bluuebunny/crossref_metadata_2025 huggingface dataset:
The Relation Between Primary Osteoarthritis of the Trapeziometacarpal Joint and Supernumerary Slips of the Abductor Pollicis Longus Tendon
Authors: SCHULZ C. U. , ANETZBERGER H. , PFAHLER M. , MAIER M. , REFIOR H. J.
Published: September 2002

We have studied whether accessory abductor pollicis longus slips inserting into the thenar eminence or trapezium influence the incidence and severity of trapeziometacarpal joint osteoarthritis. The right first extensor compartment of 73 cadavers was dissected and trapeziometacarpal degeneration was graded macroscopically. The main abductor pollicis longus tendon which inserted at the metacarpal base was accompanied by supernumerary APL slips in 96% of cases. Thenar or trapezial slips occurred frequently but coexisted in only one case. The incidence of trapeziometacarpal arthritis was not influenced by the number of accessory slips or whether they inserted onto the thenar eminence or the trapezium.
Reactive and inelastic scattering dynamics of hyperthermal oxygen atoms on a saturated hydrocarbon surface
Authors: Zhang Jianming , Garton Donna J. , Minton Timothy K.
Published: September 2002

The dynamics of the initial interactions of hyperthermal O atoms with a saturated hydrocarbon surface have been investigated by directing an O-atom beam at a continuously refreshed liquid squalane surface and monitoring time-of-flight and angular distributions of inelastically scattered O atoms and reactively scattered OH and H2O. These products are formed through thermal and nonthermal processes. The inelastic scattering processes may be described in terms of the limiting cases of direct inelastic scattering (nonthermal) and trapping desorption (thermal). The initial step leading to production of volatile OH and H2O is believed to be direct H-atom abstraction to form OH. Once formed, the OH may scatter directly into the gas phase before thermal equilibrium with the surface is reached, or it may undergo further collisions and reactions with the surface. These secondary interactions include trapping and desorption of OH and abstraction of a second hydrogen atom to form H2O. Interactions that occur before thermal equilibrium with the surface can be reached lead to products that exit the surface at hyperthermal velocities, while those that occur in thermal equilibrium with the surface yield products that leave the surface at thermal velocities given by the surface temperature. Direct, single-collision scattering events that produce O and OH are described with a kinematic picture that allows the determination of the effective surface mass encountered by an incident O atom, the atom–surface collision energy in the center-of-mass frame, and the fraction of the center-of-mass collision energy that goes into translation of the scattered gaseous product and the recoiling surface fragment. Center-of-mass velocity-flux maps for OH indicate either single-collision events through a largely collinear O–H–C transition state or multiple-collision events in which initially formed OH scatters inelastically from the surface.
Recommended Vapor–Liquid Equilibrium Data. Part 1: Binary n-Alkanol–n-Alkane Systems
Authors: Góral Marian , Oracz Paweł , Skrzecz Adam , Bok Andrzej , Ma̧czyński Andrzej
Published: September 2002

The recommended vapor–liquid equilibrium (VLE) data for 39 binary n-alcohol–n-alkane systems have been obtained after critical evaluation of all data (490 data sets) reported in the open literature up to the middle of 2001. The evaluation procedure consisted in combining the thermodynamic consistency tests, data correlation, comparison with enthalpy of mixing data, and comparison of VLE data for various mixtures. The data were correlated with equations based on the local compositions concept as well as with the equation of state appended with a chemical term (EoSC) proposed by Góral. The recommended data are presented in the form of individual pages containing tables of data, figures, and auxiliary information. Each page corresponds to one system and contains three isotherms (spaced by at least 15 K) and one isobar (preferably at 101.32 kPa). Experimental gaps were completed with the predicted data.
Doppler Broadening and its Contribution to Compton Energy-Absorption Cross Sections: An Analysis of the Compton Component in Terms of Mass-Energy Absorption Coefficient
Authors: Rao D. V. , Takeda T. , Itai Y. , Akatsuka T. , Cesareo R. , Brunetti A. , Gigante G. E.
Published: September 2002

Compton energy absorption cross sections are calculated using the formulas based on a relativistic impulse approximation to assess the contribution of Doppler broadening and to examine the Compton profile literature and explore what, if any, effect our knowledge of this line broadening has on the Compton component in terms of mass–energy absorption coefficient. Compton energy-absorption cross sections are evaluated for all elements, Z=1–100, and for photon energies 1 keV–100 MeV. Using these cross sections, the Compton component of the mass–energy absorption coefficient is derived in the energy region from 1 keV to 1 MeV for all the elements Z=1–100. The electron momentum prior to the scattering event should cause a Doppler broadening of the Compton line. The momentum resolution function is evaluated in terms of incident and scattered photon energy and scattering angle. The overall momentum resolution of each contribution is estimated for x-ray and γ-ray energies of experimental interest in the angular region 1°–180°. Also estimated is the Compton broadening using nonrelativistic formula in the angular region 1°–180°, for 17.44, 22.1, 58.83, and 60 keV photons for a few elements (H, C, N, O, P, S, K, and Ca) of biological importance.
Luminescence studies of a Si/SiO2 superlattice
Authors: Averboukh B. , Huber R. , Cheah K. W. , Shen Y. R. , Qin G. G. , Ma Z. C. , Zong W. H.
Published: September 2002

Photoluminescence and electroluminescence from a Si/SiO2 superlattice have been measured. They show similar characteristics and exhibit an inhomogeneously broadened photoluminescence band peaked at 2.06 eV. The excitation spectrum indicates that excitations occur in the Si layers. The insensitivity of the luminescence spectrum and decay to temperature and excitation wavelength suggests that luminescence originates from transitions between localized defect states. These localized states are most likely defect states residing at the Si/SiO2 interfaces, because there should be a significant concentration of defects at the interface and SiO2 due to the large lattice mismatch and the amorphous state. The close proximity of these states offers a more rapid transition path for the excited electrons. An energy band diagram of the superlattice is constructed based on our results.
Intraband relaxation and temperature dependence of the fluorescence decay time of one-dimensional Frenkel excitons: The Pauli master equation approach
Authors: Bednarz M. , Malyshev V. A. , Knoester J.
Published: September 2002

In molecular J-aggregates one often observes an increase of the fluorescence decay time when increasing the temperature from 0 K. This phenomenon is usually attributed to the thermal population of the dark Frenkel exciton states that lie above the superradiant bottom state of the exciton band. In this paper, we study this effect for a homogeneous one-dimensional aggregate in a host medium and we model the scattering between different exciton states as arising from their coupling to the host vibrations. A Pauli master equation is used to describe the redistribution of excitons over the band. The rates entering this equation are calculated within the framework of first-order perturbation theory, assuming a linear on-site interaction between excitons and acoustic phonons. Solving the master equation numerically for aggregates of up to 100 molecules, we calculate the temperature dependence of the fluorescence kinetics in general and the decay time scale in particular. The proper definition of the fluorescence decay time is discussed in detail. We demonstrate that, even at a quantum yield of unity, the possibility to directly interpret fluorescence experiments in terms of a simple radiative time scale depends crucially on the initial excitation conditions in combination with the competition between spontaneous emission and intraband phonon-assisted relaxation.
A density functional study of van der Waals interactions
Authors: Kamiya Muneaki , Tsuneda Takao , Hirao Kimihiko
Published: September 2002

The applicability of density functional theory (DFT) to van der Waals (vdW) calculations are investigated by using the long-range exchange correction scheme and the Andersson–Langreth–Lundqvist vdW functional. By calculating bond energy potentials of rare-gas dimers, it was found that the present scheme gives much more accurate potentials for all dimers than conventional sophisticated DFT methods do. We therefore confirmed that vdW bonds are constructed under the balance of long-range exchange and vdW correlation interactions, although neither of these interactions are usually contained in pure exchange–correlation functionals. It was also found that calculated vdW potentials are obviously affected by functional forms for rapidly varying densities. Especially in vdW calculations, we must employ a correlation functional that satisfies the fundamental condition for rapidly varying density.
Cross-sectional scanning tunneling microscopy of GaAsSb/GaAs quantum well structures
Authors: Zuo S. L. , Hong Y. G. , Yu E. T. , Klem J. F.
Published: September 2002

We have used cross-sectional scanning tunneling microscopy (STM) to perform nanometer-scale characterization of compositional structure and interfacial properties within GaAs1−xSbx/GaAs double-quantum well structures. An algorithm has been devised based on analysis of strain effects in STM data to obtain detailed, quantitative compositional profiles within alloy layers. Using this and other analysis techniques, we have assessed the influence of group V anion soaks at each heterojunction interface on interface roughness and abruptness. An As soak at the GaAs–on–GaAs1−xSbx interfaces reduces interface roughness but leads to a slight loss of abruptness at the interface, while an As+Sb soak at GaAs1−xSbx–on–GaAs interfaces improves abruptness while leaving interface roughness largely unaffected. Significant compositional grading at the nanometer scale is observed within the GaAs1−xSbx layers.
Ballistic transport and photoluminescence in silicon nanocrystallites
Authors: Torchynska Tatiana V.
Published: September 2002

One of the most interesting problems of modern solid-state physics is the emission mechanism of bright photoluminescence in the red spectral range discovered in silicon nanocrystallite structures, particularly in wires and dots. This article presents an interpretation of strong “red” photoluminescence in silicon wires and dots based on hot carrier ballistic transport in the process of photoluminescence excitation. Photoluminescence (PL), its excitation, electron paramagnetic resonance, infrared absorption and Raman scattering spectra of as-prepared Si wires have been examined. Silicon wire layers (porous silicon) were obtained by electrochemical etching of p-type Si wafers in a HF-ethanol solution. An atomic force microscope is used for porous silicon morphology analysis. It is shown that the very low PL intensity could be attributed to carrier radiative recombination between localized states quantum confined inside Si nanocrystallites. It is revealed that the ballistic effect can enhance the effective hot carrier excitation of interface defect-related photoluminescence in Si nanocrystallite structures. PL excitation spectrum modification depending on the Si crystallite size confirms the role of the ballistic effect in PL excitation of Si low-dimensional structures.
Spin–spin coupling tensors by density-functional linear response theory
Authors: Lantto Perttu , Vaara Juha , Helgaker Trygve
Published: September 2002

Density-functional theory (DFT) calculations of indirect nuclear magnetic resonance spin–spin coupling tensors J, with the anisotropic but symmetric parts being the particular concern, are carried out for a series of molecules with the linear response (LR) method. For the first time, the anisotropic components of J are reported for a hybrid functional. Spin–spin tensors calculated using the local density approximation (LDA), the gradient-corrected Becke–Lee–Yang–Parr (BLYP) functional, and the hybrid three-parameter BLYP (B3LYP) functional are compared with previous ab initio multiconfiguration self-consistent-field (MCSCF) LR results and experimental data. In general, the B3LYP functional provides reasonable accuracy not only for the isotropic coupling constants but also for the anisotropic components of J, with the results improving in the sequence LDA→BLYP→B3LYP. Error cancellation often improves the total DFT spin–spin coupling when the magnitude of the paramagnetic spin–orbit contribution is overestimated, or when the spin–dipole (SD) and Fermi-contact (FC) contributions are far from the MCSCF values. For the F19 nucleus, known to be difficult for DFT, the anisotropic properties of heteronuclear, in particular F1319C couplings are often more accurate than the poorly described isotropic coupling constants. This happens since the FC contribution is small at fluorine compared with carbon, leading to a small error in the total SD/FC term. With the recent implementation of the hybrid B3LYP functional, calculations of predictive quality for the J tensors are no longer restricted to small model molecules, opening up the possibility of studying the anisotropic components of J in large organic and biomolecules of experimental interest.
Reactive ion etching of quartz and Pyrex for microelectronic applications
Authors: Zeze D. A. , Forrest R. D. , Carey J. D. , Cox D. C. , Robertson I. D. , Weiss B. L. , Silva S. R. P.
Published: September 2002

The reactive ion etching of quartz and Pyrex substrates was carried out using CF4/Ar and CF4/O2 gas mixtures in a combined radio frequency (rf)/microwave (μw) plasma. It was observed that the etch rate and the surface morphology of the etched regions depended on the gas mixture (CF4/Ar or CF4/O2), the relative concentration of CF4 in the gas mixture, the rf power (and the associated self-induced bias) and microwave power. An etch rate of 95 nm/min for quartz was achieved. For samples covered with a thin metal layer, ex situ high resolution scanning electron microscopy and atomic force microscopy imaging indicated that, during etching, surface roughness is produced on the surface beneath the thin metallic mask. Near vertical sidewalls with a taper angle greater than 80° and smooth etched surfaces at the nanometric scale were fabricated by carefully controlling the etching parameters and the masking technique. A simulation of the electrostatic field distribution was carried out to understand the etching process using these masks for the fabrication of high definition features.
Band structure engineering of superlattice-based short-, mid-, and long-wavelength infrared avalanche photodiodes for improved impact ionization rates
Authors: El-Rub K. Abu , Grein C. H. , Flatte M. E. , Ehrenreich H.
Published: September 2002

We study the effects of the electronic band structure on the hole- and electron-initiated impact ionization in Sb-based superlattice avalanche photodiodes. Earlier calculations have revealed that bulk alloy AlGaSb avalanche photodiodes with alloy composition near the resonance between the energy gap and the spin-orbit splitting have an enhanced hole to electron impact ionization coefficient ratio for a low electric field but not for a high electric field. The absence of an enhancement under high fields is due to carrier heating spreading the hole distribution in the splitoff band. A strategy to extend this type of enhancement to high fields in a superlattice involves band engineering the superlattice to place flat bands at approximately one energy gap below the top of the valence band. This prevents holes from spreading in energy and hence gives rise to strong hole-initiated impact ionization. Quantitative results are presented for short-infrared AlAs/InGaAs/AlAs/InGaSb, midinfrared InAs/InGaSb/AlSb, and long-infrared InAs/InGaSb/AlSb superlattices.
Ultrafast photodissociation of Br2: Laser-generated high-harmonic soft x-ray probing of the transient photoelectron spectra and ionization cross sections
Authors: Nugent-Glandorf Lora , Scheer Michael , Samuels David A. , Bierbaum Veronica M. , Leone Stephen R.
Published: September 2002

The ultrafast dissociation of gas-phase Br2 is probed via a 400 nm pump soft-x-ray probe scheme at five different high-order harmonic wavelengths (13th, 15th, 17th, 19th, and 21st of an 800 nm Ti:sapphire laser). A series of time-resolved ultrafast photoelectron spectra reveals prompt two-photon ionization features, which allow in situ measurement of the cross correlation between the pump and probe pulses. Transient features are attributed to ionization of the dissociative excited state wave packet, and new spectral peaks are associated with the formation of atomic Br. Deconvolution of time-trace plots of the atomic signals with the cross-correlation pulse durations reveal similar dissociation times (∼40 fs) at two probe wavelengths (47 and 42 nm). Analysis of the transient wave packet photoelectron signal suggests an ionization process that occurs during dissociation, with a broad electron kinetic energy distribution at an extended Br–Br bond length (R ⩾3 Å). At long delay times (⩾500 fs), an enhancement of the ionization cross section of the Br atom compared to the Br2 molecule is observed with each of the probe wavelengths, the ratio increasing from a factor of 21±1 to 56±5 for probe wavelengths of 61.5 to 38 nm, respectively. The intensity of the transient wave packet signal on the dissociative state remains nearly constant between the 17th and 19th harmonic probes, indicating that the ionization cross section of the dissociative state has an entirely different wavelength dependence than the Br atom. The transient wave packet ionization signal is qualitatively 10%–20% of the simultaneous two-photon (400 nm+soft x-ray) ionization signal. The results are discussed in terms of the transient dynamics of dissociative state photoelectron spectroscopy, the correlation between molecular and atomic ionization probabilities, and above threshold ionization probabilities.
Folding/unfolding kinetics on a semiflexible polymer chain
Authors: Sakaue T. , Yoshikawa K.
Published: September 2002

We studied the kinetic process of a folding/unfolding transition of a long semiflexible polymer chain by Brownian dynamics simulation. A semiflexible chain with an elongated coil conformation is folded into a compact and ordered structure, such as a toroid or rod, through the processes of nucleation and growth. This transition is characterized as a disorder–order transition. The folded morphology is not necessarily the global minimum of free energy, which demonstrates the crucial effect of kinetics on the semiflexible chain folding. The growth process of toroid formation is characterized by a constant growth rate reflecting the dimensionality of a chain, which corresponds well with experimental observations of DNA folding. It is also shown that the path of the unfolding process is much different from that of folding.
Grand canonical Monte Carlo simulation of hydration forces between nonorienting and orienting structureless walls
Authors: Hayashi Tomohiro , Pertsin Alexander J. , Grunze Michael
Published: September 2002

The hydration forces between structureless model walls were calculated using the grand canonical Monte Carlo technique. Several wall–water interaction potentials were tried, including both orientation independent and strongly directional potentials which reflected the preference of water for tetrahedral hydrogen bonding coordination. Primary attention was given to large wall-to-wall separations (4 nm and more), where the oscillations of the hydration force due to layering effects decayed. The hydration force was found to be highly sensitive to the presence of orientation-dependent terms in the wall–water interaction potential. Strongly directional potentials led to hydrophobic attraction of the walls even when the wall–water interaction was substantially stronger than the water–water interaction. The reason had to do with the orientational ordering induced by the walls in the adjacent water layers.
Atomic force microscopy study of surface roughening of sputter-deposited TiN thin films
Authors: Liu Z.-J. , Jiang N. , Shen Y. G. , Mai Y.-W.
Published: September 2002

The kinetic surface roughening of TiN thin films sputter-deposited on silicon substrates at room temperature was studied. Scaling analyses were made by surface measurements of atomic force microscopy (AFM). The roughness exponent α and growth exponent β that characterize scaling behaviors of surface growth were calculated using the height–height correlation function H(r) and power spectra P(f). The exponent values of α=∼0.98 and β=∼0.28 indicated that the surface growth behavior of sputtered TiN thin films could be adequately explained by a simple linear growth model showing surface diffusion as a smoothing effect and shot noise as a roughening mechanism. An inverse Fourier transformation technique was also used to generate the evolution of theoretical surface profiles that showed good agreement with AFM measurements.
Coexisting ferro- and antiferromagnetism in Ni2MnAl Heusler alloys
Authors: Acet Mehmet , Duman Eyup , Wassermann Eberhard F. , Mañosa Lluis , Planes Antoni
Published: September 2002

The structural and magnetic properties of stoichiometric Ni2MnAl are studied to clarify the conditions for ferromagnetic and antiferromagnetic ordering claimed to occur in this compound. X-ray and magnetization measurements show that although a single phase B2 structure can be stabilized at room temperature, a single L21 phase is not readily stabilized, but rather a mixed L21+B2 state occurs. The mixed state incorporates ferromagnetic and antiferromagnetic parts for which close-lying Curie and a Néel temperatures can be identified from magnetization measurements.
MgO-mixed Ba0.6Sr0.4TiO3 bulk ceramics and thin films for tunable microwave applications
Authors: Chang Wontae , Sengupta Louise
Published: September 2002

The dielectric properties of Ba0.6Sr0.4TiO3 (BST) and 1.0, 20.0, 40.0, and 60.0 wt % MgO-mixed BST bulk ceramics and thin films were investigated for tunable microwave applications. The effects of MgO mixing with BST on BST phase transitions were examined. It is observed that Mg substitution into BST causes a shift in the cubic-tetragonal BST phase transition peak to a lower temperature. Mg-substituted BST and MgO-mixed phases exhibit depressed and broadened BST phase transition peaks, resulting in decreased dielectric constants and dielectric losses at room temperature. BST and 1.0, 20.0, 40.0, and 60.0 wt % MgO-mixed BST thin films (∼0.3 μm thick) were deposited on (100) MgO single-crystal substrates at 750°C in an oxygen ambient pressure of 200 mTorr by pulsed laser deposition. The MgO–BST composite thin films showed a relatively high dielectric Q (=1/tan δ) compared to the pure BST and Mg-substituted BST thin films while retaining useful dielectric tuning.
High resolution measurements of ion temperatures in z-pinch plasmas
Authors: Yadlowsky E. J. , Barakat F. , Carlson E. P. , Hazelton R. C. , Keitz M. , Klepper C. C. , Failor B. H. , Levine J. S. , Song Y. , Whitten B. L. , Coverdale C. R. , Deeney C. , Spielman R. B.
Published: September 2002

The Doppler broadening of ion line profiles emitted by z-pinch plasma provides information about the thermalization of the implosion kinetic energy and the radiation efficiency of the pinch. Measurements of these line profiles are often complicated by source broadening in the instrument and opacity broadening of the emitted radiation. A high resolution concave crystal spectrometer in the Johann geometry was used to record the time averaged spectra of optically thin trace elements in the load. An imaging slit provided radially resolved but axially averaged spectra. The measurements indicate that lower ion temperatures (3–5 keV) are observed for Al wire loads on both the Saturn and Double EAGLE accelerators in the short current pulse mode (60–100 ns) than in the long pulse mode (125–225 ns) where values of 6.3–9.5 keV are observed. These values are smaller than those observed on Saturn by others. Furthermore, the wavelength at the line center of axially resolved ion line profiles on the DM-2 accelerator at Titan was observed to vary about some average value which implies an axially varying fluid motion of the plasma column transverse to the pinch axis.
Predictive model of the optical response of amorphous WO3 to ion intercalation
Authors: Lehan J. P. , Yu P. C. , Backfisch D. L. , Chambers J. P.
Published: September 2002

The optical response of an amorphous tungsten oxide half cell upon varying degrees of protenation is examined. First, the indium tin oxide transparent conductor’s dielectric function is determined from a parameterized version of the ionized impurity scattering model of Hamberg and Granqvist [I. Hamberg and C. G. Granqvist, Appl. Phys. Lett. 44, 721 (1984)]. Then the tungsten oxide data are interpreted using two theoretical optical dispersion formulas. The first is the polaron conductivity theory of Reik and Reese [H. G. Reik and D. Reese, J. Phys. Chem. Solids 28, 581 (1967)] and the second is the parametric semiconductor model of Johs et al. [B. Johs et al., Thin Solid Films 313–314, 137 (1998)]. It is found that the parametric semiconductor model is able to reproduce the measured optical spectra extremely well. The resulting set of dielectric functions is interpreted in terms of the intercalated charge. An empirical model is constructed to explain the observed behavior of the imaginary part of the dielectric function, which should be appropriate for device modeling. The real part of the dielectric function is then readily determined by application of the Kramers–Krönig relations, which are inherent to the parametric semiconductor model.
X-ray analysis of temperature induced defect structures in boron implanted silicon
Authors: Sztucki M. , Metzger T. H. , Kegel I. , Tilke A. , Rouvière J. L. , Lübbert D. , Arthur J. , Patel J. R.
Published: September 2002

We demonstrate the application of surface sensitive diffuse x-ray scattering under the condition of grazing incidence and exit angles to investigate growth and dissolution of near-surface defects after boron implantation in silicon(001) and annealing. Silicon wafers were implanted with a boron dose of 6×1015 ions/cm2 at 32 keV and went through different annealing treatments. From the diffuse intensity close to the (220) surface Bragg peak we reveal the nature and kinetic behavior of the implantation induced defects. Analyzing the q dependence of the diffuse scattering, we are able to distinguish between point defect clusters and extrinsic stacking faults on {111} planes. Characteristic for stacking faults are diffuse x-ray intensity streaks along 〈111〉 directions, which allow for the determination of their growth and dissolution kinetics. For the annealing conditions of our crystals, we conclude that the kinetics of growth can be described by an Ostwald ripening model in which smaller faults shrink at the expense of the larger stacking faults. The growth is found to be limited by the self-diffusion of silicon interstitials. After longer rapid thermal annealing the stacking faults disappear almost completely without shrinking, most likely by transformation into perfect loops via a dislocation reaction. This model is confirmed by complementary cross-sectional transmission electron microscopy.
Optical pump-and-probe measurement of the thermal conductivity of nitride thin films
Authors: Daly B. C. , Maris H. J. , Nurmikko A. V. , Kuball M. , Han J.
Published: September 2002

We report on measurements of the thermal conductivity of epitaxially grown nitride thin films. These semiconductor materials are of considerable technological importance for applications such as blue-light emitters and high-power, high frequency electronic devices. Measurements were made in the temperature range of 150–400 K using an optical technique in which the sample is heated with an ultrashort (∼150 fs) light pulse, and a time-delayed probe light pulse is used to measure the temperature of the sample as a function of time. The conductivity of the polycrystalline sample and the alloys are found to be significantly reduced compared to published values for bulk GaN.
Evidence of a ternary Co1−xFexSi2 phase with a CaF2-type structure: High-resolution transmission electron microscopy and diffraction anomalous fine structure study
Authors: Ersen O. , Ulhaq-Bouillet C. , Pierron-Bohnes V. , Tuilier M. H. , Berling D. , Bertoncini P. , Pirri C. , Gailhanou M. , Thiaudière D.
Published: September 2002

A ternary silicide phase (Co0.6Fe0.4Si2) with a cubic CaF2-type structure, grown in epitaxy on Si(111), is investigated by using diffraction anomalous fine structure and high-resolution transmission electron microscopy. This cubic phase is formed by annealing at 930 K a room-temperature-grown epitaxial ternary layer with ratios of 0.7:2 for Fe:Si and 0.3:2 for Co:Si. This phase is mixed with a tetragonal α-FeSi2-type phase, but both phases are ternary. It is shown that a large amount of Fe (about 40%) substitutes for Co atoms on the metallic sites of the CaF2-type lattice of the cubic silicide phase.
Transmission spectroscopy of photonic crystals in a silicon-on-insulator waveguide structure
Authors: Zelsmann M. , Picard E. , Charvolin T. , Hadji E. , Dal’zotto B. , Nier M. E. , Seassal C. , Rojo-Romeo P. , Letartre X.
Published: September 2002

Optical properties of two-dimensional photonic crystals (PCs) integrated in a silicon-on-insulator stripe waveguide are reported. Transmission measurements are done on a wide wavelength range (1.1–1.7 μm) by coupling a white-light source in the cleaved edge of the sample and collecting light at the other cleaved side of the waveguide. PC mirrors and one-dimensional (1D) Fabry–Pérot cavities formed between two PC reflectors have been fabricated and characterized. The photonic band gap of the mirror is observed in the Γ–M direction for the transverse electric like guided modes. For the waveguide with the 1D Fabry–Pérot cavity, resonant modes appear within the gap. It is found that the experimental spectra are in very good agreement with both the theoretical photonic band structure and the theoretical transmission calculated by finite difference time domain.
Generation of ballistic electrons in nanocrystalline porous silicon layers and its application to a solid-state planar luminescent device
Authors: Nakajima Yoshiki , Kojima Akira , Koshida Nobuyoshi
Published: September 2002

A principle of planar-type visible light emission is presented using ballistic electrons as excitation source. The device is composed of a semitransparent top electrode, a thin film of fluorescent material, a nanocrystalline porous silicon (nc-PS) layer, an n-type silicon wafer, and an ohmic back contact. When a positive dc voltage is applied to the top electrode with respect to the substrate, electrons injected into the nc-PS layer are accelerated via multiple-tunneling through interconnected silicon nanocrystallites, and reach the outer surface as energetic hot or quasiballistic electrons. They directly excite the fluorescent film, and then induce uniform visible luminescence. This solid-state light-emitting device, regarded as a “vacuum-less cathode-ray tube,” has many technological advantages over the conventional luminescent devices. It may lead to big innovations in the development of large-area thin flat-panel display and other electronic devices.
Field-controlled optical profile of a waveguide having a liquid-crystalline core
Authors: Marangoni M. , Osellame R. , Ramponi R. , Buscaglia M. , Bellini T. , Mantegazza F.
Published: September 2002

The optical properties of a nematic liquid-crystal waveguide in a hybrid configuration have been dynamically reshaped in a straightforward and controlled way by applying an external electric field. The anisotropic refractive index profile of the waveguide has been determined for different electric-field strengths by means of m-lines spectroscopy. The experimental results are in very good agreement with the values predicted by a simple model that takes into account the dielectric, optical, and elastic properties of the liquid-crystal guiding layer.
Operation of high-temperature superconductor magnetometer with submicrometer bicrystal junctions
Authors: Faley M. I. , Poppe U. , Urban K. , Slobodchikov V. Yu. , Maslennikov Yu. V. , Gapelyuk A. , Sawitzki B. , Schirdewan A.
Published: September 2002

We investigated the noise properties of dc superconducting quantum interference device flip-chip magnetometers with submicrometer-wide bicrystal junctions operating at 77.4 K. The noise of the magnetometers with electronics was about 6 fT/√Hz at frequencies above 100 Hz increasing up to about 20 fT/√Hz at 1 Hz. The operation of the magnetometers was characterized in an electronic axial first order gradiometer system, which was employed for biomagnetic measurements. The system demonstrated a gradient resolution of about 1 fT/cm√Hz at 77.4 K and stable operation in a standard magnetically shielded room under clinical conditions.
Hydrogen redistribution induced by negative-bias-temperature stress in metal–oxide–silicon diodes
Authors: Liu Ziyuan , Fujieda Shinji , Terashima Koichi , Wilde Markus , Fukutani Katsuyuki
Published: September 2002

Poly-Si/SiO2/Si diodes in which oxides were grown thermally under wet oxidation conditions and subsequently treated by a post-oxidation anneal (POA) have been characterized electrically and chemically before and after applying negative-bias-temperature stress (NBTS). It was confirmed that NBTS produces interface states and that POA suppresses the interface state production. Nuclear reaction analysis indicated that NBTS results in hydrogen redistribution within the oxide layer. POA was shown to partly suppress such hydrogen accumulation. Hydrogen is thus clearly shown to influence the stability against NBTS.
Resolution of photonic crystal superprism
Authors: Baba Toshihiko , Matsumoto Takashi
Published: September 2002

We theoretically investigated the performance of the photonic crystal superprism, that is, the propagating beam quality, the wavelength sensitivity, and the resolution as a narrow band filter at 1.5-μm-wavelength range. First, we defined the equi-incident-angle curve in the Brillouin zone. Next, we mapped three parameters that represented the abovementioned performance over the Brillouin zone. As a result, we found a narrow design window that allows a high resolution of 0.4 nm along an equi-incident-angle curve but requires an incident beam width of over 100 μm and a device length of centimeter order. It can be an essential high efficiency filter if the input end of the crystal is optimized and the propagation loss is suppressed.
Control of surface morphology through variation of growth rate in SiGe/Si(100) epitaxial films: Nucleation of “quantum fortresses”
Authors: Gray Jennifer L. , Hull Robert , Floro Jerrold A.
Published: September 2002

The surface morphology of Si0.7Ge0.3 films grown at 550 °C by molecular-beam epitaxy is found to be highly controllable through changes in growth rate. A growth rate of 0.9 Å/s results in a surface morphology that begins as shallow pyramidal pits, which then become decorated by ordered quadruplets of islands that surround the edges of the pits. This “quantum fortress” structure represents a symmetry with potential application to quantum cellular automata geometries. A higher growth rate of 3 Å/s produces similar results. However, when the growth rate is reduced to 0.15 Å/s, the surface morphology that develops instead consists of elongated ridges.
Twinning in TiSi2-island catalyzed Si nanowires grown by gas-source molecular-beam epitaxy
Authors: Tang Qiang , Liu Xian , Kamins Theodore I. , Solomon Glenn S. , Harris James S.
Published: September 2002

Using TiSi2 islands as a catalyst, we have grown Si nanowires by gas-source molecular-beam epitaxy using Si2H6 as the gas source. The dominant TiSi2 islands are C49 phase with the orientation: Si[110]//C49-TiSi2[100] and Si(001)//C49-TiSi2(010). Twinning in the grown Si nanowires is observed by reflection high-energy electron diffraction and transmission electron microscopy. The twining also causes kinking, i.e., an abrupt change of growth direction of the Si nanowires. Lattice mismatch stress between the TiSi2 islands and the Si nanowires possibly leads to twinning and kinking of the Si nanowires.
Rapid imaging of nanotubes on insulating substrates
Authors: Brintlinger T. , Chen Yung-Fu , Dürkop T. , Cobas Enrique , Fuhrer M. S. , Barry John D. , Melngailis John
Published: September 2002

We demonstrate the use of field-emission scanning electron microscopy for rapid imaging of small-diameter carbon nanotubes on insulating SiO2 substrates. The image contrast stems from local potential differences between the nanotube and substrate and is insensitive to surface roughness and defects. This technique may also be used as a probe of the electrical connectivity of small structures without external leads.
Controlling the size and density of self-assembled PbSe quantum dots by adjusting the substrate temperature and layer thickness
Authors: Raab A. , Springholz G.
Published: September 2002

The formation of self-assembled PbSe quantum dots by molecular-beam epitaxy of PbSe on PbTe (111) is investigated in dependence of growth temperature and layer thickness. It is shown that in the temperature range of 240 °C to 420 °C, the dot density and dot height vary exponentially with temperature, whereas the wetting layer thickness and the dot shapes remain essentially constant. A different behavior is observed for the dependence on the PbSe thickness, which linearly changes the average dot height but only slightly affects the dot density. Both parameters allow an efficient control of the quantum dot sizes as is essential for device applications.
Surface Fermi-level position and gap state distribution of InGaP surface grown by metalorganic vapor-phase epitaxy
Authors: Hashizume Tamotsu
Published: September 2002

Electronic properties of “free” n-In0.49Ga0.51P surfaces grown by metalorganic vapor-phase epitaxy were directly characterized using the contactless capacitance–voltage technique. The HCl-treated surface showed a wide and continuous distribution of surface state density (Dss) in energy with relatively low densities, leading to no pronounced Fermi-level pinning effect on the surface. The minimum Dss value was determined to be 8×1011 cm−2 eV−1. The surface Fermi-level position was found at 1.2 eV above the valence band maximum, consistent with the x-ray photoelectron spectroscopy results.
Optical properties of self-assembled Ge wires grown on Si(113)
Authors: Halsall M. P. , Omi H. , Ogino T.
Published: September 2002

We report photoluminescence and Raman scattering measurements of Ge wires formed by self-assembly on Si(113) substrates. The samples were grown at a growth temperature of 500 °C on Si(113) substrates by solid-source molecular-beam epitaxy. Atomic force microscopy results clearly show the formation of coherent wire-shaped islands elongated in the [33-2] direction, some with lengths exceeding 500 nm. Micro-Raman measurements indicate that at this low growth temperature intermixing of the silicon and germanium is restricted with an average Ge fraction exceeding 0.7. Capping of the wires with a 20 nm Si epilayer enables the observation of low-temperature photoluminescence. A series of samples with increasing Ge coverage were studied and the onset of Ge islanding is observed to occur at a coverage of 5 monolayers. Wire formation occurs at coverages of 6 monolayers or greater. The observed emission band from the wires has a line shape quite different from that observed from Ge islands on Si[100], being substantially narrower in energy. A stochastic calculation based on idealized quantum wires is presented which reproduces the observed photoluminescence line shape well.
Synthesis of multiwalled carbon nanotubes from carbon black
Authors: Doherty S. P. , Chang R. P. H.
Published: September 2002

We describe a method to produce high-crystalline quality multiwalled carbon nanotubes from carbon black. By modifying the arc into a high-temperature oven, carbon black is converted into carbon nanotubes by a solid-state transformation without a catalyst. This process sheds new light onto the growth mechanism of carbon nanotubes and could lead to a scalable method of making multiwall nanotubes.
Formation of Co nanoclusters in epitaxial Ti0.96Co0.04O2 thin films and their ferromagnetism
Authors: Kim D. H. , Yang J. S. , Lee K. W. , Bu S. D. , Noh T. W. , Oh S.-J. , Kim Y.-W. , Chung J.-S. , Tanaka H. , Lee H. Y. , Kawai T.
Published: September 2002

Anatase Ti0.96Co0.04O2 films were grown epitaxially on SrTiO3 (001) substrates by using pulsed laser deposition with in-situ reflection high-energy electron diffraction. The oxygen partial pressure, PO2, during the growth was systematically varied. As PO2 decreased, the growth behavior was changed from a two-dimensional layer-by-layer-like growth to a three-dimensional island-like one, which resulted in an increase in the saturation magnetization. These structural and magnetic changes were explained in terms of the formation of cobalt clusters whose existence was proved by transmission-electron-microscope studies. Our work clearly indicates that the cobalt clustering will cause room-temperature ferromagnetism in the Co-doped TiO2 films.
High-repetition rate femtosecond laser-driven hard-x-ray source
Authors: Egbert A. , Mader B. , Tkachenko B. , Fallnich C. , Chichkov B. N. , Stiel H. , Nickles P. V.
Published: September 2002

A compact, high-repetition rate, ultrashort-pulse laser-driven hard-x-ray source based on the combination of a femtosecond laser system with an x-ray diode is demonstrated. A comparison with available laser-plasma sources is presented. Numerical modeling is performed which proves that picosecond and subpicosecond hard-x-ray pulses can be produced with this source.
Polarized Raman scattering of epitaxial Pb(Zr,Ti)O3 thin films in the tetragonal-phase field
Authors: Lee Sun-Hwa , Jang Hyun M. , Sung Hyun H. , Yi Hyunjung
Published: September 2002

In view of the difficulty in preparing single crystals, a c-axis oriented epitaxial lead zirconate titanate (PZT) film was prepared as a model system for the single-crystalline PZT. By employing an extraordinary backscattering configuration in which the relevant phonon wave vector, k, is parallel to the film/substrate interface, we have successfully isolated the E [transverse optical (TO)] symmetry phonons from A1(TO) phonons. Compared with polarized Raman spectra of the c-axis oriented PbTiO3 film, the polarized spectra of the epitaxial PZT film (with Zr/Ti=40/60) exhibited significant asymmetric line broadening with a noticeable downward shift of the mode frequencies. In addition to this, we observed a splitting of the “silent” mode into the B1-symmetry mode and the E(TO) mode using the parallel and cross polarization configurations, respectively.
Minor and major-loop studies of magnetic and reversal properties for synthetic antiferromagnetically coupled media
Authors: Shan Z. S. , Malhotra S. S. , Stafford D. C. , Bertero G. , Wachenschwanz D.
Published: September 2002

An approach has been developed to determine the magnetic properties for both the top and bottom layers of synthetic antiferromagnetically coupled (SAF) media by measuring the minor and major loops at different H field sweep rates with an alternating gradient force magnetometer. Using this approach, the effects of the bottom layer thickness on the magnetic and thermally activated properties of both the top and bottom layers were investigated systematically. These results are valuable for optimal design of SAF media.
Self-formation of microdomains by the topographical and fringe field effects in a liquid crystal display with dielectric surface gratings
Authors: Yoon Tae-Young , Park Jae-Hong , Sim JaeSung , Lee Sin-Doo
Published: September 2002

We report on the self-formation of microdomains by the topographical and fringe field effects in a twisted nematic liquid crystal display (LCD) with dielectric surface gratings (DSG). A regular array of the DSG produces periodically aligned microdomains in each pixel because of the topographical alignment of the LC and the spatial variations of the effective voltage across the LC layer. The mutual optical compensation within each pixel is naturally achieved and thus the range of viewing in the LCD is significantly extended without complex surface treatments.
Soft anisotropic high magnetization Cu/FeCo films
Authors: Jung H. S. , Doyle W. D. , Wittig J. E. , Al-Sharab J. F. , Bentley J.
Published: September 2002

A remarkable reduction in the coercivity Hc of sputtered Fe65Co35 films from 9.6 to 0.7 kA/m was observed using a Cu underlayer as thin as 2.5 nm. The FeCo without Cu exhibited a wide distribution of anisotropy fields up to >80 kA/m while the FeCo with Cu showed a well-defined in-plane uniaxial anisotropy field of 2.3 kA/m up to FeCo thicknesses of at least 1 μm. The saturation magnetostriction was (4.7±0.4)×10−5, independent of Cu thickness while the in-plane tensile stress gradually decreased from 2 to 0.2 GPa as the Cu thickness increased to 10 nm. The Cu changed the preferred orientation of the FeCo from (100) to (110) but more significantly reduced the average grain size from ∼50 to ∼9 nm. This alone is sufficient to explain quantitatively the reduction in Hc using Hoffmann’s ripple theory.
Issues of just‐in‐time (access) v. just‐in‐case (ownership) for libraries in developing countries: lessons to be learnt from developed countries
Authors: Moahi Kgomotso H.
Published: September 2002

The information age, where ICT is an essential tool for harnessing and disseminating information, has brought with it a number of very attractive innovations for libraries, such as the provision of information in electronic form, and the gradual move away from the just‐in‐case model, to the just‐in‐time service model, adopted by many libraries in the developed world. Many libraries in developing countries are still pondering the implications of going down the just‐in‐time route. Discusses the advantages and disadvantages for academic and research libraries, considers the experience of libraries in developed countries that have adopted the just‐in‐time model (using electronic resources) for services and draws lessons that academic and research libraries in developing countries can learn from.
Annual CREMRU‐JCI survey of corporate real estate practices in Europe and North America: 1993‐2001
Authors: Bon Ranko , Gibson Virginia , Luck Rachael
Published: September 2002

The annual survey of corporate real estate practices has been conducted by CREMRU since 1993, and in collaboration with JCI since 1997. IDRC and NACORE, two leading professional associations concerned with corporate real estate have supported the survey. In 1999 IDRC endorsed the survey and opened it to a wider audience. This summary of the nine annual surveys focuses on the incidence of corporate real estate management (CREM) policies, functions and activities, as well as the assessment of knowledge or skills relevant to the CREM function in the future. Both are of vital interest to educational institutions concerned with this field, as well as the personnel and training functions within organisations concerned with better management of their property.