bluuebunny/crossref_metadata_2025 huggingface dataset:
Stearic acid‐induced cardiac lipotoxicity is independent of cellular lipid and is mitigated by the fatty acids oleic and capric acid but not by the PPAR agonist troglitazone
Authors: Rabkin Simon W. , Lodha Parth
Published: May 2009

The objective of this study was to examine the potential of stearic acid to induce cardiomyocyte cell death and the hypothesis that the amount of cellular lipid is a determinant of cell death. In cardiomyocytes from embryonic chick heart, stearic acid (SA) produced a significant (P < 0.001) concentration‐dependent increase in cell death with an ED50 of 71 μm. In contrast, capric (C10:0) or oleic acid (OA; C18:1), at <200 μm, did not alter cell viability. Stearic acid‐induced cell death was significantly reduced by OA and to a lesser extent by capric acid. Neither OA nor capric acid altered cell death produced by potassium cyanide and deoxyglucose. Stearic acid (100 μm) induced a significant (P < 0.05) twofold increase in cellular lipid as assessed by Nile blue and Sudan Black staining. A role for cellular lipid in cardiomyocyte death was excluded because OA increased cellular lipid, at concentrations that did not induce cell death; OA did not alter SA‐induced cellular fat stores but reduced cell death; and the PPARγ agonist troglitazone at concentrations that reduced cellular lipid content did not alter cell death. High concentrations of troglitazone, however, induced cell death. In summary, SA is a potent inducer of cardiac cell death and intracellular lipid accumulation. The amount of intracellular lipid, however, is not a determinant of cardiomyocyte cell death. Troglitazone has potential cardiotoxicity at high doses but, at lower concentrations, does not prevent cardiac lipotoxicity, which can be completely prevented by low concentrations of oleic acid.
Adsorption mechanism of arg-gly-asp on rutile TiO2 (110) surface in aqueous solution
Authors: Liang Ying-Chun , Song Dai-Ping , Chen Ming-Jun , Bai Qing-Shun
Published: May 2009

Molecular dynamics simulations were performed to investigate the adsorption mechanism of arg-gly-asp (RGD) tripeptide on pit and perfect rutile TiO2 (110) surfaces in aqueous solution and the competitive mechanism of RGD and water. It is shown that the adsorption of RGD on pit surface is more stable than that on perfect surface, and the adsorption energy of the pit surface is −106.14 kcal mol−1, which is 1.8 times as big as that of the perfect surface. Water influences significantly RGD adsorption on the surface. The water molecules reach first the surface and occupy the adsorption sites, i.e., the water oxygen atoms bond to the surface fivefold titanium atoms to form the stable first hydration layer and interact with the surface bridging oxygen atoms to form the second hydration layer. The subsequent arrival RGD edges out the adsorbed water molecules bonding to the surface oxygen atoms and forms hydrogen bonds with these oxygen atoms. Electrostatic and van der Waals interactions are the main interactions between RGD and hydrophilic TiO2 surfaces.
Long-working-distance Linnik microscopic interferometry for measuring the surface profile of microstructures
Authors: Hu Xiaodong , Deng Shujuan , Wang Wenan , Hu Xiaotang
Published: May 2009

The surface profile is an important specification that influences the performance and stability of a microelectromechanical system device. Microscopic interferometry is, up to now, the most widely used technique for surface profiles of microstructures. A long working distance is needed when it is necessary to place components such as probes or transparency windows between microstructures and the objective. In this paper, a long-working-distance Linnik microscopic interferometer system was developed for meeting above requirements. Because it is difficult to ensure that the sample and the reference objectives are completely identical, the surface profile is modulated by unmatched optical path length between measurement and reference arms. This paper puts forward compensation process for demodulating the surface profile. Experiment results show that this method can provide correct measurement of the surface profile of microstructures effectively.
Diamond milling of nitrided steels for optical mold making
Authors: Osmer J. , Gläbe R. , Riemer O. , Brinksmeier E. , Bütepage S. , Hoffmann F.
Published: May 2009

So far ultraprecision diamond machining of steel molds for optical applications is not possible because of excessive wear of the applied diamond tools. This article discusses a thermochemical approach for steel machining with single crystal diamond tools as well as the process of material modification. Ultraprecision raster milling experiments for the nitrided carbon steel C45 (AISI 1045) and the tempering steel 42CrMo4 (AISI 4140) are presented. In both materials a surface roughness of Ra<10nm could be achieved. The observed flank wear of the cutting tools was VB<2μm for all experiments after cutting work pieces with a diameter of 30mm.
Development of a fine tool servo with force monitoring system for nanomachining applications
Authors: Gan S. W. , Rahman M. , Lim H. S.
Published: May 2009

The strong demand for ultraprecision components in today’s industries has gradually delivered focus in the research area of diamond turning. A new technique called tool servosystem, an auxiliary servoaxis of the lathe, has become the best solution in machining the ultraprecision surfaces more effectively. This article presents a newly developed piezoelectric-based fine tool servo (FTS) system for a miniature ultraprecision lathe. The FTS system is specially designed by installing a small-size and high sensitivity force transducer which measures the thrust force along the in-feed direction during diamond turning, and also detects the initial contact point of tool/workpiece. A new flexure mechanism of the FTS is presented which is built to measure the cutting force and guide the piezoelectric actuator movement. By employing this flexure mechanism, the cutting force can be measured accurately without sacrificing the desired displacement of the cutting tool during turning process. In order to achieve the optimized tracking performance, the FTS system is controlled by the proportional-integral-derivative feedback and feedforward algorithm that is available with the motion controller. The nonferrous workpiece materials such as aluminum alloys and brass have been machined in this study to investigate the performance characteristics of the developed FTS system. In addition, an example of a nanosurface with microfeatures has been machined and thereby successfully verified the capability of the FTS system. The results show a significant improvement in the surface finish of the machined workpiece and also confirm that this system can successfully generate nanosurfaces effectively.
Controlled morphology of microtools shaped using focused ion beam milling technique
Authors: Zhang S. J. , Fang F. Z. , Xu Z. W. , Hu X. T.
Published: May 2009

Advantages of focused ion beam (FIB) technology in micromachining are high feature resolution, capable of maskless processing, rapid prototyping, and adaptive for various materials and geometries. FIB was extensively used to fabricate a variety of microtools for ultraprecision machining and micromachining with typical dimensions ranging from 10 to 40 μm and a curvature radius of 25 nm or even smaller. The microtools with controlled geometries, such as arc and sawtooth shapes, were shaped using FIB milling technique corresponding to different cutting requirements. The FIB milling is able to shape desired tool geometries with microscale features by means of controlling suitable ion beam parameters and precise orientation of the tools with respect to projection direction of ion beam. The cutting microtools used here are made from hard alloy. Testing experiments were carried out using a microtool with arc-shaped cross section to machine concentric rings and an annular plane in planar metal workpiece. Another microtool with sawtooth-shaped cross section was used to fabricate microdiffractive optical elements. The machining results demonstrated that the FIB-fabricated microtools can accurately machine desired microstructures. This fabrication method shows significant advantages of higher precision and lower cost than that of the conventional tool lapped finishing methods. It is promising to be an effective method for fabricating the microtools with complex shapes.
Efficient and smooth grinding characteristics of monocrystalline 4H-SiC wafer
Authors: Kasuga Hiroshi , Ohmori Hitoshi , Lin Weimin , Watanabe Yutaka , Mishima Taketoshi , Doi Toshiro
Published: May 2009

Semiconductors have a broad range of uses. In particular, semiconductors used for power conversion are generically called “power devices.” Silicon carbide (SiC) power devices have been gaining attention as next-generation semiconductors because they have excellent electrical characteristics compared to silicon power devices. However, SiC is difficult to grind efficiently because of its hard and brittle characteristic. In this study, the authors used some effective grinding methods and investigated efficient grinding conditions. As a result of their experiments, the average removal volume was 80.0% for 40μm of grinding with a 1200 mesh-size wheel.
Development of three-axis desktop milling machine
Authors: Wang Q. Y. , Fang F. Z. , Hu X. T.
Published: May 2009

With a trend toward miniaturization, miniaturized machine tools turn to be more and more reasonable than conventional machine tools in fabricating scaled-down work parts with better quality, higher efficiency, and less expense. In the past 20years, various miniaturized machine tools have been developed. For the purpose of studying machine tool miniaturization technology and micromachining mechanism, a three-axis desktop milling machine tool is presented in this article. Typical microfeatures such as microgears, microthin walls, and microelectrode made from copper alloy or aluminum alloy have been machined by end milling tools in diameters of 0.1, 0.2, and 0.4mm. Meanwhile, the profile and roughness of these microstructures are also analysed. By these experiments, the machining performance of this three-axis desktop milling machine tool in aspect of three-dimensional complex microstructures is demonstrated.
Tool runout effects on wear and mechanics behavior in microend milling
Authors: Bai Q. S. , Yang K. , Liang Y. C. , Yang C. L. , Wang B.
Published: May 2009

In this article, three-dimensional micro-end-milling finite element models were built to analyze the mechanics behavior and wear of microtool while machining aluminum alloy (Al 2024-T6). The cutting force, equivalent stress, and wear characteristics of microend cutter were dynamically simulated to investigate the tool runout effects. The simulation results show that the cutting forces in micromilling are very small as compared to conventional scale cutting. The maximal equivalent stress located on the tip of cutting edge, which produces distinct size effect on tool wear. Tool runout is found to have a significant influence on the mechanics behaviors and wear of microend cutter. Experimental verification of the simulation model was carried out by micromilling experiments. It is shown that the wear of microend cutter mainly occurs in tool nose. The small tool runout causes considerable rapid tool wear and breakage while deflection plane is parallel to the cutting edges of tool (γ=0°). In order to minimize the equivalent stress and tool wear, it is recommended that the axis of microend cutter should be consistent with the spindle axis and the deflection plane is perpendicular to the cutting edges (γ=90°).
Characterization of the Ag∕Fe nanocomposite fluid
Authors: Chang Ho , Wu Yan-Chyuan , Kao Mu-Jung , Shieh Tung-Jung , Jwo Ching-Song
Published: May 2009

In this article, an arc discharge nanofluid synthesis system with complex ultrasonic orthogonal vibration and vortex stirring is proposed and developed for a Ag∕Fe nanocomposite fluid. For this, one of the electrodes and the ultrasonic vibrator are assembled together to form an orthogonal model with the other electrode and together installed inside the vacuum chamber of the arc discharge system, with de-ionized water as the dielectric liquid. In the fabrication process, the positive electrode uses a Ag rod and the negative electrode uses an Fe rod to apply electrical energy, producing a heating source to generate an adequate arc with a high temperature that can melt and vaporize the two electrodes. The vaporized metal is then rapidly quenched by the designed cooling system, thus nucleating and forming nanocomposite fluid. During arc discharge, through the vibration of the ultrasonic vibrator, disturbance occurs to the insulating liquid. Thus, the vaporized metal can leave the high-temperature gap zone easily and can be rapidly condensed by the low-temperature insulating liquid. The nanocomposite fluid generated by the synthesis system is analyzed by morphology, heat transfer, zeta potential, and magnetism analysis.
Silicon-on-insulation-based deformable mirror array for adaptive optics
Authors: Wang D. J. , Yao J. , Qiu C. K. , Hu F. R. , Fan T. Q.
Published: May 2009

In this paper, the authors present a continuous membrane deformable mirror array based on silicon-on-insulator (SOI) bulk micromachining technology for applications in adaptive optics. In order to facilitate the use of the device layers of SOI wafers for the reflective surface and electrostatic actuators, the fabrication of the micromirror array is separated from the electronics chip, and then they are bonded together using the flip-chip assembly. The optical reflective membrane formed by the device layer of one SOI wafer is of high quality in terms of flatness and surface roughness; the stroke space is mainly determined by the height of the device layer of another wafer. The simulation results of the actuator performance by the finite element analysis method shows that the stroke is up to 2μm at about 70V actuation voltage and the frequency is about 17.8kHz.
Fabrication of cutting tools for ultraprecision machining of tantalum and their cutting characteristics
Authors: Mizutani M. , Naruse T. , Kameyama Y. , Koma Y. , Ohmori H. , Sasaki C.
Published: May 2009

To investigate the cutting characteristics of tantalum, three types of cutting tools were prepared. From the cutting experiments, it is found that the tool with the rake angle of 28° is the most suitable for precision machining of tantalum.
Impact of channel width and dummy length on performance enhancement in p-type metal oxide semiconductor field effect transistor with a silicon-germanium alloy stressor
Authors: Lee Chang-Chun , Huang Jacky , Chang Shu-Tong , Wang Wei-Ching
Published: May 2009

The stress distribution in the Si channel regions of silicon-germanium (SiGe) source/drain p-type metal oxide semiconductor field effect transistor of various widths and dummy lengths was studied using ANSYS simulations. The drain current enhancement is dominated by the compressive stress along the transport direction. Stress perpendicular to the channel was found to have the least effect on the drain current in wide-width devices. However, this stress component cannot be neglected in narrower devices. The tensile stress along the vertical direction contributes to the drain current enhancement in wide devices but can be neglected when the width is very small. The impact of channel width and dummy length effects on improvements in device performance such as the drive current gain was also analyzed.
Three-dimensional molecular dynamics modeling of nanocutting
Authors: Zhang Z. G. , Fang F. Z. , Hu X. T. , Sun C. K.
Published: May 2009

Molecular dynamics (MD) analysis at the nanometric scale is a powerful tool for understanding the deformation mechanisms of materials when undeformed chip thickness is at atomic or nanometric scale. Until now, two-dimensional and 2.5D MD models have been employed in the MD analysis. With advances in computer performance, it is possible to simulate larger-scale MD in a reasonable time. This article presents a three-dimensional (3D) tool with a cutting-edge radius of 3 nm and a nose radius of 25 nm to reduce computation time. Taper cut is carried out on monocrystalline silicon to verify the model proposed. A smooth surface is achieved before fracture surfaces occur when the depth of cut is below a critical value. The 3D model is also verified by comparing with results obtained by other studies.
Prediction and simulation of surface topomorphy in ultraprecision milling for optical freeform surface
Authors: Luo Zhong-Cheng , Peng Fang-Yu , Chen Xu-Bing , Wei Li-Feng
Published: May 2009

The successful development of the surface topomorphy model and the model-based simulation system is helpful in identifying the optimal cutting conditions of machining optical freeform surfaces without the costly trial-and-error cutting tests. This article presents a novel model that describes the path-interval and feed-interval scallops generating mechanism in ultraprecision milling process. The topomorphy value of any point on the machined surface can be calculated directly by simulating the tool kinematics precisely and discretizing the cutting edge and meshing the workpiece. Through analyzing the effect of the feed per tooth on the surface scallop height and simulating the machined surface topomorphy, it can be found that the scallop height increases greatly when the feed/pick ratio is above 1 and the feed-interval scallop plays a more important role to surface roughness than the path-interval scallop in ultraprecision milling process.
Finite-element analysis of aerostatic lubrication with porous restrictors based on HYPERMESH
Authors: Zhang Xiaofeng , Lin Bin , Wang Taiyong
Published: May 2009

In this article, the authors numerically analyzed the aerostatic thrust bearing with porous restrictors using the finite-element method. After the existing methods were considered, a new analysis procedure is developed for improving the efficiency and application of the finite-element analysis program. In this procedure, HYPERMESH is used for preprocessing and postprocessing with the solver programed with C. The one-dimensional (1D)/three-dimensional (3D) source flow model derived from D’Arcy’s law and the partial porous-bearing model are both supported by the solver. The matrix compress storage arithmetic and INTEL MATH KERNEL LIBRARY linear sparse solvers are used for improving the utilization ratio of memory and the solution efficiency. Therefore, the solver can be used to analyze the different applications of the porous restrictors in engineering. The program is validated by comparing the results obtained by different methods. The calculation efficiency and results of the 1D/3D source flow model are analyzed and compared with experimental results. The 1D model is shown to be suitable for engineering issues.
Hybrid machining of microstructures using a combination of electrical discharge machining milling and laser ablation
Authors: Weber Patricia , Haupt Sebastian , Schulze Volker
Published: May 2009

Using laser beam machining with ultrashort laser pulses, microstructures in the micrometer region can be manufactured in virtually all materials, regardless of their mechanical properties. However, machining times are slow if good surface qualities are required. Micro electrical discharge machining (EDM) is also capable of removing material nearly without process forces, but with a higher processing speed if structure sizes exceed a certain value. With the combination of both processes, specific advantages can be realized while disadvantages can be partially eliminated. Therefore, a hybrid machine tool was developed that combines the two processes of ultrashort pulsed laser ablation and EDM milling. No reclamping is necessary. In this study, the limitations and challenges of the single processes are investigated. After that, the novel hybrid machine tool is presented, along with strategies for the efficient and economic manufacturing of microstructures in materials that are difficult to machine by conventional processes.
Strong exciton-photon coupling in ZnO based resonators
Authors: Sturm C. , Hilmer H. , Schmidt-Grund R. , Czekalla C. , Sellmann J. , Lenzner J. , Lorenz M. , Grundmann M.
Published: May 2009

The authors report on the fabrication of high quality all-oxide Bragg reflectors (BRs) and ZnO based resonators. The resonator consists of a bulk half-wavelength ZnO microcavity embedded between two BRs, each made of 10.5 layer pairs of yttria stabilized zirconia and Al2O3. Scanning transmission electron microscopy and atomic force microscopy, yield smooth interfaces and low surface roughness for the BR as well as the resonator. For the BR with 10.5 layer pairs the authors obtain reflectivities up to 99.2% within the Bragg stop band. The exciton-polariton dispersion was determined by both, polarization- and angle-resolved photoluminescence (PL) and reflectivity (R) measurements. The detuning between the uncoupled exciton mode and photon mode was changed by shifting the exciton mode energy in the temperature range of 10–290 K. Thereby we observed that a strong exciton-photon coupling regime up to room temperature is present in our resonators with maximum values of the Rabi splitting of about 68 meV (PL, T=10 K) and 76 meV (R,T=10 K).
Properties of reactively sputtered Ag, Au, Pd, and Pt Schottky contacts on n-type ZnO
Authors: Lajn A. , Wenckstern H. v. , Zhang Z. , Czekalla C. , Biehne G. , Lenzner J. , Hochmuth H. , Lorenz M. , Grundmann M. , Wickert S. , Vogt C. , Denecke R.
Published: May 2009

Highly rectifying Ag, Au, Pd, and Pt Schottky contacts have been fabricated on heteroepitaxial pulsed-laser deposited ZnO-thin films by reactive sputtering. X-ray photoelectron spectroscopy revealed an oxidation of the Ag, Pd, and Pt contact material; the gold contacts are purely metallic. The necessity of a conductive capping of the oxidized contacts is proven by photocurrent measurements of AgxO contacts. The ideality factors and the effective barrier heights were determined by current-voltage measurements. Capacitance-voltage and temperature dependent current-voltage measurements were furthermore carried out to determine the mean barrier height, the standard deviation and the respective voltage dependencies taking lateral fluctuations of the barrier height into account.
Surfactant assisted solution spray synthesis of stabilized prussian blue and iron oxide for preparation of nanolatex composites
Authors: Kulkarni R. D. , Ghosh N. , Patil U. D. , Mishra S.
Published: May 2009

Nanoparticles find wide applications as nanopigments in the field of surface coatings. Their role in enhancement of durability, transparency, scratch resistance, thixotropy, dispersion stability, etc., has been discussed. The aim of the present investigation was to conduct synthesis of nanoparticles, viz., prussian blue (Fe4[Fe(CN)6]3) and iron oxide, which are widely used as prime pigments in paints. The syntheses of nanosize pigments by different routes, however, were associated with difficulties of regulating particle size distribution and stabilizing this distribution. In the present work, use of cetyl trimethyl ammonium bromide, sodium dodecyl sulfate, Tween 80, and potassium dodecyl benzene sulfonate as surfactant and contact of precursor and precipitator in atomized mode as means of stabilizing particle size within the range of 12–32nm has been established. IR, x-ray powder diffraction, and color matching monitored the synthesis. It was observed that finer tuning of particle size of prussian blue and ferric oxide in the presence of surfactant was governed by viscosity, spray pressure, degree of atomization, and surfactant/reactant concentration. Acrylate latex nanocomposites were prepared through emulsion polymerization of methyl methacrylate, butyl acrylate, and methylacrylic acid in the presence of prussian blue. The mechanical, stability, and rheological characteristics of nanolatex paints were determined and interpreted. Single step surfactant modified solution spray synthesis at ambient temperature thus presents a feasible technique suitable for the production of nanoparticles at industrial scale.
Effects of annealing in N2 on sputtered Al-doped ZnO thin films
Authors: Lennon C. , Kodama R. , Chang Y. , Sivananthan S. , Deshpande M.
Published: May 2009

Transparent conductive oxides (TCOs) are a unique class of materials that exhibit both low electrical resistivity and high optical transmittance. Al-doped ZnO thin films have the potential to replace the widely used TCO indium tin oxide at a fraction of the current cost. Thin ZnO:Al films have been deposited by rf magnetron sputtering at room temperature onto fused quartz substrates. An ex situ anneal at 350°C in N2 was employed to improve both the electrical and optical properties of as-deposited films. The calculated average grain size increased from 25.6to28.3nm following the anneal. The resistivity was found to decrease from 3.7×10−3to7.1×10−4Ωcm as a result of postdeposition processing. An average optical transmittance of >85% was routinely observed for annealed films. X-ray photoelectron spectroscopy measurements were conducted in order to investigate the degree of oxygen deficiency of both as-deposited and annealed films. It was found that the annealing procedure generated an oxygen poor region near the film surface. The authors propose that the formation of oxygen vacancies in conjunction with improved crystalline quality is responsible for the measured improvement in film resistivity.
Nickel-germanium soft x-ray zone plates
Authors: Lindblom Magnus , Reinspach Julia , von Hofsten Olov , Bertilson Michael , Hertz Hans M. , Holmberg Anders
Published: May 2009

This article presents a fabrication process for soft x-ray zone plates in which nickel and germanium are combined to achieve high diffraction efficiency. A nickel zone plate is first fabricated on a germanium film and then used as a hardmask for a CHF3-plasma etch into the germanium. Zone plates with 50–60 nm nickel and 110–150 nm of germanium are presented. The measured diffraction efficiencies were 10%–11% at λ=2.88 nm, which shows that high efficiency is possible even with thin nickel. Thus, the method has a potential for improving the efficiency of high-resolution zone plates for which the high-aspect-ratio structuring of nickel is difficult.
New technology for the trueing of microgrinding wheels
Authors: Hoffmeister H.-W. , Hlavac M. , Schnell C.
Published: May 2009

Microgrinding wheels are suitable for the microstructuring of hard and brittle materials but usually they can only manufacture structures with rectangular geometries because of their limited profile geometries. The use of microgrinding wheels with a special profile is uncommon. This is due to the fact that microgrinding wheels with a profile are difficult to manufacture; furthermore, the renewing process after the profile has worn is difficult to accomplish. A new and successful approach is to true the microgrinding wheels by miniaturized diamond profile rollers. The technology of trueing grinding wheels by diamond profile rollers is highly favored and well established in macroscopic grinding technology. Easy kinematics, high quality, and short processing times make this technology very efficient. Moreover, this technology allows for a periodical renewing of the profile inside the grinding machine. Confirmed by those technological advantages, the authors developed diamond tools in order to realize a truing process for microgrinding wheels.
Research on NC interpolation algorithm for rotary symmetric aspheric ultrasonic-magnetorheological compound finishing
Authors: Zhang Yong , Zhang Feihu , Zhang Guangyu , Luan Dianrong
Published: May 2009

Ultrasonic-magnetorheological compound finishing (UMC finishing) is a new technique for the ultraprecision machining of aspheric surfaces, especially for the ultraprecision machining of small-radiused concave surfaces and freeform surfaces. In this article, an UMC finishing equipment with five axes, four of which perform linkage movement, was developed. According to characteristic of UMC finishing, NC interpolation algorithm for rotary symmetric aspheric based on this equipment was researched. The derivation process and computer simulation result of the algorithm were also presented. The interpolation error of this algorithm was analyzed and the calculation formula was also proposed. According to the result of analysis, the precision of the interpolation algorithm is high and the algorithm is very useful. A great number of polishing experiments prove that high quality aspheric surface can be machined using this numerical interpolation algorithm. The profile accuracy of 58.32nm and surface roughness Ra of 0.746nm can be obtained stably.
Large-scale assembly of periodic nanostructures with metastable square lattices
Authors: Sun Chih-Hung , Min Wei-Lun , Linn Nicholas C. , Jiang Peng , Jiang Bin
Published: May 2009

This article reports a simple and scalable spin-coating technique for assembling non-close-packed colloidal crystals with metastable square lattices over wafer-scale areas. The authors observe the alternate formation of hexagonal and square diffraction patterns when the thickness of the colloidal crystals is gradually reduced during spin coating. No prepatterned templates are needed to induce the formation of the resulting metastable crystals with square arrangement. This bottom-up technology also enables the large-scale production of a variety of squarely ordered nanostructures that are consistent with the industry-standard rectilinear coordinate system for simplified addressing and circuit interconnection. Broadband moth-eye antireflection gratings with square lattices have been fabricated by using the shear-aligned colloidal monolayers as structural templates. Optical reflection measurement shows the squarely ordered arrays exhibit lower reflection than the nature-inspired hexagonal arrays with the similar structural parameters.
Realization of nanosecond pulse laser micromachining system
Authors: Liu Chunyang , Fu Xing , Wu Yong , Li Yi , Sun Fengming , Hu Xiaotang
Published: May 2009

In this article a new nanosecond pulse laser micromachining system has been designed, which consists of laser, mechanical and optical structure, three-dimensional (3D) work platform, and control system. 355nm ultraviolet nanosecond pulse laser, with 40ns pulse duration, is chosen as the light source. The repetition frequency can be set from single shot to 100kHz. Mechanical and optical structures are designed for laser beam focusing. Computer software resolves the graphics. Moreover, control system based on digital signal processing and field programmable gate array is designed to drive the 3D work platform. With the designed system, some processing parameters have been analyzed and optimized in experiments. Some measures are also taken to improve the microfabrication quality and minimize the splashes of the heat-affected zone. Finally, some microstructures are fabricated by the designed nanosecond pulse laser micromachining system. The width of processing line is about 40μm with less splashes.
Study on structure optimization of a piezoelectric cantilever with a proof mass for vibration-powered energy harvesting system
Authors: Li Yanning , Li Wen , Guo Tong , Yan Zhidan , Fu Xing , Hu Xiaotang
Published: May 2009

The study of micropower supply has become a key issue in the development of wireless sensor networks using microelectromechanical system technology. Vibration-powered energy harvesting system is considered as a good source for generating micropower. A general layout of a vibration energy harvesting system based on a sandwiched (PZT–Si–PZT) rectangle cantilever with a nickel proof mass was proposed. For the optimization of the system, formula of the voltage and power output based upon an equivalent circuit of piezoelectric layer and ac-dc converter was deduced. For the vibration harvesting structure, lower resonance frequencies are usually preferred. In order to find the relationship of the cantilever length and proof mass on the resonance frequencies of the energy harvesting structure, computations using Microsoft Excel software were conducted. The results show that it would be advisable not to increase the cantilever length only in order to get lower resonance frequency. However, the resonance frequency of the structure can be reduced dramatically by the accession of a proof mass with reasonable weight, so that the whole structure can be optimized to fit its application in natural environment. This study provides some basic considerations for the design of piezoelectric-based vibration energy harvesting system for converting ambient vibrational energy into electricity.
Topography of epitaxial GaAs surfaces for growth
Authors: Lehman S. Y. , Roshko A. , Mirin R. P. , Bertness K. A. , Harvey T. E. , Cobry K. D.
Published: May 2009

The topography and surface roughness of (100) GaAs substrates and buffers after different preparation procedures were determined from atomic force microscopy (AFM) measurements. In order to characterize the topography over a wide range of length scales, multiple large 5×5 μm2 AFM scans were acquired for each sample. These scans were analyzed both by histogramming the distribution of pixel heights and by finding the rms roughness at length scales from 10 nm to 5 μm using a tiling analysis. The influence of substrate aging and chemical etching on buffers grown by molecular beam epitaxy was studied, as was the effect of different buffer growth procedures. Immediately after thermal desorption of the surface oxide, all wafers were extremely rough, as expected, with wafers etched in HCl:H20 (1:1) somewhat smoother than untreated epiready wafers, while wafers etched in H2O2:NH4OH:H2O (3:1:10) were rougher. After as little as 100 nm of buffer growth, however, there was no significant difference in roughness of etched or as-received substrates, and all samples were quite smooth with a rms roughness around 0.27 nm. The buffer growth conditions were found to significantly affect surface roughness. Interrupting the supply of Ga at the start of the growth enhanced mounding on the wafer surface, while postgrowth annealing at the growth temperature reduced the surface roughness and changed the characteristic topography of the surface.
Enhanced surface blistering of germanium with B+∕H+ coimplantation
Authors: Ma Xiaobo , Du Xiaofeng , Liu Weili , Chen Chao , Song Zhitang , Lin Chenglu
Published: May 2009

The surface blisters in B+∕H+ coimplanted germanium (Ge) and H-only-implanted Ge were compared. The surface-blister phenomenon in B+∕H+ coimplanted Ge emerged after annealing at 330–340°C; but in H-only-implanted Ge, the blistering emerged after annealing at over 400°C. The results indicate that the preimplanted boron can facilitate the coalescence of implanted H into bubbles, and so, it decreases the temperature for surface-blister formation. The exfoliation mechanism of B+∕H+ coimplanted Ge during the annealing step was investigated. The transmission electron microscopy results indicate that the B+∕H+ coimplantation creates both (100) and {111} platelet defects, and the nucleation of H bubbles occurs at regions where the (100) defects are concentrated. The bottoms of popped-off blisters show a very rough surface because the (100) and {111} platelets occur at different depths, and the wide distribution of (100) platelets also contributes to this roughness. The results show that boron appears to be one of the choices for prebonding implantation because it reduces the splitting temperature of the H-implanted Ge wafer.
Improved field emission via laser processing of carbon nanotubes on paper substrates
Authors: Lyth S. M. , Henley S. J. , Silva S. R. P.
Published: May 2009

The authors report excellent electron field emission characteristics from acid-oxidized multiwalled carbon nanotubes printed onto paper substrates and subjected to a postdeposition laser treatment. A distinct change in the morphology of the nanotube layer was observed after laser irradiation, and threshold fields improved from 4.8V∕μm before laser irradiation to 2.1V∕μm after laser irradiation. This study shows how field emission cathodes can be fabricated in a straightforward manner on cheap, flexible substrates and that the field emission characteristics can be tailored readily via postdeposition laser treatment.
Pd-catalyzed hydrogen sensing with InN nanobelts
Authors: Wright J. S. , Lim Wantae , Gila B. P. , Pearton S. J. , Ren F. , Lai Wei-Ta , Chen Li-Chyong , Hu Ming-Shien , Chen Kuei-Hsien
Published: May 2009

The use of Pd coatings on multiple InN nanobelts is shown to enhance their sensitivity for hydrogen sensing at hundreds of ppm level at 25°C. Without the metal coating to catalyze dissociation of the hydrogen molecules, the InN nanobelts with Ohmic contacts at either end showed no detectable change in current when exposed to hydrogen under the same conditions. Moreover, the Pd-coated InN showed no response to CO2, C2H6, NH3, and O2 (all in N2 ambient). The relative resistance change in the Pd-coated sensors was not linearly dependent on the hydrogen concentration at dilute levels, i.e., 8% at 100ppm H2 and 9.5% at 1000ppm H2. The recovery characteristics of the sensors at room temperature after hydrogen sensing were also examined and ∼50% of the initial InN resistance was recovered 10min after sensor exposure to air. At higher temperatures, larger resistance changes and faster response and recovery were obtained. Pd-coated InN nanobelt sensors displayed much higher relative response than Pt-coated sensors.
Theory of space charge limited regime of thermionic energy converter with negative electron affinity emitter
Authors: Smith Joshua Ryan , Bilbro Griff L. , Nemanich Robert J.
Published: May 2009

A theory of the space charge limited output current regime of a vacuum thermionic energy conversion device (TEC) employing a negative electron affinity (NEA) diamond emitter electrode is derived. The theory is developed by assuming that the electrons behave as a collisionless gas and self-consistently solving Vlaslov’s equation and Poisson’s equation. Special cases of the theory are addressed. Calculations are performed to model a TEC with a nitrogen doped diamond emitter material under various conditions. It is shown that the NEA material outperforms a similar positive electron affinity material in terms of output power and efficiency because the NEA lowers the electrostatic boundary condition at the emitter and therefore mitigates the negative space charge effect.
Commercial molecular beam epitaxy production of high quality SrTiO3 on large diameter Si substrates
Authors: Gu X. , Lubyshev D. , Batzel J. , Fastenau J. M. , Liu W. K. , Pelzel R. , Magana J. F. , Ma Q. , Wang L. P. , Zhang P. , Rao V. R.
Published: May 2009

The authors report on the development of a molecular beam epitaxy production process for the epitaxial growth of high quality, single crystal, single phase SrTiO3 (STO) films on Si substrates with diameter up to 8in. Reflection high-energy electron diffraction indicated that the STO growths proceeded two dimensionally with excellent stoichiometric control, as confirmed by Rutherford backscattering spectroscopy measurement. Excellent crystalline quality has been confirmed by x-ray diffraction rocking curves of the STO (200) reflection with narrow full width at half maximum of 0.06° for a 1200Å thin film. Atomic force microscopy images show smooth, defect-free STO surface with a root-mean-square roughness value as low as ∼0.6Å. Cross-sectional transmission electron microscope images reveal an abrupt interface between STO and Si, with a very thin SiO2 interfacial layer.
Fabrication of functional structures at Si (100) surface by mechanical scribing in the presence of aryl diazonium salts
Authors: Shi Liqiu , Sun Tao , Yan Yongda , Zhao Jianwei , Dong Shen
Published: May 2009

A combination of chemical and mechanical method has been proposed to fabricate modified surface on the oxide-coated silicon. When the diamond tool scribes the silicon sample in the presence of 4-benzoic acid diazonium tetrafluoroborate (COOHC6H4N2BF4), the chemoactive COOHC6H4 radical can be generated from aryldiazonium salt due to the breaking of chemical bond of silicon substrate. They may then induce grafting of an organic monolayer on the substrate via Si–C connection. The surface morphologies before and after chemomechanical reaction are characterized with atomic force microscopy. X-ray photoelectron spectroscopy confirms the presence of COOHC6H4 and shows a steady increase in the amount of carbon on the exposed fresh Si surface. Infrared spectroscopy suggests that COOHC6H4 groups bond with surface Si atoms via Si–C covalent bonds. To the best of the authors knowledge, this is the first report of the chemomechanical preparation of self-assembled monolayers on oxide-coated silicon in the presence of aryldiazonium salt. The method described in this article will have important implications for building nano- or microscale functional structures.
Fabrication of crystalline Si spheres with atomic-scale surface smoothness using homogenized KrF excimer laser reformation system
Authors: Hung Shih-Che , Shiu Shu-Chia , Chao Cha-Hsin , Lin Ching-Fuh
Published: May 2009

A technique applying the homogenized KrF excimer laser reformation to fabricate Si spheres on the silicon on insulator platform is presented. High-power excimer laser was used to illuminate the Si rods which were fabricated using typical procedures. The Si rods were then melted and reshaped to spheres due to surface tension. This method is capable of fabricating submicrometer Si spheres with extremely smooth surface. Atomic force microscopy was used to reveal the atomic-scale surface smoothness of the fabricated Si spheres. It shows that root-mean-square roughness is smaller than 0.1nm. In addition, tunneling electron microscopy was used to investigate crystalline property of the Si spheres, showing that single-crystalline Si with lattice plane spacing of about 0.24nm was formed after the transformation of the Si rod into the sphere.
Investigation on feedback control of linear motors in ultraprecision-machine feed-drive systems
Authors: Guan Chao-Liang , Dai Yi-Fan , Xie Xu-Hui , Yin Zi-Qiang
Published: May 2009

Linear motors offer many advantages over ac or dc servo motors. More and more ultraprecision machines use linear motors in their feed-drive systems. The distance measured by the linear encoder is used to calculate the linear motor’s velocity. A linear-motor controller needs a high-resolution position sensor for smooth velocity control. However, the high-resolution position sensor may sense the vibration of the mechanical structure and therefore cause instability. This article presents a simulation model to analyze the impact of linear encoder feedback on a linear motor’s motion control and stability. Experiments are designed to validate the simulation model. Both simulation and experiment demonstrate that proper selection of linear encoder’s resolution can satisfy a smooth velocity control and stability requirements.
Microstructural compositional, and optical characterization of GaN grown by metal organic vapor phase epitaxy on ZnO epilayers
Authors: Rogers D. J. , Hosseini Teherani F. , Moudakir T. , Gautier S. , Jomard F. , Molinari M. , Troyon M. , McGrouther D. , Chapman J. N. , Razeghi M. , Ougazzaden A.
Published: May 2009

This article presents the results of microstructural, compositional, and optical characterization of GaN films grown on ZnO buffered c-sapphire substrates. Transmission electron microscopy showed epitaxy between the GaN and the ZnO, no degradation of the ZnO buffer layer, and no evidence of any interfacial compounds. Secondary ion mass spectroscopy revealed negligible Zn signal in the GaN layer away from the GaN∕ZnO interface. After chemical removal of the ZnO, room temperature (RT) cathodoluminescence spectra had a single main peak centered at ∼368nm (∼3.37eV), which was indexed as near-band-edge (NBE) emission from the GaN layer. There was no evidence of the ZnO NBE peak, centered at ∼379nm (∼3.28eV), which had been observed in RT photoluminescence spectra prior to removal of the ZnO.
Evolutionary Relationships among theFusarium oxysporumf. sp.cubenseVegetative Compatibility Groups
Authors: Fourie Gerda , Steenkamp E. T. , Gordon T. R. , Viljoen A.
Published: May 2009

Fusarium oxysporumf. sp.cubense, the causal agent of fusarium wilt of banana (Musaspp.), is one of the most destructive strains of the vascular wilt fungusF. oxysporum. Genetic relatedness among and within vegetative compatibility groups (VCGs) ofF. oxysporumf. sp.cubensewas studied by sequencing two nuclear and two mitochondrial DNA regions in a collection of 70F. oxysporumisolates that include representatives of 20 VCGs ofF. oxysporumf. sp.cubense, other formae speciales, and nonpathogens. To determine the ability ofF. oxysporumf. sp.cubenseto sexually recombine, crosses were made between isolates of opposite mating types. Phylogenetic analysis separated theF. oxysporumisolates into two clades and eight lineages. Phylogenetic relationships betweenF. oxysporumf. sp.cubenseand other formae speciales ofF. oxysporumand the relationships among VCGs and races ofF. oxysporumf. sp.cubenseclearly showed thatF. oxysporumf. sp.cubense's ability to cause disease on banana has emerged multiple times, independently, and that the ability to cause disease to a specific banana cultivar is also a polyphyletic trait. These analyses further suggest that both coevolution with the host and horizontal gene transfer may have played important roles in the evolutionary history of the pathogen. All examined isolates harbored one of the two mating-type idiomorphs, but never both, which suggests a heterothallic mating system should sexual reproduction occur. Although, no sexual structures were observed, some lineages ofF. oxysporumf. sp.cubenseharboredMAT-1andMAT-2isolates, suggesting a potential that these lineages have a sexual origin that might be more recent than initially anticipated.
Comparative Genomics of the IncA/C Multidrug Resistance Plasmid Family
Authors: Fricke W. Florian , Welch Timothy J. , McDermott Patrick F. , Mammel Mark K. , LeClerc J. Eugene , White David G. , Cebula Thomas A. , Ravel Jacques
Published: May 2009

Multidrug resistance (MDR) plasmids belonging to the IncA/C plasmid family are widely distributed among
Salmonella
and other enterobacterial isolates from agricultural sources and have, at least once, also been identified in a drug-resistant
Yersinia pestis
isolate (IP275) from Madagascar. Here, we present the complete plasmid sequences of the IncA/C reference plasmid pRA1 (143,963 bp), isolated in 1971 from the fish pathogen
Aeromonas hydrophila
, and of the cryptic IncA/C plasmid pRAx (49,763 bp), isolated from
Escherichia coli
transconjugant D7-3, which was obtained through pRA1 transfer in 1980. Using comparative sequence analysis of pRA1 and pRAx with recent members of the IncA/C plasmid family, we show that both plasmids provide novel insights into the evolution of the IncA/C MDR plasmid family and the minimal machinery necessary for stable IncA/C plasmid maintenance. Our results indicate that recent members of the IncA/C plasmid family evolved from a common ancestor, similar in composition to pRA1, through stepwise integration of horizontally acquired resistance gene arrays into a conserved plasmid backbone. Phylogenetic comparisons predict type IV secretion-like conjugative transfer operons encoded on the shared plasmid backbones to be closely related to a group of integrating conjugative elements, which use conjugative transfer for horizontal propagation but stably integrate into the host chromosome during vegetative growth. A
hipAB
toxin-antitoxin gene cluster found on pRA1, which in
Escherichia coli
is involved in the formation of persister cell subpopulations, suggests persistence as an early broad-spectrum antimicrobial resistance mechanism in the evolution of IncA/C resistance plasmids.