Fluorescence Enhancements on Silver Colloid Coated Surfaces

We observed a strong, more than 16-fold, enhancement of Texas Red-labeled BSA fluorescence emission when deposited on silver colloid coated surfaces (SCCS). The same labeled protein deposited on silver island films (SIFs) showed an approximate 8-fold fluorescence enhancement. The lifetimes of Texas Red-BSA fluorescence are significantly shorter on silvered surfaces than on uncoated quartz substrate indicating a strong change in radiative decay rate of the dyes. We also observed a 36-fold increased brightness of overlabeled fluorescein-HSA deposited on silver colloid coated surface. Stronger enhancement observed for overlabeled Fl-HSA protein indicates that presence of silver particles partially decreased self-quenching. Our results indicate that surfaces coated with silver colloids are valuable substrates for metal-enhanced fluorescence.     

Multiple trapping using a focused hybrid vector beam

We propose a simple and efficient method that uses a single focused hybrid vector beam to confine metallic Rayleigh particles at multiple positions.We study the force mechanisms of multiple trapping by analyzing the gradient and scattering forces.It is observed that the wavelength and topological charges of the hybrid vector beam regulate the trapping positions and number of optical trap sites.The proposed method can be implemented easily in three-dimensional space, and it facilitates both trapping and organization of particles.Thus, it can provide an effective and controllable means for nanoparticle manipulation.     

Multifocal optical trapping using counter-propagating radially-polarized beams

A model of optical tweezers which can trap a chain of Rayleigh particles is proposed by using two counter-propagating equal highly focused radial polarized beams. Calculations show that a multifocal distribution along the optical axis is formed and the scattering force is equal to zero in the total focal filed, consequently a chain of metallic Rayleigh particles can be stably trapped. The trap force and the trap stiffness using two counter-propagating Radially-polarized beams are larger than those using two counter-propagating linearly-polarized beams. The trapping stability is calculated and analyzed in detail. The trapping number of particles in a trapping chain can be controlled by adjusting the aperture angle of the objective and the parameters of the filter used in the proposed trap system.     

Optical absorption of ultrafine metal spheres with dielectric cores

We compute the optical absorption of a glass containing a small fraction of silver particles with dielectric cores. The results are based on the Maxwell Garnett formalism. The dielectric permeability of the metallic shells is obtained by modifying experimental data for bulk silver to account for size dependent scattering of the conduction electrons. We find an absorption maximum in the visible range at a wavelength which, for sufficiently minute particles, depends rather strongly on the size of the cores and on their dielectric constant. The relevance of these results to recent experimental data by Smithard and by Genzel et al. is pointed out. We argue that their observed absorption maxima can be explained without invoking any quantum effects.     

Optical characterization of metallic aerosols

Airborne metallic particulates from industry and urban sources are highly conducting aerosols. The characterization of these pollutant particles is important for environment monitoring and protection. Because these metallic particulates are highly reflective, their effect on local weather or regional radiation budget may also need to be studied. In this work, light scattering characteristics of these metallic aerosols are studied using exact solutions on perfectly conducting spherical and cylindrical particles. It is found that for perfectly conducting spheres and cylinders, when scattering angle is larger than 90° the linear polarization degree of the scattered light is very close to zero. This light scattering characteristics of perfectly conducting particles is significantly different from that of other aerosols. When these perfectly conducting particles are immersed in an absorbing medium, this light scattering characteristics does not show significant change. Therefore, measuring the linear polarization of scattered lights at backward scattering angles can detect and distinguish metallic particulates from other aerosols. This result provides a great potential of metallic aerosol detection and monitoring for environmental protection.     

Optomagnetically Controlled Microparticles Manufactured with Glancing Angle Deposition

Optical trapping and magnetic trapping are common micromanipulation techniques for controlling colloids including micro‐ and nanoparticles. Combining these two manipulation strategies allows a larger range of applied forces and decoupled control of rotation and translation; each of which are beneficial properties for many applications including force spectroscopy and advanced manufacturing. However, optical trapping and magnetic trapping have conflicting material requirements inhibiting the combination of these methodologies. In this paper, anisotropic microscaled particles capable of being simultaneously controlled by optical and magnetic trapping are synthesized using a glancing angle deposition (GLAD) technique. The anisotropic alignment of dielectric and ferromagnetic materials limits the optical scattering from the metallic components which typically prevents stable optical trapping in three dimensions. Compared to the current state of the art, the benefits of this approach are twofold. First, the composite structure allows larger volumes of ferromagnetic material so that larger magnetic moments may be applied without inhibiting the stability of optical trapping. Second, the robustness of the synthesis process is greatly improved. The dual optical and magnetic functionality of the synthesized colloids is demonstrated by simultaneously optically translating and magnetically rotating a magnetic GLAD particle using a custom designed optomagnetic trapping system.     

A simple method for the preparation of colloidal polymer-supported silver nanoparticles

Polysulfone?silver composite nanoparticles have been prepared by combining polymer nanoprecipitation and redox synthesis of silver, in the presence of a glucose-modified cyclosiloxane as stabilizing agent. Based on previous kinetic investigations and on model reactions, we concluded that the reducing agent in this case is the tetrahydrofuran (THF) used as solvent for polysulfone. Dynamic light scattering measurements on the obtained polymer-silver composite particles indicated particle average diameter of 176 nm with a polydispersity index of 0.25. The UV–vis spectrum exhibited the silver plasmon resonance. By different microscopic methods (atomic force microscopy—AFM, high resolution transmission electron microscopy—HRTEM, and scanning electron microscopy—SEM), larger polymer particles coated with silver nanoprticles were observed. The Energy Dispersive X-Ray analysis—EDX; confirmed the presence of Ag on the surface of the particles, while the selected area electron diffraction showed single crystalline silver nanospheres with face-centered cubic structure.     

Image enhancement in near-field scanning optical microscopy with laser-trapped metallic particles

A trapped-particle near-field scanning optical microscope is constructed by use of submicrometer- or micrometer-sized metallic particles (gold and silver) to increase scattering efficiency. The image contrast of the evanescent-wave interference pattern on the surface of a prism upon total internal reflection, obtained with trapped gold particles of diameter 0.1 and 2microm , is improved by a factor of approximately 2 and 1.5, respectively, compared with that obtained with trapped polystyrene particles of similar size. The use of a 2-microm gold particle leads to image contrast that is approximately three times as great as that obtained with a 0.1-microm gold particle, and interference patterns of a subwavelength period are obtained in both cases.     

Stable optical trapping based on optical binding forces

Various trapping configurations have been realized so far, either based on the scattering force or the gradient force. In this Letter, we propose a new trapping regime based on the equilibrium between a scattering force and optical binding forces only. The trap is realized from the interaction between a single plane wave and a series of fixed small particles, and is efficient at trapping multiple free particles. The effects are demonstrated analytically upon computing the exact scattering from a collection of cylindrical particles and calculating the Lorentz force on each free particle via the Maxwell stress tensor.     

Light scattering by slightly nonspherical particles on surfaces

We investigate the shape dependence of the scattering by dielectric and metallic particles on surfaces by considering particles whose free-space scattering properties are nearly identical. The scattering by metallic particles is strongly dependent on the shape of the particle in the region near where the particle touches the surface. The scattering by dielectric particles displays a weaker, but nonetheless significant, dependence on particle shape. These results have a significant effect on the use of light scattering to size and identify particles on surfaces.     

Zn/ZnO纳米颗粒的表面声子Raman散射

Ｚｎ／ＺｎＯ纳米颗粒的表面声子Ｒａｍａｎ散射许建峰黄亚彬莫育俊（河南大学物理系开封４７５００１）ＲａｍａｎＳｃａｔｅｒｉｎｇｆｒｏｍＳｕｒｆａｃｅＰｈｏｎｏｎｓｉｎＺｎ／ＺｎＯＮａｎｏｐａｒｔｉｃｌｅｓＸｕＪｉａｎｆｅｎｇ，ＨｕａｎｇＹａｂｉｎ，Ｍｏ...     

Monitoring small defects on surface microstructures through backscattering measurements

The detection and characterization of small defects on particles or structures of a size comparable with the incident wavelength and located on flat substrates is numerically analyzed. For metallic scattering systems, calculations based on the extinction theorem of physical optics show that geometrical information about a small Gaussian defect can be obtained by partially integrating the backscattering patterns.     

Particle Shape Effects in the Extinction Spectra of Gold and Silver Nanoparticles

Particle shape effects in the absorption and scattering spectra of gold and silver nanoparticles are studied for optical-range radiation. Numerical calculations of extinction cross section are performed using the FDTD approach for particles of three shapes: disks, triangular prisms, and triradial-base prisms. It is established that the spectra of nanoparticles of different shapes differ qualitatively even if they are of the same characteristic dimensions. The obtained results can be used to develop a spectroscopic procedure for determining the shape of metallic nanoparticles and producing quantitative estimates of their characteristic dimensions.     

Ultra‐subwavelength focusing of light by a monolayer of metallic nanoshells with an adsorbed defect

We study theoretically the focusing properties of a two‐dimensional periodic array of silver‐coated silica nanospheres. The array contains an adsorbed nanosphere of the same type which serves as point source when the array is illuminated by a plane wave. By using a rigorous multiple‐scattering theory we show that under plane wave illumination, the array focuses the incident light in a tight area with size of about 1/70 of the wavelength. At the same time, the near‐field is amplified by three orders of magnitude. The frequency corresponding to the focusing and amplification effects depends on the thickness of the silver nanoshell offering a tunable response of the structure. The latter can find application in optical trapping, lithography and imaging below the diffraction limit. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

相干和非相干合成光束对金属瑞利粒子的光学俘获

研究了两光束的合成方式(相干和非相干合成)对俘获金属瑞利粒子的辐射力和稳定性的影响,着重研究了辐射力与合成方式、离轴距离、相干参数和粒子半径的关系.结果表明,不同合成方式下,离轴距离和相干参数都分别存在临界值d_c和α_c,在0d_c或α>α_c时,焦面处光强呈中心凹陷分布,此时横向梯度力不能作为回复力俘获金属瑞利粒子.在0<d≤d_c时,与非相干合成光束比较,相干合成光束在焦面处光强、辐射力、俘获刚性和纵向俘获范围更大.因此,适当选择合成方式,较小离轴距离和较低相干参数可有利于合成光束对金属瑞利粒子的俘获.     

The scattering of hydrogen,deuterium, and the rare gases from silver (111) single crystals

The scattering of hydrogen, deuterium, and the rare gases from the (111) face of silver has been studied at ultrahigh vacuum. The surfaces were prepared by argon ion bombardment and high temperature annealing. Incident angles between 20° and 65° and surface temperatures between room temperature and 573°K have been investigated. The scattering data exhibit quasi-elastic scattering (He, H₂, D₂), inelastic scattering (Ne, Ar, Kr), and trapping dominated scattering (Xe). Identification of these scattering regimes correlates with D/kT_g and is consistent with similar data from Pt(111) and W(110). The separate effects of microscopic surface roughness and thermal roughening have been identified and thermal attenuation in the elastic regime correlated with dynamical interactions rather than thermal roughening. Trapping and rotational coupling are discussed. Comparison of the data with scattering from epitaxial (111) silver indicates that the epitaxial surfaces are significantly more disordered than the single crystal surfaces.     

随机取向双层椭球粒子偏振散射特性研究

基于T矩阵方法,给出了随机取向、轴对称、含核椭球粒子的散射计算方法.散射体的核和外壳均可为非球形粒子,整个粒子具有轴对称性.以含核椭球粒子为模型,计算了含有吸收性内核(黑炭,black carbon)的水凝物气溶胶的散射特性,分析了核的大小、形状对消光系数、散射系数、吸收系数、不对称因子、单次散射反照率以及Muller矩阵等的影响. 关键词： 光散射 T矩阵 Muller矩阵 椭球粒子     

SERS characterization of metallic silver nanoparticle self‐assembly within thin films

Clusters of silver nanoparticles are generated by the thermally initiated reduction of silver carboxylates (long‐chain fatty acids) in the thin polymer films. The size, shape, and aggregation of these nanoparticles are affected by the reduction reaction in the presence of capping agents. In order to understand the mechanism(s) controlling the silver structure formation, it is essential to understand the surface coordination chemistry occurring during this process. We now report the first application of surface‐enhanced Raman spectroscopy (SERS) to directly characterize adsorbates on the surfaces of silver nanoparticles within a thin film imaging construction containing multiple components. In addition, SERS investigation of model silver substrates was used to confirm the identify of specific adsorbates of silver complexes. This is a powerful tool for revealing the chemistry involved with the control of silver nanoparticle aggregation during thermally induced metallic silver formation within thin films. Both the catechol‐reducing agent and the phthalazinone (PAZ) particle aggregation agent are observed on the metallic silver surface at the initial particle formation and during its crystal growth. However, careful attention to excitation wavelength is required in order to observe all the surface species. PAZ appears to be more effective at stabilizing individual silver particles than other aggregation agents investigated. An understanding of the roles of the aggregation/reducing agents in the growth and aggregation of silver nanoparticles is important for preparing different types of silver particles for specific applications including silver‐based thermal imaging systems. Copyright © 2008 John Wiley & Sons, Ltd.     

层析滤纸拉曼光谱特性研究

为了研究层析滤纸在表面增强拉曼光谱和层析技术联用中的影响。在785 nm激发波长下分别测试了层析滤纸, 涂布银胶后层析滤纸的拉曼特征谱, 以及氧化乐果在层析滤纸上的拉曼光谱和表面增强拉曼光谱(SERS)。结果表明, 层析滤纸在800~1500 cm-1光谱区域具有丰富的拉曼特征峰, 分析认为主要来源于纤维素, 并对其进行了归属; 涂布银胶后, 由于银颗粒的作用, 层析滤纸拉曼强度整体降低, 并发生特征峰相对强度的变化; 同时, 氧化乐果在层析滤纸上的SERS谱也表明涂布银胶能够有效抑制层析滤纸拉曼特征峰, 增强待测物质拉曼强度, 但在800~1500 cm-1光谱区域仍需考虑层析滤纸的影响。     

The effect of radiation on dye-doped polystyrene microspheres coated by a thin silver layer

The heat conduction equation is analyzed theoretically and numerically for the case of the effect of laser radiation on two-layer spherical particles. The internal heat sources and the temperature distribution are calculated for particles whose core of dye-doped polystyrene is coated by a deposited silver layer. The distribution of heat sources inside such a two-component microsphere is shown to depend significantly on the core radius and the shell thickness. Therefore, these parameters strongly affect the heating of particles. In particular, an increase in the thickness of the deposited silver layer may either reduce or strongly increase the heating time of two-layer microspheres.