Nanoscale structures of circle - MgCl2 constructed by plasmid DNA templates

Circular nanoscale structures of inorganic salt, MgCl₂, are constructed by extended plasmid DNA pBR322 as a template on mica substrates, and these nanosized structures of 6.2±1.3 to 8.2±1.8 nm in height, and 1.35±0.18 to 2.93±0.25 μm in length are investigated by atomic force microscopy (AFM). The chemical element components of these nanostructures are characterized by XPS. We also discuss a possible formation mechanism of these circle nanostructures.     

Nanoscale control of low-dimensional spin structures in manganites

Due to the upcoming demands of next-generation electronic/magnetoelectronic devices with low-energy consumption,emerging correlated materials(such as superconductors,topological insulators and manganites) are one of the highly promising candidates for the applications.For the past decades,manganites have attracted great interest due to the colossal magnetoresistance effect,charge-spin-orbital ordering,and electronic phase separation.However,the incapable of deterministic control of those emerging low-dimensional spin structures at ambient condition restrict their possible applications.Therefore,the understanding and control of the dynamic behaviors of spin order parameters at nanoscale in manganites under external stimuli with low energy consumption,especially at room temperature is highly desired.In this review,we collected recent major progresses of nanoscale control of spin structures in manganites at low dimension,especially focusing on the control of their phase boundaries,domain walls as well as the topological spin structures(e.g.,skyrmions).In addition,capacitor-based prototype spintronic devices are proposed by taking advantage of the above control methods in manganites.This capacitor-based structure may provide a new platform for the design of future spintronic devices with low-energy consumption.     

多个CCD交汇测量系统的理论研究

本文介绍了采用多个线阵ＣＣＤ 组成交汇测量系统的基本原理,导出了测量坐标的计算公式,并利用有关的误差理论对该方法的测量精度进行了详细分析。研究结果表明,多个ＣＣＤ 交汇测量系统能够得到较高的目标捕获几率,同时还能有效地提高坐标测量精度。对大靶面、高速小目标物体的精密测量具有重要意义     

Direct opal-like structures consisting of monodisperse polymer particles and synthesis of the related inverse structures

Three-dimensional periodic solid-state film structures with a face-centered cubic lattice and a high degree of perfection have been prepared from monodisperse particles of styrene copolymers with methacrylic acid. It has been shown that these structures can be successfully used not only as model objects for studying specific features of light propagation in photonic crystals but also as templates for synthesizing inverse opal-like structures. The influence of the degree of hydrophilization of the surface layer of polymer particles forming a polymer template and the template synthesis conditions on the quality of an inverse opal-like TiO₂-based structure has been analyzed.     

Nanoscale continuum calculation of basal dislocation core structures in graphite

In this work, we calculate the core structures of basal dislocations in graphite in a nanoscale continuum framework. The model consists of a stack of buffered Kirchhoff plates where the plates represent the covalent interactions within individual graphene sheets and the buffer layers represent the secondary interactions between them. In the mid-plane of the buffer layers, cohesive surfaces are introduced to account for the nonlinear deformations due to basal dislocations. The cohesive surface separation is governed by using an empirical 4-8 Lennard–Jones potential. Meanwhile, their relative shear sliding is governed by using a newly proposed empirical periodic stacking-fault potential. With these potentials, the core structures of full dislocations and partials are calculated and examined. It is shown that the full dislocations automatically split into partials that repel each other. The core sizes of individual partials, measured between peak stresses, are about 5?nm wide for the edge component and slightly narrower for the screw component. Since these sizes are about 10 times the lattice constant, they lend credence to our continuum model of basal dislocation cores in graphite. It is also shown that when the dislocations are densely packed on the same glide plane, i.e. in a pile-up, with spacing one to two times the core size, the split partials retain their individual identity with well-defined and well-separated stress peaks. Meanwhile, the membrane normal stresses in the graphene sheets rise considerably at the pile-up tips which, in turn, may provoke further deformation and damage modes such as kinking and delamination.     

Nanoscale resistive random access memory consisting of a NiO nanodot and Au nanowires formed by dip-pen nanolithography

We demonstrate the nanoscale resistive random access memory (RRAM) element consisting of an approximately 30 nm diameter NiO nanodot and two bridging Au nanowires, formed by a dip-pen nanolithography technique using nickel carbonate (Ni₂(CO₃)(OH)₂) and [AuCl₄]⁻ complex solutions, respectively. The Au/NiO/Au nanowire resistive switch exhibits typical unipolar switching characteristics with high performance at low Set and Reset voltages.     

Fabrication of size-controlled three-dimensional structures consisting of electrohydrodynamically produced polycaprolactone micro/nanofibers

In this paper, we report a facile method of fabricating size-controlled three-dimensional (3D) polycaprolactone (PCL) micro/nanofiber structure using a modified electrospinning supplemented with a specially designed solvent bath in which the flow rate of the solvent (EtOH) was controlled. By varying the flow rate of the EtOH into the grounded bath and the electrospinning parameters including a distance between the nozzle and target, the height, diameter, porosity, and micro/nanofiber size of the 3D structures were controlled. To show stable micro/nanofibrous structures under the fabricating conditions, we characterized a process diagram for various flow rates of EtOH and weight percents of PCL. We believe that this modified electrospinning process may be a new means of fabricating micro/nanofibrous 3D structures.     

Quasi-phase-matched frequency conversion in KNbO3 structures consisting of 90° ferroelectric domains

Periodic 90° domain structure with 18.6 μm periodicity was fabricated by applying a 200 V/mm electric field over (1̄01)-cut KNbO₃ plate. The blue light generation by quasi-phase-matched frequency doubling in this periodic 90° domain structure is demonstrated. The 90° domain structure completely compensates for a Poynting vector walk-off of the second-harmonic beam. Moreover, these structures exhibit amphoteric Poynting vector refraction properties, i.e., the refraction can be negative or positive depending on the angle of incidence at the 90° domain boundary. PACS 42.65.ky; 42.70.Mp; 77.80.Dj     

More complex DNA structures

Fibrous polynucleotide duplexes are very polymorphic. Detailed x-ray analysis of the D forms of poly d(AT) ·poly d(AT) and poly d(IC) ·poly d(IC) and of the B form of poly d(GC) ·poly d(GC) show that 5′RpY3′ dinucleoside monophosphates in these molecules have either t,t or t,g conformations at C3′–03′, 03′-P which lead to similar orientations of phosphate groups. On the other hand, 5′YpR3′ fragments commonly have g,t conformations and hence a markedly different orientation of the phosphate group. Studies of the more complex structures of the C form of poly d(ACC) ·poly d(GGT) and of a pleiomeric D form of poly d(AT) ·poly d(AT) where the repeated structural motifs are hexanucleotides reveal further details of the surface “wrinkles” on DNA. In the case of the H form of poly d(A) ·poly d(T), the sugar rings in each strand are puckered differently-C2′-endo in poly d(T) and C3′-endo in poly d(A). Such heteromerous duplexes have unusually pronounced directional properties. Similar structure ma be present in some DNA-RNA hybrids. These surface feature might enable regulatory proteins and enzymes to recognize their host DNA sequences more easily in the blinding process.     

Nanoscale smoothing of plasmonic films and structures using gas cluster ion beam irradiation

We present a novel method of using gas cluster ion beam irradiation (GCIB) to flatten and widen grains in silver films and structures, while simultaneously, reducing the film thickness with nanometer precision. Ultrathin Ag films produced by GCIB have lower absorbance and better adhesion compared to as-deposited films. By applying the technique post-fabrication to plasmonic color filters, waveguides and disks, we show that an enhanced surface plasmon resonance and propagation length can be achieved.     

Nanoscale imaging of buried structures with elemental specificity using resonant x-ray diffraction microscopy

We report the first demonstration of resonant x-ray diffraction microscopy for element specific imaging of buried structures with a pixel resolution of approximately 15 nm by exploiting the abrupt change in the scattering cross section near electronic resonances. We performed nondestructive and quantitative imaging of buried Bi structures inside a Si crystal by directly phasing coherent x-ray diffraction patterns acquired below and above the Bi M5 edge. We anticipate that resonant x-ray diffraction microscopy will be applied to element and chemical state specific imaging of a broad range of systems including magnetic materials, semiconductors, organic materials, biominerals, and biological specimens.     

由介质球构成的三维光子晶体能带结构的平面波研究

采用平面波展开方法计算由介质球构成的面心立方三维光子晶体的能带结构及透射性质.选 用合适的平面波个数研究了SiO₂蛋白石结构光子晶体的能带及透射性质，并采 用转移矩阵 方法计算了电磁波沿［111］方向的传输特性，两种方法得到的结果相符合.还研究了反蛋白 石结构光子晶体的全带隙.最后，研究了壳层介质球构成的面心立方结构光子晶体的能带特 性，发现在高介质球外面包裹适当厚度的低介电常数介质壳层所构成的光子晶体，可以增大 L点相对带隙宽度50％，并证明了其优化内外半径比值约为0．69. 关键词： 光子晶体 光子能带 平面波展开方法 Core-Shell结构     

Modification of a SAXS camera to study structures on multiple scales

A compact small-angle X-ray scattering (SAXS) camera was modified in order to cover a significantly wider size range than that typically covered by conventional lab-based devices. A new housing with a larger sample-to-detector distance (230 → 1300 mm) was developed and a new focusing Göbel mirror was installed to provide a narrower beam width needed to detect scattering intensities very close to the primary beam. A new photon-counting detector was applied to probe the intensity at small scattering vectors while an imaging plate detector serves to simultaneously collect data at large scattering angles up to 90°. The relevant features of the camera are shown and discussed based on raytracing simulations and SAXS measurements, respectively. The minimum scattering vector could be decreased by a factor of 10 to a value of 0.008 nm^?1 corresponding to structures up to 780 nm in size. Structural analyses of selected particle systems demonstrate ability of the modified camera to probe various structural parameters on multiple scales, e.g., crystallite size, primary particle size, aggregate size, and fractal dimensions. The modified camera system is promising for structural studies of particle formation and growth/aggregation mechanisms since it provides information on multiple scales ranging from angstroms to several hundred nanometers.     

Nanoscale imaging with resonant coherent X rays: extension of multiple-wavelength anomalous diffraction to nonperiodic structures

The methodology of multiple-wavelength anomalous diffraction, widely used for macromolecular structure determination, is extended to the imaging of nonperiodic nanostructures. We demonstrate the solution of the phase problem by a combination of two resonantly recorded coherent scattering patterns at the carbon K edge (285 eV). Our approach merges iterative phase retrieval and x-ray holography approaches, yielding unique and rapid reconstructions. The element, chemical, and magnetic state specificity of our method further renders it widely applicable to a broad range of nanostructures, providing a spatial resolution that is limited, in principle, by wavelength only.     

Scalable InP integrated wavelength selector based on binary search

We present an InP monolithically integrated wavelength selector that implements a binary search for selecting one from N modulated wavelengths. The InP chip requires only log(2)N optical filters and log(2)N optical switches. Experimental results show nanosecond reconfiguration and error-free wavelength selection of four modulated wavelengths with 2 dB of power penalty.     

Physics of multiple level hairpin vortex structures in turbulence

Previous experimental and numerical studies have revealed that the hairpin vortex is a basic flow element of transitional boundary layer. The hairpin vortex is believed to have legs, necks and a ring head. Based on our DNS study, the legs and the ring head are generated separately by different mechanisms. The legs function like an engine to generate low speed zones by rotation, create shear layers with surrounding high speed neighbor fluids, and further cause vortex ring formation through shear layer instability. In addition, the ring head is ?-shaped and separated from quasi-streamwise legs from the beginning. Contrary to the classical concept of "vortex breakdown", we believe transition from laminar flow to turbulence is a "buildup" process of multiple level vortical structures. The vortex rings of first level hairpins are mostly responsible for positive spikes, which cause new vorticity rollup, second level vortex leg formation and finally smaller second level vortex ring generation. The third and lower level vortices are generated following the same mechanism. In this paper, the physical process from ?-vortex to multi-level hairpin vortices is described in detail.     

Analysis of coupling effect on valence band structures of strained multiple quantum wells

The multi-well energy representation technique is presented for the analysis of the valence band structures of multiple quantum well (MQW) lasers. In terms of this technique and its relative formulae, calculations are performed for InGaAs/InGaAsP strained MQW structures. It is found that the coupling exists between the wells, and causes the energy split. So, on the basis of the computed results, the coupling between the wells is analysed, and the split of both the quantized energy levels at the Γ point and the quantized energy bands at the non-Γ points is described. It is also found that the structural parameters of the MQW system strongly influence the coupling property and the energy split, and hence these effects are also discussed in relation to the periodic length, the well width, the distance between the wells, and the ratio of the well width to the periodic length. This revised version was published online in June 2006 with corrections to the Cover Date.