bluuebunny/crossref_metadata_2025 huggingface dataset:
Arterial Input Function Derived from Pairwise Correlations Between PET-image Voxels
Authors: Schain Martin , Benjaminsson Simon , Varnäs Katarina , Forsberg Anton , Halldin Christer , Lansner Anders , Farde Lars , Varrone Andrea
Published: April 2013

A metabolite corrected arterial input function is a prerequisite for quantification of positron emission tomography (PET) data by compartmental analysis. This quantitative approach is also necessary for radioligands without suitable reference regions in brain. The measurement is laborious and requires cannulation of a peripheral artery, a procedure that can be associated with patient discomfort and potential adverse events. A non invasive procedure for obtaining the arterial input function is thus preferable. In this study, we present a novel method to obtain image-derived input functions (IDIFs). The method is based on calculation of the Pearson correlation coefficient between the time-activity curves of voxel pairs in the PET image to localize voxels displaying blood-like behavior. The method was evaluated using data obtained in human studies with the radioligands [ 11 C]flumazenil and [ 11 C]AZ10419369, and its performance was compared with three previously published methods. The distribution volumes ( VT) obtained using IDIFs were compared with those obtained using traditional arterial measurements. Overall, the agreement in VT was good (~3% difference) for input functions obtained using the pairwise correlation approach. This approach performed similarly or even better than the other methods, and could be considered in applied clinical studies. Applications to other radioligands are needed for further verification.
Early Identification of Potentially Salvageable Tissue with MRI-Based Predictive Algorithms after Experimental Ischemic Stroke
Authors: Bouts Mark JRJ , Tiebosch Ivo ACW , van der Toorn Annette , Viergever Max A , Wu Ona , Dijkhuizen Rick M
Published: April 2013

Individualized stroke treatment decisions can be improved by accurate identification of the extent of salvageable tissue. Magnetic resonance imaging (MRI)-based approaches, including measurement of a ‘perfusion-diffusion mismatch’ and calculation of infarction probability, allow assessment of tissue-at-risk;however, the ability to explicitly depict potentially salvageable tissue remains uncertain. In this study, five predictive algorithms (generalized linear model (GLM), generalized additive model, support vector machine, adaptive boosting, and random forest) were tested in their potency to depict acute cerebral ischemic tissue that can recover after reperfusion. Acute T2-, diffusion-, and perfusion-weighted MRI, and follow-up T2 maps were collected from rats subjected to right-sided middle cerebral artery occlusion without subsequent reperfusion, for training of algorithms (Group I), and with spontaneous (Group II) or thrombolysis-induced reperfusion (Group III), to determine infarction probability-based viability thresholds and prediction accuracies. The infarction probability difference between irreversible—i.e., infarcted after reperfusion— and salvageable tissue injury—i.e., noninfarcted after reperfusion—was largest for GLM (20 ± 7%) with highest accuracy of risk-based identification of acutely ischemic tissue that could recover on subsequent reperfusion (Dice's similarity index = 0.79 ± 0.14). Our study shows that assessment of the heterogeneity of infarction probability with MRI-based algorithms enables estimation of the extent of potentially salvageable tissue after acute ischemic stroke.
Chronic Imaging of Cortical Blood Flow using Multi-Exposure Speckle Imaging
Authors: Kazmi Syed Mohammad Shams , Parthasarthy Ashwin B , Song Nelly E , Jones Theresa A , Dunn Andrew K
Published: April 2013

Chronic imaging of cerebral blood flow (CBF) is an important tool for investigating vascular remodeling after injury such as stroke. Although techniques such as Laser Speckle Contrast Imaging (LSCI) have emerged as valuable tools for imaging CBF in acute experiments, their utility for chronic measurements or cross-animal comparisons has been limited. Recently, an extension to LSCI called Multi-Exposure Speckle Imaging (MESI) was introduced that increases the quantitative accuracy of CBF images. In this paper, we show that estimates of chronic blood flow are better with MESI than with traditional LSCI. We evaluate the accuracy of the MESI flow estimates using red blood cell (RBC) photographic tracking as an absolute flow calibration in mice over several days. The flow measures computed using the MESI and LSCI techniques were found to be on average 10% and 24% deviant ( n = 9 mice), respectively, compared with RBC velocity changes. We also map CBF dynamics after photo-thrombosis of selected cortical microvasculature. Correlations of flow dynamics with RBC tracking were closer with MESI ( r = 0.88) than with LSCI ( r = 0.65) up to 2 weeks from baseline. With the increased quantitative accuracy, MESI can provide a platform for studying the efficacy of stroke therapies aimed at flow restoration.
Anisotropic low field magnetoimpedance in (001) oriented La0.7Sr0.3MnO3 thin films
Authors: Joshi R. S. , Sylvinson M. R. Daniel , Anil Kumar P. S.
Published: April 2013

We report the evidence for the anisotropic magnetoimpedance behavior in (001) oriented La0.7Sr0.3MnO3 (LSMO) thin films, in low frequency–low magnetic field regime. (001) oriented LSMO thin films were deposited using pulsed laser deposition and characterized with X-ray diffraction and temperature dependent magnetization studies. In the in-plain configuration, an ac magnetoresistance (MRac) of ∼−0.5% was observed at 1000 Oe, at 100 Hz frequency in these films. The MRac was found to decrease with increase in frequency. We observe increases in MRac at low frequency, indicating major contribution for change of permeability from domain wall motion. At higher frequencies, it decreases due to decrease in transverse permeability, resulting from dampening of domain wall motion. Out-of-plane configuration showed MRac ∼ 5.5% at 1000 Oe, at 100 Hz frequency. The MRac turned from positive to negative with increase in frequency in out-of-plane configuration. These changes are attributed to the change in permeability of the film with the frequency and applied magnetic field.
Magnetic field induced polarization and magnetoelectric effect of Ba0.8Ca0.2TiO3-Ni0.2Cu0.3Zn0.5Fe2O4 nanomultiferroic
Authors: Sadhana Katlakunta , Ramana Murthy Sarabu , Jie Shang , Xie Yali , Liu Yiwei , Zhan Qingfeng , Li Run-Wei
Published: April 2013

The xBa0.8Ca0.2TiO3-(1 − x)NiCuZn ferrite (x = 0.1, 0.3, 0.5, 0.7, and 0.9) nanocomposites were prepared by using sol-gel method. The densification of these composites was carried out using microwave sintering method. The magnetic field induced changes in the ferroelectric polarization loop may support the possible magnetoelectric coupling between Ba0.8Ca0.2TiO3 and NiCuZn ferrite phases. The observed change in ferroelectric polarization with applied magnetic field proves the coupling between magnetic and ferroelectric order parameters. The loop change is observed with the composition and with magnetic field. The magnetoelectric coefficient of the nanocomposite with x = 0.3 shows a value of 280 mV/cm Oe is obtained.
Effect of three dimensional interface in determination of spin polarization using Andreev reflection spectroscopy
Authors: Gifford J. A. , Snider C. N. , Martinez J. , Chen T. Y.
Published: April 2013

A theoretical study of a three-dimensional (3D) normal metal/superconductor interface with arbitrary spin polarization and interface geometry is presented. The interface geometry can drastically affect the Andreev spectrum due to the 3D injection. The 3D effect can be attributed to a larger interfacial scattering factor in the 1D model, yielding the same intrinsic spin polarization and superconducting gap as the 3D model. This demonstrates that the 1D model can be utilized to extract the intrinsic spin polarization and the superconducting gap values for a 3D interface as long as the interfacial scattering factor is not concerned.
Improved sliced velocity map imaging apparatus optimized for H photofragments
Authors: Ryazanov Mikhail , Reisler Hanna
Published: April 2013

Time-sliced velocity map imaging (SVMI), a high-resolution method for measuring kinetic energy distributions of products in scattering and photodissociation reactions, is challenging to implement for atomic hydrogen products. We describe an ion optics design aimed at achieving SVMI of H fragments in a broad range of kinetic energies (KE), from a fraction of an electronvolt to a few electronvolts. In order to enable consistently thin slicing for any imaged KE range, an additional electrostatic lens is introduced in the drift region for radial magnification control without affecting temporal stretching of the ion cloud. Time slices of ∼5 ns out of a cloud stretched to ⩾50 ns are used. An accelerator region with variable dimensions (using multiple electrodes) is employed for better optimization of radial and temporal space focusing characteristics at each magnification level. The implemented system was successfully tested by recording images of H fragments from the photodissociation of HBr, H2S, and the CH2OH radical, with kinetic energies ranging from <0.4 eV to >3 eV. It demonstrated KE resolution ≲1%–2%, similar to that obtained in traditional velocity map imaging followed by reconstruction, and to KE resolution achieved previously in SVMI of heavier products. We expect it to perform just as well up to at least 6 eV of kinetic energy. The tests showed that numerical simulations of the electric fields and ion trajectories in the system, used for optimization of the design and operating parameters, provide an accurate and reliable description of all aspects of system performance. This offers the advantage of selecting the best operating conditions in each measurement without the need for additional calibration experiments.
Elastic scattering by finitely many point-like obstacles
Authors: Hu Guanghui , Sini Mourad
Published: April 2013

This paper is concerned with the time-harmonic elastic scattering by a finite number N of point-like obstacles in \documentclass[12pt]{minimal}\begin{document}${\mathbb {R}}^n$\end{document}Rn (n = 2, 3). We analyze the N-point interactions model in elasticity and derive the associated Green's tensor (integral kernel) in terms of the point positions and the scattering coefficients attached to them, following the approach in quantum mechanics for modeling N-particle interactions. In particular, explicit expressions are given for the scattered near and far fields corresponding to elastic plane waves or point-source incidences. As a result, we rigorously justify the Foldy method for modeling the multiple scattering by finitely many point-like obstacles for the Lamé model. The arguments are based on the Fourier analysis and the Weinstein-Aronszajn inversion formula of the resolvent for the finite rank perturbations of closed operators in Hilbert spaces.
Magnetic behavior of reduced graphene oxide/metal nanocomposites
Authors: Sahoo P. K. , Panigrahy Bharati , Li Dan , Bahadur D.
Published: April 2013

The dispersion of metal nanoparticles on reduced graphene oxide (RGO) sheets potentially provides a new way to develop novel catalytic, magnetic, adsorbing, and electrode materials. In this work, we report the structural and magnetic properties of RGO/metal (Bi, Pt, Ni, and Pt-Ni) nanocomposites. Such nanocomposites are successfully synthesized by a facile in situ co-reduction route. The structure, composition, and morphology of the synthesized materials are systematically investigated by X-ray diffraction, inductively coupled plasma-atomic emission spectrometer , and high resolution transmission electronic microscopy. The M–H curve and zero-field-cooled and field-cooled data for RGO, RGO/Ni, and RGO/Pt-Ni nanocomposites exhibit ferromagnetic behaviour. RGO/Pt nanocomposite shows diamagnetic, while RGO/Bi nanocomposite shows lower magnetization compared to that of RGO. Detailed magnetic studies on these nanocomposites and its correlation with microstructural features are presented here.
Coarse-grain molecular dynamics simulations of nanoparticle-polymer melt: Dispersion vs. agglomeration
Authors: Patra Tarak K. , Singh Jayant K.
Published: April 2013

In this work, we study the influence of polymer chain length (m), based on Lennard-Jones potential, and nanoparticle (NP)-polymer interaction strength (ɛnp) on aggregation and dispersion of soft repulsive spherically structured NPs in polymer melt using coarse-grain molecular dynamics simulations. A phase diagram is proposed where transitions between different structures in the NP-polymer system are shown to depend on m and ɛnp. At a very weak interaction strength ɛnp = 0.1, a transition from dispersed state to collapsed state of NPs is found with increasing m, due to the polymer's excluded volume effect. NPs are well dispersed at intermediate interaction strengths (0.5 ⩽ ɛnp ⩽ 2.0), independent of m. A transition from dispersion to agglomeration of NPs, at a moderately high NP-polymer interaction strength ɛnp = 5.0, for m = 1–30, is identified by a significant decrease in the second virial coefficient, excess entropy, and potential energy, and a sharp increase in the Kirkwood-Buff integral. We also find that NPs undergo the following transitions with increasing m at ɛnp ⩾ 5.0: string-like → branch-like → sphere-like → dispersed state.
Measurement of area density of vertically aligned carbon nanotube forests by the weight-gain method
Authors: Esconjauregui Santiago , Xie Rongsie , Fouquet Martin , Cartwright Richard , Hardeman David , Yang Junwei , Robertson John
Published: April 2013

The area density of vertically aligned carbon nanotubes forests is measured and analysed by the weight gain method. The mass density of a close packed array of single- and multi-walled nanotubes is analysed as a function of the average nanotube diameter and number of walls, and this is used to derive the area density, from which the filling factor can be extracted. Densities of order 1013 cm−2 tubes are grown from cyclic catalyst methods.
Magnetic anisotropy and thermal stability study of perpendicular Co/Ni multilayers
Authors: Wang Guangzhong , Zhang Zongzhi , Ma Bin , Jin Q. Y.
Published: April 2013

The perpendicular magnetic anisotropy (PMA) and thermal stability of Ta (3.0 nm)/Cu (tCu)/[Co (0.29 nm)/Ni (0.65 nm)]N/Ta (3.0 nm) multilayers are investigated with various Cu thicknesses (tCu) and Co/Ni periodic numbers (N). A relatively thick Cu seed layer and a suitable Co/Ni repetition number benefit the PMA with larger coercivity and remanence ratio. But the magnetic hysteresis loop for the structure with N in excess of 10 exhibits a bow-tie shape due to the formation of multi-domains, which may cause a significant drop of the remanence ratio. The post-annealing experiments show that the thermal stability of PMA increases with increasing N. In addition to the intermixing of Co and Ni atoms at interfaces, we consider that the diffusion of nonmagnetic atoms into the magnetic layers is also responsible for the PMA decay with increasing annealing temperature.
Studying exothermic reactions in the Ni-Al system at rapid heating rates using a nanocalorimeter
Authors: Swaminathan P. , Grapes M. D. , Woll K. , Barron S. C. , LaVan D. A. , Weihs T. P.
Published: April 2013

Heats of reaction and heat capacity changes were measured using scanning nanocalorimetry for a nickel and aluminum bilayer where initial heating rates of 104 K/s were achieved. Multiple exotherms were observed on the initial heating, but the number of intermediate exotherms decreased with increasing heating rate. The final phase was the B2 NiAl intermetallic. Results from the nanocalorimeter were compared with a conventional differential scanning calorimeter (operating at 0.7 K/s) to understand the effect of significant (10 000×) increases in heating rate on the phase transformation sequence. The high heating rate in the nanocalorimeter delays reaction initiation, causes the exothermic peaks to shift to higher temperatures, and appears to suppress the formation of intermediate, metastable phases. Potential explanations for this apparent suppression are discussed.
Accurate determination of interface trap state parameters by admittance spectroscopy in the presence of a Schottky barrier contact: Application to ZnO-based solar cells
Authors: Marin Andrew T. , Musselman Kevin P. , MacManus-Driscoll Judith L.
Published: April 2013

This work shows that when a Schottky barrier is present in a photovoltaic device, such as in a device with an ITO/ZnO contact, equivalent circuit analysis must be performed with admittance spectroscopy to accurately determine the pn junction interface recombination parameters (i.e., capture cross section and density of trap states). Without equivalent circuit analysis, a Schottky barrier can produce an error of ∼4-orders of magnitude in the capture cross section and ∼50% error in the measured density of trap states. Using a solution processed ZnO/Cu2O photovoltaic test system, we apply our analysis to clearly separate the contributions of interface states at the pn junction from the Schottky barrier at the ITO/ZnO contact so that the interface state recombination parameters can be accurately characterized. This work is widely applicable to the multitude of photovoltaic devices, which use ZnO adjacent to ITO.
Tuning donut profile for spatial resolution in stimulated emission depletion microscopy
Authors: Neupane Bhanu , Chen Fang , Sun Wei , Chiu Daniel T. , Wang Gufeng
Published: April 2013

In stimulated emission depletion (STED)-based or up-conversion depletion-based super-resolution optical microscopy, the donut-shaped depletion beam profile is of critical importance to its resolution. In this study, we investigate the transformation of the donut-shaped depletion beam focused by a high numerical aperture (NA) microscope objective, and model STED point spread function (PSF) as a function of donut beam profile. We show experimentally that the intensity profile of the dark kernel of the donut can be approximated as a parabolic function, whose slope is determined by the donut beam size before the objective back aperture, or the effective NA. Based on this, we derive the mathematical expression for continuous wave (CW) STED PSF as a function of focal plane donut and excitation beam profiles, as well as dye properties. We find that the effective NA and the residual intensity at the center are critical factors for STED imaging quality and the resolution. The effective NA is critical for STED resolution in that it not only determines the donut shape but also the area the depletion laser power is dispersed. An improperly expanded depletion beam will have negligible improvement in resolution. The polarization of the depletion beam also plays an important role as it affects the residual intensity in the center of the donut. Finally, we construct a CW STED microscope operating at 488 nm excitation and 592 nm depletion with a resolution of 70 nm. Our study provides detailed insight to the property of donut beam, and parameters that are important for the optimal performance of STED microscopes. This paper will provide a useful guide for the construction and future development of STED microscopes.
Electrodeposition and characterization of magnetostrictive galfenol (FeGa) thin films for use in microelectromechanical systems
Authors: Estrine Eliot C. , Robbins William P. , Maqableh Mazin M. , Stadler Bethanie J. H.
Published: April 2013

In this paper, we investigate the challenges related to electrodeposition and characterization of magnetostrictive galfenol thin films as well as techniques used to overcome these issues. Successful deposition and evaluation of galfenol thin films is necessary for the design of galfenol based microelectromechanical devices. Stress is a primary concern because thick films and poor adhesion to substrates (e.g., silicon oxide) can lead to delamination and peeling. In addition, magnetostriction measurements require films that are uniform in thickness and composition over the sample area. Various adhesion layers were tested, and delamination was eliminated with Cr/Cu, which provided robust adhesion to the glass substrates used in capacitance bridge measurements. Uniformity and composition were controlled by the use of a rotating disk electrode for electrodeposition, which created a uniform boundary condition across the sample during deposition. The capacitance bridge technique was calibrated with Ni/glass samples, after which a magnetostriction of 140 ppm was measured for Fe83Ga17 films. These results represent the first magnetostriction measurements of electrodeposited galfenol.
The tail effect on the shape of an electrical double layer differential capacitance curve
Authors: Henderson Douglas , Lamperski Stanisław , Bari Bhuiyan Lutful , Wu Jianzhong
Published: April 2013

The differential capacitance curve for the double layer formed by an electrolyte dissolved in a solvent is commonly believed to be parabolic-like with a minimum at low electrolyte charge concentration and low electrode surface charge density, and independent of electrolyte concentration at high electrolyte concentrations and high electrode charge and would be, in the absence of solvent effects, featureless at these latter conditions. This is the prediction of the popular Gouy-Chapman-Stern theory. In contrast, for an ionic liquid this curve can have a single or a double hump (or a bell or camel shape). Fedorov et al. [Electrochem. Commun. 12, 296 (2010)]10.1016/j.elecom.2009.12.019 have related these humps, particularly the double hump, to the neutral tails of ions in many ionic liquids. Evidence presented here shows, however, that such humps are general features of the differential capacitance of a double layer, whether it be formed by ions with or without a neutral tail. The presence of a double or single hump results from the magnitude of the electrolyte charge concentration. For both spherical ions or non-spherical ions consisting of charged heads and neutral tails, the shape of the differential capacitance transforms continuously from a double hump to a single hump as the electrolyte concentration is increased.
Strain effect of multilayer FeN structure on GaAs substrate
Authors: Zhang Xiaowei , Ji Nian , Lauter Valeria , Ambaye Hailemariam , Wang Jian-Ping
Published: April 2013

Overly doped FeN multilayer structure on GaAs substrate was fabricated. After the post-annealing process, FeN martensite in each Fe/FeN layer formed partially chemically ordered Fe16N2, which was observed by X-ray diffraction. To detect the saturation magnetization (Ms) depth profile, polarized neutron reflectivity was conducted. Fe/FeN layer showed a significant improvement of Ms for each layer compared to Ms of Fe. More importantly, different FeN layers showed different Ms according to the physical distance to the substrate GaAs. The most enhanced Ms (exceeding the limit of Fe65Co35 Ms) observed at the bottom part of the film, consistent with previous reports, should be attributed to the lattice strain by GaAs substrate. In order to detect the lattice constant, In-plane X-ray Diffraction was done and a large in-plane lattice constant was determined.
Pull-out simulations of a capped carbon nanotube in carbon nanotube-reinforced nanocomposites
Authors: Li Y. , Liu S. , Hu N. , Han X. , Zhou L. , Ning H. , Wu L. , Alamusi  , Yamamoto G. , Chang C. , Hashida T. , Atobe S. , Fukunaga H.
Published: April 2013

Systematic atomic simulations based on molecular mechanics were conducted to investigate the pull-out behavior of a capped carbon nanotube (CNT) in CNT-reinforced nanocomposites. Two common cases were studied: the pull-out of a complete CNT from a polymer matrix in a CNT/polymer nanocomposite and the pull-out of the broken outer walls of a CNT from the intact inner walls (i.e., the sword-in-sheath mode) in a CNT/alumina nanocomposite. By analyzing the obtained relationship between the energy increment (i.e., the difference in the potential energy between two consecutive pull-out steps) and the pull-out displacement, a set of simple empirical formulas based on the nanotube diameter was developed to predict the corresponding pull-out force. The predictions from these formulas are quite consistent with the experimental results. Moreover, the much higher pull-out force for a capped CNT than that of the corresponding open-ended CNT implies a significant contribution from the CNT cap to the interfacial properties of the CNT-reinforced nanocomposites. This finding provides a valuable insight for designing nanocomposites with desirable mechanical properties.
Excitation energies and ionization potentials at high electric fields for molecules relevant for electrically insulating liquids
Authors: Davari N. , Åstrand P.-O. , Ingebrigtsen S. , Unge M.
Published: April 2013

The electric-field dependence of the molecular ionization potential and excitation energies is investigated by density-functional theory calculations. It is demonstrated that the ionization potential has a strong field dependence and decreases with increasing field. The excitation energies depend weakly on the field and the number of available excited states decreases with increasing field since the ionization potential has a stronger field dependence. Above a specific field, different for each molecule, a two-state model is obtained consisting of the electronic ground state and the ionized state. Implications for streamer propagation and electrically insulating materials are discussed.
Magnetic field effect spectroscopy of C60-based films and devices
Authors: Gautam Bhoj R. , Nguyen Tho D. , Ehrenfreund Eitan , Vardeny Z. Valy
Published: April 2013

We performed spectroscopy of the magnetic field effect (MFE) including magneto-photoinduced absorption (MPA) and magneto-photoluminescence (MPL) at steady state conditions in annealed and pristine fullerene C60 thin films, as well as magneto-conductance (MC) in organic diodes based on C60 interlayer. The hyperfine interaction has been shown to be the primary spin mixing mechanism for the MFE in the organics. In this respect, C60 is a unique material because 98.9% of the carbon atoms are 12C isotope, having spinless nucleus and thus lack hyperfine interaction. In spite of this, we obtained substantial MPA (up to ∼15%) and significant MC and MPL in C60 films and devices, and thus mechanisms other than the hyperfine interaction are responsible for the MFE in this material. Specifically, we found that the MFE(B) response is composed of narrow (∼10 mT) and broad (>100 mT) components. The narrow MFE(B) component is due to spin-dependent triplet exciton recombination in C60, which dominates the MPA(B) response at low pump intensities in films, or the MC response at small current densities in devices. In contrast, the broad MFE(B) component dominates the MPA(B) response at high pump intensities (or large current densities for MC(B)) and is attributed to spin mixing in the polaron pairs spin manifold due to g-factor mismatch between the electron- and hole-polarons in C60. Our results show that the organic MFE has a much broader scope than believed before.
The soft magnetic properties of ring-shaped (Co0.6Fe0.3Ni0.1)68(B0.811Si0.189)27Nb5 bulk metallic glasses
Authors: Dong Yaqiang , Man Qikui , Zhang Zhidong , Shen Baolong
Published: April 2013

Ring-shaped (Co0.6Fe0.3Ni0.1)68(B0.811Si0.189)27Nb5 bulk samples with an outer diameter of 10 mm, an inner diameter of 6 mm, and a thickness of 1 mm were successfully prepared by copper mold casting. The effects of annealing treatments on magnetic properties of the ring-shaped bulk sample were investigated. After the optimum annealing treatment, the resulting ring-shaped bulk sample exhibits good magnetic properties, i.e., low coercive force of 0.55 A/m, high maximum permeability of 433 000, and high permeability of 19 400 at 50 Hz under an AC field amplitude of 1.2 A/m, respectively. In addition, the ring-shaped bulk sample also shows low core loss of 0.09 W/kg at 50 Hz under induction of 0.5 T. The synthesis of ring-shaped bulk samples with good magnetic properties is encouraging for their potential applications as functional materials in the future.
Thermoelectric performance of p-type skutterudites YbxFe4−yPtySb12 (0.8 ≤ x ≤ 1, y = 1 and 0.5)
Authors: Young Cho Jung , Ye Zuxin , Tessema Misle M. , Salvador James R. , Waldo Richard A. , Yang Jiong , Zhang Wenqing , Yang Jihui , Cai W. , Wang H.
Published: April 2013

Thermoelectric performance of p-type skutterudites currently lags that of the corresponding n-type materials, and improvement of this important class of materials has become the focus of considerable research effort world-wide. Recent calculations find promising band structure features in p-type skutterudite materials of the type AFe3NiSb12 (A = Ca, Sr, or Ba), which could potentially lead to excellent thermoelectric properties. Recent work on the Yb-filled analogs of these formulations (YbFe3NiSb12) however, finds that the onset of intrinsic conduction at lower than expected temperatures deteriorates the performance above 500 K. This leads to performance in the temperature range of interest for automotive waste heat recovery applications. We, therefore, seek a way to increase the band gap in order to find a way to minimize the deleterious effects of intrinsic conduction on thermoelectric performance. Here, we present ab initio band structure calculations, the synthesis and thermoelectric properties of YbxFe4−yPtySb12 (0.8 ≤ x ≤ 1, y = 1 and 0.5). Ab initio calculations find that the band gap increases for YbFe3PtSb12 as compared to the Ni-containing analog, though no such increase in the band gap energy was found for YbFe3.5Pt0.5Sb12 as compared to YbFe3.5Ni0.5Sb12. The y = 1 sample shows a characteristic transition to intrinsic conduction with a decrease in the Seebeck coefficient at temperatures above 700 K. The increased carrier concentration in y = 0.5 virtually eliminates any evidence of intrinsic conduction, and the Seebeck coefficients for these samples increase monotonically up to 750 K, resulting in power factors approaching 27 μW/cm·K2 at 750 K. These power factors combined with low thermal conductivity result in a ZT = 0.9 at 750 K for Yb0.95Fe3.5Pt0.5Sb12.
Mode space approach for tight-binding transport simulations in graphene nanoribbon field-effect transistors including phonon scattering
Authors: Grassi R. , Gnudi A. , Imperiale I. , Gnani E. , Reggiani S. , Baccarani G.
Published: April 2013

In this paper, we present a mode space method for atomistic non-equilibrium Green's function simulations of armchair graphene nanoribbon field effect transistors (FETs) that includes electron-phonon scattering. With reference to both conventional and tunnel FET structures, we show that, in the ideal case of a smooth electrostatic potential, the modes can be decoupled in different groups without any loss of accuracy. Thus, inter-subband scattering due to electron-phonon interactions is properly accounted for, while the overall simulation time considerably improves with respect to real-space, with a speed-up factor of 40 for a 1.5-nm-wide device. Such factor increases with the square of the device width. We also discuss the accuracy of two commonly used approximations of the scattering self-energies: the neglect of the off-diagonal entries in the mode-space expressions and the neglect of the Hermitian part of the retarded self-energy. While the latter is an acceptable approximation in most bias conditions, the former is somewhat inaccurate when the device is in the off-state and optical phonon scattering is essential in determining the current via band-to-band tunneling. Finally, we show that, in the presence of a disordered potential, a coupled mode space approach is necessary, but the results are still accurate compared to the real-space solution.
Metallic spintronic thin film as a hydrogen sensor
Authors: Chang Crosby S. , Kostylev Mikhail , Ivanov Eugene
Published: April 2013

We investigate the ferromagnetic resonance response of palladium-cobalt bi-layer thin films to hydrogen charging at atmospheric pressure. We find that hydrogen absorption by the palladium capping layer results in the narrowing and shifting of the ferromagnetic resonance line of the underlying cobalt. We explain the observed phenomena as originating from reduction in the spin pumping effect and from variation in the magnetic anisotropy of the cobalt layer through an interface effect. The shift of the resonance frequency or field is the easiest to detect. We utilize this to demonstrate functionality of the bi-layer film as a hydrogen sensor.
Formation of Pd2Si on single-crystalline Si (100) at ultrafast heating rates: An in-situ analysis by nanocalorimetry
Authors: Molina-Ruiz M. , Lopeandía A. F. , González-Silveira M. , Anahory Y. , Guihard M. , Garcia G. , Clavaguera-Mora M. T. , Schiettekatte F. , Rodríguez-Viejo J.
Published: April 2013

The kinetics of intermediate phase formation between ultrathin films of Pd (12 nm) and single-crystalline Si (100) is monitored by in-situ nanocalorimetry at ultrafast heating rates. The heat capacity curves show an exothermic peak related to the formation of Pd2Si. A kinetic model which goes beyond the conventional linear-parabolic growth to consider independent nucleation and lateral growth of Pd2Si along the interface and vertical growth mechanisms is developed to fit the calorimetric curves. The model is used to extract the effective interfacial nucleation/growth and diffusion coefficients at the unusually high temperatures of silicide formation achieved at very fast heating rates.
Vacuum annealed cerium-substituted yttrium iron garnet films on non-garnet substrates for integrated optical circuits
Authors: Goto Taichi , Eto Yu , Kobayashi Keiichi , Haga Yoji , Inoue Mitsuteru , Ross C. A.
Published: April 2013

Polycrystalline cerium-substituted yttrium iron garnet (CeYIG) showing large Faraday rotation (FR) in the near-IR region was grown on non-garnet (synthetic fused silica, Si, and Si-on-insulator) substrates by sputtering followed by thermal annealing in vacuum. The FR of the films is comparable to the single crystal value. Structural characterization, magnetic properties, refractive index, extinction coefficient, surface topography, and FR vs. wavelength were measured and the magnetooptical figure of merit was compared with that of CeYIG films on garnet substrates.
Versatile fluoride substrates for Fe-based superconducting thin films
Authors: Kurth F. , Reich E. , Hänisch J. , Ichinose A. , Tsukada I. , Hühne R. , Trommler S. , Engelmann J. , Schultz L. , Holzapfel B. , Iida K.
Published: April 2013

We demonstrate the growth of Co-doped BaFe2As2 (Ba-122) thin films on CaF2 (001), SrF2 (001), and BaF2 (001) single crystal substrates using pulsed laser deposition. All films are grown epitaxially despite of a large misfit of −10.6% for BaF2 substrate. For all films, a reaction layer is formed at the interface confirmed by X-ray diffraction and for the films grown on CaF2 and BaF2 additionally by transmission electron microscopy. The superconducting transition temperature of the film on CaF2 is around 27 K, whereas the corresponding values of the films on SrF2 and BaF2 are around 22 K and 21 K, respectively. The Ba-122 on CaF2 shows almost identical crystalline quality and superconducting properties as films on Fe-buffered MgO.
Magnetostrictive properties of the heavy-rare-earth-free Sm1-xNdxFe2 compounds
Authors: Wang Y. , Ren W. J. , Yang Y. H. , Li B. , Li J. , Zhang Z. D.
Published: April 2013

In this work, we report the magnetostrictive properties of Sm1-xNdxFe2 compounds, which are free of (expensive) heavy rare earths. Anomalies are observed in the temperature dependence of both the magnetization and the magnetostriction of these compounds, which are ascribed to spin-reorientation transitions. At low fields, the quasi-static magnetostriction and the piezomagnetic coefficient d33 of Sm0.88Nd0.12Fe2 are larger than those of SmFe2, which is due to the compensation of the anisotropy of the Sm3+ and Nd3+ ions. At a magnetic-field strength of 6 kOe, the static magnetostriction of Sm0.88Nd0.12Fe2 is −1244 ppm at 225 K and −1022 ppm at 290 K and, at a bias magnetic field of 700 Oe, the d33 equals 0.55 ppm/Oe (6.8 nm/A).
Strong excitation intensity dependence of the photoluminescence line shape in GaAs1−xBix single quantum well samples
Authors: Mazur Yu. I. , Dorogan V. G. , Schmidbauer M. , Tarasov G. G. , Johnson S. R. , Lu X. , Ware M. E. , Yu S.-Q. , Tiedje T. , Salamo G. J.
Published: April 2013

A set of high quality single quantum well samples of GaAs1−xBix with bismuth concentrations not exceeding 6% and well widths ranging from 7.5 to 13 nm grown by molecular beam epitaxy on a GaAs substrate at low temperature is studied by means of photoluminescence (PL). It is shown that the PL line shape changes when the exciton reduced mass behavior changes from an anomalous increase (x < 5%) to a conventional decrease (x > 5%). Strongly non-monotonous PL bandwidth dependence on the excitation intensity is revealed and interpreted in terms of optically unresolved contributions from the saturable emission of bound free excitons.
Research on an optimal site selection model for desert photovoltaic power plants based on analytic hierarchy process and geographic information system
Authors: Xiao Jianhua , Yao Zhengyi , Qu Jianjun , Sun Jiahuan
Published: April 2013

Optimal site selection for desert photovoltaic power plants is important to energy output and involves a multicriteria evaluation of many factors. This paper analyzes the factors influencing desert photovoltaic power station site selection and establishes an optimal site selection model for desert photovoltaic power plants using an analytic hierarchy process and geographic information system technology. We selected a typical desert area in northwestern China as the research location to test the model. Validation results were ideal, and the model successfully displayed the optimal site for desert photovoltaic power plants, from which the most suitable site for desert photovoltaic power plants could be selected.
Electron channeling contrast imaging studies of nonpolar nitrides using a scanning electron microscope
Authors: Naresh-Kumar G. , Mauder C. , Wang K. R. , Kraeusel S. , Bruckbauer J. , Edwards P. R. , Hourahine B. , Kalisch H. , Vescan A. , Giesen C. , Heuken M. , Trampert A. , Day A. P. , Trager-Cowan C.
Published: April 2013

Threading dislocations, stacking faults, and associated partial dislocations significantly degrade the optical and electrical properties of materials such as non-polar III-nitride semiconductor thin films. Stacking faults are generally difficult to detect and quantify with existing characterization techniques. We demonstrate the use of electron channeling contrast imaging in the scanning electron microscope to non-destructively reveal basal plane stacking faults terminated by partial dislocations in m-plane GaN and InGaN/GaN multiple quantum well structures grown on γ-LiAlO2 by metal organic vapor phase epitaxy.
Efficiency enhancement in ultraviolet light-emitting diodes by manipulating polarization effect in electron blocking layer
Authors: Lu Yu-Hsuan , Fu Yi-Keng , Huang Shyh-Jer , Su Yan-Kuin , Xuan Rong , Pilkuhn Manfred H.
Published: April 2013

The characteristics of the ultraviolet light-emitting diode (LED) with conventional and specifically designed electron blocking layers (EBLs) are investigated numerically and experimentally in this work. Simulation results show that delicately designed EBLs can not only capably perform the electron blocking function but also eliminate the incidental drawback of obstruction of hole injection caused by the nature of the large polarization field at the c-plane nitride heterojunction. It is shown that the polarization induced downward band bending can be mitigated when the portion of conventional EBL lying adjacent to the active region is replaced by a graduated AlGaN layer. The conduction band profile indicates that this replacement structure could have the capability of electron confinement similar to the conventional structure, and the valence band profile indicates that the spike induced by the polarization field is simultaneously eliminated, assisting the process of hole injection and distribution in the active region. Electron leakage over the EBL is thus obviously reduced, and the consumption efficiency of the injection carriers is improved, as expressed in the distribution of the electron current density. The experimental results show that the light output power can be significantly enhanced from 29.3 mW for the conventional device to 54.7 mW for the LED with the redesigned EBL structure.
Inkjet printing of aligned single-walled carbon-nanotube thin films
Authors: Takagi Yuki , Nobusa Yuki , Gocho Shota , Kudou Hikaru , Yanagi Kazuhiro , Kataura Hiromichi , Takenobu Taishi
Published: April 2013

We report a method for the inkjet printing of aligned single-walled carbon-nanotube (SWCNT) films by combining inkjet technology with the strong wettability contrast between hydrophobic and hydrophilic areas based on the patterning of self-assembled monolayers. Both the drying process control using the strong wettability boundary and the coffee-stain effect strongly promote the aggregation of SWCNTs along the contact line of a SWCNT ink droplet, thereby demonstrating our achievement of inkjet-printed aligned SWCNT films. This method could open routes for developing high-performance and environmentally friendly SWCNT printed electronics.
Strong coupling between Rhodamine 6G and localized surface plasmon resonance of immobile Ag nanoclusters fabricated by direct current sputtering
Authors: Fang Yingcui , Blinn Kevin , Li Xiaxi , Weng Guojun , Liu Meilin
Published: April 2013

We made clean silver nano-clusters (AgNCs) on glass substrates by DC magnetron sputtering of a high purity Ag target in a high vacuum chamber. The AgNCs film shows strong localized surface plasmon resonance (LSPR) due to the coupling among Ag nanoparticles in the AgNCs and the coupling between AgNCs. The LSPR indicates strong coupling with Rhodamine 6G (R6G) adsorbed on the AgNC surface, which enhances the R6G absorption intensity and broadens the absorption wavelength range. This result promotes plasmonic nanoparticles to be better used in solar cells.
Negative refraction of acoustic waves using a foam-like metallic structure
Authors: Hladky-Hennion A.-C. , Vasseur J. O. , Haw G. , Croënne C. , Haumesser L. , Norris A. N.
Published: April 2013

A phononic crystal (PC) slab made of a single metallic phase is shown, theoretically and experimentally, to display perfect negative index matching and focusing capability when surrounded with water. The proposed PC slab is a centimeter scale hollow metallic foam-like structure in which acoustic energy is mediated via the metal lattice. The negative index property arises from an isolated branch of the dispersion curves corresponding to a mode that can be coupled to incident acoustic waves in surrounding water. This band also intercepts the water sound line at a frequency in the ultrasonic range. The metallic structure is consequently a candidate for the negative refraction of incident longitudinal waves.
Direct observation of minority carrier lifetime improvement in InAs/GaSb type-II superlattice photodiodes via interfacial layer control
Authors: Zuo Daniel , Qiao Pengfei , Wasserman Daniel , Lien Chuang Shun
Published: April 2013

We present improved performance in strain-balanced InAs/GaSb type-II superlattice photodetectors grown using InSb interfacial layers, measured using a cross-sectional electron beam induced current (EBIC) technique to obtain minority carrier diffusion characteristics. We detail a modified EBIC model that accounts for the long absorber regions in photodetectors and fit the experimental data. We find a significant increase in the minority hole lifetime (up to 157 ns) and increased minority electron lifetime due to the interfacial layers. Additionally, electrical characterization of the device temperature-dependent resistance-area product reveals that the interfacial treatment improves the device dark current at lower temperatures.
Direct laser initiation and improved thermal stability of nitrocellulose/graphene oxide nanocomposites
Authors: Zhang Xin , Hikal Walid M. , Zhang Yue , Bhattacharia Sanjoy K. , Li Li , Panditrao Siddharth , Wang Shiren , Weeks Brandon L.
Published: April 2013

We report on the enhancement and possible control of both laser ignition and burn rates of Nitrocellulose (NC) microfilms when doped with graphene oxide (GO). A Nd:YAG (1064 nm, 20 ns) laser is used to ignite GO-doped NC films at low temperatures. The effect of GO on the doping concentration of the activation energies of laser ignition and thermal stability of the NC films is studied. The activation energy of laser ignition decreases with increasing GO/NC weight ratio and attains a constant value with higher concentrations. This behavior is accompanied by an increase in the thermal stability.
Improved Si0.5Ge0.5/Si interface quality achieved by the process of low energy hydrogen plasma cleaning and investigation of interface quality with positron annihilation spectroscopy
Authors: Liao M.-H. , Chen C.-H.
Published: April 2013

The Positron Annihilation Spectra(PAS), Raman, and Photoluminescencespectroscopy reveal that Si0.5Ge0.5/Si interface quality can be significantly improved by the low energy plasma cleaning process using hydrogen. In the PAS, the particularly small value of lifetime and intensity near the Si0.5Ge0.5/Si interface in the sample with the treatment indicate that the defect concentration is successfully reduced 2.25 times, respectively. Fewer defects existed in the Si0.5Ge0.5/Si interface result in the high compressive strain about 0.36% in the top epi-Si0.5Ge0.5 layer, which can be observed in Raman spectra and stronger radiative recombination rate about 1.39 times for the infrared emission, which can be observed in the photoluminescencespectra. With better Si0.5Ge0.5/Si interface quality, the SiGe-based devices can have better optical and electrical characteristics for more applications in the industry. The PAS is also demonstrated that it is the useful methodology tool to quantify the defect information in the SiGe-based material.
Influence of monsoon-driven hydrographic features on siphonophore assemblages in the Taiwan Strait, western North Pacific Ocean
Authors: Hsieh Hung-Yen , Yu Shwu-Feng , Lo Wen-Tseng
Published: April 2013

The spatial patterns of siphonophores were analysed in relation to local hydrographic features during two different monsoon seasons (the north-easterly monsoon in winter v. the south-westerly monsoon in summer) in the Taiwan Strait. Forty-eight species were identified, with five types of calycophoran siphonophores (Lensia subtiloides, Chelophyes appendiculata, Chelophyes contorta, Bassia bassensis, and Diphyes chamissonis) being most common in both seasons. Significantly higher abundances of four of the five common species were recorded in summer than in winter. Differences in the siphonophore species compositions were also observed between the northern and southern part of Taiwan Strait, with significantly higher diversity occurring in the southern waters. The distribution patterns of siphonophore assemblages were closely linked to the hydrographic features, influenced by the dynamic nature of the currents in the study area, with temperature, salinity and zooplankton biomass being the three most important factors.