bluuebunny/crossref_metadata_2025 huggingface dataset:
Inclusion of selected higher excitations involving active orbitals in the state-specific multireference coupled-cluster theory
Authors: Das Sanghamitra , Kállay Mihály , Mukherjee Debashis
Published: December 2010

The parent state-specific multireference coupled-cluster (SS-MRCC) theory proposed by Mukherjee et al. [J. Chem. Phys. 110, 6171 (1999)], though rigorously size-extensive and also size-consistent with localized orbitals, has some deficiencies in the minimal truncation scheme, viz. at the singles and doubles (SD) level (SS-MRCCSD). SS-MRCCSD does not involve the direct coupling of all the model functions with a given virtual function belonging to the uncontracted multiconfiguration CISD space. It also does not involve, even in the linear power of a cluster operator \documentclass[12pt]{minimal}\begin{document}$T_\mu$\end{document}Tμ, the direct coupling of the virtual functions \documentclass[12pt]{minimal}\begin{document}$\chi _{l_\mu }$\end{document}χlμ, which are up to doubly excited with respect to a model function \documentclass[12pt]{minimal}\begin{document}$\phi _\mu$\end{document}φμ to the other virtual functions of the MRCISD space which can be generated by triple and quadruple excitations from \documentclass[12pt]{minimal}\begin{document}$\phi _\mu$\end{document}φμ. We argue that inclusion of a selection of triples and quadruples involving at most two inactive orbital excitations from every \documentclass[12pt]{minimal}\begin{document}$\phi _\mu$\end{document}φμ would ameliorate the shortcoming of the incomplete coupling of the triply and quadruply excited virtual functions which can couple with the singly and doubly excited ones. This extended ansatz for our SS-MRCC theory, to be called SS-MRCCSDtq by us, would still miss the direct coupling of the manifold of the model functions \documentclass[12pt]{minimal}\begin{document}$\lbrace \phi _\lambda , \lambda \ne \mu \rbrace$\end{document}{φλ,λ≠μ} to singly and doubly excited virtual functions. However, this effect is expected to be less significant than the lack of the more complete virtual space couplings, these functions being many more numerous, suggesting the new methods to be significantly improved schemes. Excellent results on the potential energy surfaces of small molecules involving single, double, and triple bond dissociation bear out our expectations fully.
Reduced mobility of di-propylene glycol methylether in its aqueous mixtures by quasielastic neutron scattering
Authors: Swenson Jan , Sjöström Johan , Fernandez-Alonso Felix
Published: December 2010

The hydrogen (H-) bonding interplay between water and other organic molecules is important both in nature and in a wide range of technological applications. Structural relaxation and, thus, diffusion in aqueous mixtures are generally dependent on both the strength and the structure of the H-bonds. To investigate diffusion in H-bonding mixtures, we present a quasielastic neutron scattering study of di-propylene glycol methylether (2PGME) mixed with H2O (or D2O) over the concentration range 0–90 wt.% water. We observe a nonmonotonic behavior of the dynamics with a maximum in average relaxation time for the mixture with 30 wt.% water, which is more than a factor 2 larger compared to that of either of the pure constituents. This is a result in qualitative agreement with previous calorimetric studies and the behavior of aqueous mixtures of simple mono-alcohols. More surprisingly, we notice that the dynamics of the 2PGME molecules in the mixture is slowed down by more than a factor 3 at 30 wt.% water but that the water dynamics indicates an almost monotonous behavior. Furthermore, in the low momentum transfer (Q) range of the 2PGME, where the intermediate scattering function I(Q,t) is considerably stretched in time (i.e., the stretching parameter β ≪ 1), it is evident for the 2PGME–D2O samples that the Q-dependence of the inverse average relaxation time, 〈τ〉−1, is greater than 2. This implies that the relaxation dynamics is partly homogenously stretched, i.e., the relaxation of each relaxing unit is somewhat intrinsically stretched in time.
Interferometric imaging of surface acoustic waves on a glass sphere
Authors: Otsuka P. H. , Matsuda O. , Tomoda M. , Wright O. B.
Published: December 2010

We use an ultrafast optical pump and probe technique to investigate the propagation of subgigahertz surface acoustic waves on a 1 mm diameter glass sphere with an aluminum coating. A fiber-based pump setup generates the surface waves and a common-path interferometer images them in the time domain over the sphere surface as they pass through the pole opposite the source of excitation. Fourier analysis allows the acoustic spectrum of the acoustic source to be extracted and waves traveling in opposite directions to be isolated.
Approach to the physical origin of breakdown in silicon solar cells by optical spectroscopy
Authors: Gundel Paul , Kwapil Wolfram , Schubert Martin C. , Seifert Holger , Warta Wilhelm
Published: December 2010

The electrical breakdown of silicon solar cells at low reverse currents has recently gained increased attention. In this study we investigate the physical properties of prebreakdown sites with high resolution spectroscopy techniques. These techniques comprise the measurement of the electroluminescence under reverse voltage, microphotoluminescence spectroscopy, and micro-Raman spectroscopy. The measurements show very high levels of stress at the prebreakdown sites, an increase in the breakdown size with applied reverse bias and redshift in the breakdown electroluminescence spectrum with increasing onset voltage. The results are tentatively explained by a lower bandgap energy at the breakdown sites, which could be caused by stress.
Application of domain structures elements of ferrite-garnet films for transport of magnetic microparticles
Authors: Gorobets Yu. I. , Dzhezherya Yu. I. , Melnichuk I. A. , Cherepov S. V. , Kuz' A. P.
Published: December 2010

The physical background of the device for the transportation of magnetic microparticles which is using a domain structure of garnete-ferrite films with easy-plane anisotropy are developed and experimentally proved in the present paper. The proposed device can be used in microbiology, medicine, and genetic engineering.
A coupled cluster approach with a hybrid treatment of connected triple excitations: Implementation and applications for open-shell systems
Authors: Shen Jun , Kou Zhuangfei , Xu Enhua , Li Shuhua
Published: December 2010

An implementation of the coupled cluster (CC) singles, doubles, and a hybrid treatment of connected triples [denoted as CCSD(T)-h], based on the unrestricted Hartree–Fock (UHF) reference, is presented. Based on the spin-integrated formulation, we have developed a computer program to achieve the automatic derivation and implementation of the CCSD(T)-h approach. The CCSD(T)-h approach computationally scales as the seventh power of the system size, and is affordable for many medium-sized systems. The present approach has been applied to study the equilibrium geometries and harmonic vibrational frequencies in a number of open-shell diatomic molecules and bond breaking potential energy profiles in several open-shell molecules, including CH3, NH2, and SiH2. For all systems under study, the overall performance of the UHF-based CCSD(T)-h approach is very close to that of the corresponding CCSDT (CC singles, doubles, and triples), and much better than that of the UHF-based CCSD(T) (CC singles, doubles, and perturbative triples).
Charge density identification in ion channels
Authors: Wolansky G. , Taflia A.
Published: December 2010

Biological channels permeate ions through cell membranes. Ion channels carry a permanent charge that has a significant role in determining channel's permeation properties such as selectivity to certain ions, current amplitude, etc. In this paper we deal with the determination of the permanent charge from current-voltage curves. The ion channel current behavior is modelled by Poisson–Nernst–Planck (PNP) equations system. Previous works on the fixed charge density identification problem contain several ill-posed steps and linearization of the nonlinear PNP system. We suggest here several methods to make these algorithms more stable and accurate.
Recombination-pumped triatomic hydrogen infrared lasers
Authors: Saykally R. J. , Michael E. A. , Wang J. , Greene Chris H.
Published: December 2010

Mid-infrared laser lines observed in hydrogen/rare gas discharges are assigned to three-body recombination processes involving an electron, a rare gas (He or Ne) atom, and the triatomic hydrogen ion (H3+). Calculations of radiative transitions between neutral H3 Rydberg states support this interpretation, and link it to recent results for hydrogenic/rare gas afterglow plasmas. A mechanism for the population inversion is proposed, and the potential generality and astrophysical implications of such molecular recombination laser systems are briefly discussed.
Crosslinking of porous SiOCH films involving Si–O–C bonds: Impact of deposition and curing
Authors: Gourhant O. , Gerbaud G. , Zenasni A. , Favennec L. , Gonon P. , Jousseaume V.
Published: December 2010

This paper focuses on the properties of nanoporous SiOCH thin films deposited using a porogen approach by plasma enhanced chemical vapor deposition. The impact of deposition temperature, porogen loading and porogen removal treatment is investigated using Fourier transform infrared spectroscopy, solid-state nuclear magnetic resonance analysis, and electrical and mechanical measurements. This work shows that a higher deposition temperature allows limiting the film shrinkage during the porogen removal treatment and leads to the best compromise in term of electrical and mechanical properties. Beside, the effect of Si–O–C bonds on the enhancement of mechanical properties is promoted since a typical crosslinking mechanism is highlighted in case of ultraviolet curing.
Thermoelectric properties of nanostructured Si1−xGex and potential for further improvement
Authors: Bera Chandan , Soulier M. , Navone C. , Roux Guilhem , Simon J. , Volz S. , Mingo Natalio
Published: December 2010

We theoretically investigate the thermoelectric properties of sintered SiGe alloys, compare them with new and previous experimental measurements, and evaluate their potential for further improvement. The theoretical approach is validated by extensive comparison of predicted bulk mobility, thermopower, and thermal conductivity, for varying Ge and doping concentrations, in the 300–1000K temperature range. The effect of grain boundaries is then included for Si0.8Ge0.2 sintered nanopowders and used to predict optimized values of the thermoelectric figure of merit at different grain sizes. Our calculations suggest that further optimization of current state of the art n-type (p-type) material would be feasible, possibly leading to ∼5% (4%) ZT enhancement at 1000 K and 16% (6%) at room temperature. Even larger enhancements should be possible if the phonon scattering probability of the grain boundaries could be increased beyond its present value.
Portable fiber sensors based on surface-enhanced Raman scattering
Authors: Yang Xuan , Tanaka Zuki , Newhouse Rebecca , Xu Qiao , Chen Bin , Chen Shaowei , Zhang Jin Z. , Gu Claire
Published: December 2010

Two portable molecular sensing systems based on surface-enhanced Raman scattering (SERS) have been experimentally demonstrated using either a tip-coated multimode fiber (TCMMF) or a liquid core photonic crystal fiber (LCPCF) as the SERS probe. With Rhodamine 6G as a test molecule, the TCMMF-portable SERS system achieved 2–3 times better sensitivity than direct sampling (focusing the laser light directly into the sample without the fiber probe), and a highly sensitive LCPCF-portable SERS system reached a sensitivity up to 59 times that of direct sampling, comparable to the sensitivity enhancement achieved using fiber probes in the bulky Renishaw system. These fiber SERS probes integrated with a portable Raman spectrometer provide a promising scheme for a compact and flexible molecular sensing system with high sensitivity and portability.
Systematic investigation of global phase behavior of polymer mixtures in the pressure-temperature plane
Authors: Gençaslan Mustafa , Bilgin Yüksel , Keskin Mustafa
Published: December 2010

We investigate the critical lines of polymer mixtures in the presence of their vapor phase at the mathematical double point, where two critical lines meet and exchange branches, and its environment. The model used combines the lattice gas model of Schouten, ten Seldam and Trappeniers with the Flory-Huggins theory. The critical line structure is displayed for various combinations of the chain length and system parameters in the pressure (P)-temperature (T) plane, as is usually done with experimental results. This type of work sheds light on the essential transition mechanism involved in the phase diagram's change of character, such as multi-critical points and mathematical double points, which are of great practical importance in supercritical fluid extraction processes. The P, T diagrams are discussed in accordance with the Scott and van Konynenburg binary phase diagram classification. We found that our P, T plots were in agreement with type II, type III, or type IV phase diagram behaviors. We also found that some of our phase diagrams represent the liquid-liquid equilibria in polymer solutions and mixtures.
Ion irradiation induced structural and electrical transition in graphene
Authors: Zhou Yang-Bo , Liao Zhi-Min , Wang Yi-Fan , Duesberg Georg S. , Xu Jun , Fu Qiang , Wu Xiao-Song , Yu Da-Peng
Published: December 2010

The relationship between the electrical properties and structure evolution of single layer graphene was studied by gradually introducing the gallium ion irradiation. Raman spectrums show a structural transition from nano-crystalline graphene to amorphous carbon as escalating the degree of disorder of the graphene sample, which is in correspondence with the electrical transition from a Boltzmann diffusion transport to a carrier hopping transport. The results show a controllable method to tune the properties of graphene.
Nucleation process in Cu3Au(001) surface region around the order-disorder phase transition
Authors: Zasada I. , Rok Ł. , Mróz S. , Rychtelska T.
Published: December 2010

The element distribution in the Cu3Au(001) surface region has been determined on the basis of directional Auger electron spectroscopy polar profiles measurements and interpreted in the frame of thermodynamic approach formulated for the inhomogeneous systems by using the Néel sublattices concept. Both approaches, experimental and theoretical, allowed us to present the temperature dependence of element concentration in a layer resolved mode. The wide temperature range explored in the experiment ensured the large data base for the theoretical analysis which enabled us to propose the distribution of intra–layer and inter-layer pairwise interactions leading to proper temperature dependence of segregation profiles in the surface region. This kind of interaction distribution can be understood as strain induced.
Kinetics following addition of sulfur fluorides to a weakly ionized plasma from 300 to 500 K: Rate constants and product determinations for ion–ion mutual neutralization and thermal electron attachment to SF5, SF3, and SF2
Authors: Shuman Nicholas S. , Miller Thomas M. , Hazari Nilay , Luzik Eddie D. , Viggiano A. A.
Published: December 2010

Rate constants for several processes including electron attachment to SF2, SF3, and SF5 and individual product channels of ion-ion mutual neutralization between SF6−, SF5−, and SF4− with Ar+ were determined by variable electron and neutral density attachment mass spectrometry. The experiments were conducted with a series of related neutral precursors (SF6, SF4, SF5Cl, SF5C6H5, and SF3C6F5) over a temperature range of 300–500 K. Mutual neutralization rate constants for SF6−, SF5−, and SF4− with Ar+ are reported with uncertainties of 10–25% and show temperature dependencies in agreement with the theoretical value of T−0.5. Product branching in the mutual neutralizations is temperature independent and dependent on the electron binding energy of the anion. A larger fraction of product neutrals from the SF6− mutual neutralization (0.9 ±0.1) are dissociated than in the SF5− mutual neutralization (0.65 ± 0.2), with the SF4− (0.7 ± 0.3) likely lying in between. Electron attachment to SF5 (k = 2.0 × 10−8 $\pm^{2}_{1}$±12 cm3 s−1 at 300 K) and SF3 (4 ± 3 × 10−9 cm3 s−1 at 300 K) show little temperature dependence. Rate constants of electron attachment to closed-shell SFn species decrease as the complexity of the neutral decreases.
Vertically arrayed Si nanowire/nanorod-based core-shell p-n junction solar cells
Authors: Wang X. , Pey K. L. , Yip C. H. , Fitzgerald E. A. , Antoniadis D. A.
Published: December 2010

Vertically arrayed Si nanowire/nanorod-based core-shell p-n junction solar cells have been fabricated by a solid-state phosphorus diffusion to convert the shell of the boron-doped p-type Si nanowires to n-type, thus forming a core-shell p-n junction structure. The nanowires with a nanosphere defined diameter were fabricated by an Au-film assisted electrochemical etching method, enabling controlled junction formation. The Si nanowire arrays show superior optical properties over a wide range of spectrum. In addition, longer nanowires are more effective for light trapping and absorption which is more advantageous for efficient energy harvesting. The cells show a high energy conversion efficiency of 1.47%, a significant improvement from the previously reported Si nanowire-based core-shell junction solar cells where the core-shell junctions were formed by an oppositely doped Si deposition on preformed Si nanowires. The relatively high efficiency might be mainly attributed to the extremely low reflectivity of the nanowire arrays for efficient energy harvesting and a pristine junction formation by the diffusion method.
Scale-dependent vibration analysis of prestressed carbon nanotubes undergoing rotation
Authors: Murmu T. , Adhikari S.
Published: December 2010

Understanding the dynamic behavior of rotating nanostructures is important for practical development of nanomachines. At the nanoscale, the nonlocal effects often become prominent. In this study, we investigate the nonlocal effects in bending-vibration of an initially prestressed single-walled carbon nanotube via nonlocal elasticity. The carbon nanotube is assumed to be attached to a molecular hub and is undergoing rotation. Nonlocal Euler–Bernoulli beam theory is employed to formulate the governing equations. Differential quadrature method is being utilized and the nonlocal bending frequencies of the rotating system are determined. The effects of the initial preload on vibration characteristics of rotating carbon nanotube are examined. Further, influence of (a) nonlocal effects (b) angular velocities, (c) hub radii and (d) higher mode frequencies are studied. It is explicitly shown that the bending vibration of a rotating carbon nanotube is significantly influenced by the existence of a preload, angular velocity and the nonlocal parameter.
Influence of confinement on solvation of ethanol in water studied by Raman spectroscopy
Authors: Ratajska-Gadomska B. , Gadomski W.
Published: December 2010

Herewith we present the results of our studies on the effect of confinement on the solvation of ethyl alcohol in aqueous solutions using Raman spectroscopy of the O–H stretching band. Based on Gaussian–Lorentzian deconvolution of the O–H band Raman spectra we investigate the local structures created between water–water, water–alcohol, and alcohol–alcohol molecules, which are directly related to the solubility of the liquids. Comparison of the responses in bulk solutions and in solutions confined in the pores of the gelatin gel shows that for high ethanol concentrations solubility significantly increases with decrease of the pore sizes.
Enhanced photoluminescence from condensed electron-hole pairs in trenched Si
Authors: Cheng Yung-Chen , Sun Chi-Yuan , Sun Edward , Chen Miin-Jang
Published: December 2010

In this paper, we report the characteristics of low-temperature photoluminescence (PL) from condensed electron-hole (e-h) pairs in p-type silicon substrates with and without high-aspect-ratio trench structures. The average hole diameters of trenches were 140 and 170 nm, and the depth of trenches were about 5 μm. An Al2O3 surface passivation layer with thickness of 10 nm was grown by atomic layer deposition on surfaces of all samples to reduce nonradiative recombination and provide nucleation centers of condensed e-h pairs at Si/Al2O3 interface. Significant enhancement of PL intensity from e-h liquid/droplet (EHL/EHD) was observed in the trenched silicon at temperature below 30 K. Dominant PL from EHL/EHD at 14 K in the trenched silicon with larger hole diameters may be attributed to stronger spatial confinement of condensed e-h pairs in a smaller volume.
Modeling electron flow produced by a three-dimensional spatially periodic field emitter
Authors: Rokhlenko A. , Lebowitz J. L.
Published: December 2010

We study the space charge limited field emission from an emitter whose surface has a simple periodic structure with bumps. The shape of each bump is represented by a smooth function and the emission is governed by the Fowler–Nordheim–Schottky law. A mathematical scheme for modeling the potential and current structure by a set of elementary functions is developed and implemented numerically with the help of a special least square procedure. Our results show that such emitters are more efficient than emitters with long ridges only in weak electric fields. In stronger fields the latter give larger currents and they should be more durable. The emission by an individual bump in our periodic structure is compared also with that of a single emitter bump of the same shape, they appear to be quite close.
Control of the strain and magnetoresistance of LaMnO3+δ thin films using the magnetostriction of Terfenol-D alloy
Authors: Zheng R. K. , Wang Y. , Chan H. L. W. , Choy C. L. , Luo H. S.
Published: December 2010

We have fabricated a magnetoelectric laminate structure composed of magnetostrictive Tb0.3Dy0.7Fe1.92 (Terfenol-D) alloy and LaMnO3+δ (LMO)/0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 (PMN–PT) structure where the LMO film is epitaxially grown on the piezoelectric PMN–PT single-crystal substrate. When an external dc magnetic field is applied perpendicular to the film plane, the magnetoresistance of the LMO film at 220 K under a magnetic field of 1.2 T for the LMO/PMN–PT/Terfenol-D structure is enhanced by 31.6% with respect to that for the LMO/PMN–PT structure without Terfenol-D. Measurements of the magnetoelectric effects of the LMO/PMN–PT/Terfenol-D structure indicate that the strain induced by the magnetostriction of the Terfenol-D alloy is transferred to the PMN–PT substrate, which induces changes in the strain state of the PMN–PT substrate, thereby modifying the strain and magnetoresistance of the epitaxial LMO film.
The renormalized Jellium model of colloidal suspensions with multivalent counterions
Authors: Colla Thiago E. , Levin Yan
Published: December 2010

An extension of the renormalized Jellium model which allows to study colloidal suspensions containing trivalent counterions is proposed. The theory is based on a modified Poisson–Boltzmann equation which incorporates the effects of counterion correlations near the colloidal surfaces using a new boundary condition. The renormalized charges, the counterion density profiles, and osmotic pressures can be easily calculated using the modified renormalized Jellium model. The results are compared with the ones obtained using the traditional Wigner–Seitz (WS) cell approximation also with a new boundary condition. We find that while the thermodynamic functions obtained within the renormalized Jellium model are in a good agreement with their WS counterpart, the effective charges predicted by the two theories can be significantly different.
Time-resolved photoelectron spectroscopy of low-energy excitations of 4×4 C60/Cu(111)
Authors: Rosenfeldt Arne C. , Göhler Benjamin , Zacharias Helmut
Published: December 2010

Time-resolved two-photon photoemission is applied to investigate electron dynamics in multiple monolayers (MLs) of ordered fullerite on a copper substrate. The experimental data are analyzed assuming coupled excited state dynamics. Rate equations fitted to these dynamics yield lifetimes of about 80 ps for the lowest unoccupied molecular orbital (LUMO), about 1.2 ns for the singlet exciton and 22 μs for the triplet exciton at a surface temperature of 140 K. For trapped triplet excitons lifetimes up to 200 μs are observed. An increased excitation fluence reduces the lifetime of the excitons due to annihilation. An increased sample temperature slightly reduces the lifetime of the triplet exciton. There is no evident dependence of the exciton lifetimes on the pump photon energy in the range of hν = 2.9 to 3.3 eV. A dependence on the layer thickness (10–20 ML) is not observed as long as more than 9 ML are prepared.
An axiomatic characterization of a two-parameter extended relative entropy
Authors: Furuichi Shigeru
Published: December 2010

The uniqueness theorem for a two-parameter extended relative entropy is proven. This result extends our previous one, the uniqueness theorem for a one-parameter extended relative entropy to a two-parameter case. In addition, the properties of a two-parameter extended relative entropy are studied.
Investigation of the time evolutions of some log-periodic oscillators
Authors: Özeren Serhat F.
Published: December 2010

We consider the time evolution of the one dimensional classical and quantum oscillator systems according to its mass and spring constant with fluctuating time. By using the SU(1,1) coherent states, the classical equations of motion of the quantum oscillator have been obtained. Also, the effects of fluctuating mass and spring constant have been illustrated with the figures.
Subbandgap absorption in polymer-fullerene solar cells
Authors: Presselt M. , Bärenklau M. , Rösch R. , Beenken W. J. D. , Runge E. , Shokhovets S. , Hoppe H. , Gobsch G.
Published: December 2010

We present external quantum efficiency (EQE) studies of poly(3-hexylthiophene-2,5-diyl):[6,6]-phenylC61-butyric acid methyl ester (P3HT:PCBM) based bulk heterojunction polymer solar cells with improved intensity resolution in the subbandgap (SBG) region, i.e., the energy range below the optical bandgaps of the pristine materials. Varying the P3HT:PCBM blending ratio, we find that in addition to a Gaussian profile an exponential tail is needed for a quantitative description of the SBG EQE spectra. While the exponential contribution can be reliably assigned to disorder effects, the SBG EQE Gaussian profile can be due to charge-transfer absorption between P3HT and PCBM or due to absorption of PCBM at the interface or in the polymer-rich phase.
Reactive solid-state dewetting of Cu–Ni films on silicon
Authors: Clearfield Raphael , Railsback Justin G. , Pearce Ryan C. , Hensley Dale K. , Fowlkes Jason D. , Fuentes-Cabrera Miguel , Simpson Michael L. , Rack Philip D. , Melechko Anatoli V.
Published: December 2010

The behavior of a 50 nm Cu–Ni alloy film on Si in a process of reactive solid-state dewetting is presented. The films were annealed at a range of temperatures (300–700 °C) in 1% H2 99% N2 reducing atmosphere. The resulting alloy and silicide particles formed by film dewetting and film reaction with the substrate were distinguished by selective wet etching and examined by scanning electron microscopy and spectroscopy. After potassium hydroxide etch, regions that etch slower than silicon substrate have distribution statistics similar to the alloy and silicide particles prior to their removal, indicating strong coupling between mass transport across the interface and along the surface.
Scanning transmission electron microscopy investigation of the Si(111)/AlN interface grown by metalorganic vapor phase epitaxy
Authors: Radtke G. , Couillard M. , Botton G. A. , Zhu D. , Humphreys C. J.
Published: December 2010

The structure and chemistry of the interface between a Si(111) substrate and an AlN(0001) thin film grown by metalorganic vapor phase epitaxy have been investigated at a subnanometer scale using high-angle annular dark field imaging and electron energy-loss spectroscopy. ⟨112¯0⟩AlN∥⟨110⟩Si and ⟨0001⟩AlN∥⟨111⟩Si epitaxial relations were observed and an Al-face polarity of the AlN thin film was determined. Despite the use of Al deposition on the Si surface prior to the growth, an amorphous interlayer of composition SiNx was identified at the interface. Mechanisms leading to its formation are discussed.
Magnetostructural influences of thin Mg insert layers in crystalline CoFe(B)/MgO/CoFe(B) magnetic tunnel junctions
Authors: Hindmarch A. T. , Harnchana V. , Ciudad D. , Negusse E. , Arena D. A. , Brown A. P. , Brydson R. M. D. , Marrows C. H.
Published: December 2010

It is common to find a thin (∼0.5 nm) layer of Mg deposited prior to the MgO tunnel barrier in crystalline CoFe(B)/MgO/CoFe(B) magnetic tunnel junctions, due to the improved device performance that results. However, despite their common usage, the reasons why such layers are effective are unclear. We use structures that model the lower electrode of such devices to show that a suitably thick Mg insert layer enhances the crystal quality of both MgO and CoFe(B), permits interfacial oxides to reduce back to a metallic ferromagnetic state, and hence improves magnetic switching of the CoFe(B) electrode, properties which are inextricably linked to device performance.
Synchronized single electron emission from dynamical quantum dots
Authors: Mirovsky P. , Kaestner B. , Leicht C. , Welker A. C. , Weimann T. , Pierz K. , Schumacher H. W.
Published: December 2010

We study synchronized quantized charge pumping through several dynamical quantum dots (QDs) driven by a single time modulated gate signal. We show that the main obstacle for synchronization being the lack of uniformity can be overcome by operating the QDs in the decay cascade regime. We discuss the mechanism responsible for lifting the stringent uniformity requirements. This enhanced functionality of dynamical QDs might find applications in nanoelectronics and quantum metrology.
Giant magnetic domain-wall resistance in phase-separated manganite films
Authors: Granja L. , Hueso L. E. , Prieto J. L. , Levy P. , Mathur N. D.
Published: December 2010

The top and bottom electrodes of the ferromagnetic manganite La0.7Ca0.3MnO3 may be magnetically decoupled by a La0.59Ca0.41MnO3 interlayer in which ferromagnetic and paramagnetic phases coexist. In mesas fabricated from these trilayer films, in-plane magnetic domain walls associated with the antiparallel magnetic electrode configuration show a giant resistance-area product >10−10 Ω m2. This is almost two orders of magnitude larger than our devices with interlayer composition La0.6Ca0.4MnO3 [C. Israel et al., Phys. Rev. B 78, 054409 (2008)] where phase separation is less extreme. High-field treatments modify the ferromagnetic phase fraction of the interlayer.
Passively harmonically mode-locked vertical-external-cavity surface-emitting laser emitting 1.1 ps pulses at 147 GHz repetition rate
Authors: Quarterman A. H. , Perevedentsev A. , Wilcox K. G. , Apostolopoulos V. , Beere H. E. , Farrer I. , Ritchie D. A. , Tropper A. C.
Published: December 2010

Coupled-cavity passive harmonic mode-locking of a quantum well based vertical-external-cavity surface-emitting laser has been demonstrated, yielding an output pulse train of 1.5 ps pulses at a repetition rate of 80 GHz and with an average power of 80 mW. Harmonic mode-locking results from coupling between the main laser cavity and a cavity formed within the substrate of the saturable absorber structure. Mode-locking on the second harmonic of the substrate cavity allows a train of 1.1 ps pulses to be generated at a repetition rate of 147 GHz with 40 mW average power.
High responsivity ultraviolet photodetector realized via a carrier-trapping process
Authors: Liu J. S. , Shan C. X. , Li B. H. , Zhang Z. Z. , Yang C. L. , Shen D. Z. , Fan X. W.
Published: December 2010

Metal-semiconductor-metal structured ultraviolet (UV) photodetector has been fabricated from zinc oxide films. The responsivity of the photodetector can reach 26 000 A/W at 8 V bias, which is the highest value ever reported for a semiconductor ultraviolet photodetector. The origin of the high responsivity has been attributed to the carrier-trapping process occurred in the metal-semiconductor interface, which has been confirmed by the asymmetric barrier height at the two sides of the metal-semiconductor interdigital electrodes. The results reported in this paper provide a way to high responsivity UV photodetectors, which thus may address a step toward future applications of UV photodetectors.
Tunneling characteristics of graphene
Authors: Shin Young Jun , Kalon Gopinadhan , Son Jaesung , Kwon Jae Hyun , Niu Jing , Bhatia Charanjit S. , Liang Gengchiau , Yang Hyunsoo
Published: December 2010

Negative differential conductance and tunneling characteristics of two-terminal graphene devices are observed before and after electric breakdown, respectively. The former is caused by the strong scattering under a high E-field, and the latter is due to the appearance of a tunneling barrier in graphene channel induced by a structural transformation from crystalline graphene to disordered graphene because of the breakdown. Using Raman spectroscopy and imaging, the presence of nonuniform disordered graphene is confirmed. A memory switching effect of 100 000% ON/OFF ratio is demonstrated in the tunneling regime, which can be employed in various applications.
Modeling of plasma turbulence and transport in the Large Plasma Device
Authors: Popovich P. , Umansky M. V. , Carter T. A. , Friedman B.
Published: December 2010

Numerical simulation of plasma turbulence in the Large Plasma Device (LAPD) [W. Gekelman, H. Pfister, Z. Lucky et al., Rev. Sci. Instrum. 62, 2875 (1991)] is presented. The model, implemented in the BOUndary Turbulence code [M. Umansky, X. Xu, B. Dudson et al., Contrib. Plasma Phys. 180, 887 (2009)], includes three-dimensional (3D) collisional fluid equations for plasma density, electron parallel momentum, and current continuity, and also includes the effects of ion-neutral collisions. In nonlinear simulations using measured LAPD density profiles but assuming constant temperature profile for simplicity, self-consistent evolution of instabilities and nonlinearly generated zonal flows results in a saturated turbulent state. Comparisons of these simulations with measurements in LAPD plasmas reveal good qualitative and reasonable quantitative agreement, in particular in frequency spectrum, spatial correlation, and amplitude probability distribution function of density fluctuations. For comparison with LAPD measurements, the plasma density profile in simulations is maintained either by direct azimuthal averaging on each time step, or by adding particle source/sink function. The inferred source/sink values are consistent with the estimated ionization source and parallel losses in LAPD. These simulations lay the groundwork for more a comprehensive effort to test fluid turbulence simulation against LAPD data.
Dissipative surface stress effects on free vibrations of nanowires
Authors: Hasheminejad Seyyed M. , Gheshlaghi Behnam
Published: December 2010

A dissipative surface stress model is adopted to study the effect of size-dependent surface dissipation on natural frequencies of vibrating elastic nanowires (NWs). Euler–Bernoulli beam theory along with the classic Zener model for interior friction in the presence of an initial surface tension [C. Zener, Elasticity and Anelasticity of Metals (University of Chicago Press, Chicago, 1948)] are employed to derive a fifth order differential equation of motion describing the flexural vibrations of the NW. Numerical results include the natural frequencies of vibration for selected nanowire lengths ranging from nanometers to microns, for three common boundary conditions: simply supported, cantilever, and fully clamped.
Low contact resistivity and strain in suspended multilayer graphene
Authors: Rouxinol Francisco P. , Gelamo Rogério V. , Amici Renato G. , Vaz Alfredo R. , Moshkalev Stanislav A.
Published: December 2010

Method to prepare suspended multilayer graphene (MLG) flakes and to form highly conductive (contact resistivity of ∼0.1 kΩ μm2) and tight mechanical connection between MLG and metal electrodes is described. MLG flakes prepared from natural graphite were precisely deposited over tungsten electrodes using dielectrophoresis, followed by high-temperature thermal annealing in high-vacuum. Considerable strain induced in the suspended part of flakes was revealed by Raman imaging.
Using competitive protein adsorption to measure fibrinogen in undiluted human serum
Authors: Choi Seokheun , Wang Ran , Lajevardi-Khosh Arad , Chae Junseok
Published: December 2010

We report a unique sensing mechanism based on competitive protein adsorption to measure fibrinogen, a cardiovascular biomarker, in undiluted human serum. The method uses physical adsorption of proteins to a surface rather than complex and time-consuming immobilization procedures. Two fibrinogen concentrations were differentiated in spiked in human serum [3.0 mg/ml (normal concentration) versus 3.2 mg/ml (abnormal concentration with heart disease)]. Real-time surface plasmon resonance signals were monitored as fibrinogen displaced a preadsorbed protein, IgM, on a hydrophobic gold surface. The relatively strong-affinity protein, IgM, was displaced primarily by fibrinogen and much less by other proteins in human serum.
Adsorption geometry of individual fullerene on Si surface at room-temperature
Authors: Du Xinli , Chen Feng , Chen Xiu , Wu Xianxin , Cai Yingxiang , Liu Xiaoqing , Wang Li
Published: December 2010

The adsorption properties of individual fullerene molecules at room-temperature have been investigated by scanning tunneling microscopy. Statistical analysis of the images demonstrates that fullerene molecules prefer to adsorb on five specific sites: corner hole, the middle of the faulted and unfaulted parts, and the top of the rest atoms within the faulted and unfaulted parts. High-resolution images of individual fullerene molecules on each of the adsorption sites show distinct intramolecular structures. By combining these internal fine structures with theoretical simulations, the molecular orientations at each of the adsorption sites can be unambiguously determined.
Highly temperature insensitive quantum cascade lasers
Authors: Bai Y. , Bandyopadhyay N. , Tsao S. , Selcuk E. , Slivken S. , Razeghi M.
Published: December 2010

An InP based quantum cascade laser (QCL) heterostructure emitting around 5 μm is grown with gas-source molecular beam epitaxy. The QCL core design takes a shallow-well approach to maximize the characteristic temperatures, T0 and T1, for operations above room temperature. A T0 value of 383 K and a T1 value of 645 K are obtained within a temperature range of 298–373 K. In room temperature continuous wave operation, this design gives a single facet output power of 3 W and a wall plug efficiency of 16% from a device with a cavity length of 5 mm and a ridge width of 8 μm.
Organic-inorganic magnetic tunnel heterojunctions based on dithiapyrannylidene ultrathin films grown on Fe3O4(111)
Authors: Berny Stéphane , Tortech Ludovic , Fichou Denis , Matzen Sylvia , Moussy Jean-Baptiste
Published: December 2010

We report on the morphology, transport, and magnetic properties of ultrathin films of 4,4′-bis(diphenyl-2,6-thiapyrannylidene) (DITPY-Ph4), a planar quinoïd organic compound with potential applications in electronics. Atomic force microscopy (AFM) shows that highly homogeneous and continuous DITPY-Ph4 ultrathin films with thicknesses as low as 2 nm can be grown on epitaxial Fe3O4(111). Current-sensing AFM performed on ultrathin layers evidences an insulating behavior with a nonresonant tunneling conduction regime. Vibrating sample magnetometry achieved on Fe3O4/DITPY-Ph4/Co organic-inorganic heterojunctions reveals the decoupling between the two magnetic electrodes and demonstrates that DITPY-Ph4 can be used to build magnetic tunnel junctions.
The atomic structure and polarization of strained SrTiO3/Si
Authors: Kumah D. P. , Reiner J. W. , Segal Y. , Kolpak A. M. , Zhang Z. , Su D. , Zhu Y. , Sawicki M. S. , Broadbridge C. C. , Ahn C. H. , Walker F. J.
Published: December 2010

For thin film devices based on coupling ferroelectric polarization to charge carriers in semiconductors, the role of the interface is critical. To elucidate this role, we use synchrotron x-ray diffraction to determine the interface structure of epitaxial SrTiO3 grown on the (001) surface of Si. The average displacement of the O octahedral sublattice relative to the Sr sublattice determines the film polarization and is measured to be about 0.05 nm toward the Si, with Ti off-center displacements 0.009 nm away from the substrate. Measurements of films with different boundary conditions on the top of the SrTiO3 show that the polarization at the SrTiO3/Si interface is dominated by oxide-Si chemical interactions.
Multigenic System Controlling Viral Systemic Infection Determined by the Interactions Between Cucumber mosaic virus Genes and Quantitative Trait Loci of Soybean Cultivars
Authors: Ohnishi Shizen , Echizenya Issei , Yoshimoto Eri , Boumin Kim , Inukai Tsuyoshi , Masuta Chikara
Published: December 2010

Soybean ‘Harosoy’ is resistant to Cucumber mosaic virus soybean strain C (CMV-SC) and susceptible to CMV-S strain D (CMV-SD). Using enzyme-linked immunosorbent assay and Northern hybridization, we characterized the Harosoy resistance and found that CMV-SC did not spread systemically but was restricted to the inoculated leaves in Harosoy. Harosoy resistance was not controlled by either a dominant or recessive single gene. To dissect this system controlling long-distance movement of CMV in soybean, we constructed infectious cDNA clones of CMV-SC and CMV-SD. Using these constructs and the chimeric RNAs, we demonstrated that two viral components were required for systemic infection by the virus. The region including the entire 2b gene and the 5′ region of RNA3 (mainly the 5′ untranslated region) together were required. By quantitative trait locus (QTL) analysis using an F2 population and the F3 families derived from Harosoy and susceptible ‘Nemashirazu’, we also showed that at least three QTLs affected systemic infection of CMV in soybean. Our study on Harosoy resistance to CMV-SC revealed an interesting mechanism, in which multiple host and viral genes coordinately controlled viral systemic infection.
A hermeneutic interpretation of a controlled laboratory experiment: a case study of decision‐making with a group support system
Authors: Lee Allen S. , Dennis Alan R.
Published: December 2010

We conduct a case study of a laboratory experiment involving a group support system and explain how it went awry. We take the perspectives of the experiment's human subjects and the researchers themselves as the basis on which to interpret what happened in the experiment. We interpret the researchers as imputing, to the human subjects, the ‘conduit model’ of communication and the ‘calculator model’ of human information processing, which together constitute an instance of Ricoeur's hermeneutic ‘world behind the text’. We interpret the human subjects as importing, into the laboratory, their socially constructed world of personal friends, their histories and even their popular culture – a world that is an instance of Ricoeur's hermeneutic ‘world in front of the text’. We explain the experiment's going awry as following from the researchers' not accounting for, much less being aware of, the disparity between the two worlds. In taking the human subjects and the researchers seriously as human beings, we make recommendations about how such experiments might be better conducted, particularly in information systems research.
Classification of patients by severity grades during triage in the emergency department using data mining methods
Authors: Zmiri Dror , Shahar Yuval , Taieb‐Maimon Meirav
Published: December 2010

Objective  To test the feasibility of classifying emergency department patients into severity grades using data mining methods.

Design  Emergency department records of 402 patients were classified into five severity grades by two expert physicians. The Naïve Bayes and C4.5 algorithms were applied to produce classifiers from patient data into severity grades. The classifiers' results over several subsets of the data were compared with the physicians' assessments, with a random classifier, and with a classifier that selects the maximal‐prevalence class.

Measurements  Positive predictive value, multiple‐class extensions of sensitivity and specificity combinations, and entropy change.

Results  The mean accuracy of the data mining classifiers was 52.94 ± 5.89%, significantly better (P < 0.05) than the mean accuracy of a random classifier (34.60 ± 2.40%). The entropy of the input data sets was reduced through classification by a mean of 10.1%. Allowing for classification deviations of one severity grade led to mean accuracy of 85.42 ± 1.42%. The classifiers' accuracy in that case was similar to the physicians' consensus rate. Learning from consensus records led to better performance. Reducing the number of severity grades improved results in certain cases. The performance of the Naïve Bayes and C4.5 algorithms was similar; in unbalanced data sets, Naïve Bayes performed better.

Conclusions  It is possible to produce a computerized classification model for the severity grade of triage patients, using data mining methods. Learning from patient records regarding which there is a consensus of several physicians is preferable to learning from each physician's patients. Either Naïve Bayes or C4.5 can be used; Naïve Bayes is preferable for unbalanced data sets. An ambiguity in the intermediate severity grades seems to hamper both the physicians' agreement and the classifiers' accuracy.
Thermal ecology and behaviour of the nomadic social forager Malacosoma disstria
Authors: McCLURE MELANIE , CANNELL ELIZABETH , DESPLAND EMMA
Published: December 2010

The present study examines whether the nomadic social caterpillar Malacosoma disstria Hübner (Lepidoptera: Lasiocampidae) can thermoregulate despite the lack of a tent, and evaluates the role of thermoregulation in directing the colony's behaviour. The presence of a radiant heat and light source (i.e. a lamp in the laboratory experiments and the sun in the field observations) enables caterpillar colonies to increase body temperature by basking (remaining still under a heat source) and this is only effective when caterpillars cluster in groups. Body temperatures achieved when basking in a group coincide with the temperatures at which the development rate is maximal for this species. Indeed, in the laboratory experiments, the presence of a lamp results in higher growth rates, confirming that thermoregulation is an advantage to group living. When a radiant heat/light source is provided at a distance from the food in the laboratory, caterpillars behave to maximize thermal gains: colonies move away from the food to bivouac (i.e. group together and remain still on a silk mat) under the lamp, spend more time on the bivouac and cluster in a more cohesive group. Thermal needs thus influence habitat selection and colony aggregation. Malacosoma disstria relies on developing rapidly, despite low seasonal temperatures, aiming to benefit from springtime high food quality and low predation rates; however, unlike others in its genus, it does not build a tent but instead exhibits collective nomadic foraging (i.e. the whole colony moves together between temporary resting and feeding sites). In this species, collective thermoregulatory behaviour is not only possible and advantageous, but also drives much of the colony's behaviour, in large part dictating the temporal and spatial patterns of movement. These findings suggest that thermoregulation may be an important selection pressure keeping colonies together.