48 h consisted of voids, which were originated by the detachment of ZnTe microspheres from Te rods after their growth.

Highly productive solvothermal synthesis of hexagonal Sb2Te3 fine-platelets using solution with high precursor concentration and added glucose

High-purity hexagonal Sb2Te3 fine-platelets were successfully synthesized with high efficiency via a solvothermal route using a high precursor concentration with the assistance of glucose. The solvothermal synthesis was carried out at 180 °C for 16 h while the solution was stirred at 500 rpm. To clarify the role of the chemical compounds, we replaced glucose in the precursor solution with polyvinyl pyrrolidone (PVP). Hexagonal Sb2Te3 platelets with a size of 3–6 μm and approximate thickness of 0.25 μm were obtained when an optimal amount of glucose (0.8 g) was used, and the production efficiency reached 90%. In contrast, the solvothermal synthesis route using various amounts of PVP produced mainly Te rods, and the production efficiency was as low as 40%. A possible reason for the successful growth of hexagonal Sb2Te3 platelets via glucose-assisted solvothermal synthesis was the double role of glucose as a reducing catalyst as well as a surfactant.

Rod-like Te as excellent microwave absorber: a new exploration

In this study, we report a facile method to prepare rod-like Te material, which can be used as a novel microwave absorber. Diameter of the Te rods can be tuned in the range of 46–51 nm by changing the reaction time. With the increase of Te particle diameter in the composites, the microwave absorbing property gets worse. As for the Te-0.5 sample with diameter of 45.7 nm, a maximum reflection loss value of −53.8 dB at 16.0 GHz and an effective absorption bandwidth (4.8 GHz) ranging from 13.2 to 18 GHz at the thickness of only 1.55 mm can be achieved. To the best of our knowledge, it is the first time to investigate the microwave response of Te rods. These rods show obvious potential for lightweight, highly efficient microwave absorption in high frequency.

STUDY OF BAND STRUCTURE OF TWO-DIMENSIONAL ANISOTROPIC HONEYCOMB PHOTONIC CRYSTALS

Using the plane wave expansion method, we have calculated, for both E and H polarizations, the band structure of 2D anisotropic photonic crystals with honeycomb lattice composed of anisotropic tellurium ( Te ) rods embedded in air background. The two rods in the unit cell are chosen square and circular in shape. Here, from a practical point of view, in order to obtain maximum band gaps, we have also studied the band structure as a function of size of rods.

Two-step synthesis of Bi 2Te 3–Te nanoarrays with sheet–rod multiple heterostructure

Bi 2Te 3–Te arrays with sheet –rod multiple heterostructure were obtained in large scale, using Te nanorod arrays as the in-situ templates under solvothermal process. The array is formed by the ordered Bi 2Te 3–Te rods where Bi 2Te 3 sheets distribute from the top face to the bottom face along the Te rod vertically. The microstructure of the heterostructure was studied through X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The electrical conductivity and Seebeck coefficient of the arrays were also studied. The course of reaction was monitored so as to propose a possible growth mechanism of such novel heterostructure. The key for the preparation of such heterostructure is to balance the velocity between the dissolution of Te rods and the formation of Bi 2Te 3 sheets. This synthetic approach could be promising to prepare self-assembled low-dimensional nanoarrays of metals and semiconductors with high yield.

Biomolecule-Assisted Hydrothermal Synthesis and Self-Assembly of Bi2Te3 Nanostring-Cluster Hierarchical Structure

A simple biomolecule-assisted hydrothermal approach has been developed for the fabrication of Bi(2)Te(3) thermoelectric nanomaterials. The product has a nanostring-cluster hierarchical structure which is composed of ordered and aligned platelet-like crystals. The platelets are approximately 100 nm in diameter and only approximately 10 nm thick even though a high reaction temperature of 220 degrees C and a long reaction time of 24 h were applied to prepare the sample. The growth of the Bi(2)Te(3) hierarchical structure appears to be a self-assembly process. Initially, Te nanorods are formed using alginic acid as both reductant and template. Subsequently, Bi(2)Te(3) grows in a certain direction on the surface of the Te rods, resulting in the nanostring structure. The nanostrings further recombine side-by-side with each other to achieve the ordered nanostring clusters. The particle size and morphology can be controlled by adjusting the concentration of NaOH, which plays a crucial role on the formation mechanism of Bi(2)Te(3). An even smaller polycrystalline Bi(2)Te(3) superstructure composed of polycrystalline nanorods with some nanoplatelets attached to the nanorods is achieved at lower NaOH concentration. The room temperature thermoelectric properties have been evaluated with an average Seebeck coefficient of -172 microV K(-1), an electrical resistivity of 1.97 x 10(-3) Omegam, and a thermal conductivity of 0.29 W m(-1) K(-1).

Creation of large band gap with anisotropic annular photonic crystal slab structure

A two-dimensional anisotropic annular photonic crystal slab structure composed of circular air holes and dielectric rods with finite thickness in a triangular lattice is presented to achieve an absolute photonic band gap. Positive uniaxial crystal Tellurium is introduced to the structure with the extraordinary axis parallel to the extension direction of rods. The role of each geometric parameter is investigated by employing the conjugate-gradient method. A large mid-gap ratio is realized by the parameter optimization. A flat band called as anomalous group velocity within two large gaps is discovered and can be widely applied in many fields. A hybrid structure with GaAs slab and Te rods is designed to achieve a large gap and demonstrates that the annular structure can improve the gap effectively.

Effect of Photonic Crystal Band Gap on Rotation of Hollow Oval Te Rods in Triangular Lattice

The band structures and field patterns of two-dimensional (2D) triangular photonic crystals with hollow tellurium (Te) rods are calculated using the plane-wave method. Inner-rod and whole-rod rotations are considered to investigate how the rotational and structural symmetries affect E- and H-polarization modes. It is indicated that the H-polarization modes are strongly affected by the shape and interaction between the fields of the rods. In addition, the effect of rotational symmetry on H-polarization modes must be considered when whole rods are rotated. The E-polarization modes for both types of rotations are strongly related to the shape of the rods. Moreover, H-polarization modes determine the absolute photonic band gap (PBG) width when whole rods are rotated, while E-polarization modes determine the absolute PBG width when inner rods are rotated.

Spontaneous Transformation of CdTe Nanoparticles into Angled Te Nanocrystals: From Particles and Rods to Checkmarks, X-Marks, and Other Unusual Shapes

CdTe nanoparticles spontaneously transform into the branched Te nanocrystals with the unique, highly anisotropic shape of checkmarks after partial removal of the stabilizers of L-cysteine. The Te checkmarks are made in a relatively high yield and uniformity; the length of the arms is ca. 150 nm, whereas the angle between the arms is 74 degrees . Subsequent growth of the particle yields mothlike nanocrystals retaining geometrical anisotropy. Unlike the previous synthesis methods of branched nanocrystals, they are formed via a merger of individual rod-shaped crystallites. High-energy crystal faces on their apexes act as the sticky points causing the particles to join in the ends. This is the first demonstration of spontaneous transformation of binary semiconductor particles into highly anisotropic nanocolloids in an angled conformation. The end reactivity of starting Te rods can be used both for bottom-up fabrication of nanoscale electronics and relatively safe and nontoxic method of synthesis of Te-based optical and other materials.

Bi 2Te 3–Te nanocomposite formed by epitaxial growth of Bi 2Te 3 sheets on Te rod

Single-crystal Bi 2Te 3–Te nanocomposites with heterostructure were synthesized using a two-step solvothermal process in the presence of ethylenediaminetetraacetic acid disodium salt. The first step is the formation of the Te nanorods and the second step is to grow the Bi 2Te 3 sheets off the Te rods surface to form the Bi 2Te 3–Te nanocomposites. The products were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. We demonstrate a method of an epitaxial growth of Bi 2Te 3 nanosheets perpendicular to the axis of the central Te rod and a formation process of Bi 2Te 3–Te nanocomposites is also proposed.

Absolute photonic band gaps in a two-dimensional photonic crystal with hollow anisotropic rods

The plane-wave expansion method is used to calculate photonic band gaps for two structures with hollow anisotropic tellurium (Te) rods. Both structures are found to have absolute band gaps at the low- and high-frequency regions. Compared with the photonic crystal with solid Te rods, the photonic crystal with hollow Te rods has a large absolute band gap at the high-frequency region: for the triangular lattice of oval hollow Te rods, there is an absolute band gap of 0.058 w e ( w e=2 πc/ a), and for the square lattice of square hollow Te rods, there is an absolute band gap of 0.056 w e.

Limitations in Producing Nanocrystals Using Reverse Micelles as Nanoreactors

In this paper the synthesis and characterization of CdTe nanocrystals are presented. Opposite to what has been observed with Cd1–yMnyS, it has been impossible to include manganese ions in CdTe matrices. Only large rods of telluride were seen. ZnTe could also not be formed and again only Te rods were perceived. This clearly indicates that chemistry in colloidal self-assemblies is not always similar to that in homogeneous solutions.

Limitations in Producing Nanocrystals Using Reverse Micelles as Nanoreactors

In this paper the synthesis and characterization of CdTe nanocrystals are presented. Opposite to what has been observed with Cd1–yMnyS, it has been impossible to include manganese ions in CdTe matrices. Only large rods of telluride were seen. ZnTe could also not be formed and again only Te rods were perceived. This clearly indicates that chemistry in colloidal self-assemblies is not always similar to that in homogeneous solutions.