Computer-aided process planning for fabrication of three-dimensional microstructures for bioMEMS applications

In recent years, there has been increasing interest from both academies and industries in developing micro-electromechanical system (MEMS) technology for biological applications, known as bioMEMS or biochips. Targeting at high throughput biomolecule analysis, drug compound screening, and reduction of reagent and sample volume, today's bioMEMS devices come with miniaturised design and increased complexity of microstructures. Fabrication of such a complex bioMEMS structure involves a number of layer fabrication cycles. Moreover, a two-dimensional (2D) mask is required for each process. Thus, manually generating such a complex process plan has become a difficult task. With recent advances in material technology, polydimethylsiloxane (PDMS) silicone material has been widely applied in nowadays bioMEMS fabrication. This paper proposes a novel automated process planning approach for fabrication of three-dimensional (3D) microstructures in bioMEMS. This approach can handle both PDMS casting and traditional micro fabrication processes. It integrates a novel solid decomposition method and a feasibility search algorithm. Also, it can directly handle the solid model of an integrated microstructure with B-rep representation, and automatically generate the data of the fabrication process plan along with masks. A process planner prototype has been implemented. An application example is presented to demonstrate the functionality of the prototype.     

Biomimetics of photonic nanostructures

Biomimetics is the extraction of good design from nature. One approach to optical biomimetics focuses on the use of conventional engineering methods to make direct analogues of the reflectors and anti-reflectors found in nature. However, recent collaborations between biologists, physicists, engineers, chemists and materials scientists have ventured beyond experiments that merely mimic what happens in nature, leading to a thriving new area of research involving biomimetics through cell culture. In this new approach, the nanoengineering efficiency of living cells is harnessed and natural organisms such as diatoms and viruses are used to make nanostructures that could have commercial applications.     

One-dimensional ZnO nanostructures: fabrication, optoelectronic properties, and device applications

One-dimensional (1D) zinc oxide (ZnO) nanostructures have been extensively and intensively studied for several decades not only for their extraordinary chemical and physical properties, but also for their current and future different electronic and optoelectronic device applications. This review provides a brief overview of the progress of different synthesis methods and applications of 1D-ZnO nanostructures. Morphology of ZnO nanostructures grown by various methods and progress in the optical properties are briefly described. Using low-temperature photoluminescence (LTPL) study, detailed informations about the defect states and impurity of such nanostructures are reported. Improvement of field emission properties by modifying the edge of 1D-ZnO nanostructures is briefly discussed. Applications such as different sensors, field effect transistor, light-emitting diodes (LEDs), and photodetector are briefly reviewed. ZnO has large exciton binding energy (60 meV) and wide band gap (3.37 eV), which could lead to lasing action based on exciton recombination. As semiconductor devices are being aggressively scaled down, ZnO 1D nanostructures based resistive switching (RS) memory (resistance random access memory) is very attractive for nonvolatile memory applications. Switching properties and mechanisms of Ga-doped and undoped ZnO nanorods/NWs are briefly discussed. The present paper reviews the recent activities of the growth and applications of various 1D-ZnO nanostructures for sensor, LED, photodetector, laser, and RS memory devices.     

The fabrication of carbon nanostructures using electron beam resist pyrolysis and nanomachining processes for biosensing applications

We present a facile, yet versatile carbon nanofabrication method using electron beam lithography and resist pyrolysis. Various resist nanopatterns were fabricated using a negative electron beam resist, SAL-601, and they were then subjected to heat treatment in an inert atmosphere to obtain carbon nanopatterns. Suspended carbon nanostructures were fabricated by the wet-etching of an underlying sacrificial oxide layer. Free-standing carbon nanostructures, which contain 130?nm wide, 15?nm thick, and 4?μm long nanobridges, were fabricated by resist pyrolysis and nanomachining processes. Electron beam exposure dose effects on resist thickness and pattern widening were studied. The thickness of the carbon nanostructures was thinned down by etching with oxygen plasma. An electrical biosensor utilizing carbon nanostructures as a conducting channel was studied. Conductance modulations of the carbon device due to streptavidin-biotin binding and pH variations were observed.     

Fully three-dimensional modeling of the fabrication and behavior of photonic crystals formed by holographic lithography

A comprehensive and fully three-dimensional model of holographic lithography is used to predict more rigorously the geometry and transmission spectra of photonic crystals formed in Epon SU-8 photoresist. It is the first effort known to the authors to incorporate physics of exposure, postexposure baking, and developing into three-dimensional models of photonic crystals. Optical absorption, reflections, standing waves, refraction, beam coherence, acid diffusion, resist shrinkage, and developing effects combine to distort lattices from their ideal geometry. These are completely neglected by intensity-threshold methods used throughout the literature to predict lattices. Numerical simulations compare remarkably well with experimental results for a face-centered-cube (FCC) photonic crystal. Absorption is shown to produce chirped lattices with broadened bandgaps. Reflections are shown to significantly alter lattice geometry and reduce image contrast. Through simulation, a diamond lattice is formed by multiple exposures, and a hybrid trigonal-FCC lattice is formed that exhibits properties of both component lattices.     

Rigorous calculations and fabrication by self-assembly techniques of 2D subwavelength structures of gold for photonic applications

The use of metal 2D subwavelength structures (SWSs) is a promising solution for all those applications where a selective emission from a thermal source is desirable, e.g., photovoltaic and blackbody emission. The investigation of the SWS's photonic bandgap properties is challenging, especially for the infrared and visible spectra, where the fabrication difficulties have always represented an obstacle. In this paper, the anodization of aluminum films as a self-assembly method for the SWS fabrication is proposed. A rigorous calculation of 2D SWSs of gold having high absorptivity in the visible and low absorptivity in the NIR, their fabrication by DC-sputtering deposition through anodic porous alumina templates, and their optical and topographic characterization are presented.     

Hydrophobicity of templated silica xerogels for molecular sieving applications

Silica xerogels were prepared by a sol-gel process catalyzed by acid with tetraethylorthosilicate, and using an organic covalent ligand template (methyltriethoxysilane) or a noncovalent template C6 surfactant (triethylhexylammonium bromide). The influence of hydrotreatment on the structure of templated xerogels is examined in terms of surface area, micropore volume, average pore size, and pore size distribution, and compared against a blank xerogel (nontemplated). The role of surface functional groups was evaluated using 29Si nuclear magnetic resonance. The structural integrity of the xerogel was maintained to a large extent in samples that had a high contribution of Q4 species (siloxane groups). Xerogel matrix densification occurred when there was a large concentration of Q3 and Q2 species (silanol groups), which also were responsible for increased hydrophilicity. The templated xerogels resulted in up to a 25% concentration of methyl functional groups (T3 and T2 species), leading to hydrophobic xerogels. The best results in terms of structural integrity and hydrophobicity were obtained with templated xerogels prepared with the C6 surfactant. The results in this study suggest that surfactant-enhanced condensation reactions lead to structures with a high contribution of Q4 groups, which are not susceptible to water attack, but are strong enough to oppose matrix densification during rehydration.     

Controllable fabrication of porous alumina templates for nanostructures synthesis

Porous alumina templates (AAO) has attracted significant interest due to the fact that they are readily fabricated through a simple procedure and are extremely popular templates in nanoscience studies. In this paper, the effects of different pore-widening treatments on the pore quality of the AAO templates were investigated. Results show that, through a highly controllable chemical pore-widening process at low temperature, different pore dimensions and diameters of the AAO templates can be easily achieved in a nanometer-scale way without changing the interpore distance. Combining with anodization voltage control, AAO templates with desired size distribution can be obtained, which will be extremely useful in template technology and masks for lithographic application. Also, silver nanorods/wires of different dimensions have been fabricated from above AAO templates after pore diameter adjustments. Such nanostructure materials hold high potential for electronics, optics, mechanics and sensing technology.     

有机光子晶体的制备

本文主要介绍了有机材料在制备光子晶体中的应用以及几种常用的制备方法.     

A facile method for fabrication of large area graphene nanostructures

In this study, we introduce a novel method to produce large area interconnected graphene nanostructures. A single layer CVD (Chemical Vapor Deposition) grown graphene was nanostructured by employing dewetted Ni thin film as an etching mask for the underlying graphene. As a result, a network of graphene nanostructures with irregular shapes and widths down to 10 nm is obtained. The FET (field effect transistor) devices fabricated employing the nanostructured graphene as channel material exhibit increased on/off current ratio compared to pristine graphene indicating a slight band gap opening due to the quantum confinement effect in such narrow graphene nanostructures. This technique can be useful for the large scale fabrication of graphene based electronic devices such as FETs and sensors.     

Fast photonic switches based on GaAs nanostructures

Fast photonic switches, in which light controls light, can be created based on high-voltage GaAs nanostructures with a thin (nanodimensional) surface dielectric layer. The switches offer a high operation speed that ensures optical data recording and transmission at a rate of 10⁴-10⁵ cps, possess a large modulation amplitude, and can operate at a relatively low optical control signal power (I<1 W/cm²). These devices can be used in systems of optical data processing, optical computation systems, all-optical communication lines with optical addressing of informative signals, etc.     

三维光子晶体的制备技术研究进展

光子晶体是周期性介电结构．它能象周期性原子结构中的电子禁带一样．产生光子禁带。自从1987年Yablonovitch提出光子晶体的概念以来，有关光子晶体的各种研究非常活跃。本文回顾了三维光子晶体的制备技术研究现状，旨在激发不同学科领域研究人员的想象力和创造力．使他们从一些可能的光子晶体制造途径中有所裨益．并将这种可能性转变为现实。     

Fabrication of photonic nanostructures in nonlinear optical polymers

Two experimental techniques have been developed for creating photonic structures in nonlinear optical (NLO) polymers with precisions down to nanoscale. The first technique uses nanoimprinting technology to directly pattern the guest-host NLO polymers. It can be applied to the fabrication of photonic bandgap structures in NLO materials, as well as many other photonic structures in both linear and nonlinear polymers. The second technique utilizes self-assembly of NLO polymer monolayers onto a nanostructured template. This approach provides a highly effective means to implement practical waveguide devices using high performance self-assembled polymers with large electro-optic activity and inherent long-term stability. An optical switching device is proposed, based on nanofabricated NLO polymers.     

Long term storage of virus templated fluorescent materials for sensing applications

Wild type, mutant, and chemically modified Cowpea mosaic viruses (CPMV) were studied for long term preservation in the presence and absence of cryoprotectants. Viral complexes were reconstituted and tested via fluorescence spectroscopy and a UV/vis-based RNase assay for structural integrity. When viruses lyophilized in the absence of cryoprotectant were rehydrated and RNase treated, UV absorption increased, indicating that the capsids were damaged. The addition of trehalose during lyophilization protected capsid integrity for at least 7 weeks. Measurements of the fluorescence peak maximum of CPMV lyophilized with trehalose and reconstituted also indicate that the virus remained intact. Microarray binding assays indicated that CPMV particles chemically modified for use as a fluorescent tracer were intact and retained binding specificity after lyophilization in the presence of trehalose. Thus, we demonstrate that functionalized CPMV nanostructures can be stored for the long term, enabling their use in practical sensing applications.     

Nanopatterning of Si(001) for bottom-up fabrication of nanostructures

The epitaxial growth of Si on Si(001) under conditions at which the (2?×?n) superstructure is forming has been investigated by scanning tunneling microscopy and Monte Carlo simulations. Our experiments reveal a periodic change of the surface morphology with the surface coverage of Si. A regular (2?×?n) stripe pattern is observed at coverages of 0.7-0.9 monolayers that periodically alternates with less dense surface structures at lower Si surface coverages. The MC simulations show that the growth of Si is affected by step-edge barriers, which favors the formation of a rather uniform two-dimensional framework-like configuration. Subsequent deposition of Ge onto the (2?×?n) stripe pattern yields a dense array of small Ge nanostructures.     

Microassembly of semiconductor three-dimensional photonic crystals

Electronic devices and their highly integrated components formed from semiconductor crystals contain complex three-dimensional (3D) arrangements of elements and wiring. Photonic crystals, being analogous to semiconductor crystals, are expected to require a 3D structure to form successful optoelectronic devices. Here, we report a novel fabrication technology for a semiconductor 3D photonic crystal by uniting integrated circuit processing technology with micromanipulation. Four- to twenty-layered (five periods) crystals, including one with a controlled defect, for infrared wavelengths of 3-4.5 microm, were integrated at predetermined positions on a chip (structural error <50 nm). Numerical calculations revealed that a transmission peak observed at the upper frequency edge of the bandgap originated from the excitation of a resonant guided mode in the defective layers. Despite their importance, detailed discussions on the defective modes of 3D photonic crystals for such short wavelengths have not been reported before. This technology offers great potential for the production of optical wavelength photonic crystal devices.     

Cu2S nanostructures prepared by Cu-cysteine precursor templated route

A facile Cu-cysteine precursor templated route for the synthesis of Cu₂S nanowires, dendritic-like and flowerlike nanostructures is reported. The Cu-cysteine precursors are prepared through the reaction between Cu²⁺, l-cysteine and ethanolamine at room temperature, and the morphologies of Cu-cysteine precursors can be controlled by adjusting the molar ratio of l-cysteine to Cu²⁺. The Cu-cysteine precursors are used as both templates and source materials for the subsequent preparation of polycrystalline Cu₂S nanostructures by thermal treatment, and the morphologies of the precursors can be well preserved after the thermal transformation to Cu₂S nanostructures. The samples are characterized using X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy.     

Electrodeposition and optical properties of silver infiltrated photonic nanostructures

In this work we report about the preparation and optical characterization of technologically relevant silver based nanostructures by metal infiltration of monolayered or opal-like templates of polystyrene (PS) latex spheres. Low toxicity electrolytic baths present obvious advantages and facilitate the synthesis, and are therefore, desirable methods for this kind of processes. Silver was reduced from an environmentally friendly solution based on ethylendiaminetetraacetic acid or EDTA using pulse plating electrochemical methods. The morphology of the deposits may be controlled by the pre-treatment process performed before the electrodeposition. Optical reflectance spectroscopy analysis shows that high quality films may be obtained by this method.     

Chiral metamaterial composed of three-dimensional plasmonic nanostructures

We introduce a top-down fabricated metamaterial composed of three-dimensional, chiral, plasmonic nanostructures for visible and near-infrared wavelengths. Based on a combined spectroscopic and interferometric characterization, the entire complex transmission response in terms of a Jones matrix is disclosed. Particularly, the polarization output state of light after propagation through the nanostructures can be decoded from the measurements for any excitation configuration. We experimentally found a rotation of the polarization azimuth of linearly polarized light exceeding 50° at wavelengths around 1.08 μm. This corresponds to a specific rotation which is significantly larger than that of any linear, passive, and reciprocal medium reported to date.