Group-theoretic approach to enhancing the Fourier modal method for crossed gratings with square symmetry

The Fourier modal method for crossed gratings with square symmetry is reformulated by use of a group-theoretic approach that we developed recently. In the new formulation, a crossed-grating problem is decomposed into six symmetrical basis problems whose field distributions are the symmetry modes of the grating. Then the symmetrical basis problems are solved with symmetry simplifications, whose solutions are superposed to get the solution of the original problem. Theoretical and numerical results show that when the grating is at some Littrow mountings, the computation efficiency can be improved effectively: The memory occupation is reduced by 3/4 and the computation time is reduced by a factor from 25.6 to 64 in different incident cases. Numerical examples are given to show the effectiveness of the new formulation.     

Fabrication of periodic nickel silicide nanodot arrays using nanosphere lithography

The interfacial reactions of the 2D-ordered nickel metal nanodots that were prepared by polystyrene nanosphere lithography (NSL) on Si substrates after different heat treatments have been investigated. Epitaxial NiSi₂ nanodot arrays were found to form at a temperature as low as 350 °C. The results indicated that the growth of epitaxial NiSi₂ is more favorable for the Ni metal dot array samples. The sizes of these epitaxial NiSi₂ nanodots in samples annealed at 350–800 °C are in the range of 84–110 nm. The shape of the epitaxial NiSi₂ nanodot was found to be pyramidal. Furthermore, for the samples annealed at 900 °C, amorphous SiO_x nanowires were found to grow on individual nickel silicide nanoparticles. The diameters of these nanowires are in the range of 15–20 nm. As the size of metal nanodot can be adjusted by tuning the diameter of the polystyrene (PS) spheres, the NSL technique promises to be an effective patterning method without complex lithography.     

基于溶胶-凝胶的两种旋涂方法制备PZT厚膜

采用溶胶-凝胶法,研究了两种在Au/Cr/SiO2/Si基底上沉积PZT(Pb(Zr0.52Ti0.48)O3)厚膜的方法.把与PZT澄清溶胶成分相同的PZT纳米粉混入澄清PZT溶胶,然后超声混合形成PZT浆料,PZT纳米粉的粒径为50～100nm.XRD分析表明两种方法得到的PZT厚膜都获得了单相钙钛矿结构.SEM结果显示两种厚膜厚度大约4μm,第一种旋涂方法制得的PZT厚膜表面粗糙,第二种旋涂方法制得的厚膜表面致密,无裂纹.在1 kHz的测试频率下,第一种和第二种厚膜的矫顽场分别为30 kV/cm和50 kV/cm,饱和极化分别为45 μC/cm2和54 μC/cm2,剩余极化分别为25μC/cm2 and 30μC/cm2.第二种厚膜有较高的直流耐压性能,在300 kV/cm的电场下,仍然保持较好的铁电性能.因而,第二种旋涂方法能够改善PZT厚膜的表面形貌和铁电性能.     

Preparation of YBCO superconductor thin film by spin-coating method with metal-organic precursors

YBCO thin film was prepared by the spin-coating method with metal-organic precursors. The precursors were synthesized by reacting metal acetates with 2-ethylhexanic acid or by reacting metal halides with ammonium 2-ethylhexanate directly. After proper heat treatments, YBCO film with T _{c, onset} = 80 K and T _c,zero = 77 K was obtained. SEM studies of a sample prepared at 990 °C showed the presence of CuO and Ba₂YCuO₅ (211 phase). This suggested the transient presence of a liquid phase which had been observed in preparing YBCO bulk material by the melt-texture method before the formation of YBCO phase. Furthermore, many voids were observed in the as-obtained film. These might be the origin of the relatively low T _c,zero, temperature.     

Fabrication of patterned multicomponent protein gradients and gradient arrays using microfluidic depletion

We demonstrate that depletion effects in the fluids used to fill a poly(dimethylsiloxane) microfluidic device can be used in conjunction with its design rules to generate patterned protein gradients. The linear portions of these structures can be designed to present gradients of bound protein coverage-varying from near-saturation to effectively zero-over distances ranging from a few hundred micrometers to more than 1 cm by design. Such patterns can be developed in a simple, single-channel form as well as in a multichannel gradient array of more complex design. The patterning protocols also support the use of multiple protein sources, and we demonstrate an assembly process mediated by a protein that inhibits adsorption to generate a gradient array in pixel form. We describe examples of multiple protein gradient patterns along with simple immunoassays to illustrate the scope of the methodology, the activity of the patterned proteins, and their recognition in gradient form on a surface. These gradients should prove useful to studies in biosensor and bioassay development and as substrates for cell culture to study growth and motility.     

Fabrication of p-type silicon nanowire arrays with a high aspect ratio using electrochemical and alkaline etching

We report on the fabrication of silicon nanostructures with a high aspect ratio that were created using a combination of electrochemical etching and alkaline etching. With this technique, we were able to fabricate nano- and/or micro-wire structures that are perfectly periodic over large areas of 3.14 cm2. After porous silicon was created by electrochemical etching, the effect of post-alkaline etching was investigated to determine how changes in the etching time, solution concentration and temperature of the etchant influenced the silicon morphology. As a result, periodic silicon wire arrays with good vertical alignment were obtained, and these arrays had a width of less than 500 nm and/or a high aspect ratio of more than 20.     

Fabrication of suspended silicon nanowire arrays

A method to fabricate suspended silicon nanowires that are applicable to electronic and electromechanical nanowire devices is reported. The method allows for the wafer-level production of suspended silicon nanowires using anisotropic etching and thermal oxidation of single-crystal silicon. The deviation in width of the silicon nanowire bridges produced using the proposed method is evaluated. The NW field-effect transistor (FET) properties of the device obtained by transferring suspended nanowires are shown to be practical for useful functions.     

Diagnostic of phased arrays with faulty elements using the mutual coupling method

The ability to calibrate phased array antennas by utilising the mutual coupling method (MCM), which takes advantage of the mutual coupling effect between adjacent elements, is addressed. The basic assumption of the method is that the mutual coupling between adjacent elements is equal for all elements in the array and its major deficiency is its failure in the case of faulty elements. A parametric study to identify the effect of faulty elements in the array has been conducted. It has been shown that displacement of one element in the array may cause a significant error in the calibration, which affects its radiation characteristics (increase in the far side lobe level). The main contribution is the presentation of the effect of faulty elements in the calibration process and the proposal of a way to detect and bypass the faulty elements in a phased array calibrated by the MCM.     

Fabrication and characterization of sputtered-carbon microelectrode arrays

This paper describes a robust and reliable process for fabricating a novel sputter-deposited, thin-film carbon microelectrode array using standard integrated circuit technologies and silicon micromachining. Sputter-deposited carbon films were investigated as potential candidates for microelectrode materials. The surface properties and cross section of the microelectrode arrays were studied by atomic force microscopy and scanning electron microscopy, respectively. Electrical site impedance, crosstalk, and lifetime (dielectric integrity) of microelectrodes in the array were characterized. Electrochemical response of the microelectrodes to hexaammineruthenium(III) chloride and dopamine were investigated by fast-scan cyclic voltammetry and high-speed, computer-based chronoamperometry; results show that thin-film carbon microelectrodes are well-behaved electrochemically. The thin carbon films offer extremely good electrical, mechanical, and chemical properties and thus qualify as viable candidates for various electroanalytical applications, particularly acute neurophysiological studies.     

Fabrication of extreme-ultraviolet point-diffraction interferometer aperture arrays

Interferometric testing at the design wavelength is required for accurately characterizing the wave front of an imaging system operating in the extreme ultraviolet. The fabrication of point-diffraction interferometer apertures for extreme ultraviolet wave-front aberration analysis is described. The apertures are formed in a 200-nm-thick low-pressure chemical-vapor-deposited Si(3)N(4) film and vary in size from approximately 0.10 to 0.50 μm to generate a reference wave front of varying numerical aperture. A graded absorber overcoat is used to control the intensity of the aberrated wave front.Optimal fringe contrast can be obtained when the aperture that provides the maximum uniformity and contrast in the interference plane is selected.     

Fabrication of ordered hollow ZnO-NiO oxide arrays

We have combined colloidal templating and pulsed laser deposition (PLD) to fabricate arrays of ordered two-dimensional hollow ZnO-NiO mixed oxides. The underlying principle involved in producing colloidal templates by a spin-coating method has been investigated with the use of radial distribution functions. To deposit mixed oxide in a facile manner, we have designed and fabricated a novel PLD target, which has an alternating sequence of pie-shaped ZnO and NiO pieces. Structural characterizations reveal a surface morphology of protruding nano-crystallites, which consist of würtzite ZnO and rock salt NiO. The electrical properties have been discussed from the viewpoint of junction effects.     

Fabrication of discrete polystyrene nanoparticle arrays with controllable their structural parameters

We have demonstrated the fabrication of two-dimensionally periodic non-close packed arrays of spherical polystyrene nanoparticles with controllable their structural parameters including diameter and interpartcile distance. The principle of this procedure relies on stepwise integration of spin-coat-assisted colloidal self-assembly of the single layer of close-packed polystyrene nanoparticle on a substrate, and subsequent etching of the particle under atmospheric pressure helium plasma. The plasma process converted the close-packed nanoparticle array into non-close-packed arrangement remaining with unchanged their original spherical shape and periodicity. Owing to the etching process underwent isotropically, the structural parameters could be controlled with nanometric accuracy by the treatment time. The etching rate strongly depended on the working pressure conditions, and the etching rate under 250 Torr was ca. 3 times faster than that of the 760 Torr. The effects of the working pressure indicated the neutral helium radicals and photons diffused from the plasma might be primarily responsible for the etching.     

Optical method of measuring angular displacement using four photodiode arrays

A method of measuring angular displacement is investigated that uses two pairs of photodiode arrays arranged in a square and crossed linear images produced with two cylindrical mirrors. According to this method the measurement error can be greatly reduced even when inclination of the rotation axis exists.     

Fabrication of oriented arrays of porous gold microsheaths using aligned silver nanowires as sacrificial template

A simple one-step process for preparation of oriented arrays of porous gold microsheaths has been developed by dissolution of sacrificial templates of aligned Ag nanowires in a mixture solution of HAuCl₄ and NaCl at room temperature. The morphology and crystal structure of the product were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Its composition was estimated by energy dispersive X-ray spectroscopy (EDX). The results indicated that the gold microsheaths had generally preserved the original orientation of Ag nanowires and their orientation was robust enough to survive the centrifugal process. The gold microsheaths consist of nanoparticles (ca. 100 nm) that form nanovoids (tens to hundreds of nanometers) between them, giving them a porous nature. Such arrays of well oriented gold microsheaths are expected to show interesting anisotropic optical and electronic properties, and their hollow porous structures might find broad potential applications in surface plasma resonance (SPR), catalysis and chemical sensing.     

Fabrication of polypyrrole-based nanoelectrode arrays by colloidal lithography

This paper describes a novel technique to produce polypyrrole-based nanoelectrodes for electrochemical detection purpose. The fabrication process relies on the creation of patterned nanotemplates i.e., nanometric gold spots surrounded by an electrically insulating material (SiO(x)). From these templates, polypyrrole nanopillars are grown by classical electrochemical methods. Atomic force microscopy demonstrates that polypyrrole grows selectively inside the gold nanotemplates. The electrochemical characterization by cyclic voltammetry showed a sigmoidal-shaped voltammogram characterizing the typical nanoelectrode array behavior.     

模板渗透法制备氧化锌纳米管阵列

采用溶胶-凝胶法,以醋酸锌和氢氧化锂为主要原料制备了纳米氧化锌溶胶;再以其为构造单元在阳极氧化铝模板(AAO)中通过减压渗透法制备了氧化锌纳米管阵列.同时利用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线衍射(XRD)和能谱(EDS)对所得的氧化锌纳米颗粒、纳米管进行了分析.结果表明,所得的氧化锌纳米颗粒,粒径为2～5nm,分布较窄,属于纤锌矿型六方晶系;所得氧化锌纳米管,阵列结构规整,外径约为300nm,壁厚约为50nm,长度可以达到5μm以上.