bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogeomorphic processes in a steep debris flow initiation zone
Authors: Imaizumi Fumitoshi , Sidle Roy C. , Tsuchiya Satoshi , Ohsaka Okihiro
Published: May 2006

Many debris flows initiate in steep channels (>20 degrees), yet studies have focused on lower‐gradient streams where failure is controlled by water height above channel deposits. Multiple debris flows in a steep channel in Ohya landslide, central Japan, were linked to infilling processes (i.e., freeze‐thaw and dry ravel) and partial saturation of accumulated sediment. Because of very active geomorphic processes in this catchment, 39 debris flows were observed in the past 6 yr. Pre‐ and post event imagery indicates selective transport of finer materials during most debris flows that comprise saturated and unsaturated flows; however, fluvial sediment processes, important in relation to debris flow initiation in gentler channels, were minimal. Critical conditions for the movement of such unsaturated materials are derived by equating shear stress with solid friction of the channel bed.
Inertial confinement fusion neutron images
Authors: Disdier L. , Rouyer A. , Lantuéjoul I. , Landoas O. , Bourgade J. L. , Sangster T. C. , Glebov V. Yu. , Lerche R. A.
Published: May 2006

At the OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)], 14-MeV neutron images are acquired with a 20-μm resolution and a large signal-to-noise ratio (SNR) using penumbral and ring apertures. The two aperture types produce coded images of the source that are unfolded using a similar autocorrelation method. The techniques provide comparable images for various deuterium-tritium filled target implosions, with glass and plastic (CH) shells. SNR analysis reveals that the annular (ring) technique will achieve a good image quality at the 10-μm resolution level with the planned upgrade of our novel detector. The detector is an array of 85-μm-diam capillary tubes filled with a liquid scintillator. Its resolution is limited to 650μm by the track length of the elastically scattered recoil protons. Replacing the hydrogen in the scintillator with deuterium improves detector spatial resolution to 325μm, and makes high source resolution achievable. The readout design provides an efficient light collection of the scintillation photons by relaying the image through a fiber optic taper. Improved efficiency produces images with better SNR. Also, the increased detector sensitivity allows single event recording of 2.45-MeV neutron interactions. For the first time ever, we show neutron images of deuterium filled, warm, and cryogenic target implosions.
Compact single and nested tungsten-wire-array dynamics at 14–19MA and applications to inertial confinement fusion
Authors: Cuneo M. E. , Sinars D. B. , Waisman E. M. , Bliss D. E. , Stygar W. A. , Vesey R. A. , Lemke R. W. , Smith I. C. , Rambo P. K. , Porter J. L. , Chandler G. A. , Nash T. J. , Mazarakis M. G. , Adams R. G. , Yu E. P. , Struve K. W. , Mehlhorn T. A. , Lebedev S. V. , Chittenden J. P. , Jennings C. A.
Published: May 2006

Wire-array z pinches show promise as a high-power, efficient, reproducible, and low-cost x-ray source for high-yield indirect-drive inertial confinement fusion. Recently, rapid progress has been made in our understanding of the implosion dynamics of compact (20-mm-diam), high-current (11–19MA), single and nested wire arrays. As at lower currents (1–3MA), a single wire array (and both the outer and inner array of a nested system), show a variety of effects that arise from the initially discrete nature of the wires: a long wire ablation phase for 50%-80% of the current pulse width, an axial modulation of the ablation rate prior to array motion, a larger ablation rate for larger diameter wires, trailing mass, and trailing current. Compact nested wire arrays operate in current-transfer or transparent mode because the inner wires remain discrete during the outer array implosion, even for interwire gaps in the outer and inner arrays as small as 0.21mm. These array physics insights have led to nested arrays that produce radiation pulse shapes required for three-shock low-adiabat compression of high-yield inertial confinement fusion capsules.
Modeling of field-reversed configuration experiment with large safety factor
Authors: Steinhauer Loren , Guo Houyang , Hoffman Alan , Ishida Akio , Ryutov Dmitri
Published: May 2006

The Translation-Confinement-Sustainment facility has been operated in the “translation-formation” mode in which a plasma is ejected at high-speed from a θ-pinch-like source into a confinement chamber where it settles into a field-reversed-configuration state. Measurements of the poloidal and toroidal field have been the basis of modeling to infer the safety factor. It is found that the edge safety factor exceeds two, and that there is strong forward magnetic shear. The high-q arises because the large elongation compensates for the modest ratio of toroidal-to-poloidal field in the plasma. This is the first known instance of a very high-β plasma with a safety factor greater than unity. Two-fluid modeling of the measurements also indicate several other significant features: a broad “transition layer” at the plasma boundary with probable line-tying effects, complex high-speed flows, and the appearance of a two-fluid minimum-energy state in the plasma core. All these features may contribute to both the stability and good confinement of the plasma.
Gas-filled hohlraum experiments at the National Ignition Facility
Authors: Fernández Juan C. , Goldman S. R. , Kline J. L. , Dodd E. S. , Gautier C. , Grim G. P. , Hegelich B. M. , Montgomery D. S. , Lanier N. E. , Rose H. , Schmidt D. W. , Workman J. B. , Braun D. G. , Dewald E. L. , Landen O. L. , Campbell K. M. , Holder J. P. , MacKinnon A. J. , Niemann C. , Schein J. , Young B. K. , Celeste J. R. , Dixit S. N. , Eder D. C. , Glenzer S. H. , Haynam C. A. , Hinkel D. , Kalantar D. , Kamperschroer J. , Kauffman R. L. , Kirkwood R. , Koniges A. E. , Lee F. D. , MacGowan B. J. , Manes K. R. , McDonald J. W. , Schneider M. B. , Shaw M. J. , Suter L. J. , Wallace R. J. , Weber F. A. , Kaae J. L.
Published: May 2006

Experiments done at the National Ignition Facility laser [J. A. Paisner, E. M. Campbell, and W. Hogan, Fusion Technol. 26, 755 (1994)] using gas-filled hohlraums demonstrate a key ignition design feature, i.e., using plasma pressure from a gas fill to tamp the hohlraum-wall expansion for the duration of the laser pulse. Moreover, our understanding of hohlraum energetics and the ability to predict the hohlraum soft-x-ray drive has been validated in ignition-relevant conditions. Finally, the laser reflectivity from stimulated Raman scattering in the fill plasma, a key threat to hohlraum performance, is shown to be suppressed by choosing a design with a sufficiently high ratio of electron temperature to density.
Measurements of shock-induced guided and surface acoustic waves along boreholes in poroelastic materials
Authors: Chao Gabriel , Smeulders D. M. J. , van Dongen M. E. H.
Published: May 2006

Acoustic experiments on the propagation of guided waves along water-filled boreholes in water-saturated porous materials are reported. The experiments were conducted using a shock tube technique. An acoustic funnel structure was placed inside the tube just above the sample in order to enhance the excitation of the surface modes. A fast Fourier transform-Prony-spectral ratio method is implemented to transform the data from the time-space domain to the frequency-wave-number domain. Frequency-dependent phase velocities and attenuation coefficients were measured using this technique. The results for a Berea sandstone material show a clear excitation of the fundamental surface mode, the pseudo-Stoneley wave. The comparison of the experimental results with numerical predictions based on Biot’s theory of poromechanics [J. Acoust. Soc. Am. 28, 168 (1956)], shows that the oscillating fluid flow at the borehole wall is the dominant loss mechanism governing the pseudo-Stoneley wave and it is properly described by the Biot’s model at frequencies below 40kHz. At higher frequencies, a systematic underestimation of the theoretical predictions is found, which can be attributed to the existence of other losses mechanisms neglected in the Biot formulation. Higher-order guided modes associated with the compressional wave in the porous formation and the cylindrical geometry of the shock tube were excited, and detailed information was obtained on the frequency-dependent phase velocity and attenuation in highly porous and permeable materials. The measured attenuation of the guided wave associated with the compressional wave reveals the presence of regular oscillatory patterns that can be attributed to radial resonances. This oscillatory behavior is also numerically predicted, although the measured attenuation values are one order of magnitude higher than the corresponding theoretical values. The phase velocities of the higher-order modes are generally well predicted by theory.
13.5
nm
extreme ultraviolet emission from tin based laser produced plasma sources
Authors: Hayden Paddy , Cummings Anthony , Murphy Nicola , O’Sullivan Gerry , Sheridan Paul , White John , Dunne Padraig
Published: May 2006

An examination of the influence of target composition and viewing angle on the extreme ultraviolet spectra of laser produced plasmas formed from tin and tin doped planar targets is reported. Spectra have been recorded in the 9–17nm region from plasmas created by a 700mJ, 15ns full width at half maximum intensity, 1064nm Nd:YAG laser pulse using an absolutely calibrated 0.25m grazing incidence vacuum spectrograph. The influence of absorption by tin ions (SnI–SnX) in the plasma is clearly seen in the shape of the peak feature at 13.5nm, while the density of tin ions in the target is also seen to influence the level of radiation in the 9–17nm region.
Optical manipulation of neutral nanoparticles suspended in a microfluidic channel
Authors: Ben-Abdallah Philippe , Ould El Moctar Ahmed , Ni Bo , Aubry Nadine , Singh Pushpendra
Published: May 2006

An optical method to deterministically manipulate nanosized particles in suspensions within confined microfluidic devices is introduced. We show that under appropriate conditions strong dielectrophoretic forces several orders of magnitude larger than the Brownian force can be generated using an external optical actuation. A self-consistent coupled point-dipole model that includes the redistribution of charges on the channel boundaries allows us to specify the underlying mechanisms and estimate the optical forces experienced by a nanoparticle.
Real-time coarsening dynamics of Ge∕Si(100) nanostructures
Authors: Mckay Michael R. , Shumway John , Drucker Jeff
Published: May 2006

The coarsening dynamics of Ge∕Si(100) nanostructures were monitored using real-time, elevated temperature scanning tunneling microscopy (STM). Gas-source molecular beam epitaxy from digermane onto Si(100) was used to produce mixed hut and pyramid cluster ensembles. The width of the most elongated rectangular-based hut clusters was always less than the side length of square-based pyramid clusters for the growth conditions employed. This suggests that pyramid elongation to form hut clusters occurred at early growth stages for some smaller clusters. A previously unidentified coarsening mechanism was characterized during growth temperature annealing and was interpreted using atomistic elastic modeling. Pyramid clusters were more stable than narrow hut clusters with larger volumes. These larger volume huts decayed by reducing their length at a constant width, finally becoming small pyramids. These small pyramids are less stable than those that never elongated to form huts and consequently dissolve. The decrease in the total island volume identified using STM was attributed to large (diameter>1μm), low chemical potential clusters. These clusters depleted the surface of Ge adatoms as evidenced by denuded zones devoid of smaller clusters observed for growth and annealing at higher temperatures. These results suggest that a preferred island size for pyramids and huts does not exist.
Thermionic trap-assisted tunneling model and its application to leakage current in nitrided oxides and AlGaN∕GaN high electron mobility transistors
Authors: Mahaveer Sathaiya D. , Karmalkar Shreepad
Published: May 2006

We propose two models of electron tunneling from metal to a semiconductor via traps. In addition to the electrons below the metal Fermi level, the models also include the thermally activated electrons above the Fermi level. The first model is called generalized thermionic trap-assisted tunneling (GTTT), which considers tunneling through both triangular and trapezoidal barriers present in metal insulator semiconductor (MIS) structures. The second model is called thermionic trap-assisted tunneling (TTT), which considers tunneling through triangular barriers present in modern Schottky junctions. The GTTT model is shown to predict the low field leakage currents in MIS structures with nitrided oxide as insulator, and the TTT model is shown to predict the reverse gate leakage in AlGaN∕GaN high electron mobility transistors.
Effective transport properties of arrays of multicoated or graded spheres with spherically transversely isotropic constituents
Authors: Kuo Hsin-Yi , Chen Tungyang
Published: May 2006

This work is concerned with the determination of the effective conductivity and potential fields of a periodic array of spherically transversely isotropic spheres in an isotropic matrix. We generalize Rayleigh’s method to account for the periodic arrangements of the inclusions. The inclusions considered in the formulation could be multicoated, generally graded, or exponentially graded. For the multicoated spheres, we derive a recurrence procedure valid for any number of coatings. We show that a (2×2) array alone can mathematically represent the effect of the multiple coatings. For a graded inclusion, the method of Frobenius is adopted to obtain series solutions for the potential fields. For an exponentially graded sphere, we show that the admissible potential field in the inclusion admits a closed-form expression in terms of confluent hypergeometric functions. All these types of inclusions can be characterized by simple scalar coefficients Tl in the estimate of effective conductivities. Simple orthorhombic, body-centered orthorhombic, and face-centered orthorhombic lattice structures are considered in the formulation. Numerical results are presented for selected systems with sufficient accuracy. We demonstrate that the anisotropy of the spheres can strongly influence the potential fields inside the inclusions. The effects of spherical anisotropy, multiple coatings, and the grading factor are also studied.
The role of antimony on properties of widely varying GaInNAsSb compositions
Authors: Yuen Homan B. , Bank Seth R. , Bae Hopil , Wistey Mark A. , Harris James S.
Published: May 2006

Antimony has been used as a surfactant to improve the quality of GaInNAs∕GaAs quantum wells for long-wavelength optoelectronics. We demonstrate the importance of antimony as a reactive surfactant and the proper usage of it with dilute nitrides in order to tailor the properties of solar cell and laser devices. The effects of the addition of antimony to low indium concentration (∼8%) and low strain GaInNAs material (for 1.0eV solar cell applications) were investigated. It was assumed previously that adding antimony helped all GaInNAs alloys, but the validity of this was not previously tested. The addition of antimony to high indium concentration (∼32%) and high strain GaInNAs samples led to a dramatic improvement in optical quality and a widening of the growth window, while it led to a degradation in the low indium (low strain) composition samples. The addition of indium under constant antimony flux also improved the optical quality of the GaInNAs material. Variations in the indium and antimony compositions revealed a competition in atomic incorporation into the GaInNAsSb alloy. This interaction will be discussed. Increasing indium and/or strain confirmed the reactive surfactant properties of antimony on GaInNAsSb alloys.
The energy level spacing from InAs∕GaAs quantum dots: Its relation to the emission wavelength, carrier lifetime, and zero dimensionality
Authors: Jang Y. D. , Lee H. , Lee D. , Kim J. S. , Leem J. Y. , Noh S. K.
Published: May 2006

We have found that the level spacing between the ground and first excited states of InAs∕GaAs quantum dots (QDs) increases as the photoluminescence peak energy decreases, that is, as the QD increases in size. By means of simple numerical calculations, we confirm that this seemingly unusual level-spacing behavior originates from the low aspect ratio of typical QDs with a finite potential barrier. Carrier lifetime measurements show that QDs with a lower photoluminescence peak energy tend to have a shorter decay time, which can be attributed to better confinement of the electron wave function and the resultant increase in electron-hole wave function overlap.
Strong in-plane optical anisotropy of asymmetric (001) quantum wells
Authors: Chen Y. H. , Ye X. L. , Xu B. , Wang Z. G.
Published: May 2006

It is well known that asymmetry in the (001) direction can induce in-plane optical anisotropy (IPOA) in (001) quantum wells (QWs). In this letter, asymmetry is introduced in (001) GaAs∕AlGaAs QWs by inserting 1 ML (monolayer) of InAs or AlAs at interfaces. Strong IPOA, which is comparable to that in the InGaAs∕InP QWs with no common atom, is observed in the asymmetric GaAs∕AlGaAs QW by reflectance difference spectroscopy.
Preparation of metastable Sr3Co4O9 epitaxial thin films with controlled orientation and their anisotropic thermoelectric properties
Authors: Sakai Akihiro , Kanno Tsutomu , Yotsuhashi Satoshi , Okada Satoshi , Adachi Hideaki
Published: May 2006

We have prepared metastable misfit-type Sr3Co4O9 epitaxial films by rf-planar magnetron sputtering. Anisotropic electric resistivity and Seebeck coefficient (parallel and perpendicular to the CoO2 layers) were measured using a-axis-oriented Sr3Co4O9 films where the layer structure stands perpendicularly to the substrate surface. The parallel resistivity exhibited considerable low value of about 2.5mΩcm at room temperature. Although the parallel Seebeck coefficient was a little lower than that of the Ca3Co4O9 film at room temperature, the thermoelectric power factor was estimated to be two times higher than that of Ca3Co4O9 owing to lower resistivity in Sr3Co4O9.
Growth of thicker zinc-blende CrSb layers by using (In,Ga)As buffer layers
Authors: Deng J. J. , Zhao J. H. , Bi J. F. , Niu Z. C. , Yang F. H. , Wu X. G. , Zheng H. Z.
Published: May 2006

Zinc-blende CrSb (zb-CrSb) layers with room-temperature ferromagnetism have been grown on (In,Ga)As buffer layers epitaxially prepared on (001) GaAs substrates by molecular-beam epitaxy. Compared with the typical thickness [2–3 ML (ML denotes monolayers)] of zb-CrSb grown directly on GaAs, the thickness of zb-CrSb grown on (In,Ga)As has been increased largely; the maximum can be up to ∼9 ML. High-resolution cross sectional transmission electron microscopy images show that the zb-CrSb layer is combined with (In,Ga)As buffer layer without any dislocations at the interface.
Effect of hydroxyl groups on erbium-doped bismuth-oxide-based glasses for fiber amplifiers
Authors: Hayashi Hideaki , Sugimoto Naoki , Tanabe Setsuhisa , Ohara Seiki
Published: May 2006

The interactions between Er3+ ions OH groups in Er-doped Bi2O3-based glasses were investigated for samples with various Er OH concentrations. From the analyses of the total decay rate of the I13∕24 level of Er3+ it was confirmed that the OH groups are dominant quenching centers of excited Er3+ and a cause of concentration quenching of 1.5μm band emission. The attempts to remove the OH groups in the melting process were then performed. Highly dehydrated glass was obtained by keeping the dew point of the melting atmosphere at the order of −30°C. The solution of the OH groups in reheating processes for fiber fabrication was also investigated. It was revealed that they diffused from the glass surface to the inside with an order of millimeters when the glasses were annealed above softening temperature. Finally, we fabricated highly Er-doped, 5cm length compact C-band fiber amplifiers with various OH concentrations. By removing the OH groups in the core glasses, the gain characteristics drastically improved and a 10dB gain at 1560nm was achieved with 150mW pumping at 980nm.
Thermal donors formation via isothermal annealing in magnetic Czochralski high resistivity silicon
Authors: Bruzzi Mara , Menichelli David , Scaringella Monica , Härkönen Jaakko , Tuovinen Esa , Li Zheng
Published: May 2006

A quantitative study about the thermal activation of oxygen related thermal donors in high resistivity p-type magnetic Czochralski silicon has been carried out. Thermal donor formation has been performed through isothermal annealing at 430°C up to a total time of 120min. Space charge density after each annealing step has been measured by transient current technique. The localized energy levels related to thermal double donors (TD) have been observed and studied in details by thermally stimulated currents (TSCs) in the range of 10–70K, and activation energies E and effective cross sections σ have been determined for both the emissions TD0∕+ (E=75±5meV, σ=4×10−14cm2) and TD+∕+ (E=170±5meV, σ=2×10−12cm2). The evolution of the space charge density caused by annealing has been unambiguously related to the activation of TDs by means of current deep level transient spectroscopy TSC, and current transients at constant temperature i(t,T). Our results show that TDs compensate the initial boron doping, eventually provoking the sign inversion of the space charge density. TD’s generation rate has been found to be linear with the annealing time and to depend critically on the initial interstitial oxygen concentration, in agreement with previous models developed on low resistivity silicon.
Does the molecular orientation induce an electric dipole in Cu-phthalocyanine thin films?
Authors: Yamane H. , Yabuuchi Y. , Fukagawa H. , Kera S. , Okudaira K. K. , Ueno N.
Published: May 2006

The effect of the molecular orientation on the molecular electronic structure is studied on the Cu-phthalocyanine∕graphite system via film thickness dependences of metastable-atom electron spectra and ultraviolet photoelectron spectra. We observed a decrease in the vacuum-level position and a corresponding band-bending-like shift in the highest occupied state only for thick films where the molecular tilt angle increases gradually with the film thickness. These shifts are explained by electric dipoles produced in the film by a gradient of the intermolecular electronic interaction along the surface normal due to the continuous increase in the molecular tilt angle. The result indicates that the change in the molecular orientation is an important origin of the band-bending-like shift in the molecular electronic states even if the molecule has no permanent electric dipole.
Role of poly(styrene-acrylonitrile) copolymer interface layer in controlling charge storage and decay properties of amorphous selenium films
Authors: Chand S. , Sharma G. D. , Dwivedi S.
Published: May 2006

We report here the effect of poly(styrene-acrylonitrile) copolymer interface barrier layer films on the charge storage and decay characteristics of amorphous selenium (a-Se) films studied by the thermally stimulated discharge current and potential decay techniques, respectively. Incorporation of copolymer interface barrier layer reduces the charge storage capacity/built-up of residual potential in a-Se film and enhances its x-ray sensitivity. These effects have been attributed to the blocking and field assisted enhanced mobility role of the copolymer interface barrier film.
Effect of annealing on the mobility and morphology of thermally activated pentacene thin film transistors
Authors: Guo Dong , Ikeda Susumu , Saiki Koichiro , Miyazoe Hiroyuki , Terashima Kazuo
Published: May 2006

Pentacene thin film transistors (TFTs) were fabricated by the organic molecular beam deposition method. The TFTs were characterized in order to study the effect of thermal annealing on the morphology and carrier mobility of the transistors. For all the TFT samples the mobility exhibited an Arrhenius relationship with temperature, indicating a thermally activated transport that could be explained by the carrier trap and thermal release transport mechanism. Therefore, in order to investigate the annealing effect, we tested the data for a significant period of time after annealing until the temperature recovered to room temperature, so that the thermal activation effect was screened and possible effects of thermal expansion and stress were also ruled out. As a result, we found that only with a temperature below a critical temperature of approximately 45°C could annealing improve the mobility, while annealing with T>50°C would decrease the mobility compared to the value before annealing. Atomic force microscopy observation and x-ray diffraction (XRD) data indicated that annealing caused decreased grain size and decreased XRD peak intensity for all samples. Increasing the annealing temperature to 70°C caused obvious desorption because of the low van der Waals intermolecular forces in the organic film. The mobility deterioration after high temperature annealing may be ascribed to the deteriorated microstructure, while the improved mobility may result from the increased crystallinity in the bottom several layers near the substrate film interface. The results also suggested that the influence of possible structure evolution should be distinguished when investigating temperature dependent transport properties.
Photoinduced interdiffusion in nanolayered Se∕As2S3 films: Optical and x-ray photoelectron spectroscopic studies
Authors: Adarsh K. V. , Sangunni K. S. , Shripathi T. , Kokenyesi S. , Shipljak M.
Published: May 2006

Photoinduced interdiffusion was observed with above band gap light in nanolayered Se∕As2S3 films. It is discussed in terms of the optical parameters such as band gap, Urbach edge (Ee) [F. Urbach, Phys. Rev. 92, 1324 (1953)], and B1∕2 (Tauc’s parameter) [J. Tauc et al., Phys. Status Solidi 15, 627 (1966)]. Experimental data of B1∕2 and Ee for as-prepared samples do not show clear correlation implied by the Mott-Davis model [N. F. Mott and E. A. Davis, Electronic Process in Non-crystalline Materials (Clarendon, Oxford 1979), p. 287]. It is also shown that the optical parameters can be changed with a change in the Se sublayer thickness. Variations of these optical parameters as a function of modulation period and photoinduced interdiffusion were discussed in terms of the quantum confinement effect and changes in the valence and conduction bands. We proposed a model to explain the mechanism of Se diffusion in As2S3, which suggests that diffusion takes place through the wrong bonds. X-ray photoelectron spectroscopy (XPS) is used to investigate the chemical alternations in the bonding. The proposed model was supported by the XPS data.
Operation of the intermediate band solar cell under nonideal space charge region conditions and half filling of the intermediate band
Authors: Luque A. , Martí A. , López N. , Antolín E. , Cánovas E. , Stanley C. , Farmer C. , Díaz P.
Published: May 2006

A photovoltaic device based on an intermediate electronic band located within the otherwise conventional band gap of a semiconductor, the so-called intermediate band solar cell (IBSC), has been proposed for a better utilization of the solar spectrum. Experimental IBSC devices have been engineered using quantum dot technology, but their practical implementation results in a departure of key underpinning theoretical principles, assumed to describe the operation of the IBSC, away from the ideal. Two principles which are only partially fulfilled are that (i) the intermediate band should be half filled with electrons and (ii) the region containing the quantum dots should not be located fully within the junction depletion region. A model to describe the operation of the devices under these nonidealized conditions is presented and is used to interpret experimental results for IBSCs with ten layers of quantum dots. Values for the electron and hole lifetimes, associated with recombination from the conduction band to the intermediate band and from the intermediate band to the valence band (0.5 and 40ps, respectively) are thus obtained.
Terahertz amplification in delta-doped germanium films with in-plane transport
Authors: Dolguikh M. V. , Muravjov A. V. , Peale R. E.
Published: May 2006

Amplification of terahertz radiation on intersubband transitions has been analyzed by numerical Monte Carlo simulation for p-type delta-doped Ge films with in-plane transport configuration of applied electric and magnetic fields. A significant increase of the gain is found, compared to existing bulk p-Ge lasers, due to spatial separation of light and heavy hole streams, which reduces scattering of light holes on ionized impurities and heavy holes. The considered device has potential as a widely tunable (2–4THz) laser with high duty cycle and operating temperatures up to 50K.
Deep drilling of metals with ultrashort laser pulses: A two-stage process
Authors: Nielsen C. S. , Balling P.
Published: May 2006

Ultrashort laser pulses have been investigated as a means for the generation of deep narrow holes in metal samples. The drilling is observed to occur in two stages: the rapid formation of a narrow channel and the subsequent broadening of this channel to its final width. An in situ depth-gauging technique shows that this broadening develops regularly down through the hole. The coupling of light energy to the sample during this second stage of drilling and its polarization dependence are discussed.
Optical and electrical properties of undoped ZnO films
Authors: Lin Yow-Jon , Tsai Chia-Lung , Lu Yang-Ming , Liu Chia-Jyi
Published: May 2006

Optical and electrical properties of undoped ZnO films were investigated in this study. We find that the conductivity increased with increasing the ratio of (blue luminescence+green luminescence) to ultraviolet luminescence [i.e., (BL+GL)∕UVL] defect emission intensities, due to the increase of the singly ionized oxygen vacancy. We deduce that the BL and GL are related to the oxygen-vacancy deep level and the yellow luminescence is attributed to the band-acceptor transition. We also find that poorer crystal quality may lead to the reduction of the optical transmittance. This suggests that these defects and the crystal quality interact to change the conductivity and optical transmittance of ZnO. The spectroscopic correlations may be used as a predictive tool to identify the quality of ZnO.
ZnO-nanoparticle-coated carbon nanotubes demonstrating enhanced electron field-emission properties
Authors: Green Joshua M. , Dong Lifeng , Gutu Timothy , Jiao Jun , Conley John F. , Ono Yoshi
Published: May 2006

Multiwalled carbon nanotubes (CNTs) were coated, using atomic layer deposition, with a thin layer of ZnO and subsequently annealed. Studies of the morphologies of the ZnO-coated CNTs revealed no significant change in the internal structures (multiwalled graphite sheets) and the diameters of the CNTs, but the ZnO appeared to form bead-shaped single crystalline particles attaching to the surface of the nanotubes. The electron field-emission properties of the ZnO-coated CNTs were dramatically improved over both uncoated CNTs and ZnO nanowires. It is reasoned that numerous ZnO “nanobeads” on the surface of the nanotubes serve as additional emission sites, in addition to the tips of CNTs, and result in the enhancement of electron field emission.
Enhancement of cancer chemotherapy in vitro by intense ultrawideband electric field pulses
Authors: Jordan David W. , Uhler Michael D. , Gilgenbach Ronald M. , Lau Y. Y.
Published: May 2006

Experiments have been performed to enhance the Jurkat cell-killing effects of the cancer chemotherapy agent bleomycin using electric field pulses of 50–200kV∕cm peak electric field strength, ∼150ns duration, and nanosecond rise time. Dramatic increases in cell killing (factors of ∼1000) were observed with a low dose of bleomycin after treatment with trains of ten or more pulses at all electric field strengths tested, compared to pulse-only or drug-only treatments. Cell death occurred within 24h for treated cells, with some evidence of membrane phosphatidylserine externalization at 6h postexposure but no significant increase in caspase activity, indicating that the primary mode of cell death was not caspase-mediated apoptosis.
The influence of nano-oxide layer on magnetostriction of sensing layer in bottom spin valves
Authors: Qiu J. J. , Han G. C. , Li K. B. , Liu Z. Y. , Zong B. Y. , Wu Y. H.
Published: May 2006

The magnetostriction coefficient (λs) of ultrathin sputtered polycrystalline as-deposited and annealed Ta∕Ni81Fe19(t)∕Ta films was studied as a function of the thickness. λs and magnetoresistance (MR) of bottom-type spin valves (SVs) with nano-oxide layer (NOL) added in the pinned layer were investigated by using NiFe, Co90Fe10, and CoFe∕NiFe∕CoFe layers as free layer (FL), respectively. λs of SV with NOL increased slightly except that of CoFe FL. NOLs were added at different positions to study the effects of NOL on λs of CoFe FL. All λs of CoFe FL change from negative to positive and its absolute value also increases significantly with CoFeOx related NOL added below. Our λs and surface roughness results indicated that the structure of the film not the roughness dominates λs of ultrathin FL in SVs.
Band structure of honeycomb photonic crystal slabs
Authors: Weng Tai-I , Guo G. Y.
Published: May 2006

Two-dimensional (2D) honeycomb photonic crystals with cylinders and connecting walls have the potential to have a large full band gap. In experiments, 2D photonic crystals do not have an infinite height, and therefore, we investigate the effects of the thickness of the walls, the height of the slabs, and the type of the substrates on the photonic bands and gap maps of 2D honeycomb photonic crystal slabs. The band structures are calculated by the plane wave expansion method and the supercell approach. We find that the slab thickness is a key parameter affecting the band gap size, while on the other hand the wall thickness hardly affects the gap size. For symmetric photonic crystal slabs with lower dielectric claddings, the height of the slabs needs to be sufficiently large to maintain a band gap. For asymmetric claddings, the projected band diagrams are similar to that of symmetric slabs as long as the dielectric constants of the claddings do not differ greatly.
Raman study of anharmonic phonons in SrBi4Ti4O15 thin films
Authors: Du C. L. , Zhang S. T. , Gu Z. B. , Cheng G. X. , Wang J. , Lu M. H. , Zhao J. , Chen Y. F.
Published: May 2006

Raman spectra of SrBi4Ti4O15 (SBTi4) thin films were measured as a function of temperature from 80to820K. Below room temperature, no phonon modes were detected between 200 and 815cm−1, which indicates the existence of a phonon band gap in this material. Differences between the Raman spectra of the thin film and bulk polycrystalline samples are discussed. The asymmetric Raman band at high frequency can be interpreted as the superposition of two main distinct Raman lines. Temperature dependence of the Raman shifts and full widths at half maximum (FWHMs) for the two phonon modes is discussed as well, which provides information about the vibration energy levels within the film. Theoretical fittings of their FWHMs indicate that the higher-energy phonon mode is apparently more anharmonic than the lower one.
Monolithically fabricated double-ended tuning-fork-based force sensor
Authors: Fukuzawa Kenji , Ando Takamasa , Shibamoto Masami , Mitsuya Yasunaga , Zhang Hedong
Published: May 2006

A highly sensitive force sensor that is suitable for precise gap control is presented. It combines a double-ended tuning fork (DETF) resonator with a cantilever beam. When the force to be measured is applied to the cantilever beam, the resonant frequency of the DETF beam changes due to the change in axial force. The DETF-based sensor can detect the force as an amplitude change due to the resonant frequency change. The performance of the sensor was theoretically and experimentally investigated. The sensor is rigid and can measure the force with a change in the sample or probe height of less than about 1nm. The experimentally attained minimum detection limit of the force was 19μN and this can be improved by more than one order of magnitude according to theoretical estimation. The combination of the DETF-based sensor and the fixed probe or sample is expected to provide the measurement of the surface force with precise gap control. It can be useful for various fields such as interface science, probe microscopy, and microtribology.
Intensity-dependent refractive index of a Pöschl-Teller quantum well
Authors: Yildirim Hasan , Tomak Mehmet
Published: May 2006

The linear and nonlinear changes in the refractive index of a Pöschl-Teller quantum well are studied. The Pöschl-Teller potential can easily become asymmetric by a correct choice of its parameter set. We use this feature to investigate the intensity-dependent refractive index of a GaAs quantum well within the density matrix formalism. Numerical results reveal large values of linear and nonlinear changes in the refractive index.
Use of thermally induced higher order modes of a microcantilever for mercury vapor detection
Authors: Kadam Ashwini R. , Nordin Gregory P. , George Michael A.
Published: May 2006

We demonstrate the use of thermally induced higher order modes of a microcantilever as an alternate detection technique by studying Au–Hg interactions. The first four thermally induced flexural modes (i.e., the fundamental and first three higher order modes) have been examined for two different Au coatings. In the first case, 50nm thick Au is sputter deposited along the entire length of a rectangular Si microcantilever. In the second case the Au is confined to a 30μm length at the tip of the Si microcantilever. In both cases the microcantilever spectral response and deflection has been studied as a function of Hg concentration and total exposure time. For the low doses studied, the higher order modes show a distinct Hg sensing response whereas the fundamental mode does not. The frequency shift for the fourth order mode for a total exposure of 300s to approximately 15ppb Hg in N2 is found to be −320 and −70Hz for the first and second cases, respectively.
The evolution of microstructure and photoluminescence of SiCN films with annealing temperature
Authors: Du Xi-Wen , Fu Yang , Sun Jing , Yao Pei
Published: May 2006

Silicon carbonitride (SiCN) films were deposited by radio-frequency magnetron sputtering and then annealed at different temperatures from 1100to1300°C in hydrogen atmosphere. The as-deposited films and films annealed at 1100°C did not show photoluminescence (PL), whereas strong PL peaks appeared at 355 and 469nm after annealing at 1200 and 1300°C. X-ray diffraction, transmission electron microscope, and Fourier transform infrared spectrometer results show that the enhancement of PL properties is due to the change of microstructure and composition.
Absorption spectrum and assignment of the Chappuis band of ozone
Authors: Grebenshchikov S. Yu. , Schinke R. , Qu Z.-W. , Zhu H.
Published: May 2006

New global diabatic potential energy surfaces of the electronic states B11 and A21 of ozone and the non-adiabatic coupling surface between them are constructed from electronic structure calculations. These surfaces are used to study the visible photodissociation in the Chappuis band by means of quantum mechanical calculations. The calculated absorption spectrum and its absolute intensity are in good agreement with the experimental results. A vibrational assignment of the diffuse structures in the Chappuis band system is proposed on the basis of the nodal structures of the underlying resonance states.
Nested sequence of projectors. II. Multiparameter multistate statistical models, Hamiltonians, S-matrices
Authors: Abdesselam B. , Chakrabarti A.
Published: May 2006

Our starting point is a class of braid matrices, presented in a previous paper, constructed on a basis of a nested sequence of projectors. Statistical models associated to such N2×N2 matrices for odd N are studied here. Presence of 12(N+3)(N−1) free parameters is the crucial feature of our models, setting them apart from other well-known ones. There are N possible states at each site. The trace of the transfer matrix is shown to depend on 12(N−1) parameters. For order r, N eigenvalues constitute the trace and the remaining (Nr−N) eigenvalues involving the full range of parameters come in zero-sum multiplets formed by the rth roots of unity, or lower dimensional multiplets corresponding to factors of the order r when r is not a prime number. The modulus of any eigenvalue is of the form eμθ, where μ is a linear combination of the free parameters, θ being the spectral parameter. For r a prime number an amusing relation of the number of multiplets with a theorem of Fermat is pointed out. Chain Hamiltonians and potentials corresponding to factorizable S-matrices are constructed starting from our braid matrices. Perspectives are discussed.
Microsolvation effects on the electron capturing ability of thymine: Thymine-water clusters
Authors: Kim Sunghwan , Wheeler Steven E. , Schaefer Henry F.
Published: May 2006

The effects of solvation on the stability of thymine and its negative ion have been investigated by explicitly considering the structures of complexes of thymine with up to five water molecules and the respective anions at the B3LYP/DZP++ level of theory. The vertical detachment energy of thymine was predicted to increase gradually with the hydration number, consistent with experimental observations from a photodetachment-photoelectron spectroscopy study J. Schiedt et al., [Chem. Phys. 239, 511 (1998)]. The adiabatic electron affinity of thymine was also found to increase with the hydration number, which implies that while the conventional valence anion of thymine is only marginally bound in the gas phase, it may form a stable anion in aqueous solution.
Computational studies on the ground and excited states of BrOOBr
Authors: Li Yumin , Vo Christopher K.
Published: May 2006

In this work, theoretical computations for the ground and excited states of BrOOBr have been performed at high-level ab initio molecular orbital theories. The ground-state geometries of BrOOBr in different forms (trans, cis, and twist form) have been optimized at the couple-cluster CCSD(T) level of theory with cc-pVTZ and aug-cc-pVTZ basis sets, which indicates that at CCSD(T)/cc-pVTZ level of theory, the twist form is 4.96kcal∕mol more stable than the trans form and 10.67kcal∕mol more stable than the cis form; at the CCSD(T)/aug-cc-pVTZ basis set the twist form is 4.33kcal∕mol more stable than the trans form and 9.54kcal∕mol more stable than the cis form. The vertical excitation energies and potential-energy curves for the singlet and triplet low-lying excited states of BrOOBr were calculated at both the complete active space self-consistent-field (CASSCF) level of theory and the multireference internally contracted configuration interaction (MRCI) level of theory. The differences of potential-energy curves at CASSCF and MRCI levels of theory are found for the BrOOBr excited states. At CASSCF level of theory, none of the BrOOBr excited states are bound. However, at MRCI level of theory, all the BrOOBr states studied in this work are bound or slightly bound at the Frank-Condon region. In addition, the scalar relativistic effect and the spin-orbital coupling effect on the vertical excitation energies of the electronic states of BrOOBr were estimated.
Exploration of NVE classical trajectories as a tool for molecular crystal structure prediction, with tests on ice polymorphs
Authors: Buch V. , Martoňák R. , Parrinello M.
Published: May 2006

Following an initial Communication [Buch et al., J. Chem. Phys. 123, 051108 (2005)], a new molecular-dynamics-based approach is explored to search for candidate crystal structures of molecular solids corresponding to minima of the enthalpy. The approach is based on the observation of phase transitions in an artificial periodic system with a small unit cell and relies on the existence of an optimal energy range for observing freezing to low-lying minima in the course of classical trajectories. Tests are carried out for O structures of nine H2O-ice polymorphs. NVE trajectories for a range of preimposed box shapes display freezing to the different crystal polymorphs whenever the box dimensions approximate roughly the appropriate unit cell; the exception is ice II for which freezing requires unit cell dimensions close to the correct ones. In an alternate version of the algorithm, an initial box shape is picked at random and subsequently readjusted at short trajectory intervals by enthalpy minimization. Tests reveal the existence of ice forms which are “difficult” and “easy” to locate in this way. The former include ice IV, which is also difficult to crystallize experimentally from the liquid, and ice II, which does not interface with the liquid in the phase diagram. On the other hand, the latter crystal search procedure located successfully the remaining seven ice polymorphs, including ice V, which corresponds to the most complicated structure of all ice phases, with a monoclinic cell of 28molecules.
A consistent calculation of the chemical potential for dense simple fluids
Authors: Bomont Jean-Marc
Published: May 2006

A general method to calculate the excess chemical potential βμex, that is based on the Kirkwood coupling parameter’s dependence of the correlation functions, is presented. The expression for the one particle bridge function B(1)(r) is derived for simple fluids with spherical interactions. Only the knowledge of the bridge function B(2)(r) is required. The accuracy of our approach is illustrated for a dense hard sphere fluid. As far as B(2)(r) is considered as exact, B(1)(r) is found to be, at high densities, the normalized bridge function −B(2)(r)∕B(2)(r=0). This expression ensures a consistent calculation of the excess chemical potential by satisfying implicitly the Gibbs-Duhem constraint. Only the pressure-consistency condition is necessary to calculate the structural and thermodynamic properties of the fluid.
Quadrupolar solvatochromism: 4-amino-phthalimide in toluene
Authors: Milischuk Anatoli A. , Matyushov Dmitry V.
Published: May 2006

We present calculations of the temperature dependence of the solvent reorganization energy of 4-amino-phthalimide chromophore in quadrupolar toluene. The reorganization energy is a sum of the contributions from quadrupolar and induction solvation. We employ several calculation formalisms in order to evaluate their performance against the experiment. The point-dipole and full atomic distributions of solute charge are compared to show that the point-dipole approximation works well for this chromophore. We also show that most of the reorganization entropy comes from the quadrupolar response. Induction solvation amounts to about 10% of the entropy. Both the reorganization energy and the reorganization entropy are greatly affected by the local solute-solvent density profile (density reorganization) which contributes about half of their values. The induction reorganization energy is strongly affected by the microscopic, nonlocal nature of the density fluctuations of the solvent around the solute.
On the quantum mechanics for one photon
Authors: Hu Yapeng , Qiu Weigang , Zhang Hongbao
Published: May 2006

This paper revisits the quantum mechanics for one photon from the modern viewpoint and by the geometrical method. Especially, besides the ordinary (rectangular) momentum representation, we provide an explicit derivation for the other two important representations, called the cylindrically symmetrical representation and the spherically symmetrical representation, respectively. These other two representations are relevant to some current photon experiments in quantum optics. In addition, the latter is useful for us to extract the information on the quantized black holes. The framework and approach presented here are also applicable to other particles with arbitrary mass and spin, such as the particle with spin 12.