Direct micro/nano metal patterning based on two-step transfer printing of ionic metal nano-ink

We present a direct metal patterning method by a two-step transfer printing process of non-particle, ionic metal nano-ink solution. This fabrication method allows a simple direct patterning of various micro/nanoscale metallic structures. Complex structures such as multilayer line arrays, patterns along non-flat topologies, and micro/nanoscale hybrid patterns can be achieved by using this process. Also, the low temperature and pressure process conditions are compatible with the fabrication of electronic structures and devices on flexible substrates such as polyimide film and photographic papers. As an application of this process, we fabricated ZnO nanowire-based flexible UV sensors, where metal electrodes were fabricated by two-step transfer printing. In the case of ZnO nanowire sensors, highly sensitive and fast responding performances to UV illumination and good mechanical robustness against repeated bending conditions could be verified.     

Cross-reactive metal ion sensor array in a micro titer plate format

A cross-reactive array in a micro titer plate (MTP) format is described that is based on a versatile and highly flexible scheme. It makes use of rather unspecific metal ions probes having almost identical fluorescence spectra, thus enabling (a) interrogation at identical analytical wavelengths, and (b) imaging of the probes contained in the wells of the MTP using a CCD camera and an array of blue-light-emitting diodes as a light source. The unselective response of the indicators in the presence of mixtures of five divalent cations generates a characteristic pattern that was analyzed by chemometric tools. The fluorescence intensity of the indicators was transferred into a time-dependent parameter applying a scheme called dual lifetime referencing. In this method, the fluorescence decay profile of the indicator is referenced against the phosphorescence of an inert reference dye added to the system. The intrinsically referenced measurements also were performed using blue LEDs as light sources and a CCD camera without intensifiers as the detector. The best performance was observed if each well was excited by a single LED. The assembly allows the detection of dye concentrations in the nanomoles-per-liter range without amplification and the acquisition of 96 wells simultaneously. The pictures obtained form the basis for evaluation by pattern recognition algorithms. Support vector machines are capable of predicting the presence of significant concentrations of metal ions with high accuracy.     

Effect of substrate patterning on hydroxyapatite sol-gel thin film growth

The effect of substrate patterning on hydroxyapatite (HA) sol-gel thin film growth is investigated. Sol-gel derived HA was spun onto wet and dry etched micro-patterned titanium substrates to obtain thin films of thickness ~ 400 nm. The amorphous films were made crystalline by firing at temperatures ranging from 650 to 850 °C for 5 min. Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), and atomic force microscopy (AFM) were used to characterize the films. Crystal sizes calculated from XRD data show that films on patterned substrates contained larger grains than those on un-patterned substrates. The films on wet etched substrates contained larger grains than the films on dry etched substrates. AFM results confirm XRD results. A marked difference between the films on patterned and unpatterned substrates was observed, with those on the patterned substrates being much rougher than those on the unpatterned substrates. The films inside the channels contained larger grains than those outside of channels, on the polished, unetched portion of the substrate.     

Reduction of titanium and other metal oxides using electrodeoxidation

Abstract

Many reactive and refractory metals are currently produced industrially by reducing their compounds, including oxides, using a more reactive metal. In some cases, where there is substantial oxygen solubility in the metal, the oxygen is first removed by carbochlorination followed by reduction. Titanium and zirconium are made by reduction of the volatile tetrachlorides by magnesium. The processes consist essentially of two reduction steps: reducing magnesium chloride to magnesium metal and then reduction of the metal compound; this makes the overall reduction process relatively expensive. Electrodeoxidation is very simple in that the oxide to be reduced is rendered cathodic in molten alkaline earth chloride. By applying a voltage below the decomposition potential of the salt, it has been found that ionisation of oxygen is the dominant cathode reaction, rather than alkaline earth metal deposition. In the laboratory, this technique has been applied to reduce a large number of metal oxides to the metals, including titanium, zirconium, chromium, niobium, tantalum, uranium and nickel. Furthermore, when mixed oxides are used as the cathode, alloys or intermetallic compounds of uniform composition are obtained. This may offer advantages over conventional technology for those alloys that are difficult to prepare at present, owing to differences in either density or vapour pressure.     

Synthesis of metal chalcogenide nanodot arrays using block copolymer-derived nanoreactors

Soluble metal chalcogenide precursors are used to fabricate arrays of metal chalcogenide nanodots by spin-coating. Nanodots are formed after thermal decomposition of the precursors, which are collected in patterned nanowell arrays. These arrays are derived from block copolymer patterns and may consist of the polymer itself or result from etching to transfer the pattern to an inorganic substrate. Etching provides enhanced control over nanowell shape and the morphology of the resulting metal chalcogenide array.     

Tunable MEMS capacitors using vertical carbon nanotube arrays grown on metal lines

In this work, tunable MEMS capacitors are realized using a vertically grown carbon nanotube array. The vertical CNT array forms an effective CNT membrane, which can be electrostatically actuated like the conventional metal plates used in MEMS capacitors. The CNT membrane is grown on titanium nitride metal lines, with a Al/Fe bi-layer as buffer layer and catalyst material respectively, using chemical vapor deposition process. Two different anchor configurations are investigated. A maximum capacitance of 400 fF and maximum tunability of 5.8% is extracted from the S-parameter measurements. Using the tunable MEMS vertical array capacitor a voltage controlled oscillator (VCO) is demonstrated showing promise for integrating CNTs for communications applications.     

Photonic crystal patterning of luminescent sol-gel films for light extraction

Structured luminescent thin films are investigated in the context of improved light extraction of phosphors for solid-state-lighting applications. Thin films composed of a sol-gel titania matrix doped with europium chelates are studied as a model system. These films, patterned with a square photonic lattice by soft nanoimprint lithography, are characterized by angle-resolved fluorescence. Modeling of this simple technique is shown to fit well the experimental data, revealing in great detail the guided modes of the film and their extraction parameters. An eightfold extraction enhancement factor of the film emission is measured. To further improve the extraction efficiency, we investigate the role of an additional low-index mesoporous silica underlayer through its influence on the guided modes of different polarizations and their interactions with the photonic crystal. Results obtained on model systems open the way towards the optimization of light-emitting devices, using a strategy of dielectric microstructure engineering using the sol-gel process.     

The design of SAW RAC's using arrays of thin metal dots

Many successful dot array SAW devices including RAC's, resonators and band-pass filters have been reported, but the wide range of dot parameters, including dot dimensions, spacing and pattern, which allows flexibility in design, has not previously been utilized. This paper reports on the design of an RAC (reflecting array compressor) with a TB product of 1000, the emphasis being to exploit some of this flexibility. The design has been implemented using YZ LiNbO₃ with thin metal dots as the reflectors. It makes use of the wide range of reflectivities available from electrical effects in a novel weighting scheme based on dot size. The dots have been designed so that the sensitivity to over-etch is minimal. The array, which is sparse and near-periodic, has been designed to reduce unwanted reflections. This is least successful in the case of SAW to bulk wave reflection and the consequent loss due to this cause is accounted for in the design. The design approach is quite general and should be of use for other devices     

The fabrication of metal silicide nanodot arrays using localized ion implantation

We propose a process for fabricating nanodot arrays with a pitch size of less than 25?nm. The process consists of localized ion implantation in a metal thin film on a Si wafer using a focused ion beam (FIB), followed by chemical etching. This process utilizes the etching resistivity changes of the ion beam irradiated region that result from metal silicide formation by ion implantation. To control the nanodot diameter, a threshold ion dose model is proposed using the Gaussian distribution of the ion beam intensities. The process is verified by fabricating nanodots with various diameters. The mechanism of etching resistivity is investigated via x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES).     

Generation of midfield concentrated beam arrays using periodic metal annular apertures

Generation of minimally diffracting beam arrays in the midfield region using periodic metal annular apertures is investigated. The relations between the patterns of the diffraction fields and the structural parameters of the periodic metal annular aperture are numerically analyzed. Material dependent transmission characteristics are also studied with finite difference time-domain simulation. The results reveal that the beam concentration efficiency and axial intensity uniformity have a trade-off restriction due to strong inter-aperture interference and surface plasmon mediates the transmission efficiency of the periodic annular apertures. The design criteria of the metal annular aperture to achieve the strong and uniform beam arrays are addressed.     

Simple, large-scale patterning of hydrophobic ZnO nanorod arrays

Here we describe a simple, versatile technique to produce large-scale arrays of highly ordered ZnO nanorods. Patterning of three distinct ZnO crystal morphologies is demonstrated through use of different ZnO seed layers. Array formation is accomplished through a simple variation on nanosphere lithography that imprints a thickness variation across a PMMA mask layer. The area of exposed seed layer is controlled through etching time in an oxygen plasma. Subsequent hydrothermal growth from the patterned seed layer produces high-quality ZnO crystals in uniform arrays. The high uniformity of the patterned array is shown to induce a high contact angle hydrophobic state even without the need for chemical modification of the ZnO surface. This technique provides a straightforward way to integrate the optical and electrical properties of high-quality ZnO nanorods with the tunable fluidic properties at the surface of well-ordered arrays.     

Universal energy-level alignment of molecules on metal oxides

Transition-metal oxides improve power conversion efficiencies in organic photovoltaics and are used as low-resistance contacts in organic light-emitting diodes and organic thin-film transistors. What makes metal oxides useful in these technologies is the fact that their chemical and electronic properties can be tuned to enable charge exchange with a wide variety of organic molecules. Although it is known that charge exchange relies on the alignment of donor and acceptor energy levels, the mechanism for level alignment remains under debate. Here, we conclusively establish the principle of energy alignment between oxides and molecules. We observe a universal energy-alignment trend for a set of transition-metal oxides--representing a broad diversity in electronic properties--with several organic semiconductors. The trend demonstrates that, despite the variance in their electronic properties, oxide energy alignment is governed by one driving force: electron-chemical-potential equilibration. Using a combination of simple thermodynamics, electrostatics and Fermi statistics we derive a mathematical relation that describes the alignment.     

A micro-Raman study of iron-titanium oxides obtained by sol-gel synthesis

Iron-Titanium mixed oxides in powders and thin films on glass substrates have been prepared at different composition by using the sol-gel method. The thermal evolution, revealing the formation of different crystalline phases, has been followed by means of the micro-Raman spectroscopy. Pseudobrookite was the only crystalline phase found involving both iron and titanium. The differences in the thermal behavior between powders and films and the influence of iron as impurity in the crystallization process of the titania were also studied.     

微纳结构化智能凝胶材料用于重金属离子快速检测的研究进展

智能凝胶材料由于具有特异响应环境信息的能力,被广泛应用于生物或化学传感器,包括重金属离子传感器.由于智能凝胶材料的特征尺寸越小,响应速度越快,因此研究重金属离子响应型智能凝胶材料的微纳尺度结构化对于实现其快速检测具有指导意义.综述了近年来利用微纳结构化智能凝胶材料实现重金属离子快速检测的研究进展,探寻可以制备出简单、可...     

Electrical conductivity of sol-gel derived metal nanoparticles

Electrically conducting films of thickness 2 m have been prepared on ordinary glass slides by growing ultra-fine particles of iron and copper, respectively, from a suitable precursor sol. The diameters of metal particles can be varied from 3–13 nm by controlling the heat-treatment schedule of the sol coating. Resistivity measurements (d.c.) have been carried out over the temperature range 80–300 K. The resistivity values in the range 0.0001–0.0039 cm have been obtained depending on the particle diameter and the type of metal used. The effective Debye temperature _D for the different nanoparticle systems have been estimated by fitting the experimental data to the Ziman equation. _D is found to vary from 346–408 K for iron with the particle size in the range 3.4–9.5 nm. The values obtained for copper are 243–307 K with particle diameters covering a range of 5.9–12.6 nm.     

金属纤维阵列的制备技术

为了更好地应用现有的金属纤维阵列制备技术并探究其未来发展趋势,介绍了气-液-固、拉制、模板、化学气相沉积、金属表面氧化还原等制备技术的基本原理和研究现状,重点评述模板法和化学气相沉积法,并指出其优势与不足.研究结果表明,模板法和化学气相沉积法是当前众多技术手段之中较实用的金属纤维阵列制备方法,其产品具有金属种类多样和尺寸可达纳米级的特点,发展前景良好.改进模板法和化学气相沉积法是金属纤维阵列制备技术的重要发展方向.     

Preparation of anchored ceramic coatings on metal substrates: a modified sol-gel technique using colloidal silica sol

A single-step dip-coating technique was developed to produce stable films or washcoats of controlled thickness, surface area and pore-size distribution on alumina whisker-covered metal substrates (both flat plates and monoliths). Dip-coating slurries were prepared by dispersing fine porous powder in a colloidal silica sol. The method provided control over coating thickness and coating properties, such as pore-size distribution and surface area. The coating thickness could be varied between approximately 2 and 40 m by selecting slurry composition and withdrawal speed in the dipping procedure. The pore-size distribution and surface area could be varied by changing type and amount of porous filler material in the dipping slurry. Uniform and bimodal pore-size distributions were obtained using silica and ZSM-5 molecular sieves, respectively, yielding coatings with surface areas between 60 and 400 m²g^–1.