金属纳米结构材料

<正>金属纳米结构材料是指基本结构特征尺度在纳米量级(小于100纳米)的单相或多相金属材料,如纳米晶体材料(晶粒尺寸三维均在纳米尺度)、纳米孪晶材料(孪晶-基体层片厚度在纳米尺度)、纳米层状结构(二维层片结构厚度在纳米尺度)、梯度纳米结构(晶粒尺寸从纳米尺度梯度变化到宏观尺度)及混合纳米结构     

［111］晶向银纳米杆结构稳定性的分子动力学模拟

采用分子动力学模拟方法,以超细［111］晶向银纳米杆为研究对象,基于Finnis-Sinclair型多体势,模拟研究了纳米杆在不同温度弛豫过程中的动态平衡变化过程,分析研究了弛豫后银纳米杆的稳态结构变化、平均势能的变化及其在不同时刻结构的演变过程。结果表明温度对［111］晶向银纳米杆结构稳定性将产生重大影响,［111］晶向银纳米杆存在一临界失稳温度,当温度小于临界失稳温度时,体系保持完好线状晶态,当温度大于临界失稳温度小于熔点时,体系坍塌熔化后发生重结晶,截面面积增大,长度明显缩短,随温度增加此特征更加显著,接近熔点时,体系形成由(111)和(100)面围成的多面体且势能最低;当温度大于熔点时,体系变成高度无序的球状团簇。     

银纳米片的可控光诱导化学合成及其表征

以LED灯作为光源,采用光诱导法成功制备了高产率的银纳米片,运用紫外可见光谱(UV-vis)跟踪银纳米片制备液的吸光度,采用扫描电子显微镜(SEM)和透射电子显微镜(TEM)对产物的形貌与结构进行表征,并探究了光照强度、柠檬酸钠用量和过氧化氢用量对银纳米片形貌及产率的影响.结果表明:适当增加光照强度是提高银纳米片的产率和保持其尺寸均一性的关键;柠檬酸钠能促进银纳米片的生成,但用量过多反而不利于制备均匀的银纳米片;过氧化氢的适量加入能使银纳米片更加均匀,但过量时产物中易出现其他形貌的银纳米颗粒,从而降低银纳米片的产率.     

中国科学家首次从分子层次证明纳米催化的形貌效应

中国科学院大连化物研究所的研究人员利用形貌控制概念，通过对金属氧化物纳米粒子尺寸和形貌的调控，使得制备的Co3O4纳米棒表面暴露41％的活性（110）晶面。这种晶面含有较多的CO氧化的活性位，即使在-77C仍然可以实现100％的CO的转化，其反应速率是通常氧化钴纳米粒子的10倍。     

Ti—B—N纳米复合薄膜的制备及结构和力学性能

利用反应磁控溅射方法在(100)单晶硅和高速钢(W18Cr4V)基片上制备出不同B含量的Ti--B--N纳米复合薄膜.使用X射线衍射(XRD)和高分辨透射电镜(HRTEM)研究了Ti--B--N纳米复合薄膜的组织结构,并用纳米压痕仪测试了它们的纳米硬度和弹性模量.结果表明:通过改变TiB2靶功率和Ti靶功率的方法可制备出非晶--纳米晶复合结构的Ti--B--N薄膜;Ti--B--N薄膜中主要含有TiN纳米晶,随着B含量的增加,形成的TiN纳米晶尺寸变小,非晶成分增加;当B含量很高时会出现很小的TiB2纳米晶,此时薄膜性能不好;当TiN晶粒尺寸为5 nm左右时,Ti--B--N薄膜力学性能最优,纳米硬度和弹性模量分别达到32.7 GPa和350.3 GPa.     

银纳米棒合成银纳米片的制备方法与性能表征

通过在银纳米棒前驱液中引入柠檬酸钠、双氧水以及硼氢化钠,成功制备出银纳米三角片.采用X射线衍射(X-ray diffraction,XRD)、透射电子显微镜(transmission electron microscope,TEM)和紫外-可见-近红外(ultraviolet-visible-near infrared,UV-Vis-NIR)光谱对样品进行表征.结果表明,制备的银纳米三角片的边长约为100 nm,且为面心立方晶体(face centered cubic,fcc)结构;银纳米三角片的形貌与银纳米棒前驱液的加入量有关.通过分析UV-Vis-NIR光谱,发现银纳米三角片在830 nm处具有很强的表面等离子体共振(surface plasmon resonance,SPR)峰.因其良好的红外吸收性能,银纳米三角片可被应用于硅基薄膜太阳能电池的前电极.     

Na_2CO_3调控醇热法制备规则形貌Ag纳米晶

以乙二醇为溶剂、Na2S为成核剂、聚乙烯吡喏烷酮(PVP)和Na2CO3为修饰剂,采用醇热法制备不同形貌的Ag纳米晶。通过调节反应时间、Na2CO3浓度、滴加速率以及起始滴加时间等来调控Ag纳米晶的微结构。利用场发射扫描电子显微镜(FESEM)和紫外-可见光(UV-vis)吸收光谱对Ag纳米晶的形貌和尺寸以及局域表面等离子特性(LSPR)进行表征。结果表明:浓度为50μmol/L的Na2CO3,在AgNO3滴加完毕后5.5 min时以2 mL/min的速率滴加到体系中反应3 h,能够得到平均颗粒尺寸为60 nm、尺寸分布均匀的截角立方Ag纳米晶。     

扩散火焰法制备TiO2纳米晶及其光催化活性

利用自行设计开发的扩散火焰燃烧反应器,以四氯化钛为前驱体,通过四氯化钛气相水解法,改变四氯化钛进料速率和中心环氧气含量,合成粒径和晶型组成可控的二氧化钛纳米晶。透射电镜(TEM)和X射线衍射仪(XRD)分析结果表明:制备的球形样品分散性好、粒径分布均匀、晶化完整。以罗丹明B染料在紫外光条件下的降解为模型反应,考察了球形二氧化钛纳米晶的粒径和晶型组成与光催化活性的关系。结果表明:晶型组成不变时,晶粒尺寸越小,光催化活性越好;而当晶粒尺寸不变时,随着锐钛矿型质量分数的增加,光催化降解罗丹明B的活性先增加后降低,锐钛矿型二氧化钛质量分数为0.80时,光催化活性最好。     

不同表面活性剂对Sn基底表面银纳米粒子薄膜的原位生长及其光学性能的影响

以Sn基底为活性基底,通过不同表面活性剂的作用,采用原位置换法在其表面制备出形貌各异的银纳米粒子薄膜材料.采用扫描电镜、Ｘ射线衍射仪、紫外可见分光光度计、荧光分光光度计等测试手段对样品进行分析和表征, 并考察银纳米粒子的形貌对其薄膜基底表面增强拉曼散射(SERS)活性的影响.结果表明：随着反应液中表面活性剂种类的改变,银纳米粒子的形貌发生改变.当表面活性剂为聚乙烯吡咯烷酮(PVP)时,制备出的由银纳米粒子具有极强的紫外可见吸收光谱红移;并且以此条件得到的SERS活性基底具有极强的SERS信号.     

Ag纳米棒的控制合成

在多孔氧化铝纳米孔道内,乙二醇与Ag 反应生成银核,在一定温度下并经限域生长形成银纳米棒.用X射线衍射光谱(XRD)、透射电子显微镜(TEM)以及电子选区衍射(SAED)等检测手段对产物进行了表征.TEM形貌表明,制备的银纳米棒产量丰富,半径均匀,其长度约为200 nm,平均直径为60 nm,这与所用模板的孔结构相一致;SAED图表明银纳米棒是孪晶结构;XRD数据分析指出银纳米棒具有面心立方的晶体结构.     

新型金纳米薄片的制备与生长研究

在表面活性剂PVP的辅助下,利用高温溶剂热法,合成了星形、盾形和多边形等新型Au纳米薄片.对其结构分析表明,Au纳米薄片均为单晶,边长为数微米,厚度约40 nm.这些新型的Au纳米片的形成可以理解为(111)面沿着〈211〉和其他高指数面的生长.不同晶面表面能的理论模拟可以很好解释(111)晶面沿高指数方向生长的可能性.利用堆垛层错引导晶体生长可以很好地解释选区电子衍射中的分数衍射及晶面间距.     

Strain effects and phase transitions in photonic resonator crystals

Optical structures with periodic variations of the dielectric constant in one or more directions (photonic crystals) have been employed extensively for studying optical diffraction phenomena. Practical interest in such structures arises from the possibilities they offer for tailoring photon modes, and thereby the characteristics of light propagation and light-matter interactions. Photonic resonator crystals comprising two-dimensional arrays of coupled optical microcavities have been fabricated using vertical-cavity surface-emitting laser wafers. In such structures, the light propagates mostly normal to the periodic plane. Therefore, the corresponding lateral Bragg-periodicities are larger, a feature that is advantageous for device manufacture as it allows for larger lattice constants in the lateral direction. Here we investigate strain effects in a photonic resonator crystal by shifting neighbouring lattice rows of microcavities in opposite directions, thereby introducing an alternating square or quasi-hexagonal pattern of shear strain. We find that, for strain values below a critical threshold, the lasing photon mode is virtually locked to the corresponding mode supported by the unstrained photonic crystal. At the critical strain value, we observe a phase-transition-like switching between the square and quasi-hexagonal lattice modes. The tolerance of subcritical strains suggests that the resonator crystal may be useful for applications requiring high spatial coherence across the lattice, while the mode switching could potentially be exploited in free-space optical communications.     

Computational design of direct-bandgap semiconductors that lattice-match silicon

Crystalline silicon is an indirect-bandgap semiconductor, making it an inefficient emitter of light. The successful integration of silicon-based electronics with optical components will therefore require optically active (for example, direct-bandgap) materials that can be grown on silicon with high-quality interfaces. For well ordered materials, this effectively translates into the requirement that such materials lattice-match silicon: lattice mismatch generally causes cracks and poor interface properties once the mismatched overlayer exceeds a very thin critical thickness. But no direct-bandgap semiconductor has yet been produced that can lattice-match silicon, and previously suggested structures pose formidable challenges for synthesis. Much recent work has therefore focused on introducing compliant transition layers between the mismatched components. Here we propose a more direct solution to integrating silicon electronics with optical components. We have computationally designed two hypothetical direct-bandgap semiconductor alloys, the synthesis of which should be possible through the deposition of specific group-IV precursor molecules and which lattice-match silicon to 0.5-1% along lattice planes with low Miller indices. The calculated bandgaps (and hence the frequency of emitted light) lie in the window of minimal absorption in current optical fibres.     

Anisotropy of Earth's D' layer and stacking faults in the MgSiO3 post-perovskite phase

The post-perovskite phase of (Mg,Fe)SiO3 is believed to be the main mineral phase of the Earth's lowermost mantle (the D' layer). Its properties explain numerous geophysical observations associated with this layer-for example, the D' discontinuity, its topography and seismic anisotropy within the layer. Here we use a novel simulation technique, first-principles metadynamics, to identify a family of low-energy polytypic stacking-fault structures intermediate between the perovskite and post-perovskite phases. Metadynamics trajectories identify plane sliding involving the formation of stacking faults as the most favourable pathway for the phase transition, and as a likely mechanism for plastic deformation of perovskite and post-perovskite. In particular, the predicted slip planes are {010} for perovskite (consistent with experiment) and {110} for post-perovskite (in contrast to the previously expected {010} slip planes). Dominant slip planes define the lattice preferred orientation and elastic anisotropy of the texture. The {110} slip planes in post-perovskite require a much smaller degree of lattice preferred orientation to explain geophysical observations of shear-wave anisotropy in the D' layer.     

Beta-helix structure and ice-binding properties of a hyperactive antifreeze protein from an insect

Insect antifreeze proteins (AFP) are considerably more active at inhibiting ice crystal growth than AFP from fish or plants. Several insect AFPs, also known as thermal hysteresis proteins, have been cloned and expressed. Their maximum activity is 3-4 times that of fish AFPs and they are 10-100 times more effective at micromolar concentrations. Here we report the solution structure of spruce budworm (Choristoneura fumiferana) AFP and characterize its ice-binding properties. The 9-kDa AFP is a beta-helix with a triangular cross-section and rectangular sides that form stacked parallel beta-sheets; a fold which is distinct from the three known fish AFP structures. The ice-binding side contains 9 of the 14 surface-accessible threonines organized in a regular array of TXT motifs that match the ice lattice on both prism and basal planes. In support of this model, ice crystal morphology and ice-etching experiments are consistent with AFP binding to both of these planes and thus may explain the greater activity of the spruce budworm antifreeze.     

三角晶格Ising模型Monte Carlo模拟的GPU加速算法

在分析传统Monte Carlo算法的基础上,针对三角晶格Ising模型提出了一种基于GPU的并行模拟方法,大大提高了算法的效率。对1024?024的模型,实现了69倍的加速比。通过该算法所得数据分析模型的临界行为,获得了高精度的临界点βc = 0.27466(1)和临界指数yt =1.01(2),yh = 1.8756(3)。     

镍基体上银和铜膜的择优取向及其价电子分析

目的研究在Ni（100）基体上沉积Ag和Cu膜的择优取向的形成机理。方法采用X-射线衍射进行分析,根据固体与分子经验电子理论（EET）的键距差（BLD）方法,计算Ni（100）晶面、Ag和Cu的33个晶面的平均电子密度及相对电子密度差。结果X-射线衍射分析结果表明,在Ni（100）基体上沉积Ag和Cu膜的主要择优取向为（111）,其次依次为（100）和（110）。计算结果表明,2个晶面的电子密度差越小,相应的择优取向越强。结论从界面处电子密度的连续原理成功地分析了在基体上沉积薄膜的择优取向的产生机理。     

自旋S=1键稀释蜂窝格子伊辛模型的临界温度

本文提出一种新的缀饰方法将自旋 S=1淬灭键稀释伊辛模型在交换作用参数子空间:exP(K)cosk(J)=1映象到混合自旋淬灭座稀释缀饰格子系统。对此混合自旋缀饰格子系统应用退火模型近似求得了自旋 S=1淬灭键稀释蜂窝格子伊辛系统的临界温度与键浓度之间的解析关系。所得结果在弱稀释极限下与严格解一致。     

航路交叉点动态保护区的算法研究

繁忙的航路网产生大量的航路交叉点,不仅加重了空中交通管制员的工作负荷,也大大增加了冲突碰撞的可能性。为了减小交叉点处的碰撞风险,建立了交叉点保护区与飞行速度及航线角度的动态函数关系。首先,基于速度的正态分布概率理论,在给定安全目标等级条件下,求解相应的保护区大小;同时,对两机侧向间隔进行动态研究,求出保证两机距离达到最小安全间隔时的保护区大小,双重考虑取较大保护区范围。最后仿真验证了其可行性,算法可求出满意实时间隔,并保证航路安全。     

One of the origins for curved edges of polyethylene single crystals

A new concept of lattice strain was developed to explain the origin of the curved edges of polyethylene (PE) single crystals. In the crystallization of PE from poor solvents, the length of critical nucleus generated is rather short. The thin lamellae are thermodynamically unstable especially at high temperature. Thereby, during the growth of PE single crystals an annealing process is going on simultaneously, which results in a reduction of thickness from the center to growing faces of lamellae. It is known that the thinner the single crystals, the bigger the unit-cell dimensions. Consequently, unit-cells in the central part of single crystals formed are somewhat smaller than those in the outer part of the same crystals. In order to fit in with the gradual enlargement of unit-cell dimensions from the center to the edges of single crystals, the lattice planes of a faster gmwing dominant 110 deform to be a set of parallel arcs of concentric circles. Accordingly, the edge of a slower growing subodinste 200 becomes a part of an ellipse with obvious curvature while the edge of a 11101 sector remains almost straight for it is a part of a Large circumference.