bluuebunny/crossref_metadata_2025 huggingface dataset:
East Molokai and other Kea‐trend volcanoes: Magmatic processes and sources as they migrate away from the Hawaiian hot spot
Authors: Xu Guangping , Frey Frederick A. , Clague David A. , Weis Dominique , Beeson Melvin H.
Published: May 2005

There are geochemical differences between shield lavas from the two parallel trends, Kea and Loa, defined by young Hawaiian volcanoes. The shield of East Molokai volcano, at greater than 1.5 Ma, is the oldest volcano on the Kea trend. Sequences of older tholeiitic to younger alkalic basalt that erupted as this volcano evolved from the shield to postshield stage of volcanism are well exposed. Much younger, ∼0.34–0.57 Ma, alkalic basalt and basanite erupted during rejuvenated stage volcanism. Like rejuvenated stage lavas erupted at other Hawaiian volcanoes, rejuvenated stage East Molokai lavas have relatively low 87Sr/86Sr and high 143Nd/144Nd. Such ratios reflect a source component with a long‐term depletion in abundance of incompatible elements. On the basis of positive correlations of 87Sr/86Sr versus 206Pb/204Pb and negative correlations of these isotopic ratios with Nb/Zr, a smaller proportion of this depleted component also contributed to the late shield/postshield lavas erupted at East Molokai and the other Kea‐trend volcanoes, Haleakala and Mauna Kea. At each of these Kea‐trend volcanoes, as the volcano moved away from the hot spot, the extent of melting and magma supply from the mantle decreased, the depth of melt segregation increased, and there was an increasing role for a component with long‐term relative depletion in incompatible elements. This depleted component has Kea‐trend Pb isotopic characteristics and relatively low 208Pb/204Pb at a given 206Pb/204Pb, and it is probably not related to oceanic lithosphere or the source of mid‐ocean ridge basalt. The overlap in Sr, Nd, and Pb isotope ratios of recent Kilauea shield lavas and 550 ka Mauna Kea shield lavas has been used to argue that Kea‐trend shield volcanism samples a vertically continuous, geochemically distinct stripe which persisted in the hot spot source for 550 kyr (Eisele et al., 2003; Abouchami et al., 2005). As Kea‐trend volcanoes migrate away from the hot spot and evolve from the shield to postshield stage, there are systematic changes in Sr, Nd, and Pb isotope ratios. However, the overlap of Sr, Nd, and Pb isotope ratios in late shield/postshield lavas from Mauna Kea (<350 ka) and East Molokai (∼1.5 Ma) show that the periphery of the hot spot sampled by Kea‐trend postshield lavas also had long‐term geochemical homogeneity.
Testing the IZZI protocol of geomagnetic field intensity determination
Authors: Yu Yongjae , Tauxe Lisa
Published: May 2005

A new paleointensity determination protocol (the IZZI method) was recently proposed. The IZZI technique combines the Aitken (in‐field, zero‐field; IZ) and Coe (zero‐field, in‐field; ZI) methods. The IZZI protocol of paleointensity method was experimentally tested, showing a strong angular dependence resulting from the undemagnetized portions of partial thermoremanent magnetization (pTRM) tails. The IZZI method is better than the conventional techniques (Aitken, Coe, and Thellier) in three respects: (1) it can easily detect the angular dependence; (2) it provides a quantitative estimate for the consistency of the outcome between IZ and ZI step; and (3) it is quicker because the extra pTRM tail check step is unnecessary.
A high‐precision model of first‐order reversal curve (FORC) functions for single‐domain ferromagnets with uniaxial anisotropy
Authors: Newell Andrew J.
Published: May 2005

Plots of the first‐order reversal curve (FORC) function are used to characterize ferromagnetic particles in rocks. The function is based on classical Preisach theory, which represents magnetic hysteresis by elementary loops with displacementHuand half widthHc. Using analytical and numerical integration of single‐particle magnetization curves, a high‐precision FORC function is calculated for a sample with randomly oriented, noninteracting, elongated single‐domain (SD) particles. Some properties of the FORC function are independent of the distribution of particle orientations and shapes. There is a negative peak near theHuaxis, and the FORC function is identically zero forHu> 0. The negative peak, previously attributed to particle interactions, is due to the increasing slope of a reversible magnetization curve near a jump. This peak is seen in experimental FORC functions of SD samples but not of samples with larger particles, probably because of Barkhausen jumps. The second feature is not seen in any experimental FORC function. A spread of the function toHu> 0 can be caused by particle interactions or nonuniform magnetization.
Response of seismicity to Coulomb stress triggers and shadows of the 1999 Mw = 7.6 Chi‐Chi, Taiwan, earthquake
Authors: Ma Kuo‐Fong , Chan Chung‐Han , Stein Ross S.
Published: May 2005

The correlation between static Coulomb stress increases and aftershocks has thus far provided the strongest evidence that stress changes promote seismicity, a correlation that the Chi‐Chi earthquake well exhibits. Several studies have deepened the argument by resolving stress changes on aftershock focal mechanisms, which removes the assumption that the aftershocks are optimally oriented for failure. Here one compares the percentage of planes on which failure is promoted after the main shock relative to the percentage beforehand. For Chi‐Chi we find a 28% increase for thrust and an 18% increase for strike‐slip mechanisms, commensurate with increases reported for other large main shocks. However, perhaps the chief criticism of static stress triggering is the difficulty in observing predicted seismicity rate decreases in the stress shadows, or sites of Coulomb stress decrease. Detection of sustained drops in seismicity rate demands a long catalog with a low magnitude of completeness and a high seismicity rate, conditions that are met at Chi‐Chi. We find four lobes with statistically significant seismicity rate declines of 40–90% for 50 months, and they coincide with the stress shadows calculated for strike‐slip faults, the dominant faulting mechanism. The rate drops are evident in uniform cell calculations, 100‐month time series, and by visual inspection of the M ≥ 3 seismicity. An additional reason why detection of such declines has proven so rare emerges from this study: there is a widespread increase in seismicity rate during the first 3 months after Chi‐Chi, and perhaps many other main shocks, that might be associated with a different mechanism.
Joint analysis of ISM and TES spectra: The utility of multiple wavelength regimes for Martian surface studies
Authors: Mustard John F. , Cooper Christopher D.
Published: May 2005

A number of spectroscopic instruments with high resolution and complementary wavelength ranges, including TES, THEMIS, OMEGA, and CRISM, will give an unprecedented wealth of information about the surface of Mars. In order to maximize the utility of these data sets, they need to be joined to provide pan‐spectral coverage of the surface of Mars that will give information on different types of absorption processes in surface materials. We have performed a test of this approach using ISM and TES data to provide near‐infrared and thermal infrared coverage of the selected regions observed by both instruments. Gridding and registering the two data sets to a common reference allows investigations of regional and global properties of the surface. Here we investigate the variability in the spectral properties of low‐albedo regions, particularly Type I (basaltic) and Type II regions, and relate these variations to probably mineralogic composition. ISM and TES data agree on the presence of pyroxenes in Type I regions but may indicate a lack of pyroxene in the Type II material, although this is inconclusive. Type I regions in general appear to be uniform in composition, and surface variations are primarily controlled by mixing with dust. Temporal variations in surface reflectance make analysis of the differences in spectral properties between eastern and western Syrtis Major difficult but indicate that slope differences may not be due to intimate cementing of dark and light materials but rather due to penetrative oxidation of the surfaces of basaltic materials. These results demonstrate that the complementary strengths of multiple wavelength regimes allow greater understanding of surface composition and processes.
Dust detection in the ISS environment using filmed microchannel plates
Authors: Carpenter J. D. , Stevenson T. J. , Fraser G. W. , Lapington J. S. , Brandt D.
Published: May 2005

Microchannel plates bearing a 60 nm thick aluminum film have been exposed to the external International Space Station (ISS) environment for 756 days. Postretrieval analysis has revealed holes in the aluminum film, which may have resulted from impacts by dust particles as small as a few tens of nanometers in diameter. Such particles have been undetectable by previously flown, much thicker foils. The flux of such particles appears to be consistent with the extrapolation, to this particle size regime, of current models for the near‐Earth dust and debris environment and data from previously flown foils.
North Pacific halocline and cold climate induced by Panamanian Gateway closure in a coupled ocean‐atmosphere GCM
Authors: Motoi Tatsuo , Chan Wing‐Le , Minobe Shoshiro , Sumata Hiroshi
Published: May 2005

The influence of the closure of the Panamanian Gateway during the late Cenozoic on climate in and around the North Pacific is investigated by using a coupled ocean‐atmosphere general circulation model with an open and closed gateway. In the case of an open (closed) gateway, deep convection is present (absent) in the North Pacific. The deep convection is associated with surface saline water transported from the subtropical Atlantic through the open gateway to the North Pacific. On the other hand, with the closed gateway, the lack of saline water transport from the Atlantic induces halocline formation over the subarctic Pacific with cold climate. The deep convection in the North Pacific leads to a vigorous thermohaline circulation with larger meridional heat transport, and causes warmer climate in and around the North Pacific. These results are generally consistent with paleoceanographic and paleoclimatic estimates related to the closure of the Panamanian Gateway.
Correlations between magnetic anomalies and surface geology antipodal to lunar impact basins
Authors: Richmond N. C. , Hood L. L. , Mitchell D. L. , Lin R. P. , Acuña M. H. , Binder A. B.
Published: May 2005

Previous work has shown that the strongest concentrations of lunar crustal magnetic anomalies are located antipodal to four large, similarly aged impact basins (Orientale, Serenitatis, Imbrium, and Crisium). Here, we report results of a correlation study between magnetic anomaly clusters and geology in areas antipodal to Imbrium, Orientale, and Crisium. Unusual geologic terranes, interpreted to be of seismic or ejecta origin associated with the antipodal basins, have been mapped antipodal to both Orientale and Imbrium. All three antipode regions have many high‐albedo swirl markings. Results indicate that both of the unusual antipode terranes and Mare Ingenii (antipodal to Imbrium) show a correlation with high‐magnitude crustal magnetic anomalies. A statistical correlation between all geologic units and regions of medium to high magnetization when high‐albedo features are present (antipodal to Orientale) may suggest a deep, possibly seismic origin to the anomalies. However, previous studies have provided strong evidence that basin ejecta units are the most likely sources of lunar crustal anomalies, and there is currently insufficient evidence to differentiate between an ejecta or seismic origin for the antipodal anomalies. Results indicate a strong correlation between the high‐albedo markings and regions of high magnetization for the Imbrium, Orientale, and Crisium antipodes. Combined with growing evidence for an Imbrian age to the magnetic anomalies, this supports a solar wind deflection origin for the lunar swirls.
Spatiotemporal patterns driven by autocatalytic internal reaction noise
Authors: Hochberg David , Zorzano M.-P. , Morán Federico
Published: May 2005

The influence that intrinsic local-density fluctuations can have on solutions of mean-field reaction-diffusion models is investigated numerically by means of the spatial patterns arising from two species that react and diffuse in the presence of strong internal reaction noise. The dynamics of the Gray–Scott (GS) model [P. Gray and S. K. Scott, Chem. Eng. Sci. 38, 29 (1983); P. Gray and S. K. Scott, Chem. Eng. Sci.39, 1087 (1984); P. Gray and S. K. Scott,J. Phys. Chem. 89, 22 (1985)] with a constant external source is first cast in terms of a continuum field theory representing the corresponding master equation. We then derive a Langevin description of the field theory and use these stochastic differential equations in our simulations. The nature of the multiplicative noise is specified exactly without recourse to assumptions and turns out to be of the same order as the reaction itself, and thus cannot be treated as a small perturbation. Many of the complex patterns obtained in the absence of noise for the GS model are completely obliterated by these strong internal fluctuations, but we find novel spatial patterns induced by this reaction noise in the regions of parameter space that otherwise correspond to homogeneous solutions when fluctuations are not included.
Electron density, exchange-correlation density, and bond characterization from the perspective of the valence-bond theory. II. Numerical results
Authors: Rincón Luis , Alvarellos J. E. , Almeida Rafael
Published: May 2005

In this work we have analyzed the bond character of a series of representative diatomic molecules, using valence bond and the atoms in molecules points of view. This is done using generalized valence-bond calculations. We have also employed more exigent levels, as configuration interaction with single and double excitations and complete active space self-consistent field calculations, in order to validate the generalized valence-bond results. We have explored the possibility that the known delocalization index, and a parameter that measures the excess or defect population within a given atomic basin, can be considered as indicators of the character of bond interaction. We conclude that for a proper description of the bond character, the global behavior of both the charge and two-electron densities should be considered.
Polymer distribution in connected spherical domains
Authors: Sousa A. F. , Pais A. A. C. C. , Linse P.
Published: May 2005

The distribution of neutral and charged polymers with different flexibilities between two spheres of varying volume connected by a short and narrow cylinder has been investigated by Monte Carlo simulations. The uncharged chain displayed mostly a single-sphere occupancy due to the high conformational entropy penalty of crossing the cylindrical domain, whereas for the charged polymer a double-sphere occupancy was obtained, except for very different spherical volumes. The origin of this different occupancy behavior stems from the counterion entropy. At increasing stiffness, a stronger preference for double-sphere occupancy was predicted.
Surface and bulk dissolution properties, and selectivity of DNA-linked nanoparticle assemblies
Authors: Lukatsky D. B. , Frenkel Daan
Published: May 2005

Using a simple mean-field model, we analyze the surface and bulk dissolution properties of DNA-linked nanoparticle assemblies. We find that the dissolution temperature and the sharpness of the dissolution profiles increase with the grafting density of the single-stranded DNA “probes” on the surface of colloids. The surface grafting density is controlled by the linker occupation number, in analogy with quantum particles obeying fractional statistics. The dissolution temperature increases logarithmically with the salt concentration. This is in agreement with the experimental findings [R. Jin, G. Wu, Z. Li, C. A. Mirkin, and G. C. Schatz, J. Am. Chem. Soc. 125, 1643 (2003)]. By exploiting the unique phase behavior of DNA-coated colloids, it should be possible to detect multiple “targets” in a single experiment by essentially mapping the DNA base-pair sequence onto the phase behavior of DNA-linked nanoparticle solution.
Product distributions, rate constants, and mechanisms of LiH+H reactions
Authors: Defazio Paolo , Petrongolo Carlo , Gamallo Pablo , González Miguel
Published: May 2005

We present a quantum-mechanical investigation of the LiH depletion reaction LiH+H→Li+H2 and of the H exchange reaction LiH+H′→LiH′+H. We report product distributions, rate constant, and mechanism of the former, and rate constant and mechanism of the latter reaction. We use the potential-energy surface by Dunne et al. [Chem. Phys. Lett. 336, 1 (2001)], the real-wave-packet method by Gray and Balint-Kurti [J. Chem. Phys. 108, 950 (1998)], and the J-shifting approximation. The H21 nuclear-spin statistics and progressions of vib-rotational states (v′,j′) rule both initial-state-resolved and thermal product distributions, which have saw-toothed shapes with odd j′ preferred with respect to even j′. At high collision energies and temperatures, we obtain a regular 3-to-1 intensity alternation of rotational states. At low collision energies and temperatures, the degeneracy and density of many H2 levels can, however, give more irregular distributions. During the collision, the energy flows from the reactant translational mode to the product vibration and recoil ones. The rate constants of both reactions are not Arrhenius type because the reactions are barrier-less. The low-temperature, LiH depletion rate constant is larger than the H exchange one, whereas the contrary holds at high temperature. The real-time mechanisms show the nuclear rearrangements of the nonreactive channel and of the reactive ones, and point out that the LiH depletion is preferred over the H exchange at short times. This confirms the rate-constant results.
Effect of relativity on the ionization spectra of the xenon fluorides XeFn (n=2, 4, 6)
Authors: Pernpointner Markus , Cederbaum Lorenz S.
Published: May 2005

Noble gas compounds exhibit special chemical bonding situations and have been investigated by various spectroscopic and theoretical techniques. In this work we calculate the ionization spectra of the xenon fluorides (XeF2,XeF4, and XeF6) in the valence and subvalence (down to Xe4d) areas by application of the recently developed Dirac–Hartree–Fock one-particle propagator technique. In this technique, the relativistic (four-component) and electron correlation effects are computed simultaneously. The xenon compounds show considerable spin–orbit splitting strongly influencing the photoelectron spectrum not reproducible in prior calculations. Comparison to one-component methods is made and the occurring satellite structures are interpreted. The satellite structures can be attributed either to the breakdown of the one-particle picture or to a reflection of intra-atomic and interatomic Auger decay processes within the molecule.
Delayed recombination of detrapped space-charge carriers in poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene]-based light-emitting diode
Authors: Sinha S. , Monkman A. P.
Published: May 2005

We report the observation of a spectroscopically resolved delayed electrofluorescence (DEF) in the time domain of nanosecond to microsecond (depending on temperature, in the range of 30–290 K, as well as bias) from light-emitting diodes based on poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene]. The decay kinetics of this DEF are always found to be biexponential in nature. The fast decaying component with a lifetime of ∼40ns is attributed to the back transfer of nonemissive (or very weakly emissive) interchain excited singlets (partially charge-transfer states) to emissive intrachain excited singlets (this component is called DEFCT). The relatively slower decaying component with a lifetime of ∼0.2–6.2μs (depending on temperature as well as bias) is attributed to the recombination of detrapped space-charge carriers at the polymer-electrode interfaces (this component is called DEFSC). The intensity of DEFSC increases as the temperature is increased from 30 to 290 K, although it is weak at low temperature (<100K). The temperature dependence of the recombination rate of the detrapped space-charge carriers yields two activation energies of 2.2 and 40 meV below and above ∼130K, respectively. The existence of these two activation energies is explained on the assumption of electrons being in shallow traps and holes in deep traps. Also, our data indicate that the space-charge carriers generally act as major quenching sites (especially at 290 K) for triplet excitons in polymer light-emitting diodes.
The distribution of impurities in the interfaces and window layers of thin-film solar cells
Authors: Emziane M. , Durose K. , Halliday D. P. , Romeo N. , Bosio A.
Published: May 2005

We report a systematic multielement study of impurities in CdS window layers by dynamic and quantitative secondary-ion-mass spectrometry (SIMS) with high depth resolution. The study was carried out on CdTe∕CdS solar cell structures, with the glass substrate removed. The analysis proceeded from the transparent conductive oxide free surface to the CdTe absorbing layer with a view to examining the influence of the CdCl2 heat treatment on the distribution and concentration of impurities in the structures. Special attention was paid to the impurities present in the CdS window layer that may be electrically active, and therefore affect the characteristics of the CdTe∕CdS device. It was shown that Cl, Na, and Sb impurities had higher concentrations in CdS following cadmium chloride (CdCl2) heat treatment while Pb, O, Sn, and Cu conserved the same concentration. Furthermore, Zn, Si, and In showed slightly lower concentrations on CdCl2 treatment. Possible explanations of these changes are discussed and the results compared with previous SIMS measurements from the “back wall” (i.e., from the CdTe free surface through the glass substrate) obtained from the same structures.
Misfit dislocations in nanoscale ferroelectric heterostructures
Authors: Nagarajan V. , Jia C. L. , Kohlstedt H. , Waser R. , Misirlioglu I. B. , Alpay S. P. , Ramesh R.
Published: May 2005

We present a quantitative study of the thickness dependence of the polarization and piezoelectric properties in epitaxial (001) PbZr0.52Ti0.48O3 films grown on (001) SrRuO3-buffered (001) SrTiO3 substrates. High-resolution transmission electron microscopy reveals that even the thinnest films (∼8nm) are fully relaxed with a dislocation density close to 1012cm−2 and a spacing of approximately 12 nm. Quantitative piezoelectric and ferroelectric measurements show a drastic degradation in the out-of-plane piezoelectric constant (d33) and the switched polarization (ΔP) as a function of decreasing thickness. In contrast, lattice-matched ultrathin PbZr0.2Ti0.8O3 films that have a very low dislocation density show superior ferroelectric properties. Supporting theoretical calculations show that the variations in the strain field around the core of the dislocation leads to highly localized polarization gradients and hence strong depolarizing fields, which result in suppression of ferroelectricity in the vicinity of a dislocation.
Improvement of interfacial and dielectric properties of sputtered Ta2O5 thin films by substrate biasing and the underlying mechanism
Authors: Huang A. P. , Chu Paul K.
Published: May 2005

The use of tantalum pentoxide (Ta2O5) thin films as advanced gate dielectrics in integrated circuits has been hampered by thermodynamic instability at the Ta2O5/Si interface. We have demonstrated the fabrication of crystalline Ta2O5 thin films on n-type Si (100) at lower substrate temperature by means of substrate biasing. In the work reported here, the influence of the substrate bias on the interfacial and dielectric characteristics of the Ta2O5 thin films is investigated in details. Our results show that by applying a suitable bias to the Si substrate, the dielectric properties of Ta2O5 thin films can be improved. Using a substrate bias of −200 V, the thin film has a permittivity of 34 and leakage current density of 10−7A∕cm2 at an electric field of 800 kV/cm. The effects and mechanism of the bias on the interfacial and dielectric characteristics are described.
Stationary scanning x-ray source based on carbon nanotube field emitters
Authors: Zhang J. , Yang G. , Cheng Y. , Gao B. , Qiu Q. , Lee Y. Z. , Lu J. P. , Zhou O.
Published: May 2005

We report a field emission x-ray source that can generate a scanning x-ray beam to image an object from multiple projection angles without mechanical motion. The key component of the device is a gated carbon nanotube field emission cathode with an array of electron emitting pixels that are individually addressable via a metal–oxide–semiconductor field effect transistor-based electronic circuit. The characteristics of this x-ray source are measured and its imaging capability is demonstrated. The device can potentially lead to a fast data acquisition rate for laminography and tomosynthesis with a simplified experimental setup.
Computation of electrostatic forces between solvated molecules determined by the Poisson–Boltzmann equation using a boundary element method
Authors: Lu Benzhuo , Zhang Deqiang , McCammon J. Andrew
Published: May 2005

A rigorous approach is proposed to calculate the electrostatic forces among an arbitrary number of solvated molecules in ionic solution determined by the linearized Poisson–Boltzmann equation. The variational principle is used and implemented in the frame of a boundary element method (BEM). This approach does not require the calculation of the Maxwell stress tensor on the molecular surface, therefore it totally avoids the hypersingularity problem in the direct BEM whenever one needs to calculate the gradient of the surface potential or the stress tensor. This method provides an accurate and efficient way to calculate the full intermolecular electrostatic interaction energy and force, which could potentially be used in Brownian dynamics simulation of biomolecular association. The method has been tested on some simple cases to demonstrate its reliability and efficiency, and parts of the results are compared with analytical results and with those obtained by some known methods such as adaptive Poisson–Boltzmann solver.
Low-temperature epitaxial Ni silicidation: The role of hyperthermal species
Authors: Tsubouchi Nobuteru , Horino Yuji
Published: May 2005

We present the results of Ni silicidation on a Si(111) surface employing a mass-selected hyperthermal Ni−58 ion beam at 100 eV and discuss the reaction mechanism compared with the conventional Ni silicidation process. It is found that the Ni silicide formation using this technique is different from that achieved by conventional methods such as high-energy Ni-ion implantation or evaporation with thermal species. Namely, the Ni silicide phase formed at 230 °C using hyperthermal ions in this study is Ni-rich Ni2Si, in contrast to Si-rich disilicide NiSi2, ordinarily formed when high-energy Ni ions or thermal Ni beams react with Si at elevated temperatures. In addition, this layer is formed epitaxially on Si in spite of a low substrate temperature of 230 °C, while a polycrystalline Ni silicide layer is formed with conventional Ni-rich silicidation. This suggests that the reaction mechanism of the silicide formation with hyperthermal Ni particles is different from that using higher- or thermal-energy Ni particles. The atomic rearrangement induced by the thermal spikes most likely plays an important role in the Ni silicidation process employing hyperthermal species.
Photoluminescence enhancement of Si nanocrystals embedded in SiO2 matrix by CeF3 doping
Authors: Fang Y. C. , Zhang Z. J. , Xie Z. Q. , Zhao Y. Y. , Lu M.
Published: May 2005

Ce 3 + ions were doped into Si nanocrystals (nc-Si) embedded in SiO2 matrix (nc-Si∕SiO2) by evaporation of CeF3 powder onto the surface of nc-Si∕SiO2 and followed by thermal annealing in nitrogen ambient at different temperatures. Photoluminescence (PL) properties of the doped samples were studied. It has been found that the PL intensity of nc-Si can be remarkably enhanced and the enhancement depends on the doping concentration. Photoluminescence excitation spectra of the doped and undoped nc-Si imply that the enhancement comes from energy transfer from Ce3+ ions to nc-Si when excitation wavelength ranges from 240 to 320 nm.
Electron tunneling spectroscopy study of traps in high-k gate dielectrics: Determination of physical locations and energy levels of traps
Authors: Wang Miaomiao , He Wei , Ma T. P.
Published: May 2005

It will be demonstrated that the electron tunneling spectroscopy (ETS), obtained by taking the second derivative of the current-voltage (I–V) characteristic of a tunnel barrier, is an effective technique to probe traps in ultra-thin gate dielectrics where significant tunneling currents flow. By taking the electron tunneling spectra in both polarities, one can determine the locations and energy levels of traps that appear in the ETS spectra. The procedure for the above and the associated derivation will be presented. Examples are shown to demonstrate the use of ETS to track the evolution of traps in high-k gate dielectrics under electrical stress.
Nanoindentation tests on diamond-machined silicon wafers
Authors: Yan Jiwang , Takahashi Hirokazu , Tamaki Jun’ichi , Gai Xiaohui , Harada Hirofumi , Patten John
Published: May 2005

Nanoindentation tests were performed on ultraprecision diamond-turned silicon wafers and the results were compared with those of pristine silicon wafers. Remarkable differences were found between the two kinds of test results in terms of load-displacement characteristics and indent topologies. The machining-induced amorphous layer was found to have significantly higher microplasticity and lower hardness than pristine silicon. When machining silicon in the ductile mode, we are in essence always machining amorphous silicon left behind by the preceding tool pass; thus, it is the amorphous phase that dominates the machining performance. This work indicated the feasibility of detecting the presence and the mechanical properties of the machining-induced amorphous layers by nanoindentation.
Determination of thin-film stresses on round substrates
Authors: Blech Ilan A. , Blech Iditt , Finot Marc
Published: May 2005

Thin films deposited on wafers show, in some cases, large variations in stress. The local curvature is often used in the Stoney equation [G. G. Stoney, Proc. R. Soc. London, Ser. A 82, 172 (1909)] to calculate the local stress. This practice leads to false stress results. A general method for the calculation of the film stress, for films with isotropic stress, is presented here. The stress is calculated from both the local and overall shape of the substrate. Simple examples of isotropic stress were simulated and the substrate deformation calculated. The film stress was calculated back from the substrate shape with good agreement with the initial stress distribution. The substrate shape under films with centrosymmetric stress distribution can be analytically calculated. The current method successfully calculates the stress distribution from the substrate shape. Some guidelines for the deviation of the calculated stress from that of Stoney’s are given. Finally, the case of nonisotropic stressed film cannot be generally solved since there is no unique stress distribution for any given substrate shape.
The number of Cu lamination effect on current-perpendicular-to-plane giant-magnetoresistance of spin valves with Fe50Co50 alloy
Authors: Yuasa H. , Fukuzawa H. , Iwasaki H. , Sahashi M.
Published: May 2005

The current-perpendicular-to-plane (CPP) giant-magnetoresistance (GMR) of spin valves with Fe50Co50 alloy was investigated. It has been reported that the Cu inserted in Fe50Co50 is effective for enhancing CPP-GMR. In this paper, we investigated the number of Cu lamination effect on CPP-GMR and clarified that higher CPP-GMR is obtained by decreasing the number of Cu layers. In order to ascertain the reason for this tendency, the crystalline structure and magnetization were examined. As a result, it was found that the d spacing of Fe50Co50 increases when the number of Cu layers is increased, although saturation magnetization does not change.
Capture of particles of dust by convective flow
Authors: Lyubimov Dmitry V. , Straube Arthur V. , Lyubimova Tatyana P.
Published: May 2005

Interaction of particles of dust with vortex convective flows is under theoretical consideration. It is assumed that the volume fraction of solid phase is small, variations of density due to nonuniform distribution of particles and those caused by temperature nonisothermality of medium are comparable. Equations for the description of thermal buoyancy convection of a dusty medium are developed in the framework of the generalized Boussinesq approximation taking into account finite velocity of particle sedimentation. The capture of a cloud of dust particles by a vortex convective flow is considered, general criterion for the formation of such a cloud is obtained. The peculiarities of a steady state in the form of a dust cloud and backward influence of the solid phase on the carrier flow are studied in detail for a vertical layer heated from the sidewalls. It is shown that in the case, when this backward influence is essential, a hysteresis behavior is possible. The stability analysis of the steady state is performed. It turns out that there is a narrow range of governing parameters, in which such a steady state is stable.
Critical speed for capillary-gravity surface flows in the dispersive shallow water limit
Authors: Pham Chi-Tuong , Nore Caroline , Brachet Marc-Étienne
Published: May 2005

The stability of perfect-fluid capillary-gravity surface flows past a cylindrical obstacle is studied in the shallow water limit, using the two-dimensional compressible Euler equations, with leading-order dispersive corrections. Stationary solutions with different contact angles are obtained by Newton branch following, based on Fourier pseudospectral methods, using mapped Chebychev polynomials. Stable and unstable branches are found to meet, through a saddle-node bifurcation, at a critical speed beyond which no stationary solution exists. For large obstacles, the stable branch is compared with the stationary solutions of the compressible Euler equation without dispersion. Boundary layers are investigated. In this regime, the unstable dynamics are shown to lead to a finite-time dewetting singularity.
2.45 GHz microwave-excited atmospheric pressure air microplasmas based on microstrip technology
Authors: Kim Jaeho , Terashima Kazuo
Published: May 2005

A plasma system based on microstrip technology was developed for the generation of atmospheric pressure microplasmas. A discharge gap was placed between the striplines and the ground plane on the transverse cross section in the direction of microwave propagation. This microstrip structure permits the concentration of electric fields at the discharge gap, which is confirmed by a computer simulation using the three-dimensional simulation code based on the finite-difference time-domain method, and can produce atmospheric pressure plasmas even in air. The microplasmas were sustained in the discharge gap (width: 0.2 mm, length: 6 mm) at a microwave power of 1 W. The experimentally measured rotational temperature of nitrogen molecules was 800 K, indicating these plasmas to be nonthermal plasmas. This plasma system will provide a portable microplasma system utilizing a small semiconductor microwave source and a large-scale atmospheric pressure nonthermal plasma using the array configuration.
Dust-lattice waves: Role of charge variations and anisotropy of dust-dust interaction
Authors: Kompaneets R. , Ivlev A. V. , Tsytovich V. , Morfill G.
Published: May 2005

Dust-lattice waves are studied in the framework of the one-dimensional particle string model. The dust-dust interaction potential is assumed to have an arbitrary dependence on the vertical and horizontal coordinates, which allows to take into account the wake field effects. Both the vertical and horizontal charge variations are also included into the model. The model yields the coupling between the vertical and horizontal (longitudinal) modes: the coupling coefficient is the sum of six terms, each caused by a different physical mechanism. It is shown that the coupling can trigger the resonance oscillatory instability, which has been already observed in experiments. It is also shown that a nonoscillatory instability can appear at small wave numbers due to the coupling.
Thickness-dependent optical properties of La0.7Sr0.3MnO3 thin films
Authors: Liu H. L. , Kuo M. X. , Her J. L. , Lu K. S. , Weng S. M. , Wang L. M. , Cheng S. L. , Lin J. G.
Published: May 2005

We report on a systematic study of the thickness dependence of the optical properties of La0.7Sr0.3MnO3 thin films epitaxially grown on a LaAlO3 substrate. The x-ray powder-diffraction data indicate that the c-axis lattice constant is enhanced with decreasing the film thickness due to the compressive strain in the film plane produced by lattice mismatch. Magnetization curves show a decrease of the Curie temperature (TC) for decreasing thickness of films. Optical reflectance and transmittance measurements provide evidence that the position of Mn-O stretching mode shifts toward low frequency and the energy of the charge-transfer transition between O 2p and Mn 3d states increases with the decrease of film thickness. Most importantly, an analysis of the small-polaron absorption in the mid-infrared region shows that the polaron binding energy increases with decreasing the film thickness, suggesting that the strain dependence of TC mainly results from the strain-induced electron–phonon coupling.
Spin transfer in antisymmetric exchange-biased spin-valves
Authors: Jiang Y. , Yu G. H. , Wang Y. B. , Teng J. , Ochiai T. , Tezuka N. , Inomata K.
Published: May 2005

In this letter, we report on measurements of current-induced magnetization switching (CIMS) in current-perpendicular-to-plane exchange-biased spin-valves (ESPVs). The structures of the ESPVs are all “antisymmetric,” but with different thickness of a ruthenium (Ru) layer. It is confirmed that the “antisymmetric” structures largely enhance the spin transfer effect and therefore reduce critical current densities for the CIMS. The effect of the Ru layer on the spin transfer in the ESPVs is also systematically studied. With a decrease of the Ru layer’s thickness, the critical current densities can be further reduced. The lowest critical current we achieved in an “antisymmetric” structure is 1×106A∕cm2, which realizes a reduction of more than one order of magnitude compared with all the reported works.
Characterization of turbulent jets from high-aspect-ratio rectangular nozzles
Authors: Mi J. , Deo R. C. , Nathan G. J.
Published: May 2005

Turbulent free jets issuing from rectangular slots with various high aspect ratios (15–120) are characterized. The centerline mean and rms velocities are measured using hot-wire anemometry over a downstream distance of up to 160 slot heights at a slot-height-based Reynolds number of 10 000. Experimental results suggest that a rectangular jet with sufficiently high aspect ratio (>15) may be distinguished between three flow zones: an initial quasi-plane-jet zone, a transition zone, and a final quasi-axisymmetric-jet zone. In the quasi-plane-jet zone, the turbulent velocity field is statistically similar, but not identical, to those of a plane jet.
Fluorescence quenching in tip-enhanced nonlinear optical microscopy
Authors: Krug John T. , Sánchez Erik J. , Xie X. Sunney
Published: May 2005

We describe the theoretical treatment of fluorescence quenching in tip-enhanced nonlinear optical microscopy (TENOM). Finite difference time domain simulations demonstrate that while sharp pyramidal probes yield fluorescence signal enhancement that decays monotonically as a function of probe-fluorophore distance, more commonly used conical probes cause more complex image contrast. Fluorescence quenching can thus explain the halo-type images that are sometimes observed in TENOM. Formation of a dielectric spacer layer on the TENOM probe should alleviate the complications associated with quenching.
Properties of Heusler alloy Co2Cr1−xFexAl superlattices and spin valves
Authors: Kelekar R. , Clemens B. M.
Published: May 2005

We investigate the properties of epitaxial Co2Cr1−xFexAl-based multilayers grown by dc magnetron sputtering upon MgO substrates. Co2Cr1−xFexAl/Cr superlattices of high epitaxial quality can be grown, though no evidence for antiferromagnetic coupling is observed. Simple spin-valve trilayers of the form Co2Cr1−xFexAl/Cu/Co90Fe10 show large giant magnetoresistances of up to 6.8% at room temperature, comparable to the highest achieved in conventional exchange-biased spin valves.
Better bottom contact properties in organic field-effect transistors with ultrathin layers
Authors: Muck T. , Fritz J. , Wagner V.
Published: May 2005

Organic field-effect transistors (OFETs) are very promising to realize cheap electronics for mass production. Structuring the electrodes of OFETs directly onto organic semiconductors is often prohibited, while substrates with prepatterned electrodes disturb organic film growths at the electrodes resulting in low contact quality. We report on the observation that thiophene-based ultrathin organic layers, in the monolayer range, exhibit smoother and more uniform growth characteristics close to gold contacts when compared to thicker organic layers. As a result, these ultrathin layers in bottom contact configuration exhibit superior electrical contact properties.
Carbon isotope composition and water-use efficiency in plants with crassulacean acid metabolism
Authors: Winter Klaus , Aranda Jorge , Holtum Joseph A. M.
Published: May 2005

The relationship between water-use efficiency, measured as the transpiration ratio (g H2O transpired g–1 above- plus below-ground dry mass accumulated), and 13C / 12C ratio (expressed as δ13C value) of bulk biomass carbon was compared in 15 plant species growing under tropical conditions at two field sites in the Republic of Panama. The species included five constitutive crassulacean acid metabolism (CAM) species [Aloe vera (L.) Webb & Berth., Ananas comosus (L.) Merr., Euphorbia tirucalli L., Kalanchoë daigremontiana Hamet et Perr., Kalanchoë pinnata (Lam.) Pers.], two species of tropical C3 trees (Tectona grandis Linn. f. and Swietenia macrophylla King), one C4 species (Zea mays L.), and seven arborescent species of the neotropical genus Clusia, of which two exhibited pronounced CAM. The transpiration ratios of the C3 and CAM species, which ranged between 496 g H2O g–1 dry mass in the C3–CAM species Clusia pratensis Seeman to 54 g H2O g–1 dry mass in the constitutive CAM species Aloe vera, correlated strongly with δ13C values and nocturnal CO2 gain suggesting that δ13C value can be used to estimate both water-use efficiency and the proportion of CO2 gained by CAM species during the light and the dark integrated over the lifetime of the tissues.
Transcriptional profiles of organellar metabolite transporters during induction of crassulacean acid metabolism in Mesembryanthemum crystallinum
Authors: Kore-eda Shin , Noake Chiyuki , Ohishi Masahisa , Ohnishi Jun-ichi , Cushman John C.
Published: May 2005

Metabolite transport across multiple organellar compartments is essential for the operation of crassulacean acid metabolism (CAM). To investigate potential circadian regulation of inter-organellar metabolite transport processes, we have identified eight full-length cDNAs encoding an organellar triose phosphate / Pi translocator (McTPT1), a phosphoenolpyruvate / Pi translocator (McPPT1), two glucose-6-phosphate / Pi translocators (McGPT1, 2), two plastidic Pi translocator-like proteins (McPTL1, 2), two adenylate transporters (McANT1, 2), a dicarboxylate transporter (McDCT2), and a partial cDNA encoding a second dicarboxylate transporter (McDCT1) in the model CAM plant, Mesembryanthemum crystallinum L. We next investigated day / night changes in steady-state transcript abundance of each of these transporters in plants performing either C3 photosynthesis or CAM induced by salinity or water-deficit stress. We observed that the expression of both isogenes of the glucose-6-phosphate / Pi translocator (McGPT1, 2) was enhanced by CAM induction, with McGPT2 transcripts exhibiting much more pronounced diurnal changes in transcript abundance than McGPT1. Transcripts for McTPT1, McPPT1, and McDCT1 also exhibited more pronounced diurnal changes in abundance in the CAM mode relative to the C3 mode. McGPT2 and McDCT1 transcripts exhibited sustained oscillations for at least 3 d under constant light and temperature conditions suggesting their expression is under circadian clock control. McTPT1 and McGPT2 transcripts were preferentially expressed in leaf tissues in either C3 or CAM modes. The leaf-specific and / or circadian controlled gene expression patterns are consistent with McTPT1, McGPT2 and McDCT1 playing CAM-specific metabolite transport roles.
Distinctive diel growth cycles in leaves and cladodes of CAM plants: differences from C3 plants and putative interactions with substrate availability, turgor and cytoplasmic pH
Authors: Gouws Liezel M. , Osmond C. Barry , Schurr Ulrich , Walter Achim
Published: May 2005

Distinct diel rhythms of leaf and cladode expansion growth were obtained in crassulacean acid metabolism (CAM) plants under water-limited conditions, with maxima at mid-day during phase III of CO2 assimilation. This pattern coincided with the availability of CO2 for photosynthesis and growth during the decarboxylation of malic acid, with maximum cell turgor due to the nocturnally accumulated malic acid, and with the period of low cytoplasmic pH associated with malic acid movement from vacuole to cytosol. Maximum growth rates were generally only 20% of those in C3 plants and were reached at a different time of the day compared with C3 plants. The results suggest that malic acid, as a source of carbohydrates, and a determinant of turgor and cytoplasmic pH, plays a major role in the control of diel growth dynamics in CAM plants under desert conditions. The observed plasticity in phasing of growth rhythms under situations of differing water availability suggests that a complex network of factors controls the diel growth patterns in CAM plants and needs to be investigated further.
Influence of burning intensity on water repellency and hydrological processes at forest and shrub sites in Portugal
Authors: Ferreira A. J. D. , Coelho C. O. A. , Boulet A. K. , Leighton-Boyce G. , Keizer J. J. , Ritsema C. J.
Published: May 2005

In addition to the incineration of vegetation and litter layer, fires are also responsible for the formation of a water repellent layer with significantly different severity and spatial distribution patterns following different burning intensities. Those spatial distribution patterns have an enormous influence on soil wetting patterns, and on hydrological processes at different scales.
This study attempts to understand the role of water repellence severity and spatial distribution patterns on soil, slope, and catchment water processes, and on the transmission of hydrological processes between different scales. The comparison between microplot (0.24 m2), plot (16 m2), and catchment (<1.2 km2) scales shows that water repellence spatial homogeneity enhances water fluxes transfer between the different scales. In fact, the more intense the fires, the more severe and spatially uniform the soil water repellency became. For burned areas with heterogeneous soil water repellency, overland flow produced in water repellent patches infiltrated downslope at hydrophilic sites, thereby reducing superficial water fluxes at wider scales. For the more severe and homogeneous water repellent areas following forest wildfires, overland flow was enhanced downslope, increasing fast superficial water fluxes at wider scales.