Structural and dielectrical studies on mechano-chemically synthesized indium doped CdS nanopowders

Incorporation of indium (dopant) into CdS crystals have been successfully achieved by a mechanical alloying process. Powders are prepared with various In/Cd ratio from 1 to 10 at% and milled at 300 revolution per minute (rpm) for 60 min. X-ray diffraction (XRD) analysis of milled In doped CdS compound showed that the major phase of the product was wurtzite with grain sizes varying from 37 to 42 nm corresponding to change in In/Cd compositions. High resolution transmission electron microscopy (HRTEM) images as well as Fourier transformation in reciprocal space provide a good pathway to identify the structure of individual CdS nanocrystals, whose dominant phase was determined to be wurtzite structure along with zinc blende structure. Field emission scanning electron microscopy (FESEM) images reveal that CdS crystal prefers to grow along the (001) direction rather than (110) due to its high surface energy. The Raman spectra of CdS:In particles present well-resolved lines at approximately 303 and 600 cm⁻¹, corresponding to the first and second-order scatterings, respectively, of the longitudinal optical (LO) phonon mode. Dielectrical studies showed that dielectrical constant (ε′) decreased with increase in frequency, whereas AC conductivity (σ_AC) in In doped CdS increases with increase in frequency and also both the values increased with increase in doping concentration.     

Preparation of CdS doped carbon nanotubes and their electrochemical properties

A CdS doped carbon nanotube sol was synthesised by the sol-gel technique and applied to a titanium plate to synthesise a composite electrode. Energy dispersion X-ray spectroscopy and X-ray diffraction analysis confirmed that the electrodes contain CdS. Scanning electron microscopy revealed that the carbon nanotubes were uniformly dispersed on the surface of the plate. A two-chamber microbial fuel cell was constructed using the electrode as the anode, flexible graphite as the cathode and glucose solution as the substrate in the anode chamber. The effects of CdS dose, glucose concentration and temperature on the cell efficiency and organic degradation have been analysed. At 313 K, the two-chambered fuel cell possessed the optimum output voltage of 906 mV, with a power of 19·6 mW m^?2 and a removal rate of 81% for chemical oxygen demand in treatment of wastewater. The composite electrode was found to be stable and to perform reproducibly.     

复合结构纳米晶CdS：Cu/CdS的制备及光学特性

在非配位溶剂中合成了高质量的CdS纳米晶核,并利用Cu2+离子对其进行掺杂,制备了CdS:Cu纳米晶.通过进一步采用连续离子层吸附反应的方法对CdS:Cu纳米晶进行表面修饰,得到CdS:Cu/CdS复合结构纳米晶.利用X射线衍射(XRD),透射电镜(TEM),紫外可见吸收光谱(UV-Vis)和荧光光谱(PL)对其结构、形貌以及光学性质进行了表征和分析,结果表明:所制备的复合结构CdS:Cu/CdS纳米晶为立方闪锌矿结构;与CdS纳米晶核相比,掺杂Cu2+可以使其表面态发光发生红移;在CdS:Cu纳米晶中,通过改变掺杂Cu2+的浓度,可以实现表面态发光在570和620nm之间的连续调节.与未经包覆的CdS:Cu纳米晶相比,包覆层CdS增强了纳米晶CdS:Cu的稳定性.     

Influence of the Cd/S Molar Ratio on the Optical and Structural Properties of Nanocrystalline CdS Thin Films

Nanocrystalline CdS thin films have been deposited using precursors with different thiourea concentrationonto glass substrates by sol-gel spin coating method.The crystalline nature of the films has been observedto be strongly dependent on thiourea concentration and annealing temperature.The CdS films are found tobe nanocrystalline in nature with hexagonal structure.The grain size is found to be in the range of 7.6 to11.5 nm depending on the thiourea concentration and annealing temperature.The high resolution transmissionelectron microscopy (HRTEM) results of the CdS films prepared using cadmium to thiourea molar ratio of0.3:0.3 indicate the formation of nanocrystalline CdS with grain size of 5 nm.Fourier transform infrared (FTIR)analysis shows the absorption bands corresponding to Cd and S.The optical study carried out to determinethe band gap of the nanostructured CdS thin films shows a strong blue shift.The band gap energy has beenobserved to lie in the range of 3.97 to 3.62 eV following closely the quantum confinement dependence ofenergy on crystallite radius.The dependence of band gap of the CdS films on the annealing temperature andthiourea concentration has also been studied.The photoluminescence (PL) spectra display two main emissionpeaks corresponding to the blue and green emissions of CdS.     

Preparation and characterization of hydroxyapatite synthesized from oyster shell powders

The ready availability and the low cost of oyster shells, which is composed predominantly of calcium carbonate with rare impurities, along with natural wastes are attractive features for converting the biological material into hydroxyapatite (HA) powders for biomedical applications. The HA powder was synthesized using oyster shell powders and dicalcium phosphate dihydrate (CaHPO₄·2H₂O, DCPD) through ball milling and subsequently heat treatment. The HA was initiated through sintering the 1-h milled sample at 1000 °C for 1 h, while pure HA phase is formed after sintering the 10-h milled sample. The as-prepared samples, obtained after 5 or 10 h of milling and then heat-treating at 1000 °C for 1 h, contain the phase of β-tricalcium phosphate (β-TCP). Moreover, the result of FTIR analysis showed that the as-prepared HA sample is A- and B-type carbonate-containing calcium phosphates. The as-synthesize HA powder containing trace elements Mg and Sr exhibited good crystallinity (96.3%) and high phase-purity.     

Structural and optical properties of CdS thin films grown by chemical bath deposition

Cubic cadmium sulphide (CdS) thin films with (111) preferential orientation were prepared by chemical bath deposition (CBD) technique, using the reaction between NH₄OH, CdSO₄ and CS(NH₂)₂. The films properties have been investigated as a function of bath temperature and deposition time. Structural properties of the obtained films were studied by X-ray diffraction analysis. The structural parameters such as crystallite size have been evaluated. The transmission spectra, recorded in the UV visible range reveal a relatively high transmission coefficient (70%) in the obtained films. The transmittance data analysis indicates that the optical band gap is closely related to the deposition conditions, a direct band gap ranging from 2.0 eV to 2.34 eV was deduced. The electrical characterization shows that CdS films' dark conductivities can be controlled either by the deposition time or the bath temperature.     

Structural and optical characterization of Ni-doped CdS quantum dots

Ni-doped CdS quantum dots have been prepared by chemical precipitation technique. The X-diffraction results indicated that the particle size of Ni-doped CdS nanoparticles is smaller than that of undoped CdS and no secondary phase was observed. The average grain size of the nanoparticles is found to lie in the range of 2.7–4 nm. The compositional analysis results show that Cd, Ni, and S are present in the samples. HRTEM studies reveal that the average particle size of undoped and Ni-doped CdS quantum dots is 2 and 3 nm, respectively. Raman spectra shows that 1LO, 2LO, and 3LO peaks of the Ni-doped CdS samples are slightly red shifted when compared to that of undoped CdS. The absorption edge of Ni-doped CdS nanoparticles is found to shift towards the higher-wavelength (red shift) side when compared to that of undoped CdS and the band gap is observed to lie in the range of 3.79–3.95 eV. This band gap is higher than that of the bulk CdS and is due to quantum confinement effect present in CdS nanoparticles.     

Nature and density of lattice defects in ball milled nanostructured copper

Copper powder of 99.9% purity with particle size in the micrometer range was subjected to high energy ball milling by milling times between 2 and 24 h applying stearic acid as surfactant. The nature and density of lattice defects were determined using differential scanning calorimetry (DSC) and X-ray line profile analysis (XPA). The DSC measurements exhibit a considerable drop of the total stored energy with increasing ball milling time indicating a surprising decrease of lattice defect concentrations by more than one order of magnitude. The results from XPA, however, show that neither the dislocation density, nor the crystallite size can account for this behavior. Rather it is to be attributed to a high concentration of deformation induced vacancy type defects, with their density gradually decreasing during ongoing milling.     

Sintering of copper nanopowders under hydrogen: an in situ X-ray diffraction analysis

The reduction by hydrogen gas of the cuprite layer on copper nanocrystals and the subsequent sintering of the nano-particles were studied using in-situ X-ray diffraction and dilatometry. Spherical nanocrystals produced by evaporation and condensation have an average size of 35 nm, exhibiting a large surface curvature. Each nanoparticle is coated with a 3.5 nm layer of Cu₂O, which is rough and disordered, as revealed by high-resolution electron microscopy. Reduction by hydrogen of this curved cuprite layer occurs at 363 K, which is ≈65 K lower than is observed on a layer supported by micrometer-sized or bulk copper with a flat surface. The reduction process and its effect on the sintering of nanopowders are analysed and discussed.     

Preparation of lanthanide doped CdS, ZnS quantum dots in natural polysaccharide template and their optical properties

Employing a biomimic method using polysaccharide as template, luminescent lanthanide ions doped CdS and ZnS quantum dots (QDs) were prepared. According to the results of TEM and absorbance, nanocrystals with an average size of 6 nm were formed under mild condition without any toxic and expensive agent applied. Differentiating from the un-doped CdS and ZnS QDs prepared in polysaccharide template, the lanthanide doped QDs exhibited obvious dopant emission in their photoluminescence spectrum. It was also found that the dopant PL became more prominent with increasing lanthanide doping concentration, while the highest PL intensity was obtained at a doping level of 1% for both of CdS and ZnS QDs. When different lanthanide ions were introduced into the CdS QDs in polysaccharide template, varied emission wavelength were able to be obtained. This study provides an easy, mild and environmental friendly alternative method to prepare doped quantum dots. In addition, the bioactivity and processabilities endowed by the polysaccharide template may expand the applications potential of this type of optical materials.     

The copper influence on the PL spectra of CdTe thin film as a component of the CdS/CdTe heterojunction

The influence of annealing in the presence of CdCl₂ and a thin copper layer deposited onto CdTe on the photoluminescence spectra of CdTe, as a component of CdS/CdTe heterojunction, has been studied for two excitation wavelengths: 0.337 μm and 0.6328 μm. The behavior of the PL was studied as a function of the measurement temperature and excitation intensity. At 0.6328 μm excitation, the interface PL consists of a known 1.43X band, and the chloride annealing enhances radiative transitions at 1.536 eV. The intensity of the 1.536 eV transitions increases when Cu is present. The PL of as-deposited CdTe films prepared in the presence of oxygen has the 1.45X band attenuated when excited with 0.337 μm excitation wavelength.     

原位表面修饰纳米CdS粒子的表面结构和光学性能

采用微乳液法合成了纳米尺度硫化镉粒子,并用硫醇和咪唑对粒子进行了原位表面修饰.对纳米硫化镉粒子的形貌与表面结构进行了表征,证实了表面修饰剂与粒子间的键合.电镜观察和紫外-可见吸收光谱的测定发现,表面修饰明显地提高了纳米粒子在溶剂中的分散性,改变了纳米粒子的表面结构,消除了粒子表面导致无辐射弛豫的缺陷,因而提高了纳米粒子分散于溶剂体系的荧光性能.修饰剂与溶剂间的相互作用决定了表面修饰粒子在溶剂中的分散性,对纳米粒子的光学性能也有一定的影响.     

功能化CdS纳米晶的合成及CdS/聚苯乙烯纳米杂化材料的研究

以氯化镉和硫化钠为原料,采用巯基乙醇为有机配体,在H2O/DMF的溶剂中,制得分散均匀且表面富含羟基基团CdS纳米晶溶液.我们使用γ-甲基丙烯氧丙基三甲氧基硅烷(MPS)来修饰CdS纳米晶的表面,得到双键官能团化的CdS纳米晶.通过原位自由基聚合方法,成功地得到了聚苯乙烯基CdS纳米晶复合材料.利用傅里叶红外光谱仪(FT-IR)、透射电子显微镜(TEM)、紫外-可见光吸收光谱仪(UV-vis)、X射线衍射分析仪(XRD)、热重分析仪(TGA)、荧光光谱 (PL) 考察了CdS纳米晶及CdS/聚苯乙烯复合材料的结构和光学性能的关系规律.结果表明巯基乙醇表现出良好的光学性能,其配体不是简单的物理吸附于纳米晶表面,而是以化学键的形式和纳米晶表面镉原子相结合.相比于纯的聚苯乙烯材料,聚苯乙烯基CdS纳米晶材料表现出良好的光学和热学性能.     

Field emission and photo-catalytic investigations on hierarchical nanostructures of copper doped CdS synthesized by kitchen-chemistry approach

We herein report an economical and facile technique for the synthesis of hierarchical nanostructures of Cu doped CdS nanostructures by microwave assisted solvothermal technique using a household microwave oven. We attempted to establish the effect of variation of solvents ratio on the morphological and optical properties of the obtained nanoscale structures. The field emission characteristics of the copper doped CdS nanoarchitecture have been studied and the turn on field is found to be 2.8 V/microm for an emission current density of approximately 0.1 microA/cm2. Emission current stability is determined at the preset current of approximately 1 microA and approximately 10 microA for the stable duration of approximately 4 hrs. The observed field emission results envisage the possibility of using the present emitter in the field emission sources. We believe that this is a unique report on the synthesis as well as field emission studies of copper doped CdS nanostructures. Photocatalytic dye degradation ability of the Cu doped CdS nanostructures is observed to be less than the undoped CdS counterparts.     

纳米氟硼酸钾粉末的制备及表征

探讨了高能球磨法制备纳米KBF4粉末的工艺过程及影响因素.通过选择合适的球磨工艺及表面活性剂,以普通KBF4粉末为原料成功制备出粉末的粒度均径为81.2nm、比表面积为28.26m2/g的纳米级KBF4粉末.分别采用BET比表面积测试法、X射线小角度散射法(SAXS)及扫描电镜对纳米KBF4粉末进行了表征.     

Structural and optical characterization of potassium doped zinc oxide nanosheets

This paper presents the synthesis of potassium (K) doped zinc oxide nano sheets at room temperature by wet chemical method. The structure and morphology of the crystals prepared for different molar concentrations of K were analysed by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Lattice strain and grain size were calculated from the Williamson–Hall (WH) Plot and Debye–Scherrer’s formula for different concentrations of potassium. Absorption studies reveal that absorption is minimum in the visible region and band gap energy is found to decrease with increase in K concentration. The photoluminescence (PL) spectra were used to study the luminescence behavior and the nature of defects in the samples and the overall emission is white for all the samples except the one prepared with 1.2 M potassium doping.     

Influence of Au Photodeposition and Doping in CdS Nanorods: Optical and Photocatalytic Study

Au-modified CdS nanorods (100–200 nm × 5–10 nm) are synthesized via two different techniques, namely photodeposition and doping. The prepared samples are characterized by x-ray powder diffraction, transmission electron microscopy (TEM), and UV–vis and fluorescence spectroscopy. X-ray diffraction study confirmed the hexagonal phase of bare and Au-CdS samples, whereas, 5 wt% Au³⁺ doping into CdS resulted in a slight distortion in the crystal structure toward higher degree side. TEM images revealed the fine distribution of Au nanodeposits of size in the range of 2.5–4.5 nm on to the CdS surface in the photodeposited sample. The optical spectrum shows a significant red-shift in absorption onset (485 nm → 515 nm) and band-edge emission (505 nm → 512 nm) of CdS nanorods with the replacement of certain Cd²⁺ ions with Au³⁺. The influence of Au photodeposition and doping in CdS nanorods was comparatively tested by photooxidation of RhB (50 ppm) dye aqueous solution under direct sunlight irradiation (35–40 mWcm^?2). Our results point out that 5 wt% Au³⁺ doping into CdS nanorods remarkably improved its activity and stability due to homogeneous dispersion of charge throughout the crystal, quick Fermi level equilibration, and an improvement in ionic bond formation.     

Crystallite size reduction of Cr doped Al2O3 materials via optimized high-energy ball milling method

α-Al₂O₃ based compounds have large crystals and it is very difficult to reduce the crystallite size because they are very stable and hard. One way of reducing the crystallite size of the materials is by using high-energy ball milling method. Pure and single-phase micron-sized α-Al_2−xCr_xO₃ (x = 0.1, 0.2, 0.3) materials were successfully obtained via self-propagating combustion method. These materials were then subjected to a simple milling process from their microcrystalline powders. Comparisons between the micron-sized and milled samples in terms of their phase, structure, morphology and crystallite size were discussed. The XRD results reveal that all the milled samples were pure with no impurity or other phases present. Structural parameters are extracted via the Rietveld method, revealing that the cell constant, a, of the milled samples is higher than that of the micron-sized materials by 0.09 % to 0.11 %, resulting in a 0.28 % to 0.39 % increase in cell volume. FESEM results show a gradual decrease in crystallite size with increased milling time. Notably, the method successfully reduces the crystallite size without changing the phase of the materials and preserving the stoichiometry of the Al_2−xCr_xO₃ materials which may offer improved properties in various applications.