bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for the physical basis and universality of the elimination of particulates using dual-laser ablation. I. Dynamic time-resolved target melt studies, and film growth of Y2O3 and ZnO
Authors: Mukherjee Pritish , Chen Shudong , Cuff John B. , Sakthivel Palanikumaran , Witanachchi Sarath
Published: July 2002

The application of a dual-laser ablation process, incorporating the addition of a synchronized CO2 laser to the traditional excimer (KrF) laser used for the ablation of targets in thin film deposition, has been previously demonstrated to be effective in the elimination of particulates in films of Y2O3 [J. Vac. Sci. Technol. A 13, 1171 (1995)]. It has been hypothesized that the efficacy of particulate removal is related to phase transformation from the solid to liquid phase prior to excimer laser ablation of the target material. In this series of two articles we present direct physical evidence of the dynamics of the phase transformation occurring on the target surface and its effect on the morphology of film growth. Pump–probe experiments have been conducted using the CO2 laser to probe the dynamic reflectivity of the target surface on the nanosecond timescale. These experiments were conducted for a range of materials spanning a wide range of thermal conductivity including a low thermal conductivity insulator (Y2O3), and a sublimating oxide (ZnO), as well as a high thermal conductivity metal (Zn) to assess the universal applicability of the results. In this article (Part I) the results of these dynamic reflectivity experiments are correlated with previously reported particulate-free deposition of thin films of Y2O3. Similar experiments are conducted for ZnO. In both cases, the reflectivity measurements yielded times for the onset of melt at a variety of CO2 laser fluences. Synchronization of the KrF laser to coincide with the onset of melt resulted in particulate-free film growth. The effect of mistiming on the quality of the deposited film is presented for ZnO.
Effective mass and exciton binding energy in ordered (Al)GaInP quantum wells evaluated by derivative of reflectivity
Authors: Shao Jun , Dörnen Achim , Winterhoff Rolf , Scholz Ferdinand
Published: July 2002

Low-temperature (1.8 K) magneto-optical reflectivity spectroscopy together with derivative operation has been employed in evaluating the reduced effective mass and exciton binding energy in GaxIn1−xP/AlGaInP quantum wells (QWs). Low uncertainty of the method in identifying excitonic transition energy (⩽0.3 meV) enables a simultaneous determination of both the heavy-hole (hh) and light-hole (lh) excitons in the QWs with ordering. The obtained effective masses manifest to be ordering-dependent, the dependence of which is compared with that reported for the GaInP2 bulk material. Results from the lattice-matched QWs suggest that the magnetic-field enhancement of the oscillator strength is stronger for the hh exciton than for the lh exciton.
Interaction of electrons with spin waves in the bulk and in multilayers (invited)
Authors: Berger L.
Published: July 2002

The exchange interaction between electrons and magnetic spins is considerably enhanced near interfaces, in magnetic multilayers. As a result, a dc current can be used to generate spin oscillations. We review theory and experimental evidence. The s–d exchange interaction causes a rapid precession of itinerant conduction-electron spins s around the localized spins S of magnetic electrons. This s precession has been observed directly [Weber et al., Science 291, 1015 (2001)] with electron beams through Fe, Co, and Ni films. Because of it, the time-averaged interaction torque between s and S vanishes. Thus, electrons do not interact at all with long-wavelength spin waves, in the bulk. An interface between a magnetic layer and a spacer causes a local coherence between the precession phases of different electrons, in a region within 10 nm from the interface [J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996)]; [L. Berger, Phys. Rev. B 54, 9353 (1996)]. Also, a second magnetic layer with pinned S is used to “prepare” s in a specific direction, before the electrons cross over to the active magnetic layer. The current-induced drive torque of s on S in the active layer may be calculated from the spin current or from the spin imbalance Δμ. This torque is equivalent to negative Gilbert damping, leading to instability of S. Spin current and Δμ are proportional to each other [L. Berger, J. Appl. Phys. 89, 5521 (2001)] and can arise from Fermi-surface translation, as well as from expansion/contraction. In fields H normal to layers, the critical current Ic for S instability is predicted to be proportional to the ferromagnetic-resonance frequency ω {consistent with Tsoi et al. [Tsoi et al., Phys. Rev. Lett. 80, 4281 (1998); 81, 493 (1998); Nature (London) 406, 46 (2000)] experiments}. However, for in-plane H, due to elliptic S precession, Ic is not proportional to ω, but linear in H [Katine et al., Phys. Rev. Lett. 84, 3149 (2000), experiments]. Apart from the current-induced drive torque, an extra Gilbert damping is predicted near the interface even at zero current [L. Berger, Phys. Rev. B 54, 9353 (1996)]. It has been observed by ferromagnetic resonance [Urban et al., Phys. Rev. Lett. 87, 217204 (2001)].
Synthesis and magnetic characterization of the La0.6Ln0.1Pb0.3MnO3(Ln=Pr, Nd, and Y) manganites
Authors: Horng Lance , Chang C. C. , Wu T. C. , Young S. L. , Chen Y. C. , Chen H. Z.
Published: July 2002

La 0.6 Ln 0.1 Pb 0.3 MnO 3 ( Ln=Pr, Nd, and Y) oxides have been synthesized by a standard ceramic fabrication method. The partial replacement of La ions by small amounts of Pr, Nd, or Y ions results in a considerable decrease in the ferromagnetic transition temperature and clearly irreversible behavior in the field-cooling–zero-field-cooling curve at low field, showing a short-range spin order phase. These facts are in agreement with the smaller ionic radii of Pr, Nd, and Y ions in contrast to La ions, and the corresponding larger distortion of perovskite structures. The hysteresis loops of these samples illustrate that the magnetization still remains unsaturated in high field and the saturation moments are larger for Pr-doped and Nd-doped manganites. This can be interpreted in terms of canted spins between Mn ions and magnetic Pr or Nd ions with f-shell electrons.
Transport processes in the vicinity of a magnetic island in tokamaks
Authors: Shaing K. C.
Published: July 2002

It is shown that in the vicinity of a magnetic island, the toroidal symmetry of the equilibrium magnetic field strength B is broken in tokamaks due to the finite width of the island. The magnitude of this broken symmetry is of the order of (δB/B)1/2 with δB the perturbed magnetic field strength. This leads to enhanced plasma transport. The symmetry breaking induced transport flux in the collisionless regime in tokamaks with an island is calculated. The magnitude of the island induced transport fluxes can be comparable to that of the anomalous transport fluxes.
Magnetic properties of ultrathin cobalt films grown on Ge(111) and Si(111) substrates
Authors: Tsay J. S. , Yao Y. D. , Wang K. C. , Cheng W. C. , Yang C. S.
Published: July 2002

Magnetic properties of cobalt films grown on Ge(111) and Si(111) substrates were investigated. On a Ge(111) substrate, cobalt films possess an in-plane anisotropy. On a Si(111) substrate, ultrathin cobalt films (3–9 monolayers), which were deposited at 300 K, exhibited a canted easy axis. The different orientations of the easy axis of magnetizations are attributed to the different roughness of the film/substrate interfaces. Interaction between Co layers and the substrates produces intermixed compound layers that are nonmagnetic. The thickness of this compound layer is 3.8 monolayers for Co/Ge(111), and 2.1 monolayers for Co/Si(111). A series of annealing experiments showed that the onset temperature of the disappearance of the magnetism for Co films is lower on Ge than that on Si substrate. For cobalt film, this onset temperature is 300 K on Ge(111) and 575 K on Si(111).
Monte Carlo simulations of ordering in ferromagnetic–antiferromagnetic bilayers
Authors: Tsai Shan-Ho , Landau D. P. , Schulthess Thomas C.
Published: July 2002

Monte Carlo simulations have been used to study phase transitions on coupled anisotropic ferro/antiferromagnetic (FM/AFM) films of classical Heisenberg spins. We consider films of different thicknesses, with fully compensated exchange across the FM/AFM interface. We find indications of a phase transition on each film, occuring at different temperatures. It appears that both transition temperatures depend on the film thickness.
Large exchange bias in interdiffused NiFe/Mn bilayers
Authors: Youssef Jamal Ben , Spenato David , Gall Henri Le , Ostoréro Jean
Published: July 2002

The effect of the annealing temperature a well as the antiferromagnetic (AF) and ferromagnetic (F) thickness on exchange coupling in Ni81Fe19/Mn single bilayers was systematically studied. We then show that a large exchange coupling is observed when the bilayers are annealed at 300 °C: it corresponds to an exchange field of about 290 Oe. This large exchange field is induced with a rather thick F layer of 46 nm. Both the exchange field Hex and coercive field Hc increase with Mn thickness reaching saturation around 100 nm of Mn. The exchange coupling is associated with interfacial diffusion at the NiFe/Mn interface. This result is confirmed by a large change in magnetization and resistivity before and after annealing. We show that the existence of the exchange field is associated with the clear evidence of a new FeMnNi phase in the x-ray spectrum.
Evidence of a tilted and herringbone structure in cadmium behenate Langmuir–Blodgett ultrathin films: Comparison with Langmuir monolayers
Authors: Dupres V. , Cantin S. , Perrot F. , Fontaine P. , Goldmann M.
Published: July 2002

The molecular arrangement of monolayers and multilayers of cadmium behenate deposited at the air–water interface or on air-oxidized silicon wafers was investigated by means of grazing incidence x-ray diffraction. Even though it is frequently mentioned that the Langmuir–Blodgett (LB) monolayers of fatty acid salts have usually an in-plane hexagonal packing, we obtained two first-order peaks in all the investigated films, indicating a distorted hexagonal lattice. Whereas these peaks are in-plane in the Langmuir or LB monolayers implying no molecular tilt, they are slightly out of the plane in the 3 and 5 layers samples indicating tilted molecules. In these few layers LB films, second-order peaks are detected and the molecules are tilted towards a next-nearest neighbor (NNN structure), as in the L2′ phase of fatty acids. Using two angles of incidence of the x-ray beam allowing to probe either all the layers or only the external layers, a distribution of the tilt angle in the range 1°–6° is evidenced within each layer of the LB films. Moreover, the herringbone peak is measured in this NNN structure corresponding to the L2′ phase, implying that the herringbone order is long-range in the LB films.
Determination of three-dimensional equilibria from flux surface knowledge only
Authors: Mynick H. E. , Pomphrey N.
Published: July 2002

It is shown that the method of Christiansen and Taylor, from which complete tokamak equilibria can be determined given only knowledge of the shape of the flux surfaces, can be extended to three-dimensional equilibria, such as those of stellarators. As for the tokamak case, the given geometric knowledge has a high degree of redundancy, so that the full equilibrium can be obtained using only a small portion of that information.
Current drive experiments in the helicity injected torus (HIT-II)
Authors: Redd A. J. , Nelson B. A. , Jarboe T. R. , Gu P. , Raman R. , Smith R. J. , McCollam K. J.
Published: July 2002

The Helicity Injected Torus [HIT-II: T. Jarboe et al., Phys. Plasmas 5, 1807 (1998)] is a low-aspect-ratio tokamak capable of both inductive (ohmic) and Coaxial Helicity Injection (CHI) current drive. HIT-II is modest in size (major radius R=0.3 m, minor radius a=0.2 m, and on-axis toroidal field of up to 0.5 T), but has demonstrated 200 kA of toroidal plasma current, using either CHI or induction separately. The loop voltage, boundary flux, and plasma equilibrium are controlled by a real-time flux feedback system. HIT-II ohmic plasmas exhibit reconnection events during both the current ramp-up and decay, events that relax the current profile while conserving the magnetic helicity. A new operating regime for CHI plasmas, using a double-null divertor (DND) boundary flux, has been explored. DND CHI plasmas exhibit good shot-to-shot reproducibility, low impurity content, minimal shorting current in the absorber region, and EFIT-reconstructed equilibria consistent with significant closed-flux core regions [EFIT: L. Lao et al., Nucl. Fusion 25, 1611 (1985)]. HIT-II DND CHI discharges also exhibit a continuous n=1 mode at the outer midplane, a mode that has been correlated experimentally with current-profile relaxation. A detailed explanation of helicity injection current drive has been developed, which is consistent with experimental observations of HIT and HIT-II discharges. According to this mechanism, asymmetric distortion of the n=1 mode structure generates current drive in the core plasma by dynamo action, relaxing the CHI-driven current profile.
Heterodyne mixing in diffusion-cooled superconducting aluminum hot-electron bolometers
Authors: Siddiqi I. , Verevkin A. , Prober D. E. , Skalare A. , McGrath W. R. , Echternach P. M. , LeDuc H. G.
Published: July 2002

We present microwave (30 GHz) measurements on aluminum superconducting hot-electron bolometer (HEB) mixers. Aluminum HEB mixers have a lower superconducting transition temperature than niobium and niobium nitride devices, and are predicted to have improved sensitivity and require less local oscillator power. The devices studied consist of a narrow superconducting aluminum microbridge with contacts comprised of thick aluminum, titanium, and gold. A perpendicular magnetic field is used to suppress superconductivity in the contacts. The device length is much shorter than the electron–phonon inelastic length [L≪(Dτe–ph)1/2] and thus the intermediate frequency (IF) bandwidth is set by the diffusion time of hot electrons from the microbridge into the contacts. We discuss limitations on the IF bandwidth in very short HEB mixers with fully normal contacts. Overall, the microwave heterodyne mixing results show good performance with a mixer noise temperature inferred from the conversion efficiency and output noise of TM⩾4 K, double side band (DSB). Measurements at 618 GHz yield a conversion efficiency approximately 10 dB lower than observed at 30 GHz. Output saturation by background radiation is postulated to contribute significantly to this difference. A similar decrease in conversion efficiency in the microwave mixing measurements is observed when broadband noise is added to the rf input signal. We discuss the tradeoff between increased sensitivity and the occurrence of saturation effects in low transition temperature HEBs.
Dependence of band gap energy shift of In0.2Ga0.8As/GaAs multiple quantum well structures by impurity-free vacancy disordering on stoichiometry of SiOx and SiNx capping layers
Authors: Su Yu Jae , Dong Song Jin , Tak Lee Yong , Lim H.
Published: July 2002

We have investigated the effects of the stoichiometry of SiOx and SiNx capping layers on the band gap energy shift induced by impurity-free vacancy disordering of the In0.2Ga0.8As/GaAs multiple quantum well structures. The stoichiometry of the SiOx and SiNx capping layers was changed by varying the flow rate of silane (SiH4) gas, and argon gas was employed as the carrier gas of the diluted SiH4 gas to eliminate any possible incorporation of nitrogen into the deposited film when nitrogen gas is employed as the carrier gas. A blueshift of photoluminescence peak of up to 112 meV is observed after rapid thermal annealing at 950 °C for 50 s from the sample capped with SiOx (provided with a SiH4 flow rate of 20 sccm). It is observed that the magnitude of the blueshift increases with the decrease of SiH4 flow rate for the SiOx and SiNx capping layer because of the increased porosity of dielectric capping layers. The insertion of intermediate GaAs cap layer reduces the band gap energy shift irrespective of the SiOx or SiNx capping layer.
Large absolute and polarization-independent photonic band gaps for various lattice structures and rod shapes
Authors: Susa Nobuhiko
Published: July 2002

Despite the considerable amount of research undertaken on various lattice structures, the photonic band gap (PBG) for a triangular lattice remains the largest both in the transverse magnetic (TM) and transverse electric (TE) modes. The PBG for a square lattice can be doubled by using square air holes rather than air cylinders. Reducing the symmetry was effective in terms of a honeycomb lattice in that the PBG can be increased 40% by deforming the lattice and using oval dielectric rods instead of cylindrical rods. The PBGs for all the examined structures increase monotonously as the refractive index is increased. The overlap PBG between the TM and TE gaps (polarization-independent PBG) is the largest for a triangular lattice of circular air rods. The overlap PBG for a hybrid square lattice of air rods is the next largest, and is twice as large as that for the well-known honeycomb lattice consisting of dielectric cylinders. When the refractive index of a dielectric material is increased to more than 3.50, the magnitude of the overlap PBG for almost all the photonic crystals that exhibit an overlap PBG saturates or decreases, except for the largest and next largest overlap PBG’s mentioned above.
Electric field effect on positronium formation in liquids
Authors: Stepanov Sergey V. , Byakov Vsevolod M.
Published: July 2002

The comparison of different models (the Ore, spur, and blob models) of positronium (Ps) formation is presented. Because in molecular media Ps is formed in the terminal positron blob and not in an ordinary spur, the application of the blob model seems to be the most adequate. We extend this model for consideration of the Ps formation in the presence of an external electric field (<100 kV/cm). In the simplified limiting case, this approach provides a formula similar to the Onsager one for the geminate recombination probability. The influence of ion–electron recombination and other intrablob processes on Ps formation is taken into account. The role of quasifree positronium in the Ps formation process is discussed.
Production of monodispersed particles by using effective size selection
Authors: Perales-Perez O. , Sasaki H. , Kasuya A. , Jeyadevan B. , Tohji K. , Hihara T. , Sumiyama K.
Published: July 2002

In this article we report the results of two size selection methods that are based on interfacial interaction between nanosize particles, magnetite in this case, anionic surfactants, and nonpolar solvents. It is proposed that by selecting a suitable surfactant type and/or conditions to modify the particle–particle separation distance, only smaller particles can be stabilized against aggregation and settling making a size sensitive separation possible. Using this phenomenon, an effective size selection at the nanosize level has been achieved and the preliminary results are presented here. Depending on the conditions, stable suspensions of nearly monodispersed nanoparticles of magnetite (diameter less than 10 nm and standard deviation, σ, below 0.2) were obtained from polydispersed powders (less than 40 nm in diameter and σ around 0.6) synthesized from aqueous solutions at 25 °C. Magnetization measurements of the fractions confirmed the effectiveness of the developed size selection methods.
On photochemistry of water in solid Xe: Thermal and light-induced decomposition of HXeOH and HXeH and formation of H2O2
Authors: Khriachtchev Leonid , Tanskanen Hanna , Pettersson Mika , Räsänen Markku , Ahokas Jussi , Kunttu Henrik , Feldman Vladimir
Published: July 2002

A photochemical study of water (H2 16O, H2 18O, D2 16O, and D2 18O) in solid Xe is described. The water–Xe samples were irradiated at 193 nm and then annealed at 40–50 K, which led to formation of various isotopomers of Xe-containing molecules, HXeOH and HXeH. This diffusion-controlled formation of HXeH and HXeOH consumes the main part of hydrogen atoms generated in the matrix during photolysis. Both photodecomposition profiles and ultraviolet (UV) absorption spectra of HXeOH and HXeH feature a broad absorption band of these species around 240 nm corresponding to the transition to the repulsive excited states. It is also found that HXeOH and HXeH molecules can be thermally destroyed in similar time scales of ∼10 min at about 54 and 66 K, respectively. This clear difference between the decomposition temperatures for HXeOH and HXeH suggests the intrinsic basis of the decomposition process, which possibly occurs over the barriers of the bending coordinates. The absence of strong H–D isotope effect in this thermal decomposition indicates that tunneling of hydrogen is not essentially involved in the process at these temperatures. However, the local disorder of a Xe matrix seems to produce inhomogeneous broadening of the activation energies of the decomposition as indicated by the observed nonexponential decay kinetics. Upon photolysis and annealing of the H2O–Xe samples, monomeric and complexed hydrogen peroxide is formed originating, at least partially, from water clusters stabilized in solid Xe. In addition, we report the vibrational data on various isotopomers of HXeH, HXeOH, H2O, OH, and OH⋯H2O isolated in solid Xe.
Magnetic and mechanical properties of (Fe, Co)–Pt bulk alloys prepared through various processing techniques
Authors: Saha S. , Thong C. J. , Huang M. Q. , Obermyer R. T. , Zande B. J. , Chandhok V. K. , Simizu S. , Sankar S. G.
Published: July 2002

Magnetic and mechanical properties of Fe60Pt40, Fe60.5Pt39.5 and (Fe1−xCox)60.5Pt39.5 bulk alloys prepared by a number of processing techniques have been examined. Processing techniques include induction melting, mechanical milling (at ∼77 K), hot and cold work, and melt extraction. Magnetic properties were determined in the temperature range from 300 to 1100 K using a vibrating sample magnetometer. Melt extracted Fe60.5P39.5 sample appeared to be fully dense and the magnetic properties found to be 4πMs (at 1.5 T)∼1.08 T, Hc∼270.6 kA/m, and (BH)max∼55.7 kJ/m3. Freezer milled Fe60.5Pt39.5 sample (loose powder) showed a saturation induction of 1.33 T, and coercivity of 270.6 kA/m at room temperature. Curie temperature for this sample is found to be 450 °C. For the Fe45.37Co15.13Pt39.5 (loose powder) sample, coercivity increases to 318 kA/m and the Curie temperature increases to 540 °C. Tensile strength was measured for selected samples. It is found that Fe–Pt and (Fe,Co)–Pt magnets are about 5–10 times mechanically stronger than the rare earth based permanent magnets. Preliminary examination of the structural and magnetic properties of these alloys indicates that the (Fe,Co)–Pt bulk alloys are an excellent system to explore exchange coupling mechanism in permanent magnets.
Dust charging effects on the sheath equilibrium of a plasma with energetic electron beam
Authors: Goedert J. , Garcia L. G.
Published: July 2002

Recently the dust charging and levitating in a collisionless cathode sheath with energetic electron beam were analyzed theoretically [D. Wang et al. J. Appl. Phys. 88, 1276 (2000)]. In this article, the model is extended in order to take into account the effects of the dust charge density on the plasma sheath equilibrium. The results show that dust density plays an important role both in the dust charging process and on the sheath potential profile.
Growth and characterization of GaInNxAs1−x thin films with band-gap energies in the red-blue portion of the visible spectrum
Authors: Cardona-Bedoya Jairo A. , Gordillo-Delgado Fernando , Zelaya-Angel Orlando , Cruz-Orea Alfredo , Mendoza-Álvarez Julio G.
Published: July 2002

Using the radio-frequency (rf) sputtering deposition technique, we have grown GaInNxAs1−x thin films on glass substrates at room temperature. The concentration of nitrogen in the films was found to depend mainly on the rf power used to excite the growth plasma. X-ray diffractograms show that the films have small grain sizes and present a broad diffraction band centered close to the (002) diffraction peak of hexagonal GaN. Electron dispersive spectroscopy measurements report N concentrations of x∼0.8 and In concentrations of about 3% indicating that we have grown GaInNxAs1−x alloys in the GaN-rich side. The absorption spectra measured by the photoacoustic technique show that these semiconductor films have band-gap energies ranging between 1.69 and 2.56 eV, when the rf sputtering power is varied in the range 30–80 W. Thus, we show the feasibility to grow GaInNxAs1−x thin films with high N concentrations in which we can tune the band-gap energy in the red-blue portion of the visible spectrum, by a careful control of the growth parameters.
Nano-oxide-layer specular spin valve heads with synthetic pinned layer: Head performance and reliability
Authors: Hasegawa N. , Koike F. , Ikarashi K. , Ishizone M. , Kawamura M. , Nakazawa Y. , Takahashi A. , Tomita H. , Iwasaki H. , Sahashi M.
Published: July 2002

To implement the specular nano-oxide-layer (NOL) spin valve (SV) heads for use in practical applications, it is key to simultaneously achieve a good specular effect of the NOL inserted in the synthetic ferrimagnet pinned layer (i.e., high magnetoresistance MR performance) and a strong pinning field through the NOL. By using CoFe+X as a substance to be subjected to oxidation, we obtained the NOL specular SV films simultaneously achieving a high MR ratio of 17%–18% and a high pinning field of 1100–1500 Oe. Narrow track (0.12 μm) heads were fabricated and they showed a high sensitivity of 10 mV/μm. Several reliability tests were done both at the sheet film level and the actual head level. The oxygen inside NOL was found to be stable up to 350 °C, and pinned layer magnetization canting after orthogonal field annealing was found to be almost the same as today’s non-NOL SV films. An electrostatic discharge test and accelerated lifetime test were also performed and NOL specular heads were demonstrated to have almost the same robustness as today’s non-NOL heads.
Optical gaps of alkali borate and alkali fluoroborate glasses
Authors: Suzuki Takenobu , Hirano Masahiro , Hosono Hideo
Published: July 2002

The optical gaps of B2O3 alkali borate, and alkali fluoroborate glasses were determined by using blown films. The gap of B2O3 glass was 8.0 eV and the value decreased monotonically with decreasing the B2O3 content in both fluoroborate and borate glasses. When compared at a constant B2O3 content, the gap is in the order Li>Na>K and fluoroborate>borate. Ab initio molecular orbital calculation on the model clusters of the glasses revealed that the lowest excitations in B2O3 and alkali (fluoro) borate glasses are the transitions from nonbonding 2p orbitals of oxygen atoms in boroxol rings to vacant nonbonding 2p orbitals of boron atoms on “loose” BO3 triangles and from nonbonding 2p orbitals of oxygen atoms bonded with borons in tetrahedral coordination to the vacant ns orbitals of neighboring alkali ions, respectively. The vacant ns orbitals of the alkali ions neighboring oxygen atoms attached to tetrahedral borons primarily contribute to the lowest unoccupied molecular orbital (LUMO) levels. On the other hand, fluorine indirectly contributes to lowering the highest occupied molecular orbital (HOMO) levels via inductive effect (polarization of B–F σ-bond). It was therefore concluded that the effect of alkali addition on lowering LUMO levels is larger than that of fluorine addition on lowering the HOMO level.
Solitons in parametrically driven discrete nonlinear Schrödinger systems with the exploding range of intersite interactions
Authors: Vakhnenko Oleksiy O.
Published: July 2002

We present the sequence of parametrically driven discrete nonlinear Schrödinger systems with the progressively extending range of intersite couplings. In the case of time-independent coupling parameters the sequence is reduced to the Ablowitz–Ladik hierarchy, which is known to be integrable by the inverse scattering transform. However the models with the time-dependent intersite interactions are shown to be integrable too irrespective of a particular form of time dependencies of coupling parameters. Any of such parametrically driven systems might exhibit rather complex soliton dynamics and is described by the unconserved Hamiltonian function. We reveal an important subclass of parametrically driven systems demonstrating the parametrical localization of soliton dynamics on a confined domain of space. Meanwhile an appropriate choice of time dependencies in intersite interactions allow us to transform the original parametrically driven system into another one but subjected to the linear external potential. As a result the latter system can be readily integrated as well. In particular the peculiarities of Bloch oscillations in the systems with time-independent long range intersite interactions and linear external potential of constant strength are analyzed. In general, regulating the range of intersite couplings, the strengths and time dependencies of coupling parameters, we are able to model a number of physically important quasi-one-dimensional systems. We develop an alternative approach to solve the Marchenko equations permitting one to obtain the multisoliton solutions in the most simple and natural way. Finally, we point out how to reformulate any model in row in terms of corrected amplitudes with the standard Poisson brackets.
Laser-induced fluorescence studies of excited Sr reactions. III. Sr(3P1)+CHF=CH2, CF2=CH2, CHF=CHF, and C6H5F
Authors: Teule J. M. , Janssen M. H. M. , Stolte S. , Bulthuis J.
Published: July 2002

Laser-induced fluorescence spectra reveal the internal energy distributions of SrF(X 2Σ) formed in the reactions of electronically excited Sr(3P1) with various unsaturated fluorohydrocarbons, i.e., CHF=CH2, CF2=CH2, CHF=CHF, and C6H5F. The internal energy distribution of the ground state diatomic product typically shows less vibrational excitation, without inversion, and somewhat lower rotational excitation than the reactions of Sr(3P1) with HF and saturated hydrocarbons. The different behavior of the two groups of reactants is rationalized by a simple MO picture, assuming that an electron from Sr is transferred to a σ* orbital in HF and the saturated fluorohydrocarbons and to a π* orbital in the unsaturated fluorohydrocarbons with a subsequent transfer to a σ* orbital of the C–F bond. The latter transfer constitutes an extension of the reaction path, leading to less vibrational excitation. This would explain why the energy disposal in the reaction with C6H5F behaves similar to that in the reactions with the fluoroethenes. Even if the shape of the vibrational distribution of the SrF product is the same for all unsaturated fluorohydrocarbons studied, the degree of vibrational excitation varies strongly. This even holds when comparing cis- and transCHF=CHF, where the distributions can be characterized by distinct surprisal parameters.
Short- and long-lived electronic states of BF−
Authors: Dreuw A. , Sommerfeld T. , Cederbaum L. S.
Published: July 2002

Resonance states of BF− are studied with high-level ab initio methods. In analogy to the fundamental anions N2− and CO−, the Π2 ground state of BF− has been found to be a short-lived shape-type resonance state exhibiting a lifetime of less than a femtosecond. In contrast, the lowest quartet state Σ−4 of BF− is clearly long-lived, since the decay channels via direct electron emission and dissociation are closed and all other possible decay channels are spin-forbidden. The lowest sextet state of BF− is also investigated. Connection to recently identified long-lived high-spin states of N2− and CO− is made and their relations are discussed.
On higher-dimensional dynamics
Authors: Wesson Paul S.
Published: July 2002

Technical results are presented on motion in N(>4)D manifolds to clarify the physics of brane theory, Kaluza–Klein theory, induced-matter theory, and string theory. The so-called canonical or warp metric in five dimensions (5D) effectively converts the manifold from a coordinate space to a momentum space, resulting in a new force (per unit mass) parallel to the four-dimensional (4D) velocity. The form of this extra force is actually independent of the form of the metric, but for an unbound particle is tiny because it is set by the energy density of the vacuum or cosmological constant. It can be related to a small change in the rest mass of a particle, and can be evaluated in two convenient gauges relevant to gravitational and quantum systems. In the quantum gauge, the extra force leads to Heisenberg’s relation between increments in the position and momenta. If the 4D action is quantized then so is the higher-dimensional part, implying that particle mass is quantized, though only at a level of 10−65 g or less, which is unobservably small. It is noted that massive particles which move on timeline paths in 4D can move on null paths in 5D. This agrees with the view from inflationary quantum field theory, that particles acquire mass dynamically in 4D but are intrinsically massless. A general prescription for dynamics is outlined, wherein particles move on null paths in an N(>4)D manifold which may be flat, but have masses set by an embedded 4D manifold which is curved.
Compatibility and decompositions of effects
Authors: Pulmannová Sylvia
Published: July 2002

Compatibility relations in effect algebras and their connections with refinements of the orthogonal partitions of unity are studied. Properties of blocks as maximal sets of compatible elements are discussed. Some special kinds of effect algebras are characterized using properties of compatibility. Using refinements, an additional structure on the effect test spaces is introduced and used to a characterization of different types of effect algebras.
High-performance polymer light-emitting diodes doped with a red phosphorescent iridium complex
Authors: Chen Fang-Chung , Yang Yang , Thompson Mark E. , Kido Junji
Published: July 2002

High efficiency has been achieved in polymer light-emitting diodes (PLEDs) exhibiting red emission by doping a fluorescence host material, poly(vinylcarbazole) (PVK), with an iridium(III) complex, bis[2-(2′-benzothienyl)-pyridinato-N,C3′]iridium(acetylacetonate) (BtpIr). The electroluminescence spectrum has a maximum wavelength of 614 nm. The highest external quantum efficiency is 3.3%. Due to its short triplet excited lifetime (∼5 μs), the quenching of the triplet exciton in BtpIr-doped PVK PLEDs has been shown to be suppressed compared to platinum(II)-2,8,12,17-tetraethyl- 3,7,13,18-tetramethylporphyrin-doped PVK PLEDs. 65% of the peak efficiency can be sustained at high-current density and at the very high brightness of 1350 cd/m2. We suggest that both triplet–triplet annihilation and polaron–triplet annihilation involves exciton quenching.
A second look at Uq(Sl2) at third root of unity
Authors: Kastler Daniel
Published: July 2002

We revisit the 27-dimensional quotient of Uq(Sl2) at third roots of unity within a presentation adapted to a Hopf bar-operation. We describe in detail the regular representation and display the Hopf automorphisms and the Hopf bar-operations.
Electrical properties of highly reliable plug buffer layer for high-density ferroelectric memory
Authors: Song Yoon J. , Koo B. J. , Lee J. K. , Kim C. J. , Jang N. W. , Kim H. H. , Jung D. J. , Lee S. Y. , Kim Kinam
Published: July 2002

A CoSi2 buffer layer was prepared in polycrystalline silicon (polysilicon) plug for preventing an undesired microvoid between the polysilicon plug and Ir/Ti diffusion barrier. Since the microvoid generates random function fail, resulting in low wafer yield of a 4 Mb ferroelectric random access memory device, we developed the thermally stable CoSi2 buffer layer for eliminating the random single bit fails. The ferroelectric capacitors using the CoSi2 buffer layer showed a low contact resistance of 96 Ω per contact in 1k serial contact array with contact size of 0.6 μm, and also exhibited great ferroelectric properties such as remnant polarization and coercive voltage of 20 μC/cm2 and 1.2 V, respectively. Scanning electron microscopy analyses confirmed that no microvoid was formed between the interface between the Ir/Ti barrier layer and the CoSi2 buffer layer.
Nonlinear Fokker–Planck equation exhibiting bifurcation phenomena and generalized thermostatistics
Authors: Shiino Masatoshi
Published: July 2002

A nonlinear Fokker–Planck equation exhibiting bifurcation phenomena is proposed within the framework of generalized thermostatistics. The nonlinearity responsible for the occurrence of bifurcation of solutions is assumed to be of the form appearing in the standard mean field model. A Liapunov function is defined that takes the form of free energy involving generalized entropies of Tsallis and an H-theorem is proved to show that the free energy, which is bounded below, continues to decrease until the system approaches one of the equilibrium distributions. The H-theorem ensures, instead of uniqueness of the equilibrium distribution, global stability of the system in that either one of multisolutions must be approached for large times. Local stability analysis is conducted and the second-order variation of the Liapunov function is computed to find its relevant part whose sign governs stability of the equilibrium distribution of the system. The case with a bistable potential is investigated, as an example of confirming the theory, to give the bifurcation diagram displaying the order parameter as a function of the coefficient of the nonlinear diffusion term.
Magnetic field in a thick superconducting solenoid for dynamic levitation of objects
Authors: Dushkin C. , Nawa M. , Fujita T. , Nakabayashi S.
Published: July 2002

High-field superconducting magnets are of increasing importance for the levitation of objects and materials processing, whose success depends on the detailed knowledge of the magnetic field and force distribution in the solenoid. Here we propose an elegant analytical approach for calculation based on a simple equation for the axial field of thick solenoid. Experimental examples illustrate its application to the design of magnets and the simulation of the complex motion of water droplets and plastic balls levitating in liquid medium under dynamic conditions.
Admittance of axially polarized lossy piezoceramic cylinders loaded with a viscoelastic liquid
Authors: Kiełczyński P. , Pajewski W. , Szalewski M.
Published: July 2002

Analytical formulas for the electrical admittance of a viscoelastically loaded cylindrical piezoceramic resonator vibrating in a shear mode are established. In the analysis, mechanical losses in a piezoelectric ceramic and in a liquid were taken into account. The admittance was calculated based on the solutions of the equations of motion of the piezoelectric ceramics and viscoelastic liquid. These solutions fulfilled the appropriate boundary conditions on the cylindrical surfaces of the resonator. In this way, analytical formulas for admittance dependent on the material parameters of ceramics and viscoelastic liquid were established. Analyzing the obtained admittance diagrams, the changes in resonant frequencies Δfs and Δfm as a function of the liquid viscosity η were evaluated. From the numerical calculations of the authors it follows that the Kanazawa–Gordon formula, which is derived for planar resonators and relates the shift in resonant frequency to the viscosity of the Newtonian liquid, can also be valid for cylindrical resonators. The work shows that piezoelectric cylindrical resonator with a moderately low mechanical quality factor and high electromechanical coupling coefficient can be useful for measuring liquids of large viscosity. The results of this work can constitute the basis for the design and construction of viscosity sensors.
Polarized Raman scattering of epitaxial PbTiO3 thin film with coexisting c and a domains
Authors: Lee Sun-Hwa , Jang Hyun M. , Cho Seong M. , Yi Gyu-Chul
Published: July 2002

Effects of the orientation of ferroelectric domains on the characteristics of polarized Raman spectra were studied using an epitaxially grown PbTiO3 thin film in which the c-axis oriented domains coexist with the a-axis oriented domains on MgO (001). To obtain polarized spectra for both two distinctive c and a domains, we have employed scattering configurations in which the relevant phonon wave vector, k, is perpendicular to the c axis of the tetragonal unit cell. Compared with the mode frequencies of single-crystal PbTiO3, a softening of the E(TO) phonons was evident for both c and a domains, suggesting the presence of a strong tensile film stress. In addition to this, we observed a splitting of the degenerate “silent” mode into two distinctive B1 and E modes in an epitaxially grown film on MgO (001).
Vibrational overtones and rotational structure of HCl in rare gas matrices
Authors: Berghof V. , Martins M. , Schmidt B. , Schwentner N.
Published: July 2002

The rotational structure in the vibrational transitions from v=0 to v=1, 2, 3, 4 of H35Cl and H37Cl is studied in Xe, Kr, and Ar matrices with high spectral resolution. A consistent set of rotational constants Bv for the vibrational levels v=0 to 4 is derived. B0 decreases with the tightness of the cage from 9.78 cm−1 in Xe to 8.83 cm−1 in Ar for H35Cl (gas phase 10.44 cm−1). The values for B0 to B4 decrease linearly with v due to the vibration-rotation-coupling constant α which increases from 0.37 cm−1 in Xe to 0.479 cm−1 in Ar (gas 0.303) according to the cage tightness. The splitting of the R(1) transition which originates from the hindering of rotation is analyzed in Xe using the T2g–T1u and T2g–Eg transition energies. A comparison with force field calculations yields a dominant contribution of the sixth spherical harmonic YA1g6 of the octahedral matrix potential. The modulation of the potential takes a value of K6/B=17 which corresponds to a barrier for the rotation of 160 cm−1. The splitting increases with the vibrational level v which can be interpreted as a weak admixture of the YA1g4 spherical harmonic. A large isotope effect and a reduction of the T1u–A1g transition energy [R(0)-transition] beyond the crystal field value are attributed to an eccentric rotation with a displacement of the center-of-mass of the order of 0.05 Å. The vibrational energies ωe show an opposite trend with matrix atom size and decrease with polarizability from 2970 cm−1 in Ar to 2945.4 cm−1 in Xe (gas 2989.9 cm−1) while the anharmonicity ωexe of the free molecule lies close to the Kr value and thus between that of Ar and Xe.
SVRT calculation for bond-selective reaction H+HOD→H2+OD, HD+OH
Authors: Zhang Xin , Han KeLi , Zhang John Z. H.
Published: July 2002

The semirigid vibrating rotor target (SVRT) model is applied to study bond-selective branching reaction H+HOD→H2+OD, HD+OH on the Schatz–Elgersma potential energy surface when one of the stretching modes of HOD is excited. Using the SVRT model, the time-dependent wavepacket calculation is carried out in four-mathematical dimensions with the remaining two internal coordinates fixed. The reaction probabilities for producing two product branches are calculated from two separate dynamics calculations. The results show that for reaction H+HOD(100)→HD+OH when O–D stretching mode is excited, the SVRT calculation gives excellent results. The SVRT result is slightly worse for reaction H+HOD(001)→H2+OD when the O–H stretching mode is excited. The current study demonstrates that the SVRT model is also applicable for giving accurate results for polyatomic reactions when the chemical bond that is broken is vibrationally excited.
Sharp tip geometry and its effect on hardness in nanoindentation experiments
Authors: Ikezawa Kazuhiro , Maruyama Tadashi
Published: July 2002

In this article, we used an indenter, sharper than a Berkovich indenter, consisting of a triangular pyramid with a face angle of 80°, and compared the difference between our own and the Berkovich indenters. First, the cross-sectional shapes of the indenters were analyzed by the Shih, Yang, and Li model [C. W. Shih, M. Yang, and J. C. M. Li, J. Mater. Res. 6, 2623 (1991)]. The result suggested that our sharp indenter has more deviation from the ideal triangular pyramid than the Berkovich indenter, resulting from the difference in sharpness of the indenters. Second, we determined an area function for our indenter using fused silica and compared it with those of an ideal triangular pyramid and a Berkovich indenter. There was a larger difference between the real and ideal indenters in our indenter than in the Berkovich case. Third, hardness measurements indicated that hardness increases with increases in depth and reaches a constant value in both cases of fused silica and single-crystal Si. This dependence of hardness on depth is explained herein in a qualitative manner.
Cross-sectional scanning tunneling microscopy study of InGaAs quantum dots on GaAs(001) grown by heterogeneous droplet epitaxy
Authors: Liu N. , Lyeo H. K. , Shih C. K. , Oshima M. , Mano T. , Koguchi N.
Published: July 2002

We present a cross-sectional scanning tunneling microscopy (STM) study of heterogeneous-droplet-epitaxy (HDE)-grown InGaAs quantum dots (QDs). We found that the structural properties of HDE-grown QDs such as size, shape, etc., are quite different from that of Stranski–Krastanov (SK)-grown InGaAs QDs. HDE-grown InGaAs QDs exhibit a reverse trapezoidal shape, opposite to the SK-grown QDs. In addition, the In concentration within individual HDE QDs is rather uniform, contrary to the case in SK QDs. These HDE QDs also show large size fluctuation. However, we found that there is a size dependence in the In concentration within the QD—the larger QD has lower In concentration, suggesting a self-compensation effect which gives rise to a sharp photoluminescence linewidth.
Field-enhanced piezoelectric deformation during the high temperature/low temperature rhombohedral (FERh/FERL) phase transformation for tin modified lead zirconate titanate ceramics
Authors: Yang Pin , Moore Roger H. , Burns George R.
Published: July 2002

An unusual field-enhanced piezoelectric deformation near the FERH/FERL structural phase transformation was observed in a tin modified lead zirconate titanate solid solution. In addition to the typical field-induced domain reorientation and the piezoelectric strain, this additional field-enhanced deformation only observed near the phase transformation increases linearly with external electric field strength. A 78% increase in field-enhanced strain was observed at a field strength of 32 kV/cm. Comparison of the dielectric susceptibility at low and high field conditions suggests that the observed unusual behavior is created by a field-induced lattice softening during the structural phase transformation. Experimental observations on the field-induced softening phenomena are reported.
Exponentially small splittings in Hamiltonian systems
Authors: Gelfreich V. G. , Lazutkin V. F. , Tabanov M. B.
Published: July 2002

Families of area preserving analytical maps, depending on a small parameter ε, are considered, with the case ε=0 corresponding to an integrable map. The asymptotic formulas for the splittings of separatrices are derived by the method of analytical continuation of the separatrices to the complex domain. The main terms of the asymptotics are exponentially small with respect to the size of the perturbation. As ε tends to zero, the intersection angle of the separatrices can oscillate. The exponent and the oscillatory multiplier of the asymptotic formulas are determined by the position of poles of the homoclinic (heteroclinic) orbit of the limiting flow. Pre-exponential coefficients in the asymptotic formulas contain a multiplier obtained by the numerical study of separatrices of ‘‘model’’ maps in the complex domain.