铝纳米晶的低温导电特性研究

采用真空热压技术将电磁感应加热-自悬浮定向流法制备的铝纳米粉末压制成块体样品.通过X射线衍射、透射电子显微镜、扫描电子显微镜及X射线能谱分析了铝纳米晶的微观结构,并用四探针法测量了不同温度下(8—300 K)样品的电阻率,研究了铝纳米晶的电阻率(ρ)随温度的变化规律.结果表明:由于晶界(非晶氧化铝)对电子的散射以及晶界声子对电子的散射效应,低温(40 K)下,铝纳米晶的本征电阻率随温度变化关系明显不同于粗晶铝,不仅呈现出T~4变化,还表现出显著的T3变化规律.因晶界等缺陷和非晶氧化铝杂质对电子的散射,铝纳米晶残余电阻率比粗晶铝电阻率大5—6个数量级.     

电子束诱导的纳米颗粒表面等离激元激发模拟

本文基于离散偶极子近似方法,发展出了一套计算任意纳米结构材料的电子能量损失谱的方法和程序. 模拟了在单个银纳米颗粒附近不同入射位置下的电子能量损失谱,其计算结果与实验能谱非常吻合. 虽然离散偶极子近似法早在很多年前就已经被应用到处理外加光场激发的情形,但这套方法才真正提供了一个研究电子束诱导金属纳米颗粒局域表面等离激元激发的计算工具.     

Nanocomposites for electromagnetic radiation protection

Specific features that characterize nanoparticles and which are due to their small size and allow one to enhance the interaction between the electromagnetic radiation and nanostructured materials and to develop the effective protection of man and equipment against harmful uncontrolled radiation are reported. Examples of the development of nanocomposite radar absorbing materials that can be used for protection of man and equipment are presented.     

铝纳米颗粒的热物性及相变行为的分子动力学模拟

采用分子动力学方法模拟了纳米金属铝在粒径为0.8-3.2 nm 时的熔点、密度和声子热导率的变化, 研究了粒径为1.6 nm的铝纳米颗粒的密度、比热和声子热导率随温度的变化. 采用原子嵌入势较好地模拟了纳米金属铝的热物性及相变行为, 根据能量-温度曲线和比热容-温度曲线对铝纳米颗粒的相变温度进行了研究, 并利用表面能理论、尺寸效应理论对铝纳米颗粒熔点的变化进行了分析. 随着纳米粒径的不断增大, 铝纳米颗粒的熔点呈递增状态, 当粒径在2.2-3.2 nm时, 熔点的增幅减缓, 但仍处于递增趋势. 随着纳米粒径的增大, 铝纳米颗粒的密度呈单调递减, 热导率则呈线性单调递增, 且热导率的变化情况符合声子理论. 随着温度的升高, 粒径为1.6 nm的铝纳米颗粒的密度、热导率均减小. 该模拟从微观原子角度对纳米材料的热物性进行了研究, 对设计基于铝纳米颗粒的相变材料具有指导意义.     

Investigation of Bioimpacts of Metallic and Metallic Oxide Nanostructured Materials: Size,Shape, Chemical Composition,and Surface Functionality: A Review

Nanotechnology is set to impact a wide range of various fields, including medicine, materials technology, environmental sciences, and engineering/manufacturing. Nanoparticles are categorized depending on their size, composition, shape, and surface functionality. Due to the excessive growth of nanostructured materials (NSMs) in production and industrial applications, human and environmental exposure to them and their possible toxicity issues are inevitable. The main objective of this review is to study NSMs, in particular metallic and metallic oxide nanoparticles, and properties that have a determinative role in their bioimpacts. Nevertheless, the main focus is to provide an overview of NSMs toxicology. Medical and environmental applications of the NSMs are discussed here. Also, key factors on the toxicity of the nanoparticles such as shape, size, chemical composition, and surface functionality are discussed. Finally, toxicity of the nanoparticles is going to be highlighted, and relevant studies are critically compared. This review gives a broad scientific view for improving the functional efficiency of nanomaterials while mitigating their possible adverse and unintended effects on biological systems.     

PdPt Nanocubes: A High‐Performance Catalyst for Hydrolytic Dehydrogenation of Ammonia Borane

An effective way to improve the catalytic activity of metal‐based nanostructured materials is to control the size, shape, or composition. Here, the bimetallic PdPt nanoparticles (NPs) show significant dependency on the shape for catalytic hydrolysis of ammonia borane. The catalytic activity of PdPt cubic nanoparticles (cNPs) is found to be the best compared with the activities of spherical nanoparticles (sNPs) of Pd, Pt, and PdPt and cNPs of Pd under the same reaction conditions. The turnover frequency (50.02 min^?1) of PdPt cNPs for ammonia borane hydrolysis is among the values of the most active catalysts. This high catalytic performance of PdPt cNPs encourages the approach of shape and composition control for various catalytic applications.     

Size distribution effect on the magnetization and magneto-resistance in ferromagnetic nanostructured manganites

We present experimental data of magnetization and magneto-resistance of nanostructured La_2/3B_1/3MnO₃ with B=Ca, Sr, which present difference between the coercive field in the magnetization loop with their corresponding maximum value in the magneto-resistance. This difference is described by a model that include, size distribution of magnetic particles, randomly oriented anisotropy axis and electronic transfer between the particles, which is mediated by spin-polarized tunneling process. Also, the model predicts that the maximum magneto-resistance can be, in the magnetic disorder state, two times larger than the experimental value. The model results can be used to estimate the size dispersion of nanoparticles in similar systems.     

Deposition of Aerosol Nanoparticles on Flat Substrate Surfaces

The deposition process in a homogeneous electric field, and the subsequent microscopic arrangement of charged, metallic aerosol nanoparticles in the size range of 30 nm on flat substrate surfaces is described. The first aspect of the investigation is the transfer of the particles from a three-dimensional distribution in the gas phase into their arrangement on the substrate surface, in dependence on particle-particle interactions and on Brownian motion. The theoretical results obtained with a trajectory model are compared with experimental results obtained by scanning electron microscope investigation of the deposition patterns. The second aspect of the investigation is the nanostructured arrangement of nanoparticles by means of inhomogeneous electric microfields. We demonstrate a parallel process for the transfer of charge patterns on oxidized silicon surfaces followed by the deposition of monodisperse singly charged nanoparticles, which allows the creation of particle arrangements reaching from 100 nm resolution up to structures in the upper micrometer range. The charge patterns are transferred using a polydimethylsiloxane (PDMS)-stamp, which is covered with a metal layer.     

Atomic dynamics of lead embedded into nanoporous glass

The thermal atomic vibration spectrum of lead nanostructured in porous glass with an average pore size of 7 nm and the thermal vibration spectrum of conventional bulk lead (taken for comparison) are measured using inelastic neutron scattering. The density of states in the phonon spectrum of lead nanoparticles is found to exceed the density of states in the spectrum of bulk lead at both low (E < 2.5 meV) and high (E > 9.5 meV) energies. These data are used to propose a model for the structure of a porous glass-lead nano-composite.     

Electric conductivity of nanocluster PbTe structures with controlled topology: Manifestation of macroscopic quantum effects

Methods of laser modification allow us to observe macroscopic quantum phenomena in nanostructured (cluster) materials. The laser synthesis of nanoparticles/nanoclusters with different topologies in semiconductor PbTe samples is performed via direct laser modification of thin films under the action of continuous laser radiation with a wavelength of 1.06 μm and a power density of ~10⁵ W/cm². Nanoparticles with bimodal distribution in lateral dimensions are obtained on the surfaces of the samples. The electrophysical properties of such structures can be controlled as desired by modifying their topology. Variations in electric properties depending on the particle location density are demonstrated. The results are interpreted based on the existence of quantum coherent processes with tunneling transitions and hopping conductivity. This approach is promising for the fabrication of elements and devices in optoelectronics and photonics based on new physical principles, and of different hybrid optoelectrical schemes.     

In situ TEM study of mechanical behaviour of twinned nanoparticles

There is strong interest in studying changes in mechanical properties with reducing grain size. The rational is that consequent dislocation glide cannot be sustained, resulting in an increase in material strength. However, this comes with the cost of a reduction in ductility. It has been shown that coherent twin boundaries in nanostructured Cu improve the ductility to 14% [Lu et al., Science 324 (2009) p. 349]. In this paper, we report for the first time the compression of individual nanoparticles using an in situ force probing holder in the transmission electron microscope. Four types of nanoparticles were tested, three with twin boundaries (decahedra, icosahedra and a single twin) and one free of defects (octahedral). Our results indicate the yield strength of the twinned nanoparticles is between 0.5 and 2.0 GPa. The total malleability for the twinned particles range from 80 to 100%. In addition, experimental results were reproduced by MD simulations of the compression phenomena and suggest that the outstanding mechanical properties are related with partial dislocation multiplication at twin boundaries.     

New highly fluorescent biolabels based on II-VI semiconductor hybrid organic-inorganic nanostructures for bioimaging

Semiconductor quantum dots based on II-VI materials may be prepared to develop good biolabeling properties. In this study we present some well-succeeded results related to the preparation, functionalization and bioconjugation of CdY (Y = S, Se and Te) to biological systems (live cells and fixed tissues). These nanostructured materials were prepared using colloidal synthesis in aqueous media resulting nanoparticles with very good optical properties and an excellent resistance to photodegradation.     

Modifier effects on chemical reduction synthesis of nanostructured copper

Size-controlled chemical reduction synthesis of nanostructured Cu was studied in the presence of a single modifier such as polyethylene glycols, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate or a mixture of two different types of modifiers. The Cu nanoparticles were characterized by powder X-ray diffraction, transmission electron microscopy, selected area electron diffraction and Fourier transform infrared spectroscopy. The average particle size and particle size distribution of the nanostructured Cu depend upon the type of modifiers and the modifier effect follows the order: PEG-2000 > SDBS > PEG-600 > SDS > PEG-6000. The experimental results indicate that due to the existence of a synergistic action, a mixture of two types of modifiers has a significant effect on the particle size and the size distribution of Cu nanoparticles.     

The effect of solvent on the crystal structure and size distribution of cadmium sulfide nanocrystals

CdS nanocrystals with different structures were synthesized by the method of solution precipitation using thiourea and cadmium acetate as starting materials in different solvents: water, methanol and N,N-dimethylformamide (DMF). Our results show that the solvent has direct effect on the structure and size of the final nanoparticles. It was found that using DMF, as a solvent, results in producing smaller nanoparticles with the cubic structures, while using the other solvents gives rise to larger nanoparticles with the hexagonal structure. It was also found that using heat during washing the precipitate results in a more homogenous size distribution of CdS nanocrystals. On the basis of our experimental results we also suggest a critical structure transformation size.     

Electronic States of Nanostructured Systems: Titanium and Zirconia

The density functional method with pseudopotentials are used to study the electron states of nanoparticles and nanostructured systems: chains, films, and three-dimensional nanosystems of titanium and zirconia. It is shown that all studied titanium nanosystems have the density of electronic states (DES) of the metallic type, but zirconia nanosystem demonstrates a dielectric energy gap in the vicinity of the Fermi level. The density of states of nanostructured titanium is close in shape to DES of the single crystal but has a smoother shape due to disordering of the atomic arrangement. The forbidden band width of the nanostructured zirconia is smaller as compared to the corresponding width in crystalline ZrO₂, supposedly because of incomplete saturation of ionic bonds.     

Preparation and Dielectric Properties of Nanostructured ZnO Whiskers

By a novel controlled combustion synthesis method, a large number of nanostructured ZnO whiskers with different morphologies, such as tetra-needles, long-leg tetra-needles and multi-needles, are prepared without any additive in open air at high temperature. The morphologies and crystalline structures of the as-prepared ZnO nanostructured whiskers are investigated by SEM and XRD. The possible growth mechanism on the nanostructured ZnO whiskers is proposed. The experimental results indicate that the dielectric constants and losses of the nanostructured ZnO whiskers are very low, demonstrating that the nanostructured ZnO whiskers are low-loss materials for microwave absorption in X-band. However, obvious microwave absorption in nanostructured ZnO whiskers is observed. The quasi-microantenna model may be attributed to the microwave absorption of the ZnO whiskers.     

Investigation of the optical characteristics of composite materials based on cadmium sulfide nanoparticles stabilized in a high-pressure polyethylene matrix

Composite materials based on cadmium sulfide nanoparticles in an inert dielectric matrix of high-pressure (low-density) polyethylene are experimentally studied. It is shown how the size and weight concentration of nanoparticles in the bulk of the stabilizing matrix affect the nanocomposite absorption. The experimental results are interpreted based on the two-flux Kubelka-Munk model.     

Thermal plasma deposition of nanostructured films

A thermal plasma process for the synthesis of nanoparticles and their immediate assembly into nanostructured films is discussed. In this process, known as hypersonic plasma particle deposition, a thermal plasma with injected precursors is expanded through a nozzle to nucleate nanoparticles, which are then inertially deposited onto a cooled substrate in vacuum. A lightly consolidated nanostructured film results. Particle and film diagnostics along with images of the plasma flow are used to explain the formation of nanostructured silicon carbide films by this process     

Effect of deposition parameters on morphology and size of FeCo nanoparticles synthesized by pulsed laser ablation deposition

The experimental parameters that control the surface morphology and size of iron cobalt nanoparticles synthesized at room temperature by pulsed laser ablation deposition (PLAD) technique have been systematically investigated. The nanoparticle synthesis has been achieved at higher operating gas pressures of argon. It was found that nanoparticles upon deposition formed small clusters, the size of which increases with decreasing pressure, increasing laser-energy density, and decreasing target-to-substrate distance. This trend could be attributed to change in the kinetic energy of deposited nanoparticles with varying argon pressure, laser-energy, and target-to-substrate distance. The nanoparticles size and size distribution showed strong dependence on argon pressure and weak dependence on laser-energy density and target-to-substrate distance.     

Effect of tunneling on the thermoelectric efficiency of bulk nanostructured materials

The possibility of increasing the thermoelectric figure of merit for bulk nanostructured materials has been investigated theoretically. The kinetic coefficients of the nanostructured material have been calculated and evaluated under the assumption that the dominant role in the transfer is played by the tunneling of electrons between nanoparticles. The limiting case of the absence of phonon thermal conductivity through barrier layers has been considered. It has been demonstrated using the estimates obtained for materials based on Bi₂Te₃ that the thermopower in the nanostructured material can be sufficiently high and that, despite the low electrical conductivity, the dimensionless thermoelectric figure of merit can be as large as 3–4 at room temperature.