Manipulation of the Morphology of CdSe Nanostructures: The Effect of Si

The morphological manipulation, structural characterization, and photoluminescence properties of different CdSe nanocrystals are reported. Several different CdSe structures, including nanowires, nanorods, nanoparticles, and tetrapod crystals, have been grown on silicon substrates by means of simple, Si‐assisted chemical vapor deposition. By manipulating the growth driving force (i.e., the degree of supersaturation), the morphology of the CdSe nanocrystals can be varied sequentially from nanowires/nanorods to nanoparticles to tetrapod structures. The optical properties of the CdSe nanocrystals are investigated using photoluminescence spectroscopy. Some thermodynamic models are proposed to explain the results.     

用N2O-C2H2火焰原子吸收光谱法测定电解液中锂

简述运用N2O-C2H2火焰原子吸收光谱法进行镉镍电池电解液中锂含量的测定，并介绍了锂最佳测定条件及呈良好线性范围的浓度。同时对样品的干扰因素、消化处理条件，在综合分析的基础上提出了有效的测定方案。该测定方法灵敏度好，准确度与精密度均能满足镉镍电池研制工作的要求。测定样品锂含量相对标准偏差均小于1．0％（测定次数n=10），标准加入回收率均在97．0％，100．0％（n=6）范围内，达到了实验室分析质量与质量控制的要求，适用于电解液中锂含量的控制分析和样品系统分析。     

Multi-component adsorption of Ag(I), Cd(II) and Cu(II) by natural carbonaceous materials

Adsorption of silver, cadmium and copper from aqueous solutions by natural carbonaceous materials was investigated. The studied series of natural materials (spruce wood, pine bark, cork, peat, fusinite, lignite, oxidised lignite, bituminous coal and anthracite) was extended to include industrial carbon-rich materials: coke, activated carbon F-400 and Multisorb 100. Adsorption was tested on a single-component system and on the binary and ternary mixtures. All the materials used differ in their ability to adsorb selected metals. The adsorption of metals is significantly affected by the presence of other ions in solution. Total metal uptake was considerably higher in a mixture than single-ion adsorption. Chemical reactions, such as precipitation and reduction of metallic silver, play a role in metal uptake by bituminous coal, coke and activated carbon.     

Doping behavior of iodine in Hg0.8Cd0.2Te+

Iodine doped single crystal samples of Hg_0.8Cd_0.2Te were annealed at temperatures varying from 450 to 600°C in Hg vapor and quenched to room temperature. Hall effect measurements at 77 K on the crystals cooled to room temperature indicate the samples to be n-type after anneals at high Hg pressures whereas they turn p-type after anneals at low Hg pressures; the electron concentration increases with increase in Hg pressure. The results are explained on the basis that the crystals are saturated with (Hg,Cd)I₂, with the iodine being present as donors occupying tellurium lattice sites (I_Te) and a fraction being present as (I_TeV_Hg)’ species formed from the iodine on tellurium lattice sites (I_Te) pairing with the doubly ionized native acceptor defects (V^Hg/11). The solubility of the I_Te species increases with increase in Hg pressure, whereas that of the (I_TeV_Hg)’ species increases with decrease in Hg This work was supported by NASA under contract NAS8-33245 pressure. Equilibrium constants for the incorporation of the iodine species as well as the pairing reaction have been established     

Effect of formate and methanol on photoreduction/removal of toxic cadmium ions using TiO2 semiconductor as photocatalyst

Photoreduction/removal of cadmium was studied at pH 7 using TiO₂ Degussa as photocatalyst, and either formate or methanol as hole scavengers. In the absence of organic additives, approximately 60% of cadmium was found to be removed from the solution by adsorption. Addition of formate resulted in the photoreduction of cadmium to its metallic form. No cadmium reduction was observed when methanol was added as the hole scavenger. Zeta potential measurements of the catalyst suspensions and studies on the extent of organic additive adsorption and mineralisation were used to prove the photoreduction process. It was found that the adsorption of both cadmium and the organic hole scavenger is crucial for the photoreduction of cadmium. It is postulated that to be an effective hole scavenger the organic additive needs to be easily photooxidised under an anoxic environment. In addition, the presence of formate radicals could be responsible for the Cd photoreduction.     

The formation of different phases of CuxTe and their effects on CdTe/CdS solar cells

Material studies and device applications of Cu_xTe in an NREL-developed CdTe solar cell structured as glass/Cd₂SnO₄/ZnSnO_x/CdS/CdTe are presented. The Cu_xTe primary back contact was formed by evaporating a Cu layer with various thicknesses at room temperature on HNO₃/H₃PO₄ (NP) solution etched CdTe layer. A post-annealing was then followed. The structural evolution and electrical properties of Cu_xTe were investigated. Cu/Te ratio and post-annealing temperature are two processing parameters in this study. The Cu_xTe phases are mainly controlled by the Cu/Te ratio. After a post-annealing at a low temperature, such as 100 °C, no Cu_xTe phase transformation from its as-deposited phase was observed. A post-annealing treatment at a higher temperature, such as 250 °C, can reveal the stoichiometric Cu_xTe phases based on the Cu/Te ratio used in the devices. But a post-annealing at a further higher temperature, such as 400 °C, resulted in a complicated Cu_xTe phase appearance. CuTe, Cu_1.4Te, and Cu₂Te are three major phases detected by X-ray diffraction (XRD) for different Cu thickness application annealed at 250 °C. Application of Cu thicker than 60 nm degrades open-circuit voltage (V_oc) and shunting resistance (R_sh), but increases series resistance (R_s). The correlation between device performance and the Cu_xTe back contact illustrates that the process used for forming the Cu₂Te back contact failed to produce good fill factor (FF) and also introduced higher barrier height. The best device was observed for a back contact with a mixed Cu_1.4Te and CuTe phases.     

Effects of CdCl2 treatment on the properties of CdS films prepared by r.f. magnetron sputtering

Effects of the thickness of CdCl₂ layer and the annealing on structural and optical properties of sputter-deposited CdS films were investigated. The annealing process of evaporated CdCl₂ was carried out by heating the sample in air at 350-500 °C for 20 min. As the thickness of the CdCl₂ increases, the (002) peak of CdS becomes weak and the other peaks of CdS increases. Especially, for 200 nm CdCl₂, the preferential orientation of the (002) plane disappears and the c-axis of the CdS film tends to orient parallel to the substrate. As the CdCl₂ layer is thicker, the grains are enlarged significantly. The improvement of optical properties of CdS films with thicker CdCl₂ layer might be successfully employed in achieving better conversion efficiencies in solar cells.     

杂交苏丹草镉的吸收与分布规律研究

随着土壤中添加镉量的增加,杂交苏丹草的株高明显降低,生物量显著下降。镉添加量为40mg kg土的处理,杂交苏丹草株高和地上部的生物量分别只有对照的48%和8.4%。不加镉的对照,杂交苏丹草根、茎、叶的含镉量分别为3.2,2.7,3.2μg g-1,各部位含镉量没有显著差异;而在添加镉的土壤中,则呈现出根>茎>叶的变化规律;土壤添加镉的量越大,杂交苏丹草各部位含镉量越高,当镉添加量为40mg kg-1土时,根、茎、叶的含镉量分别为451.9,132.5,79.4μg g-1。杂交苏丹草植株中镉含量与土壤中镉的添加量呈现为显著的直线正相关,镉的累积量呈现为先上升后下降的规律。