bluuebunny/crossref_metadata_2025 huggingface dataset:
Stretching and slipping of liquid bridges near plates and cavities
Authors: Dodds Shawn , Carvalho Marcio da Silveira , Kumar Satish
Published: September 2009

The dynamics of liquid bridges are relevant to a wide variety of applications including high-speed printing, extensional rheometry, and floating-zone crystallization. Although many studies assume that the contact lines of a bridge are pinned, this is not the case for printing processes such as gravure, lithography, and microcontacting. To address this issue, we use the Galerkin/finite element method to study the stretching of a finite volume of Newtonian liquid confined between two flat plates, one of which is stationary and the other moving. The steady Stokes equations are solved, with time dependence entering the problem through the kinematic boundary condition. The contact lines are allowed to slip, and we evaluate the effect of the capillary number and contact angle on the amount of liquid transferred to the moving plate. At fixed capillary number, liquid transfer to the moving plate is found to increase as the contact angle on the stationary plate increases relative to that on the moving plate. When the contact angle is fixed and the capillary number is increased, the liquid transfer improves if the stationary plate is wetting, but worsens if it is nonwetting. The presence of a cavity on the stationary plate significantly affects the contact line motion, often causing pinning along the cavity wall. In these cases, liquid transfer is controlled primarily by the cavity shape, suggesting that the effects of surface topography dominate over those of surface wettability. At low capillary numbers, bridge breakup can be understood in terms of the Rayleigh–Plateau stability limit, regardless of the combination of contact angles or the plate geometry. At higher capillary numbers, the bridge is able to stretch beyond this limit although the deviation from this limit appears to depend on contact line pinning, and not directly on the combination of contact angles or the plate geometry.
Modification of magnetic properties and structure of Kr+ ion-irradiated CrPt3 films for planar bit patterned media
Authors: Kato T. , Iwata S. , Yamauchi Y. , Tsunashima S.
Published: September 2009

30 keV Kr+ ions were irradiated onto L12 ordered CrPt3 (20 nm) alloy films fabricated by a magnetron sputtering deposition followed by an appropriate heat treatment, and the modification of the structure and magnetic properties of the CrPt3 films was investigated in detail. The fabricated L12 CrPt3 (20 nm) onto a fused quartz substrate exhibited a quite large perpendicular anisotropy of 5×106 ergs/cc, due to the large lattice distortion of 1%. The large perpendicular anisotropy decreased with increasing the ion dose, and became almost zero at the ion dose of 2×1014 ions/cm2 due to the loss of the magnetic order of CrPt3. The suppression of the magnetic order of CrPt3 by the Kr+ ion irradiation is attributed to the transformation of the structure from the L12 phase to a disordered fcc phase, which was confirmed by x-ray diffraction analysis. Unlike the magnetization and perpendicular anisotropy, the anisotropy field of CrPt3 does not decrease significantly with the increase in the Kr+ ion dose, and exhibited more than 20 kOe even at the ion dose of 1×1014 ions/cm2. This is considered to be attributed that the lattice distortion of CrPt3 unchanged even at the Kr+ ion dose of 2×1014 ions/cm2.
Controllable spin-dependent transport in armchair graphene nanoribbon structures
Authors: Nguyen V. Hung , Nam Do V. , Bournel A. , Nguyen V. Lien , Dollfus P.
Published: September 2009

Using the nonequilibrium Green’s functions formalism in a tight binding model, the spin-dependent transport in armchair graphene nanoribbons controlled by a ferromagnetic gate is investigated. Beyond the oscillatory behavior of conductance and spin polarization with respect to the barrier height, which can be tuned by the gate voltage, we especially analyze the effects of width-dependent band gap and of the nature of contacts. The oscillation of spin polarization in graphene nanoribbons with a large band gap is strong in comparison with that in infinite graphene sheets. Very high spin polarization (close to 100%) is observed in normal-conductor/graphene/normal-conductor junctions. Moreover, we find that the difference in electronic structure between normal conductor and graphene generates confined states which have a strong influence on the transport properties of the device. This study suggests that the device should be carefully designed to obtain a high controllability of spin-polarized current.
Photo-induced charge state conversion of Eu2+ in Ca2ZnSi2O7
Authors: Kamioka Hayato , Hirano Masahiro , Hosono Hideo
Published: September 2009

Eu 2 + doped sorosilicate Ca2ZnSi2O7 (melilite) exhibits a broad band emission peaking at ∼600 nm (∼2 eV) due to the electric dipole allowed transition of 4f65d1 to 4f7 of Eu2+ by an excitation with blue light (460 nm). Strong O2− ligand field with low symmetry due to the layered tetragonal crystallographic structure of the melilite may play a dominant role in lowering the emission band energy to ∼2 eV. In addition, line emissions attributable to the transitions from D50 to F7J of Eu3+ ions are detected by an excitation with deep UV light with sub-360 nm wavelengths. This is due to the formation of transient Eu3+ ions via charge transfer from Eu2+ to the matrix. The lifetime of the transient Eu3+ ion is found to be 58 ms by a pump-probe measurement, in which UV pulse laser and green continuous wave laser are employed as pump and probe lights, respectively. Based on these results, the energy diagram of Eu2+ in Ca2ZnSi2O7 is proposed.
Band alignment at SrCu2O2/ZnO heterointerface
Authors: Konovalov I. , Hesse R.
Published: September 2009

SrCu 2 O 2 / ZnO interface is interesting for application in blue and UV light emission devices. Measurements of the valence band offset at SrCu2O2/ZnO interface using photoelectron spectroscopy result in an offset of 2.0 eV (cliff), meaning that the interface band gap is reduced to 1.4 eV. Blue and UV light emission observed previously can be attained in this material system presumably by injection of minority carriers involving tunneling through a narrow barrier at the interface. Additional intensive infrared light emission due to interface recombination can be predicted.
Dynamics of electron transfer reactions in the presence of mode mixing: Comparison of a generalized master equation approach with the numerically exact simulation
Authors: Velizhanin Kirill A. , Wang Haobin
Published: September 2009

A generalized master equation approach is developed to describe electron transfer (ET) dynamics in the presence of mode mixing. Results from this approximate approach are compared to the numerically exact simulations using the multilayer multiconfiguration time-dependent Hartree theory. The generalized master equation approach is found to work well for nonadiabatic resonant ET. Depending on the specific situation, it is found that the introduction of mode mixing may either increase or decrease the ET time scale. The master equation fails in the adiabatic ET regime, where the introduction of mode mixing may lead to electron trapping. From both the approximate theory and the numerically exact simulation it is shown how neglecting mode mixing in practical calculations may lead to inaccurate predictions of the ET dynamics.
Evidence for a liquid-solid critical point in a simple monatomic system
Authors: Elenius Måns , Dzugutov Mikhail
Published: September 2009

It is commonly believed that the transition line separating a liquid and a solid cannot be interrupted by a critical point. This opinion is based on the traditional symmetry argument that an isotropic liquid cannot be continuously transformed into a crystal with a discrete rotational and translational symmetry. We present here a molecular-dynamics simulation of a simple monatomic system suggesting the existence of a liquid-solid spinodal terminating at a critical point. We show that, in the critical region, the isotropic liquid continuously transforms into a phase with a mesoscopic order similar to that of the smectic liquid crystals. We argue that the existence of both the spinodal and the critical point can be explained by the close structural proximity between the mesophase and the crystal. This indicates a possibility of finding a similar thermodynamic behavior in gelating colloids, liquid crystals, and polymers.
A converse approach to the calculation of NMR shielding tensors
Authors: Thonhauser T. , Ceresoli D. , Mostofi Arash A. , Marzari Nicola , Resta R. , Vanderbilt David
Published: September 2009

We introduce an alternative approach to the first-principles calculation of NMR shielding tensors. These are obtained from the derivative of the orbital magnetization with respect to the application of a microscopic, localized magnetic dipole. The approach is simple, general, and can be applied to either isolated or periodic systems. Calculated results for simple hydrocarbons, crystalline diamond, and liquid water show very good agreement with established methods and experimental results.
Electrostatics of capsid-induced viral RNA organization
Authors: Forrey Christopher , Muthukumar M.
Published: September 2009

We have addressed the role of electrostatics in the formation of genome structure in the Pariacoto virus, where substantial experimental data are available. We have used Langevin dynamics simulation of a coarse-grained model, based on the published crystal structure of the rigid portion of the Pariacoto capsid and including flexible N-terminal protein arms, attached to the rigid capsid at the appropriate locations. The inclusion of charged residues in our model was dictated solely by the location of charges inherent in the Pariacoto sequence itself. Although the viral genome and other exogenous RNA sequences used in experimental studies can assume secondary structures, we have intentionally used uniformly charged flexible polyelectrolyte lacking predetermined secondary structures as the substitute for the viral genome, in order to see whether the same final assembled genome structure emerges without invoking secondary RNA structures. The intent of our study was to investigate the internal environment presented by the capsid proteins of Pariacoto virus, specifically whether the topological features and electrostatic potential at the inner capsid surface can induce complexation of generic negatively charged polyelectrolyte into structures similar to those observed experimentally with packaged RNA. We find that the charge decoration on the interior of the capsid templates the assembly of the flexible polyelectrolyte, allowing hybridizationlike folding of similarly charged strands, and eventually organizing dodecahedral assembly of the polymer. Our results from a generic flexible polyelectrolyte for the assembled structure and bimodal monomer distribution are remarkably matched to that of the viral RNA found experimentally. Results of our work can be interpreted primarily as a consequence of electrostatics, as consideration of base-pairing has been omitted. We propose that our work supports the growing body of evidence that electrostatic interactions play a crucial role in RNA viral assembly and structure.
Room-temperature green upconversion luminescence in LaMgAl11O19:Mn2+, Yb3+ upon infrared excitation
Authors: Martín-Rodríguez R. , Valiente R. , Bettinelli M.
Published: September 2009

We present a spectroscopic study of the green upconversion luminescence of Mn2+ upon near infrared Yb3+ excitation in LaMgAl11O19 codoped with manganese and ytterbium. Excitation at 975 nm with a diode laser resonant with the F27/2→F25/2 Yb3+ transition induces a broad emission band centered at 514 nm and assigned to the T41→A61 transition of tetrahedral Mn2+. The upconversion luminescence can be seen by the naked eye up to 500 K. This finding is a promising step in order to use the Mn2+–Yb3+ system as a potential candidate for display phosphors by upconversion.
A spatial averaging approach to rare-event sampling
Authors: Doll J. D. , Gubernatis J. E. , Plattner Nuria , Meuwly Markus , Dupuis P. , Wang H.
Published: September 2009

We describe a method for treating the sparse or rare-event sampling problem. Our approach is based on the introduction of a family of modified importance functions, functions that are related to but easier to sample than the original statistical distribution. We quantify the performance of the approach for a series of example problems using an asymptotic convergence analysis based on transition matrix methods.
Room temperature ferromagnetism of bulk polycrystalline (In0.85−xSnxFe0.15)2O3: Charge carrier mediated or oxygen vacancy mediated?
Authors: Li S. C. , Ren P. , Zhao B. C. , Xia B. , Wang L.
Published: September 2009

Four bulk polycrystalline (In0.85−xSnxFe0.15)2O3 samples with x=0, 0.01, 0.03, and 0.05 were synthesized, where carrier concentration n was controlled by varying Sn doping concentration x. Strong room temperature ferromagnetism was observed. A systematic characterization and analysis of structure, purity, magnetic, and transport properties indicates that ferromagnetism is due to neither impurities nor charge carriers. The four samples were annealed in air and high vacuum alternately. The ferromagnetism signal disappears and appears accordingly. Based on these results, we conclude that room temperature ferromagnetism in (In0.85−xSnxFe0.15)2O3 system is closely and directly related to oxygen vacancies in the samples.
Mapping bias-induced phase stability and random fields in relaxor ferroelectrics
Authors: Rodriguez B. J. , Jesse S. , Bokov A. A. , Ye Z.-G. , Kalinin S. V.
Published: September 2009

The spatial variability of polarization reversal behavior in the relaxor 0.9Pb(Mg1/3Nb2/3O3)–0.1PbTiO3 crystal, is revealed on the ∼100 nm scale using switching spectroscopy piezoresponse force microscopy. Quenched fields conjugate to polarization are found, which show mesoscopic (∼100–200 nm) spatial fluctuations around near-zero bias values. The mapping of the stability gap of the bias-induced phase and conjugate random fields is demonstrated. The origin of the observed nanoscale domains and the field-induced part of the polarization are discussed.
Crystallization kinetics in electron-beam evaporated amorphous silicon on ZnO:Al-coated glass for thin film solar cells
Authors: Sontheimer T. , Becker C. , Bloeck U. , Gall S. , Rech B.
Published: September 2009

To systematically study the crystallization process of electron-beam evaporated amorphous silicon on ZnO:Al-coated glass for polycrystalline silicon thin film solar cells, transmission electron microscopy and optical microscopy were employed. A time and temperature dependent analysis allowed the individual investigation of the growth and nucleation processes. The growth velocities of Si-crystals on ZnO:Al and SiN-coated glass were found to be identical within the investigated temperature regime of 500–600 °C. However, with a high steady state nucleation rate and a low activation energy, the nucleation process of Si on ZnO:Al-coated glass has shown to differ significantly from nucleation on glass.
Size-dependent yield stress in twinned gold nanowires mediated by site-specific surface dislocation emission
Authors: Deng Chuang , Sansoz Frederic
Published: September 2009

Large-scale molecular dynamics simulations were performed to demonstrate the synergistic effects of twin boundaries and free surfaces on dislocation emission in gold nanowires under tensile loading. It is revealed that the addition of nanoscale twins to crystalline nanowires can act to either increase or decrease their resistance to slip in tension, depending on both sample diameter and number of twins per unit length. Site-specific surface dislocation emission and image forces due to twin boundaries are used to explain the size-dependence of yield stress in twinned gold nanowires.
Power gain up to gigahertz frequencies in three-terminal nanojunctions at room temperature
Authors: Spanheimer D. , Müller C. R. , Heinrich J. , Höfling S. , Worschech L. , Forchel A.
Published: September 2009

Direct current and alternating current characteristics of three-terminal nanojunctions (TTJs) are studied at room temperature. The TTJs are based on a modulation-doped GaAs∕AlGaAs heterostructure and were structured by applying mask techniques and wet chemical etching. Devices with lateral dimensions of a few tens of nanometers and with narrow gold contacts were fabricated and transistor characteristics with maximum transconductance values exceeding 100μA∕V are demonstrated. By analyzing the scattering parameters of the TTJs, power gain up to 1.5GHz is observed. This gigahertz amplification is related to the implemented narrow gold contacts which control the quantum capacitance of the electron reservoirs.
Influence of the donor/acceptor interface on the open-circuit voltage in organic solar cells
Authors: Liu Z. T. , Lo M. F. , Wang H. B. , Ng T. W. , Roy V. A. L. , Lee C. S. , Lee S. T.
Published: September 2009

The donor/acceptor interface in a standard CuPc/C60 organic solar cell was modified by insertion of a thin layer of molybdenum trioxide (MoO3). An ultrathin layer of MoO3 between the donor and acceptor increased the open-circuit voltage (VOC) from 0.45 to 0.85 V. The enhancement in VOC is explained by the increase in the energy level offset between the lowest unoccupied molecular orbital of the acceptor and the highest occupied molecular orbital of the donor (EDHOMO-EALUMO). The explanation is supported by the energy level analysis of the donor/acceptor interface by ultraviolet photoemission spectroscopy and x-ray photoemission spectroscopy.
Photoimpedance characterization of polymer field-effect transistor
Authors: Sangeeth C. S. Suchand , Jaiswal Manu , Menon Reghu
Published: September 2009

The small signal ac response is measured across the source-drain terminals of poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) field-effect transistor under dc bias to obtain the equivalent circuit parameters in the dark, and under a monochromatic light (540 nm) of various intensities. The numerically simulated response based on these parameters shows deviation at low frequency which is related to the charge accumulation at the interface and the contact resistance at the electrodes. This method can be used to differentiate the photophysical phenomena occurring in the bulk from that at the metal-semiconductor interface for polymer field-effect transistors.
Selective excitation of laser modes in an organic photonic dot microcavity
Authors: Langner M. , Sudzius M. , Fröb H. , Lyssenko V. G. , Leo K.
Published: September 2009

We experimentally investigate variable laser mode excitation in an organic photonic dot microcavity by shifting the excitation beam position. The sample comprises two highly reflective dielectric mirrors (R>99.9%) and a square-shaped organic dye mesa of a DCM doped (2 wt %) Alq3-matrix. Its wavelength-size (≈5×5 μm2) transforms the cavity mode dispersion to a set of discrete states, each with a different intensity distribution of the electromagnetic field in space. Numerical simulations, including absorption and gain, confirm the experimentally observed relation between mode distribution and progression on the excitation condition.
Stress tensor field near the edge of a slit with dispersion forces
Authors: Rusanov A. I. , Kuni F. M.
Published: September 2009

Classical problem of interaction through a slit is complemented by estimating stress tensor field near the edge of an empty slit between solids with dispersion forces. All four nonzero components of the Irving–Kirkwood stress tensor are calculated as functions of distances from the slit walls and slit edge.
Structural response of a highly viscous aluminoborosilicate melt to isotropic and anisotropic compressions
Authors: Wu Jingshi , Deubener Joachim , Stebbins Jonathan F. , Grygarova Lenka , Behrens Harald , Wondraczek Lothar , Yue Yuanzheng
Published: September 2009

Aluminoborosilicate melts of E-glass composition have been compressed at pressures up to 500 MPa and subsequently cooled (4–5 K min−1) under pressure from well above the glass transition to room temperature. It is found that increasing uniaxial pressure lead to anisotropic glasses with increasing permanent birefringence, while increasing isostatic pressure resulted in isotropic glasses with increasing density (compaction of 2.1% at 500 MPa). Static and magic-angle spinning nuclear magnetic resonance spectroscopy of B11, N23a, A27l, and S29i were performed to explore pressure-induced changes in the short-range structure of these glasses. NMR experiments readily detected increasing BIV, AVl, and AVIl concentrations with pressure as well as a decrease in the mean distance of sodium to oxygen atoms (0.7% at 500 MPa), but no detectible evidence of short-range structural orientation around these atoms in the birefringent glasses were found. Quantifying the changes in the local boron, aluminum, silicon, and sodium environments revealed that the measured increase of recovered density with pressure in E-glass can only be partly explained by increase in B and Al coordination, and that overall compression of the network and of the network modifier cation volumes must also be important. Structural changes in the intermediate range, which were not detected by NMR, are discussed as a source of birefringence in anisotropic E-glass.
Excited state relaxation in poly(spirobifluorene-co-benzothiadiazole) films
Authors: Devižis A. , Serbenta A. , Meerholz K. , Hertel D. , Gulbinas V.
Published: September 2009

Excited state relaxation of the poly(spirobifluorene-co-benzothiadiazole) has been investigated by means of the time resolved fluorescence and femtosecond transient absorption. The experimental results and their comparison with the similar data obtained for poly(fluorene-co-benzothiadiazole) show that the long-lived excited state with the reduced dipole moment of the transition to the ground state is formed on a subpicosecond time scale due to the exciton localization on a polymer backbone and spirobifuorene side group. Excited state stabilization reduces the transition dipole moment still further, causing fluorescence relaxation faster than the relaxation of the excited state.
Six-fold in-plane magnetic anisotropy in Co-implanted ZnO (0001)
Authors: Akdoğan Numan , Rameev Bulat , Güler Sümeyra , Öztürk Osman , Aktaş Bekir , Zabel Hartmut , Khaibullin Rustam , Tagirov Lenar
Published: September 2009

Magnetic anisotropies of Co-implanted ZnO (0001) films grown on single-crystalline Al2O3 (112¯0) substrates have been studied by ferromagnetic resonance (FMR) technique for different cobalt implantation doses. The FMR data show that the easy and hard axes have a periodicity of 60° in the film plane, in agreement with the hexagonal structure of the ZnO films. This six-fold in-plane magnetic anisotropy, which is observed for the first time in ZnO-based diluted magnetic semiconductors, is attributed to the substitution of cobalt on Zn sites in the ZnO structure, and a clear indication for long range ferromagnetic ordering between substitutional cobalt ions in the single-crystalline ZnO films.
Design and performance of a simple, room-temperature Ga2O3 nanowire gas sensor
Authors: Arnold S. P. , Prokes S. M. , Perkins F. K. , Zaghloul M. E.
Published: September 2009

Ga 2 O 3 nanowire gas sensors were fabricated using the vapor-liquid-solid method of nanowire growth over platinum interdigitated electrodes. While cheaply and easily fabricated, the sensors are capable of detecting various analytes at room temperature. As analyte is adsorbed onto the nanowire surfaces, a change in the device capacitance is measured. Fast recovery of the sensing devices, without the use of an external heat source, allows these devices to operate at low power. Capacitance is seen to increase following a Freundlich isotherm in response to increasing concentrations of analyte vapors.
Semiconductor behaviors of low loading multiwall carbon nanotube/poly(dimethylsiloxane) composites
Authors: Hu C. H. , Liu C. H. , Chen L. Z. , Fan S. S.
Published: September 2009

We present a flexible electronic material fabricated by incorporating multiwall carbon nanotubes (MWNTs) into poly(dimethylsiloxane) rubber (0.35 wt % MWNT loading is most appropriate in our study). Resistance-temperature data for different composites (0.35–5 wt %) are analyzed within Coulomb gap variable range hopping model, which well explains the semiconductor behaviors in low MWNT loading composites. Field effect transistors fabricated using 0.35 wt % composite show a p-type behavior with a high effective mobility of 1.98 cm2 V s and linear transconductance 8.34×10−8 S at 2.5 V drain voltage. These results suggest an optional way of seeking for high-quality flexible electronic materials.
The effect of gas flow on argon plasma discharge generated with a single-electrode configuration at atmospheric pressure
Authors: Li Shou-Zhe , Huang Wen-Tong , Wang Dezhen
Published: September 2009

A long atmospheric-pressure plasma column confined in a dielectric tube is generated in argon with use of a single-electrode configuration driven with a sinusoidal power supply operating at 45 kHz. The electrical characteristics are investigated by means of measuring voltage-current and voltage-power curves at two gas flow states, turbulent and laminar. The gas temperatures of plasma discharge at various gas flow rates are determined by the spectroscopic analysis of OH A-X spectrum. The discussion about effect of gas flow on electrical discharge characteristics is presented and it is found that the heat removal by gas flow plays the most important role in determining its electrical characteristics.
Metal coordination converts the tub-shaped cyclo-octatetraene into an aromatic molecule: Electronic states and half-sandwich structures of group III metal-cyclo-octatetraene complexes
Authors: Lee Jung Sup , Lei Yuxiu , Kumari Sudesh , Yang Dong-Sheng
Published: September 2009

Group III (Sc, Y, and La) metal-(1,3,5,7-cyclo-octatetraene) (COT) complexes were produced in a laser-vaporization molecular beam source and studied by pulsed-field-ionization zero-electron-kinetic-energy (ZEKE) spectroscopy. Adiabatic ionization energies and metal-ligand stretching frequencies were measured from the ZEKE spectra. Metal-ligand bonding and low-lying electronic states of the neutral and ionized complexes were analyzed by combining the spectroscopic measurements with the molecular orbital treatment and density functional theory calculations. The ionization energies and metal-ligand stretching frequencies of these complexes are in the order of Sc>Y>La. The ground electronic state of the neutral complexes is A21, whereas the ground state of the ions is A11. The molecular symmetry is C8v in both neutral and ionic ground states. Although free COT is a nonaromatic molecule with a tublike structure, coordination of the group III metal atoms converts the tub-shaped molecule into a planar, aromatic structure. This conversion is induced by a two-electron transfer from the metal atoms to the ligand upon the formation of the complexes.
Verification of p-n junctions in polymer light-emitting electrochemical cells via electrical characterization
Authors: Lei Yueqing , Teng Feng , Hou Yanbing , Lou Zhidong , Wang Yongsheng
Published: September 2009

We report micrometer thick sandwich light-emitting electrochemical cells (LECs) based on a blend of poly[5-(2′-ethylhexyloxy)-2-methoxy-1, 4-phenylene vinylene] and poly(ethylene oxide) complexed with lithium trifluoromethanesulfonate. These LECs exhibit very similar properties as those of thin LECs including bipolar current-voltage characteristics and light emission. Mixing of aluminum nanoparticles into polymer layers improves electroluminescence because of smaller series resistance and larger light-emitting area. Taking series resistance into account, we confirm the operating mechanism of an LEC is the formation of a p-n junction by in situ electrochemical doping via fitting the steady state current-voltage characteristics to the expression for the Shockley model of a p-n diode.
Raman investigation of oxidation mechanism of silicon nanowires
Authors: Liu L. Z. , Wu X. L. , Zhang Z. Y. , Li T. H. , Chu Paul K.
Published: September 2009

Raman spectra are acquired from Si nanowires (NWs) with diameters of 2–15 nm oxidized for different time durations. The Si TO optical phonon peak downshifts asymmetrically finally becoming an amorphous Si peak after a long oxidation time. The spectral changes cannot be correlated using the phonon confinement model of cylindrical NWs. Microstructural observations disclose that the strain induced by oxidization breaks the NWs into small nanocrystals. By considering the morphological transformation, we adopt the phonon confinement models on wires and dots to explain very well the Raman spectra acquired from Si NWs with different diameters.
Interaction of phosphorus with dislocations in heavily phosphorus doped silicon
Authors: Ohno Y. , Shirakawa T. , Taishi T. , Yonenaga I.
Published: September 2009

Effects of annealing at 1173 K, that is comparable to the typical temperatures for the fabrication of Si-based devices, on the dissociated dislocations in Czochralski-grown silicon crystals heavily doped with phosphorus atoms were determined. Dislocation segments with edge component are constricted. They climbed out of the slip plane toward the compression side, forming complete dislocation segments. The dissociation width of the rest segments is increased. These results suggest that phosphorus atoms segregate nearby dislocations and the high doping level at the dislocations lowers the formation energy of negatively charged vacancies.
Multilevel unipolar resistance switching in TiO2 thin films
Authors: Chae S. C. , Lee J. S. , Choi W. S. , Lee S. B. , Chang S. H. , Shin H. , Kahng B. , Noh T. W.
Published: September 2009

We report on multilevel switching behavior in the unipolar resistance switching of TiO2 thin films. Multiple metastable states were observed during the reset process by measuring I-V curves. As observed using a conducting atomic force microscope, the multilevel resistance switching was accompanied by decreases in area and in the conductance of the top surface conducting regions. These experimental observations at both the macroscopic and microscopic levels could be explained by using the “random circuit breaker network” model, which is a dynamic bond percolation model.
Efficient multiple triplet quantum well structures in organic light-emitting devices
Authors: Park Tae Jin , Jeon Woo Sik , Choi Jin Woo , Pode Ramchandra , Jang Jin , Kwon Jang Hyuk
Published: September 2009

We demonstrate the multiple quantum well (MQW) structures with the charge control layers (CCLs) to produce highly efficient red phosphorescent organic light-emitting devices (OLEDs). Various triplet quantum well devices from a single to five quantum wells are realized using wide band-gap hole and electron transporting layers, narrow band-gap host and dopant materials, and CCLs. Triplet energies in such MQW devices are confined at the emitting layers. The maximum external quantum efficiency of 14.8% with a two quantum well device structure is obtained. The described MQW device concept has been proposed to be very useful to future OLED display and lighting applications.
Internal quantum efficiency of c-plane InGaN and m-plane InGaN on Si and GaN
Authors: Ni X. , Lee J. , Wu M. , Li X. , Shimada R. , Özgür Ü. , Baski A. A. , Morkoç H. , Paskova T. , Mulholland G. , Evans K. R.
Published: September 2009

We investigated internal quantum efficiency (IQE) of polar (0001) InGaN on c-sapphire, and (11¯00) nonpolar m-plane InGaN on both m-plane GaN and specially patterned Si. The IQE values were extracted from the resonant photoluminescence intensity versus the excitation power. Data indicate that at comparable generated carrier concentrations the efficiency of the m-plane InGaN on patterned Si is approximately a factor of 2 higher than that of the highly optimized c-plane layer. At the highest laser excitation employed (∼1.2×1018 cm−3), the IQE of m-plane InGaN double heterostructure on Si is approximately 65%. We believe that the m-plane would remain inherently advantageous, particularly at high electrical injection levels, even with respect to highly optimized c-plane varieties. The observations could be attributed to the lack of polarization induced field and the predicted increased optical matrix elements in m-plane orientation.
Universality in phase diagram of (K,Na)NbO3–MTiO3 solid solutions
Authors: Wang Ruiping , Bando Hiroshi , Itoh Mitsuru
Published: September 2009

Detailed phase diagrams are necessary for improving the temperature stability of piezoelectric properties of (Na,K)NbO3-based solid solutions. We report the phase diagrams of the (1−x)Na0.5K0.5NbO3–xMTiO3 (M=Pb, Ba, Sr, Ca, and Bi0.5Li0.5) solid solutions over a broad temperature range of 10 K≤T≤∼770 K. It is found that the phase diagrams show several universal characteristics: (a) Curie temperature TC-T decreases sharply at low x range; (b) the relation between TC-T and x deviates from Vegard’s law; and (c) the tetragonal-orthorhombic phase transition temperature TT-O and the orthorhombic-rhombohedral phase transition temperature TO-R are almost independent of M. We suggest that valence mismatch is the main reason for the rapid decrease in TC-T and the deviation of TC-T from Vegard’s law. It is also found that TC-T is mainly affected by the A-site cations, whereas TT-O and TO-R are mainly affected by the B-site cations.
Paper transistor made with covalently bonded multiwalled carbon nanotube and cellulose
Authors: Yun Sungryul , Jang Sang-Dong , Yun Gyu-Young , Kim Joo-Hyung , Kim Jaehwan
Published: September 2009

We report a flexible paper transistor made with regenerated cellulose and covalently bonded multiwalled carbon nanotube (RC-MWCNT). MWCNT bonded to cellulose chains can act as electron channel paths in dielectric cellulose layers. It is found that the covalent bonding between cellulose and MWCNT can be modulated by reaction time and temperature. The RC-MWCNT paper transistor shows that the leakage current and the on/off ratio are strongly associated with the concentration of MWCNTs. The estimated electron mobility of RC-MWCNT paper is comparable to other organic transistor materials. The RC-MWCNT paper transistor has a potential for flexible electronic paper.
Investigation of three-terminal organic-based devices with memory effect and negative differential resistance
Authors: Yu Li-Zhen , Lee Ching-Ting
Published: September 2009

The current-voltage characteristics of the gate-controlled three-terminal organic-based devices with memory effect and negative differential resistances (NDR) were studied. Gold and 9,10-di(2-naphthyl)anthracene (ADN) were used as the metal electrode and active channel layer of the devices, respectively. By using various gate-source voltages, the memory and NDR characteristics of the devices can be modulated. The memory and NDR characteristics of the devices were attributed to the formation of trapping sites in the interface between Au electrode and ADN active layer caused by the defects, when Au metal deposited on the ADN active layer.
Highly luminescent garnets for magneto-optical photonic crystals
Authors: Grishin A. M. , Khartsev S. I.
Published: September 2009

We compare luminescent properties of several Er-doped garnets as building blocks in all-garnet heteroepitaxial magneto-optical photonic crystals. Pulsed laser deposited La3Ga5O12, Gd3Ga5O12, Y3Fe5O12, and rf-magnetron sputtered Bi3Fe5O12 were chosen to host Er3+ ions on dodecahedral lattice sites. Er substituents with the concentration of 0.5 at. % (0.1 garnet formula units) do not decrease giant Faraday rotation in Bi2.9Er0.1Fe5O12 garnet; meanwhile providing intense room temperature C-band photoluminescence (PL). Fe3+ ion works as a sensitizer for Er resulting in fivefold PL enhancement in iron garnets compared to gallium ones. PL lifetime in gallium garnets is in millisecond range reaching almost 6 ms in Gd2.9Er0.1Ga5O12. We conclude Er substitution in gallium and iron garnet layers used both as Bragg mirrors and microcavities promises magneto-optical photonic crystals to become an active lasing medium.
Pentacene as protection layers of graphene on SiC surfaces
Authors: Jee Hae-geun , Han Jin-Hee , Hwang Han-Na , Kim Bongsoo , Kim Hee-seob , Kim Young Dok , Hwang Chan-Cuk
Published: September 2009

We report that pentacene can be used as a protection layer of graphene using synchrotron radiation-based photoemission spectroscopy. When pentacene was deposited on a single layer graphene, molecular states of pentacene were clearly observed, yet no change in the band structure of graphene could be identified. Unique electronic properties of graphene can be preserved in the presence of pentacene layers, and this finding can be exploited for fundamental research as well as application of graphene in electronic devices. After exposing the pentacene-covered graphene to air followed by a subsequent annealing under vacuum, band structure of graphene was completely maintained.
Influence of crystal quality of underlying GaN buffer on the formation and optical properties of InGaN/GaN quantum dots
Authors: Davies S. C. , Mowbray D. J. , Wang Q. , Ranalli F. , Wang T.
Published: September 2009

A study of InGaN quantum dots (QDs) grown on two different GaN templates—GaN growth using a conventional two-step approach and growth using our recently developed high temperature (HT) AlN as a buffer—is reported. The HT AlN buffer leads to a significant reduction in the dislocation density, particularly screw dislocations, in subsequently deposited GaN. This reduction is confirmed by a significant decrease in the (0002) x-ray diffraction rocking curve width. The GaN on the HT AlN buffer leads to a high density (1010/cm2) of InGaN QDs, whereas in contrast InGaN QDs on the conventional GaN layer grown using the two-step approach have a much smaller density (∼108/cm2). Furthermore, the carrier lifetimes for the QDs on the GaN/HT AlN have been found to be up to nine times longer than those for the QDs on the conventional GaN.
Characterization of terahertz emission from a dc-biased filament in air
Authors: Chen Yanping , Wang Tie-jun , Marceau Claude , Théberge Francis , Châteauneuf Marc , Dubois Jacques , Kosareva Olga , Chin See Leang
Published: September 2009

We demonstrate that the terahertz emission from a dc-biased filament can be regarded as a sum of an elliptically polarized terahertz source (generated by a filament without external electric field) and a linearly polarized terahertz source induced by the external electric field applied to the filament. The peak frequency and linewidth of the linearly polarized terahertz source are related to the average plasma density of the filament.
Relative permeabilities and coupling effects in steady-state gas-liquid flow in porous media: A lattice Boltzmann study
Authors: Huang Haibo , Lu Xi-yun
Published: September 2009

In this paper, the viscous coupling effects for immiscible two-phase (gas-liquid) flow in porous media were studied using the Shan–Chen-type single-component multiphase lattice Boltzmann model. Using the model, the two-phase flows in porous media with density ratio as high as 56 could be simulated and the contact angle of the gas-liquid interface at a solid wall is adjustable. To investigate viscous coupling effects, the co- and countercurrent steady-state two-phase flow patterns and relative permeabilities as a function of wetting saturation were obtained for different capillary numbers, wettabilities, and viscosity ratios. The cocurrent relative permeabilities seem usually larger than the countercurrent ones. The opposing drag-force effect and different pore-level saturation distributions in co- and countercurrent flows may contribute to this difference. It is found that for both co- and countercurrent flows, for strongly wet cases and viscosity ratio M>1, knw increase with the driving force and the viscosity ratio. However, for neutrally wet cases, the variations of knw and kw are more complex. It is also observed that different initial pore-level saturation distributions may affect final steady-state distribution, and hence the relative permeabilities. Using the cocurrent and countercurrent steady flow experiments to determine the generalized relative permeabilities seems not correct.
Effects of film dimension on the phase transformation behavior of NiTi thin films
Authors: Huang Xu , Ramirez A. G.
Published: September 2009

This letter demonstrates the role of film geometry on the phase transformation and shape memory behaviors of NiTi thin films. Lithographically patterned lines possess a strain profile that significantly alters their phase transformation behavior and surface morphology in comparison to continuous films, although the microstructures remain the same. The stress profile causes the film curvature to change with direction: concave parallel to the line and convex when perpendicular. Additionally, patterned lines require higher temperature excursions for complete phase transformations; their transformation temperature interval doubled that of the continuous film. Such observations illuminate how microelectromechanical system embodiments of these materials may behave.
Kicking to Bigger Uprights: Field Goal Kicking Performance Influences Perceived Size
Authors: Witt Jessica K , Dorsch Travis E
Published: September 2009

Perception relates not only to the optical information from the environment but also to the perceiver's performance on a given task. We present evidence that the perceived height and width of an American-football field goal post relates to the perceiver's kicking performance. Participants who made more successful kicks perceived the field goal posts to be farther apart and perceived the crossbar to be closer to the ground compared with participants who made fewer kicks. Interestingly, the current results show perceptual effects related to performance only after kicking the football but not before kicking. We also found that the types of performance errors influenced specific aspects of perception. The more kicks that were missed left or right of the target, the narrower the field goal posts looked. The more kicks that were missed short of the target, the taller the field goal crossbar looked. These results demonstrate that performance is a factor in size perception.
Economic benefits of variable rate technology: case studies from Australian grain farms
Authors: Robertson Michael , Carberry Peter , Brennan Lisa
Published: September 2009

In this study we attempt to quantify the economic benefits of the adoption of variable rate application of fertiliser on six case study farms from the Australian wheatbelt. The farm case studies covered a range of agro-climatic regions (Mediterranean, uniform, and summer-dominant rainfall patterns), cropping systems (wheat–lupin, wheat–canola, and winter and summer crops), farm sizes (1250–5800 ha cropping program), soil types (shallow gravels to deep cracking clays), and production levels (average wheat yields from 1.8 to 3.5 t/ha). The farmers had been practising some form of variable rate technology (VRT) management of fertiliser for 2–10 years.
Capital investment in VRT equipment ranged from $37 000 to $73 000, which is at the medium to high end of investment for Australian farmers, and when expressed as investment per cropped hectare it varied from $11 to $30/ha. All farmers were able to quantify benefits of VRT, ranging from $1 to $22/ha across the six farms, and a break-even analysis showed that the initial capital outlay was recovered within 2–5 years. On a per paddock basis, benefits ranged from –$28 to +$57/ha.year, and reasons for this wide range could be explained by fertiliser management practices and the degree of within-paddock yield variation. Where VRT benefits were able to be estimated across a run of seasons for a given paddock, it was noticeable that benefits, albeit diminished, still occurred in below-average yielding years. This suggests that, once zones have been defined, benefits from VRT will occur in most seasons.
This study demonstrates that the participating Australian grain growers have adopted VRT systems that are profitable and recover the initial capital outlay within a few years. The use of, and benefits from, VRT technology vary farm to farm, in line with farmer preferences and circumstances.
Managing soil-borne crop diseases using precision agriculture in Australia
Authors: Heap J. W. , McKay A. C.
Published: September 2009

Field experiments in southern Australia examined the spatial distribution of soil-borne disease inoculum within paddocks using DNA-based soil assays. Paddocks were divided into zones using cluster analysis for a range of combinations of digital data layers. Inoculum levels differed among zones in 33–64% of the 108 cases examined, depending on the zone model used. It was concluded that zone models used for precision agriculture (PA) most commonly in Australia (viz. zones based on cluster analysis of grain yield maps, ECa, and elevation, and zones based on satellite biomass imagery) were most suitable for partitioning inoculum distribution within paddocks. Generally there was a correlation between pre-sowing levels of inoculum and crop root damage and shoot biomass; however, there was not always a strong correlation between inoculum level and grain yield. There was some evidence that damage/unit soil inoculum varied among zones, but difficulties in predicting this a priori suggest that the damage rate should be assumed to be equal among zones.
It is suggested that crop managers divide paddocks into yield or management zones and test each zone before every crop, using an appropriate soil sampling protocol. The disease risk and yield potential for each zone should then be considered to decide whether differential management is feasible or warranted. A soil test based on one composite paddock sample gives a paddock average only, which in many cases gives insufficient information about varying inoculum levels for robust zone management. If testing of every zone is not possible, then zones with the highest risk to profit from disease damage should be tested, to minimise risk. As PA technologies and biological understanding of disease behaviour improve, crop managers will have greater opportunities to exploit the non-random spatial distribution of soil-borne disease inoculum in new and imaginative ways at the zone level.
Advances in precision agriculture in south-eastern Australia. II. Spatio-temporal prediction of crop yield using terrain derivatives and proximally sensed data
Authors: Robinson N. J. , Rampant P. C. , Callinan A. P. L. , Rab M. A. , Fisher P. D.
Published: September 2009

The effects of seasonal as well as spatial variability in yield maps for precision farming are poorly understood, and as a consequence may lead to low predictability of future crop yield. The potential to utilise terrain derivatives and proximally sensed datasets to improve this situation was explored. Yield data for four seasons between 1996 and 2005, proximal datasets including EM38, EM31, and γ-ray spectra for 2003–06, were collected from a site near Birchip. Elevation data were obtained from a Differential Global Positioning System and terrain derivatives were formulated. Yield zones developed from grain yield data and yield biomass estimations were included in this analysis. Statistical analysis methods, including spatial regression modelling, discriminant analysis via canonical variates analysis, and Bayesian spatial modelling, were undertaken to examine predictive capabilities of these datasets. Modelling of proximal data in association with crop yield found that EM38h, EM38v, and γ-ray total count were significantly correlated with yield for all seasons, while the terrain derivatives, relative elevation, slope, and elevation, were associated with yield for one season (1996, 1998, or 2005) only. Terrain derivatives, aspect, and profile and planimetric curvature were not associated with yield. Modest predictions of crop yield were established using these variables for the 1996 yield, while poor predictions were established in modelling yield zones.