Geometrically tuned and chemically switched wetting properties of silicon nanotips

The wetting properties of silicon nanotips (SiNTs) are discussed. SiNTs were prepared by single step dry etching of silicon wafers in an electron cyclotron resonance plasma of silane, methane, argon and hydrogen and water contact angles were measured as a function of their aspect ratio (α) and the inter-tip distance. The hydrophilic nature of the SiNTs is tunable with α and the inter-tip distance. Super-hydrophilicity with water contact angles close to 2° was observed with α>12 (length ～1500?nm). Upon coating a 1500?nm long SiNT with TiO(2), the water contact angle jumped from 2° to ～140°, demonstrating a switchover from super-hydrophilic to hydrophobic surface properties.     

Modeling and experimental validation of pressure drop for pneumatic plug conveying

This paper indicates that a variety of models exist to calculate the pressure drop of pneumatic plug conveying. Unfortunately these models are limited in their flexibility and calculate pressure drop only for two extremes, the active and passive case of bulk solid. Until now the stress state within the plug cannot be determined. Therefore a sensor was built to detect wall shear stress, normal stress and the stress state along a moving plug. Beginning with vertical pneumatic plug conveying, the previous models were verified and modified to get new perceptions about formation, stability and pressure drop of plugs.The DFG (German Research Community) is gratefully appreciated for the financial support to this work.Received October 2003     

Top-down fabrication of vertical silicon nano-rings based on Poisson diffraction

Vertical Si nano-rings with a uniform thickness of about 100 nm have been fabricated by conventional optical photolithography with a low cost based on Poisson diffraction. Moreover, the roughness of the Si nano-rings can be effectively reduced by sacrificial oxidation. In order to increase the density of the nano-rings, coaxial twin Si nano-rings have been fabricated by the Poisson diffraction method combined with the spacer technique. The thickness of both the inner and outer Si nano-rings is about 60 nm, and the gap between the twin nano-rings is about 100 nm.     

MOS-junction-based nanostructures by thermal oxidation of silicon wires for hydrogen detection

Heavily p-doped monocrystalline silicon wires have been fabricated by employing isotropic Si wet etch and thermal oxidation to achieve a nanometric cross section-a gate-oxide growth and a final palladium evaporation made up the MOS junction able to detect hydrogen concentration in air. Several types of wire dimensions have been designed and fabricated: length ranges from 5 to 70 /spl mu/m; the smallest widths obtained are around 250-300 nm, while the biggest are up to 7 /spl mu/m. Preliminary experimental results show a high signal/noise ratio sensor response to 100 ppm concentration of H/sub 2/ at room temperature, 1-atm air.     

Fabrication of silicon oxide nanotips by mechanical contact and elongation methods

We investigated the thinning process of silicon oxide tips by mechanical contact and elongation by in situ high-resolution transmission electron microscopy with functions of atomic force microscopy and scanning tunneling microscopy. The processing precision of thinning reached the atomic scale. However, the stability of the thinned tips determined their minimum size; the size of the produced tips was at least approximately 1 nm. We produced thin, long nanotips for optical fiber probes by this method. We also performed the aperture opening of optical fiber probes for scanning near-field optical microscopy. Scraping produced an aperture of approximately 15 nm.     

Modeling and fabrication of three-dimensional silicon substrates with tailored shape and microtopography parameters for CdTe films

Seven models were constructed for the surface of three-dimensional silicon substrates. We proposed models of upright and inverted pyramids (and frusta) and models of substrates with triangular and prismatic cross sections. In modeling, we took into account the capabilities of photolithography and anisotropic etching of silicon wafers. We modeled the light ray trajectory in a thin-film three-dimensional CdS/CdTe solar cell with a large surface area. Three-dimensional microtextured substrates were fabricated using photomasks and modeling and calculation results. Their surface morphology was studied by scanning electron microscopy. The elemental composition of the microtextured silicon substrates was determined.     

基于EDTA-Cu的柔性阴极制备试验与机理研究

为制备低成本和环保的柔性阴极,研究柔性电极的制备机理,本文以EDTA-Cu为活性材料,利用激光诱导化学镀铜工艺,制备了电解加工柔性阴极并进行了系统表征,对相关机理进行了探讨.试验结果表明,基于EDTA-Cu和改性聚氨酯的柔性阴极具有较好的激光诱导化学镀铜选择性,活性材料的成分和颗粒形貌、激光功率、扫描速度、激光波长、激...     

The effect of thermal oxidation on the luminescence properties of nanostructured silicon

Herein is reported a detailed study of the luminescence properties of nanostructured Si using X-ray excited optical luminescence (XEOL) in combination with X-ray absorption near-edge structures (XANES). P-type Si nanowires synthesized via electroless chemical etching from Si wafers of different doping levels and porous Si synthesized using electrochemical method are examined under X-ray excitation across the Si K-, L(3,2) -, and O K-edges. It is found that while as-prepared Si nanostructures are weak light emitters, intense visible luminescence is observed from thermally oxidized Si nanowires and porous Si. The luminescence mechanism of Si upon oxidation is investigated by oxidizing nanostructured Si at different temperatures. Interestingly, the two luminescence bands observed show different response with the variation of absorption coefficient upon Si and O core-electron excitation in elemental silicon and silicon oxide. A correlation between luminescence properties and electronic structures is thus established. The implications of the finding are discussed in terms of the behavior of the oxygen deficient center (OCD) and non-bridging oxygen hole center (NBOHC).     

A molecular dynamics-stochastic model for thermal conductivity of nanofluids and its experimental validation

A model to predict the enhanced thermal conductivity of water based copper nanofluid on the basis of molecular dynamics simulation coupled with stochastic simulation shows for the first time that the temperature of a copper nanoparticle colliding with a heat source can rise rapidly within the short collision period (e.g., 10-50 ps) estimated by impact dynamics due to phonon transfer. Thereafter the particles undergo Brownian movement in the base fluid and transfer the excess heat in about 2 to 3 ms to the surrounding fluid resulting in an appreciable enhancement of the thermal conductivity of the fluid. Microconvection has minor contribution to the enhanced thermal conductivity of nanofluids. The predicted thermal conductivity of nanofluid and its variation with the volume fraction of the nanoparticles agree well with the present experiments, as well as, with the data reported in the literature.     

Influence of thermal oxidation on the interfacial properties of ultrathin strained silicon layers

In this work we examine the influence of thermal oxidation on the electrical characteristics of ultra-thin strained silicon layers grown on relaxed Si_0.78Ge_0.22 substrates under moderate to high thermal budget conditions in N₂O ambient at 800 °C. The results reveal the presence of a large density of interfacial traps which depends on the oxidation process. As long as the strained silicon layer remains between the growing oxide and the underlying Si_0.78Ge_0.22 layer, the density of interface traps increases with increasing oxidation time. When the oxidation process consumes the s-Si layer the interface state density undergoes a significant reduction of the order of 40%. This experimental evidence signifies that the strained silicon-Si_0.78Ge_0.22 interface is a major source of the measured interfacial defects. This situation can be detected only when the front SiO₂-strained silicon interface and the rear strained silicon-Si_0.78Ge_0.22 interface are in close proximity, i.e. within a distance of 5 nm or less. Finally, the influence of the material quality deterioration—as a result of the thermal treatment—to the interfacial properties of the structure is discussed.     

Modeling of diffusion and oxidation in two dimensions during silicon device processing

A process simulator named “2D-DIFFUSE” has been developed where the coupled diffusion equation of dopant impurity and point defects: interstitials and vacancies, has been solved numerically in two-dimension. The interaction of point defects has been modeled assuming quasi (i.e. local) equilibrium,C ₁ C _v=C ₁*C*_V and constant vacancy,C _v=C _v*, conditions. Indeed, these two assumptions decouple the two point defects diffusion equations. The processes modeled in the present version of the simulator include pre-deposition, diffusion and oxidation. The simulator is quite successful at modeling each process individually as well as integrating various processes and models. The program has also been applied to the simulation of phenomena as the dopant diffusion under various ambients, oxidation enhanced and retarded diffusion, emitter push effect etc. Comparisons between simulation based on point defect parameters from various sources have been made.     

大气中烧结多孔氮化硅的相变和氧化机理研究

以α—Si3N4为原料，分别以Y2O3-Al2O3和MgO-Al2O3-SiO2两个体系作为烧结助剂，在大气中对氮化硅坯体在1400～1550℃进行烧结。研究了烧结温度、烧结助剂体系对氮化硅的氧化程度、氧化产物的影响。结果表明，以MgO-Al2O3-SiO2作烧结助剂有利于α-Si3N4转变为β-Si3N4，且该烧结助剂体系的的抗氧化能力也明显优于Y2O3-Al2O3体系。氮化硅在不同温度烧结时形成的氧化产物不同。     

Fast fabrication of silicon based microstructures using 355 nm UV laser

Abstract

In this study, a 355 nm UV Nd:YAG laser is used to process silicon wafers. In order to obtain microstructures with high aspect ratio, a dual prism optical system is set up to control the cutting linewidth of the UV laser beam. During the laser beam propagation through the prisms, the two prisms are rotated with the same angular velocity, which results in the focal spot of the laser beam moving in a circular path on the silicon substrates. When the laser beam moves relative to the holder (workstation), a laser cutting process can be carried out. With this laser system, the cutting linewidth is controllable ranging from 10 μm to 1 mm by adjusting the initial phase difference in the two prisms. The experimental results show that arbitrary shaped silicon based microstructures with high aspect ratio can be fabricated by this 355 nm UV laser system, and the aspect ratio over 10 can be obtained.     

Modeling and experimental validation of a new type of tuned liquid damper

This paper introduces a new type of tuned liquid damper (TLD) having a relatively simple, easy-to-model behavior and high effectiveness in controlling structural vibrations. It consists of a traditional TLD with addition of a floating roof. Since the roof is much stiffer than water, it prevents wave breaking, hence making the response linear even at large amplitudes. The roof also facilitates the incorporation of supplemental devices with which the level of damping of the liquid vibration can be substantially augmented. This newly proposed TLD, denoted as tuned liquid damper with floating roof (TLD-FR), maintains the traditional advantages of TLDs (low cost, easy installation and tuning), but its numerical characterization is much simpler because the floating roof suppresses higher sloshing vibration modes, resulting in a system that can be represented by a single-degree-of-freedom model. An efficient numerical scheme, where the dynamic behavior of the TLD-FR is expressed as a second-order lineal system of equations, is discussed and validated by scaled experimental tests. The equations of motion of a structure equipped with a TLD-FR are then derived and manipulated to offer a unifying representation dependent upon only four model characteristics of the TLD-FR: The first three (mass, frequency and damping ratios) are common for all type of mass dampers, whereas the final one, termed efficiency index, is related to a similar parameter used to characterize liquid column dampers. Through this approach, the behavior of the proposed TLD-FR can be easily correlated with the behavior of other well-known linear mass damper devices. The relationship between these parameters and the geometrical characteristics of the TLD-FR is also examined. Finally, the identification of the optimal characteristic of the TLD-FR (natural frequency and damping) under stationary stochastic excitation is discussed.     

Multiple thermal oxidation of silicon and the electrophysical properties of silicon oxide films and the Si-SiO2 bonding layer

Epitaxial films of CdS, CdSe and CdTe grown by evaporation in vacuum onto (110) surfaces of Ge had the sphalerite structure in parallel or nearly parallel alignment with the substrate. In the case of the CdS films it was found that there was a critical temperature of about 370°C. Annealing or growth above this temperature resulted in a domain-form transformed structure. The CdSe and CdTe films were found to have the domain-form structure as-grown at any temperature in the epitaxial range. Films of sphalerite-structure CdS grown on (110) surfaces of NaCl could also be annealed to produce the domain-form transformed structure. There were found to be two types of domain in the films with this structure. Each type of domain was faulted on one of the two {111} planes inclined at 35°19′ to the [110] film normal. In CdTe the faulting was random, giving rise only to streaks in the diffraction pattern. In CdSe and CdS, however, the faulting was partly regular, giving rise to extra spots along the 〈111〉 streaks in the diffraction pattern.In CdSe the faults could be annealed out and the domain boundaries were then found to be antiphase boundaries. The origin of the two types of domains at least in CdSe was therefore a particular form of double positioning, leading to polarity reversal between regions of the film growing from the two types of nuclei.A lath-form transformed structure was found only in some CdS films that were grown on (110) NaCl, floated off and annealed on gold grids. This structure is dealt with in the second paper in this series.