bluuebunny/crossref_metadata_2025 huggingface dataset:
Combinatorial synthesis and high throughput evaluation of ferroelectric/dielectric thin-film libraries for microwave applications
Authors: Chang H. , Gao C. , Takeuchi I. , Yoo Y. , Wang J. , Schultz P. G. , Xiang X.-D. , Sharma R. P. , Downes M. , Venkatesan T.
Published: July 2002

A library of 256 differently doped thin films of (BaxSr1−x)TiO3 (where 0.5<x<1.0) was generated on a 1 in.×1 in. LaAlO3 substrate using multistep thin-film deposition techniques together with a quaternary masking strategy. Appropriate postannealing processing afforded high-quality epitaxial thin films. The microwave properties, i.e., dielectric constant and loss tangent, of samples in the library were characterized with a scanning-tip microwave near-field microscope at 1 GHz, and the results were found to be consistent with measurements made with interdigital electrodes. Specific dopants were found to significantly affect the dielectric constant and tangent loss. Tungsten, in particular, reduces the tangent loss.
Lasing mechanism of InGaN/GaN/AlGaN multiquantum well laser diode
Authors: Domen K. , Kuramata A. , Tanahashi T.
Published: July 2002

We investigated the lasing mechanism of an InGaN/GaN/AlGaN multiquantum well (MQW) laser diode on SiC grown by low-pressure metalorganic vapor phase epitaxy. Surface emission and edge emission are compared by optical pumping on the laser chip for which electrical pumping was made. Excitation power dependence of photoluminescence (PL) and PL mapping are also taken on the same chip. From the results, we demonstrate that lasing phenomena in our laser are dominated by free carriers and that the observed various stimulated emission lines are caused by the inhomogeneity of the InGaN MQW.
Film thickness and composition monitoring during growth by molecular beam epitaxy using alpha particle energy loss
Authors: Beaudoin M. , Adamcyk M. , Gelbart Z. , Giesen U. , Kelson I. , Levy Y. , MacKenzie J. A. , Tiedje T.
Published: July 2002

The α-particle energy loss method (AEL) has been implemented in situ to monitor film thickness during growth by molecular beam epitaxy. For InP and GaAs substrates recoil implanted with α-particle emitters, we have been able to measure thickness and composition of deposited GaAs, AlGaAs and InGaAs in real time. The AEL method yields in situ real time results comparable in accuracy to those obtained by ex situ scanning electron microscope and high-resolution x-ray diffraction measurements.
SrCu
2
O
2
:
A p-type conductive oxide with wide band gap
Authors: Kudo Atsushi , Yanagi Hiroshi , Hosono Hideo , Kawazoe Hiroshi
Published: July 2002

SrCu 2 O 2 thin films were prepared on SiO2 glass substrates by pulsed laser deposition. The film deposited in O2 atmosphere of 7×10−4 Pa at 573 K showed high optical transmission in visible and near-infrared regions. Potassium was doped at Sr site for substitutional doping. The optical band gap of the K-doped film was estimated to be ∼3.3 eV. The dc electrical conductivity of the K-doped film at 300 K was 4.8×10−2 S cm−1 and the activation energy was 0.10 eV. Positive sign of Seebeck and Hall coefficients demonstrated the p-type conduction of the film. Hole concentration and mobility at 300 K were 6.1×1017 cm−3 and 0.46 cm2 V−1 s−1, respectively.
High-finesse disk microcavity based on a circular Bragg reflector
Authors: Labilloy D. , Benisty H. , Weisbuch C. , Krauss T. F. , Smith C. J. M. , Houdré R. , Oesterle U.
Published: July 2002

We made disk-shaped microcavities of approximately 10 μm2 in area in a GaAs/AlGaAs waveguide structure by etching deep vertical concentric trenches. The trenches form a circular Bragg-like reflector that confines light in the remaining two lateral dimensions. We demonstrate from photoluminescence excited in the waveguide the confinement of discrete disk modes whose wave vector is mainly radial, in contrast with whispering gallery modes. Their quality factors up to Q=650 indicate in-plane reflectivities approaching 90%. In the near infrared, this represents a demonstration of wavelength-scale light confinement based on photonic crystal effects in two dimensions.
Optical data storage in C60 doped polystyrene film by photo-oxidation
Authors: Xia A. D. , Wada S. , Tashiro H.
Published: July 2002

A potential application of C60 for three-dimensional optical data storage in read only memory recorded by photo-oxidation is investigated. Photo-oxidation significantly enhances the fluorescence intensity of C60 molecules; therefore, one bit data can be recorded by the photo-oxidation of C60 doped polystyrene film at individual points by a focused laser beam and be read nondestructively as a brilliant fluorescence spot, in contrast to the nonoxidized areas after photo-oxidation is blocked. This enables three-dimensional recording using a laser scanning microscope. As a result, a pattern consisting of three layers of bit data was written and read in a C60 doped polystyrene film. We also discuss the time course of photo-oxidation of C60.
Temperature-induced changes in photopolymer volume holograms
Authors: Dhar Lisa , Schnoes Melinda G. , Wysocki Theresa L. , Bair Harvey , Schilling Marcia , Boyd Carol
Published: July 2002

Temperature-induced distortions of plane-wave holographic gratings recorded in low glass transition temperature (Tg∼26 °C) photopolymer media were measured. Changes in temperature affect the refractive index and dimensions of photopolymer materials, thereby rotating the angular Bragg selectivity of recorded volume holograms. From temperature-dependent measurements on a set of angularly multiplexed holograms, the out-of-plane coefficient of thermal expansion of a thin photopolymer film constrained between two rigid glass substrates is found to be 500 ppm/°C. These experiments suggest that the temperature sensitivity of photopolymer volume holograms may limit their use in many applications.
Charge stability of pulsed-laser deposited polytetrafluoroethylene film electrets
Authors: Schwödiauer Reinhard , Bauer-Gogonea Simona , Bauer Siegfried , Heitz Johannes , Arenholz Enno , Bäuerle Dieter
Published: July 2002

Pulsed-laser deposited (PLD) polytetrafluoroethylene (Teflon-PTFE) films from press-sintered powder targets are found to be highly crystalline, with spherulite sizes adjustable over more than one order of magnitude by suitable thermal annealing. Films with large spherulites show an excellent charge stability, comparable and even superior to commercially available Teflon-PTFE foils. PLD-PTFE enlarges the family of Teflon materials and may thus become interesting for potential miniaturized electret devices.
A method for liquid crystal alignment using in situ ultraviolet exposure during imidization of polyimide
Authors: Kim Jae-Hoon , Acharya Bharat R. , Kumar Satyendra , Ha Ki Ryong
Published: July 2002

Homogeneous alignment of liquid crystals can be achieved by a technique using polyimide films and in situ exposure to linearly polarized ultraviolet (LPUV) light during imidization. The alignment layers prepared by this method exhibit higher thermal stability while requiring shorter processing time than the conventional UV alignment method which employs UV exposure after the imidization of polyimide is complete. Multidomain cells can be easily fabricated with the use of a photomask and multistep in situ LPUV exposure during hard bake.
High-speed force sensor for force microscopy and profilometry utilizing a quartz tuning fork
Authors: Giessibl Franz J.
Published: July 2002

Force sensors are key elements of atomic force microscopes and surface profilometers. Sensors with an integrated deflection meter are particularly desirable. Here, quartz tuning forks as used in watches are utilized as force sensors. A novel technique is employed which simplifies the interpretation of the data and increases the imaging speed by at least one order of magnitude compared to previous implementations. The variation of the imaging signal with distance fits well to a Hertzian contact model. Images of compact discs and calibration gratings, which have been obtained with scanning speeds up to 230 μm/s, are presented.
Electrical and optical properties of Ge–implanted 4H–SiC
Authors: Katulka G. , Guedj C. , Kolodzey J. , Wilson R. G. , Swann C. , Tsao M. W. , Rabolt J.
Published: July 2002

The structural, electronic, and optical properties of single crystalline n-type 4H–SiC implanted with Ge atoms have been investigated through x-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), Raman spectroscopy, and sheet resistivity measurements. Ge atoms are implanted under the conditions of a 300 keV ion beam energy with a dose of 2×1016 cm−2. X-ray diffraction of the Ge-implanted sample showed broadening of the Bragg peaks. A shoulder on the (0004) reflection indicated an increase in the lattice constant corresponding to substitutional Ge and implantation induced lattice damage, which was repaired through thermal annealing at 1000 °C. The diffraction pattern after annealing indicated improved crystal structure and a peak shift to a lower reflection angle of 35.2°. The composition of Ge detected through XRD was reasonably consistent with RBS measurements that indicated 1.2% Ge in a 1600-Å-thick layer near the SiC surface. Raman spectroscopy also showed fundamental differences in the spectra obtained for the Ge-implanted SiC (SiC:Ge) compared to a pure sample of SiC. Sheet resistivity measurements indicate a higher conductivity in the Ge implant by a factor of 1.94 compared to unimplanted SiC. These results have demonstrated the possibility of substitutional implantation of Ge atoms into the crystalline lattice of 4H–SiC substrates. The change in composition and properties may have numerous electronic device applications including high power, high temperature, optoelectronic, as well as high frequency device structures.
Tunable midinfrared source by difference frequency generation in bulk periodically poled KTiOPO4
Authors: Fradkin K. , Arie A. , Skliar A. , Rosenman G.
Published: July 2002

We demonstrate quasi-phase-matched difference frequency generation in periodically poled KTiOPO4. A midinfrared (3.2–3.4 μm) idler with a power level of 0.17 μW is generated by mixing a Nd:YAG laser and tunable external cavity laser near 1550 nm which is amplified by an erbium-doped fiber amplifier. The wavelength, temperature, and angle tuning characteristics of this device are determined. The experimental results are used to derive a Sellmeier equation with improved accuracy in the midinfrared range for the extraordinary refractive index of flux-grown KTiOPO4.
Ultrashort laser pulse induced deformation of silver nanoparticles in glass
Authors: Kaempfe M. , Rainer T. , Berg K.-J. , Seifert G. , Graener H.
Published: July 2002

Irradiating intense femtosecond laser pulses on a glass sample containing silver nanoparticles results in permanent sample color changes if the laser wavelength is in the region of the particles’ surface plasmon resonance. In particular, even a single pulse of appropriate intensity can modify the initially isotropic extinction of glass containing spherical particles to a dichroic sample behavior in the irradiated area. This observation is interpreted as ultrafast particle deformation induced by the laser pulse creating nonspherical particles of uniform orientation.
Hall potentiometer in the ballistic regime
Authors: Baelus B. J. , Peeters F. M.
Published: July 2002

We demonstrate theoretically how a two-dimensional electron gas can be used to probe local potential profiles using the Hall effect. For small magnetic fields, the Hall resistance is inversely proportional to the average potential profile in the Hall cross and is independent of the shape and the position of this profile in the junction. The bend resistance, on the other hand, is much more sensitive on the exact details of the local potential profile in the cross junction.
Bistability and self-pulsation in quantum-dot lasers with intracavity quantum-dot saturable absorbers
Authors: Qasaimeh O. , Zhou W.-D. , Phillips J. , Krishna S. , Bhattacharya P. , Dutta M.
Published: July 2002

Self-organized In0.4Ga0.6As/GaAs quantum-dot single-mode ridge waveguide lasers with intracavity absorber were grown by molecular beam epitaxy. Bistability in the light–current characteristics of 3 μm single-mode edge-emitting laser was obtained by controlling the intracavity absorber voltage. Self-pulsation was also observed with a center frequency of 1.6 GHz and linewidth <10 MHz.
Argon ion-induced dissociation of acetylene in an expanding Ar/C2H2 plasma
Authors: de Graaf A. , van Hest M. F. A. M. , van de Sanden M. C. M. , Letourneur K. G. Y. , Schram D. C.
Published: July 2002

Mass spectrometric and Langmuir probe measurements reveal that the plasma chemistry of an expanding Ar/C2H2 plasma which is used for deposition of hydrogenated amorphous carbon is dominated by argon ion-induced dissociation of the precursor gas. The ion-induced dissociation is very efficient leading to complete depletion under certain conditions. The ion fluence as determined from modeling the mass spectrometry results is in good agreement with Langmuir probe measurements suggesting a one-to-one relation between the argon ion and acetylene consumption. The good correlation found between the growth rate and the acetylene consumption rate expresses the efficient use of the dissociation products.
Cross-sectional scanning-tunneling microscopy of stacked InAs quantum dots
Authors: Eisele H. , Flebbe O. , Kalka T. , Preinesberger C. , Heinrichsdorff F. , Krost A. , Bimberg D. , Dähne-Prietsch M.
Published: July 2002

We present cross-sectional scanning-tunneling microscopy results of threefold stacked InAs quantum dots prepared by metal-organic chemical-vapor deposition at 485 °C and a growth rate of 0.18 nm/s. The dots consist of stoichiometrically pure InAs and show a layer-dependent size. The images indicate a prismatic dot shape with {101} and additional {111} side faces as well as a (001) top face.
Organic multilayers as distributed Bragg reflectors
Authors: Convertino A. , Valentini A. , Cingolani R.
Published: July 2002

We report on a distributed Bragg reflector (DBR) operating in the IR spectral region, based on a fluorocarbon polymer (CFx) multilayer. In this organic structure, the periodic variation of the refractive index is obtained by embedding gold clusters in the CFx, resulting in a periodic CFx/CFx(Au) layered structure with a refractive index discontinuity in the infrared spectral region of about Δn∼0.4. We have fabricated a quarter-wavelength stack consisting of 4 CFx/CFx(Au) pairs, with a nominal Au concentration equal to 17%. The DBR shows a reflectance peak of about 70% at 1.7 μm and a full width at half maximum of about 0.4 μm.
Phase jumps and interferometric surface plasmon resonance imaging
Authors: Grigorenko A. N. , Nikitin P. I. , Kabashin A. V.
Published: July 2002

Conditions at which phase of light demonstrates a markedly different behavior for close values of system parameters as well as the Heaviside jump are discussed and explained in terms of phase topology. On this basis, a method of interferometric surface plasmon resonance imaging is proposed and applied to develop ultrasensitive affinity array sensors with a monoatomic thickness resolution.
Current–voltage characteristics of a GaAs Schottky diode accounting for leakage paths
Authors: Ellis J. A. , Barnes P. A.
Published: July 2002

Many fabricated Schottky diodes exhibit significant deviations from the theoretically calculated current–voltage (I–V) characteristics of ideal Schottky diodes. Attempts have been made to account for this deviation using interface states or surface state densities. Previous models have used the interfacial layer model to analyze the nonideal I–V characteristics of a GaAs Schottky barrier. We show here how nonideal behavior can be explained by considering surface leakage currents and material resistance. The standard figure of merit of Schottky diodes is the ideality factor, which can be obtained from measurements of δV/δ ln(I). By taking into account device resistance and shunt leakage paths with physically appropriate parameters, a relationship between δV/δ ln(I) and voltage can be established, which yields a better understanding of transport across the interface(s) of real Schottky diodes.
Anisotropic magnetic susceptibility of multiwalled carbon nanotubes
Authors: Tsui F. , Jin L. , Zhou O.
Published: July 2002

Magnetic susceptibility of partially aligned multiwalled carbon nanotubes has been studied using superconducting quantum interference device magnetometry. Partial alignment of multiwalled nanotubes was produced by uniaxially straining composites of carbon nanotubes embedded in polymer matrices. The degree of alignment was determined by x-ray diffraction. The observed magnetic response is diamagnetic and anisotropic with the component along the nanotubes less diamagnetic than that of the perpendicular. The observed anisotropy is consistent with theoretical predictions, but it contradicts earlier experimental findings.
Single-mode waveguide propagation and reshaping of sub-ps terahertz pulses in sapphire fibers
Authors: Jamison S. P. , McGowan R. W. , Grischkowsky D.
Published: July 2002

Waveguide propagation of sub-ps terahertz pulses in single-crystal sapphire fibers is reported. An incident THz pulse of approximately 0.6 ps duration undergoes considerable reshaping due to the absorptive and dispersive waveguide propagation, resulting in transmitted chirped pulse durations of 10–30 ps. Good agreement between theory and experiment is obtained by analyzing the propagation in terms of the single HE11 waveguide mode. The dominance of the single HE11 mode, despite the fiber dimensions allowing for multimode propagation, is attributed to the free-space to waveguide coupling.
Precise velocity measurement of surface acoustic waves on a bearing ball
Authors: Yamanaka Kazushi , Cho Hideo , Tsukahara Yusuke
Published: July 2002

Using the photoacoustic effect of interference fringes scanned at the phase velocity of surface acoustic waves (SAW), we excited tone bursts of SAW with a center frequency of around 30 MHz on a 8 mm φ steel bearing ball. A surprisingly large number (around 20 turns) of round-trip propagations was observed. The time interval between the SAW at the first and the twelfth turn was as large as 93 μs, however it could be determined with a 2 ns resolution since an exact overlapping of the two wave forms was possible. Thus, we achieved a very high resolution of 0.002% in the velocity measurement, and a velocity change of 2 m/s due to the deposition of a 50-nm-thick Ag film was easily detected. Because of its noncontact nature, this method would be useful for nondestructive evaluation of bearing balls.
Double fitting of Maker fringes to characterize near-surface and bulk second-order nonlinearities in poled silica
Authors: Qiu Mingxin , Vilaseca Ramon , Botey Muriel , Sellarès Jordi , Pi Francesc , Orriols Gaspar
Published: July 2002

An experimental analysis of the distribution and thickness of the bulk nonlinearity induced in poled silica is reported. The second-order susceptibility decreases exponentially from the anodic interface. Maker fringe patterns showing a double structure are interpreted in relation to the presence of two nonlinear profiles, one concentrated near the anodic surface and another extending into the bulk of the sample. The Maker fringe theory is properly generalized and a double fitting technique reproducing well the experimental results is used to characterize the induced nonlinearities. The dependence of the second-harmonic signal on the poling temperature is given, which is different from that of sol-gel silica.
High quality Ge on Si by epitaxial necking
Authors: Langdo T. A. , Leitz C. W. , Currie M. T. , Fitzgerald E. A. , Lochtefeld A. , Antoniadis D. A.
Published: July 2002

We show that pure Ge grown selectively on SiO2/Si substrates in 100 nm holes is highly perfect at the top surface compared to conventional Ge lattice-mismatched growth on planar Si substrates. This result is achieved through a combination of interferometric lithography SiO2/Si substrate patterning and ultrahigh vacuum chemical vapor deposition Ge selective epitaxial growth. This “epitaxial necking,” in which threading dislocations are blocked at oxide sidewalls, shows promise for dislocation filtering and the fabrication of low-defect density Ge on Si. Defects at the Ge film surface only arise at the merging of epitaxial lateral overgrowth fronts from neighboring holes. These results confirm that epitaxial necking can be used to reduce threading dislocation density in lattice-mismatched systems.
Molecular alignment in submicron patterned polymer matrix using nanoimprint lithography
Authors: Wang Jian , Sun Xiaoyun , Chen Lei , Zhuang Lei , Chou Stephen Y.
Published: July 2002

We report a promising approach to align molecules in a polymer film patterned by nanoimprint lithography. We found that molecules and chromophores are spontaneously aligned in the plane of the film during the nanopatterning process. Since the polymer–chromophore (called guest–host) system plays an important role in the field of nonlinear optics and organic optoelectronics, in this letter we present a technique to combine the high-resolution patterning capability of nanoimprint lithography with the ability to control molecule and chromophore orientation. It opens up a way to realize new molecular electronic and optoelectronic devices.
Interdiffusion in NiFe/Cu/NiFe trilayers: Possible failure mechanism for magnetoelectronic devices
Authors: Brückner W. , Baunack S. , Hecker M. , Mönch J.-I. , van Loyen L. , Schneider C. M.
Published: July 2002

The evolution of electrical resistance, stress, and microstructure during annealing has been studied on 100 nm NiFe(20 wt %)/200 nm Cu/100 nm NiFe trilayers. Irreversible resistance changes and the concentration-depth profiles show that, at and above 200 °C, diffusion of Ni into Cu as well as of Cu into NiFe occurs. The interdiffusion is held for an important failure mechanism of Cu/NiFe-based magnetoelectronic system at elevated temperatures.
Experimental observation of the mobility edge in a waveguide with correlated disorder
Authors: Kuhl U. , Izrailev F. M. , Krokhin A. A. , Stöckmann H.-J.
Published: July 2002

The tight-binding model with correlated disorder introduced by Izrailev and Krokhin [Phys. Rev. Lett. 82, 4062 (1999)] has been extended to the Kronig–Penney model. The results of the calculations have been compared with microwave transmission spectra through a single-mode waveguide with inserted correlated scatterers. All predicted bands and mobility edges have been found in the experiment, thus demonstrating that any wanted combination of transparent and nontransparent frequency intervals can be realized experimentally by introducing appropriate correlations between scatterers.
Ensemble dependence of the transient fluctuation theorem
Authors: Searles Debra J. , Evans Denis J.
Published: July 2002

The fluctuation theorem gives an analytical expression for the probability of observing second law violating dynamical fluctuations in nonequilibrium systems. At equilibrium, statistical mechanical fluctuations are known to be ensemble dependent. In this paper we generalize the transient and steady-state fluctuation theorems to various nonequilibrium dynamical ensembles. The transient and steady-state fluctuation theorem for an isokinetic ensemble of isokinetic trajectories is tested using nonequilibrium molecular dynamics simulations of shear flow.
A new form of the elliptic relaxation equation to account for wall effects in RANS modeling
Authors: Manceau Rémi , Hanjalić Kemal
Published: July 2002

Different methods for improving the behavior in the logarithmic layer of the elliptic relaxation equation, which enable the extension of Reynolds stress models or eddy viscosity models down to the wall, are tested in a channel flow at Reτ=590 and compared with direct numerical simulation (DNS) data. First, a priori tests are performed in order to confirm the improvement predicted by the theory, either with the Rotta+IP (isotropization of production) model or the Speziale–Sarkar–Gatski (SSG) model as the source term of the elliptic relaxation equation. The best form of the model is then used for full simulations, in Durbin second moment closure or in the frame of the v2¯−f model. It is shown that the results can be significantly improved, in particular by using a formulation based on the refinement of the modeling of the two-point correlations involved in the redistribution term.
Polarization-induced electron populations
Authors: Ridley B. K.
Published: July 2002

Electron populations induced by spontaneous and piezoelectric polarization in semiconductor heterostructures can be estimated simply by using elementary electrostatic theory. The method is illustrated for the AlGaN/GaN system in which the AlGaN barrier is either undoped, or doped n type, and the effect of a GaN overlayer is described.
Structure and stability of the N-hydroxyurea dimer: Post-Hartree–Fock quantum mechanical study
Authors: Jabalameli Ali , Venkatraman Ramaiyer , Nowek Andrzej , Sullivan Richard H.
Published: July 2002

The potential energy surface (PES) search of the N-hydroxyurea dimer was searched with second-order Møller–Plesset perturbation theory (MP2) and the 6-31G(d,p) basis set. Eight local minimum energy structures have been found. Four of them have relatively strong (ΔE∼−10 to −13 kcal/mol) intermolecular interactions and the others are moderately strongly interacting species (ΔE∼−3 to −7 kcal/mol). Final estimation of interaction energies was performed using the larger 6-311G(df,pd) and 6-311G(2df,2pd) basis sets. The predicted interaction energies are ΔE=−14.26 kcal/mol and −3.43 kcal/mol for the strongest and the weakest interacting forms of the studied complex, respectively, at the MP2/6-311G(2df,2pd)//MP2/6-31G(d,p) level of theory. The self-consistent field (SCF) interaction energy decomposition indicates the important influence of the deformation term magnitude on ΔE(SCF). The calculated electron correlation contribution to ΔE(MP2) depends on the geometry of the system and varies from −0.5 to −5 kcal/mol. The estimated influence of water on the stability (free energy of hydration) of N-hydroxyurea dimers using the self-consistent isodensity polarized continuum (SCI-PCM) model of solvation varies from ∼−11 kcal/mol to ∼−21 kcal/mol. The forms predicted to be more strongly interacting species in gas phase are less influenced by hydration than the more weakly interacting ones.
Scanning tunneling microscope measurements of the amplitude of vibration of a quartz crystal oscillator
Authors: Borovsky B. , Mason B. L. , Krim J.
Published: July 2002

We report highly accurate measurements of the vibrational amplitude of a transverse shear mode quartz resonator, obtained by directly imaging the surface oscillatory motion with a scanning tunneling microscope. Amplitude measurements, performed over a range of resonator drive levels and quality factors, agree with theoretical predictions to within a factor of two.
Stable integration of isolated cell membrane patches in a nanomachined aperture
Authors: Fertig N. , Tilke A. , Blick R. H. , Kotthaus J. P. , Behrends J. C. , ten Bruggencate G.
Published: July 2002

We present a method for integrating an isolated cell membrane patch into a semiconductor device. The semiconductor is nanostructured for probing native cell membranes for scanning probe microscopy in situ. Apertures were etched into suspended silicon-nitride layers on a silicon substrate using standard optical lithography as well as electron-beam lithography in combination with reactive ion etching. Apertures of 1 μm diam were routinely fabricated and a reduction in size down to 50 nm was achieved. The stable integration of cell membranes was verified by confocal fluorescence microscopy in situ.
Two-dimensional numerical equilibria of field-reversed configuration in the strong mirror field
Authors: Suzuki Y. , Okada S. , Goto S.
Published: July 2002

Two-dimensional numerical equilibria of field-reversed configuration (FRC) plasmas in the strong mirror field applied externally are studied by means of the Grad–Shafranov equation. Appropriate choice of the pressure function is necessary to obtain a thin and elongated equilibrium, as observed in the FRC Injection Experiment (FIX) [H. Himura et al., Phys. Plasmas 2, 191 (1995)]. To solve the Grad–Shafranov equation, the finite difference method is used, applying the boundary-fitted curvilinear coordinates and the attracted grids near the separatrix. The outstanding feature of the equilibria is the presence of a narrow and sharp spike in the toroidal current profile near the separatrix.
Ultrathin layer alkaline earth metals as stable electron-injecting electrodes for polymer light emitting diodes
Authors: Cao Yong , Yu Gang , Parker Ian D. , Heeger Alan J.
Published: July 2002

Polymer light emitting diodes in which the cathode comprises an ultrathin layer of alkaline earth metal show much better operating lifetime, especially at high temperatures, in comparison with devices fabricated with cathodes from the same metals with thickness greater than 100 Å. The operating lifetime is dependent on the specific low work function metal used. Among the alkali and alkaline earth metals, devices with ∼30 Å Ba as cathode show the best half life during continuous operation. Using an ultrathin Ba cathode with an Al or Ag capping layer and poly[2-(3,7-dimethyloctyloxy)-5-methoxy-1,4-phenylenevinylene] as luminescent polymer, the half life reaches 400 h at 85 °C and exceeds 10 000 h at room temperature when operated at a current density of 8.3 mA/cm2 with a luminance of 100–140 cd/cm2.
Ice nanotube: What does the unit cell look like?
Authors: Koga Kenichiro , Parra Ruben D. , Tanaka Hideki , Zeng X. C.
Published: July 2002

It is discovered that for an n-gonal ice nanotube built from stacking a single type of n-gonal rings of water, the unit cell consists of two stacked n-gonal rings. In one ring the O–H bonds of water molecules line up clockwise whereas in the other ring the O-H bonds line up counterclockwise. Among the n-gonal ice nanotubes examined, the pentagonal or hexagonal ice nanotube appears to be the most stable.
Piezoelectric properties and poling effect of Pb(Zr, Ti)O3 thick films prepared for microactuators by aerosol deposition
Authors: Akedo J. , Lebedev M.
Published: July 2002

Crack-free [Pb(Zr0.52, Ti0.48)O3] (PZT) films with more than 10 μm thickness as the piezoelectric material, were formed on stainless-steel (SUS304) and Pt/Ti/SiO2/Si substrates by aerosol deposition and then annealed at 600 °C in air. The deposition rate was 20 μm/min in an area of 5×5 mm2. To estimate the piezoelectric and mechanical properties of PZT films, a unimorph structured PZT and a free-standing cantilever were fabricated. The Young’s modulus (Y11) of the PZT film was 80 GPa. Poling at 40 kV/cm, 250 °C for 20 min increased the properties by a factor of 4.0–5.5, resulting in the piezoelectric coefficient (−d31) varying from 80 to 180 pm/V.
Uniaxial locked epitaxy of ZnO on the a face of sapphire
Authors: Fons P. , Iwata K. , Yamada A. , Matsubara K. , Niki S. , Nakahara K. , Tanabe T. , Takasu H.
Published: July 2002

High-quality, c-oriented ZnO epitaxial films have been grown on the a surface using molecular-beam epitaxy. The use of a-oriented sapphire eliminates rotational domains and related structural defects which have limited the use of ZnO in electronic applications. The ZnO epitaxial layers are uniquely oriented with the ZnO/sapphire orientational relationship [0001]‖[112̄0] and 〈112̄0〉‖[0001]. This unique orientation is a consequence of the anisotropy of the a-sapphire surface in conjunction with a strong correlation along a single direction leading to the term uniaxial locked epitaxy. High-resolution x-ray diffraction measurements show an increase in x-ray lateral coherence length from several tens of nanometers to >0.7 μm for growth of c-oriented ZnO on the a surface as opposed to the c surface of sapphire.
Spectroscopy of yttrium dimers in argon matrices
Authors: Fang L. , Chen X. , Shen X. , Liu Y. , Lindsay D. M. , Lombardi J. R.
Published: July 2002

The absorption and resonance Raman spectra of yttrium dimers (Y2) in argon matrices are measured for the first time. The absorption spectrum (scattering depletion spectrum SDS) shows a weak, broad transition centered near 485 nm. Resonance Raman spectra obtained by exciting into this absorption band with several visible laser lines (465.5–496.5 nm) give a single, sharp progression with up to ten Stokes transitions. These data give ωe=184.4(4) cm−1, with ωexe=0.30(3) cm−1, leading to a spectroscopic dissociation energy of De=3.5(4) eV. Comparison of our results with several ab initio calculations adds confirmation to the assignment of the ground state of Y2 to be the Σg+1 state.
Thermal conductivity of solid krypton with methane admixture
Authors: Dudkin V. V. , Gorodilov B. Ya. , Krivchikov A. I. , Manzhelii V. G.
Published: July 2002

The thermal conductivity of CH4–Kr solid solutions is investigated at CH4 concentrations 0.2–5.0% in the temperature range 1.8–40 K. It is found that the temperature dependence of the thermal conductivity has features typical of resonance phonon scattering. The analysis of the experimental results shows that the main contribution to the impurity-caused scattering of phonons is made by the scattering on rotational excitations of the nuclear spin T-species of CH4 molecules. The phonon–rotation interaction parameter is estimated.
Direct determination of molecular constants from rovibronic spectra with genetic algorithms
Authors: Hageman J. A. , Wehrens R. , de Gelder R. , Leo Meerts W. , Buydens L. M. C.
Published: July 2002

It is shown that a new procedure, based on genetic algorithms (GA’s), can be used for direct determination of molecular constants, in particular rotational constants, from rovibronic spectra. This new approach only requires an estimate of the acceptable range of the parameters. The power of the method is demonstrated on the rotationally resolved fluorescence spectra of indole, indazole, benzimidazole, and 4-aminobenzonitril. A rigid asymmetric rotor Hamiltonian is used to calculate the theoretical spectra. The GA matches the generated spectra with an experimental spectrum with the use of a new method for spectra comparison. This spectra comparison function is able to deal with frequency shifts which are caused by (small) changes in the rotational constants and it yields better results in comparison with traditional spectra comparison methods, like RMS. In addition, the robustness of the method is tested.
Simultaneous determination of optical and acoustic thicknesses of protein layers using surface plasmon resonance spectroscopy and quartz crystal microweighing
Authors: Laschitsch Alexander , Menges Bernhard , Johannsmann Diethelm
Published: July 2002

The optical and the acoustic thicknesses of protein layers during adsorption were simultaneously determined by a combination of surface plasmon resonance spectroscopy and quartz crystal microweighing. Coupling of the surface plasmon was achieved by etching a diffraction grating into the quartz surface prior to the deposition of the metal electrode. The evolution of the acoustic and the optical thickness was markedly different, which is attributed to surface roughness and partial coverage.
Comparison of planar shear flow and planar elongational flow for systems of small molecules
Authors: Matin M. L. , Daivis P. J. , Todd B. D.
Published: July 2002

We use nonequilibrium molecular dynamics to simulate steady state planar shear flow and planar elongational flow of fluids of small molecules at constant volume and temperature. The systems studied are Lennard–Jones diatomic molecules (chlorine), and a series of linear Lennard–Jones molecules with one, two, and four sites. In our simulations of planar elongational flow, we employ Kraynik–Reinelt periodic boundary conditions, which allow us to obtain precise values of the steady state planar elongational viscosity. We validate our application of Kraynik–Reinelt periodic boundary conditions by comparing the zero strain rate shear and elongational viscosities. The results show that the elongational viscosity is proportional to the shear viscosity in the zero strain rate limit, as expected. The viscosity, pressure, and internal energy of the atomic Lennard–Jones fluid show exactly the same behavior for the two types of flow when both sets of results are plotted against the second scalar invariant of the strain rate tensor. The results for the diatomic and four-site molecules show differences in the pressure, energy, and viscosity outside the Newtonian regime when plotted against the second scalar invariant of the strain rate tensor. The differences in the properties in the nonlinear regime increase with both strain rate and molecular length.
Electron beam and optical depth profiling of quasibulk GaN
Authors: Chernyak L. , Osinsky A. , Nootz G. , Schulte A. , Jasinski J. , Benamara M. , Liliental-Weber Z. , Look D. C. , Molnar R. J.
Published: July 2002

Electron beam and optical depth profiling of thick (5.5–64 μm) quasibulk n-type GaN samples, grown by hydride vapor-phase epitaxy, were carried out using electron beam induced current (EBIC), microphotoluminescence (PL), and transmission electron microscopy (TEM). The minority carrier diffusion length, L, was found to increase linearly from 0.25 μm, at a distance of about 5 μm from the GaN/sapphire interface, to 0.63 μm at the GaN surface, for a 36-μm-thick sample. The increase in L was accompanied by a corresponding increase in PL band-to-band radiative transition intensity as a function of distance from the GaN/sapphire interface. We attribute the latter changes in PL intensity and minority carrier diffusion length to a reduced carrier mobility and lifetime at the interface, due to scattering at threading dislocations. The results of EBIC and PL measurements are in good agreement with the values for dislocation density obtained using TEM.
Three-dimensional simulations of ion thruster beam neutralization
Authors: Othmer C. , Glassmeier K. H. , Motschmann U. , Schüle J. , Frick Ch.
Published: July 2002

Motivated by the recently revived interest in electric propulsion, the neutralization regime of an ion thruster is investigated by means of a three-dimensional particle-in-cell simulation. Electrons enter the simulation box with a half-Maxwellian velocity distribution, while the ions are injected with a uniform bulk velocity. Focus is put on the dynamics of the electrons, and the actual electron to ion mass ratio of 1:250 000 is used. The injection velocity ratio η≔ve0th/vi0 between electron thermal velocity and ion bulk velocity turned out to be a crucial parameter for the electron dynamics within the plasma beam: For η<1.7 a moving electrostatic shock forms with a potential jump of a few kTe0/e. Downstream of the shock front, the electron plasma becomes fully Maxwellian and drifts with the ion bulk velocity. For η>1.7, the electrons still obtain a drift velocity roughly equal to vi0 within a few electron inertia lengths behind the emitting plane. However, a shock front does not form, and the electron velocity distribution does not become Maxwellian. On the basis of a tentative model, in which the plasma beam is regarded as a self-similarly expanding electron diode, the shock front can be identified with a kind of virtual cathode and the dependence of the shock velocity on the beam cross section can be explained.
Effects of gamma-ray irradiation on the microstructural and luminescent properties of radio-frequency magnetron-sputtered GaN thin films
Authors: Wang Ching-Wu , Soong Bo-Shao , Chen Jing-Yu , Chen Chih-Liang , Su Yan-Kuin
Published: July 2002

The microstructural and luminescent properties of sputtered GaN thin films preiiradiated and γ-ray irradiated were systematically investigated. Analytical results revealed that the increasing doses of γ rays could enhance the occurrence of more nitrogen vacancies, which not only created a prominent deep level luminescence but also destroyed the crystallinity of GaN thin films. For low dose of γ-ray irradiation [≦4 Mrad (GaN)], evidence showed that by raising the irradiation dose, more associated Ga–H complexes would be effectively promoted, yielding an enhanced yellow band emission. However, for high dose of γ-ray irradiation [>4 Mrad (GaN)], further higher doses of γ rays could lead to the dissociation of Ga–H complexes in GaN samples, resulting in a repressed yellow band emission. From both the Fourier transform infrared spectroscopy and yellow band emission results, it is strongly suggested that Ga–H complexes in the vicinity of N most probably act as the origin of yellow band emission in GaN material.
Empty-space-in-silicon technique for fabricating a silicon-on-nothing structure
Authors: Mizushima I. , Sato T. , Taniguchi S. , Tsunashima Y.
Published: July 2002

A promising technique to form the silicon-on-nothing structure is presented as an alternative to the silicon-on-insulator structure. A large plate-shaped empty space in silicon (ESS) below the surface of the silicon substrate can be fabricated by connecting the spherical empty spaces, which are formed by surface migration of Si on the patterned Si substrate. The ESS technique has the potential to change the microprocess for the fabrication of large-scale integrated circuits and it can be applied to various manufacturing technologies.
Epitaxial growth of ferromagnetic Ni2MnGa on GaAs(001) using NiGa interlayers
Authors: Dong J. W. , Chen L. C. , Xie J. Q. , Müller T. A. R. , Carr D. M. , Palmstrøm C. J. , McKernan S. , Pan Q. , James R. D.
Published: July 2002

Heusler alloy Ni2MnGa thin films have been grown pseudomorphically on a relaxed NiGa interlayer on GaAs(001) by molecular-beam epitaxy. In situ reflection high-energy electron diffraction patterns, ex situ x-ray diffraction, and cross-sectional view transmission electron microscopy electron diffraction patterns confirm the single-crystal growth of Ni2MnGa. The films grow pseudomorphically on the relaxed NiGa interlayer with a tetragonal structure (a=b=5.79 Å and c=6.07 Å). Magnetic measurements using vibrating sample and superconducting quantum interference device magnetometers reveal Ni2MnGa to have an in-plane easy axis and a Curie temperature ∼350 K.
Time-dependent quantum mechanical calculations on H+O2 for total angular momentum J>0. III. Total cross sections
Authors: Goldfield Evelyn M. , Meijer Anthony J. H. M.
Published: July 2002

The H+O2→OH+O reaction has been studied with a time-dependent wave packet method for total angular momentum J=15, 20, 25, 35. This work is a continuation of previous studies for J⩽10. The calculations were performed combining a real wave packet method with the Coriolis coupled method on parallel computers. We find that for most energies there is a monotonic decrease of reaction probability with increasing J. Nevertheless, due to the 2J+1 degeneracy, higher angular momentum states contribute significantly to the total reaction cross section. A smoothing/interpolation/extrapolation scheme is employed to compute total reaction cross sections. These cross sections are compared with quasiclassical results on the same potential energy surface, and the most recent experimental cross sections. Comparisons with quasiclassical results show the significance of zero-point energy constraints. The quantum mechanical theoretical cross sections are smaller than the experimental ones everywhere, suggesting that a more accurate potential energy surface is required. There is also some possibility that nonadiabatic effects play a role in this reaction.
Structure and distribution of secondary defects in high energy ion implanted 4H-SiC
Authors: Ohno Toshiyuki , Kobayashi Naoto
Published: July 2002

The structure, size, and distribution of the secondary defects in high-energy B+ or Al+ implanted 4H-SiC were investigated by cross-sectional transmission electron microscope observations and secondary ion mass spectrometry analyses. Three types of defect structure were detected. The first (type I) is an extrinsic Frank partial dislocation loop parallel to {0001} and is same as that observed in kilo-electron-volt energy B+ or Al+ implanted SiC. The second (type II) is also an extrinsic dislocation loop with an extra Si–C bilayer parallel to {0001} but it has not been previously reported. The last type (type III) has no extra Si–C bilayer. The type of defect is correlated to the size of it. When the size is larger than about 12 nm, the defect becomes type I or type II and the defects which are smaller than about 12 nm are type III. The range of the secondary defect size depends on implanted ions and its dose. The maximum size of defects grows with dopant concentration and that in B+ implanted sample is larger than that in Al+ implanted one at the same volume concentration of dopant. But the minimum size of defects seems independent of dopant concentration and ion species. It is 2–4 nm in any case. These defects are distributed in the deeper region of projected range for low dose implantation. On the contrary, they are distributed from near surface for high dose implanted samples.
Mechanisms of injection enhancement in organic light-emitting diodes through an Al/LiF electrode
Authors: Heil H. , Steiger J. , Karg S. , Gastel M. , Ortner H. , von Seggern H. , Stößel M.
Published: July 2002

The mechanisms of enhanced electron injection into the electron transport layer of Alq3 [tris(8-hydroxyquinoline)-aluminum] via LiF interlayers are studied by means of I–V characteristics, secondary ion mass spectroscopy (SIMS), and Kelvin probe measurements. Devices for single carrier injection were prepared using aluminum electrodes, Alq3 electron transport layers, and thin intermediate layers of LiF. It was found that devices deposited in the order Alq3-LiF-aluminum have a much higher electron injection capability than structures deposited in the order aluminum-LiF-Alq3. SIMS depth profile analysis reveals that the evaporation of Al on LiF leads to a spatial separation of Li and F probably induced by a chemical reaction of Al with LiF. Simple thermodynamic calculations support the energetic feasibility of such a reaction. Titanium cathodes in the same layer sequence also exhibit electron injection enhancement, probably due to their similar chemical reactivity. However, electron injection from Ag electrodes is not significantly improved by the introduction of a LiF interlayer.
Preliminary experiments on apparatus for in situ studies of microwave-driven reactions by small angle neutron scattering
Authors: Whittaker A. G. , Harrison A. , Oakley G. S. , Youngson I. D. , Heenan R. K. , King S. M.
Published: July 2002

In this article we describe apparatus for the study of the microwave-driven growth of particles in solution by in situ small angle neutron scattering (SANS). This apparatus has enabled the first preliminary experiments using microwave-activated in situ diffraction. We take iron oxide as the prototype system, but the technique may be extended to a wide variety of chemical reactions that deposit solids from solution. The key features of the apparatus are a microwave cavity with a modular construction that may be adapted to the geometric constraints of the diffractometer, and a computer-controlled microwave generator that may be set to maintain either constant pressure or temperature in the reaction vessel. In this particular piece of equipment the reaction vessel is adapted so that part of the sample fills a cell of identical construction to those commonly used in SANS measurements for optimal transmission of the neutron beam.