Tellurium Nanostructures Research Articles

Dependence of excited-state properties of tellurium on dimensionality: From bulk to two dimensions to one dimensions

The dependence of excited-state properties on dimensionality is the most prominent character of nanostructures. Using first-principles many-body perturbation theory, we show how those excited-state properties, i.e., quasiparticle energies and excitons, evolve with the dimensionality of tellurium nanostructures that have attracted significant interest because of their high carrier mobility and air stability. Even though the elementary atomistic structures are similar, dimensionality dictates many-electron interactions and excited-state properties: the self-energy correction to the band gap is increased from 0.22 eV in bulk to 0.90 eV in a two-dimensional (2D) monolayer, and ultimately to 2.70 eV in a one-dimensional (1D) spiral tube; excitonic effects are weak in bulk with an exciton binding energy less than 10 meV, while the exciton binding energy is substantially enhanced to be 0.67 eV in the monolayer and 2.40 eV in the 1D structure. Interestingly, reduced dimensionality also produces substantial anisotropic optical response through many-electron interactions: local-field effects dominate the optical spectra of 2D and 1D structures and induce highly anisotropic optical responses. These results not only reveal a systematic picture for understanding the evolution of excited-state properties with dimensionality but also suggest the possibility of designing macroscopic electronic and optical properties by engineering nanosized building blocks.

Large-scale synthesis of Tellurium nanostructures via galvanic displacement of metals

Tellurium (Te) is an attractive semiconductor material for a wide range of applications in various functional devices including, radiation dosimeters, optical storage materials, thermoelectric or piezoelectric generators. In this work, large scale synthesis of tellurium (Te) nanostructures have been successfully carried out in different concentrations of aqueous solutions containing TeO2 and NaOH, by galvanic displacements of Zn and Al which served as the sacrificial materials. Galvanic displacement process is cost-effective and it requires no template or surfactant for the synthesis of nanostructures. By varying the concentrations of TeO2 and NaOH, etching temperatures and etching times, Te nanostructures of various forms of nanostructures were successfully obtained, ranging from one-dimensional needles and rod-like structures to more complex hierarchical structures. Microscopy examinations on the nanostructures obtained have shown that both the diameters and lengths of the Te nanostructures increased with increasing etching temperature and etching time.

A Generalized Crystallographic Description of All Tellurium Nanostructures.

Despite tellurium being less abundant in the Earth's crust than gold, platinum, or rare-earth elements, the number of industrial applications of tellurium has rapidly increased in recent years. However, to date, many properties of tellurium and its associated compounds remain unknown. For example, formation mechanisms of many tellurium nanostructures synthesized so far have not yet been verified, and it is unclear why tellurium can readily transform to other compounds like silver telluride by simply mixing with solutions containing silver ions. This uncertainty appears to be due to previous misunderstandings about the tellurium structure. Here, a new approach to the tellurium structure via synthesized structures is proposed. It is found that the proposed approach applies not only to these structures but to all other tellurium nanostructures. Moreover, some unique tellurium nanostructures whose formation mechanism are, until now, unconfirmed can be explained.

Synthesis of tunable tellurium nanoparticles

Tellurium is a chalcogenide element, essential, in the development of renewable energy solutions. However, substantial problems remain to synthesize zero-dimensional tellurium nanostructures in a facile and environmentally friendly way. This communication reports the first successful synthesis of pure tellurium nanoparticles by laser ablation in liquids. Two solvents were used i.e. de-ionized water and acetone. The effect of wavelength on the size and crystallinity of the produced nanoparticles has been investigated. The thermal stability and the size-dependent energy bandgap has also been predicted using nano-thermodynamics. Finally, the most stable colloidal solution as well as the smallest size distribution was obtained in acetone.

Facile sonochemical synthesis of tellurium and tellurium dioxide nanoparticles: Reducing Te(IV) to Te via ultrasonic irradiation in methanol

In this study, tellurium (Te) nanostructures were synthesized via a facile sonochemical method by reducing TeCl4 to Te under ultrasonic irradiation in methanol. Moreover, by carrying out the reaction in an alkaline environment TeO2 nanoparticles were produced. According to our knowledge, it is the first time that without secondary reducing agent Te4+ are reduced to Te. Also, the effects of ultrasonic power, irradiation time, solvent, and surfactant on the morphology and particle size of Te nanostructures were investigated. The obtained products were characterized by XRD, SEM, EDS, FT-IR and DRS.

Emerging tellurium nanostructures: controllable synthesis and their applications

Tellurium (Te) is a rare element in trace amounts of about one part per billion, comparable to that of platinum and ranked 75th in the abundance of the elements in the earth crust. Te nanostructures, as narrow bandgap semiconductors, have numerous potential applications in the fabrication of many modern devices. The past decades have witnessed an explosion in new strategies for synthesizing diverse emerging Te nanostructures with controlled compositions, sizes, shapes, and structures. Their structure-determined nature makes functional Te nanomaterials an attractive candidate for modern applications. This review focuses on the synthesis and morphology control of emerging Te nanostructures and summarizes the latest developments in the applications of Te nanostructures, such as their use as chemical transformation templates to access a huge family of nanowires/nanotubes, batteries, photodetectors, ion detection and removal, element doping, piezoelectric energy harvesting, gas sensing, thermoelectric devices and many other device applications. Various Te nanostructures with different shapes and structures will exploit the beneficial properties associated with their assembly process and nanofabrication. Finally, the prospects for future applications of Te nanomaterials are summarized and highlighted.

A simple method for the deposition of nanostructured tellurium synthesized in ammonia solution

In this work, we report a highly adherent, and uniform deposition of nanostructured tellurium. The deposition of the nanostructured tellurium was realized by the dripping of a modified solution of NaHTe based on the dissolution of NaBH4 and tellurium powder in an aqueous solution of NH4OH. This method allowed the relatively simple manipulation of tellurium nanostructures under laboratory ambient, without requiring the use of organic stabilizers. Transmission electron microscopy (TEM) was realized on a powder sample obtained by the reaction between H2Te and aqueous solution of NH4OH. TEM analysis indicated that tellurium nanorods and Y-type nanostructures are grown from tellurium nanoparticles, such as in a hydrothermal system. Then, the nanoparticles serve as seeds for the growth of more extended tellurium nanostructures. Electron diffraction and X-ray diffraction analysis showed that depositions have the hexagonal structure of tellurium highly oriented on (101) direction.

Systematic Synthesis of Tellurium Nanostructures and Their Optical Properties: From Nanoparticles to Nanorods, Nanowires, and Nanotubes

AbstractIn the past two decades, tremendous efforts have been made towards the development of synthetic strategies for nanostructured materials with well‐controlled size, shape, composition, and spatial arrangement. Herein, we report a systematic study on the synthesis of tellurium nanostructures, which can evolve from nanoparticles to nanorods, nanowires, and nanotubes by a simple solution‐based process. The size‐ and diameter‐dependent optical properties of Te nanowires have been explained based on the modeling calculations using the joint density of states (JDOS).

Size Controlled Synthesis of Tellurium Nanorices by Galvanic Displacement Reaction of Aluminum

ABSTRACT Tellurium nanostructures were synthesized by galvanic displacement reaction (GDR) of aluminum in an alkaline solution containing TeO 3 2− ions. Due to negative redox potential of Al/AlO 2 − ( i.e. , −2.50 V vs. sat. Ag/AgCl), TeO 3 2− (+IV) can be reduced to Te 2 2− (-I) and Te 2− (-II), which resulted in the deposition of Te (0) nanostructures in the solution via chemical reaction between Te 2 2− or Te 2− and TeO 3 2− . The deposition mechanism led to the formation of unique “rice-like” nanostructures in the solution instead of branched structures on the substrate. The sharp tips of the “rice-like” nanostructures may be attributed to the high density of surface charges at the tips. The morphology, diameter and aspect ratio of Te “rice-like” nanostructures were altered by the TeO 3 2− concentration, solution pH, reaction time and the reaction temperature. Electrochemical analytical methods, including open circuit potential (OCP) and linear polarizations (LPs), were used to investigate the reaction mechanisms. The enhancement of piezoelectric constant (d 11 ) of nanorices at small diameter was probably due to a flexoelectric effect.

Simple and rapid methods based microwave and sonochemistry for synthesizing of tellurium nanostructures using novel starting reagents for solar cells

Herein, tellurium (Te) nanostructures were successfully synthesized via microwave and sonochemical routes in which tellurium tetrachloride as a tellurium source and hydrazine, potassium borohydride, and thioglycolic acid (TGA) as reducing reagents were used. TGA can be easily oxidized to the corresponding disulfide [SCH2CO2H]2, which in turn can reduce TeCl4 to Te. The obtained Te was characterized by XRD, SEM, EDS, and DRS. Additionally, the effects of reducing agent as well as solvent and surfactant on morphology and size of the products were studied. Tellurium thin film was deposited on the FTO–TiO2 by Dr-blading then employed to solar cell application and measured open circuit voltage (Voc), short circuit current (Isc), and fill factor were determined as well. The studies showed that preparation method play crucial role on particle morphology and sizes. As result, various solar cell efficiencies will be achieved for the obtained nanostructures.

Microbial-assisted synthesis and evaluation the cytotoxic effect of tellurium nanorods.

The present study was designed to isolate bacterial strain capable of tellurium nanorods' (Te NRs) production followed by purification and evaluation of the cytotoxic effect of Te NRs. Among 25 environmental samples collected for screening of Te NR-producer bacterial strains one bacterial colony (isolated from hot spring and identified as Pseudomonas pseudoalcaligenes strain Te) was selected and applied for biosynthesis of Te NRs. Thereafter, an organic-aqueous partitioning system was applied for the purification of the biogenic Te NRs and the purified Te NRs were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction spectroscopy (XRD), UV-visible spectroscopy, and Fourier transform infrared spectroscopy (FTIR) techniques. The cytotoxic effect of biologically synthesized Te NRs and potassium tellurite on four cell lines of MCF-7, HT1080, HepG2 and A549 was then determined using the MTT assay method. The obtained results revealed lower toxicity for the rod-shaped biogenic tellurium nanostructures (~22nm diameter by 185nm length) compared to K2TeO3.

Synthesis of Tellurium Heterostructures by Galvanic Displacement Reaction of Zinc in Alkaline Baths

Tellurium (Te) nanostructures, including nanowires and branched nanorods, were synthesized by galvanic displacement reaction (GDR) of zinc foils in alkaline baths containing TeO32− ions. The dimension, morphology, and crystal structure of the Te nanostructures were controlled by varying the electrolyte composition, pH, and the reaction temperature. For examples, single crystalline Te nanowires were synthesized at low TeO32− concentrations (e.g., 2 mM), whereas 3-D branched nanorods were obtained at higher TeO32− concentrations (e.g., >10 mM) at a fixed pH of 13.1. The diameter of the branches was increased by increasing TeO32− concentration. Solution pH also effected the morphology of Te heterostructures where the pH range from 12.8 to 13.1 yielded branched nanorods whereas higher pH (i.e., 14.7) yielded nanowires at a fixed TeO32− concentration (i.e., 10 mM). Reaction temperature predominately effected on the dimension where the average diameter increased from 49 nm to 200 nm with increasing temperature from 4 °C to 50 °C. Various electrochemical analytical methods including open circuit potential (OCP), linear sweep voltammograms (LSVs) as well as linear potentiodynamic polarizations (LPs) were carried out to understand the underlying reaction mechanism. Based on these analysis, the formation of branched nanorods was attributed to secondary nucleation at the crystal imperfections.

Facile Hydrothermal Synthesis of Tellurium Nanostructures for Solar Cells

Tellurium (Te) nanostructures have been successfully synthesized via a simple hydrothermal methodfrom the reaction of a TeCl4 aqueous solution with thioglycolic acid (TGA) as a reductant. TGA can be easily oxidized to the corresponding disulfide [SCH2CO2H]2, which in turn can reduce TeCl4 to Te. The obtained Te was characterized by XRD, SEM, EDS, and DRS. The effect of reducing agent on morphology and size of the products were also studied. Additionally, Te thin film was deposited on the FTO-TiO2 by Dr- blading then employed to solar cell application and measured open circuit voltage (Voc), short circuit current (Isc), and fill factor (FF) were determined as well. The studies showed that particle morphology and sizes play crucial role on solar cell efficiencies.

Tellurium nanostructures: Simple chemical reduction synthesis, characterization and photovoltaic measurements

Herein, we report a simple chemical reduction method at low temperature to synthesize different tellurium (Te) nanostructures including nanorods and nanospheres. In addition, the effect of preparation parameters such as solvent, surfactant and reducing agent on the morphology of Te was studied. The as-produced Te nanostructures were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and photoluminescence spectroscopy (PL). Based on the morphological studies, it was found that sphere-like and rod-like nanostructures of Te could be obtained by using potassium borohydride (KBH4) and hydrazine hydrate (N2H4·H2O) as reducing agents, respectively. On the other hand, very uniform nanoparticles of Te have been formed in the presence of thioglycolic acid (TGA) as surfactant. We have also investigated the photocurrent density–voltage (J–V) curve of Te nanorods.

Theoretical studies of geometry asymmetry in tellurium nanostructures: intrinsic dipole, charge separation, and semiconductor–metal transition

Bulk tellurium (Te) presents a threefold screw axis with highly anisotropic chain structure, where every Te atom forms strong covalent bonds in the chain and much weaker bonds in the adjacent chains. The bonds in the adjacent chains are critical to the total energies of Te nanostructures since the nearest neighbors are always saturated. Confirmed by our model simulation and first-principles calculations, the nanobelts would be stabilized at the temperature of 600 K due to the entropy effect, though the hexagonal nanowires have the smallest surface-to-volume ratio. Attributed to the geometry asymmetry of the highly anisotropic chain, we showed that the difference of weaker bonds' distribution induces an intrinsic dipole, and thus a charge separation at the two ends of Te nanobelts. Interestingly, it further leads to a semiconductor–metal transition which is also verified by our first-principles calculations. Our finding provides a new mechanism of charge separation and semiconductor–metal transition, due to the unique asymmetry of geometry in Te nanostructures.

Self-assembly of nanoparticles to form tree-like tellurium nanostructures using novel starting reagents

A new rapid and single step thermal method was successfully developed to synthesize tree-like tellurium (Te) nanostructures at mild condition. Te nanostructures were synthesized using tellurium tetrachloride (TeCl4) as a Te precursor and thioglycolic acid (TGA) as reducing and caping agent. No secondary chemical reducing agent is required to proceed and complete the reaction. A preliminary study on the possibility of developing a solar cell having the fluorine-doped tin oxide (FTO)/TiO2/Te/Pt–FTO structure was also investigated to produce an inexpensive solar cell by Te nanostructures.

Enantioselective control of lattice and shape chirality in inorganic nanostructures using chiral biomolecules.

A large number of inorganic materials form crystals with chiral symmetry groups. Enantioselectively synthesizing nanostructures of such materials should lead to interesting optical activity effects. Here we report the synthesis of colloidal tellurium and selenium nanostructures using thiolated chiral biomolecules. The synthesis conditions are tuned to obtain tellurium nanostructures with chiral shapes and large optical activity. These nanostructures exhibit visible optical and chiroptical responses that shift with size and are successfully simulated by an electromagnetic model. The model shows that they behave as chiral optical resonators. The chiral tellurium nanostructures are transformed into chiral gold and silver telluride nanostructures with very large chiroptical activity, demonstrating a simple colloidal chemistry path to chiral plasmonic and semiconductor metamaterials. These materials are natural candidates for studies related to interactions of chiral (bio)molecules with chiral inorganic surfaces, with relevance to asymmetric catalysis, chiral crystallization and the evolution of homochirality in biomolecules.

Synthesis and antimicrobial activity of gold/silver-tellurium nanostructures.

Gold-tellurium nanostructures (Au-Te NSs), silver-tellurium nanostructures (Ag-Te NSs), and gold/silver-tellurium nanostructures (Au/Ag-Te NSs) have been prepared through galvanic reactions of tellurium nanotubes (Te NTs) with Au(3+), Ag(+), and both ions, respectively. Unlike the use of less environmentally friendly hydrazine, fructose as a reducing agent has been used to prepare Te NTs from TeO2 powders under alkaline conditions. The Au/Ag-Te NSs have highly catlaytic activity to convert nonfluorescent Amplex Red to form fluorescent product, revealing their great strength of generating reactive oxygen species (ROS). Au/Ag-Te NSs relative to the other two NSs exhibit greater antimicrobial activity toward the growth of E. coli, S. enteritidis, and S. aureus; the minimal inhibitory concentration (MIC) values of Au/Ag-Te NSs were much lower (>10-fold) than that of Ag-Te NSs and Au-Te NSs. The antibacterial activity of Au/Ag-Te NSs is mainly due to the release of Ag(+) ions and Te-related ions and also may be due to the generated ROS which destroys the bacteria membrane. In vitro cytotoxicity and hemolysis analyses have revealed their low toxicity in selected human cell lines and insignificant hemolysis in red blood cells. In addition, inhibition zone measurements using a Au/Ag-Te NSs-loaded konjac jelly film have suggested that it has great potential in practial application such as wound dressing for reducing bacterial wound infection. Having great antibacterial activitiy and excellent biocompatibility, the low-cost Au/Ag-Te NSs hold great potential as effective antimicrobial drugs.

Trifold Tellurium One-Dimensional Nanostructures and Their Formation Mechanism

Uniform trifold tellurium nanostructures have been synthesized through a facile and green solvothermal method. Their structural characteristics were investigated by using various electron microscopy techniques. The results showed that tellurium nanostructures are well-crystallized and grow along the [0001] direction. They have the hexagonal crystal structure and trifold morphology with a lateral dimension of less than 100 nm. Through detailed structural analysis of intermediate products and structural modeling, the formation mechanism of trifold tellurium nanostructures has been well illustrated; that is, the trifold Te nanostructures shared two {112̅0} sidewalls of nanowire components with each other to reduce the entire system energy.

Morphology change of galvanically displaced one-dimensional tellurium nanostructures via controlling the microstructure of sacrificial Ni thin films

One-dimensional Tellurium (Te) nanostructures with controlled dimensions and morphologies have been synthesized by the galvanic displacement reaction (GDR) of electrodeposited nickel (Ni) thin films. The effects of sacrificial Ni microstructure and HTeO2+ ion concentration on the resulting Te nanostructures were systematically investigated. The preferred crystal orientation of sacrificial Ni thin films was varied to synthesize Te nanostructures with various levels of distinctiveness. By adjusting the concentration of HTeO2+ ions in the galvanic displacement electrolyte, well-aligned one-dimensional (1-D) Te nanostructures such as conical and hexagonal pillars were prepared where the diameter ranged from ∼70 to ∼900nm and the length ranged from 1 to 3.6μm.