Electrospray deposit structure of nanoparticle suspensions

Electrospray atomization has unique capabilities for deploying colloidal suspensions to create nanoparticle films and coatings. This technique can deliver precise quantities of particles in a dry state to a target substrate and overcomes many limitations of other printing and coating technologies. Since the structure of a nanoparticle layer governs its functionalities, it is essential to understand the relationship between the key operating parameters and the macro- and microstructure of an electrospray deposit. We investigated the role of three key parameters on the deposit structure: electrospray time, the target substrate electrical properties, and the polydispersity of the colloidal suspension. The macrostructure of the nanoparticle deposits was similar for all spray times and substrates. In particular, the deposited particles segregate to the center and edge of a deposit, leaving a depletion region in between. We speculate that the mutual Coulombic forces due to the space charge inside the plume play a key role in governing the trajectory of the nanoparticles and the ensuing deposit morphology. Since particles emitted by electrospray are highly charged, the microstructure of a deposit was strongly influenced by the electrical conductivity of the target substrate. By maintaining a net charge, particles deposited on to a dielectric substrate could influence the deposition of subsequent in-flight particles, which opens new routes for exerting control over the deposit structure.     

The effect of excess surfactants on the adsorption of iron oxide nanoparticles during a dip-coating process

The effect of excess surfactants (oleic acids) in a colloidal solution on the adsorption behavior of 9.5-nm-sized, sterically stabilized iron oxide (γ-Fe₂O₃) nanoparticles on hydrogen terminated Si (Si:H) substrates during a dip-coating process is examined. While the particle coverage follows a type of Langmuir adsorption isotherm as initially increasing and subsequently saturating with increasing particle concentration, it also critically depends on the excess surfactant concentration in the solution. For instance, it is noted that by adding the oleic acids from 0.06 to 2.80 × 10¹⁸ ml⁻¹ in the solution with 4.65 × 10¹³ ml⁻¹ particle concentration, the coverage is gradually reduced from 0.42 to 0.25. In addition, increasing surfactant concentration distinctly changes the morphology of a self-assembled particle layer from densely distributed smaller clusters to sparsely connected, larger ones with enlarged space. The reduced coverage and enlarged cluster size with increasing oleic acid concentration are explained by the reduced interaction energy between particle and substrate and the increased capillary force between particles.     

Self-assembled silver nanoparticle films at an air-liquid interface and their applications in SERS and electrochemistry

In this paper, we present a novel technique to prepare silver nanoparticle films by controlling the self-assembly of nanoparticles at an air-liquid interface. In an ethanol-water phase, silver nanoparticles were prepared by reduction of AgNO₃ aqueous solution with NaBH₄ in the presence of cinnamic acid. It was found that the silver nanoparticles in this process could be trapped at the air-liquid interface to form 2-dimensional nanoparticle films. The morphology of nanoparticle films could be controlled by systematic variation of the experimental parameters. It is worth noting that the nanoparticle films could serve as the active substrates for surface-enhanced Raman scattering (SERS). 4-Aminothiophenol (4-ATP) molecule was used as a test probe to investigate the SERS sensitivity of different nanoparticle films. The results indicated that the nanoparticle films showed excellent Raman enhancement effect. Furthermore, the nanoparticle films prepared by our strategy were found to be efficient electrocatalysts for anodic oxidation of formaldehyde in alkaline medium.     

Dispersion tailoring in single mode optical fiber by doping silver nanoparticle

We propose an optical fiber which has very low dispersion loss (typically ~ 6.7 ps²/km at 1,550 nm) that can be achieved by doping Ag nanoparticle into the core glass. At low absorption loss approximation, dispersion free propagation can be achieved up to 64 km for a 20 ps pulse. Enhanced third order nonlinearity due to the presence of Ag nanoparticle (typically ~ 3.82 × 10^?20 W/m²) compensates for long length dispersion broadening that is not possible in conventional fused silica step index fiber.     

Effect of chromium interlayer deposition on periodic silver nanoparticle array structure fabricated by nanosphere lithography

Effect of chromium interlayer deposition on 2-dimensional, periodic silver nanoparticle array structure was systematically investigated. The silver nanoparticle array was fabricated by nanosphere lithography with assembled polystyrene nanospheres being as a deposition mask. The chromium interlayer was deposited by thermal evaporation either on the nanosphere mask or directly on the silicon substrate. The structures of the achieved silver nanoparticle arrays were characterized by scanning electron microscope and were compared with that of silver nanoparticle array without the interlayer. With analysis of the anomalies among the structures the critical role of the interlayer in the periodic nanoparticle array fabrication was revealed.     

Electrodeposition of silver nanoparticle arrays on ITO coated glass and their application as reproducible surface-enhanced Raman scattering substrate

In this paper, a double-potentiostatic method is used for preparation of highly efficient and uniform surface-enhanced Raman scattering (SERS) substrate. The method takes advantage of the quick nucleation and slow growth process, yielding silver nanoparticle arrays (NAs) containing large amount of hot spots, which bring about these dense silver NAs for reproducible SERS application.     

硅狭缝光波导的色散特性及其色散补偿应用的研究

对硅狭缝光波导色散特性进行了数值研究.研究结果表明,在1.55μm工作波长附近,硅狭缝光波导色散随结构参量的改变而改变,一般在-1000ps/(nm·km)以下,最大可达到-6700ps/(nm·km)左右,同时其相对色散斜率可小于0.009nm-1.因此,选取合适的结构参量,硅狭缝光波导可被用于补偿高速宽带光通信链路的残余色散,且比现有的色散补偿光纤具有一定的优势.     

A Dispersion Flattening Dispersion Compensating Fiber Design for Broadband Dispersion Compensation

An efficient dispersion compensating fiber (DCF) design is proposed based on a coaxial fiber structure, which provides dispersion compensation over a broad wavelength region matching that of an erbium-doped fiber amplifier gain spectrum. The design can provide dispersion coefficient that is nearly twice those of existing DCF designs. Due to the basic nature of the dispersion curve of this design, the total link dispersion cannot only be compensated but also can be flattened.     

Fluctuations and rheology in active bacterial suspensions

We probe nonequilibrium properties of an active bacterial bath through measurements of correlations of passive tracer particles and the response function of a driven, optically trapped tracer. These measurements demonstrate violation of the fluctuation-dissipation theorem and enable us to extract the power spectrum of the active stress fluctuations. In some cases, we observe 1/sqrt[omega] scaling in the noise spectrum which we show can be derived from a theoretical model incorporating coupled stress, orientation, and concentration fluctuations of the bacteria.     

优化二元相位取样光纤布喇格光栅及对色散和色散斜率补偿的应用

利用粒子群算法对二元相位取样光栅的周期相位调制进行优化设计，在此基础上提出了基于二元相位取样光纤布喇格光栅的色散和色散斜率补偿技术.通过光栅周期啁啾可以调整每个信道的带宽，色散量由子光栅长度决定，调整取样函数的啁啾系数可以改变色散斜率，因此可以设计出用于波分复用系统的多信道色散补偿器件.     

Origin and System Effects of Polarization Mode Dispersion in Chirped Bragg Gratings

Polarization mode dispersion of chirped Bragg gratings is analyzed in terms of key birefringence phenomena and impact on telecommunication systems performance. The influence on polarization mode dispersion (PMD) of fiber birefringence, grating chromatic dispersion, and ripples of the group delay curve is pointed out. Polarization mode dispersion influence on systems performance is investigated by numerical simulations and transmission experiments at 10 Gbit/s. The deterministic nature of Bragg gratings PMD determines a moderate, upper-limited system penalty for a transmission line employing a single compensating device. However, in the case of broadband components, a non-negligible PMD penalty may be observed due to the difficulty of controlling accurately the group delay linearity.     

Flow and fracture in drying nanoparticle suspensions

Drying aqueous suspensions of monodisperse silica nanoparticles can fracture in remarkable patterns. As the material solidifies, evenly spaced cracks invade from the drying surface, with individual cracks undergoing intermittent motion. We show that the growth of cracks is limited by the advancement of the compaction front, which is governed by a balance of evaporation and flow of fluid at the drying surface. Surprisingly, the macroscopic dynamics of drying show signatures of molecular-scale fluid effects.     

Sedimentation of nanoparticles in nanoscale colloidal suspensions

A theoretical model is developed to study the sedimentation characteristics of nanoscale colloidal suspensions (nanofluids). The influences of various deterministic and stochastic forcing parameters in the transport characteristics of the suspended nanoparticles are investigated by employing a Langevin formalism of particle transport. The role of collective particle interaction phenomena in the sedimentation of nanoparticles is analyzed by invoking the fundamental considerations of agglomeration-deagglomeration kinetics of the particulate phases. The model demonstrates the effect of particle volume fraction, particle size, and aggregate structure on the sedimentation velocity of the suspended nanoparticles. Predictions from the present model agree well with the experimental results reported in the literature.     

Structural properties of silver nanoparticle agglomerates based on transmission electron microscopy: relationship to particle mobility analysis

In this work, the structural properties of silver nanoparticle agglomerates generated using condensation and evaporation method in an electric tube furnace followed by a coagulation process are analyzed using Transmission Electron Microscopy (TEM). Agglomerates with mobility diameters of 80, 120, and 150 nm are sampled using the electrostatic method and then imaged by TEM. The primary particle diameter of silver agglomerates was 13.8 nm with a standard deviation of 2.5 nm. We obtained the relationship between the projected area equivalent diameter (d _pa) and the mobility diameter (d _m), i.e., d _pa = 0.92 ± 0.03 d _m for particles from 80 to 150 nm. We obtained fractal dimensions of silver agglomerates using three different methods: (1) D _f = 1.84 ± 0.03, 1.75 ± 0.06, and 1.74 ± 0.03 for d _m = 80, 120, and 150 nm, respectively from projected TEM images using a box counting algorithm; (2) fractal dimension (D _fL) = 1.47 based on maximum projected length from projected TEM images using an empirical equation proposed by Koylu et al. (1995) Combust Flame 100:621–633; and (3) mass fractal-like dimension (D _fm) = 1.71 theoretically derived from the mobility analysis proposed by Lall and Friedlander (2006) J Aerosol Sci 37:260–271. We also compared the number of primary particles in agglomerate and found that the number of primary particles obtained from the projected surface area using an empirical equation proposed by Koylu et al. (1995) Combust Flame 100:621–633 is larger than that from using the relationship, d _pa = 0.92 ± 0.03 d _m or from using the mobility analysis.     

高功率离子束在漂移管中的中性化传输

介绍了“闪光二号”加速器产生的高功率离子束在漂移管中的传输实验。对比了采用中性化措施前后的传输情况，分析了中性化措施对离子束束斑半径、束流均匀性的影响。根据实测的二极管电压模拟得到了传输一定距离后的束流波形，与实测结果符合较好。采取适当的中性化措施后，高功率离子束可以有效传输80 cm以上，束流发散得到抑制，束流均匀性得到改善。     

Rationalisation of distribution functions for models of nanoparticle magnetism

A formalism is presented which reconciles the use of different distribution functions of particle diameter in analytical models of the magnetic properties of nanoparticle systems. For the lognormal distribution a transformation is derived which shows that a distribution of volume fraction transforms into a lognormal distribution of particle number albeit with a modified median diameter. This transformation resolves an apparent discrepancy reported in Tournus and Tamion [Journal of Magnetism and Magnetic Materials 323 (2011) 1118].     

Low-frequency laser spectroscopy of cylindrical nanoparticle suspensions

A theory of generation of anti-Stokes radiation on the eigenvibrations in a suspension of cylindrical nanoparticles in the field of two copropagating electromagnetic pump waves has been developed. Surface ponderomotive forces are shown to induce acoustic vibrations and dipolemoments of nanoparticles at the anti-Stokes frequency. Under these conditions, the scattering efficiency depends on the dielectric characteristics of the solution and the acoustic parameters of the liquid and solid fractions of the suspension. Experiments on stimulated low-frequency Raman scattering of laser radiation in aqueous suspensions of tobacco mosaic virus in a buffer solution have been performed. A coherent signal of the Stokes component with a frequency shift of ≈60GHz is detected; this value is in good agreement with the estimated frequency shift for stimulated excitation of eigenvibrations of cylindrical nanoparticles in a liquid: ≈50 GHz.     

Approximate and Exact Small Signal Analysis for Single-Mode Fiber Near Zero Dispersion Wavelength with Higher Order Dispersion

This article presents the comparison of approximate and exact small-signal theories for analyzing the influence of the higher-order dispersion terms on dispersive optical communication systems operating near zero dispersion wavelength for linear single-mode fiber. For the approximate theory, the generalized conversion matrix has been reported and gives the transfer function of intensity and phase from the fiber input to fiber output for a laser source including the influence of any higher-order dispersion term. In addition, expressions for the small-signal frequency response and the relative intensity noise (RIN) response of an ultrafast laser diode including noises are derived. However, it is observed that the approximation assumed for the second-order dispersion term for the approximate analysis is not valid. From the approximate theory, the exact generalized conversion matrix and exact expressions for small-signal frequency response and relative intensity noise (RIN) are obtained. We show that for the exact theory, the second-order dispersion term has no effect on intensity and frequency response even at large modulating frequencies and large propagation distances contrary to the approximate theory as reported by other authors. But we show that third-order dispersion term certainly has some minute impact on the frequency and RIN response for long distance links at high modulating frequencies.     

Approximate and Exact Small Signal Analysis for Single-Mode Fiber Near Zero Dispersion Wavelength with Higher Order Dispersion

This article presents the comparison of approximate and exact small-signal theories for analyzing the influence of the higher-order dispersion terms on dispersive optical communication systems operating near zero dispersion wavelength for linear single-mode fiber. For the approximate theory, the generalized conversion matrix has been reported and gives the transfer function of intensity and phase from the fiber input to fiber output for a laser source including the influence of any higher-order dispersion term. In addition, expressions for the small-signal frequency response and the relative intensity noise (RIN) response of an ultrafast laser diode including noises are derived. However, it is observed that the approximation assumed for the second-order dispersion term for the approximate analysis is not valid. From the approximate theory, the exact generalized conversion matrix and exact expressions for small-signal frequency response and relative intensity noise (RIN) are obtained. We show that for the exact theory, the second-order dispersion term has no effect on intensity and frequency response even at large modulating frequencies and large propagation distances contrary to the approximate theory as reported by other authors. But we show that third-order dispersion term certainly has some minute impact on the frequency and RIN response for long distance links at high modulating frequencies.     

Dependence of the viscosity of nanofluids on nanoparticle size and material

The viscosity of nanofluids as a function of nanoparticle size and material is modeled and analyzed. Dependences of the viscosity of nanofluids based on liquid argon with aluminum and lithium nanoparticles are obtained. The nanoparticle size ranges from 1 to 4 nm. The volume concentration of nanoparticles is varied from 1% to 12%. It is shown that the viscosity of the nanofluid increases with decreasing nanoparticle size and, in addition, depends on the nanoparticle material.