Fabrication of metal nanodot arrays using a porous alumina membrane as a template

Thin nanodotstructured metal films and heterostructured nanodot arrays (metal nanodot arrays/Si) with a high density and uniform distribution for various kinds of metals (Au, Al, Ag, Pb, Cu, Sn, and Zn) were fabricated by thermal vacuum evaporation using an anodic porous alumina membrane as a template. However, for such metals as Sn, Zn, and Pb with relatively lower melting point as compared with Al it was found that heterostructured nanodot arrays were not formed by a single stage of evaporation. For these metals, we developed a new method termed “two step evaporation method”. The size and the arrays of dots were depended on the pore structure in the anodic porous alumina template. The technique demonstrated in this report is simple and suitable for the preparation of nanodot arrays in the large area for materials which could be vacuum evaporated.     

Replication of mold for UV-nanoimprint lithography using AAO membrane

A simple and highly effective method to the replication of soft mold based on the anodic aluminum oxide (AAO) membrane was developed. The soft mold with nanopillar arrays was composed of the toluene diluted PDMS layer supported by the soft PDMS. A water contact angle as high as 114° was achieved. The hexagonally well-order arrays of holes of nanometer dimensions, ∼100 nm pore diameter and 125 nm center-to-center pore, could be gained over large areas by UV-nanoimprint lithography (UV-NIL) with the replicated soft PDMS mold. It is expected that the developed soft mold would find applications in light emitting diodes devices.     

场发射冷阴极微栅孔阵列制备技术

实现了一种采用聚苯乙烯纳米球自组装技术和微机械制造技术加工的场发射阴极用亚微米栅极微孔阵列。设计了一套完整的工艺实验方案,首先采用微球自组装技术获得了亚微米级金属网孔掩膜,然后通过反应离子刻蚀技术获得了亚微米栅极孔阵列,从而实现了集成度高、分布均匀的周期性亚微米孔洞阵列的制备,微孔集成度达到108cm-2。实验研究了氧气刻蚀聚苯乙烯微球的规律。采用金属掩膜,四氟化碳干法刻蚀二氧化硅,获得了深度为500 nm的微孔。实验结果证明该工艺方案是一种获得大面积、均匀分布、集成度高的场发射冷阴极栅孔阵列的有效方法。     

高矫顽力的Co70Cu30合金纳米线阵列的制备及磁性研究

利用直流电化学沉积法, 在多孔阳极氧化铝模板中首次制备出了具有[220]取向的单晶 面心立方结构的CoCu固溶体合金纳米线阵列, 其Co含量高达70%.透射电子显微镜显示纳米线均匀连续, 具有较高的长径比, 约为300. 磁性测量表明所制备的Co₇₀Cu₃₀ 合金纳米线具有超高的矫顽力H_c//=2438 Oe(1 Oe=79.5775 A/m)和较高的矩形比S//=0.76, 远高于以往报道的CoCu合金纳米线的磁性, 分析表明磁性好的主要原因是由于较高Co含量和高形状各向异性. 通过磁性测量和模型计算, 得到Co₇₀Cu₃₀ 合金纳米线阵列在反磁化过程中遵从对称扇型转动的球链模型, 并从结构的角度分析了Co₇₀Cu₃₀合金纳米线阵列的反磁化行为.     

A high‐throughput method for controlled hot‐spot fabrication in SERS‐active gold nanoparticle dimer arrays

We present a high‐throughput method for fabricating large arrays of surface‐enhanced Raman scattering (SERS) active gold dimers. Using a large‐area/low‐cost nanopatterning method in conjunction with a meniscus force deposition technique, we were able to create large arrays of uniformly spaced nanoclusters comprising two 60‐nm gold nanospheres. Raman measurements of a thiophenol monolayer deposited on smaller scale arrays of aligned dimers yielded enhancement factors as high as 10⁹. Polarization‐controlled measurements show spectral peak heights to be 10–100 times smaller when the incident beam is polarized perpendicularly to the dimer axis, confirming that the measured enhancements arise from the ‘hot spots’ between the two nanospheres. Copyright © 2009 John Wiley & Sons, Ltd.     

ZnS nanorod arrays synthesized by an aqua-solution hydrothermal process upon pulse-plating Zn nanocrystallines

Via a simple aqua-solution hydrothermal route, uniform ZnS nanorod arrays were fabricated upon pulse-plating Zn nanocrystallines. Particularly, low temperature (95 °C) and short time (1 h) were employed in the hydrothermal reaction. ZnS nanorods were found to be grown along certain Zn crystalline direction. Control experiments which were performed by replacing Zn nanocrystallines with Zn plate found no one-dimensional ZnS nanostructure on the substrate. Therefore, it was proposed that pulse-plating Zn nanocrystallines acted as both reactant and seed during the hydrothermal process. ZnS nanorod arrays could be theoretically fabricated on almost any raw base plate as long as Zn nanocrystallines could be pulse-plated on the plate. The ZnS nanorod arrays with high length-to-diameter ratio were expected to be a potential candidate for future field-emission devices.     

The effects of catalyst treatment on fast growth of millimeter-long multi-walled carbon nanotube arrays

An optimized strategy was developed for fast growth of millimeter-long CNT arrays using chemical vapor deposition (CVD). Growth temperature of 800 °C was firstly determined, and catalyst heat treatment conditions were then optimized to probe the full potential of growth rate. 1.5 mm long CNT arrays were obtained in 10 min under optimized growth and catalyst heat treatment conditions. The growth rate of CNT arrays strongly depends on the growth temperature and catalyst heat treatment. Insufficient reduction could not reduce iron oxide into metallic state or/and crack down catalyst film into particles, but excessive treatment may result in large particles due to Ostwald ripening process. This method would offer more freedoms in designing the fast growth of high-purity, long CNT arrays.     

Multiplexed Readout of Superconducting Bolometers

Studies of emission in the far-infrared and submillimeter from astrophysical sources require large arrays of detectors containing hundreds to thousands of elements. A multiplexed readout is necessary for practical implementation of such arrays, and can be developed using SQUIDS, such that, e.g., a 32 × 32 array of bolometers can be read out using 100 wires rather than the >2000 needed with a brute force expansion of existing arrays. These bolometer arrays are made by micromachining techniques, using superconducting transition edge sensors as the thermistors. We describe the development of this multiplexed superconducting bolometer array architecture as a step toward bringing about the first astronomically useful arrays of this design. This technology will be used in the SAFIRE instrument on SOFIA, and is a candidate for a wide variety of other spectroscopic and photometric instruments.     

Direct laser interference patterning of poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT-PSS) thin films

We have developed a patterning procedure based on selective ablation using interference patterns with ns-laser pulses to fabricate periodic arrays on large areas of poly(3,4-ethylene dioxythiophene)-poly(4-styrene sulfonic acid) (PEDOT-PSS) thin films over a metallic gold–palladium layer. Single pulse laser-ablation experiments were performed to study the ablation characteristics of the thin films as a function of the film thickness. The ablation threshold fluence of the PEDOT-PSS films was found to be dependent on thickness with values ranging from 43 mJ/cm² to 252 mJ/cm². Additionally, fluences at which the PEDOT-PSS films could be ablated without inducing damage in the underlying metallic films were observed (128 mJ/cm² and 402 mJ/cm² for film thicknesses of 70 nm and 825 nm, respectively). Linear periodic arrays with line spacings of 7.82 μm and 13.50 μm were also fabricated. The surface topography of these arrays was analyzed using scanning electron and atomic force microscopy. For thicker polymeric layers, several peeled sub-layers of the conjugated polymer with average thicknesses of about 165–185 nm were observed in the ablation experiments. The size and scale of structures produced by this technique could be suitable for several biomedical applications and devices in which controlling cell adhesion, promoting cell alignment, or improving biocompatibility are important.     

Growth of self-assembled ZnO nanowire arrays

This paper reports on ZnO nanowires arrays synthesized using Sn as a catalyst. The Sn particles were produced from the reduction of SnO₂ powders via a vapour-solid growth process. Control of growth conditions led to the formation of ZnO nanowire arrays, radial nanowire ‘flowers’ and uniaxial fuzzy nanowires. ZnO nanowire–nanobelt junctions were also grown by changing the growth direction. As-grown nanowire arrays could be fundamental materials for investigating physical and chemical properties at nano-scale dimensions.     

Efficient large-array k-domain parallel MRI using channel-by-channel array reduction

This article presents a method to explore the flexibility of channel reduction in k-domain parallel imaging (PI) with massive arrays to improve the computation efficiency. In PI, computation cost increases with the number of channels. For the k-domain methods requiring channel-by-channel reconstruction, this increase can be significant with massive arrays. In this article, a method for efficient k-domain PI reconstruction in large array systems is proposed. The method is based on the fact that in large arrays the channel sensitivity is localized, which allows channel reduction through channel cross correlation. The method is tested with simulated and in vivo MRI data from a 32-channel and 64-channel systems using the multicolumn multiline interpolation (MCMLI) method. Results show that the proposed algorithm can achieve similar or improved reconstruction quality with significantly reduced computation time for massive arrays with localized sensitivity.     

A two-step hydrothermally grown ZnO microtube array for CO gas sensing

Tubular ZnO microstructure arrays were fabricated on a large scale by a two-step hydrothermal method. The porous ZnO tubular structures were then used to construct a gas sensor for CO detection. The microtube array gas sensor showed sensitive response to different concentration of CO with an optimum temperature of 250 °C. Because of the large surface to volume ratio, the sensitivity of the microtube arrays was about twice of that of the ZnO rods. Our results indicate that this simple two-step method for fabrication of large-scale tubular microstructure arrays can be potentially used in gas sensor applications with improved performance. PACS 81.07.Bc; 78.55.Et; 07.07.Df     

三维大型任意阵列宽带波束指向性图的快速计算

为解决常规频域直接方法计算大型三维阵列宽带波束图(BP)速度较慢,无法满足大型三维宽带阵优化设计需求的问题,提出了一种适用于大型三维任意阵列的宽带BP图的快速算法.在利用二维非均匀快速傅里叶变换(NUFFT)伴随操作实现二维阵列BP频域快速计算方法的基础上,引入第三空间频率变量,将与阵元纵向坐标有关的相位因子转化为第三...     

FIB快速加工纳米孔点阵的新方法

纳米尺度的点阵在纳米器件和基础科学研究方面都具有非常重要的应用.目前普遍采用的聚焦离子束和电子束曝光技术可以很方便的在衬底上加工纳米量级的微细结构，但大面积的图形加工过程需要花费太多的机时.介绍一种利用设计图形BMP文件的像素点阵和实际加工区域之间的匹配关系，通过聚焦离子束加工获得所需要的纳米孔点阵的新方法.采用这种方法可以在短时间内获得大面积的纳米点阵结构. 关键词： 聚焦离子束 电子束曝光 纳米孔点阵     

Universal phenomenon of self-organized criticality in magnetic flux dynamics

Magnetization curves of square arrays of Josephson junctions of two basic types were investigated: superconductor–insulator–superconductor (SIS) and superconductor–normal metal–superconductor (SNS).

Magnetic flux avalanches were observed in SIS arrays. A statistical analysis of flux avalanches showed that their size distribution can be described by a power law with a crossover where the exponent n varies from −1.2 for small avalanches to −3.5 for the large ones. Such a behavior of avalanches is interpreted as the self-organized criticality (SOC) manifestation. In SNS arrays, the flux avalanches were not observed, but a considerable asymmetry of a hysteresis curve was revealed.     

碱溶液修饰硅纳米线阵列绒面

提出用碱溶液修饰硅纳米线阵列制作太阳能绒面的方法。实验中首先采用金属催化化学腐蚀法在Si(100)基底上制备了定向排列的硅纳米线阵列,然后将纳米线阵列浸入碱溶液中进行修饰,修饰时间分别为10,30,50,60,90s。通过扫描电子显微镜(SEM)对硅纳米线阵列进行形貌分析,采用太阳能测试系统附带的积分球测量纳米线阵列绒面结构的反射光谱。通过测量和分析发现硅纳线阵列在碱溶液中修饰30s时表面分布均匀,在400～1000nm波段的综合反射率低于4%。结果表明碱溶液修饰纳米线阵列的方法能够有效分散束状硅纳米线阵列,明显降低绒面的反射率,并且初步分析了碱溶液修饰硅纳米线阵列的分散机理。     

One step synthesis of vertically aligned ZnO nanowire arrays with tunable length

Length control of ZnO nanowire arrays is a valuable concern for both fundamental research and future device application. In this article, vertically aligned ZnO nanowire arrays were synthesized by a seed layer catalyzed vapor phase transport method in a single experiment cycle. The length of these nanowire arrays exhibits a quasi-continuous evolution. It was found that the type and flow rate of carrier gas have a significant influence on the length modulation of ZnO arrays along the tube. A feasible route to tune the length of ZnO nanowire arrays from several micrometers to nearly 100 μm could be achieved by adjusting proper deposition position and carrier gas.     

Approach flow direction effects on the cross-flow induced vibrations of a square array of tubes

Water tunnel experiments were conducted on a square array of tubes with a pitch ratio of 1·5. The array could be rotated about an axis perpendicular to the direction of flow so that the effects of incident flow direction on cross-flow tube response could be studied. Constant Strouhal number vorticity response was observed over a range of orientations with some Strouhal number dependence on orientation angle. While incident flow direction was found to have some effect on the fluid-elastic stability threshold, no dramatic changes, such as occurred for triangular arrays, were found. Experiments were also conducted to determine the stability behaviour of a single flexible tube in otherwise rigid arrays.     

Current mirror effect and correlated cooper-pair transport in coupled arrays of small Josephson junctions

We have measured the transport properties of capacitively coupled one-dimensional arrays of small aluminum Josephson junctions. Under suitable biasing conditions, the samples act as current mirrors; the currents in the two arrays couple to each other and become equally large. The coupling is found both for currents flowing in the same direction and in opposite directions. We have also measured the time dependent fluctuations of the currents in the two arrays, and we find a strong correlation or anticorrelation of the fluctuations depending on the relative direction of the two currents.     

Trapped rainbow techniques for spectroscopy on a chip and fluorescence enhancement

We report on the experimental demonstration of the broadband “trapped rainbow” in the visible range using arrays of adiabatically tapered optical nanowaveguides. Being a distinct case of the slow light phenomenon, the trapped rainbow effect could be applied to optical signal processing, sensing in such applications as spectroscopy on a chip, and to providing enhanced light-matter interactions. As an example of the latter applications, we have fabricated a large area array of tapered nanowaveguides, which exhibit broadband “trapped rainbow” effect. Considerable fluorescence enhancement due to slow light behavior in the array has been observed.