Interfacial hybridization kinetics of oligonucleotides immobilized onto fused silica surfaces

Fused silica optical fibers have been used in an intrinsic mode optical configuration as biosensors for fluorescence based detection of hybridization of nucleic acids. In this work, the kinetics of hybridization of single-stranded oligonucleotides that were covalently immobilized were studied. The probe DNA was dT₂₀, and the target was Fluorescein-labeled non-complementary (dT₂₀) or complementary (dA₂₀) oligonucleotide. Chronofluorimetric monitoring of the adsorption and hybridization processes was used to investigate oligonucleotide films of different density, in different salt concentrations, at temperatures of 25 and 40 °C, with the concentration of the target DNA being 0.005–0.1 μM. Mathematical models based on first- and second-order Langmuir adsorption have been examined to describe both the adsorption and the hybridization processes. Experimental data were processed using the models, and the hybridization kinetics were calculated. Hybridization kinetics on these optical fiber DNA sensors was found to be up to three orders faster than results presented for a number of other experiments using different immobilization chemistries.     

A route to fractal DNA-assembly

Crystallization is periodic self-assembly onthe molecular scale. Individual DNA componentshave been used several times to achieveself-assembled crystalline arrangements in twodimensions. The design of a fractal system isa much more difficult goal to achieve withmolecular components. We present DNAcomponents whose cohesive portions arecompatible with a fractal assembly. Thesecomponents are DNA parallelograms that havebeen used previously to produce two dimensionalarrays. To obtain a fractal arrangement,however, we find it necessary to combine theseparallelograms with glue-like constructs. Theassembly of the individual parallelograms and aseries of glues and protecting groups appear toensure the fractal growth of the system in twodimensions. Synthetic protocols are suggestedfor the implementation of this approach tofractal assembly.     

A silicon transconductance light emitting device (TRANSLED)

A novel multi-terminal silicon light emitting device (TRANSLED) is described where both the light intensity and spatial light pattern of the device are controlled by an insulated MOS gate voltage. This presents a major advantage over two terminals Si-LEDs, which require direct modulation of the relatively high avalanche current. It is found that, depending on the bias conditions, the light intensity is either a linear or a quadratic function of the applied gate voltage. The nonlinear relationship facilitates new applications such as the mixing of electrical input signals and modulating the optical output signal, which cannot readily be achieved with two terminal Si-LEDs, since they exhibit a linear relationship between diode avalanche current and light intensity. Furthermore, the control gate voltage can also modulate the emission pattern of the light emitting regions, for example, changing the TRANSLED from an optical line source to two point sources.     

A 400°C silicon Hall sensor

The maximum operating temperature of conventional silicon sensors is limited to about 200°C, due to excessive thermal generation of carriers at higher temperatures. The minority-carrier exclusion effect can be exploited to reduce the number of thermally generated carriers, ultimately maintaining extrinsic carrier concentrations at intrinsic temperatures. Based on this effect, a silicon magnetic-field sensor with a maximum operating temperature of about 400°C is presented. The sensitivity has been improved by about 500% with respect to a previously reported version, and now measures about 60 V (A T)⁻¹ at room temperature. Additionally, the theoretical support of the exclusion effect has been improved with a more accurate analytical model.     

电力机车硅机组均压检测装置的研制

针对机务段现场检修工作的实际需要,研究电力机车硅机组均压特性检测装置,介绍了装置构成,并分析了工作原理。     

Measurements of thermoelectric properties of silicon pillars

Nanostructured silicon as a material for thermoelectrics provides several advantages over conventional materials, such as bismuth telluride or lead telluride. The technological processing of silicon is well advanced due to the rapid development of microelectronics in recent decades. Silicon is largely available and environmentally friendly. The operating temperature of silicon thermoelectric generators is higher (>250 °C) compared to bismuth telluride. So far silicon is rarely used as a thermoelectric material because of its high thermal conductivity. The figure of merit Z, which is the commonly used measure of the thermoelectric properties of materials, is thereby too small for device applications. In order to introduce silicon as an efficient thermoelectric material thermal conductivity has to be drastically reduced. Nanostructuring into wires, i.e. restriction of the device geometry in both dimensions perpendicular to the heat propagation path indicates a route towards lower thermal conductivity. In this study we investigated silicon pillars produced in a wafer-scale top-down process by ICP (Inductive Coupled Plasma) cryogenic dry etching followed by thermal oxidation and oxide stripping. The pillars have diameters from 2 μm down to 170 nm. Their heights vary from 26.7 μm to 32.1 μm. We measured the reduction of thermal conductivity due to decreasing of pillar diameter. 3ω measurements were performed using a Wollaston probe with pillars of diameters down to 700 nm showing a reduction of thermal conductivity of 27% compared to bulk silicon.     

Mathematical-model-based design of silicon burst neurons

Conventionally, silicon neurons have been designed based on two major principles, namely phenomenological and conductance-based principles. In previous studies [T. Kohno, K. Aihara, Parameter tuning of a MOSFET-based nerve membrane, in: Proceedings of the 10th International Symposium on Artificial Life and Robotics 2005, 2005, pp. 91–94; T. Kohno, K. Aihara, A MOSFET-based model of a Class 2 Nerve membrane, IEEE Trans. Neural Networks 16 (3) (2005) 754–773; T. Kohno, K. Aihara, Bottom-up design of Class 2 silicon nerve membrane, J. Intell. Fuzzy Syst., in press], we proposed a mathematical-model-based design principle that is based on phase plane and bifurcation analyses. It reproduces the mathematical structures of biological neuron models, thus making the silicon neurons simple and biologically realistic. In this study, we demonstrate that square-wave and another type of silicon bursters can be constructed by adding simple circuitries and tuning the system parameters for the silicon nerve membrane designed in our previous studies. Our simple square-wave burster exhibits various firing patterns, including chaotic spiking and bursting.     

Wet etching of silicon gratings with triangular profiles

Triangular silicon gratings of different size (periods from 0.8 to 25.0 m) are manufactured by wet chemical etching. Two main principles of preparation are used and improved. The received gratings are investigated and characterized by SEM concerning the uniformity and the sharpness of the convex edges and the concave notches. Their very small radii determined by TEM are reported for the first time. The gratings can be applied to optical purposes or as standards for surface metrology.     

Humidity sensing behavior of silicon nanowires with hexamethyldisilazane modification

In this paper, the sensing behavior of the capacitive humidity sensors based on silicon nanowires with and without hexamethyldisilazane (HMDS) modification has been investigated. The sensing mechanism is based on the capacitance variations due to the adsorption/desorption of water molecules among silicon nanowires. The effect of HMDS modification on the sensor's performance was discussed. The study indicated that after HMDS treatment, the sensor's surface turns into hydrophobic and the sensor's performance such as the linearity, hysteresis and response time can be improved remarkably.     

Micromachined silicon bolometers as detectors of soft X-ray, ultraviolet, visible and infrared radiation

This paper presents the development of micromachined thin-film silicon microbolometers which can be used for detection of soft X-ray, UV, visible and infrared radiation. The detector structure is a 1 μm thick polysilicon/Si₃N₄ membrane suspended over a cavity. This structure has been obtained by anisotropic etching of silicon with a previously deposited polysilicon/Si₃N₄ sandwich. Alternatively, porous silicon has been used as the sacrificial layer. Devices have been characterized. Good values of the voltage responsivity and detectivity have been obtained.     

Fabrication of improved piezoresistive silicon cantilever probes for the atomic force microscope

This paper describes an improved design for a monolithic silicon atomic force microscope (AFM) probe using piezoresistive sensing. The probe is V shaped, with a sharp tip at the free end and two piezoresistors at the root, and is fabricated using silicon-on-insulator (SOI) starting material. The maximum sensitivity of the AFM probe is measured to be 4.0(± 0.1) × 10⁻⁷ Å⁻¹, which is larger than that of the previous parallel-arm piezoresistive AFM probe. The measured results are in reasonable agreement with the values predicted by theory. The minimum detectable force and minimum detectable deflection of the AFM probes are predicted to be 1.0 × 10⁻¹⁰ N and 0.29 Å_r.m.s., respectively, using a Wheatstone bridge arrangement biased at a voltage of ± 5 V and bandwidth of 10 Hz–1 kHz.     

The effect of DNA probe distribution on the reliability of label-free biosensors

As the design of label-free DNA biosensors matures, and their sizes reduced to enhance their sensitivity, not much has been researched about the variations in the received signal with the positioning of the probes on the sensitive surface. We approach this issue computationally in this paper. By adopting the finite-element model on a three-dimensional biological field-effect transistor (BioFET) slice, and running Monte-Carlo simulations on the positions of the DNA molecules, we extract the expected variations in the signal. Then, we show that signal-to-noise (SNR) ratio can be low enough to hinder the functionality of the device, placing a limitation on how low the sensitivity of a sensor of a certain size can be.     

应用等温吸附曲线判断水稻土供硅能力Ⅰ等温曲线方程参数与水稻相对产量的关系

选取低浓度系列平衡液进行等温吸附解吸试验,并结合田间试验的效果,研究了不同水稻土对硅的吸附解吸特征及其与土壤理化性质水稻土供硅能力之间的关系。结果表明:在低浓度梯度条件下,直线方程y=bx-a可以很好地描述土壤对硅的吸附过程。水稻相对产量与a之间存在着极显著的幂指数函数正相关关系,所以,a可以作为评价水稻土供硅能力的指标。     

An integrated circuit design of a silicon neuron and its measurement results

A novel MOSFET-based silicon nerve membrane model and its measurement results are described in this paper. This model is designed based on a mathematical structure that is characterized by phase plane analysis and bifurcation theory. The circuit is fabricated through MOSIS TSMC 0.35 μm CMOS process. Measurement results demonstrate that our circuit shows fundamental abilities of excitable cells such as a) a resting state, b) an action potential, c) a threshold, and d) a refractoriness. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Micromachining of (hhl) silicon structures: experiments and 3D simulation of etched shapes

The micromachining of various (hhl) silicon plates in a 35% KOH-water etchant is studied. Experimental shapes for membranes and mesa etched with initially circular masks are discussed. Theoretical 3D etched shapes for such microstructures are derived from a numerical simulation based on the tensorial model for the anisotropic wet etching. Experimental and theoretical shapes show a fair agreement, indicating a satisfactory adjustment of the dissolution slowness surface related to the etching of silicon in KOH etchant. The interest of the 3D simulation for designing mask patterns is outlined.     

Molecular dynamics simulation of salt rejection through silicon carbide nanotubes as a nanostructure membrane

Salt rejection phenomenon was investigated using armchair silicon carbide (SiC) nanotubes under applied electric fields. The systems included the (7,7) and (8,8) SiC nanotubes surrounded by silicon nitride membrane immersed in a 0.4 mol/L aqueous solution of sodium chloride. Results of molecular dynamics (MD) simulations for selective separation of Na⁺ and Cl⁻ ions showed that the (7,7) SiC nanotube is suitable for separation of cations and the (8,8) SiC nanotube can be used for separating anions. The water desalination by SiC nanotubes was demonstrated by potential of mean force for Na⁺ and Cl⁻ ions in each SiC nanotube. Furthermore, the ionic current, ion residence time, and the radial distribution functions of species were measured to evaluate the properties of the system. Based on the results of this research, the studied SiC nanotubes can be recommended as a nanostructure model for water desalination.     

Microstructuring of silicon by electro-discharge machining (EDM) — part I: theory

Currently, nearly all microcomponents are fabricated by micro-electronic production technologies like etching, deposition and other (photo) lithographic techniques. In this way, main emphasis has been put on surface micromechanics. The major challenge for the future will be the development of real three-dimensional microstructures. The main objective of the proposed research is the development of a production technology for three-dimensional micromechanical structures together with a study of the mechanical properties of these structures. Electrodischarge machining (EDM) is a versatile technique which is very well suited for machining complex microstructures. This paper starts with an overview of EDM technology, the current state-of-the-art of micro EDM, and a comparison of EDM with other micromachining technologies. Afterwards, the basic parameters for EDM of silicon are derived. It will be demonstrated that EDM of silicon is not only feasible, but also forms an interesting, powerful and complementary alternative to traditional silicon micromachining.     

Effect of electrode size and silicon residue on piezoelectric thin-film membrane actuators

Piezoelectric micro-electromechanical systems (MEMS) often adopt a membrane structure to facilitate sensing or actuation. Design parameters, such as membrane size, thickness of the piezoelectric thin film, and electrode types, have been studied to maximize actuation, sensitivity, or coupling coefficient. This paper is to demonstrate numerically and experimentally that the size of silicon residue and its relative size to the top electrode are two critical yet unrecognized parameters in maximizing the actuation displacement of PZT thin-film membrane actuators. To study effects of the silicon residue, we have developed a finite element model using ANSYS. The model consists of five components: a square passive silicon membrane, a silicon substrate, a PZT thin film, a square top electrode, and a silicon residue region. In particular, the silicon residue has a circular inner diameter and a square outer perimeter with a trapezoidal cross section. Predictions of the finite element model lead to several major results. First, when the silicon residue is present, there exists an optimal size of the top electrode maximizing the actuator displacement. Second, the optimal electrode size is roughly 50–60% of the inner diameters of the silicon residue. The displacement of the membrane actuator declines significantly as the electrode overlaps with the silicon residue. Third, the maximal actuator displacement decreases as the inner diameter of the silicon residue decreases. Aside from the finite element analysis, a mechanics-of-material model is also developed to predict the electrode size that maximizes the actuator displacement. To verify the simulation results, eight PZT thin-film membrane actuators with progressive electrode sizes are fabricated. These actuators all have a square membrane of 800 μm × 800 μm with the inner diameter of the silicon residue controlled between 500 and 750 μm. A laser Doppler vibrometer is used to measure the actuator displacements. The experimental measurements confirm that there exists an optimal size of the top electrode maximizing the actuator displacement.