Te Precursor Research Articles

One-Step Hydrothermal Controlled Synthesis of HgTe Nanorods

This paper describes a one-step hydrothermal synthesis of rod-shaped HgTe nanocrystals (NCs). X-ray powder diffraction (XRD), field scanning electron microscopy (FE-SEM), transition electron microscopy (TEM) and energy-dispersive X-ray analysis (EDX) have been used to characterize the HgTe NCs. The length, diameter, surface roughness and the aspect ratio of the HgTe nanorods are well controlled through Te precursor, reaction time and reductant.

A totally phosphine-free synthesis of metal telluride nanocrystals by employing alkylamides to replace alkylphosphines for preparing highly reactive tellurium precursors

Despite the developments in the wet chemical synthesis of high-quality semiconductor nanocrystals (NCs) with diverse elemental compositions, telluride NCs are still irreplaceable materials owing to their excellent photovoltaic and thermoelectric performances. Herein we demonstrate the dissolution of elemental tellurium (Te) in a series of alkylamides by sodium borohydride (NaBH4) reduction at relatively low temperature to produce highly reactive precursors for hot-injection synthesis of telluride NCs. The capability to tune the reactivity of Te precursors by selecting injection temperature permits control of NC size over a broad range. The current preparation of Te precursors is simple, economical, and totally phosphine-free, which will promote the commercial synthesis and applications of telluride NCs.

Characterization of Cd0.9Zn0.1Te based virtual Frisch grid detectors for high energy gamma ray detection

Detector grade CZT single crystals have been grown from zone refined Cd, Zn, and Te (∼7N) precursor materials using a tellurium solvent method. Infrared transmission imaging has shown an average tellurium inclusion size of ∼8μm in the as-grown crystal. Radiation detectors were fabricated in planar and virtual Frisch grid geometry and characterized for their spectroscopic performance. Charge transport properties revealed a high drift mobility of∼1200cm2/Vs and a mobility–lifetime product of ∼2.8×10−3cm2/V. A detector with planar configuration (dimensions 6.9×6.9×4.8mm3) showed an energy resolution of 4.7% for 59.5keV gamma rays. The detector in a Frisch grid configuration (dimensions 4.2×6.2×6.5mm3) exhibited an energy resolution of 1.4% for 662keV gamma rays. Digital spectroscopic measurements were carried out using a high-resolution digitizer card. A biparametric correlation scheme was employed to study the effect of charge loss on energy resolution of the planar detector. Based on this correlation scheme, a digital correction method was applied and improved pulse-height spectrum was obtained for 662keV gamma rays using the planar detector with spectral features comparable to those of the virtual Frisch grid detector.

Fabrication and Characterization of ${\rm Cd}_{0.9}{\rm Zn}_{0.1}{\rm Te}$ Schottky Diodes for High Resolution Nuclear Radiation Detectors

Cadmium zinc telluride (CZT) Schottky diodes with very low reverse leakage current have been fabricated and characterized for high resolution gamma ray detectors. The diodes were made using <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm Cd}_{0.9}{\rm Zn}_{0.1}{\rm Te}$</tex></formula> detector grade crystals grown from zone refined Cd, Zn, and Te (7N) precursor materials using low temperature tellurium solvent method. Various crystallographic defects including Te-inclusions/precipitates were identified and characterized using electron beam induced current (EBIC) measurement and thermally stimulated current (TSC) spectroscopy. The EBIC images were correlated with transmission infrared (TIR) images of CZT crystals and the EBIC contrast was attributed to the nonuniformities in spatial distribution of Te inclusions. Characterization by TSC revealed shallow and deep level centers with activation energies 0.25–0.4 eV and 0.65–0.8 eV respectively, which were attributed to intrinsic defects associated with Te inclusions. Pulse height measurements were carried out using <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$^{137}{\rm Cs}$</tex></formula> (662 keV) radiation source and energy resolution of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim 1.51}\%$</tex></formula> full width at half maximum (FWHM) was obtained from the as-grown boule.

Microwave‐assisted aqueous synthesis of new quaternary‐alloyed CdSeTeS quantum dots; and their bioapplications in targeted imaging of cancer cells

In this study, we report for the first time a one-pot approach for the synthesis of new CdSeTeS quaternary-alloyed quantum dots (QDs) in aqueous phase by microwave irradiation. CdCl2 was used as a Cd precursor during synthesis, NaHTe and NaHSe were used as Te and Se precursors and mercaptopropionic acid (MPA) was used as a stabilizer and source of sulfur. A series of quaternary-alloyed QDs of different sizes were prepared. CdSeTeS QDs exhibited a wide emission range from 549 to 709 nm and high quantum yield (QY) up to 57.7 %. Most importantly, the quaternary-alloyed QDs possessed significantly long fluorescence lifetimes > 100 ns as well as excellent photostability. Results of high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX) and powder X-ray diffraction (XRD) spectroscopy showed that the nanocrystals possessed a quaternary alloy structure with good crystallinity. Fluorescence correlation spectroscopy (FCS) showed that QDs possessed good water solubility and monodispersity in aqueous solution. Furthermore, CdSeTeS QDs were modified with alpha-thio-omega-carboxy poly(ethylene glycol) (HS-PEG-COOH) and the modified QDs were linked to anti-epidermal growth factor receptor (EGFR) antibodies. QDs with the EGFR antibodies as labeling probes were successfully applied to targeted imaging for EGFR on the surface of SiHa cervical cancer cells. We believe that CdSeTeS QDs can become useful probes for in vivo targeted imaging and clinical diagnosis.

Aqueous Synthesis of Highly Monodispersed Thiol-Capped CdTe Quantum Dots Through Electrochemical Approach

A facile green approach has been developed to control the growth regime in the aqueous synthesis of CdTe semiconductor Quantum dots (QDs) via the electrochemistry method. The Low growth temperature and slow injection of Te precursors are used to prolong the diffusion controlled stage and thus suppress Ostwald ripening during nanocrystal growth. The experimental results showed that a low concentration of Te precursor would definitely influence the growth procedure. The narrow absorption peaks in the UV-visible absorption spectra, as well as transmission electron microscopy images indicated that the as-prepared CdTe QDs had a good monodispersity. The high-resolution transmission electron microscopy (HRTEM) images and powder X-ray diffraction (XRD) pattern suggested that the as-prepared QDs have high crystallinity and cubic structure. The QDs exhibited high fluorescence QYs about 50% and the best of QY 67% without any postpreparative treatment over a broad spectral range of 516-609 nm, which could be further broadened by long-term refluxing. The current work suggested that electrochemical method was an attractive approach to the synthesis of high-quality II-VI semiconductor QDs at a large scale.

AQUEOUS SYNTHESIS OF HIGH QUANTUM YIELD AND MONODISPERSED THIOL-CAPPED CdxZn1-xTe QUANTUM DOTS BASED ON ELECTROCHEMICAL METHOD

A facile green approach has been developed to control the growth regime in the aqueous synthesis of CdxZn1-xTe semiconductor quantum dots (QDs) based on the electrochemistry method. The Low growth temperature and slow injection of Te precursor are used to prolong the diffusion controlled stage and thus suppress Ostwald ripening during the nanocrystal growth. The experimental results showed that a low concentration of Te precursor will definitely influence the growth procedure. The UV–visible absorption spectra, as well as transmission electron microscopy (TEM) shows the QDs a good monodispersity at any interval of the reaction procedure. The high-resolution transmission electron microscopy (HRTEM) images and powder X-ray diffraction (XRD) pattern suggested that the as-prepared QDs have high crystallinity and cubic structure. The size and composition-dependent fluorescent emission wavelength of the resultant CdxZn1-xTe alloyed QDs can be tuned from 460 to 610 nm, and their photoluminescent quantum yield can reach up to 70%. Especially in the wavelength range of 510–578 nm, the overall PL QYs of the as-prepared CdxZn1-xTe QDs were above 50%. The current work suggests that electrochemical method is an attractive approach to the synthesis of high-quality II-VI ternary alloyed semiconductor QDs at large-scale with a prominent cost advantage.

Facile preparation of metal telluride nanocrystals using di-n-octylphosphine oxide (DOPO) as an air-stable and less toxic alternative to the common tri-alkylphosphines

In this paper, we have developed a “green” method for the synthesis of metal telluride nanocrystals. In this method, di-n-octylphosphine oxide (DOPO) has been used to disperse Te and form Te–DOPO precursor. This new Te precursor was found to be highly reactive and suitable for the synthesis of metal telluride nanocrystals in various monodispersity, size, and shape. Dot-/tetrapod-shaped CdTe, dot-shaped ZnTe, dot-/cubic-shaped PbTe, dot-/rod-shaped Ag2Te, cubic-shaped Cu2−xTe, ternary alloyed CuInTe2, and quaternary alloyed Cu2ZnSnTe4 semiconductor nanocrystals all have been well-controlled synthesized. The photoluminescence emission of as-synthesized CdTe nanocrystals covered a wide range (570–735 nm) and the quality of as-synthesized metal telluride nanocrystals were reached or exceed the level compared with the traditional method using phosphine–Te precursor. The possible dissolving molecular mechanism of Te in DOPO in this synthesis was specially studied and illustrated that intramolecular proton transfer from the phosphorus (formation of DOPO–Te complex) was essential in the synthesis of metal telluride nanocrystals. This method provided a greener and less expensive route to large-scale synthesis of all kinds of high quality metal telluride nanocrystals.

Size controlled synthesis of monodisperse PbTe quantum dots: using oleylamine as the capping ligand

We report a simple method to synthesize monodisperse hydrophobic PbTe quantum dots followed by a stability study of the as-synthesized quantum dots in air. We provide evidence that air-stable PbTe quantum dots can be synthesized using this method. PbCl2 complexed with oleylamine was used as the Pb precursor. Tellurium powder dissolved in tri-n-octylphosphine was used as the Te precursor. Oleylamine was used as the only capping ligand. The size and shape of the PbTe quantum dots were controlled by changing variables such as injection temperature, growth temperature, and growth time. Both Pb to oleylamine and Pb to Te feed mole ratios have been examined to obtain the optimal synthetic conditions. The PbTe quantum dots can be changed from hydrophobic to hydrophilic through ligand exchange using 4-mercaptopyridine to replace oleylamine as the capping ligand. The colloidal PbTe quantum dots were characterized by transmission electron microscopy, high resolution transmission electron microscopy, selected area X-ray diffraction, energy-dispersive X-ray spectroscopy, FT-IR spectrometer, 31PNMR spectrometer, and powder X-ray diffraction. The sizes of the PbTe quantum dots synthesized ranged from 2.6 nm to 14.0 nm with a relative standard deviation of ∼5.6 to 9.1%. The shape of the PbTe quantum dots was either spherical ( ∼9 to 10 nm).

Hydrothermal synthesis and thermoelectric transport property of PbS–PbTe core–shell heterostructures

We report a facile hydrothermal route for the synthesis of PbS–PbTe core–shell heterostructured nanorods. The phase ratio of PbS to PbTe can be tuned by introducing different molar ratios of PbS to the Te precursor (molar ratio of PbS to Te precursor, R). The as-prepared samples were characterized by the X-ray diffraction pattern (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and X-ray photoelectron spectroscopy (XPS). Thermoelectric transport measurements present that the obtained PbS–PbTe core–shell nano-structured composites have an enhanced power factor compared to that of pure PbS. The maximum power factor of 294 μW (m K2)−1 can be achieved for the sample with R = 20. In addition, the power factor can be tuned by changing the phase ratio of PbS to PbTe.

Synthesis and Characterization of Rutile Nanocrystals Prepared in Aqueous Media at Low Temperature

Rutile powder was synthesized via sol–gel processing of Tyzor TE precursor in an aqueous solution at 40°C–50°C. A suite of characterization techniques, including FTIR, Raman, X‐ray, and electron diffraction, were employed to investigate the microstructural evolution. The synthesized powder was phase‐pure rutile possessing high surface area (144.7 m2/g), an average pore size of 24.9 nm, and pore volume of 0.66 cm3/g. A reaction mechanism is proposed for the preferential evolution of rutile over other titania polymorphs (i.e. amorphous or anatase).

Electrodeposition and characterization of thermoelectric Bi 2Te 2Se/Te multilayer nanowire arrays

Multilayer nanowire arrays of a new heterogeneous thermoelectric material, Bi 2Te 2Se/Te, were successfully fabricated by a template-assisted pulsed electrodeposition method. The nanowires were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, and energy dispersive X-ray spectroscopy, respectively. The diameter of the nanowires is in the range of 60–85 nm. By adjusting the concentration of Te precursor, the length of the Te segment can be modulated. At sufficient low concentration of Te precursor, the phase composition of the other segment can even be changed from Bi 2Te 2Se to Bi 2Se 2Te. The formation and growth mechanisms of the nanowires were proposed.

Layered GaTe Crystals for Radiation Detectors

In this work we investigated a new method of growing detector grade large GaTe layered chalcogenide single crystals. GaTe ingots (2" diameter) were grown by a novel method using graphite crucible by slow crystallization from a melt of high purity (7 N) Ga and zone refined (ZR) Te precursors in an argon atmosphere. GaTe samples from the monocrystalline area of the ingot have been cleaved mechanically and characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis by x-rays (EDX), atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), transfer length method (TLM), resistivity measurements using van der Pauw technique, Hall effect, and capacitance-voltage (C-V) measurements. Our investigations reveal a novel method of growing superior quality GaTe crystals for large volume inexpensive nuclear radiation detectors.

Cathodic Stripping Synthesis and Cytotoxity Studies of Glutathione-Capped CdTe Quantum Dots

A cathodic stripping of Te precursor in the presence of Cd2+ and biocompatible glutathione (GSH) was reported for facile synthesis of lowly cytotoxic and highly luminescent CdTe quantum dots (QDs) in aqueous solution. The photoluminescence, electrogenerated chemiluminescence (ECL), toxicity, and cyto-osmosis of the QDs were evaluated to reveal their potential bio-applications. The morphology and composition of as-prepared QDs were investigated by HRTEM and powder XRD spectroscopy, which indicated that the QDs consisted of a CdTe core coated with a CdS shell. The obtained CdTe/CdS core/shell QDs possessed good crystallinity, narrow monodispersity and long-term stability. These QDs showed high fluorescence quantum yields of 49% to 63% over a broad spectral range of 540-650 nm. Efficient and stable ECL of QDs was observed on the anodic potential region upon the electrode potential cycled between 1.5 and -2.0 V versus Ag/AgCl. Furthermore, human liver cancer HepG2 cells were chosen as model cells for toxicity assay of QDs. Effects of the concentration, size, and incubation time of CdTe QDs capped with GSH or mercaptoacetic acid (MAA) on the cell metabolic viability and cyto-osmosis were evaluated. GSH-capped CdTe QDs could infiltrate cytomembrane and karyothecas, and were less cytotoxic than MAA-capped ones under the same experimental conditions. The reported CdTe QDs could be good candidates of fluorescent and ECL probes for biosensing and cell imaging.

Layer-by-layer self-assembly CdTe quantum dots and molecularly imprinted polymers modified chemiluminescence sensor for deltamethrin detection

A novel chemiluminescence sensor for determination deltamethrin was firstly reported based on CdTe quantum dots and deltamethrin imprinted polymers by layer-by-layer assembly modified on the surface of slide glass, whose shape was the same as the bottom of 96 well micro-plate. The binding characteristic of the imprinted polymers to deltamethrin was evaluated by equilibrium binding experiments and the morphology was studied by scanning electronic microscope. Scatchard analysis was carried out to estimate the binding parameters of the imprinted polymers. The water-soluble TGA-capped CdTe quantum dots were prepared. NaHTe was used as the Te precursor for CdTe quantum dots synthesis. Under the optimum conditions, the chemiluminescence intensity had a linear relationship against the concentration of deltamethrin over the range of 0.053–46.5 μg mL −1 with a lower detection limit of 0.018 μg mL −1. The regression equation was Δ I = 2225 + 107 c ( c: μg mL −1) with a correlation coefficient of 0.9973. The relative standard deviation was 4.7%. The presented method was applied successfully to the determination of deltamethrin in real samples with satisfactory results.

Formation of 1-D ZnTe nanocrystals by aerosol-assisted spray pyrolysis

One-dimensional (1-D) ZnTe nanowires were prepared by aerosol-assisted spray pyrolysis using a mixture of ZnO (1 mmol)/OA (4 mL)/TOPO (0.8 g)/ODE (4 mL) as Zn precursor and Te/TOP (3 mL of 0.75M) as Te precursor. The shape, size, and crystal structure of products were characterized by means of transmission electron microscope (TEM) and X-ray diffraction (XRD). The shape evolution of ZnTe nanocrystals from nanodots to nanowires was achieved by controlling the reaction temperature. ZnTe nanodots with average diameter of 8.3 nm were synthesized at 300 °C. “Earthworm-like” shaped ZnTe (linear ZnTe aggregates) consisting of primary ZnTe nanodots of about 16 nm in diameter were obtained at 400 °C. In addition, 1-D ZnTe nanowires were prepared at reaction temperature higher than 450 °C. Those experimental results suggest that ZnTe nanowires with zinc blende structure are formed from ZnTe nanodots by the oriented attachment due to insufficient surface capping of surfactant molecules and by strong dipole-dipole interaction of nanodots, followed by self-organization of linear aggregates at higher reaction temperatures. The linear ZnTe aggregates consisting of primary ZnTe nanodots may be an intermediate stage in the formation process of nanowires from nanodots.

Electrical phase change of CVD-grown Ge-Sb-Te thin-film device

A prototype Ge-Sb-Te thin-film phase-change memory device has been fabricated and reversible threshold and phase change switching demonstrated electrically, with a threshold voltage of 1.5–1.7 V. The Ge-Sb-Te thin film was fabricated by chemical vapour deposition (CVD) at atmospheric pressure using GeCl4, SbCl5, and Te precursors with reactive gas H2 at reaction temperature 780°C and substrate temperature 250°C. The surface morphology and composition of the CVD-grown Ge-Sb-Te thin film has been characterised by scanning electron microscopy and energy dispersive X-ray analysis. The CVD-grown Ge-Sb-Te thin film shows promise for phase change memory applications.

Low Temperature Crystal Growth and Characterization of Cd0.9Zn0.1Te for Radiation Detection Applications

ABSTRACTCd0.9Zn0.1Te (CZT) detector grade crystals were grown from zone refined Cd, Zn, and Te (7N) precursor materials, using the tellurium solvent method. These crystals were grown using a high temperature vertical furnace designed and installed in our laboratory. The furnace is capable of growing up to 8” diameter crystals, and custom pulling and ampoule rotation functions using custom electronics were furnished for this setup. CZT crystals were grown using excess Te as a solvent with growth temperatures lower than the melting temperatures of CZT (1092°C). Tellurium inclusions were characterized through IR transmittance maps for the grown CZT ingots. The crystals from the grown ingots were processed and characterized using I-V measurements for electrical resistivity, thermally stimulated current (TSC), and electron beam induced current (EBIC). Pulse height spectra (PHS) measurements were carried out using a 241Am (59.6 keV) radiation source, and an energy resolution of ~4.2% FWHM was obtained. Our investigation demonstrates high quality detector grade CZT crystals growth using this low temperature solvent method.

The role of hydrogen in hot wire chemical vapor deposition of Ge-Sb-Te thin films

Ge-Sb-Te (GST) thin films were deposited by hot wire chemical vapor deposition using metalorganic Ge, Sb, and Te precursors. The hydrogen flow was varied in order to investigate the hydrogen influence on the deposition of GST films. A decrease of the temperature (from 450 to 350 °C) and an increase of the hydrogen concentration (from 0 to 50%) of the total gas flow result in a lowering of the deposition rate. Additionally, a higher hydrogen flow can be used to obtain smooth GST films (mean roughness—5 nm). The chemical composition of the films significantly depends on the hydrogen content. The tellurium content decreases and the antimony content increases with increasing hydrogen flow.

Size- and Shape-Controlled Synthesis of CdTe and PbTe Nanocrystals Using Tellurium Dioxide as the Tellurium Precursor

We have developed a new method for the synthesis of CdTe and PbTe nanocrystals by using TeO2 with trioctylphosphine oxide as Te precursor. Using this method, uniform-sized CdTe nanocrystals are suc...