bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared spectra and second-harmonic generation in barium strontium titanate and lead zirconate-titanate thin films: “Polaron” artifacts
Authors: Scott J. F. , Jiang A. Q. , Redfern S. A. T. , Zhang Ming , Dawber M.
Published: August 2003

We report infrared absorption spectroscopy and second-harmonic generation data for barium strontium titanate (BST) and lead zirconate-titanate (PZT) ceramic films in the 3000−5500 cm−1 region. Second-harmonic generation experiments give temperature dependences in accord with oxygen vacancy cluster theory [S. A. Prosandeev, Sov. Phys. JETP 83, 747 (1996); S. A. Prosandeev, V. S. Vikhnin, and S. Kapphan, Integr. Ferroelectr. 32, 1047 (2001); J. Phys. Condens. Matter 14, 4407 (2002)]. A percolation model of vacancy ordering is discussed. The present work shows that earlier data interpreted as polaron spectra in these films were actually artifacts due to interference in the optical apparatus used [B. Guettler, U. Bismayer, P. Groves, and E. Salje, Semicond. Sci. Technol. 10, 245 (1950]; more recent “polaron” spectra in WO3 films may also be artifacts [L. Berggren, A. Azens, and G. A. Niklassson, J. Appl. Phys. 90, 1860 (2001)]. Numerical estimates of the polaron mass m**=16 me in SrTiO3 and BST help prove that dielectric data in strontium titanate interpreted as bipolarons [A. Levstik et al., Appl. Phys. Lett. 81, 4046 (2002)] are also artifacts.
Modeling of poling, piezoelectric, and pyroelectric properties of ferroelectric –3 composites
Authors: Or Y. T. , Wong C. K. , Ploss B. , Shin F. G.
Published: August 2003

A model for the piezoelectric and pyroelectric activities of 0–3 composites of ferroelectric particles in a linear matrix has been developed based on the polarization behavior of the inclusions. The model is applied to simulate the piezoelectric activity of a lead zirconate titanate/epoxy system polarized under different fields and the piezo- and the pyroelectric properties of lead titanate/polyvinylidene fluoride–trifluoroethylene 70/30 mol %] composites polarized with different poling times. The model predictions show reasonably good agreement with experimental data. The ability to predict the gross properties of 0–3 composites in terms of the poling field and poling time may be especially helpful in the making of practical composites with particular properties.
Ferroelectric transition in an epitaxial barium titanate thin film: Raman spectroscopy and x-ray diffraction study
Authors: El Marssi M. , Le Marrec F. , Lukyanchuk I. A. , Karkut M. G.
Published: August 2003

We have performed x-ray diffraction and Raman spectroscopy measurements in the temperature range of 300–873 K on a single phase epitaxially oriented BaTiO3 thin film grown by pulsed laser deposition on a single crystal MgO substrate. The θ–2θ room temperature diffraction measurements and asymmetric rocking curves indicate that the film is very weakly tetragonal with the c-axis parallel to the plane of the film. X-ray diffraction measurements up to high temperature reveal only a change in slope in the perpendicular to the plane lattice parameter around 450 K (in bulk Tc=395 K) indicating that a diffuse-like of phase transition is taking place. Room temperature polarized Raman spectra show that the film is indeed tetragonal with C4v symmetry and with the a-axis perpendicular to the film plane. Monitoring of the overdamped soft mode and the 308 cm−1 mode confirms that the phase transition is taking place over a wide temperature range according to the x-ray results. The increase of the phase transition temperature is attributed to the stress effect induced by the substrate.
Toroidal electron temperature gradient mode structure in the presence of nonuniform background flows
Authors: Davydova Tatiana , Bateman Glenn , Kritz Arnold H. , Pankin Alexei
Published: August 2003

The influence of nonuniform poloidal and toroidal background plasma flows on the spatial structure and growth rate of the electrostatic electron temperature gradient (ETG) mode is investigated in the linear approximation. This derivation includes the ballooning mode formalism and a more recently developed version of the direct method by Taylor and Wilson [Plasma Phys. Controlled Fusion 38, 1999 (1996)]. It is shown that the growth rate of the ETG mode is not changed significantly by flow shear. However, it is found that the spatial structure of the ETG mode depends crucially on the derivative of the flow shear rate with respect to the minor radius of the tokamak cross section and also depends crucially on the magnetic shear. For moderate magnetic shear, the unstable ETG mode is strongly localized in the poloidal direction and is elongated along the radial direction, with a characteristic radial width much larger than the electron Larmor radius. This may explain the formation of streamer structures above the threshold of ETG mode instability. Streamers are believed to enhance electron thermal transport beyond the values provided by simple mixing length estimates. For very low values of magnetic shear, the ETG mode structure becomes extended in the poloidal direction, and the ballooning formalism does not apply. In this case, the direct method is used and it is shown that the ETG mode is strongly localized in the radial direction. The small radial extent of these modes may considerably reduce electron heat transport, which would enhance the formation of an electron thermal transport barrier.
Resonance Raman spectroscopic study of fused multiporphyrin linear arrays
Authors: Jeong Dae Hong , Jang Sung Moon , Hwang In-Wook , Kim Dongho , Matsuzaki Yoichi , Tanaka Kazuyoshi , Tsuda Akihiko , Nakamura Takeshi , Osuka Atsuhiro
Published: August 2003

For prospective applications as molecular electric wires, triply linked fused porphyrin arrays have been prepared. As expected from their completely flat molecular structures, π-electron delocalization can be extended to the whole array manifested by a continuous redshift of the HOMO-LUMO transition band to infrared region up to a few μm as the number of porphyrin units in the array increases. To gain an insight into the relationship between the molecular structures and electronic properties, we have investigated resonance Raman spectra of fused porphyrin arrays depending on the number of porphyrin pigments in the array. We have carried out the normal mode analysis of fused porphyrin dimer based on the experimental results including Raman frequency shifts of two types of C13-isotope substituted dimers, Raman enhancement pattern by changing excitation wavelength, and depolarization ratio measurements as well as normal-mode calculations at the B3LYP/6-31G level. In order to find the origins for the resonance Raman mode enhancement mechanism, we have predicted both the excited state geometry changes (A-term) and the vibronic coupling efficiencies (B-term) for the relevant electronic transitions based on the INDO/S-SCI method. A detailed normal mode analysis of the fused dimer allows us to extend successfully our exploration to longer fused porphyrin arrays. Overall, our investigations have provided a firm basis in understanding the molecular vibrations of fused porphyrin arrays in relation to their unique flat molecular structures and rich electronic transitions.
Quantitative analysis of orientational order in the molecular monolayer by surface second harmonic generation
Authors: Rao Yi , Tao Yi-song , Wang Hong-fei
Published: August 2003

We have developed a systematic approach to quantitatively determine the orientational order of molecular monolayer based on surface second harmonic generation (SHG) measurement. Traditionally, the experimentally obtainable orientational parameter D=〈cos θ〉/〈cos3 θ〉 has been used to determine the averaged orientational angle θ with SHG. Also, it has been widely accepted that without the help from other techniques, SHG was insufficient for determination of both the orientational angle θ0 and its distribution Δθ. Here, we derived an explicit and general functional form, R(θ)=|〈cos θ〉−c * 〈cos3 θ〉|2, which is orientationally dependent and is proportional to the SH intensity measured from the molecular monolayer. We further showed that R(θ) contains the full information of the orientational order of the molecular monolayer, and the orientational parameter D represents only a special case of R(θ). Through orientationally sensitive R(θ) and D, both the orientational angle and its distribution could be uniquely and accurately determined from the SHG-only measurements in chosen polarization configurations. Using this approach, we were able to accurately determine both the orientational angle and its distribution in the Langmuir monolayer of a liquid crystal molecule 4′-n-octyl-4-cyanobiphenyl (8CB) at the air/water interface. With such information, we were not only able to show that the phase transition of 8CB from the gas–liquid coexistence region to liquid region is accompanied with a continuous orientational angular distribution narrowing process, but also for the first time we were able to accurately determine a less than 3° tilt angle change of the 8CB chromophore in the whole liquid phase region of the 8CB monolayer. This quantitative approach to orientational analysis of molecular monolayer or multilayer is general for both SHG and sum frequency generation, and should lead the way to more quantitative understanding of the orientational order of molecular films per se.
Identification of new adsorption sites of H and D on rhodium(100)
Authors: Pauer G. , Eichler A. , Sock M. , Ramsey M. G. , Netzer F. , Winkler A.
Published: August 2003

Exposure of Rh(100) to hydrogen (deuterium) in atomic form leads to the population of adsorption sites, not attainable with molecular species. Quantitative thermal desorption spectroscopy (TDS), high resolution electron energy loss spectroscopy (HREELS), and density functional theory (DFT) calculations have been applied to investigate these new adsorption sites. In addition to the fourfold hollow sites (1 ML), which can be populated by dissociative adsorption, occupation of subsurface sites and the population of additional surface sites (for deuterium) have been observed (maximum coverage 3.4 ML). In TDS individual adsorption states show up in the form of three different peaks: Recombination of H (D) atoms from hollow sites around 300 K, desorption of subsurface species between 150–200 K, and recombinative desorption via a molecular precursor at about 120 K (for deuterium only). The exposure of the Rh(100) surface to atomic H (D) leads to a pronounced roughening of the surface, as evidenced in the HREELS spectra. Zero point corrected adsorption energies, activation barriers for adsorption, desorption, and diffusion into the subsurface sites, as well as vibrational energies have been calculated by DFT for a variety of adsorbate configurations of H and D and compared with the experimental data.
Generalized variational principle of Herglotz for several independent variables. First Noether-type theorem
Authors: Georgieva Bogdana , Guenther Ronald , Bodurov Theodore
Published: August 2003

This paper extends the generalized variational principle of Herglotz to one with several independent variables and derives the corresponding generalized Euler–Lagrange equations. The extended principle contains the classical variational principle with several independent variables and the variational principle of Herglotz as special cases. A first Noether-type theorem is proven for the new variational principle, which gives the conserved quantities corresponding to symmetries of the associated functional. This theorem contains the classical first Noether theorem as a special case. As examples for applications we calculate a conserved quantity for the damped nonlinear Klein–Gordon equation and we show that the equations which describe the propagation of electromagnetic fields in a conductive medium can be derived from the generalized variational principle of Herglotz (but not from a classical variational principle).
Improved Epstein–Glaser renormalization. II. Lorentz invariant framework
Authors: Lazzarini Serge , Gracia-Bondı́a José M.
Published: August 2003

The Epstein–Glaser type T-subtraction introduced by one of the authors in a previous paper is extended to the Lorentz invariant framework. The advantage of using our subtraction instead of the Epstein and Glaser standard W-subtraction method is especially important when working in Minkowski space, as then the counterterms necessary to keep Lorentz invariance are simplified. We show how T-renormalization of primitive diagrams in the Lorentz invariant framework directly relates to causal Riesz distributions. A covariant subtraction rule in momentum space is found, sharply improving upon the BPHZL method for massless theories.
Polymer-specific effects of bulk relaxation and stringlike correlated motion in the dynamics of a supercooled polymer melt
Authors: Aichele M. , Gebremichael Y. , Starr F. W. , Baschnagel J. , Glotzer S. C.
Published: August 2003

We analyze dynamical heterogeneities in a simulated “bead-spring” model of a nonentangled, supercooled polymer melt. We explore the importance of chain connectivity on the spatially heterogeneous motion of the monomers. We find that when monomers move, they tend to follow each other in one-dimensional paths, forming strings as previously reported in atomic liquids and colloidal suspensions. The mean string length is largest at a time close to the peak time of the mean cluster size of mobile monomers. This maximum string length increases, roughly in an exponential fashion, on cooling toward the critical temperature TMCT of the mode-coupling theory, but generally remains small, although large strings involving ten or more monomers are observed. An important contribution to this replacement comes from directly bonded neighbors in the chain. However, mobility is not concentrated along the backbone of the chains. Thus, a relaxation mechanism in which neighboring mobile monomers along the chain move predominantly along the backbone of the chains, seems unlikely for the system studied.
The 1,5-H-shift in 1-butoxy: A case study in the rigorous implementation of transition state theory for a multirotamer system
Authors: Vereecken Luc , Peeters Jozef
Published: August 2003

The rigorous implementation of transition state theory (TST) for a reaction system with multiple reactant rotamers and multiple transition state conformers is discussed by way of a statistical rate analysis of the 1,5-H-shift in 1-butoxy radicals, a prototype reaction for the important class of H-shift reactions in atmospheric chemistry. Several approaches for deriving a multirotamer TST expression are treated: oscillator versus (hindered) internal rotor models; distinguishable versus indistinguishable atoms; and direct count methods versus degeneracy factors calculated by (simplified) direct count methods or from symmetry numbers and number of enantiomers, where applicable. It is shown that the various treatments are fully consistent, even if the TST expressions themselves appear different. The 1-butoxy H-shift reaction is characterized quantum chemically using B3LYP-DFT; the performance of this level of theory is compared to other methods. Rigorous application of the multirotamer TST methodology in an harmonic oscillator approximation based on this data yields a rate coefficient of k(298 K,1 atm)=1.4×105 s−1, and an Arrhenius expression k(T,1 atm)=1.43×1011 exp(−8.17 kcal mol−1/RT) s−1, which both closely match the experimental recommendations in the literature. The T-dependence is substantially influenced by the multirotamer treatment, as well as by the tunneling and fall-off corrections. The present results are compared to those of simplified TST calculations based solely on the properties of the lowest energy 1-butoxy rotamer.
Theory of a two-step enantiomeric purification of racemic mixtures by optical means: The D2S2 molecule
Authors: Thanopulos Ioannis , Král Petr , Shapiro Moshe
Published: August 2003

We present an optical “enantio-purification switch” that turns in two steps a racemic mixture of left-handed and right-handed chiral molecules into a pure sample containing the enantiomer of interest. The optical switch is composed of an “enantio discriminator” and an “enantio converter” acting in tandem. The method is robust, insensitive to decay processes, and does not require molecular preorientation. We demonstrate the method for the nanosecond purification of a racemate of (transiently chiral) D2S2 molecules. The energies of the rovibrational states and the related dipole elements are obtained by ab initio calculations.
Simulation of quantum processes using entangled trajectory molecular dynamics
Authors: Donoso Arnaldo , Zheng Yujun , Martens Craig C.
Published: August 2003

In this paper, we describe a new method for simulating quantum processes using classical-like molecular dynamics. The approach is based on solving the quantum Liouville equation in the Wigner representation using ensembles of classical trajectories in phase space. The nonlocality of quantum mechanics is incorporated in the trajectory representation as nonclassical interactions between the members of the ensemble, leading to an entanglement of their evolution. The statistical independence of the individual trajectories making up an ensemble in the classical limit is lost when quantum effects are included, and the entire state of the system must be propagated as a unified whole. We develop the formalism and its numerical implementation, and illustrate its application on two model problems of quantum mechanical tunneling: escape from a metastable well and wave packet penetration of the Eckhart barrier.
Characterization of dihydrogen-bonded D–H⋯H–A complexes on the basis of infrared and magnetic resonance spectroscopic parameters
Authors: Cybulski Hubert , Pecul Magdalena , Sadlej Joanna , Helgaker Trygve
Published: August 2003

The structural, energetic, and spectroscopic properties of the dihydrogen-bonded complexes LiH⋯H2, LiH⋯CH4, LiH⋯C2H6, and LiH⋯C2H2 are investigated. In particular, the interaction energy is decomposed into physically meaningful contributions, and the calculated vibrational frequencies, the magnetic resonance shielding constants, and inter- and intramolecular spin–spin coupling constants are analyzed in terms of their correlation with the interaction energy. Unlike the other three complexes, which can be classified as weak van der Waals complexes, the LiH⋯C2H2 complex resembles a conventional hydrogen-bonded system. The complexation-induced changes in the vibrational frequencies and in the magnetic resonance shielding constants correlate with the interaction energy, as does the reduced coupling JHX2h between the proton of LiH and hydrogen or carbon nucleus of the proton donor, while JHH1h do not correlate with the interaction energy. The calculations have been carried out using Møller–Plesset perturbation theory, coupled-cluster theory, and density-functional theory.
Relativistic correlating basis sets for the main group elements from Cs to Ra
Authors: Noro Takeshi , Sekiya Masahiro , Osanai You , Miyoshi Eisaku , Koga Toshikatsu
Published: August 2003

Contracted Gaussian-type function sets are developed for correlating functions of the ten main group elements from Cs to Ra. A segmented contraction scheme is used for its compactness and efficiency. Contraction coefficients and exponents are determined by minimizing the deviation from accurate natural orbitals or K-orbitals, incorporating the relativistic effect by the third-order Douglas–Kroll approximation. The present basis sets yield more than 98% of atomic correlation energies predicted by accurate natural orbitals of the same size. The use of the present set with the model core potential methods gives more than 99% of the correlation energies obtained by the atomic natural orbitals optimized for the model core potential itself. The present correlating sets applied to relativistic model core potential methods including spin–orbit effects predict the spectroscopic constants of the BiH molecule in excellent agreement with experimental results.
Bound states of positron with urea and acetone molecules using configuration interaction ab initio molecular orbital approach
Authors: Tachikawa Masanori , Buenker Robert J. , Kimura Mineo
Published: August 2003

Characteristic features of the positron binding structure of the urea and acetone molecules are discussed based on the results obtained by the configuration interaction scheme of quantum chemical molecular orbital calculations. This method takes the positron–electron correlation contribution into account explicitly. We have found that the positron distribution is concentrated behind the carbonyl oxygen atom. The positron affinity of urea is larger than that of acetone, which is consistent with the stronger dipole moment of urea.
Analysis of the bonding and reactivity of H and the Al13 cluster using density functional concepts
Authors: Mañanes A. , Duque F. , Méndez F. , López M. J. , Alonso J. A.
Published: August 2003

The bonding of hydrogen in the Al13H aggregate is analyzed in the framework of density functional theory using the local density approximation. The interaction between the H-1s orbital and only certain molecular orbitals of Al13 is responsible for the binding. Different measures of the charge transfer give consistent results and predict the stabilization of a sizable amount of electronic charge, about two electrons, around the proton site. The state of the H atom can be described as a negatively charged impurity screened by the surrounding electron gas, similarly to a H impurity embedded in a vacancy in metallic aluminum. Friedel-type oscillations can be appreciated in the screening charge. Local Fukui functions and condensed Fukui indexes associated to the ground state of the cluster Al13 are used as indicators of molecular reactivity. Those indices allow to predict and understand the equilibrium location of H found in the total energy calculations for Al13H.
Plasma–surface interaction at sharp edges and corners during ion-assisted physical vapor deposition. Part II: Enhancement of the edge-related effects at sharp corners
Authors: Macak E. B. , Münz W.-D. , Rodenburg J. M.
Published: August 2003

In the companion article, E. B. Macak et al., J. Appl. Phys. (2003) (Part I), we demonstrated that changes in the plasma sheath surrounding a sharp edge during ion-assisted physical vapor deposition (PVD) can lead to significant changes in the coating properties in the edge region. In this article, we examine the ion–surface interaction in the case of sharp corners. The three-dimensional corner geometry is shown—both experimentally and theoretically—to cause significant enhancement of the edge-related effects due to substantial increase in the ion flux density close to the corner. For TiAlN/VN coatings deposited on sharp corners of various geometries by closed-field unbalanced magnetron (CF UBM) sputtering using high flux low-energy Ar+-ion irradiation (Ji/Jme∼4, Ei=75−150 eV), the coatings in the corner region deteriorate rapidly with increasing the substrate bias during the deposition. At −75 V, delamination of the coatings, and at −105 V, partial resputtering can be observed. At −150 V, the coatings are completely resputtered from the corner area and the ion bombardment causes a significant erosion of the substrate creating complex topographical structures such as ripples and cones. Significant Al depletion (up to ∼70%) is found at the corners. The spatial extent of the morphological and compositional changes is also greatly enhanced (up to 3 mm from the edge in our conditions). We model the difference between the two-dimensional plasma sheath around an edge and the three-dimensional plasma sheath around a corner. The characteristic shape of the different plasma sheaths is used to calculate the corresponding magnitude of the ion bombardment and the spatial extent of the affected region. In the case of a 30° wedge coated by CF UBM at −150 V, the sputtering rate of the ions in the corner region is found to be up to ∼40 times higher than on flat parts—which explains the observed severe changes.
Structure of high-Tc/manganite perovskite superlattices
Authors: Haberkorn N. , Guimpel J. , Steren L. B. , Campillo G. , Saldarriaga W. , Gómez M. E.
Published: August 2003

We study the crystalline and interface structure of RBa2Cu3O7/La1−xAxMnO3 superlattices (R=Y, Gd; A=Ca, Sr) grown on mismatched MgO substrates by means of nondestructive x-ray diffraction. The diffraction patterns are adjusted to a model of the structure which includes interface roughness and interdiffusion. Our results show that these disorder mechanisms cannot be neglected and should be taken into account to understand the physical properties of these superlattices.
Transport and magnetic properties of La0.7Pb0.3MnO3+x Ag (x=0−20 wt %) nanocomposites
Authors: Pal Sudipta , Banerjee Aritra , Chatterjee S. , Nigam A. K. , Chaudhuri B. K. , Yang H. D.
Published: August 2003

Magnetization and transport properties of La0.7Pb0.3MnO3+x Ag (x=0−20 wt %) nanocomposites have been reported. In this Ag-containing colossal magnetoresistive (CMR) La0.7Pb0.3MnO3 composite (referred to as CMR-Ag), conductivity (σ) and metal–insulator transition temperature (Tp) increase with increasing Ag. Electron microscopy and elemental mapping indicated a uniform distribution of Ag nanoparticles/clusters. The enhancement of Tp is accompanied by a reduction of the c-axis lattice constant. Coexistence of interfacial tunneling with intrinsic transport behavior has been observed at the grain boundaries in the samples with a higher (⩾10 wt %) Ag content. Due to the presence of nonmagnetic Ag in the ferromagnetic La0.7Pb0.3MnO3 material, dc magnetization decreases but the corresponding Tp increases. In the low-temperature (T<Tp) phase, resistivity data follow a T2 dependent behavior for the samples with higher Ag concentration (x⩽5 wt %). On the other hand, for lower Ag (⩽5 wt %) containing samples, a T2.5 dependent behavior is observed. This suggests the importance of both the electron–electron (T2 dependence behavior) and the electron–magnon (T2.5 dependence behavior) interactions for explaining low-temperature (TTp), conductivity data follow the adiabatic polaron hopping conduction mechanism. Unlike the Ag free sample, the variable-range-hopping model is found to be inapplicable for the present Ag containing nanocomposites.
Controlling alloy composition of InAsP self-assembled quantum dots embedded in GaAs
Authors: Maltez R. L. , Ribeiro E. , Carvalho W. , Ugarte D. , Medeiros-Ribeiro G.
Published: August 2003

We report on the growth of quantum dot (QD) layers of InAsP alloys buried in GaAs by low-pressure metalorganic chemical vapor deposition. Ternary QDs were obtained by the addition of a PH3 flux during the InAs QD growth, exhibiting recombination energies lying between those of InAs and InP QDs. The electronic properties of these QDs, as evaluated by photoluminescence spectroscopy, could be tailored by varying both the growth rate and the PH3 flux for a constant AsH3 flux. The morphology of these QDs was investigated by transmission electron microscopy from which the formation of an InAsP ternary alloy QDs was inferred. Based on electron microscopy results, the fundamental role of As incorporation on the morphology of and on the defect nucleation associated to InAsP QDs could be then evaluated. From this optical–structural combined analysis, we were able to identify the growth conditions that produce good quality InAsP QDs embedded in GaAs.
Variable single electron charging energies and percolation effects in molecularly linked nanoparticle films
Authors: Trudeau P.-E. , Escorcia A. , Dhirani A.-A.
Published: August 2003

We study electrical transport in strongly coupled, molecularly linked, gold nanoparticle (NP) films whose bulk dc conductances are governed by percolation phenomena. Films with fewer NPs exhibit current suppression below a threshold voltage, likely due to single-electron charging of NP clusters. In some cases, the thresholds are very large (∼1 V) and suppression persists to room temperature. The thresholds tend to decrease with increasing amounts of NPs in the film, and eventually, metal-like conductance is observed down to at least 10 K. The observed trend toward metal-like conductance, despite the presence of film disorder, is enabled by strong inter-NP coupling and increasing film connectivity. The latter is an inherent property of molecularly linked NP films due to both robust chemical inter-NP linkages provided by alkane dithiol linker molecules, coupled with the ability to grow chains of connected NPs to arbitrary lengths through cyclical Au/dithol treatments. In the case of small thresholds, our data is well described by a high-temperature approximation of “orthodox” theory for a linear array of tunnel junctions.
Analytical and simulation studies of nonlinear effects caused by upper-hybrid waves in plasmas
Authors: Eliasson B. , Shukla P. K.
Published: August 2003

Nonlinear interactions between large amplitude upper-hybrid waves and low-frequency electromagnetic waves in a magnetized plasma have been considered. Specifically, the decay of upper-hybrid waves into lower-hybrid and magnetosonic waves, as well as the modulational instabilities leading to the formation of density cavities which trap upper-hybrid wave envelopes, are investigated both theoretically and numerically. It is found that the three-wave process between two upper-hybrid waves and the lower-hybrid wave, which is the fastest growing instability of the system, is important for the generation of waves of small wave numbers, via the self-interaction of the generated decay products from the three-wave interaction. A comparison between the theory of the parametric decay, simulations of a generalized Zakharov system of equations modeling the interaction between upper-hybrid, lower-hybrid and magnetosonic (fast Alfvénic) waves is presented. Comparisons are made with a simulation of the fully electromagnetic Vlasov–Maxwell system for ions and electrons where a sudden onset of cavities and long wavelength magnetosonic wave emission could be seen, similar as in the simulation of the Zakharov-type system.
Femtosecond response of J aggregates adsorbed onto silver colloid surfaces
Authors: Yaǧlioǧlu Gül , Dorsinville Roger , Özçelik Serdar
Published: August 2003

We have performed femtosecond pump-probe spectroscopy measurements in 1,1’-diethyl- 3,3’-bis(4-sulfobutyl)-5,5’,6,6’-tetrachlorobenz imidazolocarbocyanine (also known as TDBC) J aggregates adsorbed onto silver colloidal surfaces. We show that the dependence on probe power and wavelength of the induced emission band dynamics, intensity, and position can only be explained by assuming stimulated emission from the one-exciton state. The stimulated emission originates from the amplification of the one-exciton state emission by an induced transition from the two-exciton state to the one-exciton state. One of the key causes of the stimulated emission is the formation of coherently coupled TDBC molecules on colloidal silver surfaces.
Effects of exciton and charge confinement on the performance of white organic p−i−n electrophosphorescent emissive excimer devices
Authors: D’Andrade Brian W. , Forrest Stephen R.
Published: August 2003

The quantum efficiency of triplet excimer-based white organic p−i−n light-emitting devices (WOLEDs) is shown to depend exponentially on the thickness of the emissive layer (EML), while the voltage increases approximately linearly with EML thickness. The EML consists of the square planar Pt excimer emitting complex, platinum(II) [2-(4’,6’-difluorophenyl-N, C2′) (2,4-pentanedionato)] doped into N,N’-dicarbazolyl-3,5-benzene, and the electron capture length within the EML is found to vary from 90±10 to 120±10 Å, depending on whether or not the transport layers are p or n doped. The p−i−n WOLED exhibits peak external quantum and power efficiencies of (5.2±0.5)% and (11±1) lm/W, respectively, and at 500 cd/m2 these efficiencies decrease to (4.2±0.4)% and (4.3±0.4) lm/W. The device has color coordinates of (0.35, 0.43) and a color rendering index of 75. We also demonstrate the importance of an electron blocking layer that reduces the leakage of excitons and charge out of thin EMLs, thereby improving the quantum efficiency of devices by a factor approaching 3, as compared to devices lacking the blocking layer.
Nanopatterning of periodically strained surfaces: Predictive kinetic Monte Carlo simulation study
Authors: Larsson M. I. , Sabiryanov R. F. , Cho K. , Clemens B. M.
Published: August 2003

We present a method based on kinetic Monte Carlo simulations to atomically control the nanopatterning by using strain-assisted nucleation of adatom islands on periodically strained surfaces. It is presumed in the model that there is a capping layer of optional thickness terminated by an atomically flat surface above a dislocated interface. By varying the dislocation spacing and geometry as well as the capping layer material and thickness, the surface strain field can be modified. For the model system Co on Pt(111) the optimal growth condition is demonstrated for a surface strain field of period 9 nm for structures with an 8–10-ML-thick Pt capping layer. For these parameters strongly enhanced nucleation at maxima in the periodic strain field is achieved. We study also the effects on the self-organization of strain-relaxed adatom islands and the effects of modified potential energy barriers at step edges, i.e., the Ehrlich–Schwoebel (ES) barriers. Both strain relaxation and ES barriers are found to be of large importance for the nanopatterning. Finally, various nanostructures obtained for different strain fields including parallel, rhomboid, and hexagonal geometries are considered. The method described in this investigation is not restricted to the “Co on Pt(111)” and “Ag on Ag(111)” model systems. The simulation model is of general interest to predict strain-assisted growth of metals and also of semiconductors.
Integrable hydrodynamic chains
Authors: Pavlov Maxim V.
Published: August 2003

A new approach for derivation of Benney-type moment chains and integrable hydrodynamic type systems is presented. New integrable hydrodynamic chains are constructed; all their hydrodynamical reductions are described and integrated. New (2+1) integrable hydrodynamic type systems are found.
Revision of TV Thomson scattering data analysis and detection of profile structure
Authors: van Milligen B. Ph. , Classen I. G. J. , Barth C. J.
Published: August 2003

The determination of electron temperature and density profiles with high resolution Thomson Scattering is reconsidered, focusing on the correct treatment of the statistics and error estimation. Based on this, methods are proposed to decide whether spatial structures observed in the measured profiles are significant. A detailed statistical analysis of the detection process is given. It is shown that a maximum likelihood method must be used to fit the theoretical scattering spectra to the data, in order to obtain electron temperature and density. Furthermore, an existing calibration procedure for the detector, based exclusively on the statistics of the detected scattering image, is perfected. This self-consistent analysis leads to a precise definition of the confidence limits. Based on these, statistical tests are designed to determine whether structures seen on the Thomson scattering profiles are significant or not. To test the statistical method, some TEXTOR discharges were analyzed.
Magnetic calorimeters for high resolution x-ray spectroscopy
Authors: Fleischmann A. , Daniyarov T. , Rotzinger H. , Linck M. , Enss C. , Seidel G. M.
Published: August 2003

Microcalorimeters operating at low temperatures have proven to be suitable tools for high resolution x-ray spectroscopy. Metallic magnetic calorimeters (MMCs) are one kind of such detectors. The operation of a MMC is based on the temperature dependence of the magnetization of a paramagnetic material such as Au doped with Er in a small magnetic field. The temperature of a x-ray absorber, in thermal contact with the paramagnetic material, can be monitored with high sensitivity by using a dc superconducting quantum interference device. An energy resolution of one part in 1000 at 6 keV has now been demonstrated for MMCs. We report on the recent progress in the development of MMCs and discuss the limitations of such devices resulting from fundamental noise sources.
Comparative study of the influence of the gas injection system on the Nd:yttrium-aluminum-garnet laser cutting of advanced oxide ceramics
Authors: Quintero F. , Pou J. , Lusquiños F. , Boutinguiza M. , Soto R. , Pérez-Amor M.
Published: August 2003

Cutting of advanced oxide ceramics is still a difficult task. In this work, the possibility to effectively cut them using a Nd:YAG laser guided by an optical fiber is demonstrated. The key points are the aerodynamic interactions of the assist gas jet in the fusion laser cutting of ceramics. A comprehensive study of the influence of these aerodynamic interactions on the laser cutting of advanced oxide ceramics has been carried out. The characteristics of the heat affected zone (HAZ) were studied related to the efficiency of the assist gas to eject the molten material. It has been demonstrated that the HAZ can be avoided with a suitable design of the gas injection system combined with an appropriate selection of the values of the processing parameters. With the aim of improving the efficiency of the assist gas injection system, a new cutting head with an off-axis supersonic nozzle was developed. Furthermore, a comparison between the utilization of a conventional coaxial conical nozzle to inject the assist gas and the new system is presented. The results obtained give clear proof that the use of the new gas injection system leads to a great improvement on the cut quality by means of a more efficient removing of the molten material out of the cutting front. This result is of special interest in the laser fusion cutting of thick ceramic plates at high processing rates.
In situ manipulation and characterizations using nanomanipulators inside a field emission-scanning electron microscope
Authors: Kim Keun Soo , Lim Seong Chu , Lee Im Bok , An Key Heyok , Bae Dong Jae , Choi Shinje , Yoo Jae-Eun , Lee Young Hee
Published: August 2003

We have used two piezoelectric nanomanipulators to manage the multiwalled carbon nanotubes (MWCNTs) within the field emission-scanning electron microscope (FE-SEM). For an easy access of a tungsten tip to MWCNTs, we prepared the tungsten tip in sharp and long tip geometry using different electrochemical etching parameters. In addition, the sample stage was tilted by 45° from the normal direction of the surface to allow a better incident angle to the approaching tungsten tip. For manipulations, a nanotube or the bundles were attached at the tungsten tip using an electron beam-induced deposition (EBID). Using two manipulators, we have then fabricated a CNT-based transistor, a cross-junction of MWCNTs, and a CNT-attached atomic force microscopy tip. After these fabrications, the field emission properties of the MWCNT and junction properties of the MWCNT and the tungsten tip have been investigated. We found that the EBID approach was very useful to weld the nanostructured materials on the tungsten tip by simply irradiating the electron beam, although this sometimes increased the contact resistance by depositing hydrocarbon materials.
Light amplification in polymer field effect transistor structures
Authors: Pauchard Marc , Swensen James , Moses Daniel , Heeger Alan J. , Perzon Erik , Andersson Mats R.
Published: August 2003

The amplified spontaneous emission (ASE) of optically pumped films of poly(2-(2′,5′-bis(octyloxy)benzene)-1,4-phenylenevinylene (BOP-PPV) was studied in structures comprising a gate electrode, a thin film of gate insulator material (SiO2) and the polymer film as luminescent semiconducting layer (i.e. a field effect transistor without the source and drain electrodes). The influences of different gate electrodes on the threshold and the wavelength of the amplified emission were measured for variable thickness of the gate insulator. An exponential increase in ASE threshold (It) with decreasing separation between electrode and polymer layer was observed. In structures with 200 nm SiO2 gate insulator, It=300 kW/cm2 with an n-Si gate electrode and 200 kW/cm2 with Au electrode (100 nm thick). Compared to the same polymer film on pure SiO2 (It=2 kW/cm2), this increase results from waveguide losses in the nearby gate electrode. With an indium–tin–oxide (ITO) gate electrode (140 nm thick) on glass, again with a 200 nm SiO2 gate insulator, It=30 kW/cm2. The ITO electrode acts as a second waveguide, and the light is distributed into two modes. The observed wavelength shift and the increasing It with decreasing SiO2 thickness result from this mode structure. When the thickness of the ITO electrode is less than 60 nm, the mode traveling mainly in the ITO is cutoff, and a single waveguide structure is formed with an associated reduction in It. For an ITO thickness of 12 nm, It=4 kW/cm2, only two times bigger than that observed in a pure BOP-PPV film on fused silica.
Development of a multistage laser frequency stabilization for an interferometric gravitational-wave detector
Authors: Nagano Shigeo , Kawamura Seiji , Ando Masaki , Takahashi Ryutaro , Arai Koji , Musha Mitsuru , Telada Souichi , Fujimoto Masa-Katsu , Fukushima Mitsuhiro , Kozai Yoshihide , Miyama Shoken , Ueda Akitoshi , Waseda Koichi , Yamazaki Toshitaka , Ishizuka Hideki , Kuroda Kazuaki , Matsumura Sumihiro , Miyakawa Osamu , Miyoki Shinji , Ohashi Masatake , Sato Shuichi , Tatsumi Daisuke , Tomaru Takayuki , Uchiyama Takashi , Kawabe Keita , Ohishi Naoko , Otsuka Shigemi , Sekiya Atsushi , Takamori Akiteru , Taniguchi Shinsuke , Tochikubo Kuniharu , Tsubono Kimio , Ueda Kozo , Yamamoto Kazuhiro , Mio Norikatsu , Moriwaki Shigenori , Horikoshi Gen’ichi , Kamikubota Norihiko , Ogawa Yujiro , Saito Yoshio , Suzuki Toshikazu , Nakagawa Ken’ichi , Ueda Ken-ichi , Araya Akito , Kanda Nobuyuki , Kawashima Nobuki , Mizuno Eiichi , Barton Mark A. , Tsuda Nobuhiro , Matsuda Namio , Nakamura Takashi , Sasaki Misao , Shibata Masaru , Tagoshi Hideyuki , Tanaka Takahiro , Nakao Ken-ichi , Oohara Ken-ichi , Kojima Yasufumi , Futamase Toshifumi , Asada Hideki
Published: August 2003

Laser frequency stabilization is essential for interferometric gravitational-wave detectors to attain their target sensitivity. We have designed a multistage laser frequency stabilization system which has been applied in the development of the TAMA 300 gravitational-wave detector in Japan. The control topology consisting of two cascaded loops were employed to secure high feedback gain and reliable detector operation and thus allow the best frequency stability and uninterrupted long-term observation. We achieved simultaneously a frequency stability of 5×10−5 Hz/Hz, and a common-mode rejection ratio (which reduces the coupling of frequency noise to spurious signals in the detector) of 37 dB. The developed system enabled us to operate TAMA 300 with sufficient sensitivity and stability that it had the potential to register gravitational-wave events. The system was confirmed to be suitable for a gravitational-wave detector from the observation run of TAMA 300.
High pressure view-cell for simultaneous in situ infrared spectroscopy and phase behavior monitoring of multiphase chemical reactions
Authors: Schneider M. S. , Grunwaldt J.-D. , Bürgi T. , Baiker A.
Published: August 2003

A new type of high pressure spectroscopy view-cell for investigation of multiphase reactions is presented. It allows visual observation of the reaction mixture at conditions up to 200 °C and 200 bar. Measurements of the reactor cell’s upper part by transmission spectroscopy with variable path length and of the cell’s bottom part by attenuated total reflection (ATR) spectroscopy can be performed quasi-simultaneously. By coating the internal reflection element with a catalyst film, in situ investigations of heterogeneous catalysts can be performed. The potential of this new experimental setup is demonstrated using examples of heterogeneous and homogeneous catalytic reactions. For the heterogeneously catalyzed hydrogenation of ethyl pyruvate over Pt/Al2O3 in “supercritical” ethane the reaction progress could be monitored by spectroscopic investigation of the fluid phase. Quantitative evaluation of the spectra combined with digital imaging of the reaction mixture allowed simultaneous determination of phase behavior and reaction kinetics. ATR-IR spectra of the catalyst film could be measured at the same time. In the homogeneously catalyzed formylation of morpholine with “supercritical” carbon dioxide and hydrogen, not only number and nature, but also the composition of the different phases could be determined. The catalyst was found to be confined to the liquid phase. Although the aim of these preliminary studies was to test the functionality of the new cell, already significant new insight on the investigated catalytic reactions could be gained.
Correlation of microwave dielectric properties and normal vibration modes of xBa(Mg1/3Ta2/3)O3–(1−x)Ba(Mg1/3Nb2/3)O3 ceramics: I. Raman spectroscopy
Authors: Chia Chih-Ta , Chen Yi-Chun , Cheng Hsiu-Fung , Lin I-Nan
Published: August 2003

Micro-Raman measurements of xBa(Mg1/3Ta2/3)O3–(1−x)Ba(Mg1/3Nb2/3)O3 perovskite ceramics, with x=0, 0.25, 0.50, 0.75, and 1.0, were taken at room temperature. Raman results clearly show the 1:2 ordered structures of these compounds. Four A1g and five Eg Raman modes were unambiguously assigned. The A1g(O) phonon of the oxygen-octahedron stretch mode, which possesses the largest energy and width of all the observed Raman phonons, significantly influences the microwave dielectric properties of the materials. A higher vibration frequency of A1g(O) mode results in a lower dielectric constant, and a wider width of the mode corresponds to a lower Q×f value.
Structural and morphological control of nanosized Cu islands on SiO2 using a Ti underlayer
Authors: Hu Minghui , Noda Suguru , Okubo Tatsuya , Yamaguchi Yukio , Komiyama Hiroshi
Published: August 2003

The structure and morphology of nanosized Cu islands grown by sputter deposition on clean SiO2 substrates and Ti-underlayered SiO2 substrates are investigated using transmission electron microscopy. On SiO2, spherical Cu islands with a random crystalline orientation are formed, whereas on Ti/SiO2, semispherical islands with a preferred 〈111〉 crystalline orientation are formed. Moreover, the Cu islands on Ti/SiO2 have smaller sizes, shorter interisland distances, and a higher number density than those on SiO2. These structural and morphological changes at the nanoscale are discussed from the viewpoint of interfacial interactions. Our study suggests that by using an appropriate metal underlayer, it is possible to fabricate nanosized islands with the desired wettability, crystalline orientation, as well as morphology of island ensembles.
Time-resolved photoluminescence studies of CdTe solar cells
Authors: Metzger W. K. , Albin D. , Levi D. , Sheldon P. , Li X. , Keyes B. M. , Ahrenkiel R. K.
Published: August 2003

We show that time-resolved photoluminescence measurements of completed polycrystalline CdTe solar cells provide a measure of recombination near the CdTe/CdS metallurgical interface that is strongly correlated to the open-circuit voltage in spite of complex carrier dynamics in the junction region. Oxygen in the growth ambient during close-spaced sublimation generally reduces this recombination rate; grain size does not have a strong effect.