bluuebunny/crossref_metadata_2025 huggingface dataset:
Free energy profiles for penetration of methane and water molecules into spherical sodium dodecyl sulfate micelles obtained using the thermodynamic integration method combined with molecular dynamics calculations
Authors: Fujimoto K. , Yoshii N. , Okazaki S.
Published: January 2012

The free energy profiles, ΔG(r), for penetration of methane and water molecules into sodium dodecyl sulfate (SDS) micelles have been calculated as a function of distance r from the SDS micelle to the methane and water molecules, using the thermodynamic integration method combined with molecular dynamics calculations. The calculations showed that methane is about 6–12 kJ mol−1 more stable in the SDS micelle than in the water phase, and no ΔG(r) barrier is observed in the vicinity of the sulfate ions of the SDS micelle, implying that methane is easily drawn into the SDS micelle. Based on analysis of the contributions from hydrophobic groups, sulfate ions, sodium ions, and solvent water to ΔG(r), it is clear that methane in the SDS micelle is about 25 kJ mol−1 more stable than it is in the water phase because of the contribution from the solvent water itself. This can be understood by the hydrophobic effect. In contrast, methane is destabilized by 5–15 kJ mol−1 by the contribution from the hydrophobic groups of the SDS micelle because of the repulsive interactions between the methane and the crowded hydrophobic groups of the SDS. The large stabilizing effect of the solvent water is higher than the repulsion by the hydrophobic groups, driving methane to become solubilized into the SDS micelle. A good correlation was found between the distribution of cavities and the distribution of methane molecules in the micelle. The methane may move about in the SDS micelle by diffusing between cavities. In contrast, with respect to the water, ΔG(r) has a large positive value of 24–35 kJ mol−1, so water is not stabilized in the micelle. Analysis showed that the contributions change in complex ways as a function of r and cancel each other out. Reference calculations of the mean forces on a penetrating water molecule into a dodecane droplet clearly showed the same free energy behavior. The common feature is that water is less stable in the hydrophobic core than in the water phase because of the energetic disadvantage of breaking hydrogen bonds formed in the water phase. The difference between the behaviors of the SDS micelles and the dodecane droplets is found just at the interface; this is caused by the strong surface dipole moment formed by sulfate ions and sodium ions in the SDS micelles.
Ultrasensitive anomalous Hall effect in SiO2/Fe-Pt/SiO2 sandwich structure films
Authors: Lu Y. M. , Cai J. W. , Pan H. Y. , Sun Li
Published: January 2012

Ultrasensitive anomalous Hall effect has been demonstrated in a SiO2/Fe-Pt/SiO2 sandwich structure. Owing to the interfacial electron scattering, the Hall resistivity is appreciably enhanced for the thin Fe-Pt layers of high quality; meanwhile, a large interfacial anisotropy is formed and further enhanced through annealing, leading to a room temperature Hall slope up to 2160 μΩ cm/T and field sensitivity of 12 000 Ω/T at Fe-Pt thickness ∼1.8 nm. This number is an order magnitude higher than the best semiconductor sensitivity. Other important technical characteristics, such as electrical resistivity and temperature coefficient, are also suitable to practical magnetic Hall sensor development.
Importance of the correlation contribution for local hybrid functionals: Range separation and self-interaction corrections
Authors: Arbuznikov Alexei V. , Kaupp Martin
Published: January 2012

Local hybrid functionals with their position-dependent exact-exchange admixture are a conceptually simple and promising extension of the concept of a hybrid functional. Local hybrids based on a simple mixing of the local spin density approximation (LSDA) with exact exchange have been shown to be successful for thermochemistry, reaction barriers, and a range of other properties. So far, the combination of this generation of local hybrids with an LSDA correlation functional has been found to give the most favorable results for atomization energies, for a range of local mixing functions (LMFs) governing the exact-exchange admixture. Here, we show that the choice of correlation functional to be used with local hybrid exchange crucially influences the parameterization also of the exchange part as well as the overall performance. A novel ansatz for the correlation part of local hybrids is suggested based on (i) range-separation of LSDA correlation into short-range (SR) and long-range (LR) parts, and (ii) partial or full elimination of the one-electron self-correlation from the SR part. It is shown that such modified correlation functionals allow overall larger exact exchange admixture in thermochemically competitive local hybrids than before. This results in improvements for reaction barriers and for other properties crucially influenced by self-interaction errors, as demonstrated by a number of examples. Based on the range-separation approach, a fresh view on the breakdown of the correlation energy into dynamical and non-dynamical parts is suggested.
Quadratic finite volume element method for the improved Boussinesq equation
Authors: Zhang Zhiyue , lu Fuqiang
Published: January 2012

In this paper, a new numerical procedure is developed for solving the initial boundary value problems for the improved Boussinesq equation. The quadratic finite volume element method is used to discretize the nonlinear partial differential equation in space and a system involving only time parameter is derived. The resulting coefficient matrix for the semi-discrete scheme is tridiagonal and can be solved efficiently. For time derivative terms, central difference approximation is preferred. Various numerical experiments are given to test and validate our method and show its capacity to simulate single-wave splitting, wave interaction, and blow-up behavior.
Hybrid time dependent/independent solution for the He I line ratio temperature and density diagnostic for a thermal helium beam with applications in the scrape-off layer-edge regions in tokamaks
Authors: Muñoz Burgos J. M. , Schmitz O. , Loch S. D. , Ballance C. P.
Published: January 2012

Spectroscopic studies of line emission intensities and ratios offer an attractive option in the development of non-invasive plasma diagnostics. Evaluating ratios of selected He I line emission profiles from the singlet and triplet neutral helium spin systems allows for simultaneous measurement of electron density (ne) and temperature (Te) profiles. Typically, this powerful diagnostic tool is limited by the relatively long relaxation times of the 3S metastable term of helium that populates the triplet spin system, and on which electron temperature sensitive lines are based. By developing a time dependent analytical solution, we model the time evolution of the two spin systems. We present a hybrid time dependent/independent line ratio solution that improves the range of application of this diagnostic technique in the scrape-off layer (SOL) and edge plasma regions when comparing it against the current equilibrium line ratio helium model used at TEXTOR.
Adiabatic nonlinear waves with trapped particles. III. Wave dynamics
Authors: Dodin I. Y. , Fisch N. J.
Published: January 2012

The evolution of adiabatic waves with autoresonant trapped particles is described within the Lagrangian model developed in Paper I, under the assumption that the action distribution of these particles is conserved, and, in particular, that their number within each wavelength is a fixed independent parameter of the problem. One-dimensional nonlinear Langmuir waves with deeply trapped electrons are addressed as a paradigmatic example. For a stationary wave, tunneling into overcritical plasma is explained from the standpoint of the action conservation theorem. For a nonstationary wave, qualitatively different regimes are realized depending on the initial parameter S, which is the ratio of the energy flux carried by trapped particles to that carried by passing particles. At S < 1/2, a wave is stable and exhibits group velocity splitting. At S > 1/2, the trapped-particle modulational instability (TPMI) develops, in contrast with the existing theories of the TPMI yet in agreement with the general sideband instability theory. Remarkably, these effects are not captured by the nonlinear Schrödinger equation, which is traditionally considered as a universal model of wave self-action but misses the trapped-particle oscillation-center inertia.
Mid-gap trap states in CdTe nanoparticle solar cells
Authors: Bezryadina A. , France C. , Graham R. , Yang L. , Carter S. A. , Alers G. B.
Published: January 2012

Thin film solar cells comprised of quantum-confined CdTe nanoparticles are shown to have a low intrinsic density of mid-gap trap states relative to their equivalent bulk film, indicating that the ligands are effective at electrically passivating surface states. Sintering the nanoparticles into a poly-crystalline thin film increases device performance but also increases the density of mid-gap trap states due to doping from the CdCl treatment and the formation of long range disorder such as grain boundaries and dislocations. Long term aging under illumination increases the density of mid-gap traps in the unsintered films due to degradation of the ligands.
Experimental realization of the porous silicon optical multilayers based on the 1-s sequence
Authors: Estevez J. O. , Arriaga J. , Méndez-Blas A. , Robles-Cháirez M. G. , Contreras-Solorio D. A.
Published: January 2012

We report experimental results of the reflectance spectra of deterministic aperiodic multilayer structures fabricated with porous silicon. The refractive index of the layers forming the structures follows the values generated by the self-similar sequence called “the 1s-counting sequence.” We fabricated samples with 64, 128, and 256 layers with different thicknesses and porosities by controlling the applied current density and the etching time. The measured reflectance spectra exhibit properties of self-similarity, which are in good agreement with theoretical results reported previously.
Enhancement of superconducting properties in FeSe wires using a quenching technique
Authors: Ozaki Toshinori , Mizuguchi Yoshikazu , Demura Satoshi , Deguchi Keita , Kawasaki Yasuna , Watanabe Tohru , Okazaki Hiroyuki , Hara Hiroshi , Takeya Hiroyuki , Yamaguchi Takahide , Kumakura Hiroaki , Takano Yoshihiko
Published: January 2012

Enhancements of superconducting properties were observed in FeSe wires using a quenching technique. Zero resistivity was achieved at about 10 K in quenched wires, which is about 2 K higher than that of polycrystalline FeSe bulk. Furthermore, transport Jc of quenched wires showed three times higher than that of furnace-cooled wires. In contrast, the quenched polycrystalline FeSe bulks did not show the enhancement of Tc. The quenching technique is greatly promising for fabricating FeSe wires with high Tc and high Jc, and quenched FeSe wires have high potential for superconducting wire applications.
Low activation energy for the removal of excess nitrogen in nitrogen rich indium nitride
Authors: Butcher Kenneth S. A. , Chen Patrick P.-T. , Downes James E.
Published: January 2012

For some InN films large amounts of excess nitrogen are seen at low growth temperatures. Recent studies have revised downward the defect formation energies for several forms of nitrogen rich point-defects in InN. Here we calculate an activation energy of 0.4 ± 0.1 eV for the thermally activated removal of much of the excess nitrogen, believed to be interstitial nitrogen. This low energy barrier is shown to support the case for a low defect formation energy of the same native defect, although it is pointed out that non-equilibrium plasma based conditions are required to reach these lower defect formation energies.
Effects of hydrogen adsorption on mechanical properties of chiral single-walled zinc oxide nanotubes
Authors: Mirnezhad M. , Ansari R. , Rouhi H.
Published: January 2012

Size- and chirality-dependent mechanical properties of single-walled zinc oxide nanotubes (ZnONTs) under four different states of hydrogen adsorption have been investigated in this paper. A molecular mechanics model is developed to derive analytical expressions for surface Young’s modulus and Poisson’s ratio of chiral hydrogenated ZnONTs (H-ZnONTs). On the basis of quantum mechanics, density functional theory (DFT) is utilized to obtain the force constants of molecular mechanics theory. Also, the values of surface Young’s modulus, bending stiffness, Poisson’s ratio, and atomic structure of a hydrogenated zinc oxide (H-ZnO) sheet associated with the four positions of adsorption are determined via the DFT calculations. The related results indicate that the bending stiffness of a H-ZnO sheet is chirality-independent. The present analysis provides the possibility of considering nanotubes with different types of chirality. It is indicated that, for all positions of hydrogen adsorption, the values of surface Young’s modulus for armchair H-ZnONTs are higher than those of zigzag H-ZnONTs and the results of chiral H-ZnONTs are between the results of armchair and zigzag nanotubes. Also, the maximum stability happens when the hydrogen atoms are adsorbed on zinc and oxygen atoms at the two opposite sides of a ZnO sheet.
Structure factors in granular experiments with homogeneous fluidization
Authors: Puglisi Andrea , Gnoli Andrea , Gradenigo Giacomo , Sarracino Alessandro , Villamaina Dario
Published: January 2012

Velocity and density structure factors are measured over a hydrodynamic range of scales in a horizontal quasi-2D fluidized granular experiment, with packing fractions ϕ ∈ [10%, 40%]. The fluidization is realized by vertically vibrating a rough plate, on top of which particles perform a Brownian-like horizontal motion in addition to inelastic collisions. On one hand, the density structure factor is equal to that of elastic hard spheres, except in the limit of large length-scales, as it occurs in the presence of an effective interaction. On the other hand, the velocity field shows a more complex structure which is a genuine expression of a non-equilibrium steady state and which can be compared to a recent fluctuating hydrodynamic theory with non-equilibrium noise. The temporal decay of velocity modes autocorrelations is compatible with linear hydrodynamic equations with rates dictated by viscous momentum diffusion, corrected by a typical interaction time with the thermostat. Equal-time velocity structure factors display a peculiar shape with a plateau at large length-scales and another one at small scales, marking two different temperatures: the “bath” temperature Tb, depending on shaking parameters, and the “granular” temperature Tg < Tb, which is affected by collisions. The two ranges of scales are separated by a correlation length which grows with ϕ, after proper rescaling with the mean free path.
Self-metalation of 2H-tetraphenylporphyrin on Cu(111): An x-ray spectroscopy study
Authors: Diller K. , Klappenberger F. , Marschall M. , Hermann K. , Nefedov A. , Wöll Ch. , Barth J. V.
Published: January 2012

The bonding and the temperature-driven metalation of 2H-tetraphenylporphyrin (2H-TPP) on the Cu(111) surface under ultrahigh vacuum conditions were investigated by a combination of x-ray photoelectron spectroscopy (XPS) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy with density functional theory calculations. Thin films were prepared by organic molecular beam epitaxy and subsequent annealing. Our systematic study provides an understanding of the changes of the spectroscopic signature during adsorption and metalation. Specifically, we achieved a detailed peak assignment of the 2H-TPP multilayer data of the C1s and the N1s region. After annealing to 420 K both XPS and NEXAFS show the signatures of a metalloporphyrin, which indicates self-metalation at the porphyrin-substrate interface, resulting in Cu-TPP. Furthermore, for 2H-TPP monolayer samples we show how the strong influence of the copper surface is reflected in the spectroscopic signatures. Adsorption results in a strongly deformed macrocycle and a quenching of the first NEXAFS resonance in the nitrogen edge suggesting electron transfer into the LUMO. For Cu-TPP the spectroscopic data indicate a reduced interaction of first-layer molecules with the substrate as demonstrated by the relaxed macrocycle geometry.
Influence of electric fields on the depolarization temperature of Mn-doped (1-x)Bi1/2Na1/2TiO3-xBaTiO3
Authors: Sapper Eva , Schaab Silke , Jo Wook , Granzow Torsten , Rödel Jürgen
Published: January 2012

The transition between induced long-range order and relaxor-like behavior upon heating is investigated in lead-free (1-x)Bi1/2Na1/2(Ti0.995Mn0.005)O3-xBa(Ti0.995Mn0.005)O3 piezoceramics with x = 0.03, 0.06, and 0.09 (BNT-100xBT:Mn). Temperature-dependent permittivity ɛ′(T) and thermally stimulated depolarization currents (TSDC) of poled samples were measured under identical heating conditions to clarify the depolarization mechanism. In both methods, the influence of electric bias fields on the transition temperature was investigated. Fields applied in the poling direction shift the transition to higher temperatures, with corresponding results in ɛ′(T) and TSDC measurements. While the response of transition temperature to external fields displays a similar trend in all investigated compositions, the shape of TSDC is clearly connected with the composition and, hence, the crystal symmetry of the sample. Furthermore, the comparison of ɛ′(T) and TSDC data reveals a systematic shift between transition temperatures obtained with the two different methods.
Forced wave motion with internal and boundary damping
Authors: Louw Tobias , Whitney Scott , Subramanian Anu , Viljoen Hendrik
Published: January 2012

A d’Alembert-based solution of forced wave motion with internal and boundary damping is presented with the specific intention of investigating the transient response. The dynamic boundary condition is a convenient method to model the absorption and reflection effects of an interface without considering coupled PDE’s. Problems with boundary condition of the form ∂w∂z+α̃∂w∂t=0 are not self-adjoint which greatly complicates solution by spectral analysis. However, exact solutions are found with d’Alembert’s method. Solutions are also derived for a time-harmonically forced problem with internal damping and are used to investigate the effect of ultrasound in a bioreactor, particularly the amount of energy delivered to cultured cells. The concise form of the solution simplifies the analysis of acoustic field problems.
Free surface domain nucleation in a ferroelectric under an electrically charged tip
Authors: Yang Lun , Dayal Kaushik
Published: January 2012

This paper examines the process of domain nucleation in ferroelectric perovskites at a free surface due to electrical fields applied through a charged tip above the surface. We use a real-space phase-field model to model the ferroelectric, and apply a boundary element-based numerical method that enables us to accurately account for the stray electric fields outside the ferroelectric and the interactions through electric fields between the external tip and ferroelectric. We calculate the induced domain patterns, the stress and internal electric fields, and the induced surface displacement for various relative orientations of the crystal lattice with respect to the free surface. The effect of the external spatially inhomogeneous electric field leads to the formation of complex domain patterns and nominally incompatible microstructures. Two key findings are: first, in c axis films, a new domain forms beneath the tip through 180° switching and this new domain has the opposite piezo-response as the original domain, leading to a distinct displacement signature on the surface; and second, in a axis films, domain nucleation occurs at lower applied field because polarization rotates to align with the applied field, whereas in c axis films, the polarization magnitude reduces until 180° switching occurs at a higher applied field. We also see that the calculated domain patterns differ significantly from analytical approximations that are often used.
Reentrant spin-glass behavior induced by the frustration of Fe-Fe interactions in Laves phase Nb1−xHfxFe2 alloys
Authors: Gao Tian , Nishimura Katsuhiko , Namiki Takahiro , Okimoto Hiroshi
Published: January 2012

We carried out magnetization and specific-heat measurements of metallic compounds Nb1−xHfxFe2 (x = 0 and 0.65), which exhibit reentrant spin-glass freezing. The frequency dependence of ac susceptibility and the bifurcation between zero-field-cooled and field-cooled magnetization curves suggest the complex coexistence of magnetic phases at low temperatures. A long-time relaxation of magnetization is possibly due to the cluster-type and traditional reentrant spin-glass transition, which may be induced by the frustration of long-range Fe-Fe interactions. We did not observe any discontinuity indicating long-range magnetic phase transition in the data of specific heat versus temperature, but a broad hump characteristic of spin-glass freezing. The difference between the behaviors of two samples proves the existence of two types of reentrant spin-glass in alloys. The moment arrangements are briefly discussed.
Temperature-induced exciton switching in long alkyl chain based inorganic-organic hybrids
Authors: Pradeesh K. , Baumberg J. J. , Vijaya Prakash G.
Published: January 2012

Photoluminescence and transmission is systematically explored in thin films of long–alkyl-chain-based inorganic-organic (IO) hybrids (CnH2n+1NH3)2PbI4 (n = 12, 16, 18) (CnPI) and NH3C12H22NH3PbI4 (DDPI). Such IO-hybrids, which form natural multiple quantum well structures stacked up along c-axis, possess strong room-temperature exciton transitions. These hybrids exhibit reversible phase transition of two different crystal phase transitions at easily accessible device temperatures. Flipping the structural phase is clearly reflected in switching of the excitons with corresponding photoluminescence and transmission changes showing clear thermal hysteresis. The phase-dependent switching of excitons is predominantly due to reversible crumpling of the inorganic PbI sheet networks. Systematic temperature dependent studies establish a correlation between the structure and optical exciton features. Such thermo-optic exciton switching suggests possible new photonic devices.
Role of n-dopant based electron injection layer in n-doped organic light-emitting diodes and its simple alternative
Authors: Wook Park Young , Hwan Choi Jin , Hyun Park Tae , Ho Song Eun , Kim Hakkoo , Jun Lee Hyun , Joong Shin Se , Ju Byeong-Kwon , Song Won Jun
Published: January 2012

We investigate the enhancement mechanism of the electroluminescence (EL) of alkali metal based n-doped organic light-emitting diodes (OLEDs). The dual role of the n-dopant (carrier transport and lowering of the injection barrier) induces a trade-off. When the electron transport layer (ETL) is optimally doped by the n-dopant for the highest conductivity, the amount of n-dopant at the ETL/cathode interface is insufficient to form enough chemical bonds with the cathode for efficient carrier injection. This insufficient amount of n-dopant limits the carrier injection properties. To solve this problem, we demonstrated that the addition of an electron injection layer (EIL) comprised of the n-dopant could increase its presence at the interface and, thereby, improve the carrier injection properties and, consequently, the EL efficiency. Moreover, simply using an alkali-metal alloy (rather than co-deposition) on the n-doped ETL as a cathode, instead of using the additional EIL, greatly improves the EL efficiency of the OLEDs. The alkali-metal alloy cathode increased the interfaced states at the ETL/cathode. The proposed model was confirmed by x-ray photoemission spectroscopy experiments on the alkali-metal n-dopant/electrode interface.
Hysteretic anomalous Hall effect in a ferromagnetic, Mn-rich Ge:Mn nanonet
Authors: Bürger Danilo , Zhou Shengqiang , Höwler Marcel , Ou Xin , Kovacs György J. , Reuther Helfried , Mücklich Arndt , Skorupa Wolfgang , Helm Manfred , Schmidt Heidemarie
Published: January 2012

Ferromagnetic Ge:Mn has been fabricated by Mn implantation in intrinsic Ge wafers and by pulsed laser annealing with a pulse duration of 300 ns. Due to a segregation instability during laser annealing, Mn segregates at the liquid-solid interface and an approximately 40 nm thick Ge:Mn surface layer is strongly enriched with Mn. Plan-view images reveal a percolating Mn-rich nanonet. Hysteretic anomalous Hall effect has been observed up to 30 K, but it vanishes after etching away the 40 nm thick Mn-rich Ge:Mn surface layer. The nanonet seems to support the correlation between magnetization and hysteretic Hall resistance. Intrinsic scattering in the threads or vertices of this nanonet may lead to the observed anomalous Hall effect.
Nonthermal effects on the electron-atom bremsstrahlung process in generalized Lorentzian plasmas
Authors: Jung Young-Dae , Hong Woo-Pyo
Published: January 2012

The nonthermal effects on the electron-atom bremsstrahlung process are investigated in generalized Lorentzian plasmas. The screened atomic wave function and energy for the hydrogen atom in Lorentzian plasmas are obtained by the Ritz variational method. The electron-atom bremsstrahlung radiation cross section in Lorentzian plasmas is also obtained as a function of the spectral index and plasma parameters. It is shown that the nonthermal character of the Lorentzian plasma strongly suppresses the electron-atom bremsstrahlung cross section. In addition, it is shown that the nonthermal effect on the bremsstrahlung process decreases with increasing radiation photon energy. It is also shown that the nonthermal effect on the bremsstrahlung cross section is more significant in plasmas with higher densities.
X-band microwave generation caused by plasma-sheath instability
Authors: Bliokh Y. , Felsteiner J. , Slutsker Ya. Z.
Published: January 2012

It is well known that oscillations at the electron plasma frequency may appear due to instability of the plasma sheath near a positively biased electrode immersed in plasma. This instability is caused by transit-time effects when electrons, collected by this electrode, pass through the sheath. Such oscillations appear as low-power short spikes due to additional ionization of a neutral gas in the electrode vicinity. Herein we present first results obtained when the additional ionization was eliminated. We succeeded in prolonging the oscillations during the whole time a positive bias was applied to the electrode. These oscillations could be obtained at much higher frequency than previously reported (tens of GHz compared to few hundreds of MHz) and power of tens of mW. These results in combination with presented theoretical estimations may be useful, e.g., for plasma diagnostics.
Native cation vacancies in Si-doped AlGaN studied by monoenergetic positron beams
Authors: Uedono A. , Tenjinbayashi K. , Tsutsui T. , Shimahara Y. , Miyake H. , Hiramatsu K. , Oshima N. , Suzuki R. , Ishibashi S.
Published: January 2012

Native defects in Si-doped AlGaN grown by metalorganic vapor phase epitaxy were probed by monoenergetic positron beams. Doppler broadening spectra of the annihilation radiation and positron lifetimes were measured, and these were compared with results obtained using first-principles calculation. For Si-doped AlxGa1−xN (4 × 1017 Si/cm3), the vacancy-type defects were introduced at above x = 0.54, and this was attributed to the transition of the growth mode to the Stranski-Krastanov mechanism from the Frank-van der Merwe mechanism. For Si-doped Al0.6Ga0.4N, the vacancy concentration increased with increasing Si concentration, and the major defect species was identified as Al vacancies. A clear correlation between the suppression of cathodoluminescence and the defect concentration was obtained, suggesting the cation vacancies act as nonradiative centers in AlGaN.
Optical and structural characterization of thermal oxidation effects of erbium thin films deposited by electron beam on silicon
Authors: Kamineni Himani S. , Kamineni Vimal K. , Moore Richard L. , Gallis Spyros , Diebold Alain C. , Huang Mengbing , Kaloyeros Alain E.
Published: January 2012

Thermal oxidation effects on the structural, compositional, and optical properties of erbium films deposited on silicon via electron beam evaporation were analyzed by x-ray diffraction, x-ray photoelectron spectroscopy, Auger electron spectroscopy, and spectroscopic ellipsometry. A gradual rise in oxidation temperature from 700 to 900 °C resulted in a transition from ErO- to Er2O3-rich phase. Additional increase in oxidation temperature above 1000°C led to the formation of erbium silicate due to further oxygen incorporation, as well as silicon out-diffusion from the substrate. A silicon oxide interfacial layer was also detected, with its thickness increasing with higher oxidation temperature. Additionally, film refractive index decreased, while its Tauc bandgap value increased from ∼5.2 eV to ∼6.4 eV, as the oxidation temperature was raised from 700 °C to above 900 °C. These transformations were accompanied by the appearance of an intense and broad absorption band below the optical gap. Thermal oxidation effects are discussed in the context of film structural characteristics and defect states.
The equation of state, shock-induced molecule dissociation, and transparency loss for multi-compressed dense gaseous H2 + D2 mixtures
Authors: Gu Y. J. , Chen Q. F. , Zheng J. , Cai L. C. , Jia O. H. , Chen Z. Y. , Jing F. Q.
Published: January 2012

The experimental equation of state and temperature data of the dense gaseous H2 + D2 mixtures under multi-shock compression were presented in a pressure range of 2–36 GPa and a temperature range of 2300–5300 K. The strong shock wave was produced using the flyer plate impact by accelerated up to 5.1–6.2 km/s with a two-stage light-gas gun and introduced into the plenum gas sample, which was pre-compressed from environmental pressure to 30–40 MPa. Time-resolved spectral radiation histories were acquired with two sets of multi-wavelength channel pyrometers, which were used to determine the shock velocity and shock temperature in the sample. Shock pressure and particle velocity were obtained by the impedance matching method. The experimental data prove the validity of self-consistent fluid variational theory (SFVT) model in the partial dissociation region. The time-resolved spectral radiation histories along with the SFVT calculation show that the shocked gas samples lose their transparency in visible light wavelength ranges of 400–800 nm at about 12.99 GPa and 4413 K or higher.
Leaky-mode effects in plasmonic-coupled quantum dot infrared photodetectors
Authors: Lee S. C. , Sharma Y. D. , Krishna S. , Brueck S. R. J.
Published: January 2012

The effects of a heavily doped GaAs top contact layer on a plasmonics-integrated InAs quantum dot infrared photodetector (QDIP) are investigated. A metal photonic crystal (MPC), a 100 nm-thick gold film perforated with a 2.5 μm-period, 2-dimensional square hole array, is employed as a plasmonic coupler. The MPC is fabricated on QDIPs with identical structures except for the thickness (0.1 and 1.3 μm) of the top contact layer (doping concentration ∼2 × 1018 cm−3). For the lowest order surface plasma wave (SPW) resonance, the resonance wavelength undergoes a blue shift of 0.27 μm from 8.26 μm, and the responsivity and detectivity drop by ∼50% for the thicker contact layer. These effects are explained by leaky mode characteristics resulting from the free-carrier-reduced dielectric constant in the contact region that impacts the SPW resonance.
Atomic-level study of twin nucleation from face-centered-cubic/body-centered-cubic interfaces in nanolamellar composites
Authors: Han W. Z. , Carpenter J. S. , Wang J. , Beyerlein I. J. , Mara N. A.
Published: January 2012

We report deformation twinning in Cu within accumulative roll-bonded Cu-Nb nanolamellar composites. Twins appear connected to the Nb{112}//Cu{112} interface with the Kurdjumov-Sachs orientation relationship, which we show to be ordered and faceted. The interface adopts a different faceted structure after twinning. Our analysis suggests that deformation twinning involves facet dissociation and slip-transfer from the Nb layer to the Cu layer due to a geometrically favorable slip transmission pathway.
Carbon-mediated growth of thin, fully relaxed germanium films on silicon
Authors: Tetzlaff D. , Wietler T. F. , Bugiel E. , Osten H. J.
Published: January 2012

Smooth, fully relaxed Ge layers (thickness below 100 nm) were grown directly on Si(001) in a cyclic process flow. Each cycle consists of a low temperature epitaxy step followed by the deposition of less than a monolayer of carbon and subsequent thermal annealing. Full strain relaxation was achieved for 65 nm thin Ge films. Carbon, which is not incorporated homogenously into the Ge layer, prevents the formation of islands during thermal annealing. The lattice mismatch is accommodated via a regular dislocation array of complete edge dislocations localized at the Si/Ge interface.
Pulsed metal organic chemical vapor deposition of nearly latticed-matched InAlN/GaN/InAlN/GaN double-channel high electron mobility transistors
Authors: Xue JunShuai , Zhang JinCheng , Hou YaoWei , Zhou Hao , Zhang JinFeng , Hao Yue
Published: January 2012

High quality, nearly lattice-matched InAlN/GaN/InAlN/GaN double-channel heterostructures were grown on sapphire by pulsed-metal-organic-chemical-vapor-deposition (PMOCVD). High electron mobility of 1414 cm2/Vs was achieved along with a two-dimensional-electron-gas density of 2.55 × 1013 cm−2. We attribute it to the high quality PMOCVD-grown InAlN barriers and, additionally, to the novel GaN layer growth between two InAlN barriers, which consists of a thin GaN spacer to prevent indium-redistribution and indium-cluster formation during the subsequent growth and a relatively thick GaN channel to enhance electron mobility. High-electron-mobility-transistors fabricated on these heterostructures with 0.8-μm-length gate exhibit a maximum drain current of 906 mA/mm and a transconductance of 186 mS/mm.
Influence of structure disorder on the lattice thermal conductivity of polycrystals: A frequency-dependent phonon-transport study
Authors: Hao Qing
Published: January 2012

It is widely accepted that the lattice thermal conductivity of a polycrystal mainly depends on its grain sizes, phonon mean free paths, and grain-boundary thermal resistance. However, uncertainties always exist on how much grain misalignment and a wide grain size distribution in a real polycrystal could affect the thermal analysis. Considering frequency-dependent phonon mean free paths, the influence of these factors is carefully examined by phonon Monte Carlo simulations for a series of disordered silicon polycrystals with grain sizes ranging from 1 to 400 nm. More generally, simulations are also performed on thermally anisotropic polycrystals. Despite all structure variation, this work suggests that the “direction-averaged” lattice thermal conductivity of a polycrystal is always close to that of an aligned polycrystal, with an effective grain size matching the interface density of the studied polycrystal.
Adsorption dynamics and angular dependency of contaminants on Ru mirror surfaces
Authors: Catalfano M. , Kanjilal A. , Al-Ajlony A. , Harilal S. S. , Hassanein A.
Published: January 2012

A real time contamination of the Ru surface and corresponding effect on its work function were studied using extreme ultraviolet photoelectron spectroscopy with a 13.5-nm wavelength of light. The change in work function indicates formation of molecular dipoles, oriented outward from the Ru surface. X-ray photoelectron spectroscopy investigations suggest variation in electromagnetic interaction with the components of the adsorbed foreign species when the emission angle from the target surface was changed from 0° to 50°; H2O and C-On show a strong coupling at lower angles and OH dominates at higher angles, whereas carbon is found in the mid-range peaking at 30°.
Numerical simulations of runaway electron generation in pressurized gases
Authors: Levko D. , Yatom S. , Vekselman V. , Gleizer J. Z. , Gurovich V. Tz. , Krasik Ya. E.
Published: January 2012

The results of a numerical simulation of the generation of runaway electrons in pressurized nitrogen and helium gases are presented. It was shown that runaway electrons generation occurs in two stages. In the first stage, runaway electrons are composed of the electrons emitted by the cathode and produced in gas ionization in the vicinity of the cathode. This stage is terminated with the formation of the virtual cathode, which becomes the primary source of runaway electrons in the second stage. Also, it was shown that runaway electrons current is limited by both the shielding of the field emission by the space charge of the emitted electrons and the formation of a virtual cathode. In addition, the influence of the initial conditions, such as voltage rise time and amplitude, gas pressure, and the type of gas, on the processes that accompany runaway electrons generation is presented.
Extended spectral response in organic photomultiple photodetectors using multiple near-infrared dopants
Authors: Chuang Shao-Tang , Chien Shang-Chieh , Chen Fang-Chung
Published: January 2012

We demonstrate highly sensitive polymer photodetectors (OPDs) with spectral response extending from the ultraviolet to the near-infrared (NIR) region (∼1200 nm). After doping two NIR dopants, high external quantum efficiencies (∼5500%) and high responsivities (23.0 A/W) are achieved under a low reverse bias (−3.7 V). The high gains could be attributed to unbalanced carrier transport in the photoactive layer arising from the electron traps at the NIR dopants. This approach allows the ready preparation of OPDs exhibiting broad spectral responses and high quantum efficiencies simultaneously.
Unified (p, q; α, β, ν; γ) −deformed oscillator algebra: Irreducible representations and induced deformed harmonic oscillator
Authors: Baloitcha E. , Hounkonnou M. N. , Nkouankam E. B. Ngompe
Published: January 2012

A new deformed canonical commutation relation, generalizing various known deformations, is defined together with its structure function of deformation. Then, the related irreducible representations are characterized and classified. Finally, the discrete spectrum of the corresponding deformed harmonic oscillator Hamiltonian is investigated and discussed.
Surface plasmon-enhanced electroluminescence in organic light-emitting diodes incorporating Au nanoparticles
Authors: Xiao Y. , Yang J. P. , Cheng P. P. , Zhu J. J. , Xu Z. Q. , Deng Y. H. , Lee S. T. , Li Y. Q. , Tang J. X.
Published: January 2012

Surface plasmon-enhanced electroluminescence (EL) in an organic light-emitting diode is demonstrated by incorporating the synthesized Au nanoparticles (NPs) in the hole injection layer of poly(3,4-ethylene dioxythiophene):polystyrene sulfonic acid. An increase of ∼25% in the EL intensity and efficiency are achieved for devices with Au NPs, whereas the spectral and electrical properties remain almost identical to the control device. Time-resolved photoluminescence spectroscopy reveals that the EL enhancement is ascribed to the increase in spontaneous emission rate due to the plasmonic near-field effect induced by Au NPs.
Quasi-coherent states for harmonic oscillator with time-dependent parameters
Authors: Ünal Nuri
Published: January 2012

In this study, we discuss the harmonic oscillator with the time-dependent frequency, ω(t), and the mass, M(t), by generalizing the holomorphic coordinates for the harmonic oscillator. In general cases, we solve the Schrödinger equation by reducing it into the Riccati equation and discuss the uncertainties for the quasi-coherent states of the time-dependent harmonic oscillator. In special cases, we find the following results: First, for a time-dependent harmonic oscillator, if [ω(t)M(t)] is constant, then the coherent states will evolve as the coherent states. Second, for the driven harmonic oscillator, the coherent states will evolve as the coherent states with new eigenvalues. Third, we derive quasi-coherent states for the Caldirola–Kanai Hamiltonian and show that the product of uncertainties, ΔxΔp, is larger than minimum value; however, it is constant. We also discuss the classical equations of motion for the system.
Production of bio-oil from mahua de-oiled cake by thermal pyrolysis
Authors: Volli Vikranth , Singh R. K.
Published: January 2012

De-oiled cakes, a source of biomass in the form of agriculture residue, could be an ideal source for the production of bio-fuels that can be substituted with conventional fossil fuels. In this study, pyrolysis of mahua de-oiled cake (Madhuca indica) was carried in a semi-batch reactor at the temperatures of 350, 400, 450, 500, 550, and 600 °C. The optimum temperature at which maximum yield of 41.36% (by weight) liquid product obtained was 550 °C. Empirical formula of the bio-oil was established as CH1.379N0.0576S0.004O0.614. The thermal degradation of mahua de-oiled cake was studied in inert atmosphere from ambient temperature to a temperature of 600 °C at a heating rate of 25 °C min−1. The chemical composition of bio-char was investigated by using SEM-EDX and its heating value was determined to be 26 MJ/kg. Characterization showed that the bio-oil obtained can potentially be valued as fuel and chemical feedstock.
Classical ladder operators, polynomial Poisson algebras, and classification of superintegrable systems
Authors: Marquette Ian
Published: January 2012

We recall results concerning one-dimensional classical and quantum systems with ladder operators. We obtain the most general one-dimensional classical systems, respectively, with a third and a fourth-order ladder operators satisfying polynomial Heisenberg algebras. These systems are written in terms of the solutions of quartic and quintic equations. They are the classical equivalent of quantum systems involving the fourth and fifth Painlevé transcendents. We use these results to present two new families of superintegrable systems and examples of trajectories that are deformation of Lissajous's figures.
Arc discharge regulation of a megawatt hot cathode bucket ion source for the experimental advanced superconducting tokamak neutral beam injector
Authors: Xie Yahong , Hu Chundong , Liu Sheng , Jiang Caichao , Li Jun , Liang Lizhen , Team NBI
Published: January 2012

Arc discharge of a hot cathode bucket ion source tends to be unstable what attributes to the filament self-heating and energetic electrons backstreaming from the accelerator. A regulation method, which based on the ion density measurement by a Langmuir probe, is employed for stable arc discharge operation and long pulse ion beam generation. Long pulse arc discharge of 100 s is obtained based on this regulation method of arc power. It establishes a foundation for the long pulse arc discharge of a megawatt ion source, which will be utilized a high power neutral beam injection device.
Grid-point requirements for large eddy simulation: Chapman’s estimates revisited
Authors: Choi Haecheon , Moin Parviz
Published: January 2012

Resolution requirements for large eddy simulation (LES), estimated by Chapman [AIAA J. 17, 1293 (1979)], are modified using accurate formulae for high Reynolds number boundary layer flow. The new estimates indicate that the number of grid points (N) required for wall-modeled LES is proportional to ReLx, but a wall-resolving LES requires ÑReLx13/7, where Lx is the flat-plate length in the streamwise direction. On the other hand, direct numerical simulation, resolving the Kolmogorov length scale, requires ÑReLx37/14.
Full-length myosin Va exhibits altered gating during processive movement on actin
Authors: Armstrong Jessica M. , Krementsova Elena , Michalek Arthur J. , Heaslip Aoife T. , Nelson Shane R. , Trybus Kathleen M. , Warshaw David M.
Published: January 2012

Myosin Va (myoV) is a processive molecular motor that transports intracellular cargo along actin tracks with each head taking multiple 72-nm hand-over-hand steps. This stepping behavior was observed with a constitutively active, truncated myoV, in which the autoinhibitory interactions between the globular tail and motor domains (i.e., heads) that regulate the full-length molecule no longer exist. Without cargo at near physiologic ionic strength (100 mM KCl), full-length myoV adopts a folded (approximately 15 S), enzymatically-inhibited state that unfolds to an extended (approximately 11 S), active conformation at higher salt (250 mM). Under conditions favoring the folded, inhibited state, we show that Quantum-dot-labeled myoV exhibits two types of interaction with actin in the presence of MgATP. Most motors bind to actin and remain stationary, but surprisingly, approximately 20% are processive. The moving motors transition between a strictly gated and hand-over-hand stepping pattern typical of a constitutively active motor, and a new mode with a highly variable stepping pattern suggestive of altered gating. Each head of this partially inhibited motor takes longer-lived, short forward (35 nm) and backward (28 nm) steps, presumably due to globular tail-head interactions that modify the gating of the individual heads. This unique mechanical state may be an intermediate in the pathway between the inhibited and active states of the motor.
p63–microRNA feedback in keratinocyte senescence
Authors: Rivetti di Val Cervo Pia , Lena Anna Maria , Nicoloso Milena , Rossi Simona , Mancini Mara , Zhou Huiqing , Saintigny Gaelle , Dellambra Elena , Odorisio Teresa , Mahé Christian , Calin George Adrian , Candi Eleonora , Melino Gerry
Published: January 2012

We investigated the expression of microRNAs (miRNAs) associated with replicative senescence in human primary keratinocytes. A cohort of miRNAs up-regulated in senescence was identified by genome-wide miRNA profiling, and their change in expression was validated in proliferative versus senescent cells. Among these, miRNA (miR)-138, -181a, -181b, and -130b expression increased with serial passages. miR-138, -181a, and -181b, but not miR-130b, overexpression in proliferating cells was sufficient per se to induce senescence, as evaluated by inhibition of BrdU incorporation and quantification of senescence-activated β-galactosidase staining. We identified Sirt1 as a direct target of miR-138, -181a, and -181b, whereas ΔNp63 expression was inhibited by miR-130b. We also found that ΔNp63α inhibits miR-138, -181a, -181b, and -130b expression by binding directly to p63-responsive elements located in close proximity to the genomic loci of these miRNAs in primary keratinocytes. These findings suggest that changes in miRNA expression, by modulating the levels of regulatory proteins such as p63 and Sirt1, strongly contribute to induction of senescence in primary human keratinocytes, thus linking these two proteins. Our data also indicate that suppression of miR-138, -181a, -181b, and -130b expression is part of a growth-promoting strategy of ΔNp63α in epidermal proliferating cells.