Nanostructured Deposition of Nanoparticles from the Gas Phase

For many applications, nanoparticles from the gas phase are of interest due to their physical properties. Especially for electronic or optoelectronic applications, the transfer from their random distribution in the gas phase onto flat substrate surfaces has to be controlled because the particles are needed in exactly defined areas on the substrate. 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. By applying different voltages to the stamp, negative or positive charges can be transferred. Thus, nanoparticles of different polarities can be guided to certain places.     

电场辅助溶解法实现玻璃表面金纳米粒子的形貌控制

贵金属纳米粒子由于其非常独特的光学特性和表面活性, 在光子学、 催化和生物标识等方面都有非常重要的应用. 采用离子溅射和后续热处理相结合的方法在玻璃表面形成了尺寸大约为60-80 nm的单分散的球形金纳米粒子. 在适当的温度条件下, 采用步进式增加的强直流电场, 实现了金纳米粒子的电场辅助溶解过程. 在玻璃表面的不同颜色区域, 初始球形的金纳米粒子溶解成月蚀状形貌. 结合不同颜色区域内金纳米粒子的表面等离子体共振吸收性质和扫描电镜照片, 研究了实验条件对金纳米粒子性质的影响. 结合电场辅助溶解实验过程中的电流-电压特性, 分析了金纳米粒子在强直流电场辅助下溶解的物理过程: 金粒子中动出的电子向阳极的隧穿过程作为开始, 随后是金阳离子向玻璃基体中的传输过程和阴极提供的电子与带有正电荷的金粒子相结合的过程. 详细讨论了电场辅助溶解法实现金纳米粒子形貌控制的物理机制.     

Quasi-nanowires from fluorescent semiconductor nanocrystals on the surface of oriented DNA molecules

Ordered structures in the form of quasi-nanowires were obtained from CdSe/ZnS fluorescent semiconductor nanoparticles of spherical (quantum dots) or rodlike (quantum rods) form by their electrostatic deposition on DNA molecules with subsequent stretching of the molecules on a solid substrate. Positively charged nanoparticles were fixed along the negatively charged backbones of DNA molecules by electrostatic interactions in an aqueous solution of a mixture of DNA with quantum particles at different stoichiometric ratios. Strands of single DNA molecules with quantum particles fixed along them were immobilized and stretched on hydrophobic surfaces using the molecular combing technique. It is shown that, by varying the nanoparticle charge and the stoichiometry of complexes of DNA with particles, it is possible to create fluorescent structures with predetermined morphology and properties.     

Control of nanoparticle size and amount by using the mesh grid and applying DC-bias to the substrate in silane ICP-CVD process

The effect of applying a bias to the substrate on the size and amount of charged crystalline silicon nanoparticles deposited on the substrate was investigated in the inductively coupled plasma chemical vapor deposition process. By inserting the grounded grid with meshes above the substrate, the region just above the substrate was separated from the plasma. Thereby, crystalline Si nanoparticles formed by the gas-phase reaction in the plasma could be deposited directly on the substrate, successfully avoiding the formation of a film. Moreover, the size and the amount of deposited nanoparticles could be changed by applying direct current bias to the substrate. When the grid of 1 × 1-mm-sized mesh was used, the nanoparticle flux was increased as the negative substrate bias increased from 0 to – 50 V. On the other hand, when a positive bias was applied to the substrate, Si nanoparticles were not deposited at all. Regardless of substrate bias voltages, the most frequently observed nanoparticles synthesized with the grid of 1 × 1-mm-sized mesh had the size range of 10–12 nm in common. When the square mesh grid of 2-mm size was used, as the substrate bias was increased from – 50 to 50 V, the size of the nanoparticles observed most frequently increased from the range of 8–10 to 40–45 nm but the amount that was deposited on the substrate decreased.     

Estimation of zeta potentials of titania nanoparticles by molecular simulation

Non-equilibrium molecular dynamics (NEMD) simulations have been performed for static electric fields for a range of positively charged spherical rutile-titania nanoparticles with radii of 1.5 to 2.9 nm for two different salt concentrations in water, in order to simulate electrophoresis directly. Using the observed limiting drag velocities, Helmholtz-Smoluchowski (HS) theory was used to estimate their ζ potentials. These estimates were compared to values from numerical solution of the non-linear Poisson-Boltzmann (PB) equation for representative configurations of the nanoparticles, in addition to idealised analytic and Debye-Hückel (DH) solutions about spherical particles of the same geometry and charge state, for the given salt concentrations. It was found that reasonable agreement was obtained between the various approaches, with the NEMD-HS results some 15%-15% smaller than the numerical PB results for more highly charged nanoparticles.     

Electron‐transfer transparency of graphene: Fast reduction of metal ions on graphene‐covered donor surfaces

The mechanism of charge transfer through nanomaterials such as graphene remains unclear, and the amount of charge that can be transferred from/to graphene without damaging its structural integrity is unknown. In this communication, we show that metallic nanoparticles can be decorated onto graphene surfaces as a result of charge transfer from the supporting substrate to an adjoining solution containing metal ions. Au or Pt nanoparticles were formed with relatively high yield on graphene‐coated substrates that can reduce these metal ions, such as Ge, Si, GaAs, Al, and Cu. However, metal ions were not reduced on graphene surfaces coated onto non‐reducing substrates such as SiO₂ or ZnO. These results confirm that graphene can be doped by exploiting charge transfer from the underlying substrate; thus graphene is not only transparent with respect to visible light, but also with respect to the charge transfer. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Nanoparticle electrostatic loss within corona needle charger during particle-charging process

A numerical investigation has been carried out to examine the electrostatic loss of nanoparticles in a corona needle charger. Two-dimensional flow field, electric field, particle charge, and particle trajectory were simulated to obtain the electrostatic deposition loss at different conditions. Simulation of particle trajectories shows that the number of charges per particle during the charging process depends on the particle diameter, radial position from the symmetry axis, applied voltage, Reynolds number, and axial distance along the charger. The numerical results of nanoparticle electrostatic loss agreed fairly well with available experimental data. The results reveal that the electrostatic loss of nanoparticles increases with increasing applied voltage and electrical mobility of particles; and with decreasing particle diameter and Reynolds number. A regression equation closely fitted the obtained numerical results for different conditions. The equation is useful for directly calculating the electrostatic loss of nanoparticles in the corona needle charger during particle-charging process.     

A comparative STM study of Ru nanoparticles deposited on HOPG by mass-selected gas aggregation versus thermal evaporation

Scanning tunneling microscopy was used to compare the morphologies of Ru nanoparticles deposited onto highly-oriented graphite surfaces using two different physical vapour deposition methods; (1) pre-formed mass-selected Ru nanoparticles with diameters between 2 nm and 15 nm were soft-landed onto HOPG surfaces using a gas-aggregation source and (2) nanoparticles were formed by e-beam evaporation of Ru films onto HOPG. The particles generated by the gas-aggregation source are round in shape with evidence of facets resolved on the larger particles. Annealing these nanoparticles when they are supported on unsputtered HOPG resulted in the sintering of smaller nanoparticles, while larger particles remained immobile. Nanoparticles deposited onto sputtered HOPG surfaces were found to be stable against sintering when annealed. The size and shape of nanoparticles deposited by e-beam evaporation depend to a large extent on the state of the graphite support and the temperature. Ru deposition onto unsputtered HOPG is characterised by bimodal growth with large flat particles formed on the substrate terraces and smaller diameter particles aligned along the substrate steps. Evaporation onto sputtered HOPG results in the formation of 2 nm round particles with a narrow size distribution. Finally, thermal deposition onto both sputtered and unsputtered HOPG at 660 °C results in larger particles showing a flat Ru(0 0 0 1) top facet.     

Carbon nanotubes decorated by graphitic shells encapsulated Cu nanoparticles

Carbon nanotubes (CNTs) decorated by graphitic shells encapsulated Cu nanoparticles were fabricated by low-energy hydrocarbon ion deposition with using Cu as hold substrate at 900°C. Scanning electron microscopy shows that the surface of CNTs becomes very coarse by hydrocarbon ion treatment. The investigation of transmission electron microscope shows that the full surfaces of CNTs are coated by dense graphitic shells encapsulated Cu nanoparticles. The graphitic shells consist of 7–10 layers and the size of Cu core is 1–2 nm.     

用双极坐标求解带电导体圆柱和无限大接地导体平板间的电势

利用双极坐标求解了带电导体圆柱和无限大接地导体平板间的电势分布,并对带电导体圆柱表面的电荷分布及无限大接地导体平板表面的电荷分布作了讨论.     

Multiwall carbon nanotubes decorated with FeCr2O4, a new selective electrochemical sensor for amoxicillin determination

Direct writing aims to deposit materials onto substrates in localised positions. In this paper, we demonstrate a new method for direct writing of nanoparticles at ambient-air-pressure. An electrical discharge is used to generate gold nanoparticles of the order of 10?nm diameter, which are then transported and ??focused?? by an electric field in air, through the process of electric field-assisted diffusion, as opposed to normal ballistic focusing since the mean free path in air is very short. This process is novel and allows for practical normal atmospheric-pressure focused deposition of nanoparticles. The focusing mechanism is capable of producing patterned arrays of deposited nanoparticles with widths that are less than 10?% of the diameter of the focusing apparatus; in the present experimental configuration, gold spots with diameters of a few tens of micrometres were achieved, with ultimate size being limited by transverse diffusion and by charged particle mutual repulsion. In this study, the process of generating nanoparticles from bulk material, transporting and focusing these particles takes place in one operation, which is a key advantage in rapid prototyping and manufacturing techniques.     

Parameters optimization for biological molecules patterning using 248-nm ultrafast lasers

Laser-induced forward transfer has been used for the deposition of photoactive biotin in micron-scale patterns. The process uses a 500 fs pulsed KrF laser beam to transfer small amounts of a liquid solution target as micron-size droplets to a substrate placed parallel and in close proximity to it. The biomolecules remain active after the transfer; this is demonstrated through fluorescence assays. In addition to the laser parameters, those regarding the target composition and the receiving surface for the miniaturization of the transferred patterns have been studied and optimized. Droplets as small as 5 μm have been obtained by reducing the target thickness and transfer energy; by increasing the percentage of glycerol added in the biomolecules solution and by using hydrophobic surfaces as receiving substrates. The influence of the glycerol addition and the hydrophobicity of the receiving surfaces on the activity of the transferred biomolecules have also been studied.     

Particles in laser ablation of polytetrafluoroethylene

KrF-laser ablation of pressed polytetrafluoroethylene (PTFE) targets is accompanied by the ejection of submicron- to micron-sized particles. Collected ejecta consist of four basic particle morphologies ranging from small particles 50-200 nm in diameter to larger particles ~10 7m in diameter. Many particles carry electric charge as measured by using charged electrodes and by the Millikan technique. Thin PTFE films deposited by pulsed laser deposition (PLD) from the same targets onto heated Si substrates are highly crystalline and show only a minor but detectable increase of defects compared with the target material. The transferred particulates mainly consist of long PTFE molecule chains. The low molecular weight material that is also transferred to the substrate mainly either links with other low molecular weight material or evaporates during deposition.     

工业中粉体颗粒的荷电机理及数值模拟方法

工业过程中粉体颗粒不可避免地会相互摩擦碰撞而荷电. 荷电颗粒的存在可能会危害正常的工业生产过程, 也可能对工业过程起促进作用. 因此, 荷电粉体颗粒及其特性受到了广泛的关注, 但目前对粉体颗粒的荷电机理依然缺乏透彻的了解, 尤其是在气固两相流动中的粉体颗粒荷电现象. 事实上, 工业中存在的粉体颗粒的运动都受到流体的影响, 是典型的气固两相流系统, 流体对粉体颗粒的作用使粉体颗粒接触的荷电现象变得更为复杂, 因此从两相流动的观点来研究粉体颗粒荷电的物理本质就显得越来越重要. 本文介绍了工业过程中的几种不同类型的粉体颗粒荷电行为, 回顾了颗粒的荷电机理与描述颗粒荷电的数学模型. 对于工业过程中颗粒的荷电现象及颗粒在多相流体中的动力学行为, 介绍了研究颗粒受流体影响时荷电特性的数值模拟方法. 本文旨在对粉体颗粒的荷电机理、应用以及研究方法进行梳理与探讨, 为正确认识工业过程中粉体颗粒的荷电现象并加以控制利用提供理论借鉴.     

Monolayer deposition of L10 FePt nanoparticles via electrospray route

The deposition monolayers of L1₀ FePt nanoparticles via an electrospraying method and the magnetic properties of the deposited film were studied. FePt nanoparticles in a size of around 2.5 nm in diameter, prepared by a liquid process, were used as a precursor. The size of the deposited particles can be controlled up to 35 nm by controlling the sprayed droplet size that is formed by adjusting the precursor concentration and the precursor flow rate. The droplets were heated in a tubular furnace at a temperature of up to 900 °C to remove all organic compounds and to transform the FePt particles from disordered face centered cubic to an ordered FCT phase. Finally, the particles were deposited in the form of a monolayer film on a silicon substrate by electrostatic force and characterized by scanning electron microscopy. The monolayer of particles was obtained by the high charge on particles obtained during the electrospraying process. The magnetic properties of the monolayer were investigated by magneto-optic Kerr effect measurements. Coercivity up to 650 Oe for a film consisting of 35 nm L1₀ FePt nanoparticles was observed after heat treatment at a temperature of 800 °C.     

Increase in the molecular component of the adhesive pressure in polymer composites induced by electric charge

The effect of electric charge, present at a glass fiber–polymer interface during the composite material formation, on the adhesive pressure between the components was studied. Additional electric charge was delivered to the interface by means of the deposition of charged polymer particles onto the fiber surface from a fluidized bed in an electric field. The adhesive pressure was calculated using the results of the variational mechanics analysis by Scheer and Nairn from the data obtained with a single fiber microbond test. Our experiments showed that the adhesive pressure increased by 15–20% in the case of charged polymer matrices. This can be attributed to both intensification of van der Waals forces due to extra interfacial pressure and, for polar polymers, the increase of the surface concentration of local adhesive bonds. The mechanical and kinetic models have been proposed to describe the observed behavior of the adhesive pressure; theoretical curves for the adhesive pressure as a function of the time and temperature of the contact formation, including the effect of electric factors, have been obtained. From the kinetic model, the activation energies for the process of adhesive contact formation were determined. The effect of acceleration of adhesive bonding in the presence of electric charge can be explained in terms of a decrease of the activation energy for local bond formation in an electric field.     

Electron correlations in the chemisorption theory: Self-consistent calculations of the adatom charge

The single hydrogen-like adatom chemisorption on transition metal surfaces is studied by using the generalized model Hamiltonian. This Hamiltonian includes the possibility of influence of the adatom orbital occupancy on the charge transfer between the adatom and the substrate metal. The correlation effects were included up to second order in V (the single particle coupling strength). The numerical calculations of the charge transfer between an adatom and a substrate metal, as well as the comparison with results obtained for the standard Newns-Anderson model indicate that this generalized Hamiltonian can be more efficient in describing the chemisorption process.     

Silver nanoparticles deposited on dielectric surfaces

Surface plasmon polaritons in nanoparticles were used as a sensitive indicator of structural and electronic properties of metallic nanoparticles deposited upon various dielectric substrates. Quantum size and cluster–substrate interactions were separated. The latter were modelled with the dynamic charge transfer effect. For calibration purposes, the free surfaces of the same clusters exposed to a UHV beam were also investigated. The particles were slightly deformed during deposition; their final shapes and, in particular, their contact areas were determined. The width of the plasmon excitation band was roughly doubled compared to that of the free particles, but proved to depend only slightly on the chemical nature of the substrates, in drastic contrast to the case of fully embedded particles. The analogy holds for the dephasing lifetimes. One reason for this is that the contact area varies strongly with the substrate material, while it is constant in systems of matrix-embedded particles. Received: 26 July 2001 / Revised version: 10 September 2001 / Published online: 15 October 2001     

Strategy for improved analysis of peptides by surface‐enhanced Raman spectroscopy (SERS) involving positively charged nanoparticles

A strategy for improved surface‐enhanced Raman spectroscopy (SERS) measurements that extends the variety of analytes accessible to SERS analysis is developed. The strategy involves inducing aggregation by mixing positively charged nanoparticles which form SERS‐active clusters when mixed with negatively charged silver nanoparticles fabricated using the Lee–Meisel process. To make positively charged nanoparticles, silver nanoparticles using the traditional Lee–Meisel process are fabricated and coated with a thin layer of silica and the silica modified with silane chemistry. Analytes with a significant amount of negative charge exhibit strong Raman bands when the strategy using these fabricated, positively charged nanoparticles for inducing cluster formation is used, enabling their detection and analysis. We envision the use of positively charged nanoparticles in cluster formation for expanding the range of analytes that can be detected using SERS and hence the range of applications SERS can play a role in. Copyright © 2008 John Wiley & Sons, Ltd.     

Optical properties of gold electrode surfaces covered with metal monolayers

The relative reflectivity changes ΔR/R of a gold electrode surface caused by the deposition of monolayers of thallium, copper and lead from electrolytic solutions at underpotentials have been studied in situ in the photon energy range between 1.8 and 5.2 eV. The optical constants of the surface layer giving rise to this measured reflectivity change have been calculated and compared to the results of the electroreflectance effect on bare gold surfaces. It is shown that the reflectance change observed during the monolayer deposition is to first order due to a change in the gold electrode surface layer and not to absorption processes in the monolayer itself. The latter ones cause a fine structure superimposed to the substrate spectrum. The relatively strong change in the gold surface optical constants upon metal monolayer deposition is explained in terms of an enhanced electroreflectance effect due to the partially ionic character of the metal adatoms, which alters the free electron concentration in the substrate surface layer. Electroreflectance spectra obtained on gold surfaces covered with a monolayer of thallium compare favourably with dielectric loss functions computed for charged gold surfaces. This supports the assumption that the reflectivity changes observed upon metal monolayer deposition are mostly due to changes in the optical properties of the substrate metal surface.