bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of prostaglandin receptors in mitochondria on apoptosis of human lung carcinoma cell line A549
Authors: Fang K.M. , Shu W.H. , Chang H.C. , Wang J.J. , Mak O.T.
Published: October 2004

PGs (prostaglandins) are synthesized through the cyclo-oxygenase (COX-1 and -2) pathway in a variety of cells in response to various physiological stimuli. All cells require at least one pathway for apoptosis, and mitochondrial play a central role in regulation of apoptosis. In a previous study, incubation of A549 cells with NS-398 (a COX-2-specific inhibitor) induced apoptosis and inhibited cell proliferation, and the concentrations of different PGs between various cellular compartments were found to be changed. To determine whether PG receptors are involved in this regulation, Western-blot analyses were performed specific for PGE2 (EP receptors) and PGF2α (FP receptor) receptors, which were expressed in A549 cells. Western-blot analysis revealed that mitochondria that were isolated from A549 cells expressed EP receptors (EP2, EP3 and EP4), whereas FP receptors were undetectable. EP receptors (EP1, EP3 and EP4) and FP receptors were detected from A549 cell membrane. These results suggest that the change of PG production in A549-cells-induced cancer cell apoptosis might be related to the different expressions of EP and FP receptors in cell and mitochondrial membrane.
Programmed −1 ribosomal frameshifting in the SARS coronavirus
Authors: Ramos F. Dos , Carrasco M. , Doyle T. , Brierley I.
Published: October 2004

Programmed −1 ribosomal frameshifting is an alternate mechanism of translation used by coronavirus to synthesize replication proteins encoded by two overlapping open reading frames. For some coronaviruses, the mRNA cis-acting stimulatory structures involved in this process have been characterized, but their precise contribution to ribosomal frameshifting is not completely understood. Recently, a novel coronavirus was identified as the causative agent of the severe acute respiratory syndrome. This review describes the mRNA motifs involved in programmed −1 ribosomal frameshifting in this virus.
Transcriptional control of Nramp1: a paradigm for the repressive action of c-Myc
Authors: Lapham A.S. , Phillips E.S. , Barton C.H.
Published: October 2004

Slc11a1/Nramp1 (solute carrier family 11 member a1/murine natural resistance-associated macrophage protein 1 gene) encodes a divalent cation transporter that resides within lysosomes/late endosomes of macrophages. Nramp1 modulates the cellular distribution of divalent cations in response to cell activation by intracellular pathogens. Nramp1 expression is repressed and activated by the proto-oncogene c-Myc and Miz-1 (c-Myc-interacting zinc finger protein 1) respectively. Here we demonstrate, using a c-Myc mutant (V394D, Val394→Asp) that is incapable of binding Miz-1, that c-Myc repression of Nramp1 transcription is dependent on its interaction with Miz-1. An oligo pull-down assay demonstrates specific binding of recombinant Miz-1 to the Nramp1 Miz-1-binding site or initiator element(s), and Miz-1-dependent c-Myc recruitment.
Post-translational modification of RelA(p65) NF-κB
Authors: Campbell K.J. , Perkins N.D.
Published: October 2004

Stimulation with diverse agents activates the NF-κB (nuclear factor κB) transcription factor, affecting inflammatory and immune responses, proliferation, differentiation, apoptosis and tumourigenesis. Determining how NF-κB elicits such distinct responses is essential to understanding NF-κB function in diseased tissues. Recent developments illustrating that post-translational modification of NF-κB subunits influences their nuclear role are discussed. These observations suggest that diagnosis and new therapies based on reprogramming NF-κB activity could be more efficient than total NF-κB inhibition.
Haem oxygenase-1 in inflammation
Authors: Rushworth S.A. , O'Connell M.A.
Published: October 2004

HO-1 (haem oxygenase-1) is a stress-inducible enzyme that plays a protective role in inflammation. Pro-inflammatory mediators, including lipopolysaccharide and cytokines, induce HO-1 expression. The 5′-flanking region of the HO-1 gene contains binding sites for the transcription factors that regulate inflammation, including nuclear factor-κB and activator protein 1. However, these do not appear to mediate lipopolysaccharide-induced HO-1 gene expression. In response to haem and antioxidants, murine HO-1 is regulated by the transcription factor Nrf2 (NF-E2-related factor 2). This transcription factor may also be important in the regulation of HO-1 by pro-inflammatory stimuli.
In vitro regulation of reporter gene transcription by the androgen receptor AF1 domain
Authors: Choudhry M.A. , McEwan I.J.
Published: October 2004

The androgen receptor (AR) is a ligand-activated transcription factor that regulates gene expression in response to the steroids testosterone and dihydrotestosterone. AR-dependent gene expression is likely to play an important role in a number of receptor-associated disorders, such as prostate cancer, spinal bulbar muscular atrophy, male type baldness and hirsutism. The AR contains two transactivation domains, termed AF1 (activation function 1) located in the N-terminus and AF2 (activation function 2) in the C-terminal ligand-binding domain. AF2 exhibits weak transcriptional activity, whereas AF1 is a strong regulator of transcription. Transcriptional regulation by AF1 is thought to be modulated by a number of proteins that interact with this region, and by post-translational modifications. Our focus is on the N-terminal-interacting proteins and their regulation of transcription via interaction with the receptor. To better understand the mechanism of AR-AF1 action, we have reconstituted AR activity in HeLa nuclear extracts using a unique dual reporter gene assay. Multiple LexA-binding sites in the promoter allow transcription to be driven by a recombinant AR-AF1–Lex fusion protein. The findings from initial experiments suggest an increase in transcription initiation and elongation rates by AR-AF1–Lex. The role of protein–protein interactions involving co-activators and basal transcription factors and AR-AF1 activity are discussed.
A PLCδ1-binding protein, p122RhoGAP, is localized in focal adhesions
Authors: Kawai K. , Yamaga M. , Iwamae Y. , Kiyota M. , Kamata H. , Hirata H. , Homma Y. , Yagisawa H.
Published: October 2004

We have investigated the cellular distribution of p122RhoGAP, a GTPase-activating protein of Rho small GTPase and an activator of phospholipase C-δ1. Immunofluorescence studies demonstrated that endogenous p122 is localized at the tips of actin stress fibres and co-localizes with vinculin in normal rat kidney cells. In immunoprecipitation studies, p122 co-precipitated with vinculin, indicating that p122 is localized at the sites of focal adhesion. We have also shown that the N-terminal half of p122 is responsible for this localization. It is conceivable, therefore, that p122 is involved in the reorganization of the actin cytoskeleton and focal adhesions that regulate cell–substratum adhesion and cell migration.
Filling the GAPs in cell dynamics control: BPGAP1 promotes cortactin translocation to the cell periphery for enhanced cell migration
Authors: Lua B.L. , Low B.C.
Published: October 2004

Cells undergo dynamic changes in morphology or motility during cellular division and proliferation, differentiation, neuronal pathfinding, wound healing, apoptosis, host defense and organ development. These processes are controlled by signalling events relayed through cascades of protein interactions leading to the establishment and maintenance of cytoskeletal networks of microtubules and actin. Various regulators, including the Rho small GTPases (guanine nucleotide triphosphatases), serve as master switches to fine-tune the amplitude, duration as well as the integration of such circuitry responses. Rho GTPases are activated by guanine nucleotide-exchange factors and inactivated by GAPs (GTPase-activating proteins). Although normally down-regulating signalling pathways by catalysing their GTPase activity, many GAPs exist with various protein modules, the functions of which still largely remain unknown. BPGAP1 is a novel RhoGAP that co-ordinately regulates pseudopodia and cell migration through the interplay of its BNIP-2 and Cdc42GAP homology domains serving as a homophilic/heterophilic interaction device, an enzymic RhoGAP domain that inactivates RhoA and a proline-rich region that binds the Src homology-3 domain of cortactin. Both proteins co-localize to cell periphery and enhance cell migration. As a molecular scaffold in cortical actin assembly and organization, cortactin and its interaction with small GTPases, GAPs and tyrosine kinases seems set to provide further insights to the multiplicity and complexity of cell dynamics control. Elucidating how these processes might be individually or co-ordinately regulated through cortactin remains an exciting future challenge.
Control of SCAR activity in Dictyostelium discoideum
Authors: Blagg S.L. , Insall R.H.
Published: October 2004

The WASP (Wiskott–Aldrich syndrome protein)/SCAR (suppressor of cAMP receptor) family of adaptor proteins regulate actin polymerization by coupling Rho-family GTPases to the activation of the Arp2/3 complex. SCAR exists within a complex of proteins, including Nap1 (Nck-associated protein 1), PIR121 (p53-inducible mRNA 121), Abi2 (Abl-interactor 2) and HSPC300. This complex was first reported to inhibit SCAR activity, but there is now some controversy over whether the complex is inhibitory or activatory. This complex is currently being studied in a wide range of different systems, and model organisms such as the amoeba Dictyostelium discoideum have been used to remove genetically SCAR complex members to ascertain their specific roles.
Lymphocyte activation receptors: new structural paradigms in group V of C-type animal lectins
Authors: Pavlíček J. , Kavan D. , Pompach P. , Novák P. , Lukšan O. , Bezouška K.
Published: October 2004

The structure–function relationship in group V of C-type animal lectins remains incompletely understood despite the new structures of NK (natural killer) cell receptors that have been solved recently. Recombinant, soluble forms of rat and human NKR-P1 and CD69 that we obtained after in vitro refolding were analysed by Fourier transform–ion cyclotron resonance MS and heteronuclear NMR (1H-15N correlation). In NKR-P1, calcium may not be removed by chelating agents because of the very high affinity of binding. In CD69, incorporation of calcium causes a structural shift in several amino acids important for the interaction with carbohydrates. Structural studies have also allowed us to understand an interesting preference of these receptors for either linear (NKR-P1) or branched (CD69) carbohydrate sequences.
Absence of room temperature ferromagnetism in bulk Mn-doped ZnO
Authors: Kolesnik S. , Dabrowski B.
Published: October 2004

Structural and magnetic properties have been studied for polycrystalline Zn1−xMnxO (x=0.02,0.03,0.05). Low-temperature (∼500 °C) synthesis leaves unreacted starting ZnO and manganese oxides. Contrary to a recent report, no bulk ferromagnetism was observed for single-phase materials synthesized in air at temperatures above 900 °C. Single-phase samples show paramagnetic Curie–Weiss behavior.
Epitaxial growth and physical properties of a room temperature ferromagnetic semiconductor: Anatase phase Ti1−xCoxO2
Authors: Yamada Y. , Toyosaki H. , Tsukazaki A. , Fukumura T. , Tamura K. , Segawa Y. , Nakajima K. , Aoyama T. , Chikyow T. , Hasegawa T. , Koinuma H. , Kawasaki M.
Published: October 2004

There has been considerable debate regarding the origin of ferromagnetism in the ferromagnetic semiconductor anatase phase TiO2 doped with Co, ranging from carrier induced ferromagnetism in a framework of diluted magnetic semiconductor to merely the precipitation of ferromagnetic and metallic Co precipitates in the TiO2 matrix. This paper reports on a systematic investigation of the structures, together with the electronic and magneto-optical properties, of thin films of anatase phase TiO2, doped with Co. Films of anatase Ti1−xCoxO2 (x=0–0.10) were grown epitaxially on LaSrAlO4 (001) substrates, using pulsed laser deposition method. In order to control n-type carrier concentration, the oxygen pressure during the growth was systematically varied, yielding films with insulative, semiconductive (carrier concentration n∼1×1017 cm−3), and metallic (n∼2×1019 cm−3) properties. Reflection high energy electron diffraction patterns, atomic force microscopy, and transmission electron microscopy show no evidence of Co segregation in these films. Magneto-optical response was examined by measuring magneto-optical circular dichroism (MCD) spectra at room temperature. A large MCD peak appears at a photon energy close to the band gap of TiO2. The magnetic field dependence of MCD signal indicates ferromagnetic behavior, which is similar to that of the magnetization. The MCD intensity increases systematically with the increase of n or x. Since MCD response originates from charge carriers at the band edge, one can conclude that interaction between the charge carriers and Co impurities is essential to realize ferromagnetism.
Growth of pinhole-free epitaxial Yb and Er silicide thin films on atomically clean (111)Si
Authors: Tsai W. C. , Chi K. S. , Chen L. J.
Published: October 2004

The growth of pinhole-free epitaxial Yb and Er silicide thin films on (111)Si has been achieved by capping appropriate amorphous Si(a-Si) layer at room temperature followed by annealing at 700°C in an ultrahigh vacuum chamber. The thickness of the a-Si capping layer was selected to be such that the consumption of Si atoms from the substrate is minimized. The design and reimplementation of the scheme involving appropriate thickness of a-Si capping layer was based on an understanding of the formation mechanism of the pinholes with epitaxial rare-earth islands as diffusion barriers for Si diffusion at the silicide∕Si interfaces.
Formation, structure, and phonon confinement effect of nanocrystalline Si1−xGex in SiO2-Si-Ge cosputtered films
Authors: Yang Y. M. , Wu X. L. , Siu G. G. , Huang G. S. , Shen J. C. , Hu D. S.
Published: October 2004

Using magnetron cosputtering of SiO2, Ge, and Si targets, Si-based SiO2:Ge:Si films were fabricated for exploring the influence of Si target proportion (PSi) and annealing temperature (Ta) on formation, local structure, and phonon properties of nanocrystalline Si1−xGex (nc-Si1−xGex). At low PSi and Ta higher than 800°C, no nc-Si1−xGex but a kind of composite nanocrystal consisting of a Ge core, GeSi shell, and amorphous Si outer shell is formed in the SiO2 matrix. At moderate PSi, nc-Si1−xGex begins to be formed at Ta=800°C and coexists with nc-Ge at Ta=1100°C. At high PSi, it was disclosed that both optical phonon frequency and lattice spacing of nc-Si1−xGex increase with raising Ta. The possible origin of this phenomenon is discussed by considering three factors, the phonon confinement, strain effect, and composition variation of nc-Si1−xGex. This work will be helpful in understanding the growth process of ternary GeSiO films and beneficial to further investigations on optical properties of nc-Ge1−xSix in the ternary matrix.
Aluminum, oxide, and silicon phonons by inelastic electron tunneling spectroscopy on metal-oxide-semiconductor tunnel junctions: Accurate determination and effect of electrical stress
Authors: Petit C. , Salace G. , Vuillaume D.
Published: October 2004

We do inelastic electrical tunneling spectroscopy (IETS) to provide information concerning the vibrational and excitational modes present in silicon dioxide and phonon modes of the electrodes, and of silicon dioxide in metal-oxide-silicon tunnel junction. We analyze the phonon spectra coming from different parts of the metal-oxide-semiconductor (MOS) junction: the aluminum gate, the SiO2 ultrathin film, and the silicon substrate. We compare the phonon modes for the (100) and (111) silicon orientations. We show that IETS can reveal the modifications of Si-SiO2 interface induced by electrical stresses. After a constant voltage stress, the silicon longitudinal phonon modes are significantly shifted in energy, while the transversal phonon modes stay unaffected. Interface healing after annealing is also observed by IETS. These features make IETS a useful tool for MOS reliability studies.
Structural study of FeSi2 under pressure
Authors: Takarabe K. , Ikai T. , Mori Y. , Udono H. , Kikuma I.
Published: October 2004

The structural properties of β- and α-FeSi2 were examined by high-pressure x-ray diffraction at room temperature. In β-FeSi2, the lattice compression in the longest a axis is larger than in the b and c axes. The expected pressure-induced quenching by the Jahn-Teller effect on γ-FeSi2 was not achieved in the pressure range investigated. The bulk modulus B0 of β-FeSi2 and its derivative B0′ were determined to be 243.5GPa and 3.2GPa, respectively. A high-pressure phase, tentatively assigned to be tetragonal, appeared at about 20GPa. For α-FeSi2, a higher temperature phase of β-FeSi2, the bulk modulus B0 and its derivative B0′ were determined to be 183GPa and 6.2GPa, respectively. The experimental values of B0 are compared with the values estimated by various first-principles calculations, where the characteristic tendency is shown.
Analog performance of the nanoscale double-gate metal-oxide-semiconductor field-effect-transistor near the ultimate scaling limits
Authors: Jiménez D. , Iñíguez B. , Suñé J. , Sáenz J. J.
Published: October 2004

We explore the prospective behavior of the nanoscale double-gate metal-oxide-semiconductor field-effect-transistor (DG-MOSFET) when used as the basis for building analog circuits. Results for transconductance, output conductance, and related parameters, such as transconductance efficiency, and Early voltage, are presented in the ballistic and diffusive regimes using the non-equilibrium Green’s function method (NEGF) and the scattering theory of the nanoscale MOSFET. Very high transconductance (∼20mS∕μm), approaching the ballistic limit, can be achieved provided that technological improvements further increase the electron mobility in the silicon film. For the ballistic limit a cutoff frequency of about 1–4THz is possible. The transconductance efficiency is not to much affected by length scaling and temperature. The output conductance and Early voltage are severely affected by length scaling as channel length-modulation (CLM) and drain-induced barrier lowering (DIBL) effects become more important, but they are acceptable for channel lengths above 15nm. Finally, it is shown that the International Technology Roadmap requirements for small-signal parameters, in mixed-signals systems, near the ultimate scaling limit, could be accomplished using the DG-MOSFET.
Deep levels created by low energy electron irradiation in 4H-SiC
Authors: Storasta L. , Bergman J. P. , Janzén E. , Henry A. , Lu J.
Published: October 2004

With low energy electron irradiation in the 80–250keV range, we were able to create only those intrinsic defects related to the initial displacements of carbon atoms in the silicon carbide lattice. Radiation induced majority and minority carrier traps were analyzed using capacitance transient techniques. Four electron traps (EH1, Z1∕Z2, EH3, and EH7) and one hole trap (HS2) were detected in the measured temperature range. Their concentrations show linear increase with the irradiation dose, indicating that no divacancies or di-interstitials are generated. None of the observed defects was found to be an intrinsic defect–impurity complex. The energy dependence of the defect introduction rates and annealing behavior are presented and possible microscopic models for the defects are discussed. No further defects were detected for electron energies above the previously assigned threshold for the displacement of the silicon atom at 250keV.
Instrumentation for analysis and utilization of extreme-ultraviolet and soft x-ray high-order harmonics
Authors: Poletto L. , Bonora S. , Pascolini M. , Villoresi P.
Published: October 2004

The design and the performances of an extreme ultraviolet (EUV)spectrometer/monochromator for generation and diagnostics of high-order harmonics of an ultrashort (<30 fs) pulsed laser focused onto a gas jet are presented. The harmonic generation is optimized using an adaptive mirror before the laser focusing stage. A toroidal mirror is used to focus the XUV radiation in an intermediate stage for pump/probe experiments. A grazing-incidence flat-field spectrometer for the 5–75 nm spectral region has been designed: it adopts a stigmatic toroidal mirror and a varied line-space flat grating mounted in converging light. The almost flat stigmatic spectrum is acquired by a 40-mm-diameter microchannel plate intensifier; the whole detector can be moved to scan various portions of the spectrum. Different detectors allow one to acquire both integrated and single shot spectra at 1 kHz repetition rate. The absolute calibration of the spectrometer is provided. The same optical scheme can be applied to the design of a constant deviation angle EUV monochromator by substituting the detector block with an exit slit.
Studies on high resolution x-ray diffraction, optical and transport properties of InAsxSb1−x∕GaAs (x⩽0.06) heterostructure grown using liquid phase epitaxy
Authors: Dixit V. K. , Bansal Bhavtosh , Venkataraman V. , Bhat H. L. , Chandrasekharan K. S. , Arora B. M.
Published: October 2004

The growth of InAsxSb1−x∕GaAs (x⩽0.06) heterostructures has been achieved using liquid phase epitaxy. High resolution x-ray diffraction studies reveal that the films are single crystalline and structurally coherent with the substrate. It is also inferred from these measurements that the in-plane and out-of-plane strain arising out of mismatched epitaxy is almost completely relaxed, leading to a high dislocation density. The room temperature energy gap is measured to be 0.13eV for InAs0.06Sb0.94∕GaAs. Temperature dependence of the energy gap is studied between 93 and 433K through the absorption spectra. Temperature dependent Hall and mobility measurements carried out between 10 and 370K on these samples are discussed.
Exploitation of the thermotunnel effect for energy scavenging
Authors: Despesse Ghislain , Jager Thomas
Published: October 2004

Over the past few years, MEMS and smart material technologies improvements have allowed autonomous sensor devices to become more and more widespread. As batteries are not always appropriate to power these systems, energy scavenging solutions from ambient power are currently being developed. In particular, many researches have been carried out to improve thermal to electrical energy conversion in ambient temperature gradients. Until now, thermoelectric materials are still the most employed for this application. However, the recent developments in nanoscale device structures open different perspectives. In these nanoscale systems, the heat transport is achieved between two electrodes thanks to electron tunneling. The thermotunnel effect is currently widely studied in the cooling configuration where it has already been shown that it is more efficient than the Peltier effect. We have decided to evaluate this effect in the reciprocal way of work with the objective of being able to power a small sensor node. Considering a device with a simplicial geometrical structure, a modeling has been developed in order to evaluate the feasibility of conversion of a thermal flow into an electrical power based on thermotunneling effect. Comparisons with thermoelectric performances at ambient temperature have been performed.
An experimental study on the ZnO/sapphire layered surface acoustic wave device
Authors: Wu Tsung-Tsong , Wang Wei-Shan
Published: October 2004

In this study, ZnO thin films with different thicknesses were deposited on C-plane sapphire substrates by radio-frequency magnetron sputtering. Properties of interdigital transducer/ZnO/sapphire layered surface acoustic wave device including surface wave velocity, electromechanical coupling coefficient, and propagatiion loss were measured and discussed. Combining the effective permittivity approach and the coupling-of-modes (COM) model, the dispersion characteristics and frequency responses of the ZnO/sapphire layered structure were simulated. By substituting the measured parameters into the COM model, the simulated frequency response has shown good agreement with the experimental results.
In situ synthesis of carbon nanotubes decorated with palladium nanoparticles using arc-discharge in solution method
Authors: Bera Debasis , Kuiry Suresh C. , McCutchen Matthew , Seal Sudipta , Heinrich Helge , Slane Grady C.
Published: October 2004

A unique, simple, inexpensive, and one-step synthesis route to produce carbon nanotubes (CNTs) decorated with palladium nanoparticles using a simplified dc arc-discharge in solution is reported. Zero-loss energy filtered transmission electron microscopy and scanning transmission electron microscopy confirm the presence of 3nm palladium nanoparticles. Such palladium nanoparticles form during the reduction of palladium tetra-chloro-square-planar complex. The deconvoluted x-ray photoelectron spectroscopy envelope shows the presence of palladium on the decorated CNTs. The energy dispersive spectroscopy suggests no functionalization of atomic chlorine to the sidewall of the CNTs. The presence of dislodged graphene sheets with wavy morphology supports the formation of CNTs through the “scroll mechanism.”
Modeling and regrowth mechanisms of flash lamp processing of SiC-on-silicon heterostructures
Authors: Smith M. , McMahon R. A. , Voelskow M. , Skorupa W.
Published: October 2004

This paper describes the development of a thermal model for flash lamp processing of 3C-SiC on silicon substrates in the millisecond regime, the FLASiC process. The model is a numerical solution of the enthalpy equation, using a modified implicit Crank-Nicholson scheme to combine accurate prediction of melt depths with reasonable computation times. The model has been calibrated against experiments and then used to compute the temperature distribution in the wafer during annealing. The results show the time and extent of melting as a function of layer thickness, wafer preheat temperature, and pulse intensity and duration. The kinetics of melting and regrowth have also been considered.
Spectral self-interference fluorescence microscopy
Authors: Moiseev L. , Cantor C. R. , Aksun M. I. , Dogan M. , Goldberg B. B. , Swan A. K. , Ünlü M. S.
Published: October 2004

Spontaneous emission of fluorophores located close to a reflecting surface is modified by the interference between direct and reflected waves. The spectral patterns of fluorescent emission near reflecting surfaces can be precisely described with a classical model that considers the relative intensity and polarization state of direct and reflected waves depending on dipole orientation. An algorithm based on the emission model and polynomial fitting built into a software application can be used for fast and efficient analysis of self-interference spectra, yielding information about the location of the emitters with subnanometer precision. Spectral information was used to study thin films of fluorescent substances on surfaces.
A physically based model for the spatial and temporal evolution of self-interstitial agglomerates in ion-implanted silicon
Authors: Ortiz Christophe J. , Pichler Peter , Fühner Tim , Cristiano Filadelfo , Colombeau Benjamin , Cowern Nicholas E. B. , Claverie Alain
Published: October 2004

A physically motivated model that accounts for the spatial and temporal evolution of self-interstitial agglomerates in ion-implanted Si is presented. For the calibration of the model, a genetic algorithm is used to find the optimum set of physical parameters from experimental data. Mean-size evolution of {113} defects obtained by transmission electron microscopy and self-interstitial oversaturation results measured in the vicinity of extended defects are combined in the same fitting procedure. The calibration of parameters shows that binding energies of small self-interstitial clusters exhibit strong maxima, as reported in other investigations. Results of the calibrated model are compared to experimental data obtained in complementary investigations. It is demonstrated that the model is able to predict a wide variety of physical phenomena, from the oversaturation of self-interstitials via the mean-size evolution of {113} defects to the depth distribution of the density of the latter.
Growth of crack-free GaN films on Si(111) substrate by using Al-rich AlN buffer layer
Authors: Lu Yuan , Cong Guangwei , Liu Xianglin , Lu Da-Cheng , Zhu Qinsheng , Wang Xiaohui , Wu Jiejun , Wang Zhanguo
Published: October 2004

GaN epilayers were grown on Si(111) substrate by metalorganic chemical vapor deposition. By using the Al-rich AlN buffer which contains Al beyond stoichiometry, crack-free GaN epilayers with 1 μm thickness were obtained. Through x-ray diffraction (XRD) and secondary ion mass spectroscopy analyses, it was found that a lot of Al atoms have diffused into the under part of the GaN epilayer from the Al-rich AlN buffer, which results in the formation of an AlxGa1−xN layer at least with 300 nm thickness in the 1 μm thick GaN epilayer. The Al fraction x was estimated by XRD to be about 2.5%. X-ray photoelectron spectroscopy depth analysis was also applied to investigate the stoichiometry in the Al-rich buffer before GaN growth. It is suggested that the underlayer AlxGa1−xN originated from Al diffusion probably provides a compressive stress to the upper part of the GaN epilayer, which counterbalances a part of tensile stress in the GaN epilayer during cooling down and consequently reduces the cracks of the film effectively. The method using the Al diffusion effect to form a thick AlGaN layer is really feasible to achieve the crack-free GaN films and obtain a high crystal quality simultaneously.
Atomic force microscopy and x-ray photoelectron spectroscopy investigations of the morphology and chemistry of a PdCl2∕SnCl2 electroless plating catalysis system adsorbed onto shape memory alloy particles
Authors: Silvain J. F. , Fouassier O. , Lescaux S.
Published: October 2004

A study of the different stages of the electroless deposition of copper on micronic NiTi shape memory alloy particles activated by one-step and two-step methods has been conducted from both a chemical and a morphological point of view. The combination of x-ray photoelectron spectroscopy (XPS) measurements and atomic force microscopy (AFM) imaging has allowed detection of the distribution of the formed compounds and depth quantification and estimation of the surface topographic parameters. For the two-step method, at the sensitization of the early stages, it is observed by AFM that Sn is absorbed in form of clusters that tend to completely cover the surface and form a continuous film. XPS analysis have shown that Sn and Pd are first absorbed in form of oxide (SnO2 and PdO) and hydroxide [Sn(OH)4]. After the entire sensitization step, the NiTi substrate is covered with Sn-based compounds. After the sensitization and the activation steps the powder roughness increases. Behavior of the Sn and Pd growth for the one-step method does not follow the behavior found for the two-step method. Indeed, XPS analysis shows a three-dimensional (3D) growth of Pd clusters on top of a mixture of metallic tin, oxide (SnO) and hydroxide [Sn(OH)2]. These Pd clusters are covered with a thin layer of Pd-oxide contamination induced by the electroless process. The mean roughness for the one-step and two-step processes are equivalent. After copper deposition, the decrease of mean roughness is attributed to a filling of surface valleys, observed after the Sn-Pd coating step.
The channel effect: Coupling of the detonation and the precursor shock wave by precompression of the explosive
Authors: Tanguay V. , Higgins A. J.
Published: October 2004

The high-explosive channel effect is investigated to study the coupling dynamics of the precursor shock wave with the detonation. This is achieved experimentally by using porous pentaerythritol tetranitrate (PETN) powder in square channels. It is found that the precursor shock wave causes the detonation to accelerate to approximately 1.5 times the detonation velocity of the porous PETN. This phenomenon is found to be almost independent of the fill gas and the initial pressure in the channel. It is found that the precursor shock wave is insufficiently strong to initiate the PETN layer before the arrival of the main detonation front, and that the mechanism responsible for the observed acceleration is precompression of the explosive layer by the precursor shock wave. This mechanism is modeled analytically by generalizing an existing model for the precursor shock wave dynamics with boundary layers. The results agree well qualitatively and relatively well quantitatively considering the assumptions that are made.
Deposition and structure of chemically vapor deposited nanoscale Ti-Si islands on Si
Authors: Kamins T. I. , Ohlberg D. A. A. , Williams R. Stanley
Published: October 2004

Nanoscale islands of Ti-Si were formed by chemical vapor deposition onto a Si substrate. The islands were deposited by the H2 reduction of TiCl4 either without or with a Si-containing gas added during deposition. The Ti deposition rate increases strongly with increasing deposition temperature below 690 °C, but it increases only slowly at higher temperatures. For a fixed deposition time at the lower temperatures, the number of islands after deposition changes only slowly as the amount of Ti deposited (and the deposition temperature) varies, but the number of Ti atoms in each island changes rapidly. Adding Si from the gas phase during deposition does not change the amount of Ti deposited, but it increases the height of the deposited islands above the substrate surface plane. The amount of Si-containing gas needed to form stoichiometric TiSi2 increases with decreasing deposition temperature. The island position can be controlled by depositing on a structured Si surface.
Effects of radio-frequency driving power, gas pressure, and nitrogen seeding on the transition dynamics in argon inductively coupled plasmas
Authors: Razzak M. Abdur , Takamura Shuichi , Uesugi Yoshihiko
Published: October 2004

The influences of rf driving power, neutral gas pressure, and nitrogen seeding on the electrostatic-to-electromagnetic (E-H) mode transition dynamics in radio-frequency argon inductively coupled plasmas (ICPs) in a pressure range of 50–100kPa are investigated, both experimentally and theoretically. The E-H mode transition dynamics and its characteristic transition time scale are investigated by observing the high-speed imaging (13500fps) as well as the temporal change of plasma loading impedance. The experimental results reveal that the E-H mode transition time is not fixed at any operating conditions rather it depends on some important parameters such as the rf driving power, neutral gas pressure, gas type. It is found that the E-H mode transition time depends on the unique parameter Eθ∕p; the so-called effective induced electric field, rather than the independent parameter: the rf power or neutral gas pressure. It is also found that longer E-H mode transition time is required to ignite the high-pressure Ar-N2 plasmas with a 2.5%–10% N2 seeding than that of pure Ar plasmas with the same operating conditions. The experimental results are compared with that of the recently developed theoretical models, and a good agreement is found between them.
Ultrafast nonlinear tuning of the reflection properties of AlGaAs photonic crystal waveguides by two-photon absorption
Authors: Bristow A. D. , Kundys D. O. , García-Déniz A. Z. , Wells J.-P. R. , Fox A. M. , Skolnick M. S. , Whittaker D. M. , Tahraoui A. , Krauss T. F. , Roberts J. S.
Published: October 2004

We have studied the power-dependent wavelength shift of photonic coupling resonances of a two-dimensional photonic crystal waveguide by reflection geometry pump-probe measurements. The quadratic response is indicative of two-photon induced carrier creation, which alters the refractive index of the semiconductor core of the photonic lattice. A free-carrier model is used to simulate the phenomenon, giving values of the change in refractive index per unit carrier density that satisfactorily compare to values calculated for bulk AlGaAs under similar conditions. Time-resolved spectra are also presented, showing relaxation times of <10ps which are consistent with surface recombination times in the patterned waveguide.
Growth of Ti3SiC2 thin films by elemental target magnetron sputtering
Authors: Emmerlich Jens , Högberg Hans , Sasvári Szilvia , Persson Per O. Å. , Hultman Lars , Palmquist Jens-Petter , Jansson Ulf , Molina-Aldareguia Jon M. , Czigány Zsolt
Published: October 2004

Epitaxial Ti3SiC2(0001) thin films have been deposited by dc magnetron sputtering from three elemental targets of Ti, C, and Si onto MgO(111) and Al2O3(0001) substrates at temperatures of 800–900°C. This process allows composition control to synthesize Mn+1AXn (MAX) phases (M: early transition metal; A: A-group element; X: C and∕or N; n=1–3) including Ti4SiC3. Depositions on MgO(100) substrates yielding the Ti–Si–C MAX phases with (101¯5), as the preferred orientation. Samples grown at different substrate temperatures, studied by means of transmission electron microscopy and x-ray diffraction investigations, revealed the constraints of Ti3SiC2 nucleation due to kinetic limitations at substrate temperatures below 700°C. Instead, there is a competitive TiCx growth with Si segregation to form twin boundaries or Si substitutional incorporation in TiCx. Physical properties of the as-deposited single-crystal Ti3SiC2 films were determined. A low resistivity of 25μΩcm was measured. The Young’s modulus, ascertained by nanoindentation, yielded a value of 343–370GPa. For the mechanical deformation response of the material, probing with cube corner and Berkovich indenters showed an initial high hardness of almost 30GPa. With increased maximum indentation loads, the hardness was observed to decrease toward bulk values as the characteristic kink formation sets in with dislocation ordering and delamination at basal planes.
Polarized Raman scattering of highly [111]-oriented Pb(Zr,Ti)O3 thin films in the rhombohedral-phase field
Authors: Yi Hyunjung , Kim Min G. , Park Jung H. , Jang Hyun M.
Published: October 2004

Highly [111]-oriented rhombohedral lead zirconate titanate [Pb(Zr1−xTix)O3;PZT] thin films were prepared on Pt(111)∕Ti∕SiO2∕Si substrates by suitably combining pulsed laser deposition with sol-gel coating. Two distinctive types of the backscattering geometry were employed for the polarized Raman scattering study: (i) normal backscattering in which the propagation direction of relevant phonons is parallel to the principal [111] polar axis of the rhombohedral 3m(C3v) point group for observing E(TO) phonons, and (ii) side-view backscattering in which the phonon-propagation direction is normal to the [111] direction for isolating A1(TO) phonons. Room-temperature Raman spectra of the [111]-oriented PZT60∕40 film (with Zr∕Ti=60∕40) having the high-temperature rhombohedral form were examined and compared with those of the [111]-oriented low-temperature rhombohedral PZT90∕10 film which is characterized by the tilting of oxygen octahedra about the principal [111] direction. Similarities and differences in the observed Raman spectra between these two distinctive films were examined in the light of the Raman selection rules for R3m and R3c space groups.
Error mechanisms and rates in tunable-barrier single-electron turnstiles and charge-coupled devices
Authors: Zimmerman Neil M. , Hourdakis Emmanouel , Ono Yuki , Fujiwara Akira , Takahashi Yasuo
Published: October 2004

Si -based single-electron tunneling (SET) devices have of late become an important alternative to the metal-based ones, both for ultralarge scale integration (ULSI) electronics and for electrical metrology. We have very recently been designing, fabricating, and measuring SET turnstiles, pumps, and charge-coupled devices using tunable barriers in silicon. Having shown the potential of these devices, we wish to understand the error mechanisms which may manifest themselves, and to predict the level of these errors, in order to decide how feasible these devices will be. In this paper, we devote a substantial amount of analysis to the consideration of the “dynamical” error mechanism. This particular error considers how electrons split up as the barrier is raised, or alternatively how the Coulomb blockade is formed. We then consider a wide variety of other errors, including thermal, frequency, leakage, and heating errors. We show the dependence of the error rate on each of those mechanisms, and predict maxima or minima for the corresponding parameters. In the conclusion, we discuss the various advantages Si-based turnstiles or pumps would offer with respect to the metal-based ones.
Raman scattering and photoluminescence studies of Er-implanted and Er+O coimplanted GaN
Authors: Song S. F. , Chen W. D. , Zhang Chunguang , Bian Liufang , Hsu C. C. , Ma Baoshan , Li G. H. , Zhu Jianjun
Published: October 2004

Raman measurements and photoluminescence (PL) were performed on the metal-organic chemical-vapor deposition epitaxially grown GaN before and after the implantation with Er and Er+O. Several Raman defect modes have emerged from the implantation-damaged samples. The structures around 300 and 595cm−1 modes are attributed to the disorder-activated Raman scattering, whereas the 670cm−1 peak is assigned to nitrogen-vacancy-related defect scattering. One additional peak at 360cm−1 arises after Er+O coimplantation. This Raman peak is attributed to the O-implantation-induced defect complex. The appearance of the 360cm−1 mode results in the decrease of the Er3+ -related infrared PL intensity for the GaN:Er+O samples.
Structural and electrical properties of trimethylboron-doped silicon nanowires
Authors: Lew Kok-Keong , Pan Ling , Bogart Timothy E. , Dilts Sarah M. , Dickey Elizabeth C. , Redwing Joan M. , Wang Yanfeng , Cabassi Marco , Mayer Theresa S. , Novak Steven W.
Published: October 2004

Trimethylboron (TMB) was investigated as a p-type dopant source for the vapor–liquid–solid growth of boron-doped silicon nanowires (SiNWs). The boron concentration in the nanowires was measured using secondary ion mass spectrometry and results were compared for boron-doping using TMB and diborane (B2H6) sources. Boron concentrations ranging from 1×1018 to 4×1019cm−3 were obtained by varying the inlet dopant∕SiH4 gas ratio. TEM characterization revealed that the B2H6-doped SiNWs consisted of a crystalline core with a thick amorphous Si coating, while the TMB-doped SiNWs were predominantly single crystal even at high boron concentrations. The difference in structural properties was attributed to the higher thermal stability and reduced reactivity of TMB compared to B2H6. Four-point resistivity and gate-dependent conductance measurements were used to confirm p-type conductivity in the TMB-doped nanowires and to investigate the effect of dopant concentration on nanowire resistivity.
Optical response of mixed Ag-Cu nanocrystals produced by pulsed laser deposition
Authors: Gonzalo J. , Babonneau D. , Afonso C. N. , Barnes J.-P.
Published: October 2004

Ag - Cu mixed nanocrystals (NCs) have been embedded in an amorphous Al2O3 matrix by alternate ablation of pure metal and Al2O3 targets. The composition of the NCs has been varied from pure Cu to pure Ag. Structural analysis by high-resolution electron microscopy (HREM) has shown that in the whole range of compositions, the NCs have average in-plane diameters in the range 3–4nm and are wider in the in-plane direction than their height, the aspect ratio being 1.4–1.6. The optical properties of the resulting nanocomposite films have instead a strong dependence on the NCs composition. A single surface plasmon resonance (SPR) has been observed whose wavelength blueshifts from that of Cu to that of Ag as the Ag content increases, thus allowing the SPR to be tuned over a broad interval (424–572nm). Although the nucleation and growth mechanisms have been found to depend on the metal that was deposited first, the optical response has no significant sensitivity to the deposition sequence and thus, it is concluded that more controllable results are achieved by depositing the lighter element first. Finally, HREM together with selective area electron diffraction show that the Ag-CuNCs are most likely formed by metastable solid solutions of Ag and Cu.
Improved method for measuring absolute O2(a1Δg) concentration by O2(a1Δg→X3Σg−) IR radiation
Authors: Deng Liezheng , Shi Wenbo , Yang Heping , Sha Guohe , Zhang Cunhao
Published: October 2004

We describe an improved technique for measuring the absolute O2(a1Δ) concentration via the quantitative determination of IR radiation from O2(a1Δg→X3Σg−) transition. An exact geometrical optical model was first established, in which the influence of reflection and refraction on the radiation characteristics of a luminous volume source was given full consideration, making possible the accurate calculation of the coupling efficiency between the volume source and a receiving area. Then, an IR radiation receiving apparatus (IRRRA) was constructed and its responsivity (mV/W) to the power of IR radiation calibrated by a tungsten standard lamp. An optical detection system was, in turn, built according to the optical model with fine alignment between the IRRRA and an optical cell. We then demonstrate the procedure to obtain the absolute concentration of O2(a1Δ) flowing through the optical cell from a jet singlet oxygen generator from the signal of the IRRRA, the optical cell volume, and the coupling efficiency between the cell and the IRRRA. Moreover, to verify the accuracy of this method, the absolute O2(a1Δ) concentration was compared to that measured by an established isothermal calorimetry method. Based on the comparison of the O2(a1Δ) concentrations determined by the two methods, the Einstein A-coefficient was estimated as (2.70±0.84)×10−4 s−1, which agrees with Badger’s value of 2.58×10−4, Špalek’s of 2.24×10−4, Newman’s of 2.19×10−4, and Miller’s of 2.3×10−4 within the uncertainty of the experimental techniques. The method advanced in this article is worthwhile for the measurement of absolute O2(a1Δ) concentration in a chemical oxygen iodine laser or a singlet oxygen generator. It can also provide a general technique for the measurement of absolute concentrations of long-lifetime luminous species other than O2(a1Δ).
Continuous scanning from picoseconds to microseconds in time resolved linear and nonlinear spectroscopy
Authors: Bredenbeck Jens , Helbing Jan , Hamm Peter
Published: October 2004

We describe a setup of two synchronized femtosecond 1 kHz oscillator/regenerative amplifier laser systems that allows to continuously delay the amplified pulses up to 50 μs, with a jitter of ⩽2 ps. It can be realized by facile modification and combination of equipment that already exists in many femtosecond laser laboratories. It opens up a variety of experimental possibilities, particularly for the investigation of systems that display dynamics over a wide range of time scales, such as peptides and proteins. As an example we discuss the application of this setup for time resolved IR spectroscopy.
Nearly strain-free heteroepitaxial system for fundamental studies of pulsed laser deposition: EuTiO3 on SrTiO3
Authors: Wang Huan-Hua , Fleet Aaron , Brock J. D. , Dale Darren , Suzuki Yuri
Published: October 2004

High-quality epitaxial thin films of EuTiO3 have been grown on the (001) surface of SrTiO3 using pulsed laser deposition. In situ x-ray reflectivity measurements reveal that the growth is two dimensional and enable real-time monitoring of the film thickness and roughness during growth. The film thickness, surface mosaic, surface roughness, and strain were characterized in detail by using ex situ x-ray diffraction. The thickness and composition were confirmed with Rutherford backscattering spectroscopy. The EuTiO3 thin films grow two dimensionally, epitaxially, and pseudomorphically, with no measurable in-plane lattice mismatch.