bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical and spectroscopic study of infrared spectra of hydrogen-bonded 1-methyluracil crystal and its deuterated derivative
Authors: Boczar Marek , Kwiendacz Jacek , Wójcik Marek J.
Published: April 2008

Theoretical simulation of the band shape and fine structure of the N–H(D) stretching band is presented for 1-methyluracil and its deuterated derivative taking into account anharmonic coupling between the high-frequency N–H(D) stretching and the low-frequency N⋯O stretching vibrations, resonance interaction between two equivalent hydrogen bonds in the dimer, anharmonicity of the potentials for the low-frequency vibrations in the ground and excited state of the N–H(D) stretching mode, Fermi resonance between the N–H(D) stretching and the first overtone of the N–H(D) bending vibrations, and electrical anharmonicity. The effect of deuteration has been successfully reproduced by our model calculations. Infrared, far-infrared, Raman, and low-frequency Raman spectra of the polycrystalline 1-methyluracil have been recorded. The geometry and experimental frequencies are compared with the results of harmonic and anharmonic B3LYP∕6-311++G** calculations.
Analysis of broadband microwave conductivity and permittivity measurements of semiconducting materials
Authors: Ritz Elvira , Dressel Martin
Published: April 2008

We perform broadband phase sensitive measurements of the reflection coefficient from 45MHz up to 20GHz by employing a vector network analyzer with a 2.4mm coaxial sensor which is terminated by the sample under test. While the material parameters (conductivity and permittivity) can be easily extracted from the obtained impedance data if the sample is metallic, no direct solution is possible if the material under investigation is an insulator. Focusing on doped semiconductors with largely varying conductivity, here we present a closed calibration and evaluation procedure for frequencies up to 5GHz, based on the rigorous solution for the electromagnetic field distribution inside the sample combined with the variational principle; basically, no limiting assumptions are necessary. A simple static model based on the electric current distribution proves to yield the same frequency dependence of the complex conductivity up to 1GHz. After a critical discussion, we apply the developed method to the hopping transport in Si:P at temperature down to 1K.
Characterization of the donor-acceptor-pair transition in Nitrogen-implanted zinc oxide
Authors: Stichtenoth D. , Dürr J. , Ronning C. , Wischmeier L. , Voss T.
Published: April 2008

Zinc oxide bulk crystals were doped with nitrogen by ion beam implantation. After postimplantation annealing, a luminescent transition appears at 3.230eV. Power-dependent photoluminescence studies and time-resolved measurements at several spectral positions within this band can be described by a model for donor-acceptor-pair (DAP) transitions. By tracing the luminescence in a temperature-dependent study, a connection to phonon replicas could be excluded. Based on these results, this luminescence line could be clearly assigned to a DAP transition. In order to increase the doping efficiency, various approaches are considered and discussed. A slight increase could be obtained by high-temperature implantation without postimplantation annealing.
Determination of buried interface composition and magnetism profiles using standing-wave excited soft x-ray emission and inelastic scattering
Authors: Sell B. C. , Ritchey S. B. , Yang S.-H. , Parkin S. S. P. , Watanabe M. , Mun B. S. , Plucinski L. , Mannella N. , Nambu A. , Guo J. , West M. W. , Salmassi F. , Kortright J. B. , Fadley C. S.
Published: April 2008

We demonstrate that a standing-wave/wedge (swedge) method for probing buried solid-solid interfaces can be carried out using soft x-ray emission spectroscopy (XES) and resonant inelastic x-ray scattering (RIXS). For the particular case of an Al2O3∕Fe∕Cr structure of relevance to giant magnetoresistance, measurements of Fe L and Cr L total intensities and Fe L magnetic circular dichroism are used to derive for both the top and bottom Fe interfaces the depth profile of composition and the depth dependence of the atom-specific Fe contribution to magnetization. Using XES and RIXS in this method, as compared to photoelectron spectroscopy in prior work, permits studying more deeply buried interfaces, and suggests future applications to a wide variety of magnetic and nonmagnetic nanostructures.
Sensitivity of porous silicon rugate filters for chemical vapor detection
Authors: Salem M. S. , Sailor M. J. , Fukami K. , Sakka T. , Ogata Y. H.
Published: April 2008

The characteristics of chemical vapor sensors constructed from porous Si rugate filters are examined. The peak position of the resonant wavelength exhibits a redshift response upon exposure to ethanol vapors. The filter response scales with the vapor partial pressure; the concentration level is estimated based on theoretical calculations. The formation of two stacked rugate filters with similar index contrast but different periodicities is used to test the extent of liquid infiltration into each individual filter. The penetration length of the condensate is found to be comparable to the thickness of the filter; in a 11.3-μm-thick filter, a steady-state response is achieved in 4min.
Density-functional-theory calculations for silicon vacancy migration
Authors: Wright A. F. , Wixom R. R.
Published: April 2008

The saddle-point configurations and associated formation energies of a migrating silicon vacancy in the +2, +1, 0, −1, and −2 charge states were computed using density-functional theory with a plane wave basis set, norm-conserving pseudopotentials, and the generalized-gradient approximation for exchange and correlation. Spurious electrostatic and strain contributions arising from use of periodic boundary conditions were removed by performing maximum likelihood fits on results from 215-, 511-, and 999-atom supercells, and thereby obtaining formation energies corresponding to isolated vacancies. Migration enthalpies were computed by subtracting similarly obtained formation energies for vacancies in local-energy minimum configurations. The results (0.27eV in the +2 charge state, 0.19eV in the +1 charge state, 0.36eV in the 0 charge state, 0.04eV in the −1 charge state, and 0.15eV in the −2 charge state) are in good overall agreement with experimental results obtained at low temperatures.
Electromagnetic emission memory phenomena related to LiF ionic crystal deformation
Authors: Mavromatou C. , Tombras G. S. , Ninos D. , Hadjicontis V.
Published: April 2008

During the uniaxial compression of LiF ionic monocrystals, acoustic and electromagnetic emissions (EME) are detected. We observed that when the compression is performed in successive loading, unloading cycles and these emissions are being monitored, no new emissions will occur unless the maximum stress of the previous cycle is exceeded, meaning that the material presents memory characteristics. This is observed not only for the acoustic emission (AE), which is the well known Kaiser effect, but for the EME as well. In other words, the material appears to memorize and reveal the previously maximum stress it suffered while being deformed. The importance of an electromagnetic memory feature of a material can be related to various applications in material science, especially when the detection of AE is not feasible or gives false alert. Such cases may very well be earthquakes’ predictive indications, monitoring of mines’ stability, imminent landslides, etc.
Annealing effects on Czochralski grown Lu2Si2O7:Ce3+ crystals under different atmospheres
Authors: Feng He , Ding Dongzhou , Li Huanying , Lu Sheng , Pan Shangke , Chen Xiaofeng , Ren Guohao
Published: April 2008

Cerium-doped lutetium pyrosilicate Lu2Si2O7:Ce3+ (LPS:Ce) single crystal samples grown via Czochralski method were annealed under air and H2 atmospheres from 350to1600°C. The x-ray excited luminescence spectra and UV as well as thermal stimulated luminescence spectra were measured. It was found that the luminescence efficiency after annealing in air at 1400°C was significantly enhanced compared to the unannealed samples. This phenomenon was suggested to be caused by the existence of some oxygen vacancies in the LPS:Ce crystals, and these oxygen vacancies can be effectively eliminated by means of annealing in air. Although the annealing will lead to the oxidization of cerium ions from Ce3+ ions to Ce4+, which is harmful to the luminescent efficiency, the annealing treatment does enhance the luminescent efficiency of LPS:Ce, without changing its luminescence mechanics.
Carrier induced ferromagnetism in Mn-doped ZnO: Monte Carlo simulations
Authors: Souza T. M. , da Cunha Lima I. C. , Boselli M. A.
Published: April 2008

Ferromagnetism in Mn-doped ZnO is investigated by Monte Carlo simulations assuming indirect exchange interaction via two different competing mechanisms: (i) antiferromagnetic superexchange and (ii) an oscillating carrier mediated interaction. The calculations are performed for p- and n-type samples. The Mn ion is taken as a substitutional impurity and its concentrations varied from 3% to 20%. The carrier concentrations (holes or electrons) were tested in the range of 1×1016–1×1020cm−3. These simulations showed paramagnetic, ferromagnetic, and spin-glass behaviors for the p-type samples depending on the Mn and hole concentrations. On the other hand, no phase transition was observed for the n-type samples, whatever the Mn and electron concentrations used in the simulations.
Global convective cell formation in pair-ion plasmas
Authors: Vranjes J. , Poedts S.
Published: April 2008

The global electrostatic mode in pair-ion plasmas is discussed for cylindric geometry and for a radially inhomogeneous equilibrium density. In the case of a Gaussian radial density profile, exact analytical eigensolutions are found in terms of the Kummer confluent hypergeometric functions. The mode is identified as a convective cell propagating in the poloidal and axial direction, having at the same time a standing wave structure in the radial direction.
Effect of an axial jet on vortex merging
Authors: Marles David , Gursul Ismet
Published: April 2008

Experiments were conducted to understand the effect of an axial jet on the merging process of a simulated flap-edge and wing-tip corotating vortex pair in the near wake. Cross-flow velocity measurements and flow visualization were performed for the three realistic jet positions on both equal and unequal strength like-signed vortices for a range of momentum coefficients. The main finding was that the initial jet position has a vastly contrasting effect on the merging process. If the jet turbulence rapidly interacts with only one of the vortices, severe diffusion of that vortex occurs which ultimately wraps around and becomes consumed by the unaffected vortex structure. The jet causes a reduction in the vortex spacing and an increase in the rotation angle; hence, merging is promoted. If the jet turbulence does not directly interact with either vortex but instead interferes with the mechanism in the outer-recirculation region that advects vorticity to a larger radius, then merging can be retarded. In this case, an increase in vortex spacing and reduction in rotation angle were observed. Increasing the momentum coefficient, hence, introducing more turbulence into the flow, has a greater effect on the merging process.
Stochastic synchronization of the near wall turbulence
Authors: Tardu Sedat F.
Published: April 2008

We investigate the characteristics of the instantaneous phases and amplitudes of the wavelet coefficients applied to the fluctuating wall shear stress and longitudinal velocity in the low buffer layer of a fully developed turbulent boundary layer. We show that the instantaneous phase exhibits long quiescent periods of constant values separated by sudden phase jumps. We establish a similarity with the stochastic synchronization of chaotic systems in the presence of noise that plays a role similar to the incoherent turbulence. We analyze the statistical characteristics of the constant phase periods and show the existence of type-I intermittency of the constant phase lengths related to a saddle-node bifurcation of the unstable periodic orbit embedded in the wall turbulent attractor. The period of the later is closely related to that of the cyclic regeneration of shear stress producing eddies.
Coarse graining of master equations with fast and slow states
Authors: Pigolotti Simone , Vulpiani Angelo
Published: April 2008

We propose a general method for simplifying master equations by eliminating from the description rapidly evolving states. The physical recipe we impose is the suppression of these states and a renormalization of the rates of all the surviving states. In some cases, this decimation procedure can be analytically carried out and is consistent with other analytical approaches, such as in the problem of the random walk in a double well potential. We discuss the application of our method to nontrivial examples: diffusion in a lattice with defects and a model of an enzymatic reaction outside the steady state regime.
Surface photovoltage and photoluminescence excitation spectroscopy of stacked self-assembled InAs quantum dots with InGaAs overgrown layers
Authors: Chan C. H. , Kao C. W. , Hsu H. P. , Huang Y. S. , Wang J. S. , Shen J. L. , Tiong K. K.
Published: April 2008

Surface photovoltage (SPV) and photoluminescence excitation (PLE) spectroscopy have been used to characterize multiple stacked self-assembled InAs quantum dot (QD) structures with and without InGaAs overgrown layers. The SPV spectra contain rich optical features that originate from every relevant portion of the samples, including the QDs, wetting layer (WL), hybrid quantum well (HQW), and GaAs barrier. The excited state peak positions detected by PLE coincide with those from SPV measurements, which indicates that the QD ensembles are of monomodal distribution. The redshifts of the QD transitions have been attributed to the altered strain distribution, and the reduction in the linewidth of the WL signals indicates a partial alleviation of the surface roughness effect by the incorporation of InGaAs overgrown layers. An additional spectral feature situated between the highest lying QD state and the WL signals has been attributed to the electronic transition in the InAs/InGaAs dots-in-well structure.
Electronic and atomic structures of Ti1−xAlxN thin films related to their damage behavior
Authors: Tuilier M.-H. , Pac M.-J. , Gîrleanu M. , Covarel G. , Arnold G. , Louis P. , Rousselot C. , Flank A.-M.
Published: April 2008

Ti and AlK-edge x-ray absorption spectroscopy is used to investigate the electronic structure of Ti1−xAlxN thin films deposited by reactive magnetron sputtering. The experimental near edge spectra of TiN and AlN are interpreted in the light of unoccupied density of state band structure calculations. The comparison of the structural parameters derived from x-ray absorption fine structure and x-ray diffraction reveals segregation between Al-rich and Ti-rich domains within the Ti1−xAlxN films. Whereas x-ray diffraction probes only the crystallized domains, the structural information derived from extended x-ray absorption fine structure analysis turns on both crystalline and grain boundaries. The results are discussed by considering the damage behavior of the films depending on the composition.
Noncommutative fields and actions of twisted Poincaré algebra
Authors: Chaichian M. , Kulish P. P. , Tureanu A. , Zhang R. B. , Zhang Xiao
Published: April 2008

Within the context of the twisted Poincaré algebra, there exists no noncommutative analog of the Minkowski space interpreted as the homogeneous space of the Poincaré group quotiented by the Lorentz group. The usual definition of commutative classical fields as sections of associated vector bundles on the homogeneous space does not generalize to the noncommutative setting, and the twisted Poincaré algebra does not act on noncommutative fields in a canonical way. We make a tentative proposal for the definition of noncommutative classical fields of any spin over the Moyal space, which has the desired representation theoretical properties. We also suggest a way to search for noncommutative Minkowski spaces suitable for studying noncommutative field theory with deformed Poincaré symmetries.
Growth and electrical properties of N,N′-bis(n-pentyl)terrylene- 3,4:11,12-tetracarboximide thin films
Authors: Petit Matthieu , Hayakawa Ryoma , Shirai Yasuhiro , Wakayama Yutaka , Hill Jonathan P. , Ariga Katsuhiko , Chikyow Toyohiro
Published: April 2008

A n-type semiconductor molecule N,N′-bis(n-pentyl)terrylene-3,4:11,12-tetracarboximide (TTCDI-5C) was synthesized. Theoretical calculations predict several advantages in electrical properties, including large adiabatic electron affinity and small reorganization energy. The molecule was deposited on SiO2 surfaces and the structure of the resultant thin film was studied. Grain size and thin film crystallinity improve as the temperature increases. Top-contact organic field effect transistors (OFETs) using TTCDI-5C as the semiconductor layer were fabricated using SiO2 as the gate dielectric. Values of charge carrier mobility up to 7.24×10−2cm2V−1s−1 and current on/off ratios higher than 104 were obtained, demonstrating the potential of TTCD-5C for use in OFETs.
Determination of the conduction band offset between hydrogenated amorphous silicon and crystalline silicon from surface inversion layer conductance measurements
Authors: Kleider J. P. , Gudovskikh A. S. , Roca i Cabarrocas P.
Published: April 2008

The presence of an electron rich inversion layer in p-type crystalline silicon (c-Si) at the interface with n-type hydrogenated amorphous silicon (a-Si:H) is experimentally demonstrated from the coplanar conductance of (n) a-Si:H∕(p) c-Si structures, which is shown to be very sensitive to the band mismatch between the two semiconductors. The temperature dependence of the corresponding sheet electron density allows to determine with a very good precision the conduction band offset ΔEC between a-Si:H and c-Si:ΔEC=0.15±0.04eV.
A simple model of stiff and flexible polymer chain adsorption: The influence of the internal chain architecture
Authors: Adamczyk Piotr , Romiszowski Piotr , Sikorski Andrzej
Published: April 2008

In this study, we investigated the process of random sequential adsorption of stiff and flexible polymer chains on a two-dimensional square lattice. The polymer chains were represented by sequence of lattice points forming needles, T shapes, and crosses as well as flexible linear chains and star-branched chains consisted of three and four arms. The Monte Carlo method was employed to generate the model systems. The percolation threshold and the jamming threshold were determined for all systems under consideration. The influence of the chain length and the chain architecture on both thresholds was calculated and discussed. The changes in the ordering of the system were also studied.
Self-focused ZnO transducers for ultrasonic biomicroscopy
Authors: Cannata J. M. , Williams J. A. , Zhou Q. F. , Sun L. , Shung K. K. , Yu H. , Kim E. S.
Published: April 2008

A simple fabrication technique was developed to produce high frequency (100MHz) self-focused single element transducers with sputtered zinc oxide (ZnO) crystal films. This technique requires the sputtering of a ZnO film directly onto a curved backing substrate. Transducers were fabricated by sputtering an 18μm thick ZnO layer on 2mm diameter aluminum rods with ends shaped and polished to produce a 2mm focus or f-number equal to one. The aluminum rod served a dual purpose as the backing layer and positive electrode for the resultant transducers. A 4μm Parylene matching layer was deposited on the transducers after housing and interconnect. This matching layer was used to protect the substrate and condition the transfer of acoustic energy between the ZnO film and the load medium. The pulse-echo response for a representative transducer was centered at 101MHz with a −6dB bandwidth of 49%. The measured two way insertion loss was 44dB. A tungsten wire phantom and an adult zebrafish eye were imaged to show the capability of these transducers.
A compact quantum model for fin-shaped field effect transistors valid from dc to high frequency and noise simulations
Authors: Lázaro A. , Nae B. , Iñiguez B. , Garcia F. , Tienda-Luna I. M. , Godoy A.
Published: April 2008

Fin-shaped field effect transistors (FinFETs) are considered to be a very attractive option to improve the performance of complementary metal-oxide-semiconductor devices into the sub-50-nm gate length regime. However, for those dimensions, quantum effects must be considered in order to develop accurate compact models useful for circuit simulations. In this paper, we study the influence of the quantum effects on dc, Radio frequency (rf), and microwave noise for nanoscale FinFET transistors including nonstationary effects. We present an analytical charge model to adjust the charge control computed from the self-consistent solution of the two-dimensional Schrödinger and Poisson equations. rf and noise performances are calculated using the active transmission line method. Comparison between classical and quantum charge control and between drift-diffusion and hydrodynamic models is carried out.
Magnetic behavior of single La0.67Ca0.33MnO3 nanotubes: Surface and shape effects
Authors: Dolz M. I. , Bast W. , Antonio D. , Pastoriza H. , Curiale J. , Sánchez R. D. , Leyva A. G.
Published: April 2008

We report magnetization experiments in two magnetically isolated ferromagnetic nanotubes of perovskite La0.67Ca0.33MnO3. The results show that the magnetic anisotropy is determined by the sample shape, although the coercive field is reduced by incoherent magnetization reversal modes. The temperature dependence of the magnetization reveals that the magnetic behavior is dominated by grain surface properties. These measurements were acquired using a silicon micromechanical oscillator working in its resonant mode. The sensitivity was enough to measure the magnetic properties of these two samples with a mass lower than 14pg and to obtain for the first time the magnetization loop for one isolated nanotube.
Vibrational overtone spectra of N–H stretches and intramolecular dynamics on the ground and electronically excited states of methylamine
Authors: Marom Ran , Zecharia Uzi , Rosenwaks Salman , Bar Ilana
Published: April 2008

The vibrational pattern and energy flow in the N–H stretch manifolds and the dissociation dynamics of methylamine (CH3NH2) were investigated via vibrationally mediated photodissociation. Action spectra and Doppler profiles, reflecting the yield of the ensuing H photofragments, versus near infrared/visible vibrational excitation and UV excitation, respectively, were measured. The jet-cooled action spectra and the simultaneously measured room temperature photoacoustic spectra of the first to third N–H stretching overtones exhibit broad features, somewhat narrower in the former, consisting of barely recognized multiple bands. Two phases of fitting of the spectroscopic data were performed. In the first phase, the raw data were analyzed to obtain band positions, types, intensities, and transition linewidths. In the second, the information derived from the first phase was then used as data in a fit to joint local mode/normal mode (LM/NM) and NM Hamiltonian parameters. The derived parameters predicted well band positions and allowed band assignment. The LM/NM Hamiltonian and the extracted Lorentzian linewidths enabled the determination of the initial pathways for energy redistribution and the overall temporal behavior of the N–H stretch and doorway states, as a result of Fermi couplings and interactions with bath states. The results indicate a nonstatistical energy flow in the V=2 manifold region, pointing to the dependence of the coupling on specific low order resonances rather than on the total density of bath states. The Doppler profiles suggest lower average translational energies for the released H photofragments, in particular, for V=3 and 4 as compared to V=1 and 2, implying a change in the mechanism for bond cleavage.
Control of the magnetic and magnetotransport properties of La0.67Sr0.33MnO3 thin films through epitaxial strain
Authors: Takamura Y. , Chopdekar R. V. , Arenholz E. , Suzuki Y.
Published: April 2008

The influence of epitaxial strain, in the form of tetragonal distortions, on the magnetic and magnetotransport properties of La0.67Sr0.33MnO3 thin films was studied. The tetragonal distortion (c∕a ratio) was modulated through the choice of the substrate, ranging from c∕a=1.007 on (001)-oriented (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates to 0.952 on (110)-oriented GdScO3 substrates. In agreement with previous theoretical predictions, these large values of tensile strain cause the Curie temperature and the saturation magnetization to decrease, alter the temperature dependence of the resistivity and magnetoresistance, and increase the resistivity by several orders of magnitude.
On the mode stability of a self-similar wave map
Authors: Donninger Roland , Aichelburg Peter C.
Published: April 2008

We study linear perturbations of a self-similar wave map from Minkowski space to the three-sphere which is conjectured to be linearly stable. By considering analytic mode solutions of the evolution equation for the perturbations, we prove that there are no real unstable eigenvalues apart from the well-known gauge instability.
Thermal effect on piezoelectric stick-slip actuator systems
Authors: Li J. W. , Yang G. S. , Zhang W. J. , Tu S. D. , Chen X. B.
Published: April 2008

The piezoelectric stick-slip (PZT-SS) actuator is known to achieve motion with a theoretically unlimited range yet high resolution (several nanometers). In this type of actuator, friction plays an active role in producing a meaningful stick-slip motion. However, friction is a source of heat which may cause significant temperature rise, affecting the dynamic performance of the actuator. Our study aimed to measure temperature rise in the stick-slip motion and to understand whether such a rise could significantly affect the displacement of the stick-slip motion. In this study, a temperature measurement system was developed using the off-the-shelf components, with which the temperature rise up to 0.436°C was successfully measured on a proprietary PZT-SS actuator. The experiment further shows that the temperature rise affects the displacement of the actuator when operating voltage is at the low end (∼6V). Therefore, one of the design recommendations for such an actuator system is that the operating voltage should be at the high end (∼30V). The study also measured the temperature rise (∼0.263°C after the system worked for 6300s) at the friction interface due to the piezoelectric element which is a part of the whole PZT-SS actuator. This means that temperature rise is due to both the friction at two interacting surface and the operation of the piezoelectric element.
Strain and composition mapping of epitaxial nanostructures
Authors: Cionca C. N. , Riposan A. , Kumah D. P. , Husseini N. S. , Walko D. A. , Yacoby Y. , Millunchick J. M. , Clarke R.
Published: April 2008

We have used surface x-ray diffraction and a direct method of phase reconstruction to obtain subangström resolution maps of an ion-beam milled In0.27Ga0.73As∕GaAs(001) thin film exhibiting three-dimensional (3D) epitaxial nanostructures. The 3D electron density was calculated based on the diffraction pattern along the Bragg rods measured with synchrotron radiation, from which the chemical composition, strain profile, and average nanostructure shape were extracted. The film maintained a wetting layer exhibiting a sharp strain gradient, which extended into the substrate. Atop the wetting layer, the ion-beam milled islands possessed an apical shape and were depleted in indium.
In depth fiber optic trapping of low-index microscopic objects
Authors: Mohanty K. S. , Liberale C. , Mohanty S. K. , Degiorgio V.
Published: April 2008

We demonstrate that a focused beam through a microaxicon built on the tip of a single mode optical fiber can trap low-index objects at much larger depths as compared to the vortex beam tweezers generated using high numerical aperture microscope objectives. The measured transverse trapping force for low-index objects in Mie regime was found to depend on particle size and on distance of trapped objects from the fiber tip. While axial movement of trapped low-index objects was achieved by variation in trap beam power, transportation in three dimensions was achieved by maneuvering the fiber.
Further investigation of the photodissociation dynamics of dichlorocarbene near 248nm
Authors: Shin Seung Keun , Dagdigian Paul J.
Published: April 2008

A further investigation of the 248nm photodissociation of CCl2, which expands upon our original study of this process [S. K. Shin and P. J. Dagdigian, Phys. Chem. Chem. Phys. 8, 3446 (2006)], is presented. The CCl2 parent molecule and the CCl photofragment were detected by laser fluorescence excitation in a molecular beam experiment. From the dependence of the CCl2 signals on the photolysis laser fluence, attenuation cross sections of the 00, 11, and 21 vibrational levels were determined; the cross sections for the excited vibrational levels were found to be significantly smaller than those for the ground vibrational level. The previously observed fragment CCl bimodal rotational state distribution was found to arise from the photolysis of more than one parent molecule. At low CHCl3 mole fractions in the gas supplied to the pyrolysis beam source, it was concluded that CCl2 is the photolysis precursor for both low-J and high-J CCl fragments. On the basis of the dependence of the CCl signals on the photolysis laser fluence, ground and vibrationally excited CCl2, respectively, were assigned as the precursors to these two classes of fragments. The photofragment excitation spectra for low-J and high-J CCl fragments from the photolysis of CCl2 were recorded in the wavelength range around 248nm; both were found to be structureless. The 248nm photodissociation dynamics of CCl2 is discussed in light of our experimental observations and quantum chemical calculations of the CCl2 excited electronic states.
Measurements of NOx, acyl peroxynitrates, and NOy with automatic interference corrections using a NO2 analyzer and gas phase titration
Authors: Hargrove James , Zhang Jingsong
Published: April 2008

N O 2 analyzers are much more valuable if they can also measure NO since the two (NO+NO2=NOx) are often found together. NO can be quantitatively converted to NO2 by reaction with ozone and subsequent thermal decomposition of the N2O5 that may form from further oxidation. The conversion of NO, along with decomposition of N2O5 and removal of the remaining unreacted ozone with a heated chamber, allows for quantitative determination of NOx using a NO2 analyzer and the determination of decomposed acyl peroxynitrates. Ambient tests are performed to demonstrate these methods.
Misfit strain dependence of electrocaloric effect in epitaxial Pb(Zr1−xTix)O3 thin films
Authors: Qiu J. H. , Jiang Q.
Published: April 2008

A phenomenological Landau–Devonshire thermodynamic theory is employed to investigate the effect of the misfit strain on the electrocaloric effect of single domain epitaxial Pb(Zr1−xTix)O3 thin films grown on thick cubic substrates. Theoretical analysis indicates that the epitaxial Pb(Zr1−xTix)O3 thin films have the large electrocaloric coefficient at room temperature and the electrocaloric properties largely depend on the misfit strain and the applied electric field. Furthermore, the applied field decreases the electrocaloric coefficient and reduces its misfit strain dependence.
Alignment of cellulose chains of regenerated cellulose by corona poling and its piezoelectricity
Authors: Yun Sungryul , Kim Jung Hwan , Li Yuanxie , Kim Jaehwan
Published: April 2008

Cellulose based electroactive paper has been developed as smart material. In this paper, corona poled cellulose films were prepared to improve their piezoelectricity and the influence of grid voltage to the corona poling was investigated. Cellulose was regenerated by dissolving cellulose natural fibers using a solvent, and removing it. During the regeneration process, alignment of cellulose was attempted by applying corona electrical poling. These characteristics were investigated by field emission scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. As increasing the grid voltage of the corona poling, the generation of cellulose nanofibers in the cellulose layered structures was observed, which influenced the increased crystallinity resulting in improved piezoelectric charge constant of cellulose films.
Microring resonator based modulator made by direct photodefinition of an electro-optic polymer
Authors: Balakrishnan M. , Faccini M. , Diemeer M. B. J. , Klein E. J. , Sengo G. , Driessen A. , Verboom W. , Reinhoudt D. N.
Published: April 2008

A laterally coupled microring resonator was fabricated by direct photodefinition of negative photoresist SU8, containing tricyanovinylidenediphenylaminobenzene chromophore, by exploiting the low ultraviolet absorption window of this chromophore. The ring resonator was first photodefined by slight cross-linking. Thereafter, poling (to align the chromophores) and further cross-linking (to increase the glass transition temperature) were simultaneously carried out. The material showed excellent photostability and the electro-optic modulation with an r33 of 11pm∕V was demonstrated at 10MHz.
Formation of cobalt-silicide nanocrystals in Ge-doped dielectric layer for the application on nonvolatile memory
Authors: Hu Chih-Wei , Chang Ting-Chang , Liu Po-Tsun , Tu Chun-Hao , Lee Sheng-Kai , Sze Simon M. , Chang Chun-Yen , Chiou Bi-Shiou , Tseng Tseung-Yuan
Published: April 2008

In this work, Ge-doped cobalt-silicon thin film was synthesized using a cosputter system (Co and Si0.5Ge0.5). The deposited film was annealed in oxygen ambient at 650°C to form cobalt-silicide nanocrystals. The formation of isolated silicide nanocrystals was confirmed by transmission electron microscopy and x-ray photoelectron spectroscopy analysis. In metal-oxide-insulator-oxide-silicon structure, a significant electrical hysteresis is observed and attributed by the presence of the cobalt-silicide nanocrystals and the oxidized Ge elements.
Transformation of premixed flame behavior with hydrodynamic and body-force instabilities
Authors: Pan Kuo-Long
Published: April 2008

Flame dynamics such as the formation of wrinkles is caused by instabilities such as thermal expansion and buoyancy. We have studied the combined thermal and buoyancy effects on the propagation of a premixed flame by using a front-tracking method. It was found that though wrinkled surface could be stabilized by a strong upward buoyancy force (negative gravity) in a downward propagating flame, wrinkles with short wavelengths remained intact, while those with long wavelengths were suppressed as the magnitude of gravity became sufficiently small. As such, compared to the zero-gravity condition, reduced ranges of cellular scales result in weaker interactions between multiscale wrinkles; consequently, the chaotic motion characterized by incessant merging and dividing of cells is also weakened. With downward buoyancy (positive gravity) as well as flame propagation, a steady flame structure is established. This is in contrast to the general realization of gravitational destabilization in that while a flame is readily deformed to a large wrinkle at the incipient stage of Darrieus–Landau instability, ensuing stability due to the coupling of Darrieus–Landau and Rayleigh–Taylor instabilities prevents further excitation of secondary Darrieus–Landau instability and hence associated unsteady evolution. However, if the positive gravity is sufficiently large, the ordered pattern degenerates and the highly irregular geometry of flame surface is formed without a specific cell structure. This is the typical manifestation of Rayleigh–Taylor instability caused by the buoyancy force exerted on an interface with a density jump.
Concentrating colloids with electric field gradients. I. Particle transport and growth mechanism of hard-sphere-like crystals in an electric bottle
Authors: Leunissen Mirjam E. , Sullivan Matthew T. , Chaikin Paul M. , van Blaaderen Alfons
Published: April 2008

This work concerns the use of electric field gradients to manipulate the local particle concentration in a hard-sphere-like suspension. Inside a specially designed “electric bottle,” we observed our colloids to collect in the regions of lowest field strength (“negative dielectrophoresis”). This allows for the use of larger field gradients and stronger dielectrophoretic forces than in the original electric bottle design, which was based on positive dielectrophoresis [M. T. Sullivan et al., Phys. Rev. Lett. 96, 015703 (2006)]. We used confocal scanning laser microscopy to quantitatively follow the time-dependent change in the particle density and the suspension structure. Within a few days, the dielectrophoretic compression was seen to initiate a heterogeneouslike growth of large single crystals, which took place far out-of-equilibrium. The crystals had a random hexagonal close-packed structure and displayed an intriguing growth mechanism, during which the entire crystal was continuously transported, while growing both on the “high-field” and the “low-field” sides, although at different rates. After switching off the electric field, the compressed crystals were found to relax to a lower packing fraction and melt, at a much slower rate than the crystal growth. Besides revealing the particular (far out-of-equilibrium) crystal growth mechanism in these electric bottles, our observations also shed light on the role of the different particle transport processes in the cell and some of the relevant tuning parameters. This is useful for different types of experiments, for instance, focusing more on melting, homogeneous crystallization, or the glass transition.
Waveguide coupled terahertz photoconductive antennas: Toward integrated photonic terahertz devices
Authors: Page H. , Malik S. , Evans M. , Gregory I. , Farrer I. , Ritchie D.
Published: April 2008

We demonstrate the operation of a low temperature GaAs photoconductive antenna pumped via a monolitically integrated AlGaAs based dielectric waveguide using 100fs pulses at 860nm. This technology demonstrates the feasibility of monolithically integrating dielectric waveguides and fast photoconductivity terahertz materials. We also demonstrate convenient pumping normal to the surface of the waveguide device via a surface grating coupler fabriacted using a gallium focused ion beam. Our initial results show a ∼10% optical coupling efficiency into the photomixer element. We attribute this low coupling efficiency to unoptimized processing techniques.
Structural and magnetic properties in Mn-doped GaN grown by metal organic chemical vapor deposition
Authors: Cui X. G. , Tao Z. K. , Zhang R. , Li X. , Xiu X. Q. , Xie Z. L. , Gu S. L. , Han P. , Shi Y. , Zheng Y. D.
Published: April 2008

Mn-doped GaN epitaxial films (Ga1−xMnxN) were grown on sapphire (0001) by metal organic chemical vapor deposition. Mn concentration was determined by energy dispersive spectrometry. For Ga1−xMnxN with x up to 0.027, no secondary phases except for GaN were detected by high resolution x-ray diffractometer. Raman scattering spectra show that the longitudinal optical phonon mode A1(LO) of Ga1−xMnxN shifts toward lower frequency with increasing Mn concentration due to substitutional Mn incorporation. Electron spin resonance (ESR) measurements were performed and highly anisotropic sixfold hyperfine line indicates that the ionized Mn2+ substitutes for Ga3+ ions. However, magnetometry reveals that all homogenous Ga1−xMnxN show paramagneticlike behaviors. From Brillouin function fit and ESR spectra, it is concluded that Mn ions are present as isolated paramagnetic centers.
Silicon nanowire array photoelectrochemical solar cells
Authors: Peng Kuiqing , Wang Xin , Lee Shuit-Tong
Published: April 2008

Silicon nanowires (SiNWs) arrays prepared by electroless etching show excellent optical antireflectivity over a wide spectral bandwidth from 300to1000nm and surface defect-induced electrical conductivity. Both characteristics make the SiNWs a promising material for photovoltaic cell applications. Photoelectrochemical (PEC) measurements showed the electroless etching SiNWs are remarkably photoactive and effective in enhancing photovoltaic properties including photocurrent and photovoltage. Since electroless etching can enable simple, wafer-scale fabrication of SiNWs without the need of doping. SiNWs array thus prepared show great promise as low-cost and scalable photovoltaic-type PEC materials.
Effects of molecular versus atomic oxygen on NiSi and Ni(Pt)Si films grown on both p- and n-doped Si(100)
Authors: Manandhar Sudha , Kelber Jeffry
Published: April 2008

Effects of mixed atomic/molecular oxygen (O+O2) and pure O2 on the surface compositions of Ni(Pt)Si (on n-doped substrates) and NiSi films on p- or n-doped Si(100) substrates have been characterized by x-ray photoemission spectroscopy. Exposure to O+O2 results in rapid silicon consumption and the kinetically driven oxidation of the transition metal(s), with oxides >35Å thick formed on all samples without passivation. The addition of Pt retards but does not eliminate oxide growth or Ni oxidation. Substrate dopant type has no effect on oxidation rate except at high exposures where there is a slight enhancement of n-type oxidation. Exposure to O2 yields rapid passivation after the formation of a SiO2 film 6–7Å thick on all samples.
Magnetic domain observation in writer pole tip for perpendicular recording head by electron holography
Authors: Kim J. J. , Hirata K. , Ishida Y. , Shindo D. , Takahashi M. , Tonomura A.
Published: April 2008

Electron holographic observations were performed in order to clarify the magnetic domain structures in nanosized pole tips for perpendicular recording heads made from Ni–Fe and Co–Ni–Fe. While an external magnetic field was applied, the magnetic fields leaking from the pole tips as well as the detailed magnetic flux distribution inside them were visualized for the first time. In addition, we report the direct observation result that implies the pole erasure characteristic of the Co–Ni–Fe pole tip. The observations have revealed that electron holography provides useful information for understanding the magnetic characteristics of nanosized pole tips for perpendicular recording heads.
Metal-semiconductor-metal Ge photodetectors integrated in silicon waveguides
Authors: Vivien Laurent , Marris-Morini Delphine , Fédéli Jean-Marc , Rouvière Mathieu , Damlencourt Jean-François , El Melhaoui Loubna , Le Roux Xavier , Crozat Paul , Mangeney Juliette , Cassan Eric , Laval Suzanne
Published: April 2008

Metal-semiconductor-metal (MSM) Ge photodetectors integrated in silicon-on-insulator waveguides using butt coupling configuration have been experimentally demonstrated. Bandwidths reach 28GHz under 6V bias at wavelengths of 1.31 and 1.55μm for a photodetector with 1μm electrode spacing, which is almost compatible with a 40Gb∕s operation. High responsivity of about 1A∕W at both wavelengths for a 10μm long photodetector has been obtained. Under 1V bias, MSM photodetectors with 1 and 0.7μm electrode spacings have bandwidths of 9 and 17GHz, respectively, which is compatible with a data transmission speed of 10Gb∕s.
Single zinc-doped indium oxide nanowire as driving transistor for organic light-emitting diode
Authors: Zhang Wenfeng , Jie Jiansheng , He Zhubing , Tao Silu , Fan Xia , Zhou Yechun , Yuan Guodong , Luo Linbao , Zhang Wenjun , Lee Chun-Sing , Lee Shuit-Tong
Published: April 2008

Zn-doped In2O3 nanowires (NWs) were prepared by simple chemical vapor deposition and were systematically characterized. Field-effect transistors (FETs) constructed from the Zn-doped In2O3 nanowires exhibit excellent performance characteristics such as high mobility, “high-on-state” current of 105A and large on/off current ratio of 107. Single-NW-FETs can successfully drive an organic light-emitting diode, revealing the application potential of Zn-doped In2O3 NW-FETs in high-performance displays.
Intense photoluminescence of thin films of porous hydrogenated microcrystalline silicon
Authors: Solomon I. , Rerbal K. , Chazalviel J.-N. , Ozanam F. , Cortès R.
Published: April 2008

We report the preparation of highly photoluminescent porous silicon in the form of thin films with thicknesses of around 1 μm. These films are obtained by stain etching thin films of microcrystalline silicon deposited by plasma-enhanced chemical vapor deposition with a flow of silane gas (SiH4) that is highly diluted in hydrogen. Stain etching is performed with aqueous solutions of hydrofluoric acid and Fe(III) in the form of ferric chloride (FeCl3). The porous silicon obtained shows a strong photoluminescence with a quantum efficiency estimated in the 1%–10% range. It could be used for the design of inexpensive large-surface electroluminescent devices.
Observation of one magnon and magnon-phonon-electric dipole coupling in multiferroics bismuth ferrite thin films
Authors: Kumar Ashok , Murari N. M. , Katiyar R. S.
Published: April 2008

We observed “one magnon,” scattering in multiferroic polycrystalline BiFeO3 thin films near 17.2cm−1 at 90K employing Raman spectroscopy. It is seen with a kink in magnon intensity at 150K and with strong anomaly near 210K illustrating spin reorientation transition. The spectral weight of one magnon transferred to the lowest phonon mode near the spin reorientation temperature suggests magnon-phonon coupling. Dielectric constant and dielectric loss as function of temperature showed anomaly at 210K suggesting magnon-phonon-electric dipole coupling. The one magnon becomes overdamped or overcome by elastic scattering at elevated temperatures.
Negative bias temperature instability and relaxation in HfSiON gate stack field effect devices
Authors: Devine R. A. B. , Hjalmarson H. P. , Alshareef H. N. , Quevedo-Lopez M.
Published: April 2008

Negative bias temperature instability and relaxation measurements have been performed on HfSiON gate stack devices. The time exponent for threshold voltage shift evolution is observed to be temperature dependent. The dominant source of the positive charge induced threshold voltage variation is determined to be dielectric trapped charge and this is the source of variation during relaxation. Nonlinear threshold voltage shift versus inversion channel carrier mobility is observed. Its magnitude is inconsistent with expectations from existing models.
A comparative study of write field distribution of trailing-edge shielded and unshielded perpendicular write heads by quantitative magnetic force microscopy
Authors: Chen Y. J. , Leong S. H. , Huang T. L. , Ng K. W. , Hu S. B. , Yuan Z. M. , Ng V.
Published: April 2008

Three-dimensional write field distributions of trailing-edge shielded and unshielded perpendicular write heads with applied direct current write currents were studied by magnetic force microscopy (MFM) measurements. A quantitative MFM approach of two times integrating measured frequency shift at a series of tip scan heights over the perpendicular direction was proposed to measure the magnetic field strength and field gradient. Results indicate shielded heads in addition to smaller saturation write currents, exhibited more than two to three times higher write field gradients over a wide range of moderate field strength over unshielded heads, thus, producing sharper bit transition and improved signal to noise ratio as theoretically predicted.