bluuebunny/crossref_metadata_2025 huggingface dataset:
Strength and texture of Pt compressed to 63 GPa
Authors: Dorfman Susannah M. , Shieh Sean R. , Duffy Thomas S.
Published: February 2015

Angle- and energy-dispersive X-ray diffraction experiments in a radial geometry were performed in the diamond anvil cell on polycrystalline platinum samples at pressures up to 63 GPa. Observed yield strength and texture depend on grain size. For samples with 70–300-nm particle size, the yield strength is 5–6 GPa at ∼60 GPa. Coarse-grained (∼2-μm particles) Pt has a much lower yield strength of 1–1.5 GPa at ∼60 GPa. Face-centered cubic metals Pt and Au have lower strength to shear modulus ratio than body-centered cubic or hexagonal close-packed metals. While a 300-nm particle sample exhibits the 〈110〉 texture expected of face-centered-cubic metals under compression, smaller and larger particles show a weak mixed 〈110〉 and 〈100〉 texture under compression. Differences in texture development may also occur due to deviations from uniaxial stress under compression in the diamond anvil cell.
Horizontal molecular orientation in solution-processed organic light-emitting diodes
Authors: Zhao L. , Komino T. , Inoue M. , Kim J.-H. , Ribierre J. C. , Adachi C.
Published: February 2015

Horizontal orientation of the emission transition dipole moments achieved in glassy vapor-deposited organic thin films leads to an enhancement of the light out-coupling efficiency in organic light-emitting diodes (OLEDs). Here, our combined study of variable angle spectroscopic ellipsometry and angle dependent photoluminescence demonstrates that such a horizontal orientation can be achieved in glassy spin-coated organic films based on a composite blend of a heptafluorene derivative as a dopant and a 4,4′-bis(N-carbazolyl)-1,1′-biphenyl as a host. Solution-processed fluorescent OLEDs with horizontally oriented heptafluorene emitters were then fabricated and emitted deep blue electroluminescence with an external quantum efficiency as high as 5.3%.
Zonal flow formation in the presence of ambient mean shear
Authors: Hsu Pei-Chun , Diamond P. H.
Published: February 2015

The effect of mean shear flows on zonal flow formation is considered in the contexts of plasma drift wave turbulence and quasi-geostrophic turbulence models. The generation of zonal flows by modulational instability in the presence of large-scale mean shear flows is studied using the method of characteristics as applied to the wave kinetic equation. It is shown that mean shear flows reduce the modulational instability growth rate by shortening the coherency time of the wave spectrum with the zonal shear. The scalings of zonal flow growth rate and turbulent vorticity flux with mean shear are determined in the strong shear limit.
High mobility epitaxial graphene devices via aqueous-ozone processing
Authors: Yager Tom , Webb Matthew J. , Grennberg Helena , Yakimova Rositsa , Lara-Avila Samuel , Kubatkin Sergey
Published: February 2015

We find that monolayer epitaxial graphene devices exposed to aggressive aqueous-ozone processing and annealing became cleaner from post-fabrication organic resist residuals and, significantly, maintain their high carrier mobility. Additionally, we observe a decrease in carrier density from inherent strong n-type doping to extremely low p-type doping after processing. This transition is explained to be a consequence of the cleaning effect of aqueous-ozone processing and annealing, since the observed removal of resist residuals from SiC/G enables the exposure of the bare graphene to dopants present in ambient conditions. The resulting combination of charge neutrality, high mobility, large area clean surfaces, and susceptibility to environmental species suggest this processed graphene system as an ideal candidate for gas sensing applications.
Gate-modulated weak anti-localization and carrier trapping in individual Bi2Se3 nanoribbons
Authors: Wang Li-Xian , Yan Yuan , Liao Zhi-Min , Yu Da-Peng
Published: February 2015

We report a gate-voltage modulation on the weak anti-localization of individual topological insulator Bi2Se3 nanoribbons. The phase coherence length decreases with decreasing the carrier density of the surface states on the bottom surface of the Bi2Se3 nanoribbon as tuning the gate voltage from 0 to −100 V, indicating that the electron-electron interaction dominates the decoherence at low carrier density. Furthermore, we observe an abnormal conductance decline at positive gate voltage regime, which is ascribed to the capture of surface carriers by the trapping centers in the surface oxidation layer.
Principles of femtosecond X-ray/optical cross-correlation with X-ray induced transient optical reflectivity in solids
Authors: Eckert S. , Beye M. , Pietzsch A. , Quevedo W. , Hantschmann M. , Ochmann M. , Ross M. , Minitti M. P. , Turner J. J. , Moeller S. P. , Schlotter W. F. , Dakovski G. L. , Khalil M. , Huse N. , Föhlisch A.
Published: February 2015

The discovery of ultrafast X-ray induced optical reflectivity changes enabled the development of X-ray/optical cross correlation techniques at X-ray free electron lasers worldwide. We have now linked through experiment and theory the fundamental excitation and relaxation steps with the transient optical properties in finite solid samples. Therefore, we gain a thorough interpretation and an optimized detection scheme of X-ray induced changes to the refractive index and the X-ray/optical cross correlation response.
In situ measurement of fixed charge evolution at silicon surfaces during atomic layer deposition
Authors: Ju Ling , Watt Morgan R. , Strandwitz Nicholas C.
Published: February 2015

Interfacial fixed charge or interfacial dipoles are present at many semiconductor-dielectric interfaces and have important effects upon device behavior, yet the chemical origins of these electrostatic phenomena are not fully understood. We report the measurement of changes in Si channel conduction in situ during atomic layer deposition (ALD) of aluminum oxide using trimethylaluminum and water to probe changes in surface electrostatics. Current-voltage data were acquired continually before, during, and after the self-limiting chemical reactions that result in film growth. Our measurements indicated an increase in conductance on p-type samples with p+ ohmic contacts and a decrease in conductance on analogous n-type samples. Further, p+ contacted samples with n-type channels exhibited an increase in measured current and n+ contacted p-type samples exhibited a decrease in current under applied voltage. Device physics simulations, where a fixed surface charge was parameterized on the channel surface, connect the surface charge to changes in current-voltage behavior. The simulations and analogous analytical relationships for near-surface conductance were used to explain the experimental results. Specifically, the changes in current-voltage behavior can be attributed to the formation of a fixed negative charge or the modification of a surface dipole upon chemisorption of trimethylaluminum. These measurements allow for the observation of fixed charge or dipole formation during ALD and provide further insight into the electrostatic behavior at semiconductor-dielectric interfaces during film nucleation.
Repulsion-based model for contact angle saturation in electrowetting
Authors: Ali Hassan Abdelmoumen Abdellah , Mohamed Hany Ahmed , Abdelgawad Mohamed
Published: February 2015

We introduce a new model for contact angle saturation phenomenon in electrowetting on dielectric systems. This new model attributes contact angle saturation to repulsion between trapped charges on the cap and base surfaces of the droplet in the vicinity of the three-phase contact line, which prevents these surfaces from converging during contact angle reduction. This repulsion-based saturation is similar to repulsion between charges accumulated on the surfaces of conducting droplets which causes the well known Coulombic fission and Taylor cone formation phenomena. In our model, both the droplet and dielectric coating were treated as lossy dielectric media (i.e., having finite electrical conductivities and permittivities) contrary to the more common assumption of a perfectly conducting droplet and perfectly insulating dielectric. We used theoretical analysis and numerical simulations to find actual charge distribution on droplet surface, calculate repulsion energy, and minimize energy of the total system as a function of droplet contact angle. Resulting saturation curves were in good agreement with previously reported experimental results. We used this proposed model to predict effect of changing liquid properties, such as electrical conductivity, and system parameters, such as thickness of the dielectric layer, on the saturation angle, which also matched experimental results.
Creating femtosecond-laser-hyperdoped silicon with a homogeneous doping profile
Authors: Lin Yu-Ting , Mangan Niall , Marbach Sophie , Schneider Tobias M. , Deng Guoliang , Zhou Shouhuan , Brenner Michael P. , Mazur Eric
Published: February 2015

Femtosecond-laser hyperdoping of sulfur in silicon typically produces a concentration gradient that results in undesirable inhomogeneous material properties. Using a mathematical model of the doping process, we design a fabrication method consisting of a sequence of laser pulses with varying sulfur concentrations in the atmosphere, which produces hyperdoped silicon with a uniform concentration depth profile. Our measurements of the evolution of the concentration profiles with each laser pulse are consistent with our mathematical model of the doping mechanism, based on classical heat and solute diffusion coupled to the far-from-equilibrium dopant incorporation. The use of optimization methods opens an avenue for creating controllable hyperdoped materials on demand.
An improved three-dimensional two-temperature model for multi-pulse femtosecond laser ablation of aluminum
Authors: Zhang Jinping , Chen Yuping , Hu Mengning , Chen Xianfeng
Published: February 2015

In this paper, an improved three-dimensional two-temperature model for multi-pulse femtosecond laser ablation of aluminum was proposed and proved in our experiment. Aiming to achieve hole-drilling with a high ratio of depth/entrance diameter in vacuum, this model can predict the depth and radius of the drilled holes precisely when employing different laser parameters. Additionally, for multi-pulse laser ablation, we found that the laser fluence and number of pulses are the dominant parameters and the multi-pulse ablation threshold is much lower than the single-pulse one, which will help to obtain high-quality holes.
Effect of a direct current bias on the electrohydrodynamic performance of a surface dielectric barrier discharge actuator for airflow control
Authors: Yan Huijie , Yang Liang , Qi Xiaohua , Ren Chunsheng
Published: February 2015

The effect of a DC bias on the electrohydrodynamics (EHD) force induced by a surface dielectric barrier AC discharge actuator for airflow control at the atmospheric pressure is investigated. The measurement of the surface potential due to charge deposition at different DC biases is carried out by using a special designed corona like discharge potential probe. From the surface potential data, the plasma electromotive force is shown not affected much by the DC biases except for some reduction of the DC bias near the exposed electrode edge for the sheath-like configuration. The total thrust is measured by an analytical balance, and an almost linear relationship to the potential voltage at the exposed electrode edge is found for the direct thrust force. The temporally averaged ionic wind characteristics are investigated by Pitot tube sensor and schlieren visualization system. It is found that the ionic wind velocity profiles with different DC biases are almost the same in the AC discharge plasma area but gradually diversified in the further downstream area as well as the upper space away from the discharge plasma area. Also, the DC bias can significantly modify the topology of the ionic wind produced by the AC discharge actuator. These results can provide an insight into how the DC biases to affect the force generation.
Mechanical and photo-fragmentation processes for nanonization of melanin to improve its efficacy in protecting cells from reactive oxygen species stress
Authors: Liu Yi-Cheng , Chen Sih-Min , Liu Jhong-Han , Hsu Hsiang-Wei , Lin Hoang-Yan , Chen Szu-yuan
Published: February 2015

It has been well established ex vivo that melanin has the ability of scavenging free radicals and reactive oxygen species (ROS), besides other functions. Therefore, we propose to utilize nanonized melanin as medication against acute oxidative stress. For this purpose, we developed and characterized two techniques based on mechanical stir and photo-fragmentation using femtosecond laser pulses, respectively, for disintegration of suspended melanin powder to produce nanometer-sized and water-dispersible melanin. This resolves a major obstacle in the medical and industrial applications of melanin. The viabilities of cultured retinal pigment epithelium (RPE) cells exposed to exogenous H2O2 stress and treated with various conditions of melanin and irradiation were compared. It was found that melanin could be nanonized very effectively with the techniques, and nanonized melanin exhibited a much stronger effect than unprocessed melanin on raising the viability of cultured RPE cells under acute ROS stress. The effect was even more prominent without simultaneous light irradiation, promising for effective in vivo application to the whole body.
Tunable microwave magnetic properties in oblique deposited CoHf/Ta multilayers
Authors: Chai Guozhi , Wang Xinhua , Wang Zhiling , Xue Desheng
Published: February 2015

In this work, the microwave magnetic properties of oblique deposited CoHf/Ta multilayers were investigated. The high frequency magnetic properties of CoHf/Ta multilayers showed different behaviors with oblique angle for different Ta interlayer thickness t. For example, when the Ta interlayer thickness fixed as 5.0 nm, the resonance frequency fr increased from 2.1 to 3.4 GHz with the oblique deposition angle θ changing from 10° to 30°. However, when the Ta layer fixed as 15.0 nm, the fr decreased from 2.5 to 1.7 GHz with the oblique deposition angle changing in the same range. The opposite behavior of the fr with θ is supposed to result from the existence of the Ta buffer layer, in which the thicker Ta interlayer may hinder the self-shadow effects of the CoHf magnetic layers.
On size-dependent stability and infectivity of λ bacterial phages
Authors: Li Long , Wang Jizeng
Published: February 2015

The elastic icosahedral capsid of λ phages plays an important role in the life cycle of these phages, such as holding the viral genome and releasing confinement for DNA ejection. Understanding how a nanosized elastic capsid guarantees the stability and infectivity of λ phages is challenging. In this article, we propose a combined nonlinear continuum and statistical mechanics model by considering the effects of DNA bending deformation, electrostatic repulsion between DNA–DNA strands, and elastic deformation of phage capsid to investigate the coupled process between capsid and DNA in packaging and ejection. Based on this model, we show that packaging DNA into immature λ phage capsid uses less force than packaging DNA into mature λ phage because of the deformability and softness of the former. Consequently, resistance to DNA packaging inside capsid decreases compared with mature ones. We also observe relationships between phage capsid size and the maximum shear stress on the inner surface of capsid and required osmotic pressure for the complete inhibition of DNA ejection. An optimized radius of capsid, i.e., around 30 nm, is found for both stable DNA packaging and effective viral infection from mechanical standpoints, which may result from physical evolution. All these findings may be interesting to toxicologists, nanotechnologists, and virologists.
Polymer-ceramic composite filler selection using mixing rules
Authors: Tuhkala M. , Juuti J. , Teirikangas M. , Jantunen H.
Published: February 2015

In this work, classical Bruggeman symmetric and Looyenga mixing rules were used together with a general mixing model to estimate the permittivities and loss tangents of polymer composites in order to make rational filler selections. Eight different fillers were used and compared with theoretical polymer composites. Permittivity levels of the composites were between 2.1 and 70 in the frequency range of 2.5−8 GHz. Results showed that rational selections of fillers also provided better properties of composites when using low permittivity instead of high permittivity filler. However, in certain permittivity targets, better properties were achieved with high permittivity filler. The selections were based on the required volume ratios of fillers and total loss tangents of the composites. Theoretical results correlated well with previously reported values.
Room temperature nonlinear magnetoelectric effect in lead-free and Nb-doped AlFeO3 compositions
Authors: Cótica Luiz F. , Santos Guilherme M. , Freitas Valdirlei F. , Coelho Adelino A. , Pal Madhuparna , Santos Ivair A. , Garcia Ducinei , Eiras José A. , Guo Ruyan , Bhalla Amar S.
Published: February 2015

It is still a challenging problem to obtain technologically useful materials displaying strong magnetoelectric coupling at room temperature. In the search for new effects and materials to achieve this kind of coupling, a nonlinear magnetoelectric effect was proposed in the magnetically disordered relaxor ferroelectric materials. In this context, the aluminum iron oxide (AlFeO3), a room temperature ferroelectric relaxor and magnetic spin glass compound, emerges as an attractive lead-free magnetoelectric material along with nonlinear magnetoelectric effects. In this work, static, dynamic, and temperature dependent ferroic and magnetoelectric properties in lead-free AlFeO3 and 2 at. % Nb-doped AlFeO3 multiferroic magnetoelectric compositions are studied. Pyroelectric and magnetic measurements show changes in ferroelectric and magnetic states close to each other (∼200 K). The magnetoelectric coefficient behavior as a function of Hbias suggests a room temperature nonlinear magnetoelectric coupling in both single-phase and Nb-doped AlFeO3-based ceramic compositions.
Mechanical properties and magnetocaloric effects in La(Fe, Si)13 hydrides bonded with different epoxy resins
Authors: Zhang Hu , Sun YuJie , Li YaWei , Wu YuanYuan , Long Yi , Shen Jun , Hu FengXia , Sun JiRong , Shen BaoGen
Published: February 2015

The mechanical properties and magnetocaloric effect (MCE) of bonded La(Fe, Si)13 hydrides have been studied in detail. The mechanical strength increases with increasing the grade of epoxy resin from E-20 to E-51. This occurs because more pores and boundaries are filled with high grade resin since high epoxide content increases the degree of crosslinking and reduces the viscosity and shrinkage of resin. The compressive strength reaches 162 MPa for the bonded LaFe11.7Si1.3C0.2H1.8 with 3 wt. % E-51, which is 35% higher than that of bulk LaFe11.7Si1.3C0.2 compound (120 MPa). The mass ΔSM values remain almost same in bonded hydrides and are in a good agreement with the theoretical value. The maximum volumetric ΔSM values are 61.8, 58.0, and 54.7 mJ/cm3 K for bonded hydrides with epoxy resins E-20, E-44, and E-51, respectively, much higher than those of some magnetocaloric materials in same temperature range. The improved mechanical properties and large MCE indicate that bonded LaFe11.7Si1.3C0.2H1.8 is a promising material for room temperature magnetic refrigeration.
Correlative transmission electron microscopy and electrical properties study of switchable phase-change random access memory line cells
Authors: Oosthoek J. L. M. , Voogt F. C. , Attenborough K. , Verheijen M. A. , Hurkx G. A. M. , Gravesteijn D. J. , Kooi B. J.
Published: February 2015

Phase-change memory line cells, where the active material has a thickness of 15 nm, were prepared for transmission electron microscopy (TEM) observation such that they still could be switched and characterized electrically after the preparation. The result of these observations in comparison with detailed electrical characterization showed (i) normal behavior for relatively long amorphous marks, resulting in a hyperbolic dependence between SET resistance and SET current, indicating a switching mechanism based on initially long and thin nanoscale crystalline filaments which thicken gradually, and (ii) anomalous behavior, which holds for relatively short amorphous marks, where initially directly a massive crystalline filament is formed that consumes most of the width of the amorphous mark only leaving minor residual amorphous regions at its edges. The present results demonstrate that even in (purposely) thick TEM samples, the TEM sample preparation hampers the probability to observe normal behavior and it can be debated whether it is possible to produce electrically switchable TEM specimen in which the memory cells behave the same as in their original bulk embedded state.
Poor fluorinated graphene sheets carboxymethylcellulose polymer composite mode locker for erbium doped fiber laser
Authors: Mou Chengbo , Arif Raz , Lobach Anatoly S. , Khudyakov Dmitry V. , Spitsina Nataliya G. , Kazakov Valery A. , Turitsyn Sergei , Rozhin Aleksey
Published: February 2015

We report poor fluorinated graphene sheets produced by thermal exfoliation embedding in carboxymethylcellulose polymer composite (GCMC) as an efficient mode locker for erbium doped fiber laser. Two GCMC mode lockers with different concentration have been fabricated. The GCMC based mode locked fiber laser shows stable soliton output pulse shaping with repetition rate of 28.5 MHz and output power of 5.5 mW was achieved with the high concentration GCMC, while a slightly higher output power of 6.9 mW was obtained using the low concentration GCMC mode locker.
Vibrational modes of ultrathin carbon nanomembrane mechanical resonators
Authors: Zhang Xianghui , Waitz Reimar , Yang Fan , Lutz Carolin , Angelova Polina , Gölzhäuser Armin , Scheer Elke
Published: February 2015

We report measurements of vibrational mode shapes of mechanical resonators made from ultrathin carbon nanomembranes (CNMs) with a thickness of approximately 1 nm. CNMs are prepared from electron irradiation induced cross-linking of aromatic self-assembled monolayers and the variation of membrane thickness and/or density can be achieved by varying the precursor molecule. Single- and triple-layer freestanding CNMs were made by transferring them onto Si substrates with square/rectangular orifices. The vibration of the membrane was actuated by applying a sinusoidal voltage to a piezoelectric disk on which the sample was glued. The vibrational mode shapes were visualized with an imaging Mirau interferometer using a stroboscopic light source. Several mode shapes of a square membrane can be readily identified and their dynamic behavior can be well described by linear response theory of a membrane with negligible bending rigidity. By applying Fourier transformations to the time-dependent surface profiles, the dispersion relation of the transverse membrane waves can be obtained and its linear behavior verifies the membrane model. By comparing the dispersion relation to an analytical model, the static stress of the membranes was determined and found to be caused by the fabrication process.
Front grid optimization of Cu(In,Ga)Se2 solar cells using hybrid modeling approach
Authors: Bednar N. , Severino N. , Adamovic N.
Published: February 2015

This paper describes the hybrid approach to modeling and simulation of thin film solar cells with a metal front grid. A 3D model with high aspect ratio of device thickness (100 s of nm) and its length and width (mm and cm range) was divided into two coupled models with different number of spatial dimensions (a 1D and a 3D model) on different length scales. The first one is modeling of the material level of solar cell which is then coupled with the second model taking into account the photovoltaic (PV) cell/module geometry. It calculates the photo-current flow through the transparent electrode dictated by the shape of metal front grid. This approach enables the separation of the technology-dependent material simulation from the front grid design simulation. In this paper, the use of the developed model to simulate solar cells based on Cu(In,Ga)Se2 technology is described. The metallization in the form of parallel fingers was investigated and optimized for the described case study. Finally, the efficiency of solar thin-film modules using optimized cells with different widths was explored, thus enabling the tuning of the output voltage of the solar module while the power output remains unchanged.
Enhanced ferroelectric and ferromagnetic properties in lead-free multilayer composite films based on ferroelectric (Bi0.5Na0.5)0.945Ba0.055TiO3 and multiferroic BiFeO3
Authors: Perez-Rivero A. , Ricote J. , Bretos I. , García-Hernández M. , Calzada M. L. , Jiménez R.
Published: February 2015

The study of the functional properties of the multilayer composite films of ferroelectric (Bi0.5Na0.5)0.945Ba0.055TiO3 (BNBT) and multiferroic BiFeO3 (BF) obtained by chemical solution deposition has been performed in this work. First, it has been observed a significant improvement of the remnant polarization of the multilayer composite with respect to the single phase film of BNBT: Pr = 32 μC × cm−2, which is comparable with the values reported for bulk BNBT. This is a consequence of the stabilization of the ferroelectric domains of BNBT, although the relaxor character is still present. The leakage currents, which prevent the full exploitation of the properties of BF films, are reduced thanks to the combination with insulator BNBT layers. Besides, the magnetic behavior shows values of remnant magnetization at room temperature that makes this multilayer composites promising for multiferroic applications.
Thermal and electromechanical properties of melilite-type piezoelectric single crystals
Authors: Shen Chuanying , Zhang Shujun , Cao Wenwu , Cong Hengjiang , Yu Haohai , Wang Jiyang , Zhang Huaijin
Published: February 2015

Melilite-type crystals, including Ca2Ga2SiO7, Ca2MgSi2O7, and CaNdGa3O7, were successfully grown by the Czochralski technique. Thermal properties were investigated and full matrices of electromechanical constants of these melilite crystals were evaluated by impedance method, with d14 being on the order of 5.3–9.3 pC/N. The relationship between microstructure and electromechanical properties of the three kinds of crystals was established, in order to explore the piezoelectric origin and further optimize the piezoelectric properties. The distortion of eight-fold antiprisms and the distortion/rotation of tetrahedrons were thought to contribute to the piezoelectric d14 and d36, respectively. In addition, the layered structure leads to strong anisotropic behavior, accounts for the high resistivity along Z direction in Ca2MgSi2O7, while the disordered structure accounts for the degraded resistivity in CaNdGa3O7. The properties at elevated temperature were investigated, where the elastic constants show high thermal stability over the range of 25–500 °C, with minimal variation of 6%.
Crack propagation in viscoplastic polymers: Heat generation in near-tip zone and viscoplastic cohesive model
Authors: Chen Y. T. , Liu K. X.
Published: February 2015

We develop a precise experimental method to measure the full-field heat-generating process near moving (mode I) crack tips in polycarbonate films and present the experimental image of crack tip structure in viscoplastic polymers. A viscoplastic cohesive model is constructed to analyze the mechanical state and temperature increase in near-tip zone during steady crack propagation. The cohesive stress in this model is uniquely characterized by viscoplastic constitutive equation instead of traction-separation displacement relationship or constant yield stress, which greatly differs from previous models. Our proposed model's prediction of temperature increase agrees well with the experimental result.
Highly sensitive and stable relative humidity sensors based on WO3 modified mesoporous silica
Authors: Tomer Vijay K. , Duhan Surender
Published: February 2015

This study investigates the effectiveness of using WO3 loaded mesoporous silica nanocomposite developed using one step hydrothermal method for measuring relative humidity (RH) at room temperature. On measuring the sensing response, the nanocomposite sensor exhibits excellent linearity, negligible hysteresis, swift response and recovery time, good repeatability, and outstanding stability in 11%–98% RH range. The complex impedance spectra of the sensor at different RHs were used to explore the humidity sensing mechanism. This work could encourage a right approach to blueprint practical humidity sensors with high sensitivity, long stability and fast response/recovery time.
A hole modulator for InGaN/GaN light-emitting diodes
Authors: Zhang Zi-Hui , Kyaw Zabu , Liu Wei , Ji Yun , Wang Liancheng , Tan Swee Tiam , Sun Xiao Wei , Demir Hilmi Volkan
Published: February 2015

The low p-type doping efficiency of the p-GaN layer has severely limited the performance of InGaN/GaN light-emitting diodes (LEDs) due to the ineffective hole injection into the InGaN/GaN multiple quantum well (MQW) active region. The essence of improving the hole injection efficiency is to increase the hole concentration in the p-GaN layer. Therefore, in this work, we have proposed a hole modulator and studied it both theoretically and experimentally. In the hole modulator, the holes in a remote p-type doped layer are depleted by the built-in electric field and stored in the p-GaN layer. By this means, the overall hole concentration in the p-GaN layer can be enhanced. Furthermore, the hole modulator is adopted in the InGaN/GaN LEDs, which reduces the effective valance band barrier height for the p-type electron blocking layer from ∼332 meV to ∼294 meV at 80 A/cm2 and demonstrates an improved optical performance, thanks to the increased hole concentration in the p-GaN layer and thus the improved hole injection into the MQWs.
Tuning of Fano resonances in terahertz metamaterials
Authors: Cao Y. P. , Wang Y. Y. , Geng Z. X. , Liu J. , Yang Y. P. , Chen H. D.
Published: February 2015

To overcome the large linewidth in the transmission spectra of metamaterials which have been applied in fields such as bio-sensing and light modulating in terahertz regime, a set of terahertz metamaterials which are composed of two different split ring resonators are designed and fabricated to explore the characteristics such as Fano resonances and quality factors by changing the geometry structure. The results illustrate that the Fano resonance is tuned both in the depth and in the width when the gap position of the metamaterial with asymmetric structure varies. Meanwhile, to obtain extremely sharp Fano resonances, the gap width is reduced, which greatly improves the quality factor of the Fano line shape in the transmission spectra, presenting a narrow linewidth of merely 11 GHz in the simulation and 23 GHz in the experiment.
Thickness effect on magnetocrystalline anisotropy of Co/Pd(111) films: A density functional study
Authors: Jekal Soyoung , Rhim S. H. , Kwon Oryong , Hong Soon Cheol
Published: February 2015

In this study, we carried out first-principles calculations on magnetocrystalline anisotropy (MCA) of Co/Pd thin films by adopting two different systems of (i) n-Co/3-Pd and (ii) n-Pd/3-Co. In one system, we vary the thickness of Co layer, fixing the thickness of the Pd layer to 3-monolayers, and in the other system vice versa. MCA is mainly governed by the surface and interface Co atoms, while contributions from other Co atoms are smaller. MCA energy (EMCA) of the Co/Pd thin film shows oscillatory behavior with the thickness of the Co layer, but is insensitive to the thickness of the Pd layer. In particular, the n-Co/3-Pd films of n = 2, 4, and 6 exhibit strong perpendicular MCA of about 1 meV. Our results suggest that controlling the thickness of the Co layer in Co/Pd (111) is crucial in achieving strong perpendicular MCA.
Structural, magnetic, and dielectric properties of graphene oxide/ZnxFe1−xFe2O4 composites
Authors: Khurana Geetika , Kumar Nitu , Kooriyattil Sudheendran , Katiyar Ram S.
Published: February 2015

Graphene oxide (GO)/ZnxFe1−xFe2O4 (ZFO) (x = 0.1, 0.3, 0.5, and 0.7) composites were synthesized using a facile two-step synthesis process. GO bulk powder was synthesized by the modified Hummer's method and the ZFO nanoparticles (NPs) (particle size 3–12 nm) by chemical co-precipitation method. Structural analysis of GOZFO composites confirms the coexistence of both phases without any additional impurity phase. The saturation magnetization was found to increase with increasing particle size of ZFO in composite samples. Semiconducting nature of the resistance was found to increase with decreasing particle size of ZFO due to enhanced scattering. The dielectric properties of the composite system were also improved by the addition of ZFO NPs and the maximum enhancement was observed in the composite having ultrafine ZFO NPs. These results indicate that GOZFO composites can be seen as the potential candidates for magnetic and capacitive applications.
Tracing the transition of a macro electron shuttle into nonlinear response
Authors: Kim Chulki , Prada Marta , Qin Hua , Kim Hyun-Seok , Blick Robert H.
Published: February 2015

We present a study on a macroscopic electron shuttle in the transition from linear to nonlinear response. The shuttle consists of a classical mechanical pendulum situated between two capacitor plates. The metallic pendulum enables mechanical transfer of electrons between the plates, hence allowing to directly trace electron shuttling in the time domain. By applying a high voltage to the plates, we drive the system into a controlled nonlinear response, where we observe period doubling.
Thermally activated domain wall motion in [Co/Ni](111) superlattices with perpendicular magnetic anisotropy
Authors: Le Gall S. , Vernier N. , Montaigne F. , Gottwald M. , Lacour D. , Hehn M. , Ravelosona D. , Mangin S. , Andrieu S. , Hauet T.
Published: February 2015

Field-induced magnetization dynamics in a [Co/Ni] superlattice exhibiting strong perpendicular magnetic anisotropy is studied using Kerr microscopy. We report domain wall velocity over 8 decades within thermally activated, transitory, and flow dynamical regimes. At low field, the thermally activated regime is characterized by dendritic domain growth that differs from the creep mechanism usually observed for the interaction of domains wall with a 2D random pinning potential for layers grown by sputtering. This result is explained by the epitaxial nature of the [Co/Ni] superlattices involving a single-type defect. The transition from the thermally activated to the flow regime is characterized by a reduction of the density of non-reversed domains which exists after domain wall displacement.
Quasi-unipolar pentacene films embedded with fullerene for non-volatile organic transistor memories
Authors: Lee Juhee , Lee Sungpyo , Lee Moo Hyung , Kang Moon Sung
Published: February 2015

Quasi-unipolar non-volatile organic transistor memory (NOTM) can combine the best characteristics of conventional unipolar and ambipolar NOTMs and, as a result, exhibit improved device performance. Unipolar NOTMs typically exhibit a large signal ratio between the programmed and erased current signals but also require a large voltage to program and erase the memory cells. Meanwhile, an ambipolar NOTM can be programmed and erased at lower voltages, but the resulting signal ratio is small. By embedding a discontinuous n-type fullerene layer within a p-type pentacene film, quasi-unipolar NOTMs are fabricated, of which the signal storage utilizes both electrons and holes while the electrical signal relies on only hole conduction. These devices exhibit superior memory performance relative to both pristine unipolar pentacene devices and ambipolar fullerene/pentacene bilayer devices. The quasi-unipolar NOTM exhibited a larger signal ratio between the programmed and erased states while also reducing the voltage required to program and erase a memory cell. This simple approach should be readily applicable for various combinations of advanced organic semiconductors that have been recently developed and thereby should make a significant impact on organic memory research.
Thermal self-oscillations in radiative heat exchange
Authors: Dyakov S. A. , Dai J. , Yan M. , Qiu M.
Published: February 2015

We report the effect of relaxation-type self-induced temperature oscillations in the system of two parallel plates of SiO2 and VO2 which exchange heat by thermal radiation in vacuum. The non-linear feedback in the self-oscillating system is provided by metal-insulator transition in VO2. Using the method of fluctuational electrodynamics, we show that under the action of an external laser of a constant power, the temperature of VO2 plate oscillates around its phase transition value. The period and amplitude of oscillations depend on the geometry of the structure. We found that at 500 nm vacuum gap separating bulk SiO2 plate and 50 nm thick VO2 plate, the period of self-oscillations is 2 s and the amplitude is 4 K, which is determined by phase switching at threshold temperatures of phase transition.
Monitoring non-pseudomorphic epitaxial growth of spinel/perovskite oxide heterostructures by reflection high-energy electron diffraction
Authors: Schütz P. , Pfaff F. , Scheiderer P. , Sing M. , Claessen R.
Published: February 2015

Pulsed laser deposition of spinel γ-Al2O3 thin films on bulk perovskite SrTiO3 is monitored by high-pressure reflection high-energy electron diffraction (RHEED). The heteroepitaxial combination of two materials with different crystal structures is found to be inherently accompanied by a strong intensity modulation of bulk diffraction patterns from inelastically scattered electrons, which impedes the observation of RHEED intensity oscillations. Avoiding such electron surface-wave resonance enhancement by de-tuning the RHEED geometry allows for the separate observation of the surface-diffracted specular RHEED signal and thus the real-time monitoring of sub-unit cell two-dimensional layer-by-layer growth. Since these challenges are essentially rooted in the difference between film and substrate crystal structure, our findings are of relevance for the growth of any heterostructure combining oxides with different crystal symmetry and may thus facilitate the search for novel oxide heterointerfaces.
Conductive rubber based flexible metamaterial
Authors: Zhang Fuli , Liu Zijun , Qiu Kepeng , Zhang Weihong , Wu Chen , Feng Shuqi
Published: February 2015

In this letter, we present experimentally flexible split ring resonator (SRR) metamaterial made of conductive rubber. Different from most conventional flexible metamaterials whose mechanical advantage relied on ultrathin soft substrates, compliance property of conductive rubber based SRR results from its intrinsic property. Experimental results show that unique property of negative effective parameter is preserved by conductive rubber based SRR. Moreover, strain property of conductive rubber not only allows SRR to be compliant but also provides extra means to frequency tunability. When SRR is deformed along its symmetric axis, an extra capacitance is formed by gap-bearing side, resulting in a decreasing resonance trend with enhanced deformation.
Absorption properties of type-II InAs/InAsSb superlattices measured by spectroscopic ellipsometry
Authors: Webster P. T. , Riordan N. A. , Liu S. , Steenbergen E. H. , Synowicki R. A. , Zhang Y.-H. , Johnson S. R.
Published: February 2015

Strain-balanced InAs/InAsSb superlattices offer access to the mid- to long-wavelength infrared region with what is essentially a ternary material system at the GaSb lattice constant. The absorption coefficients of InAs/InAsSb superlattices grown by molecular beam epitaxy on (100)-oriented GaSb substrates are measured at room temperature over the 30 to 800 meV photon energy range using spectroscopic ellipsometry, and the miniband structure of each superlattice is calculated using a Kronig-Penney model. The InAs/InAsSb conduction band offset is used as a fitting parameter to align the calculated superlattice ground state transition energy to the measured absorption onset at room temperature and to the photoluminescence peak energy at low temperature. It is observed that the ground state absorption coefficient and transition strength are proportional to the square of the wavefunction overlap and the ground state absorption coefficient approaches a maximum value of around 5780 cm−1 as the wavefunction overlap approaches 100%. The absorption analysis of these samples indicates that the optical joint density of states is weakly dependent on the period thickness and Sb content of the superlattice, and that wavefunction overlap is the principal design parameter in terms of obtaining strong absorption in these structures.
Wavelength-selective plasmonics for enhanced cultivation of microalgae
Authors: Ooms Matthew D. , Jeyaram Yogesh , Sinton David
Published: February 2015

Optimal photon management is a key challenge for photobioreactor design, since light gradients and varying spectral sensitivities between organisms result in uneven illumination and unused photons. This paper demonstrates wavelength specific scattering from plasmonic nano-patterned surfaces as a means of addressing the challenge of photon management in photobioreactors. Modular photobioreactors were constructed with different reflective substrates including arrays of plasmonic nanodisks, broadband reflectors, and untreated glass. It was found that the growth rate of cyanobacterium S. elongatus in photobioreactors equipped with a plasmonic substrate (R623 nm ∼ 35%) was enhanced by 6.5% compared to photobioreactors equipped with untreated glass. Furthermore, plasmonic reflectors showed a normalized power efficiency improvement of 52% over broadband reflectors. Wavelength-specific reflection from plasmonic reflectors increases the flux of useful light to cultures without sacrificing the full spectrum.
Estimates of repeatability and heritability of methane production in sheep using portable accumulation chambers
Authors: Goopy J. P. , Robinson D. L. , Woodgate R. T. , Donaldson A. J. , Oddy V. H. , Vercoe P. E. , Hegarty R. S.
Published: February 2015

This study was designed to screen a large number of sheep to identify individuals with high and low methane (CH4) production, and to estimate repeatability and heritability of CH4 emissions in sheep, utilising portable accumulation chambers (PAC) designed for in-field use. Mature ewes (n = 710) selected from a research flock with known sires had their CH4 production over 1 h measured in PAC [CH4 (g1h)]. Individuals with High (n = 103) or Low (n = 104) CH4 (g1h), adjusted for liveweight (LW), were selected and re-measured on three occasions 1–4 months later, at another site with more abundant and better quality pasture. Mean of the selected (207) ewes CH4 (g1h) emissions were ~50% higher than at the first measurement site (0.66 g vs 0.42 g). LW was a significant correlate of CH4 production (r = 0.47). Correlations between CH4 (g1h) for the three PAC measurements at Site 2, before adjusting for LW ranged from 0.44 to 0.55. After adjusting for the effect of LW, repeatability was 0.33 at the first and 0.43 at the second site. The correlation between estimates of an animal’s emissions at the first and second sites, adjusted for LW, was 0.24. Initial CH4 production of the selected High group was 32% greater than the Low group (P < 0.0001). On re-measurement there was still a significant difference (9–15%, P < 0.006) between Low and High groups. The initial estimate of heritability of CH4 (g1h), based on variation between the ewes’ sires (0.13), was not maintained across the two sites. This may be due to genotype × environment interactions. We postulate that aspects of rumen physiology, which modulate CH4 production, could be expressed differently in different nutritional environments. Our results indicate that field use of PAC to screen sheep populations for CH4 production is both robust and repeatable. However, further investigations are required into the relationship between CH4 output of individual animals in PAC compared with the more controlled conditions in respiration chambers.
Determination and prediction of the net energy content of seven feed ingredients fed to growing pigs based on chemical composition
Authors: Liu D. W. , Liu L. , Li D. F. , Wang F. L.
Published: February 2015

Two experiments were conducted to determine the net energy (NE) content of various feed ingredients (Exp. 1) and to establish prediction equations for NE for these same ingredients (Exp. 2). In Exp. 1, 36 barrows (27.5 ± 0.5 kg) were assigned to six diets (in a completely randomised design) to give six replicates per diet. The diets were a corn-soybean meal basal diet and five experimental diets containing either wheat, wheat bran, corn dried distillers grains with solubles (cDDGS), canola meal or cottonseed meal. The pigs were housed in six open-circuit chambers (six pigs at a time balanced for dietary treatment) for 16 days, the first 7 days were used for an adaptation to the diets, while for the next 5 days pigs were fed ad libitum (2400 kJ/kg BW0.6·day–1), then fed at 1 × metabolisable energy (ME) for maintenance for 3 days, followed by fasting for 24 h. The NE content of wheat, wheat bran, cDDGS, canola meal, and cottonseed meal were 11.44, 7.78, 10.21, 8.38, and 7.32 MJ/kg DM, respectively. Stepwise regression analysis performed between the chemical composition and the energy value of the ingredients, allowed for the NE to be accurately predicted from chemical characteristics. The best fit equation was: NE = 1.46 + (0.63 × gross energy) – (0.37 × acid detergent fibre), with a R2 of 0.94, a residual standard deviation (RSD) of 0.54 MJ/kg, and P < 0.01. In Exp. 2, 36 barrows (34.6 ± 1.5 kg) were randomly allotted to six diets containing various combinations of corn, soybean meal, wheat, wheat bran, cDDGS, canola meal, or cottonseed meal. The chemical composition of each diet was determined and the results were used to establish prediction equations for the NE in the six diets and 16 diets (including six diets from Exp. 1, six diets from Exp. 2 and four diets from our laboratory published data). The best fit equations were as follows: NE = –0.47 + (0.84 × ME) with an R2 of 0.94, a RSD of 0.20 MJ/kg, and P < 0.01; NE = –10.19 + (0.97 × digestible energy) + (0.08 × starch) + (0.05 × acid detergent fibre) with an R2 of 0.84, a RSD of 0.46 MJ/kg, and P < 0.01, respectively. In summary, the NE of the seven ingredients could be better measured by the respiration calorimetry estimated by substitution method. The NE prediction equation determined based on the chemical characteristics of the test ingredients was better than when determined using the chemical characteristics of the diets.
Ketenes from N-(2-Pyridyl)amides
Authors: Plüg Carsten , Kanaani Hussein , Wentrup Curt
Published: February 2015

Methoxycarbonylketene 4a, methoxycarbonyl(methyl)ketene 4b, chloroketene 4c, cyanoketene 4d, diphenylketene 4e, and 2-pyridylketene 4f have been generated by flash vacuum thermolysis of the corresponding 2-pyridylacetamide derivatives 3a–f and isolated in Ar matrices for FT-IR spectroscopic characterisation. The N-(2-pyridyl)-2-pyridylacetamide 3f yielded 2-pyridyl isocyanate in addition to 2-pyridylketene.