High-temperature edge luminescence from cubic cadmium selenide layers

High-temperature electrical and luminescent properties of β-CdSe layers synthesized by the solid-state substitution reaction were studied. In the temperature interval from 290 to 450 K, the edge emission band related to the annihilation of free excitons inelastically scattered from free charge carriers dominates in the photoluminescence spectrum. The binding energies of the excitons and optical phonons were measured. The bandgap width and the temperature coefficient of its variation were determined.     

Physical properties of cadmium selenide layers produced by solid-state substitution reactions

Hexagonal and cubic CdSe layers were produced on single-crystal CdS and ZnSe substrates by solid-state substitution reactions. The room-temperature conductivity of the layers is dominated by donor levels with ionization energies of 0.7 and 0.16 eV for α- and β-CdSe, respectively. The 300-K photoluminescence spectra of the layers show two emissions differing in origin: one is due to interband transitions, and the other to dissociation of excitons upon inelastic scattering from electrons.     

X-ray topographic studies of cadmium selenide

The perfection of single crystal platelets of cadmium selenide, as grown from the vapour phase, has been investigated by X-ray projection topography. Individual dislocations, stacking faults, fringe patterns, curvature of the lattice planes, and the effects of precipitates, have been detected. Dislocations have been identified having Burgers vectors 1/31 1¯20 and 0 0 01 with screw, edge, mixed and 60° configurations.     

Synthesis of cadmium selenide nanorods by polyethylene glycol-assisted solvothermal process

Cadmium selenide nanorods were successfully synthesised using Cd(NO₃)₂ and Se powder in ethylenediamine by the polyethylene glycol-assisted solvothermal reaction at 200°C for 72?h. Phase of the product was detected using X-ray powder diffractometer and selected area electron diffractometer. The XRD and electron diffraction patterns were simulated by CaRIne Crystallography 3.1 program and were found to be in accordance with those of the interpretation. The product analysed using scanning electron microscope, transmission electron microscope and high-resolution transmission electron microscopy, appeared as the nanorods with their growth in the [1?1?1] direction. The direct energy band gap, determined from the UV–visible absorbance, was 1.82?eV.     

Quantitative analysis of cadmium selenide nanocrystal concentration by comparative techniques

In this paper, we compared atomic absorption spectroscopy (AAS), anodic stripping voltammetry (ASV), and UV-vis spectroscopy for the determination of the concentration of CdSe nanocrystal (NC) solutions. The experimental results were combined with crystallographic calculations of the NC size, which led to a very accurate determination of the nanocrystal concentration--a crucial parameter for bioanalytical applications. Furthermore, such a combined approach can be extended to the determination of shell thickness of core/shell materials (e.g., CdSe/ZnS).     

Nanopatterned cadmium selenide Langmuir-Blodgett platform for leukemia detection

We present results of the studies relating to preparation of Langmuir-Blodgett (LB) monolayers of tri-n-octylphosphine oxide-capped cadmium selenide quantum dots (QCdSe) onto indium-tin oxide (ITO) coated glass substrate. The monolayer behavior has been studied at the air-water interface under various subphase conditions. This nanopatterned platform has been explored to fabricate an electrochemical DNA biosensor for detection of chronic myelogenous leukemia (CML) by covalently immobilizing the thiol-terminated oligonucleotide probe sequence via a displacement reaction. The results of electrochemical response studies reveal that this biosensor can detect target DNA in the range of 10(-6) to 10(-14) M within 120 s, has a shelf life of 2 months, and can be used about 8 times. Further, this nucleic acid sensor has been found to distinguish the CML-positive and the control negative clinical patient samples.     

Electrochemical deposition of zinc selenide and cadmium selenide onto porous silicon from aqueous acidic solutions

An electrochemical deposition process of ZnSe and CdSe compound semiconductors from aqueous acidic solutions onto silicon substrates with porous silicon layers formed on their surfaces was studied by the voltammetry method. The experimental data obtained were compared with the deposition data onto metal and silicon substrates, and the optimal conditions for the binary compound deposition onto porous silicon were determined. Semiconductor films deposited were studied by scanning electron microscopy, X-ray diffractometry, and X-ray microanalysis. The films are shown to have the crystalline structure and a nearly stoichiometric composition with a minor Se excess. Further annealing in air for 15 min allowed the Se concentration to be decreased.     

Space-charge-limited conductivity in evaporated cadmium selenide thin films

We have studied the basic d.c. electrical properties of evaporated CdSe films in the context of the development of inexpensive solar cells. Earlier measurements have shown significant variations, which depend on the preparation and previous treatment of the films. In the present work Al---CdSe---Al sandwich structures were studied, with the CdSe thickness in the range 0.1–1.0 (μm. D.c. capacitance varied inversely with film thickness, yielding a permittivity of 7.82 × 10⁻¹¹ F m⁻¹ (relative permittivity 8.83). Current density was proportional to applied voltage at low voltage levels, but followed a power law at higher voltages with exponent typically 2.5; the transitional voltage was directly proportional to the square of the film thickness. The results were interpreted as ohmic conduction at low voltages and space-charge-limited conductivity (SCLC) dominated by an exponential trap distribution, at higher voltage levels. Measurements of current density as a function of inverse temperature for different applied voltages in the SCLC region enabled the derivation of typical mobilities in the range of ( 7.65–10.15) × 10⁻⁵ m² V⁻¹ s⁻¹ using the results of our existing theory. This value of mobility and the derived trapping parameters were in general agreement with some earlier measurements.     

The structure and semiconducting properties of cadmium selenide films

CdSe films about 1 μm thick were vacuum deposited on unheated glass substrates. Reflection electron diffraction studies showed the growth of a one-dimensional {00.1} texture orientation of the hexagonal phase. Films of lower resistivity were characterized by a larger grain size and better ordering, whilst films of higher resistivity contained amorphous regions and were less ordered. A study of the carrier type, the concentration, the Hall mobility and the variation in the bond length u along the hexagonal c axis of “as-deposited” and heat-treated films showed that the lower resistivity films incorporated a small cadmium excess, which increased with heat treatment, resulting in higher carrier concentrations and a further lowering of the resistivity. Large increases in the resistivities of films deposited at high rates were attributed to the depletion of the small individual grains.     

Synthesis and characterization of poly(N-vinylpyrrolidine)-silica hybrid shell coated cadmium selenide / cadmium sulphide and cadmium selenide / zinc sulfide nanoparticles

Poly(N-vinylpyrrolidine)-silica hybrid shell coated cadmium selenide / cadmium sulphide and cadmium selenide / zinc sulfide nanoparticles were synthesized by combining the organometallic and single “step” modified Stober method. The synthesized nanoparticles were characterized by atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, and a spectrofluorometer. Concluding, this report has provided important insights into the design of new water-soluble polymer silica hybrid shell coated quantum dots nanoparticles for biomedical, analytical and catalytic applications.     

Preparation of colloidal cadmium selenide nanoparticles by pulsed laser ablation in methanol and toluene

Colloidal spherical nanoparticles (NPs) of cadmium selenide (CdSe) have been prepared by laser ablation of cadmium target in methanol and toluene solutions. The properties of CdSe nanoparticles ablated in methanol and toluene were investigated and compared. The morphology and structure of synthesised CdSe NPs were analyzed by X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscope (TEM). XRD investigation revealed that the nanoparticles are crystalline and have hexagonal structure. Optical absorption showed that the value of optical energy gap of ablated CdSe nanoparticles depends on the solution type. TEM measurements showed that CdSe NPs with diameters ranging from 25 to 35 nm were synthesised in methanol while, the nanoparticles ablated in toluene have diameters in the range of (40–50) nm.     

Studies on hexagonal cadmium selenide thin film deposited by chemical route using ascorbic acid

We have successfully deposited cadmium selenide (CdSe) thin films by simple dip method using ascorbic acid as complexing agent. Variation of thickness with time and temperature were studied. Deposited samples were characterized by X-ray diffraction, scanning electron microscopy. The absorption, electrical and photoelectrochemical properties are also studied. The X-ray diffraction analysis shows that the film samples are in hexagonal structure. The optical band gap energy was found to be 1.70 eV. Activation energy was found to be 0.447 and 0.034 eV for higher temperature and lower temperature respectively. For CdSe photoelectrode, the open circuit voltage and short circuit current are found to be 267 mV and 175 mA respectively. The calculation shows the fill factor is 28.67 %. The power conversion efficiency is found to be 1.01 %.     

Successively pulse plated cadmium selenide films and their photoelectrochemical behaviour

In successive pulse plating, the pulse deposition is repeated after a definite duration of plating preceded by a mild cleaning of the electrode and with a fresh deposition bath for the same duration. In this study, CdSe films were deposited on Ti substrates by successive pulse plating from a bath containing CdSO₄ and SeO₂ at a current density of 80 mA cm⁻² and a duty cycle of 3·3% for a duration of 30 min. The films heat-treated to 550°C for 20 min in argon atmosphere, were polycrystalline with a hexagonal structure. At an illumination of 60 mW cm⁻², a conversion efficiency of 4·5% for the photoetched film and 1·7% for the chemically etched one were determined.     

Structural and optical characterizations of chemically deposited cadmium selenide thin films

Synthesis of cadmium selenide thin films by CBD method has been presented. The deposited film samples were subjected to XRD, SEM, UV-vis-NIR and TEP characterization. X-ray diffraction analysis showed that CdSe film sample crystallized in zinc blende or cubic phase structure. SEM studies reveal that the grains are spherical in shape and uniformly distributed all over the surface of the substrates. The optical band gap energy of as deposited film sample was found to be in the order of 1.8 eV. The electrical conductivity of the film sample was found to be 10⁻⁶ (Ω cm)⁻¹ with n-type of conduction mechanism.     

Growth and characterization of lead selenide thin films

Growth of lead selenide thin films has been carried out electrochemically on indium doped tin oxide coated conducting glass substrates from an aqueous acidic bath consists of Pb(CH₃COO)₂ and SeO₂. X-ray diffraction analysis has been carried out to determine the crystal structure and phases of the deposited films. Microstructural parameters such as crystallite size, strain and dislocation density which have been evaluated from X-ray diffraction data. Surface morphology and film composition have been analyzed using scanning electron microscopy and energy dispersive analysis by X-rays. The effect of bath temperature on structural, microstructural, morphological and compositional properties of the films are studied and the results are discussed. Optical absorption measurements shows that the deposited films possess a direct band gap value of 0.38?eV.