bluuebunny/crossref_metadata_2025 huggingface dataset:
Snell’s law of refraction observed in thermal frontal polymerization
Authors: Pojman John A. , Viner Veronika , Binici Burcu , Lavergne Shanna , Winsper Melanie , Golovaty Dmitry , Gross Laura
Published: September 2007

We demonstrate that Snell’s law of refraction can be applied to thermal fronts propagating through a boundary between regions that support distinct frontal velocities. We use the free-radical frontal polymerization of a triacrylate with clay filler that allows for two domains containing two different concentrations of a peroxide initiator to be molded together. Because the polymerization reaction rates depend on the initiator concentration, the propagation speed is different in each domain. We study fronts propagating in two parallel strips in which the incident angle is 90°. Our data fit Snell’s law vr∕vi=sinθr∕sinθi, where vr is the refracted velocity, vi is the incident velocity, θr is the angle of refraction, and θi is the incident angle. Further, we study circular fronts propagating radially from an initiation point in a high-velocity region into a low-velocity region (and vice versa). We demonstrate the close resemblance between the numerically simulated and experimentally observed thermal reaction fronts. By measuring the normal velocity and the angle of refraction of both simulated and experimental fronts, we establish that Snell’s law holds for thermal frontal polymerization in our experimental system. Finally we discuss the regimes in which Snell’s law may not be valid.
A strong micropillar containing a low angle grain boundary
Authors: Maaß R. , Van Petegem S. , Grolimund D. , Van Swygenhoven H. , Uchic M. D.
Published: September 2007

In situ white beam Laue diffraction experiments on focused ion beam machined single crystal 10μm Ni pillars are performed to explore the relation between the initial and evolving microstructures and the subsequent flow response. The pillar has a flow stress that is at least in the upper bound of the scatter of the flow stresses obtained for similar Ni pillars. Detailed analysis of the Laue pattern suggests that the strength is in part due to the low angle grain boundary acting as a dislocation barrier.
Competition between coexisting phases in (La,Pr)CaMnO3 manganites
Authors: Masunaga S. H. , Jardim R. F.
Published: October 2007

Polycrystalline La5∕8−yPryCa3∕8MnO3, 0⩽y⩽0.625, samples were synthesized by the solid-state reaction method and studied using x-ray powder diffraction, magnetic susceptibility [χ(T)], and magnetoresistivity [ρ(T,H)] measurements. Some features such as an appreciable thermal hysteresis observed in both ρ(T) and χ(T) curves indicated a competing scenario due to the coexistence of different phases. We have also found that there is a critical region in the phase diagram, for the Pr concentration ranging from ∼0.30 to 0.40, where the magnitude of the insulator to metal transition temperature (TMI), the Curie temperature (TC), the magnetoresistance, and the residual resistivity (ρ0) are characterized by abrupt changes with little increase in y. Our data also indicate that the physical properties of these manganites in this critical region are dominated by a strong competition between coexisting ferromagnetic metallic and charge-ordered insulating phases.
Determination of deformation potential constant of the conduction band in Si from electron heating experiments on Si metal-oxide-semiconductor field-effect transistors
Authors: Park K. H. , Unuma T. , Hirakawa K. , Takagi S.
Published: September 2007

The authors have investigated the heating process of two-dimensional electrons in conventional n-type Si metal-oxide-semiconductor field-effect transistors by analyzing the amplitudes of Shubnikov-de Haas oscillations at low temperatures. It is found that the observed carrier heating behavior is well explained by the energy relaxation due to acoustic phonon emission via deformation potential coupling. From detailed comparison between experiment and theory, we have determined the deformation potential constant of the conduction band in Si to be 12±2eV, which is larger than commonly accepted value 9eV for bulk Si.
Introduction: Dissipative localized structures in extended systems
Authors: Tlidi Mustapha , Taki Majid , Kolokolnikov Theodore
Published: September 2007

Localized structures belong to the class of dissipative structures found far from equilibrium. Contributions from the most representative groups working on a various fields of natural science such as biology, chemistry, plant ecology, mathematics, optics, and laser physics are presented. The aim of this issue is to gather specialists from these fields towards a cross-fertilization among these active areas of research and thereby to present an overview of the state of art in the formation and the characterization of dissipative localized structures. Nonlinear optics and laser physics have an important part in this issue because of potential applications in information technology. In particular, localized structures could be used as “bits” for parallel information storage and processing.
Impact of V/III ratio on electrical properties of GaN thick films grown by hydride vapor-phase epitaxy
Authors: Oh D. C. , Lee S. W. , Goto H. , Park S. H. , Im I. H. , Hanada T. , Cho M. W. , Yao T.
Published: September 2007

Impact of V/III ratio on electrical properties of GaN thick films are investigated, which are grown by hydride vapor-phase epitaxy. The authors note that the electron concentration of GaN films decreases with the increase of V/III ratio, while their electrical resistivity and electron mobility increase simultaneously. These indicate that enhancing V/III ratio suppresses electron-feeding sources in GaN films, which is not by generating electron-trapping centers but by reducing donor-type defects. On the other hand, it is shown that the linewidth of x-ray rocking curves in GaN films decreases and the near-band edge emission intensity of 10K photoluminescence spectra increases as V/III ratio increases. These mean that higher V/III ratio condition helps for reducing crystalline point defects in GaN films. In terms of theoretical fitting into the temperature-dependence curves of electron mobilities, it is found that the electron transport of GaN films grown in lower V/III ratio condition is more hampered by defect scatterings. Consequently, it is suggested that the generation of donor-type defects in the GaN thick films is more suppressed by higher V/III ratios, which induces lower background electron concentration and higher electron mobility.
The structures and electrical transport properties of germanium nanowires encapsulated in carbon nanotubes
Authors: Zhang X. Q. , Li H. , Liew K. M.
Published: October 2007

The structures of Ge nanowires are studied by means of geometry optimization method in this paper. As the radii of carbon nanotubes increase, the structures of the Ge nanowires transform from a monoatomic chain to helical and multishell coaxial cylinders. The physical properties, such as density of states, transmission functions, current-voltage (I-V) characteristics, and conductance spectra (G-V) of optimized nanowires sandwiched between two gold contacts are also obtained. The transport properties of a carbon-coated Ge atomic chain are significantly different from those of Ge single atomic chain. Furthermore, some nonequilibrium properties of Ge nanowires are compared with those of Sn and Si nanowires.
The effect of self-assembled monolayers on polarization-dependent two-photon photoemission and on the angular distribution of the photoelectrons
Authors: Fradkin Z. , Oron D. , Naaman R.
Published: September 2007

The effect of a self-assembled organized organic monolayer on the two-photon photoemission from semiconductor substrates was investigated. It has been found that the monolayer affects the relative yield of photoelectrons emitted by p-polarized versus s-polarized light. In addition, the monolayer affects the angular distribution of the ejected electrons. The effect on the photoelectron yield is attributed to the monolayer “smoothing” the electronic potential on the surface by eliminating surface states and dangling bonds. The effect on the angular distribution is attributed to a post-ejection interaction between the photoelectrons and the adsorbed molecules.
Relativity group for noninertial frames in Hamilton’s mechanics
Authors: Low Stephen G.
Published: October 2007

The group E(3)=SO(3)⊗sT(3), that is the homogeneous subgroup of the Galilei group parametrized by rotation angles and velocities, defines the continuous group of transformations between the frames of inertial particles in Newtonian mechanics. We show in this paper that the continuous group of transformations between the frames of noninertial particles following trajectories that satisfy Hamilton’s equations is given by the Hamilton group Ha(3)=SO(3)⊗sH(3), where H(3) is the Weyl-Heisenberg group that is parametrized by rates of change of position, momentum, and energy, i.e., velocity, force, and power. The group E(3) is the inertial special case of the Hamilton group.
Theoretical analysis for the design of the French watt balance experiment force comparator
Authors: Pinot Patrick , Genevès Gerard , Haddad Darine , David Jean , Juncar Patrick , Lecollinet Michel , Macé Stéphane , Villar François
Published: September 2007

This paper presents a preliminary analysis for designing a force comparator to be used in the French watt balance experiment. The first stage of this experiment consists in a static equilibrium, by means of a mechanical beam balance, between a gravitational force (a weight of an artefact having a known mass submitted to the acceleration due to the gravity) and a vertical electromagnetic force acting on a coil driven by a current subject to the magnetic induction field provided by a permanent magnet. The principle of the force comparison in the French experiment is explained. The general design configuration of the force balance using flexure strips as pivots is discussed and theoretical calculation results based on realistic assumptions of the static and dynamic behaviors of the balance are presented.
Concomitant speed-of-sound tomography in photoacoustic imaging
Authors: Manohar Srirang , Willemink René G. H. , van der Heijden Ferdi , Slump Cornelis H. , van Leeuwen Ton G.
Published: September 2007

We present a method to generate quantitative cross-sectional maps of acoustic propagation speed in tissue using the photoacoustic principle. The method is based on the interaction of laser-induced ultrasound from an extraneous absorber with the object under photoacoustic investigation. The propagation times of the ultrasound transients through the object at angles around 360° are measured using a multielement ultrasound detector. The geometry lends itself to fan-beam reconstruction allowing speed-of-sound tomograms to be generated. Simultaneously, conventional photoacoustic computed tomography can be performed as well. We demonstrate the concept showing results on phantoms carrying speed-of-sound distributions.
A dynamic approach to liquid crystal simulations
Authors: Wan Jones T. K.
Published: September 2007

An efficient simulation scheme is proposed to determine liquid crystal configurations in complex physical environments. In this simulation scheme, liquid crystal elastic energy, electrostatic interaction, and the surface anchoring effect are calculated via a dynamic approach that is analogous to molecular dynamics simulation. As a result, various techniques that have been established for molecular dynamics are readily adopted in the proposed scheme. The method is demonstrated by calculating the director field of a liquid crystal interacting with a patchy pattern.
Small reversible axial-strain window for the critical current of a high performance Nb3Sn superconducting strand
Authors: Lu Xi Feng , Pragnell Stephen , Hampshire Damian P.
Published: September 2007

The engineering critical current density (JC) of a Nb3Sn restacked-rod-process superconducting strand is reported as a function of magnetic field (B⩽28T), applied axial strain (−0.9%⩽εA⩽0.2%), and temperature (4.2K⩽T⩽14K). Although the strain tolerance of JC is similar to other strands, the strain range over which JC is reversible is limited in both tension and compression. Samples were partially damaged when the intrinsic strain (εI) was increased from −0.74% to −0.97% in compression and grossly damaged when εI was only 0.13% in tension.
Effect of void propagation on bump resistance due to electromigration in flip-chip solder joints using Kelvin structure
Authors: Chang Y. W. , Chiang T. H. , Chen Chih
Published: September 2007

Three-dimensional modeling is employed to simulate various Kelvin structures for detecting the change in bump resistance due to void formation and propagation during electromigration in flip-chip solder joints. It is found that the Kelvin structures can sense the highest voltage drop when its voltage probes are placed at the current entrance into the bump on the chip side, and it is thus the most sensitive design to monitor void formation and propagation. When the bump resistance increases 20% of its initial value, the depletion percentage of contact opening ranges from 21.0% to 65.0%, depending on the position of the probes.
Fermi level pinning by defects in HfO2-metal gate stacks
Authors: Robertson J. , Sharia O. , Demkov A. A.
Published: September 2007

Various mechanisms for the Fermi level pinning of p-gate metals on HfO2 are analyzed in detail. It is found that for Fermi energies below the Si valence band, HfO2 can oxidize Si by creating positively charged O vacancies. The band bending due to this vacancy concentration can account for the observed Fermi level pinning of p metals on HfO2.
Evolution of InAs branches in InAs∕GaAs nanowire heterostructures
Authors: Paladugu M. , Zou J. , Auchterlonie G. J. , Guo Y. N. , Kim Y. , Joyce H. J. , Gao Q. , Tan H. H. , Jagadish C.
Published: September 2007

Branched nanowire heterostructures of InAs∕GaAs were observed during Au-assisted growth of InAs on GaAs nanowires. The evolution of these branches has been determined through detailed electron microscopy characterization with the following sequence: (1) in the initial stage of InAs growth, the Au droplet is observed to slide down the side of the GaAs nanowire, (2) the downward movement of Au nanoparticle later terminates when the nanoparticle encounters InAs growing radially on the GaAs nanowire sidewalls, and (3) with further supply of In and As vapor reactants, the Au nanoparticles assist the formation of InAs branches with a well-defined orientation relationship with GaAs∕InAs core/shell stems. We anticipate that these observations advance the understanding of the kink formation in axial nanowire heterostructures.
Element specific separation of bulk and interfacial magnetic hysteresis loops
Authors: Suszka A. K. , Kinane C. J. , Marrows C. H. , Hickey B. J. , Arena D. A. , Dvorak J. , Lamperti A. , Tanner B. K. , Langridge S.
Published: September 2007

We have studied the reversal of the bulk and interfacial magnetizations of the free layer of a spin valve using soft x-ray resonant magnetic scattering. By dusting the interface of the NiFe free layer with a few angströms of Co, we were able to distinguish between the interfacial and bulk magnetisms by tuning the x-ray photon energy. We measured hysteresis loops of reflected x-ray intensity at selected points in reciprocal space. We find no difference in the switching fields, showing that in transition metal ferromagnets, the exchange interactions are sufficiently strong to prevent a separate interfacial coercivity from arising.
A polymer-stabilized single-layer color cholesteric liquid crystal display with anisotropic reflection
Authors: Lu Shin-Ying , Chien Liang-Chy
Published: September 2007

The authors report a method of fabricating single-layer color cholesteric liquid crystal displays from a polymer-stabilized cholesteric liquid crystal. The reflective wavelength can be electrically switched to reflect blue or green from a cell initially reflecting a red color. The color change is a result of the compression to the helical pitches in planar layers in response to the applied voltage. The unique feature of the polymer stabilization is in the fact that the electrically switched colors preserve good reflectivity and the colors are reversible with voltage ramping. Conspicuously, the polymer-stabilized cholesteric display exhibits anisotropic reflection and has a temperature independent of reflected color.
Direct observation of Schottky to Ohmic transition in Al-diamond contacts using real-time photoelectron spectroscopy
Authors: Evans D. A. , Roberts O. R. , Vearey-Roberts A. R. , Langstaff D. P. , Twitchen D. J. , Schwitters M.
Published: September 2007

Real-time photoelectron spectroscopy and in situ electrical measurements have been applied to the formation of Al contacts on p-type diamond. At 294K, an initially uniform Al film induces band bending in the diamond consistent with the measured (current-voltage) barrier height of 1.05V. The temperature-induced transition to an Ohmic contact has been monitored in real time revealing a direct correlation between the onset of surface bonding at 755K and an abrupt change in surface band bending. The reaction temperature is lower than previously believed, and there is a second transition point at 1020K where the rates of change of both reaction and band bending increase sharply.
Tuning the contact resistance in nanoscale oligothiophene field effect transistors
Authors: Hoppe A. , Seekamp J. , Balster T. , Götz G. , Bäuerle P. , Wagner V.
Published: September 2007

Nanoscale organic transistors for high frequency applications are often limited by contact resistances. We report on tuning of those resistances by shifting the transport level for dihexyl-n-thiophene (DHnT) semiconductors by variation of the number of thiophenes n from 4 to 7. The intrinsic mobility as well as contact resistance were determined from individual transfer curves of bottom-contact transistors with channel lengths down to 50nm. Best values were found for DH7T with μ=0.12cm2∕Vs and Rc=1kΩcm. While the contact resistance remains fairly constant for a given n as expected, the intrinsic mobility still decreases with decreasing channel length.
Field-effect modulation of contact resistance between carbon nanotubes
Authors: Kodama Yoshihiro , Sato Ryota , Inami Nobuhito , Shikoh Eiji , Yamamoto Yoshiyuki , Hori Hidenobu , Kataura Hiromichi , Fujiwara Akihiko
Published: September 2007

Local transport properties of a carbon nanotube (CNT) thin-film transistor (TFT) have been investigated by conducting atomic force microscopy. The current in a CNT bundle is almost constant, whereas it drastically decreases at the contacts between CNTs. Current drops at the contacts are reduced with increasing negative gate voltage VG. The results show that the contact resistance between CNTs can be modified by VG, and the operation of CNT-TFT is mainly governed by the modulation of contact resistance.
Optical parametric generation in periodically poled KTiOPO4 via extended phase matching
Authors: Pu Ye , Wu Jie , Tsang Mankei , Psaltis Demetri
Published: September 2007

We report an experimental demonstration of optical parametric generation in a periodically poled KTiOPO4 crystal based on the principle of mirrorless optical parametric oscillation. A femtosecond pump pulse spectrally centered at 792nm from a Ti:sapphire amplifier is prechirped to minimize Kerr effects. The pump pulse is then injected into the nonlinear crystal and down converted to signal and idler pulses, approximately centered at 1584nm, via amplified spontaneous parametric down conversion in a copropagating type-II quasiphase matching configuration. The maximum internal downconversion efficiency is 43%, the highest ever reported for optical parametric generators based on KTiOPO4 crystals. Such a device may find applications in optical signal processing and biological imaging.
Coupling in concentric double quantum rings
Authors: Mühle A. , Wegscheider W. , Haug R. J.
Published: September 2007

We designed a device consisting of two concentric quantum rings in a GaAs∕AlGaAs heterostructure. The outer ring is connected to leads while the inner ring is only capacitively coupled to the rest of the system. Measuring electronic transport in a regime with strong coupling to the leads we found that the conductivity not only shows an Aharonov-Bohm effect with a periodicity fitting to the diameter of the outer ring but also another component matching the inner ring. This can be explained by magnetic-field dependent charge redistributions in the inner ring which affect the outer ring via Coulomb interaction.
Fano resonance mediated by intersubband-phonon coupling
Authors: Liu H. C. , Song C. Y. , Wasilewski Z. R. , Gupta J. A. , Buchanan M.
Published: September 2007

We present direct experimental evidence of Fano resonance mediated by intersubband and phonon coupling in a specially designed GaAs∕AlGaAs quantum-well infrared photodetector. This work presents an approach for realizing quantum interference in an artificially designed structure and opens possibilities for making use of Fano resonance in infrared devices.
Electron tunneling from quantum dots characterized by deep level transient spectroscopy
Authors: Engström O. , Kaniewska M. , Kaczmarczyk M. , Jung W.
Published: September 2007

Electron tunneling from InAs∕GaAs quantum dots has been studied by deep level transient spectroscopy (DLTS). Comparing DLTS data with theory, we demonstrate how the results can be interpreted for situations where the emission mechanism is pure tunneling. An illusory anomalous tunneling dependence on electric field is resolved by taking into account the energy level distribution originating from size fluctuations in the quantum dot ensemble.
Quantum cascade lasers operating from 1.2to1.6THz
Authors: Walther Christoph , Fischer Milan , Scalari Giacomo , Terazzi Romain , Hoyler Nicolas , Faist Jérôme
Published: September 2007

Two terahertz quantum cascade lasers based on GaAs∕Al0.1Ga0.9As heterostructures are reported. Pulsed mode operation up to 84K and continuous wave (cw) power of 0.36mW at 10K are demonstrated for the laser which emits from 1.34to1.58THz. The other laser shows emission from 1.2to1.32THz with pulsed mode operation up to 69K and cw power of 0.12mW at 10K.
Optoelectronic properties in quantum-confined germanium dots
Authors: Scarselli M. , Masala S. , Castrucci P. , De Crescenzi M. , Gatto E. , Venanzi M. , Karmous A. , Szkutnik P. D. , Ronda A. , Berbezier I.
Published: October 2007

Photocurrent generation of nanometric Ge dots has been investigated by using electrochemical measurements. Photocurrent features have been ascribed, for large Ge dots, to Ge bulk direct electronic transitions at L and X points as evidenced by their close correspondence with the optical absorption coefficient. A blueshift of the photocurrent features has been detected by reducing the Ge dot size. These changes have been interpreted as due to quantum confinement effect. This result suggests that Ge dots could be applied in photovoltaic nanodevices and quantum dot based lasers.
Design and characterization of GaN∕InGaN solar cells
Authors: Jani Omkar , Ferguson Ian , Honsberg Christiana , Kurtz Sarah
Published: September 2007

We experimentally demonstrate the III-V nitrides as a high-performance photovoltaic material with open-circuit voltages up to 2.4V and internal quantum efficiencies as high as 60%. GaN and high-band gap InGaN solar cells are designed by modifying PC1D software, grown by standard commercial metal-organic chemical vapor deposition, fabricated into devices of variable sizes and contact configurations, and characterized for material quality and performance. The material is primarily characterized by x-ray diffraction and photoluminescence to understand the implications of crystalline imperfections on photovoltaic performance. Two major challenges facing the III-V nitride photovoltaic technology are phase separation within the material and high-contact resistances.
Simplified experimental technique to extract the acoustic radiation induced static strain in solids
Authors: Thimmavajjula Narasimha Karthik , Kannan Elankumaran , Balasubramaniam Krishnan
Published: September 2007

A simplified experimental technique to measure the acoustic radiation induced static strain during the longitudinal acoustic wave propagation in solids is proposed. Experiments have been carried out to extract the static displacement (dc) component without resorting to electronic filters, as in the case of previously reported experimental measurements. This prevents the influence of the filter time response characteristics on the measurement. The dependence of the static displacement amplitude on the square of the fundamental amplitude of the input wave, its being independent of the burst width of the tone burst, and its abnormal variation at low input amplitudes are reported.
Epitaxial growth of AlN films on Rh ultraviolet mirrors
Authors: Inoue S. , Okamoto K. , Nakano T. , Ohta J. , Fujioka H.
Published: September 2007

Epitaxial growth of AlN films on mirror polished Rh(111) substrates, with high reflectivity in the ultraviolet (UV) region and high thermal conductivity, was demonstrated using a low temperature growth technique employing pulsed laser deposition. It was found that AlN(0001) grows epitaxially on Rh(111) at 450°C with an in-plane epitaxial relationship of AlN[112¯0]‖Rh[11¯0] Electron backscattering diffraction observations revealed that neither 30° rotational domains nor cubic phase domains were present in the AlN. X-ray reflectivity measurements revealed that no interfacial layer was present between the AlN films and Rh substrates and that the heterointerface was atomically abrupt, indicating that the Rh substrate still functioned as an UV mirror, even after AlN growth.
Indium selenide nanowire phase-change memory
Authors: Yu Bin , Ju Sanghyun , Sun Xuhui , Ng Garrick , Nguyen Thuc Dinh , Meyyappan M. , Janes David B.
Published: September 2007

Nonvolatile memory device using indium selenide nanowire as programmable resistive element was fabricated and its resistive switching property was studied as functions of electrical pulse width and voltage magnitude. The nanowire memory can be repeatedly switched between high-resistance (∼1011Ω) and low-resistance (∼6×105Ω) states which are attributed to amorphous and crystalline states, respectively. Once set to a specific state, the nanowire resistance is stable as measured at voltages up to 2V. This observation suggests that the nanowire can be programed into two distinct states with a large on-off resistance ratio of ∼105 with significant potential for nonvolatile information storage.
Effects of Ag content on the phase structure and piezoelectric properties of (K0.44−xNa0.52Li0.04Agx)(Nb0.91Ta0.05Sb0.04)O3 lead-free ceramics
Authors: Wu Jiagang , Wang Yuanyu , Xiao Dingquan , Zhu Jianguo , Pu Zhaohui
Published: September 2007

( K 0.44 − x Na 0.52 Li 0.04 Ag x ) ( Nb 0.91 Ta 0.05 Sb 0.04 ) O 3 lead-free piezoelectric ceramics were prepared by normal sintering. The effects of Ag content on the phase structure and piezoelectric properties of the ceramics were mainly studied. These results show that the phase structure undergoes a transition from orthorhombic to tetragonal phase with increasing x from 0.00 to 0.06. The optimum Ag content enhances the piezoelectric properties, and the Curie temperature increases with increasing x. The ceramics with x=0.02 exhibit enhanced electrical properties (d33∼263pC∕N, kp∼45.3%, TC∼353°C, εr∼1478, and tanδ∼2.3%) and good aging characteristics. These results show that the ceramic with x=0.02 is a promising lead-free piezoelectric material.
The rectification of radio-frequency signal by magnetic domain wall in a single-layered ferromagnetic nanowire
Authors: Yamaguchi A. , Miyajima H. , Ono T. , Suzuki Y. , Yuasa S.
Published: September 2007

The rectifying effect of a constant-wave radio frequency (rf) current by a magnetic domain wall (DW) in a single-layered ferromagnetic wire is presented. A direct-current (dc) voltage is generated by the spin torque diode effect, which is a consequence of magnetoresistance oscillation due to the resonant spin wave excitation induced by the spin-polarized rf current. The dc voltage spectrum strongly depends on the internal spin structure in the DW, which corresponds to the magnetic fingerprint of the spin structure in the ferromagnetic wire.
Understanding the switching-off mechanism in Ag+ migration based resistively switching model systems
Authors: Guo Xin , Schindler Christina , Menzel Stephan , Waser Rainer
Published: September 2007

Different coplanar Pt∕Ag structures were prepared by photolithography on SiO2 substrates, and Pt∕H2O∕Ag cells were formed by adding de-ionized H2O to the coplanar Pt∕Ag structures. The Pt∕H2O∕Ag cell is utilized here as a model system, due to the feasibility of visual inspection of the switching process. Bipolar switching was achieved for the cell. Scanning electron microscopy (SEM) investigations demonstrated that the growth and dissolution of Ag dendrites are responsible for the resistive switching. The Ag dendrite morphology is proposed to be the origin of the asymmetrical dissolution during the switching-off process, hence the bipolar nature of the switching characteristics.
InAs nanocrystals on SiO2∕Si by molecular beam epitaxy for memory applications
Authors: Hocevar Moïra , Regreny Philippe , Descamps Armel , Albertini David , Saint-Girons Guillaume , Souifi Abdelkader , Gendry Michel , Patriarche Gilles
Published: September 2007

We studied a memory structure based on InAs nanocrystals grown by molecular beam epitaxy directly on thermal SiO2 on silicon. Both nanocrystal diameter and density can be controlled by growth parameters. Transmission electron microscopy analysis shows high crystallinity and low size dispersion. In an electrical test structure with a 3.5nm tunnel oxide, we observed that 80% of the initial injected electrons remain stored in the InAs nanocrystals after 3months and that the retention time for electrons in InAs nanocrystals is four orders of magnitude higher than in silicon nanocrystals.
A double filtering method for measuring the translational velocity of fluorescently stained cells
Authors: Yasokawa Toshiki , Ishimaru Ichirou , Kuriyama Shigeki , Masaki Tsutomu , Takegawa Kaoru , Tanaka Naotaka
Published: September 2007

The authors propose a double filtering method to measure translational velocity for tracking fluorescently stained cells. This method employs two diffraction gratings installed in the infinity space through which the parallel pencil beam of the fluorescence passes. With this method, the change in light intensity whose period is proportional to the translational velocity of the sample can be obtained at the imaging surface. By using a sample that has a random distribution of fluorescence intensity, the authors verified that translational velocity measurements could be achieved using the proposed method.
Coulomb blockade in a Si channel gated by an Al single-electron transistor
Authors: Sun L. , Brown K. R. , Kane B. E.
Published: October 2007

We incorporate an Al–AlOx–Al single-electron transistor as the gate of a narrow (∼100nm) metal-oxide-semiconductor field-effect transistor (MOSFET). Near the MOSFET channel conductance threshold, we observe oscillations in the conductance associated with Coulomb blockade in the channel, revealing the formation of a Si single-electron transistor. Abrupt steps present in sweeps of the Al transistor conductance versus gate voltage are correlated with single-electron charging events in the Si transistor, and vice versa. Analysis of these correlations using a simple electrostatic model demonstrates that the two single-electron transistor islands are closely aligned, with an interisland capacitance approximately equal to 1∕3 of the total capacitance of the Si transistor island, indicating that the Si transistor is strongly coupled to the Al transistor.
Temperature dependence of current-voltage characteristics of npn-type GaN∕InGaN double heterojunction bipolar transistors
Authors: Nishikawa Atsushi , Kumakura Kazuhide , Makimoto Toshiki
Published: September 2007

We investigated the temperature dependence of the common-emitter current-voltage (I-V) characteristics of npn-type GaN∕InGaN double heterojunction bipolar transistors. Although the current gain decreases with increasing measurement temperature, the current gain measured at 300°C is still as high as 308. The reduction of the current gain with temperature is attributed not only to the hole back-injection current from the base into the emitter but also to the shorter minority carrier diffusion length due to the increase in the carrier concentration of the p-InGaN base.
Surface encapsulation for low-loss silicon photonics
Authors: Borselli M. , Johnson T. J. , Michael C. P. , Henry M. D. , Painter O.
Published: September 2007

Encapsulation layers are explored for passivating the surfaces of silicon to reduce optical absorption in the 1500nm wavelength band. Surface-sensitive test structures consisting of microdisk resonators are fabricated for this purpose. Based on previous work in silicon photovoltaics, coatings of SiNx and SiO2 are applied under varying deposition and annealing conditions. A short dry thermal oxidation followed by a long high-temperature N2 anneal is found to be most effective at long-term encapsulation and reduction of interface absorption. Minimization of the optical loss is attributed to simultaneous reduction in sub-band-gap silicon surface states and hydrogen in the capping material.
Midinfrared GaInSb∕AlGaInSb quantum well laser diodes grown on GaAs
Authors: Nash G. R. , Smith S. J. , Coomber S. D. , Przeslak S. , Andreev A. , Carrington P. , Yin M. , Krier A. , Buckle L. , Emeny M. T. , Ashley T.
Published: September 2007

The realization of midinfrared GaInSb∕AlGaInSb type I quantum well diode lasers grown on GaAs is reported. Lasing was observed up to 95K, at an emission wavelength of ∼3.5μm, threshold current density of 115A∕cm2, and with a characteristic temperature T0∼51K.
Modified (K0.5Na0.5)NbO3 based lead-free piezoelectrics with broad temperature usage range
Authors: Zhang Shujun , Xia Ru , Shrout Thomas R.
Published: September 2007

( K 0.5 Na 0.5 ) Nb O 3 (KNN) based lead-free materials exhibit arguably, comparable piezoelectric properties to conventional Pb(Zr,Ti)O3 ceramics owing to an orthorhombic to tetragonal polymorphic phase transition (TO-T) occurring near room temperature. However, this transition correspondingly results in a strong temperature dependence of the dielectric and piezoelectric properties, being limited further by domain instability, during thermal cycling between the two ferroelectric phases. Analogous to BaTiO3 based piezoelectrics, the addition of CaTiO3 in KNN materials was found to shift the TO-T well below room temperature. Piezoelectric and electromechanical values of KNN–LiSbO3–CaTiO3 material were found to be d33∼210pC∕N, d15∼268pC∕N and k33∼61%, k15∼56%, respectively, with greatly improved temperature stability over the temperature range of −50–200°C, demonstrating practical potential for actuator and/or ultrasonic transducer applications.
High electron mobility in nearly lattice-matched AlInN∕AlN∕GaN heterostructure field effect transistors
Authors: Xie Jinqiao , Ni Xianfeng , Wu Mo , Leach Jacob H. , Özgür Ümit , Morkoç Hadis
Published: September 2007

High electron mobility was achieved in Al1−xInxN∕AlN∕GaN (x=0.20–0.12) heterostructure field effect transistors (HFETs) grown by metal-organic chemical vapor deposition. Reduction of In composition from 20% to 12% increased the room temperature equivalent two-dimensional-electron-gas density from 0.90×1013to1.64×1013cm−2 with corresponding electron mobilities of 1600 and 1410cm2∕Vs, respectively. The 10K mobility reached 17600cm2∕Vs for the nearly lattice-matched Al0.82In0.18N∕AlN∕GaN heterostructure with a sheet carrier density of 9.6×1012cm−2. For comparison, the AlInN∕GaN heterostructure without the AlN spacer exhibited a high sheet carrier density (2.42×1013cm−2) with low mobility (120cm2∕Vs) at room temperature. The high mobility in our samples is in part attributed to ∼1nm AlN spacer which significantly reduces the alloy scattering as well as provides a smooth interface. The HFETs having gate dimensions of 1.5×40μm2 and a 5μm source-drain separation exhibited a maximum transconductance of ∼200mS∕mm with good pinch-off characteristics and over 10GHz current gain cutoff frequency.
Diffraction-limited phonon thermal conductance of nanoconstrictions
Authors: Prasher Ravi , Tong Tao , Majumdar Arun
Published: October 2007

Thermal transport across nanosized constrictions is calculated considering wave effects. It is shown that Rayleigh-type phonon diffraction reduces thermal transport across nanosized constrictions at low temperatures. We show that for aT∕vDebye<0.01×10−9Ks, where a is the radius of the constriction, T the temperature, and vDebye the Debye velocity of the solid material, diffraction effects are important.
Estimation of Mn4+ ion content ratio in self-doped compound La1−xMnO3−δ
Authors: Tang G. D. , Hou D. L. , Chen W. , Hao P. , Liu G. H. , Liu S. P. , Zhang X. L. , Xu L. Q.
Published: October 2007

A method based on the thermal equilibrium theory of crystal defects for estimating the Mn4+ ion content ratio (RM4) at B sites in ABO3 self-doped manganite La1−xMnO3−δ is presented. For this kind of manganite, the relationship between the Curie temperature (TC) and RM4 can be explained by the double exchange mechanism of Zener, which is similar to that in the perovskite manganite La1−xCaxMnO3.
Optical detection of anchoring at free and fluid surfaces using a nematic liquid crystal sensor
Authors: McCamley Maureen K. , Crawford Gregory P. , Ravnik Miha , Žumer Slobodan , Artenstein Andrew W. , Opal Steven M.
Published: October 2007

Polarizing micrographs of the free and fluid surfaces in contact with nematic liquid crystals were collected and compared with simulated textures to quantitatively understand surface anchoring direction and strength. Wells with square cross section and an open upper surface were filled with a nematic liquid crystal, and free energy calculations were performed to determine the existing structures and their corresponding simulated optical textures. Homeotropic, uniform planar, and degenerate planar anchorings were differentiated based on comparisons with simulations, and surface anchoring strength was estimated.
Magnetic patterning of (Ga,Mn)As by hydrogen passivation
Authors: Thevenard L. , Miard A. , Vila L. , Faini G. , Lemaître A. , Vernier N. , Ferré J. , Fusil S.
Published: October 2007

We present a method to create magnetic patterns in thin layers of (Ga,Mn)As. It relies on local hydrogen passivation to significantly lower the hole density, and thereby locally suppress the carrier-mediated ferromagnetic phase. The sample surface is thus maintained continuous, and the minimal structure size is of about 200nm. In micron-sized ferromagnetic dots fabricated by hydrogen passivation on perpendicularly magnetized layers, the switching fields can be maintained closer to the continuous film coercivity, compared to dots made by usual dry etch techniques.
Electrical conductivity of a bulk metallic glass composite
Authors: Wang K. , Fujita T. , Chen M. W. , Nieh T. G. , Okada H. , Koyama K. , Zhang W. , Inoue A.
Published: October 2007

The authors report the electrical conductivity of a bulk metallic glass (BMG) based composite fabricated by warm extrusion of a mixture of gas-atomized glassy powders and ductile α-brass powders. The conductivity of the BMG composite can be well modeled by the percolation theory and the critical percolation threshold volume of the high-conductive brass phase was estimated to be about 10%. It was found that the short irregular brass fibers can dramatically reduce the resistivity of the BMG, leading to an improved material with both high strength and good conductivity for functional applications.
Enhanced quality factors in aperiodic reflector resonators
Authors: Breeze Jonathan , Krupka Jerzy , Alford Neil McN
Published: October 2007

Cavity resonators that employ the high reflectivity of periodic arrays of dielectric layers exhibit enhanced quality factors compared with dielectric resonators. Their quality factor is limited by the exponential decay of the electric field penetrating the structure. We show that an aperiodic reflector array with dielectric layers thinner than a quarter-wave near the defect site and asymptotically approaching quarter-wave thickness distant from the site can exhibit very high quality factors. A spherical aperiodic reflector resonator consisting of nested alumina shells is simulated and shown to exhibit quality factors greater than 107 at 10GHz and room temperature.
Chimeric constructs endow the human CFTR Cl
−
channel with the gating behavior of murine CFTR
Authors: Scott-Ward Toby S. , Cai Zhiwei , Dawson Elizabeth S. , Doherty Ann , Carina Da Paula Ana , Davidson Heather , Porteous David J. , Wainwright Brandon J. , Amaral Margarida D. , Sheppard David N. , Boyd A. Christopher
Published: October 2007

The cystic fibrosis transmembrane conductance regulator (CFTR) is a Cl
−
channel gated by ATP-driven nucleotide-binding domain (NBD) dimerization. Here we exploit species differences between human and murine CFTR to investigate CFTR channel gating. Using homologous recombination, we constructed human-murine CFTR (hmCFTR) chimeras with sequences from NBD1, NBD2, or the regulatory domain (RD) of human CFTR replaced by the equivalent regions of murine CFTR. The gating behavior of hmRD and human CFTR were indistinguishable, whereas hmNBD1 and hmNBD2 had subtle effects on channel gating, prolonging both burst duration and interburst interval. By contrast, hmNBD1+2, containing both NBDs of murine CFTR, reproduced the gating behavior of the subconductance state of murine CFTR, which has dramatically prolonged channel openings. The CFTR potentiator pyrophosphate (PP
i
) enhanced human, hmRD, and hmNBD1 CFTR Cl
−
currents, but not those of hmNBD2, hmNBD1+2, and murine CFTR. By analyzing the rate-equilibrium free-energy relationships of chimeric channels, we obtained snapshots of the conformation of the NBDs during ATP-driven dimerization. Our data demonstrate that the conformation of NBD1 changes before that of NBD2 during channel opening. This finding suggests that NBD dimerization does not proceed by a symmetric tweezer-like motion, but instead in an asymmetric fashion led by NBD1. We conclude that the NBDs of murine CFTR determine the unique gating behavior of its subconductance state, whereas NBD2 controls channel potentiation by PP
i
.
Protein kinase C δ is essential for optimal macrophage-mediated phagosomal containment ofListeria monocytogenes
Authors: Schwegmann Anita , Guler Reto , Cutler Antony J. , Arendse Berenice , Horsnell William G. C. , Flemming Alexandra , Kottmann Andreas H. , Ryan Gregory , Hide Winston , Leitges Michael , Seoighe Cathal , Brombacher Frank
Published: October 2007

Activation of macrophages and subsequent “killing” effector functions against infectious pathogens are essential for the establishment of protective immunity. NF-IL6 is a transcription factor downstream of IFN-γ and TNF in the macrophage activation pathway required for bacterial killing. Comparison of microarray expression profiles ofListeria monocytogenes(LM)-infected macrophages from WT and NF-IL6-deficient mice enabled us to identify candidate genes downstream of NF-IL6 involved in the unknown pathways of LM killing independent of reactive oxygen intermediates and reactive nitrogen intermediates. One differentially expressed gene, PKCδ, had higher mRNA levels in the LM-infected NF-IL6-deficient macrophages as compared with WT. To define the role of PKCδ during listeriosis, we infected PKCδ-deficient mice with LM. PKCδ-deficient mice were highly susceptible to LM infection with increased bacterial burden and enhanced histopathology despite enhanced NF-IL6 mRNA expression. Subsequent studies in PKCδ-deficient macrophages demonstrated that, despite elevated levels of proinflammatory cytokines and NO production, increased escape of LM from the phagosome into the cytoplasm and uncontrolled bacterial growth occurred. Taken together these data identified PKCδ as a critical factor for confinement of LM within macrophage phagosomes.
CULTURE AND WORK ORGANIZATION: THE CHINESE CASE *
Authors: Chao Y.T.
Published: September 2007

This paper discusses the role of the indigenous values in facilitating the development of managerial and organizational systems underlying the success of indigenous enterprises in the newly industrialized societies. One illustration is the Chinese culture or, more specifically, the Confucian tradition and ethos, and their implication for management and worker performance in work organizations within the ‘Confucian league’ of Asian societies. The affective rational approach to the paternalistic style of the Japanese and Chinese management coupled with such normative values as trust, subtlety and loyalty of the employees explain the individuals' commitment to their work organization and the excellence in leadership. With reference to the leading steel plant, the China Steel Corporation in Taiwan, this paper examines how such a cherished system of managerial philosophy and practices, in the context of its indigenous Chinese cultural and normative heritage, has been successfully applied to the integration of its labour force, and the upgrading of their morale, performance and productivity.
MODERNIZATION OF THE CHINESE FAMILY BUSINESS
Authors: Hwang Kwang‐Kuo
Published: September 2007

In order to study the modernization of the Chinese family business, the contrast between formal rationality and substantive rationality was used to characterize significant features of Western culture and Chinese culture respectively. A theoretical model of Chinese social behaviors as influenced by the substantive ethics of Confucianism was adopted to describe the organizational behaviors which were frequently observed in Chinese family business. Several empirical studies comparing organizational climates as perceived by employees working in foreign‐invested business, private business with formal regulations, and family business were cited to support the argument that such Confucian virtues as loyalty to the organization, working hard, maintaining interpersonal harmony, etc., are most likely to be manifested in organizations where formal regulations of Western‐style management were enforced.
CHINESE VALUE SYSTEM AND MANAGERIAL BEHAVIOUR*
Authors: Jou Jacob Yih‐Heng , Sung Kai
Published: September 2007

This is a paper which reviews and discusses the implications of Chinese value systems for managerial behaviour in Taiwan. With a central assumption that managerial behaviour and styles are largely shaped by the values and normative systems of senior members of corporate management, a study of 43 industrial firms in Taiwan investigating their organisational structure and the managerial assumptions, values and other socio‐demographical features of their senior managers was conducted. The results of the research lead to the construction of a typology of four managerial patterns in Taiwan today, viz. the ‘grass‐roots’ type, the ‘Mainlander’ type, the ‘specialist’ type and the ‘transitional’ type. While the ‘transitional’ type is more or less by definition ‘transient’, a tendency is postulated by the authors for both the ‘grass‐roots’ and ‘Mainlander’ types to move gradually to converge with the ‘specialist’ type which will become increasingly widespread in Taiwan.