bluuebunny/crossref_metadata_2025 huggingface dataset:
Stearoyl‐CoA desaturase as a new drug target for obesity treatment
Authors: Dobrzyn A. , Ntambi J. M.
Published: April 2005

Stearoyl‐CoA desaturase (SCD), the rate‐limiting enzyme in monounsaturated fatty acid synthesis, has recently been shown to be the critical control point regulating hepatic lipogenesis and lipid oxidation. As several manifestations of the metabolic syndrome and type 2 diabetes mellitus are associated with alterations in intracellular lipid partitioning, we propose that SCD1 may be a potential therapeutic target in the treatment of obesity and the metabolic syndrome. In support of this notion, we have shown that SCD1‐deficient mice have increased energy expenditure, reduced body adiposity, increased insulin sensitivity and are resistant to diet‐induced obesity and liver steatosis. Furthermore, SCD1 was found to be specifically repressed during leptin‐mediated weight loss, and leptin‐deficient ob/ob mice lacking SCD1 showed marked correction of the hypometabolic phenotype and hepatic steatosis. Much evidence indicates that the direct anti‐steatotic effect of SCD1 deficiency stems from increased fatty acid oxidation and decreased lipid synthesis. All of these findings reveal that pharmacological manipulation of SCD activity might be of benefit in the treatment of obesity, diabetes, liver steatosis and other diseases of the metabolic syndrome.
Fabrication of Si field emitter array in local vacuum package
Authors: Noda Daiji , Hatakeyama Masanori , Kyogoku Masanori , Ikushima Kimiya , Sawada Kazuaki , Ishida Makoto
Published: April 2005

We have fabricated a local vacuum package enclosing a Si field emitter array on Si substrate. To maintain the low pressure required for electron emission, a titanium evaporation getter was made as a bridge structure with the Si field emitter array in local vacuum package. The local vacuum package technique was adapted to the IC process for on-chip device fabrication. This technique will be very useful for many applications with high performance.
Screen printed carbon nanotube field emitter array for lighting source application
Authors: Park Jae-Hong , Son Gil-Hwan , Moon Jin-San , Han Jae-Hee , Berdinsky Alexander S. , Kuvshinov D. G. , Yoo Ji-Beom , Park Chong-Yun , Nam Joong-Woo , Park Jonghwan , Lee Chun Gyoo , Choe Deok Hyeon
Published: April 2005

We have investigated carbon nanotube (CNT)-field emitter array (FEA) for the application of lighting system like back light unit (BLU) in liquid crystal display (LCD). The photosensitive CNT paste was synthesized by mixing of multiwalled carbon nanotubes (MWNTs), spin on glass (SOG), organic vehicle, photosensitive monomers, photosensitive oligomers and photo initiators. Uniform CNT paste films were obtained by using backside exposure technique and emission properties of CNT paste were evaluated depending on variation in SOG content and firing conditions. Then we prepared line patterned CNT-FEAs using photolithography and measured their I–V characteristics and brightness.
High intensity pulse x-ray generation by using graphite-nanocrater cold cathode
Authors: Matsumoto Takahiro , Mimura Hidenori
Published: April 2005

Graphite nanostructures fabricated by a simple plasma etching onto a graphite substrate provide an intense emission source of electrons. This cathode does not have the adherence problem commonly seen in carbon deposited emission layera such as carbon nanotubes and graphite nanofibers, thus making it promising for applications in high power devices. The performance of this cold cathode was demonstrated by obtaining high-intensity pulse x-ray generation. High-speed x-ray radiography images of dynamical processes of the order of 10 μs were also shown by using the pulse x-ray source.
Fabrication of a nanosized current-driven spin valve device using proximity correction in electron-beam lithography
Authors: Yi Hyunjung , Nguyen T. H. Y. , Chang Joonyeon , Shin K. H.
Published: April 2005

Nanosized junctions of 100×200nm2 size were successfully fabricated on magnetic metallic multilayers in a current-driven spin-valve device by the suitable choice of the electron-beam resist, as well as careful control of back-scattering effects in electron-beam lithography. ZEP520A was chosen as an e-beam sensitive resist because its dry-etching resistance is high enough to act as an etching mask during the ion milling. The severe back-scattering effect from the underlying metallic multilayers was reasonably modified by employing the doughnut-pattern method. The doughnut-pattern method gave a set of proximity parameters (α,β, and η) with which we did the simulation to obtain the effective dose factors of each segment of the pattern. The magnetotransport signals from our devices were quite comparable to previous results from those made by different methods of other research groups. Consequently, the fabrication of nanosized current driven spin valves can be performed less complicatedly by using ZEP520A as an etching mask.
Effect of Ti interlayer on the growth of carbon nanotubes on Si by microwave-heated chemical vapor deposition
Authors: Huang J. H. , Chen Y. S. , Chuang C. C. , Wong Y. M. , Kang W. P.
Published: April 2005

The effect of Ti layer on the growth of aligned carbon nanotubes on Si using Pd, Ni, or Co as catalysts by microwave-heated chemical vapor deposition was systematically studied. For all growths, a thin Ti layer of 16 or 22 nm, a thin catalyst layer of 6–30 nm, a growth time of 15–45 min, and a growth temperature of 590 or 690 °C were varying deposition parameters. It was found that the growths with Ni or Co as the catalyst on Ti-coated Si could always produce well-aligned carbon nanotubes. However, a carbonaceouslike film was found to exist on the top of nanotubes in most Ni-catalyzed carbon nanotube films. In contrast, carbon nanotubes grown from Pd catalyst were generally not aligned. Furthermore, the nanotubes grown from Pd at 590 °C are crooked or twist, and very short.
Fourier transform infrared spectroscopy studies of water-polymer interactions in chemically amplified photoresists
Authors: McDonough Laurie A. , Chikan Viktor , Hwan Kim Zee , Leone Stephen R. , Hinsberg William D.
Published: April 2005

Fourier-transform infrared absorption spectroscopy is implemented to measure the infrared spectrum of water absorbed by the poly(t-butoxycarbonylstyrene) and the ketal-protected poly(hydroxystyrene) polymer photoresists. The shape and intensity of the OH stretching band of the water spectrum is monitored in a variety of humidity conditions in order to obtain information on the hydrogen-bonding interactions between the water and the polymer chains. The band is deconvoluted into four subbands, which represent four types of water molecules in different environments. Because of the hydrophilicity of the polymers studied, a large portion of the sorbed water molecules is believed to be strongly bound to the polar sites of the polymer. The ratios of each type of water are found to be dependent on the humidity conditions to which the sample was exposed. At higher humidities, there is an increase in the fraction of free and weakly bound water molecules. These findings are used to explain the humidity dependence of the deprotection reaction rates, since certain types of water may slow transport of reactive species within the polymer network.
Effect of plasma interactions with low-κ films as a function of porosity, plasma chemistry, and temperature
Authors: Worsley Marcus A. , Bent Stacey F. , Gates Stephen M. , Fuller Nicholas C. M. , Volksen Willi , Steen Michelle , Dalton Timothy
Published: April 2005

Integration of new low-κ interlayer dielectrics (ILD) with current damascene schemes is a continuing issue in the microelectronics industry. During integration of the ILD, processing steps such as plasma etching, resist strip, and chemical-mechanical planarization are known to chemically alter a layer of the dielectric. Here, porous organosilicate glass (OSG) ILD films, which—according to the 2004 edition of the International Technology Roadmap for Semiconductors—are projected for use in the 65 and 45 nm nodes, are investigated. spectroscopic ellipsometry, x-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy are used to characterize the modified layer of the ILD after exposure to O2 or H2 resist strip plasmas. The effects of the two types of plasma etch chemistries on the formation of the modified layer were found to differ significantly. These effects include both the degree of modification (i.e., chemical composition) and depth of the modified layer. A key difference between the O2 and H2 plasmas is that silicon hydride groups are present in the modified layer after exposure to H2 plasma but not after exposure to the O2 plasma. In addition, the influence of OSG porosity on the etch rate and modified layer thickness was investigated for porosities ranging from 0–45 %. As expected, the etch rate was found to increase rapidly with porosity. Finally, conditions including reactive gas concentrations and substrate temperature for the H2 plasma were varied. These parameters produced considerable changes in the chemistry of the modified layer, especially in the amount of hydrogen incorporated into the film. Details of these results will be discussed in the context of the mechanism by which modification and etching occurs as well as which process variables dominate those phenomena.
Time dependent models of field-assisted photoemission
Authors: Jensen Kevin L. , Feldman Donald W. , O’Shea Patrick G.
Published: April 2005

A time-dependent model of photoemission, developed to analyze current from and laser heating of metals and dispenser photocathodes, is here applied to examine the impact of geometrical field enhancement and the contribution of tunneling to the photocurrent from a tungsten needle in terms of temporal response, quantum efficiency, and cathode performance. First, a review is given of an updated Fowler–Dubridge model of quantum efficiency including quantum mechanical effects. Second, a prolate spheroidal model of a tungsten needle is given to determine applied fields and incident angles necessary to evaluate emitted current and laser heating effects. Third, a time-dependent model of laser heating of an electron distribution is given which affects the photoemitted current and (if conditions are right) gives field and thermal components as well. Finally, the methodology is related to the experimental findings of Garcia and Brau [Nucl. Instrum. Methods Phys. Res. A 483, 273 (2002)], in which an intense laser illuminates a tungsten needle under sufficiently high fields that the photoemitted current contains field and thermal emission components and effects.
Characterization of nano-size YVO4:Eu and (Y,Gd)VO4:Eu phosphors by low voltage cathodo- and photoluminescence
Authors: Kang Jong Hyuk , Nazarov Michael , Im Won Bin , Kim Jin Young , Jeon Duk Young
Published: April 2005

Low voltage cathodoluminescence (LVCL) and photoluminescence measurement were carried out to better understand the role of Gd in (Y,Gd)VO4:Eu phosphor and to compare two different synthesis methods (solid-state reaction, coprecipitation reaction) and their preparing conditions. From the analysis of LVCL measurement, it is understood that the luminescence of YVO4:Eu and (Y,Gd)VO4:Eu phosphors might be interpreted as originating from a two-level system and for reasons of enhanced luminescence intensity of (Y,Gd)VO4:Eu phosphor, the effect of Gd on the symmetry of Eu sites dominates over that of interaction between Gd and Eu. It is also found that nano-size phosphor of YVO4:Eu synthesized by coprecipitation reaction shows lower quantum yield in comparison with that synthesized by solid-state reaction due to the presence of secondary phase produced after heat treatment.
Performance improvement of diamondlike carbon membrane masks for electron projection lithography
Authors: Amemiya Isao , Yamashita Hiroshi , Taniguchi Kazutake , Nakatsuka Sakae , Kimura Ikuru , Nagarekawa Osamu
Published: April 2005

This article describes the fabrication of eight-inch continuous membrane masks with a 15-nm-thick support membrane for electron projection lithography (EPL). In order to develop an extremely thin support membrane with a tensional stress, two techniques were applied; one is a low pressure deposition process to improve the membrane bulk density, and the other is Si addition during the conventional carbon membrane deposition for improving the atomic distance mismatch between substrate and deposited film, and also to address the membrane volume strain cause by the rise in the tensional stress under the low pressure deposition condition. By using Si-additional techniques, an extremely thin membrane with a tensional stress was formed under the conditions of less than 0.5Pa chamber pressure. Long-term membrane stress stability of Si-added extremely thin membranes were particularly improved. It was less than 3MPa in elapsed times of 400h. The zero-loss electron transmittance for the fabricated 15-nm-thick membrane mask was measured to be 70.4%. Due to the development of an extremely thin membrane with high zero-loss electron transmittance of more than 50%, our high-performance membrane masks are superior to the complementary stencil masks in terms of exposure throughput.
Noise and emission characteristics of NbC∕Nb field emitters
Authors: Charbonnier F. M. , Southall L. A. , Mackie W. A.
Published: April 2005

Several applications require single field emitters with adequate long-term stability and life in a moderate vacuum. Our previous studies have shown that the refractory carbides of transition metals are capable of higher currents and are more environmentally tolerant than common field emitter materials such as W, Mo, or Si. We undertook a systematic study of the emission characteristics and stability of individual NbC∕Nb microtips at low currents and at residual pressures ranging from 10−9 to 10−5Torr. We reported preliminary results one year ago [J. Vac. Sci. Technol. B 22, 1643 (2004)]. We now present additional data and interpretations. These experimental data were obtained by two types of measurement: (a) continuous recording of the field emitted current at a fixed voltage and (b) recording of the emitted current with a saw-tooth applied voltage, which yields a large number of Fowler–Nordheim plots which are analyzed by the slop-intercept method. Our experimental results show greater instability than we expected. We conclude that for NbC∕Nb emitters fabricated by physical vapor deposition, emission is dominated by a very small number of extremely sharp but unstable nanoprotrusions, with an effective emitting area (from the slope-intercept charts) of the order of a few nm2. Consequently, we lack the stability and control of the beam directional intensity which are required for most applications. Prior to stable operation, single emitters should be conditioned to eliminate sharp protrusions, enhance paraxial emission, and increase the effective emitter area. We are now studying effective conditioning techniques for microtips.
Effect of sidewall properties on the bottom microtrench during SiO2 etching in a CF4 plasma
Authors: Min Jae-Ho , Lee Gye-Re , Lee Jin-Kwan , Moon Sang Heup , Kim Chang-Koo
Published: April 2005

Factors that affect microtrench formation during the etching of SiO2 in a CF4 plasma were investigated using an experimental set-up, which comprised a Faraday cage and step-shaped substrates consisting of a SiO2 bottom and slanted sidewalls of different materials. This set-up permitted the etched micropattern to be observed on a magnified scale under conditions that are similar to actual processes. SiO2 and fluorocarbon polymer were used as sidewall surface materials to investigate the effect of sidewall properties on the microtrench. The depth of the microtrench characteristically changed with the sidewall angle, reaching a maximum at 70° under the condition used in this study. This can be explained by the effect of two competitive factors: secondary etching of the bottom by ions reflected from the sidewall, which contributes to the bottom etch rate, and the shadowing effect of the sidewall, which decreases the etch rate. Secondary etching, as estimated from the difference in the bottom etch rates between two cases of an ordinary sidewall and a sidewall with an extremely rough surface, showed a maximum at a sidewall angle of 80°–82.5°, while the shadowing effect was increased monotonously with sidewall angle. The rates of secondary etching were higher for the polymer sidewall than for the SiO2 sidewall for sidewall angles lower than 70°, but opposite relative magnitudes were observed for angles higher than 70°. The result obtained at angles lower than 70° can be explained based on a model in which a fluorocarbon film formed on the sidewall, which was particularly thick for a polymer sidewall, acted as a source of etchant radicals, thus contributing to bottom etching. The opposite trend observed at angles higher than 70° can be attributed to the roughness of the sidewall surface, which was higher for the polymer sidewall, which affected the reflection of ions on the surface and, eventually, secondary etching.
In situ fabrication of metal gate/high-κ dielectric gate stacks using a potential lower cost front-end process for the sub-90nm CMOS technology node
Authors: Damjanovic Daniel , Singh Rajendra , Poole Kelvin F.
Published: April 2005

In this article we discuss the advantages of in situ fabrication of metal gate/high-κ gate stacks using single wafer processing. The aim was to develop an in situ process for the sub-90nm CMOS regime, which allows for a reduction in the number of processing steps and consequently the number of processing tools, while also providing for improved device performance, yield and reliability. In this work, we demonstrate improved electrical characteristics of ultrathin high dielectric constant films processed by rapid thermal processing (RTP) assisted metal-oxide chemical vapor deposition (MOCVD), where the silicon wafer underwent an in situ precleaning treatment followed by an in situ oxide deposition, in situ oxide anneal, and an in situ metallization step. Gate leakage currents on the order of 10−11A∕cm2 at a gate voltage of 1V and an EOT of 1.5nm were measured across the Al2O3 gate oxide of the gate stacks. These results present an improvement of two orders of magnitude over gate leakage currents measured across Al2O3 gate oxides with comparable EOT values reported in literature.
Influence of mechanical stress on electron field emission of multiwalled carbon nanotube–polymer composites
Authors: Poa C. H. P. , Smith R. C. , Silva S. R. P. , Sun C. Q.
Published: April 2005

Field emission properties of carbon nanotubes under mechanical stress have been investigated. The emission threshold fields initially decrease from 2.3to0.6V∕μm before rising back to 3.1V∕μm with increasing mechanical stress applied externally to the film. This behavior from nanotube composites has not been reported and is believed to be associated with modification to the work function of the nanotubes. This work suggests a possible application for these composite films as electromechanical high power switches.
Effects of nickel and titanium thickness on nickel/titanium ohmic contacts to n-type silicon carbide
Authors: Park Jae Hyun , Holloway Paul H.
Published: April 2005

Titanium/nickel/titanium ohmic contacts to 4H n-SiC nitrogen doped to 3.55×1018 and 1.22×1019cm−3 have been studied. As-deposited Ti∕Ni∕Ti∕SiC structures were rectifying, but became ohmic upon annealing at 1000°C for 2min in a N2 ambient. A nickel silicide phase (Ni2Si) was formed during annealing, and smooth interfaces were observed when a Ti layer was present between the Ni and SiC. The dependence of ohmic contact resistance on Ni and Ti layer thickness was studied. Contacts with a 20nm bottom Ti layer showed a contact resistance of 1×10−4Ωcm2, while maintaining an interfacial rms roughness of 7.5nm. Contacts with thicker bottom Ti layers (>20nm) were rectifying with a nonlinear current–voltage behavior even after annealing, and there was still a distinct Ti layer between the Ni and SiC. The lack of an ohmic contact was attributed to the Ti layer acting as a diffusion barrier restricting the formation of Ni2Si. The Ni thickness was varied from 90to30nm over a 20nm Ti bottom layer, but the specific contact resistances (ρC) (3.3×10−4±2.5×10−4Ωcm2) did not vary significantly with Ni thickness. Thicker Ni(>30nm) contacts showed a nonuniform carbon distribution with graphite-rich zones at the silicide/SiC interface. Thin Ni contacts (30nm) showed more uniform carbon distribution than in the contacts with thicker Ni, and no significant carbon-rich zone at the silicide/SiC interface.
Fabrication of polysilicon thin-film transistors using nickel/copper double-layer-induced lateral crystallization
Authors: Chen Chi-Chieh , Yang Bo-Chuan , Lee Si-Chen
Published: April 2005

The material properties and thin-film transistors characteristics of nickel/copper-induced polysilicon are investigated. It was discovered that by combining Cu and Ni, the lateral growth rate of polysilicon is about an order of magnitude higher than that induced by Ni alone, and much better than the Cu-induced case. The grain size of Ni∕Cu-induced polysilicon is 1.5 times larger than that of Ni alone, and also 30 times larger than that of the Cu induced case. The mechanism is attributed to the Cu-enhanced Ni silicide migration. The Ni∕Cu-induced low-temperature polysilicon thin-film transistor shows a field-effect mobility of 10–25cm2∕Vs, a threshold voltage of 8–22V, and an on/off current ratio about 106–107.
Effect of aspect ratio and anode location on the field emission properties of a single tip based emitter
Authors: Smith R. C. , Carey J. D. , Forrest R. D. , Silva S. R. P.
Published: April 2005

The effect on the field emission characteristics of the aspect ratio of an isolated emitter, together with the position of the anode electrode are reported. We show by computational simulation that the field enhancement factor β is only dependant on the emitter height h, radius r, when the anode to cathode separation D is greater than three times the height of the emitter away from the tip. In this regime the enhancement factor is independent of the anode location and approaches a value depicted by h and r alone and is described by the expression β0=(1+h∕αr)m where α=2 and m=1. As the anode is brought close to the tip of the emitter, the emitter tip and anode approximate a parallel plate configuration and the enhancement factor tends to unity. Extracted enhancement factor and threshold fields are described by a modified applied electric field taking D−h as the separation. Comparison with previously reported experimental results is also given.
Electron optics and electrical studies of a single Spindt-type field emitter
Authors: Désières Y. , Nicolas P. , Sermet F. , Geffraye F. , Gidon S.
Published: April 2005

Experimental and numerical investigations of the field emission of a single molybdenum Spindt emitter are presented. Experimental results show that the emission is localized at nanometric areas on the top of the tip. An effective numerical model of the tip has been developed to describe the main characteristics of the experimental beam pattern. The Lagrange constant of this model has been estimated to 15nmV1∕2.
Growth aspects of nanocrystalline diamond films and their effects on electron field emissions
Authors: Subramanian K. , Kang W. P. , Davidson J. L. , Hofmeister W. H.
Published: April 2005

In this article, we report aspects of the growth of nanocrystalline diamond films using microwave-assisted plasma chemical vapor deposition and their relation to electron field emission. Nanodiamond films with grain size as small as 5–10nm by CH4∕H2∕N2 microwave plasma enhanced chemical vapor deposition (MPECVD) and 10–20nm by CH4∕H2 MPECVD have been achieved. An effective means to grow nanodiamond films is to increase the nucleation rate and decrease the growth rate by adjusting the CVD process parameters. With its relation to field emission, we infer that the combination of high dopant concentration resulting in lower electrical resistance of the diamond film and increased sp2 bonded nondiamond carbon content contributes effectively to the enhancement of field emission characteristics, while the reduction in grain size of the nanodiamond film has no similar effect.
Stable and high emission current from carbon nanotube paste with spin on glass
Authors: Park Jae-Hong , Moon Jin-San , Han Jae-Hee , Berdinsky Alexander S. , Yoo Ji-Beom , Park Chong-Yun , Nam Joong-Woo , Park Jonghwan , Lee Chun Gyoo , Choe Deok Hyeon
Published: April 2005

A carbon nanotube (CNT) paste was synthesized by mixing multiwalled CNTs (MWNTs), organic vehicles, and inorganic binder. The paste with spin on glass (SOG) showed improved uniformity, dispersion, and adhesion characteristics of the CNT paste layer. The emission characteristics of CNT paste with SOG were improved, and compared to those of a CNT paste with a glass frit. When the organic vehicle was changed from ethyl cellulose to acryl solution, current density of CNT paste increased. The firing condition for CNT pastes was investigated and optimized. It was found that firing at 450 °C under N2 was the most suitable condition for pastes with MWNTs. We obtained stable and high emission current of 100 mA at an electric field of 8.35V∕μm from CNT paste with SOG printed on a Ni plate.
Study of neutral-beam etching conditions for the fabrication of 7-nm-diameter nanocolumn structures using ferritin iron-core masks
Authors: Kubota Tomohiro , Baba Tomohiro , Kawashima Hiroyuki , Uraoka Yukiharu , Fuyuki Takashi , Yamashita Ichiro , Samukawa Seiji
Published: April 2005

We fabricated nanocolumn structure by using a low energy neutral beam and a ferritin iron-core mask. By using Cl2 gas plasma for generating neutral beam, we obtained a better etching profile than with SF6 gas plasma. Though Cl2:SF6=90:10 enabled faster etching than Cl2 gas without degrading the etching profile when the etching depth was 25 nm, a mixture with any quantity of SF6 gas resulted in a poor etching profile when the etching depth was 50 nm. The beam energy was optimized for the 50-nm depth using Cl2 gas by changing the rf bias power to the bottom electrode of the neutral-beam source. Using the optimum beam energy, extremely high etching selectivity of the Si to ferritin iron-core masks (about 80) as well as highly anisotropic etching profile could be realized. As a result, the diameter of the top of the Si nanocolumn structure was 7 nm, which was identical to that of the iron core in the ferritin. Additionally, the etching profile was almost vertical. We were also able to achieve a high aspect ratio of about 4.6. It is very difficult for conventional plasma etching processes to fabricate such fine structure, because the high-energy photons enhanced the etching of the iron-core mask in the conventional plasma processes.
Development and characterization of silane antisticking layers on nickel-based stamps designed for nanoimprint lithography
Authors: Keil M. , Beck M. , Ling T. G. I. , Graczyk M. , Montelius L. , Heidari B.
Published: April 2005

In this study we will report on the development of a process to establish antisticking layers on nickel-based stamps, which are used in several industrial applications of nanoimprint lithography or related methods. The fluorinated alkyl silane films have been deposited onto different Ni-based stamp surfaces in order to minimize the adhesion tendency at the stamp/polymer interface. Film thickness, chemical composition, purity, and binding mechanisms of the silane groups to different stamp surface materials have been determined by photoelectron spectroscopy (XPS). In the case of electroplated nickel stamps—where low imprint qualities are observed—multilayer thick films cover the stamp surfaces, consisting of polymerized, cross-linked alkyl silanes, which are poorly bound to the surface. In order to overcome these restrictions a 100 Å thick polycrystalline titanium layer has been established in a sandwich position between the nickel substrate and the silane film. Here, silane film thicknesses in the monomolecular region together with evidences for strong covalent linkage between the silane groups and the oxidized Ti surface can be concluded from the XPS results, leading to film properties and imprint qualities, which are comparable to those formerly observed for silicon stamps.
Carbon nanotube field emitter manufactured by anodic-alumina template and Ni-CNT composite plating
Authors: Kang Hyungdong , Lee Sangmoon , Lee Haisung
Published: April 2005

We present a method of manufacturing carbon nanotube (CNT) field emitters using anodic-alumina templates and Ni-CNT composite plating. Using the anodized aluminum sheet as a substrate affects a reduction of field deformation near the film surface during the electroplating. This improves the emission uniformity considerably and also enhances the emission-site density by nearly an order of magnitude compared to the emitter prepared on a plain Cu plate. The emission characteristics are discussed in terms of the surface morphology and the interlayer resistance.
Dielectric properties enhancement of ZrO2 thin films induced by substrate biasing
Authors: Huang A. P. , Chu Paul K. , Yan H. , Zhu M. K.
Published: April 2005

We have fabricated zirconia (ZrO2) thin films on Si (100) wafers that possess excellent dielectric properties such as high permittivity up to 53 and excellent frequency stability. The good performance is mainly attributed to the improvement in the crystallinity and orientation of the thin films and the interfacial structure using substrate biasing. The bias endues positive ions with high energy and diffusion of the incident particles and relaxation of the surface are enhanced by collisions between the impinging positive ions accelerated through the plasma sheath and substrate atoms. In addition, the higher nuclei density on the surface as a result of substrate biasing is beneficial to the fabrication of oriented thin films and the dielectric properties of the thin films are improved as the substrate bias goes up. The results increase our understanding of the factors leading to the deposition of high-quality ZrO2 dielectric thin films that are able to meet the requirements for capacitors in next-generation memory devices.
A Primer on Work-Energy Relationships for Introductory Physics
Authors: Mungan Carl E.
Published: April 2005

There has been and continues to be considerable discussion in the educational community about different ways of relating the concepts of work and energy in introductory physics.1 The present article reviews a consistent and streamlined treatment of the subject, drawing particular attention to aspects seldom covered in textbooks. The paper is intended to clarify the central equations for introductory courses and to put the wider literature in context. It is specifically designed to tie closely in terminology and order of presentation to standard texts, so that it complements rather than supplants them. In brief, the key point is that there are two major categories of work, center-of-mass work and particle work.2 After an overview of these two approaches, I illustrate them with a couple of instructive examples that can be used in group problem-solving sessions in class.
Wheatstone's Bridge
Authors: Greenslade Thomas B.
Published: April 2005

The arrangement of four resistors, a source of emf, and a galvanometer, known as Wheatstone's bridge, has been in existence for more than 170 years. The only other piece of apparatus with its staying power is Atwood's machine. Now that it has reached mature status, it seems only fitting to describe its origin, analysis, circuit topology, and past and future uses.
Sand Diver
Authors: Scott Alan J.
Published: April 2005

A few years ago, I was preparing to teach a summer enrichment program for middle school students at the University of Wisconsin-Stout. With swimming on the minds of most kids during the summer, I thought buoyancy would be a fun topic to discuss. An interesting way to introduce this concept is by discussing the beer-drinking balloonist who, in a lawn chair, floated to 11,000 feet above Los Angeles in 1997. However, I needed a hands-on project and was not about to go purchase some lawn chairs to duplicate this experiment. A simple submersible called the “Sand Diver” was designed and is now used as a hands-on activity for my introductory physics course.
The DotL Protein, a Member of the TraG-Coupling Protein Family, Is Essential for Viability ofLegionella pneumophilaStrain Lp02
Authors: Buscher Benjamin A. , Conover Gloria M. , Miller Jennifer L. , Vogel Sinae A. , Meyers Stacey N. , Isberg Ralph R. , Vogel Joseph P.
Published: April 2005

Legionella pneumophilais able to survive inside phagocytic cells by an internalization route that bypasses fusion of the nascent phagosome with the endocytic pathway to allow formation of a replicative phagosome. Thedot/icmgenes, a major virulence system ofL. pneumophila, encode a type IVB secretion system that is required for intracellular growth. One Dot protein, DotL, has sequence similarity to type IV secretion system coupling proteins (T4CPs). In other systems, coupling proteins are not required for viability of the organism. Here we report the first example of a strain,L. pneumophilaLp02, in which a putative T4CP is essential for viability of the organism on bacteriological media. This result is particularly surprising since the majority of thedot/icmgenes in Lp02 are dispensable for growth outside of a host cell, a condition that does not require a functional Dot/Icm secretion complex. We were able to isolate suppressors of theΔdotLlethality and found that many contained mutations in other components of the Dot/Icm secretion system. A systematic analysis ofdot/icmdeletion mutants revealed that the majority of them (20 of 26) suppressed the lethality phenotype, indicating a partially assembled secretion system may be the source ofΔdotLtoxicity in the wild-type strain. These results are consistent with a model in which the DotL protein plays a role in regulating the activity of theL. pneumophilatype IV secretion apparatus.
Staphylococcus epidermidis
Polysaccharide Intercellular Adhesin Production Significantly Increases during Tricarboxylic Acid Cycle Stress
Authors: Vuong Cuong , Kidder Joshua B. , Jacobson Erik R. , Otto Michael , Proctor Richard A. , Somerville Greg A.
Published: April 2005

Staphylococcal polysaccharide intercellular adhesin (PIA) is important for the development of a mature biofilm. PIA production is increased during growth in a nutrient-replete or iron-limited medium and under conditions of low oxygen availability. Additionally, stress-inducing stimuli such as heat, ethanol, and high concentrations of salt increase the production of PIA. These same environmental conditions are known to repress tricarboxylic acid (TCA) cycle activity, leading us to hypothesize that altering TCA cycle activity would affect PIA production. Culturing
Staphylococcus epidermidis
with a low concentration of the TCA cycle inhibitor fluorocitrate dramatically increased PIA production without impairing glucose catabolism, the growth rate, or the growth yields. These data lead us to speculate that one mechanism by which staphylococci perceive external environmental change is through alterations in TCA cycle activity leading to changes in the intracellular levels of biosynthetic intermediates, ATP, or the redox status of the cell. These changes in the metabolic status of the bacteria result in the attenuation or augmentation of PIA production.
Requirements for
Vibrio cholerae
HapR Binding and Transcriptional Repression at the
hapR
Promoter Are Distinct from Those at the
aphA
Promoter
Authors: Lin Wei , Kovacikova Gabriela , Skorupski Karen
Published: April 2005

Virulence gene expression in certain strains of
Vibrio cholerae
is regulated in response to cell density by a quorum-sensing cascade that influences the levels of the LuxR homolog HapR through small regulatory RNAs that control the stability of its message. At high cell density, HapR represses the expression of the gene encoding the virulence gene activator AphA by binding to a site between −85 and −58 in the
aphA
promoter. We show here that a second binding site for HapR lies within the
hapR
promoter from which it functions to repress its own transcription. This site, as determined by gel mobility shift assay and DNaseI footprinting, is located between +8 and +36 from the transcriptional start and is not strongly conserved with the site at the
aphA
promoter. At low cell density, when the expression of a transcriptional
hapR-lacZ
fusion was low, no autorepression was observed. However, at high cell density, when the expression of the
hapR-lacZ
fusion was approximately 15-fold higher, the presence of HapR reduced its expression. Introduction of a single base pair change within the binding site at +18 prevented HapR binding in gel mobility shift assays. In the absence of HapR, this mutation did not significantly influence the expression of the
hapR
promoter, but in its presence, the expression of the promoter was increased at high cell density. These results indicate that HapR autorepresses from a single binding site in the
hapR
promoter and suggest a model for the temporal regulation of its expression as its intracellular levels increase.
Functional Characterization of a Novel ArgA from
Mycobacterium tuberculosis
Authors: Errey James C. , Blanchard John S.
Published: April 2005

The
Mycobacterium tuberculosis
gene
Rv2747
encodes a novel 19-kDa ArgA that catalyzes the initial step in
l
-arginine biosynthesis, namely the conversion of
l
-glutamate to α-
N
-acetyl-
l
-glutamate. Initial velocity studies reveal that Rv2747 proceeds through a sequential kinetic mechanism, with

K
m

values of 280 mM for
l
-glutamine and 150 μM for acetyl-coenzyme A and with a
k
cat
value of 200 min
−1
. Initial velocity studies with
l
-glutamate showed that even at concentrations of 600 mM, saturation was not observed. Therefore, only a
k
cat
/

K
m

value of 125 M
−1
min
−1
can be calculated. Inhibition studies reveal that the enzyme is strongly regulated by
l
-arginine, the end product of the pathway (50% inhibitory concentration, 26 μM). The enzyme was completely inhibited by 500 μM arginine, with a Hill coefficient of 0.60, indicating negatively cooperative binding of
l
-arginine.
Polyphosphate Kinase Protects
Salmonella enterica
from Weak Organic Acid Stress
Authors: Price-Carter Marian , Fazzio Thomas G. , Vallbona Ester Ibañez , Roth John R.
Published: April 2005

Mutants of
Salmonella enterica
lacking polyphosphate kinase (
ppk
) grow poorly in the presence of the weak organic acids acetate, propionate, and benzoate. This sensitivity is corrected by methionine and seems to result from destabilization of MetA (homoserine transsuccinylase), the first enzyme in methionine biosynthesis. The MetA protein is known to be sensitive to thermal inactivation, and
ppk
mutants are more sensitive to heat-induced methionine auxotrophy. Peroxide increases the sensitivity of
ppk
mutants to both heat and acid and may oxidatively damage (carbonylate) destabilized MetA. While acid appears to impair methionine biosynthesis, it leads to derepression of MetA and may inhibit growth by causing toxic accumulation of denatured protein. This is supported by the observation that the overexpression of MetA in
ppk
mutants causes acid sensitivity that is not corrected by methionine. We propose that polyphosphate acts as a chemical chaperone that helps refold MetA and/or may stimulate proteolysis of toxic denatured protein. The instability of MetA protein may provide a metabolic fuse that blocks growth under conditions that denature proteins; the sensitivity of this fuse is modulated by polyphosphate.
The Soluble NAD+-Reducing [NiFe]-Hydrogenase fromRalstonia eutrophaH16 Consists of Six Subunits and Can Be Specifically Activated by NADPH
Authors: Burgdorf Tanja , van der Linden Eddy , Bernhard Michael , Yin Qing Yuan , Back Jaap W. , Hartog Aloysius F. , Muijsers Anton O. , de Koster Chris G. , Albracht Simon P. J. , Friedrich Bärbel
Published: April 2005

The soluble [NiFe]-hydrogenase (SH) of the facultative lithoautotrophic proteobacteriumRalstonia eutrophaH16 has up to now been described as a heterotetrameric enzyme. The purified protein consists of two functionally distinct heterodimeric moieties. The HoxHY dimer represents the hydrogenase module, and the HoxFU dimer constitutes an NADH-dehydrogenase. In the bimodular form, the SH mediates reduction of NAD+at the expense of H2. We have purified a new high-molecular-weight form of the SH which contains an additional subunit. This extra subunit was identified as the product ofhoxI, a member of the SH gene cluster (hoxFUYHWI). Edman degradation, in combination with protein sequencing of the SH high-molecular-weight complex, established a subunit stoichiometry of HoxFUYHI2. Cross-linking experiments indicated that the two HoxI subunits are the closest neighbors. The stability of the hexameric SH depended on the pH and the ionic strength of the buffer. The tetrameric form of the SH can be instantaneously activated with small amounts of NADH but not with NADPH. The hexameric form, however, was also activated by adding small amounts of NADPH. This suggests that HoxI provides a binding domain for NADPH. A specific reaction site for NADPH adds to the list of similarities between the SH and mitochondrial NADH:ubiquinone oxidoreductase (Complex I).
Characterization of Enhancer Binding by the
Vibrio cholerae
Flagellar Regulatory Protein FlrC
Authors: Correa Nidia E. , Klose Karl E.
Published: April 2005

The human pathogen
Vibrio cholerae
is a highly motile organism by virtue of a polar flagellum, and motility has been inferred to be an important aspect of virulence. It has previously been demonstrated that the σ
54
-dependent activator FlrC is necessary for both flagellar synthesis and for enhanced intestinal colonization. In order to characterize FlrC binding, we analyzed two FlrC-dependent promoters, the highly transcribed
flaA
promoter and the weakly transcribed
flgK
promoter, utilizing transcriptional
lacZ
fusions, mobility shift assays, and DNase I footprinting. Promoter fusion studies showed that the smallest fragment with wild-type transcriptional activity for
flaAp
was from positions −54 to +137 with respect to the start site, and from −63 to +144 for
flgKp
. Gel mobility shift assays indicated that FlrC binds to a fragment containing the region from positions +24 to +95 in the
flaAp
, and DNase I footprinting identified a protected region between positions +24 and +85. Mobility shift and DNase I footprinting indicated weak binding of FlrC to a region downstream of the
flgKp
transcription start site. These results demonstrate a relatively novel σ
54
-dependent promoter architecture, with the activator FlrC binding downstream of the σ
54
-dependent transcription start sites. When the FlrC binding site(s) in the
flaA
promoter was moved a large distance (285 bp) upstream of the transcription start site of either
flaAp
or
flgKp
, high levels of FlrC-dependent transcription resulted, indicating that this binding region functions as an enhancer element. In contrast, the relatively weak FlrC binding site(s) in the
flgK
promoter failed to function as an enhancer element at either promoter, suggesting that FlrC binding strength contributes to enhancer activity. Our results suggest that the differences in FlrC binding to various flagellar promoters results in the differences in transcription levels that mirror the relative requirement for the flagellar components within the flagellum.
Expression of the
melC
Operon in Several
Streptomyces
Strains Is Positively Regulated by AdpA, an AraC Family Transcriptional Regulator Involved in Morphological Development in
Streptomyces coelicolor
Authors: Zhu Dongqing , He Xinyi , Zhou Xiufen , Deng Zixin
Published: April 2005

Dark brown haloes of melanin around colonies are an easily visualized phenotype displayed by many
Streptomyces
strains harboring plasmid pIJ702 carrying the
melC
operon of
Streptomyces antibioticus
IMRU3270. Spontaneous melanin-negative mutants of pIJ702 occur with a frequency of ca. 1%, and often mutation occurs in the
melC
operon, which removes the BglII site as part of an inverted repeat. Other melanin-negative mutations seem to occur spontaneously in
Streptomyces lividans
, resulting in white colonies from which intact, melanin-producing pIJ702 can be isolated by introduction into a new host.
S. lividans
ZX66 was found to be such a mutant and to have a secondary mutation influencing expression of the
melC
operon on the chromosome. A 3.3-kb DNA fragment was isolated from its progenitor strain, JT46, and a gene able to restore
melC
operon expression was found to encode a member of an AraC family of transcriptional regulators, which was equivalent to AdpA
c
in
Streptomyces coelicolor
and therefore was designated AdpA
l
. Lack of
melC
operon expression was correlated with a single A-to-C transversion, which altered a single key amino acid residue from Thr to Pro. The transcription of the
melC
operon was found to be greatly reduced in the
adpA
mutant background. The counterpart gene (
adpA
a
) in the
S. antibioticus
strain in which the
melC
operon carried on pIJ702 originated was also isolated and was found to have an identical regulatory role. Thus, we concluded that the
melC
operon is under general direct positive control by AdpA family proteins, perhaps at the transcriptional level and certainly at the translational level via
bldA
, in
Streptomyces
.
Exopolysaccharide Sugars Contribute to Biofilm Formation bySalmonella entericaSerovar Typhimurium on HEp-2 Cells and Chicken Intestinal Epithelium
Authors: Ledeboer Nathan A. , Jones Bradley D.
Published: April 2005

Recently, we demonstrated thatSalmonella entericaserovar Typhimurium can form biofilm on HEp-2 cells in a type 1 fimbria-dependent manner. Previous work onSalmonellaexopolysaccharide (EPS) in biofilm indicated that the EPS composition can vary based upon the substratum on which the bacterial biofilm forms. We have investigated the role of genes important in the production of colanic acid and cellulose, common components of EPS. A mutation in the colanic acid biosynthetic gene,wcaM, was introduced intoS. entericaserovar Typhimurium strain BJ2710 and was found to disrupt biofilm formation on HEp-2 cells and chicken intestinal tissue, although biofilm formation on a plastic surface was unaffected. Complementation of thewcaMmutant with the functional gene restored the biofilm phenotype observed in the parent strain. A mutation in the putative cellulose biosynthetic gene,yhjN, was found to disrupt biofilm formation on HEp-2 cells and chicken intestinal epithelium, as well as on a plastic surface. Our data indicate thatSalmonellaattachment to, and growth on, eukaryotic cells represent complex interactions that are facilitated by species of EPS.