bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarization interactions and boroxol ring formation in boron oxide: A molecular dynamics study
Authors: Maranas Janna K. , Chen Yingzi , Stillinger Dorothea K. , Stillinger Frank H.
Published: July 2002

We employ molecular dynamics (MD) simulations to study the structure of vitreous boron oxide. Although six-membered boroxol rings have been observed at fractions over 60% by various experimental techniques, simulation methods have not produced similar results. We adapt the polarization model, which includes many body polarization effects thought to stabilize such structures, for boron–oxygen interactions. This model is then used in MD simulations of boron oxide glass at various temperatures. We find a variation in the fraction of rings depending on the temperature of the system during network formation. The maximum ring fraction (∼33%) occurs when the sample is prepared at low temperatures. At these temperatures, the energy level of boron atoms in rings is 1.6% lower than the energies of boron atoms outside of rings. When higher equilibration temperatures are used, the fraction drops to 11%. Thus, two factors are relevant to boroxol ring formation in simulations of boron oxide, a model which incorporates polarization effects or their equivalent, and the appropriate manipulation of temperature history.
Room temperature aging behavior of thermally imprinted Pt/SrBi2Ta2O9/Pt ferroelectric thin film capacitors
Authors: Wu Di , Li Aidong , Ling Huiqin , Yu Tao , Liu Zhiguo , Ming Naiben
Published: July 2002

Metalorganic-decomposition-derived SrBi2Ta2O9 (SBT) ferroelectric thin films, sandwiched between Pt electrodes, were imprinted by heat treatment at 130 °C in air. The aging behavior at room temperature of these imprinted SBT capacitors was observed. The voltage shifts of imprinted P–V hysteresis loops increased with the increase of aging time, which indicated the strengthening of the internal bias created by the thermal treatment. With the strengthening of the internal bias, asymmetry of data loss was observed to increase with increasing aging time. The mechanism of the internal bias strengthening, the resultant asymmetric data loss and possible function failure due to this aging behavior were briefly discussed.
Interface photoluminescence in type II broken-gap P–Ga0.84In0.16As0.22Sb0.78/p-InAs single heterostructures
Authors: Moiseev K. D. , Krier A. , Yakovlev Yu. P.
Published: July 2002

Mid-infrared photoluminescence has been observed from interface transitions in high quality, abrupt P–Ga0.84In0.16As0.22Sb0.78/p-InAs heterojunctions grown by liquid phase epitaxy from an In-rich melt. The Ga0.84In0.16As0.22Sb0.78 quaternary epitaxial layer was unintentionally doped and grown lattice matched on to a (100) oriented p-type InAs substrate, resulting in a P–p isotype heterojunction. The photoluminescence emission spectra were investigated and exhibited three pronounced emission bands in the spectral region from 0.30 to 0.68 eV; hν1=0.317 eV, hν2=0.380 eV, and hνL=0.622 eV. The emission band hν1 was identified with radiative transitions between electron and hole quantum well subbands in the semimetal channel at the P–GaIn0.03As0.10Sb/p-InAs interface, while the hν2 band originates from radiative transitions involving deep acceptor states in the InAs substrate. The high-energy recombination hνL is characteristic of the Ga0.84In0.16As0.22Sb0.78 bulk quaternary layer.
Xerographic and electroabsorption study of primary photocarrier generation process in x-form metal-free phthalocyanine
Authors: Umeda Minoru , Mohamedi Mohamed , Itoh Takashi , Uchida Isamu
Published: July 2002

Using a dual-layered photoconductor, we have investigated the primary photocarrier generation process in x-form metal-free phthalocyanine (x-H2Pc) over a wide range of illumination wavelengths. According to the results of quantum efficiency measurements, it has been established that the photocarrier generation mechanism in x-H2Pc occurs via two processes: (i) production of an intermediate that depends solely on the excitation energy, and (ii) subsequent free carrier production in the presence of an electric field. In addition, the spectral quantum efficiency and the electroabsorption spectrum were measured and compared. Based on that, the primary process efficiency was divided into four regions in terms of photon energy, which explained well the relationship between them. The excitation energy dependence of the primary efficiency was semiquantitatively validated based on the electron transfer theory.
Absorption of extreme ultraviolet light in a laser produced gas-jet plasma source
Authors: Kanouff Michael , Shields Harry , Bernardez Luis , Chenoweth Donald , Kubiak Glenn
Published: July 2002

Laser produced plasmas (LPPs) provide a stable source of extreme ultraviolet (EUV) light making them well suited for use in next-generation lithography tools. The plasma is generated by directing a laser at a target composed of a partially condensed gas after it undergoes a supersonic expansion through a nozzle and enters a vacuum chamber. The expansion process results in very cold temperatures such that the gas partially condenses forming a mixture of gas and small clusters. The clusters absorb the laser energy leading to the formation of the plasma, but the excess gas absorbs some of the emitted EUV light reducing the net output of the LPP. Calculations were carried out to determine the amount of EUV light absorbed by the gaseous xenon that surrounds the plasma. The Navier–Stokes equations were solved to obtain the gas density field. Observations from experiments were used for the shape of the plasma, which showed it to be approximately that of a prolate spheroid. The relative EUV signal strength was obtained as a function of the direction angle by calculating the absorption of EUV light in the gas surrounding the plasma and integrating over the plasma surface. Calculated results for the normalized EUV energy distribution compare well with measurements of the EUV angular distribution obtained in the experiments.
A recommended modification to the dynamic two-parameter mixed subgrid scale model for large eddy simulation of wall bounded turbulent flow
Authors: Morinishi Youhei , Vasilyev Oleg V.
Published: July 2002

It is well known that the correlation between the Smagorinsky model and the subgrid scale stress is low, while the model based on the scale similarity assumption has considerably higher correlation. However, the scale similarity model by itself was found to be insufficiently dissipative. Therefore, the model is usually used together with the Smagorinsky model. Model coefficients are commonly computed using the two-parameter dynamic procedure. Nevertheless, the dynamic two-parameter mixed model still does not work well for wall bounded flows, since the model predicts a high value of the wall shear stress. In this study, we propose a modification to the two-parameter dynamic procedure for wall bounded flows, which removes that defect: the Smagorinsky parameter, CS, is computed exactly the same way as in the dynamic Smagorinsky model, then the other parameter, CL, is computed dynamically as CS is known. This ensures that the mixed model provides proper wall shear stress and mean velocity profile. Computational tests are done for turbulent channel flow where the Reynolds numbers based on the channel half-width and wall friction velocity are 395 and 1400. To remove the ambiguity regarding the accuracy of the finite difference scheme, we use high (up to 12th) order accurate fully conservative finite difference schemes in a staggered grid system.
Practical implementation of the instanton theory for the ground-state tunneling splitting
Authors: Mil’nikov Gennady V. , Nakamura Hiroki
Published: July 2002

The instanton theory is reformulated with use of the path integral approach and the Wentzel–Kramers–Brillouin approximation to the Schrödinger equation. Both approaches are shown to provide the same results. A new practically useful semiclassical formula is derived for the tunneling splitting of the ground state, which can be implemented for high-dimensional systems. The theory is applicable to systems of arbitrary Riemannian metric and is also supplemented by a practical numerical recipe to evaluate the instanton trajectory, i.e., periodic orbit, in multidimensional space. Numerical examples are presented for three-dimensional (3D) and 21D systems of HO2 and malonaldehyde, respectively.
Time domain radiation by scalar sources: Plane wave to multipole transform
Authors: Shlivinski Amir , Heyman Ehud , Devaney Anthony J.
Published: July 2002

The radiation from a pulsed source distribution can be described by a spectrum of time-dependent plane waves or of spherical waves (multipoles). These two fundamental representations are based on the slant stack transform and on the time-dependent multipole moment, respectively. In this article, we present a direct transformation relating these two representations.
Asymptotic expansion of 2F1(a,b;c;x) in terms of confluent hypergeometric functions
Authors: Chidichimo Marita C. , Thorsley Michael D.
Published: July 2002

We have developed a new asymptotic formula for 2F1(a,b;c;x) in which a and c are finite, |b| tends to infinity and the argument x tends to zero. We make use of this result to obtain asymptotic expansions of the electric dipole (E1) quantal differential excitation function for the adiabaticity parameter ξ=ηf−ηi and the Sommerfeld parameter ηf tending to infinity simultaneously, while the parameter ηi remains finite.
Propagation matrix formalism and efficient linear potential solution to Schrödinger’s equation
Authors: Demers Jean-Guy S. , Maciejko Romain
Published: July 2002

The one-dimensional Schrödinger equation for an arbitrary potential with position-dependent mass is often solved by the transfer-matrix method. While the usual definition relates wave-function coefficients on two sides of an interface, this article presents an alternative approach, in which a propagation matrix evolves the wave function and its derivative between a pair of points. The formalism is developed without an a priori commitment to a breakdown of the potential into a series of flat, linear, or other types of segments. We obtain a Wick-expansion form for the matrix and also provide a geometrical interpretation based on the SL(2,R) group. Turning to a variably spaced discretized potential we show how this approach can be flexibly applied to any potential segments. We discuss explicitly the case of constant potential and the Wentzel–Kramers–Brillouin approximation, as well as the linear potential segment. For the latter, the obtained propagation matrix has definite advantages, from both speed and robustness standpoints. Applications to transport in the ballistic regime are discussed and explicit results are presented for a InP–InGaAs junction.
Scalar quantum field coupled to boundaries and to a background magnetic field
Authors: Actor A. A. , Bender I.
Published: July 2002

The stationary states of a charged scalar quantum field interacting with a background consisting of both boundaries and a static magnetic field are investigated. Following the development of some general theory, the example of a uniform magnetic field perpendicular to two parallel Dirichlet boundaries is worked through in detail.
Electromagnetic propagators in hyperbolic Robertson–Walker cosmologies
Authors: Tomaschitz Roman
Published: July 2002

Green functions (retarded, advanced, Feynman and Dyson propagators) are calculated for the electromagnetic field in Robertson–Walker cosmologies with hyperbolic 3-manifolds as spacelike slices. The starting point is the Proca equation, i.e., the Maxwell field with a finite photon mass for infrared regularization, in a static cosmology with simply connected hyperbolic 3-sections. The time and space components of the resolvent kernel are scalar and vectorial point-pair invariants, respectively, and this symmetry allows for an explicit evaluation in the spectral representation. It is found that the quantum propagators have a logarithmic infrared singularity, which drops out in the zero curvature limit. Retarded and advanced Green functions remain well defined in the limit of zero photon mass, and they admit a simple generalization, by conformal scaling, to expanding 3-spaces. In cosmologies with multiply connected hyperbolic 3-manifolds as spacelike sections, the four enumerated propagators are constructed by means of Poincaré series. The spectral decomposition of the Green functions is given in terms of Eisenstein series for a certain class of open hyperbolic 3-spaces, including those with Schottky covering groups corresponding to solid handle-bodies as spacelike slices.
Electrical characterization of 1.8 MeV proton-bombarded ZnO
Authors: Auret F. D. , Goodman S. A. , Hayes M. , Legodi M. J. , van Laarhoven H. A. , Look D. C.
Published: July 2002

We report on the electrical characterization of single-crystal ZnO and Au Schottky contacts formed thereon before and after bombarding them with 1.8 MeV protons. From capacitance–voltage measurements, we found that ZnO is remarkably resistant to high-energy proton bombardment and that each incident proton removes about two orders of magnitude less carriers than in GaN. Deep level transient spectroscopy indicates a similar effect: the two electron traps detected are introduced in extremely low rates. One possible interpretation of these results is that the primary radiation-induced defects in ZnO may be unstable at room temperature and anneal out without leaving harmful defects that are responsible for carrier compensation.
Spherically symmetric solutions of the sixth order SU(N) Skyrme models
Authors: Floratos I. , Piette B. M. A. G.
Published: July 2002

Following the construction described by Ioannidou et al. [J. Math. Phys. 40, 6353 (1999)], we use the rational map ansatz to construct analytically some topologically nontrivial solutions of the generalized SU(3) Skyrme model defined by adding a sixth order term to the usual Lagrangian. These solutions are radially symmetric and some of them can be interpreted as bound states of Skyrmions. The same ansatz is used to construct low-energy configuration of the SU(N) Skyrme model.
Operation of ceramic cathodes with bipolar pulse excitation
Authors: Boscolo I. , Cialdi S.
Published: July 2002

The emission from ferroelectric cathodes excited by bipolar pulses does not suffer the hysteretic behavior shown with monopolar pulse excitation. This is because the bipolar pulse forces a neat charging–discharging cycle of the whole surface of the sample, and, therefore, the flipping of the polarization. The emission becomes definitely stable, whereas it was erratic in current amplitude, pulse shape and starting time with monopolar excitation. The emission yield of energetic electrons from ferroelectric cathodes of doped lead–titanate–zirconate–lanthanum increased from a few hundreds of milliamperes to some amperes (with current density of 30–50 A/cm2) in passing from monopolar to bipolar voltage pulse excitation.
Modulation of transverse magnetic mode surface wave
Authors: Hong Hee Sook , Lee Hee J.
Published: July 2002

A nonlinear Schrödinger equation is derived by perturbation analysis for a transverse magnetic mode surface wave propagating on a fixed semi-infinite plasma with slowly varying density, taking into account all the electron nonlinear dynamics, and especially the surface currents. The effects of the dynamic nonlinearities and the surface currents on the nonlinear behavior of the surface wave is assessed in comparison to the effects of the slow density perturbation.
A new class of exact solutions of the Vlasov equation
Authors: Yu M. Y. , Chen Zhaoyang , Stenflo L.
Published: July 2002

A class of exact one-dimensional oscillating solutions of the Vlasov–Poisson system describing a one-component plasma in a parabolic electrostatic potential well is considered. Through a separation of variables procedure, a system of ordinary differential equations describing the moments of the velocity distribution function is obtained. The moment equations can be decoupled at any order from the higher ones without approximations. Oscillating-pattern solutions for the resulting finite and exact systems are found.
Ab initio characterization of low-lying triplet state potential-energy surfaces and vibrational frequencies in the Wulf band of ozone
Authors: Xie Daiqian , Guo Hua , Peterson Kirk A.
Published: July 2002

Accurate ab initio potential-energy surfaces of the A23 and B13 states of ozone and their nonadiabatic coupling are reported near the ground-state equilibrium geometry using an internally contracted multireference configuration interaction method. These coupled three-dimensional potential-energy surfaces enable the first theoretical characterization of all three vibrational modes in the Wulf band. Reasonably good agreement with recent experimental observations is obtained.
Comment on “Taylor dispersion of a solute in a microfluidic channel” [J. Appl. Phys. 89, 4667 (2001)]
Authors: Dorfman Kevin D. , Brenner Howard
Published: July 2002

In a recent article [J. Appl. Phys. 89, 4667 (2001)], Beard applies Taylor dispersion theory for two-dimensional Poiseuille flow between flat plates to analyze mixing processes occurring at the entrance of a microfluidic T sensor. The classical value of the coefficient of the Taylor dispersivity, 1/210, differs from Beard’s result, and this Comment points out elements of Beard’s derivation which lead to his erroneous value of 33/560. Moreover, the lateral boundedness of the actual device and the long-time asymptotic nature of Taylor dispersion theory call into question the use of the latter model in the context of the T sensor described in Beard’s analysis.
Energy recovery linacs as synchrotron radiation sources (invited)
Authors: Gruner Sol M. , Bilderback Don , Bazarov Ivan , Finkelstein Ken , Krafft Geoffrey , Merminga Lia , Padamsee Hasan , Shen Qun , Sinclair Charles , Tigner Maury
Published: July 2002

Practically all synchrotron x-ray sources to data are based on the use of storage rings to produce the high current electron (or positron) beams needed for synchrotron radiation (SR). The ultimate limitations on the quality of the electron beam, which are directly reflected in many of the most important characteristics of the SR beams, arise from the physics of equilibrium processes fundamental to the operation of storage rings. It is possible to produce electron beams with superior characteristics for SR via photoinjected electron sources and high-energy linacs; however, the energy consumption of such machines is prohibitive. This limitation can be overcome by the use of an energy recovery linac (ERL), which involves configuring the electron-beam path to use the same superconducting linac as a decelerator of the electron beam after SR production, thereby recovering the beam energy for acceleration of new electrons. ERLs have the potential to produce SR beams with brilliance, coherence, time structure, and source size and shape which are superior to even the best third-generation storage ring sources, while maintaining flexible machine operation and competitive costs. Here, we describe a project to produce a hard x-ray ERL SR source at Cornell University, with emphasis on the characteristics, promise, and challenges of such an ERL machine.
Three-dimensional thermal noise imaging
Authors: Tischer Christian , Altmann Stephan , Fis̆inger Samo , Hörber J. K. Heinrich , Stelzer Ernst H. K. , Florin Ernst-Ludwig
Published: July 2002

We present a scanning probe microscope based on optical tweezers for three-dimensional imaging of the topology of transparent material in the nanometer range. A spherical nanoparticle serves as a probe. An optical trap moves it through the sample (e.g., a polymer network), while the position of the particle center is recorded by three-dimensional interferometry. Accessible volumes are reconstructed from the histogram of thermal position fluctuations of the particle. The resolution in determining the position of surfaces in three dimensions is about 20 nm.
Recording of transmission phase gratings in glass by ion implantation
Authors: Bányász I. , Fried M. , Dücsö Cs. , Vértesy Z.
Published: July 2002

Transmission phase gratings of grating constants of 4–12 μm have been designed and fabricated in glass via implantation of helium and nitrogen ions of energies in the 500 keV–1.6 MeV range, through photoresist masks of thickness of 3.3 μm. Multienergy implantations were applied, too. Phase profiles of the gratings were measured via interference and phase contrast microscopy and scanning electron microscopy. Quasisinusoidal profiles were obtained for the finest gratings. The highest first order diffraction efficiencies were around 20%. Dependence of the efficiencies of the gratings on the energy and dose of the implantation have been determined.
OD–N
2
:
Infrared spectroscopy, potential anisotropy, and predissociation dynamics from infared-ultraviolet double resonance studies
Authors: Tsiouris Maria , Pollack Ilana B. , Leung Helen O. , Marshall Mark D. , Lester Marsha I.
Published: July 2002

The infrared spectrum of the linear OD–N2 complex has been recorded in the OD overtone region near 1.9 μm using an infrared-ultraviolet double resonance technique. The pure overtone band of OD–N2(2νOD) was observed at 5173.99(1) cm−1, and combination bands involving the simultaneous excitation of OD stretch and geared bend were identified at 5209.02(1) cm−1 and 5214.59(2) cm−1. Assignments and spectroscopic constants have been derived from the rotationally resolved structure of each band, which are in good accord with model calculations based on an electrostatic interaction potential. Direct time–domain measurements yielded a vibrational predissociation lifetime of 150±16 ns for OD–N2 (2νOD) and a three fold decrease in lifetime upon intermolecular excitation of the lower-energy geared bending state. The OD (v=1) fragments of vibrational predissociation were found to be highly rotationally excited, indicating that predissociation proceeds by vibrational to rotational/translational energy transfer. The results obtained for OD–N2 are compared with an analogous study of OH–N2 [Marshall et al., J. Chem. Phys. 114, 7001 (2001)], revealing insights on the potential anisotropy along the geared bending coordinate and a change in the vibrational predissociation mechanism.
Numerical simulations of stress induced void evolution and growth in interconnects
Authors: Fridline Daniel , Bower Allan
Published: July 2002

We model stress driven void growth and evolution in representative interconnect microstructures. Our computations account for several kinetic processes involved in interconnect failures, including surface diffusion, interface and grain boundary diffusion, as well as sliding on grain boundaries or the interconnect/passivation interface. Depending on the relative rates of these processes, we predict several different regimes of behavior for the void. In some cases the void remains rounded, leading to a long interconnect life. For critical combinations of material properties, however, the void propagates across the line as a narrow slit, causing rapid failure. Our analysis suggests that the extent of inelastic slip between the interconnect and the surrounding passivation plays a central role in this transition. Implications for interconnect reliability are discussed.
Reversal mechanism in permanent magnetic materials
Authors: Zhao G. P. , Lim H. S. , Feng Y. P. , Ong C. K. , Liu G. R.
Published: July 2002

The phenomenon of magnetization reversal in a hard magnet is studied analytically within a framework of a simplified energy minimization model for a two grain system. The transition region (a domain wall-like moment structure) is found to play a crucial role in nucleating a reversed domain and in the subsequent formation of a domain wall near the grain boundary. This is shown to result in a considerable reduction in coercivity. Temperature effects are taken into account by considering thermally activated jumps over energy barriers that hinder the motion of the transition region. We found that thermal fluctuations at room temperature can substantially reduce coercivity provided the grains are sufficiently small.
Spin valves with canted pinning field
Authors: Lu Z. Q. , Pan G. , Zheng Y. K.
Published: July 2002

Spin valves with a canted pinning field were studied. Magnetoresistance (MR) and planar Hall effect (PHE) in the spin valves were simultaneously measured in fields applied in the film plane at different angles (α) with respect to the easy axis of the free layer. The Boltzmann transport equation was used to simulate MR and PHE curves, and to determine the magnetization orientation of the free layer at different α. Results showed that in the magnetization configuration in which the pinning field was perpendicular to the easy axis of the free layer, there existed two distinct magnetization reversal modes when the applied field angle α was near 90°. The magnetization reversal was an incoherent rotation when α<90°, which gave rise to Barkhausen noises, but was a coherent rotation when α>90°. However, in the configuration in which the angle between the pinning field and the easy axis of the free layer was about 45°, there was only one magnetization reversal mode. The interlayer coupling kept the free layer in a single domain state and constrained the magnetization reversal of the free layer in coherent rotation. Consequently, the MR response exhibited excellent linearity without Barkhauson noise when α was in the range from 75°–105°.
Dielectric relaxation in Pb0.9La0.1TiO3 ceramics in the temperature range of 400–700 °C
Authors: Kang Byung Sung , Choi Si Kyung
Published: July 2002

The dielectric properties of Pb0.9La0.1TiO3 ceramics were investigated at intermediate frequencies (102⩽f⩽106 Hz) in the temperature range of 400–700 °C. The limitation of the application of Debye relaxation model was discussed to explain the temperature-dependent behavior of the dielectric relaxation. The dielectric relaxation strength was considered as an important fitting variable through the modified Debye equation. The diffuse dielectric anomaly was successfully described by introducing the exponential decay form for the relaxation strength in the modified Debye equation.
Low-frequency and microwave performances of laser-ablated epitaxial Na0.5K0.5NbO3 films on high-resistivity SiO2/Si substrates
Authors: Abadei S. , Gevorgian S. , Cho C.-R. , Grishin A.
Published: July 2002

The dielectric properties of laser-ablated 0.5-μm-thick c-axis epitaxial Na0.5K0.5NbO3 (NKN) films on high-resistivity (>7.7 kΩ cm) silicon SiO2/Si substrates are studied experimentally in the temperature interval of 30–320 K and at frequencies of 1.0 MHz–40 GHz. The films are grown by laser ablation from a stoichiometric target. For the measurements, planar 0.5-μm-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of NKN films. The slot width between the electrodes is 2.0 or 4.0 μm. At low frequencies (f<1.0 GHz), the structure performance is that of a typical metal–dielectric–semiconductor type, where two of this type of capacitor are connected back to back. At these frequencies, the large change in the capacitance (more than 10 times at 1.0 MHz), due to the applied dc field, is mainly due to the changes in depletion layer thickness at the surface of silicon. The associated losses are also large, tan δ>1. At microwave frequencies (f>10 GHz), the voltage dependence of the capacitance is given by the NKN film. More than a 13% capacitance change at 40 V dc bias and a Q factor of more than 15 are observed at 40 GHz, which make the structure useful for applications in electrically tunable millimeter-wave devices.
High-temperature healing of interfacial voids in GaAs wafer bonding
Authors: Wu YewChung Sermon , Liu Po Chun , Feigelson R. S. , Route R. K.
Published: July 2002

Artificial voids were introduced at bonding interfaces to study how processing parameters affected the healing mechanism of interfacial voids in GaAs wafer bonding. These voids were created by placing unpatterned wafers in contact with topographically patterned wafers. During the bonding process, crystallites formed within these voids and corresponded to bonded regions within the voids. Their formation depended strongly on the height of the surface irregularities at the wafer interfaces. When the void depth (h) was ⩾200 nm, most of the crystallites were diamond shaped. The edges of the diamond features were elongated in the 〈100〉 direction. On the other hand, when the void depth was small (h⩽70 nm), dendrites grew quickly in the 〈110〉 direction.
Quantum mechanical behavior of an H atom on Cu(111) and Pt(111)
Authors: Nobuhara K. , Nakanishi H. , Kasai H. , Okiji A.
Published: July 2002

The quantum mechanical behavior of an H atom adsorbed on Cu(111) and on Pt(111) is investigated. The potential energy curves (PECs) for the H atom motion on these surfaces are calculated within the density functional theory, and the adiabatic three-dimensional potential energy surfaces (PESs) are constructed based on the obtained PECs. The wave functions and their energies for the H atom motion on the PESs are calculated within the framework of the variation method. The results show that, in the case of Cu(111), the ground state wave function is strongly localized around the fcc hollow site, the first-excited state wave function is strongly localized around the hcp hollow site, and these states almost energetically degenerate. On the other hand, the second-excited state wave function is delocalized and extends from the fcc hollow site to the bridge site and further to the hcp hollow site. Then, there is a significant energy gap between the first- excited and the second-excited state. In the case of Pt(111), the ground and the first-excited state wave functions are delocalized and extend from the hollow site to the bridge site. The second-excited state wave function further extends over the top site. The energy differences between the ground and the first-excited state, and between the first-excited and the second-excited state are very small. Thus, the H atom adsorbed on Pt(111) has a delocalized nature.
Theory of the lifetime of the MgO protecting layer in ac plasma display panels
Authors: Yoon Sean J. , Lee Insook
Published: July 2002

We have theoretically studied the lifetime of the protecting layer in an ac plasma display panel (ac-PDP) under various discharge gas conditions. The sputtering of the protecting layer by energetic plasma particles is one of the most important elements limiting the lifetime of ac-PDPs. Because of its importance in the lifetime of ac-PDPs, the sputtering yields of the MgO protecting layer by various ions are investigated as a function of their kinetic energies. We calculate the energy distribution of ions bombarding the protecting layer and perform simulations for the discharge characteristics of ac-PDPs under various gas conditions in order to estimate the lifetime of ac-PDPs. By comparing the lifetime for various gas conditions, we can also optimize the gas mixture and pressure to achieve an extended lifetime of the protecting layer.
Origin of substrate hole current after gate oxide breakdown
Authors: Rasras Mahmoud , Wolf Ingrid De , Groeseneken Guido , Degraeve Robin , Maes Herman E.
Published: July 2002

The origin of the substrate hole currents after gate oxide breakdown in metal-oxide-semiconductor field-effect transistor (nMosFET) devices is investigated, using spectroscopic and conventional photon emission microscopy. Spectral analysis of light from the breakdown locations, under positive gate bias, indicates that hot electrons mediate the light emitted from the breakdown spots. These hot electrons are generated by the high electric fields at the location of the breakdown. Furthermore, light emission due to substrate hole recombination with electrons injected from the gate through the leakage path (breakdown location) dominates the light emission spectrum under negative gate bias. This finding is further verified using carrier separation measurements. In these measurements, minority carrier currents induced by the light emitted at the breakdown location and measured at a remote pn junction are compared with the substrate hole currents before and after oxide breakdown. These measurements prove that under positive gate bias, the substrate hole current and the light emission from the breakdown locations, are dominated by hot electron impact ionization mechanism in the substrate.
Wake patterns behind boulders in the rings of Saturn
Authors: Brattli A. , Havnes O. , Melandsø F.
Published: July 2002

The flow of charged dust around an electrically charged boulder moving through an environment thought to be typical of planatery rings is studied. As the boulder moves through the ring dust it will excite a V-shaped Mach cone pattern of a form and complexity which varies significantly with boulder size, relative velocity between the boulder and the dust, and with dust plasma conditions. Parameters relevant to the Saturnian ring system are used to compute examples which demonstrate the change in Mach cone patterns with the relevant parameters. Shortcomings of the model are discussed and ways to improve the calculations of Mach cone patterns are pointed out.
A systematic study on the pulsed wire system for magnetic field measurements on the long undulator with high field
Authors: Fan T. C. , Hwang C. S. , Chang C. H. , Hsu Ian C.
Published: July 2002

The pulsed wire method for magnetic field measurement has been developed by several groups. In most cases the thin wires were used and only the short magnets were measured to ignore the dispersion due to stiffness of the wires. In the application to the long insertion devices, a lot of spurious signals occurred and contaminated the normal field signals. In this article we demonstrate a new approach to applying the pulsed wire method to a long insertion undulator with a high field. Thick wire is used instead. Then we can cancel the dispersion and trace back the normal field signal by using the fast Fourier transform calculation. The results are quite comparable to Hall probe measurement.
Effect of temperature on nonlinear optical properties of composite media with shape distribution
Authors: Gao L. , Li Z. Y.
Published: July 2002

The temperature dependence of the effective nonlinear optical properties is investigated in random metal/dielectric composites with a shape distribution of particles through the spectral representation. We adopt the Maxwell–Garnett model with a uniform shape distribution and obtain an analytical expression for the spectral density function. Numerical results show that the optical nonlinearity enhancement decreases with the increase of temperature, accompanied by a slight blueshift of the resonant peak. Such a temperature dependence results from the following changes: the conduction electron scattering frequency (due to electron–electron and electron–phonon interaction) and the plasmon frequency (due to the expansion of metal) with the temperature. We find that the former change plays a more important role in understanding the temperature-dependent optical nonlinearity. Moreover, exact results in the dilute limit show a larger magnitude and a more rapid decrease of the optical nonlinearity with temperature, in comparison with the predictions of the mean field approximation. Our results indicate that by decreasing the temperature, it is possible to achieve a large optical nonlinearity.
Electrostatic potential and plasma flow near the edge of a divertor tokamak
Authors: Weitzner Harold , Feneberg Winfried
Published: July 2002

Explicit expressions are given to determine the electrostatic potential and ion parallel flow velocity in the region of an axisymmetric low collisionality tokamak with moderately large ion flow, electrostatic potential, and safety factor Q.
Energy dispersive x-ray diffractometry as a tool alternative to differential scanning calorimetry for investigating polymer phase transitions
Authors: Rossi-Albertini V. , Isopo A. , Caminiti R. , Tentolini U.
Published: July 2002

Recently, a technique based on energy dispersive x-ray diffraction has been proposed to follow the polymer phase transitions. However, the potentialities of this method were not clear, as well as the experimental conditions in which it is more convenient than differential scanning calorimetry, generally used for the same purpose. In the present letter, the answer to this question is provided. It is shown that the two methods are complementary, rather than equivalent, the heating rate being the relevant parameter to establish which is preferable. The demonstration of this statement is given through the observation of the complex thermal properties of a reference sample studied in both ways at progressively lower heating rates. The connection between such unusual application of x-ray diffraction and the differential scanning calorimetry is discussed in terms of the two possible definitions of entropy.
Comparison of particle-in-cell simulations and a wave-population model of electron-beam-plasma interactions
Authors: Rose D. V. , Guillory J. U. , Beall J. H.
Published: July 2002

A spatially independent beam stability model [W. K. Rose et al., Astrophys. J. 280, 550 (1984)] is compared with one-dimensional particle-in-cell (PIC) simulations. The model uses rate equations to evaluate the coupling of longitudinal waves created by beam-plasma instabilities. Equilibrium solutions of the stability model are examined and wave energies from the model are compared with PIC simulations. The PIC simulations enable the stability model to be benchmarked and to explore the temporal evolution of the background plasma electron energy distribution, a capability not presently treated in the stability model. The generation of hot plasma electron tails is examined in the PIC simulations. The scalable, spatially independent model can be used in laboratory and astrophysical parameter regimes while numerical constraints limit the parameter regimes treatable in the PIC simulations.
Multipoint optical fiber vibrometer
Authors: Di Sante Raffaella , Scalise Lorenzo
Published: July 2002

A simple fiber-optic Michelson interferometer for vibration measurement and analysis is presented in this article. It has been conceived and realized with the purpose of using it as the basic measuring element of a complete system for multiple point vibration measurements. One of its main features is that it is operated in the homodyne mode allowing the detection of the direction of motion without using Bragg cells or other optical or mechanical frequency shifting devices, which usually present some inconveniences (alignment problems, dimensions, complexity of the signal processing electronic, and costs). The capability of the fiber interferometer in detecting periodic signals and a comparison with a commercial laser Doppler vibrometer is reported.
Adsorption structure of 1,4-cyclohexadiene on Si(001)
Authors: Cho Jun-Hyung , Oh Dong-Hwa , Kim Kwang S. , Kleinman Leonard
Published: July 2002

The adsorption of 1,4-cyclohexadiene on the Si(001) surface is studied by first-principles density-functional calculations within the generalized gradient approximation. The “pedestal” structure where the two C=C double bonds react with different Si dimers is found to be more stable than the “upright” structure where only one of the two C=C bonds reacts with a Si dimer. However, the [2+2] cycloaddition reaction can easily form the upright structure but not the pedestal one. The latter structure can be obtained from the former through a high energy barrier of ∼0.95 eV, indicating a small reaction rate at room temperature. Our results provide the theoretical basis for the interpretation of recent low-energy electron diffraction and photoelectron spectroscopy data in which the upright structure was seen.
Hot zones evolution and dynamics in heterogeneous catalytic systems
Authors: Luss D. , Marwaha B.
Published: July 2002

Stationary and complex moving hot regions formed for temperatures close to the extinction temperature of uniformly ignited states of several catalytic systems, such as thin rings and hollow cylinders, a thin radial flow reactor (RFR) and a shallow packed bed. IR imaging revealed that the hot and cold regions (temperature difference of the order of 100 °C) were separated by a sharp (about 3 mm wide) temperature front. The transition from the branch of uniformly ignited to the states with a hot region was usually supercritical. In some experiments a disjoint branch of states with hot regions existed and two qualitatively different states with hot zones existed under the same operating conditions. A very intricate periodic motion of a hot zone was observed in a shallow packed bed reactor. For example, Fig. 16 shows a hot zone which splits and later coalesces several times during the long (14 h) period. Hot pulse motions were observed on a single catalytic pellet. These were caused by global coupling between the surface reaction rate and the ambient reactant concentration and the inherent nonuniformity of the catalytic activity. It is not yet clear what rate processes generate the transversal hot zones in uniform packed bed reactors.
Transient electroluminescence of organic quantum-well light-emitting diodes
Authors: Xie Zhi-yuan , Wong Tsz-cheung , Hung Liang-Sun , Lee Shuit-tong
Published: July 2002

Time-resolved electroluminescence (EL) is used for to investigate the dynamic distribution of charge carriers in organic quantum-well light-emitting diodes (QWLEDs). In organic QWLEDs, N,N′-bis-(1-naphthl)-diphenyl-1,1′-biphenyl-4,4′-diamine and 2,9-dimethyl-4,7-diphenyl-1,10phenanthroline (BCP) act as a hole-transporting layer and a potential barrier layer, respectively. Tris(8-quinolinolato) aluminum is used as a potential well, a light-emitting layer, and an electron-transporting layer. Both traditional bilayer LED and QWLEDs with one, two, and four wells are investigated. For the QWLED with one well, the transient EL spectra are similar to those of traditional LEDs. In the transient EL spectra of QWLEDs with two and four wells, two distinct peaks are observed. This is due to the fact that holes first distribute in two different wells next to the NPB layer and recombine with electrons that subsequently move in when a voltage pulse is applied. This accounts for the time-resolved light emission in different recombination zones. The interval between the cutoffs of the two EL peaks is considered to be the transit time for electrons to cross the BCP layer, corresponding to electron mobility of 6×10−7 cm2 V−1 S−1 at 7×105 V/cm.
Observation of size-dependent features in the photoluminescence of zinc oxide nanocrystallites by near-field ultraviolet spectroscopy
Authors: Yatsui T. , Kawazoe T. , Shimizu T. , Yamamoto Y. , Ueda M. , Kourogi M. , Ohtsu M. , Lee G. H.
Published: July 2002

The optical properties of single zinc oxide (ZnO) nanocrystallites were investigated at room temperature by extending the optical near-field technique to the UV region. Using a UV fiber probe with a subwavelength aperture, we performed spatially- and spectrally-resolved photoluminescence (PL) imaging of individual ZnO nanocrystallites with a spatial resolution of 55 nm. Furthermore, decreasing the spot size increased the intensities of higher-energy components of the PL spectrum due to the quantum size effect.
Investigation of noise sources in platinum silicide Schottky barrier diodes
Authors: Papatzika S. , Hastas N. A. , Angelis C. T. , Dimitriadis C. A. , Kamarinos G. , Lee J. I.
Published: July 2002

Low-frequency noise measurements have been carried out in platinum silicide Schottky diodes on n-type silicon in the forward conduction regime and with the forward current IF as a parameter. The power spectral density of the current fluctuations shows a 1/f behavior and is proportional to IFβ (with 1<β⩽2). The experimental noise data have been successfully explained by an existing model of the random walk of electrons via the interface states, modified by taking into account the Schottky barrier inhomogeneity across the interface.
Analysis of a dynamic speaker in mobile phones by considering mechanical, electrical, and magnetic coupling effects
Authors: Hwang G. Y. , Kim K. T. , Chung S. U. , Hwang S. M. , Kang B. S. , Hwang I. C.
Published: July 2002

With the advent of 3G mobile phones, a combined laptop personal computer and mobile phone can be realized that enables multimedia data communication such as TV streaming, web searching, music play, etc. A dynamic speaker is an essential part to generate high quality sound in the next generation mobile phones. Noting that characteristics of a dynamic speaker are a coupled phenomenon of mechanical, electrical, and magnetic system, a systematic analysis must be implemented to fully consider the coupling effects for an improved design. This paper presents a complete analysis of a dynamic speaker by considering mechanical, electrical and magnetic coupling effects. Results of the analysis are confirmed by the experiments. An improved design of a dynamic speaker is also proposed with enhanced performance.
High-purity and high-quality 4H–SiC grown at high speed by chimney-type vertical hot-wall chemical vapor deposition
Authors: Fujihira K. , Kimoto T. , Matsunami H.
Published: July 2002

4H–SiC layers have been homoepitaxially grown at a high growth rate of 25 μm/h by chimney-type vertical hot-wall chemical vapor deposition at 1700 °C. Through photoluminescence measurement, the intrinsic defect, so-called L1 peak, was found to be reduced under a C-rich condition. In the deep level transient spectroscopy measurement, the Z1 center was also found to be suppressed under a C-rich condition. For a 75-μm-thick epilayer, the net donor concentration was reduced to as low as 5×1012 cm−3. In low-temperature photoluminescence, free exciton peaks are dominant, indicating high purity of the epilayer.
A wide-field time-domain fluorescence lifetime imaging microscope with optical sectioning
Authors: Webb S. E. D. , Gu Y. , Lévêque-Fort S. , Siegel J. , Cole M. J. , Dowling K. , Jones R. , French P. M. W. , Neil M. A. A. , Juškaitis R. , Sucharov L. O. D. , Wilson T. , Lever M. J.
Published: July 2002

This article describes a wide-field time-domain fluorescence lifetime imaging (FLIM) microscope with optical sectioning. The FLIM system utilizes a wide-field time-gated optical image intensifier, with a minimum gate width of 85 ps, to achieve high temporal resolution of fluorescence decays induced by ultrashort laser pulses. Different configurations, using excitation pulses of picojoule energy at 80 MHz repetition rate and of nanojoule energy at 10 kHz, are compared. The instrument has a temporal dynamic range spanning from 100 ps to tens of μs and is shown to have a temporal discrimination better than 10 ps. When applied to laser dye samples, it has produced FLIM maps demonstrating sensitivity to variations in both chemical species and local environment, e.g., viscosity. Wide-field optical sectioning is achieved using the technique of structured illumination, which is applied to remove out-of-focus light that can result in lifetime artifacts. The sectioning strength, which may be adjusted by choosing an appropriate spatial modulation frequency, is characterized and shown to be comparable to that of a confocal microscope. Practical considerations concerned with improving the quality of sectioned fluorescence lifetime maps, including using a large bit depth camera, are discussed.