bluuebunny/crossref_metadata_2025 huggingface dataset:
Femtosecond probing of photodissociation dynamics in acyl cyanides
Authors: Lee I-Ren , Chung Yu-Chieh , Chen Wei-Kan , Hong Xiu-Ping , Cheng Po-Yuan
Published: July 2002

The photodissociation of two acyl cyanide compounds, R–C(O)–CN, where R=methyl and tert-butyl groups, has been investigated using femtosecond time-resolved laser-induced fluorescence (LIF) spectroscopy. Both compounds were excited by two-photon excitation at a total energy of ∼6.4 eV and the formation of the free CN(X) radical products was probed in real time by monitoring the CN X→B LIF signal. The results revealed that the temporal evolution of the CN(X) formation can be well characterized by delayed biexponential rise functions with time constants in the picosecond time scale, indicating that the dissociation occurs via a complex-mode mechanism. We proposed a dissociation mechanism involving two discernable stages to account for the observed temporal behaviors as well as previous photofragment translational spectroscopic results reported by other groups. Our analyses suggested that the selectivity between the C–CN and C–R bond cleavage is determined by the competition between the adiabatic and nonadiabatic dynamics of the S2 state. The results also indicated that the adiabatic dissociation process occurring on the S2 surface is not statistical. We speculate that this nonstatistical dissociation behavior is due to an initial nonuniform phase space distribution and a slow intramolecular vibrational energy redistribution process that prevents the system from sampling the entire phase space before the reaction completes.
Noncommutative cohomological field theory and GMS soliton
Authors: Sako Akifumi , Kuroki Shin-Ichiro , Ishikawa Tomomi
Published: July 2002

We show that it is possible to construct a quantum field theory that is invariant under the translation of the noncommutative parameter θμν. This is realized in a noncommutative cohomological field theory. As an example, a noncommutative cohomological scalar field theory is constructed, and its partition function is calculated. The partition function is the Euler number of Gopakumar, Minwalla, and Strominger (GMS) soliton space.
Vibrational spectroscopy of shock-compressed nitromethane-d3
Authors: Kobayashi Takamichi , Sekine Toshimori , He Hongliang
Published: July 2002

Real-time vibrational spectra of shock-compressed nitromethane-d3 (CD3NO2) up to 10 GPa have been measured using a single-pulse laser Raman spectrometer in conjunction with a propellant gun and vibrational mode-dependent behavior has been examined. The NO2 stretching mode shows small frequency shift compared to other stretching modes, which may be attributed to increased intermolecular interaction under pressure. Pressure-induced Raman frequency shift of all the investigated stretching modes shows monotonic increase up to ∼5.0 GPa. Above 5 GPa, however, an abrupt drop in Raman frequency shift is observed for the CN and the CD3 stretching modes. At higher pressures, Raman frequencies of these two modes increase again until all Raman bands disappear at above ∼8.5 GPa, where a strong background emerges over the whole spectral range (500–2600 cm−1). This strong emission appears to indicate an onset of a single shock induced chemical reaction at ∼8.5 GPa.
A bending elasticity approach to the three-phase coexistence of microemulsions
Authors: Lade O. , Krawietz A.
Published: July 2002

In mixtures of water, oil, and surfactant, a microemulsion phase with a bicontinuous microstructure may coexist with water and oil excess phases. A common theoretical description of microemulsion properties is based on the energy of the curved bending elastic interface. The aim of the article in hand is to model the microstructures and phase behavior of microemulsions in the vicinity of the three-phase region. To this end, we compare the energy of several microstructures as function of volumetric constraints and preferred curvature parameters. Two major developments were necessary to do so: (i) A new bending energy function is introduced capable of explaining the coexistence of the bicontinuous microemulsion with both water and oil. (ii) An analytical geometric model of bicontinuous structures with variable volume ratios of the two domains is presented suitable for computing the local curvatures over the whole interface.
Radio-frequency-driven electron spin echo envelope modulation spectroscopy on spin systems with isotropic hyperfine interactions
Authors: Kälin M. , Schweiger A.
Published: July 2002

Three-pulse radio-frequency (rf) driven electron spin echo envelope modulation (ESEEM) is introduced as a method to measure hyperfine couplings of electron–nuclear spin systems in liquids. It is distinguished from the corresponding two-pulse experiment by narrower lines. Numerical simulations of rf-driven ESEEM based on Floquet theory are given and compared with average Hamiltonian theory. Artifacts which appear in rf-driven ESEEM spectra are discussed, and approaches for the removal of these artifacts such as time-proportional phase incrementation (TPPI) of the rf phase and an rf phase cycle (0, π) are presented. The validity of the analytical description of the rf-driven ESEEM experiment is shown by comparison with experimental results.
Making use of Connolly’s molecular surface program in the isodensity adapted polarizable continuum model
Authors: Höfinger Siegfried , Steinhauser Othmar
Published: July 2002

We present a general method to obtain well shaped cavities for treating solvation within the polarizable continuum model (PCM). The cavities are built with Connolly’s molecular surface program MSROLL, that allows easy evaluation of all the critical parameters involved in present day PCM technology. The procedure basically works in adapting the isodensity of the solutes at different threshold values. The important features to realize are, that on the one hand there is no uniform threshold value applicable for a reliable description of the solvation effect, and that on the other hand, there are two types of characteristic points to be found when plotting Δ Gel versus isodensity threshold value of the solute, which are, a minimum for neutral and anionic molecules, or a shoulder for cationic molecules. Taking the respective cavity dimensions at these characteristic points, the experimental values of Δ Gsolv are modeled within chemical accuracy and thus a true ab initio treatment of any arbitrary chemical system should be conceivable within this so-called isodensity adapted polarizable continuum model (IDAPCM).
The inertial lift on a small particle in a weak-shear parabolic flow
Authors: Asmolov Evgeny S.
Published: July 2002

The lateral migration of a small spherical particle translating within a vertical channel flow with large channel Reynolds numbers Rc is investigated. The weak-shear case is studied when the ratio of the slip velocity to maximum velocity of the channel flow, Vs, is finite, while two other dimensionless groups, particle Reynolds number Rs and Rc−1, are asymptotically small. The disturbance flow at large distances from the sphere is governed by Oseen-like equations. The ratio of Oseen length to channel width is ε=ls/l=(Rc|Vs|)−1≪1, i.e., the Oseen region is only a small part of the channel while the major portion of the disturbance flow is inviscid. A solution of the governing equations is constructed in terms of two-dimensional Fourier transform of the disturbance field in a plane parallel to the channel walls. The ordinary differential equation for Fourier transform of lateral velocity Γz(k,z) is solved using the method of matched asymptotic expansions based on ε. Several domains in (k,z) space are distinguished that correspond to different regions in physical space: Oseen region, inviscid region, viscous wake, boundary, and critical layers. For the weak-shear case the dominant contribution to the lift gives not velocity disturbances within the Oseen region but the large-scale inviscid disturbances. For such disturbances both effects due to an inviscid interaction with the walls and the curvature of the undisturbed velocity profile should be taken into account. The particle equilibrium positions at the distances from the wall of the order of the channel width arise for both negative and positive slip velocities.
Comparing simulation of plasma turbulence with experiment
Authors: Ross David W. , Bravenec Ronald V. , Dorland William , Beer Michael A. , Hammett G. W. , McKee George R. , Fonck Raymond J. , Murakami Masanori , Burrell Keith H. , Jackson Gary L. , Staebler Gary M.
Published: July 2002

The direct quantitative correspondence between theoretical predictions and the measured plasma fluctuations and transport is tested by performing nonlinear gyro-Landau-fluid simulations with the GRYFFIN (or ITG) code [W. Dorland and G. W. Hammett, Phys. Fluids B 5, 812 (1993); M. A. Beer and G. W. Hammett, Phys. Plasmas 3, 4046 (1996)]. In an L-mode reference discharge in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)], which has relatively large fluctuations and transport, the turbulence is dominated by ion temperature gradient (ITG) modes. Trapped electron modes and impurity drift waves also play a role. Density fluctuations are measured by beam emission spectroscopy [R. J. Fonck, P. A. Duperrex, and S. F. Paul, Rev. Sci. Instrum. 61, 3487 (1990)]. Experimental fluxes and corresponding diffusivities are analyzed by the TRANSP code [R. J. Hawryluk, in Physics of Plasmas Close to Thermonuclear Conditions, edited by B. Coppi, G. G. Leotta, D. Pfirsch, R. Pozzoli, and E. Sindoni (Pergamon, Oxford, 1980), Vol. 1, p. 19]. The shape of the simulated wave number spectrum is close to the measured one. The simulated ion thermal transport, corrected for E×B low shear, exceeds the experimental value by a factor of 1.5 to 2.0. The simulation overestimates the density fluctuation level by an even larger factor. On the other hand, the simulation underestimates the electron thermal transport, which may be accounted for by modes that are not accessible to the simulation or to the BES measurement.
Granular fingering patterns in horizontal rotating cylinders
Authors: Shen Amy Q.
Published: July 2002

We performed systematic experiments involving a thin layer of a granular medium flowing within a horizontally rotating cylinder. The cylinder aspect ratio, the particle size, and the percentage of cylinder volume occupied by particles were varied. The flow phenomena observed in these experiments were diverse and complicated. In particular, in most cases, frontal fingers were found. Dimensional analysis was used to gain insight regarding the mechanisms underlying the formation of these fingers. This analysis shows that the dimensionless granular wavelength can be expressed as a function of cylinder aspect ratio, granular Reynolds number, granular Froude number, and granular filling percentage.
Relationship between wall pressure fluctuations and streamwise vortices in a turbulent boundary layer
Authors: Kim Joongnyon , Choi Jung-Il , Sung Hyung Jin
Published: July 2002

A direct numerical simulation is performed to examine the relationship between wall pressure fluctuations and near-wall streamwise vortices in a spatially developing turbulent boundary layer. It is found that wall pressure fluctuations are closely linked with the upstream quasistreamwise vortices in the buffer region. The maximum correlation occurs with the spanwise displacement from the location of wall pressure fluctuations. The space–time correlation reveals that wall pressure fluctuations lag behind streamwise vorticity in the upstream, while streamwise vorticity lag behind wall pressure fluctuations in the downstream. The contributions of high-amplitude wall pressure event to the turbulent energy production mechanism are examined by the quadrant analysis of Reynolds shear stress.
An application of the least-squares method to system parameters extraction from experimental data
Authors: Oprisan Sorinel Adrian
Published: July 2002

We explore the possibility and the limits of extracting the parameters of the model from simulated logistic and Henon time series. For the models considered, the least-squares approach provides accurate values of the recurrence order and polynomial degree along with the model parameters. We found that the number of data points increases the accuracy of the estimation only for noise-free data. With the white noise added to the data, the accuracy could not be improved above a certain threshold that is almost independent of the number of data points. The additive noise flattened the global minimum of the least-squares function such that above a noise threshold it is no longer possible to discern the optimum values of the recurrence order and/or polynomial degree.
Correlation between photoluminescence properties and morphology of laser-ablated Si/SiOx nanostructured films
Authors: Kabashin A. V. , Sylvestre J.-P. , Patskovsky S. , Meunier M.
Published: July 2002

Pulsed laser ablation in an inert gas has been used to fabricate films containing silicon nanocrystals. We show that film microstructure is one of the main factors, determining long-term photoluminescence (PL) properties. Films with different porosity were found to exhibit PL signals with quite different peak energies, integral intensities and time-dependent evolutions. The distinction of these PL properties is attributed to the different efficiency of surface chemistry interactions between Si nanocrystallites and the ambient atmosphere for films having different porosities. Oxygen-related defects and other mechanisms are discussed to explain the PL properties of the films.
Statistical mechanics and thermodynamics of magnetic and dielectric systems based on magnetization and polarization fluctuations: Application of the quasi-Gaussian entropy theory
Authors: Apol M. E. F. , Amadei A. , Di Nola A.
Published: July 2002

The quasi-Gaussian entropy (QGE) theory employs the fact that a free-energy change can be written as the moment-generating function of the appropriate probability distribution function of macroscopic fluctuations of an extensive property. In this article we derive the relation between the free energy of a system in an external magnetic or electric field and the distribution of the “instantaneous” magnetization or polarization at zero field. The physical-mathematical conditions of these distributions are discussed, and for several continuous and discrete model distributions the corresponding thermodynamics, or “statistical state,” is derived. Some of these statistical states correspond to well-known descriptions, such as the Langevin and Brillouin models. All statistical states have been tested on several magnetic and dielectric systems: antiferromagnetic MnCl2, the two-dimensional Ising spin model, and the simulated extended simple point charge (SPC/E) water under an electric field. The results indicate that discrete modeling of magnetization and polarization is rather essential for all systems. For the Ising model the “discrete uniform” state (corresponding to a Brillouin function) gives the best description. MnCl2 is best described by a “symmetrized binomial state,” which reflects the two opposing magnetic sublattices. For simulated water it is found that the polarization, as well as the type of distribution of the fluctuations, is strongly affected by the shape of the system.
Photoluminescence spectroscopy of single silicon quantum dots
Authors: Valenta Jan , Juhasz Robert , Linnros Jan
Published: July 2002

Photoluminescence (PL) from single silicon quantum dots have been recorded and spectrally resolved at room temperature. The Si nanocrystals (NCs) were fabricated using electron-beam lithography and reactive ion etching resulting in Si nanopillars that were subsequently oxidized to produce luminescent silicon cores. The NCs are organized in a regular matrix which enables repeated observation of a specific single NC. By reflection and PL imaging, the emission is shown to originate from the Si nanopillars. The single-NC PL spectrum has a single band with a width of ∼130 meV. The emission is polarized in arbitrary directions suggestive of geometrical differences in the shape of the nanocrystals. The quantum efficiency of the PL has been found to reach as much as 35% for some nanocrystals. Our experiments support the quantum-confinement model for the PL emission of Si nanocrystals and elucidate the critical role of defect passivation.
Separation of contributions to spin valve interlayer exchange coupling field by temperature dependent coupling field measurements
Authors: Lee Chih-Ling , Bain James A. , Chu Shaoyan , McHenry Michael E.
Published: July 2002

In this work, interlayer exchange coupling fields of spin valve samples have been measured as a function of temperature, and fit to a temperature dependent combination of RKKY and Neel coupling fields. The RKKY coupling strength is assumed proportional to the form (T/T0)/sinh(T/T0), where T is temperature and T0 is characteristic temperature. [N. Persat and A. Dinia, Phys. Rev. B 56, 2676 (1997)] This allows the RKKY coupling and Neel coupling field to be separated quantitatively. The results of such an analysis on various CoFe/Cu/CoFe spin valve structures allow the extraction of a roughness parameter from the Neel model and the T0 parameter from the RKKY model. The measured roughness on the top surface was generally 2–3 times greater than the value obtained from the Neel analysis. The extracted T0 parameter was one order of magnitude smaller than that measured for bulk Cu by the de Hass–van Alphen effect. [N. Persat and A. Dinia, Phys. Rev. B. 56, 2676 (1997); B. Lengeler and W. R. Wampler, Phys. Rev. B 15, 5493 (1977)] Part of this reduction may be due to the 2D nature of the electron gas, as justified by an estimate of the 2D free electron Fermi energy calculation. However a factor of four difference remains, with the experimental value of T0 being around 100 K. This behavior, while not fully explained, is consistent with the measurements of other workers.
Hysteretic characteristics of giant magnetoimpedance due to the exchange coupling in annealed amorphous materials
Authors: Rheem Y. W. , Kim C. G. , Kim C. O. , Yoon S. S.
Published: July 2002

Experiments of the giant magnetoimpedance (GMI) profile have been performed in annealed amorphous Co66Fe4B15Si15 ribbons in open air to characterize the role of the bias field on the GMI. The GMI ratio profile measured at 0.1 MHz exhibits a drastic step-like change, the so-called GMI valve, in an 8 h annealed sample at 380 °C. The GMI valve is related to exchange coupling of the bias field with magnetization of the soft amorphous phase, where the bias field is caused by hcp-Co and fcc-Co crystalline phases on the surface B and Si depleted layer. The bias field is stable for an external field less than 100 Oe, but its direction is entirely changed according to the external field over 400 Oe. The GMI profile begins to reveal hysteresis for increasing and decreasing cyclic fields when the maximum field strength exceeds 200 Oe. The peak for the increasing field is positioned in the negative field region, but in the positive field region for decreasing field. This behavior is opposite to general magnetic hysteretic characteristics, suggesting that there is an antiferromagnetic coupling of the bias field with magnetization of the inside amorphous phase.
Growth and interfacial studies of conjugated oligomer films on Si and SiO2 substrates
Authors: Papaefthimiou V. , Siokou A. , Kennou S.
Published: July 2002

The growth of [2,5-bis(4-styryl)styryl] 1,4-dioctyloxybenzene, (Ooct-OPV5) oligomer films on Si (100)-(2×1) and Si (111)-(7×7) reconstructed surfaces as well as on a SiO2 film over a Si (100) wafer was studied by x-ray photoelectron spectroscopy (XPS). Ooct-OPV5 resembles poly (p-phenylenevinylene) (PPV), a polymer that is widely used in organic light emitting diodes. High purity oligomer films of up to 18 nm thickness were prepared on the clean substrates by stepwise evaporation in ultrahigh vacuum conditions and a layerwise growth of films was observed on all substrates. The electronic structure of the oligomer interface with n-doped Si (111) was investigated by combined x ray and ultraviolet photoelectron spectroscopies (XPS) and (UPS). The C 1s XPS peak of the bulk oligomer consisted of three components, all associated with oligomer functional groups at binding energies 285.05, 285.75, and 287.15 eV, respectively. During growth, both C 1s and O 1s peaks in the film exhibited an upward BE shift of 0.45±0.05 eV, from which the total band bending at the interface was evaluated. The depletion region in the organic film during the interface was found to be ∼90 Å thick. The UP spectra of the oligomeric film exhibited characteristic peaks that resemble those of PPV, and the oligomer work function was found to be 4.00±0.05 eV. The interface between the two materials in contact proved to be nonreactive and no detectable electric dipole was observed.
Structural study of CoCrPt films by anomalous x-ray scattering and extended x-ray absorption fine structure
Authors: Chow G. M. , Sun C. J. , Soo E. W. , Wang J. P. , Lee H. H. , Noh D. Y. , Cho T. S. , Je J. H. , Hwu Y. K.
Published: July 2002

The correlation of elemental chemistry with the particular long-range order in question cannot be obtained by common conventional characterization techniques. Here we report a study of determining the elemental concentrations of the textured Bragg diffraction peak and the averaged local atomic environment of sputtered CoCrPt films using anomalous x-ray scattering and extended x-ray absorption fine structures. The elemental compositions of the textured peak in these polycrystalline nanostructured films differed from the average global film composition. The higher Cr concentration in the textured peak indicated that a significant amount of Cr did not segregate towards the grain boundaries as a result of the low sputtering temperature and pressure used. The structural observations were consistent with the magnetic results.
The permanent electric dipole moments for the A 2Π and B 2Σ+ states and the hyperfine interactions in the A 2Π state of lanthanum monoxide, LaO
Authors: Steimle T. C. , Virgo Wilton
Published: July 2002

The optical Stark effect in the (0,0) A 2Π3/2–X 2Σ+, A 2Π1/2–X 2Σ+, and B 2Σ+–X 2Σ+ band systems of a lanthanum monoxide, LaO, supersonic molecular beam sample have been analyzed to produce permanent dipole moments, μ, for the A 2Π3/2, A 2Π1/2, and B 2Σ+ states of 1.89(6) D, 2.44(2) D, and 0.2(1) D, respectively. Fine structure splitting in the field free A 2Π3/2–X 2Σ+ and A 2Π1/2–X 2Σ+ spectra were analyzed to produce the magnetic hyperfine spectroscopic parameters a=233(4) MHz, c=−261(12) MHz, and d=410(4) MHz. A comparison with other group IIIA monoxides is made.
The invalidity of a Mach probe model
Authors: Hutchinson I. H.
Published: July 2002

Despite its recent application to the interpretation of directional Langmuir probe measurements, the model of Hudis and Lidsky [J. Appl. Phys. 41, 5001 (1970)] for ion collection in a flowing plasma is no more than an ad hoc mathematical ansatz. A reliable theoretical interpretation of directional Langmuir probe measurements in unmagnetized plasmas is still lacking.
Micro-Raman scattering in laterally epitaxial overgrown GaN
Authors: Tripathy S. , Chua S. J. , Hao M. S. , Sia E. K. , Ramam A. , Zhang J. , Sun W. H. , Wang L. S.
Published: July 2002

In this study, micro-Raman spectroscopy has been used to investigate the vibrational properties of laterally epitaxial overgrown (LEO) GaN. The LEO GaN films were grown by metal organic chemical vapor deposition on a 2 in. sapphire substrate with SiN mask. Photoluminescence and polarized Raman scattering measurements have been performed in the two regions of GaN growth (wing and window regions). Raman scattering results are consistent with the lateral growth of GaN in the overgrown region. We have observed second-order Raman scattering in the wing and window regions of GaN. The observations of longitudinal optical phonon plasmon modes in the overgrown region demonstrate that LEO GaN is doped. We have carried out micro-Raman mapping of the local strain and free carrier concentration in the LEO GaN. Anharmonicity due to temperature in LEO GaN has also been investigated. The anharmonicity was found to increase with increasing temperature, and such temperature-induced anharmonicity introduces changes in the linewidth and line center position of the Raman active phonons. The phonon lifetimes in GaN are estimated in the LEO region as well as in the coherently grown region (window region).
Stark effect modeling in strained n-type Si/Si1−xGex resonant tunneling heterostructures
Authors: Zid F. Ben , Bhouri A. , Mejri H. , Tlili R. , Said M. , Lazzari J.-L. , d’Avitaya F. Arnaud , Derrien J.
Published: July 2002

We present calculations of band discontinuities for Si1−xGex/Si1−yGey strained/relaxed heterointerfaces using the model-solid theory. From the obtained results, we then report a numerical simulation of the conduction-band diagram of a resonant tunneling diode in the Si/Si1−yGey system by solving self-consistently Schrödinger and Poisson equations with and without an applied electric field. An analysis of the Stark effect was made in the investigated heterostructure. Two main features have been extrapolated: (i) two sheets of a two-dimensional electron gas are created, leading to a resonant tunneling through the structure, (ii) a charge transfer can occur due to this tunneling effect. In addition, it is found that this charge transfer is highly sensitive to temperature and tends to saturate as the applied electric field increases.
Rate equations of vertical-cavity semiconductor optical amplifiers
Authors: Royo P. , Koda R. , Coldren L. A.
Published: July 2002

We rigorously establish the rate equations for vertical-cavity semiconductor optical amplifiers, starting from a general energy rate equation. Our results show that the conventional rate equation used so far in the literature is incorrect because of an inappropriate calculation of the mirror losses. Our calculations include the effect of amplified spontaneous emission and can be used to describe the properties of resonant-cavity-enhanced photodetectors.
A six-degree-of-freedom precision motion stage
Authors: Seugling Richard M. , LeBrun Thomas , Smith Stuart T. , Howard Lowell P.
Published: July 2002

This article presents the design and performance evaluation of a six-degree-of-freedom piezoelectrically actuated fine motion stage that will be used for three dimensional error compensation of a long-range translation mechanism. Development of a single element, piezoelectric linear displacement actuator capable of translations of 1.67 μm with 900 V potential across the electrodes and under a 27.4 N axial load and 0.5 mm lateral distortion is presented. Finite element methods have been developed and used to evaluate resonant frequencies of the stage platform and the complete assembly with and without a platform payload. In general, an error of approximately 10.0% between the finite element results and the experimentally measured values were observed. The complete fine motion stage provided approximately ±0.93 μm of translation and ±38.0 μrad of rotation in all three planes of motion using an excitation range of 1000 V. An impulse response indicating a fundamental mode resonance at 162 Hz was measured with a 0.650 kg payload rigidly mounted to the top of the stage.
Tremor: Is Parkinson’s disease a dynamical disease?
Authors: Beuter Anne , Vasilakos Konstantinon
Published: July 2002

Experimental evidence has shown a plethora of short-term fluctuations in patients with Parkinson’s disease. We investigate these transitory events using the concept of dynamical disease. Several examples of short-term fluctuations in tremor are analyzed, and in two cases, other systemic variables (i.e., respiration and blood pressure) are examined as well. A model for tremor, based on negative feedback with delays is proposed, and the transient events are simulated. The theoretical implications of the model suggest that interactions between the central and peripheral loops, as well as interactions between the control loops and other systemic signals, can give rise to transitory events in tremor, both in the pathological and in the normal case.
Least-squares orthogonal polynomial approximation in several independent variables
Authors: Caprari Robert S.
Published: July 2002

A systematic technique for generating orthonormal polynomials in two independent variables by application of the Gram–Schmidt orthogonalization procedure of linear algebra is presented. A linear least-squares approximation for experimental data or an arbitrary function is generated from these polynomials. The least-squares coefficients are computed without recourse to matrix arithmetic, which ensures both numerical stability and simplicity of implementation as a self-contained numerical algorithm. The Gram–Schmidt procedure is then utilized to generate a complete set of orthogonal polynomials of fourth degree. A general technique for the transformation of the polynomial representation from an arbitrary basis into the familiar sum of products form is presented, together with a specific implementation for fourth degree polynomials. The computational integrity of this algorithm is verified by reconstructing arbitrary fourth degree polynomials from their values at randomly chosen points in their domain.
Is C++ fast enough for Scientific Computing?
Authors: Haney Scott W.
Published: July 2002

The performance of C++ in solving physics problems is discussed. One of the attractive features of using C++ language is its ability to translate physics concepts into computer instructions. This may lead to fewer programming errors and greater productivity. (AIP)
Noncontact photoacoustic measurements of semiconductors with Michelson interferometry
Authors: Suemune I. , Yamamoto H. , Yamanishi M.
Published: July 2002

Noncontact photoacoustic measurements were performed on GaAs samples with Michelson interferometry. The detection sensitivity of the vibration amplitude up to 0.01 Å was achieved. It is demonstrated that the sensitivity is increased drastically by the resonance of the sample itself. The sensitivity for the temperature rise is estimated to be on the order of 2×10−5 °C.
Growth, characterization, and optical spectroscopy of Al2O3:Ti3+
Authors: Powell Richard C. , Caslavsky Jaroslav L. , AlShaieb Zuhair , Bowen John M.
Published: July 2002

The process of growing large diameter single crystals of Al2O3:Ti3+ by vertical solidification of the melt is described, and some of the problems in producing high-optical quality material are discussed. The characterization of the distribution and valance state of titanium ions was performed by x-ray techniques and laser Raman microprobe methods. The presence of other impurity ions, specifically iron, was also determined. In some cases titanium was found in the grown crystal to be in the rutile form. In addition, Ti-Fe pairs, and concentrated regions of titanium on the surface of the boule were also observed. Some procedures for minimizing these problems are discussed. The results of optical absorption, fluorescence, and lifetime measurements are reported. The addition of Fe is shown to produce a broad absorption band in the red region of the spectrum, and two-photon laser excitation terminating in the ultraviolet spectral region produces a broad blue emission band.
Distributions of light ions and foil destruction after irradiation of organic polymers
Authors: Fink D. , Biersack J. P. , Chen J. T. , Städele M. , Tjan K. , Behar M. , Olivieri C. A. , Zawislak F. C.
Published: July 2002

It is found that light ions (6Li, 10B) distribute neither according to their calculated range nor to their nuclear damage distributions but according to their ionization distributions after implantation into organic polymers. Also, the profile of chemical destruction after low dose light ion implantation (typically 1012–1014 ions/cm2) into organic foils obeys the ionization distribution rather than the range or nuclear damage distributions. After annealing, or at higher implanted doses, a slight shift of the implantation or destruction profiles towards the nuclear damage distribution is found. The reason for this implantation behavior may be partly understood in terms of diffusion and subsequent recombination with the created radicals. Li and B distributions in carbon (which may be regarded as the final product of polymer destruction) show a shape which can be described by range profiles with subsequent diffusion and trapping at homogeneously distributed defects. In contrast to light ions, implanted heavy ions distribute in polymers essentially according to their range profiles, due to negligible diffusion after implantation.
Theory of cathodoluminescence contrast from localized defects in semiconductors
Authors: Jakubowicz A.
Published: July 2002

An analytical solution is given for the contrast from an individual pointlike defect in the cathodoluminescence mode of a scanning electron microscope. This solution takes into account the influence of recombination at the surface and the internal optical absorption. The cathodoluminescence contrast is shown to differ from the electron-beam-induced current contrast. The pointlike defect is then treated as an elementary segment of an extended defect. Computational results are given for dislocations at various angles to the surface. Some advantages of a simultaneous cathodoluminescence and electron-beam-induced current experiment are pointed out.
Depth distribution of secondary defects in 2-MeV boron-implanted silicon
Authors: Tamura M. , Natsuaki N. , Wada Y. , Mitani E.
Published: July 2002

Annealing behavior of secondary defects in 2-MeV boron ion-implanted (100) silicon has been investigated mainly through cross-sectional TEM observations. The maximum defect density is located at a mean depth of 3.2 μm from the surface and the location is 0.3 μm deeper than that of the projected range of boron ions. This defect position in the crystal is constant under all annealing conditions (e.g., a temperature range of between 700 and 1000 °C, annealing time of up to 6780 min at 1000 °C), although the vertical distribution width of defects changes with both annealing temperature and time.
The effect of pressure on phase selection during nucleation in undercooled bismuth
Authors: Yoon W. , Paik J. S. , LaCourt D. , Perepezko J. H.
Published: July 2002

At a sufficiently large liquid undercooling, the solidification of fine Bi droplet samples at ambient pressure yields a metastable phase instead of the stable structure. The metastable Bi phase is observed to melt at 174 °C at ambient pressure. Thermal analysis measurements on droplet samples subjected to hydrostatic pressures ranging up to 400 MPa demonstrate that the melting temperature of the metastable Bi phase increases by 20.8 K/GPa with pressure, while that of the stable Bi phase decreases by 38.8 K/GPa. The trend of the measured melting temperature of the metastable Bi phase joins smoothly to the melting curve of the Bi(II) high-pressure phase. Differential scanning-calorimetry measurements on a liquid Bi droplet sample at undercoolings up to 220 °C support the identification of the metastable Bi phase as the Bi(II) high-pressure phase with a heat of fusion 5.98 kJ/g-at. A shift of the nucleation temperature under pressure, which follows the trend of the melting temperature, characterizes the nucleation onset of both Bi(I) and Bi(II) phases and provides information on the kinetic competition controlling phase selection.
C-V measurement and modelization of GaInAs/InP heterointerface with traps
Authors: Kazmierski K. , Philippe P. , Poulain P. , de Cremoux B.
Published: July 2002

GaInAs/InP heterojunction grown by metalorganic vapor-phase epitaxy has been studied by C-V measurements against temperature and frequency. The apparent concentration profiles led to the deduction that both the apparent band discontinuity and the interface charge density are dependent on both the temperature and the frequency. This behavior is explained by assuming a null actual conduction-band discontinuity and the important presence of traps at the heterojunction. A model of C-V measurement has been developed in order to account for the presence of traps and the effect of frequency. Simulation results confirm the consistency of the hypothesis of a null actual conduction-band discontinuity.
The effects of the nonabrupt depletion edge on deep-trap profiles determined by deep-level transient spectroscopy
Authors: Zhao Jian H. , Lee Jyh-Chwen , Fang Z. Q. , Schlesinger T. E. , Milnes A. G.
Published: July 2002

The effects of the nonabrupt depletion edge (the Debye tail) on the trap concentrations obtained by deep-level transient spectroscopy are discussed. In depth profiling of traps it is shown that a dramatic drop in the apparent deep-trap concentration is obtained near the edge of the total depth probed. This is an artifact of the measurement and is a consequence of the Debye tail in the depletion edge. It is shown that experimentally one can avoid this problem by using sufficiently large reverse biases and forward filling pulses to determine the deep-trap concentration in any particular region of the semiconductor.
Improved laser pumping by intense electron beams via a backscattering reflector
Authors: Sauerbrey R. , Zhu Y. , Millar P. , Tittel F. K. , Wilson W. L.
Published: July 2002

Experiments demonstrating improved laser media pumping using electron-beam concentration by means of a backscattering mirror are reported. The backscattering mirror increases the electron pumping density by as much as a factor of 3 at low gas pressures. Use of the concentrator resulted in more than a 50% increase in Ar*2 excimer emission. The N2(C→B) amplified spontaneous emission can be saturated on a gain length of only 10 cm.
Surface stability of NbN single-crystal films
Authors: Talvacchio J. , Sinharoy S. , Braginski A. I.
Published: July 2002

The surfaces of NbN(100) and NbN(111) single-crystal films were analyzed as a function of annealing temperature in ultrahigh vacuum by low-energy electron diffraction and x-ray photoelectron spectroscopy. The NbN(100) surface changed from a (1×1) to a ((2)1/2×(2)1/2)45° structure at 900 °C accompanied by a loss of nitrogen. The NbN(111) surface, initially richer in nitrogen, transformed from a (1×1) to a (2×2) structure at 800 °C with an even greater loss of nitrogen from the surface. Increasing the carbon content of the films increased the temperatures at which reconstructions were observed. Structural models of the surfaces are presented that are consistent with these observations. At higher temperatures (up to 1100 °C), additional nitrogen was lost from films of both orientations. Measurements of superconducting transition temperatures and energy gaps indicated that the entire film was nitrogen deficient after annealing, with the greatest nitrogen loss at the surface.
Optical determination of the characteristics of a pulsed-gas jet
Authors: Lompré L. A. , Ferray M. , Lrsquo;Huillier A. , Li X. F. , Mainfray G.
Published: July 2002

A pulsed-gas jet with interesting properties has been developed. A typical pressure obtained at the output of this pulsed-gas jet is 25 Torr for a backing pressure of 150 Torr. At a repetition rate of 10 Hz, the background pressure stays below 1.5×10−4 Torr. Laser-induced fluoresence measurements permit one to determine the pressure and the divergence of the gas jet accurately.
Effect of temperature on the uniform field breakdown strength of electronegative gases
Authors: Christophorou L. G. , Mathis R. A. , Hunter S. R. , Carter J. G.
Published: July 2002

In general, the electron attachment rate constant ka (〈ε〉, T), as a function of the mean electron energy 〈ε〉 and temperature T for electronegative gases which attach electrons nondissociative ily, decreases greatly with T from room temperature to T≲600 K, while the ka (〈ε〉, T) of electronegative gases which attach electrons dissociatively increases with increasing T. Based on recent studies at our laboratory on ka (〈ε〉, T), we investigated the variation with T (∼295–575 K) of the uniform field breakdown strength, (E/N)lim, for three classes of electronegative gases: (a) gases such as c-C4F8 (and c-C4F6, 1−C3F6) which attach strongly low-energy (≲1 eV) electrons nondissociatively and for which ka (〈ε〉, T) decreases precipitously with T above ambient: (b) gases such as C2F6 and CF3Cl which attach electrons exclusively dissociatively and whose ka (〈ε〉, T) increases with T; and (c) gases such as C3F8 and n-C4F10 which attach electrons both nondissociatively and dissociatively over a common low-energy range and whose ka (〈ε〉, T) first decreases and then increases with T above ambient. The (E/N)lim(T) has been found to decrease significantly with T for (a), to decrease slowly with T for (c), and to increase slightly with T for (b). These changes in (E/N)lim follow those in ka (〈ε〉, T). A similar behavior is expected for other electronegative gaseous dielectrics in the respective three groups.
Low-dimensional magnetic systems; from 1D to 3D ferrimagnets
Authors: Drillon M. , Coronado E. , Belaiche M. , Carlin R. L.
Published: July 2002

One-dimensional (1D) ferrimagnetism has recently been reported in ordered bimetallic compounds. Actually, such a behavior is not exclusive of this type of system. Ferrimagnetism can also occur in homometallic chains formed by alternating sites, or by discrete species containing an odd number of interacting metal ions. We report in this paper several examples of bimetallic or homometallic chains featuring 1D ferrimagnetism. We will also discuss the conditions for the occurrence of a long-range ferrimagnetic ordering at low temperatures.
Platinum silicide formation using rapid thermal processing
Authors: Naem A. A.
Published: July 2002

The thermal reaction of sputtered platinum with silicon to form platinum silicide by rapid thermal processing (RTP) has been investigated. A platinum film of 800 Å was sputter deposited on undoped single-crystal silicon substrates. A wide range of RTP cycles were used in N2 ambient to study the formation kinetics and determine the phase growth sequence. The composition, thickness, impurity content, platinum-silicon interface quality, grain size, and surface oxide of the Ptx Siy layer were characterized by Auger electron spectroscopy, transmission electron microscopy, and x-ray diffraction analysis. All the analysis techniques used were consistent in determining the platinum silicide system evolution. Initially, the reaction between platinum and silicon results in the formation of an intermediate phase of Pt2Si, the growth of which continues until the entire platinum film has been transformed into Pt2Si. Then the evolution of a final phase of PtSi starts at the Pt2 Si/Si interface and the reaction between Pt2 Si and Si proceeds towards the surface until the entire Pt2 Si is converted to PtSi film. No simultaneous presence of the three phases, Pt, Pt2Si, and PtSi, was observed in any sample studied. An enhanced diffusion coefficient of Pt through Pt2 Si was observed as a result of rapid thermal processing. It was determined that 1 Å of Pt results in the formation of 1.9 Å of PtSi and 1 Å of Si results in 1.44 Å of PtSi. This small rate of Si consumption is desirable for silicidation of shallow junctions formation. The resistivity of PtSi was determined to be in the range 31–38 μΩ cm which is similar to furnace annealed values. Reactive ion etching selectivity between silicon dioxide and PtSi was determined to be 33:1. The high etching selectivity combined with small Si consumption make PtSi a potential candidate for submicron applications.
Intrinsic and extrinsic photoluminescence spectra of ZnTe films on GaAs deposited by molecular-beam and organo-metallic vapor-phase epitaxy
Authors: Wilson B. A. , Bonner Carl E. , Feldman R. D. , Austin R. F. , Kisker D. W. , Krajewski J. J. , Bridenbaugh P. M.
Published: July 2002

We present low-temperature photoluminescence spectra of molecular-beam epitaxy (MBE) and organo-metallic vapor-phase epitaxy (OMVPE) ZnTe layers deposited on GaAs substrates under different growth conditions. Strong bands associated with Zn vacancies are observed in the MBE materials, while the OMVPE spectra are dominated by sharp impurity-related lines. A number of instrinsic and extrinsic emission lines are identified. No significant shift of these lines is observed relative to their positions in bulk ZnTe, implying stress levels less than 0.1 kbar for both the MBE and OMVPE layers. A study of the effects of the Zn:Te ratio in the MBE growth chamber reveals that for a growth temperature of 325 °C, an optimal value of ∼2.2 produces the highest photoluminescence efficiencies and the strongest intrinsic features. The relative intensity of the vacancy-related emission decreases as the Zn:Te ratio is increased.
Nitrogen implantation of AISI 304 stainless steel with a coaxial plasma gun
Authors: Feugeas J. N. , Llonch E. C. , de González C. O. , Galambos G.
Published: July 2002

The application of a plasma focus (PF) device operated at 1 kJ and 25 kV as a pulsed ion implanter is described. Samples of AISI 304 stainless steel implanted with nitrogen with this device show a reduction of wear of 42 times with respect to the implanted ones, with a reduction, at the same time of the friction coefficient. X-ray diffraction and x-ray photoelectron spectroscopy analyses of nitrided samples show the Fe2N precipitate formation, in an almost homogeneous ∼0.4-μm-thick superficial layer. The feasibility of the use of the PF as an implanter arises from these results as well as the possibility of designing and constructing similar systems that could perform the whole process (e.g., nitriding) in short time intervals (∼10 s).
Electron attachment and ionization coefficients and electron drift velocities in BF3 and SiF4
Authors: Hunter S. R. , Carter J. G. , Christophorou L. G.
Published: July 2002

The drift velocity of electrons (w) in SiF4 and BF3 has been measured over the density-reduced electric field (E/N) range 0.5×10−17 V cm2 ≤E/N≤300×10−17 V cm2 using a pulsed Townsend experimental technique. The electron attachment (η/N) and ionization (α/N) coefficients have also been measured in SiF4 and BF3 over the E/N range 30×10−17 V cm2 ≤E/N≤300×10−17 V cm2 in the same experiment. The electron drift velocities in these two gases exhibit regions of negative differential conductivity (NDC) similar to but smaller in magnitude than those in CH4 and CF4 . The effective ionization coefficient (ᾱ/N) has been obtained from the η/N and α/N measurements in both gases, from which the high-voltage limiting electric field strengths (E/N)lim have been found to be 123×10−17 V cm2 for BF3 and 121×10−17 V cm2 for SiF4. The significance of these results in modeling gas discharges for a number of technological applications is indicated.
Experimental analysis of phase-mode Josephson digital circuits
Authors: Nakajima K. , Sugahara H. , Fujimaki A. , Sawada Y.
Published: July 2002

We present experimental results on elementary phase-mode Josephson circuits whose combinations enable us to construct a total data processing system which is expected to be superior to the ordinary voltage-mode Josephson computer in several respects. In the phase-mode system a device depends for its operation on the existence of many stable states differing from one another by integer multiples of 2π in the phase plane. The total system is considered to be a prototype of quantum computer systems where physical quantum states are employed as logic states of information processing. By using the fabricated elementary circuits composed of SQUIDs and two types of branching points we have experimentally confirmed and, fan-out, fan-in operations, etc. We have also proposed an inhibit circuit, and presented the experimental results on the inhibit circuit.