Steady Patterns of Microparticles Formed by Optical Tweezers

In this paper, we propose a method for forming steady patterns of microparticles in a dispersion using optical tweezers. We demonstrate how to control the congregation of particles in a dispersion and to manually fabricate a pattern, The steady pattern (nay be useful for in-depth research, and the method will have applications in biology and nanotechnology.

Implication of scaling hierarchy associated with nonequilibrium: field and particulate

The advent of nanotechnology has necessitated a better understanding of how material microstructure changes at the atomic level would affect the macroscopic properties that control the performance. Such a challenge has uncovered many phenomena that were not previously understood and taken for granted. Among them are the basic foundation of dislocation theories which are now known to be inadequate. Simplifying assumptions invoked at the macroscale may not be applicable at the micro- and/or nanoscale. There are implications of scaling hierrachy associated with in-homegeneity and nonequilibrium. of physical systems. What is taken to be homogeneous and equilibrium at the macroscale may not be so when the physical size of the material is reduced to microns. These fundamental issues cannot be dispensed at will for the sake of convenience because they could alter the outcome of predictions. Even more unsatisfying is the lack of consistency in modeling physical systems. This could translate to the inability for identifying the relevant manufacturing parameters and rendering the end product unpractical because of high cost. Advanced composite and ceramic materials are cases in point. Discussed are potential pitfalls for applying models at both the atomic and continuum levels. No encouragement is made to unravel the truth of nature. Let it be partiuclates, a smooth continuum or a combination of both. The present trend of development in scaling tends to seek for different characteristic lengths of material microstructures with or without the influence of time effects. Much will be learned from atomistic simulation models to show how results could differ as boundary conditions and scales are changed. Quantum mechanics, continuum and cosmological models provide evidence that no general approach is in sight. Of immediate interest is perhaps the establishment of greater precision in terminology so as to better communicate results involving multiscale physical events.

Rapidly Infrared-Assisted Cooperatively Self-Assembled Highly Ordered Multiscale Porous Materials

In this paper, cooperative self-assembly (CSA) of colloidal spheres with different sizes was studied. It was found that a complicated jamming effect makes it difficult to achieve an optimal self-assembling condition for construction of a well-ordered stacking of colloidal spheres in a relatively short growth time by CSA. Through the use of a characteristic infrared (IR) technique to significantly accelerate local evaporation on the growing interface without changing the bulk growing environment, a concise three-parameter (temperature, pressure, and IR intensity) CSA method to effectively overcome the jamming effect has been developed. Mono- and multiscale inverse opals in a large range of lattice scales can be prepared within a growth time (15-30 min) that is remarkably shorter than the growth times of several hours for previous methods. Scanning electron microscopy images and transmittance spectra demonstrated the superior crystalline and optical qualities of the resulting materials. More importantly, the new method enables optimal conditions for CSA without limitations on sizes and materials of multiple colloids. This strategy not only makes a meaningful advance in the applicability and universality of colloidal crystals and ordered porous materials but also can be an inspiration to the self-assembly systems widely used in many other fields, such as nanotechnology and molecular bioengineering.

Molecular/Cluster Statistical Thermodynamics Methods To Simulate Quasi-Static Deformations At Finite Temperature

The rapid evolution of nanotechnology appeals for the understanding of global response of nanoscale systems based on atomic interactions, hence necessitates novel, sophisticated, and physically based approaches to bridge the gaps between various length and time scales. In this paper, we propose a group of statistical thermodynamics methods for the simulations of nanoscale systems under quasi-static loading at finite temperature, that is, molecular statistical thermodynamics (MST) method, cluster statistical thermodynamics (CST) method, and the hybrid molecular/cluster statistical thermodynamics (HMCST) method. These methods, by treating atoms as oscillators and particles simultaneously, as well as clusters, comprise different spatial and temporal scales in a unified framework. One appealing feature of these methods is their "seamlessness" or consistency in the same underlying atomistic model in all regions consisting of atoms and clusters, and hence can avoid the ghost force in the simulation. On the other hand, compared with conventional MD simulations, their high computational efficiency appears very attractive, as manifested by the simulations of uniaxial compression and nanoindenation. (C) 2008 Elsevier Ltd. All rights reserved.

The size-dependent bending elastic properties of nanobeams with surface effects

A theoretical model is presented to investigate the size-dependent bending elastic properties of a nanobeam with the influence of the surface relaxation and the surface tension taken into consideration. The surface layer and its thickness of a nanostructure are defined unambiguously. A three-dimensional (3D) crystal model for a nanofilm with n layers of relaxed atoms is investigated. The four nonzero elastic constants of the nanofilm are derived, and then the Young's modulus for simple tension is obtained. Using the relation of energy equilibrium, the size-dependent effective elastic modulus and effective flexural rigidity of a nanobeam with two kinds of cross sections are derived, and their dependence on the surface relaxation and the surface tension is analysed.

Adsorption of His-tagged peptide to Ni, Cu and Au (100) surfaces: Molecular dynamics simulation

Molecular dynamics (MD) simulations are performed to study the interaction of His-tagged peptide with three different metal surfaces in explicit water. The equilibrium properties are analyzed by using pair correlation functions (PCF) to give an insight into the behavior of the peptide adsorption to metal surfaces in water solvent. The intermolecular interactions between peptide residues and the metal surfaces are evaluated. By pulling the peptide away from the peptide in the presence of solvent water, peeling forces are obtained and reveal the binding strength of peptide adsorption on nickel, copper and gold. From the analysis of the dynamics properties of the peptide interaction with the metal surfaces, it is shown that the affinity of peptide to Ni surface is the strongest, while on Cu and An the affinity is a little weaker. In MD simulations including metals, the His-tagged region interacts with the substrate to an extent greater than the other regions. The work presented here reveals various interactions between His-tagged peptide and Ni/Cu/Au surfaces. The interesting affinities and dynamical properties of the peptide are also derived. The results give predictions for the structure of His-tagged peptide adsorbing on three different metal surfaces and show the different affinities between them, which assist the understanding of how peptides behave on metal surfaces and of how designers select amino sequences in molecule devices design. (c) 2007 Elsevier Ltd. All rights reserved.

Growth of deformation twins in room-temperature rolled nanocrystalline nickel

Deformation twinning has been observed in room-temperature rolled nanocrystalline Ni. The growth of the deformation twins via the emission of partial dislocations from a grain boundary has been examined in detail. Partial dislocations on neighboring slip planes may migrate for different distances and then remain in the grain interior, leading to the formation of a steplike twin boundary TB . With continued twin growth, the TBs become gradually distorted and lose their coherent character due to accumulated high stresses. Moreover, we propose that microtwins may form near such TBs due to the emission of partial dislocations from the TB.

Coherent linking of periodic nano-ripples on a ZnO crystal surface induced by femtosecond laser pulses

We demonstrate the coherent linking of periodic nano-ripples formed on the surface of ZnO crystals induced by femtosecond laser pulses. By adjusting the distance between two laser scanning zones, the periodic nano-ripples induced by two separated laser writing processes can be coherently linked and the ZnO nanograting with much longer grooves is therefore produced. The length limitation of this kind of nanograting previously set by the laser focus size is thus overcome. The micro-Raman mapping technique is used to evaluate the quality of coherent linking, and the underlying physics is discussed. The demonstrated scheme is promising for producing large-size self-organized nanogratings induced by femtosecond laser pulses.

Photoluminescence of Ag nanoparticle embedded Tb3+/Ce3+ codoped NaYF4/PVP nanofibers prepared by electrospinning

Ag nanoparticle embedded NaYF4:0.05Tb center dot chi Ce/ PVP (PVP stands for poly(vinyl pyrrolidone)) composite nanofibers have been prepared by electrospinning. A field emission scanning electron microscope and x-ray diffraction have been utilized to characterize the size, morphology and structure of the as-prepared electrospun nanofibers. Obvious photoluminescence (PL) of NaYF4:0.05Tb center dot 0.05Ce/PVP electrospun nanofibers due to the efficient energy transfer from Ce3+ to Tb3+ ions is observed. The PL intensity of the electrospun nanofibers decreases gradually with the addition of Ag nanoparticles. No obvious surface plasmon resonance enhanced luminescence is observed. The reasons for the weakening of the emission intensity with the addition of Ag nanoparticles have also been discussed in this work.

A uniform 290 nm periodic square structure on ZnO fabricated by two-beam femtosecond laser ablation

A uniform submicron periodic square structure was fabricated on the surface of ZnO by a technique of two linearly polarized femtosecond laser beams with orthogonal polarizations ablating material alternately. The formed two-dimensional ordering submicron structure consists of close-packed submicron squares with a spacial periodicity of 290 nm, which arises from the intercrossing of two orthogonal submicron ripple structures induced by the two beams respectively. The result demonstrates a noninterference effect of two-beam ablation based on the alternate technique, which should come from the polarization-dependent enhancement of the subwavelength ripple structure and the large interval of two alternate pulses. This two-beam alternate ablation technique is expected to open up prospects for the submicron fabrication of wide-bandgap materials.

Talbot-SNOM method for non-contact evaluation of high-density gratings

A Talbot scanning near-field optical microscopy (SNOM) method for non-contact evaluating of high-density gratings was described. This method combines the Talbot self-imaging effect of the gratings and the conventional SNOM technique without damage. The significant advantages of this method are its simple structure, reliable and fast measurement for the surface quality of the tested gratings. Experimental results of three different kinds of gratings were demonstrated to indicate that this method is effective for evaluation surface quality of high-density gratings. (c) 2004 Elsevier B.V. All rights reserved.

Electroless-plated gold films for sensitive surface plasmon resonance detection of white spot syndrome virus

The paper describes the rapid and label-free detection of the white spot syndrome virus (WSSV) using a surface plasmon resonance (SPR) device based on gold films prepared by electroless plating. The plating condition for obtaining films suitable for SPR measurements was optimized. Gold nanoparticles adsorbed on glass slides were characterized by transmission electron microscopy (TEM). Detection of the WSSV was performed through the binding between WSSV in solution and the anti-WSSV single chain variable fragment (scFv antibody) preimmobilized onto the sensor surface. Morphologies of the as-prepared gold films, gold films modified with self-assembled alkanethiol monolayers, and films covered with antibody were examined using an atomic force microscope (AFM). To demonstrate the viability of the method for real sample analysis, WSSV of different concentrations present in a shrimp hemolymph matrix was determined upon optimizing the surface density of the antibody molecules. The SPR device based on the electroless-plated gold films is capable of detecting concentration of WSSV as low as 2.5 ng/mL in 2% shrimp hemolymph, which is one to two orders of magnitude lower than the level measurable by enzyme-linked immunosorbant assays. (c) 2007 Elsevier B.V. All rights reserved.

Identification and characterization of Bacillus anthracis by multiplex PCR on DNA chip

Bacillus anthracis can be identified by detecting virulence factor genes located on two plasmids, pXO1 and pXO2. Combining multiplex PCR with arrayed anchored primer PCR and biotin-avidin alkaline phosphatase indicator system, we developed a qualitative DNA chip method for characterization of B. anthracis, and simultaneous confirmation of the species identity independent of plasmid contents. The assay amplifies pag gene (in pXO1), cap gene (in pXO2) and Ba813 gene (a B. anthracis specific chromosomal marker), and the results were indicated by an easy-to-read profile based on the color reaction of alkaline phosphatase. About 1 pg of specific DNA fragments on the chip wells could be detected after PCR. With the proposed method, the avirulent (pXO1(+)/2(-), pXO1(-)/2(+) and pXO1(-)/2(-)) strains of B. anthracis and distinguished 'anthrax-like' strains from other B. cereus group bacteria were unambiguously identified, while the genera other than Bacillus gave no positive signal. (C) 2004 Elsevier B.V. All rights reserved.