Wurtzite CdS Research Articles

Solvothermal Synthesis of High Yield CdS Nanowires in Ethylenediamine

Abstract High yield CdS nanowires were synthesized by a solvothermal method using thiourea and cadmium nitrate tetrahydrate as precursors in ethylenediamine. The products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), and UV-vis absorption spectroscopic techniques. XRD pattern indicates that the product is the hexagonal wurtzite CdS phase. SEM images show that the product is highly uniform CdS nanowires, and TEM images indicate that the diameter of the nanowires is about 50 nm and the length is up to several micrometers. Selected area electron diffraction (SAED) pattern reveals the as-prepared CdS nanowires’ single crystals with a preferential growth direction of (001). According to the experiments, the mechanism of the growth of CdS nanowires is discussed. The UV-vis absorption spectrum is shown to blueshift compared with that of bulk CdS due to the quantum size effect.

Synthesis of ZnO/CdS hierarchical heterostructure with enhanced photocatalytic efficiency under nature sunlight

Hierarchical ZnO composed of ultrathin nanosheets as secondary structures were fabricated through a hydrothermal method. Afterwards, hexagonal wurtzite CdS with diameter between 50–100 nm were incorporated on the wurtzite ZnO sheets with the assistance of ultrasonic irradiation. The hybrid ZnO/CdS samples were intensively investigated by SEM, TEM, HRTEM, XRD, XPS, PL and the UV-Vis absorption spectrum. The photocatalytic trials confirmed that the ZnO/CdS hierarchical heterostructures exhibit improved degradation efficiency compared to pure ZnO sample under natural sunlight. CdS nanoparticles are believed to serve as photo-sensitizers to extend the absorption spectrum to the visible region and the loading amount was also found to play a crucial role in influencing the degradation efficiency. Moreover, the photodegradation kinetics of RhB via using CdS/ZnO as photocatalysts were also systematically discussed. Finally, a mechanism based on this band-gap alignment was proposed to elucidate the efficiency enhancement of the hybrid photocatalysts.

Synthesis, structure and electronic properties of ultranarrow CdS nanorods

We report on the one-step synthesis of ultra narrow wurtzite CdS nanorods using bench top chemical decomposition route. The synthesized CdS nanorods are of 1.8 nm in diameter and show major confinement along the radial dimension, which is well below the exciton Bohr radius of bulk CdS (2.5 nm). Structural and self-assembly properties of nanorods are studied using X-ray Diffraction (XRD) and small angle X-ray scattering (SAXS) measurements, which reveal preferred orientation of the nanorods along direction with 2D supercrystalline spatial distribution. The estimated nanorod dimensions from XRD is corroborated with the transmission electron microscopy observations. UV–vis and photoluminescence spectroscopy reveals significant increase in the band gap in comparison to bulk CdS which is further tallied with the simulations using effective mass approximation (EMA). Formation of discrete structure of valence band and conduction band due to strongly quantum confined excitons in the radial direction is evidenced from EMA simulation. Combination of experimental and theoretical approach helps in understanding the structure–property relationship for ultranarrow CdS rods which might lead to nanorod based applications.

Influence of anionic concentration and deposition temperature on formation of wurtzite CdS thin films by in situ chemical reaction method

Nanocrystalline CdS thin films were deposited on glass substrates by a new in situ chemical reaction synthesis using cadmium precursor solid films as reaction source and sodium sulfide based solutions as anionic reaction medium. The influence of the S:Cd molar concentrations in separate cationic and anionic precursor solutions and the deposition temperature on the crystallized structure, morphologies, chemical component and optical properties of the deposited CdS films was investigated by X-ray diffraction, field emission scanning electron microscope, energy dispersive X-ray analysis and UV–Vis spectra measurements. The results show that CdS thin films deposited by the in situ chemical reaction synthesis have wurtzite structure with (002) plane preferential orientation and this tendency gradually enhances with increase of S:Cd molar concentration ratio. The deposition rate was 80–100nm thickness per cycle in the range of deposition temperature from 20°C to 60°C.

Birth and Growth of Octapod-Shaped Colloidal Nanocrystals Studied by Electron Tomography

The growth of octapod-shaped colloidal nanocrystals is analyzed in detail by electron tomography. The 3D shape of the starting cubic berzelianite Cu2–xSe seeds is studied, and their evolution into the final structure composed of a sphalerite CdSe core and eight wurtzite CdS pods is followed. The 3D reconstruction shows markedly different shapes of the pods, four of them having sharp tips and four flat ends. Also, the combination of the tomography results with high-resolution and energy-filtered transmission electron microscopy analyses leads to a precise identification of the structure and composition of the final particles. An interpretation of the different shapes of the pod ends is given based on the intrinsic anisotropy of both the sphalerite CdSe and the wurtzite CdS crystal structures and the different reactivity of their facets in the growth environment.

Facile Microwave-Combustion Synthesis of Wurtzite CdS Nanoparticles

In this study we first report microwave-combustion synthesis of faceted CdS nanoparticles by using cadmium thiocyanate complex as a single source precursor. This is the first example of a metal-thiocyanate (M-SCN) complex being used as a source for metal sulfides (M-S) preparation in a microwave-combustion process. The synthesized CdS was characterized using X-ray diffraction (XRD), field mission scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM). The by-product assisted combustion synthesis yields CdS nanoparticles with the mixtures of octahedral geometries, hexagonal, and triangle plate morphologies and the sizes were found to be 100 nm to 5 microm. The XRD patterns imply the formation of well crystallized wurtzite CdS. The influence of cadmium and sulfur precursors and microwave irradiation time on the morphology of CdS nanoparticle was also investigated. The cadmium and sulfur precursors strongly influenced the CdS morphology and increasing the microwave irradiation time and intensity has no effect on the CdS morphology. In addition, a plausible mechanism of CdS nanoparticle formation has been proposed in this research.

Glycolthermal synthesis and characterization of hexagonal CdS round microparticles in flower-like clusters

Hexagonal CdS round microparticles in flower-like clusters were synthesized by glycolthermal reactions of CdCl 2 and thiourea as cadmium and sulphur sources in 1,2-propylene glycol (PG) at 100–200 °C for 10–30 h. Phase and morphology were detected using X-ray diffraction (XRD), and scanning and transmission electron microscopy (SEM, TEM). The products were pure phase of hexagonal wurtzite CdS. The quantitative elemental analysis of Cd:S ratio was detected using energy dispersive X-ray (EDX) analyzer. Raman spectrometer revealed the presence of fundamental and overtone modes at 296 and 595 cm −1, corresponding to the strong 1LO and weak 2LO modes, respectively. Photonic properties were investigated using UV–visible and photoluminescence (PL) spectroscopy. They showed the same absorption at 493–498 nm, and emission at 431 nm due to the excitonic recombination process. A possible formation mechanism was also proposed, according to experimental results.

Synthesis and photoluminescence of wurtzite CdS and ZnS architectural structures via a facile solvothermal approach in mixed solvents

CdS and ZnS nanostructures with complex urchinlike morphology were synthesized by a facile solvothermal approach in a mixed solvent made of ethylenediamine, ethanolamine and distilled water. No extra capping agent was used in the process. The structure, morphologies and optical properties of these nanostructures were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy. The as-synthesized urchinlike architectures were composed of nanorods with wurtzite structure. The preferred growth direction of nanorods was found to be the [0 0 1] direction. The PL spectrum of CdS nanostructures exhibited a highly intense red emission band centered at about 706 nm. On the basis of the experimental results, a possible growth process has been discussed for the formation of the CdS and ZnS urchinlike structures.

Cation Exchange Reactions in Colloidal Branched Nanocrystals

Octapod-shaped colloidal nanocrystals composed of a central "core" region of cubic sphalerite CdSe and pods of hexagonal wurtzite CdS are subject to a cation exchange reaction in which Cd(2+) ions are progressively exchanged by Cu(+) ions. The reaction starts from the tip regions of the CdS pods and proceeds toward the center of the nanocrystals. It preserves both the shape and the anionic lattices of the heterostructures. During the exchange, the hexagonal wurtzite CdS pods are converted gradually into pods of hexagonal Cu(2)S chalcocite. Therefore, the partial cation exchange reactions lead to the formation of a ternary nanostructure, consisting of an octapod in which the central core is still CdSe, while the pods have a segmented CdS/Cu(2)S composition. When the cation exchange reaches the core, the cubic sphalerite CdSe core is converted into a core of cubic Cu(2-x)Se berzelianite phase. Therefore fully exchanged octapods are composed of a core of Cu(2-x)Se and eight pods of Cu(2)S. All these structures are stable, and the epitaxial interfaces between the various domains are characterized by low lattice mismatch. The Cu(2-x)Se(core)/Cu(2)S(pods) octapod represents another example of a nanostructure in which branching is achieved by proper organization of cubic and hexagonal domains in a single nanocrystal.

Formation of Ag 2S nanowires and Ag 2S/CdS heterostructures via simple solvothermal route

In our present work, Ag 2S nanowires and Ag 2S/CdS heterostructures have been successfully prepared in anhydrous ethanol through a simple solvothermal route. From the transmission electron microscopy (TEM) analysis, it is found that the factors influenced the final product are the concentration of Ag +, reaction temperature, reaction time, and solvent. Ag 2S nanowires are formed by complete Ag + cation exchange. Because of the selectivity for partial cation exchange, the reaction starts preferentially at the ends of the CdS nanowires to produce novel Ag 2S/CdS heterostructures. In addition, as the two end facets of wurtzite CdS nanowires are crystallographically nonequivalent, the produced Ag 2S/CdS heterostructures are asymmetric.

Phase and Shape Evolution of CdS Nanocrystallites under Solvothermal Conditions

CdS nanocrystallites with different morphologies have solvothermally prepared with ethylenediamine (en) and glycol as solvents. Solvent-dependent experiments were carried out by adjusting the ratios of en/glycol to investigate the effects of the solvents on the product phase formation and morphology. It was found that the morphology of CdS nanocrystallite develops from a rough spherical nanoparticle to a rod-, twinrod-, and tetrapod-shaped nanoparticle by increasing the ratio of en/glycol, meanwhile the phase composition changes from coexistence of tetragonal zinc blende CdS and hexagonal wurtzite CdS to pure hexagonal wurtzite CdS. Based on the experimental results, a possible shape evolution mechanism of CdS nanocrystallites is simply discussed.

Synthesis and photoluminescence of CdS QDs in ZrO2 nanotubes by sequential chemical bath deposition

Highly ordered ZrO2 nanotube (NT) arrays were fabricated by anodization in organic electrolyte containing NH4F. A facile sequential-chemical bath deposition technique was used to prepare CdS quantum dots (QDs) in the pores of ZrO2 NTs. XRD and HRTEM results confirmed the formation of single-phase wurtzite CdS nanoparticles with uniform size around 10 nm. UV–vis absorption and photoluminescence spectra proved that the CdS QD coating strongly enhanced the photon absorption of the NT arrays, as well as their PL signals in the visible broadband section which mostly arose from structure-dependent defects and oxygen vacancies in the nanohybrid layers.

Electrospun nanofibers of TiO2/CdS heteroarchitectures with enhanced photocatalytic activity by visible light

Herein, we have demonstrated that the electrospun nanofibers of TiO2/CdS heteroarchitectures could be fabricated through combining electrospinning technique with hydrothermal process. The configuration, crystal structure, and element composition of the as-prepared TiO2/CdS heteroarchitectures were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), resonant Raman spectrometer, X-ray photoelectron spectroscopy (XPS). The results indicated that the high-density hexagonal wurtzite CdS crystalline particles of ca. 6–40nm in diameter were uniformly and closely grown on anatase TiO2 nanofibers. Especially, the light-absorption properties as well as photocatalytic characteristics of pure TiO2 nanofibers and TiO2/CdS heteroarchitectures with different amount loading of CdS were also investigated. The absorption of TiO2/CdS heteroarchitectures was extended to the visible due to effective immobilization of sensitizing agent CdS on TiO2. In contrast with the pure TiO2 nanofibers, the TiO2/CdS heteroarchitectures showed excellent photocatalytic activity by using rhodamine B dye as a model organic substrate under visible-light irradiation. It was worth noting that the cooperative photocatalytic mechanism of the TiO2/CdS heteroarchitectures was also discussed.

Synthesis and photochemical performance of morphology-controlled CdS photocatalysts for hydrogen evolution under visible light

Novel CdS nanomaterials were synthesized by a simple “one-pot” hydrothermal biomolecule-assisted method using glutathione (GSH) as the sulfur source and structure-directing reagent. Various morphologies of CdS photocatalysts, such as solid nanospheres (s-CdS), hollow nanospheres (h-CdS) and nanorods (r-CdS), were obtained by controlling only the hydrothermal temperatures. The X-ray diffraction patterns confirmed that all of the samples were typical hexagonal wurtzite CdS. It was found that the absorption edge of s-CdS was at 465 nm with a greater blue shift compared to that of h-CdS and r-CdS. The photocatalytic activity of s-CdS was superior to that of h-CdS and r-CdS under visible light. Photoluminescence measurements revealed their different photogenerated electron/hole recombination ability, which was in accordance with the order of s-CdS < h-CdS < r-CdS. The excellent photocatalytic activity of s-CdS was ascribed to the small sizes of sub-nanocrystallites, which make it easy for photoinduced electrons and holes on the solid sphere to migrate to the surface and react with water and the sacrificial agent quickly. It was crucial to control the temperature for preparing CdS photocatalysts via hydrothermal methods. The formation mechanism of different morphology might be due to complexation, S–C bond rupture, spherical aggregation and Ostwald ripening processes.

Cadmium sulfide rod-bundle structures decorated with nanoparticles from an inorganic/organic composite

We report a new morphology of wurzite cadmium sulfide with nanoparticles decorated on rod-bundle structures, which were synthesized via calcinations of an inorganic/organic composite at 400 °C in air. The composite was hydrothermally synthesized at 180 °C using thioglycolic acid (TGA) and cadmium acetate as starting materials. The structure, composition, and morphology of the prepared material were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscope, FT-IR spectrometry, photoluminescence spectrometry, and UV–visible spectrometry. Results indicated that the composite could be defined as CdS 0.65/Cd–TGA0.35. X-ray diffraction revealed that the annealed product is CdS with wurtizite phase. The diameter of the rod is about 150–400 nm and the length from the top to the bottom of the decorated nanoparticle is about 100 nm. The composite showed high intensity of photoluminescence with similar peak position, compared to that of wurtzite CdS, because of the structure defects.

One-Pot Synthesis of Cu1.94S−CdS and Cu1.94S−ZnxCd1−xS Nanodisk Heterostructures

Nanodisk heterostructures consisting of monoclinic Cu(1.94)S and wurtzite CdS have been colloidally synthesized for the first time. Initially, hexagonal-shaped nanodisks of Cu(1.94)S were produced upon thermolysis of a copper complex in a solvent mixture of HDA and TOA at 250 °C. Rapid addition of Cd precursor to the reaction mixture resulted in the partial conversion of Cu(1.94)S into CdS, yielding Cu(1.94)S-CdS nanoheterostructures. The original morphology of the Cu(1.94)S nanodisks was conserved during the transformation. When Zn precursor was added together with the Cd precursor, Cu(1.94)S-Zn(x)Cd(1-x)S nanodisks were generated. These two-component nanostructures are potentially useful in the fabrication of heterojunction solar cells.

Off‐resonance Raman analysis of wurtzite CdS ground to the nanoscale: structural and size‐related effects

AbstractDifferent techniques were used to follow the transformation of CdS platelets during grinding and under hydrostatic pressure. X‐ray diffraction and transmission electron microscopy revealed that the platelets included zinc blende (cubic) CdS nanodomains dispersed in a wurtzite (hexagonal) single‐crystalline matrix. Extended grinding led to a decrease of the grain size and to a progressive transformation of the hexagonal stacking into a cubic one. The same phase transition was observed up to 9 GPa under hydrostatic pressure.Off‐resonance Raman spectra collected at different stages of the transition led us to connect band groups that were usually overlooked (in resonance conditions) or considered separately. They all probe the stacking disorder and their intensity can be related to the density of stacking faults. Off‐resonance Raman spectroscopy offers a way of probing the optical properties of CdS (and, more generally, layered semiconductors) as a function of the structure and of the confinement of vibrations by structural defects. Copyright © 2011 John Wiley &amp; Sons, Ltd.

CdSxTe1-x Alloying in CdS/CdTe Solar Cells

ABSTRACTA CdSxTe1-x layer forms by interdiffusion of CdS and CdTe during the fabrication of thinfilm CdTe photovoltaic (PV) devices. The CdSxTe1-x layer is thought to be important because it relieves strain at the CdS/CdTe interface that would otherwise exist due to the 10% lattice mismatch between these two materials. Our previous work [1] has indicated that the electrical junction is located in this interdiffused CdSxTe1-x region. Further understanding, however, is essential to predict the role of this CdSxTe1-x layer in the operation of CdS/CdTe devices. In this study, CdSxTe1-x alloy films were deposited by radio-frequency magnetron sputtering and coevaporation from CdTe and CdS sources. Both radio-frequency-magnetron-sputtered and coevaporated CdSxTe1-x films of lower S content (x&lt;0.3) have a cubic zincblende (ZB) structure akin to CdTe, whereas those of higher S content have a hexagonal wurtzite (WZ) structure like that of CdS. Films become less preferentially oriented as a result of a CdCl2 heat treatment at ∼400°C for 5 min. Films sputtered in a 1% O2/Ar ambient are amorphous as deposited, but show CdTe ZB, CdS WZ, and CdTe oxide phases after a CdCl2 heat treatment. Films sputtered in O2 partial pressure have a much wider bandgap than expected. This may be explained by nanocrystalline size effects seen previously [2] for sputtered oxygenated CdS (CdS:O) films.

Gas-phase substitution synthesis of Cu1.8S and Cu2S superlattice nanowires from CdS nanowires

Single-crystalline wurtzite CdS nanowires underwent gas-phase substitution to form unique superlattice cubic Cu1.8S (digenite) and hexagonal Cu2S (chalcocite) structures, using thermal evaporation of CuCl2 at 500∼600 °C. The Cu1.8S nanowires consisted of superlattices along the 〈111〉 direction, with controlled growth direction ([110], [211], [100], [111]) and superlattice periods of 1.6 and 1.9 nm. As the temperature decreased, the growth direction evolved from [100] to the higher surface-energy [110] or [211] directions, with longer superlattice periods. The Cu2S nanowires also exhibited a superlattice along the [0001] growth direction, with a periodicity of 2.7 nm and could be irreversibly converted into superlattice Cu1.8S by electron-beam irradiation.

Optical rectification and current injection in unbiased semiconductors

We present a full band-structure calculation of the electronic contribution to the second-order susceptibility in the limit of a sum frequency that vanishes. We give a sum-over-states expression for the optical rectification coefficient ${\ensuremath{\chi}}_{\text{rect}}(\ensuremath{\omega})\ensuremath{\equiv}{\ensuremath{\chi}}_{\text{rect}}(0;\ensuremath{\omega},\ensuremath{-}\ensuremath{\omega})$, which includes intraband contributions. Intraband transitions additionally lead to shift and injection currents, which we identify in the total response and separate from the optical rectification. The approach applies to all crystal classes and over a wide range of applied optical frequencies. We apply our results to a full band-structure calculation of the optical rectification, shift current, and injection current susceptibilities for wurtzite CdS and CdSe.