Analytical characterization of gold nanoparticle primary particles,aggregates, agglomerates,and agglomerated aggregates

Gold nanoparticles have been studied for many biomedical applications. However, alterations in the gold nanoparticles’ environment frequently lead to the formation of aggregates and agglomerates, which have not been well characterized. These new structures could significantly change the biological impact of the nanoparticles, so the appropriate characterization of these structures prior to biological administration is vital for the correct interpretation of toxicology results. By varying the solvent or heating under pressure, four reproducible gold nanoparticles structures were created: 10 nm primary particles, aggregates of the primary particles that contain non-reversible bonds between the individual nanoparticles, agglomerates of primary particles that contain reversible interactions between the individual nanoparticles, and agglomerated aggregates that have reversible bonds linking individual aggregates. Ultraviolet–visible (UV–Vis) spectroscopy, thermal gravitational analysis, and neutron activation analysis were each found to accurately measure the concentration of the primary particles. The primary particles measured 10 nm by dynamic light scattering (DLS) and had a spherical morphology by transmission electron microscopy (TEM) while the aggregates measured 110 nm by DLS and had a distorted morphology by TEM. The agglomerate and aggregated agglomerate samples both measured >1,000 nm by DLS, but the individual particles had significantly different morphologies by TEM. Multiple other analytical techniques, including ultracentrifugation, gel electrophoresis, and X-ray diffraction, also showed unique traits for each structure. The structural differences did not change in the presence of cell culture media or rat serum. In addition, the primary particles, aggregates, and agglomerates each had a unique UV–Vis spectrum, allowing for an inexpensive, rapid method to differentiate between the structures.     

Classification Performance of a Low Pressure Differential Mobility Analyzer for Nanometer-sized Particles

Size distribution measurements and classification tests by a low pressure differential mobility analyzer (LPDMA) for nanometer-sized silver particles and cesium iodide particles under low pressure conditions (123–300 Torr) were performed using a transmission electron microscope (TEM) and the tandem DMA technique. When the ratio of the sheath gas flow rate and the aerosol gas flow rate was set at 5 : 1, the targeted sizes calculated from the classification voltage applied to the LPDMA at 160 Torr are found to be in good correlation with the count mean Feret diameter obtained from the TEM observation of the particles collected after a classification ranging from 6 to 25 nm, although the targeted sizes set by the LPDMA were approximately 15% greater than the count mean Feret diameter measured by the TEM after classification. The geometric standard deviations of DMA-classified particles measured by TEM and those obtained from the tandem DMA method ranged from 1.08 to 1.17 and from 1.05 to 1.13, respectively. They were slightly greater than the ideal geometric standard deviations (1.05) of the particles classified with the LPDMA, which was calculated by neglecting the broadening effects due to Brownian diffusion. We experimentally demonstrated the validity of our LPDMA system for size measurements and classification of the nanometer-sized particles under low pressure conditions.     

Ni nanoparticles fabricated by laser ablation in water

Nickel nanoparticles were fabricated by ablating a bulk Ni target with pulsed 337-nm laser radiation in distilled water. Transmission electron microscope images of the removed material show spherical particles with two size scales: tens of nm and hundreds of nm. Phase explosion and Rayleigh–Plateau hydrodynamic instability are suggested as being responsible for this distribution. An X-ray diffraction pattern of the ablated material demonstrates the presence of both nickel and nickel oxide.     

Deriving the mean primary-particle diameter and related quantities from the size distribution and the gravimetric mass of spark generated nanoparticles

Spark generated carbon and iridium nanoparticles were characterised by their electrical-mobility diameter D and by the mass of particulate matter collected in parallel on filter. The particles exhibited slightly skewed lognormal size distributions with mean mobility diameters between 18 and 74 nm. The masses calculated from the measured distributions under the assumption that the particles were spherical (diameter D) and of bulk mass density turned out to be much higher than the gravimetric mass, by factors between 8 and as high as 340. This very pronounced difference initiated a search for an improved relation between particle size and mass. Data analysis suggested that the mass increases linearly with increasing D. Hence the measured distributions were evaluated under the assumption that the spark generated matter was composed of spherical primary nanoparticles of mean diameter d, aggregated in the form of chains of joint length βD, with β>1. Using reasonable values of β between 2 and 4, the mean diameter of carbon primary particles turned out to be 10±1.8 nm, in excellent agreement with size data recently obtained by transmission electron microscopy (TEM). The primary iridium particles were found to be distinctly smaller, with diameters between 3.5±0.6 nm and 5.4±0.9 nm. The comparatively small uncertainty is due to the fact that the primary-particle diameter is proportional to the square root of β. The calculated volume specific surface areas range between 500 and 1700 m²/cm³. These numbers are close to the ‘active’ surface areas previously measured by the BET method. The good agreement with TEM and BET data suggests that the novel approach of nanoparticle characterisation is meaningful. Accordingly, the number concentrations of all individual primary particles rather than the concentrations measured by the mobility analyser should be␣considered the correct dose metric in studies on animal exposure to spark generated nanoparticles. The␣evaluated data imply that the numbers quoted in the literature must be enlarged by factors ranging between about 10 and a maximum as high as 80. An erratum to this article can be found at     

Size of three‐dimensional objects measured by means of photoemission electron microscopy

Pb particles on a Si(111) substrate were investigated using a photoemission electron microscope (PEEM). The electrons have been excited by a linearly polarised femtosecond laser beam with a wavelength of λ = 400 nm. The PEEM images exhibit an unusually high contrast. They arise due to photoemission being of a nontrivial nature because the photon energy is lower than the work function of the sample. It may be caused by the following processes: two‐ or multi‐photon absorption, tunnel‐photoeffect induced by a strong lowering of the potential barrier owing to enhancement of the electrical field of the powerful incident light wave on a rough surface, generation of second harmonic with its following absorption, or electron gas heating. Images obtained with orthogonal directions of the photon polarisation were compared to estimate the shape of different Pb particles. The size of the islands was determined by two methods, either from the shape of the spatial brightness distribution or from the area under the curve of this distribution.     

大气压下石英毛细管内氩等离子体放电的发射光谱诊断

在长度为20 cm的石英毛细管内利用两个边缘锋利的中空的针型电极之间的氩气放电产生了高电子密度的大气压等离子体。利用发射光谱对所获得的等离子体的几个重要参数进行了诊断。利用计算机谱线拟合法合成了300 nm附近OH(A-X)的(0-0)转动谱带并通过与测量谱线的比较确定了等离子体的气体温度,根据H_β谱线Stark展宽法计算了等离子体的电子密度,采用玻尔兹曼曲线斜率法依据测得的有关氩的发射光谱估算了等离子体的电子温度。研究结果表明,这种石英毛细管内弧光放电等离子体的气体温度约为(1 100±50)K;电子密度数量级在1014 cm-3;电子温度约为(14 515±500)K。     

Characterization of Low Pressure DMA System for the size selection of magnetic nano-particles

For the size selection of magnetic nano particles produced in laser ablation, a low pressure differential mobility analyzer (LPDMA) was constructed. The LPDMA was characterized using the transmission electron microscopy (TEM) image of laser-ablated CoPt nano particles. Using TEM image, the geometrical standard deviation, _g, was measured to be around 1.13. The dependence of the performance of LPDMA on the gas path temperature and the pressure was measured using an electrode which measures the number of the selected particles.The size-selected magnetic nano-particles were deposited on Si substrates, whose magnetizations were measured by SQUID. It was found that nano-particles with a diameter of 20 nm have different temperature dependences from nano-particles with a diameter of 40 nm and the coercivity of 40 nm dia. nano-particles is smaller than that of 20 nm dia. nano-particles. PACS 74.25.Ha; 78.67.Bf; 81.09.-b     

氩气中铝丝电爆炸沉积能量对制备铝纳米粉体特性的影响

研制了基于脉冲电容器放电回路的亚微秒金属丝电爆炸纳米粉体制备实验平台,包括电爆炸过程电流和电压测量系统。利用透射电子显微镜(TEM)观察纳米粉体的形态与结构,并通过电镜统计观察法分析TEM图像得到纳米粉体的粒度大小及其分布。在氩气中电爆炸铝丝制备铝纳米粉体,通过改变电容器充电电压,即初始储能,实验研究沉积能量对铝纳米粉体特性的影响规律。结果表明：铝纳米粉体颗粒形态与结构主要由氩气气压的高低决定,与沉积能量基本无关。增大丝爆过程的沉积能量可显著缩小铝纳米粉体粒度分布范围,减小颗粒平均粒径,并有效地抑制纳米粉体中亚微米颗粒的形成。随着沉积能量E与氩气气压p比值(Ep-1)增大,铝纳米粉体颗粒平均粒径、最大粒径和粒径大于100 nm颗粒所占比例均呈指数函数单调减小。     

The intrinsic structure of spherical particles of opal

The intrinsic structure of spherical SiO₂ particles synthesized by hydrolysis of tetraethyl orthosilicate in an alcohol-water-ammonia medium was studied using transmission electron microscopy. It was established that the relatively large spherical silica particles were “tertiary” structures made up of smaller spherical particles (“ secondary” particles), which in turn consisted of even smaller primary spherical particles 5–10 nm in diameter. It was shown that, under the experimental conditions, the large SiO₂ particles can contain a central core comprising primary particles surrounded by several layers of secondary particles smaller than the core diameter.     

Evaluation of Morphology and Size Distribution of Silicon and Titanium Oxide Nanoparticles Generated by Laser Ablation

Nanometer-sized particles of silicon and titanium oxide were generated by irradiating solid targets using a nanosecond pulsed-Nd : YAG laser in a low pressure atmosphere. A low pressure differential mobility analyzer (LP-DMA) was used to classify the size of the generated particles. The LP-DMA and electron microscopes (SEM and TEM) were used to measure the change in the size distribution and morphology of the generated particles with laser power density and system pressure. The size distribution of both silicon and titanium oxide ranged from two to one hundred nanometers in diameter depending on the laser power density and pressure. From the high resolution TEM observation and electron diffraction, it was found that the generated titanium oxide nanoparticles were composed of a core of faceted metallic single crystals with an oxide layer 'shell.     

Microscopic investigation of soot and ash particulate matter derived from biofuel and diesel: implications for the reactivity of soot

Investigation of soot and ash particulate matter deposited in diesel particulate filters (DPFs) operating with biofuel (B100) and diesel (pure diesel: B0 and diesel₈₀/biofuel₂₀ blend: B20) by means of optical microscopy, scanning electron microscopy, and high resolution transmission electron microscopy (HRTEM) reveals the following: the rapeseed methyl ester biofuel used for this study contributes to ash production, mainly of Ca?CS?C and P-bearing compounds ranging in size between 50 and 300?nm. Smaller ash particles are less common and build aggregates. Ash is deposited on the inlet DPF surface, the inlet channel walls, and in B100-DPF at the plugged ends of inlet channels. The presence of Fe?CCr?CNi fragments, down to tens of nanometers in size within the ash is attributed to engine wear. Pt particles (50?C400?nm large) within the ash indicate that the diesel oxidation catalyst (DOC) upstream of the DPF shows aging effects. Radial cracks on the coating layer of the DOC confirm this assumption. The B100-DPF contains significantly less soot than B20 and B0. Based on the generally accepted view that soot reactivity correlates with the nanostructure of its primary particles, the length and curvature of graphene sheets from biofuel- and diesel-derived soot were measured and computed on the basis of HRTEM images. The results show that biofuel-derived soot can be more easily oxidized than diesel soot, not only during early formation but also during and after considerable particle growth. Differences in the graphene sheet separation distance, degree of crystalline order and size of primary soot particles between the two fuel types are in line with this inference.     

Plasma property effects on spectral line broadening in double-pulse laser-induced breakdown spectroscopy

Double-pulse Laser-Induced Breakdown Spectroscopy (LIBS) in an orthogonal configuration was used to investigate plasma temperature and electron density effects on Mg II emission spectral line broadening. The experiments were carried out with two Nd:YAG lasers, one operating at 355 nm for ablation and the other one at 1064 nm for plasma reheating in air at atmospheric pressure. Temporally resolved plasma temperature and electron density were measured at various delay times. Data in this study show prolonged emission of Mg II (280.27 nm) as well as enhancement of the signal intensity when using double-pulse excitation compared to the single-pulse case. An enhancement of ～8× was attained with a delay between the laser pulses equal to 1 μs. The enhancement was accompanied by higher plasma temperature and increased electron density. The double-pulse LIBS configuration provides energy to sustain the plasma emission at a period in time when the linewidth is minimum, thereby improving the analytical capabilities of low spectral resolution instrumentation typically used in LIBS system.     

Particle‐in‐cell/Monte Carlo simulation of electron and ion currents to cylindrical Langmuir probe

Electron and ion currents to a cylindrical Langmuir (electrostatic) probe were calculated using the particle‐in‐cell/Monte Carlo (PIC/MC) self‐consistent simulation for a neutral gas in the pressure range 2–3,000 Pa. The simulation enables us to calculate the probe currents even at high neutral gas pressures when the collisions of collected charged particles with neutral gas particles near the probe are important. The main aim of this paper is the calculation of probe currents at such high gas pressures and the comparison of the results with experimentally measured probe currents. Simulations were performed for two cases: (a) probes with varying radii in a non‐thermal plasma with high electron temperature at low neutral gas pressure of 2 Pa (in order to verify the correctness of our simulations), and (b) probe with the radius of 10 μm in the afterglow plasma with low electron temperature and a higher neutral gas pressure (up to 3,000 Pa). The electron probe currents obtained in case (a) show good agreement with those predicted by the orbital motion limited current (OMLC) theory for probes with radii up to 100 μm for the given plasma conditions. At larger probe radii and/or at higher probe voltages, the OMLC theory incorrectly predicts too high an electron probe current for the plasma parameters studied. Additionally, a formula describing the spatial dependence of the electron density in the presheath in the collisionless case is derived. The simulation at higher neutral gas pressures, i.e. case (b), shows a decrease of the electron probe current with increasing gas pressure and the creation of a large presheath around the probe. The simulated electron probe currents are compared with those of measurements by other authors, and the differences are discussed.     

Particle Size Characterization of an Extra Fine Milled Product

The present research aims to characterize the particle size distribution of sub micron particles suspended in a liquid. The particles milled are an organic poorly water soluble crystalline product. To characterize the size of these particles, different techniques have been tested: imaging techniques (SEM, CryoTEM), static light scattering techniques, dynamic light scattering techniques, centrifugation and flow field flow fractionation. The results indicate that the studied milled particles have a primary particle size close to 180nm and there is strong evidence of larger particles which are very likely aggregates. This is clearly seen from the Cryo TEM results. All the above mentioned techniques should in principle be able to measure samples of dispersion containing particles of ca 180 nm but several are disturbed by the presence of large aggregates. It is difficult to estimate the amount of aggregate present, but most of the time one is interested in what the primary particle size distribution is. It is clear that no single piece of equipment is capable of exactly determining the particle size distribution of our samples, but the static light scattering with low shear on mixing does give a good representation of what is seen with the image analysis by cryo TEM.     

Assisted spray pyrolysis production and characterisation of ZnO nanoparticles with narrow size distribution

Nano-sized ZnO particles with a narrow size distribution and high crystallinity were prepared from aqueous solutions with high concentrations of Zn²⁺ containing salts and citric acid in a conventional spray pyrolysis setup. Structure, morphology and size of the produced material were compared to ZnO material produced by simple spray pyrolysis of zinc nitrates in the same experimental setup. Using transmission electron microscopy and electron tomography it has been shown that citric acid-assisted spray pyrolysed material is made up of micron sized secondary particles comprising a shell of lightly agglomerated, monocrystalline primary ZnO nanoparticles with sizes in the 20–30 nm range, separable by a simple ultrasonic treatment step.     

Production of cobalt and nickel particles by hydrogen reduction

Cobalt and nickel nanoparticles were produced by hydrogen reduction reaction from cobalt or nickel chloride precursor vapour in nitrogen carrier gas. This aerosol phase method to produce nanoparticles is a scalable one-step process. Two different setups were introduced in particle production: a batch type reactor and a continuously operated reactor. Common feature in these setups was hydrogen mixing in a vertical flow reactor. The process was monitored on-line for particle mass concentration and for gas phase chemical reactions. Tapered element oscillating microbalance measured the particle mass concentration and Fourier transform infrared spectroscopy was used to monitor relevant gas phase species. The produced cobalt and nickel particles were characterised using transmission electron microscopy and x-ray diffraction. The produced cobalt and nickel particles were crystalline with cubic fcc structure. Twinning was often observed in cobalt particles while nickel particles were mostly single crystals. The cobalt particles formed typically long agglomerates. No significant neck growth between the primary particles was observed. The primary particle size for cobalt and nickel was below 100 nm.     

Emission measurement and safety assessment for the production process of silicon nanoparticles in a pilot-scale facility

Emission into the workplace was measured for the production process of silicon nanoparticles in a pilot-scale facility at the Institute of Energy and Environmental Technology e.V. (IUTA). The silicon nanoparticles were produced in a hot-wall reactor and consisted of primary particles around 60 nm in diameter. We employed real-time aerosol instruments to measure particle number and lung-deposited surface area concentrations and size distribution; airborne particles were also collected for off-line electron microscopic analysis. Emission of silicon nanoparticles was not detected during the processes of synthesis, collection, and bagging. This was attributed to the completely closed production system and other safety measures against particle release which will be discussed briefly. Emission of silicon nanoparticles significantly above the detection limit was only observed during the cleaning process when the production system was open and manually cleaned. The majority of the detected particles was in the size range of 100–400 nm and were silicon nanoparticle agglomerates first deposited in the tubing then re-suspended during the cleaning process. Appropriate personal protection equipment is recommended for safety protection of the workers during cleaning.     

The coherency of synchrotron radiation at Pohang Accelerator Laboratory

The coherency of the synchrotron radiation at Pohang Accelerator Laboratory has been investigated using Young's interferometer. The electron beam size can be measured precisely using the interferometer. An interferogram using 650 nm light at the diagnostics beamline at Pohang Light Source (PLS) has been measured to determine the electron beam distribution and the spatial coherence length. Interferograms obtained by numerical study are compared with experimental results in order to understand the measured data. From this comparison, the electron beam at PLS is revealed to be a Gaussian distribution with a standard deviation of 210 µm. The spatial coherency length of 650 nm light at PLS is measured to be 0.57 cm, and that of 0.1 nm light at PLS is predicted to be 0.88 µm by the same numerical study.     

Synthesis of Ultrafine Silicon Carbide Powders in Thermal Arc Plasmas

Ultrafine ?-SiC powders are synthesized in thermal plasmas by a reaction between methane and silicon monoxide. The reaction is carried out in an unconfined plasma jet (22.5 kW) operating at atmospheric Ar pressure. High temperatures (> 10 000 K) combined with ultrarapid quench rates (? 106 K/s) of the plasma lead to a high degree of supersaturation of the chemical vapor, resulting in homogeneous nucleation of ultrafine particles. Product characterizations are pursued with X-ray diffraction analysis, X-ray photoelectron spectroscopy (XPS), scanning, and transmission electron microscopy. The maximum SiC yield determined by thermogravimetric analysis (TGA) is 97.3 percent. Particle size analyses show a bimodal distribution with the majority of the particles falling in a size range from 2 to 40 nm. Triangular and hexagonal SiC particles are observed throughout this work and the nucleation and growth of these particles are discussed.     

Au-BaTiO3复合薄膜的脉冲激光沉积制备及其非线性光学效应

利用脉冲激光沉积技术制备了掺杂金纳米颗粒的钛酸钡复合薄膜Au-BaTiO3,用高分辨透射电镜和X射线光电子能谱对薄膜进行了表征。从透射电镜照片可以看出,制备的样品中金颗粒大小约为2~3 nm,呈球形,均匀分布在载体介质中。X射线光电子能谱给出了Ba3d、Ti2p和Au4f电子芯能级结合能,结果表明载体介质是以BaTiO3的形式存在,而Au以金属的状态掺杂其中。330~800 nm范围的线性吸收谱表明样品中Au颗粒的共振吸收峰在500 nm附近。用单光束纵向扫描方法测量了样品的三阶非线性光学效应,使用的光源为调Q的YAG激光器,波长为532 nm,脉宽为10 ns,得到的非线性折射率和非线性吸收系数分别为-2.42×10-6esu和2.22×10-6m/W,表明了Au-BaTiO3复合薄膜有较大的非线性光学响应。