bluuebunny/crossref_metadata_2025 huggingface dataset:
On the width‐amplitude inequality of electron phase space holes
Authors: Chen Li‐Jen , Pickett Jolene , Kintner Paul , Franz Jason , Gurnett Donald
Published: September 2005

Electron phase space holes are analyzed in terms of solitary‐wave solutions to the nonlinear Vlasov‐Poisson equations in a collisionless plasma. Width‐amplitude relations for one‐dimensional and three‐dimensional electron holes are derived to be inequalities that allow existence of the holes in regions to one side of a bound. The theoretical origin of the width‐amplitude inequality is elucidated to show that the inequality nature is independent of specific functional forms of the solitary potential and ambient plasma distribution functions. Ion dynamics and effects of finite hole velocity and finite perpendicular size are subsequently included. Finally, we show that the electron holes reported by Franz et al. (2005) populate an allowed region in the solution space that is significantly away from the bounding curve. These electron holes evidence the accessibility of electron holes whose widths and amplitudes are only loosely constrained and open up the possibility of spontaneous generation of phase‐space holes in turbulent fluctuations.
Comparison of geosynchronous energetic particle flux responses to solar wind dynamic pressure enhancements and substorms
Authors: Lee D.‐Y. , Lyons L. R. , Reeves G. D.
Published: September 2005

Geosynchronous energetic particle fluxes are used to examine the differences and similarities between the particle disturbances due to an enhancement in solar wind dynamic pressure Pdyn and those caused by substorms. Disturbances are also distinguished by IMF conditions. First, for not strongly southward IMF conditions (weakly southward or northward IMF), we find that the magnetospheric compression by a Pdyn enhancement usually causes particle fluxes to increase simultaneously at all energy channels. The increase is global around the Earth, but it usually occurs first on the dayside and then propagates to the nightside within a few minutes. We also find that a magnetospheric compression sometimes leads to a flux decrease or no flux change for at least one energy channel at some MLTs, which we attribute to the shape of radial profiles at constant adiabatic invariants. However, we find no evidence for substorm‐like injections in our Pdyn enhancement events when the IMF is not strongly southward. Following prolonged strongly southward IMF, substorms caused by IMF changes that lead to convection electric field reduction and are not associated with a Pdyn change generate flux disturbances that are quite similar to typical substorm flux disturbances for less strongly southward IMF conditions. However, the dispersionless injection front is found over a much wider azimuthal region, sometimes extending to the late afternoonside for protons. We find that under prolonged steady, strongly southward IMF conditions, a Pdyn enhancement leads to a two‐mode type disturbance. The disturbance due to magnetospheric compression can be clearly identified and is seen primarily on the dayside, and a substorm‐like injection associated with current wedge formation is seen on the nightside. The dayside compression effect is seen in both species, but is often more easily identified in the proton fluxes than in the electron fluxes. The substorm‐like injection feature is also seen in both species but is usually more evident in the electron fluxes. In the events studied here, the dayside compression disturbance precedes the substorm‐like injection on the nightside by a few minutes.
Properties of small‐amplitude electron phase‐space holes observed by Polar
Authors: Franz J. R. , Kintner P. M. , Pickett J. S. , Chen L.‐J.
Published: September 2005

We present Polar Plasma Wave Instrument (PWI) measurements of electrostatic solitary waves in the high‐altitude polar magnetosphere. These waves are electrostatic pulses that move parallel (and antiparallel) to the geomagnetic field and are similar to waves detected in many regions of the magnetosphere by other spacecraft. The PWI instantaneous dynamic range was 72 dB with an added 30 dB obtained by changing gain states. This large dynamic range enables the study of amplitude‐size relations up to a maximum electric field of 44 mV/m in the lowest gain state as well as enabling the investigation of small‐amplitude waves (<0.1 mV/m). The Polar PWI data indicate that these small‐amplitude solitary waves have typical scale sizes the order of the Debye length, velocities the order of the electron thermal speed, and electrostatic potentials that are small compared with the electron thermal energy per charge (ϕ ≪ kBTe/e). Statistical distributions of the wave properties are presented, and the properties are compared with theoretical predictions of electron phase‐space holes and electron‐acoustic solitons. BGK‐type analysis of electron holes predicts a relationship between the minimum allowed scale size and the amplitude and velocity. The observed solitary waves are consistent with these predictions.
Synchronized oscillations in energetic electron fluxes and whistler wave intensity in Jupiter's middle magnetosphere
Authors: Bespalov P. A. , Savina O. N. , Cowley S. W. H.
Published: September 2005

Synchronized oscillations in energetic electron fluxes and electromagnetic wave emissions at the planetary rotation period have been observed in and near Jupiter's magnetosphere. In this work we theoretically examine time‐dependent processes in Jupiter's middle magnetosphere energetic electron radiation belts which are relevant to these oscillations, where intervals of particle accumulation are followed by precipitation into the ionosphere during a whistler electromagnetic radiation pulse. These oscillations are described by a relativistic system of quasi‐linear equations, in which diffusion of particles in adiabatic invariant space and evolution of the electromagnetic radiation are taken into account. Linear analysis shows that the natural oscillation frequency of the Jovian radiation belt is almost independent of magnetic shell and is close in magnitude to the planet's rotation frequency, thus suggesting the possibility of a global resonance. We propose that such near‐resonant oscillations can be excited by periodic modulations of the whistler decay rate due to ionospheric absorption, which has components that depend both on local time in the magnetosphere and on asymmetries that rotate with the planet. These dependencies are shown to combine to produce a modulation at the planetary rotation period that is independent of local time and also independent of the angular velocity of rotation of the plasma. The response to this synchronized driving is investigated in both the linear and nonlinear regimes, and the conditions required for a synchronized response at the planetary period are examined.
Solar wind control of the radial distance of the magnetic reconnection site in the magnetotail
Authors: Nagai T. , Fujimoto M. , Nakamura R. , Baumjohann W. , Ieda A. , Shinohara I. , Machida S. , Saito Y. , Mukai T.
Published: September 2005

To understand magnetotail dynamics, it is essential to determine where magnetic reconnection takes place in the near‐Earth magnetotail during substorms. The Geotail spacecraft thoroughly surveyed the near‐Earth plasma sheet at radial distances of 10–31 RE during the years 1995–2003. Thirty‐four clear reconnection events were identified using the criterion of strong electron acceleration. Various solar wind parameters prior to each reconnection event were examined in order to find the factor controlling the location of the magnetic reconnection site in the magnetotail. The same analyses were carried out for fast tailward flow events. The most important factor was determined to be the solar wind energy input, which can be expressed by −Vx × Bs, where Vx is the x component of the solar wind velocity and Bs is the southward component of the interplanetary magnetic field. It is likely that higher efficiency of energy input, rather than the total amount of energy input, primarily controls the location of magnetic reconnection; magnetic reconnection takes place closer to the Earth when efficiency of energy input is higher. The effect of solar wind dynamic pressure is minor. The present result suggests that the tail magnetic reconnection location during substorms is controlled by solar cycle variations in the solar wind.
Role of the Hudson Bay lowland as a source of atmospheric methane
Authors: Roulet Nigel T. , Jano A. , Kelly C. A. , Klinger L. F. , Moore T. R. , Protz R. , Ritter J. A. , Rouse W. R.
Published: September 2005

Based on point measurements of methane flux from wetlands in the boreal and subarctic regions, northern wetlands are a major source of atmospheric methane. However, measurements have not been carried out in large continuous peatlands such as the the Hudson Bay Lowland (HBL) (320,000 km2) and the Western Siberian lowland (540,000 km2), which together account for over 30% of‐the wetlands north of 40°N. To determine the role the Hudson Bay Lowland as a source of atmospheric methane, fluxes were measured by enclosures throughout the 1990 snow‐free period in all the major wetland types and also by an aircraft in July. Two detailed survey areas were investigated: one (≈900km2) was in the high subarctic region of the northern lowland and the second area (≈4,800 km2) straddled the Low Subarctic and High Boreal regions of the southern lowland. The fluxes were integrated over the study period to produce annual methane emissions for each wetland type. The fluxes were then weighted by the area of 16 different habitats for the southern area and 5 habitats for the northern area, as determined from Landsat thematic mapper to yield an annual habitat‐weighted emission. On a per unit area basis, 1.31±0.11 and 2.79±0.39 g CH4 m−2 yr−1 were emitted from the southern and northern survey areas, respectively. The extrapolated enclosure estimates for a 3‐week period in July were compared to within 10% of the flux derived by airborne eddy correlation measurements made during the same period. The aircraft mean flux of 10±9 mg CH4 m−2 d−1 was not statistically different from the extrapolated mean flux of 20±16 mg CH4 m−2 d−1. The annual habitat‐weighted emission for the entire HBL using six wetland classes is estimated as 0.538±0.187 Tg CH4 yr−1 (range of extreme cases is 0.057 to 2.112 Tg CH4 yr−1). This value is much lower than expected, based on previous emission estimates from northern wetlands.
Channeling instability of upwelling melt in the mantle
Authors: Aharonov E. , Whitehead J. A. , Kelemen P. B. , Spiegelman M.
Published: September 2005

We present results of a theoretical study aimed at understanding melt extraction from the upper mantle. Specifically, we address mechanisms for focusing of porous flow of melt into conduits beneath mid‐ocean ridges in order to explain the observation that most oceanic residual peridotites are not in equilibrium with mid‐ocean ridge basalt. The existence of such conduits might also explain geological features, termed replacive dunites, that are observed in exposed mantle sections. We show here, by linear analysis, that flow in a chemically reactive porous media is unstable in the presence of a solubility gradient, such as induced by adiabatic ascent of melt underneath mid‐ocean ridges. The initially homogeneous flow becomes focused in time to produce elongated high‐porosity fingers that act as conduits for transport of fast flowing melt. This instability arises due to a positive feedback mechanism in which a region of slightly higher than average porosity causes increased influx of unsaturated flow, leading to increased dissolution which further reduces the Porosity. Even in the presence of matrix compaction and chemical diffusion the instability is demonstrated to be robust. Our analysis also indicates the existence of growing, traveling waves which transport and amplify porosity and concentration perturbations.
Intraplate stresses and plate‐driving forces in the Philippine Sea Plate
Authors: Pacanovsky Kim M. , Davis Dan M. , Richardson Randall M. , Coblentz David D.
Published: September 2005

We use a spherical shell elastic finite element analysis to characterize intraplate stresses and plate‐driving forces in the Philippine Sea Plate. Our finite element mesh is comprised of 489 nodes and 914 elements, and provide a spatial resolution of about 1°. The Philippine Sea Plate is unusual in that it does not have large numbers of seismic or tectonic stress indicators, and there are no midplate borehole stress data which can be used as constraints in this finite element study. However, it does possess a unique boundary configuration which potentially can lend more insight to plate forces and stresses than can similar studies on plates with more seismically active interiors. Because the plate's boundary consists primarily of subduction zones with roughly equal proportions of boundary on the overlying and downgoing sides of trench, the resultant plate stress field is very sensitive to subduction‐related forces. As a result, borehole stress measurements in certain parts of the plate would be useful in further constraining these forces. We find that trench pull forces can explain a large component of the velocity of the Philippine Sea Plate. However, trench pull has somewhat less overall effect on the stresses across the plate than do the lateral density and topographic variations within the plate (i.e., gravitational or potential energy force), and trench suction forces are probably about an order of magnitude smaller than the net trench pull forces. Collisional forces may dominate the stress fields near Taiwan and the Izu Peninsula, but they are of only secondary importance in determining the motion and deformation of the Philippine Sea Plate. The forces that generate stress orientations most closely matching the observed stress indicators produce a lithospheric stress field across the plate that averages about 15 MPa over a 70 km thick lithosphere, scaling inversely with lithosphere thickness. Values up to four times as great are produced locally.
Modeling of aerosol properties related to direct climate forcing
Authors: Koloutsou‐Vakakis Sotiria , Rood Mark J. , Nenes Athanasios , Pilinis Christodoulos
Published: September 2005

A long‐term local experiment was designed with the purpose to accurately quantify aerosol parameters needed in order to estimate aerosol climate forcing at an anthropogenically perturbed continental site. Total light‐scattering σλ,sp and backscattering σλ,bsp coefficients at wavelength λ, the hygroscopic growth factors with respect to scattering, ƒ(RH)λ,s, and the backscatter ratio bλ are the parameters considered in the paper. Reference and controlled relative humidity nephelometry measurements were taken at a ground level field sampling station, located near Bondville Illinois (40°03′12″N, W 88°22′19″W). Aerosol particle chemical composition and mass particle size distributions were also measured. The target parameters were also estimated from models. The modeling approach involved a two‐step process. In the first step, aerosol properties were parameterized with an approach that made use of a modified thermodynamic equilibrium model, published laboratory measurements of single hygroscopic particle properties, and empirical mixing rules. In the second step, the parameterized aerosol properties were used as inputs into a code that calculate σλ,sp and σλ,bsp as functions of λ, RH, particle size, and composition. Comparison between the measured and the modeled results showed that depending on the assumptions, the differences between the modeled and observed results were within 5 to 28% for ƒ(RH)λ,s and within 22–35% for bλ at low RH and 0–20% for bλ at high RH. The temporal variation of the particle size distribution, the equilibrium state of the particles, and the hygroscopicity of the material characterized as residual were the major factors limiting the predictive ability of the models.
Photofragment translation spectroscopy of ClN3 at 248 nm: Determination of the primary and secondary dissociation pathways
Authors: Hansen N. , Wodtke A. M. , Goncher S. J. , Robinson J. C. , Sveum N. E. , Neumark D. M.
Published: September 2005

Photofragmentation translational spectroscopy was used to identify the primary and secondary reaction pathways in the KrF laser (248 nm) photodissociation of chlorine azide (ClN3) under collision-free conditions. Both the molecular channel producing NCl (XΣ3,aΔ1)+N2 and the radical channel producing Cl (PJ2)+N3 were analyzed in detail. Consistent with previously reported velocity map ion imaging experiments [N. Hansen and A. M. Wodtke, J. Phys. Chem. A 107, 10608 (2003)] a bimodal translational energy distribution is seen when Cl atoms are monitored at m∕z=35(Cl+). Momentum-matched N3 counterfragments can be seen at m∕z=42(N3+). The characteristics of the observed radical-channel data reflect the formation of linear azide radical and another high-energy form of N3 (HEF-N3) that exhibits many of the characteristics one would expect from cyclic N3. HEF-N3 can be directly detected by electron-impact ionization more than 100μs after its formation. Products of the unimolecular dissociation of HEF-N3 are observed in the m∕z=14(N+) and m∕z=28(N2+) data. Anisotropy parameters were determined for the primary channels to be β=−0.3 for the NCl forming channel and β=1.7 and β=0.4 for the linear N3 and HEF-N3 forming channels, respectively. There is additional evidence for secondary photodissociation of N3 and of NCl.
Thermodynamic properties of lattice hard-sphere models
Authors: Panagiotopoulos A. Z.
Published: September 2005

Thermodynamic properties of several lattice hard-sphere models were obtained from grand canonical histogram- reweighting Monte Carlo simulations. Sphere centers occupy positions on a simple cubic lattice of unit spacing and exclude neighboring sites up to a distance σ. The nearestneighbor exclusion model, σ=√2, was previously found to have a second-order transition. Models with integer values of σ=1 or 2 do not have any transitions. Models with σ=√3 and σ=3 have weak first-order fluid-solid transitions while those with σ=2√2, 2√3, and 3√2 have strong fluid-solid transitions. Pressure, chemical potential, and density are reported for all models and compared to the results for the continuum, theoretical predictions, and prior simulations when available.
Calibration of the high-frequency magnetic fluctuation diagnostic in plasma devices
Authors: Appel L. C. , Hole M. J.
Published: September 2005

The increasing reservoirs of energetic particles which drive high-frequency modes, together with advances in the understanding of magnetohydrodynamics, have led to a need for higher-frequency (50 kHz to >20MHz) measurements of magnetic field fluctuations in magnetic fusion devices such as tokamaks. This article uses transmission line equations to derive the voltage response of a Mirnov coil at the digitizer end of a transmission line of length ℓ. It is shown that, depending on the terminations of the line, resonances can occur even for ℓ∕λ⪡1, with λ the wavelength of a fluctuation in the transmission line. A lumped-circuit model based on the approach of Heeter et al. [R. F. Heeter, A. F. Fasoli, S. Ali-Arshad, and J. M. Moret. Rev. Sci. Instrum. 71, 4092 (2000)] is extended to enable the inclusion simultaneously of both serial resistance and parallel conductance elements. As originally proposed by Heeter et al. the lumped-circuit model offers the advantage of remote calibration; this may be of particular value when upgrading existing systems to operate at frequencies above the original design specification. It is formally shown that the transmission line equations for the transfer function and measured impedance reduce to those of the lumped circuit model of Heeter et al. under specific conditions. The result extends the use of the lumped-circuit model of Heeter et al., which can be used to extract the transfer function from measurement of the impedance, beyond the case of an open-circuit termination. Although the numerical procedure does exhibit some problems associated with non-uniqueness, it provides a simple calibration method for systems that are not well defined. Using typical parameters for a high-frequency Mirnov coil installed on the Joint European Torus (JET) tokamak, the lumped-circuit approximation agrees with the steady-state transmission line model to within 0.015° in phase and 22% in amplitude for frequencies up to 1 MHz. A matched termination, though eliminating line resonances and reducing the length of time for the system to reach steady state, is inappropriate for the JET-type coils which exhibit significant temperature-dependent resistance. Finally, for fluctuations of finite duration, a method of computing the discrepancy due to the simplifying assumption of Fourier-stationary conditions is described.
Non-Born–Oppenheimer calculations of the pure vibrational spectrum of HeH+
Authors: Pavanello Michele , Bubin Sergiy , Molski Marcin , Adamowicz Ludwik
Published: September 2005

Very accurate calculations of the pure vibrational spectrum of the HeH+ ion are reported. The method used does not assume the Born–Oppenheimer approximation, and the motion of both the electrons and the nuclei are treated on equal footing. In such an approach the vibrational motion cannot be decoupled from the motion of electrons, and thus the pure vibrational states are calculated as the states of the system with zero total angular momentum. The wave functions of the states are expanded in terms of explicitly correlated Gaussian basis functions multipled by even powers of the internuclear distance. The calculations yielded twelve bound states and corresponding eleven transition energies. Those are compared with the pure vibrational transition energies extracted from the experimental rovibrational spectrum.
Nonlinear Thomson scattering in the strong radiation damping regime
Authors: Koga James , Esirkepov Timur Zh. , Bulanov Sergei V.
Published: September 2005

The motion of an electron can be strongly influenced by the radiation emitted by the electron during the interaction with petawatt class lasers focused to small spot sizes. In order to study this problem we have numerically integrated the equation of motion of a single electron interacting with an intense electromagnetic wave and calculated the backscattered spectra. Large differences are found between the case where damping is included and not included. In particular, the first harmonic of the backscattered radiation is downshifted and the overall amplitude of the spectra is smaller than in the case with no damping. An analytical expression for the downshift is obtained and found to agree fairly well with the numerical calculations.
Electron trajectories and gain in free-electron lasers with three-dimensional helical wiggler and ion-channel guiding
Authors: Mirzanejhad Saeed , Asri Mehdi
Published: September 2005

Deformation of steady-state trajectories of an electron, due to transverse inhomogeneity in a realizable three-dimensional helical wiggler field with ion-channel guiding, is studied. The Φ function that determines the rate of change of axial velocity with energy is derived and shows that transition to negative mass regime remains approximately unchanged under the influence of the three-dimensional effect of the wiggler. A detailed stability analysis of orbits is performed, with variation in relativistic factor γ included in the formalism, and a new stable branch is found for group-II orbit. Finally a formula for the small signal gain is derived with radiation forces in transverse components of the equation of motion included and results are compared with previous works in one-dimensional case.
Plasma sheaths in Hall discharge
Authors: Taccogna Francesco , Longo Savino , Capitelli Mario
Published: September 2005

The sheath region of a Hall discharge is studied in a four-dimensional phase space which consists of one spatial (radial in cylindrical metrics) and three velocity dimensions by means of a particle-in-cell∕Monte Carlo model coupled with a probabilistic method for the secondary electron emission. Different axial regions (anode, ionization, and acceleration zones) of the channel have been investigated using the local field approximation and distinguishing between inner and outer walls. The presheath and sheath structures are different in the three regions simulated showing a charge saturated regime in the acceleration region. Small differences in behavior for the external and internal walls of the channel are detected. Further, trapped ions are found near the walls in the acceleration region which could have an important effect on the wall recombination enhancing the axial electron current. The results could be used to obtain boundary conditions and lateral wall losses which are suitable for incorporation into one-axial and two-dimensional macroscopic models which simulate the bulk neutral plasma in Hall discharge.
A theoretical study of the structure of the liquid Ga-diamond (111) interface
Authors: Jiang Xu , Rice Stuart A.
Published: September 2005

We present the results of a computer simulation study of the structure of the interface between liquid Ga and the (111) face of diamond, with which we reinterpret the findings from an x-ray reflectivity study of that interface [W. J. Huisman, J. F. Peters, M. J. Zwanenburg, S. A. de Vries, T. E. Derry, D. Abernathy, and J. F. van der Veen, Nature (London) 390, 379 (1997); Surf. Sci. 402–404, 866 (1998)]. That experimental study has been interpreted to show that the contact of Ga with the (111) face of diamond induces the formation of Ga2 molecules for several layers into the bulk liquid, with the axes of the Ga2 molecules in successive layers oriented perpendicular to the diamond surface. No driving force for the proposed formation of Ga2 molecules is identified. The simulations reported in this paper are based on a model that permits chemical binding of Ga, as a dimer, to the CC double bonds in the reconstructed (111) face of diamond, thereby identifying the driving force for dimerization. We show that an isolated π complex with the Ga2 axis perpendicular to the CC double bond is stable. We then modify the pseudopotential-based self-consistent Monte Carlo simulation scheme for describing inhomogeneous liquid metals, using the calculated potential-energy surface of Ga2(CC) in the region close to the diamond surface. In this model only the Ga adjacent to the diamond is composed of dimers. The interfacial density distribution obtained from the simulations predicts an x-ray reflectivity that is in good agreement with that observed.
Localized modes in a one-dimensional diatomic chain of coupled spheres
Authors: Hladky-Hennion Anne-Christine , Allan Guy , de Billy Michel
Published: September 2005

This paper presents the propagation of waves along a one-dimensional “diatomic” chain made up to welded spheres, i.e., with two steel spheres of different diameters alternating. First, a theoretical analysis is presented, which gives the vibration modes of an infinite chain, leading to two low-frequency branches, separated by a band gap. A theoretical analysis is then performed on a finite chain, containing an even or an odd number of spheres. Depending on the parity of the number of spheres in the finite chain and on the ratio between the masses of the spheres, it points out that localized modes may appear in the band gap. The theoretical results have been validated by a comparison between numerical and experimental results. Many applications of such systems can therefore be found: acoustic filters, noise and vibration isolation, acoustic wave guiding, etc.
Effect of transverse nonuniformity of the rf field on the efficiency of microwave sources driven by linear electron beams
Authors: Nusinovich G. S. , Sinitsyn O. V.
Published: September 2005

This paper contains a simple analytical theory that allows one to evaluate the effect of transverse nonuniformity of the rf field on the interaction efficiency in various microwave sources driven by linear electron beams. The theory is, first, applied to the systems where the beams of cylindrical symmetry interact with rf fields of microwave circuits having Cartesian geometry. Also, various kinds of microwave devices driven by sheet electron beams (orotrons, clinotrons) are considered. The theory can be used for evaluating the efficiency of novel sources of coherent terahertz radiation.
Selective attachment of benzaldehyde on Si(100)-2×1: Structure, selectivity, and mechanism
Authors: Huang Hai Gou , Zhang Yong Ping , Cai Ying Hui , Huang Jing Yan , Yong Kian Soon , Xu Guo Qin
Published: September 2005

The interaction of benzaldehyde with the Si(100) surface has been investigated as a model system for understanding the interaction of conjugated π-electron systems with semiconductor surfaces. Vibrational features of chemisorbed benzaldehyde unambiguously demonstrate that the carbonyl group directly interacts with the Si surface dangling bonds, evidenced in the disappearance of the CO stretching mode around 1713cm−1 coupled with the retention of all vibrational signatures of its phenyl ring. X-ray photoemission spectroscopy shows that both C 1s and O 1s binding energies of the carbonyl group display large downshifts by 1.9 and 1.3 eV, respectively. Vibrational and electronic results show that the covalent attachment of benzaldehyde on Si(100) occurs in a highly selective manner through the direct interaction of both C and O atoms of the carbonyl group with a SiSi dimer to form a four-membered Si–C–O–Si ring at the interface, leaving a nearly unperturbed phenyl ring protruding into vacuum. This conclusion is further confirmed by the observation of a predominant protrusion for benzaldehyde adsorbed on Si(100)-2×1 in scanning tunneling microscopy experiments, consistent with the predication of density-functional theory calculation.
Extended x-ray absorption fine structure measurement of phase transformation in iron shocked by nanosecond laser
Authors: Yaakobi B. , Boehly T. R. , Meyerhofer D. D. , Collins T. J. B. , Remington B. A. , Allen P. G. , Pollaine S. M. , Lorenzana H. E. , Eggert J. H.
Published: September 2005

Extended x-ray absorption fine structure (EXAFS) measurements have been used to demonstrate the phase transformation from body-centered-cubic (bcc) to hexagonal-closely packed (hcp) iron due to nanosecond, laser-generated shocks. The EXAFS spectra are also used to determine the volume compression and temperature in the shocked iron, which are consistent with hydrodynamic simulations and with the compression inferred from velocity interferometric (VISAR) measurements. This is a direct, atomic-level and in situ proof of shock-induced transformation in iron. Thus, the EXAFS data can be used both for studying the phase transformation as well as for characterizing the crystal conditions (density, temperature) during the transformation.
Effect of dispersion on the relaxation-retardation time scale ratio
Authors: Ito Naoki , Richert Ranko
Published: September 2005

A simple relation between relaxation (modulus) and retardation (permittivity and compliance) times is determined for cases of dispersive instead of purely exponential response functions. An analytical solution for the Cole-Cole case and numerical treatments of the Cole-Davidson function reveal that the ratio of the relaxation- to retardation time constant is given by the ratio of the high- to low-frequency dielectric constant raised to the power of 1∕x, where x is the exponent that gauges the deviation from exponentiality.
Kinetics of crystal nucleation in undercooled droplets of Sb- and Te-based alloys used for phase change recording
Authors: Kalb J. A. , Spaepen F. , Wuttig M.
Published: September 2005

Droplets of molten alloys of composition Ge12Sb88, Ag0.055In0.065Sb0.59Te0.29, Ge4Sb1Te5, and Ge2Sb2Te5, used for optical data storage, surrounded by a molten dehydrated B2O3 flux were undercooled to 40–80K below their liquidus temperature in a differential thermal analyzer. The crystal-melt interfacial energy was calculated from the nucleation temperature using the classical nucleation theory, which gave values of around 0.20 times the heat of fusion per atom in the interface for all alloys. This value should be a lower limit since we did not establish that nucleation was homogeneous in the experiments. The steady-state nucleation rate was calculated between the liquidus and glass transition temperatures and was higher for the GeSbTe alloys than for the Sb-rich alloys. Nevertheless, the nucleation rates appear too high to allow amorphization under operating conditions for the highest achievable cooling rates. Therefore, we conclude that it is the presence of an incubation time that makes amorphization and therefore phase change recording possible in both optical and electronic media.
Time domain reflectometry-based liquid level sensor
Authors: Di Sante Raffaella
Published: September 2005

An innovative system based on the time domain reflectometry (TDR) principle for the measurement of liquid level and interface is presented in this paper. The application of time domain reflectometry in liquid level monitoring is relatively recent and most promising due to the achievement of very high levels of accuracy and repeatability and to the substantial advantages over traditional sensors used for level sensing. After a brief review and description of the operating principle and a comparison to traditional techniques, the system is described with the results obtained using water as a sample liquid and water and diesel fuel to show the system capability of detecting liquid-liquid interfaces.
Aliasing errors in measurements of beam position and ellipticity
Authors: Ekdahl Carl
Published: September 2005

Beam position monitors (BPMs) are used in accelerators and ion experiments to measure currents, position, and azimuthal asymmetry. These usually consist of discrete arrays of electromagnetic field detectors, with detectors located at several equally spaced azimuthal positions at the beam tube wall. The discrete nature of these arrays introduces systematic errors into the data, independent of uncertainties resulting from signal noise, lack of recording dynamic range, etc. Computer simulations were used to understand and quantify these aliasing errors. If required, aliasing errors can be significantly reduced by employing more than the usual four detectors in the BPMs. These simulations show that the error in measurements of the centroid position of a large beam is indistinguishable from the error in the position of a filament. The simulations also show that aliasing errors in the measurement of beam ellipticity are very large unless the beam is accurately centered. The simulations were used to quantify the aliasing errors in beam parameter measurements during early experiments on the DARHT-II accelerator, demonstrating that they affected the measurements only slightly, if at all.
Electrical and material characterizations of high-permittivity HfxTi1−xO2 gate insulators
Authors: Li M. , Zhang Z. , Campbell S. A. , Gladfelter W. L. , Agustin M. P. , Klenov D. O. , Stemmer S.
Published: September 2005

High-permittivity hafnium titanate (HfxTi1−xO2) films of various compositions have been investigated. Chemical-vapor deposited thin films have well-controlled composition and a smooth surface. Thicker films show large, highly anisotropic grains with their long axis in the plane of the film. Electrical measurements showed that the interfacial layer equivalent oxide thickness (EOT) decreases linearly with increasing Hf content. Electron energy-loss spectroscopy in scanning transmission electron microscopy indicates that the interfacial layer is primarily SiO2. In the composition range of 0.3<x<0.5, the permittivity of the high-κ films increases linearly with increasing Ti content. For values of x<0.3, the film’s permittivity is close to that of pure HfO2(∼20), while for Ti-rich films the permittivity is close to that of pure TiO2(∼50). For films with a physical thickness less than 10 nm, the leakage current decreases as Ti increases for a fixed EOT.
Structural variation of cubic and hexagonal MgxZn1−xO layers grown on MgO(111)∕c-sapphire
Authors: Vashaei Z. , Minegishi T. , Suzuki H. , Hanada T. , Cho M. W. , Yao T. , Setiawan A.
Published: September 2005

We report on the structure study of MgxZn1−xO films and, in particular, we will focus on MgxZn1−xO layers with x=0.28 and 0.41 MgxZn1−xO layers with different crystal structures of cubic and wurtzite that have been grown by plasma-assisted molecular-beam epitaxy on MgO∕c-sapphire with Mg∕Zn flux ratio control. The MgxZn1−xO films have been characterized by high-resolution transmission electron microscopy (HRTEM) and high-resolution x-ray diffraction. The dependence of the cation-anion bond length to Mg content has been studied. A virtual crystal model of MgZnO has been applied to interpret the bond-length variation. HRTEM results indicate that the initial stage of the MgZnO growth on a MgO buffer layer starts with a cubic structure even in the case of a wurtzite structure at the end of growth.
Pulsed-laser deposition of high-k titanium silicate thin films
Authors: Brassard D. , El Khakani M. A.
Published: September 2005

We report on the growth of high-k titanium silicate (TiSiO4) thin films by means of the pulsed-laser ablation of a TiO2∕SiO2 composite target. We present a systematic investigation of the effect of the oxygen background pressure [P(O2)] and the substrate deposition temperature (Td) on both the structural and electrical properties of the films. Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy analyses revealed the presence of Ti–O–Si bonds in the films, confirming thereby the formation of the titanium silicate phase. In particular, the P(O2) is shown to be a key factor for controlling the morphology, the oxygen content, and consequently the electrical properties of the titanium silicate films. Indeed, while the films deposited at P(O2)⩾50mTorr present some porosity, a high roughness, and poor dielectric and breakdown field characteristics, those grown at P(O2)<10mTorr and postannealed (at 600°C in O2) are shown to exhibit a dense and smooth microstructure together with excellent dielectric properties. On the other hand, the resistivity of the vacuum-deposited films is found to decrease remarkably when Td is raised from 20to600°C. Indeed, a strong correlation (over 14 decades) is established between the resistivity of the titanium silicate films and their oxygen content, pointing up the crucial role of their full oxidization. Thus, by identifying the optimal growth conditions, we were able to achieve dense and stoichiometric high-k titanium silicate films combining not only a dielectric constant as high as 33 and a dissipation factor as low as 0.01 but also a high breakdown field of 4MV∕cm.
Simulation of a semitransparent conducting mesh electrode for plasma immersion ion implantation
Authors: Powles R. C. , Kwok D. T. K. , McKenzie D. R. , Bilek M. M. M.
Published: September 2005

Particle-in-cell simulations of plasma evolution in the vicinity of a mesh electrode that is semitransparent to ions are presented. Space-charge accumulation and ion focusing have an important effect on the ion trajectories and ion energy distribution inside the mesh. The results indicate that when such an electrode is used to assist plasma immersion ion implantation of insulating targets, the initial plasma conditions and mesh geometry are key factors in achieving optimum dose uniformity and implanted ion energy.
Simple theory of the interband optical absorption in an external electric field for optoelectronic materials
Authors: Chakraborty P. K. , Bhattacharya S. , Ghatak K. P.
Published: September 2005

We study theoretically the interband optical-absorption coefficient (OAC) of optoelectronic materials within the framework of the three-band model of Kane [J. Phys. Chem. Solids 12, 181 (1959)] in the presence of an external electric field for modified photon energy (ℏω1) below and above the band gap (Eg), respectively. The optical matrix element depends on the electron wave vector k and this practical aspect has been incorporated in the present analysis. It has been found, taking InAs, InSb, Hg1−xCdxTe, and In1−xGaxAsyP1−y lattice matched to InP as examples of optoelectronic compounds for numerical computations, that for modified photon energies below the band gap, the OAC exhibits an exponential fall off with the electric field and the photon energy, respectively. For the opposite inequality, the OAC oscillates with the modified photon energy without the consideration of the Wannier-Stark levels, which generally exist in a band due to the presence of an external electric field. In both cases, the OAC exhibits the singularity when the incident photon energy (ℏω0) tends to Eg and the magnitude of the OAC depends to a large extent on the numerical values of the energy-band constants of the said compounds. In addition, the simplified results of the OAC for materials having parabolic energy bands have also been obtained from the present generalized analysis under certain limiting conditions.
Higher-order contribution to obliquely nonlinear electron-acoustic waves with electron beam in a magnetized plasma
Authors: El-Labany S. K. , El-Taibany W. F. , El-Abbasy O. M.
Published: September 2005

Propagation of electron-acoustic waves in a strongly magnetized four-component plasma consisting of cold and hot electrons, a warm electron beam, and stationary ions is investigated. The present model considered weakly dispersive and strongly magnetized plasma in the limit of long wavelengths. The introduction of an electron beam allows the existence of electron-acoustic solitons with velocity related to the beam velocity. With increasing the beam velocity and the beam temperature, both the soliton amplitude and the width increase. Applying a reductive perturbation theory, a nonlinear Zakharov-Kuznetsov (ZK) equation for the first-order perturbed potential and a linear inhomogeneous Zakharov-Kuznetsov (ZK-type) equation for the second-order perturbed potential are derived. Stationary solutions of these coupled equations are obtained using a renormalization method. These solutions admit either compressive or rarefactive soliton type depending on the electron-beam parameters. Moreover, the dependence of the solution on the beam parameters, obliqueness on the magnetic field, and the magnetic field itself is also investigated. The application of the present investigation to the broadband electrostatic noise in the dayside auroral zone of the Earth’s magnetosphere is considered.
Improvement of the thickness distribution of a quartz crystal wafer by numerically controlled plasma chemical vaporization machining
Authors: Shibahara Masafumi , Yamamura Kazuya , Sano Yasuhisa , Sugiyama Tsuyoshi , Endo Katsuyoshi , Mori Yuzo
Published: September 2005

To improve the thickness uniformity of thin quartz crystal wafer, a new machining process that utilizes an atmospheric pressure plasma was developed. In an atmospheric pressure plasma process, since the kinetic energy of ions that impinge to the wafer surface is small and the density of the reactive species is large, high-efficiency machining without damage is realized, and the thickness distribution is corrected by numerically controlled scanning of the quartz wafer to the localized high-density plasma. By using our developed machining process, the thickness distribution of an AT cut wafer was improved from 174 nm [peak to valley (p-v)] to 67 nm (p-v) within 94 s. Since there are no unwanted spurious modes in the machined quartz wafer, it was proved that the developed machining method has a high machining efficiency without any damage.
Fermi-level effects in semiconductor processing: A modeling scheme for atomistic kinetic Monte Carlo simulators
Authors: Martin-Bragado I. , Castrillo P. , Jaraiz M. , Pinacho R. , Rubio J. E. , Barbolla J. , Moroz V.
Published: September 2005

Atomistic process simulation is expected to play an important role for the development of next generations of integrated circuits. This work describes an approach for modeling electric charge effects in a three-dimensional atomistic kinetic Monte Carlo process simulator. The proposed model has been applied to the diffusion of electrically active boron and arsenic atoms in silicon. Several key aspects of the underlying physical mechanisms are discussed: (i) the use of the local Debye length to smooth out the atomistic point-charge distribution, (ii) algorithms to correctly update the charge state in a physically accurate and computationally efficient way, and (iii) an efficient implementation of the drift of charged particles in an electric field. High-concentration effects such as band-gap narrowing and degenerate statistics are also taken into account. The efficiency, accuracy, and relevance of the model are discussed.
Current instability and plasma waves generation in ungated two-dimensional electron layers
Authors: Dyakonov Michel , Shur Michael S.
Published: September 2005

We predict instability of the steady state with a direct current for an ungated two-dimensional (2D) electron layer. This instability caused by the current flow is similar to the “shallow water” instability in the gated 2D electron gas [see M. Dyakonov and M. S. Shur, Phys. Rev. Lett. 71, 2465 (1993)]. The mathematics of the problem correspond to “deep water” solutions for plasma waves. Just like in the “shallow water” case, this instability occurs when the boundary conditions correspond to zero ac voltage at the source and zero ac current at the drain. Such boundary conditions can be realized using either an external circuit or a depleted region at the drain. For the same device dimensions and electron mobility, the plasma wave generated in an ungated 2D device has a much higher frequency and, as a consequence, a much higher resonance quality factor, which makes the ungated devices promising for applications in resonant terahertz detectors.
Effects of the oxygen precursor on the electrical and structural properties of HfO2 films grown by atomic layer deposition on Ge
Authors: Spiga S. , Wiemer C. , Tallarida G. , Scarel G. , Ferrari S. , Seguini G. , Fanciulli M.
Published: September 2005

We report on the growth by atomic layer deposition of HfO2 films on HF-last treated Ge(001) substrates using HfCl4 as a Hf source and either O3 or H2O as oxygen sources. The choice of the oxygen precursor strongly influences the structural, chemical, and electrical properties of the HfO2 films: Those grown using H2O exhibit local epitaxial growth, a large amount of contaminants such as chlorine and carbon, and a large frequency dispersion of the capacitance-voltage (C–V) characteristics. Films grown using O3 are good insulators and exhibit well-shaped C–V curves with a minimum frequency dispersion of the accumulation capacitance. Moreover, they are smoother, less crystallized, and with a lower contaminant content than those grown using H2O. However, the use of O3 leads to the formation of a 2nm thick layer, possibly GeOx, at the HfO2∕Ge interface.
Field-programmable data acquisition and processing channel for optical tomography systems
Authors: Castillo Sergio Garcia , Ozanyan Krikor B.
Published: September 2005

This article introduces the design and implementation of an affordable high-performance set of identical data acquisition channels with digital processing capabilities. Each channel incorporates a versatile 16-bit sigma-delta analog-to-digital converter (ADC) with reconfigurable filter characteristics. The main component of each channel, a low-cost field-programmable gate array (FPGA), controls the ADC, serves as a random access memory to store the ADCs user-defined filters, and performs digital processing. A special case is illustrated, with the FPGA software configured to perform lock-in detection, which is widely applied in a number of tomography modalities. The detection scheme, based on a quadrature demodulator, utilizes only a fraction of the FPGA resources and introduces errors orders of magnitude less than the quantization error of the ADC. Implementations other than a lock-in amplifier can be realized without additional hardware intervention.