bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and fabrication of a superconducting magnet for an 18 GHz electron cyclotron resonance ion/photon source NFRI-ECRIPS
Authors: You H.-J. , Jang S.-W. , Jung Y.-H. , Lho T.-H. , Lee S.-J.
Published: February 2012

A superconducting magnet was designed and fabricated for an 18 GHz ECR ion/photon source, which will be installed at National Fusion Research Institute (NFRI) in South Korea. The magnetic system consists of a set of four superconducting coils for axial mirror field and 36 pieces of permanent magnets for hexapolar field. The superconducting coils with a cryocooler (1.5 W @ 4.2 K) allow one to reach peak mirror fields of 2.2 T in the injection and those of 1.5 T in the extraction regions on the source axis, and the resultant hexapolar field gives 1.35 T on the plasma chamber wall. The unbalanced magnetic force between the coils and surrounding yoke has been minimized to 16 ton by a coil arrangement and their electrical connection, and then was successfully suspended by 12 strong thermal insulating supports made of large numbers of carbon fibers. In order to block radiative thermal losses, multilayer thermal insulations are covered on the coil windings as well as 40-K aluminum thermal shield. Also new schemes of quench detection and safety system (coil divisions, quench detection coils, and heaters) were employed. For impregnation of the windings a special epoxy has been selected and treated to have a higher breaking strength and a higher thermal conductivity, which enables the superconductors to be uniformly and rapidly cooled down or heated during a quench.
Improvement of efficiency and temperature control of induction heating vapor source on electron cyclotron resonance ion source
Authors: Takenaka T. , Kiriyama R. , Muramatsu M. , Kitagawa A. , Uchida T. , Kurisu Y. , Nozaki D. , Yano K. , Yoshida Y. , Sato F. , Kato Y. , Iida T.
Published: February 2012

An electron cyclotron resonance ion source (ECRIS) is used to generate multicharged ions for many kinds of the fields. We have developed an evaporator by using induction heating method that can generate pure vapor from solid state materials in ECRIS. We develop the new matching and protecting circuit by which we can precisely control the temperature of the induction heating evaporator. We can control the temperature within ±15 °C around 1400 °C under the operation pressure about 10−4 Pa. We are able to use this evaporator for experiment of synthesizing process to need pure vapor under enough low pressure, e.g., experiment of generation of endohedral Fe-fullerene at the ECRIS.
A close-coupling multi-antenna type radio frequency driven ion source
Authors: Oka Y. , Shoji T.
Published: February 2012

A newly close coupling multi-antenna type radio frequency driven ion source is tested for the purpose of essentially improving plasma coupling on the basis of our old type ion source, which reuses a NNBI (negative ion source for neutral beam injection) ion source used in 1/5th scale of the Large Helical Device NNBI. The ion source and the antenna structure are described, and the efficient plasma production in terms of the positive ion saturation current (the current density) is studied. The source is made of a metal-walled plasma chamber which is desirable from the point of view of the structural toughness for fusion and industrial application, etc. At around 160 kW of rf input power, the ion saturation current density successfully reaches the 5 A/cm2 level with a gas pressure of 0.6–2 Pa in hydrogen for 10 ms pulse duration. The rf power efficiency of the plasma production with a close coupling configuration of the antenna is improved substantially compared to that with the previous antenna unit in the old type ion source. The power efficiency is assessed as competing with that of other types of sources.
Concepts for the magnetic design of the MITICA neutral beam test facility ion accelerator
Authors: Chitarin G. , Agostinetti P. , Marconato N. , Marcuzzi D. , Sartori E. , Serianni G. , Sonato P.
Published: February 2012

The megavolt ITER injector concept advancement neutral injector test facility will be constituted by a RF-driven negative ion source and by an electrostatic Accelerator, designed to produce a negative Ion with a specific energy up to 1 MeV. The beam is then neutralized in order to obtain a focused 17 MW neutral beam. The magnetic configuration inside the accelerator is of crucial importance for the achievement of a good beam efficiency, with the early deflection of the co-extracted and stripped electrons, and also of the required beam optic quality, with the correction of undesired ion beamlet deflections. Several alternative magnetic design concepts have been considered, comparing in detail the magnetic and beam optics simulation results, evidencing the advantages and drawbacks of each solution both from the physics and engineering point of view.
A 2.45 GHz electron cyclotron resonance proton ion source and a dual-lens low energy beam transport
Authors: Zhang W. H. , Ma H. Y. , Yang Y. , Wu Q. , Zhang X. Z. , Wang H. , Ma B. H. , Feng Y. C. , Fang X. , Guo J. W. , Cao Y. , Li X. X. , Zhu Y. H. , Li J. Y. , Sha S. , Lu W. , Lin S. H. , Guo X. H. , Zhao H. Y. , Sun L. T. , Xie D. Z. , Peng S. X. , Liu Z. W. , Zhao H. W.
Published: February 2012

The structure and preliminary commissioning results of a new 2.45 GHz ECR proton ion source and a dual-lens low energy beam transport (LEBT) system are presented in this paper. The main magnetic field of the ion source is provided by a set of permanent magnets with two small electro-solenoid magnets at the injection and the extraction to fine tune the magnetic field for better microwave coupling. A 50 keV pulsed proton beam extracted by a three-electrode mechanism passes through the LEBT system of length of 1183 mm. This LEBT consists of a diagnosis chamber, two Glaser lenses, two steering magnets, and a final beam defining cone. A set of inner permanent magnetic rings is embedded in each of the two Glaser lenses to produce a flatter axial-field to reduce the lens aberrations.
Sheath structure in negative ion sources for fusion (invited)
Authors: McAdams R. , King D. B. , Holmes A. J. T. , Surrey E.
Published: February 2012

In fusion negative ion sources, the negative ions are formed on the caesiated plasma grid predominantly by hydrogen atoms from the plasma. The space charge of the negative ions leaving the wall is not fully compensated by incoming positive ions and at high enough emission a virtual cathode is formed. This virtual cathode limits the flux of negative ions transported across the sheath to the plasma. A 1D collisionless model of the sheath is presented taking into account the virtual cathode. The model will be applied to examples of the ion source operation. Extension of the model to the bulk plasma shows good agreement with experimental data. A possible role for fast ions is discussed.
Nanostructure operations by means of the liquid metal ion sources
Authors: Gasanov I. S. , Gurbanov I. I.
Published: February 2012

Characteristics of a disperse phase of liquid metal ion source on the basis of various working substances are investigated. It is revealed that generation of the charged particles occurs in the threshold image and is simultaneously accompanied by excitation of capillary instability on a surface of the emitter. The majority of particles has the size about 2 nm (Sn) and a specific charge of 5 × 104 C/kg. If the working liquid possesses high viscosity (Ni), generation of nanodroplets does not occur. Gold nanoparticles are used for deposition on a surface of quartz cantilevers with the purpose of increase in sensitivity of biosensors and on an external surface of carbon nanotubes for creation pressure sensors. By means of an ion source nanostructures can be etched on a flat surface of conductive materials without difficult ion optics.
Study of space charge compensation phenomena in charged particle beams
Authors: Veltri P. , Cavenago M. , Serianni G.
Published: February 2012

The propagation of a charged particle beam is accompanied by the production of secondary particles created in the interaction of the beam itself with the background gas flowing in the accelerator tube. In the drift region, where the electric field of the electrodes is negligible, secondary particles may accumulate giving a plasma which shields the self-induced potential of the charged beam. This phenomenon, known as space charge compensation is a typical issue in accelerator physics, where it is usually addressed by means of 1D radial transport codes or Monte Carlo codes. The present paper describes some theoretical studies on this phenomenon, presenting a Particle in Cell-Monte Carlo (PIC-MC) Code developed ad hoc where both radial and axial confinements of secondary particles are calculated. The features of the model, offering a new insight on the problem, are described and some results discussed.
Volume exchange in soft FeCo films of high magnetization
Authors: Mathieu Christoph , Liu Hau-Jian , Buchanan Kristen S. , Inturi Venkateswara R.
Published: February 2012

Soft FeCo films of high magnetization are a well known integral part of today’s magnetic recording heads. Values for the volume exchange, an important parameter since it determines exchange length, domain wall width, and energy are, however, available for few compositions of FeCo in spite of the widespread use of these alloys. This paper presents results for volume exchange on Fe65Co35 determined by means of a detailed Brillouin light scattering study, one of a few methods that permit the measurement of exchange. A set of Fe65Co35 films of various thickness values was examined, and volume exchange was found to be 3.5 × 10–6 erg/cm, far higher than what is often assumed.
Investigation of easy axis orientation of Nd–Fe–B melt-spun ribbons produced by hot rolling and influence of Ti–C addition
Authors: Takezawa M. , Nakanishi Y. , Morimoto Y. , Yamasaki J. , Yagi M.
Published: February 2012

The c-axis orientation of Nd–Fe–B melt-spun ribbons caused by hot rolling and the influence of Ti–C addition were investigated. A small roll was placed on a steel wheel near a quartz tube in such a manner that the melt-spun ribbons were hot rolled immediately after quenching. X-ray diffraction patterns measured on both surfaces of the Nd–Fe–B–Ti ribbon indicate that the c-axis is oriented normal to the ribbon plane. The domain pattern of the Nd–Fe–B–Ti–C ribbon was observed with a Kerr microscope. Most of the grains exhibit a maze domain configuration, indicating that the c-axis is oriented normal to the ribbon plane. Furthermore, it was demonstrated that hot rolling and the addition of Ti–C promote c-axis orientation and high coercivity of Nd–Fe–B melt-spun ribbons.
Bulk nanocomposite using self-forming core/shell nanoparticles and its magnetic properties for high-frequency applications
Authors: Suetsuna Tomohiro , Harada Koichi , Takahashi Toshihide , Suenaga Seiichi
Published: February 2012

A bulk nanocomposite composed of tightly packed self-forming core/shell nanoparticles of metal/oxide was fabricated. The crystalline grain size of the nanoparticles, the packing ratio, and the composition were controlled in the nanocomposite, and their effects on the magnetic properties were investigated. The crystalline grain size of the nanoparticles, the packing ratio, and the composition strongly influenced the magnetic anisotropy field, magnetic coercivity, relative permeability, and loss factor at GHz bands. High permeability with a low loss factor of less than 1.5% at up to 1 GHz was obtained in the nanocomposite in which the nanoparticles with a crystalline grain size of approximately 15 nm were tightly packed.
Controlling the core-to-core distance of vortex pairs in exchange-biased iron elliptical nanoelements
Authors: Oliveira Felipe F. , Moura Thiago R. S. , Carriço A. S. , Dantas Ana L. , Rebouças G. O. G.
Published: February 2012

We report a theoretical study of vortex pairs in exchange-biased elliptical iron nanoelements. We show that the remanent state may be tailored to fit vortex pairs with opposite chiralities separated by a diamond-like domain. Flat nanoelements with lateral dimensions ranging from 115 nm × 425 nm to 195 nm × 425 nm have the core-to-core distance tunable by the interface field strength.
E-field tuning microwave frequency performance of Co2FeSi/lead zinc niobate–lead titanate magnetoelectric coupling composites
Authors: Li Shandong , Liu Ming , Lou J. , Beguhn Shawn , Wu Jianpeng , Qiu Jie , Lin Jianhua , Cai Zhiyi , Hu Yi , Xu Feng , Duh Jenq-Gong , Sun Nian X.
Published: February 2012

Nanocrystalline Co2FeSi Heusler alloy films were deposited on single crystal lead zinc niobate–lead titanate substrates. It is revealed that this multiferroic composite exhibits very strong continuously electric field (E-field) tunable microwave frequency characteristics. With an increase of the E-field intensity from 0 to 6 kV/cm, the ferromagnetic resonance field Hr shifts by 348 Oe along the easy axis direction, being equivalent to 58 Oe cm/kV, and the ferromagnetic resonance frequency fFMR dramatically increases from 2.2 to 6.1 GHz with an increment of 3.9 GHz or an increment ratio of 177%; moreover, the damping constant α decreases from 0.0150 to 0.0085. These features demonstrate that this multiferroic structure is promising in the fabrication of E-field tunable microwave components.
Effect of deviation from stoichiometric composition on structural and magnetic properties of cobalt ferrite, CoxFe3−xO4 (x = 0.2 to 1.0)
Authors: Nlebedim I. C. , Snyder J. E. , Moses A. J. , Jiles D. C.
Published: February 2012

The effects of deviation from stoichiometric composition on the structural and magnetic properties of cobalt ferrite, CoxFe3−xO4 (x = 0.2 to 1.0), are presented. Both CoFe2O4 and Fe3O4 have a spinel crystal structure, and it might be expected that intermediate compositions would have the same structure. However, results show that synthesis via the ceramic method leads to the development of a secondary α-Fe2O3 phase. Both structural and magnetic properties are altered depending on the concentration of the α-Fe2O3 phase. Saturation magnetization is at a maximum for the stoichiometric composition (i.e., x = 1.0) and thereafter decreases with x. In attempts to achieve the properties required for application, the ceramic method offers the ability to selectively adjust the concentrations of both CoFe2O4 and α-Fe2O3 phases.
Spin-flip effect on transport properties of a Mn3 molecule
Authors: Hao Hua , Zheng XiaoHong , Wang RuiNing , Zeng Zhi , Lin H. Q.
Published: February 2012

Electron transport through a single-molecule magnet [NEt4]3[Mn3Zn2(salox)3O(N3)6Cl2] is investigated by spin-polarized density functional theory combined with the Keldysh nonequilibrium Green’s function technique. Our study demonstrates that spin-filtering effect and negative differential resistance exist in the ground state of this molecule. When the magnetic state of the molecule is changed from its ground state to the spin-flip state, substantial changes are induced not only in energy levels of the molecule, but also in the coupling of molecular states with eigenstates of Ag(100) nano-electrodes, which lead to the disappearance of spin-filtering effect and negative differential resistance.
Magnetocaloric materials with first-order phase transition: thermal and magnetic hysteresis in LaFe11.8Si1.2 and Ni2.21Mn0.77Ga1.02 (invited)
Authors: Skokov K. P. , Khovaylo V. V. , Müller K.-H. , Moore J. D. , Liu J. , Gutfleisch O.
Published: February 2012

This is a report on a comparative study of thermal and magnetic hysteresis in LaFe11.8Si1.2 and Ni2.21Mn0.77Ga1.02 polycrystalline samples near their first-order phase transitions by measurements of magnetization and direct measurements of the adiabatic temperature change, ΔTad(H). Based on the obtained M(T) and M(H) dependencies, H-T diagrams were constructed for both alloys and used to explain the ΔTad(H) dependencies. For low thermal hysteresis and a sharp transition in the temperature dependence of magnetization (LaFe11.8Si1.2), the field dependencies of ΔTad(H) are governed by the phase boundary between ferromagnetic and paramagnetic states. For large thermal hysteresis and a broad transition width in temperature (Ni2.21Mn0.77Ga1.02), the phase boundary has little impact on ΔTad(H). It is also shown that, in the phase transition region, ΔTad measured upon the first application of magnetic field (virgin ΔTad(H) leg) can differ from that measured upon subsequent runs of the field. This can lead to an overestimation of the magnetocaloric effect, if only the virgin leg of ΔTad(H) is considered.
Enhanced magnetic and electrical properties in amorphous Ge:Mn thin films by non-magnetic codoping
Authors: Yin Wenjing , Kell Copeland D. , He Li , Dolph Melissa C. , Duska Chris , Lu Jiwei , Hull Robert , Floro Jerrold A. , Wolf Stuart A.
Published: February 2012

Amorphous Ge1−xMnx thin films have been prepared by co-depositing Ge and Mn on SiO2/Si using an ultrahigh vacuum molecular beam epitaxy system. Across a range of growth temperatures and Mn concentrations (2.8 at. %, 10.9 at. %, and 21.3 at. %), we achieved enhanced magnetic and electrical properties with non-magnetic codopants dispersed in the films. Self-assembled Mn-rich amorphous nanostructures were observed in the amorphous Ge matrix, either as isolated nanoclusters or as nanocolumns, depending on Mn concentration. The ferromagnetic saturation moments were found to increase with Mn concentration and reached a maximum of 0.7 μB/Mn in the as-grown samples. Two magnetic transition temperatures around 15 K and 200 K were observed in these amorphous MBE-grown samples. Coercivity is considered within the context of local magnetic anisotropy. The anomalous Hall effect confirmed a strong correlation between the magnetization and transport properties, indicating that global ferromagnetic coupling was carrier-mediated rather than through direct exchange. In addition, negative magnetoresistance was detected from 5 K to room temperature.
Absorption by DNA single strands of adenine isolated in vacuo: The role of multiple chromophores
Authors: Nielsen Lisbeth Munksgaard , Pedersen Sara Øvad , Kirketerp Maj-Britt Suhr , Nielsen Steen Brøndsted
Published: February 2012

The degree of electronic coupling between DNA bases is a topic being up for much debate. Here we report on the intrinsic electronic properties of isolated DNA strands in vacuo free of solvent, which is a good starting point for high-level excited states calculations. Action spectra of DNA single strands of adenine reveal sign of exciton coupling between stacked bases from blueshifted absorption bands (∼3 nm) relative to that of the dAMP mononucleotide (one adenine base). The bands are blueshifted by about 10 nm compared to those of solvated strands, which is a shift similar to that for the adenine molecule and the dAMP mononucleotide. Desolvation has little effect on the bandwidth, which implies that inhomogenous broadening of the absorption bands in aqueous solution is of minor importance compared to, e.g., conformational disorder. Finally, at high photon energies, internal conversion competes with electron detachment since dissociation of the bare photoexcited ions on the microsecond time scale is measured.
Charge density waves condensate as measure of charge order and disorder in Eu1-xSrxMnO3 (x = 0.50, 0.58) manganites
Authors: Pandey Parul , Awari Nilesh , Rana Rakesh , Singh Abhishek , Prabhu S. S. , Rana D. S.
Published: February 2012

We have explored the low-energy excitations in epitaxial thin films of Eu1-xSrxMnO3 [x = 0.50: spin-glass with short range charge-order and x = 0.58: long range charge-order] using terahertz time-domain spectroscopy. A finite frequency peak structure in optical conductivity is observed at ∼3.5 meV for both the films. While peak structure of x = 0.58 film possesses distinct properties of low-energy collective excitations of charge-density waves, the same is subtle and shallower with weaker peak conductivity for x = 0.50 film. These data, corroborated by magnetization, provide unambiguous evidence of the effect of range of charge-ordering, pinning, and disorder (induced by spin-glass state) on the manifestation of charge-density waves.
Fluctuation-induced conductivity analyses of Be-doped (Bi0.25Cu0.25Li0.25Tl0.25)Ba2Ca2Cu3O10-δ superconductors in the critical regime and beyond
Authors: Khan Nawazish A. , Qurat-ul-Ain  , Firdous Umber , Shaheryar
Published: February 2012

We have successfully synthesized (Bi0.25Cu0.25Li0.25Tl0.25)Ba2Ca2Cu3O10−δ and (Bi0.25Cu0.25Li0.25Tl0.25)Ba2(Ca1.5Be0.5)Cu3O10−δ samples and studied their excess conductivity analyses (fluctuation-induced conductivity) of resistivity data. The main objective of such analyses is to investigate the influence of Be-substitution on the superconductivity parameters at the microscopic level. The width of the 3D-2D Lawrence-Doniach regime is increased with the doping of Be at the Ca sites. The energy required to break apart the Cooper pairs is increased from 0.03 eV to 0.08 eV in Be-doped samples. Using the Ginzburg-Landau number (NG) and GL equations, the thermodynamic critical magnetic field Bc(0), the lower critical field Bc1(0), the upper critical field Bc2(0), the critical current density Jc(0), and penetration depth λp.d are also calculated from these analyses. The values of critical fields [Bc(0) Bc1(0)], Jc(0), and phase relaxation time τϕ are increased whereas the penetration depth λp.d and κ values are suppressed with Be-doping. It is most likely that as a result of the enhancement in the density of the carriers in the (Bi0.25Cu0.25Li0.25Tl0.25)Ba2(Ca1.5Be0.5)Cu3O10−δ sample, this charge density gap is suppressed, which in turn suppresses the pseudo-gap resulting into enhancement of Bc (0), Bc1(0), and Jc(0).
InAs/InAsSb strain balanced superlattices for optical detectors: Material properties and energy band simulations
Authors: Lackner D. , Steger M. , Thewalt M. L. W. , Pitts O. J. , Cherng Y. T. , Watkins S. P. , Plis E. , Krishna S.
Published: February 2012

InAsSb/InAs type II strain balanced superlattices lattice matched to GaSb have recently been proposed as an alternative to InAs/(In)GaSb short period superlattices for mid- to long infrared photodetectors. Photoluminescence data at 4 K of OMVPE grown InAsSb (multi-) quantum wells in an InAs matrix on InAs and GaSb substrates is presented for Sb compositions between 4% and 27%. The measured transition energies are simulated with a self-consistent Poisson and Schroedinger equation solver that includes strain and band-offsets. The fitted parameters are then used to predict the type II transition energies of InAsSb/InAs strain balanced superlattice absorber stacks at 77 K for different compositions and periods. The optical matrix element was calculated and compared with InAs/(In)GaSb superlattices. The InAsSb/InAs structures can be designed with higher or equal matrix elements for longer periods. Finally, the initial optical response data of an unoptimized strain balanced InAs0.79Sb0.21/InAs detector with a 40 nm period are shown. Its cutoff wavelength is 0.15 eV (8.5 μm), in good agreement with the predicted type II transition energy of 0.17 eV.
On the energy distribution of interface states and their relaxation time profiles in Al/pentacene/p-GaAs heterojunction diode
Authors: Şafak Yasemin , Soylu Murat , Yakuphanoğlu Fahrettin , Altındal Şemsettin
Published: February 2012

The energy density distribution profile of the interface states (Nss) and their relaxation time (τ) of Al/pentacene/p-GaAs heterojunction diodes were obtained from the admittance spectroscopy method, which is included in capacitance/conductance-voltage measurements in the frequency range of 10 kHz-1 MHz at room temperature. The values of Nss were also obtained from the forward bias current-voltage measurements by taking into account voltage-dependent barrier height, and the results were compared with those obtained using admittance method. The values of Nss and τ obtained from admittance measurements range from 1.53 × 1011 eV–1 cm–2 and 1.33 µs in (0.596-Ev) eV to 1.90 × 1011 eV–1 cm–2 and 8.18 µs in (0.673-Ev) eV, respectively. In addition, the values of Nss were obtained using Hill-Coleman method as a function of frequency. The values of Nss obtained from these three methods are in the same order and in good agreement with one another. Low values of Nss can be attributed to the interfacial pentacene layer between metal and semiconductor. This magnitude of Nss is very suitable for the fabrication of electronic devices. The C values of these diodes decrease with increasing frequency both in inversion and depletion regions, but give a peak in the accumulation region due to the effect of series resistance. The increase in C, especially at low frequencies, results from the presence of interface states at GaAs/pentacene interface.
Tracer-encapsulated solid pellet injection system
Authors: Sudo Shigeru , Tamura Naoki
Published: February 2012

The method of tracer-encapsulated solid pellet (TESPEL) is now flourishing in various fields. The original purpose to study impurity transport without giving substantial perturbation on the plasma is implemented successfully for years. In addition to this, TESPEL is being intensively applied to study thermal (especially non-local) transport, high energy particles with the use of TESPEL ablation cloud, and spectroscopy from the viewpoint of atomic data. It is now further growing up to the utilization of multiple tracer methods which was not planned at the initial phase of the project. The proof-of-principle experiment using triple tracers has been successfully implemented. This opens a way to compare the Z dependence or mass dependence of impurity transport. In this article, as TESPEL is used in a variety of fields, the TESPEL injection system is summarized together with the method of TESPEL production, TESPEL storage disk, TESPEL guide system, and the differential pumping system. Also, the observation system for TESPEL flight and TESPEL ablation is explained.
The coincidence limit of the graviton propagator in de Donder gauge on de Sitter background
Authors: Kahya E. O. , Miao S. P. , Woodard R. P.
Published: February 2012

We explicitly work out the de Sitter breaking contributions to the recent solution for the de Donder gauge graviton propagator on de Sitter. We also provide explicit power series expansions for the two structure functions, which are suitable for implementing dimensional regularization. And we evaluate the coincidence limit of the propagator.
Calculations of nonlinear response properties using the intermediate state representation and the algebraic-diagrammatic construction polarization propagator approach: Two-photon absorption spectra
Authors: Knippenberg S. , Rehn D. R. , Wormit M. , Starcke J. H. , Rusakova I. L. , Trofimov A. B. , Dreuw A.
Published: February 2012

An earlier proposed approach to molecular response functions based on the intermediate state representation (ISR) of polarization propagator and algebraic-diagrammatic construction (ADC) approximations is for the first time employed for calculations of nonlinear response properties. The two-photon absorption (TPA) spectra are considered. The hierarchy of the first- and second-order ADC/ISR computational schemes, ADC(1), ADC(2), ADC(2)-x, and ADC(3/2), is tested in applications to H2O, HF, and C2H4 (ethylene). The calculated TPA spectra are compared with the results of coupled cluster (CC) models and time-dependent density-functional theory (TDDFT) calculations, using the results of the CC3 model as benchmarks. As a more realistic example, the TPA spectrum of C8H10 (octatetraene) is calculated using the ADC(2)-x and ADC(2) methods. The results are compared with the results of TDDFT method and earlier calculations, as well as to the available experimental data. A prominent feature of octatetraene and other polyene molecules is the existence of low-lying excited states with increased double excitation character. We demonstrate that the two-photon absorption involving such states can be adequately studied using the ADC(2)-x scheme, explicitly accounting for interaction of doubly excited configurations. Observed peaks in the experimental TPA spectrum of octatetraene are assigned based on our calculations.
Local structural models of complex oxygen- and hydroxyl-rich GaP/InP(001) surfaces
Authors: Wood Brandon C. , Ogitsu Tadashi , Schwegler Eric
Published: February 2012

We perform density-functional theory calculations on model surfaces to investigate the interplay between the morphology, electronic structure, and chemistry of oxygen- and hydroxyl-rich surfaces of InP(001) and GaP(001). Four dominant local oxygen topologies are identified based on the coordination environment: M–O–M and M–O–P bridges for the oxygen-decorated surface; and M–[OH]–M bridges and atop M–OH structures for the hydroxyl-decorated surface (M = In, Ga). Unique signatures in the electronic structure are linked to each of the bond topologies, defining a map to structural models that can be used to aid the interpretation of experimental probes of native oxide morphology. The M–O–M bridge can create a trap for hole carriers upon imposition of strain or chemical modification of the bonding environment of the M atoms, which may contribute to the observed photocorrosion of GaP/InP-based electrodes in photoelectrochemical cells. Our results suggest that a simplified model incorporating the dominant local bond topologies within an oxygen adlayer should reproduce the essential chemistry of complex oxygen-rich InP(001) or GaP(001) surfaces, representing a significant advantage from a modeling standpoint.
Strain analysis of a wrinkled SiGe bilayer thin film
Authors: Chang Guo-En , Chang Chia-Ou , Cheng H. H.
Published: February 2012

We report a strain analysis on a wrinkled semiconductor pattern formed by a p-doped bilayer thin film that is compressively strained. The strain distribution is studied with a theoretical analysis using a non-linear plate theory in conjunction with a detailed morphology measurement. The results show that the normal strain reduces continuously as the wrinkle amplitude increases, due to the stretching effect, and that the variation in the strain along the wrinkle edge is dominated by the bending effect, which agrees reasonably with the Raman measurement.
A new fabrication technique to form complex polymethylmethacrylate microchannel for bioseparation
Authors: Jubery Talukder Z. , Hossan Mohammad R. , Bottenus Danny R. , Ivory Cornelius F. , Dong Wenji , Dutta Prashanta
Published: February 2012

Recent studies show that reduction in cross-sectional area can be used to improve the concentration factor in microscale bioseparations. Due to simplicity in fabrication process, a step reduction in cross-sectional area is generally implemented in microchip to increase the concentration factor. But the sudden change in cross-sectional area can introduce significant band dispersion and distortion. This paper reports a new fabrication technique to form a gradual reduction in cross-sectional area in polymethylmethacrylate (PMMA) microchannel for both anionic and cationic isotachophoresis (ITP). The fabrication technique is based on hot embossing and surface modification assisted bonding method. Both one-dimensional and two-dimensional gradual reduction in cross-sectional area microchannels were formed on PMMA with high fidelity using proposed techniques. ITP experiments were conducted to separate and preconcentrate fluorescent proteins in these microchips. Thousand fold and ten thousand fold increase in concentrations were obtained when 10 × and 100 × gradual reduction in cross-sectional area microchannels were used for ITP.
Critical lines for an unequal size of molecules in a binary gas-liquid mixture around the van Laar point using the combination of the Tompa model and the van der Waals equation
Authors: Gençaslan Mustafa , Keskin Mustafa
Published: February 2012

We combine the modified Tompa model with the van der Waals equation to study critical lines for an unequal size of molecules in a binary gas-liquid mixture around the van Laar point. The van Laar point is coined by Meijer and it is the only point at which the mathematical double point curve is stable. It is the intersection of the tricritical point and the double critical end point. We calculate the critical lines as a function of x1 and x2, the density of type I molecules and the density of type II molecules for various values of the system parameters; hence the global phase diagrams are presented and discussed in the density-density plane. We also investigate the connectivity of critical lines at the van Laar point and its vicinity and discuss these connections according to the Scott and van Konynenburg classifications. It is also found that the critical lines and phase behavior are extremely sensitive to small modifications in the system parameters.
Formation of an extended CoSi2 thin nanohexagons array coherently buried in silicon single crystal
Authors: Kellermann Guinther , Montoro Luciano A. , Giovanetti Lisandro J. , dos Santos Claro Paula C. , Zhang Liang , Ramirez Antonio J. , Requejo Félix G. , Craievich Aldo F.
Published: February 2012

A Co-doped silica film was deposited on the surface of a Si(100) wafer and isothermally annealed at 750 °C to form spherical Co nanoparticles embedded in the silica film and a few atomic layer thick CoSi2 nanoplatelets within the wafer. The structure, morphology, and spatial orientation of the nanoplatelets were characterized. The experimental results indicate that the nanoplatelets exhibit hexagonal shape and a uniform thickness. The CoSi2 nanostructures lattice is coherent with the Si lattice, and each of them is parallel to one of the four planes belonging to the {111} crystallographic form of the host lattice.
Vortex-assisted figure-eight wing power system
Authors: Labrecque David , Wheeler Dan , Katsman Eugene
Published: February 2012

Due to the rising demand for low-cost clean energy, the development of efficient wind and water energy-generating systems is one of the major goals of this century. A novel approach for extracting energy efficiently from wind and water currents utilizes a tail-weighted wing following a figure-eight trajectory. Our prototype consists of a vertical ribbon-type wing suspended at its endpoints by swivel bearings. Energy is extracted from the longitudinal pumping motion that occurs at the endpoints of this flexing wing. Since the forces in these wings are in tension like a suspension bridge, the design can potentially be scaled up to much larger sizes than current systems and sweep across enormous areas of moving fluid with a relatively small amount of material. High-speed photography is used to map out the trajectory of a prototype wing and to monitor water flow around the wing. These observations along with data from an interactive computer simulation program are used to study the vortices and hydrodynamic forces that propel the wing along the figure-eight trajectory. Our prototype is low-cost, simple to fabricate and extracts a high amount, 30%, of the total energy in the water that flows through it.
Thermal behavior of encapsulated phase change material energy storage
Authors: Al-Kayiem Hussain H. , Alhamdo Mohammed H.
Published: February 2012

The performance of thermal solar systems can be enhanced by extending its operational time by the aid of thermal energy storage. In the present work, the transient behavior of packed bed thermal energy storage (TES) was investigated experimentally and numerically. An experimental setup was designed and fabricated to simulate the charging and discharging operational modes of the system. 101 spherical capsules were filled with wax paraffin as PCM and packed in cylindrical container bed of 105 mm diameter and 420 mm long. The processes of the experimented storage system were simulated mathematically and solved numerically by finite difference technique. The analyses were carried out at two different mass velocity of the working fluid. The numerical model described the transient behavior of the system and it was in acceptable agreement with the experimental results. The transient period in the charging mode of the tested storage was around 30 min, while the energy recovery period in the discharging mode was around 60 min. The achieved results demonstrated that the tested TES could be used to enhance the performance of the thermal solar systems. The proposed packed bed thermal energy storage is easy to implement with low cost.
Nonlinearity in the high-electric-field piezoelectricity of epitaxial BiFeO3 on SrTiO3
Authors: Chen Pice , Sichel-Tissot Rebecca J. , Young Jo Ji , Smith Ryan T. , Baek Seung-Hyub , Saenrang Wittawat , Eom Chang-Beom , Sakata Osami , Dufresne Eric M. , Evans Paul G.
Published: February 2012

The piezoelectricity of a multiferroic BiFeO3 thin film deviates from its low-field linear response in electric fields higher than 150 MV/m. Time-resolved synchrotron x-ray microdiffraction reveals a low-field piezoelectric coefficient of 55 pm/V and a steeper increase in strain at higher fields, with an effective piezoelectric coefficient of 86 pm/V. The strain reaches 2% at 281 MV/m, a factor of 1.3 higher than expected based on an extrapolation from low fields. The peak intensity of the BiFeO3 (002) Bragg reflection decreases throughout the high-electric-field regime, accompanied by increased diffuse scattering, consistent with lattice softening lattice near a field-induced phase transition.
Enhanced spontaneous emission from quantum dots in short photonic crystal waveguides
Authors: Ba Hoang Thang , Beetz Johannes , Midolo Leonardo , Skacel Matthias , Lermer Matthias , Kamp Martin , Höfling Sven , Balet Laurent , Chauvin Nicolas , Fiore Andrea
Published: February 2012

We report a study of the quantum dot (QD) emission in short photonic crystal waveguides. We observe that the quantum dot photoluminescence intensity and decay rate are strongly enhanced when the emission energy is in resonance with Fabry-Perot (FP) cavity modes in the slow-light regime of the dispersion curve. The experimental results are in agreement with previous theoretical predictions and are further supported by three-dimensional finite element simulations. Our results show that the combination of slow group velocity and Fabry-Perot cavity resonance provide an avenue to efficiently channel photons from quantum dots into waveguides for integrated quantum photonic applications.
Resonantly enhanced optical nonlinearity in hybrid semiconductor quantum dot – metal nanoparticle structures
Authors: Fu Ming , Wang Kai , Long Hua , Yang Guang , Lu Peixiang , Hetsch Frederik , Susha Andrei S. , Rogach Andrey L.
Published: February 2012

The optical nonlinearity of hybrid structures composed of CdTe quantum dots and periodical particle array of gold is studied using Z-scan method. The optical nonlinearity is dramatically affected by the interaction between exciton in CdTe quantum dots and surface plasmons in Au periodical particle array. When the Au surface plasmon is tuned to be in resonance with the exciton transition in CdTe quantum dots, the largest nonlinear refractive index and the smallest two-photon absorption coefficient, n2 = −0.53 cm2/GW and β = 25 cm/GW, which are about 8 times larger and 50 times smaller than that of bare CdTe quantum dots, can be achieved.
Suppression of microwave rectification effects in electrically detected magnetic resonance measurements
Authors: Lo C. C. , Bradbury F. R. , Tyryshkin A. M. , Weis C. D. , Bokor J. , Schenkel T. , Lyon S. A.
Published: February 2012

Spin-dependent transport properties of micro- and nano-scale electronic devices are commonly studied by electrically detected magnetic resonance (EDMR). However, the applied microwave fields in EDMR experiments can induce large rectification effects and result in perturbations of the device bias conditions and excessive noise in the EDMR spectra. Here we examine rectification effects of silicon metal-oxide-semiconductor field-effect transistors exposed to X-band microwave irradiation and show that the rectification effects can be effectively suppressed by incorporating a global capacitive shunt covering the device. We demonstrate that the signal-to-noise ratio in the EDMR spectra improves by over a factor of ten in the shunted devices.
Bloch surface waves-controlled fluorescence emission: Coupling into nanometer-sized polymeric waveguides
Authors: Ballarini Mirko , Frascella Francesca , Enrico Emanuele , Mandracci Pietro , De Leo Natascia , Michelotti Francesco , Giorgis Fabrizio , Descrovi Emiliano
Published: February 2012

The lateral confinement of Bloch surface waves on a patterned multilayer is investigated by means of leakage radiation microscopy (LRM). Arrays of nanometric polymeric waveguides are fabricated on a proper silicon-nitride/silicon-oxide multilayer grown on a standard glass coverslip. By exploiting the functional properties of the polymer, fluorescent proteins are grafted onto the waveguides. A fluorescence LRM analysis of both the direct and the Fourier image plane reveals that a substantial amount of emitted radiation couples into a guided mode and then propagates into the nanometric waveguide. The observations of the mode are supported by numerical simulations.
Half-harmonic Kelvin probe force microscopy with transfer function correction
Authors: Guo Senli , Kalinin Sergei V. , Jesse Stephen
Published: February 2012

An approach for surface potential imaging based on half-harmonic band excitation (BE) in Kelvin probe force microscopy is demonstrated. Using linear and half-harmonic BE enables quantitative correction of the cantilever transfer function. Half-harmonic band excitation Kelvin probe force microscopy (HBE KPFM) thus allows quantitative separation of surface potential and topographic contributions to the signal, obviating the primary sources of topographic cross-talk. HBE KPFM imaging and voltage spectroscopy methods are illustrated for several model systems.
Electronic rectification devices from carbon nanocones
Authors: Ming Chen , Lin Zheng-Zhe , Zhuang Jun , Ning Xi-Jing
Published: February 2012

The electronic rectification effects of single wall carbon nanocones (SWCNCs) with cone angles 113°, 60°, and 39° are shown by density functional theory calculation and non-equilibrium Green’s functional method, and the 113° cone owns the best rectification. Based on this result, the experiment on the rectification effects of cone-like structures is explained. To realize the rectification device, a scheme for fabricating single wall carbon nanocones standing on substrates with the controlled cone shapes is suggested and was verified via molecular dynamics simulations.
Domain rotation induced strain effect on the magnetic and magneto-electric response in CoFe2O4/Pb(Mg,Nb)O3-PbTiO3 heterostructures
Authors: Wang Zhiguang , Viswan Ravindranath , Hu Bolin , Li Jie-Fang , Harris V. G. , Viehland D.
Published: February 2012

The present work shows good control of both magnetic and electric properties with electric and magnetic fields, respectively, for epitaxial CoFe2O4 (CFO) films on Pb(Mg,Nb)O3-PbTiO3 (PMN-PT). X-ray reciprocal space mapping revealed a transformation between a- and c-domains in the PMN-PT under electric field (E). Magnetic hysteresis loop and magnetic force microscopy (MFM) measurements showed a considerable change in the magnetic properties in specific areas of CFO layers poled by MFM probe tips. Furthermore, a pulsed electric field applied to the substrate was found to switch the magnetization of CFO between high and low values, depending on the polarity of E.
Influence of size/crystallinity effects on the cation ordering and magnetism of α-lithium ferrite nanoparticles
Authors: Jović N. , Prekajski M. , Kremenović A. , Jančar B. , Kahlenberg V. , Antić B.
Published: February 2012

α-lithium ferrite (Li0.5Fe2.5O4) nanoparticles have been prepared using two synthesis routes: citrate gel decomposition as well as the Pechini method. Analysis of HRTEM images of the particles showed that they have a core/shell structure, an average size of ∼10 nm and stacking faults parallel to the (110) planes. In both samples, the distribution of the Li and Fe cations was found to be partially ordered on the octahedral sites (Wyckoff positions 4b and 12d of space group P4332). According to literature data, Li0.5Fe2.5O4 should adopt a disordered spinel structure (so called β-phase, space group Fd3¯m) for crystallites of 10 nm or less in size. In this study it is shown that (a) the symmetry of the Li0.5Fe2.5O4 nanoparticles depends on the degree of their crystallinity and (b) the ordered crystal structures can be formed even for crystallites of 5–6 nm in size. By fitting the room temperature Mössbauer spectra it was obtained that the hyperfine field values are lower in the sample synthesized by the Pechini method. The Pechini process probably resulted in larger distortions of the cation environments than the citrate gel decomposition method. The saturation magnetization in turn was higher for the material obtained by the gel decomposition approach.
Virtual ghost imaging through turbulence and obscurants using Bessel beam illumination
Authors: Meyers Ronald E. , Deacon Keith S. , Tunick Arnold D. , Shih Yanhua
Published: February 2012

We experimentally demonstrate a single sensor virtual ghost imaging (VGI) configuration that uses the physics of nearly diffraction free light sources to penetrate partially obscuring media or turbulent media and generate images of remote opaque objects. Randomly displaced nearly diffraction free Bessel beams provided improved illumination patterns for VGI and resolving small distant targets. VGI recovered the image of objects even when the coarse illuminating Bessel beam was transmitted through obscuring and turbulent media or through a small transversely displaced aperture. Bessel beam experiments are compared with Gaussian beam experiments under similar conditions.
Epitaxial NiO gate dielectric on AlGaN/GaN heterostructures
Authors: Roccaforte Fabrizio , Greco Giuseppe , Fiorenza Patrick , Raineri Vito , Malandrino Graziella , Lo Nigro Raffaella
Published: February 2012

This letter reports on epitaxial nickel oxide (NiO) films grown by metal-organic chemichal vapor deposition on AlGaN/GaN heterostructures. The grown material was epitaxial, free from voids and exhibited a permittivity of 11.7, close to bulk NiO. This approach is advantageous with respect other methods such as the thermal oxidation of Ni films due to a better reproducibility and film quality. A reduction of the leakage current in Schottky diodes with an interfacial NiO layer has been observed and described using the metal-insulator-semiconductor Schottky model. The results indicate that these films are promising as gate dielectric for AlGaN/GaN transistors technology.
Transient-time correlation function applied to mixed shear and elongational flows
Authors: Hartkamp Remco , Bernardi Stefano , Todd B. D.
Published: February 2012

The transient-time correlation function (TTCF) method is used to calculate the nonlinear response of a homogeneous atomic fluid close to equilibrium. The TTCF response of the pressure tensor subjected to a time-independent planar mixed flow of shear and elongation is compared to directly averaged non-equilibrium molecular dynamics (NEMD) simulations. We discuss the consequence of noise in simulations with a small rate of deformation. The generalized viscosity for planar mixed flow is also calculated with TTCF. We find that for small rates of deformation, TTCF is far more efficient than direct averages of NEMD simulations. Therefore, TTCF can be applied to fluids with deformation rates which are much smaller than those commonly used in NEMD simulations. Ultimately, TTCF applied to molecular systems is amenable to direct comparison between NEMD simulations and experiments and so in principle can be used to study the rheology of polymer melts in industrial processes.