福建物构所等在团簇负载型MOF薄膜材料研究中获进展

正纳米团簇和金属有机框架(MOF)材料都是当前国际研究的热点,如何将两者在一个体系内复合发展新的功能材料是一个具有挑战性的课题。受限于MOF材料有限的窗口尺寸,与孔道尺寸匹配的纳米团簇分子均难以直接负载到MOF孔结构中。中国科学院福建物质结构研究所结构化学国家重点实验室研究员张健和张磊领导的无机合成化学团队     

四氧化三铁纳米团簇的表面修饰及生物毒性研究

采用微波辅助溶剂热法制备了四氧化三铁(Fe3O4)纳米团簇.为了改善团簇的稳定性,用改进的St(o)ber法,在Fe3O4团簇的表面包覆—层氧化硅(SiO2),成功制备出核-壳结构的Fe3O4@SiO2粒子.用透射电镜(TEM)、X射线衍射仪(XRD)、纳米粒度仪、Zeta电位、振动样品磁强计(VSM)、MTT比色法等测试手段,对样品的形貌、结构、粒径分布、胶体稳定性、磁学性质及生物毒性进行了研究,结果表明:所制备的Fe3O4纳米团簇平均尺寸约为60nm,尺寸均匀,在室温下表现出超顺磁性.包覆后的核-壳结构Fe3O4@SiO2粒子平均尺寸约为150 rn,具有良好的水分散性和胶体稳定性,包覆前后的样品均具有低的生物毒性.     

中介尺度Au纳米团簇凝固过程的分子动力学模拟

采用分子动力学模拟技术,研究了原子个数N=1088的Au纳米团簇的凝固过程的微观结构、热力学和动力学参数的变化.模型采用的是Johnson的EAM作用势.模拟结果表明:液态团簇在两种不同的冷速下冷却得到两种不同的固态组织:晶体团簇和非晶团簇.当冷速为1.5625×1013K/s时,能量随温度的变化呈线性关系,且偶分布函数的第二峰发生劈裂,体系形成非晶态;当冷速为1.5625×1012K/s时,能量-温度曲线上出现拐点,且偶分布函数显示明显的晶体峰特征,说明体系形成了晶体.另外,计算了不同冷速下原子的平均平方位移随温度的变化,发现原子位置的重排对冷却速度非常敏感.当冷速较快时,原子只在很小的范围内运动;而结晶过程是原子不断扩散重新排列的过程.     

Co掺杂ZnO薄膜的湿化学法制备及其光致发光光谱

采用湿化学法在Si衬底上生长了纳米棒结构的Co掺杂ZnO薄膜,并研究了掺杂浓度对生成样品结构和性能的影响.研究表明这种湿化学法成本低廉、收益高、重复性良好.样品的XRD结果表明掺杂的ZnO没有出现杂相.SEM结果表明掺杂样品是由ZnO纳米棒团簇结构组成,且团簇的密度随着Co掺杂浓度的增大而增大.薄膜的光致发光光谱结果表明Co掺杂导致薄膜的带隙发生红移,同时也证明了Co原子有效地进入了ZnO晶格.     

(TiO2)3n（n=1～4）纳米团簇的几何结构和电子性质研究

本文采用广义梯度近似(GGA)方法,对(TiO2)3及增长后的(TiO2)3n(n=1～4)纳米团簇进行了结构优化,计算并分析其几何结构、结合能、能级、态密度以及HOMO-LUMO的电子云密度分布。结果表明:随n增加,(TiO2)3n(n=1～4)纳米团簇结合能、HOMO轨道能量和态密度峰值逐渐增加。当团簇受到激发时,电子从HOMO轨道向LUMO轨道跃迁,同时,悬挂键以及连接键氧原子上的电子向Ti原子转移。     

微波辅助溶剂热法制备纳米Fe3O4团簇

采用微波辅助溶剂热法制备了纳米Fe3O4团簇,其中乙二醇和二甘醇作为反应溶剂和还原剂,乙酸钠和聚乙烯吡咯烷酮(PVP)作为表面活性剂和稳定剂.采用X射线衍射仪(XRD)、透射电镜(TEM)对样品的结构和形貌进行了表征,利用样品振动磁强计(VSM)对样品的磁学性能进行了表征.结果表明,微波加热2h和4h,获得的是尺寸为40 ～ 50 nm的纳米Fe3O4团簇,而在微波加热5 min的条件下,获得的是10 nm的Fe3O4纳米颗粒.所制备样品在室温下表现出超顺磁性.     

Cu薄膜生长过程的Monte Carlo模拟

用动力学晶格蒙特卡洛模型(Kinetic Lattice Monte Carlo,KLMC)模拟Cu薄膜的生长过程,讨论了基底温度、沉积原子数、单原子最大迁移步数和原子相互作用范围等参数对薄膜表面形貌的影响,并与实验结果进行了比较.结果表明:基底温度升高或沉积原子数增加时,沉积在基底上的原子逐步由众多各自独立的离散型分布向聚集状态过渡形成团簇,并且温度越低,团簇越趋于分散生长.当最大迁移步数减小或相互作用范围增大时,团簇亦趋于分散生长.     

扶手椅型石墨烯纳米带吸附镍、铜原子链的电子结构

采用基于密度泛函理论的第一性原理方法,研究了扶手椅型石墨烯纳米带吸附3d过渡金属磁性Ni和非磁性Cu单原子链的结构、电子性质和磁性.吸附体系经过弛豫后,不同宽度纳米带吸附单原子链的稳定结构是不同的.Ni比Cu原子链在石墨烯纳米带表面的吸附更为稳定.原子链吸附在纳米带的边缘洞位(即5AG-1、6AG-1和7AG-1位置)时较为稳定,且稳定程度随着纳米带宽度的增加而增加.原子链和石墨烯纳米带的相互作用使得Ni单原子链吸附体系的磁矩为零.Cu原子链吸附5AG-1的复合体系具有磁性.Ni原子链的吸附体系呈现出带隙较小的半导体性质,而Cu原子链的吸附体系全都表现出金属性质.     

粒子束注入单晶硅尺寸效应的机理研究

使用分子动力学方法研究硅粒子注入技术.系统比较分析了团簇粒子的包含反射,扩散和植入基底在内的全部运动过程,同时使用可视化方法观测记录基底表面形貌演化过程.所建立模型直观地显示了低注入能量域内的新特征.注入过程中,团簇粒子由不同粒径(数量)的硅原子组成.通过对粒径变化在注入过程的影响研究揭示了注入技术机理.仿真结果表明提出方法可用于定量预测注入粒子表面分布.本文工作可作为原子尺度下生成基底表面特征或设计图案的参考,并对可控表面沉积技术提供理论指导.     

(TiO_2)_n(n=3~8)团簇的几何结构和电子性质研究

采用广义梯度近似(GGA)方法,对(TiO2)n(n=3~8)团簇进行了结构优化,计算并分析了其几何结构,平均结合能,能级,态密度以及最高占据分子轨道-最低未占据分子轨道(HOMO-LUMO)的电子云密度分布。结果表明:随着n的增加,TiO2团簇(除了(TiO2)7团簇外)的平均结合能都在逐渐缓慢增加。(TiO2)n(n=4~8)团簇的HOMOLUMO能隙随n的增大而减小,而HOMO能量随n的增大而增加。(TiO2)n(n=3~8)团簇的HOMO的电子云主要集中在悬挂及连接的氧原子上,相反,LUMO上的电子云主要集中在钛原子以及少量部分氧原子上。     

Molecular dynamics study of the melting and crystallization of nanoparticles

Crystallography Reports - The size effects during the melting and crystallization of Lennard-Jones nanoparticles and metal clusters are investigated using two independently developed computer...     

The temperature dependent collective dynamics of liquid Rubidium

Liquids alkali metals show near the melting point at small momentum transfer values an upward bending of the dispersion relation. This so-called positive dispersion can be described within generalised hydrodynamics as a visco-elastic reaction of the liquid. There is a speculation that long-living clusters could be the physical reason behind this phenomenon. To shed light on this question a coherent inelastic neutron scattering experiment on liquid Rubidium was performed at four temperatures starting at the melting point. Distinct deviations from molecular dynamics simulation results occur at the lowest accessible momentum transfer values. With rising temperature the excitation frequencies soften at a momentum transfer value which is correlated with the dimensions of the supposed clusters.     

Formation of structure in small lead clusters under thermal effect

The thermal effect on lead clusters with radii up to 5.5 nm has been investigated by the molecular dynamics method using a modified tight-binding potential TB-SMA. The melting of Pb nanoparticles of these sizes is strictly homogeneous, without the formation of a surface liquidlike layer. The primary fcc phase in the particles is retained upon heating in the overwhelming majority of model experiments. An analysis of the structure formation during crystallization has shown that structures with pentagonal symmetry are preferred for lead clusters in this case. It is noted that an increase in the nanoparticle size leads to the dominance of the dodecahedral structure over the icosahedral one.     

Formation and stability criteria for amorphous Ge alloy films

Formation and stability of room-temperature deposited amorphous (a-) alloy films of Ge with Ag, Au, Cu, Ni, Fe, Ga, In, Sn, Sb, Ni, Bi and Nb have been studied, using differential thermal analysis and electron microscopy, as a function of various parameters such as: solubility of alloying element (in c-Ge), its melting point, atomic size and electonegativity. It has been shown that the composition range R, up to which amorphous alloy films are obtained, is affected by the solubility of the alloying element and its melting point. The effect of solubility S is dominant when S > 1 at%. However, for $\text{S ? 1}\text{at}\text{\%}$, the range is entirely governed by the melting point of the alloying element. Solubility and melting point have also been found to play a decisive role in stabilizing the amorphous phase of Ge. However, atomic size and electronegativity differences do not seem to play any important role in either the formation or stability of the amorphous phase.     

Electronic structure and properties of liquid caesium up to critical point by LMTO calculations

It is well-known that liquid caesium shows some unusual properties at low densities. We used supercell technique within linear muffin-tin orbital method to investigate this phenomenon. Electronic structure of liquid caesium for different temperatures from the melting point up to critical point was obtained. The atomic structure was simulated for a cluster of 2000 atoms by the Reatto method on the base of experimental structure factors of Cs obtained by Winter and co-workers for different temperatures (from 323 K up to 1923 K). The Kubo–Greenwood formula was applied for the calculations of melts conductivity. The received results indicate that metal–nonmetal transition in liquid cesium is connected not to the gap at Fermi energy in density of electronic states, but more likely with electrons localization on some kind of atomic clusters.     

The formation of tin oxides in thin-film Sn/C/KCl(100) structures

The formation of oxides upon the thermal annealing (both in air and vacuum) of island tin films grown on a KCl(100) substrate, which was coated by a thin layer of amorphous carbon, has been investigated by transmission electron microscopy. It is established that thermal annealing at temperatures below the tin melting point (T _m) does not lead to phase transitions with the formation of new crystalline oxide phases. At the same time, the films undergo structural changes: the average size of blocks in the substrate plane decreases compared to those in an as-deposited film. Thermal annealing in air at temperatures above the tin melting point leads to the formation of multiphase oxide structures and increases the average size of blocks and islands in the substrate plane. It is shown that preliminary thermal annealing in air at temperatures below T _m hinders oxidation upon subsequent heat treatment.     

The liquid state of large clusters with pairwise atomic interactions

Formation of the liquid state for clusters with a pair interaction between atoms is examined within the framework of the void model, in which configurational excitation of atoms results from formation of voids. Void parameters are found from computer simulation by molecular dynamics methods for Lennard-Jones clusters and from real thermodynamic parameters of the liquid states of condensed inert gases. Phase transitions are analyzed in terms of two aggregate states. This information allows us to divide the entropy jump during the solid-liquid phase transitions in two parts, so that one corresponds to configuration excitation at zero temperature, and the other is a contribution from thermal vibrations of atoms. The latter part contributes from approximately 40% for Lennard-Jones clusters consisting of 13 and 55 atoms up to 56% for bulk inert gases. These magnitudes explain the validity of melting criteria based on thermal motion of atoms, even though this phase transition results from configurational excitation of ensembles of bound atoms. It is shown that the void concept allows us to analyze various aspects of the liquid state of clusters including the existence of the freezing temperature below which no metastable liquid state exists, and the properties of glassy states which may exist below the freezing point.     

多孔TiC陶瓷的制备、性能及机理研究

以TiO2和炭黑为反应物,TiC为添加物,通过反应烧结法制备出多孔TiC陶瓷.研究了TiC的添加量对晶粒大小、孔径尺寸、开气孔率及抗弯强度的影响.研究结果表明:随着TiC的添加量从0;增大到100;,反应生成TiC的粒径从0.17μm增大到0.71μm,孔径尺寸从0.15μm增大到1.51μm,开气孔率从78;持续降到38;,抗弯强度先增加后减小,添加量为80;时最高(86 MPa).TiC生长机理主要是由于添加的TiC使TiO2周围的碳含量减少,从而导致反应生成TiC的熔点降低,扩散能力提高,晶粒粒径增大.     

Phase diagram calculation on Sn-Zn-Ga solders

Sn-Zn eutectic system is one of the most promising lead-free solders with the advantages of low melting points, excellent mechanical properties and acceptable costs, whereas its poor wetting ability confines its applications in many substrates. In this paper, gallium (Ga) was added to the Sn-Zn eutectic system in order to improve its melting properties and wetting abilities. Piecing binary phase diagram method was employed to calculate the uncharted Sn-Zn-Ga ternary phase diagram and the eutectic point of this ternary system. Differential scanning calorimeter (DSC) method was used to exam the melting point of the solder system. The SnZn6Ga solder has a melting point of 174.4 °C, with wetting rate of 48.9%, while the melting point of Sn-Zn alloy is 198.5 °C and melting rate is only about 20%. In addition, the method of piecing binary phase diagrams proves to be feasible to clarify certain unknown ternary phase systems.     

Effect of the temperature on the TMOS sono-hydrolysis and a study of the structure of the resulting aged sonogels

The effect of temperature on the oxalic acid catalyzed sono-hydrolysis of tetramethoxysilane (TMOS) was studied by means of a heat flux calorimetric method. The activation energy of the process was measured as (24.5 ± 0.8) kJ/mol in the temperature range between 10 and 50 °C. The structural characteristics of the resulting sonogels, after long period of aging in saturated conditions, were studied by means of small angle X-ray scattering. The structure can be described as formed by ∼2.7 nm mean size mass fractal-like aggregates (clusters) of primary silica particles of ∼0.3 nm mean size, all imbibed in a liquid phase. The average mass fractal dimension of the clusters was found to be 2.58. The primary particle density was estimated as 2.23 g/cm³, in good agreement with the value frequently quoted for fused silica. The volume fraction of the clusters in the saturated sonogels was estimated as about 28%. The moment in which the meniscus of the liquid phase penetrates into the clusters under rapid evaporation process has been detected by an inflection in the first derivative of the curve of weight loss in a simple thermogravimetric test.