bluuebunny/crossref_metadata_2025 huggingface dataset:
Shock-Tube Study of the Recombination of O Atoms by Ar Catalysts at High Temperatures
Authors: Wray Kurt L.
Published: January 2005

The three-body recombination of O atoms by Ar catalysts was measured over a temperature range of 1340–2920°K in a shock-tube experiment. The excess amount of O atoms was produced by shocking dilute O3–Ar mixtures. Under the experimental conditions, the O atoms in excess of equilibrium produced by the reaction O3+M→O+O2+M had to recombine via the reaction O+O+M→O2+M. The reaction O3+O→2O2 was ineffective due to the high temperature and high concentration of Ar. The O2 formed by the recombination of the O atoms was monitored behind the shock wave by absorption of 1270-Å radiation. The data scatter by about a factor of 2, but a slight negative temperature dependence is apparent. At 2000°K the recombination coefficient is about 0.7×10−34 cm6/particle2-sec. The experimental results are compared with calculated curves based on various authors' dissociation-rate constants divided by the equilibrium constant. A dissociation-rate constant given by kd = 2.5×1016T−½ exp (−D/RT) cc/mole-sec, which is shown to fit dissociation data obtained in previous work and covering a temperature range of 5000–18 000°K, was found to fit best the present recombination data.
Anharmonic Corrections in Triatomic Molecules Exhibiting the Renner Effect
Authors: Hougen J. T. , Jesson J. P.
Published: January 2005

The effect of anharmonicity in linear triatomic molecules in II electronic states has been considered. Expressions for the anharmonic corrections to the vibrational energy are presented for molecules exhibiting a very small Renner effect and a small spin—orbit interaction.
Photochemistry in the Photo-Ionization Region. II. Photochemistry of Methane, Ethane, and Ethylene at Wavelengths below 900 Å
Authors: Walker D. C. , Back R. A.
Published: January 2005

The photolysis of methane has been investigated, using light from a microwave discharge through helium which is thought to have consisted mostly of the strongly self-reversed 584-Å resonance line. A windowless fast-flow separation system was used to separate the light source from the photolysis vessel. Methane pressure was varied from 0.001 to 0.3 mm, with helium as a carrier gas making up a total pressure of 1.85 mm.

Products were correlated with saturation ion-currents, ranging up to 25 μA, which were measured in the photolysis vessel. The main products were hydrogen, ethane, ethylene, and acetylene, with estimated yields of 4.0, 0.37, 0.31, and 0.11 molecules per ion-pair, respectively. Smaller amounts of propane and propylene, and traces of C4 hydrocarbons, were also observed. Formation of unsaturated polymer was inferred from the carbon deficit of the volatile products. The effects of adding ethylene and neon to the system were studied, and in some experiments an electric field was applied.

The photolyses of ethane and ethylene were also briefly investigated. Hydrogen was the only product measured, with yields ranging from 1.0 to 1.9 and from 0.8 to 1.2 molecules per ion pair from ethane and ethylene, respectively.

Mechanisms are presented to account for the observed results. It was concluded that both direct photolysis and helium sensitization were important primary processes in all three hydrocarbons.
Potential-Energy Curves of the Excited States of Alkali Hydride Molecules
Authors: Jain D. C. , Sah P.
Published: January 2005

The potential-energy curves of the excited states of NaH and KH have been obtained by the Rydberg-Klein-Rees method as described by Singh and Jain. The simple-harmonic curves and ionic curves for LiH, NaH, KH, and RbH have also been calculated. It has been found that the potential-energy curves mostly agree with Mulliken's findings as to the anomalous behavior of the excited states of alkali hydrides.
Medium Effects in NMR. III. Fluorine Resonance in Gases
Authors: Petrakis L. , Bernstein H. J.
Published: January 2005

The fluorine resonance of CF4, SiF4, SF6, and CHF3, and in a variety of gas mixtures have been measured at pressures up to 50 atm at room temperature. The pressure dependence of the chemical shift is much more pronounced than for protons [W. T. Raynes, A. D. Buckingham, and H. J. Bernstein, J. Chem. Phys. 36, 3481 (1962)]. The results are interpreted in the same manner as for the proton work (see reference above) in terms of a field and field square contribution to the medium shift. The field square contribution is primarily due to dispersive forces and is 15 to 44 times as large as for hydrogen in CH bonds. The polar contribution (first power of the field) for CF bonds is also larger than for CH bonds but of opposite sign, being responsible for high-field medium shifts for CF bonds.
Some Solid-State Studies of Tungsten Trioxide and Their Significance to Tungsten Bronze Theory
Authors: Crowder Billy Lee , Sienko M. J.
Published: January 2005

The Hall voltage, resistivity, and thermoelectric power have been measured on single crystals of tungstic oxide (γ phase: 10° to 330°C). The electrical transport properties can be explained quantitatively on the basis of a shallow donor model (ED=0.04 eV) in which carrier mobility is limited primarily by polar scattering from optical mode lattice vibrations. The interaction between electron and phonon is describable by the perturbation theory of Howarth and Sondheimer (replacing the effective mass by the polaron mass) or by the intermediate coupling theory of Lee, Low, and Pines. The model has been extended successfully to calculate the thermal and composition dependences of resistivity and Seebeck coefficient for the cubic sodium tungsten bronzes.
Vibrations of the OH Ions in Muscovite
Authors: Vedder W. , McDonald R. S.
Published: January 2005

Pleochroism of the infrared absorption of muscovite has been measured under moderate resolution. The results are discussed in terms of the idealized mica structure.

From the pleochroism of the OH stretching band, orientation of the vibrational transition moments can be determined. These moments are tilted out of the cleavage plane by about 16°. Their projection onto the cleavage plane makes an angle of about 32° with the b axis. These directions furnish approximations to the orientation of the OH ions, but the danger of equating the two is stressed. Vibrational coupling is small. This result has been used to decide rather conclusively between two models of muscovite which differ in the orientation of the OH ions.

The librational motion has been studied directly, as well as in combination bands with the OH fundamental. It is shown that the SiO lattice also gives rise to combination bands with νOH.
Fundamental Vibrational Frequencies in Ketene and the Deuteroketenes
Authors: Cox A. Peter , Esbitt Alan S.
Published: January 2005

Accurate microwave relative intensity measurements have been made on rotational transitions of ketene and its deutero derivatives in the ground and first vibrational states. The results allow the three lowest fundamental frequencies of these molecules to be positively determined. For CH2CO these modes are found to be 443, 527, and 617 cm−1. The lowest frequency is nearly 100 cm−1 lower than any fundamental previously cited from infrared data for ketene.

To substantiate the microwave results solid-state infrared spectra of the molecules at −192° have been investigated in the region 300–4000 cm−1. The low-frequency spectra are in good agreement with the microwave data, and a complete analysis allows the nine fundamentals of CH2CO, CHDCO, and CD2CO to be evaluated. The three lowest fundamentals of CH2CO in the solid are found at 433, 513, and 613 cm−1.

The thermodynamic properties of ketene have been recalculated.
Thermoelectric Power of NaCl Containing CdCl2
Authors: Christy R. W. , Hsueh Y. W. , Mueller R. C.
Published: January 2005

The thermoelectric power of NaCl has been measured as a function of temperature between 550°C and the melting point, using Pt-metal electrodes. Measurements were made on pure material, and also on material doped with 0.1% CdCl2. Compared with the theory of Howard and Lidiard, the results yield a value of the order of −1 eV for the sum of the cation and anion vacancy heats of transport, although the accuracy is low because of reactions occurring at the electrodes and uncertainties in the ratio of defect mobilities.
Collisional Transition Probabilities for Vibrational Deactivation of Chemically Activated sec-Butyl Radicals. Diatomic and Polyatomic Molecules
Authors: Kohlmaier G. H. , Rabinovitch B. S.
Published: January 2005

The study of collisional transitional probabilities for the de-excitation by inert gases of chemically activated sec-butyl radicals, excited to internal energies in excess of 40 kcal mole−1, has been extended to H2, D2, N2, CO2, CH4, CD3F, CH3Cl, and SF6. The diatomic gases display behavior similar to the rare gases, and on a preferred exponential model of collisional transition probabilities the average amount of energy transferred per collision is 〈ΔE〉expon≃1.3 kcal mole−1. On a stepladder model the corresponding amount is ΔE≃2.5 kcal mole−1. From higher-pressure data, the efficiency for CD3F, CH3Cl, and SF6 is deduced to be comparable with that for butene and, on a preferred stepladder model, ΔE>9 kcal. For CO2 and CH4 the behavior is intermediate. The possible importance of the role of internal rotation of butyl in facilitating energy transfer is noted; some uncertainty concerning the role of over-all rotations and vibrational modes of the deactivator in the relaxation process exists.
Extended Hole Theory of Liquids. II. Approximate Calculation of the Partition Function
Authors: Blomgren G. E.
Published: January 2005

Theoretical expressions from an earlier paper for the partition function and thermodynamic properties and a linear approximation for the dependence of the cell free volume on the number of nearest neighbors in a given local configuration are used in order to calculate thermodynamic properties and an equation of state for the hole theory of liquids. The region of validity of the linear free volume approximation is discussed. Among the properties calculated are the second virial coefficient for the dilute gas, the equation of state, excess entropy and internal energy of the liquid and compressed gas, and critical properties. The results are found to be in better agreement with experiment than other liquid theories. Possible extension and corrections to the theory are discussed.
Many-Electron Theory of Atoms and Molecules. III. Effect of Correlation on Orbitals
Authors: Sinanoğlu Oktay , Tuan Debbie Fu-tai
Published: January 2005

The exact wavefunction of an N-electron atom or molecule contains, after the Hartree-Fock (HF) part, correlation terms involving successively one, two, … N electrons at a time. Particularly in closed shells, one-electron terms f̂i result mainly from pair correlations. The f̂i were previously neglected in the many-electron theory. Reasons for the smallness of f̂i are summarized. Different types of correlation effects are classified, and methods for estimating each type of f̂i are given. f̂i in closed form, i.e., including infinitely many single excitations is less than 2.8% of the Hartree-Fock orbital in He with an energy contribution 0.0001 a.u. (63 cal/mole). In the H2 molecule f̂i is negligible for (R/Re) <2. At larger R, as (1σg)2 becomes degenerate with (1σu)2 the f̂i effect increases to ∼0.4 eV at dissociation. However, in such cases and in actual nonclosed shells, these nondynamical f̂i are removed if HF orbitals are obtained after the removal of degeneracies. Dynamical correlation effects give negligible f̂i and so generalized SCF methods are not necessary. Qualitative quantum chemistry can be based on just HF orbitals or approximations to them, though energies include localized pair correlations.
Spin Resonance Spectra of Substituted Aromatic Ions: Perturbation Model
Authors: Brown Thomas H. , Karplus Martin , Schug John C.
Published: January 2005

By use of a perturbation approach, the valence-bond method is applied to weakly substituted benzene positive and negative ion radicals. Small changes in the Coulomb integrals are introduced to remove the degeneracy present in the unsubstituted case. The case of D2 symmetry, which corresponds to para-disubstituted benzene, is treated in detail in terms of a basis set consisting of eighteen valence-bond functions. Previously given formulas are used in obtaining the secular equation, spin densities, and charge densities for these ion-radical systems.

To test the usefulness of the method, spin densities of several of the methyl-benzene negative ions are compared with hyperfine constants determined from the ESR spectra of these ions. The theory accounts qualitatively for all of the experimental results, and in most cases the agreement between the measured and the calculated hyperfine constants is semiquantitative. Still better agreement may come with improved knowledge of the molecular integrals involved and of the degree of mixing of nearly degenerative states. Predictions are made for the spin densities in other methyl-benzene negative ions as well as the yet to be observed positive ions.
Creation and annihilation of free volume during homogeneous flow of a metallic glass
Authors: Heggen Marc , Spaepen Frans , Feuerbacher Michael
Published: January 2005

Bulk samples of Pd41Ni10Cu29P20 glass were tested at constant true stress (20–636MPa) in compression at 550, 555, and 565K to study the transition from steady-state creep at low stress to deformation-induced softening at high stress. In the high-stress regime strongly accelerating creep was observed. All deformation was homogeneous. The activation volume was 106Å3. The isoconfigurational activation energy was 9.03±0.64eV. The disordering rate is proportional to the applied power density (stress×strain rate). The disordering process is inefficient in energy and in the production of free volume.
Influence of gaseous annealing environment on the properties of indium-tin-oxide thin films
Authors: Wang R. X. , Beling C. D. , Fung S. , Djurišić A. B. , Ling C. C. , Li S.
Published: January 2005

The influence of postannealing in different gaseous environments on the optical properties of indiu-tin-oxide (ITO) thin films deposited on glass substrates using e-beam evaporation has been systematically investigated. It is found that the annealing conditions affect the optical and electrical properties of the films. Atomic force microscopy, x-ray diffraction, and x-ray photoemission spectroscopy (XPS) were employed to obtain information on the chemical state and crystallization of the films. These data suggest that the chemical states and surface morphology of the ITO film are strongly influenced by the gaseous environment during the annealing process. The XPS data indicate that the observed variations in the optical transmittance can be explained by oxygen incorporation into the film, decomposition of the indium oxide phases, as well as the removal of metallic In.
In-plane optical anisotropy in InxGa1−xN∕GaN multiple quantum wells induced by Pockels effect
Authors: Chang H. J. , Chen C. H. , Huang L. Y. , Chen Y. F. , Lin T. Y.
Published: January 2005

We have investigated the crystal orientation dependence of optical properties in InxGa1−xN∕GaN multiple quantum wells. The spectral peaks and intensity of the microphotoluminescence signal for different crystal orientations were found to have six-fold symmetry. Quite interestingly, the refractive index, obtained from the interference pattern, also varies with the crystal orientation. The 60° periodic anisotropy of electronic transitions as well as optical parameters was interpreted in terms of the Pockels effect induced by the strong built-in field in nitride heterojunctions. The linear dependence of the change of the refractive index on electric field is consistent with the prediction of the Pockels effect. Our result provides an alternative solution to improve the designs of photonic and electronic devices based on nitride semiconductors.
Probing two-dimensional magnetic switching in Co∕SiO2 multilayers using reversible susceptibility experiments
Authors: Spinu L. , Pham H. , Radu C. , Denardin J. C. , Dumitru I. , Knobel M. , Dorneles L. S. , Schelp L. F. , Stancu A.
Published: January 2005

The magnetic switching behavior of Co∕SiO2 multilayers has been studied using reversible susceptibility experiments performed along different orientations in the sample’s plane. A sensitive method for critical curve determination of two-dimensional magnetic systems was proposed. It was shown that this method, based on reversible susceptibility’s singularities detection, is general and can be applied independent of the expression of free energy describing the magnetic system under study. It is found that as the Co∕SiO2 ratio increases in the samples, the switching mechanism is governed by a noncoherent rotation mechanism.
Phase separation in La5∕8Sr3∕8MnO3(30%)+LuMnO3(70%) bulk sample studied by scanning microwave microscopy
Authors: Lee Jino , Park Jewook , Kim Ahram , Char K. , Park Soonyong , Hur Namjung , Cheong S.-W.
Published: January 2005

Using a scanning microwave microscope (SMM), we have investigated the phase separation in a 30%La5∕8Sr3∕8MnO3(LSMO)+70%LuMnO3(LMO) polycrystalline pressed powder sample, in which the LSMO phase is a perovskite ferromagnetic metal while the LMO phase is a hexagonal ferroelectric insulator. When the electrical properties of the sample were imaged using our SMM, the sample showed a significant contrast between the metallic LSMO and the insulating LMO grains, indicating a clear phase separation between the two phases. The metallic phase identified by the SMM clearly showed a ferromagnetic signal when investigated by a magnetic force microscope (MFM), providing solid evidence that the metallic phase is indeed the ferromagnetic LSMO. In addition, we have noticed a slight difference between the images generated by SMM and MFM, and we believe that this is due to the different depth scales probed by the two microscopy techniques.
Splitting of excitons and biexcitons in coupled InAs quantum dot molecules
Authors: Xu Xiulai , Williams D. A. , Cleaver J. R. A.
Published: January 2005

Coupling in laterally coupled InAs quantum dot molecules has been observed by conventional microscopic photoluminescence spectroscopy. At low excitation intensity, splitting of exciton emission is observed, and this is ascribed to recombination of bonding and antibonding states when two quantum dots are coupled. With increasing excitation intensity, splitting of biexciton emission because of coupling is observed on both sides of the exciton peaks. The splitting of both exciton and biexciton peaks increases with increasing energy, which implies a large wave function overlap at high energy.
Backscattering limitation for fiber-optic quantum key distribution systems
Authors: Subacius Darius , Zavriyev Anton , Trifonov Alexei
Published: January 2005

We characterized backscattering effects in optical fiber using a photon counting technique and considered its implications for quantum key distribution (QKD). We found that Rayleigh (elastic) backscattering can put strong limitations on a two-way QKD system’s performance. Raman (inelastic) scattering can restrict the ability of wavelength multiplexing of a quantum channel with strong classical data channel(s).
High-transmission solid-immersion apertured optical probes for near-field scanning optical microscopy
Authors: Dechant A. , Dew S. K. , Irvine S. E. , Elezzabi A. Y.
Published: January 2005

We demonstrate significantly increased intensity transmission for two hybrid apertured near-field optical probe designs. The probes, based on traditional atomic force microscopy tips, incorporate light-confining mechanisms that yield intensity throughput several orders of magnitude greater than conventional fiber-based probes. A microlayer probe features a high-index gallium phosphide evaporated layer, while a microsphere probe incorporates a silica microsphere lens. The increase in transmitted intensity is attributed to surface plasmon field enhancement effects as well as the decreased wavelength cutoff and focusing effects of the high-index layer and integrated solid-immersion lens, respectively.
Electron and hole moveable islands in pyroelectric/semiconductor granular systems
Authors: Kachorovskii V. Yu. , Shur M. S.
Published: January 2005

Spontaneous pyroelectric polarization induces strong built-in electric field in pyroelectric-semiconductor granular systems (pyroelectric grains in a semiconductor matrix or semiconductor grains in a pyroelectric matrix). At some critical value of the grain radius R=Rc, the built-in voltage drop across the grains becomes larger than the energy gap. In the intrinsic semiconductor, two moveable (electron and hole) islands with the size a∼Rc(R−Rc) appear at the grain surface for R>Rc. The plasma oscillations of such islands correspond to the terahertz range of frequencies. In an n-type semiconductor, the depletion and accumulation regions are formed due to a built-in electric field. For R>Rc, an inversion hole island might appear in the depletion region close to the grain interface.
The role of Cr substitution on the ferromagnetic properties of Ga1−xCrxN
Authors: Singh R. K. , Wu Stephen Y. , Liu H. X. , Gu Lin , Smith David J. , Newman N.
Published: January 2005

Angular-dependent channeling Rutherford backscattering spectroscopy (c-RBS) has been used to quantify the fraction of Cr atoms on substitutional, interstitial, and random sites in epitaxial Ga1−xCrxN films grown by reactive molecular-beam epitaxy. The morphology of these films and correlation with their magnetic properties has been investigated. Films grown at temperatures below ∼750°C have up to 90% of Cr occupying substitutional sites. Post-growth annealing at 825°C results in a systematic drop in the fraction of substitutional Cr as well as a fall off in the ferromagnetic signal. The roles of nonsubstitutional Cr in transferring charge from the Crt2 band and segregation of substitutional Cr in the loss of magnetism are discussed. Overall, these results provide strong microscopic evidence that Cr-doped III–N systems are dilute magnetic semiconductors.
Atomic force microscopy with time resolution of microseconds
Authors: Anwar M. , Rousso I.
Published: January 2005

The atomic force microscope (AFM) can acquire high-resolution images under nondestructive conditions albeit at a very poor temporal resolution. This work presents two AFM mapping techniques, stroboscopic, and continuous, for imaging rapid periodical processes with nanometer spatial resolution and microsecond time resolution. Application of these methods is demonstrated for imaging very rapid cyclic changes in the position of a microfabricated grid. Motion was resolved with 10nm spatial resolution, and 5 and 25μs temporal resolution using the stroboscopic and continuous mode, respectively. The proposed methods have the potential to image wide variety of rapid processes with unparalleled combination of lateral and temporal resolutions.
X-ray high-resolution diffraction using refractive lenses
Authors: Drakopoulos Michael , Snigirev Anatoly , Snigireva Irina , Schilling Jörg
Published: January 2005

Refractive x-ray lenses have recently been applied for imaging and scanning microscopy with hard x rays. We report the application of refractive lenses in an optical scheme for high-resolution x-ray diffraction, performed at a high brilliance synchrotron radiation source. An experimental proof of principle and a theoretical discussion are presented. In particular, we observe the x-ray diffraction pattern from a two-dimensional photonic crystal with 4.2μm periodicity, which normally is employed to scatter light in the infrared.
Nanometer-scale studies of point defect distributions in GaMnAs alloys
Authors: Gleason J. N. , Hjelmstad M. E. , Dasika V. D. , Goldman R. S. , Fathpour S. , Charkrabarti S. , Bhattacharya P. K.
Published: January 2005

We have investigated the concentrations and distributions of point defects in GaMnAs alloys grown by low-temperature molecular-beam epitaxy, using ultrahigh-vacuum cross-sectional scanning tunneling microscopy (XSTM). High-resolution constant-current XSTM reveals “A,” “M,” and “V” defects, associated with AsGa, MnGa, and VAs, respectively. A and V defects are present in all low-temperature-grown layers, while M defects are predominantly located within the GaMnAs alloy layers. In the GaMnAs layers, the concentration of V defects ([V]) increases with the concentration of M defects ([M]), consistent with a Fermi-level-dependent vacancy formation energy. Furthermore, [M] is typically two to three times [A] and [V], suggesting significant compensation of the free carriers associated with MnGa. A quantitative defect pair correlation analysis reveals clustering of nearest V–V pairs and anti-clustering of nearest M–M, M–V, and M–A pairs. For all pair separations greater than 2nm, random distributions of defects are apparent.
Ferroelectricity and local currents in epitaxial 5- and 9-nm-thick Pb(Zr,Ti)O3 ultrathin films by scanning probe microscopy
Authors: Fujisawa Hironori , Shimizu Masaru , Niu Hirohiko , Nonomura Hajime , Honda Koichiro
Published: January 2005

Ferroelectricity and local currents in 5- and 9-nm-thick Pb(Zr,Ti)O3 ultrathin films epitaxially grown on SrRuO3∕SrTiO3(100) are investigated by current-sensitive atomic force microscopy (CS-AFM) and contact-resonance piezoresponse force microscopy (CR-PFM). CS-AFM observations reveal that large local currents flowed at the step edge of SrRuO3 bottom electrodes. Using CR-PFM, clear contrasts were observed for antiparallel domains, which were not observable by conventional PFM. The observed difference in the deflection signals of flexural vibrations of the cantilever between antiparallel domains is qualitatively explained by coupled contributions from piezoelectric vibrations of the PZT and electrostatic interaction between the cantilever and bottom electrodes. Based on this interpretation, both the 5- and 9-nm-ultrathin PZT films are concluded to exhibit a stable ferroelectric state.
Diffraction effects in optical interferometric displacement detection in nanoelectromechanical systems
Authors: Kouh T. , Karabacak D. , Kim D. H. , Ekinci K. L.
Published: January 2005

Optical interferometric displacement detection techniques have recently found use in the study of nanoelectromechanical systems (NEMS). Here, we study the effectiveness of these techniques as the relevant NEMS dimensions are reduced beyond the optical wavelength used. We first demonstrate that optical cavities formed in the sacrificial gaps of subwavelength NEMS enable enhanced displacement detection sensitivity. In a second set of measurements, we show that the displacement sensitivity of conventional path-stabilized Michelson interferometry degrades rapidly beyond the diffraction limit. Both experiments are consistent with numerical models.
Ab initio prediction of a multiferroic with large polarization and magnetization
Authors: Baettig Pio , Spaldin Nicola A.
Published: January 2005

We describe the design of a magnetic ferroelectric with large spontaneous magnetization and polarization using first-principles density functional theory. The usual difficulties associated with the production of robustly insulating ferromagnets are circumvented by incorporating the magnetism through ferrimagnetic behavior. We show that the ordered perovskite Bi2FeCrO6 will have a polarization of ∼80μC∕cm2, a piezoelectric coefficient of 283μC∕cm2, and a magnetization of ∼160emu∕cm3 (2μB per formula unit), far exceeding the properties of any known multiferroic.
Efficiency improvement in solid-state-dye-sensitized photovoltaics with an amphiphilic Ruthenium-dye
Authors: Schmidt-Mende Lukas , Zakeeruddin Shaik M. , Grätzel Michael
Published: January 2005

We report a solid-state-dye-sensitized solar cell with an efficiency of 4% over the standard air mass 1.5 spectrum (100mW∕cm2). This was made possible by using an amphiphilic dye with hydrophobic spacers. We attribute the performance to the self-assembly of the dye to a dense layer on the TiO2 surface with its carboxylate groups as anchors and with its hydrophobic isolating chains as blocking layer between hole conductor and TiO2. In addition we studied the dependence of the thickness of the nanoporous TiO2 layer and the device performance. These results show the high potential for solid-state-dye-sensitized solar cells to compete with amorphous silicon cells as low-cost alternative.
Minority carrier transport in p-type Zn0.9Mg0.1O doped with phosphorus
Authors: Lopatiuk O. , Burdett W. , Chernyak L. , Ip K. P. , Heo Y. W. , Norton D. P. , Pearton S. J. , Hertog B. , Chow P. P. , Osinsky A.
Published: January 2005

Minority carrier diffusion length and lifetime in p-Zn0.9Mg0.1O doped with phosphorus were obtained from local electron beam irradiation measurements. The irradiation resulted in an increase of up to 25% in minority electron diffusion length from the initial value of ∼2.12μm and in a simultaneous decrease of the peak near-bandedge cathodoluminescence intensity. The observed phenomena are attributed to charging of phosphorus-related deep acceptor level(s), which is consistent with the activation energy of 256±20meV found for the effect of electron injection in Zn0.9Mg0.1O.
Electric-field-enhanced electron capture coefficient of EL2 level in semi-insulating GaAs
Authors: Kiyama M. , Tatsumi M. , Yamada M.
Published: January 2005

The electric-field dependence of electron capture coefficient to EL2 donor level in semi-insulating GaAs has been quantitatively determined from the analysis of the sublinear J–E characteristics up to 1150V∕cm before the onset of the low-frequency current oscillation. The three-probe guard-ring method was employed to obtain precise J–E characteristics. By considering the rate equation of the capture and emission process in the steady state, a simplified formula was derived to determine the electric-field dependence of capture coefficient. Our results agree well with those calculated from the multiphonon emission capture model.
Room-temperature 3.9–4.3 μm photoluminescence from InSb submonolayers grown by molecular beam epitaxy in an InAs matrix
Authors: Solov’ev V. A. , Lyublinskaya O. G. , Semenov A. N. , Meltser B. Ya. , Solnyshkov D. D. , Terent’ev Ya. V. , Prokopova L. A. , Toropov A. A. , Ivanov S. V. , Kop’ev P. S.
Published: January 2005

We report on molecular beam epitaxial growth of InSb submonolayer insertions in an InAs matrix, exhibiting intense mid-IR photoluminescence (PL) up to room temperature (RT). The InSb insertions are fabricated by an exposure of InAs surface to an antimony Sb4 flux. The nominal thickness of insertions grown at different temperatures (TS=400–485°C) ranges from 0.6 to 1.4 monolayer, as estimated from x-ray diffraction measurements of InSb∕InAs multiple submonolayer structures. This gives rise to the variation of the emission wavelength within the 3.9–4.3 μm range at RT. An integral PL intensity drop from 77 K to RT does not exceed 20 times.
Influence of band alignment on recombination in pseudomorphic Si1−xGex∕Si quantum wells
Authors: Sugawara Y. , Kishimoto Y. , Akai Y. , Fukatsu S.
Published: January 2005

Unique potential lineup of pseudomorphic Si1−xGex∕Si quantum wells (QWs) allows negative charge buildup in the near-surface region. Significant local charge imbalance created thereby between electrons and holes diminishes the efficiency of the otherwise dominating, nonradiative Shockley-Read-Hall recombination in the QWs at a low level of photoexcitation, which is evidenced by anomalous evolution of photoluminescence intensity and internal quantum efficiency with increasing excitation density.
Direct observation of enhanced residual thermal energy coupling to solids in femtosecond laser ablation
Authors: Vorobyev A. Y. , Guo Chunlei
Published: January 2005

We perform direct measurement of the thermal energy remaining in the bulk of Cu, Mg, Au, and Si samples following multi-pulse femtosecond laser ablation. In contrast to the previous belief that the thermal energy remaining in the ablated sample is negligible using femtosecond pulses, we show a significant amount of residual thermal energy deposited in various materials. In fact, with a sufficiently large number of pulses at high fluence, virtually all the incident laser energy can be retained in the sample. Several possible mechanisms are investigated for their role in residual heating, including laser-induced surface modification, exothermic chemical processes, and pressure effects.
Large polar pretilt for the liquid crystal homologous series alkylcyanobiphenyl
Authors: Huang Zhibin , Rosenblatt Charles
Published: January 2005

Sufficiently strong rubbing of the polyimide alignment layer SE-1211 (Nissan Chemical Industries, Ltd.) results in a large pretilt of the liquid crystal director from the homeotropic orientation. The threshold rubbing strength required to induce nonzero pretilt is found to be a monotonic function of the number of methylene units in the homologous liquid crystal series alkylcyanobiphenyl. The results are discussed in terms of the dual easy axis model for alignment.
Thermal stimulation of aqueous volumes contained in carbon nanotubes: Experiment and modeling
Authors: Yarin Alexander L. , Yazicioglu Almila G. , Megaridis Constantine M.
Published: January 2005

The dynamic response, as caused by thermal stimulation, of aqueous liquid attoliter volumes contained inside multiwall carbon nanotubes is investigated theoretically and experimentally. The experiments indicate an energetically driven mechanism responsible for the dynamic multiphase fluid behavior visualized under high resolution in the transmission electron microscope. The theoretical model is formulated using a continuum approach, which combines temperature-dependent diffusion with intermolecular interactions in the fluid bulk, as well as in the vicinity of the carbon wall. Intermolecular van der Waals forces are modeled by Lennard-Jones 12-6 potentials. Comparisons between theoretical predictions and experimental data demonstrate the ability of the model to describe the major trends observed in the experiments.
Fermi level pinning and Hf–Si bonds at HfO2: Polycrystalline silicon gate electrode interfaces
Authors: Xiong K. , Peacock P. W. , Robertson J.
Published: January 2005

Doped polycrystalline Si (poly-Si) gate electrodes on HfO2 films on Si substrates are found not to cause as large shifts in the flat band voltage as those of SiO2 on Si. This effect has been attributed to a weak pinning of the Fermi level at the top poly-Si HfO2 interface. The effect is shown to be consistent with the formation of Hf–Si bonds at an otherwise O-terminated oxide interface. Vacancies, divacancies, and substitutional Si atoms are introduced into models of oxygen-terminated Si–HfO2 (100) interfaces and the resulting Hf–Si bonds are found to create a metallic interface with the Fermi level pinned at about 0.3 eV below the Si conduction band-edge.
Effects of 1:1 B-cation order on Raman scattering in complex perovskites AB′B″0.5O30.5
Authors: Levin Igor , Prosandeev Sergey A. , Maslar James E.
Published: January 2005

Effects of 1:1 B-cation ordering on Raman spectra were analyzed for a double-perovskite CaAl0.5Nb0.5O3 substituted with 5mol% CaTiO3. Raman measurements were conducted on a series of well-equilibrated polycrystalline samples quenched from various annealing temperatures to produce a broad range of a cation order parameter, η. The results demonstrated surprisingly different sensitivities of the ordering-related Raman-active modes, F2g, Eg, and A1g, to the variations of η. The differences were attributed to a dissimilar coupling of these vibrations to the mean value (ηe) and to the fluctuations (Δη) of η(η=ηe+Δη). In particular, the integrated intensities of both the F2g and Eg Raman peaks were found to depend primarily on ηe, while that of the A1g peak appeared to be strongly influenced by Δη. These differences were ascribed to the distinct symmetries of the three modes: Only the A1g mode has the same symmetry as η resulting in linear coupling of these oxygen displacements to η.
Low-dissipation capillary switches at small scales
Authors: Hirsa Amir H. , López Carlos A. , Laytin Michael A. , Vogel Michael J. , Steen Paul H.
Published: January 2005

A system of two coupled capillary surfaces is made to switch between its stable states via mechanical and electrochemical disturbances. The bistable switch is experimentally demonstrated using water droplets, where the mechanical activation or “toggle” is achieved by a momentary air-pressure change. Requirements for capillary switches to avoid viscous dissipation are described and strategies for utilizing capillary switches for transporting other liquids or solids are discussed. Addressability of individual switches is achieved using electrochemical activation via a redox surfactant, where surface tension of one element of the switch is changed relative to the other.
Microscopic aspects of the region-by-region polarization reversal kinetics of polycrystalline ferroelectric Pb(Zr,Ti)O3 films
Authors: Stolichnov Igor , Malin Lisa , Colla Enrico , Tagantsev Alexander K. , Setter Nava
Published: January 2005

The region-by-region polarization switching in ferroelectric Pb(Zr,Ti)O3 thin films sandwiched between Pt electrodes has been directly observed using piezoelectric scanning probe microscopy. A resolution improved by one order-of-magnitude compared to the standard piezoelectric response imaging technique for ferroelectric capacitors was achieved by reducing the top electrode thickness to 10–15nm through polishing. It was demonstrated that the individually switched regions correspond to single grains or clusters of grains where the grain boundaries act as frontiers limiting the propagation of the switched state. The study of the propagation of the reversed polarization state as a function of voltage applied shows a rather discontinuous growth of the switched areas, the movement of the domain walls being triggered abruptly by different threshold voltages. This result agrees with the earlier proposed nucleation-limited switching model. The observation of the frozen regions that do not switch even at higher voltages provides significant insight into the “bits-failure” problem in submicron ferroelectric capacitors used for nonvolatile memory applications.
Effects of tantalum penetration through hafnium oxide layer on carrier generation rate in silicon substrate and carrier mobility degradation
Authors: Kang Chang Yong , Rhee Se Jong , Choi Chang Hwan , Akvar M. S. , Zhang Manhong , Lee Taekhwi , Ok Injo , Lee Jack C.
Published: January 2005

This letter presents the effects of tantalum penetration through hafnium oxide on bulk carrier generation rates and carrier mobility degradation. The penetration of Ta atoms degraded the bulk carrier lifetime in the Si substrate. Surface nitrogen incorporation can be useful to mitigate Ta penetration into the Si substrate. The incorporated Ta in the dielectric was found to have no effect on the effective κ value. On the other hand, it increased pre-existing traps and interface states. Thus, mobility degradation for tantalum nitride gate devices was primarily caused by pre-existing traps and interface states of the high-k dielectrics.
Effect of amplified spontaneous emission and absorber mirror recovery time on the dynamics of mode-locked fiber lasers
Authors: Herda Robert , Okhotnikov Oleg G.
Published: January 2005

The effect of the amplified spontaneous emission (ASE) on the performance of the semiconductor saturable absorber mirrors (SESAMs) in mode-locked fiber lasers has been investigated. We show that high level of ASE intensity typical for fiber lasers can saturate the absorption and degrade significantly the nonlinear response of the SESAM. We studied the effect of the absorber recovery time and demonstrated that the ion-irradiated SESAMs with fast nonlinear response are less affected by the ASE radiation and, consequently, in the presence of the high-power ASE they exhibit better self-starting capability compared with slow absorbers.
Influence of chemical short-range order on atomic diffusion in Al–Ni melts
Authors: Das S. K. , Horbach J. , Koza M. M. , Mavila Chatoth S. , Meyer A.
Published: January 2005

We use inelastic neutron scattering and molecular dynamics simulation to investigate the chemical short-range order (CSRO), visible through prepeaks in the structure factors, and its relation to self-diffusion in Al–Ni melts. As a function of composition at 1795K, Ni self-diffusion coefficients from experiment and simulation exhibit a nonlinear dependence with a pronounced increase on the Al-rich side. This comes along with a change in CSRO with increasing Al content that is related to a more dense packing of the atoms in Ni-rich Al–Ni systems.
White organic light-emitting devices based on 4,4′-bis(2,2′-diphenyl vinyl)-1,1′-biphenyl and phosphorescence sensitized 5,6,11,12-tetraphenylnaphthacene
Authors: Zhang Yingfang , Cheng Gang , Zhao Yi , Hou Jingying , Liu Shiyong
Published: January 2005

We report white organic light-emitting devices (WOLEDs) based on 4,4′-bis(2,2′-diphenyl vinyl)-1,1′-biphenyl (DPVBi) and phosphorescence sensitized 5,6,11,12-tetraphenylnaphthacene (rubrene). In the devices, DPVBi acts as a blue light-emitting layer, and rubrene sensitized by a phosphorescent material, fac tris (2-phenylpyridine) iridium [Ir(ppy)3], acts as a yellow light-emitting layer. The devices have a maximum brightness of 8633cd∕m2 (at a driving voltage of 22V). The maximum luminous efficiency is 9.22cd∕A (at a current density of 0.90mA∕cm2). Commission international De L’Eclairage coordination of (0.30,0.37) is obtained for luminance ranging from 100 to 1000cd∕m2.
Large blueshift of the band gap of GaAsSb∕AlSb quantum wells with ion implantation
Authors: Sun Xiaolan , Peyghambarian Nasser , Kost Alan R. , Eradat Nayer
Published: January 2005

We describe studies of intermixing in GaAsSb∕AlSb quantum wells with 18.8% and 31% arsenic, grown on GaSb substrates. Samples were implanted with a 1×1013cm−2 dose of 330keV boron ions and annealed. The band gap for the samples was determined from photoluminescence. The maximum blueshift of the band gap was 141nm (86meV) for the quantum wells with 18.8% arsenic and 198nm (124meV) for the quantum wells with 31% arsenic. The blueshifts are attributed to interdiffusion of both group-III and group-V constituents. Photoluminescence strength generally increased with annealing temperature.
Theoretical investigation of scaling effects from macro-to-microscale convection due to variations in incompressible fluid properties
Authors: Mahulikar Shripad P. , Herwig Heinz
Published: January 2005

We re-examine the governing continuum-based conservation equations for single-phase laminar forced convection of liquids, incorporating temperature dependence of fluid viscosity and thermal conductivity. The effects of property variations become highly significant from macro-to-microscale convection. Further, the effects of property variations along the flow become more significant relative to property variations over the cross section; thereby necessitating consideration of additional convection mechanisms at the microscale, in addition to mechanisms known at the macroscale. The same Brinkman number that determines convection with viscous dissipation, also determines convection with variations in fluid properties; but now the significance in convection increases with decreasing Brinkman number.
Hysteretic current–voltage characteristics and resistance switching at an epitaxial oxide Schottky junction SrRuO3∕SrTi0.99Nb0.01O3
Authors: Fujii T. , Kawasaki M. , Sawa A. , Akoh H. , Kawazoe Y. , Tokura Y.
Published: January 2005

Transport properties have been studied for a perovskite heterojunction consisting of SrRuO3 (SRO) film epitaxially grown on SrTi0.99Nb0.01O3 (Nb:STO) substrate. The SRO/Nb:STO interface exhibits rectifying current–voltage (I–V) characteristics agreeing with those of a Schottky junction composed of a deep work-function metal (SRO) and an n-type semiconductor (Nb:STO). A hysteresis appears in the I–V characteristics, where high resistance and low resistance states are induced by reverse and forward bias stresses, respectively. The resistance switching is also triggered by applying short voltage pulses of 1μs–10ms duration.
Crystalline γ-Al2O3 barrier for magnetite-based magnetic tunnel junctions
Authors: Bataille A. M. , Moussy J.-B. , Paumier F. , Gota S. , Guittet M.-J. , Gautier-Soyer M. , Warin P. , Bayle-Guillemaud P. , Seneor P. , Bouzehouane K. , Petroff F.
Published: January 2005

We report on the elaboration and physical properties of fully epitaxial Fe3O4∕Al2O3 bilayers to be included in magnetic tunnel junctions. Uncovered Fe3O4(111) single layers and bilayers were epitaxially grown onto sapphire (0001) substrates. Appropriate growth conditions lead to a stoichiometric Fe3O4 layer both at the Fe3O4∕Al2O3 interface and on the whole thickness, as checked by in situ x-ray photoelectron spectroscopy and by the observation of the Verwey transition, respectively. Transmission electron microscopy demonstrates the epitaxial growth of a γ-Al2O3 layer on top of Fe3O4(111), which insulating properties have been monitored by conductive tip atomic force microscopy.
Time-gated backscattered ballistic light imaging of objects in turbid water
Authors: Zevallos L. Manuel E. , Gayen S. K. , Alrubaiee M. , Alfano R. R.
Published: January 2005

Time-gated optical imaging of objects in turbid water was carried out in a backscattering geometry using light pulses of different pulse widths and a time-gated detection scheme with variable gate widths. Experimental results demonstrate that ultrashort pulsed illumination with ultrashort gated detection significantly improve image contrast as compared to any other combinations. These results are important for imaging objects embedded in turbid media, such as cloud, fog, smoke, murky water, and biological tissues for military, civilian, and medical applications.
Visualization using scanning nonlinear dielectric microscopy of electrons and holes localized in the thin gate film of a metal–SiO2–Si3N4–SiO2–semiconductor flash memory
Authors: Honda Koichiro , Cho Yasuo
Published: January 2005

We have used scanning nonlinear dielectric microscopy to clarify the position of electrons and holes in the gate SiO2–Si3N4–SiO2 (ONO) film of a metal–ONO–semiconductor flash memory. The electrons were detected in the Si3N4 part of the ONO film, while the holes were found in the bottom SiO2 film as well as in the Si3N4 film. This suggests that the injected electrons and holes did not always recombine with each other.
Enhancement of hole injection using O2 plasma-treated Ag anode for top-emitting organic light-emitting diodes
Authors: Won Choi Ho , Young Kim Soo , Kim Ki-Beom , Tak Yoon-Heung , Lee Jong-Lam
Published: January 2005

We report the enhancement of hole injection using AgOx layer between Ag anode and 4,4′-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl in top-emitting organic light-emitting diode (OLED). The turn-on voltage of OLEDs decreased from 17 to 7V as Ag changed to AgOx by the surface treatment using O2 plasma. Synchrotron radiation photoelectron spectroscopy results showed that the work function increased about 0.4eV by the O2 plasma treatment. This led to the decrease of the energy barrier for hole injection, reducing the turn-on voltage of OLEDs.