bluuebunny/crossref_metadata_2025 huggingface dataset:
Second-harmonic generation in two-dimensional periodically poled lithium niobate using second-order quasiphase matching
Authors: Ni Peigen , Ma Boqin , Wang Xuehua , Cheng Bingying , Zhang Daozhong
Published: June 2003

Two-dimensional nonlinear photonic crystals of lithium niobate with square lattices were fabricated. In these crystals, efficient quasiphase-matched second-harmonic generation was demonstrated by using second-order quasiphase matching. As a mode-locked Nd:yttritium–aluminum–garnet laser at 1064 nm with 35 ps pulse was used, we obtained an average power of 0.86 mW at 532 nm with 2.73 mW input, which corresponds to 42% internal conversion efficiency. The variations of second-harmonic output with crystal temperature and incident angle were measured. In addition, the relation between the second-harmonic output and reversed duty cycle was studied. All the experimental results are well consistent with simulations.
Self-embedded nanocrystalline chromium carbides on well-aligned carbon nanotips
Authors: Tsai C. L. , Hsu J. H. , Chen C. F.
Published: June 2003

Well-aligned carbon nanotips embedded with nanocrystalline chromium carbide were directly grown on a substrate by microwave plasma chemical vapor deposition. These nanomaterials grew up to about 1 μm long and 60 nm in diameter, yielding a high aspect ratio. In comparison between carbon nanotubes with hollow structure, transmission electron microscopy images show its solid body, which is made of graphite along with nanocrystalline chromium carbide on the tip. These nanomaterials perform well in field emission applications with a turn-on field of 1.38 V/μm and 565 μA/cm2 at 2.2 V/μm. Our result confirms the possibility of the self-embedded nanocrystalline materials on the top of carbon nanotips.
Phase shift ellipses for pulsating flows
Authors: Yakhot Alexander , Grinberg Leopold
Published: June 2003

A pulsating laminar flow of a viscous, incompressible fluid through a pipe with an orifice has been studied at relatively low Reynolds numbers. The motion is caused by an imposed sinusoidally varying pressure difference, Δp(t). The induced flow rate, Q(t), has a phase shift, φQ, with respect to the imposed pressure oscillations. We have used that a phase (x,y)-plane instantaneous state plot of two phase-shifted trajectories: x(t)=sin(ωt+φx) and y(t)=sin(ωl+φy), is an ellipse. The ellipses of the instantaneous states Q(t) vs Δp(t) during a cycle allow readily computing the phase shift, φQ.
Prediction of electrokinetic and pressure flow in a microchannel T-junction
Authors: MacInnes J. M. , Du X. , Allen R. W. K.
Published: June 2003

It is generally accepted that in simple microchannel flows the electrical double layer at walls is thin enough for “slip velocity” boundary conditions to be used with good approximation. Recent theoretical work by one of the authors has considered the limits of this approach in cases characterized by nonuniform liquid properties and complex channel geometries. In that work, the chemically reacting flow in an arbitrary channel geometry produced by electric potential and pressure differences with heat transfer and electrophoresis is considered. The present work undertakes a broad test of the model approach in a complex channel network geometry, in the case of nonreacting uniform-property liquid. Velocity is measured by particle tracking with correction for electrophoretic motion. Measured and predicted velocities in a three-dimensional experimental T-junction within a network of five channel segments are compared for three cases of steady flow including electrically driven flow, pressure-driven flow, and mixed pressure and electrical flow. All conditions of the experiment required to determine the flow uniquely have been measured. The computational methodology used combines local three-dimensional representation with overall circuit analysis of the channel network. Comparisons are found to be within the 5% experimental scatter of the velocity measurement method used. The work emphasizes the care required in fabrication, measurement, flow control, and numerical solution if prediction of actual fabricated devices is to be achieved.
Impact of drops of polymer solutions on small targets
Authors: Rozhkov A. , Prunet-Foch B. , Vignes-Adler M.
Published: June 2003

The collision of drops of polymer solutions with small targets was studied experimentally. The tested liquids were aqueous solutions of polyethylene oxide (MW=4 000 000) at concentrations of 10, 100, 1000 wt ppm. The drop impact velocity was about 3.5 m/s, and the drop diameters were in the range of 2.6–3.8 mm. The target was a stainless steel disk of 3.9 mm diameter. The collision was monitored by means of high-speed photography technique. As in the case of pure water, a circular liquid lamella was formed, and then it retracted with formation of outwards-directed secondary jets. There was no significant difference between the values of the maximum diameter and the retraction velocity of the lamella in the cases of water and polymeric liquids. On the contrary, the polymeric additives drastically changed the character of the lamella retraction. The secondary jets were transformed into thinning filaments submitted to elastic stresses with an attached droplet. Then, depending on the polymer concentration, the filaments ruptured and the attached droplets escaped, or the liquid filaments pulled the attached droplets back and the whole liquid returned to the target. A splashing threshold has been derived for polymeric liquids based on the liquid relaxation time and the impact conditions.
SiGe-free strained Si on insulator by wafer bonding and layer transfer
Authors: Langdo T. A. , Currie M. T. , Lochtefeld A. , Hammond R. , Carlin J. A. , Erdtmann M. , Braithwaite G. , Yang V. K. , Vineis C. J. , Badawi H. , Bulsara M. T.
Published: June 2003

SiGe-free strained Si on insulator substrates were fabricated by wafer bonding and hydrogen-induced layer transfer of strained Si grown on bulk relaxed Si0.68Ge0.32 graded layers. Raman spectroscopy shows that the 49-nm thick strained Si on insulator structure maintains a 1.15% tensile strain even after SiGe layer removal. The strain in the structure is thermally stable during 1000 °C anneals for at least 3 min, while more extreme thermal treatments at 1100 °C cause slight film relaxation. The fabrication of epitaxially defined, thin strained Si layers directly on a buried insulator forms an ideal platform for future generations of Si-based microelectronics.
Photocurrent noise in multi-quantum-well infrared photodetectors
Authors: Carbone A. , Introzzi R. , Liu H. C.
Published: June 2003

We report on photocurrent noise in AlGaAs/GaAs quantum-well infrared photodetectors having nominally the same design, except the number of wells N. The power spectral density does not scale as the inverse of the number of wells N in the presence of infrared radiation. These features can be understood by taking into account the nonlinearity arising at high infrared power as a consequence of the nonuniform potential distribution through the quantum-well structure.
Vortices on a cylinder
Authors: Haslam Michael C. , Mallier Roland
Published: June 2003

We consider flows on a cylinder and use a streamfunction formulation to derive a nonlinear equation governing steady-state flows in that geometry. Comparing this equation to the counterpart for plane flows allows us to write down vortex solutions for flow on a cylinder.
Lattice expansion in nanocrystalline niobium thin films
Authors: Banerjee R. , Sperling E. A. , Thompson G. B. , Fraser H. L. , Bose S. , Ayyub P.
Published: June 2003

High-purity nanocrystalline niobium (Nb) thin films have been deposited using high-pressure magnetron sputter deposition. Increasing the pressure of the sputtering gas during deposition has systematically led to reduced crystallite sizes in these films. Based on x-ray and electron diffraction results, it is observed that the nanocrystalline Nb films exhibit a significantly large lattice expansion with reduction in crystallite size. There is however, no change in the bcc crystal structure on reduction in crystallite size to below 5 nm. The lattice expansion in nanocrystalline Nb has been simulated by employing a recently proposed model based on linear elasticity and by appropriately modifying it to incorporate a crystallite-size-dependent width of the grain boundary.
Effect of Si delta doping on the luminescence properties of InP/InAlP quantum dots
Authors: Zhang X. B. , Heller R. D. , Noh M. S. , Dupuis R. D. , Walter G. , Holonyak N.
Published: June 2003

We show that the cathodoluminescence (CL) properties of InP quantum dots (QDs) grown on In0.5Al0.5P matrix layers, lattice-matched to (001) GaAs substrates, can be greatly improved by introducing silicon delta doping in the layer adjacent to the QDs. Under optimized conditions, the room-temperature CL intensity of QDs can be improved by ∼16 times. We speculate that the increased CL intensity is caused by the efficient capture of electrons from the reservoir of the delta-doped layer into the QDs, which, to some extent, counterbalances the thermal escape of electrons from the QDs. A temperature-dependent CL study of InP QDs grown without Si delta doping shows a quenching of the CL at high temperatures, which supports the unipolar escape of electrons from QDs, while delta-doped QDs show an anomalous behavior. The QD integrated CL intensity increases with temperature and then decreases after 200 K. This anomalous behavior is interpreted as caused by competition between two processes: (1) thermal activation of carriers out of the potential well introduced by delta doping and then capture by QDs, which enhances the CL intensity; and (2) quenching of the CL due to thermal activation of carriers out of the QDs.
Nanoscale polarization manipulation and conductance switching in ultrathin films of a ferroelectric copolymer
Authors: Qu Hongwei , Yao Wei , Garcia T. , Zhang Jiandi , Sorokin A. V. , Ducharme S. , Dowben P. A. , Fridkin V. M.
Published: June 2003

We report the direct observation of induced molecular reorientation on a ferroelectric copolymer with a scanning tunneling microscope (STM). Ultrathin copolymer films of vinylidene fluoride (70%) with trifluoroethylene (30%) revealed a quasihexagonal close-packing structure with long-range polymer chain ordering. By flipping the polarity of the STM tip bias voltage, a reversal of local polarization was observed through an apparent lattice shift and was accompanied by an asymmetric “diode-like” character in tunneling current I(V). These results clearly demonstrated conductance switching behavior on nanoscale with local polarization reversal.
Formation of ring patterns surrounded by ripples by single-shot laser irradiation with ultrashort pulse width at the solid/liquid interface
Authors: Katayama Kenji , Yonekubo Hideaki , Sawada Tsuguo
Published: June 2003

A single pulse (pulse width: 200 fs) was irradiated onto a water/silicon interface. The processed surface had many ring patterns surrounded by sinusoidal patterns within the irradiated spot. The diameter of their rings ranged from 500 nm to 10 μm. It was proposed that the oscillation of a bubble at the interface emitted an acoustic wave around itself and that the melted silicon surface, deformed due to acoustic pressure, solidified instantaneously in the course of the propagation of the acoustic wave on the silicon surface.
Interaction of two flapping filaments in a flowing soap film
Authors: Zhu Luoding , Peskin Charles S.
Published: June 2003

Using the immersed boundary method, we have simulated the motion of two flexible filaments in a flowing soap film, which was experimentally studied by Zhang et al. [Nature (London) 408, 835 (2000)]. We found numerically two distinct modes of sustained oscillation of the two filaments: parallel flapping and mirror-image clapping, depending on the separation distance between the two filaments. Our simulation results agree with that of the experiment at least qualitatively, even though the Reynolds number of the flowing soap film in our simulation is about two orders of magnitude lower than that of the experiment.
Low temperature single molecule spectroscopy using vibronic excitation and dispersed fluorescence detection
Authors: Kiraz Alper , Ehrl Moritz , Bräuchle Christoph , Zumbusch Andreas
Published: June 2003

We demonstrate vibronic excitation combined with spectrally resolved zero phonon line detection of single terrylenediimide (TDI) molecules in both the Shpol’skii matrix hexadecane and the polymer PMMA at cryogenic temperatures. Spectral jumps as large as 80 cm−1 are recorded with a 1 s time resolution. This technique does not require a weak electron–phonon coupling, and promises applications in spectroscopy of a wide-range of single nanostructures in amorphous hosts including fluorescing proteins. Vibronic excitation is also used to determine vibrational spectra of the excited state of single TDI molecules.
Experimental probing of the anisotropy of the empty p states near the Fermi level in MgB2
Authors: Klie R. F. , Zhu Y. , Schneider G. , Tafto J.
Published: June 2003

We have studied the boron K edge in the superconductor MgB2 by electron energy loss spectroscopy (EELS) and experimentally resolved the empty p states at the Fermi level that have previously been observed within an energy window of 0.8 eV by soft x-ray absorption spectroscopy. Using angular-resolved EELS, we find that these states at the immediate edge onset have pxy character in agreement with predictions from first-principle electronic structure calculations.
Epitaxial colossal magnetoresistive La0.67(Sr,Ca)0.33MnO3 films on Si
Authors: Kim J.-H. , Khartsev S. I. , Grishin A. M.
Published: June 2003

La 0.67 ( Sr,Ca ) 0.33 MnO 3 (LSCMO) films have been grown by a pulsed-laser deposition technique on Si(001) substrates buffered with Bi4Ti3O12/CeO2/yttrium-stabilized zirconia (YSZ) heteroepitaxial layers. X-ray diffraction has revealed cube-on-cube growth of an epitaxial Bi4Ti3O12/CeO2/YSZ/Si heterostructure whereas the LSCMO layer grows in the “diagonal-on-side” manner on top of the Bi4Ti3O12 (BTO) template. The maximum temperature coefficient of resistivity (TCR)=4.4% K−1 and colossal magnetoresistance (CMR) Δρ/ρ∼2.9% kOe−1 have been reached at 294 K. This was achieved due to the successive improvement of c-axis orientation of the layers: Full widths at half-maximum 0.65°, 0.58°, 0.65°, 1.13°, and 0.18° in LSCMO/BTO/CeO2/YSZ/Si stack, respectively. As a prototype of an uncooled bolometer, heteroepitaxial CMR structure on Si demonstrates, at 294 K, the noise equivalent temperature difference of 1.2 μK/√Hz@30 Hz.
Acoustic waves generated by a laser line pulse in a transversely isotropic cylinder
Authors: Pan Y. , Rossignol C. , Audoin B.
Published: June 2003

The acoustic field of a homogeneous and transversely isotropic cylinder generated by a laser line pulse in either ablation or thermoelastic regime is obtained theoretically. A two-dimensional Fourier transform is used to calculate the acoustic displacement at the cylinder surface. Experimental and theoretical normal displacements under either regime are obtained and compared for aluminum cylinders. Very good agreements are observed in the time, shape, and relative amplitude (i) of the cylindrical Rayleigh waves with different roundtrips and (ii) of the various longitudinal and transverse bulk waves propagating through the cylinder or reflected at the free circular surface.
Ferroelectric properties of (Ba0.5Sr0.5)TiO3/Pb(Zr0.52Ti0.48)O3/ (Ba0.5Sr0.5)TiO3 thin films with platinum electrodes
Authors: Yan Feng , Wang Yening , Chan Helen L. W. , Choy Chung Loong
Published: June 2003

Multilayered Pt/(Ba0.5Sr0.5)TiO3/Pb(Zr0.52Ti0.48)O3/(Ba0.5Sr0.5)TiO3/Pt (BST/PZT/BST) thin films with different thicknesses of the BST layers were prepared by the pulsed-laser deposition method. The existence of a BST layer between the PZT and Pt electrode can greatly improve the fatigue properties of the PZT film. However, the heterostructure with thicker BST layers exhibits lower remnant polarization because of a lower electric field applied on the PZT layer. So, the thickness of BST layers should be decreased to decrease the working voltage of the multilayered film. A heterostructure with very thin BST layers (thickness ∼7.5 nm) has good ferroelectric properties, such as high remnant polarization and rare fatigue resistance after 1010 switching cycles. A possible reason for the effect of BST is that the BST layer can absorb oxygen vacancies or other point defects from the PZT layer and greatly improve its fatigue properties.
Supercritical carbon dioxide extraction of porogens for the preparation of ultralow-dielectric-constant films
Authors: Rajagopalan T. , Lahlouh B. , Lubguban J. A. , Biswas N. , Gangopadhyay S. , Sun J. , Huang D. H. , Simon S. L. , Mallikarjunan A. , Kim H.-C. , Volksen W. , Toney M. F. , Huang E. , Rice P. M. , Delenia E. , Miller R. D.
Published: June 2003

Supercritical carbon dioxide extraction of poly(propylene glycol) porogen from poly(methylsilsesquioxane) (PMSSQ) cured to temperatures adequate to initiate matrix condensation, but still below the decomposition temperature of the porogen, is demonstrated to produce nanoporous, ultralow-dielectric-constant thin films. Both closed and open cell porous structures were prepared simply by varying the porogen load in the organic/inorganic hybrid films. 25 and 55 wt % porogen loads were investigated in the present work. Structural characterization of the samples conducted using transmission electron microscope, small angle x-ray scattering, and Fourier transform infrared spectroscopy, confirms the extraction of the porogen from the PMSSQ matrix at relatively low temperatures (⩽200 °C). The standard thermal decomposition process is performed at much higher temperatures (typically in the range of 400 °C–450 °C). The values of dielectric constants and refractive indices measured are in good agreement with the structural properties of these samples.
II–VI quantum dot formation induced by surface energy change of a strained layer
Authors: Tinjod F. , Gilles B. , Moehl S. , Kheng K. , Mariette H.
Published: June 2003

A method for growing self-assembled II–VI quantum dots (QDs) is demonstrated: A highly strained CdTe layer, grown onto Zn(Mg)Te, is covered with an amorphous Te layer which is then desorbed. This induces QD formation, observed as an abrupt change of both the reflection high-energy electron diffraction pattern and the surface morphology studied by atomic force microscopy in an ultrahigh vacuum. The dots are also characterized after capping by microphotoluminescence. This morphology transition, which occurs after and not during the growth, can be understood in terms of variation of the surface energy in presence of the group-VI element, which compensates for the natural trend toward plastic relaxation in II–VI compounds. This method shows the strong influence of the surface energy (and not just the lattice mismatch) in inducing the formation of coherent islands for mismatched systems having a low dislocation formation energy such as CdTe/ZnTe and CdSe/ZnSe.
Thickness dependence of the properties of epitaxial MgB2 thin films grown by hybrid physical-chemical vapor deposition
Authors: Pogrebnyakov A. V. , Redwing J. M. , Jones J. E. , Xi X. X. , Xu S. Y. , Li Qi , Vaithyanathan V. , Schlom D. G.
Published: June 2003

We have studied the effect of deposition rate and layer thickness on the properties of epitaxial MgB2 thin films grown by hybrid physical-chemical vapor deposition on 4H-SiC substrates. The MgB2 film deposition rate depends linearly on the concentration of B2H6 in the inlet gas mixture. We found that the superconducting and normal-state properties of the MgB2 films are determined by the film thickness, not by the deposition rate. When the film thickness was increased, the transition temperature Tc increased and the residual resistivity ρ0 decreased. Above 3000 Å, a Tc of 41.8 K, a ρ0 of 0.28 μΩ cm, and a residual resistance ratio RRR of over 30 were obtained.
Electron localization by self-assembled GaSb/GaAs quantum dots
Authors: Hayne M. , Maes J. , Bersier S. , Moshchalkov V. V. , Schliwa A. , Müller-Kirsch L. , Kapteyn C. , Heitz R. , Bimberg D.
Published: June 2003

We have studied the photoluminescence from type-II GaSb/GaAs self-assembled quantum dots in magnetic fields up to 50 T. Our results show that at low laser power, electrons are more weakly bound to the dots than to the wetting layer, but that at high laser power, the situation is reversed. We attribute this effect to an enhanced Coulomb interaction between a single electron and dots that are multiply charged with holes.
Strain-induced ordering in InxGa1−xN alloys
Authors: Teles L. K. , Ferreira L. G. , Leite J. R. , Scolfaro L. M. R. , Kharchenko A. , Husberg O. , As D. J. , Schikora D. , Lischka K.
Published: June 2003

The energetics and thermodynamic properties of cubic (c-)InxGa1−xN alloys are investigated by combining first-principles total energy calculations, a concentration-dependent cluster-based model, and Monte Carlo simulations. The search for the ground-state energies leads to the conclusion that biaxial strain suppresses phase separation, and acts as a driving force for chemical ordering in c-InxGa1−xN alloys. Ordered superlattice structures, with composition x≅0.5 and stable up to T=1000 K, arises as the relevant thermodynamic property of the strained alloy. We suggest that the In-rich phases recently observed by us in c-GaN/InxGa1−xN/GaN double heterostructures are ordered domains formed in the alloy layers due to biaxial strain.
Emissions from single localized states observed in ZnCdS ternary alloy mesa structures
Authors: Kumano H. , Hitaka Y. , Suemune I.
Published: June 2003

Sharp and discrete emission lines from single localized states in ZnCdS ternary alloys were clearly observed from selectively grown mesa structures. This is a demonstration that compound semiconductor alloy systems, which usually show broad emission spectra due to alloy fluctuations, are able to exhibit emissions from discrete energy levels with quasi-zero-dimensional density of states in limited mesa areas where limited number of deeper localized states will contribute. Introduction of ZnCdS/MgS short-period superlattices is found to play a significant role for the exciton migration enhancement from shallower to deeper localized states, which makes the observation of the emission lines from the single localized states possible in the ZnCdS alloy layers.
Selective modification of band gap in GaInNAs/GaAs structures by quantum-well intermixing
Authors: Macaluso R. , Sun H. D. , Dawson M. D. , Robert F. , Bryce A. C. , Marsh J. H. , Riechert H.
Published: June 2003

We report an investigation of selective quantum-well intermixing (QWI) in 1.3-μm GaInNAs/GaAs multi quantum wells by silica-cap-induced disordering processes. After thermal annealing under specific conditions, controlled shifts of band gap at room temperature of over 200 nm have been observed in sputtered SiO2-capped samples, while uncapped and SiO2-capped samples by plasma-enhanced chemical vapor deposition demonstrated negligible shift. This selective modification of the band gap in GaInNAs quantum wells has been confirmed by detailed photoluminescence and photoluminescence excitation spectroscopy, and by secondary ion mass spectrometry. The controlled tuning of the band gap of GaInNAs/GaAs by QWI is important for a wide range of photonic integrated circuits and advanced device applications.
Copper thin film of alternating textures
Authors: Huang Hanchen , Wei H. L. , Woo C. H. , Zhang X. X.
Published: June 2003

It is common for thin films to have a predominant texture, but not alternating textures. In this letter, we report a copper film of alternating textures through self-organization. Using dc magnetron sputtering technique, we deposit copper films on a SiO2/Si(111) substrate. A thin layer of copper of 〈111〉 texture is first developed, and another thin layer of 〈110〉 ensued. As deposition continues, a third layer of copper of 〈111〉 texture is formed on the top, leading to a sandwich copper thin film of alternating 〈111〉 and 〈110〉 textures. The film morphology is characterized with scanning electron microscopy and atomic force microscopy and the texture with x-ray diffraction. Based on anisotropic elastic analyses and molecular dynamics simulations, we propose a model of texture evolution during the formation of multilayers, attributing the texture evolution to the competition of surface and strain energies.
Flexible organic field-effect transistors fabricated by the electrode-peeling transfer with an assist of self-assembled monolayer
Authors: Fujita Katsuhiko , Yasuda Takeshi , Tsutsui Tetsuo
Published: June 2003

We propose a way to fabricate a flexible organic field-effect transistor: an electrode-peeling transfer method. In this method, source–drain metal electrodes were formed finely on rigid temporary substrate, where a micropatterning process such as photolithography is applicable. The electrodes were treated with an alkane thiol to form a self-assembled monolayer followed by complete covering of the temporary substrate via chemical vapor deposition of an organic dielectric layer. After the gate electrode was deposited on the top, the multilayer of the source–drain electrodes/dielectric layer/gate electrode was peeled off from the temporary substrate by an adhesive Scotch tape substrate without deletion. The peeling-transfer was completed with an assist of a self-assembled monolayer as a connecting buffer layer between the electrodes and the dielectric layer. Any organic semiconductor materials can be deposited on freshly peeled-off surface of the flexible substrate. In the present case, pentacene was used as the semiconductor material. It showed a hole mobility exceeding 0.1 cm2/V s even after the substrate was rolled.
Surface band-bending effects on the optical properties of indium gallium nitride multiple quantum wells
Authors: Peng L.-H. , Shih C.-W. , Lai C.-M. , Chuo C.-C. , Chyi J.-I.
Published: June 2003

We report the use of selective wavelength excitation to examine the surface band-bending effects on the optical properties of 3.0-nm-thick indium gallium nitride (InGaN) multiple quantum wells (MQWs). Under a 355-nm excitation, the In0.18Ga0.82N well emission exhibits a linear dependence on the injected carrier density (Ninj) with a coefficient of (i) 8.5×10−18 meV cm3 for the spectral blueshift and (ii) 3×10−14 V cm2 for the change of internal field at a density up to Ninj∼1019 cm−3 at 77 K. When excited by a shorter wavelength at 248 nm, the emission from the thin GaN cap layer quenches, but that from the InGaN wells prevails. These observations are attributed to the transportation of photogenerated carriers from the bent GaN surface and redistribution in the InGaN wells. By solving the rate and Poisson equations with a Fermi-level pinning in the band-structure analysis, the emission from the InGaN/GaN MQWs is shown dominant by the recombination between the high-lying subbands and the screening of internal field effects.
CuO-doped SnO2 thin films as hydrogen sulfide gas sensor
Authors: Khanna Atul , Kumar Rajesh , Bhatti S. S.
Published: June 2003

CuO-loaded SnO2 element was earlier identified as a highly sensitive and selective H2S gas sensor. A number of techniques have been used by different authors for preparing thick and thin films of SnO2 doped with CuO, which among various metal oxides has outstanding promoter action for the sensitive detection of H2S by SnO2. Here we report the growth and characterization of CuO-doped SnO2 thin films by a thermal evaporation technique. These thin films show an extremely high sensitivity of ∼106 to few parts per million levels of H2S gas in air. The gas sensor is characterized at four operating temperatures and its long-term stability in response to H2S gas is tested over a period of 3 years.
Void-mediated formation of Sn quantum dots in a Si matrix
Authors: Lei Y. , Möck P. , Topuria T. , Browning N. D. , Ragan R. , Min K. S. , Atwater H. A.
Published: June 2003

Atomic scale analysis of Sn quantum dots (QDs) formed during the molecular beam-epitaxy (MBE) growth of SnxSi1−x (0.05⩽x⩽0.1) multilayers in a Si matrix revealed a void-mediated formation mechanism. Voids below the Si surface are induced by the lattice mismatch strain between SnxSi1−x layers and Si, taking on their equilibrium tetrakaidecahedron shape. The diffusion of Sn atoms into these voids leads to an initial rapid coarsening of quantum dots during annealing. Since this formation process is not restricted to Sn, a method to grow QDs may be developed by controlling the formation of voids and the diffusion of materials into these voids during MBE growth.
White organic light-emitting devices using a phosphorescent sensitizer
Authors: Cheng Gang , Li Feng , Duan Yu , Feng Jing , Liu Shiyong , Qiu Song , Lin Dong , Ma Yuguang , Lee S. T.
Published: June 2003

The efficiency of white organic light-emitting devices has been improved dramatically by the introduction of a phosphorescent material, fac tris (2-phenylpyridine) iridium [Ir(ppy)3] as a sensitizer. Ir(ppy)3 and 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl) are codoped into 4,4′-N,N′-dicarbazole-biphenyl (CBP) host. The chromaticity of white emission can be tuned by adjusting the thickness of the codoped CBP layer or the concentration of Ir(ppy)3. The luminance efficiency of these devices is affected at the same time due to the severe difference in efficiency between the two primary emission peaks.
Bioceramic hydroxyapatite at high pressures
Authors: Velisavljevic Nenad , Vohra Yogesh K.
Published: June 2003

A bioceramic hydroxyapatite, Ca10(PO4)6(OH)2 polycrystalline sample was studied under high pressures in a diamond anvil cell to investigate its structural, electrical, and mechanical properties under compression. Anisotropic compression effects were observed in x-ray diffraction studies below 8 GPa. Nanoindentation hardness measurements on pressure-treated hydroxyapatite samples show hardness value of 4.0±0.5 GPa which is comparable to the plasma-sprayed samples. Electrical studies show that the bioceramic sample retained its insulating properties to 65 GPa. The present studies demonstrate that a fully dense and translucent hydroxyapatite sample is attained above 10 GPa at 300 K.
Schottky nanocontacts on ZnO nanorod arrays
Authors: Park W. I. , Yi Gyu-Chul , Kim J.-W. , Park S.-M.
Published: June 2003

We report on fabrication and electrical characteristics of ZnO nanorod Schottky diode arrays. High quality ZnO nanorods were grown for the fabrication of the Schottky diodes using noncatalytic metalorganic vapor phase epitaxy and Au was evaporated on the tips of the vertically well-aligned ZnO nanorods. I–V characteristics of both bare ZnO and Au/ZnO heterostructure nanorod arrays were measured using current-sensing atomic force microscopy. Although both nanorods exhibited nonlinear and asymmetric I–V characteristic curves, Au/ZnO heterostructure nanorods demonstrated much improved electrical characteristics: the reverse-bias breakdown voltage was improved from −3 to −8 V by capping a Au layer on the nanorod tips. The origin of the enhanced electrical characteristics for the heterostructure nanorods is suggested.
Experimental synthesis of fiber Bragg gratings using optical low coherence reflectometry
Authors: Chapeleau Xavier , Leduc Dominique , Lupi Cyril , Le Ny Roger , Douay Marc , Niay Pierre , Boisrobert Christian
Published: June 2003

We apply a combination of optical low coherence reflectometry and a layer-peeling method to the synthesis of a fiber grating. The index modulation amplitude we obtain is compared with a Krug measurement result and the dc refractive index is derived from the phase measurement.
Vortex ring pinchoff in the presence of simultaneously initiated uniform background co-flow
Authors: Krueger Paul S. , Dabiri John O. , Gharib Morteza
Published: June 2003

Vortex rings were formed with a piston-cylinder mechanism in the presence of uniform background co-flow supplied through a shroud surrounding the cylinder. The jet and co-flow were started simultaneously. Ratios of the co-flow to jet velocity (Rv) in the range 0–1 were considered. The formation number (F) as a function of Rv was determined using the procedure of Gharib et al. [J. Fluid Mech. 360, 121 (1998)] and a generalized definition of formation time. The results show a sharp decrease in F as Rv increases from 0.5–0.75, suggesting possible performance limitations for pulsed-jet propulsion.
Controlled self-assembly of semiconductor quantum dots using shadow masks
Authors: Schallenberg T. , Borzenko T. , Schmidt G. , Obert M. , Bacher G. , Schumacher C. , Karczewski G. , Molenkamp L. W. , Rodt S. , Heitz R. , Bimberg D.
Published: June 2003

An effective method for controlling the position and number of self-assembled quantum dots (QDs) grown by molecular-beam epitaxy has been developed. Epitaxially grown shadow masks are used to realize selective area growth, which exploits different incidence angles of the molecular beams. We applied this method to control the position and number of self-assembled CdSe QDs in a ZnSe matrix. Bright cathodoluminescence shows the presence of regularly distributed ensembles of QDs and that single QDs can be reliably grown.
Metal–oxide–semiconductor devices using Ga2O3 dielectrics on n-type GaN
Authors: Lee Ching-Ting , Chen Hong-Wei , Lee Hsin-Ying
Published: June 2003

Using a photoelectrochemical method involving a He–Cd laser, Ga2O3 oxide layers were directly grown on n-type GaN. We demonstrated the performance of the resultant metal–oxide–semiconductor devices based on the grown Ga2O3 layer. An extremely low reverse leakage current of 200 pA was achieved when devices operated at −20 V. Furthermore, high forward and reverse breakdown electric fields of 2.80 MV/cm and 5.70 MV/cm, respectively, were obtained. Using a photoassisted current–voltage method, a low interface state density of 2.53×1011 cm−2 eV−1 was estimated. The varactor devices permit formation of inversion layers, so that they may be applied for the fabrication of metal–oxide–semiconductor field-effect transistors.
Gain switching of an external cavity grating-coupled surface emitting laser with wide tunability
Authors: Hu Y. , Gubenko A. , Venus G. , Gadjiev I. , Il’inskaja N. , Nesterov S. , Portnoi E. , Dubov M. , Khrushchev I.
Published: June 2003

Gain-switched, single frequency operation of an external cavity grating-coupled surface emitting laser with a wavelength tuning range of 100 nm is presented. A short pulse duration of 41 ps and a high peak power of 0.88 W have been obtained.
Quantum design and synthesis of a boron–oxygen–yttrium phase
Authors: Music Denis , Chirita Valeriu , Kreissig Ulrich , Czigány Zsolt , Schneider Jochen M. , Helmersson Ulf
Published: June 2003

Ab initio calculations are used to design a crystalline boron–oxygen–yttrium (BOY) phase. The essential constituent is yttrium substituting for oxygen in the boron suboxide structure (BO0.17) with Y/B and O/B ratios of 0.07. The calculations predict that the BOY phase is 0.36 eV/atom more stable than crystalline BO0.17 and experiments confirm the formation of crystalline thin films. The BOY phase was synthesized with reactive rf magnetron sputtering and identified with x-ray and selected area electron diffraction. Films with Y/B ratios ranging from 0.10 to 0.32, as determined via elastic recoil detection analysis, were grown over a wide range of temperatures (300–600 °C) and found to withstand 1000 °C.
Fabrication of monodispersive FePt nanoparticle films stabilized on rigid substrates
Authors: Yu Andrew C. C. , Mizuno Mikihisa , Sasaki Yuichi , Inoue Makoto , Kondo Hirofumi , Ohta Ippei , Djayaprawira David , Takahashi Migaku
Published: June 2003

Monodispersive FePt nanoparticle films can be stabilized firmly on rigid Si substrates using amino-functional silane, such as [3-(2-aminoethlyamino) propyl]trimethoxysilane, as a coupling layer. The Si substrate/SiO2/APTS/FePt nanoparticles heterostructure was confirmed using high-resolution electron microscopy (HREM). The HREM result agreed well with the x-ray reflectivity measurement upon the individual layer thickness. The as-made superparamagnetic FePt nanoparticle film transformed from chemically disordered fcc structure to chemically ordered L10 phase upon annealing at 800 °C for 30 min under a vacuum of 10−8 Torr. Plan-view high-resolution scanning electron microscopy (HRSEM) observation indicated that under high-vacuum annealing, coalescence of the monodispersive nanoparticle film was not significant. The HRSEM result was consistent with the in-plane x-ray diffractometry measurement, in which sharpening of the diffraction peaks occurred only very slightly for the annealed films.
Theory of avalanche multiplication and excess noise in quantum-well infrared photodetectors
Authors: Schneider Harald
Published: June 2003

A theoretical treatment of the noise current of quantum-well infrared photodetectors in the presence of avalanche multiplication is presented. Avalanche multiplication results in a characteristic excess noise which is expressed as a function of the avalanche multiplication factor and the capture probability. The multiplication factor can thus be determined from the photoconductive gain and the noise gain.
Comparison of an Australian food-frequency questionnaire with diet records: implications for nutrition surveillance
Authors: Ambrosini GL , Mackerras D , de Klerk NH , Musk AW
Published: June 2003

Objectives:

To compare a widely used Australian food-frequency questionnaire (FFQ) with diet records and consider the results in relation to its use in nutrition surveillance.

Design:

Inter-method reliability study.

Setting:

A randomised trial in subjects with past asbestos exposure.

Subjects:

Seventy-two adults living in Western Australia.

Methods:

A semi-quantitative FFQ developed by the Commonwealth Scientific Industrial Research Organisation in South Australia was administered after the completion of four 7-day diet records (DRs).

Results:

Mean agreement between methods was not significantly different from 100% for many nutrients, but the limits of agreement indicated that, at the individual level, the FFQ over- or underestimated the DR by at least 50%. Mean agreement between methods decreased significantly with increasing intakes for the majority of nutrients. Pearson's correlation coefficients were less informative indicators of agreement compared with the limits of agreement.

Conclusions:

These results indicate poor agreement between the FFQ and DR when estimating absolute intakes. Therefore, comparing intakes collected using this FFQ with specific cut-off points such as Recommended Dietary Intakes for nutrition surveillance may lead to seriously flawed conclusions about population intakes.
Seasonal misclassification error and magnitude of true between-person variation in dietary nutrient intake: a random coefficients analysis and implications for the Japan Public Health Center (JPHC) Cohort Study
Authors: Fahey Michael T , Sasaki Satoshi , Kobayashi Minatsu , Akabane Masayuki , Tsugane Shoichiro
Published: June 2003

Objective:

We examine (1) the extent to which seasonal diet assessments correctly classify individuals with respect to their usual nutrient intake, and (2) whether the magnitude of true variation in intake between individuals is seasonal. These effects could lead, respectively, to bias in estimates of relative risk for associations between usual nutrient exposure and disease, and to an increase in required sample size.

Subjects and setting:

One hundred and twenty-seven families in four regions of the Japan Public Health Center (JPHC) Cohort Study.

Design:

On average, 48 weighed daily food records were collected per family over six seasons of 1994 and 1995.

Results:

A random slopes regression model was used to predict the correlation between seasonal and annual average intakes, and to estimate true between-person variation in intakes by season. Mean vitamin C intake was greatest in summer and autumn, and seasonal variation was attributable to the consumption of fruit and vegetables. Predicted correlations between seasonal and annual average vitamin C intake ranged from 0.62 to 0.87, with greatest correlations in summer and autumn. True between-person variation in vitamin C intake was also strongly seasonal, ranging from 45 to 78% of total variance, and was again greatest in summer and autumn. These effects were less seasonal among energy and 13 other nutrients.

Conclusions:

It may be possible substantially to reduce both seasonal misclassification of individuals with respect to their usual vitamin C intake, and required sample size, by asking subjects to report high-season intake of fruit and vegetables in the JPHC Study.
Yoghurt in the Spanish diet: nutritional implications and socio-cultural aspects of its consumption
Authors: Capdevila Francesca , Martí-Henneberg Carles , Closa Ricardo , Subías Joaquín Escribano , Fernández-Ballart Joan
Published: June 2003

Objectives:

This study aims to analyse the differences, with regard to socio-cultural characteristics and dietary habits, between low and high consumers of yoghurt and other fermented dairy product desserts, and the nutritional significance of these differences.

Methods:

We analysed the diet of a healthy population (4–65 years), using the 24-hour recall method, on three non-consecutive days. The participants were grouped by age and sex and were also divided into tertiles on the basis of yoghurt consumption. We compared energy and nutrient intakes, educational level and socio-economic status in the low consumption (LC) group and the high consumption (HC) group.

Results:

In general there were no significant differences in energy intake or nutritional profile between LC and HC groups. The only significant difference was in the percentage of energy provided by lipids, which was significantly lower in HC women, possibly due to the high number of women in this group who consumed low-fat yoghurt. There were significant differences in the distribution of HC and LC subjects according to the three educational levels (P < 0.05) but n according to socio-economic status.

Conclusion:

The fact of being a high consumer of fermented dairy products took place in the framework of other dietary changes that compensated for this high consumption, resulting in the absence of significant differences in energy intake and nutritional profile between HC and LC subjects. The only exception was found in women who consumed low-fat dairy products. There was a relationship between high consumption of fermented dairy products and educational level.
Misclassification associated with measurement error in the assessment of dietary intake
Authors: de Moor Carl , Baranowski Tom , Cullen Karen W , Nicklas Theresa
Published: June 2003

Objective:

Dietary assessment has been used for certification to receive food supplements or other nutrition services and to provide feedback for educational purposes. The proportion of individuals correctly certified as eligible is a function of the amount of error that exists in the dietary measures and the level of dietary intake used to establish eligibility. Whether individuals are correctly counselled to increase or decrease the consumption of selected foods or nutrients is a function of the same factors. It is not clear, however, what percentage of individuals would be correctly classified under what circumstances. The objective of this study is to demonstrate the extent to which measurement error and eligibility criteria affect the accuracy of classification.

Design:

Hypothetical distributions of dietary intake were generated with varying degrees of measurement error. Different eligibility criteria were applied and the expected classification rates were determined using numerical methods.

Setting and subjects:

Simulation study.

Results:

Cut points of dietary intake at decreasing levels below the 50th percentile of true intake were associated with lower sensitivity and predictive value positive rates, but higher specificity and predictive value negative rates. The correct classification rates were lower when two cut points of dietary intake were used. Using a single cut point that was higher than the targeted true consumption resulted in higher sensitivity but lower predictive value positive, and lower specificity but higher predictive value negative.

Conclusions:

Current methods of dietary assessment may not be reliable enough to attain acceptable levels of correct classification. Policy-makers and educators must consider how much misclassification error they are willing to accept and determine whether more intensive methods are necessary.
Physical activity monitoring in Europe. The European Physical Activity Surveillance System (EUPASS) approach and indicator testing
Authors: Rütten A , Vuillemin A , Ooijendijk WTM , Schena F , Sjöström M , Stahl T , Vanden Auweele Y , Welshman J , Ziemainz H
Published: June 2003

Objectives:

The main objective of this paper is to describe the approach and specific findings of the European Physical Activity Surveillance System (EUPASS) research project. In particular, the analysis presented aims at testing the reliability, comparability and predictive power of different sets of physical activity (PA) indicators.

Design:

First, a panel study based on computer-aided telephone interview (CATI) was designed to report PA data of a representative, selected group of about 100 persons per country at three points in time. Second, a CATI time series survey was carried out with the goal of realising about 100 interviews per month over six consecutive months.

Setting:

The project was carried out in eight European countries to support the development of the European Union's (EU) Health Monitoring Programme.

Subjects:

Random population samples (subjects aged 18 years and older) were drawn from each participating country.

Results:

While many PA indicators used in EU countries to date as well as the psychosocial and environmental measures tested in the present study had acceptable to good reliability coefficients, the test–retest reliability scores of the International Physical Activity Questionnaire (IPAQ) version tested (the short (last 7 days) telephone interview IPAQ; IPAQ-S7T) were rather low. The comparability between extant national PA items and the IPAQ-S7T was low for all countries. The strongest predictors of perceived health were the psychosocial and environmental PA indicators.

Conclusions:

According to the results of the present study, more research is needed to further investigate and improve the quality of the IPAQ. In addition, the specific predictive power of the tested psychosocial and environmental PA indicators on perceived health should be of particular interest for designing health surveillance activities in the future.