bluuebunny/crossref_metadata_2025 huggingface dataset:
Multichannel bit error rate tester for fiber optic transceiver testing
Authors: Green Samuel I.
Published: September 2002

I describe an inexpensive and portable method used to conduct bit error rate test measurements in an aircraft at altitude to measure susceptibility of gigabit fiber optic transceivers to ionizing radiation. This method uses a built-in test feature of Texas Instruments GigaBit Ethernet transceiver chips. During a 20 min flight at 39 000 ft altitude, none of the eight test channels using Finisar FTRJ-8519-1 fiber optic transceivers indicated any bit errors.
Magneto-optical microscope magnetometer for simultaneous local probing of magnetic properties
Authors: Choe Sug-Bong , Kim Dong-Hyun , Cho Yoon-Chul , Jang Hyuk-Jae , Ryu Kwang-Su , Lee Hae-Seung , Shin Sung-Chul
Published: September 2002

The design of a magneto-optical microscope magnetometer (MOMM) for simultaneously probing local magnetic properties is described. The MOMM consists of an optical polarizing microscope capable of magneto-optical contrast that is used as a magnetometer by sweeping a magnetic field from an electromagnet. Due to full-field optical imaging, as opposed to single photodiode detection, the system is capable of simultaneous measurement of magnetic hysteresis loops and magnetization viscosity curves on 8000 individual local regions of 400×400 nm2 area in ferromagnetic materials. The most striking feature of the system is that it provides two-dimensional maps of the local magnetic properties including the coercivity, the switching time, and the activation magnetic moment from two-dimensional arrays of the hysteresis loops and the viscosity curves. We present the local magnetic properties and their correlations in Co/Pd multilayer films prepared by electron-beam evaporation.
Intrinsic and extrinsic charge carrier photogeneration in phenyl-substituted polyphenylenevinylene-trinitrofluorenone blend systems
Authors: Im C. , Emelianova E. V. , Bässler H. , Spreitzer H. , Becker H.
Published: September 2002

Spectral, field, and temperature dependencies of steady-state photoconductivity were studied in thin films of pure phenyl substituted copolymeric polyphenylenevinylene (PhPPV) and PhPPV doped by trinitrofluorenone. The films were sandwiched between indium tin oxide (ITO) and aluminum as well as between two aluminum contacts. Typical surface extrinsic carrier photogeneration was observed in ITO/PhPPV/Al samples with positively biased ITO while the intrinsic photoconductivity dominated in Al/PhPPV/Al samples and ITO/PhPPV/Al sandwiches with negatively biased ITO. Charge carrier photogeneration in both doped and undoped PhPPV at higher photon excess energies was found to be in good agreement with predictions of the hot exciton dissociation model. At low excess photon energy of the inducing light, carrier photogeneration is ascribed to dissociation of optical excitations on charge transfer centers which are either dopant molecules in the doped samples or intrinsic defects in the pure material.
Analytical time-dependent Hartree–Fock schemes for the evaluation of the hyper-Raman intensities
Authors: Quinet Olivier , Champagne Benoı̂t
Published: September 2002

Two analytical procedures based on the time-dependent Hartree–Fock (TDHF) scheme are elaborated to evaluate the first derivatives of the dynamic first hyperpolarizability with respect to atomic Cartesian coordinates. In the first scheme, the mixed third-order TDHF equations are solved iteratively to obtain the third derivatives of the linear combination of atomic orbitals coefficients twice with respect to external dynamic electric fields and once with respect to atomic Cartesian coordinates. The second takes advantage of the 2n+1 rule and interchange relations to express the first derivatives of the dynamic first hyperpolarizability with respect to atomic Cartesian coordinates in terms of lower-order derivatives. Both procedures have been implemented in the GAMESS quantum chemistry package. Applications focus on the characterization of the frequency dispersion of the first derivatives of the first hyperpolarizability with respect to vibrational normal coordinates of H2O, NH3, and CH4 as well as on the determination of nonresonant hyper-Raman intensities within the double harmonic oscillator approximation.
Synthesis and swelling behavior of a weak polyacid brush
Authors: Biesalski M. , Johannsmann D. , Rühe J.
Published: September 2002

We describe the synthesis and the swelling behavior of a weak polyacid brush attached to a solid surface. Monolayers of poly methacrylic acid are generated by using self-assembled monolayers of an azo initiator and radical chain polymerization of methacrylic acid monomer at the surface of a planar substrate in situ. The thickness of the resulting surface-attached polyelectrolyte brush can be adjusted between 5 and 400 nm in the dry, collapsed state. The swelling behavior in water as a function of pH and salt concentration is investigated by multiple-angle null-ellipsometry. At high salt concentrations the brush thickness decreases due to electrostatic screening. At low concentration, however, an increase of thickness with ion concentration is found.
Fully leaky guided wave determination of the original alignment direction for the directors at the walls in a twisted nematic liquid crystal cell
Authors: Yang F. Z. , Gao H. J. , Sambles J. R.
Published: September 2002

Fully leaky guided optical modes are used to explore the director profile in a twisted nematic liquid crystal cell built using a pair of high-index glass plates. This allows access to the pseudocritical angles corresponding to the liquid-crystal indices. Optical data is recorded over a range of angles of incidence with the cell subject to ac voltages. At higher-applied fields, the director in the cell center aligns almost homeotropically. Then the two surface regions become elastically decoupled, the directors at the surfaces realigning along the original alignment axes. Beyond the pseudo-critical angle corresponding to the low index of the liquid-crystal two minima of the polarization conserving transmission signal, for transverse electric polarization, TSS (over a particular range of incidence angles) are found as the cell rotation angle is changed. These two minima give the original alignment directions of the director, the easy axes, at the two substrates, information vital to the measurement of the torsional anchoring energies at the interfaces of the cells.
Space-charge dynamics in photorefractive polymers
Authors: Ostroverkhova Oksana , Singer Kenneth D.
Published: September 2002

The model of space-charge formation in photorefractive polymers due to Schildkraut and Buettner has been modified to include thermally accessible deep traps as well as shallow traps. The dynamic equations have been solved semiempirically using independent measurements of photoconductive properties to predict photorefractive dynamics. Dependencies of the dynamics on charge generation, mobility, trap density, acceptor density, ionized acceptor density, as well as their associated rates are examined. The magnitude of the fast time constant of photorefractive development is successfully predicted. The introduction of deep traps into the model has allowed us to qualitatively predict the reduction in speed due to deep trap filling and ionized acceptor growth. Experimental studies of photoconductivity and photorefraction (PR) in several polyvinyl carbazole photorefractive composites are carried out to demonstrate the applicability of the model. By choosing chromophores with different ionization potentials and by varying the chromophore concentrations, we investigate the influence of the chromophore ionization potential on the photoelectric and PR properties and reveal the nature of deep traps in the composites and their contribution to both photoconductivity and PR dynamics. Effects of plasticizer components are also discussed.
The asymptotic region of the potential energy surfaces relevant for the O(3P)+O2(X 3Σg−)⇌O3 reaction
Authors: Rosmus Pavel , Palmieri Paolo , Schinke Reinhard
Published: September 2002

The potential energy functions for all states of ozone correlating with the lowest O(3P)+O2(X 3Σg−) asymptote have been calculated in the asymptotic region employing correlated electronic wave functions. For linear ozone, the Σs states (s=1,3, and 5) lie above the corresponding Πs states. For bent geometries the Π states split into Renner–Teller components with A′ and A″ symmetry, respectively. While the Π1 and Π3 states lead to bent–bent Renner–Teller pairs, the Π5 state gives rise to a linear/linear pair of states. The different spin multiplets emerging from the Π states cross for valence angles around 160° and the A′1 component becomes the lowest one. The matrix elements of the spin-orbit operator have also been calculated. They are dominated by the atomic P3 contributions and their dependence on the mutual orientation of the O2 molecule and the O atom is small. In the regions where the states correlating to the linear Π1,3,5 cross, i.e., for valence angles between 150° and 180° and close to 90°, the mixing among the singlet, triplet, and quintet states is strong and the electron spin quantum number is no longer a good quantum number.
Characterization of GaAs/AlGaAs laser mesas regrown with semi-insulating GaInP by scanning capacitance microscopy
Authors: Douhéret O. , Anand S. , Barrios C. Angulo , Lourdudoss S.
Published: September 2002

In this work, cross-sectional scanning capacitance microscopy (SCM) is used to investigate GaAs/AlGaAs buried heterostructure lasers. Laser mesas are buried with GaInP:Fe selectively regrown by hydride vapor phase epitaxy. It is shown that a complete 2D map of the electrical properties of device structure including, delineation of regrown interfaces and electrical nature of the regrown GaInP layer can be obtained. The behavior of the SCM signal with ac bias is used to verify the semi-insulating nature of the regrown layer at different locations of the sample. The measured SCM signal for the regrown GaInP:Fe layer is uniformly zero, indicating very low free carrier densities and confirming semi-insulating properties. This observation strongly suggests, in addition, uniform Fe incorporation in the regrown layers, close to and far away from the mesa. Finally, a nanoscale feature in the SCM contrast appearing as a bright (dark) spot in dC/dV mode (feedback bias mode) is observed at the mesa sidewall close to the interface between the regrown GaInP:Fe and the p-cladding layer. The origin of this contrast is discussed in terms of local band-bending effects and supported by 2D Poisson simulations of the device structure.
Electrostatics in periodic slab geometries. I
Authors: Arnold Axel , de Joannis Jason , Holm Christian
Published: September 2002

We propose a new method to sum up electrostatic interactions in two-dimensional (2D) slab geometries. It consists of a combination of two recently proposed methods: the 3D Ewald variant of Yeh and Berkowitz [J. Chem. Phys. 111, 3155 (1999)] and the purely 2D method MMM2D by Arnold and Holm [Chem. Phys. Lett. 354, 324 (2002). The basic idea involves two steps: First we use a three-dimensional summation method whose summation order is changed to sum up the interactions in a slab-wise fashion. Second we subtract the unwanted interactions with the replicated layers analytically. The resulting method has full control over the introduced errors. The time to evaluate the layer correction term scales linearly with the number of charges, so that the full method scales like an ordinary 3D Ewald method, with an almost linear scaling in a mesh based implementation. In this paper we will introduce the basic ideas, derive the layer correction term, and numerically verify our analytical results.
Torque magnetometry in pulsed magnetic fields with use of a commercial microcantilever
Authors: Ohmichi E. , Osada T.
Published: September 2002

A miniature torquemeter for use in a pulsed magnetic field is developed by utilizing a commercially available piezoresistive microcantilever. The high sensitivity of ∼5×10−13 Am2 at 38 T is achieved. The response to faster signals were considerably improved due to high eigenfrequency of the cantilever (f∼250–300 kHz). In this article, we successfully demonstrate the magnetic torque data of samples of sub-μg order in pulsed magnetic fields up to 38 T with pulse duration of less than 60 ms. We also found that the de Haas–van Alphen data are in good agreement with the previous reports obtained in steady magnetic fields.
Achieving highly conductive AlGaN alloys with high Al contents
Authors: Nam K. B. , Li J. , Nakarmi M. L. , Lin J. Y. , Jiang H. X.
Published: September 2002

Si-doped n-type AlxGa1−xN alloys were grown by metalorganic chemical vapor deposition on sapphire substrates. We have achieved highly conductive n-type AlxGa1−xN alloys for x up to 0.7. A conductivity (resistivity) value of 6.7 Ω−1 cm−1 (0.15 Ω cm) (with free electron concentration 2.1×1018 cm−3 and mobility of 20 cm2/Vs at room temperature) has been achieved for Al0.65Ga0.35N, as confirmed by Hall-effect measurements. Our experimental results also revealed that (i) the conductivity of AlxGa1−xN alloys continuously increases with an increase of Si doping level for a fixed value of Al content and (ii) there exists a critical Si-dopant concentration of about 1×1018 cm−3 that is needed to convert insulating AlxGa1−xN with high Al content (x⩾0.4) to n-type.
Substrate bias effect on the formation of nanocrystalline diamond films by microwave plasma-enhanced chemical vapor deposition
Authors: Yang Tien-Syh , Lai Jir-Yon , Wong Ming-Show , Cheng Chia-Liang
Published: September 2002

The influence of negative substrate bias on the crystallinity, morphology, and growth rate of the diamond films deposited using microwave plasma-enhanced chemical vapor deposition in 1% CH4/H2 plasma were investigated. The nanocrystalline diamond films were produced exclusively under the biasing at −250 V. With −50 V biasing, faceted (111) microcrystalline diamond films at higher growth rate than no-bias samples were produced. When the biasing between −100 and −200 V, faceted (100) diamond films with decreasing grain size were favored, and the growth rates were gradually reduced along with the increasing biasing. The results indicate that the etching efficiency of H+ ions is enhanced with the increasing kinetic energy obtained from the increasing bias voltage. On the other hand, CHx+ ions at −250 V biasing would have sufficient energy to perform the ion subplantation model to grow the nanocrystalline diamond films by bias-enhanced nucleation.
In situ study of void growth kinetics in electroplated Cu lines
Authors: Liniger E. , Gignac L. , Hu C.-K. , Kaldor S.
Published: September 2002

An in situ electromigration apparatus was used to study the kinetics of void growth in unpassivated, electropolated copper damascene lines. Voids were observed to grow by consuming grains in a stepwise fashion, either by grain thinning or by an edge displacement mechanism. Surface diffusion was found to be the primary diffusion path for void growth. In addition, grain boundaries provided a secondary path for copper diffusion in polycrystalline structures and nucleation sites for void growth in bamboo structures. Void growth rate was measured as a function of sample temperature and linewidth using a scanning electron microscope. An electromigration activation energy of 0.9±0.1 eV was determined for the copper voiding process. The effect of linewidth on void growth rate was also investigated and found to be negligible, consistent with a surface-diffusion dominated model for void growth. The in situ apparatus also made it possible to directly correlate changes in electrical resistance with physical changes taking place in the test structures.
High-accuracy coupled-cluster computations of bond dissociation energies in SH, H2S, and H2O
Authors: Peebles Lynda R. , Marshall Paul
Published: September 2002

The first and second bond dissociation enthalpies of H2S have been investigated at up to the CCSD(T)/aug-ccpV6Z level of theory. Corrections for core/valence electron correlation, anharmonic zero point vibrational energy and relativistic effects were followed by extrapolation to the complete basis set limit. Analysis of direct dissociation yields D0(S–H)=349.9 and D0(HS–H)=375.8 kJ mol−1. Together these imply an atomization enthalpy for H2S about 1 kJ mol−1 larger than literature evaluations. Consideration of exchange of a second H atom from OH to SH yields D0(HS–H)=376.2 kJ mol−1. The two computations of D0(HS–H) lie within 0.5 kJ mol−1 of a recent spectroscopic measurement of D0(HS–H)=376.24±0.05 kJ mol−1 [R. C. Shiell, X. K. Hu, Q. J. Hu, and J. W. Hepburn, J. Phys. Chem. A 104, 4339 (2000)]. The deuterated analogs SD and D2S are also considered. There is also accord to within 1.5 kJ mol−1 with D0(S–H)=348.4±0.8 kJ mol−1, which we derive from the experimental literature. We propose revised enthalpies of formation, ΔfH0(2Π3/2SH)=142.6±0.8 kJ mol−1 and ΔfH298.15(SH)=143.1±0.8 kJ mol−1. The results suggest the dominant uncertainties in these high-level calculations come from the basis set extrapolation and scalar relativistic terms, and that both contribute about 1 kJ mol−1 uncertainty. We also obtain D0(H–OH)=492.6 kJ mol−1, which compares well with recent experiments.
Microscopic simulation of structure and dynamics of water and counterions in a monohydrated montmorillonite
Authors: Marry V. , Turq P. , Cartailler T. , Levesque D.
Published: September 2002

Models of swelling clays are studied by computer simulations (Monte Carlo and molecular dynamics). We focus on the comparison of structural and dynamic properties of two montmorillonites with different kinds of counterions Na+ and Cs+. The calculated values are compared with available experimental quantities such as interlayer spacing as a function of water content and diffusion coefficients of both water molecules and counterions in the monohydrated state. The results are consistent with experimental values and previous simulations. For the dynamics, the short time behavior of water as observed with quasielastic neutron scattering is in agreement with simulated one. For the ions, the experimental values are related to macroscopic long time motions and are much smaller than the short time values calculated from MD. Thus, the present study provides a detailed insight in the microscopic dynamics of ions related to the structure of the clay: it is shown that Cs+ diffuse faster than Na+ and that the arrangement of clay surfaces plays a significant role in the choice of the sites occupied by the cations as well as in their mobility.
Relation between microstructures and magnetic properties upon annealing in Fe50Mn50/Ni80Fe20 films
Authors: Xu Ming , Lu Zhengqi , Yang Tao , Liu Cuixiu , Cui Shufan , Mai Zhenhong , Lai Wuyan , Jia Quanjie , Zheng Wenli
Published: September 2002

The annealing-temperature-dependent change in the exchange bias and coercivity is investigated in Fe50Mn50/Ni80Fe20 films. It is interesting to note that, as the annealing temperature increases, the exchange bias first decreases, and then increases, and finally decreases for the case of annealing at the higher temperature. The coercivity will increase upon annealing at moderate temperature, but decrease upon higher-temperature annealing. We can qualitatively interpret the change of the magnetic properties with annealing temperature in connection to the microstructures by x-ray scattering technologies. The results show that both the large exchange bias field and low coercivity of Fe50Mn50/Ni80Fe20 films are dependent of not only the interfacial roughness but also the antiferromagnetic structure.
Investigation of two-phase nucleation in paraelectric phase of ferroelectrics with ferroelectric–antiferroelectric–paraelectric triple point
Authors: Ishchuk V. M. , Sobolev V. L.
Published: September 2002

Results of investigation of phenomena preceding the phase transition from paraelectric to dipole-ordered phases in Pb1−x(Li1/2La1/2)x(Zr1−yTiy)O3 solid solutions with compositions close to the ferroelectric–antiferroelectric–paraelectric triple point in the Ti-concentration-temperature phase diagram are presented. X-ray diffraction and piezoelectric resonance methods are used for identification of the two-phase (antiferroelectric and ferroelectric) nuclei at the temperatures above the curie temperature. The relation between the presence of these two-phase nuclei in paraelectric phase of the compound and the diffuseness of the ordering phase transition is noted. The phenomenon of ion segregation at the interdomain boundary separating regions of ferroelectric and antiferroelectric phases and its role in enabling the observation of the piezoelectric resonance are discussed.
Self-similarity, power-law scaling, and non-Gaussianity of turbulent fluctuation flux in a nonfusion magnetoplasma
Authors: Trasarti-Battistoni R. , Draghi D. , Riccardi C. , Roman H. E.
Published: September 2002

The statistical characteristics of turbulent particle flux Γturb due to the correlated fluctuations of density and E⃗×B⃗-drift velocity in the simple magnetized torus Thorello [S. Alba, M. Fontanesi, A. Galassi, C. Riccardi, and E. Sindoni, Phys. Essays 6, 225 (1993)] are studied. The focus is on the shape and the low-order moments (absolute width, rms width, skewness, and kurtosis) of the probability distribution functions (PDF), and on how they change as a function of time-resolution τ upon coarse-graining. The way the shape of the PDF and its moments change are closely linked to each other, and they lend support to the view of two distinct regimes, separated by τbreak≈50 μs. In both regimes, however, the statistical evidence for self-similarity, power-law scaling, and non-Gaussianity is rather mixed. The behavior at small τ is interpreted as due to the presence of smooth, positively correlated (and possibly coherent, i.e., long-lived) structures within the data, and the behavior at large τ as due to the standard (i.e., Gaussian, as opposed to the Levy–Gnedenko) Central Limit Theorem.
Electrical and optical properties of beryllium-implanted Mg-doped GaN
Authors: Yu Chang-Chin , Chu C. F. , Tsai J. Y. , Lin C. F. , Wang S. C.
Published: September 2002

We investigated the electrical and optical characteristics of beryllium implanted Mg-doped GaN materials. The Mg-doped GaN samples were grown by metalorganic chemical vapor deposition system and implanted with Be ions at two different energies of 50 and 150 keV and two different doses of about 1013 and 1014 cm−2. The implanted samples were subsequently rapidly thermal annealed at 900, 1000, and 1100 °C for various periods. The annealed samples showed an increase of hole concentration by three orders of magnitude from nonimplanted value of 5.5×1016 to 8.1×1019 cm−3 as obtained by Hall measurement. The high hole concentration samples also showed low specific resistance ohmic contact of about 10−3 Ω cm2 and 10−6 Ω cm2 using Ni/Au and Ni/Pd/Au metallization, respectively, without any further annealing process. It is also found from the temperature dependent photoluminescence that the activation energy of Mg dopants of the Be implanted samples has an estimated value of about 170 meV, which is nearly 30% lower than the as-grown samples of about 250 meV. The crystal quality and surface morphology of the Be implanted samples measured by x-ray diffraction and atomic force microscopy show no obvious degradation in the crystal quality and surface morphology.
Transient simulations of a resonant tunneling diode
Authors: Pinaud Olivier
Published: September 2002

Stationary and transient simulations of a resonant tunneling diode in the ballistic regime are presented. The simulated model consists in a set of Schrödinger equations for the wave functions coupled to the Poisson equation for the electrostatic interaction. The Schrödinger equations are applied with open boundary conditions that model continuous injection of electrons from reservoirs. Automatic resonance detection enables reduction of the number of Schrödinger equations to be solved. A Gummel type scheme is used to treat the Schrödinger–Poisson coupling in order to accelerate the convergence. Stationary I–V characteristics are computed and the transient regime between two stationary states is simulated.
High resolution laser-driven proton radiography
Authors: Cobble J. A. , Johnson R. P. , Cowan T. E. , Renard-Le Galloudec N. , Allen M.
Published: September 2002

Laser-accelerated beams of Mega-electron volt protons have been produced at the Los Alamos Trident laser facility and used for high-resolution point-projection proton radiography of Au grids. The effective proton source size affords an inherent resolution of 2–3 μm in the object plane. The proton beam is characterized by ion time-of-flight Faraday cup measurements and nuclear particle track detectors. Laser-driven proton radiography appears promising as a valuable research tool for probing plasmas or modest density objects.
Single molecules as nanoprobes. A study of the Shpol’skii effect
Authors: Matsushita M. , Bloeß A. , Durand Y. , Butter J. Y. P. , Schmidt J. , Groenen E. J. J.
Published: September 2002

We present a comparative study, down to the single-molecule level, of the linewidth and multiplet structure of the optical transitions of 2.3,8.9-dibenzanthanthrene (DBATT) in shock-frozen solutions of n-decane, n-undecane, and n-tetradecane. The n-alkane matrices show weak structural ordering and distinct incorporations of the DBATT molecules have been recognized. The order does not increase, nor does the ensemble optical linewidth decrease going from bulk to sub-volumes of less than 1 μm3. The relation between lateral position, orientation of the transition moment, and transition frequency has been investigated using single-molecule fluorescence-excitation and polarization spectroscopy. The distribution of the orientation is found not to depend on frequency and vice versa. Structural ordering on a microscopic scale is found not to be decisive as regards the linewidth and multiplet structure.
Infrared spectroscopy of biphenyl under hydrostatic pressure
Authors: Zhuravlev K. K. , McCluskey M. D.
Published: September 2002

Changes in the conformations of conjugated molecules affect the optical and electronic properties significantly. Hydrostatic pressure has been used to probe the conformations of biphenyl (C12H10) and deuterated biphenyl (C12D10) at liquid-helium temperatures. Infrared (IR) spectra of these materials have been taken up to a pressure of 2 GPa. A disappearance of certain IR absorption peaks has been found to occur between 0.07 and 0.45 GPa, due to the phase transition from a twisted to a planar conformation. Numerical simulations together with group-theoretical analysis have been performed to identify the nature of the vibrational modes that lose IR activity upon planarization.
Possibilities for achieving antihydrogen recombination and trapping using a nested Penning trap and a magnetic well
Authors: Ordonez C. A. , Dolliver D. D. , Chang Yongbin , Correa J. R.
Published: September 2002

A theoretical study is presented regarding some possibilities for achieving antihydrogen recombination and trapping using a nested Penning trap and a magnetic well. The work reported consists of a review, an extension, and applications of the relevant knowledge base. A nested Penning trap produces a magnetic field, which provides plasma confinement perpendicular to the magnetic field, and an electric field associated with a nested-well potential profile. The nested-well potential profile provides plasma confinement parallel to the magnetic field for oppositely signed plasma species that can have overlapping confinement regions. A configuration is considered in which the electric field is applied in two regions of uniform magnetic field that reside on opposite sides of a magnetic well region. The electric field confines overlapping positron and antiproton plasmas, which thread the magnetic well region. The magnetic well region would serve to trap a fraction of any antihydrogen atoms that are formed. Two different methods are considered for achieving overlap of positron and antiproton plasmas. For each, a set of conditions is predicted for achieving antihydrogen recombination and trapping. Although the study reported specifically considers simultaneous confinement of positron and antiproton plasmas in nested Penning traps, much of the information presented is also relevant to the prospect of merging other pairs of oppositely signed plasmas (e.g., electron and positron plasmas).
Strontium–titanate-doped lead metaniobate ferroelectric thin films
Authors: Xue J. M. , Ezhilvalavan S. , Gao X. S. , Wang J.
Published: September 2002

Ferroelectric polymorph of lead metaniobate (PbNb2O6) exhibits an orthorhombic structure, which is metastable at room temperature and can only be obtainable by quenching from high temperatures (∼1200 °C). In this letter, we report a ferroelectric PbNb2O6 thin film doped with SrTiO3 (Pb0.95Sr0.05(Nb2)0.98Ti0.05O6) with orthorhombic structure on Pt/Ti/Si substrate, which was prepared via a sol-gel route. The orthorhombic structure was developed at 900 °C at a normal heating rate of 5 °C/min and cooling rate of 10 °C/min. The PbNb2O6 film exhibited a remanent polarization (Pr) of 12.3 μC/cm2 and a coercive field (Ec) of 39 kV/cm, respectively, when measured at an applied field of 143 kV/cm. The leakage current density was 1.02×10−5 A/cm2 at 100 kV/cm. The room-temperature dielectric constant and dissipation factor was stable (∼325 and ∼1.5%, respectively) over a frequency range of 1 kHz to 1 MHz.
Analysis of interfacial silicates and silicides formed by annealing ultrathin Hf on SiO2: Effect of Hf/SiO2 thickness ratio
Authors: Lee Jung-Ho , Ichikawa Masakazu
Published: September 2002

The annealing of two different ultrathin Hf/SiO2 stacks, i.e., Hf rich (1.7 ML/0.3 nm) and SiO2 rich (1 ML/1 nm) is investigated in situ in an ultrahigh vacuum (UHV) by using scanning tunneling microscopy and x-ray photoelectron spectroscopy. To describe the interface structure formed in practical high-k processes, this approach conjectures the effects of underlying SiO2 on the stability of metal–silicon and metal–oxygen bondings, which would subsequently determine the interfacial phases. The annealing of these film stacks causes silicate formation, but the relative thickness ratio between Hf and SiO2 is found to greatly affect a phase stability of interfacial silicates in a high-temperature (⩾780 °C) regime. As the underlying SiO2 thickens, the Hf–Si bondings are expected to be replaced with Hf–O–Si (silicate) bonding units, even at room temperature deposition in an UHV. In the Hf-rich stack (Hf–Si bonding dominant), phase separation into silicides was observed at a relatively low temperature (∼780 °C) compared with a SiO2-rich one (Hf–O–Si bonding dominant) where silicidation occurs above 900 °C. Irrespective of the thickness ratio between Hf/SiO2, above 900 °C, two types of crystalline silicides, i.e., facetbars (metallic) and platelets (semiconducting), were observed and these silicides were also identified to be oxygen-free phases by analyzing their atomic structures.
Conduction-induced oxidation of silicon on silver metaphosphate glass
Authors: Doi Akira
Published: September 2002

dc biasing of silicon-anoded silver metaphosphate glass with a pulse train enabled us to follow the process of conduction-induced oxidation of silicon. Biasing with 1000 or 500 V/cm at or below 140 °C induced formation of a dielectric oxide having capacitance of around 10−7 F cm−2. From a large relaxation time of polarization involved, e.g., 10−4 s at 140 °C, it is suggested that the oxide is not the genuine silicon dioxide.
Investigation of the effect of high-temperature annealing on stability of ultrathin Al2O3 films on Si(001)
Authors: Kundu Manisha , Miyata Noriyuki , Ichikawa Masakazu
Published: September 2002

We investigated the stability of a uniform and stoichiometric 0.6-nm-thick Al2O3 film on a Si(001) surface during high-temperature annealing in ultrahigh vacuum (UHV), under low oxygen pressure (2×10−6, 5×10−6, and 2×10−5 Torr O2), and under high oxygen pressure (5×10−5 Torr O2) conditions. UHV annealing of the Al2O3/Si(001) system at 900 °C drastically degraded the Al2O3 film quality and caused atomic-scale roughness at the Al2O3/Si(001) interface. Voids formed in the oxide film as annealing progressed. A low oxygen pressure ambient during annealing, while more or less maintaining the film stoichiometry, caused atomic-scale roughness at the interface. A high oxygen pressure ambient during annealing maintained the film stoichiometry and thickness. However, this processing condition led to the formation of interfacial Si oxide, which caused substantial SiO volatilization and etching of the Si substrate at the Al2O3/Si(001) interface, thereby inducing nanometer-scale roughness at the interface. These results indicate that high-temperature processing imposes a limitation in controlling the composition of ultrathin Al2O3 films and maintaining the abruptness of the Al2O3/Si(001) interface on an atomic scale.
Layering structures at free liquid surfaces: The Fisher–Widom line and the capillary waves
Authors: Tarazona P. , Chacón E. , Reinaldo-Falagán M. , Velasco E.
Published: September 2002

We analyze the layering structure for the free liquid surface observed at low temperature in simple fluid models, with pair interaction potentials. The relationship of the surface layers with the Fisher–Widom line is discussed, by direct comparison of Monte Carlo simulation results for the liquid–vapor density profiles and the pair distribution function of the bulk liquid. Also we study the role of the capillary waves in the damping of the surface oscillatory profiles, with Monte Carlo simulations for different transverse areas, and through the theoretical scaling forms using the values of the surface tension given by our simulations. The main conclusion is that the dependence of the surface layering with the temperature is dominated by the capillary waves, even at the small transverse sizes typically used in computer simulations. In contrast, the Fisher–Widom line seems to be of minor importance for the amplitude of the layering.
Molecular dynamics studies of molecular diffusion in ice Ih
Authors: Ikeda-Fukazawa Tomoko , Horikawa Shinichiro , Hondoh Takeo , Kawamura Katsuyuki
Published: September 2002

We performed molecular dynamics simulations of the diffusion of interstitial He and H2O in ice Ih and found diffusion hops for these interstitial molecules from a stable site to an adjacent site. By observing the jumps of these diffusing species, we determined the jump frequencies, the crystal orientation dependence of the diffusion coefficients, and the diffusion activation energies. Most jumps are along the c axis, because the energy barrier for diffusion along the c axis is lower than that in the a–b plane. Furthermore, the diffusion mechanism for He significantly differ from that for H2O; interstitial H2O diffused by distorting the ice lattice, whereas He atom migrated by jumping from a stable interstitial site to an adjacent site without distorting the lattice. The transverse optic mode for translational lattice vibrations of the lattice surrounding the interstitial H2O shifts to high energy in comparison with that of the pure ice Ih. This upward shift is attributed to a strong coupling between localized translational vibrations of the interstitial H2O and lattice vibrations. The ice lattice is distorted by the translational vibration of the interstitial H2O, since the vibration energy of the mode is close to the energy region of the lattice vibrations of the ice Ih. We conclude that the localized vibrational motion of interstitial molecule is one of the dominant factors governing the diffusion mechanism of the molecule in the ice crystal.
On the search for C–H–O hydrogen bonding in aqueous acetic acid: Combined high-pressure infrared spectroscopy and ab initio calculations study
Authors: Chang Hai-Chou , Jiang Jyh-Chiang , Lin Ming-Shan , Kao Hsiang-En , Feng Chun-Min , Huang Yu-Chun , Lin Sheng Hsien
Published: September 2002

This study provides the evidence for hydrophobic hydration of CH3COOD as its aqueous solution was compressed by high pressure. On going from neat CH3COOD to diluted CH3COOD/D2O mixtures, the C–H vibration absorption bands do not reveal the solvent shift in frequency upon dilution, while the C–H absorption bands are altered into one prominent band at ∼2955 cm−1 as the pressure was applied above 0.3 GPa. The possible explanation is the enhancement of C–H–O interactions between C–H and D2O under the condition of high pressure. Ab initio calculations predict that the CH3 stretching frequencies and intensities of acetic acid are hardly affected by the presence of water, if the methyl group does not participate in the complex formation. Nevertheless, the strongest absorption peak at ∼2928 cm−1 is predicted in several low-energy (acetic acid)–(water)x complexes with the participation of C–H–O hydrogen bond. The reorganization of hydrogen-bond network or geometry is suggested to be responsible for the formation of C–H–O hydrogen bond.
Pattern-induced ripple structures at silicon-oxide/silicon interface by excimer laser irradiation
Authors: Chen X. Y. , Lu Y. F. , Cho B. J. , Zeng Y. P. , Zeng J. N. , Wu Y. H.
Published: September 2002

Ripple structures by KrF excimer laser irradiation have been observed on a silicon surface capped with a thin layer of patterned silicon oxide. The ripples are highly dependent on the patterns of the silicon oxide. They are centered and enhanced at the boundaries of the opened windows, forming a radial-wavelike structure. The formation of the ripples is attributed to the combined effect of surface stress, surface scattered wave and boundary effects.
Vibrational energy transfer and reactivity in HO+CO collisions
Authors: Billing Gert D. , Muckerman J. T. , Yu H. G.
Published: September 2002

The rate-constants for vibrational energy transfer and chemical reaction have been calculated using a recently modified potential energy surface.
DNA spintronics
Authors: Zwolak M. , Di Ventra M.
Published: September 2002

We predict, using a tight-binding model, that spin-dependent transport can be observed in short DNA molecules sandwiched between ferromagnetic contacts. In particular, we show that a DNA spin valve can be realized with magnetoresistance values of as much as 26% for Ni and 16% for Fe contacts. Spin-dependent transport can broaden the possible applications of DNA as a component in molecular electronics and shed new light into the transport properties of this important biological molecule.
Photoinduced photoluminescence intensity enhancement in poly(p-phenylene vinylene) films
Authors: Gobato Y. Galvão , Marletta A. , Faria R. M. , Guimarães F. E. G. , de Souza J. M. , Pereira E. C.
Published: September 2002

We report measurements of photoluminescence (PL) intensity enhancement in poly(p-phenylene vinylene) (PPV) films induced by light irradiation in the presence of air. This effect is dependent on laser intensity and the ratio between film thickness and excitation penetration depth. The results suggest that an efficient spectral diffusion of excited carriers to nondegraded PPV segments by Förster energy transfer is an important consideration in the PL efficiency of conjugated polymers light-irradiated in air.
Active control of a global thermocapillary instability
Authors: Shiomi Junichiro , Amberg Gustav
Published: September 2002

Active control was applied to oscillatory thermocapillary flow in an open cylindrical container filled with Silicone oil. Thermocapillary convection was driven by imposing a radial temperature gradient on a flat free surface. This is an extension of the previous work by Shiomi et al. who applied proportional feedback control by locally heating the surface at a single position using the local temperature signal at a different position fed back through a simple algorithm. Although significant attenuation of the oscillation was detected, an uncertainty remained if global stabilization was achieved. In the present paper, two sensor/heater pairs were installed to achieve the global suppression of the oscillation. Successful global stabilization of the oscillation was achieved in a range of Marangoni number, with the best performance in the weakly nonlinear regime. Using a reliable temperature measurement method, quantitative analysis is carried out to quantify the performance of the control. The optimal values of gain and relative position of sensor/heater pairs were identified.
Shear-mode piezoelectric properties of Pb(Yb1/2Nb1/2)O3–PbTiO3 single crystals
Authors: Zhang Shujun , Laurent Lebrun , Rhee Sorah , Randall Clive A. , Shrout Thomas R.
Published: September 2002

In this letter, the shear-mode piezoelectric and electromechanical properties of 0.55Pb(Yb1/2Nb1/2)O3–0.45PbTiO3 (PYNT45) single crystals are reported. The piezoelectric coefficients d15 and g15 were found to be 2100 pC/N and 0.064 Vm/N, respectively, with an electromechanical coupling coefficient k15 of 91% at room temperature. With increasing temperature, the values decreased dramatically above 168 °C, corresponding to the ferroelectric–ferroelectric phase transition temperature. In contrast to 0.955Pb(Zn1/3Nb2/3)O3–0.045PbTiO3 single crystals, PYNT45 crystals exhibit a larger g15 and the useful temperature range is significantly expanded. High-temperature aging experiments showed that PYNT45 single crystals exhibit good domain stability.
Raman spectra and optical trapping of highly refractive and nontransparent particles
Authors: Xie Changan , Li Yong-qing
Published: September 2002

We measured the Raman spectra of single optically trapped highly refractive and nontransparent microscopic particles suspended in a liquid using an inverted confocal laser-tweezers-Raman-spectroscopy system. A low-power diode-laser beam of TEM00 mode was used both for optical trapping and Raman excitation of refractive, absorptive, and reflective metal particles. To form a stable trap for a nontransparent particle, the beam focus was located near the top of the particle and the particle was pushed against a glass plate by the axial repulsive force. Raman spectra from single micron-sized crystals with high index of refraction including silicon, germanium, and KNbO3, and from absorptive particles of black and color paints were recorded. Surface-enhanced Raman scattering of R6G and phenylalanine molecules absorbed on the surface of a trapped cluster of silver particles was also demonstrated.
Effect of atmosphere during heating of substrate on the low temperature deposition of metalorganic chemical vapor deposited Pb(Zrx,Ti1−x)O3 thin films
Authors: Tokita Kouji , Aratani Masanori , Funakubo Hiroshi
Published: September 2002

The effect of the atmosphere during the heating of a substrate before starting the deposition on the characteristics of the deposited Pb(Zrx,Ti1−x)O3 (PZT) films was investigated. Rhombohedral PZT films were prepared on Pt/Ti/SiO2/Si substrates by metalorganic chemical vapor deposition (MOCVD) from 415 to 580 °C. PZT films with smooth surfaces and low leakage current densities were obtained when the substrate was heated under an Ar atmosphere at the heating rate of 7 °C/min. Moreover, a crystalline PZT film having good ferroelectricity was obtained at as low as 415 °C when the substrate was heated under the Ar atmosphere, while the film consisted of an amorphous phase when the substrate was heated under an O2 atmosphere. These results clearly show that heating the substrate under an Ar atmosphere before starting the deposition is effective for obtaining a film with a large ferroelectricity at a low deposition temperature for the MOCVD process.
Rate of intramolecular contact formation in peptides: The loop length dependence
Authors: Wang Zhisong , Makarov Dmitrii E.
Published: September 2002

We use Monte Carlo simulations to estimate the rate of formation of a contact between the ends of a peptide chain as a function of its length N. We find that this rate decreases monotonically with N, in accord with the experimental data of Lapidus, Eaton, and Hofrichter [Proc. Natl. Acad. Sci. U.S.A. 97, 7220 (2000)] and of Bieri et al. [Proc. Natl. Acad. Sci. U.S.A. 96, 9597 (1999)] but in contrast to previous theoretical work predicting a maximum of the rate for N∼10. By comparing our results with those data we estimate the diffusion coefficient for the relative diffusion of the chain ends to be D∼6×10−6 cm2/s, which is close to that found for monomer diffusion.
Global entanglement in multiparticle systems
Authors: Meyer David A. , Wallach Nolan R.
Published: September 2002

We define a polynomial measure of multiparticle entanglement which is scalable, i.e., which applies to any number of spin-12 particles. By evaluating it for three particle states, for eigenstates of the one dimensional Heisenberg antiferromagnet and on quantum error correcting code subspaces, we illustrate the extent to which it quantifies global entanglement. We also apply it to track the evolution of entanglement during a quantum computation.
Improved structure and properties of single-wall carbon nanotube spun fibers
Authors: Vigolo Brigitte , Poulin Philippe , Lucas Marcel , Launois Pascale , Bernier Patrick
Published: September 2002

This letter describes a method to improve the alignment of single-wall carbon nanotubes in macroscopic fibers produced by a simple spinning process. By contrast to classical composite fibers, where the nanotubes are embedded in a polymeric matrix, they consist of an interconnected network of polymers and nanotubes. This network can be swollen and stretched when the fibers are immersed in an appropriate solvent. The nanotubes alignment, studied by x-ray scattering, is significantly improved by the treatment. The fiber Young’s modulus can also be increased by a factor of 4.
Synthesis and Raman scattering study of rutile SnO2 nanowires
Authors: Wang Wenzhong , Xu Congkang , Wang Guanghou , Liu Yingkai , Zheng Changlin
Published: September 2002

This article reports the synthesis and Raman scattering study of rutile SnO2 nanowires obtained by a simple precursor thermal decomposition process in NaCl flux with Sn(CO3)2 as the precursor. The SnO2 nanowires have lengths up to tens of micrometers and diameters in the range of 8–25 nm, with an average of 15 nm. In addition to the fundamental Raman scattering peaks, the other two Raman scattering peaks are also observed. We have discussed the possible reasons for the appearance of two Raman scattering peaks at 300 and 601 cm−1, but the origin of these two modes is not well understood.
Solvent effects on conformational dynamics of proteins: Cytochrome c in a dried trehalose film
Authors: Ponkratov V. V. , Friedrich J. , Vanderkooi J. M.
Published: September 2002

The spectral diffusion dynamics of free base cytochrome c (H2-Cc) in a dry trehalose film is tremendously enhanced as compared to a glycerol/water glass. We show that relaxation as well as fluctuation processes contribute to the spectral diffusion dynamics. Relaxation shows up in aging phenomena which can be measured in a separate fashion. In both solvents, the spectral diffusion as well as the aging dynamics follow power laws in time. The respective exponents are quite different, yet the influence of the solvent on them is only marginal. The large difference in the magnitude of the spectral diffusion dynamics in the two solvents can be traced back to a correspondingly large difference in the inhomogeneous width which itself seems to come from the much higher glass transition temperature in trehalose, which is close to the unfolding temperature of cytochrome c.