bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of metal clusters on the swelling of gold–fluorocarbon–polymer composite films
Authors: Convertino Annalisa , Valentini Antonio , Bassi Anna , Cioffi Nicola , Torsi Luisa , Cirillo Emilio N. M.
Published: July 2002

We have investigated the swelling of acetone in fluorocarbon polymer films doped with different gold concentrations below the percolation threshold. The presence of the gold clusters in the polymer improves the mixing between the polymer and the acetone, which is not a good solvent for this kind of polymer. To explain our results, the stoichiometry and the morphology of the polymer–metal system have been studied and a modified Flory–Huggins model has been developed.
Self-assembled carbon nanotubes grown without catalyst from nanosized carbon particles adsorbed on silicon
Authors: Botti S. , Ciardi R. , Terranova M. L. , Piccirillo S. , Sessa V. , Rossi M. , Vittori-Antisari M.
Published: July 2002

Carbon nanotubes films have been prepared by low-velocity spraying of carbon nanosized particles on heated Si substrate. Studies reveal that by properly choosing the deposition temperature, well-aligned carbon nanotubes are self-assembled from the particles without a catalyst. Raman scattering and reflection high-energy electron diffraction show that the tubes are bundles of single-wall nanotubes.
Plasma screening effects on occurrence time for electron-ion scattering in strongly coupled plasmas
Authors: Jung Young-Dae
Published: July 2002

Plasma screening effects on the occurrence time for the elastic electron–ion scattering in strongly coupled plasmas are investigated using the ion-sphere model. For small scattering angles, the occurrence time advance is found to be significantly reduced with the decrease in the strength of the plasma screening. For strong plasma screening cases, the occurrence time advance is found to decrease with an increase of the scattering angle. However, for weak plasma screening cases, the occurrence time advance is increased sinusoidally with the increase scattering angle.
Secular behavior of electrostatic Kelvin–Helmholtz (diocotron) modes coupled with plasma oscillations
Authors: Hirota M. , Tatsuno T. , Kondoh S. , Yoshida Z.
Published: July 2002

Electrostatic instabilities in electron plasmas have been studied by analyzing initial value problems. The self-electric field of a non-neutral plasma produces a flow that brings about non-Hermitian property into the generating operator. Because of the nonorthogonality of eigenmodes, the evolution of the system is rather complex. Secular behavior is a typical appearance of unresolvable mode couplings that may be cast in a representation of Jordan block. The coupling of the perpendicular (with respect to the magnetic field) electrostatic modes (Kelvin–Helmholtz or diocotron modes) and parallel plasma oscillations causes a more complex phenomena.
Interface of directly bonded InP wafers for vertical couplers
Authors: Jin-Phillipp N. Y. , Liu B. , Bowers J. E. , Hu E. L. , Kelsch M. , Thomas J. , Rühle M.
Published: July 2002

Vertical directional couplers fabricated using direct wafer bonding have demonstrated a very short coupling length and a small excess optical loss introduced by the bonded interface layer. The structure of the interface of directly bonded InP wafers is investigated. Dislocations at the interface are found to accommodate the tilt misorientation between the two wafers without introducing extra misfit. Body-centered-tetragonal In inclusions of a size of few nanometers are identified at the interface. The excess optical loss of the coupler based on directly bonded InP wafers due to the formation of these inclusions may be eliminated by using lower temperature and a phosphor atmosphere for direct bonding.
Study on Zr-silicate interfacial layer of ZrO2 metal-insulator-semiconductor structure
Authors: Yamaguchi Takeshi , Satake Hideki , Fukushima Noburu , Toriumi Akira
Published: July 2002

We have investigated the physical and dielectric properties of the Zr-silicate interfacial layer of ZrO2 metal-insulator-semiconductor (MIS) structure fabricated by pulsed-laser ablation deposition. It was found that an ultrathin Zr-silicate interfacial layer is formed on a Si substrate as a result of the reaction between ZrO2 and Si. We showed that MIS capacitors consisting solely of the ultrathin Zr-silicate interfacial layer could be fabricated by selective etching of the ZrO2 layer. The Zr-silicate interfacial layer showed a small equivalent oxide thickness of 0.8 nm, a dielectric constant of 8–9, and low leakage less than 1 A/cm2 at Vg of −1 V.
Determining element-specific magnetocrystalline anisotropies using x-ray magnetic linear dichroism
Authors: Dhesi S. S. , van der Laan G. , Dudzik E.
Published: July 2002

X-ray magnetic linear dichroism (XMLD) is shown to be an element-specific probe of the magnetocrystalline anisotropy (MAE). The anisotropy in the spin-orbit interaction, determined using XMLD, is related to the MAE using a sum rule for a series of stepped Co surfaces exhibiting increasing uniaxial magnetic anisotropy. A linear relationship between the MAE, determined using XMLD, and the step density driven increase in the magnetic anisotropy proves the link between XMLD and the MAE. The element-specific nature of the technique is demonstrated by determining the individual MAE for Co/Fe bilayers.
Phase diagram of three contrasting magnetization reversal phases in uniaxial ferromagnetic thin films
Authors: Choe Sug-Bong , Shin Sung-Chul
Published: July 2002

We present an analytical description of a magnetization reversal phase diagram of ferromagnetic thin films that have uniaxial perpendicular anisotropy. The phase equilibrium lines were calculated from a micromagnetic consideration of equilibrium conditions of the wall motion, dendritic growth, and nucleation processes. The phase diagram characterizes well simulated domain evolution patterns: typical domain evolution patterns are predicted accurately in the corresponding phases accompanied by gradual phase transitions across the phase equilibrium lines.
Inverse opal with an ultraviolet photonic gap
Authors: Ni Peigen , Cheng Bingying , Zhang Daozhong
Published: July 2002

Photonic crystals composed of TiO2 and air voids fabricated by the template method exhibit an ultraviolet photonic stop band (∼380 nm) in the Γ–L direction. Scanning electron microscopy images show that the inverse opal possesses face-centered-cubic symmetry with a lattice constant of 240 nm. The transmission spectra show that the change in transmittance is one order of magnitude in the gap, which is in accord with the reflection spectrum.
Accurate measurements of quantum voltage steps on arrays of bicrystal Josephson junctions
Authors: Klushin A. M. , Behr R. , Numssen K. , Siegel M. , Niemeyer J.
Published: July 2002

Quantum voltages of an array of YBa2Cu3O7 bicrystal junctions were calibrated against a programmable Josephson array voltage standard. We demonstrated that steps of the current–voltage characteristic of an array of bicrystal junctions at voltages of about 9 mV were flat over the current range of about 80 μA to within six parts in 108. The coincidence of quantum voltages on the array of high-temperature superconductor junctions at 64 K and the reference voltage on the array of niobium junctions at 4.2 K was measured with an uncertainty of two parts in 108. With the same uncertainty, we revealed the coincidence of the Josephson constant KJ≡h/2e in YBa2Cu3O7 and in metallic superconductors.
Intraband absorption and photocurrent spectroscopy of self-assembled p-type Si/SiGe quantum dots
Authors: Fromherz T. , Mac W. , Hesse A. , Bauer G. , Miesner C. , Brunner K. , Abstreiter G.
Published: July 2002

In infrared transmission and photocurrent spectra of self-assembled SiGe quantum dot samples grown in the Stranski–Krastanow mode at temperatures around T=520 °C different types of transitions are observed: in the transmission experiments, an absorption line due to bound-to-bound transitions is measured whereas the photocurrent spectra are determined by bound-to-continuum transitions. The experimental determination of the energies of both types of transitions for the same sample allows a detailed discussion of the features observed in the spectra as well as an estimate of the average Ge content in the dots.
High-sensitivity high-resolution dual-function signal and time digitizer
Authors: Sarwana Saad , Gupta Deepnarayan , Kirichenko Alex F. , Oku Takayuki , Otani Chiko , Sato Hiromi , Shimizu Hirohiko M.
Published: July 2002

We have developed a dual-function high sensitivity/high-resolution digitizer. It consists of a superconducting digital integrated circuit, which can operate both as a time-to-digital converter (TDC) and a flux counting analog-to-digital converter (ADC). The TDC has a 30 ps multihit time resolution. The ADC has been designed with a superconducting quantum interference device based detector for a 1 μA full scale range. This digitizer is extremely useful in many applications, e.g., for time-of-flight measurements, or as a radiation resistant, low-noise, low-power ADC for detector readout.
Timing jitter reduction in modelocked semiconductor lasers with photon seeding
Authors: Jiang Leaf A. , Abedin Kazi S. , Grein Matthew E. , Ippen Erich P.
Published: July 2002

We demonstrate improvement of the noise performance of a modelocked semiconductor laser using coherent photon seeding. We show that the timing jitter can be reduced without increasing the pulse width.
Atomistic-to-continuum description of vacancy cluster properties in crystalline silicon
Authors: Prasad Manish , Sinno Talid
Published: July 2002

A synergistic combination of molecular dynamics and statics calculations based on the empirical Environment-Dependent Interatomic Potential (EDIP) is used to compute the thermodynamic properties of vacancy clusters (voids) in silicon. All cluster formation properties are found to follow a simple size scaling law, leading to a compact expression for void free energies. An estimate for the free energy of the unreconstructed Si (111) surface is found to compare well with experimental measurements. The results should be useful for the development of accurate process simulators for void formation during crystal growth and wafer thermal annealing.
In situ diffuse reflectance spectroscopy investigation of low-temperature-grown GaAs
Authors: Zhao Ri-an , Cich Michael J. , Specht Petra , Weber Eicke R.
Published: July 2002

We have utilized in situ diffuse reflectance spectroscopy (DRS) to monitor both the substrate temperature transient and the epilayer absorption during low-temperature (LT) GaAs molecular-beam epitaxy. We have found a significant increase of the sub-band-gap absorption from LT GaAs. The magnitude of absorption at 1.2 eV correlates well with the concentration of arsenic antisite defects. The incorporation rate of arsenic antisites appears uniform despite a substrate temperature transient due to the effusion cell radiation heating. The influence of absorption spectra change on the accuracy of DRS temperature measurement is also discussed. This study shows that DRS can be used for both growth temperature measurement and real-time nonstoichiometry monitoring.
Characteristics of high-quality p-type AlxGa1−xN/GaN superlattices
Authors: Yasan A. , McClintock R. , Darvish S. R. , Lin Z. , Mi K. , Kung P. , Razeghi M.
Published: July 2002

Very-high-quality p-type AlxGa1−xN/GaN superlattices have been grown by low-pressure metalorganic vapor-phase epitaxy through optimization of Mg flow and the period of the superlattice. For the superlattice with x=26%, the hole concentration reaches a high value of 4.2×1018 cm−3 with a resistivity as low as 0.19 Ω cm by Hall measurement. Admittance spectroscopy was performed in order to investigate the electrical properties of the superlattices. These measurements confirm that superlattices with a larger period and higher Al composition have higher hole concentration and lower resistivity, as predicted by theory.
Effect of H2 on nitrogen incorporation in the metalorganic chemical vapor deposition of GaAs1−yNy (0⩽y⩽0.08)
Authors: Moody B. F. , Barletta P. T. , El-Masry N. A. , Roberts J. C. , Aumer M. E. , LeBoeuf S. F. , Bedair S. M.
Published: July 2002

The effect of hydrogen on the incorporation of nitrogen in GaAs1−yNy grown by metalorganic chemical vapor deposition (MOCVD) is reported. Nitrogen content as high as y=0.081 has been achieved when the use of H2 is completely avoided in the MOCVD growth of GaAs1−yNy. When H2 is added to the growth ambient, the value of y in GaAs1−yNy decreases as the relative percent of H2 in the carrier gas increases. We will report on the properties of these GaAsN films and discuss the nature of the effect that H2 has on modulating the N content in these films.
Intense sonoimplantation of atoms from gases into metals
Authors: Arata Yoshiaki , Zhang Yue-Chang
Published: July 2002

It was found that various gaseous atoms can be easily implanted into metal powders under ultrasonic cavitation inside a vessel with water (H2O,D2O or a mixture thereof). Inert gases (He3, He4, Ne, and Ar) and others (N2, air, H2, and D2) were strongly sonoimplanted into metals such as Ti, Fe, Ni, Cu, Zr, Pd, Ag, Ta, Pt, and Au, which were originally set in the vessel as foils, and were broken into ultrafine metal powders during intense ultrasonic processing. A large amount of implanted atoms was verified to exist in these powders from mass spectroscopic analyses.
Long-aging effects on the properties of La0.5Sr0.5CoO3−δ films
Authors: Prokhorov V. G. , Lee Y. P. , Kim K. W. , Ishchuk V. M. , Chukanova I. N.
Published: July 2002

The transport and magnetic properties of as-deposited and long-aged La0.5Sr0.5CoO3−δ films prepared by pulsed laser deposition have been investigated. It was found that an oxygen deficiency in the aged film leads not only to a change in the Co3+:Co4+ ratio, but to the formation of a structural disorder in the Co–O–Co conduction channel due to the accumulated oxygen vacancies. In addition to the usual ferromagnetic transition at TC≃250 K, the second magnetic transition was observed at TM≈50 K, which is treated as a freezing of the spin-glass state provided by the weak disorder in the oxygen arrangement.
Dynamics of a nonlinear master equation: Low-dimensional manifolds and the nature of vibrational relaxation
Authors: Davis Michael J.
Published: July 2002

The dynamics of nonlinear master equations describing vibrational relaxation in shock-heated molecules are studied. The nonlinearity results principally from inclusion of self-collisions. The master equations were derived in a previous paper by fitting experimental data and besides being nonlinear they vary according to changes in the bath temperature. It is demonstrated that, except for brief transients, the dynamics lie on one-dimensional, nonlinear manifolds, including the full time of experimental observation. The one-dimensional nature of the dynamics allows for an in depth study of vibrational relaxation. It is shown that vibrational distributions cannot be characterized accurately by a vibrational temperature until they are close to equilibrium and that one-dimensional rate laws accurately describe the dynamics on the one-dimensional manifold. The latter characteristic is important, because it allows results generated from master equations which include self-collisions to be easily incorporated into kinetic modeling.
Si-doped cubic GaN grown on a Si(001) substrate with a thin flat SiC buffer layer
Authors: Wang D. , Yoshida S. , Ichikawa M.
Published: July 2002

Highly Si-doped cubic GaN films were grown on a Si(001) substrate coated with a 2.5-nm-thick flat 3C–SiC buffer layer. The Si doping concentration ranged from 1×1019 to 1×1021 cm−3. Upon Si doping, the initial nucleations easily coalesced, producing a flat surface with a 4×1 reconstruction and preferential growth in the [110] direction. The density of stacking faults also increased. The substitution of Ga atoms with Si atoms and the increased density of stacking faults help to relieve the compressive stress in GaN caused by the lattice mismatch of the GaN film and the substrate. GaN showed a strong photoluminescence intensity at room temperature.
Microscopic structure and optical properties of GaAs1−xNx/GaAs(001) interface grown by metalorganic vapor phase epitaxy
Authors: Dumont H. , Auvray L. , Monteil Y. , Bondoux C. , Largeau L. , Patriarche G.
Published: July 2002

We have investigated the structure and optical properties of GaAs0.97N0.03/GaAs produced by metalorganic vapor phase epitaxy grown on GaAs surface at 520–550 °C. Using cross-sectional transmission electron microscopy and photoluminescence spectroscopy (PL), we show the presence of a 5–6-nm-thick nitrogen-rich interfacial region. The nitrogen composition near the interface is twice higher (x=0.038) than that of the bulk epilayer (x=0.016). PL data shows two peaks located at 1.05 and 1.18 eV associated to the interfacial region and the bulk layer, respectively. We discuss several mechanisms of surface enrichment of nitrogen that occurred during the first stage of GaAsN growth.
Josephson effect in point contacts between “f-wave” superconductors
Authors: Mahmoodi R. , Shevchenko S. N. , Kolesnichenko Yu. A.
Published: July 2002

A stationary Josephson effect in point contacts between triplet superconductors is analyzed theoretically for the most-probable models of the order parameter in UPt3 and Sr2RuO4. The consequence of misorientation of the crystals in the superconducting banks on this effect is considered. We show that different models for the order parameter lead to quite different current-phase relations. For certain angles of misorientation a boundary between superconductors can generate a spontaneous current parallel to the surface. In a number of cases the state with a zero Josephson current and minimum of the free energy corresponds to a spontaneous phase difference. This phase difference depends on the misorientation angle and may possess any value. We conclude that experimental investigations of the current-phase relations of small junctions can be used for determination of the order parameter symmetry in the superconductors mentioned above.
Retrieval of the dielectric function of thin films from femtosecond pump-probe experiments
Authors: Jasapara J. , Mero M. , Rudolph W.
Published: July 2002

The retrieval of the complex dielectric function from time-resolved pump-probe reflection and transmission experiments on thin films is investigated. A general approach is presented that takes into account interference effects of both the pump and the probe pulse. The influence of the pulse duration is investigated. The retrieval technique is exemplified with experimental data from a Ta2O5 film.
Pressure-induced resonant Raman scattering in Ge/Si islands
Authors: Teo K. L. , Qin L. , Shen Z. X. , Schmidt O. G.
Published: July 2002

Self-assembled Ge islands grown by solid-source molecular-beam epitaxy were investigated by resonant Raman scattering under hydrostatic pressure at room temperature. We utilize the effect of pressure to tune the electronic transition through laser excitation energies in the Ge islands. The pressure coefficient of this resonating electronic transition thus obtained is ∼2.7±0.5 meV/kbar, which is significantly smaller than the pressure shift of the El transition in bulk Ge. This is attributed to the fact that the Ge islands are strongly constrained by the surrounding Si lattice, leading to a smaller deformation as compared to the bulk Ge, when subjected to the same pressure.
Stimulated-emission-induced enhancement of the decay rate of longitudinal optical phonons in III–V semiconductors
Authors: Chen Jing , Khurgin Jacob B. , Merlin R.
Published: July 2002

We explore the feasibility of reducing the lifetime of longitudinal optical phonons in InP by injecting coherent longitudinal acoustic modes of frequency given by the difference between those of the longitudinal and transverse optical phonons. Calculations show that a ten-fold reduction in the lifetime can be attained using a 40 mW acoustic source. The increase in the phonon decay should reduce the scattering rate of hot electrons in fast devices.
Strong chemical interaction between indium tin oxide and phthalocyanines
Authors: Peisert H. , Knupfer M. , Schwieger T. , Fink J.
Published: July 2002

We present a study of the interface properties between indium tin oxide (ITO) and the well-established molecular organic semiconductor copper phthalocyanine (CuPC) and its fluorinated relative copper tetraflourophthalocyanine (CuPCF4) using photoemission spectroscopy. It is shown that a strong chemical interaction occurs between the PC molecules and ITO which indicates the presence of interface states at these technically relevant interfaces.
Influence of interdot coupling on electron-wave interference in an open quantum-dot molecule
Authors: Aoki N. , Oonishi D. , Iwase Y. , Ochiai Y. , Ishibashi K. , Aoyagi Y. , Bird J. P.
Published: July 2002

We study the characteristics of the fluctuations, observed in the low-temperature magnetoconductance of an open quantum-dot molecule formed from a pair of split-gate quantum dots. The evolution of these fluctuations suggests a decrease in the typical area for coherent interference with decreasing dot-coupling strength. We discuss this behavior in terms of a transition from multi- to single-dot interference as a function of the interdot coupling.
Local magnetic ordering in La1−xCaxMnO3 determined by spin-polarized x-ray absorption spectroscopy
Authors: Qian Q. , Tyson T. A. , Kao C.-C. , Croft M. , Ignatov A. Yu.
Published: July 2002

A systematic study of spin-dependent Mn K-edge x-ray absorption spectra was performed on La1−xCaxMnO3. By examining the changes in the pre-edge spectra with the temperature, a model of the excitation process is developed and used to predict the temperature dependent changes in the local magnetic ordering about Mn sites. The approach is of general applicability to perovskite systems. It can be used to determine the change in the local magnetic order (ferromagnetic versus antiferromagnetic) about a transition metal site upon going through a transition or as the result of external perturbations.
Anomalous Hall effect in La1−xCaxCoO3
Authors: Baily S. A. , Salamon M. B. , Kobayashi Y. , Asai K.
Published: July 2002

La 1−x Ca x CoO 3 films show the largest anomalous Hall effect of any ferromagnetic metal. The anomalous Hall coefficient increases as x decreases. At doping below 0.2 La1−xCaxCoO3 is insulating and shows spin-glass behavior at low temperature. We have measured the Hall effect and magnetic behavior of an x=0.15 crystal. It shows cluster-glass or correlated-spin-glass behavior at intermediate temperatures. The anomalous Hall effect does not depend on the total magnetization, M, but on the ferromagnetic correlations of the glass.
Visualization of low-frequency liquid surface acoustic waves by means of optical diffraction
Authors: Miao Runcai , Yang Zongli , Zhu Jingtao , Shen Changyu
Published: July 2002

A technique for low-frequency liquid surface acoustic wave (LFLSAW) visualization is developed based on the light diffraction. The technique is capable of real-time characterization of wave amplitude, and it produces highly visible stationary diffraction pattern for a low-frequency wave (a few hundreds Hz). The disappearance of the zero-order diffraction fringe, which corresponding to the 100% diffraction efficiency, was experimentally observed for using this technique. The correlation of the diffraction pattern to the LFLSAW amplitude is also experimentally established.
Si
–
SiO
2
barrier height and its temperature dependence in metal-oxide-semiconductor structures with ultrathin gate oxide
Authors: Hadjadj A. , Simonetti O. , Maurel T. , Salace G. , Petit C.
Published: July 2002

The potential distribution across n+ polycristalline silicon (poly-Si)/SiO2/Si(p) structures, with an oxide layer thinner than 4 nm, was determined using a full quantum self-consistent model. When applied to capacitance–voltage measurements, it allows an accurate determination of the oxide thickness tox to be made. When applied to current–voltage measurements, in the Fowler–Nordheim regime, it leads to an accurate determination of the barrier height Φ at the interface between the emitting poly-Si gate electrode and the oxide, over a temperature range 20–250 °C. The results show a constant Φ(0 K) for 3 nm<tox⩽9 nm. However, the temperature sensitivity |dΦ/dT| increases from 0.35 to 0.7 meV/K with tox reduction.
Composites of C60 based poly(phenylene vinylene) dyad and conjugated polymer for polymer light-emitting devices
Authors: Wang Shu , Yang Junlin , Li Yuliang , Lin Hongzhen , Guo Zhixin , Xiao Shengxiong , Shi Zhiqiang , Zhu Daoben , Woo Hyung-Suk , Carroll David L. , Kee In-Seo , Lee Ji-Hoon
Published: July 2002

A C60-based poly(phenylene vinylene) (PPV) dyad poly{(2,5-di-pentoxyl-phenylene)-4diylvinylene-3,6-[9-(1-azafulleroid-propyl)-carbazolenevinylene]} (PPV–AFCAR) and an emissive conjugated polymer poly{1,4[2-(3,7-dimethyloctyloxy)-3,5,6-trimethoxy]phenylene vinylene} (POMPV) were prepared to investigate the role of [60]fullerene in conjugated polymer composites. Multilayer organic light-emitting devices with the configuration of indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/blends/2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole(Bu-PBD)/LiF/Al were fabricated using PPV–AFCAR as a dopant and POMPV as an emissive material.
Superconductivity in thin-film YBa2Cu3O7−δ/La0.7Ca0.3MnO3 bilayers
Authors: Allsworth M. D. , Chakalov R. A. , Colclough M. S. , Mikheenko P. , Muirhead C. M.
Published: July 2002

We report the influence of the magnetic state of thin films of La0.7Ca0.3MnO3 (LCMO) on the superconducting order parameter in LCMO/YBa2Cu3O7−δ (YBCO) thin-film bilayers. We find that the number density of Cooper pairs is enhanced at the coercive field of the LCMO layer relative to that where the magnetic moment is saturated. This effect is at most ∼10% and is only observable within a few degrees of the superconducting transition temperature. Experiments with thin SrTiO3 layers between the LCMO and YBCO layers provide strong evidence that the effect is a consequence of the spin-polarized nature of the electrons at the interface, rather than a direct magnetic effect.
Mechanisms of oxygen incorporation in indium–tin–oxide films deposited by laser ablation at room temperature
Authors: Morales-Paliza M. A. , Haglund R. F. , Feldman L. C.
Published: July 2002

The use of O218 as a background gas in pulsed-laser deposition (PLD) of indium–tin–oxide (ITO) films allows clear discrimination between the two oxygen sources in the films: target and background gas. A study of both stoichiometric and electrical properties of the ITO films in terms of the relative contributions of the two oxygen sources at different background-gas pressures is presented in this work. The film with lowest resistivity (∼4×10−4 Ω cm) incorporates 28% oxygen from the background gas as compared to the total oxygen in the film. This relatively strong oxygen incorporation from the background gas suggests a strong exchange rate between O16 from the target and O18 from the background gas in the “plume” phase of the PLD process.
Molecular patterning through high-resolution polymethylmethacrylate masks
Authors: Hang Qingling , Wang Yuliang , Lieberman Marya , Bernstein Gary H.
Published: July 2002

Electron beam lithography was used to make nanometer trenches in thin polymethylmethacrylate (PMMA). After development, the wafers were dipped in an aqueous solution of the Creutz–Taube ion [(NH3)5Ru(pyrazine)Ru(NH3)5](o-toluenesulphonate)5 (CT5), and the PMMA was removed with acetone or dichloromethane. Atomic force microscopy and x-ray photoelectron spectroscopy were used to investigate the surface characteristics of wafers after dissolution of the PMMA and to confirm the binding of a monolayer of CT5 molecules on the wafer within the areas delimited by the PMMA trenches. This masking technique has so far been demonstrated to pattern 35 nm lines of a monolayer of CT5 molecules on silicon dioxide.
Strain-induced surface segregation in In0.5Ga0.5As/GaAs heteroepitaxy
Authors: Ohtake Akihiro , Ozeki Masashi , Terauchi Masami , Sato Futami , Tanaka Michiyoshi
Published: July 2002

Surface segregation and strain relaxation processes in layer-by-layer growing InxGa1−xAs films on the GaAs(001) and GaAs(111)A substrates have been studied. While the lattice strain is almost relaxed by introducing misfit dislocations on the (111)A substrate, the in-plane lattice constant of the growing film on the (001) substrate hardly changes throughout the growth. We found that a significant amount of In atoms is segregated to the growing surface on the (001) substrate, which is induced by the lattice strain at the coherent (001) interface.
Classical microwave response of coupled quantum dots in single-wall carbon nanotubes
Authors: Ishibashi K. , Suzuki M. , Ida T. , Aoyagi Y.
Published: July 2002

The dc transport properties of coupled quantum dots in single-wall carbon nanotubes have been studied below 100 mK under microwave irradiation. The Coulomb oscillations for different microwave power were similar to those for different bias voltages without microwave. The current–voltage curves showed simple shifts as the microwave power was increased. These experimental observations may be explained by the classical response of the coupled quantum dots to the microwave irradiation.
Formation mechanism of the multilayered-structure barrier of WNx/Si(100)
Authors: Choi I. S. , Park J. C. , Choi J. T. , Kim H. J. , Lee S. Y.
Published: July 2002

The chemical bonding states, microstructure, and the formation mechanism of an interfacial layer between WNx/Si(100) treated by rapid thermal annealing at various temperatures were investigated. It was found that the ultrathin interfacial layer had the multilayered structure of SiO2/SiOxNy/nano-WSi2. The interfacial silicon nitride layer formed by lower annealing temperatures was converted into an oxide layer by increasing the annealing temperature. The thickness of the interfacial oxide layer increased from ∼34 to ∼50 Å with the annealing temperature. It was found that the interfacial layer played a role as a barrier against silicidation between W and Si(100) up to 1000 °C.
Adiabatic switching in coupled quantum dot systems facilitated by the coexistence of “molecular” and “atomic” states
Authors: Akis R. , Vasileska D. , Ferry D. K.
Published: July 2002

We model a double quantum dot system defined by a split metal gate over a GaAs/AlGaAs heterostructure, with the dots being coupled via a quantum point contact. Hybridization effects analogous to that of molecules are apparent. However, contrary to some previous studies, we find that there can be a coexistence of “atomic” and “molecular” regimes. The resulting behavior may be utilized to create a device that switches adiabatically, providing a possible route to dissipation-free computing.
Dependence of fractal conductance fluctuations on soft-wall profile in a double-layer semiconductor billiard
Authors: Micolich A. P. , Taylor R. P. , Davies A. G. , Fromhold T. M. , Linke H. , Macks L. D. , Newbury R. , Ehlert A. , Tribe W. R. , Linfield E. H. , Ritchie D. A.
Published: July 2002

We present a semiconductor system featuring two billiards located one on top of the other. We use this system to study the dependence of fractal conductance fluctuations on soft-wall potential profile and show the fluctuations to be surprisingly robust to changes in profile.
Silver photodoping into Al–ZnSe for application to white light emitters
Authors: Lee Hyun-Yong , Takai Toshiaki , Yao Takafumi
Published: July 2002

Room-temperature Ag photodoping into crystalline Al-doped ZnSe grown by molecular-beam epitaxy (MBE) has been achieved. A promising approach to apply to a patterned white light emitter has also been proposed. An Al–ZnSe with Ag islands was illuminated with a HeCd laser at 300 K and annealed in the MBE chamber. Then, their photoluminescence characteristics were measured in real time. The self-activated (SA) emission, observed in as-grown Al–ZnSe, undergoes a considerable change in intensity and band energy position through Ag photodoping and subsequent annealing. The resultant emission bands centered at 2.145 eV and 2.250 eV are assigned as a donor-to-acceptor pair transition related with Ag impurities rather than SA centers. In addition, chromaticity can be controlled by an adjustment of photoirradiated Ag-doped area.
Single-flux-quantum pump based on a three-junction superconducting quantum interference device
Authors: Mizugaki Yoshinao , Chen Jian , Nishikata Satoshi , Sugi Keiji , Nakajima Kensuke , Yamashita Tsutomu
Published: July 2002

We demonstrate the operation of a single-flux-quantum (SFQ) pump that is electromagnetically dual to the single-electron pump. The circuit is composed of a three-junction superconducting quantum interference device with three control lines. By applying two phase-shifted rf signals magnetically, the SFQ-pump transfers one SFQ per one cycle of the rf signals even at zero- and negatively-biased condition. The circuit was fabricated using a Nb/AlOx/Nb Josephson junction technology. When we fed rf signals of 4.5 GHz, we observed a Shapiro step crossing the zero-current axis. Periodic dependence of voltage at the zero-biasing state upon dc offset flux was also confirmed.
Forming silicon carbon nitride crystals and silicon carbon nitride nanotubes by microwave plasma-enhanced chemical vapor deposition
Authors: Chang Hui Lin , Hsu Chih Ming , Kuo Cheng Tzu
Published: July 2002

Catalyst-assisted silicon carbon nitride (SiCN) nanotubes and SiCN crystals are prepared. The SiCN nanotubes and SiCN crystals are formed by gaseous sources of CH4/N2/H2 and CH4/N2, respectively, and using solid Si columns arranged symmetrically around the specimen as additional Si sources. The formation of the tubular structure is related to the ambient of process that includes H2 gas, which is considered to delay the action of the so-called catalyst poisons and keep the tube end open during growth. Analysis shows that the SiCN crystals exhibit tetragonal or hexagonal shapes with sizes of about several microns, and multibonding structures. In contrast, the SiCN tubes are randomly orientated with various diameters, and graphitelike structure. The growth mechanisms of SiCN crystals and SiCN nanotubes are discussed.
Some remarks on coherent structures out of chaos in planetary atmospheres and oceans
Authors: Nezlin Mikhail V.
Published: July 2002

In the context of planetary atmospheres and oceans, it is natural to define ‘‘coherent structures’’ as ‘‘long-lived,’’ or ‘‘solitary,’’ Rossby vortices. These can be described by the generalized Charney–Obukhov equation (in fluid dynamics) or the analogous generalized Hasegawa–Mima equation (in plasma physics). These two equations contain KdV-type nonlinearities which (together with the compensating dispersive spreading) determine the formation of the coherent structures and explain the clear-cut cyclonic/anticyclonic asymmetry observed experimentally in long-lived planetary Rossby vortices. Examples are given of natural vortices which are (and which are not) coherent structures.
Pseudo-spectral methods and linear instabilities in reaction-diffusion fronts
Authors: Jones Wesley B. , O’Brien James J.
Published: July 2002

We explore the application of a pseudo-spectral Fourier method to a set of reaction-diffusion equations and compare it with a second-order finite difference method. The prototype cubic autocatalytic reaction-diffusion model as discussed by Gray and Scott [Chem. Eng. Sci. 42, 307 (1987)] with a nonequilibrium constraint is adopted. In a spatial resolution study we find that the phase speeds of one-dimensional finite amplitude waves converge more rapidly for the spectral method than for the finite difference method. Furthermore, in two dimensions the symmetry preserving properties of the spectral method are shown to be superior to those of the finite difference method. In studies of plane/axisymmetric nonlinear waves a symmetry breaking linear instability is shown to occur and is one possible route for the formation of patterns from infinitesimal perturbations to finite amplitude waves in this set of reaction-diffusion equations.
Design of magnetic-field gradient coils for imaging
Authors: Quine Richard W. , Rinard George , Rugg Donald E. , Eaton Gareth R. , Eaton Sandra S.
Published: July 2002

A computational procedure is outlined for the design of magnetic-field gradient coils for producing a gradient along one axis under realistic constraints of finite coil dimensions, wire packing in the coil windings, desired gradient strength, and desired gradient linearity.
Taking the generality out of general relativity
Authors: Bernstein R.
Published: July 2002

Although much has been written about relativity, little delves into its actual equations. Even rarer does one find relativity used in any sort of computation, such as one would find in a computer simulation. This is sad. it is hoped to be shown here not just the problems one might encounter in writing such a simulation, but also that one can perform a simulation of general relativity without too much effort. In fact, our experience has been that a program simulating geodesic motion in general relativity requires no more lines of code than a corresponding program to simulate planetary motion using Newton's laws. The relativity program is straightforward and general, but slow. However, by mechanically substituting the equations for the gravitational time-dilation metric of the Schwarzchild metric, and then performing algebraic simplifications, one can obtain a program whose simulation time is as fast as a corresponding Newtonian motion simulation. The resulting customized relativity programs are again short and simple. Customization does, however, obscure a little relation between the general equations and those actually used.
Parametric cubic spline-fitting programs for open and closed curves
Authors: Smith D. A.
Published: July 2002

Three numerical recipes are given using Ahlberg’s algorithm for the parametric fitting by cubic splines of a set of n-dimensional data points; subroutine SPLINE for an open curve, PSPLINE for a closed curve, and EPSPLINE for an axially symmetric surface (surface of revolution). Parametric routines are not troubled by intersections, and offer more flexibility in dealing with boundary conditions. One subroutine call is required for each data dimension. The execution speed of all programs is comparable to standard routines for an open curve.
Finding the needle in the haystack: Algorithms for conformational optimization
Authors: Andricioaei Ioan , Straub John E.
Published: July 2002

Algorithms are given for comformational optimization of proteins. The protein folding problems is regarded as a problem of global energy mimimization. Since proteins have hundreds of atoms, finding the lowest-energy conformation in a many-dimensional configuration space becomes a computationally demanding problem.© American Institute of Physics.
Implantation of dopants into indium phosphide
Authors: Zeisse Carl R. , Wilson Robert G. , Hopkins Craig G.
Published: July 2002

Seven donors (Si, S, Ge, Se, Sn, Te, and Pb) and nine acceptors (Be, Mg, Cr, Mn, Fe, Cu, Zn, Cd, and Hg) have been implanted into liquid-encapsulated Czochralski InP(Fe). For each dopant, the first four moments of the density profile have been extracted by fitting Pearson IV distributions to secondary ion mass spectrometry data. The results suggest that, when implanting into indium phosphide at reduced energies not too far from 1, the mean will be 1/5 larger than the theoretical prediction and the standard deviation will be twice the theoretical prediction.
An electron-beam controlled diffuse discharge switch
Authors: Schoenbach K. H. , Schaefer G. , Kristiansen M. , Krompholz H. , Harjes H. C. , Skaggs D.
Published: July 2002

The performance of externally controlled, high-pressure, diffuse discharges as switching elements in pulse power systems is strongly determined by the recombination and attachment processes in the fill gas. To obtain high control efficiency and fast response of the diffuse discharge switch the discharge must be attachment dominated with the attachment rate coefficient increasing with field strength. An electron-beam controlled diffuse discharge system was constructed to study the behavior of pulsed discharges in the submicrosecond range in gas mixtures containing N2 as a buffer gas and small additives of electronegative gases. The results of experiments in N2 plus N2O were compared with values obtained with a Monte Carlo code and a rate equation calculation.
Quantum theory of electron transport in the Wigner formalism
Authors: Lin J. , Chiu L. C.
Published: July 2002

A unified theory of electron transport in a phonon bath using the Wigner formalism is presented. The resulting quantum kinetic equation not only lends itself to a phase space description of the electron transport, but also includes higher-order effects such as degeneracy, collisional broadening, and intracollisional field effect. The equation provides a rigorous theoretical foundation for Monte Carlo simulation of high-field electron transport in submicron and quasi-two-dimensional device structures.
Correlation between chemistry and the amount of mixing in bilayers submitted to ion bombardment
Authors: d’Heurle F. , Baglin J. E. E. , Clark G. J.
Published: July 2002

Experiments conducted with bilayers of elements so chosen as to maximize chemical differences and to minimize physical differences (e.g., atomic weights) demonstrate the importance of chemistry in determining the amount of interaction which results from ion mixing experiments. These results emphasize the dominance of chemical factors which are at least neglected, if not totally ignored, in the modeling of ion mixing effects. Ion bombardment of Pd/Hf bilayers causes the formation of Pd3Hf; the existence of such compounds was not detected in other bilayers of ‘‘similar’’ elements.
Comparison of plated Co-P and sputtered Co-Re as recording media based on nucleation, growth, structure, and magnetics
Authors: Khan Mahbub R. , Lee Jae I.
Published: July 2002

The nucleation, growth, and microstructure of electroless plated Co-P and sputtered Co-Re have been studied and compared to their magnetics. Co-P starts to nucleate as islands with low nucleation density and high coercivity. The film becomes continuous at a thickness of 300 Å and has a rough surface. Co-Re, on the other hand, forms solid solutions and shows initial growth of high nucleation density and low coercivity. The superparamagneticlike range of Co-P is narrower than Co-Re. The impact of growth mechanism on the signal to noise ratio is analyzed and some recording performance data is presented.
A theory of plasma-assisted chemical vapor transport processes
Authors: Zarowin C. B.
Published: July 2002

A theory is presented for plasma-assisted chemical vapor transport (PACVT) processes, applicable to reactive ion or plasma etching, plasma-assisted chemical vapor deposition and, in the absence of a plasma, low-pressure thermally driven chemical vapor transport processes. The central results of this theory are the steady-state or nonequilibrium gas-phase chemical concentrations in the vicinity of the reacting surfaces and the rate at which the etch/deposit solid is transported into or out of the reactor volume and/or between reactor surfaces as a function of reactor geometry, (ion-bombardment-enhanced) surface reaction rates, diffusion, and flow rates. Taking the rate-limiting chemical reactions to be heterogeneous leads to a transport equation that predicts behavior for such processes that is essentially in agreement with experiment. Instead of depending on the homogeneous reaction kinetics, this behavior stems from the competition between surface reaction rates, diffusion, and flow rates, yielding a dependence on reactive surface to volume ratios or reactor loading. In contrast to the preceding loading equation, this one is applicable to the entire range of flow for which the transport rate depends on reactor loading, while the reciprocal of the etch rate still exhibits the linear dependence on loading obtained earlier. Also, the theory clarifies some previously observed, but inadequately explained, phenomena unique to PACVT, such as increased flow rate sensitivity for more exoenergetic reactions, flow-dependent ultrahigh etch selectivity between conducting and insulating films, and etch pattern sidewall deposition for endoenergetic reactions.
A structure marker study for Pd2Si formation: Pd moves in epitaxial Pd2Si
Authors: Lien C.-D. , Nicolet M-A. , Pai C. S.
Published: July 2002

A sample with the configuration Si (111)/single crystalline Pd2Si/polycrystalline Pd2Si/Pd is used to study the dominant moving species during subsequent Pd2Si formation by annealing at 275 °C. The interface between monocrystalline and polycrystalline Pd2Si is used as a marker to monitor the dominant moving species. The result shows that Pd is the dominant moving species in the monocrystal. off
Selective saturation of paramagnetic defects in electron- and neutron-irradiated GaAs
Authors: Goltzene A. , Meyer B. , Schwab C. , Beall R. B. , Newman R. C. , Whitehouse J. E. , Woodhead J.
Published: July 2002

A comparison of the electron paramagnetic resonance spectra obtained in fast neutron- and electron-irradiated GaAs crystals has confirmed the simultaneous presence of the quadruplet and singlet spectra, ascribed previously to As4+Ga and V2−Ga centers. Only in electron-irradiated material, however, are both signals separated by the selective microwave power saturation of the quadruplet. This apparent disparity is ascribed to a difference in the coupling between the two partners in the As4+Ga-V2−Ga associated complexes.
Flexible A-15 superconducting tape via the amorphous state
Authors: Clapp Mireille Treuil , Shi Donglu
Published: July 2002

The melt spinning technique was used to rapidly solidify superconducting materials. In the Ti3Nb6Mo3Si4 alloy system, it was possible to form metastable A-15 and amorphous ribbons as the quenching rate was increased. The liquid-quenched A-15 ribbons were extremely brittle, which is typical of this crystal structure. The metastable A-15 phase could also be formed by annealing the amorphous ribbons. These, however, were far more flexible, their percent elongation being up to 30 times greater than that of the liquid quenched A-15’s. The flexibility appeared to depend on grain size, and increased as the grain size decreased. This is consistent with behavior observed in other brittle materials of a brittle to ductile transition as a function of grain size.
Double-drift plasma instabilities in contiguous two-dimensional electron and hole gases: A solid-state two-stream amplifier
Authors: Crowne Frank
Published: July 2002

A new type of solid-state broad-band amplifier is proposed, which makes use of pairs of two-dimensional electron and hole gases which are created at the interfaces of a compositional-doping superlattice. It is shown that when these carrier gases are drifted in opposite directions by an applied electric field, the system is unstable against the formation of electrostatic waves. This instability is analogous to the two-stream instability of classical plasma physics, and can be used to amplify properly input signals over a wide range of frequencies. Calculations are presented for a single pair of gases side by side; considerable gain is predicted even for this single-pair configuration.
Infrared spectroscopic markers of conformational defects in polymethylene chain molecules
Authors: Jona P. , Gussoni M. , Zerbi G.
Published: July 2002

Infrared absorption bands which can be related to conformational defects in long polymethylene chains are calculated both in frequency and in intensity. End-gauche, kink, and U-fold conformational distortions are considered; a complete characterization is given in the frequency range from 700 to 1400 cm−1.