bluuebunny/crossref_metadata_2025 huggingface dataset:
Autoinhibitory control of the CaV1.2 channel by its proteolytically processed distal C‐terminal domain
Authors: Hulme Joanne T. , Yarov‐Yarovoy Vladimir , Lin Teddy W.‐C. , Scheuer Todd , Catterall William A.
Published: June 2006

Voltage‐gated Ca2+ channels of the CaV1 family initiate excitation–contraction coupling in cardiac, smooth, and skeletal muscle and are primary targets for regulation by the sympathetic nervous system in the ‘fight‐or‐flight’ response. In the heart, activation of β‐adrenergic receptors greatly increases the L‐type Ca2+ current through CaV1.2 channels, which requires phosphorylation by cyclic AMP‐dependent protein kinase (PKA) anchored via an A‐kinase anchoring protein (AKAP15). Surprisingly, the site of interaction of PKA and AKAP15 lies in the distal C‐terminus, which is cleaved from the remainder of the channel by in vivo proteolytic processing. Here we report that the proteolytically cleaved distal C‐terminal domain forms a specific molecular complex with the truncated α1 subunit and serves as a potent autoinhibitory domain. Formation of the autoinhibitory complex greatly reduces the coupling efficiency of voltage sensing to channel opening and shifts the voltage dependence of activation to more positive membrane potentials. Ab initio structural modelling and site‐directed mutagenesis revealed a binding interaction between a pair of arginine residues in a predicted α‐helix in the proximal C‐terminal domain and a set of three negatively charged amino acid residues in a predicted helix–loop–helix bundle in the distal C‐terminal domain. Disruption of this interaction by mutation abolished the inhibitory effects of the distal C‐terminus on CaV1.2 channel function. These results provide the first functional characterization of this autoinhibitory complex, which may be a major form of the CaV1 family Ca2+ channels in cardiac and skeletal muscle cells, and reveal a unique ion channel regulatory mechanism in which proteolytic processing produces a more effective autoinhibitor of CaV1.2 channel function.
Disinhibition of the cardiac limb of the arterial baroreflex in rat: a role for metabotropic glutamate receptors in the nucleus tractus solitarii
Authors: Simms Annabel E. , Paton Julian F. R. , Pickering Anthony E.
Published: June 2006

The nucleus tractus solitarii (NTS) is the first site of integration for primary baroreceptor afferents, which release glutamate to excite second‐order neurones through ionotropic receptors.In vitrostudies indicate that glutamate may also activate metabotropic receptors (mGluRs) to modulate the excitability of NTS neurones at pre‐ and postsynaptic loci. We examined the functional role of metabotropic glutamate receptors (mGluRs) in modulating the baroreceptor reflex in the rat NTS. Using the working heart–brainstem preparation, the baroreflex was activated using brief pressor stimuli and the consequent cardiac (heart rate change) and non‐cardiac sympathetic (T8–10 chain) baroreflex gains were obtained. Microinjections of glutamate antagonists were made bilaterally into the NTS at the site of termination of baroreceptor afferents. NTS microinjection of kynurenate (ionotropic antagonist) inhibited both the cardiac and sympathetic baroreflex gains (16 ± 5% and 59 ± 11% of control, respectively). The non‐selective mGluR antagonist MCPG produced a dose‐dependent inhibition of the cardiac gain (30 ± 3% of control) but not the sympathetic gain. Selective inhibitions of the cardiac gain were also seen with LY341495 and EGLU suggesting the response was mediated by group II mGluRs. This effect on cardiac gain involves attenuation of the parasympathetic baroreflex as it persists in the presence of atenolol. Prior NTS microinjection of bicuculline (GABAAantagonist) prevented the mGluR‐mediated attenuation of the cardiac gain. These results are consistent with the reported presynaptic inhibition of GABAergic transmission by group II mGluRs in the NTS and constitute a plausible mechanism allowing selective feed‐forward disinhibition to increase the gain of the cardiac limb of the baroreflex without changing the sympathoinhibitory component.
Recurrent inhibition of the bladder C fibre reflex in the cat and its response to naloxone
Authors: Mazières L. , Jiang C. H. , Lindström S.
Published: June 2006

Recurrent inhibition of the bladder C fibre reflex was studied in adult female cats anaesthetized with α‐chloralose. Test reflexes were evoked by electrical stimulation of bladder Aδ and C afferents in the right pelvic nerve and were recorded from the proximal end of a small ipsilateral pelvic nerve branch, transected close to the bladder. Such test reflexes were consistently depressed by repetitive electrical stimulation of the contralateral bladder pelvic nerve (20 Hz, 20 s) at intensities sufficient to recruit axons of bladder preganglionic neurones. The inhibition could be evoked after transection of the left dorsal roots S1–S4 and the sympathetic supply to the bladder but was abolished by transection of the pelvic nerve central to the site of stimulation. Hence, it most likely involved central recurrent collaterals of antidromically activated bladder preganglionic neurones. The reflex suppression was quite considerable – maximal C fibre reflexes were reduced to a group mean of 25% (± 9% confidence interval) of their control size. The effect had a slow onset, requiring a few seconds of conditioning stimulation to be revealed, and was very long lasting (minutes). Naloxone (0.01–0.5 mg kg−1i.v.) abolished the recurrent inhibition of both the C fibre and Aδ bladder reflexes, while inhibition from afferents in the dorsal clitoris nerve remained unchanged. It is concluded that the segmental bladder C fibre reflex and the spino‐ponto‐spinal Aδ micturition reflex are both targets of recurrent inhibition from bladder parasympathetic preganglionic neurones and that the effect involves an enkephalinergic mechanism.
Sodium–calcium exchange does not require allosteric calcium activation at high cytosolic sodium concentrations
Authors: Urbanczyk Jason , Chernysh Olga , Condrescu Madalina , Reeves John P.
Published: June 2006

The activity of the cardiac Na+–Ca2+ exchanger (NCX1.1) is allosterically regulated by Ca2+, which binds to two acidic regions in the cytosolically disposed central hydrophilic domain of the NCX protein. A mutation in one of the regulatory Ca2+ binding regions (D447V) increases the half‐activation constant (Kh) for allosteric Ca2+ activation from ∼0.3 to > 1.8 μm. Chinese hamster ovary cells expressing the D447V exchanger showed little or no activity under physiological ionic conditions unless cytosolic [Ca2+] was elevated to > 1 μm. However, when cytosolic [Na+] was increased to 20 mm or more (using ouabain‐induced inhibition of the Na+,K+‐ATPase or the ionophore gramicidin), cells expressing the D447V mutant rapidly accumulated Ca2+ or Ba2+ when the reverse (Ca2+ influx) mode of NCX activity was initiated, although initial cytosolic [Ca2+] was < 100 nm. Importantly, the time course of Ca2+ uptake did not display the lag phase that reflects allosteric Ca2+ activation of NCX activity in the wild‐type NCX1.1; indeed, at elevated [Na+], the D447V mutant behaved similarly to the constitutively active deletion mutant Δ(241–680), which lacks the regulatory Ca2+ binding sites. In cells expressing wild‐type NCX1.1, increasing concentrations of cytosolic Na+ led to a progressive shortening of the lag phase for Ca2+ uptake. The effects of elevated [Na+] developed rapidly and were fully reversible. The activity of the D447V mutant was markedly inhibited when phosphatidylinositol 4,5‐bisphosphate (PIP2) levels were reduced. We conclude that when PIP2 levels are high, elevated cytosolic [Na+] induces a mode of exchange activity that does not require allosteric Ca2+ activation.
Glutamate acts at NMDA receptors on fresh bovine and on cultured human retinal pigment epithelial cells to trigger release of ATP
Authors: Reigada David , Lu Wennan , Mitchell Claire H.
Published: June 2006

The photoreceptors lie between the inner retina and the retinal pigment epithelium (RPE). The release of glutamate by the phototoreceptors can signal changes in light levels to inner retinal neurons, but the role of glutamate in communicating with the RPE is unknown. Since RPE cells are known to release ATP, we asked whether glutamate could trigger ATP release from RPE cells and whether this altered cell signalling. Stimulation of the apical face of fresh bovine RPE eyecups with 100 μm NMDA increased ATP levels more than threefold, indicating that both receptors for NMDA and release of ATP occurred across the apical membrane of fresh RPE cells. NMDA increased ATP levels bathing cultured human ARPE‐19 cells more than twofold, with NMDA receptor inhibitors MK‐801 and d‐AP5 preventing this release. Blocking the glycine site of the NMDA receptor with 5,7‐dichlorokynurenic acid prevented ATP release from ARPE‐19 cells. Release was also blocked by channel blocker NPPB and Ca2+ chelator BAPTA, but not by cystic fibrosis transmembrane conductance regulator (CFTR) blocker glibenclamide or vesicular release inhibitor brefeldin A. Glutamate produced a dose‐dependent release of ATP from ARPE‐19 cells that was substantially inhibited by MK‐801. NMDA triggered a rise in cell Ca2+ that was blocked by MK‐801, by the ATPase apyrase, by the P2Y1 receptor antagonist MRS2179 and by depletion of intracellular Ca2+ stores with thapsigargin. These results suggest that glutamate stimulates NMDA receptors on the apical membrane of RPE cells to release ATP. This secondary release can amplify the glutaminergic signal by increasing Ca2+ inside RPE cells, and might activate Ca2+‐dependent conductances. The interplay between glutaminergic and purinergic systems may thus be important for light‐dependent interactions between photoreceptors and the RPE.
Periodic Motions in a Periodically Forced Oscillator Moving on an Oscillating Belt With Dry Friction
Authors: Luo Albert C.J. , Gegg Brandon C.
Published: July 2006

In this paper, periodic motion in an oscillator moving on a periodically oscillating belt with dry friction is investigated. The conditions of stick and nonstick motions for such an oscillator are obtained in the relative motion frame, and the grazing and stick (or sliding) bifurcations are presented as well. The periodic motions are predicted analytically and numerically, and the analytical prediction is based on the appropriate mapping structures. The eigenvalue analysis of such periodic motions is carried out. The periodic motions are illustrated through the displacement, velocity, and force responses in the absolute and relative frames. This investigation provides an efficient method to predict periodic motions of such an oscillator involving dry friction. The significance of this investigation lies in controlling motion of such a friction-induced oscillator in industry.
Dynamics of Multibody Systems With Spherical Clearance Joints
Authors: Flores P. , Ambrósio J. , Claro J. C. P. , Lankarani H. M.
Published: July 2006

This work deals with a methodology to assess the influence of the spherical clearance joints in spatial multibody systems. The methodology is based on the Cartesian coordinates, with the dynamics of the joint elements modeled as impacting bodies and controlled by contact forces. The impacts and contacts are described by a continuous contact force model that accounts for geometric and mechanical characteristics of the contacting surfaces. The contact force is evaluated as function of the elastic pseudo-penetration between the impacting bodies, coupled with a nonlinear viscous-elastic factor representing the energy dissipation during the impact process. A spatial four-bar mechanism is used as an illustrative example and some numerical results are presented, with the efficiency of the developed methodology discussed in the process of their presentation. The results obtained show that the inclusion of clearance joints in the modelization of spatial multibody systems significantly influences the prediction of components’ position and drastically increases the peaks in acceleration and reaction moments at the joints. Moreover, the system’s response clearly tends to be nonperiodic when a clearance joint is included in the simulation.
Rail Geometry and Euler Angles
Authors: Rathod Cheta , Shabana Ahmed A.
Published: July 2006

In railroad vehicle dynamics, Euler angles are often used to describe the track geometry (track centerline and rail space curves). The tangent and curvature vectors as well as local geometric properties such as the curvature and torsion can be expressed in terms of Euler angles. Some of the local geometric properties and Euler angles can be related to measured parameters that are often used to define the track geometry. The Euler angles employed, however, define a coordinate system that may differ from the Frenet frame used in the classical differential geometry. The relationship between the track frame used in railroad vehicle dynamics and the Frenet frame used in the theory of curves is developed in this paper and is used to shed light on some of the formulas and identities used in the geometric description in railroad vehicle dynamics. The conditions under which the two frames (track and Frenet) become equivalent are presented and used to obtain expressions for the curvature and torsion in terms of Euler angles and their derivatives with respect to the arc length.
Effect of Material Anisotropy and Curing Stresses on Interface Delamination Propagation Characteristics in Multiply Laminated FRP Composites
Authors: Pradhan Brajabandhu , Panda Saroja Kanta
Published: July 2006

The present study encompasses the thermoelastic effect of material anisotropy and curing stresses on interlaminar embedded elliptical delamination fracture characteristics in multiply laminated fiber-reinforced polymeric (FRP) composites. Two sets of full three-dimensional finite element analyses have been performed to calculate the displacements and interlaminar stresses along the delaminated interface responsible for the delamination onset and propagation. Modified crack closure integral methods based on the concepts of linear elastic fracture mechanics have been followed to evaluate the individual modes of strain energy release rates along the delamination front. It is shown that the individual modes of energy release rates vary along the delamination front depending on the ply sequence, orientation, and thermoelastic material anisotropy of the constituting laminae. This causes the anisotropic and non-self similar delamination propagation along the interface. The asymmetric and nonuniform variations in the nature of energy release rate plots obtained in a thermomechanical loading environment are significant when curing stress effects are included in the numerical analysis and hence should be taken into account in the designs of laminated FRP composite structures.
Numerical and Experimental Evaluation of the Damping Properties of Shape-Memory Alloys
Authors: Auricchio Ferdinando , Fugazza Davide , DesRoches Reginald
Published: July 2006

This paper presents and compares two different uniaxial constitutive models for superelastic shape-memory alloys (SMAs), suitable to study the dependence of the stress-strain relationship on the loading-unloading rate. The first model is based on the inclusion of a direct viscous term in the evolutionary equation for the martensite fraction and it shows how the material response is bounded between two distinct rate-independent models. The second model is based on a rate-independent evolutionary equation for the martensite fraction coupled with a thermal balance equation. Hence, it considers mechanical dissipation as well as latent heat and includes the temperature as a primary independent variable, which is responsible of the dynamic effects. The ability of both models to reproduce the observed reduction of damping properties through the modification of the hysteresis size is discussed by means of several numerical simulations. Finally, the capacity of the constitutive equations to simulate experimental data from uniaxial tests performed on SMA wires and bars of different size and chemical composition is shown.
Small Amplitude Dynamic Properties of Ni48Ti46Cu6 SMA Ribbons: Experimental Results and Modelling
Authors: Remillat C. , Hassan M. R. , Scarpa F.
Published: July 2006

This work illustrates viscoelastic testing and fractional derivative modelling to describe the thermally induced transformation equivalent viscoelastic damping of NiTiCu SMA ribbons. NiTiCu SMA ribbons have been recently evaluated to manufacture novel honeycombs concepts (conventional and negative Poisson’s ratio) in shape memory alloys for high damping and deployable sandwich antennas constructions. The dynamic mechanical thermal analysis (DMTA) test has been carried out at different frequencies and temperatures, with increasing and decreasing temperature gradients. Thermally induced transformations (austenitic and martensitic) provide damping peaks at low frequency range excitations. On the opposite, the storage moduli are not affected by the harmonic pulsation. As the SMA ribbon increases its stiffness, the damping capacity reduces, and the loss factor drops dramatically at austenite finish temperature. The fractional derivative models provide a compact representation of the asymmetry of the peak locations, as well as the storage modulus change from martensite to austenite phases.
Application of EDM Hole-Drilling Method to the Measurement of Residual Stress in Tool and Carbon Steels
Authors: Lee Hwa-Teng , Mayer Joachim , Hsu Fu-Chuan , Rehbach Werner P. , Weirich Thomas , Dimyati Arbi , Tai Tzu-Yao
Published: July 2006

This study adopts the application of the electrodischarge machining (EDM) hole-drilling method to the measurement of residual stress in AISI D2 cold work tool steel, AISI H13 hot work tool steel, and AISI 1045 medium carbon steel. A calibration procedure based on the thermal conductivity of the material is conducted to compensate for the additional compressive stress induced in the workpiece by the EDM hole-drilling operation. Since the formation of this white layer influences the magnitude of the induced stress, the scanning electron microscopy, transmission electron microscopy, and nanoindentation techniques are used to examine the microstructure and hardness of the white layer resolidified on the EDMed surface. The experimental results reveal that combination of the hole-drilling strain-gage method (ASTM standard E837) with an EDM drilling process provides the effective means of determining the residual stress in materials with high hardness and good wear resistance.
Comparison of Cervical Disk Implants and Cervical Disk Fusion Treatments in Human Cadaveric Models
Authors: Davies M. A. , Bryant S. C. , Larsen S. P. , Murrey D. B. , Nussman D. S. , Laxer E. B. , Darden B. V.
Published: June 2006

Articulating cervical disk implants have been proposed as an alternative to disk fusion in the treatment of cervical disk disease. To examine the mechanical effect of articulating cervical disk implants (ACDI) versus simulated cervical disk fusion, a mechanical test device was constructed and cadaveric tests were carried out. While results show little effect on the pressures above and below the treatment level, the percent hysteretic behavior of the specimens trended to be higher for the ACDI, indicating that these implants retain more of the natural energy absorption capability of the cervical spine.
Experimental Validation of an Inverse Heat Transfer Algorithm for Optimizing Hyperthermia Treatments
Authors: Gayzik F. Scott , Scott Elaine P. , Loulou Tahar
Published: June 2006

Hyperthermia is a cancer treatment modality in which body tissue is exposed to elevated temperatures to destroy cancerous cells. Hyperthermia treatment planning refers to the use of computational models to optimize the heating protocol with the goal of isolating thermal damage to predetermined treatment areas. This paper presents an algorithm to optimize a hyperthermia treatment protocol using the conjugate gradient method with the adjoint problem. The output of the minimization algorithm is a heating protocol that will cause a desired amount of thermal damage. The transient temperature distribution in a cylindrical region is simulated using the bioheat transfer equation. Temperature and time are integrated to calculate the extent of thermal damage in the region via a first-order rate process based on the Arrhenius equation. Several validation experiments are carried out by applying the results of the minimization algorithm to an albumen tissue phantom. Comparisons of metrics describing the damage region (the height and radius of the volume of thermally ablated phantom) show good agreement between the desired extent of damage and the measured extent of damage. The sensitivity of the bioheat transfer model and the Arrhenius damage model to their constituent parameters is calculated to create a tolerable range of error between the desired and measured extent of damage. The measured height and radius of the ablated region fit well within the tolerable range of error found in the sensitivity analysis.
Dynamic Response of Immature Bovine Articular Cartilage in Tension and Compression, and Nonlinear Viscoelastic Modeling of the Tensile Response
Authors: Park Seonghun , Ateshian Gerard A.
Published: June 2006

Very limited information is currently available on the constitutive modeling of the tensile response of articular cartilage and its dynamic modulus at various loading frequencies. The objectives of this study were to (1) formulate and experimentally validate a constitutive model for the intrinsic viscoelasticity of cartilage in tension, (2) confirm the hypothesis that energy dissipation in tension is less than in compression at various loading frequencies, and (3) test the hypothesis that the dynamic modulus of cartilage in unconfined compression is dependent upon the dynamic tensile modulus. Experiment 1: Immature bovine articular cartilage samples were tested in tensile stress relaxation and cyclical loading. A proposed reduced relaxation function was fitted to the stress-relaxation response and the resulting material coefficients were used to predict the response to cyclical loading. Adjoining tissue samples were tested in unconfined compression stress relaxation and cyclical loading. Experiment 2: Tensile stress relaxation experiments were performed at varying strains to explore the strain-dependence of the viscoelastic response. The proposed relaxation function successfully fit the experimental tensile stress-relaxation response, with R2=0.970±0.019 at 1% strain and R2=0.992±0.007 at 2% strain. The predicted cyclical response agreed well with experimental measurements, particularly for the dynamic modulus at various frequencies. The relaxation function, measured from 2% to 10% strain, was found to be strain dependent, indicating that cartilage is nonlinearly viscoelastic in tension. Under dynamic loading, the tensile modulus at 10Hz was ∼2.3 times the value of the equilibrium modulus. In contrast, the dynamic stiffening ratio in unconfined compression was ∼24. The energy dissipation in tension was found to be significantly smaller than in compression (dynamic phase angle of 16.7±7.4deg versus 53.5±12.8deg at 10−3Hz). A very strong linear correlation was observed between the dynamic tensile and dynamic compressive moduli at various frequencies (R2=0.908±0.100). The tensile response of cartilage is nonlinearly viscoelastic, with the relaxation response varying with strain. A proposed constitutive relation for the tensile response was successfully validated. The frequency response of the tensile modulus of cartilage was reported for the first time. Results emphasize that fluid-flow dependent viscoelasticity dominates the compressive response of cartilage, whereas intrinsic solid matrix viscoelasticity dominates the tensile response. Yet the dynamic compressive modulus of cartilage is critically dependent upon elevated values of the dynamic tensile modulus.
Theoretical and Experimental Analysis of a Base-Excited Rotor
Authors: Driot N. , Lamarque C. H. , Berlioz A.
Published: July 2006

In this study, the dynamic behavior of a flexible rotor system subjected to support excitation (imposed displacements of its base) is analyzed. The effect of an excitation on lateral displacements is investigated from theoretical and experimental points of view. The study focuses on behavior in bending. A mathematical model with two gyroscopic and parametrical coupled equations is derived using the Rayleigh-Ritz method. The theoretical study is based on both the multiple scales method and the normal form approach. An experimental setup is then developed to observe the dynamic behavior permitting the measurement of lateral displacements when the system’s support is subjected to a sinusoidal rotation. The experimental results are favorably compared with the analytical and numerical results.
Deformation and Life Estimates for a Metal Matrix—Spherical Particulate Subjected to Thermomechanical Loading
Authors: McDonald Russell J. , Kurath Peter
Published: July 2006

Thermal cycling has been experimentally demonstrated to diminish the performance of many reinforced materials. The coefficient of thermal expansion mismatch is the driving force for the development of high self-equilibrating stresses and strains in the vicinity of the reinforcement. To glean the magnitude of these stresses, a simple geometry, a spherical particulate (SiC) in a spherical domain (aluminum W319) was investigated. A set of partitioned strain rate equations considered temperature dependent material properties for thermal, elastic, mechanical plastic, and creep plastic deformation. The mechanical plasticity model utilized an improved Armstrong-Fredrick kinematic hardening algorithm and a Fisher type rate dependent yield criteria. A hyperbolic sine relation proposed by Dorn (1954, “Some Fundamental Experiments on High Temperature Creep,” J. Mech. Phys. Solids, 3, pp. 85–116) was used to model creep deformation. A multidimensional residual stress state due to cooling from the molten state was considered in the simulations. Two damage parameters, Findley and equivalent plastic strain, were employed to estimate cyclic damage. While the life estimates are crude, they both predict finite lives for reasonable service temperature ranges.
Surface and texture characterization of thin-film ZnTe formed with pulsed-laser deposition
Authors: Erlacher Artur , Lukaszew Alejandra R. , Jaeger Herbert , Ullrich Bruno
Published: July 2006

Using thin-film semiconductors as active photonic interfaces, an all-optical laser digitizer can be realized. Based on these results, zinc telluride (ZnTe) has attracted our interest since it is an appealing semiconductor for applications in photonics. Low-temperature pulsed-laser deposition (PLD), i.e., without substrate heater, was employed to deposit amorphous thin-film ZnTe on silicon (Si) and glass substrates using either the 1064 or 532 nm emission lines of a nanosecond-pulsed Nd:YAG laser. In spite of the predominantly amorphous sample textures, x-ray-diffraction experiments and analysis of the surface roughness including outgrowth distribution using atomic force microscopy reveal major differences in surface morphology and crystal textures between samples formed at these two laser wavelengths. This indicates wavelength-dependent ablation and wavelength-dependent PLD mechanisms with nanosecond pulses. Our observations contribute to a better understanding of PLD and provide tools to fine-tune and optimize the optoelectronic and photonic properties of ZnTe amorphous thin films as well as their incorporation into Si-based technologies in order to fabricate cost-effective and functional optoelectronic devices.
Interstitial oxygen-related defects and current leakage in trench metal-oxide-semiconductor field-effect transistor on epi∕As++ structure
Authors: Wang Q. , Daggubati Manmohan , Paravi Hossein , Yu Rong , Zhang Xiao Feng
Published: July 2006

Interstitial oxygen (Oi) related defect and reverse current leakage have been investigated on test trench metal-oxide-semiconductor field-effect transistors fabricated on epilayers over heavily arsenic-doped wafers (As++). The devices on the wafers sealed with polysilicon at backside exhibited an increased yield loss in reverse current leakage with increasing Oi concentration. The Oi concentration depth profiles indicate that Oi did precipitate out at the interface between the polysilicon layer and bulk silicon. This precipitation may consume the polylayer and reduce its gettering efficiency, which leads to an Oi-dependent current leakage. Similar experiments carried out with damaged backside As++ wafers show an overall low and Oi-independent current leakage yield loss. This reduced leakage yield loss is due to the intrinsic gettering effect of the Oi precipitates in these wafers close to the back surface. Transmission electron microscopy study revealed, in the junction region, the existence of intrinsic stacking faults and punch-out dislocation loop, characteristic of oxygen precipitation. The reverse current-voltage curves related to these defects have been quantitatively analyzed using the Shockley-Read-Hall model. The effective generation lifetimes of intrinsic stacking fault and punch-out dislocation loop are about 4.3 ps and 50 ns, respectively, and are significantly shorter than 2.5μs in defect-free area.
Hot electrons at metal-organic interface: Time-resolved two-photon photoemission study of phenol on Ag(111)
Authors: Ryu Sunmin , Chang Jinyoung , Kwon Hyuksang , Kim Seong Keun
Published: July 2006

We used time-resolved two-photon photoemission (2PPE) spectroscopy to investigate the excitation mechanism and dynamical behavior of the anionic molecular resonance (MR) state of phenol weakly interacting with Ag(111). The photoexcited MR state of phenol was found at 3.1 eV above the Fermi level at 1 ML (monolayer) coverage, and the binding energy of this state remained rather constant at 0.74±0.05eV for all coverages. The polarization angle dependence of the 2PPE signal clearly showed that the MR state is populated by an indirect excitation process involving scattering of photoexcited hot electrons rather than direct electronic transition from a bulk band. The lifetime of the MR state was found to increase from 33 to 60 fs upon increasing the coverage from 1 to 9 ML, implying that the MR state becomes further decoupled from the bulk at a higher coverage. These results constitute the first time-resolved 2PPE study that clearly demonstrates the hot-electron-mediated mechanism operating for molecules that are potentially active photochemically but weakly interacting with a metal surface.
Surface modification of silicon and polydimethylsiloxane surfaces with vapor-phase-deposited ultrathin fluorosilane films for biomedical nanodevices
Authors: Bhushan Bharat , Hansford Derek , Lee Kang Kug
Published: July 2006

Ultrathin coatings of fluorosilane films for silicon and polydimethylsiloxane (PDMS) nanochannels are desirable to control the hydrophobicity of the surface and reduce or prevent undesired protein adsorption or cell interactions critical for the performance of most biomedical micro/nanodevices. Surface modifications using vapor-phase deposition become increasingly important for some biomedical nanodevices and have advantages over liquid-phase deposition since the vapor phase can permeate more efficiently into silicon nanochannels. In this study, vapor-phase deposition was used to deposit ultrathin films of four fluorosilanes on silicon and PDMS and identify deposition conditions for an optimal process. The films were characterized by means of a contact angle analyzer for hydrophobicity, an ellipsometer for film thickness, and an atomic force microscope for surface roughness of these films. Results of this study and relevant mechanisms are the subject of this article.
Optical activation of implanted impurities in ZnS nanowires
Authors: Stichtenoth D. , Schwen D. , Müller S. , Borchers C. , Ronning C.
Published: July 2006

Nanostructures of zinc sulfide (ZnS), a II-VI compound semiconductor with a direct band gap of 3.66eV in the cubic phase and 3.74eV in the wurtzite phase, show interesting optical properties, making it a promising candidate for optoelectronic devices. Single-crystalline nanobelts and nanowires were synthesized in a computer-controlled process according to the vapor-liquid-solid-mechanism. We investigated the morphology, structure, and composition by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. The optical properties were studied by low-temperature photoluminescence (PL) and cathodoluminescence. The synthesized ZnS nanowires were implanted with nitrogen and boron as potential donor and acceptor, respectively. The implanted nanowires were investigated directly after ion implantation and showed a high quantity of defects resulting in nonluminescent material. Annealing procedures recovered the crystal structure and the luminescence, and we found emerging and varying PL lines indicating the activation of the implanted impurities.
Optimization and deposition of CdS thin films as applicable to TiO2∕CdS composite catalysis
Authors: Prabakar K. , Takahashi T. , Nakashima T. , Kubota Y. , Fujishima A.
Published: July 2006

Methanol decomposition has been studied by in situ Fourier transform infrared spectroscopy on a CdS∕TiO2 bilayer deposited on glass substrates. First CdS thin films were deposited by chemical bath deposition method using the CdSO4 and thiourea as the precursors and ammonia as the complexing agent and have the optical band gap of 2.2–2.29 eV for the different CdSO4 solution concentrations. The structure of the CdS films was found to have mixed cubic and hexagonal phases, while the TiO2 films were polycrystalline anatase structure with an optical band-gap energy of 3.2 eV deposited at a total sputtering pressure of 0.1 Pa in an argon and oxygen gas mixture (Ar:O2=80:20) at 200 W sputtering power. The visible light active photocatalytic degradation efficiency of methanol over a TiO2∕CdS double layer is four times higher than that of a TiO2 single layer. The decomposition of methanol pathway proceeds via formaldehyde as the intermediate product.
Effect of substrate material and bias on properties of TiN films deposited in the hybrid plasma reactor
Authors: Bárdos L. , Baránková H. , Gustavsson L.-E.
Published: July 2006

Parameters of TiN films deposited in the hybrid hollow cathode and microwave electron cyclotron resonance (ECR) plasma reactor can be strongly affected by the substrate material. Differences have been found between films grown on Si substrates and steel substrates, as well as between steel substrates from martensite and austenite steels. Temperature measurements by simple probes made from different materials with surfaces covered by wafers from Si or from steel confirmed substantial differences depending on individual materials. These differences can be explained by material-dependent absorptions of the microwave power as well as by enhanced particle bombardment of ferromagnetic substrates connected with deformation of the magnetic field in the hybrid plasma reactor. The effect of surface bombardment has been confirmed by voltage-current measurements using electrically biased probes. The results correspond well with properties of the obtained TiN films. Observed effects could be of more general importance, e.g., for microwave ECR plasmas, magnetron sputtering, as well as for most magnetized plasma systems.
Exploring the collective dynamics of lipid membranes with inelastic neutron scattering
Authors: Rheinstädter Maikel C. , Seydel Tilo , Häußler Wolfgang , Salditt Tim
Published: July 2006

While most spectroscopic techniques, as e.g., nuclear magnetic resonance or dielectric spectroscopy, probe macroscopic responses, neutron and within some restrictions also x-ray scattering experiments give the unique access to microscopic dynamics at length scales of intermolecular or atomic distances. Only recently, it has become possible to study collective dynamics of planar lipid bilayers using neutron spectroscopy techniques [M. Rheinstädter, C. Ollinger, G. Fragneto, F. Demmel, and T. Salditt, Phys. Rev. Lett. 93, 108107 (2004)]. We determined the dispersion relation of the coherent fast picosecond density fluctuations on nearest-neighbor distances of the phospholipid acyl chains in the gel and in the fluid phases of a dimyristoylphoshatidylcholine bilayer. The experiments shed light on the evolution of structure and dynamics, and the relation between them, in the range of the gel-fluid main phase transition. The scattering volume restriction for inelastic neutron experiments was overcome by stacking several thousands of highly aligned membrane bilayers. By combining different neutron-scattering techniques, namely, three-axis, backscattering, and spin-echo spectroscopies, we present measurements of short- and long-wavelength collective fluctuations in biomimetic and biological membranes in a large range in momentum and energy transfer, covering time scales from about 0.1ps to almost 1μs and length scales from 3Å to about 0.1μm. The neutron-backscattering technique gives information about slow molecular dynamics of lipid acyl chains and the “membrane-water,” i.e., the water molecules in between the stacked bilayers in the nanosecond time range [M. C. Rheinstädter, T. Seydel, F. Demmel, and T. Salditt, Phys. Rev. E 71, 061908 (2005)]. The dispersion relations of the long-wavelength undulation modes in lipid bilayers with nanosecond relaxation times can be determined by quasielastic reflectometry on spin-echo spectrometers and give direct access to the elasticity parameters of the membranes.
Characteristics of large-diameter plasma using a radial-line slot antenna
Authors: Tian C. , Nozawa T. , Ishibasi K. , Kameyama H. , Morimoto T.
Published: July 2006

Characteristics of the surface-wave plasma generated by a radial-line slot antenna (RLSA) have been studied by both direct plasma probe measurements and numerical simulations. Some unique characteristics have been found, including excellent critical radial plasma uniformity, low electron temperature under various pressure conditions, the main plasma generation area of RLSA being limited in the plasma surface, and few high-energy electrons existing in the wafer region. Numerical simulations are implemented to reveal the more essential difference in plasma generation between the RLSA and the other plasma sources, where the superiority of RLSA plasma has been confirmed. The features of high plasma uniformity and low electron temperature lead to free plasma damage in our associated etching process.
Vacuum measurement by carbon nanotube field emission
Authors: Choi In-Mook , Woo Sam-Yong , Hong Seung-Soo
Published: July 2006

A vacuum measurement technology utilizing the carbon nanotube (CNT) field-emission effect has been developed and characterized. The fabricated pressure sensor is a triode type similar to a conventional ionization gauge, but has a planar structure similar to a field-emission display. Owing to the excellent field-emission characteristics of CNTs, it is possible to make a cost effective cold cathode-type ion gauge. The triode-type CNT sensor has been manufactured by a screen-printing method and by a thermal chemical-vapor deposition growth method. A modified structure with an electron filter has also been introduced and characterized so as to improve the performances, such as sensitivity and stability. A glass grid with Cr deposited by e-beam is placed on the cathode. By the voltage applied to the grid, electrons are emitted from the CNTs and they ionize gas molecules in the chamber. Two modes are available to detect the gas density in the chamber, an electron emission mode and an ionization mode. In the electron emission mode, the collector voltage is controlled to be slightly higher than the grid voltage, whereas in the ionization mode it is controlled to be lower than the grid voltage so as to obtain a large ionization ratio. The ionized molecules are gathered at the collector and the electrons return to the grid in the triode structure. The ionization ratio increases as a function of pressure in the electron emission mode. The ionization characteristics are dependent on the gas and the combination of the voltages applied to the grid and the collector. In this article, the various metrological characteristics of the developed pressure sensor utilizing CNTs are introduced.
Dependence of power trench metal-oxide-semiconductor field-effect transistor processes on wafer thickness
Authors: Daggubati M. , Sim G. , Long D. , Paravi H. , Wang Q.
Published: July 2006

The dependence of trench metal-oxide-semiconductor field-effect transistor processes on wafer thickness has been studied. In the photolithography process, it was found that the photoresist thickness decreased with the decrease of wafer thicknesses. This is due to the fact that thinner wafer has less thermal mass and hence less dissipation time. Unless compensated for, this change in resist thickness adds to critical dimension and trench depth variations. After the rapid thermal processing, the thinner wafers exhibited a lower resistivity and higher silicide stress (i.e., 3.23E+10dyn∕cm2 for 508μm wafers and 4.60E+09dyn∕cm2 for 675μm wafers). Also, the stress is more uniform across the thinner wafers, possibly due to uniform Si-rich TixSiy (x<y) phase. Both Z-contrast transmission electron microscopy imaging and energy dispersive x-ray profiling on the silicide layers of the thicker wafers revealed a Ti-rich layer (possibly TiSi) on the top of TixSiy (x<y) layer and at the Si-silicide interface; whereas only scattered regions of Ti-enriched regions were observed in thinner wafers. Higher temperature in thinner wafers seems to assist in the removal of this Ti-rich layer.
Reduction of laser-induced roughness in a-Si:H surfaces for vacuum compatible lithography
Authors: Jacobs R. N. , Robinson E. W. , Stoltz A. J. , Dinan J. H. , Salamanca-Riba L.
Published: July 2006

A vacuum compatible lithography technique has recently been demonstrated, whereby amorphous hydrogenated silicon (a-Si:H) films are used as a resist. Following plasma deposition of the a-Si:H film, poly-Si patterns are generated on the surface by excimer laser exposure through a projection mask. Development is then carried out by hydrogen plasma etching for which etch selectivities of over 1000:1 have been achieved between a-Si:H and poly-Si regions. However, the roughness induced by excimer laser irradiation can be well over ten times that of the as-deposited a-Si:H surface. This is problematic because the roughness may be transferred to underlying device layers during subsequent pattern transfer plasma etching. We have developed a stepwise laser irradiation procedure that reduces the surface roughness by an order of magnitude to a level of ∼1nm. This value is approximately equal to the surface roughness for the as-deposited a-Si:H film. The irradiation procedure uses multiple pulses with progressive increases in the energy density, in contrast to the single high energy density pulses previously used. Transmission electron microscopy and Fourier transform infrared spectroscopy are used to understand and confirm the mechanism behind this process. Our data suggest that the observed reduction in roughness is due both to smaller grain sizes and to a slow rate of H removal from the film surface. The results may also hold significance for other applications of laser processed a-Si:H, even where different film properties are desired.
Growth of carbon nanotube bundle arrays on silicon surfaces
Authors: Bronikowski Michael J. , Manohara Harish M. , Hunt Brian D.
Published: July 2006

The growth on silicon substrates of arrayed bundles of multiwalled carbon nanotubes (CNTs) by metal catalyzed chemical vapor deposition of carbon from ethylene has been characterized and optimized. We find that, while CNTs can grow on bare Si substrates, the growth is substantially more reproducible if a thin (∼3nm) barrier layer of aluminum oxide is used between the Si surface and iron catalyst. Optimum Fe thickness and growth temperature are 3.0 nm and 650 °C, respectively. We find that the CNT length increases linearly with time at a rate of 3–4μm∕min for up to 2 h of CNT growth, after which the growth ceases. The length of the resulting CNT can thus be controlled up to a maximum length of ∼500μm. Such control over CNT bundle length will be crucial in the incorporation of these bundle arrays into high-intensity electron field emission devices.
Measuring the thickness of organic/polymer/biological films on glass substrates using spectroscopic ellipsometry
Authors: Tompkins Harland G. , Tiwald Tom , Bungay Corey , Hooper Andrew E.
Published: July 2006

In this work we discuss a method of determining film thickness for film/substrate combination where the index of refraction of the film and substrate in the transparent spectral regions is almost identical. Common examples of this situation are organic/polymer/biological films on glass substrates. Infrared ellipsometry is used and we use weight gain to provide some necessary additional information for determining the optical functions for the film material. The spectral regions of strong molecular vibrations are then used for determining film thickness.
Cold atmospheric plasma in nitrogen and air generated by the hybrid plasma source
Authors: Baránková H. , Bárdoš L. , Söderström D.
Published: July 2006

Generation of long plumes of cold atmospheric plasma in nitrogen and air has been successfully performed by the hybrid hollow electrode activated discharge (H-HEAD) source. The source with a simple cylindrical electrode terminated by a gas nozzle combines the microwave antenna plasma with the hollow cathode plasma generated inside the gas nozzle by pulsed dc power. The H-HEAD source is capable of generating up to 10 cm long plumes in air at microwave powers below 500 W and at air flow rates as low as 100 sccm (standard cubic centimeter per minute). The corresponding flow rates in the nitrogen plasma are even less than 80 sccm. The discharges in air and nitrogen have similar shapes and are comparable with the corresponding plasma columns in argon. A comparison of the optical emission spectra of the plasma in nitrogen and air is presented. The temperatures generated on steel substrates by interaction with nitrogen and air plasma columns at different microwaves and dc powers are compared with the corresponding effects in argon plasma.
Effect of nitrogen on the photocatalytic activity of TiOxNy thin films
Authors: Prabakar K. , Takahashi T. , Nezuka T. , Nakashima T. , Kubota Y. , Fujishima A.
Published: July 2006

Visible light active nitrogen doped titanium oxide (TiOxNy) thin films were deposited by dc reactive magnetron sputtering on glass substrates at different nitrogen flow rates and sputtering pressures. All the deposited films consist of composite of TiOxNy and TiO2 phases of anatase and a small portion of the rutile (R) phase was embedded in the polycrystalline films. X-ray diffraction and optical studies confirmed that the prepared films had nitrogen substituted at some of the oxygen sites in TiO2, which formed narrow N 2p band above the valence band. The surface roughness of the films varied between 5 and 25 nm for the films deposited at nitrogen flow of 0.5–5 SCCM (standard cubic centimeter per minute), respectively. The photocatalytic decomposition of methanol was investigated using fourier transform infrared as a function of irradiation time. The formaldehyde and CO species are the main intermediates by increasing the irradiation time in the presence of pure methanol and CO2 is produced after the complete decomposition. The properties of the films, including the crystallinity, surface morphology, and light absorption capability, are influenced by the nitrogen flow rate while the photocatalytic reaction on TiOxNy thin films is very sensitive to oxygen vacancy and its surface structure.