Synthesis of CdS nanocrystals with different morphologies via an ultraviolet irradiation route

A simple ultraviolet photochemical reduction synthetic approach to preparing CdS nanocrystals with different morphologies is described. Sodium dodecyl sulfate (SDS) was used as soft template for the chemical synthesis of CdS nanocrystals in a mixture solution at room temperature. It was found that the magnetic force stirring and the volume proportions of C₂H₅OH and H₂O had marked influences on the morphology of CdS nanocrystals (such as spherical, acicular-like, rod-like and worm-like shapes). The formation of CdS is via precipitation of Cd²⁺ ions with the homogeneously released S²⁻ ions from decomposition of thioacetamide under ultraviolet irradiation source. X-ray diffraction (XRD), scanning electron microscopy (SEM) and the ultraviolet–visible (UV–vis) absorption spectra were employed to characterize the products. This novel method is expected to produce various semiconductor nanocrystals with potential applications in the fields of materials science and photovoltaic cells, etc.     

Novel approach to control CdS morphology by simple microwave-solvothermal method

Nanosize CdS powders with different microstructures are prepared in different solvents by using rapid microwave irradiation. Effect of solvents and Cd²⁺ precursors are to be able to control the particle size, and microstructures of CdS have been investigated by X-ray diffraction and TEM. The different particle size and morphologies are observed using different Cd²⁺ precursors in different solvents. TEM micrographs clearly show multiarmed nanorods and spherical shape morphologies of CdS powders are obtained in polar solvent like water (H₂O), whereas non-polar polyol solvent like ethylene glycol (EG), prickle and cluster like morphologies of CdS are achieved with different Cd²⁺ precursors such as CdSO₄ and Cd (CH₃COO)₂. The spectroscopy studies of nanosize CdS are examined by photo-luminescence spectra. Band gap and the absorption co-efficient for nano CdS is also evaluated from optical absorption studies.     

Effects of CdCl2 on the electrical properties of sintered CdS films

CdS films on glass substrates with various amounts of CdCl₂ have been prepared by coating and sintering, and their microstructure, electrical resistivity, carrier concentration and mobility have been investigated. The sintering rate is strongly increased near the melting temperature of CdCl₂ and the enhancement in the sintering is via a liquid-phase sintering mechanism. Doping of chlorine also occurs during the sintering and the solubility of chlorine in CdS is of the order of 10¹⁸ cm^–3 at 650° C. The electron concentration of the sintered CdS films which contained CdCl₂ before sintering increases with increasing grain size. The electron mobility increases sharply with increasing average grain size due to a sharp decrease in the total trap density, which is proportional to the total grain-boundary area.     

Aligned tungsten oxide nanowires on tungsten (100) substrates

WO₃ nanowires in body center cubic structure were grown on W (100) substrates by heating in an argon atmosphere. Scanning electron microscope and transmission electron microscope characterizations show the WO₃ NWs grew along the [100] crystallographic orientation and were aligned in three directions. The diameter of WO₃ NWs is in the range of several to 20 nm and the length is up to 1 µm. Field emission measurements show that the field emission current density can reach 1.8 mA/cm² under electrical field 10 V/µm and the turn-on field can be as low as 2.6 V/µm.     

One-pot fabrication of hollow SiO2 nanowires via an electrospinning technique

Hollow SiO₂ nanowires (NWs) were one-pot fabricated via an electrospinning method. Their morphologies, structures, and chemical compositions were investigated by means of scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In order to fabricate optimum hollow SiO₂ NWs, the relative volume ratio of tetraethyl orthosilicate (TEOS, an alkoxide precursor) to ethanol (solvent) was systematically controlled from 0.02 to 0.36. SEM, HRTEM, XRD, and XPS results indicate that amorphous SiO₂ hollow NWs can be one-pot synthesized by using the volume ratio of 0.18 under a constant voltage of 8.0 kV.     

High aspect ratio CdS nanowires synthesized in microemulsion system

CdS nanowires with typical length more than 8 μm and width of 30 nm on average have been successfully synthesized through Cd(NO₃)₂ reacting with CS₂ and ethylenediamine in microemulsion system of sodium dodecylbenzene sulfonate (SBDS). The microstructures of the as-synthesized CdS nanowires were characterized using XRD, transmission electron microscopy (TEM) and HRTEM. The possible formation mechanism was discussed. The morphologies of CdS sample strongly depend on the concentration of surfactant in solutions.     

Dependence of photovoltaic performance of solvothermally prepared CdS/CdTe solar cells on morphology and thickness of window and absorber layers

In the present work a new strategy for straightforward fabrication of CdS/CdTe solar cells, containing CdS nanowires and nanoparticles as a window layer and CdTe nanoparticles and microparticles as an absorber layer, are reported. CdS and CdTe nanostructures were synthesized by solvothermal method. X-ray diffraction analysis revealed that highly pure and crystallized CdS nanowires and nanoparticles with hexagonal structure and CdTe nanoparticles with cubic structure were obtained. Atomic force microscope and field emission scanning electron microscope images showed that CdS nanowires with length of several μm and average diameter of 35 nm, CdS nanoparticles with average particle size of 32 nm and CdTe nanoparticles with average particle size of 43 nm, were uniformly coated on the substrate by the homemade formulated pastes. Based on ultraviolet–visible absorption spectra, the band gap energies of CdS nanowires, CdS nanoparticles and CdTe nanoparticles were calculated 2.80, 2.65 and 1.64 eV, respectively. It was found that, the photovoltaic performance of the solar cells depends on thickness of CdTe and CdS films, reaching a maximum at a specific value of 6 μm and 225 nm, respectively. For such cell made of CdS nanowires and CdTe nanoparticles the V_OC, J_SC, fill factor and power conversion efficiency were calculated 0.62 V, 6.82 mA/cm², 59.7 and 2.53 %, respectively. Moreover, photovoltaic characteristics of the solar cells were dependent on CdTe and CdS morphologies. CdS/CdTe solar cell made of CdTe and CdS nanoparticles had the highest cell efficiency (i.e., 2.73 %) amongst all fabricated solar cells. The presented strategy would open up new concept for fabrication of low-cost CdS/CdTe solar cells due to employment of a simple chemical route rather than the vapor phase methods.     

TiO2 nanowires sensitized with CdS quantum dots and the surface photovoltage properties

TiO₂ nanowires prepared by thermal annealing of anodized Ti foil were sensitized with CdS quantum dots (QDs) via chemical bath deposition (CBD). Microstructural characterizations by SEM, TEM and XRD show that the CdS nanocrystals with the cubic structure have intimate contact to the TiO₂ nanowires. The amount of CdS QDs can be controlled by varying the CBD cycles. The experiment results demonstrate that the surface photovoltage (SPV) response intensity was significantly enhanced and the surface photovoltage response region was also expanded obviously for the TiO₂ NWs sensitized by CdS QDs.     

Facile fabrication of silver nanoplates via a solvothermal method

This paper describes a simple solvothermal route to synthesize silver nanoplates by reduction of silver nitrate (AgNO₃) with N,N-dimethylformamide. In this approach, ferric chloride (FeCl₃) servers as the controlling agent, enabling the control over the concentration of free Ag⁺ ions in the solution. As the concentration of FeCl₃ added to the reaction was increased, the morphologies of silver nanostructures evolved from triangular silver nanoplates to hexagonal silver nanoplates. The structures of these nanoplates were characterized by X-ray diffraction, electron microscopy and electron diffraction. A possible mechanism is proposed to interpret the shape-controlled synthesis of silver nanostructures. Finally, our results suggest that this method provides a convenient way to prepare silver nanostructures with different morphologies.     

A hydrothermal method to prepare the spherical ZnS and flower-like CdS microcrystallites

The spherical ZnS and flower-like CdS microcrystallites are prepared by a convenient hydrothermal process through the reactions of Zn(CH₃COO)₂·2H₂O or Cd(CH₃COO)₂·2H₂O with S and NaH₂PO₂·H₂O in aqueous solution at 180 °C for 12 h. Powder X-ray diffraction (XRD) is used to confirm the cubic phases of the ZnS and CdS microcrystallites. Their chemical compositions are characterized by X-ray photoelectron spectroscopy (XPS). Scanning electron microscope (SEM) images show the morphologies of the as-synthesized ZnS and CdS. The photoluminescence spectra (PL) exhibit their optical properties.     

Metal-free indoline dye sensitized zinc oxide nanowires solar cell

Dye sensitized solar cell (DSSC) based on metal-free indoline dye D102 sensitized zinc oxide (ZnO) nanowires (NWs) derived from aqueous solution on seeded substrate was investigated. The morphology, composition and crystalline structure of the highly oriented ZnO NWs were characterized by field-emission scanning electron microscope, energy dispersive X-ray spectrum spectroscopy and X-ray diffraction, respectively. The chemical bond between D102 and ZnO NWs was confirmed by Fourier transfer infrared spectra. The photovoltaic property of DSSC was characterized at full sun intensity of 100 mW/cm² (AM 1.5) with short circuit current J_sc = 14.06 mA/cm² and energy conversion efficiency η = 2.6%.     

The effect of pH value on the synthesis and photocatalytic performance of MnWO4 nanostructure by hydrothermal method

In this study MnWO₄ nanocrystals with different morphologies were synthesised by a simple hydrothermal method with MnCl₂?·?4H₂O and Na₂WO₄?·?2H₂O as source materials. The products were characterised by X-ray powder diffraction, field-emission scanning electron microscopy, Raman spectroscopy and fluorescence spectroscopy. The results reveal that pH value plays an important role in the morphology and phase of samples. A simple reaction mechanism for the formation of MnWO₄ was presented. The photodegradation of acetone was employed as a probe reaction to test the photoactivities of the as-prepared samples.     

Improving the characteristics of CdS and CIAS films and the performances of CIAS solar cells by electrodeposition Cu–Se/CIAS binary structure precursors on FTO substrate

Cu-poor electrodeposited CuIn_1?xAl_xSe₂ (CIAS) precursor films were prepared to investigate the alteration in surface morphology of post-annealed CIAS films through post-annealing temperature adjustment. Scanning electron microscopy (SEM) and atomic force microscope (AFM) analyses demonstrated that surface morphology and root–mean–square (RMS) roughness of post-annealed CIAS films exhibited uneven and rough triangular structures. The crystal size of post-annealed CIAS films can be increased by increasing post-annealing temperature. The precursor film structure was modified by substituting Cu–Se/CIAS binary structure with CIAS single structure to proceed with the investigation. The apparent variation in surface morphology of post-annealed CIAS films changed from rough triangular structures to smooth round structures, and the RMS roughness of post-annealed CIAS films was reduced to <100 nm. The reduction was attributed to the formation of Cu–Se liquid phases during the post-annealing process, which enhanced elemental migration, recombination, and promotion of large grains and smooth surface formation. X-ray diffraction patterns showed three preferred growth orientations along the (112), (204/220), and (116/312) planes with chalcopyrite structures for all species. In addition, the characteristics of surface morphology, RMS roughness, and current measurement of subsequently deposited cadmium sulfide (CdS) film were studied and examined via SEM and AFM analyses. The surface morphology of CdS films deposited on binary structure post-annealed CIAS films exhibited smoothness, compactness, small RMS roughness, and large crystals with round and film-like structure. The AFM current images indicated that the distribution of leakage current paths was greatly diminished by changing the precursor film structure from CIAS single structure to Cu–Se/CIAS binary structure. The dark current–voltage characteristics of the CdS/CIAS heterojunctions showed that the reverse dark current density was decreased by approximately one order of magnitude from 4.02 × 10^?4 (single structure) to 4.26 × 10^?5 A/cm² (binary structure). Furthermore, the conversion efficiency of CIAS solar cells was enhanced from 0.52 (single structure) to 1.44 % (binary structure) with increase in V_oc and J_sc.     

Controlled synthesis and photoluminescence properties of hierarchical BaXO4 (X = Mo, W) nanostructures at room temperature

Controlled synthesis of hierarchical Barium molybdate (BaMoO₄) nanostructures with different morphologies, such as peanut-like, cube-like and flower-like, was successfully achieved in aqueous solution at room temperature. The obtained products were characterized by a scanning electron microscope (SEM) and an X-ray power diffractometer (XRD). The morphologies of the obtained products were found to be greatly dependent on reaction time, EDTA concentration and the [Ba²⁺]/[MoO₄²⁻] ratio. This controllable method could be readily extended to produce hierarchical Barium tungstate (BaWO₄) nanostructures with peanut-like, dumbbell-like, sphere-like and flower-like morphologies. The photoluminescence (PL) properties of the obtained BaMoO₄ and BaWO₄ nanostructures exhibited strong dependence on the morphologies and sizes, respectively.     

Preparation of ear-like, hexapod and dendritic PbS using cyclic microwave-assisted synthesis

Different morphologies of PbS were prepared using microwave-assisted synthesis of 1:4, 1:1 and 4:1 molar ratios of Pb(CH₃COO)₂ to NH₂CSNH₂ in propylene glycol. Cubic PbS was detected using X-ray diffraction (XRD) and selected area electron diffraction (SAED). Raman spectrometry revealed the presence of vibrations at 134, 274 and 430 cm^− 1. The product morphologies for different molar ratios of Pb(CH₃COO)₂ to NH₂CSNH₂ were also characterized using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The obtained morphologies changed with molar ratios used for the starting agents. The simulated diffraction pattern was also in accordance with the interpretation of the experimental results.     

Synthesis of tadpole-shaped Au nanoparticles using a Langmuir monolayer of fluorocarbon surfactant

Tadpole-shaped nanoplates, linearly arranged nanoparticles and triangular and hexagonal nanoplates were synthesized under a Langmuir monolayer of a cationic fluorocarbon surfactant, FC-4 (C₃F₇O(CF(CF₃)CF₂O)₂CF(CF₃)CONH(CH₂)₃N⁺(C₂H₅)₂CH₃I^?) through interfacial reduction of AuCl₄^? by formaldehyde gas. Reports about such tadpole-shaped nanoparticles are relatively scarce. The predominantly plate-like particles are mainly nearly perfect triangular and hexagonal nanocrystals, of micrometer scale in diameter. The Au nanoparticles are characterized using transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). The atomically flat planar surfaces of the Au nanoplates correspond to {111} planes and the lateral surfaces are {110} planes. The surface pressure strongly influences the formation of different Au nanostructures. A potential mechanism of such diverse morphologies is also discussed.     

Preparation and characterization of CdS–Bi2S3 nanocomposite thin film by successive ionic layer adsorption and reaction (SILAR) method

CdS, Bi₂S₃ and CdS–Bi₂S₃ nanocomposite thin films were grown by successive ionic layer adsorption and reaction method (SILAR) onto the glass substrates at room temperature. These films were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and electrical measurement systems. A comparative study was made between CdS, Bi₂S₃ and CdS–Bi₂S₃ nanocomposite thin films. The XRD patterns reveal that CdS, Bi₂S₃ and CdS–Bi₂S₃ nanocomposite thin film have hexagonal, orthorhombic and mixed phase of hexagonal CdS and orthorhombic Bi₂S₃ crystal structure, respectively. SEM images showed uniform deposition of the material over the entire glass substrate. The energy band gap for CdS, Bi₂S₃ and CdS–Bi₂S₃ thin films were revealed from the optical studies and were found to be 2.4, 1.6 and 1.69 eV, respectively. The thermoemf measurements of CdS–Bi₂S₃ nanocomposite thin film revealed n-type electrical conductivity, while the I–V measurement of CdS, Bi₂S₃ and CdS–Bi₂S₃ nanocomposite thin film under dark and illumination condition (100 mW/cm²) exhibited photoconductivity phenomena suggesting its applicability in photosensors devices.     

CdS annealing treatments in various atmospheres and effects on performances of CdTe/CdS solar cells

In this work, a systematic research on CdS annealing treatments under various atmospheres had been done to understand their effects on CdS/CdTe solar cells. CdS films were prepared by a standard CBD method and annealed under various atmospheres, including Ar, Ar+H₂, O₂, Ar+S and Ar+CdCl₂. Morphological, structural, optical and chemical properties were investigated using Atom force microscope (AFM), X-ray diffraction (XRD), UV–VIS spectroscopy and X-ray photoelectron spectroscopy (XPS). Annealing treatments enhanced modifications of morphology, structure and electrical properties of CdS films. AFM showed different surface morphologies and roughnesses of CdS films annealed under various atmospheres. XRD indicated the transition of CdS films from metastable cubic structure to stable hexagonal structure after annealing treatment, especially annealed in Ar+CdCl₂. From XPS analysis, Fermi levels of CdS films shifted closer to conduction band after annealing under O₂ and Ar+CdCl₂, while the levels shifted away from conduction band under Ar+H₂ and Ar+S. The relationships between those modifications by annealing treatments and effects on the performance of solar cells were discussed. Solar cell based on CdS annealed with Ar+CdCl₂ had the best performance due to the high n-doping of CdS layer introduced by annealing process.     

Solvothermal growth of single-crystal CdS nanowires

Cadmium sulfide (CdS) nanowires (NWs) were prepared by the solvothermal method using ethylenediamine as a solvent. Two sets of CdS NWs were synthesized at 160 and 200 °C for various reaction durations (3?5, 7, and 24 h). Scanning/tunneling electron microscopy was used to examine the surface morphology of the grown NWs. Their dimensions are found to depend on the reaction temperature and duration. The CdS NWs grown at 200 °C for all durations are longer than those prepared at 160 °C, with diameters ranging from 15 to 40 nm. A three-armed structure is exhibited by all the samples. The grown CdS NWs display a hexagonal wurtzite phase and grows along the \(\mathbf {\left \langle {001}\right \rangle }\) direction. The optical absorption of the grown NWs shows a sharp absorption edge with a blueshift, which indicates an expansion of the optical band gap. All prepared samples show two emission peaks in their photoluminescence spectra. The emission peak location depends on the reaction temperature and duration. The CdS NWs prepared at 160 °C show a sharp band–band emission compared with those prepared at 200 °C. Raman analysis indicates that the optical properties of the grown NWs are enhanced with increased temperature and reaction duration.     

Varied crystalline orientation of anatase TiO<Subscript>2</Subscript> nanotubes from [101] to [001] promoted by TiF<Subscript>6</Subscript><Superscript>2−</Superscript> ions and their enhanced photoelectrochemical performance

Herein, we report an ionic cross-linkage process of synthesizing [001] preferred oriented anatase TiO₂ nanowires and nanotubes hybrid structure (TWTs) based on anodization method wherein varied amounts of TiF₆ ^2? ions are added in synthetic process. We show how the TiF₆ ^2? ions switch the growth direction of TWTs from [101] to [001] (denoted as T₁₀₁WTs and T₀₀₁WTs, respectively) and change their geometrical morphologies, i.e., small ionic radii TiF₆ ^2? ions migrate and partly replace the TiO₆ ^2? octahedra under electric field, which separate out and leave vacancies during annealing process, resulting in a reconstruction of TiO₂. Importantly, absorption property and photoelectrochemical (PEC) performance of T₀₀₁WTs exceed those of T₁₀₁WTs. Furthermore, CdS QDs are assembled onto TWTs photoelectrodes by successive ionic layer adsorption and reaction technique. Likewise, T₀₀₁WT/CdS presents superior absorption capability and enhanced PEC performance to those of T₁₀₁WT/CdS. This could be attributed to their preponderances of improved light absorption capability and decreased electron recombination.