bluuebunny/crossref_metadata_2025 huggingface dataset:
X
-mode reflectometry measurements in the JET plasma core region
Authors: Hacquin S. , Meneses L. , Cupido L. , Sharapov S. , Alper B. , Fessey J. , Klein A. , Testa D. ,   JET-EFDA Contributors
Published: October 2006

The X-mode radial correlation reflectometry diagnostic on JET has long suffered from strong signal attenuation in the original transmission lines. To reach higher performances, new low-attenuation corrugated circular waveguides and a new cluster of six antennas have been successfully installed in Autumn 2005. The increase of the signal-to-noise ratio using these new transmission lines is found to be on the order of magnitude of 20 dB, thus enabling good quality of reflectometry measurement. With the benefit of this improvement, first X-mode reflectometry measurements of density fluctuations in the core region of the JET plasma are reported in this article.
Initial angle resolved measurements of fast neutrals using a multichannel linear AXUV detector system on LHD
Authors: Veshchev E. A. , Ozaki T. , Goncharov P. R. , Sudo S. ,   LHD Experimental Group
Published: October 2006

A new multichannel diagnostic for fast ion distribution studies has been developed and successfully tested on the Large Helical Device (LHD) in different plasma heating conditions. The diagnostic is based on a linear array AXUV detector consisting of 20 segments, charge sensitive preamplifiers, and a set of pulse height analysis channels. The main advantage of this system is the possibility to make time, energy, and angle-resolved measurements of charge exchange neutral particles in a single plasma discharge. This feature makes the new diagnostic a very helpful and powerful tool intended to contribute to the understanding of fast ion behavior in a complex helical plasma geometry like the one of LHD.
X-ray diagnostics for investigating electron distribution functions in the central cell of the GAMMA 10 tandem mirror
Authors: Kohagura J. , Cho T. , Hirata M. , Numakura T. , Fukai T. , Tomii Y. , Kiminami S. , Morimoto N. , Ikuno T. , Namiki S. , Shimizu K. , Ito M. , Miyata Y. , Minami R. , Miyoshi S. , Ogura K. , Saito N. , Saito T. , Kariya T.
Published: October 2006

The quantum efficiency of an ultralow-energy-sensitive pure-Ge (ULE Ge) detector is investigated using synchrotron radiation from the storage ring at AIST especially for x-ray pulse-height analyses (PHAs), down to a few hundred eV. Several types of x-ray diagnostics such as x-ray PHA, x-ray absorption methods, and x-ray tomography using the ULE Ge detector, a NaI(Tl) detector, as well as a microchannel-plate tomography system are employed for investigating electron distribution functions and electron temperature profiles with preliminary central electron-cyclotron heating in the central cell of the GAMMA 10 tandem mirror. These measurements play an important role in studying an essential physics scaling of the electron temperature as a function of electron confining potential in tandem mirror plasmas.
Cracking of III-nitride layers with strain gradients
Authors: Romanov A. E. , Beltz G. E. , Cantu P. , Wu F. , Keller S. , DenBaars S. P. , Speck J. S.
Published: October 2006

Experimental results are demonstrated for the cracking of nominally compressed AlyGa1−yN layers grown on AlxGa1−xN buffer layers with smaller lattice constants (y<x). The authors present a theoretical analysis showing that the inclination of pure edge threading dislocation lines effectively reduces the compressive stress, causing relaxation, and after reaching a certain thickness begins to generate the tensile stress gradient responsible for cracking. The critical layer thickness for crack nucleation in such a gradient elastic field has been found. The results of the modeling are in good agreement with experimental observations of crack onset in nominally compressed nitride layers.
The formation of planar ribbonlike aggregates from stiff polyanions in the presence of anisotropic cations
Authors: Komarov Pavel V. , Zherenkova Lubov V. , Khalatur Pavel G. , Reineker Peter
Published: October 2006

A dilute salt-free solution of rodlike polyanions in the presence of anisotropic (chain) cations consisting of neutral tails and charged heads is studied. Using Monte Carlo simulation within the framework of the primitive model, different Coulomb coupling regimes were considered. While aggregation in the strong coupling limit is expected, we report new morphology, namely, the formation of ribbonlike nanostructures. At strong electrostatic interaction, the system is found to undergo the self-organization resulting in the formation of planar aggregates that look like a “ladder” of polyanions sandwiched between cationic chains. We investigate the stability of different morphologies and find that these aggregates are thermodynamically stable. Focus has been made on how the chemical structure of anisotropic cations affects the morphology of the aggregates.
Structural and optical properties of highly hydroxylated fullerenes: Stability of molecular domains on the C60 surface
Authors: Guirado-López R. A. , Rincón M. E.
Published: October 2006

The excitation spectra and the structural properties of highly hydroxylated C60(OH)x fullerenes (so-called fullerenols) are analyzed by comparing optical absorption experiments on dilute fullerenol-water solutions with semiempirical and density functional theory electronic structure calculations. The optical spectrum of fullerenol molecules with 24–28 OH attached to the carbon surface is characterized by the existence of broad bands with reduced intensities near the ultraviolet region (below ∼500nm) together with a complete absence of optical transitions in the visible part of the spectra, contrasting with the intense absorption observed in C60 solutions. Our theoretical calculations of the absorption spectra, performed within the framework of the semiempirical Zerner intermediate neglect of diatomic differential overlap method [Reviews in Computational Chemistry II, edited by K. B. Lipkowitz and D. B. Boyd (VCH, Weinheim, 1991), Chap. 8, pp. 313–316] for various gas-phase-like C60(OH)26 isomers, reveal that the excitation spectra of fullerenol molecules strongly depend on the degree of surface functionalization, the precise distribution of the OH groups on the carbon structure, and the presence of impurities in the samples. Interestingly, we have surprisingly found that low energy atomic configurations are obtained when the OH groups segregate on the C60 surface forming molecular domains of different sizes. This patchy behavior for the hydroxyl molecules on the carbon surface leads in general to the formation of fullerene compounds with closed electronic shells, large highest occupied molecular orbital-lowest unoccupied molecular orbital energy gaps, and existence of an excitation spectrum that accounts for the main qualitative features observed in the experimental data.
Magnetotransport properties of Ge channels with extremely high compressive strain
Authors: Sawano K. , Kunishi Y. , Shiraki Y. , Toyama K. , Okamoto T. , Usami N. , Nakagawa K.
Published: October 2006

Ge channel structures with extremely high compressive strain up to 2.8% were fabricated and their magnetotransport properties were evaluated. It was found that at the same hole density the sample with the higher strain showed the lower hole effective mass and that the compressive strain effectively reduced the effective mass. The Dingle ratios obtained were very high (>5) for all samples, indicating that remote impurity scattering was a dominant scattering mechanism rather than high angle scatterings caused by degradation of the channel layers. This result strongly suggests that Ge channels with extremely high strain are very promising for high performance complementary-metal-oxide-semiconductor applications.
A free-energy landscape picture and Landau theory for the dynamics of disordered materials
Authors: Javaheri Mohammad Reza H. , Chamberlin Ralph V.
Published: October 2006

Landau’s theory of phase transitions [Nature (London) 138, 840 (1936); Statistical Physics (Pergamon, London, 1959)] is adapted to treat independently relaxing regions in complex systems using nanothermodynamics. The order parameter we use governs the thermal fluctuations, not a specific static structure. We find that the entropy term dominates the thermal behavior, as is reasonable for disordered systems. Consequently, the thermal equilibrium occurs at the internal-energy maximum, so that the potential-energy minima have negligible influence on the dynamics. The dynamics involves normal thermal fluctuations about the free-energy minimum, with a time scale that is governed by the curvature of the internal-energy maximum. The temperature dependence of the fluctuations yields Vogel-Tamman-Fulcher-type [Phys. Z. 22, 645 (1921); J. Am. Ceram. Soc. 8, 339 (1925); Z. Anorg. Allg. Chem. 156, 245 (1926)] relaxation rates and approximate time-temperature superposition, consistent with the Williams-Landell-Ferry [J. Am. Chem. Soc. 77, 3701 (1955)] procedure for analyzing the dynamics of complex fluids, while the size dependence of the fluctuations provides an explanation for the distribution of relaxation times and heterogeneity that are found in glass-forming liquids, thus providing a unified picture for several features in the dynamics of disordered materials.
Three-dimensional simulation of gaseous slip flow in different aspect ratio microducts
Authors: Agrawal Abhishek , Agrawal Amit
Published: October 2006

Three-dimensional lattice Boltzmann method based simulations of a microduct have been undertaken in this paper. The objectives are to understand the different physical phenomena occurring at these small scales and to investigate when the flow can be treated as two dimensional. Toward this end, the Knudsen number and aspect ratio (depth to width ratio) are varied for a fixed pressure ratio. The pressure in the microduct is nonlinear with the nonlinearity in pressure reducing with an increase in the Knudsen number. The pressure behaves somewhat similar to two-dimensional microchannels, even when the aspect ratio is unity. The slip velocity at the impenetrable wall has two components: along and perpendicular to the primary flow direction. Our results show that the streamwise velocity near the centerline is relatively invariant along the depth for an aspect ratio of more than three, suggesting that the microduct can be modeled as a two-dimensional microchannel. On the other hand, the velocity component along the depth is never identically zero, implying that the flow is not truly two dimensional, although for practical purposes a two-dimensional treatment might suffice. A curious change in the vector direction in a plane normal to the flow direction is observed around an aspect ratio of four. These three-dimensional results are significant because they will help in theoretical development and flow modeling at microscales.
Tuning of the interdot resonance in stacked InAs quantum dot arrays by an external electric field
Authors: Talalaev V. G. , Tomm J. W. , Sokolov A. S. , Shtrom I. V. , Novikov B. V. , Winzer A. T. , Goldhahn R. , Gobsch G. , Zakharov N. D. , Werner P. , Gösele U. , Cirlin G. E. , Tonkikh A. A. , Ustinov V. M. , Tarasov G. G.
Published: October 2006

Optoelectronic properties of vertically stacked InAs∕GaAs quantum dot (QD) arrays are analyzed. The arrays are grown by molecular beam epitaxy into the intrinsic region of GaAs p-i-n junctions. The structures are extensively characterized by transmission electron microscopy and steady-state and transient photoluminescences. The application of an external bias along growth direction is found to substantially impact the photoluminescence properties. Our results allow for establishing a semiquantitative model for the band structure of biased QD structure, which is used for a consistent interpretation of all data. In particular, we interpret the photoluminescence properties of the structures, which are fully explained by the bias tuning the energetic states of the QDs with respect to each other. Tuning through resonances between the ground states of QDs is found to substantially modify luminescence intensities as well as rise and decay times. This bias sensitivity paves the way for photonic applications of such structures.
Study of electromigration-induced Cu consumption in the flip-chip Sn∕Cu solder bumps
Authors: Liu C. Y. , Ke Lin , Chuang Y. C. , Wang S. J.
Published: October 2006

The Cu consumption in flip-chip Sn∕Cu solder joint structures, both with and without current stressing was studied. The Cu consumption activation energy without current stressing was determined to be 0.93eV. With current stressing, the Cu consumption activation energy decreased to 0.66eV. We believe that the enhancement of Cu consumption by current stressing is due to the electromigration (EM) Cu atoms dissolved in the Sn to electromigrate instantaneously toward the anode side, which means that the cathode’s Cu–Sn compound layer dissolves into the Sn to satisfy the Cu solubility limit. The EM-induced Cu consumption is controlled by either the dissolution of the cathode Cu–Sn compound or by EM Cu flux in Sn. The temperature defines that the controlling step of Cu consumption was found and determined to be 129°C by equating the dissolution flux in the Cu–Sn compound and the EM Cu flux in Sn. When the EM temperature is higher than the critical temperature, the Cu–Sn compound dissolution process controls the Cu consumption. In this case, a constant interfacial Cu–Sn compound thickness remains at the cathode interface, which is determined by the balance between the Cu–Sn compound dissolution and the chemical Cu flux. If the EM temperature is lower than the critical temperature, the EM Cu flux in the Sn controls the Cu consumption. The growth of Cu–Sn compound at cathode is controlled by the EM Cu flux in Sn and the chemical Cu flux.
Ultraviolet driven negative current and rectifier effect in self-assembled green fluorescent protein device
Authors: Chiragwandi Z. G. , Gillespie K. , Zhao Q. X. , Willander M. , Panas I.
Published: October 2006

UV induced negative current produced at low voltages is reported in a photocurrent rectifier device consisting of a sensing region between two nano Al∕Al2O3 electrodes placed 30nm apart, employing a droplet of enhanced green fluorescent protein as molecular electrolyte. The current-voltage characteristics are discussed in terms of the properties of the thin Al2O3 scale, the position of the Fermi level, the position of the highest occupied molecular orbital-lowest unoccupied molecular orbital gap, and dispersion of states induced by varying dielectric constants.
Auxiliary-field quantum Monte Carlo study of first- and second-row post-d elements
Authors: Al-Saidi W. A. , Krakauer Henry , Zhang Shiwei
Published: October 2006

A series of calculations for the first- and second-row post-d elements (Ga–Br and In–I) are presented using the phaseless auxiliary-field quantum Monte Carlo (AF QMC) method. This method is formulated in a Hilbert space defined by any chosen one-particle basis and maps the many-body problem into a linear combination of independent-particle solutions with external auxiliary fields. The phase/sign problem is handled approximately by the phaseless formalism using a trial wave function, which in our calculations was chosen to be the Hartree-Fock solution. We used the consistent correlated basis sets of Peterson et al. [J. Chem. Phys. 119, 11099 (2003); 119, 11113 (2003)], which employ a small-core relativistic pseudopotential. The AF QMC results are compared with experiment and with those from density functional (generalized gradient approximation and B3LYP) and CCSD(T) calculations. The AF QMC total energies agree with CCSD(T) to within a few millihartrees across the systems and over several basis sets. The calculated atomic electron affinities, ionization energies, and spectroscopic properties of dimers are, at large basis sets, in excellent agreement with experiment.
Static and high frequency magnetic and dielectric properties of ferrite-ferroelectric composite materials
Authors: Kalarickal Sangita S. , Ménard David , Das Jaydip , Patton Carl E. , Zhang Xubai , Sengupta Louise C. , Sengupta Somnath
Published: October 2006

A series of sintered composite materials was fabricated from Parascan™ barium strontium titanate (BSTO) and Trans-Tech nickel zinc ferrite powders. The ferrite loading was varied from zero (BSTO only) to 100wt% (ferrite only). X-ray diffraction data show the presence of a third, nonmagnetic phase that sets the ferrite loading at values somewhat lower than the as prepared wt % amounts. The average magnetization is found to scale linearly with the loading. The initial susceptibility, saturation field, and coercive force as obtained from hysteresis loop data show trends consistent with these data. Ferromagnetic resonance linewidth and effective linewidth measurements at 10GHz show reasonable values for the 100wt% samples, but any amount of BSTO causes a severe degradation in both loss parameters. Similarly, it is found that any amount of ferrite causes a rapid drop in the relative dielectric constant that is consistent with standard mixing models. Loss tangent measurements gave modest values in the 0.001–0.005 range at 1MHz and much larger values in the 0.02–0.03 range at 10GHz.
Theoretical and computational investigations on thermodynamic properties, effective site diameters, and molecular free volume of carbon disulfide fluid
Authors: Eskandari Nasrabad Afshin , Laghaei Rozita
Published: October 2006

A newly proposed theory [R. Laghaei et al., J. Chem. Phys. 124, 154502 (2006)] was extended to polyatomics and applied to compute the density and temperature dependence of the effective site diameters of carbon disulfide fluids. The generic van der Waals (GvdW) theory was also extended to polyatomics in order to calculate the GvdW parameters and the molecular free volume using the effective site diameters as the repulsion-attraction separation distance. A three-site Lennard-Jones potential available in the literature was slightly modified and used in Monte Carlo simulations to obtain the functions appearing in the effective site diameter and GvdW expressions. The interaction potential was examined to reproduce the fluid phase thermodynamic properties using Gibbs ensemble Monte Carlo simulations and also the equation of state in the liquid phase using NVT Monte Carlo (NVT-MC) simulations. Comparison between the simulation results and experimental data shows excellent agreement for the densities of the coexisting phases, the vapor pressure, properties of the predicted critical point, and the equation of state. NVT-MC simulations were performed over a wide range of densities and temperatures in sub- and supercritical regions to compute the effective site diameters, the GvdW parameters, and the molecular free volume. The molecular structure in terms of the site-site pair correlation functions, the density dependence of the effective site diameters, and the density and temperature dependence of the GvdW parameters and molecular free volume were studied and discussed. The GvdW parameters were fitted to empirical expressions as a function of density and temperature. The computed molecular free volume will be used in future investigations to study the transport properties of carbon disulfide.
Photoluminescence of Tb3+ doped SiNx films grown by plasma-enhanced chemical vapor deposition
Authors: Yuan Zhizhong , Li Dongsheng , Wang Minghua , Chen Peiliang , Gong Daoren , Wang Lei , Yang Deren
Published: October 2006

Room temperature photoluminescence (PL) properties of the Tb3+ ion implanted nonstoichiometric silicon nitride (Tb3+:SiNx) and silicon dioxide (Tb3+:SiOx) were studied. The films were deposited by plasma-enhanced chemical vapor deposition and then annealed at different temperatures for 1h in flowing N2 before or after the implantation. Results show that there are four intense PL peaks due to the intra-4f transitions of Tb3+ in the wavelength from 470to625nm for both kinds of films. Moreover, after postannealing at 1000°C, the integrated PL intensity of Tb3+:SiNx is much higher than that of Tb3+:SiOx. The energy transfer from the defect related energy levels to the Tb3+ ions will enhance the D45→Fk7 (k=3–6) luminescence of Tb3+ ions.
Electroluminescent orthofused thiophene dye embedded in polyvinylcarbazole
Authors: Giovanella Umberto , Botta Chiara , Bossi Alberto , Licandro Emanuela , Maiorana Stefano
Published: October 2006

The photoluminescence and electroluminescence of a molecular precursor of helicene embedded in an active matrix formed by a hole-transporter polymer mixed with an electron transporter molecule are reported. Optimization of the weight ratio between the dye and the matrix is performed by a detailed study of the absolute emission efficiencies obtained by photoexcitation and by charge injection. A 0.17wt% dye concentration gives the best compromise among energy transfer, transport properties, and quenching effects induced by dye aggregation, leading to an external blue electroluminescence efficiency of 0.4% in a single layer device.
Cooperative organic hydrogen bonds: The librational modes of cyclic methanol clusters
Authors: Wugt Larsen R. , Suhm M. A.
Published: October 2006

Intermolecular hydrogen bond libration modes of isolated cyclic methanol trimers (≈613cm−1) and tetramers (695 and 760cm−1) are observed in pulsed jet Fourier transform infrared spectra and found to exhibit sizeable anharmonicity and mode coupling effects, opening the way for a microscopic interpretation of the broad librational bands of alcohols. The correlation of experimental OH stretching and OH libration band intensities provides important constraints for theoretical band strengths, cluster densities, and size assignments.
Application of Coulomb wave function discrete variable representation to atomic systems in strong laser fields
Authors: Peng Liang-You , Starace Anthony F.
Published: October 2006

We present an efficient and accurate grid method for solving the time-dependent Schrödinger equation for an atomic system interacting with an intense laser pulse. Instead of the usual finite difference (FD) method, the radial coordinate is discretized using the discrete variable representation (DVR) constructed from Coulomb wave functions. For an accurate description of the ionization dynamics of atomic systems, the Coulomb wave function discrete variable representation (CWDVR) method needs three to ten times fewer grid points than the FD method. The resultant grid points of the CWDVR are distributed unevenly so that one has a finer grid near the origin and a coarser one at larger distances. The other important advantage of the CWDVR method is that it treats the Coulomb singularity accurately and gives a good representation of continuum wave functions. The time propagation of the wave function is implemented using the well-known Arnoldi method. As examples, the present method is applied to multiphoton ionization of both the H atom and the H− ion in intense laser fields. The short-time excitation and ionization dynamics of H by an abruptly introduced static electric field is also investigated. For a wide range of field parameters, ionization rates calculated using the present method are in excellent agreement with those from other accurate theoretical calculations.
Sharpening the shape distribution of gold nanoparticles by laser irradiation
Authors: Resta V. , Siegel J. , Bonse J. , Gonzalo J. , Afonso C. N. , Piscopiello E. , Van Tenedeloo G.
Published: October 2006

This work reports on the optical response and morphological changes of gold nanoparticles (NPs) induced by laser irradiation with single nanosecond laser pulses of different fluences and wavelengths. The as-grown specimens consist of irregularly shaped NPs (10–13nm in average dimensions) produced by pulsed laser deposition on a substrate. They exhibit a broad optical absorption band related to the surface plasmon resonance (SPR) peaking in the range of 634–685nm. After irradiation with fluences above a threshold value, a blueshift, a decrease of the overall absorption, and a narrowing of the SPR band are observed. The SPR peak wavelength and amplitude after irradiation at increasing fluences reach an approximately constant value, irrespective of the irradiation wavelength. This value is consistent with a homogeneous distribution of spherical gold NPs with a mean diameter close to the average initial dimensions as determined by transmission electron microscopy. The results demonstrate that the conversion of irregularly shaped NPs into spherical NPs with reduced dimension dispersion is a thermally driven process and occurs within a fluence interval defined by the melting threshold of all NPs and the ablation threshold. Whereas the useful fluence interval is controlled by the effective fluence absorbed, that is dependent on the laser wavelength and thermal properties of the substrate, the final shape and dimensions of the NPs are independent of the irradiation wavelength provided the fluence is within this useful interval.
Influence of distribution of additives on electrical potential barrier at grain boundaries in ZnO-based multilayered chip varistor
Authors: Hirose Sakyo , Nishita Koichi , Niimi Hideaki
Published: October 2006

The influence of the distribution of additives on the electrical potential barrier at grain boundaries in a ZnO-based multilayered chip varistor was investigated by scanning surface potential microscopy (SSPM) and transmission electron microscope (TEM). The leakage current strongly depended on the distribution of additives, and a more uniform distribution improved the electrical nonlinearity. SSPM images revealed that the grain-boundary resistance of a uniformly distributed sample was higher than that of a poorly distributed sample. The decrease in the electrical nonlinearity due to the poor distribution was attributed to a decrease in the potential barrier height instead of an increase in the inactive grain boundary. The TEM analysis indicated that the poor distribution of Pr ions interfered with the formation of the potential barrier and resulted in the decrease in its height.
Gas-phase synthesis of magnesium nanoparticles: A high-resolution transmission electron microscopy study
Authors: Kooi B. J. , Palasantzas G. , De Hosson J. Th. M.
Published: October 2006

Magnesium nanoparticles with size above 10nm, prepared by gas-phase syntheses, were investigated by high-resolution transmission electron microscopy. The dominant particle shape is a hexagonal prism terminated by Mg(0002) and Mg{101¯0} facets. Oxidation of Mg yields a MgO shell (∼3nm thick), which has an orientation relation with the Mg. Inhomogeneous facet oxidation influences their growth kinetics resulting in a relatively broad size and shape distribution. Faceted voids between Mg and MgO shells indicate a fast outward diffusion of Mg and vacancy rearrangement into voids. The faceting of polar {220} planes is assisted by electron irradiation.
Polarizability of the dielectric double-sphere
Authors: Pitkonen Mikko
Published: October 2006

An explicit solution for the longitudinal and transverse polarizability of the symmetric dielectric intersecting double sphere is obtained as a rapidly converging series of integral operators, which is fast enough for real time calculation in Java Applet.
On-off intermittency in time series of spontaneous paroxysmal activity in rats with genetic absence epilepsy
Authors: Hramov Alexander , Koronovskii Alexey A. , Midzyanovskaya I. S. , Sitnikova E. , van Rijn C. M.
Published: October 2006

In the present paper we consider the on-off intermittency phenomena observed in time series of spontaneous paroxysmal activity in rats with genetic absence epilepsy. The method to register and analyze the electroencephalogram with the help of continuous wavelet transform is also suggested.
Effects of interfacial organic layers on thin film nucleation in atomic layer deposition
Authors: Dube Abhishek , Sharma Manish , Ma Paul F. , Engstrom J. R.
Published: October 2006

Atomic layer deposition (ALD) of titanium nitride (TiN) on silicon dioxide and silicon dioxide modified by self-assembled monolayers (SAMs) with different structures and functional terminations has been investigated employing molecular beam techniques. On the –CH3 terminated SAMs, growth is significantly attenuated over that observed on clean SiO2, more than an order of magnitude for the thicker SAMs, and involves islanded, nonuniform growth. ALD is also observed on SAMs with reactive end groups, –OH and –NH2, but growth is uniform and attenuated only by approximately a factor of 3, independent of the thickness of these SAMs.
Rapid solid-phase crystallization of high-rate, hot-wire chemical-vapor-deposited hydrogenated amorphous silicon
Authors: Young David L. , Stradins Paul , Xu Yueqin , Gedvilas Lynn , Reedy Bob , Mahan A. H. , Branz Howard M. , Wang Qi , Williamson D. L.
Published: October 2006

Solid-phase crystallization of hydrogenated amorphous silicon thin films deposited by hot-wire (HW) and plasma-enhanced (PE) chemical vapor deposition was studied using in situ optical monitoring. HW films crystallized at least five times faster than PE films, independent of H and O concentration, deposition rate (2–110Å∕s), and nanovoid density due to reduced enthalpy barriers to both nucleation and final crystallization, which may be related to the presence of larger regions of highly ordered Si in the films.
Recombination zone in mixed-host organic light-emitting devices
Authors: Hsiao Chih-Hung , Chen Yan-Hau , Lin Tien-Chun , Hsiao Chia-Chiang , Lee Jiun-Haw
Published: October 2006

In this letter, the authors had quantitatively investigated the recombination zone in the mixed-host (MH) emitting layer (EML) of an organic light-emitting device with different mixed ratios experimentally and theoretically. The MH-EML consisted of a hole-transport layer (HTL) and an electron-transport layer fabricated by coevaporation. When the mixed ratio of the HTL in the EML increases, the driving voltage increases then decreases; this can be well demonstrated by an electrical model with different carrier mobilities. A blueshift was also observed due to the solid state solvation effect combined with the exciton shift from the anode to the cathode side.
High-mobility transistors based on nanoassembled carbon nanotube semiconducting layer and SiO2 nanoparticle dielectric layer
Authors: Xue Wei , Liu Yi , Cui Tianhong
Published: October 2006

The authors report the fabrication and characterization of high-mobility thin-film transistors (TFTs) using layer-by-layer (LBL) nano self-assembled single-walled carbon nanotubes (SWCNTs) as the semiconducting material and SiO2 nanoparticles as the gate dielectric material. The channel length and the effective thickness of the SWCNT semiconductor layer are 50μm and 38nm, respectively. The effective thickness of the SiO2 dielectric layer is 180nm. The SWCNT TFT exhibits p-type semiconductor characteristics and operates in the accumulation mode, with a hole mobility (μp) of 168.5cm2∕Vs, a normalized transconductance (gm∕W) of 0.5S∕m, a threshold voltage (Vth) of −3V, and an on/off current ratio (Ion∕off) of 4.2. The combination technique with LBL nano self-assembly and microlithography provides a simple, low-temperature, and highly efficient approach to fabricate inexpensive TFT devices.
Low threshold current density distributed feedback quantum cascade lasers with deep top gratings
Authors: Xu Gangyi , Li Aizhen , Li Yaoyao , Wei Lin , Zhang Yonggang , Lin Chun , Li Hua
Published: October 2006

The authors report on pulsed and continuous-wave operation of single mode tunable distributed feedback quantum cascade lasers at λ∼7.7μm. A deep top grating and a thin heavily doped InP layer beneath the grating are formed in the upper cladding to obtain simultaneously a strong feedback effect and a low waveguide loss. A “three-well vertical transition” active region is used with a low doped injector. In pulsed operation, a very low threshold current density of 970A∕cm2 and a peak power of 75mW are achieved at 300K. Reliable single mode emission with a side mode suppression ratio of ∼30dB is achieved in a large temperature range (155–320K) with a tuning range of 90nm. The lasers operate in continuous-wave mode up to 130K.
Noncontact tuning fork position sensing for hollow-pyramid near-field cantilevered probes
Authors: Ambrosio A. , Cefalì E. , Spadaro S. , Patanè S. , Allegrini M. , Albert D. , Oesterschulze E.
Published: October 2006

We demonstrate that tuning fork sensing provides a stable, noncontact mode of operation when applied to near-field optical microscopy employing cantilevered probes. Detrimental damping effects that have so far limited the practical use of these otherwise very advantageous probes are totally overcome. We validate our tuning fork setup featuring hollow-pyramid probes by an optical nanolithography application.
Anisotropic Sm–Fe–N magnets produced by compression shearing method
Authors: Saito Tetsuji , Sato Hisanobu , Takeishi Hiroyuku , Nakayama Noboru
Published: October 2006

Sm–Fe–N bulk magnet was produced by the compression shearing method. X-ray diffraction studies revealed that the magnet retained the original Sm2Fe17N3 phase structure without any appreciable decomposition of the Sm2Fe17N3 phase and that this phase had a pronounced crystallographic alignment. Magnetic measurements confirmed that the Sm–Fe–N magnet was magnetically anisotropic. The bulk anisotropic Sm–Fe–N magnet exhibited a high remanence value of 9.43kG with a high coercivity of 11.0kOe.
Nonconductive polymer microresonators actuated by the Kelvin polarization force
Authors: Schmid Silvan , Wendlandt Michael , Junker David , Hierold Christofer
Published: October 2006

The authors present a method, based on the Kelvin polarization force, to actuate nonconductive polymer microstructures. A proof of principle was conducted by finite element simulations. Microresonators made of SU-8 were fabricated and characterized under resonant conditions at applied ac voltage of 5Vpp. A quality factor of Q=87 in vacuum and a square dependence of the force on the applied voltage were obtained. The presented actuator design and fabrication do not require additional electrodes on the movable structure for actuation and thus allow for the full exploration of the exceptional variety of polymer materials for microscaled actuators and sensors.
Thermal conductivity of diamond-like carbon films
Authors: Shamsa M. , Liu W. L. , Balandin A. A. , Casiraghi C. , Milne W. I. , Ferrari A. C.
Published: October 2006

The authors report the thermal conductivity (K) of a variety of carbon films ranging from polymeric hydrogenated amorphous carbons (a-C:H) to tetrahedral amorphous carbon (ta-C). The measurements are performed using the 3ω method. They show that thermal conduction is governed by the amount and structural disorder of the sp3 phase. If the sp3 phase is amorphous, K scales linearly with the C–C sp3 content, density, and elastic constants. Polymeric and graphitic films have the lowest K (0.2–0.3W∕mK), hydrogenated ta-C:H has K∼1W∕mK, and ta-C has the highest K (3.5W∕mK). If the sp3 phase orders, even in small grains such as in micro- or nanodiamond, a strong K increase occurs for a given density, Young’s modulus, and sp3 content.
Discharge characteristics of atmospheric-pressure radio-frequency glow discharges with argon/nitrogen
Authors: Wang Hua-Bo , Sun Wen-Ting , Li He-Ping , Bao Cheng-Yu , Gao Xing , Luo Hui-Ying
Published: October 2006

In this letter, atmospheric-pressure glow discharges in γ mode with argon/nitrogen as the plasma-forming gas using water-cooled, bare copper electrodes driven by radio-frequency power supply at 13.56MHz are achieved. The preliminary studies on the discharge characteristics show that, induced by the α-γ coexisting mode or γ mode discharge of argon, argon-nitrogen mixture with any mixing ratios, even pure nitrogen, can be employed to generate the stable γ mode radio-frequency, atmospheric-pressure glow discharges and the discharge voltage rises with increasing the fraction of nitrogen in the argon-nitrogen mixture for a constant total gas flow rate.
Mode-dependent enhancement of photodissociation and photoionization in a seven atom molecule
Authors: Golan Amir , Rosenwaks Salman , Bar Ilana
Published: October 2006

We report the first experimental demonstration of vibrational mode-dependent enhancement in photodissociation and photoionization of a seven atom molecule, methylamine (CH3NH2). The fundamental C-H stretches and the overtones or combinations of CH3 bends were prepared via stimulated Raman excitation (SRE) prior to their 243.135nm one-photon dissociation or two-photon ionization. The photodissociation or photoionization of the vibrationally excited molecules was achieved via 10ns delayed or temporally overlapping SRE and UV pulses, respectively. It is shown that bending modes are more effective than stretches in promoting photodissociation and photoionization, since their UV excitation is favored by larger Franck Condon factors. This behavior provides clear evidence for vibrational mode-dependence in a relatively large molecule with a torsional degree of freedom, indicating that these modes survive intramolecular vibrational redistribution on a time scale considerably longer than hitherto inferred from previous studies.
Electron transport in semiconducting chiral carbon nanotubes
Authors: Kauser M. Z. , Ruden P. P.
Published: October 2006

The authors report on electron transport characteristics for semiconducting, single wall, chiral carbon nanotubes. The Boltzmann transport equation is solved indirectly by the ensemble Monte Carlo method. The basis for the transport calculations is provided by electronic structure calculations in the framework of a simple tight binding model. Scattering mechanisms considered are due to the electron-phonon interactions involving longitudinal acoustic, longitudinal optic, and radial breathing mode phonons. Due to the smaller Brillouin zone, Umklapp scattering processes occur with much greater frequency in chiral carbon nanotubes than in achiral nanotubes. The transient and steady-state transport characteristics are found to be dependent on the chirality for semiconducting carbon nanotubes with similar diameters.
Application of metal-doped organic layer both as exciton blocker and optical spacer for organic photovoltaic devices
Authors: Chan M. Y. , Lai S. L. , Lau K. M. , Lee C. S. , Lee S. T.
Published: October 2006

An effective optical spacer based on doping of ytterbium (Yb) metal into bathophenanthroline (BPhen) has been developed for applications in organic photovoltaic (OPV) devices. Utilizing Yb:BPhen as an optical spacer in standard copper phthalocyanine/C60 photovoltaic devices, power efficiency can be increased by four times to 3.42%. Ultraviolet photoemission spectroscopy measurements reveal that the good electron transport between C60 and Yb:BPhen is mainly related to the suitable energy level alignment at the interface. Combining with its high optical transparency and electrical conductivity, the Yb:BPhen film provides a useful means for maximizing the power conversion efficiency of OPV devices.
Conditions for designing single-mode air-core waveguides in three-dimensional photonic crystals
Authors: Lousse Virginie , Shin Jonghwa , Fan Shanhui
Published: October 2006

The authors present a general procedure that allows the design of single-mode air-core waveguides in three-dimensional photonic crystals. The procedure involves analyzing the modal profile of the band edge mode in the perfect crystal, identifying the regions of maximal electric-field intensity, and placing the air defects to enclose these regions. As an illustration, they present a detailed design of air-core waveguides in a recently proposed silicon body-center-cubic crystal structure that possesses a 25% complete band gap.
III/V ratio based selectivity between strained Stranski-Krastanov and strain-free GaSb quantum dots on GaAs
Authors: Balakrishnan G. , Tatebayashi J. , Khoshakhlagh A. , Huang S. H. , Jallipalli A. , Dawson L. R. , Huffaker D. L.
Published: October 2006

The authors demonstrate and characterize type-II GaSb quantum dot (QD) formation on GaAs by either Stranski-Krastanov (SK) or interfacial misfit (IMF) growth mode. The growth mode selection is controlled by the gallium to antimony (III/V) ratio where a high III/V ratio produces IMF and a low ratio establishes the SK growth mode. The IMF growth mode produces strain-relaxed QDs, where the SK QDs remain highly strained. Both ensembles demonstrate strong room temperature photoluminescence (PL) with the SK QDs emitting at 1180nm and the IMF QDs emitting at 1375nm. Quantized energy levels along with a spectral blueshift are observed in 77K PL. Transmission electron microscope images identify the IMF array and crystallographic shape for both types of QD formation. Atomic force microscope images characterize QD geometry and density.
Reduction of gate leakage current of HfSiON dielectrics through enhanced phonon-energy coupling
Authors: Samantaray Chandan B. , Chen Zhi
Published: October 2006

The authors have investigated the effect of phonon-energy-coupling enhancement induced by rapid thermal processing (RTP) and deuterium annealing on the leakage current characteristics of HfSiON gate dielectrics. The leakage current is reduced by one- and-a-half orders of magnitude after RTP and deuterium annealing of HfSiON gate dielectrics. The leakage current density of the HfSiON gate insulator with equivalent oxide thickness of 5.2Å was only 4×10−2Acm−2. This suggests that HfSiON with the enhanced phonon-energy coupling can be scaled down to below 5Å.
Instabilities of switching processes in synthetic antiferromagnets
Authors: Bogdanov A. N. , Rößler U. K.
Published: October 2006

It is shown that magnetic states and field-driven reorientation transitions in synthetic antiferromagnets crucially depend on contributions of higher-order anisotropies. A phenomenological macrospin model is derived to describe the magnetic states of two antiferromagnetically coupled magnetic thin-film elements. The calculated phase diagrams show that magnetic states with out-of-plane magnetization, symmetric escaped spin-flop phases, exist in a broad range of the applied magnetic field. Due to the formation of such states and concomitant multidomain patterns, the switching processes in toggle magnetic random access memory devices can radically deviate from predictions within oversimplified models.
Large tunnel magnetoresistance in tunnel junctions with Co2MnSi∕Co2FeSi multilayer electrode
Authors: Ebke D. , Schmalhorst J. , Liu N.-N. , Thomas A. , Reiss G. , Hütten A.
Published: October 2006

Two kinds of magnetic tunnel junctions with Co2FeSi electrodes are compared. Using Co2FeSi single layers a tunnel magnetoresistance of 52% is reached, whereas the magnetization of the Co2FeSi is only 75% of the expected value. By using [Co2MnSi∕Co2FeSi]x10 multilayer electrodes the magnetoresistance can be increased to 114% and the full bulk magnetization is reached. All junctions show an inverse tunnel magnetoresistance, when the electrons are tunneling from the Co–Fe into the Heusler compound electrode. This results from a special band structure feature of full Heusler compounds, which is robust even for atomic disorder in the films.
Driving frequency effect on the electron energy distribution function in capacitive discharge under constant discharge power condition
Authors: Ahn S. K. , You S. J. , Chang H. Y.
Published: October 2006

A modern trend of VHF driven plasma sources in semiconductor processing stimulates a lot of studies concerning the driving frequency effect on plasma parameters in a capacitive discharge. In spite of abundant studies, the validation and application of these results in industrial plasma processing are still questionable because these studies were performed under a fixed rf voltage condition or an assumption of Maxwellian electron energy distribution, while the fixed discharge power condition and non-Maxwellian distribution are typical in industrial plasma processing. To resolve this problem, the authors investigated the driving frequency effect on plasma parameters (electron density and temperature) under the fixed discharge power condition by measuring the electron energy distribution functions, which are the most important factor in chemical reactions during the plasma processing. A remarkable result was observed—as the driving frequency increases, the electron temperature increases and the electron density remains almost constant or decreases, which is opposite to what previous studies have suggested. This result can be tentatively explained as a result of an enhancement of collisional heating in the bulk plasma with driving frequency under the fixed discharge power condition.
High-conductance states of single benzenedithiol molecules
Authors: Tsutsui Makusu , Teramae Yumi , Kurokawa Shu , Sakai Akira
Published: October 2006

Conductance of single 1,4-benzenedithiol (BDT) molecules is investigated in a wide range (0–0.3)G0, exploiting mechanically controllable break junction technique. The authors observed a series of clear conductance steps both in low- (∼0.01G0) and high-conductance (∼0.1G0) regimes and corresponding two sets of peak structures in the conductance histograms. The two distinct conductance states are attributable to different Au–S bonding configurations of Au∕BDT∕Au junctions. The high-bias measurements reveal that the high-conductance state of single BDT molecules is stable up to 1.6V and prospective for molecular device applications.
Indium adsorption on GaN under metal-organic chemical vapor deposition conditions
Authors: Jiang F. , Wang R.-V. , Munkholm A. , Streiffer S. K. , Stephenson G. B. , Fuoss P. H. , Latifi K. , Thompson Carol
Published: October 2006

Real-time synchrotron grazing-incidence x-ray fluorescence is employed to study indium adsorption on the GaN (0001) surface under typical process conditions for InGaN metal-organic chemical vapor deposition. An indium condensation boundary is mapped as a function of trimethylindium pressure, substrate temperature, and carrier gas composition. Below the condensation boundary, indium surface coverage reaches a maximum of ∼1∕4 ML. The addition of 8% H2 to the carrier gas is found to have a significant effect on both condensation and adsorption of indium.
Controlled selective growth of ZnO nanorod and microrod arrays on Si substrates by a wet chemical method
Authors: Kim Yong-Jin , Lee Chul-Ho , Hong Young Joon , Yi Gyu-Chul , Kim Sung Soo , Cheong Hyeonsik
Published: October 2006

The use of a wet chemical method to selectively grow ZnO microrod and nanorod arrays on Si substrates is described. To control the size and position of the ZnO microrods and nanorods, polymethylmethacrylate (PMMA) submicron patterns were prepared on the Si substrates with an intermediate ZnO layer using e-beam lithography. Selective growth of the ZnO structures was achieved by the absence of ZnO nucleation sites on the PMMA mask, resulting in position-controlled growth of ZnO structures only on patterned holes where the ZnO layer was exposed. In addition, the diameters of the ZnO microrods were determined by the patterned hole size, and the diameters as small as 250nm were obtained when a hole diameter of 250nm was employed. The structural and optical characteristics of the ZnO microrods were further investigated using x-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy.
Surface polarization enhancement in (Pb0.25Ba0.15Sr0.6)TiO3 nanotubes
Authors: Liu Wei , Sun Xiaohua , Han Hongwei , Li Meiya , Zhao Xing-Zhong
Published: October 2006

( Pb 0.25 Ba 0.15 Sr 0.6 ) Ti O 3 (PBST) nanotube arrays were prepared using porous anodic aluminum oxide (AAO) template from PBST sol solution. Electron microscope results showed that uniform length and diameter of PBST nanotubes were obtained and that the diameter and length of PBST nanotubes were dependent on the pore diameter and the thickness of the applied AAO template. X-ray diffraction and electron diffraction pattern investigations demonstrated that PBST nanotubes were composed of perovskite nanocrystals. Comparison between nanotube and nanofilm polarization results showed that enhanced polarization existed in PBST nanotubes. A mechanism has been proposed to explain this polarization enhancement effect.