Computer Simulation and X-ray Diffraction of Nanocrystals

X-ray diffraction of structure in nanocrystalline alpha -Fe and Cu was studied by atomistic simulation. Atomic position equilibrium was reached by using molecular dynamics method to simulate nanocrystalline structure with Finnis potentials to model interatomic interactions. It was found that the boundary component exhibits short-range order, and the distortion in crystalline component increases with the decrease of grain size.     

纳米材料结构与性能的计算机模拟研究

先进的理论和计算技术结合计算机的威力，提供了在原子层次上了解纳米材料及其演化过程细节的可能性，具有无先例的准确性，使纳米材料设计和性能预测成为可能。本文首先概送了计算机模拟的理论方法和作用，扼要地综述了计算机模拟在纳米材料的微观结构、力学、热学、电磁学等性能的研究进展，最后阐述了纳米材料结构和性能的计算机模拟研究所面临的问题。     

Computer Experiment on Deformation of Nanocrystals of the Chromium-Niobium System. Part 2. Mechanical Properties

Molecular-dynamic simulation of the process of stretching of chromium and niobium nanocrystals and chromium-niobium bicrystals was performed to a pair-potential approximation. The authors obtained and analyzed the dependences of the potential energy, the number of pair interactions, work of deformation, stress, reduction in the cross-sectional area, and Poissons ratio on the strain with various orientations of nanocrystals with respect to the tensile force. They calculated the characteristics of elasticity, yielding, and strength of nanocrystals.__________Translated from Problemy Prochnosti, No. 2, pp. 5 – 18, March – April, 2005     

钨酸钙纳米晶的制备及性能

以钨酸钠和硝酸钙为原料,加以表面活性剂聚乙二醇200,配制出钨酸钙混浊液,将得到的沉淀物在100 ℃烘干后,制备出钨酸钙纳米晶.对样品进行了XRD分析、红外光谱分析及TEM观察.结果表明,制备的钨酸钙样品结晶良好,纳米晶颗粒间分散性良好,无团聚;在钨酸钙纳米晶的形成过程中,聚乙二醇200对钨酸钙纳米晶颗粒间的分散起着决定性作用;在265 nm波长光的激发下,钨酸钙的光致发光谱中显示一宽化的蓝色发光带.     

On Structure and Thermodynamics of Coherent Nanocrystals

Several classifications for the nanocrystalline morphologies are introduced. It is demonstrated that coherency and coherence strain are important physical quantities, which influence the stability, the morphology and the grain size of nanocrystalline domains. Examples for different nanocrystalline textures are reported     

Computer Simulation of the Structure of Disperse Systems by the Particle Method

A computer simulation model of the internal structure of disperse systems, based on the particle method, is suggested. Numerical studies of these structures are carried out with use of the developed model.     

Facet-Dependent Photocatalytic Properties of AgBr Nanocrystals

Polyhedral AgBr nanocrystals, evolved from cubes through truncated cubes and finally to high-symmetry octahedra, which corresponds to a progressive shrinkage of exposed {100} facets and enlargement of exposed {111} facets, are prepared by facile precipitation reactions. The as- prepared AgBr nanocrystals exhibit facet-dependent catalytic properties, with the {111}-dominated octahedra showing the highest photocatalytic activities.     

铸件凝固过程组织计算机模拟研究动态

介绍了铸件凝固组织模拟的3种方法,并对利用各种数值方法所取得的计算机模拟结果进行了评述.重点介绍了各模型的形核和生长的数学模型,同时也分析了这些数学模型所存在的问题.展望了铸件凝固组织模拟的发展方向.     

石墨镶嵌Co纳米晶的形成及其特性

用直流碳弧法在阳极石墨棒中加入金属Ｃｏ产生石墨镶嵌Ｃｏ纳米晶,研究在复合石墨棒中加入不同的Ｃｏ含量对石墨镶嵌Ｃｏ纳米晶的形貌、结构特性及晶粒尺寸分布的影响,探讨石墨镶嵌Ｃｏ纳米晶的形成原因及碳弧法中氦气压力和Ｃｏ含量对掺Ｃｏ阳极石墨棒所产生的碳灰的Ｃ６０／７０产率的影响。结果表明,复合阳极棒中的Ｃｏ含量决定了石墨镶嵌Ｃｏ纳米晶的数量和晶凿直径分布,碳弧法中的Ｈｅ气压力仍是影响掺Ｃｏ阳极棒所产生的碳     

计算机模拟对嵌段共聚物胶束结构的优化设计

胶束对疏水性药物的增溶作用与药物和载体材料的相容性密切相关,本文通过热力学方法判断二者的相容性。以布洛芬作为模型药物,采用Materials Studio模拟软件计算一系列疏水链段与布洛芬的混合能Emix及混合自由能ΔGmix,筛选适合布洛芬的胶束疏水链段。结果显示布洛芬与聚丙烯、聚氧丙烯等疏水链段的混合自由能为正值,与聚乳酸/乙醇酸的的混合自由能为负值,根据混合自由能原理,文中所选的嵌段共聚物胶束的疏水链段中,聚乳酸/乙醇酸与布洛芬的相容性最好。     

针状纳米CuO的制备及其催化性能研究

研究了水热反应条件对纳米CuO结构和形貌的影响.采用XRD、FTIR、TEM等测试手段对产物进行了表征,并用热分析法考察了不同粒径纳米CuO对高氯酸铵(AP)分解的催化作用.结果表明通过调节反应物浓度可以控制针状CuO直径在8～15nm,通过控制反应温度和反应时间可以得到CuO和Cu2O两种产物.不同粒径的纳米CuO均能强烈催化AP的分解,其中8nm的针状纳米CuO催化活性最强,可使AP高温分解峰降低93.64℃,分解放热量由590.12J/g增至1390J/g.     

Morphology and Structure of BN and B4C Nanocrystals

The morphology and structure of BN and B₄C nanocrystals in thin layers produced on Si substrates by plasma-enhanced chemical vapor deposition from triethylamineborane were studied before and after exposure to synchrotron radiation. The as-deposited layers consisted of two types of nanocrystals differing in shape, which all had a defect diamond-like structure. After irradiation, two types of nanocrystals were also observed, but the layers consisted of cubic BN, hexagonal BN, and rhombohedral B₄C with lattice parameters differing from those of bulk materials. These results were interpreted as evidence that the irradiated layers contained centaurs—intergrowths of different structures with coherent interfaces.     

物体面形对结构光场的空间调制：计算机模拟

提出一个实现三维面形对结构光场的空间调制的计算机仿真系统。重点讨论仿真系统的基本原理、投影光场与观察光场和三维面形的几何关系、该系统的实现方案。本文还给出了在一定系统参数条件下，几种特殊三维面形对空间结构光场调制的实验结果。     

溶剂热制备花状ZnO纳米晶及光性能表征

利用溶剂热法,以乙酸锌（Zn（CH3COO）2·2H2O）和氢氧化钠（NaOH）为源,在乙二醇和水的混合溶剂中制备出了花状氧化锌纳米晶体,用X射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）和选区电子衍射（SAED）测试分析,发现样品为六方纤锌矿结构的ZnO单晶,花状晶体的大小约为600nm,单个花瓣的长、宽分别约为300nm、100nm。对比实验发现,产物形貌对NaOH浓度的依赖性很大。紫外可见吸收光谱（UV—vis spectra）显示,产物除了本征吸收外,在长波方向（600nm处）也有一宽化的、较强的吸收峰。室温荧光光谱（PL spectra）显示,产物在400—480nm有一明显的发光带,且在405nm和472nm处有两个较强的发光峰。     

Finite-Size Effect on Band Structure and Photoluminescence of Semiconductor Nanocrystals

Based on a model for size-dependent atomic cohesive energy of nanocrystals, a simple and unified model, without any adjustable parameter, has been established for finite size effect on shifts of valence and conduction band edges [DeltaE_V(D) and DeltaE_C(D)], and bandgap expansion [DeltaE_G(D)| of semiconductor nanocrystals, where Delta denotes the expansion and D is the size of nanocrystals. In the light of this model, DeltaE_V(D), DeltaE_C(D), and DeltaE_G(D) functions increase with dropping D in comparison with the corresponding bulk counterparts. The available experimental results of Si, CdS, ZnSe, and ZnTe nanocrystals confirm the validity of model.     

不同pH值下纳米纤维素晶体悬浮液的流变性能研究

研究不同pH值下的棒状纳米纤维素晶体悬浮液体系的细微结构变化与流变行为的关系,探讨了pH调节剂的加入所引起的体系结构变化的机理,并采用线性的流变学方法研究了各体系流动性、蠕变性以及频率响应性等动态粘弹性质,分别利用Power-Law模型、Burger模型对体系的流动曲线、蠕变曲线进行了数据拟合,研究发现,pH=2的悬浮液体系具有典型的液晶结构,呈现三段式＂S＂型流动曲线;随着pH值的增加,体系逐渐形成凝胶结构且凝胶强度越来越强,＂S＂型流动曲线逐渐模糊,蠕变的弹性柔量逐渐增大,粘性柔量逐渐减小,而pH〉9后出现蠕变弹性恢复,体系储能模量G′和损耗模量G″均有明显增加,但损耗角正切tanδ值先减小然后增大,pH=7体系内耗最小。     

Facet‐Dependent Optical Properties of Semiconductor Nanocrystals

Recent observations of facet‐dependent electrical conductivity and photocatalytic activity of various semiconductor crystals are presented. Then, the discovery of facet‐dependent surface plasmon resonance absorption of metal–Cu₂O core–shell nanocrystals with tunable sizes and shapes is discussed. The Cu₂O shells also exhibit a facet‐specific optical absorption feature. The facet‐dependent electrical conductivity, photocatalytic activity, and optical properties are related phenomena, resulting from the presence of an ultrathin surface layer with different band structures and thus varying degrees of band bending for the {100}, {110}, and {111} faces of Cu₂O to absorb light of somewhat different wavelengths. Recently, it is shown that the light absorption and photoluminescence properties of pure Cu₂O cubes, octahedra, and rhombic dodecahedra also display size and facet effects because of their tunable band gaps. A modified band diagram of Cu₂O can be constructed to incorporate these optical effects. Literature also provides examples of facet‐dependent optical behaviors of semiconductor nanostructures, indicating that optical properties of nanoscale semiconductor materials are intrinsically facet‐dependent. Some applications of semiconductor optical size and facet effects are considered.     

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.