bluuebunny/crossref_metadata_2025 huggingface dataset:
Giant microwave photoresistance of two-dimensional electron gas
Authors: Ye P. D. , Engel L. W. , Tsui D. C. , Simmons J. A. , Wendt J. R. , Vawter G. A. , Reno J. L.
Published: July 2002

We measure microwave frequency (4–40 GHz) photoresistance at low magnetic field B, in high mobility two-dimensional electron gas samples, excited by signals applied to a transmission line fabricated on the sample surface. Oscillatory photoresistance vs B is observed. For excitation at the cyclotron resonance frequency, we find a giant relative photoresistance ΔR/R of up to 250%. The photoresistance is apparently proportional to the square root of applied power, and disappears as the temperature is increased.
A self-consistent trapping model of driven electron plasma waves and limits on stimulated Raman scatter
Authors: Rose Harvey A. , Russell David A.
Published: July 2002

A Vlasov equation based model is used to determine various regimes of electron plasma wave response to a source appropriate to stimulated scatter in a laser hot spot. It incorporates trapped particle effects such as the standard nonlinear frequency shift, extended beyond the weak regime, and a reduction of damping à la Zakharov and Karpman [V. E. Zakharov and V. I. Karpman, JETP 16, 351 (1963)]. The results are consistent with those of Holloway and Dorning [J. P. Holloway and J. J. Dorning, Phys. Rev. A 44, 3856 (1991)] for small amplitude Bernstein–Greene–Kruskal modes. This leads to the prediction that as long as kλD⩾0.53 for a background Maxwellian distribution function, e.g., a 5 keV plasma with ne/nc⩽0.075, anomalously large backward stimulated Raman scatter can be excluded. A similar analysis leads to density limits on stimulated Brillouin scatter.
Mechanism for linear and nonlinear optical effects in monoclinic bismuth borate (BiB3O6) crystal
Authors: Lin Zheshuai , Wang Zhizhong , Chen Chuangtian , Lee Ming-Hsie
Published: July 2002

Electronic structure calculations of BiB3O6 crystal from first principles are performed based on a plane-wave pseudopotential method. The linear refractive indices and the static second-harmonic generation (SHG) coefficients are also calculated by the SHG formula improved by our group. The calculated values are in good agreement with the experimental values. A real-space atom-cutting method is adopted to analyze the respective contributions of the cation and anionic groups to the optical response. The results show that the contribution of the (BiO4)5− anionic group to the SHG coefficients is more pronounced than that of the (BO3)3− and (BO4)5− groups.
Perovskite phase stabilization in epitaxial Pb(Mg1/3Nb2/3)O3–PbTiO3 films by deposition onto vicinal (001) SrTiO3 substrates
Authors: Bu S. D. , Lee M. K. , Eom C. B. , Tian W. , Pan X. Q. , Streiffer S. K. , Krajewski J. J.
Published: July 2002

We report the perovskite phase stabilization of 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 (PMN-PT) epitaxial thin films by deposition onto miscut substrates. Films were grown on (001) SrTiO3 substrates with miscut angles from 0 to 8 degrees toward the [100] direction using 90° off-axis magnetron sputtering. Films on high miscut substrates (>4°) showed almost the pure perovskite phase in both x-ray diffraction and transmission electron microscopy image, and were nearly stoichiometric. In contrast, films on exact (001) SrTiO3 contained a high volume fraction of pyrochlore phases with Pb deficiency. Atomic force microscopy reveals that films on 8° miscut substrates have a much smoother surface morphology than those on exact (001) SrTiO3. Cross-sectional transmission electron microscopy images reveal that the pyrochlore phases nucleate on top of the perovskite phase, and that the amount of the pyrochlore phases increase with film thickness. A film on an 8° miscut substrate exhibits a polarization hysteresis loop with a remnent polarization of 20 μC/cm2 at room temperature.
Aluminum-induced crystallization of hydrogenated amorphous germanium thin films
Authors: Chambouleyron I. , Fajardo F. , Zanatta A. R.
Published: July 2002

Al-induced crystallization of co sputtered hydrogenated amorphous germanium films, deposited at 220 °C, onto crystalline silicon substrates is investigated by Raman and infrared spectroscopies as a function of the Al concentration (2×10−6<[Al/Ge]<2.5×10−2). Aluminum induces partial crystallization of the films for metal concentrations smaller than ∼1.3 at. %. A sort of explosive crystallization of the films occurs within a narrow Al concentration range (∼1.3<[Al/Ge]<∼1.8 at. %). Raman spectra do not display any crystallization signal for metal concentrations above this narrow range. Data of the extended x-ray absorption fine structure of the coordination and of the local order around gallium, in Ga-doped a-Ge:H, are used to propose an overall picture of the microscopic mechanisms behind these results. A comparative analysis suggests that the crystallization seeds are fourfold-coordinated Al atoms sitting at the center of perfect tetrahedral Ge sites.
Elastic force analysis of functional polymer submicron oscillators
Authors: Sun Hong-Bo , Takada Kenji , Kawata Satoshi
Published: July 2002

We report in this letter an elastic force analysis of two-photon-polymerized submicron oscillators with spiral radius of 150 nm. A laser trapping force was first utilized to mechanically drive the spring of this small size. An overdamped oscillation was observed, according to which, the spring constant was measured to approximately 10−8 N/m. This value was 5-order smaller than the one calculated using oscillator parameters. Both deviated from a more reliable result, 10−6 N/m, as was estimated from the laser trapping force. The significant discrepancies were attributed to scaling effects and to the difference of condensed states of the polymer related to exposure processes.
Effects of tantalum adhesion layer on the properties of SrBi2Ta2O9 ferroelectric thin films
Authors: Leu Ching-Chich , Yang Ming-Che , Hu Chen-Ti , Chien Chao-Hsin , Yang Ming-Jui , Huang Tiao-Yuan
Published: July 2002

The effects of tantalum (Ta) adhesion layer on the ferroelectric and microstructural properties of sol-gel-derived SrBi2Ta2O9 (SBT) films are reported in this study. Compared to the traditional titanium (Ti) adhesion layer, the Ta adhesion layer results in more favorable, highly (115) textural structure of SBT films and therefore higher polarization and dielectric constant. The remnant polarization value of the SBT films crystallized at 750 °C increases from 11.1 to 14.2 μC/cm2 at 5 V, and the dielectric constant increases from 175 to 225. The observed improvement in the electrical properties of SBT films is ascribed to the superior microstructure of Pt thin film on Ta, which has been characterized by x-ray diffraction spectrum (XRD). XRD patterns clearly indicate that the Ti adhesion layer favors c-axis crystalline structure that is undesirable for ferroelectric properties. Moreover, secondary ion mass spectrometer profiles strongly indicate that Ti atoms diffuse deeply into the bulk of SBT thin films after crystallization annealing. By using Ta as the adhesion layer material, this inhomogeneous interdiffusion phenomenon can be effectively suppressed, eliminating the formation of TiOx interfacial layer, and possibly decreasing the occurrence of undesirable second phase compound.
Ab initio spin-orbit CI calculations of the potential curves and radiative lifetimes of low-lying states of lead monofluoride
Authors: Das Kalyan K. , Petsalakis Ioannis D. , Liebermann Heinz-Peter , Alekseyev Aleksey B. , Buenker Robert J.
Published: July 2002

The electronic structure of the lead monofluoride molecule is studied by means of ab initio configuration interaction (CI) calculations including the spin-orbit interaction. Potential-energy curves are generated for a large number of electronic states, of which only the X1 2Π1/2 ground and X2 2Π3/2 and A 2Σ+ excited states have been observed experimentally. Two different methods are compared for the inclusion of spin-orbit effects in the theoretical treatment, a contracted CI which employs a basis of large-scale Λ–S eigenfunctions to form a rather small matrix representation of the full relativistic Hamiltonian (two-step approach), and a more computationally laborious technique which involves solution of a secular equation of order 250 000 S2 eigenfunctions of different spin and spatial symmetry to achieve a potentially more evenly balanced description of both relativistic and electron correlation effects (one-step approach). In the present application, it is found that both methods achieve quite good agreement with measured spectroscopic constants for the X1, X2, and A states. The simpler of these methods is also employed to predict the radiative lifetimes of the latter two states. The key A 2Σ+–X 2Π transition moment in these calculations is found to vary strongly with internuclear distance and to vanish in the neighborhood of the respective equilibrium distances of both participating states. The computed lifetime for the A, v′=0 state of 16 μs overestimates the corresponding measured value by a factor of three, but those of higher vibrational states are found to decrease rather sharply with increasing v′, suggesting that only a slight displacement of the theoretical A–X transition moment curve is needed to explain the above discrepancy.
Plasmon waveguide for optical far/near-field conversion
Authors: Yatsui T. , Kourogi M. , Ohtsu M.
Published: July 2002

A plasmon waveguide was designed and fabricated using a metal-coated silicon wedge structure that converts propagating far-field light to the near field. Illumination (λ=830 nm) of the waveguide (plateau width 150 nm) caused transverse magnetic plasmon-mode excitation. Use of a near-field microscope allowed us to determine its beam width and propagation length as 150 nm and 2.5 μm, respectively.
A preconditioned inexact spectral transform method for calculating resonance energies and widths, as applied to HCO
Authors: Poirier Bill , Carrington Tucker
Published: July 2002

We present a complex-symmetric version of the preconditioned inexact spectral transform (PIST) method, for calculating resonance energies and widths. The PIST method uses an iterative linear solver to compute inexact Lanczos vectors for (EI−H)−1, and then diagonalizes the Hamiltonian in the inexact Lanczos representation. Our new version requires complex-symmetric variants of: (1) the Lanczos algorithm, (2) the linear solver, (3) the preconditioner we introduced in a previous paper [J. Chem. Phys. 114, 9254 (2001)]. The new method works extremely well for HCO, enabling us to calculate the first 17 dissociative resonances in less then 90 second of CPU time.
Triple-layer passivation for longevity of polymer light-emitting diodes
Authors: Kwon Seung Ho , Paik Sang Yoon , Kwon Oh Jun , Yoo Jae Soo
Published: July 2002

A poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene](MEH-PPV) light-emitting diode was coated with passivation layers in order to improve the longevity of conjugated polymer-based diodes. High-density polyethylene (HDPE), which is an insulator, was used as the passivation material in combination with a metal layer to minimize oxygen and water diffusion into the polymer light-emitting diodes. The simplicity of the HDPE(1 μm)/Al–Li(120 nm)/HDPE(1 μm) structure, which was successively thermal coated on the diode, was demonstrated. The longevity of this simple structure was dramatically enhanced after exposure to atmospheric oxygen and moisture.
Interpretation of the Kohn–Sham orbital energies as approximate vertical ionization potentials
Authors: Chong D. P. , Gritsenko O. V. , Baerends E. J.
Published: July 2002

Theoretical analysis and results of calculations are put forward to interpret the energies −εk of the occupied Kohn–Sham (KS) orbitals as approximate but rather accurate relaxed vertical ionization potentials (VIPs) Ik. Exact relations between εk and Ik are established with a set of linear equations for the εk, which are expressed through Ik and the matrix elements εkresp of a component of the KS exchange-correlation (xc) potential vxc, the response potential vresp. Although −Ik will be a leading contribution to εk, other Ij≠k do enter through coupling terms which are determined by the overlaps between the densities of the KS orbitals as well as by overlaps between the KS and Dyson orbital densities. The orbital energies obtained with “exact” KS potentials are compared with the experimental VIPs of the molecules N2, CO, HF, and H2O. Very good agreement between the accurate −εk of the outer valence KS orbitals and the corresponding VIPs is established. The average difference, approaching 0.1 eV, is about an order of magnitude smaller than for HF orbital energies. The lower valence KS levels are a few eV higher than the corresponding −Ik, and the core levels some 20 eV, in agreement with the theoretically deduced upshift of the KS levels compared to −Ik by the response potential matrix elements. Calculations of 64 molecules are performed with the approximate vxc obtained with the statistical averaging of (model) orbitals potentials (SAOP) and the calculated εk are compared with 406 experimental VIPs. Reasonable agreement between the SAOP −εk and the outer valence VIPs is found with an average deviation of about 0.4 eV.
High figure of merit in Eu-filled CoSb3-based skutterudites
Authors: Lamberton G. A. , Bhattacharya S. , Littleton R. T. , Kaeser M. A. , Tedstrom R. H. , Tritt T. M. , Yang J. , Nolas G. S.
Published: July 2002

We report measurements of electrical resistivity, thermopower, thermal conductivity, and Hall coefficient of polycrystalline Eu-doped CoSb3-based skutterudites with compositions Eu0.20Co4Sb12, Eu0.43Co4Sb11.59Ge0.31, and Eu0.42Co4Sb11.37Ge0.50. The relatively high mobility of these compounds, as compared to that of La- and Ce-filled skutterudites, may play a role in the large thermoelectric figure of merit (ZT>1 at 700 K) of Eu0.42Co4Sb11.37Ge0.50. We discuss the significant potential of these compounds for thermoelectric applications.
Characterization of a two-dimensional cantilever array with through-wafer electrical interconnects
Authors: Chow Eugene M. , Yaralioglu Goksen G. , Quate Calvin F. , Kenny Thomas W.
Published: July 2002

The characterization of two-dimensional micromachined silicon cantilever arrays with integrated through-wafer electrical interconnects is presented. The approach addresses alignment and density issues associated with operating two-dimensional scanning probe arrays. The tungsten based interconnect (30 μm diameter, 1 Ω resistance) is shown not to degrade the sensitivity of the piezoresistive deflection sensor embedded on each cantilever. Operation of the array (up to 2×7) as a microscope for imaging large areas (3.8×0.45 mm2) and with vertical row stitching is demonstrated with images of samples orders of magnitude larger than images possible with standard atomic force microscope techniques.
Electrical transport and magnetoresistance in thick films of lanthanum calcium manganite prepared by tape casting
Authors: Srinivasan G. , Rasmussen E. T.
Published: July 2002

The observation of unique thickness-dependent resistivity and magnetoresistance is reported in thick films of La0.7Ca0.3MnO3 synthesized by tape casting. Samples were prepared from tapes with layer thickness L ranging from 6 to 40 μm. Ferromagnetic resonance was used to probe the homogeneity of the films. The maximum zero-field electrical resistivity ρm(0) and low-field magnetoresistance (MR) data show: (i) an exponential drop in ρm(0) with increasing L (an inverse square dependence) and (ii) an exponential increase in MR with L (a square-root dependence). The results are in qualitative agreement with tunneling-assisted electrical transport.
Refractive index of sapphire at 532 nm under shock compression and release
Authors: Setchell Robert E.
Published: July 2002

The refractive index of sapphire at 532 nm has been determined along the Z axis over a range of conditions produced in shock compression and release experiments. In these experiments, a laser interferometer is used to measure particle velocity at an interface with a sapphire window. Values for refractive index are found from velocity corrections that must be made to account for refractive-index changes in the window due to shock wave motion. Early studies found that Z-cut sapphire windows resulted in much larger corrections than other window materials. These studies examined refractive-index changes at a wavelength of 633 nm, corresponding to the helium-neon lasers typically used in interferometers at that time. Because of the high shock impedance of sapphire, its use as an interferometer window since the early studies has been limited. Recent interest in the shock response of high-impedance ceramics, however, has resulted in considerable use of sapphire windows in experiments using laser interferometers operating at a wavelength of 532 nm. The current study is a careful re-examination of the refractive index of Z-cut sapphire under shock compression and release at this wavelength. As in the earlier work, symmetric-impact experiments were conducted on a gas gun facility using sapphire discs cut with their faces normal to the Z axis of the crystal. Laser interferometer measurements were made under known conditions to find the necessary velocity corrections as a function of the shocked state. A method used previously for analyzing refractive-index effects was used to determine refractive index as a function of the shocked state during single-shock motion, then extended to later events involving additional wave motions within the window. The current refractive-index measurements show a simple, linear dependence on density in the shocked state, in contrast to a more complicated dependence found previously. This difference is shown to be a consequence of small changes in the measured velocity corrections. The polarizability behavior is also examined using the present results, indicating a near balance between refractive-index changes due strictly to increasing density and those resulting from polarizability changes in the shocked state. An analysis using available sapphire data on refractive-index changes during hydrostatic compression and isobaric heating indicates that the temperature dependence of the polarizability has a relatively small effect on the changes in refractive index during shock compression. Together with the linear index–density relation, this indicates that a simple velocity correction found for single-shock motion can be accurately applied to arbitrary wave motions within sapphire windows.
On-chip manipulation and magnetization assessment of magnetic bead ensembles by integrated spin-valve sensors
Authors: Lagae L. , Wirix-Speetjens R. , Das J. , Graham D. , Ferreira H. , Freitas P. P. F. , Borghs G. , De Boeck J.
Published: July 2002

Manipulation and detection of magnetic beads on a semiconductor chip opens up new perspectives for analysis of magnetically labeled specimens in biomechanical micro-electromechanical systems for biological applications. Sensitive spin-valve sensors were integrated with magnetic field generating conductors to assess the behavior of ensembles of superparamagnetic nanoparticles 300 nm in diameter that contain 75%–80% magnetite. The spin-valve multilayer including a nanooxide layer achieves 8% magnetoresistance (MR) for an integrated device of 2×16 μm2. Motion of the magnetic particles towards and across the sensor is achieved by two tapered magnetic field generating current conductors. The spin-valve sensor detects the stray magnetic field that emanates from the ensemble of magnetic particles. We study the transients in the magnetic signal on the order of 1% MR. These results lead to a model that describes magnetization configurations of the cluster of beads.
NH
3
-annealed atomic-layer-deposited silicon nitride as a high-k gate dielectric with high reliability
Authors: Nakajima Anri , Khosru Quazi D. M. , Yoshimoto Takashi , Kidera Toshirou , Yokoyama Shin
Published: July 2002

Extremely thin (equivalent oxide thickness, Teq=1.2 nm) silicon-nitride high-k (εr=7.2) gate dielectrics have been formed at low temperatures (⩽550 °C) by an atomic-layer-deposition (ALD) technique with subsequent NH3 annealing at 550 °C. A remarkable reduction in leakage current, especially in the low dielectric voltage region, which will be the operating voltage for future technologies, has made it a highly potential gate dielectric for future ultralarge-scale integrated devices. Suppressed soft breakdown events are observed in ramped voltage stressing. This suppression is thought to be due to a strengthened structure of Si–N bonds and the smoothness and uniformity at the poly-Si/ALD-silicon-nitride interface.
Electronic characterization of n-ScN/p+ Si heterojunctions
Authors: Perjeru F. , Bai X. , Kordesch M. E.
Published: July 2002

We report the electronic characterization of n-ScN in heterojunctions, including deep level transient spectroscopy of electrically active deep levels. ScN material has been grown by plasma assisted physical vapor deposition on commercial p+ Si substrates. Current–voltage and capacitance–voltage measurements indicate that the built-in voltages for the heterojunctions used in this study are approximately 1.74 and 0.40 eV, as seen by electrons and holes. Deep level transient spectroscopy results show the presence of an electronic trap with activation energy EC−ET=0.51 eV. The trap has a higher concentration (1.2–1.6×1013 cm−3) closer to the ScN/Si interface.
Sum rules on the dynamic permeability of hexagonal ferrites
Authors: Adenot A. L. , Acher O. , Taffary T. , Longuet L.
Published: July 2002

A general sum rule has been established recently, bounding the integral of the gyromagnetic losses weighted by the frequency, by the square of the saturation magnetization [O. Acher and A. L. Adenot, Phys. Rev. B 62, 11324 (2000)]. This rule has been established for soft materials with internal anisotropy fields small compared to Bs. In this article, this result is extended to the case of hexagonal ferrites with strong planar anisotropy. It is shown that the bound on the integral is a simple expression of the saturation magnetization and of the out-of-plane anisotropy field. Experimental results on polycrystalline (Ba3Co2Fe24O41)-Co2Z and (BaCo1.25Ti1.25Fe9.5O19)-M hexagonal ferrites are presented. It is shown that the dynamic properties measured up to 18 GHz are bounded in agreement with our predictions.
Dynamic gradient-diffusion subgrid models for incompressible magnetohydrodynamic turbulence
Authors: Müller Wolf-Christian , Carati Daniele
Published: July 2002

The performance of different dynamic gradient-diffusion type subgrid models is evaluated in large-eddy simulations (LES) of magnetohydrodynamic (MHD) turbulence with a maximum of 643 collocation points. The reference data stems from high-resolution direct numerical simulations of decaying and forced MHD turbulence with up to 5123 spectral modes. Comparisons between LES’ and the grid filtered reference systems are carried out regarding the temporal evolution of the global quantities kinetic and magnetic energy, cross helicity, magnetic helicity, and the spectra of energy and energy flux. The influence of the subgrid models on the statistical properties of the simulated flows is also examined. Apart from unconditionally dissipative models, direct divergence modeling and the effects of additional explicit filtering in combination with a tensor-diffusivity term are considered. A new genuine MHD subgrid model, based on the cross-helicity invariant, is presented and observed to perform outstandingly well.
Self-assembled InAs quantum wires on InP(001)
Authors: Yang Haeyeon , Mu Xiaodong , Zotova Ioulia B. , Ding Yujie J. , Salamo Gregory J.
Published: July 2002

We report a study on self-assembled InAs quantum wires on a planar surface of InP(001), grown by molecular-beam epitaxy and examined by in situ scanning tunneling microscopy and photoluminescence (PL). The detailed morphology of the quantum wires including width and height distributions is presented. The quantum wires cover more than 95% of the surface area. The spectral range of the PL emission includes the technologically important 1.55 μm. In the PL emission, high optical anisotropy of more than 50% has been observed at 4.2 K and at room temperature indicating strong confinement.
Carbon nanotubes synthesized by Ni-assisted atmospheric pressure thermal chemical vapor deposition
Authors: Choi G. S. , Cho Y. S. , Hong S. Y. , Park J. B. , Son K. H. , Kim D. J.
Published: July 2002

A detailed systematic study on the growth morphology of carbon nanotubes (CNTs) on Si in atmospheric pressure thermal chemical vapor deposition was undertaken. The role of NH3 for vertical alignment of CNTs was investigated. The direct cause for the alignment was a dense distribution of the catalytic metal particles, but that the particles are maintained catalytically active under amorphous carbon deposits was established by NH3. It allows a dense nucleation of the CNTs, and consequently, assists vertical alignment through entanglement and mechanical leaning among the tubes. The CNTs grew in a base growth mode. Since Ni is consumed both by silicide reaction and by capture into the growing tube, the growth stops when Ni is totally depleted. It occurs earlier for smaller particles, and thus a long time of growth results in a thin bottom with poor adhesion.
Interfacial melting of thin ice films: An infrared study
Authors: Sadtchenko Vlad , Ewing George E.
Published: July 2002

Interfacial melting of ice has been examined by infrared spectroscopy for the first time. Thin ice films, from 10 to 20 nm thick, were prepared on a face of a germanium prism and studied over a range of temperatures just below the triple point. Interrogation was by attenuated total reflection (ATR) spectroscopy. Interfacial melting regions were distinguished from the underlying ice by comparisons of their spectra with the well established infrared signatures of bulk water and ice. Near the triple point, e.g., −0.15 °C, the spectroscopic profile of the surface melting region is indistinguishable from that of liquid water. This is compelling evidence that the commonly labeled quasi-liquid layer is indeed like liquid water. The extent of infrared extinction from ice films was used to determine the thickness of the quasi-liquid layers. At −0.03 °C the thickness is 15 nm corresponding to 40 monolayers of liquid but at −10 °C less than a monolayer remains. We compare our measurements of surface melting with those of others, sometimes finding discrepancies in thickness by two orders of magnitude. The promise of infrared spectroscopy to the further study of interfacial melting of ice is discussed.
Quantum phase interference (Berry phase) in single-molecule magnets of [Mn12]2−
Authors: Wernsdorfer W. , Soler M. , Christou G. , Hendrickson D. N.
Published: July 2002

Magnetization measurements of molecular clusters [Mn12]2− with a spin ground state of S=10 show resonance tunneling at avoided energy level crossings. The observed oscillations of the tunnel probability as a function of the magnetic field applied along the hard anisotropy axis are due to topological quantum phase interference of two tunnel paths of opposite windings. [Mn12]2− is therefore the second molecular cluster exhibiting quantum phase interference.
Application of the giant magnetoresistance effect of nanogranular Ag72Co28 thin film as a sensor for brushless dc motors
Authors: Takeda H. , Fujita A. , Fukamichi K.
Published: July 2002

The giant magnetoresistance (GMR) effect of nanogranular Ag72Co28 thin films made by an rf magnetron sputtering method on a glass substrate has been examined as a sensor having high temperature durability for brushless dc motors. In the temperature dependence, the MR ratio of nanogranular Ag72Co28 thin film in 10 kOe is 13% at room temperature and decreases to 4% at 573 K. On the other hand, the room temperature MR ratio of 10% was obtained by isothermal aging at 773 K for 7.2 ks or at 673 K for 100 ks. From the Arrhenius plots for the aging time versus the aging temperature, the durability of the GMR effect at 473 K is estimated to be ten years. The nanogranular Ag72Co28 film having 4% of the GMR effect set in the motor can accurately detect the rotating angle of the rotor from the quiescent state to the rotating state of 3000 rpm. This means that nanogranular Ag72Co28 films prepared under various conditions are suitable for sensors working at high temperatures. Consequently, the nanogranular Ag72Co28 films have a high potential for the higher output power of the brushless dc motors.
Calculation of thermodynamic, electronic, and optical properties of monoclinic Mg2NiH4
Authors: Myers W. R. , Wang L-W. , Richardson T. J. , Rubin M. D.
Published: July 2002

Ab initio total-energy density functional theory is used to investigate the low temperature (LT) monoclinic form of Mg2NiH4. The calculated minimum energy geometry of LT Mg2NiH4 is close to that determined from neutron diffraction data, and the NiH4 complex is close to a regular tetrahedron. The enthalpies of the phase change to high temperature (HT) pseudo-cubic Mg2NiH4 and of hydrogen absorption by Mg2Ni are calculated and compared with experimental values. LT Mg2NiH4 is found to be a semiconductor with an indirect band gap of 1.4 eV. The optical dielectric function of LT Mg2NiH4 differs somewhat from that of the HT phase. A calculated thin film transmittance spectrum is consistent with an experimental spectrum.
Ion–acoustic waves in dusty plasma with charge fluctuations
Authors: Vranješ J. , Pandey B. P. , Poedts S.
Published: July 2002

In the present investigation it is emphasized that dust particles in a plasma introduce two widely separated, slow and fast, temporal scales, namely dust acoustic and charge fluctuation time scales, which emanates from the large inertia of the dust, and from its collision with plasma particles, respectively. It is demonstrated that, at fast time scales, it is the collective behavior of plasma particles (electrons and ions) which is affected by dust charge fluctuation. The existence of an ion temperature threshold above which the ion–acoustic mode can become unstable due to the fluctuation of the dust charge is shown.
Collisional removal of O2(b 1Σg+,υ=2,3)
Authors: Kalogerakis Konstantinos S. , Copeland Richard A. , Slanger Tom G.
Published: July 2002

The temperature dependence of the collisional removal of O2 in the υ=3 level of the b 1Σg+ state by N2, O2, and CO2 was investigated at room temperature and below. Measurements on the υ=2 level with the colliders, O2, N2O, Ar, and He are also reported. For υ=3 removal by O2, the trend of sharply decreasing loss rate coefficients with increasing υ is seen to continue. For example, at 200 K the rate coefficient for collisional removal of O2 from the υ=3 level by O2 is some three orders of magnitude smaller than that for the υ=1 level. We argue that the mechanism of the deactivation is electronic–electronic (E–E) energy transfer. Observation of emission from a broad range of O2(b 1Σg+) vibrational levels in the terrestrial nightglow, recently discovered in astronomical sky spectra, show less than an order of magnitude difference in population between the more highly populated υ=3 level and the less populated υ=1 level. The implications of these two observations on the vibrational-level-specific atmospheric sources of vibrationally excited molecules in the b 1Σg+ electronic state are explored.
Polarization-graded ferroelectrics: Transpacitor push-pull amplifier
Authors: Mantese Joseph V. , Schubring Norman W. , Micheli Adolph L.
Published: July 2002

Functionally graded ferroelectric devices have been configured as transcapacitive push–pull charge amplifiers, whereby the net charge gain is a function of the difference in thermal environments of the individual device elements.
High-efficiency organic electrophophorescent devices through balance of charge injection
Authors: Jabbour G. E. , Wang J.-F. , Peyghambarian N.
Published: July 2002

Balancing the charge injection plays an important role not only in fluorescence-based organic light-emitting devices, but also in the performance of the recently introduced organic electrophosphorescent devices. By achieving a better balance in the injected charges, it is possible to fabricate devices based on the pure red emitter 2, 3, 7, 8, 12, 13, 17, 18-octaethyl-21H, 23H-porphine, PtOEP, with external quantum efficiency close to 9%.
In situ shrinkage measurement of holographic polymer dispersed liquid crystals
Authors: Qi Jun , DeSarkar Mousumi , Warren Garfield T. , Crawford Gregory P.
Published: July 2002

The formation dynamics of reflective holographic polymer dispersed liquid crystals (H-PDLCs) is investigated with in situ spectroscopy. A modified diffusion model is proposed to describe the time dependent shrinkage of the polymer matrix during formation. The relationship between polymer shrinkage and functionality in H-PDLC systems is found to be linear.
Real index-guided InGaAlP red lasers with buried tunnel junctions
Authors: Lu T. C. , Shieh H. M. , Wang S. C.
Published: July 2002

Real index-guided buried ridge InGaAlP 650 nm band lasers with p+–n+ buried tunnel junctions are demonstrated. Located on top of the buried ridges, the tunnel junctions, made of InGaAs/GaAs superlattices with modulation doping, were introduced as the current injection window areas. The large band gap In0.5Al0.5P layers were directly regrown around the ridges using metalorganic chemical vapor deposition to serve as the current blocking layers. Real index optical waveguiding in the lateral direction was also provided by the smaller refractive index of In0.5Al0.5P layers. The lasers showed lower threshold current and higher slope efficiency compared to conventional complex index-guided InGaAlP lasers with GaAs current blocking layers, and had low internal loss of about 5.4 cm−1.
Epitaxial titanium diboride films grown by pulsed-laser deposition
Authors: Zhai H. Y. , Christen H. M. , Cantoni C. , Goyal A. , Lowndes D. H.
Published: July 2002

Epitaxial, smooth, and low-resistivity titanium diboride (TiB2) films have been grown on SiC substrates using pulsed-laser deposition. Combined studies from ex situ x-ray diffraction and in situ reflection high-energy electron diffraction indicate the crystallographic alignment between TiB2 and SiC both parallel and normal to the substrate. Atomic force microscopy and scanning electron microscopy studies show that these epitaxial films have a smooth surface, and the resistivity of these films is comparable to that of single-crystal TiB2. Growth of these films is motivated by this material’s structural and chemical similarity and lattice match to the newly discovered superconductor MgB2, both to gain further insight into the physical mechanisms of diborides in general and, more specifically, as a component of MgB2-based thin-film heterostructures.
Comparison of turbulence measurements from DIII-D low-mode and high-performance plasmas to turbulence simulations and models
Authors: Rhodes T. L. , Leboeuf J.-N. , Sydora R. D. , Groebner R. J. , Doyle E. J. , McKee G. R. , Peebles W. A. , Rettig C. L. , Zeng L. , Wang G.
Published: July 2002

Measured turbulence characteristics (correlation lengths, spectra, etc.) in low-confinement (L-mode) and high-performance plasmas in the DIII-D tokamak [Luxon et al., Proceedings Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] show many similarities with the characteristics determined from turbulence simulations. Radial correlation lengths Δr of density fluctuations from L-mode discharges are found to be numerically similar to the ion poloidal gyroradius ρθ,s, or 5–10 times the ion gyroradius ρs over the radial region 0.2<r/a<1.0. Comparison of these correlation lengths to ion temperature gradient gyrokinetic simulations (the UCLA-University of Alberta, Canada UCAN code [Sydora et al., Plasma Phys. Controlled Fusion 38, A281 (1996)]) shows that without zonal flows simulation values of Δr are very long, spanning much of the 65 cm minor radius. With zonal flows included, these decrease to near the measured values in both magnitude and radial behavior. In order to determine if Δr scaled as ρθ,s or 5–10 times ρs, an experiment was performed which modified ρθs while keeping other plasma parameters approximately fixed. It was found that the experimental Δr did not scale as ρθ,s, which was similar to low-resolution UCAN simulations. Finally, both experimental measurements and gyrokinetic simulations indicate a significant reduction in the radial correlation length from high-performance quiescent double barrier discharges, as compared to normal L-mode, consistent with reduced transport in these high-performance plasmas.
Interfacial reaction between chemically vapor-deposited HfO2 thin films and a HF-cleaned Si substrate during film growth and postannealing
Authors: Park Byoung Keon , Park Jaehoo , Cho Moonju , Hwang Cheol Seong , Oh Kiyoung , Han Youngki , Yang Doo Young
Published: July 2002

Interfacial reactions between HfO2 thin films and a Si substrate during thin-film growth and postannealing under a N2 atmosphere were investigated by high-resolution transmission electron microscopy, Auger electron spectroscopy, and electrical measurements of metal–insulator–semiconductor capacitors. HfO2 thin films were deposited on HF-cleaned Si wafers by a chemical-vapor-deposition technique at a wafer temperature of 200 °C using a carbon-free precursor [Hf(NO3)4]. The film thicknesses ranged from 1.5 to 5.6 nm. During the initial stage of film growth, the Si surface oxidized to form a Si-rich hafnium silicate film. With increasing deposition time, Hf-rich hafnium silicate films grew. Postannealing resulted in a double-layered film structure with upper and interfacial layers having dielectric constants of approximately 9.3 and 5.6, respectively. The results were compared with the results from HfO2 films grown on SiO2-passivated Si wafers.
Coherent vibrational motion in metal particles: Determination of the vibrational amplitude and excitation mechanism
Authors: Hartland Gregory V.
Published: July 2002

Ultrafast laser excitation of metal particles coherently excites the symmetric breathing mode. This changes the electron density in the particle, which produces a periodic redshift in the position of the plasmon band. In this paper transient absorption data recorded over a range of wavelengths are analyzed to determine the amplitude of the breathing motion for 24.2 nm radius Au particles. The results are compared to a model calculation where the expansion coordinate is treated as a damped harmonic oscillator and the driving force is thermal expansion due to lattice heating (the temperature rise is determined from the energy absorbed by the sample). The only adjustable parameters in these calculations are the dephasing time of the oscillations and the time scale for energy transfer to the solvent. The experimental and calculated vibrational amplitudes are in excellent agreement, which shows that all the absorbed energy goes into expansion. However, the phases of the calculated and experimental traces do not match. The calculations can be brought into almost perfect agreement with the experimental results by including hot-electron pressure effects in the coefficient for thermal expansion of the particles. This contribution is significant in our experiments because laser excitation initially creates a very high electronic temperature. A simple expression for the time dependence of the transient absorption signal is also derived that explicitly accounts for sample polydispersity. In this expression the beat period is related to the mean radius, and the damping time to the mean radius and the width of the size distribution. Thus, time-resolved laser experiments can be used to obtain accurate information about the size distribution of metal particle samples.
Low-order scaling local electron correlation methods. V. Connected triples beyond (T): Linear scaling local CCSDT-1b
Authors: Schütz Martin
Published: July 2002

A new O(N ) method for the iterative treatment of connected triple substitutions in the framework of local coupled cluster theory is introduced here, which is the local equivalent of the canonical CCSDT-1b method. The effect of the triple substitutions is treated in a self-consistent manner in each coupled cluster iteration. As for the local (T) method presented earlier in this series the computational cost of the method scales asymptotically linear with molecular size. The additional computational burden due to the involvement of triples in each coupled cluster iteration hence is not nearly as dramatic as for the parental canonical method, where it implies an increase in the computational complexity of the coupled cluster iteration from O(N6) to O(N7). The method has certain advantages in comparison to the perturbative a posteriori treatment of connected triples (T) for cases where static correlation effects start to play a role. It is demonstrated that molecules with about 100 atoms and 1000 basis functions can be treated with the local CCSDT-1b method, i.e., at a level beyond local CCSD(T). The new local coupled cluster methods introduced here and in previous papers of this series are applied in a study on the energetics of the Bergman auto-cyclization and retro-Bergman ring opening of an azaenediyne derivate, which was recently proposed as a promising candidate for anti-cancer drug development.
Electrical properties of La-doped strontium titanate thin films
Authors: Olaya David , Pan Feng , Rogers Charles T. , Price John C.
Published: July 2002

We report on the properties of lanthanum-doped SrTiO3 thin films grown by off-axis laser ablation on LaAlO3 and SrTiO3 substrates in oxygen partial pressures ranging from 10−8 Torr to 55 mTorr. The La/Sr doping ratio of the ablation target was 1%. The resulting films have carrier densities measured in the range of 4.7–17.5×1019 cm−3 independent of temperature from room temperature to 4 K and low-temperature mobilities as high as 130 cm2/V s. These films are much more tolerant to the presence of oxygen during growth than were similar Nb-doped films reported previously.
Technique to enhance the throughput on a near-field aperture by the use of self-focusing effect
Authors: Song Ki-Bong , Kim Jeongyong , Park Kang-Ho
Published: July 2002

A technique to increase the throughput of a near-field aperture on a cantilever aperture is described. Using the self-focusing effect due to nonlinear optical Kerr effect in as-evaporated As2S3 glass, we found that the throughput of the near-field aperture with an aperture diameter ∼100 nm increases over 100 times compared with conventional tapered fiber tips. A theoretical qualitative analysis using the modified nonparaxial model to estimate the enhancement of the throughput is in good agreement with observed experimental results.
Energy transfer between Er3+ and Pr3+ in chalcogenide glasses for dual-wavelength fiber-optic amplifiers
Authors: Park Se Ho , Lee Dong Chin , Heo Jong , Shin Dong Wook
Published: July 2002

Ge–As–Ga–S glasses codoped with Er3+ and Pr3+ were synthesized for fiber-optic amplifiers operating in both 1.3 and 1.5 μm communication windows. The energy transfer between Er3+ and Pr3+ in Ge–As–Ga–S glasses was analyzed quantitatively using rate equations. The energy transfer coefficients responsible for two different energy transfer routes were 2.2(±0.05)×10−18 (Er3+:4I11/2→Pr3+:1G4) and 5.6(±0.05)×10−17 s−1 cm3 (Er3+:4I13/2→Pr3+:3F4,3), respectively. The former transfer process enhanced amplification efficiency in 1.3 μm band, while the latter reduced efficiency in the 1.5 μm band. Numerical simulation of the amplification characteristics demonstrated that signal gains of 30 and 40 dB were possible in 1.3 and 1.5 μm bands, respectively.
Self-assembly of star block copolymers by dynamic density functional theory
Authors: He Xuehao , Huang Lei , Liang Haojun , Pan Caiyuan
Published: July 2002

The dynamic mean-field density functional method, driven from the generalized time-dependent Ginzburg–Landau equation, was applied to the mesoscopic dynamics of the multi-arms star block copolymer melts in two-dimensional lattice model. The implicit Gaussian density functional expression of a multi-arms star block copolymer chain for the intrinsic chemical potentials was constructed for the first time. Extension of this calculation strategy to more complex systems, such as hyperbranched copolymer or dendrimer, should be straightforward. The original application of this method to 3-arms block copolymer melts in our present works led to some novel ordered microphase patterns, such as hexagonal (HEX) honeycomb lattice, core–shell HEX lattice, knitting pattern, etc. The observed core–shell HEX lattice ordered structure is qualitatively in agreement with the experiment of Thomas et al. [Macromolecules 31, 5272 (1998)].
Nuclear dynamics in electronic ground and excited states probed by spectrally resolved four wave mixing
Authors: Park June-Sik , Joo Taiha
Published: July 2002

Time-resolved ground-state bleach and excited-state stimulated emission spectra have been measured for indocyanine green dissolved in methanol by employing spectrally resolved four wave mixing (SRFWM). The separation of the SRFWM signals into the ground-state bleach and excited-state stimulated emission contributions allows observation of intramolecular vibrational wave packet motions and intermolecular solvation dynamics upon impulsive excitation, while the molecule resides either in the ground or in the excited state. Frequencies of the indocyanine green intramolecular vibrational modes in the ground and excited states are practically the same. Vibrational dephasing times in the excited state range from a few hundred fs to ∼2 ps, and they are consistently shorter than those in the ground state. When excitation frequency is centered near the 0-0 transition, center frequencies of the stimulated emission redshift due to solvation of the excited state in nonequilibrium solvent configuration, whereas those of the ground-state bleach blueshift due to equilibrium fluctuation of the solvent molecules around the chromophore in the ground state. At early times, the solvation function obtained from the time-resolved ground-state bleach spectra is slower than the solvation function obtained from the time-resolved excited-state stimulated emission spectra.
Room temperature tunneling magnetoresistance of electron beam deposited (Co50Fe50)x(Al2O3)1−x cermet granular films
Authors: Vovk Andriy Ya. , Wang Jian-Qing , Zhou Weilie , He Jibao , Pogoriliy Anatoliy M. , Shypil Olena V. , Kravets Anatoliy F. , Khan Hamid R.
Published: July 2002

A series of (Co50Fe50)x-(Al2O3)1−x cermet granular thin films deposited on glass substrates by dual electron beam evaporation was studied for their structural, magnetotransport, and magnetic properties. Upon varying the magnetic volume fraction, x, from 0.07 to 0.52 the percolation threshold (xc) was determined from resistivity measurements to be ∼0.17. This value agrees well with the theoretical prediction for a three-dimensional system of spherical particles. Values of the isotropic tunneling magnetoresistance (TMR) as high as 10% at room temperature were found for films with x<0.16. The relationship between magnetotransport (maximum TMR) and the granular film topology (the percolation threshold) is discussed.
Spectral response of boron-implanted amorphous silicon Schottky diode
Authors: Chikamura T. , Aoki Y. , Yano K. , Komeda T. , Ishihara T.
Published: July 2002

The spectral response of Schottky diodes on hydrogenated amorphous silicon implanted with boron has been investigated. The decrease in sensitivity in the short-wavelength range has been observed in samples implanted with the boron dose of more than 1.6×1013 ions/cm2. The experimental spectral responses are in good agreement with theoretical responses derived from the assumption that the photoexcited carriers are mainly transported by drift field.
Near-resonance-Rayleigh scattering measurement on a resonant laser-driven barium plasma
Authors: Nee Tsu-Jye A.
Published: July 2002

Near-resonance-Rayleigh scattering is used as a space-time-resolved density probe on a resonant laser-driven barium plasma. Feasibility of this technique was investigated. Comparison to other methods such as absorption technique is made and found to be consistent.