球形金纳米颗粒的消光特性及不同折射率环境下的共振波长

为了研究球形Au纳米颗粒的消光特性及共振波长与环境折射率的关系,采用Mie理论计算了直径为20,40,60和80nm的球形Au纳米颗粒在不同折射率的介质环境中的消光谱,并利用消光法实验测量了这4种粒径的Au纳米颗粒在不同浓度糖水中的吸光度,取得了糖水介质环境的折射率与浓度之间的关系及其色散规律,以及Au纳米颗粒的消光系数及共振波长随环境折射率变化的数据。结果表明,介质环境糖水浓度一定时,Au颗粒半径增大,消光峰值红移;颗粒半径一定时,周围介质环境糖水浓度增大,消光峰值红移;Au纳米颗粒的共振波长与糖水浓度呈线性关系,20,40,60,80nm的Au纳米颗粒对应的线性斜率分别为0.106 0,0.135 5,0.193 8,0.265 8,斜率随粒径尺寸的增大而增大。该结论为探索纳米颗粒的折射率敏感性奠定了基础。     

Revealing local variations in nanoparticle size distributions in supported catalysts: a generic TEM specimen preparation method

The specimen preparation method is crucial for how much information can be gained from transmission electron microscopy (TEM) studies of supported nanoparticle catalysts. The aim of this work is to develop a method that allows for observation of size and location of nanoparticles deposited on a porous oxide support material. A bimetallic Pt‐Pd/Al₂O₃ catalyst in powder form was embedded in acrylic resin and lift‐out specimens were extracted using combined focused ion beam/scanning electron microscopy (FIB/SEM). These specimens allow for a cross‐section view across individual oxide support particles, including the unaltered near surface region of these particles. A site‐dependent size distribution of Pt‐Pd nanoparticles was revealed along the radial direction of the support particles by scanning transmission electron microscopy (STEM) imaging. The developed specimen preparation method enables obtaining information about the spatial distribution of nanoparticles in complex support structures which commonly is a challenge in heterogeneous catalysis.     

The relative accuracy of axial and non-axial methods for the measurement of lattice spacings

The various different transmission electron microscopical techniques available for the measurement of lattice spacings are discussed, and the limited situations under which lattice fringe spacing measurement is the most appropriate approach are considered. The relative accuracy of measurements on images obtained under axial and non-axial conditions is further considered, and the generally greater accuracy of the latter technique demonstrated. Further results on the use of the method for the measurement of the carbon content of retained austenite in a dual phase steel are included.     

Characterization of nanoscaled heterogeneities in mechanically alloyed and compacted CuFe.

Cu80Fe20 and Cu50Fe50 were mechanically alloyed from the pure elements by ball milling for 36 h. The alloy powder was compacted into tablets at room temperature by applying a pressure of 5 GPa. Characterization of the Cu80Fe20) and Cu50Fe50 alloys was carried out by high-resolution transmission electron microscopy (HREM), atom probe field ion microscopy and three-dimensional atom probe (3DAP). The grain size of the nanocrystalline microstructure of the ball-milled alloys observed with HREM varies between 3 and 50 nm.Atom probe and 3DAP measurements indicate that the as-prepared state is a highly supersaturated alloy, in which the individual nanocrystals have largely varying composition. Fe concentration in Cu was found to range from about 8 to 50 at%. It is concluded that by ball milling and compacting an alloy is produced which on a nanometer scale is heterogeneous with respect to morphology and composition.     

Integrating in situ high pressure small and wide angle synchrotron x-ray scattering for exploiting new physics of nanoparticle supercrystals

Combined small and wide angle synchrotron x-ray scattering (SAXS and WAXS) techniques have been developed for in situ high pressure samples, enabling exploration of the atomic structure and nanoscale superstructure phase relations. These studies can then be used to find connections between nanoparticle surfaces and internal atomic arrangements. We developed a four-axis control system for the detector, which we then employed for the study of two supercrystals assembled from 5 nm Fe(3)O(4) and 10 nm Au nanoparticles. We optimized the x-ray energy and the sample-to-detector distance to facilitate simultaneous collection of both SAXS and WAXS. We further performed in situ high pressure SAXS and WAXS on a cubic supercrystal assembled from 4 nm wurtzite-structure CdSe nanoparticles. While wurtzite-structure CdSe nanoparticles transform into a rocksalt structure at 6.2 GPa, the cubic superstructure develops into a lamellarlike mesostructure at 9.6 GPa. Nanoparticle coupling and interaction could be enhanced, thus reducing the compressibility of the interparticle spacing above ～3?GPa. At ～6.2?GPa, the wurtzite-to-rocksalt phase transformation results in a noticeable drop of interparticle spacing. Above 6.2 GPa, a combined effect from denser CdSe nanoparticle causes the interparticle spacing to expand. These findings could be related to a series of changes including the surface structure, electronic and mechanical properties, and strain distribution of CdSe under pressure. This technique opens the way for exploring the new physics of nanoparticles and self-assembled superlattices.     

镀膜光纤探针近场捕获的模拟与实验

为提高近场捕获的能力与灵活性,研究了一种利用镀膜光纤探针对纳米微粒进行近场捕获的方法.采用麦克斯韦应力张量和三维时域有限差分方法建立了近场中纳米微粒的作用力模型,通过光阱力与其他作用力的比较讨论了近场捕获的稳定性,并根据各轴向光阱力的分布情况分析了纳米微粒的捕获尺寸与捕获位置.结果表明,只有当微粒尺寸小于探针孔径时才存...     

On the measurement of lattice parameters in a collection of nanoparticles by transmission electron diffraction

Improved accuracy in transmission electron diffraction measurements of interplanar spacings can be achieved by adding to the camera constant a term proportional to the square of the diffraction ring radius. A statistical technique using all of the diffraction rings yielded a precision better than 0.05% when measuring the lattice parameter of copper nanoparticles. Gold was used as an internal reference for copper by vapor depositing gold and copper on opposite sides of a thin amorphous carbon film. The source of the squared-radius term is consistent with distortions associated with the magnetic field of the post-objective lenses.     

Numerical study on spatial distribution of silver nanoparticles inside whole-body type inhalation toxicity chamber

Silver nanoparticles are among the fastest growing product categories in the nanotechnology industry. Several experimental studies reported earlier for its toxicity and its associated risks. Uniform distribution of nanoparticle concentration in inhalation toxicity exposure chambers is important in the conduct of inhalation experimental evaluation. However, relatively little is known. Several factors, including nanoparticle size, degree of mixing, and chamber design, may influence the nanoparticles distribution in whole-body exposure chamber. In the present work we investigated numerically the silver nanoparticles concentration distribution and particle trajectory in the whole body inhalation toxicity test chamber. A three dimensional numerical simulation was performed using the commercially available computational fluid dynamics code Fluent with two models, discrete phase model (DPM) and fine particle model (FPM) to calculate spatial particle trajectories and concentration. The simulated results show that the silver nanoparticle trajectories and concentration distribution are dependent on inhalation toxicity chamber geometry.     

HREM image contrast from supported small metal particles

HREM, image calculations and small probe diffraction/AEM have been used to characterize structure and contrast of supported small metal particles of ≤5 nm diameter. Such small particles are thought to be active species in industrial applications such as in heterogeneous catalysis where, in general, the particles employed as catalysts are supported. Image calculations (HREM and diffraction contrast) carried out at both 200 keV and 400 keV at various defoci and support thicknesses have shown that in HREM, particle images are obscured by the support contrast with the loss of edge definition and particles appear to be smaller than they actually are. The particle visibility is better at 400 keV. The calculations have also indicated that particle shape varies as a function of support thickness and defocus. The results have clear implications for identification and interpretation of surface structure of the supported small particles accurately by HREM if not performed under controlled conditions and for determining their size and shape.     

A comparative study of thin coatings of Au/Pd, Pt and Cr produced by magnetron sputtering for FE-SEM

Visualization of structural details of specimens in field emission scanning electron microscopy (FE-SEM) requires optimal conductivity. This paper reports on the differences in conductive layers of Au/Pd, Pt and Cr, with a thickness of 1.5–3.0 nm, deposited by planar magnetron sputtering devices. The coating units were used under standard conditions for source–substrate distance, current, HT and argon pressure. Carbon films, deposited by high-vacuum evaporation on small, freshly cleaved pieces of mica, were used as substrate and mounted on copper grids for TEM and SEM inspection. Au/Pd, Pt and, to a lesser extent, Cr coatings varied in particle density, size and shape. Au/Pd coatings have a slightly more granular appearance than Cr and Pt coatings, but this is strongly dependent on the type of sputtering device employed. In FE-SEM images there is almost no difference in contrast and particle size between the Au/Pd layer and the Pt layers of a similar thickness. The nuclei of Au/Pd are rather small with almost no growth to the sides or in height, making Au/Pd coatings a good alternative to chromium and platinum for FE-SEM of biological tissues because of its higher yield of secondary electrons.     

Electrical conduction of thiol modified 60bp Poly(dG)-poly DNA molecules through Au nanoparticles

A novel transport measurement scheme of 60 base pairs of poly (dG) -poly (dC) DNA molecules using Au nanoparticles is devised and implemented. Thiol (-SH) terminations are synthesized at both 5’ and 3’ ends of the double stranded DNA molecules and they can be chemisorbed on the Au surface through sulfur atoms by covalent bonding. These thiol-modified ends make chemical bindings with Au nanoparticles and Au nano-gap electrodes, forming a stable electrode-DNA-nanoparticle-DNA-electrode conduction channel. This transport channel is self-formed and is stable due to robust bonding of thiol and Au. The current-voltage characteristic measured from our device shows a nonlinear behavior and the voltage gap is comparable to the result of previous experiment using the same molecules. This self-trapping method by thiol modified DNA molecules would also be a promising technique for efficient nanoparticle trapping.     

Transmission electron microscopy and theoretical analysis of AuCu nanoparticles: atomic distribution and dynamic behavior

Though the application of bimetallic nanoparticles is becoming increasingly important, the local atomistic structure of such alloyed particles, which is critical for tailoring their properties, is not yet very clearly understood. In this work, we present detailed study on the atomistic structure of Au-Cu nanoparticles so as to determine their most stable configurations and the conditions for obtaining clusters of different structural variants. The dynamic behavior of these nanoparticles upon local heating is investigated. AuCu nanoparticles are characterized by high resolution transmission electron microscopy (HRTEM) and energy filtering elemental composition mapping (EFECM), which allowed us to study the internal structure and the elemental distribution in the particles. Quantum mechanical approaches and classic molecular dynamics methods are applied to model the structure and to determine the lowest energy configurations, the corresponding electronic structures, and understand structural transition of clusters upon heating, supported by experimental evidences. Our theoretical results demonstrate only the core/shell bimetallic structure have negative heat of formation, both for decahedra and octahedral, and energetically favoring core/shell structure is with Au covering the core of Cu, whose reverse core/shell structure is not stable and may transform back at a certain temperature. Experimental evidences corroborate these structures and their structural changes upon heating, demonstrating the possibility to manipulate the structure of such bimetallic nanoparticles using extra stimulating energy, which is in accordance with the calculated coherence energy proportions between the different configurations.     

spICP-MS准确定量多分散金纳米颗粒的颗粒数量浓度

建立了基于单颗粒电感耦合等离子体质谱（spICP-MS）法准确定量分析多分散金纳米颗粒（AuNPs）的颗粒数量浓度。以包含30 nm和60 nm AuNPs的多分散样品为研究对象,考察载气流速和采样深度对尺寸分辨率,以及采集时间和驻留时间对颗粒数量浓度测定结果的影响。研究表明：优化载气流速能显著改善尺寸分辨率,而采样深度的影响相对较小,在载气流速0.8 L/min、采样深度9 mm时,获得了最佳的尺寸分辨率;延长采集时间能有效降低测定结果的相对标准偏差（RSD）,当采集时间增加至180 s时,多分散样品中30 nm和60 nm AuNPs颗粒数量浓度测定值的相对标准偏差降至5%以下（n=3）;选取驻留时间为0.1 ms时,测定结果与配制值相符,且颗粒信号与离子信号的区分更加明显。在优化的条件下,粒径和颗粒数量浓度检出限分别为10 nm和49 NPs/g。采用本方法对不同混合比例的多分散样品进行定量分析,其测定结果与标准值相符,证明了方法的可靠性。将该方法应用于自来水、泉水和湖水中多分散纳米颗粒的定量测定,3种水样的加标回收率在80%~120%之间。本方法具有尺寸分辨率高、测量精密度好、离子干扰小等优点,可为环境基体中多分散纳米颗粒的定量测定提供方法参考。     

Nanoparticle suspension preparation using the arc spray nanoparticle synthesis system combined with ultrasonic vibration and rotating electrode

This study aims to investigate the use of a new nanoparticle preparation method, i.e., the arc spray nanoparticle synthesis system (ASNSS) combined with ultrasonic vibration and rotating electrode, to prepare TiO₂ nanoparticle suspension. For the proposed new method of nanoparticle suspension preparation, this study has designed four different process modes of experimentation for comparison, in order to obtain suspended nanoparticles with smaller particle size and relatively good dispersion. This study discusses the process modes with different settings of variables including peak current, pulse duration, breakdown voltage, temperature of the dielectric fluid and amplitude of ultrasonic vibration, in order to determine the better conditions for the preparation of TiO₂ nanoparticles suspension. The Transition Electron Microscope (TEM) image of the experiment result shows that TiO₂ nanoparticles prepared by the ultrasonic vibration assisted vacuum arc spray process has an average particle size of less than 10 nm.     

Nanoparticle shape and configuration analysis by transmission electron tomography

Tomographic reconstruction by transmission electron microscopy is used to reveal three‐dimensional nanoparticle shapes and the stacking configurations of nanoparticle ensembles. Reconstructions are generated from bright‐field image tilt series, with a sample tilt range up to ± 70°, using single or dual tilt axes. We demonstrate the feasibility of this technique for the analysis of nanomaterials, using appropriate acquisition conditions. Tomography reveals both cubic and hexagonal close‐packing configurations in multi‐layered arrays of size‐selected In nanospheres. By tomography and phase‐contrast lattice imaging, we relate the three‐dimensional shape of PbSe octahedral nanoparticles to the underlying crystal structure. We also confirm simple‐cubic packing in multi‐layers of PbSe nanocubes and see evidence that the particle shapes have cubic symmetry. The shapes of TiO₂ nanorod bundles are shown by tomographic reconstruction to resemble flattened ellipsoids.     

Precise measurements of nanostructure parameters

The precision of measurements performed by atomic-force microscopy (AFM) and high-resolution electron microscopy (HREM) for solving problems of metrology and diagnostics of solid nanostructures is discussed. The HREM-measured height of a monatomic step on a Si(111) surface covered by a thin natural oxide film is demonstrated to be 0.314 ± 0.001 nm. The same accuracy is ensured by AFM measurements through controlling the Si surface relief with heating in ultra-high vacuum on specially created test objects with the distance between the steps being approximately 2 μm. It is shown that the geometric phase method can be used to quantify the strains in the crystal lattice of strained heterostructures on the basis of HREM images with accuracy to 10⁻⁴%, and in situ irradiation by electrons in HREM measurements can be used to visualize ordered clusterization of vacancies and self-interstitial atoms in {113} planes in Si samples.     

Recent improvements to the Cambridge University 600 kV High Resolution Electron Microscope

Several recent modifications to the Cambridge University 600 kV HREM have resulted in increased levels of performance and greater operating efficiency. Changes include new Permendur pole-pieces with a reduced gap leading to improved aberration coefficients, and an attachment to the tilt/shift supplies which facilitates accurate beam alignment. Resolution figures include: (a) an axial CTF extending, without zeros, beyond 1·8 Å at 575 kV; (b) tilted beam CTFs extending beyond 1·1 Å; and (c) lattice fringes of 0·72 Å spacing.     

AFM studies of nanoparticle deposition via electrospray ionization

Electrospray ionization was used to deposit CdSe nanoparticles on graphite and InP substrates. The charge transferred to the substrate via the deposition was correlated to the number of particles found on the substrate by AFM observation. A charge per nanoparticle was determined from depositions of various lengths of time, which is approximately 1 electron per nanoparticle. This value was found to be consistent for concentrations of nanoparticle solutions, which differed by an order of magnitude. Such a value may be used for predicting the density of nanoparticles deposited on a substrate during the deposition. It was found that above a critical concentration, the deposition process produced large clumps of particles rather than individual particles. At lower concentrations, individual particles deposited on the graphite substrates were found to be mobile, arranging themselves on step edges of the graphite.     

Qualification of the tomographic reconstruction in atom probe by advanced spatial distribution map techniques

New and improved spatial distribution map (SDM) methods are developed to identify and extract crystallographic information within atom probe tomography three-dimensional (3D) reconstructions. Detailed structural information is retrieved by combining z-SDM offset distribution analyses computed in multiple crystallographic directions, accurately determining inter-planar spacings and crystallographic angles. The advantages of this technique in comparison to applying the complete z-SDM and complementary xy-SDM analysis to a single crystallographic direction are investigated. Further, in determining these multidirectional z-SDM and xy-SDM profiles, background noise reduction and automatic peak identification algorithms are adapted to attain increased accuracy and is shown to be particularly effective in cases where crystal structure is present but poorly resolved. These techniques may be used to calibrate the reconstruction parameters and investigate their dependence on the design of individual atom probe experiments.     

TEM纳米尺度石墨标样的制备

透射电镜的长度标尺或公称放大倍数是判断试样中组织细节尺寸的依据,需要应用纳米级长度标样进行校准。本文介绍了一种用石墨制备透射电镜专用纳米尺度标样的方法,对石墨的X射线衍射分析以及对石墨标样的TEM高分辨像和电子衍射分析表明,标样中石墨的高分辨像为（002）晶面的点阵像,其晶面间距为0．342nm,可作为纳米尺度的参照材料。本文对使用纳米尺度标样校正ETEM标尺的基本方法进行了简要讨论。