Silicon nanopore array structure using porous anodic alumina

A free-standing, bidirectionally permeable and ultra-thin (500-1000 nm) porous anodic alumina membrane was fabricated using a two-step aluminium anodization process, which was then placed on top of a silicon film as an etching mask. The pattern was transferred to silicon using dry-etching technology, and the silicon nanopore array structure was formed. The factors which afflct the pattern transfer process are discussed. Observation of the nanopatterned sample under a scanning electron microscope shows that the structure obtained by this method is made up of uniform and highly ordered holes, which attains to 125 nm depth. The photoluminescence spectrum from the nanopatterned sample,the surface of which has been thermal-oxidized, shows that the the luminesce is evidently enhanced, the mechanism of which is based on the normally weak TO phonon assisted bandgap light-emission process, and the physical reasons that underlic the enhancement have been analyzed. The PL results do show an attractive optical characteristic, which provides a promising pathway to achieve efficient light emission from silicon.

Fabrication and characterization of gold coated hollow silicon microneedle array for drug delivery

In this paper, we present the fabrication and characterization of Ti and Au coated hollow silicon microneedles for transdermal drug delivery applications. The hollow silicon microneedles are fabricated using isotropic etching followed by anisotropic etching to obtain a tapered tip. Silicon microneedle of 300 mu m in height, with 130 mu m outer diameter and 110 mu m inner diameter at the tip followed by 80 mu m inner diameter and 160 mu m outer diameter at the base have been fabricated. In order to improve the biocompatibility of microneedles, the fabricated microneedles were coated with Ti (500 nm) by sputtering technique followed by gold coating using electroplating. A breaking force of 225 N was obtained for the fabricated microneedles, which is 10 times higher than the skin resistive force. Hence, fabricated microneedles can easily be inserted inside the skin without breakage. The fluid flow through the microneedles was studied for different inlet pressures. A minimum inlet pressure of 0.66 kPa was required to achieve a flow rate of 50 mu l in 2 s with de-ionized water as a fluid medium. (C) 2014 Elsevier B.V. All rights reserved.

In-plane elastic responses of circular cell honeycombs and bundled circular tubes in a diamond array structure

Assemblages of circular tubes and circular honeycombs in close packed arrangement are presently both competing and complementing regular honeycomb structures (HCS). The intrinsic isotropy of bundled tubes/rings in hexagonal arrays restricts their use to applications with isotopic need. With the aim of extending the utility of tubes/rings assemblages to anisotropic needs, this paper explores the prospects of bundled tubes and circular honeycombs in a general diamond array structure (DAS) to cater these needs. To this end, effective transverse Young's moduli and Poisson's ratio for thick/thin DAS are obtained theoretically. Analysis frameworks including thin ring theory (TRT), curved beam theory (CBT) and elasticity formulations are tested and corroborated by FEA employing contact elements. Results indicate that TRT and CBT are reasonable for thin tubes and honeycombs. Nevertheless, TRT yields compact formulae to study the anisotropy ratio, moduli spectrum and sensitivity of the assemblage as a function of thicknesses and array structure. These formulae supplement designers as a guide to tailor the structures. On the other hand, elasticity formulation can estimate over a larger range including very thick tubes/rings. In addition, this formulation offers to estimate refined transverse strengths of assemblages. (C) 2015 Elsevier Ltd. All rights reserved.

In-plane effective shear modulus of generalized circular honeycomb structures and bundled tubes in a diamond array structure

Use of circular hexagonal honeycomb structures and tube assemblies in energy absorption systems has attracted a large number of literature on their characterization under crushing and impact loads. Notwithstanding these, effective shear moduli (G*) required for complete transverse elastic characterization and in analyses of hierarchical structures have received scant attention. In an attempt to fill this void, the present study undertakes to evaluate G* of a generalized circular honeycomb structures and tube assemblies in a diamond array structure (DAS) with no restriction on their thickness. These structures present a potential to realize a spectrum of moduli with minimal modifications, a point of relevance for manufactures and designers. To evaluate G* in this paper, models based on technical theories - thin ring theory and curved beam theory - and rigorous theory of elasticity are investigated and corroborated with FEA employing contact elements. Technical theories which give a good match for thin HCS offer compact expressions for moduli which can be harvested to study sensitivity of moduli on topology. On the other hand, elasticity model offers a very good match over a large range of thickness along with exact analysis of stresses by employing computationally efficient expressions. (C) 2015 Elsevier Ltd. All rights reserved.

Fabrication and Characterization of High Power InGaN Blue-Violet Lasers with an Array Structure

InGaN/GaN multi-quantum-well-structure laser diodes with an array structure are successfully fabricated on sapphire substrates. The laser diode consists of four emitter stripes which share common electrodes on one laser chip. An 800-mu m-long cavity is formed by cleaving the substrate along the < 1 (1) over bar 00 >. orientation using laser scriber. The threshold current and voltage of the laser array diode are 2A and 10.5 V, respectively. A light output peak power of 12W under pulsed current injection at room temperature is achieved. We simulate the electric properties of GaN based laser diode in a co-planar structure and the results show that minimizing the difference of distances between the different ridges and the n-electrode and increasing the electrical conductivity of the n-type GaN are two effective ways to improve the uniformity of carrier distribution in emitter stripes. Two pairs of emitters on a chip are arranged to be located near the two n-electrode pads on the left and right sides, and the four stripe emitters can laser together. The laser diode shows two sharp peaks of light output at 408 and 409 nm above the threshold current. The full widths at half maximum for the parallel and perpendicular far field patterns are 8 degrees and 32 degrees, respectively.

Size tolerance analysis of a 4X4 tapered multimode interference coupler in a silicon-on-insulator structure

Size tolerance of a 4X4 general interference tapered multimode interference (MMI) coupler in a silicon-on-insulator (SOI) structure is investigated by means of a 2-D finite difference beam propagation method (2D-FDBPM), together with an effective refractive index method (EIM). The results show that the tapered multimode interference coupler exhibits relatively larger size tolerance when light is launched from the edgeport than from midport, though it has much better output power uniformity when light is launched from midport. Besides that, it can reduce the device length greatly. The 4X4 general interference tapered MMI coupler has a slightly larger size tolerance compared with a conventional straight multimode interference coupler. (C) 2003 Society of Photo-Optical Instrumentation Engineers.

Au@Si-n: Growth behavior, stability and electronic structure

The configurations, stability, and electronic structure of AuSin (n = 1-16) clusters have been investigated within the framework of the density functional theory at the B3PW91/LanL2DZ and PW91/DNP levels. The results show that the Au atom begins to occupy the interior site for cages as small as Si-11 and for Si-12 the Au atom completely falls into the interior site forming Au@Si-12 cage. A relatively large embedding energy and small HOMO-LUMO gap are also found for this Au@Si-12 structure indicating enhanced chemical activity and good electronic transfer properties. All these make Au@Si-12 attractive for cluster-assembled materials.

Effect of rapid thermal annealing and hydrogen plasma treatment on the microstructure and light-emission of silicon-rich oxide film

Silicon-rich silicon oxide (SRSO) films are prepared by plasma-enhanced chemical vapor deposition method at the substrate temperature of 200degreesC. The effect of rapid thermal annealing and hydrogen plasma treatment on tire microstructure and light-emission of SRSO films are investigated in detail using micro-Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and photoluminescence (PL) spectra. It is found that the phase-separation degree of the films decreases with increasing annealing temperature from 300 to 600degreesC, while it increases with increasing annealing temperature from 600 to 900degreesC. The light-emission of the films are enhanced with increasing annealing temperature up to 500degreesC, while it is rapidly reduced when the annealing temperature exceeds 600degreesC. The peak position of the PL spectrum blueshifts by annealing at the temperature of 300degreesC, then it red-shifts with further raising annealing temperature. The following hydrogen plasma treatment results in a disproportionate increase of the PL intensity and a blueshift or redshift of the peak positions, depending on the pristine annealing temperature. It is thought that the size of amorphous silicon clusters, surface structure of the clusters and the distribution of hydrogen in the films can be changed during the annealing procedure. The results indicate that not only cluster size but also surface state of the clusters plays an important role in the determination of electronic structure of the amorphous silicon cluster and recombination process of light-generated carriers.

QCA Systolic array design

Quantum-dot Cellular Automata (QCA) technology is a promising potential alternative to CMOS technology. To explore the characteristics of QCA and suitable design methodologies, digital circuit design approaches have been investigated. Due to the inherent wire delay in QCA, pipelined architectures appear to be a particularly suitable design technique. Also, because of the pipeline nature of QCA technology, it is not suitable for complicated control system design. Systolic arrays take advantage of pipelining, parallelism and simple local control. Therefore, an investigation into these architectures in QCA technology is provided in this paper. Two case studies, (a matrix multiplier and a Galois Field multiplier) are designed and analyzed based on both multilayer and coplanar crossings. The performance of these two types of interconnections are compared and it is found that even though coplanar crossings are currently more practical, they tend to occupy a larger design area and incur slightly more delay. A general semi-conductor QCA systolic array design methodology is also proposed. It is found that by applying a systolic array structure in QCA design, significant benefits can be achieved particularly with large systolic arrays, even more so than when applied in CMOS-based technology.

Active surgical positioning device for a cochlear implant electrode array

Cochlear implants have been of great benefit in restoring auditory function to individuals with profound bilateral sensorineural deafness. The implants are used to directly stimulate auditory nerves and send a signal to the brain that is then interpreted as sound. This project focuses on the development of a surgical positioning tool to accurately and effectively place an array of stimulating electrodes deep within the cochlea. This will lead to improved efficiency and performance of the stimulating electrodes, reduced surgical trauma to the cochlea, and as a result, improved overall performance to the implant recipient. The positioning tool reported here consists of multiple fluidic chambers providing localized curvature control along the length of the attached silicon electrode array. The chambers consist of 200μm inner diameter PET (polyethylene therephthalate) tubes with 4μm wall thickness. The chambers are molded in a tapered helical configuration to correspond to the cochlear shape upon relaxation of the actuators. This ensures that the optimal electrode placement within the cochlea is retained after the positioning tool becomes dormant (for chronic implants). Actuation is achieved by injecting fluid into the PET chambers and regulating the fluidic pressure. The chambers are arranged in a stacked, overlapping design to provide fluid connectivity with the non-implantable pressure controller and allow for local curvature control of the device. The stacked tube configuration allows for localized curvature control of various areas along the length of the electrode and additional stiffening and actuating power towards the base. Curvature is affected along the entire length of a chamber and the result is cumulative in sections of multiple chambers. The actuating chambers are bonded to the back of a silicon electrode array.

Silicon nanopillar arrays with SiO2 overlayer for biosensing application

We present the fabrication of silicon dioxide (SiO2) coated silicon nanopillar array structures and demonstrate their application as sensitive optical biosensors. Colloidal lithography, plasma dry etching and deposition processes are used to fabricate SiO2 coated Si nanopillar arrays with two different diameters and periods. Proof of concept bio recognition experiments are carried out with the bovine serum albumin (BSA)/antiBSA model system using Fourier transform visible and IR spectrometry (FT-VIS-IR) in reflection mode. A limit of detection (LoD) value of 5.2 ng/ml is estimated taking in to account the wavenumber uncertainty in the measurements.

A wideband array antenna with beam-steering capability using real valued weights

This article presents an array antenna with beam-steering capability in azimuth over a wide frequency band using real-valued weighting coefficients that can be realized in practice by amplifiers or attenuators. The described beamforming scheme relies on a 2D (instead of 1D) array structure in order to make sure that there are enough degrees of freedom to realize a given radiation pattern in both the angular and frequency domains. In the presented approach, weights are determined using an inverse discrete Fourier transform (IDFT) technique by neglecting the mutual coupling between array elements. Because of the presence of mutual coupling, the actual array produces a radiation pattern with increased side-lobe levels. In order to counter this effect, the design aims to realize the initial radiation pattern with a lower side-lobe level. This strategy is demonstrated in the design example of 4 X 4 element array. (C) 2005 Wiley Periodicals. Inc.