CdTe Nanoclusters Research Articles

Absorption Features of CdTe Nanoclusters: Aspect Ratio Dependency of the Singlet/Doublet from First-Principles Calculations

Two categories of absorption features, singlet and doublet, have been observed in semiconductive II–VI magic-size clusters (MSCs) experimentally; however, the underlying mechanism resulting in the ...

Создание нанокластеров CdTe в трековых темплэйтах SiO 2 /Si с использованием двух типов электролита

Создание нанокластеров CdTe в трековых темплэйтах SiO 2 /Si с использованием двух типов электролита

Bonding and Spectral Character of Cr Doped Cdte, Cdse and Cds Nano-Clusters

The geometrical structures, bonding characteristics, Raman spectra, and molecular orbitals of hexagonal and tetrahedral Cr-doped CdX molecules have been investigated using density functional theory calculations at the B3LYP/LANL2DZ level. The structures of Cr-doped CdX molecules had obvious distortions compared with pure CdX clusters, especially CdCr2Se3 and CdCr2S3 clusters. The Mulliken charges of Cr atoms were negative and were lower than those of Cd atoms in the corresponding structures. Raman spectra showed that there was the vibration of the Cr–Cr bond in Cr-doped CdX molecules. Wiberg bond indices (WBI) values show that there were Cr–Cr bonds in some clusters. WBI values have also revealed that bonds between Cr and Te, Se, S were stronger than those between Cd and X atoms. Finally, molecular orbital observations indicate that the transitions in doped structures were from d orbital to d orbital, which is different from undoped structures.

DFT studies on the stability of linear, ring, and 3D structures in CdTe nanoclusters

In DFT studies with the B3LYP/LanL2DZ basis set the different structures, linear, ring, and 3D, of cadmium telluride (CdTe) n clusters for n = 2–7 were completely optimized. The stability, dipole moment, and point groups of the different clusters were studied. The HOMO–LUMO energy gap, ionization potential, electron affinity, relative stability, and binding energy of different clusters were studied and compared with values for different isomers. These results for the different properties of CdTe nanoclusters will give clear information enabling the design of new materials with potential importance in thin-film solar cells.

Crystal and electronic structure of PbTe/CdTe nanostructures

In this article, the authors reported a theoretical study of structural and electronic properties of PbTe inclusions in CdTe matrix as well as CdTe nano-clusters in PbTe matrix. The structural properties are studied by ab initio methods. A tight-binding model is constructed to calculate the electron density of states (DOS) of the systems. In contrast to the ab initio methods, the latter allows studying nanostructures with diameters comparable to the real ones. The calculations show that both kinds of inclusions lead to changes of the DOS of the carriers near the Fermi level, which may affect optical, electrical and thermoelectric properties of the material. These changes depend on the size, shape, and concentration of inclusions.

Nano Heterojunctions of Cadmium Sulfide and Cadmium Telluride for Photoelectrocemical Cell Applications

AbstractThis study presents a very cost effective template-based electrochemical technique to synthesize the nano heterojunctions of cadmium sulfide (CdS) and cadmium telluride (CdTe). SEM analysis revealed that the average length of CdS nanowires varied from 500 nm to 4 μm depending on the deposition time and voltage. Also, average diameter of the CdS nanowires ranged between 100 and 200 nm. The structures of CdS nanowires have been confirmed by XRD and EDX analysis. Photoelectrochemical performances of CdS nanowires revealed that there is a dramatic change in the photoelectrochemical performances with the change in deposition time and voltage. The maximum fill factor (FF) and power efficiency (η) of the CdS nanowires has been calculated as 45 % and 1.36 %, respectively. After the optimization of the CdS nanowire deposition conditions based on the PEC performance, CdTe nanostructures have been deposited on CdS nanowires at various deposition time. SEM analysis showed that CdTe nanostructures have a tendency to grow as nanoclusters. It was observed that the density and the average diameter of the clusters was a strong function of the deposition time. The average diameter of the CdTe nanoclusters after 9-hour deposition reached about 260 nm. The successful heterojunction of CdS nanowires with CdTe nanoclusters have been observed in the SEM analysis. It has been concluded that the PEC performances of the CdS nanowires improved significantly after CdTe deposition. The maximum η, obtained in this study is about 8.04 %. This is one of the highest efficiencies reported in the literature for the nanowire array photoelectrochemical cells.

Low temperature synthesis of thiol‐functionalized CdTe nanoclusters with different tellurium contents

AbstractIn recent years thiol‐functionalized cadmium telluride nanoparticles act as a core layers for obtaining high photovoltaic efficiency in conjugated polymer/inorganic nanocrystal solar cells and also provide easy tuning of quantum size effect by varying thiol groups and processing temperature. In this work, thiol functionalized CdTe nanoclusters were prepared for different tellurium concentrations at low temperature and its impact has been discussed. Structural parameters estimated by X‐ray diffraction revealed hexagonal phases at lower tellurium concentration and cubic phase at higher tellurium concentrations. Surface morphology of the samples analyzed by transmission electron microscopy, exhibited cluster type of morphology. Optical band gap energy estimated by diffused electron microscopy showed an increase with Te content and band edge emission has been observed in the photoluminescence spectra of CdTe nanoclusters around 620 nm. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Incorporation of Thiol-Stabilized CdTe Nanoclusters into Langmuir-Blodgett Films

The methods of incorporating thiol-stabilized CdTe nanoclusters into mono- and multilayer films produced by the Langmuir-Blodgett (LB) technique on the basis of anionic (behenic acid) and cationic (octadecyltrinonylammonium (ODTNA) iodide) surfactants were investigated. ‘Pressure-area’ isotherms, quartz crystal microbalance (QCM), FTIR, atomic force microscopy (AFM) and UV/Vis spectroscopy give evidence on the incorporation of the nanoclusters in LB films. The limiting surface area of the behenic acid monolayer increases with a simultaneous decrease of the film strength. The optical absorption of the films obtained through the incorporation of the clusters acquires the features of CdTe nanocrystals. The noticeable difference in the deposition process was observed for the two types of stabilizing ligands (thioglycerol and mercaptoethanol) used for the CdTe clusters. The bonding of the CdTe clusters with the carboxylic group of behenic acid monolayer is established for the thioglycerol-stabilized clusters.

Strongly Photoluminescent CdTe Nanocrystals by Proper Surface Modification

CdTe nanoclusters were prepared in aqueous solution by the reaction between Cd2+ and NaHTe in the presence of thioglycolic acid. Under reflux, the clusters start to crystallize and show a narrow band emission. The photoluminescence efficiency of CdTe nanocrystals strongly depends on the pH value of the colloidal solution. The maximum quantum yield at room temperature is approximately 18% when the pH value of the CdTe solution is brought to 4.5 by using thioglycolic acid. The optical spectroscopy studies imply that the pH-dependent behavior of the CdTe nanocrystals' fluorescence is caused by structural changes on the surface rather than the size of the nanocrystals. Systematic absorption and fluorescence studies on dialyzed samples suggest that in the acidic range a shell of cadmium thiol complexes is formed around the CdTe core. Thus, the fluorescence quantum yield is enhanced dramatically when the solution is made acidic. In contrast, such a shell can also be produced in the alkaline range, but only afte...

Thiol-Capped CdSe and CdTe Nanoclusters: Synthesis by a Wet Chemical Route, Structural and Optical Properties

AbstractCdSe and CdTe nanoclusters were formed in aqueous solutions at moderate temperatures by a wet chemical route in the presence of thiols as effective stabilizing agents. The nature of the stabilizing agent (thioalcohols or thioacids) had an important influence on the particle size and largely determined the photoluminescence properties. The nanoclusters were characterized by means of UV-vis absorption and photoluminescence spectroscopy, powder X-ray diffraction, high resolution transmission electron microscopy, and extended X-ray absorption fine structure measurements. CdSe and CdTe nanoclusters were crystalline, in the cubic zincblende phase, with mean sizes in the range of 2 to 5 nm depending on the preparative conditions and the postpreparative size-selective fractionation, and showed pronounced electronic transitions in the absorption spectra. Thioglycerol-stabilized CdTe nanoclusters possessed sharp band-egde photoluminescence being tunable with particle size.

Synthesis, morphology and optical properties of thiol‐stabilized CdTe nanoclusters in aqueous solution

AbstractThiol‐stabilized CdTe nanoclusters with sizes ranging from 1.3 to 2.4 nm have been prepared in aqueous solution and separated as oxidize‐stable powders. Investigation of CdTe nanoclusters by means of X‐ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) indicates the cubic (zincblende phase) CdTe crystalline structure. Pronounced electronic transitions in the absorption spectra are shifted dramatically towards higher energies in comparison with bulk CdTe as a consequence of quantum confinement in nanosized CdTe particles. Two kinds of size‐ and surface‐dependent photoluminescence (“excitonic” and trapped) of CdTe nanoclusters in aqueous solution were observed. A further growth of CdTe nanoclusters leads to a shift of both absorption edge and “excitonic” photoluminescence band towards longer wavelengths.

Synthesis and characterization of thiol‐stabilized CdTe nanocrystals

AbstractIn order to expand the range of high‐quality nanosized semiconductor materials that can be obtained as quantum dots through a wet chemical route a series of oxidize‐stable CdTe nanoclusters with narrow size distributions and extremely small particle sizes ranging from 1.3 to 2.4 nm has been prepared in aqueous solution using 2‐mercaptoethanol and 1‐thioglycerol as stabilizers. It has been investigated by means of UV‐vis absorption and photoluminescence spectroscopy, X‐ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and energy dispersive x‐ray analysis (EDX).