bluuebunny/crossref_metadata_2025 huggingface dataset:
Combination of a pulsed microwave plasma with a catalyst for acetylene oxidation
Authors: Rousseau A. , Guaitella O. , Röpcke J. , Gatilova L. V. , Tolmachev Y. A.
Published: September 2004

The potential of an approach combining a pulsed microwave discharge with a catalytic packed bed reactor for the oxidation of volatile organic compounds (VOC) has been studied. The ignition of the plasma has been made possible by inserting ferroelectric BaTiO3 pellets inside the microwave excitator. As a test VOC molecule, acetylene (C2H2) in an amount of 200ppm in dry air was used. The total oxidation products CO and CO2 have been monitored downstream of the plasma region by tuneable diode laser absorption spectroscopy in the infrared region. The oxidative efficiency was found to increase linearly with the pulse repetition rate. The oxidative efficiency and the CO2∕CO selectivity were considerably enhanced when the catalyst was located inside the plasma region, which shows the synergetic effect of the plasma–catalyst combination.
Quadratic response functions in the time-dependent four-component Hartree-Fock approximation
Authors: Norman Patrick , Jensen Hans Jørgen Aa.
Published: September 2004

The second-order response function has been implemented in the time-dependent four-component Hartree-Fock approximation. The implementation is atomic orbital direct and formulated in terms of Fock-type matrices. It employs a quaternion symmetry scheme that provides maximum computational efficiency with consideration made to time-reversal and spatial symmetries. Calculations are presented for the electric dipole first-order hyperpolarizabilities of CsAg and CsAu in the second-harmonic generation optical process β(−2ω;ω,ω). It is shown that relativistic corrections to property values are substantial in these cases—the orientationally averaged hyperpolarizabilities in the static limit β̄(0;0,0) are overestimated in nonrelativistic calculations by 18% and 66% for CsAg and CsAu, respectively. The dispersion displays anomalies in the band gap region due to one- and two-photon resonances with nonrelativistically spin-forbidden states. Although weakly absorbing these states inflict divergences in the quadratic response function, since the response theoretical approach which is used adopts the infinite excited-state lifetime approximation. This fact calls for caution in applications where knowledge of the exact positioning of all excited states in the spectrum is unknown.
The solvation structure of Pb(II) in dilute aqueous solution: An ab initio quantum mechanical/molecular mechanical molecular dynamics approach
Authors: Hofer Thomas S. , Rode Bernd M.
Published: September 2004

Structural properties of the hydrated Pb(II) ion have been investigated by ab initio quantum mechanical/molecular mechanical molecular dynamics simulations at Hartree-Fock quantum mechanical level. The first shell coordination number was found to be nine, and several other structural parameters such as angular distribution functions, radial distribution functions, and tilt- and θ-angle distributions allow the full characterization of the hydration structure of the Pb(II) ion.
Single molecule kinetics. II. Numerical Bayesian approach
Authors: Witkoskie James B. , Cao Jianshu
Published: September 2004

As discussed in the companion paper [J. B. Witkoskie and J. S. Cao, J. Chem. Phys. 121, 6361 (2004), preceding paper], quantitative extraction of information from single molecule experiments by several proposed indicators is difficult since the experiments only observe certain characteristics of the system, even though the indicators can contain all available information. This paper shows how one can circumvent the shortcomings of these indicators by combining information extracted from indicators with a numerical Bayesian statistical approach. The Bayesian approach determines the relative probability of various models reproducing the entire sequence of the single molecules trajectory, instead of binning and averaging over the data, which removes much of this information.
Direct observation of the B-site cationic order in the ferroelectric relaxor Pb(Mg1∕3Ta2∕3)O3
Authors: Cantoni Marco , Bharadwaja Srowthy , Gentil Sandrine , Setter Nava
Published: September 2004

By means of transmission electron microscopy (TEM) the structure of chemically ordered regions in Zr-doped Pb(Mg1∕3Ta2∕3)O3 has been studied. Large coherent ordered domains were obtained by the addition of 5mol%PbZrO3. The results obtained by conventional, analytical, and high-resolution TEM are consistent with the random-site description of the B-site order, the so-called random-layer model. Image simulations showed that a careful selection of the imaging conditions for high resolution transmission electron microscopy is necessary in order to determine the different B-site occupancies. By comparison of simulated with experimental images it was possible to directly distinguish between the different ordering models.
Characteristics of dislocations in ZnO layers grown by plasma-assisted molecular beam epitaxy under different Zn∕O flux ratios
Authors: Setiawan Agus , Vashaei Zahra , Cho Meoung Whan , Yao Takafumi , Kato Hiroyuki , Sano Michihiro , Miyamoto Kazuhiro , Yonenaga I. , Ko Hang Ju
Published: September 2004

We have investigated the characteristic of the dislocations in the ZnO layers grown on c sapphire by the plasma-assisted molecular beam epitaxy under the different Zn∕O flux ratios. The ZnO layers were characterized by the transmission electron microscopy (TEM) and the high-resolution x-ray diffraction (HRXRD). The TEM and HRXRD experiments revealed that the major threading dislocations (TDs) in the ZnO layers are the edge dislocations running along the c axis with Burgers vector of 1∕3⟨11–20⟩. The TD densities are determined to be 6.9×109, 2.8×109, and 2.7×109cm−2, for O-rich, stoichiometric, and Zn-rich grown ZnO, respectively. Different from the O-rich grown ZnO where the dislocations run along the c-axis, several dislocations in the stoichiometric and the Zn-rich grown ZnO are inclined to 20°∼30° from the c-axis. By considering the slip system in the wurtzite-structure ZnO, the glide planes of the dislocations are close to (10-10) for the O-rich grown ZnO and close to (10-11) for the stoichiometric and Zn-rich grown ZnO. Furthermore, the thickness of the interface dislocations in the O-rich grown ZnO is much thinner than in the stoichiometric and Zn-rich grown ZnO. In addition, the most probable origin of the inclined dislocations including c∕a ratios, growth rate, and initial growth stage of high temperature (HT)-ZnO layers are also discussed.
Optical surface second harmonic measurements of isotropic thin-film metals: Gold, silver, copper, aluminum, and tantalum
Authors: Krause Debra , Teplin Charles W. , Rogers Charles T.
Published: September 2004

We have studied optical surface second harmonic generation and have determined the magnitude and relative phase of the second-order susceptibility tensor elements for thermally evaporated gold, and sputtered silver, copper, aluminum, and tantalum. The second harmonic data are understood using an isotropic model of the surfaces. The measurements of the parameters from this nonlinear optical characterization, in conjunction with linear optical characterization of the samples, allow us to extract the elements of the tensors. The typical size of χ⊥(2), the tensor element that produces the surface current perpendicular to the surface and is the largest surface element, ranges from 3(±1)×10−12cm2∕statvolt for an aluminum sample with 24(±4)Årms surface roughness to 1.1(±0.1)×10−13cm2∕statvolt for a copper sample with 5(±1)Årms surface roughness. Film preparation and associated surface roughness can reproducibly change the values of χ(2); increasing sample roughness increases the magnitudes of the tensor elements. In agreement with previous aluminum measurements, we again find that the tensor elements associated with creating the second harmonic currents normal to the surface are of roughly the theoretically predicted magnitude, but that the elements associated with creating the second harmonic currents parallel to the surface and in the bulk are an order of magnitude smaller than expected.
Growth of Mn-Bi films on Si(111): Targeting epitaxial MnBi
Authors: Deffke U. , Ctistis G. , Paggel J. J. , Fumagalli P. , Bloeck U. , Giersig M.
Published: September 2004

MnBi is of high interest for application as active layer in magneto-optic data storage media for several decades. Here the molecular-beam-epitaxy growth of Mn-Bi films on Si(111) surfaces is investigated under ultrahigh vacuum conditions by means of reflection high-energy electron diffraction, low-energy electron diffraction with spot-profile analysis, Auger-electron spectroscopy, magneto-optic Kerr spectroscopy, and transmission electron microscopy to reveal the microscopic film structure, film composition, and magnetic properties. The film parameters and growth protocols are varied but none of the chosen conditions lead to the formation of MnBi from the two elements. The affinity of Mn to the substrate material Si must be regarded as major reason for the fact that no MnBi forms.
Response to “Comment on ‘Probing in situ the sulfur polymerization transition with Raman spectroscopy’ ” [J. Chem. Phys. 121, 6573 (2004)]
Authors: Yannopoulos S. N. , Andrikopoulos K. S. , Kalampounias A. G.
Published: September 2004

The central idea of the preceding Comment [J. Chem. Phys. xxx, xxx (2004)] is tackled from different viewpoints and arguments are presented showing its invalidity. First, we show that the presence of non-S8 rings is negligible under the conditions in which our experiment was performed. Then we prove that, even if we consider the non-S8 ring’s presence in the concentrations indicated in the Comment, their contribution to the isotropic Raman intensity is negligible and hence the accuracy of polymer content determination does not change as the authors of the Comment supposed. Finally, we briefly examine the ensuing question of the extent to which quench-and-dissolution methods can give accurate and reproducible results concerning the polymer content in liquid sulfur, demonstrating their inadequacy for reproducible and accurate data. Since reliable ex situ experimental data concerning sulfur’s polymerization do not exist, we vindicate the essence of methodologies that enable the quantification of sulfur’s polymerization from in situ experiments.
Nonrelativistic molecular quantum mechanics without approximations: Electron affinities of LiH and LiD
Authors: Bubin Sergiy , Adamowicz Ludwik
Published: September 2004

We took the complete nonrelativistic Hamiltonians for the LiH and LiH− systems, as well as their deuterated isotopomers, we separated the kinetic energy of the center of mass motion from the Hamiltonians, and with the use of the variational method we optimized the ground-state nonadiabatic wave functions for the systems expanding them in terms of n-particle explicitly correlated Gaussian functions. With 3600 functions in the expansions we obtained the lowest ever ground-state energies of LiH, LiD, LiH−, and LiD− and these values were used to determine LiH and LiD electrons affinities (EAs) yielding 0.330 30 and 0.327 13 eV, respectively. The present are the first high-accuracy ab initio quantum mechanical calculations of the LiH and LiD EAs that do not assume the Born-Oppenheimer approximation. The obtained EAs fall within the uncertainty brackets of the experimental results.
Raman study of phonons in K2Al2B2O7 crystals
Authors: Hu X. B. , Wang J. Y. , Zhang C. Q. , Xu X. G. , Loong Chun-Keung , Grimsditch Marcos
Published: September 2004

A Raman scattering study of the vibrational modes in K2Al2B2O7 crystals has been performed at room temperature. The vibrational modes are classified by the nuclear site group analysis method and the internal vibrational modes are assigned to vibrations of the BO3 triangle and AlO4 tetrahedron.
Systematic pump-probe terahertz wave emission spectroscopy of a photoconductive antenna fabricated on low-temperature grown GaAs
Authors: Yano R. , Gotoh H. , Hirayama Y. , Miyashita S.
Published: September 2004

We performed pump-probe terahertz (THz) wave emission spectroscopy for a photoconductive antenna fabricated on low-temperature grown GaAs. When the pump pulse intensity was increased, the THz wave generated by the probe pulse showed an increase of the spectral amplitude in the low-frequency regime (<0.5THz) and a decrease of the peak amplitude. The increase of the spectral amplitude and the decrease of the peak amplitude are related to the carrier density generated by the pump pulse, and are explained by the increase of the carrier trap time due to the saturation of the defect levels and by the carrier-carrier scattering process between carriers in the conduction band, respectively.
Wide band-gap silicon-carbon alloys deposited by very high frequency plasma enhanced chemical vapor deposition
Authors: Summonte C. , Rizzoli R. , Bianconi M. , Desalvo A. , Iencinella D. , Giorgis F.
Published: September 2004

The use of very high frequency (VHF) plasma enhanced chemical vapor deposition in a capacitive discharge is investigated to fabricate hydrogenated amorphous silicon carbon alloys, using silane and methane as silicon and carbon precursors, respectively, and hydrogen dilution of the gas mixture. The properties of samples differ significantly from that is normally observed for rf deposition. A wide band-gap material is obtained, with a carbon ratio ranging from 0.2 to 0.63. An energy gap up to 3.4eV is measured, indicating a large sp3 content. The most interesting properties are observed using 90% hydrogen dilution and 350°C as substrate temperature. In this case, a SiC bond concentration up to 6×1022cm−3 was measured for stoichiometric samples, associated to a highly crosslinked structure and no detectable SiCH3 bending signal. The role of hydrogen in determining the optical properties of the film is established and is shown to affect mainly the valence electron concentration. Based on the free energy model, hydrogen bonding is observed to lie in between a random and chemically ordered configuration. The results are obtained at a deposition rate much larger than both rf and electron cyclotron resonance deposition, and are associated to a limited gas consumption, both aspects being advantageous for practical applications. The large SiC bond concentration, associated to a limited silicon and carbon hydrogenation, makes the VHF deposited a-SiC:H a good starting material for subsequent crystallization.
Optimized Baxter model of protein solutions: Electrostatics versus adhesion
Authors: Prinsen Peter , Odijk Theo
Published: September 2004

A theory is set up of spherical proteins interacting by screened electrostatics and constant adhesion, in which the effective adhesion parameter is optimized by a variational principle for the free energy. An analytical approach to the second virial coefficient is first outlined by balancing the repulsive electrostatics against part of the bare adhesion. A theory similar in spirit is developed at nonzero concentrations by assuming an appropriate Baxter model as the reference state. The first-order term in a functional expansion of the free energy is set equal to zero which determines the effective adhesion as a function of salt and protein concentrations. The resulting theory is shown to have fairly good predictive power for the ionic-strength dependence of both the second virial coefficient and the osmotic pressure or compressibility of lysozyme up to about 0.2 volume fraction.
Melting, freezing, sublimation, and phase coexistence in sodium chloride nanocrystals
Authors: Breaux Gary A. , Benirschke Robert C. , Jarrold Martin F.
Published: September 2004

Calorimetry measurements, performed by multicollision induced dissociation, have been used to probe the melting of a number of (NaCl)nNa+ clusters with n=22–37. The clusters anneal at 225–325 K and melt at 750–850 K. (NaCl)22Na+ and (NaCl)37Na+, which can adopt geometries that are perfect fragments of the bulk lattice melt at around 850 K. The other clusters, which (except for n=31) must have defects, melt at temperatures which are up to 100 K lower than the perfect nanocrystals. The internal energy distributions become bimodal near the melting temperature. This is the signature of slow dynamic phase coexistence where clusters spontaneously jump back and forth between the solid and liquid states with an average period that is longer than required for thermal equilibration. The jump frequency must be between 104 and 107 s−1 for the bimodal distribution to be observable in our experiments. The (NaCl)nNa+ clusters can dissociate by an unusual thermally activated process where melting and freezing raise the internal energy to generate hot solid clusters that can sublime before they cool to the ambient temperature.
Influence of layer structure on the current-voltage characteristics of Si∕SiGe interband tunneling diodes
Authors: Khorenko E. , Prost W. , Tegude F.-J. , Stoffel M. , Duschl R. , Dashiell M. W. , Schmidt O. G.
Published: September 2004

We systematically investigated the DC-characteristics of Si∕SiGe interband tunneling diodes as a function of layer structure and device geometry. The Si spacer thicknesses XP and XN between the intrinsic SiGe layer and the p- and n-δ-doped layers were varied. We obtained a peak current density of 16kA∕cm2 and a peak-to-valley current ratio of 2.7 (with a device area of 45μm2) for a structure with XP=0nm and XN=1nm. A good homogeneity of all measured diode parameters was achieved over the wafer area.
Polytype transition of N-face GaN:Mg from wurtzite to zinc-blende
Authors: Monroy E. , Hermann M. , Sarigiannidou E. , Andreev T. , Holliger P. , Monnoye S. , Mank H. , Daudin B. , Eickhoff M.
Published: September 2004

We have investigated the polytype conversion of a GaN film from N-face wurtzite (2H) to zinc-blende (3C) structure due to Mg doping during growth by plasma-assisted molecular-beam epitaxy. Structural analysis by high-resolution transmission electron microscopy and high-resolution x-ray diffraction measurement revealed alignment of the cubic phase with the [111] axis perpendicular to the substrate surface. The optical characteristics of GaN:Mg layers are shown to be very sensitive to the presence of the cubic polytype. For low Mg doping, photoluminescence is dominated by a phonon-replicated donor-acceptor pair at ∼3.25eV, related to the shallow Mg acceptor level, accompanied by a narrow excitonic emission. For high Mg doping, the photoluminescence spectra are also dominated by a line around 3.25eV, but this emission displays the behavior of excitonic luminescence from cubic GaN. A cubic-related donor-acceptor transition at ∼3.16eV is also observed, together with a broad blue band around 2.9eV, previously reported in heavily Mg-doped 3C-GaN(001).
Energy levels and wave functions of weakly-bound Hex4 20NeyH (x+y=2) systems using Pekeris coordinates and a symmetry-adapted Lanczos approach
Authors: Liu Yong Dong , Roy Pierre-Nicholas
Published: September 2004

Energy levels and wave functions of floppy triatomic rare gas hydrides are calculated using a Pekeris coordinate system and the importance of various triangular configurations is assessed through the calculation of reduced distribution functions and relative weights. The calculations are performed using a symmetry-adapted Lanczos recursion within the discrete variable representation. For the 4He2H− anion, the present results are compared with those obtained from calculations based on other methods, and the accuracy of the present method is discussed. Calculations are also performed for the case of 4He2H and 20Ne2H, as well as for the mixed 4He20NeH neutrals. Our results show that no bound states are found for 4He2H while only one bound state is found for both the 20Ne2H and 4He20NeH complexes. Interestingly, a very important and common property of these systems is that there is a significant contribution from linear configurations to their bound states.
Complex autocorrelation function and energy spectrum by classical trajectory calculations
Authors: Z̆ďánská Petra R. , Moiseyev Nimrod
Published: September 2004

A quasiclassical method which enables evaluation of complex autocorrelation function from classical trajectory calculations is proposed. The method is applied for two highly excited nonlinearly coupled harmonic oscillators in regimes prevailed either by regular or chaotic classical motions. A good agreement of classical and quantum autocorrelation functions is found within short (Ehrnfest) time limit. Fourier transforms of the autocorrelation functions provide moderate resolved energy spectra, where classical and quantum results nearly coincide. The actual energy levels are obtained from approximate short-time autocorrelation functions with the help of filter diagonalization. This study is a follow up to our previous work [P. Zdanska and N. Moiseyev, J. Chem. Phys. 115, 10608 (2001)], where the complex autocorrelation has been obtained up to overall phase factors of recurrences.
Optical control of two-photon excitation efficiency of α-perylene crystal by pulse shaping
Authors: Okada T. , Otake I. , Mizoguchi R. , Onda K. , Kano S. S. , Wada A.
Published: September 2004

Optimized pulse shaping experiments were carried out on the control of two-photon excitation efficiency of an α-perylene crystal in the temperature region from 30 to 290 K. It was found that a pulse train with a pulse interval of 90 fs and an alternately reversing phase relation increased the excitation efficiency by a factor of 2 for the whole temperature region. The pulse shape characteristic for effective efficiency increase was educed by double pulse experiments in which the dependence of the emission intensity on the pulse interval and relative phase between pulses were measured. The mechanism of the efficiency increase is briefly discussed using a sliding-window Fourier transform of the pulse shape.
Lateral stress measurements and shear strength in shock loaded tungsten carbide
Authors: Millett J. C. F. , Bourne N. K. , Dandekar D. P.
Published: September 2004

The shear strength of a monolithic tungsten carbide has been measured as a function of impact stress. Results show that it increases with stress, in agreement with the work of others. Interestingly, it has also been shown that lateral stress increases, and thus shear strength decreases behind the shock front. Potential mechanisms are discussed, including cracking within the shock front itself, and stress relaxation due to high velocity dislocation motion within the shock front, followed by dislocation multiplication behind it.
Theoretical modeling and experimental characterization of InAs∕InGaAs quantum dots in a well detector
Authors: Amtout A. , Raghavan S. , Rotella P. , von Winckel G. , Stintz A. , Krishna S.
Published: September 2004

Theoretical modeling and experimental characterization of InGaAs∕GaAs quantum dots-in-a-well (DWELL) intersubband heterostructures, grown by molecular beam epitaxy are reported. In this heterostructure, the self-assembled dots are confined to the top half of a 110Å InGaAs well which in turn is placed in a GaAs matrix. Using transmission electron microscopy, the quantum dots are found to be pyramidal in shape with a base dimension of 110Å and height of 65Å. The band structure for the above mentioned DWELL heterostructure was theoretically modeled using a Bessel function expansion of the wave function. The energy levels of the three lowest states of the conduction band of the quantum dot are calculated as a function of the electric field. Intersubband n-i-n detectors were fabricated using a ten layer DWELL heterostructure. The spectral response of the detector is measured at a temperature between 30 and 50 K and compared with the prediction of our theoretical model.
Effects of the bead-bead potential on the restricted rotational diffusion of nonrigid macromolecules
Authors: Uvarov Alexander , Fritzsche Stephan
Published: September 2004

The influence of the bead-bead interaction on the rotational dynamics of macromolecules which are immersed into a solution has been investigated by starting from the microscopic theory of the macromolecular motion, i.e., from a Fokker-Planck equation for the phase-space distribution function. From this equation, we then derived an explicit expression for the configuration-space distribution function of a nonrigid molecule which is immobilized on a surface. This function contains all the information about the interaction among the beads as well as the effects from the surrounding solvent particles and from the surface. For the restricted rotational motion, the dynamics of the macromolecules can now be characterized in terms of a rotational diffusion coefficient as well as a radial distribution functions. Detailed computations for the rotational diffusion coefficient and the distribution functions have been carried out for HOOKEAN, finitely extensible nonlinear elastic, and a DNA type bead-bead interaction.
Persistent spectral hole burning studies of europium-doped sodium germanate glass
Authors: Kalluru Rajamohan R. , Pulluru Chandra R. , Rami Reddy B.
Published: September 2004

Persistent spectral hole burning has been observed in europium-doped sodium germanate glass. Hole-burning efficiency increased by 85% when the glasses were made in a reduced atmosphere, and hole burning was detected even at room temperature. There is evidence for photochemical as well as photophysical hole-burning mechanisms.
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noise in GaN∕AlGaN heterostructure field-effect transistors in high magnetic fields at 300K
Authors: Rumyantsev S. L. , Shur M. S. , Dyakonova N. , Knap W. , Meziani Y. , Pascal F. , Hoffman A. , Hu X. , Fareed Q. , Bilenko Yu. , Gaska R.
Published: September 2004

1 ∕ f noise in AlGaN∕GaN metal-oxide-semiconductor heterostructure field-effect transistors has been measured at 300K in strong magnetic fields up to 10T. The devices exhibited strong geometric magnetoresistance. The magnetic-field dependence of the 1∕f noise shows that fluctuations of the number of electrons is the dominant mechanism of the 1∕f noise.
Real-time study of the adiabatic energy loss in an atomic collision with a metal cluster
Authors: Baer Roi , Siam Nidal
Published: September 2004

Gas-phase hydrogen atoms are accelerated towards metallic surfaces in their vicinity. As it approaches the surface, the velocity of an atom increases and this motion excites the metallic electrons, causing energy loss to the atom. This dissipative dynamics is frequently described as atomic motion under friction, where the friction coefficient is obtained from ab initio calculations assuming a weak interaction and slow atom. This paper tests the aforementioned approach by comparing to a real-time Ehrenfest molecular dynamics simulation of such a process. The electrons are treated realistically using standard approximations to time-dependent density functional theory. We find indeed that the electronic excitations produce a frictionlike force on the atom. However, the friction coefficient strongly depends on the direction of the motion of the atom: it is large when the atom is moving towards the cluster and much smaller when the atom is moving away. It is concluded that a revision of the model for energy dissipation at metallic surfaces, at least for clusters, may be necessary.
Incorporation of manganese into semiconducting ScN using radio frequency molecular beam epitaxy
Authors: AL-Brithen Hamad A. , Yang Haiqiang , Smith Arthur R.
Published: September 2004

The incorporation of manganese into semiconducting ScN, using radio frequency molecular beam epitaxy, has been investigated. X-ray diffraction and reflection high energy electron diffraction measurements show the face-centered tetragonal rocksalt-type crystal structure with Sc and Mn cations and N anions. In addition to the solute incorporation into the lattice, which is clear from the positions of the diffraction peaks, atomic force microscopy images show that the surface of the alloy grown at TS⩽518°C contains dot-like features, indicating surface accumulation. The areal dot density is found to decrease as the growth temperature increases, whereas the Mn incorporation increases at 518 °C. This behavior is suggestive of a thermally activated process, and it is well explained by an Arrhenius law, giving an activation energy (diffusion barrier) of 0.67 eV. Increasing the growth temperature to 612 °C leads to an increased desorption rate, resulting in little Mn incorporation. It has been found that the growth is nearly optimized at TS=518°C for high Mn incorporation, smooth growth, and small accumulate density. The alloy is found to have lattice parameters which depend on the Mn∕(Mn+Sc) bulk ratio. The alloy lattice constants follow Vegard’s law depending on the Mn bulk fraction and the lattice constants of ScN and θ-phase MnN. The Mn incorporation and Mn incorporation coefficient for films grown at TS=518°C increase as the Mn∕(Mn+Sc) flux ratio increases.
The growth behavior of self-standing tungsten tips fabricated by electron-beam-induced deposition using 200keV electrons
Authors: Liu Z. Q. , Mitsuishi K. , Furuya K.
Published: September 2004

Self-standing tungsten tips were fabricated by electron-beam-induced deposition in a 200kV scanning transmission electron microscope to study their growth behavior. By increasing deposition time from 0.2to2400s, the tip growth rate decreases from 5–7nm∕s to zero and the root diameter increases from 2to60–65nm. Tips preferably grow downward at the beginning stage with a saturation length of 80–120nm. Dynamic Monte Carlo simulation was carried out, and 200keV electrons were proved to be more capable to fabricate tip with smaller lateral size and higher ratio than the 20keV electrons.
Low frequency dielectric relaxation phenomena in conducting polypyrrole and conducting polypyrrole-zeolite composites
Authors: Papathanassiou A. N. , Grammatikakis J. , Sakellis I. , Sakkopoulos S. , Vitoratos E. , Dalas E.
Published: September 2004

The dielectric properties of polypyrrole-zeolite composites up to 50%w∕w zeolite are studied in the frequency range from 10−2to2×106Hz from room temperature to liquid nitrogen temperature. The complex permittivity formalism reveals a temperature dependent relaxation in all samples except for the 25%w∕w zeolite composite. The frequency fmax where a maximum of a loss peak is located varies with temperature by the Williams-Lander-Ferry law. The values of the activation energy of the relaxation process (which are of the order of polaronic dc conductivity) have the tendency to reach a minimum in the 25%w∕w composition, which is a loss-free composite. The 50%w∕w zeolite behaves as a dielectric where ionic relaxation dominates. The temperature variation of the strength of the dielectric mechanism follows a Curie law, apart from 50%w∕w zeolite where the dielectric strength is practically constant. The frequencies, where loss peaks are maximum, as well as dc conductivity follow qualitatively the same temperature law, but the parameters are quite different. Moreover, the locations of the relaxation peaks diverge from the predictions of Barton-Nakajima-Namikawa model. Long-range electric charge transport (dc conductivity) and the relaxation that corresponds to short-range localized motion probably involve different processes.
Electron mobility in Ge and strained-Si channel ultrathin-body metal-oxide semi conductor field-effect transistors
Authors: Low Tony , Li M. F. , Shen Chen , Yeo Yee-Chia , Hou Y. T. , Zhu Chunxiang , Chin Albert , Kwong D. L.
Published: September 2004

Electron mobility in strained silicon and various surface oriented germanium ultrathin-body (UTB) metal-oxide semiconductor field-effect transistors (MOSFETs) with sub-10-nm-body thickness are systematically studied. For biaxial tensile strained-Si UTB MOSFETs, strain effects offer mobility enhancement down to a body thickness of 3nm, below which strong quantum confinement effect renders further valley splitting via application of strain redundant. For Ge channel UTB MOSFETs, electron mobility is found to be highly dependent on surface orientation. Ge⟨100⟩ and Ge⟨110⟩ surfaces have low quantization mass that leads to a lower mobility than that of Si in aggressively scaled UTB MOSFETs.
The effect of annealing environment on the luminescence of silicon nanocrystals in silica
Authors: Wilkinson A. R. , Elliman R. G.
Published: September 2004

The effect of annealing environment on the photoluminescence from silicon nanocrystals synthesized in fused silica by ion implantation and thermal annealing is examined as a function of annealing temperature and time. The choice of annealing environment (Ar, N2, or 5%H2 in N2) is found to affect the shape and intensity of luminescence emission spectra, an effect that is attributed both to variations in nanocrystal size and defect states at the nanocrystal/oxide interface. This is supported by Raman spectroscopy.
Atomistic shock Hugoniot simulation of single-crystal copper
Authors: Bringa E. M. , Cazamias J. U. , Erhart P. , Stölken J. , Tanushev N. , Wirth B. D. , Rudd R. E. , Caturla M. J.
Published: September 2004

Planar shock waves in single-crystal copper were simulated using nonequilibrium molecular dynamics with a realistic embedded atom potential. The simulation results are in good agreement with new experimental data presented here, for the Hugoniot of single-crystal copper along ⟨100⟩. Simulations were performed for Hugoniot pressures in the range 2 GPa – 800 GPa, up to well above the shock induced melting transition. Large anisotropies are found for shock propagation along ⟨100⟩,⟨110⟩, and ⟨111⟩, with quantitative differences from pair potentials results. Plastic deformation starts at Up≳0.75km∕s, and melting occurs between 200 and 220 GPa, in agreement with the experimental melting pressure of polycrystalline copper. The Voigt and Reuss averages of our simulated Hugoniot do not compare well below melting with the experimental Hugoniot of polycrystalline copper. This is possibly due to experimental targets with preferential texturing and/or a much lower Hugoniot elastic limit.
Observation of transient photocurrents on suspended nanotubes
Authors: Bunning J. C. , Donovan K. J. , Scott K.
Published: September 2004

Transient photocurrents are measured on a suspension of single walled carbon nanotubes in an applied electric field. A rapid electronic response time of 150 ps is achieved in these measurements. Attaining such a rapid response has required the development of an advanced technique to reduce impedance mismatch between the measuring equipment and sample. This technique, which incorporates the sample into a global 50Ω architecture, is described here. The technique allows the problem of contacting nanotubes to be avoided in the study of basic electronic transport properties. Some early results on transient photocurrents induced by a 25 ps mode locked laser pulse are shown along with the electric field dependence of the peak photocurrent and integrated photocharge. Problems associated with the long term evolution in the conductivity of suspended samples are also addressed.
Au as an acceptor in thermoelectric Bi1Sb3Te6 alloy prepared by mechanical alloying and pulse discharge sintering process
Authors: Lee Changho , Park Yong-Ho , Hashimoto Hitoshi
Published: September 2004

The effect of Au (0–0.3 wt. %) on the thermoelectric properties of Bi1Sb3Te6 alloy prepared by a mechanical alloying process has been investigated. The Seebeck coefficient decreased with the Au content. The Seebeck coefficient of a Au-free alloy at room temperature reaches a value of 250μV∕K, which is the maximum. The figure of merit value increased with the Au content up to 0.03 wt. %, because of the increased power factor. The figure of merit value of 0.03 wt. % Au alloy at room temperature was about 2.8×10−3/K, the highest value among the prepared alloys. The Hall measurement shows that the carrier concentration increases with the Au content, which explains the reason why the power factor increased. The x-ray diffraction patterns show that the intensities of (1 0 10), (1 1 0), (2 0 5), (0 0 18), (0 2 10), (1 0 19), (1 2 5), and (2 1 10) planes increased with the Au content. The atomic distance of these complex planes is longer than that of the other main plane, and the chemical bonding strength of these complex planes between constitutional elements is weaker than that of other main planes. As a result, a portion of electrons as minor carriers was trapped into the accepted level of Au atoms and∕or clusters. The fact that Au behaves as an acceptor is confirmed by the x-ray photoelectron spectroscopy observation result; a portion of Au atoms is chemically shifted in contrast to Bi, Sb, and Te atoms, which are not.
Microscopic analysis for water stressed by high electric fields in the prebreakdown regime
Authors: Joshi R. P. , Qian J. , Schoenbach K. H. , Schamiloglu E.
Published: September 2004

Analysis of the electrical double layer at the electrode-water interface for voltages close to the breakdown point has been carried out based on a static, Monte Carlo approach. It is shown that strong dipole realignment, ion-ion correlation, and finite-size effects can greatly modify the electric fields and local permittivity (hence, leading to optical structure) at the electrode interface. Dramatic enhancements of Schottky injection, providing a source for electronic controlled breakdown, are possible. It is also shown that large pressures associated with the Maxwell stress tensor would be created at the electrode boundaries. Our results depend on the ionic density, and are in keeping with recent observations. A simple, perturbative analysis shows that high field regions with a sharp variation in permittivity can potentially be critical spots for instability initiation. This suggests that the use of polished electrodes, or composite materials, or alternative nonpolar liquids might help enhance high-voltage operation.
Prediction of etch microtrenching using a neural network
Authors: Kim Byungwhan , Lee Duk Woo , Kwon Kwang Ho
Published: September 2004

Microtrenching during plasma etching was characterized by using a generalized regression neural network (GRNN). Plasma etching of oxide films was conducted in a magnetically enhanced reactive ion etch system. The etch process was characterized by means of a 24−1 fractional factorial experiment. The process parameters concerned include CHF3 flow rate, CF4 flow rate, radio frequency power, and pressure. Radicals collected with a dc bias were analyzed by optical emission spectroscopy while being correlated to the microtrenching depth (MD). A genetic algorithm (GA) was used to search an optimized set of multiparametrized spreads. The resultant prediction model had a root mean-squared error of 0.031 Å/min. Compared to conventional GRNN and statistical regression models, the GA-GRNN demonstrated more accurate predictions of more than 30% and 70%, respectively. The MD variation with the pressure or CHF3 flow rate was attributed to the more dominant role of polymer deposition over chemical etching as illustrated by a high correlation with [CF]/[F]. For variations in the rf power, the profile change played a critical role in understanding MD.
Spectroscopic investigation of the plasma in a hollow anode with an incorporated ferroelectric plasma source
Authors: Krokhmal A. , Gleizer J. Z. , Krasik Ya. E. , Yarmolich D. , Felsteiner J. , Bernshtam V.
Published: September 2004

Spectroscopic measurements are reported of the plasma formed inside a hollow anode (HA) with a ferroelectric plasma source (FPS) incorporated in it. The HA was used as a cathode in a diode supplied by an accelerating pulse (≤300kV, ≤400ns). It was found that the HA discharge (1.2kA, 10μs) is accompanied by the formation of a dense (≈8×1014cm−3) plasma layer at the surface of the FPS. This surface plasma serves as a practically unlimited source of electrons. In the bulk of the HA plasma the density is ≈3×1013cm−3 and it remains the same during the accelerating pulse whereas the plasma electron temperature increases from 4 to 11eV.
Effect of temperature gradient on simultaneously experimental determination of thermal expansion coefficients and elastic modulus of thin film materials
Authors: Chen Tei-Chen , Lin Wen-Jong , Chen Dao-Long
Published: September 2004

Some specific experimental methods to simultaneously determine the thermal expansion coefficients αF and biaxial elastic modulus EF∕(1−νF) of thin film materials have been reported recently. In these methods, the deflections or the curvature change of the thin films, deposited on two different types of circular disks with known material properties, generally can be measured with a variety of optical techniques. The temperature-dependent deflection behaviors of thin films are then obtained by heating the samples in the range from room temperature to a slightly higher temperature level at which the physical properties and microstructures of thin film materials still remain unchanged. By using the relations between stress, deflection, and temperature, the physical properties of thin films can be finally calculated by using the slopes of two lines in the stress versus temperature plot. These relations, however, are formulated under the condition of uniform temperature rise. If the heating processes of samples are conducted in the condition that there exists a small steady-state temperature gradient along the thickness of samples due to the effect of natural heat convection on the upper surface of thin film, the formulation mentioned above shall be modified. It is found that the deflection of sample induced by the small temperature gradient along the thickness due to natural heat convection is very significant and comparable to that induced by uniform temperature rise. Consequently, if the effect of this temperature gradient is carelessly disregarded in physical modeling, a significantly different value of elastic modulus may be misleadingly obtained. Some cases are exemplified and illustrated to show the influence of temperature gradient on the evaluation of material properties.
Onset of implant-related recombination in self-ion implanted and annealed crystalline silicon
Authors: Macdonald Daniel , Deenapanray Prakash N. K. , Diez Stephan
Published: September 2004

The impact of residual recombination centers after low-energy self-implantation of crystalline silicon wafers and annealing at 900 °C has been determined by bulk carrier lifetime measurements as a function of implant dose. Doses below 1013cm−2 resulted in no measurable increase in recombination, while higher doses caused a linear increase in the recombination center density. This threshold value corresponds to the known critical dose required for the formation of relatively stable dislocation loops during high temperature annealing. Deep level transient spectroscopy revealed a decrease in the vacancy-related defect concentration in the high-dose samples, which we interpret as reflecting an increase in the silicon interstitial concentration. This suggests that silicon interstitials, arising from the slowly dissolving dislocation loops, may be responsible for the increased recombination deep within the samples.
Quantum calculations of the O(3P)+H2→OH+H reaction
Authors: Balakrishnan N.
Published: September 2004

Quantum scattering calculations are reported for the O(3P)+H2(v=0,1) reaction using chemically accurate potential energy surfaces of A′3 and A″3 symmetry. We present state-to-state reaction cross sections and rate coefficients as well as thermal rate coefficients for the title reaction using accurate quantum calculations. Our calculations yield reaction cross sections that are in quantitative accord with results of recent crossed molecular beam experiments. Comparisons with results obtained using the J-shifting calculations show that the J-shifting approximation is quite reliable for this system. Thermal rate coefficients from the exact calculations and the J-shifting approximation agree remarkably well with experimental results. Our calculations also reproduce the markedly different OH(v′=0)/OH(v′=1) branching in O(3P)+H2(v=1) reaction, observed in experiments that use different O(3P) atom sources. In particular, we show that the branching ratio is a strong function of the kinetic energy of the O(3P) atom.
Phase space conduits for reaction in multidimensional systems: HCN isomerization in three dimensions
Authors: Waalkens Holger , Burbanks Andrew , Wiggins Stephen
Published: September 2004

The three-dimensional hydrogen cyanide/isocyanide isomerization problem is taken as an example to present a general theory for computing the phase space structures which govern classical reaction dynamics in systems with an arbitrary (finite) number of degrees of freedom. The theory, which is algorithmic in nature, comprises the construction of a dividing surface of minimal flux which is locally a “surface of no return.” The theory also allows for the computation of the global phase space transition pathways that trajectories must follow in order to react. The latter are enclosed by the stable and unstable manifolds of a so-called normally hyperbolic invariant manifold (NHIM). A detailed description of the geometrical structures and the resulting constraints on reaction dynamics is given, with particular emphasis on the three degrees of freedom case. A procedure is given which uses these structures to compute orbits homoclinic to, and heteroclinic between, NHIMs. The role of homoclinic and heteroclinic orbits in global recrossings of dividing surfaces and transport in complex systems is explained. The complete description provided here is inherently one within phase space; it cannot be inferred from a configuration space picture. A complexification of the classical phase space structures to incorporate quantum effects is also discussed. The results presented here call into question certain assumptions routinely made on the global dynamics; this paper provides methods that enable one to understand and quantify the phase space dynamics of reactions without making such assumptions.
Infrared spectral profiles in liquids and atom-diatom interactions
Authors: Medina A. , Roco J. M. M. , Calvo Hernández A. , Velasco S.
Published: September 2004

Molecular dynamics simulations of the infrared spectrum of a generic simple polar diatomic in a liquid nonpolar solvent allow to reproduce the different prototypical experimental line shapes of this kind of systems. This is feasible by using different solute-solvent anisotropic potentials at fixed thermodynamic conditions. In the limit cases, the rotation of the diatomic is explained in terms of a quasifree motion or a rotational diffusion evolution and the spectra show a doublet structure formed by P and R branches or a unique collapsed branch, respectively. When the profile contains three branches, including an intense Q branch in the vicinity of the center of the band, rotational evolution presents a particular hindering that can be understood by studying the influence on rotational spectral densities of the different time scales involved in rotational relaxation. Cancellation/enhancement effects among spectral density terms arising from intermediate and long times (0.4–1 ps) are essential to understand rotational hindering.
Nonequilibrium charge recombination from the excited adiabatic state of donor-acceptor complexes
Authors: Mikhailova Valentina A. , Ivanov Anatoly I. , Vauthey Eric
Published: September 2004

A model of nonequilibrium charge recombination from an excited adiabatic state of a donor-acceptor complex induced by the nonadiabatic interaction operator is considered. The decay of the excited state population prepared by a short laser pulse is shown to be highly nonexponential. The influence of the excitation pulse carrier frequency on the ultrafast charge recombination dynamics of excited donor-acceptor complexes is explored. The charge recombination rate constant is found to decrease with increasing excitation frequency. The variation of the excitation pulse carrier frequency within the charge transfer absorption band of the complex can alter the effective charge recombination rate by up to a factor 2. The magnitude of this spectral effect decreases strongly with increasing electronic coupling.