bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibrational dynamics of DNA. II. Deuterium exchange effects and simulated IR absorption spectra
Authors: Lee Chewook , Cho Minhaeng
Published: September 2006

In Paper I, we studied vibrational properties of normal bases, base derivatives, Watson-Crick base pairs, and multiple layer base pair stacks in the frequency range of 1400–1800cm−1. However, typical IR absorption spectra of single- and double-stranded DNA have been measured in D2O solution. Consequently, the more relevant bases and base pairs are those with deuterium atoms in replacement with labile amino hydrogen atoms. Thus, we have carried out density functional theory vibrational analyses of properly deuterated bases, base pairs, and stacked base pair systems. In the frequency range of interest, both aromatic ring deformation modes and carbonyl stretching modes appear to be strongly IR active. Basis mode frequencies and vibrational coupling constants are newly determined and used to numerically simulate IR absorption spectra. It turns out that the hydration effects on vibrational spectra are important. The numerically simulated vibrational spectra are directly compared with experiments. Also, the O18-isotope exchange effect on the poly(dG):poly(dC) spectrum is quantitatively described. The present calculation results will be used to further simulate two-dimensional IR photon echo spectra of DNA oligomers in the companion Paper III.
High energy x-ray imager for inertial confinement fusion at the National Ignition Facility
Authors: Tommasini Riccardo , Koch Jeffrey A. , Young Bruce , Ng Ed , Phillips Tom , Dauffy Lucile
Published: September 2006

X-ray imaging is a fundamental diagnostic tool for inertial confinement fusion (ICF) research and provides data on the size and the shape of the core in implosions. We report on the feasibility and performance analyses of an ignition x-ray imager to be used on cryogenic deuterium-tritium implosions at the National Ignition Facility. The system is intended to provide time-integrated, broadband, moderate-energy x-ray core images of imploding inertial confinement fusion capsules. It is optimized with respect to spatial-resolution, signal-to-background, and signal-to-noise ratios, taking into account the extreme operating conditions expected at NIF due to high expected neutrons yields, gamma rays, and x rays from laser-plasma interactions.
Calculation of re-emission diagnostic in NIF ignition Hohlraum at 1MJ laser energy
Authors: Delamater N. , Bradley P. , Magelssen G. , Wilson D.
Published: September 2006

Preliminary results of a two-dimensional design study are discussed for a SiO2 foam filled Hohlraum containing a Bi-coated re-emission capsule. The Hohlraum wall consists of a Au–U “cocktail” designed to maximize the amount of x-ray energy produced for the capsule to absorb, given the 1MJ laser energy into the Hohlraum. The foam fill acts to minimize wall expansion while maintaining symmetric drive on the capsule. Various foam densities and laser pointings for most efficient drive are considered. Sensitivities to drive asymmetries during the long “foot” portion of the laser drive are calculated and shown for the re-emission capsule. The foam fill was found to affect the re-emit symmetry much more than a H∕He gas fill. Compensating effects in beam balance or pointing are required to maintain best symmetry. The effect of the diagnostic on the Hohlraum environment with a Cu-doped Be ignition capsule is discussed. Effects of optimal filtering for maximum signal detectability are considered.
Carbon ion plume emission produced by charge exchange with neutral beams on National Spherical Torus Experiment
Authors: Bell Ronald E.
Published: September 2006

Emission from impurity ions excited by charge exchange with injected beam neutrals is widely used to provide local measurements of ion temperature, velocity, and density. Following the charge exchange process, hydrogenic impurity ions travel along magnetic field lines and may be excited by electron impact from the ground state before they are ionized, producing “plume” emission. This nonlocal emission from plume ions that drift into view can adversely affect the interpretation of charge exchange spectra. Carbon plume emission is observed in the background sightlines of the charge exchange recombination spectroscopy diagnostic of the National Spherical Torus Experiment. In plasmas with high rotation, superthermal flow of carbon ions produces a near Gaussian line shape for the plume emission. Modeling of the production, electron impact excitation, and ionization of the plume ions along the magnetic field lines yields line widths and line shifts consistent with observations. A radial shift between the measured and modeled plume brightness profiles is observed. Plume emission is observed on sightlines that equilibrium reconstruction indicates are not connected to the neutral beam volume, indicating a possible new constraint for the equilibrium reconstruction.
Initial results from the lost alpha diagnostics on Joint European Torus
Authors: Darrow Doug , Baeumel Stefan , Cecil Ed , Ellis Bob , Fullard Keith , Hill Ken , Horton Alan , Kiptily Vasily , Pedrick Les , Reich Matthias , Werner Andreas ,   JET-EFDA Contributors
Published: September 2006

Two devices have been installed in the Joint European Torus (JET) vacuum vessel near the plasma boundary to investigate the loss of energetic ions and fusion products in general and alpha particles in particular during the upcoming JET experiments. These devices are (i) a set of multichannel thin foil Faraday collectors and (ii) a well collimated scintillator, which is optically connected to a charge-coupled device. Initial results including the radial energy and poloidal dependence of lost ions from hydrogen and deuterium plasmas during the 2005-06 JET restart campaign will be presented.
Design of the Tore Supra motional Stark effect diagnostic
Authors: Lotte Ph. , Echard B. , Hess W. , Migozzi J. B.
Published: September 2006

This article describes the overall design of the motional Stark effect diagnostic on Tore Supra (not water cooled in its first version) and the results obtained. The diagnostic is composed of nine viewing lines measuring the plasma every 8cm with a spatial resolution varying from 3to6cm. A tube placed inside the port adjacent to the neutral beam contains a stainless-steel mirror and SFL6 optic lenses that carry the image of the neutral beam towards the optical fibers. On Tore Supra the diagnostics having components inside the machine have to face thermal load difficulties linked with the long shots, and this will be the case for ITER diagnostics. This is why for safety reasons the insulating window is placed at the rear side of the tube, and consequently the optics is under the machine vacuum. For motional Stark effect, before reaching the thermal limits on the components, a first limitation comes from the polarization modifications induced by the temperature gradients on the lenses (birefringence effect). This limitation is estimated in terms of plasma duration. The associated diagnostic neutral beam (60keV, 400kW, 5s) works in hydrogen for a higher velocity and a better plasma penetration. As a consequence the beam spectrum exhibits a large Doppler shift and a clear separation of the Stark components. The detection uses the classical elements of the polarimetry method, wide aperture photoelastic modulators, linear polarizer, narrow interference filters, and photomultipliers. The signal is processed digitally (250kHz) for the extraction of the Fourier components that allow the calculation of the magnetic field pitch angles. The first measurements obtained during Ohmic shots for various plasma currents are in good agreement with the current diffusion calculations done with the CRONOS code.
Plasmadynamic hypervelocity dust injector for the National Spherical Torus Experiment
Authors: Ticoş Cătălin M. , Wang Zhehui , Dorf Leonid A. , Wurden Glen A.
Published: September 2006

The design and construction of a plasmadynamic device to accelerate dust to hypervelocities is presented. High speed dust will be used to measure magnetic field lines in the National Spherical Torus Experiment. The plasma gun produces a high density (ne≈1018cm−3) and low temperature (a few eV) deuterium plasma, ejected by J×B forces which provide drag on the dust particles in its path. The dust will be entrained by the plasma to velocities of 1–30km∕s, depending on the dust mass. Carbon dust particles will be used, with diameters from 1to50μm. The key components of the plasmadynamic accelerator are a coaxial plasma gun operated at 10kV (with an estimated discharge current of 200kA), a dust dispenser activated by a piezoelectric transducer, and power and remote-control systems.
Radiative cooling of laser ablated vapor plumes: Experimental and theoretical analyses
Authors: Wen Sy-Bor , Mao Xianglei , Greif Ralph , Russo Richard F.
Published: September 2006

A study was made of the cooling of the laser induced vapor plume in background air. The temperature and size variations of the vapor plume were determined from spectroscopic measurements during the first few tens of microseconds after the laser pulse. Experiments were carried out over a range of laser spot sizes and energies. The energy transport by thermal radiation from the vapor plume to the background air and to the test sample was formulated. Spectral line by line calculations were made by (a) calculating the detailed line emission profiles (valid for all optical depths), as well as by (b) dividing the lines into being either optically thin or optically thick. The calculations agreed with one another and with the experimental results for the decreasing vapor plume temperature. It was also shown that for optically thin conditions, which are often valid for small vapor plumes, the variation of the surface reflectivity of the test sample had very little effect on the cooling process. For optically thin conditions, the temperature decrease of the vapor plume was independent of the plume size, shape, and position. For larger optical thicknesses of the vapor plume, the calculations showed that the reflectivity of the sample surface and the size of the vapor plume would dramatically affect cooling of the vapor plume.
Influence of the crystal microstructure on the dielectric response of the La0.67Li0.2Ti0.8Al0.2O3
Authors: García-Martín Susana , Morata-Orrantia Ainhoa , Alario-Franco Miguel Á.
Published: September 2006

Polycrystalline samples of La0.67Li0.2Ti0.8Al0.2 with different crystal microstructures have similar general dielectric behavior. The materials show very high dielectric permittivity (ε′≈300000) over relatively wide frequency and temperature ranges with no apparent dependence on the microstructure. The impedance spectroscopy study indicates that the origin of the high dielectric constant is a barrier layer capacitor effect due to depletion of Li ions at the grain boundaries of these Li-conducting materials. However, influence of the three dimensional microstructure domains on bulk properties such as electrical resistance and capacitance is observed.
Adsorbate coverages and surface reactivity in methanol oxidation over Cu(110): An in situ photoelectron spectroscopy study
Authors: Günther S. , Zhou L. , Hävecker M. , Knop-Gericke A. , Kleimenov E. , Schlögl R. , Imbihl R.
Published: September 2006

The adsorbate species present during partial oxidation of methanol on a Cu(110) surface have been investigated in the 10−5mbar range with in situ x-ray photoelectron spectroscopy and rate measurements. Two reaction intermediates were identified, methoxy with a C 1s binding energy (BE) of 285.4eV and formate with a C 1s BE of 287.7eV. The c(2×2) overlayer formed under reaction conditions is assigned to formate. Two states of adsorbed oxygen were found characterized by O 1s BE’s of 529.6 and 528.9eV, respectively. On the inactive surface present at low T around 300–350K formate dominates while methoxy is almost absent. Ignition of the reaction correlates with a decreasing formate coverage. A large hysteresis of ≈200K occurs in T-cycling experiments whose correlation with adsorbate species was studied with varying oxygen and methanol partial pressures. The two branches of the hysteresis differ mainly in the amount of adsorbed oxygen, the methoxy species, and a carbonaceous species. Methoxy covers only a minor part of the catalytic surface reaching at most 20%. Above 650K the surface is largely adsorbate-free.
Capillary condensation and quantum vacuum effects on the pull-in voltage of electrostatic switches with self-affine rough plates
Authors: Palasantzas George
Published: September 2006

In this work, we study the influence of capillary forces in combination with electrostatic and quantum vacuum generated forces on the pull-in voltage of microswitches having self-affine rough surfaces. This type of roughness is described by the rms roughness amplitude w, the in-plane correlation length ξ, and the roughness exponent H that quantifies the degree of surface irregularity at short length scales (<ξ). It is shown that an attractive capillary force decreases more the effective pull-in voltage when the plate surfaces are rougher. The latter corresponds to smaller roughness exponents H and/or larger long wavelength roughness ratios w∕ξ. Notably, the capillary contribution increases the sensitivity of the effective pull-in voltage on the roughness exponent H. This behavior takes place for values of H close to its experimental accuracy.
General method to evaluate substrate surface modification techniques for light extraction enhancement of organic light emitting diodes
Authors: Krummacher B. C. , Mathai M. K. , Choong V. , Choulis S. A. , So F. , Winnacker A.
Published: September 2006

The external light output of organic light emitting diodes (OLEDs) can be increased by modifying the light emitting surface. The apparent light extraction enhancement is given by the ratio between the efficiency of the unmodified device and the efficiency of the modified device. This apparent light extraction enhancement is dependent on the OLED architecture itself and is not the correct value to judge the effectiveness of a technique to enhance light outcoupling due to substrate surface modification. We propose a general method to evaluate substrate surface modification techniques for light extraction enhancement of OLEDs independent from the device architecture. This method is experimentally demonstrated using green electrophosphorescent OLEDs with different device architectures. The substrate surface of these OLEDs was modified by applying a prismatic film to increase light outcoupling from the device stack. It was demonstrated that the conventionally measured apparent light extraction enhancement by means of the prismatic film does not reflect the actual performance of the light outcoupling technique. Rather, by comparing the light extracted out of the prismatic film to that generated in the OLED layers and coupled into the substrate (before the substrate/air interface), a more accurate evaluation of light outcoupling enhancement can be achieved. Furthermore we show that substrate surface modification can change the output spectrum of a broad band emitting OLED.
Optical and structural properties of GaN nanopillar and nanostripe arrays with embedded InGaN∕GaN multi-quantum wells
Authors: Keller S. , Schaake C. , Fichtenbaum N. A. , Neufeld C. J. , Wu Y. , McGroddy K. , David A. , DenBaars S. P. , Weisbuch C. , Speck J. S. , Mishra U. K.
Published: September 2006

GaN nanopillar and nanostripe arrays with embedded InGaN∕GaN multi-quantum wells (MQWs) were fabricated by holographic lithography and subsequent reactive ion etching. Etch related damage of the nanostructures was successfully healed through annealing in NH3∕N2 mixtures under optimized conditions. The nanopatterned samples exhibited enhanced luminescence in comparison to the planar wafers. X-ray reciprocal space maps recorded around the asymmetric (101¯5) reflection revealed that the MQWs in both nanopillars and nanostripes relaxed after nanopatterning and adopted a larger in-plane lattice constant than the underlying GaN layer. The pillar relaxation process had no measurable effect on the Stokes shift typically observed in MQWs on c-plane GaN, as evaluated by excitation power dependent photoluminescence (PL) measurements. Angular-resolved PL measurements revealed the extraction of guided modes from the nanopillar arrays.
Epitaxial composites of Sr ferrite and hematite grown on Al2O3 by electron beam deposition and heat treatment
Authors: Kado Tetsuo
Published: September 2006

We prepared Sr-ferrite films by heat treating spinel ferrite films containing 2at.% of Sr at 1123K for 1h under an oxygen pressure of 4×10−3Pa. The spinel ferrites were epitaxially grown on Al2O3 (00.1) substrates by electron beam deposition using Sr ferrite and SrO2 as sources. Data measured with a vibrating sample magnetometer revealed that the film exhibited a magnetic uniaxial anisotropy axis perpendicular to the film plane and the coercivity was 2.5kOe. Measurements with x-ray diffraction and electron diffraction revealed that the films were composites of Sr ferrites and hematites, and the Sr ferrites and hematites had epitaxially grown in the form of layers. The epitaxial relations between Sr ferrite, Fe2O3, and Al2O3 were [00.1]Srferrite‖[00.1]Fe2O3‖[00.1]Al2O3 and [1−1.0]Srferrite‖[11.0]Fe2O3‖[11.0]Al2O3.
On the enhanced sampling over energy barriers in molecular dynamics simulations
Authors: Gao Yi Qin , Yang Lijiang
Published: September 2006

We present here calculations of free energies of multidimensional systems using an efficient sampling method. The method uses a transformed potential energy surface, which allows an efficient sampling of both low and high energy spaces and accelerates transitions over barriers. It allows efficient sampling of the configuration space over and only over the desired energy range(s). It does not require predetermined or selected reaction coordinate(s). We apply this method to study the dynamics of slow barrier crossing processes in a disaccharide and a dipeptide system.
Temperature dependent evolution of the local electronic structure of atmospheric plasma treated carbon nanotubes: Near edge x-ray absorption fine structure study
Authors: Roy S. S. , Papakonstantinou P. , Okpalugo T. I. T. , Murphy H.
Published: September 2006

Near edge x-ray absorption fine structure (NEXAFS) spectroscopy has been employed to obtain the temperature dependent evolution of the electronic structure of acid treated carbon nanotubes, which were further modified by dielectric barrier discharge plasma processing in an ammonia atmosphere. The NEXAFS studies were performed from room temperature up to 900°C. The presence of oxygen and nitrogen containing functional groups was observed in C K edge, N K edge, and O K edge NEXAFS spectra of the multiwalled carbon nanotubes. The N K edge spectra revealed three types of π* features, the source of which was decisively identified by their temperature dependent evolution. It was established that these features are attributed to pyridinelike, NO, and graphitelike structures, respectively. The O K edge indicated that both carbonyl (CO), π*(CO), and ether C–O–C, σ*(CO), functionalities were present. Upon heating in a vacuum to 900°C the π*(CO) resonances disappeared while the σ*(CO) resonances were still present confirming their higher thermal stability. Heating did not produce a significant change in the π* feature of the C K edge spectrum indicating that the tabular structure of the nanotubes is essentially preserved following the thermal decomposition of the functional groups on the nanotube surface.
Ultrathin amorphous Si layer for the growth of strain relaxed Si0.75Ge0.25 alloy layer
Authors: Rahman M. M. , Zheng S. Q. , Mori M. , Tambo T. , Tatsuyama C.
Published: September 2006

We propose a method for the growth of strain relaxed and smooth Si0.75Ge0.25 alloy layers on a Si(001) substrate. In this method, we have used an ultrathin amorphous Si (UTA-Si) layer as a buffer layer and implemented a two-step process to grow the top alloy layer. High-resolution x-ray diffraction studies show that the alloy layers are highly relaxed. Topographic studies by contact mode atomic force microscopy show that the surfaces are very smooth. UTA-Si works as a strain adjuster and helps to reduce residual strain introducing dislocation in the buffer and substrate regions. However, it was observed that the residual strain and the surface morphology depend on the thickness of the UTA-Si buffer layers and also on the growth mode of the alloy layer.
Elastic, anelastic, and piezoelectric coefficients of α-quartz determined by resonance ultrasound spectroscopy
Authors: Ogi Hirotsugu , Ohmori Toshinobu , Nakamura Nobutomo , Hirao Masahiko
Published: September 2006

All independent components of the elastic constants, internal friction, and piezoelectric coefficients of synthetic α-quartz have been simultaneously determined by resonance ultrasound spectroscopy coupled with laser-Doppler interferometry. Seventeen crystals obtained from Z and X regions with various infrared-absorption values were used; for each crystal, a complete set of the coefficients was determined using 72 resonance frequencies, which were measured by a needle-transducer tripod in a vacuum at a constant temperature with frequency-error limit of 0.001%. The infrared-absorption value and grown region did not strongly affect the material coefficients. Among the eight (elastic plus piezoelectric) coefficients, piezoelectric coefficients were significantly different from previously reported values. The six independent internal-friction components showed a positive correlation with the temperature derivatives of the corresponding elastic constants, indicating that the dominant damping mechanism was the phonon-phonon scattering. Our values at 30°C are C11=86.76GPa, C12=6.868GPa, C13=11.85GPa, C14=−18.02GPa, C33=105.5GPa, C44=58.14GPa, and e11=0.151C∕m2, and e14=−0.061C∕m2.
Swift heavy ion irradiation of a-Si∕Fe∕c-Si trilayers
Authors: Zhang K. , Lieb K. P. , Milinovic V. , Sahoo P. K.
Published: September 2006

Si ∕ Fe ∕ Si trilayers, with 12nm amorphous Si and 45nm polycrystalline Fe films deposited on Si(100) wafers, were irradiated with 350MeV Au26+ ions at fluences of (0.6–11.3)×1014ions∕cm2. The ion-induced modifications of their structural and magnetic properties were characterized by means of Rutherford backscattering, glancing angle x-ray diffractometry, and the magneto-optical Kerr effect. The mixing rate at the upper a-Si∕Fe interface was three times as high as that at the lower Fe∕c-Si interface. A simple formula is proposed, which on the basis of (nuclear) thermal-spike mixing reproduces the observed (electronic) mixing rates. Ion irradiation at a moderate fluence (6.7×1014∕cm2) induced a magnetic anisotropy in the sample, which was magnetically isotropic after deposition. At the highest fluence, full interface mixing occurred and the magnetic anisotropy almost disappeared. The results are compared with those obtained in Fe∕Si and Ni∕Si bilayers ion irradiated in the regimes of nuclear and electronic stopping.
Continuous-wave laser annealing of free-standing Si∕SiO2 superlattice: Modification of optical, structural, and light-emitting properties
Authors: Khriachtchev Leonid , Räsänen Markku , Novikov Sergei
Published: September 2006

Raman, optical, and photoluminescence studies of a free-standing Si∕SiO2 superlattice (SL) are described with emphasis on laser-induced thermal effects (laser annealing). The Si∕SiO2 SL (500 repeats of 2-nm-thick Si and SiO2 layers) on a Si substrate was grown by a molecular beam deposition method and annealed at 1100°C for 1h in an oven, which promoted Si nanocrystals. Then the Si substrate was partially chemically etched producing free-standing areas. Continuous-wave laser annealing (∼104W∕cm2) of the as-prepared free-standing SL strongly increases the Raman band of Si nanocrystals at ∼515cm−1, which features laser-induced crystallization and presumably originates from melting of Si nanostructures. The obtained results show that thermal annealing at 1100°C does not finish structural reorganization of the Si∕SiO2 SL material and a large proportion of Si excess can be undetectable by Raman spectroscopy in related thermally annealed materials. For the laser-crystallized samples, various material characteristics (Raman spectra, light emission, and absorption) have been measured as a function of laser-induced temperature and period of laser annealing. The light emission is found to be a straightforward function of the temperature whereas the absorption coefficient depends on the laser-annealing period suggesting additional laser-induced structural reorganization.
Nanocomposite nc-TiC∕a-C thin films for electrical contact applications
Authors: Lewin Erik , Wilhelmsson Ola , Jansson Ulf
Published: September 2006

Thin film nanocomposites of nanocrystalline TiC embedded in a matrix of amorphous carbon have been prepared by nonreactive unbalanced dc-magnetron sputtering. These samples have been tested as coating materials for electrical contacts and show great potential as an alternative to traditional metallic coatings for contacts subjected to wear and friction. Through variation of composition and deposition temperature different microstructures have been attained. The coatings have been characterized using x-ray diffraction, x-ray photoelectron spectroscopy, and Raman spectroscopy. The performance of the coatings has been coupled to the microstructure whereby tuning and optimization possibilities have been identified.
Acoustic method of investigating the material properties and humidity sensing behavior of polymer coated piezoelectric substrates
Authors: Caliendo Cinzia
Published: September 2006

The relative humidity (RH) sensing behavior of a polymeric film was investigated by means of polymer coated surface acoustic wave (SAW) delay lines implemented on single crystal piezoelectric substrates, such as quartz and LiNbO3, and on thin piezoelectric polycrystalline films, such as ZnO and AlN, on Si and GaAs. The same SAW delay line configuration was implemented on each substrate and the obtained devices’ operating frequency was in the range of 105–156MHz, depending on the type of the substrate, on its crystallographic orientation, and on the SAW propagation direction. The surface of each SAW device was covered by the same type RH sensitive film of the same thickness and the RH sensitivity of each polymer coated substrate, i.e., the SAW relative phase velocity shift per RH unit changes, was investigated in the 0%—80% RH range. The perturbational approach was used to relate the SAW sensor velocity response to the RH induced changes in the physical parameters of the sensitive polymer film: the incremental change in the mass density and shear modulus of the polymer film per unit RH change were estimated. The shift of the bare SAW delay lines operating frequency induced by the presence of the polymer film, at RH=0% and at T=−10°C, allowed the experimental estimation of the mass sensitivity values of each substrate. These values were in good accordance with those reported in the literature and with those theoretically evaluated by exact numerical calculation. The shift of the bare SAW delay lines propagation loss induced by the polymer coating of the device surface, at RH=0% and at ambient temperature, allowed the experimental estimation of the elastic sensitivity of each substrate. These values were found in good accordance with those available from the literature. The temperature coefficient of delay and the electromechanical coupling coefficient of the bare substrates were also estimated. The membrane sensitivity to ethanol, methanol and isopropylic alcohol was tested by means of a high-frequency (670MHz) high-sensitivity Si∕AlN resonator sensor.
Damage production in GaAs and GaAsN induced by light and heavy ions
Authors: Björkas C. , Nordlund K. , Arstila K. , Keinonen J. , Dhaka V. D. S. , Pessa M.
Published: September 2006

Ion irradiation causes damage in semiconductor crystal structures and affects charge carrier dynamics. We have studied the damage production by high-energy (100keV–10MeV) H, He, Ne, and Ni ions in GaAs and GaAs90N10 using molecular dynamics computer simulations. We find that the heavier Ne and Ni ions produce a larger fraction of damage in large clusters than H and He. These large clusters are either in the form of amorphous zones or (after room-temperature aging or high-temperature annealing) in the form of vacancy and antisite clusters. The total damage production in GaAs and GaAs90N10 is found to be practically the same for all the ions. A clearly smaller fraction of the damage in GaAs90N10 compared to GaAs is in large clusters, however. Our results indicate that experimentally observed differences in charge carrier lifetimes between light and heavy ion irradiations, and before and after annealing, can be understood in terms of the large defect clusters. An increasing amount of damage in large clusters decreases the carrier decay time.
UV∕ozone treated Au for air-stable, low hole injection barrier electrodes in organic electronics
Authors: Rentenberger S. , Vollmer A. , Zojer E. , Schennach R. , Koch N.
Published: September 2006

Ultraviolet and x-ray photoelectron spectroscopies were used to study electronic properties of interfaces between Au substrates and a number of organic semiconductors (small molecules and polymers). Au surface work function (ϕ) values before organic deposition were ∼4.7eV (exposed to air), ∼5.2eV (atomically clean), and ∼5.5eV (UV∕ozone treated). The high ϕ obtained for UV∕O3 treated Au was due to Au oxide formation and surface-adsorbed carbon and oxygen species. Au surface morphology remained essentially unchanged by UV∕ozone exposure, as observed by atomic force microscopy. Hole injection barriers (HIBs) at interfaces between UV∕ozone treated Au and the organic semiconductors were systematically lower than those for untreated Au (both atomically clean and air exposed). Reductions in HIB of up to 1.4eV (for p-sexiphenyl) were achieved. In addition, good long-term stability of reduced HIBs of such interfaces was observed for air storage of up to several days.
Compositional dependence of magnetic properties of Co–Pt thin films
Authors: Mani Pandey K. K. , Chen J. S. , Chow G. M.
Published: September 2006

The effects of Pt concentrations on the magnetic properties of Co100−xPtx (0⩽xat.%⩽43) films deposited on Ru underlayer were investigated. The Co72Pt28 film sputter deposited at room temperature showed out-of-plane coercivity of 5.5kOe, unit remanent squareness (Mr∕Ms=1), and uniaxial magnetic anisotropy constant (Ku) of 5.5×106ergs∕cc. The properties were attributed to the expansion of Co lattice due to Pt addition. The Pt reduced the interfacial lattice mismatch between Ru underlayer and magnetic layer. This in turn minimized the strain in Co–Pt films and induced the preferred growth of Co–Pt (0002) on Ru (0002). The Co72Pt28 film also showed the highest thermal stability factor.
Influence of the relaxation of Maxwell-Wagner-Sillars polarization and dc conductivity on the dielectric behaviors of nylon 1010
Authors: Lu Hongbo , Zhang Xingyuan , Zhang Hui
Published: September 2006

The effects of dc conductivity and Maxwell-Wagner-Sillars (MWS) polarization on the dielectric behaviors of nylon 1010 have been investigated by means of dielectric relaxation spectroscopy. The experimental dielectric data were analyzed within the formalisms of dielectric permittivity, complex electric modulus, and complex impedance. The results were discussed in terms of dc conductivity, MWS polarization, electrode polarization, and conductivity relaxation. The results revealed that the charge carrier transport is governed by the motion of the polymer chains. There was a transition temperature located between 100 and 110°C in the conductivity relaxation process, showing two different mechanisms for charge carrier movement. The change of charge carrier movement mechanisms was due to the motion of the polymeric chains in the interphase between amorphous and crystalline regions taking place at this temperature.
Bleaching and coating of organic nanofibers
Authors: Maibohm C. , Brewer J. R. , Sturm H. , Balzer F. , Rubahn H.-G.
Published: September 2006

Degradation of nanofibers made from organic molecules such as para-hexaphenylene or functionalized quaterphenylene via photoexcitation or thermal irradiation is investigated by optical and morphological studies. Under ambient air conditions and in the limit of strong excitation, the degradation of luminescence intensity is accompanied by an increasing surface roughness of the aggregates and by material depletion. Whereas the luminescence intensity is decreasing exponentially with increasing illumination time, the material removal follows a linear relationship. Ablation can be stopped and bleaching can be slowed down by irradiating the nanofibers in vacuum or by coating them with a few hundred nanometers thick layer of silicon oxide (SiOx). Since the latter treatments do not completely stop the bleaching, it is concluded that bleaching of nanofibers involves at least three independent processes, namely, intramolecular configuration change, photo-oxidation, and material removal.
Influence of surface termination morphologies on the imaging properties of a composite two-dimensional photonic crystal lens
Authors: Feng Zhifang , Feng Shuai , Li Zhi-Yuan , Ren Kun , Cheng Bing-Ying , Zhang Dao-Zhong
Published: September 2006

By the numerical simulation based on the finite-difference time-domain method, we investigate the adjustability of image distance for the same object distance in two-dimensional photonic crystals (PCs). When we add a fraction of a metallic component to the center of each dielectric bar, the PC slab lens can form a non-near-field image and the image distance changes for different surface terminations formed by introducing cylinders at the surface layers whose geometric and physical parameters are different from those of the PC bulk. Furthermore, the image distance can be further tuned by combining the two kinds of cylinders at the surface layers with different ratios of slab length. These simulation results clearly show that the imaging properties can be controlled effectively by changing the surface termination of PC slab lenses.
Control of microwave dielectric properties of CaTiO3-based high-permittivity ceramics using additives
Authors: Kipkoech Erick Rop , Zhu Jianhua , Lu Wenzhong
Published: September 2006

The effects of Li2O–Bi2O3–TiO2 (LBT) additions on the microwave dielectric properties of high-permittivity CaO–Sm2O3–Li2O–TiO2 (CSLT) ceramics have been investigated. Addition of LBT up to 10wt% simultaneously reduced the sintering temperature and improved the density of the sintered CSLT ceramics. Scanning electron microscope (SEM) analysis showed a secondary phase when up to 10wt% of LBT was added to CSLT, which disappeared at higher sintering temperatures. However, x-ray diffraction (XRD) analysis revealed that all the compositions had a distorted perovskite structure. By varying the amounts of LBT additions within 0.5–10wt% of the main component and the sintering temperature (1200–1400°C), a wide range of dielectric properties with permittivity in the range of 92–113, Qf>3000GHz, and TCf=±20ppm∕°C were obtained. For example, with 1.0wt% LBT additions sintered at 1400°C, εr=94.02, Qf=5970GHz, and TCf=6.8ppm∕°C; with 5.0wt% LBT additions sintered at 1350°C, εr=101.91, Qf=5050GHz, and TCf=0.4ppm∕°C; with 10.0wt% LBT additions sintered at 1250°C, εr=112.12, Qf=3560GHz, and TCf=1.0ppm∕°C. These combinations of advantages make LBT a very useful additive in developing a range of dielectric characteristics in CaO–Ln2O3–Li2O–TiO2 group of microwave dielectric ceramics.
Dynamic domain motion of thermal-magnetically formed marks on CoNi∕Pt multilayers
Authors: Zhang Li , Bain James A. , Zhu Jian-Gang , Abelmann Leon , Onoue Takahiro
Published: September 2006

We characterized a method of heat-assisted magnetic recording, which is potentially suitable for probe-based storage systems. The field emission current from a scanning tunneling microscope tip was used as the heating source. Various pulse voltages were applied to two types of CoNi∕Pt multilayered films: one is strongly coupled with low coercivity, and the other is weakly coupled with high coercivity. Experimental results show that marks achieved in strongly coupled medium are larger than that in granular one. An external magnetic field was then applied to those marks. For weak fields (lower than the coercivity of the medium) the size of marks changes distinctly in the strongly coupled medium but not in the granular one. A model of magnetic domain dynamics is built to quantitatively explain the experimental results. It agrees with experiments. Based on this model, we will be able to figure out the proposals to achieve small marks for ultrahigh recording density.
The effect of strong surface energy anisotropy on migrating grain-boundary grooves
Authors: Min Donghong , Wong Harris
Published: September 2006

Grain growth during material processing and synthesis is controlled by grain-boundary migration. When a grain boundary ends at a free surface, a groove will develop at the tip to reduce the combined surface and grain-boundary energies. This groove may hinder the movement of the grain boundary and its effect needs to be understood. Previous studies of migrating grooves have focused mainly on isotropic surface energy. We investigate the effect of strong surface energy anisotropy on the groove motion. We assume that the groove evolves by surface diffusion and moves at constant speed. A recently developed delta-function facet model is used to prescribe the surface energy at temperatures above the roughening temperature of the bicrystal. We find that a migrating groove tilts the grain-boundary tip by angle θ away from being perpendicular to the free surface. The angle θ depends on the crystallographic orientations of the bicrystal and is studied systematically for the full range of orientations. Most orientations yield faceted grooves; the remaining few cases generate smooth grooves that have the same shape as the corresponding isotropic grooves, but the size is much smaller. For a given bicrystal, the migrating-groove problem may have a unique solution or multiple solutions. We also show that a migrating-groove profile measured on a polycrystalline alumina surface can be well fitted by our anisotropic model.
Ferroelectric thin films: Review of materials, properties, and applications
Authors: Setter N. , Damjanovic D. , Eng L. , Fox G. , Gevorgian S. , Hong S. , Kingon A. , Kohlstedt H. , Park N. Y. , Stephenson G. B. , Stolitchnov I. , Taganstev A. K. , Taylor D. V. , Yamada T. , Streiffer S.
Published: September 2006

An overview of the state of art in ferroelectric thin films is presented. First, we review applications: microsystems’ applications, applications in high frequency electronics, and memories based on ferroelectric materials. The second section deals with materials, structure (domains, in particular), and size effects. Properties of thin films that are important for applications are then addressed: polarization reversal and properties related to the reliability of ferroelectric memories, piezoelectric nonlinearity of ferroelectric films which is relevant to microsystems’ applications, and permittivity and loss in ferroelectric films—important in all applications and essential in high frequency devices. In the context of properties we also discuss nanoscale probing of ferroelectrics. Finally, we comment on two important emerging topics: multiferroic materials and ferroelectric one-dimensional nanostructures.
Interface-induced phenomena in polarization response of ferroelectric thin films
Authors: Tagantsev A. K. , Gerra G.
Published: September 2006

This article reviews the existing theoretical models describing the interface-induced phenomena which affect the switching characteristics and dielectric properties of ferroelectric thin films. Three groups of interface-induced effects are addressed—namely, “passive-layer-type” effects, ferroelectric-electrode contact potential effects, and the poling effect of the ferroelectric-electrode interface. The existing experimental data on dielectric and switching characteristics of ferroelectric thin film capacitors are discussed in the context of the reviewed theories. Special attention is paid to the case of internal bias field effects.
Fractal dimensions of niobium oxide films probed by protons and lithium ions
Authors: Pehlivan Esat , Niklasson Gunnar A.
Published: September 2006

Cyclic voltammetry (CV) and atomic force microscopy (AFM) were used to determine fractal surface dimensions of sputter deposited niobium pentoxide films. Peak currents were determined by CV measurements. Power spectral densities obtained from AFM measurements of the films were used for calculating length scale dependent root mean square roughness. In order to compare the effect of Li and H ion intercalation at the fractal surfaces, LiClO4 based as well as propionic acid electrolytes were used. The CV measurements gave a fractal dimension of 2.36 when the films were intercalated by Li ions and 1.70 when the films were intercalated by protons. AFM measurements showed that the former value corresponds to the fractal surface roughness of the films, while the latter value is close to the dimensionality of the distribution of hillocks on the surface. We conclude that the protons are preferentially intercalated at such sites.
Study of the dynamic magnetic properties of soft CoFeB films
Authors: Bilzer C. , Devolder T. , Kim Joo-Von , Counil G. , Chappert C. , Cardoso S. , Freitas P. P.
Published: September 2006

We study the magnetization damping in ion-beam deposited Co72Fe18B10 thin films as a function of film thickness and crystalline state. As-deposited amorphous layers showed low damping (αapp=0.006) that is thickness independent. 40nm Co80Fe20 with no boron content exhibited a value twice higher (αapp=0.013). Crystallization in Co72Fe18B10, triggered by annealing at 280°C, results in increased magnetization as well as a strong increase in damping, by a factor of 5 for 40nm films. For lower thicknesses the damping increase upon annealing is less pronounced. The exchange stiffness constant for amorphous films is deduced from perpendicular standing spin waves to be 28.4×10−12J∕m. The annealing dependence of damping should have consequences for the spin-transfer switching in CoFeB∕MgO∕CoFeB magnetic tunnel junctions.
Effects of current on droplet generation and arc plasma in gas metal arc welding
Authors: Hu J. , Tsai H. L.
Published: September 2006

In gas metal arc welding (GMAW), a technology using pulsed currents has been employed to achieve the one-droplet-per-pulse (ODPP) metal transfer mode with the advantages of low average currents, a stable and controllable droplet generation, and reduced spatter. In this paper, a comprehensive model was developed to study the effects of different current profiles on the droplet formation, plasma generation, metal transfer, and weld pool dynamics in GMAW. Five types of welding currents were studied, including two constant currents and three wave form currents. In each type, the transient temperature and velocity distributions of the arc plasma and the molten metal, and the shapes of the droplet and the weld pool were calculated. The results showed that a higher current generates smaller droplets, higher droplet frequency, and higher electromagnetic force that becomes the dominant factor detaching the droplet from the electrode tip. The model has demonstrated that a stable ODPP metal transfer mode can be achieved by choosing a current with proper wave form for given welding conditions.
Electromechanical characterization of 0.55Pb(Ni1∕3Nb2∕3)O3–0.45Pb(Zr0.3Ti0.7)O3 fibers with Pt core
Authors: Sebald Gael , Benayad Abdelmjid , Qiu Jinhao , Guiffard Benoit , Guyomar Daniel
Published: September 2006

Piezoelectric fibers of composition 0.55Pb(Ni1∕3Nb2∕3)O3–0.45Pb(Zr0.3Ti0.7)O3 were fabricated by extrusion of Pb(Nb,Ni)O3–Pb(Zr,Ti)O3 (PNN–PZT) powder around a platinum wire. Their properties are compared with the same bulk material properties. Fiber’s ceramic component exhibits a d31 of −145pC∕N and a lateral coupling factor of −0.22. The bulk material properties are much higher with a d31 of −404pC∕N and a lateral coupling factor of −0.38. The origin of this discrepancy was investigated by different means: microstructure (grain size and perovskite phase ratio), density, and polarization limitations. The polarization is the main limitation. Due to the radial electric field, a radial polarization gradient is obtained that limits the polarization on the outer edge. The calculation of the expected properties are then found to be k31=−0.28 (homogenization of the properties’ gradient). The remaining discrepancy is then assumed to be due to a density problem that can explain the 30% property loss. Density effect on piezoelectric properties of PNN-PZT bulk ceramics is presented to validate this assumption.
Nanoscale studies of domain wall motion in epitaxial ferroelectric thin films
Authors: Paruch Patrycja , Giamarchi Thierry , Tybell Thomas , Triscone Jean-Marc
Published: September 2006

Atomic force microscopy was used to investigate ferroelectric switching and nanoscale domain dynamics in epitaxial Pb(Zr0.2Ti0.8)O3 thin films. Measurements of the writing time dependence of domain size reveal a two-step process in which nucleation is followed by radial domain growth. During this growth, the domain wall velocity exhibits a v∝exp−(1∕E)μ dependence on the electric field, characteristic of a creep process. The domain wall motion was analyzed both in the context of stochastic nucleation in a periodic potential as well as the canonical creep motion of an elastic manifold in a disorder potential. The dimensionality of the films suggests that disorder is at the origin of the observed domain wall creep. To investigate the effects of changing the disorder in the films, defects were introduced during crystal growth (a-axis inclusions) or by heavy ion irradiation, producing films with planar or columnar defects, respectively. The presence of these defects was found to significantly decrease the creep exponent μ, from 0.62–0.69 to 0.38–0.5 in the irradiated films and 0.19–0.31 in the films containing a-axis inclusions.