bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser surface micro-/nano-structuring by a simple transportable micro-sphere lens array
Authors: Sedao Xxx , Derrien Thibault J.-Y. , Romer Gert-willem R. B. E. , Pathiraj Belavendram , Huis in ‘t Veld Albertus J.
Published: November 2012

A micro-sphere array optic was employed for laser surface micro-structuring. This array optic consists of a hexagonally close-packed monolayer of silica micro-spheres. It was organized through a self-assembly process and held together on a glass support, without using any adhesives. The array assembly was then reversed, placed in direct contact with the substrate and exposed to 515 nm, 6.7 ps laser pulses. During the exposure, the silica spheres act as micro-lenses, which enhance the near-field light intensity underneath them. As the spheres are confined in the space between the substrate and glass support, they are not ejected during laser machining. Using this type of direct write laser machining, a large number of identical features (nano-holes) can be produced in parallel simultaneously. The holes drilled are a few hundred nanometres in diameter and the depth depends on the number of laser pulses applied. The impact of laser machining on the micro-spheres was also studied. The micro-spheres were contaminated or partially damaged after micro-structuring. Combination of a moderate laser pulse energy and multiple shots was found to ensure a good surface structuring quality and minimum damage to the spherical particles.
Enhancing heat transfer in a high Hartmann number magnetohydrodynamic channel flow via torsional oscillation of a cylindrical obstacle
Authors: Hussam Wisam K. , Thompson Mark C. , Sheard Gregory J.
Published: November 2012

An approach is studied for side-wall heat transfer enhancement in the magnetohydrodynamic flow of fluid in a rectangular duct that is damped by a strong transverse magnetic field. The mechanism employs the rotational oscillation of a cylinder placed inside the duct to encourage vortex shedding, which promotes the mixing of fluid near a hot duct wall with cooler fluid in the interior. The effectiveness of the heat transfer enhancement is investigated over a wide range of oscillation amplitudes and forcing frequencies. The motivation for exploring this mechanism is inspired by the transient growth response of this flow, which indicates that the optimal disturbances feeding the vortex shedding process are localized near the cylinder, and are characterized by an asymmetrical disturbance with respect to the wake centreline. The results show that a considerable increase in heat transfer from the heated channel wall due to rotational oscillation of the cylinder can be achieved, with the maximum enhancement of more than 30% over a zone extending 10d downstream of the cylinder. As the angular velocity amplitude of oscillation is increased, the range of oscillation frequencies for effective enhancement is widened, and the frequency at which the peak Nusselt number occurs is shifted slightly to lower frequencies. As the amplitude is increased, the formation of strong discrete wake vortices draws fluid from the wall boundary layers into the wake, enhancing heat transfer. The effect of oscillation amplitude on the distribution of local Nusselt number \documentclass[12pt]{minimal}\begin{document}$\textit {Nu}_w$\end{document}Nuw along the heated wall is significant. With an increase in Reynolds number, scope for additional heat transfer enhancement is possible.
Low density shear viscosity of Lennard-Jones chains of variable rigidities
Authors: Delage Santacreu S. , Galliero G. , Odunlami M. , Boned C.
Published: November 2012

The zero-density shear viscosity of different types of short Lennard-Jones chains, up to the hexa-decamer, has been evaluated using a non-equilibrium molecular dynamics scheme. Simulations have been performed on chains of variable rigidities going from the fully flexible to the fully rigid chains. Very interestingly, it is found that there exists a universal relation (a power law) between the zero-density viscosity of the Lennard-Jones chains and their radius of gyration whatever the rigidity of the chain and for all tested temperatures (ranging from 2.5 to 6 in reduced units). Furthermore, for the studied range of temperature, it is shown that the zero-density viscosity of both fully flexible chains and fully rigid chains models can be obtained with an accuracy of a few percents knowing only the dimer viscosity and the length of the chain.
Effects of passive control rings positioned in the shear layer and potential core of a turbulent round jet
Authors: Sadeghi H. , Pollard A.
Published: November 2012

Experimental measurements were carried out to study the effect of flow modification near the jet exit on a turbulent round free jet. To achieve this, two different fine rings, with square cross-sections, were designed and placed very close to the jet exit (x/D = 0.03). The first ring was placed in the middle of the shear layer while the second ring covered a small region of the potential core. Flying and stationary hot wire measurements were carried out to study the near- and intermediate-field development of the jet. Three Reynolds numbers (based on the jet exit mean velocity and the nozzle diameter) were used: 10 000, 30 000, and 50 000. The results show a considerable reduction in the jet spread rate and turbulence intensity when the passive rings are employed. This is more obvious for the ring placed in the shear layer. The radial profiles of the mean and rms axial velocity and third and fourth moments of fluctuations at several axial positions are considered. The power density spectra reveal the suppression of the initial shear layer instability (shear layer mode), while the jet preferred instability (preferred mode) remains active as the shear layer is modified. In the case when potential core modifications are used, the suppression of the initial shear layer instability is still considerable although there is an evidence of another vortical structure behind the ring, which, it is speculated, is due to the vortex shedding behind the ring. In this case, too, the jet preferred instability remains active. Therefore, the current paper confirms the separation of these two modes. In addition, the current contribution provides a comprehensive study of the characteristics of different length scales in the development region of the jet (e.g., integral scale, Taylor microscale, and Kolmogorov scale) for both the modified and unmodified jets.
Realizable versus non-realizable dynamic subgrid-scale stress models
Authors: Heinz Stefan , Gopalan Harish
Published: November 2012

The existence of many different dynamic large eddy simulation (LES) methods leads to questions about the theoretical foundation of dynamic LES methods. It was shown recently that the use of stochastic analysis enables a theoretically well based systematic derivation of a realizable linear dynamic model (LDM) and a realizable nonlinear dynamic model (NDM). A priori and a posteriori analyses of turbulent channel flow are used here to study the characteristic properties of these dynamic models. The LDM and NDM are compared with other dynamic models: the non-stabilized and stabilized dynamic Smagorinsky model (DSM), which is used in many applications of LES, and Wang-Bergstrom's dynamic model (WBDM), which represents an extension of the DSM. The DSM and WBDM do not represent realizable models because they are not derived as consequences of a realizable stochastic process. The comparisons reported here show that the LDM and NDM are based on a dynamic model formulation that avoids shortcomings of existing concepts. The LDM and NDM account for backscatter, and they are computationally stable without any modification. The LDM and NDM represent the instantaneous small scale structure of turbulence very well. Compared to the DSM and WBDM, respectively, the LDM and NDM are computationally more efficient.
Electron scattering from pyrazine: Elastic differential and integral cross sections
Authors: Palihawadana P. , Sullivan J. P. , Buckman S. J. , Brunger M. J.
Published: November 2012

We report on new measurements for elastic electron scattering from pyrazine. Absolute differential cross sections (DCSs) at seven discrete energies in the range 3–50 eV, and over the scattered electron angular range 10°–129°, were determined using a crossed electron-molecular beam spectrometer in conjunction with the well-established relative flow technique. Integral elastic cross sections were subsequently derived from those DCS data at each energy. Where possible comparison between the present results and those from sophisticated Schwinger multichannel and R-matrix computations is made, with generally quite good quantitative accord being found. Finally, in order to better study some of the rich resonance structure predicted by theory, results from elastic electron excitation functions are presented.
The influence of magnetic field strength in ionization stage on ion transport between two stages of a double stage Hall thruster
Authors: Yu Daren , Song Maojiang , Li Hong , Liu Hui , Han Ke
Published: November 2012

It is futile for a double stage Hall thruster to design a special ionization stage if the ionized ions cannot enter the acceleration stage. Based on this viewpoint, the ion transport under different magnetic field strengths in the ionization stage is investigated, and the physical mechanisms affecting the ion transport are analyzed in this paper. With a combined experimental and particle-in-cell simulation study, it is found that the ion transport between two stages is chiefly affected by the potential well, the potential barrier, and the potential drop at the bottom of potential well. With the increase of magnetic field strength in the ionization stage, there is larger plasma density caused by larger potential well. Furthermore, the potential barrier near the intermediate electrode declines first and then rises up while the potential drop at the bottom of potential well rises up first and then declines as the magnetic field strength increases in the ionization stage. Consequently, both the ion current entering the acceleration stage and the total ion current ejected from the thruster rise up first and then decline as the magnetic field strength increases in the ionization stage. Therefore, there is an optimal magnetic field strength in the ionization stage to guide the ion transport between two stages.
Effect of the heterogeneous neuron and information transmission delay on stochastic resonance of neuronal networks
Authors: Wang Qingyun , Zhang Honghui , Chen Guanrong
Published: November 2012

We study the effect of heterogeneous neuron and information transmission delay on stochastic resonance of scale-free neuronal networks. For this purpose, we introduce the heterogeneity to the specified neuron with the highest degree. It is shown that in the absence of delay, an intermediate noise level can optimally assist spike firings of collective neurons so as to achieve stochastic resonance on scale-free neuronal networks for small and intermediate αh, which plays a heterogeneous role. Maxima of stochastic resonance measure are enhanced as αh increases, which implies that the heterogeneity can improve stochastic resonance. However, as αh is beyond a certain large value, no obvious stochastic resonance can be observed. If the information transmission delay is introduced to neuronal networks, stochastic resonance is dramatically affected. In particular, the tuned information transmission delay can induce multiple stochastic resonance, which can be manifested as well-expressed maximum in the measure for stochastic resonance, appearing every multiple of one half of the subthreshold stimulus period. Furthermore, we can observe that stochastic resonance at odd multiple of one half of the subthreshold stimulus period is subharmonic, as opposed to the case of even multiple of one half of the subthreshold stimulus period. More interestingly, multiple stochastic resonance can also be improved by the suitable heterogeneous neuron. Presented results can provide good insights into the understanding of the heterogeneous neuron and information transmission delay on realistic neuronal networks.
Simulations of the linear plasma synthetic jet actuator utilizing a modified Suzen-Huang model
Authors: Ibrahim I. H. , Skote M.
Published: November 2012

The linear plasma synthetic jet actuator (L-PSJA) is a unique form of flow control device which harnesses the interaction of induced flows from two linear plasma actuators to form an upward jet. Since each injection can be manipulated in intensity, the synthetic jet has thrust vectoring properties. Our study simulates the L-PSJA by utilizing a modified Suzen-Huang (S-H) model that accounts for drift and diffusive properties in the surface charge. The results of the present model show that the centreline velocity is closer to the experimental values found in literature as compared to the default form of S-H modelling. Thrust vectoring simulations were also performed to demonstrate the feasibility of flow directional variation in the L-PSJA.
Analysis on performance, emission and combustion characteristics of diesel engine fueled with methyl–ethyl esters
Authors: Murugesan A. , Subramaniam D. , Vijayakumar C. , Avinash A. , Nedunchezhian N.
Published: November 2012

In this experimental study, performance, emissions, and combustion characteristics of methyl/ethyl esters of pongamia, ethyl esters of neem and diesel blends in a diesel engine were experimentally investigated. For this study, methyl esters of pongamia, ethyl esters of pongamia, and ethyl esters of neem were added to diesel by volume of 20% (B20), 40% (B40), 60% (B60) and 80% (B80), as well as pure blend (B100). Fuels were tested in single cylinder, water-cooled, direct injection kirloskar diesel engine loaded by eddy current dynamometer. The effect of blends on engine performance, exhaust emissions, and combustion were examined at different loads. It was clear, up to 40% of methyl/ethyl ester did not affect the brake thermal efficiency. On the other hand, HC emission decreased by 1.3% for B40 in comparison with base diesel operation in engine. At the same time, smoke emissions were also reduced by 1.2% compared to diesel engine fuelled with B40 blend. It was proved that B40 is a best blend ratio compared to B60, B80, and B100. The overall combustion characteristics of B40 bio diesel were similar to base diesel. The maximum cylinder pressure for B40 bio diesel was slightly less compared to maximum cylinder pressure of base diesel at the same operating condition. The heat release rate and cumulative heat release rate are higher for base diesel compared to B40 bio diesel operating at full load condition.
The wind-wave tunnel test of a tension-leg platform type floating offshore wind turbine
Authors: Ren Nianxin , Li Yugang , Ou Jinping
Published: November 2012

In this work, a tension-leg platform (TLP) type floating offshore wind turbine (FOWT) system was proposed, which was based on the National Renewable Energy Laboratory 5 MW offshore wind turbine model. Taking the coupled effect of dynamic response of the top wind turbine, support tower structure, and lower mooring system into consideration, the 1/60 scale model test for investigating the coupled wind-wave effect on performance of the floating wind turbine system was done in Harbin Institute of Technology's wind tunnel and wave flume joint laboratory. In addition, numerical simulations corresponding to the scale model tests have been performed by advanced numerical tools. The results of model tests and numerical simulations have a good agreement, so the availability of the numerical model has been verified. Furthermore, to improve the performance of the TLP system, one tentative strategy adding mooring lines to the TLP system was proposed, and the model test results of the two TLP systems were compared with each other. As a result, the motion responses of the floating platform and the force levels of tension legs were effectively reduced by the additional mooring chains. The new TLP FOWT system might play an active and instructive role in the development of future FOWT system.
A new static lighting concentrator with optical coupler
Authors: Jong-Woei Whang Allen , Lin Chia-Min , Ku Nai-Lun , Wang Ming-Cheng
Published: November 2012

Currently, energy-saving and carbon dioxide reduction are the most critical issues faced by the globe. Therefore, solar energy should be used as much as possible. A possible use is to illuminate a solar cell so as to transform light energy directly into electricity. However, due to its low efficiency and high cost, the solar cell is not presently economically feasible. Utilization of solar energy, which is considered one of the most important renewable energy sources, not only reduces consumption of fossil fuel but also slows down the pace of global warming. In addition to the use of solar cells, daylight illumination is also an important access to solar energy. Our team has developed a technique that can guide the natural light to the interior for indoor illumination. It is called the “Natural Light Guiding System.” Our system can guide sunlight to the interior, but the distribution of light at the exit of the system is disordered. To solve this problem, we have proposed an optical coupling transmission structure with right-angled prism collecting modules. We analyzed the mathematical model of coupling transmission. And, we also analyzed the efficiency of this cascade structure at the exit surface of the concentrator. In this paper, we provide a high efficiency new concentrator coupled to a transmission device. We save 75% of the optical fiber cable expense usage and we improve efficiency by 47.46% when we add an optical coupling transmission structure to our static lighting concentrator. It is better than the original cascade prism static concentrator. Taking the fiber cost into consideration, we defined a key performance index—it is a ratio of luminous flux on an illuminated area. Our system can provide more powerful light for indoor illumination than existing methods The optical coupling can provide high transmission efficiency and provide parallel light beams at the export from the optical coupling module. We used optical simulation tools to design and simulate the efficiency of the active module. We can use this system as an ecological illumination system to offer steady illumination in indoor space to provide healthy illumination, save energy, and meet safety requirements.
Development of a technology type factor for jacket structures for offshore wind turbines in Rhode Island
Authors: Hensel Jonas , Ravi Sharma M. S. , Baxter Christopher D. P. , James Hu Sau-Lon
Published: November 2012

A marine spatial planning approach was used to locate possible sites for offshore wind development in Rhode Island. In connection with the Rhode Island ocean special area management plan, a technology development index was developed by Spaulding et al. (2010) to quantify the technical challenges of a particular site relative to its potential power production. A component of this index is the technology type (TT) factor, which quantifies the relative cost of a structure/foundation system as a function of environmental loading, water depth, and soil conditions. This paper presents the development of TT factors for jacket type support structures that is proposed for supporting the offshore wind turbines in Rhode Island Sound. TT factors were calculated by the total weight of the jacket and piles for a given water depth and soil conditions normalized by the weight of a reference structure. Jacket structure weights were determined by a frequency driven finite element analysis using the program ANSYS. The structure was subjected to hydrodynamic and quasi-static turbine loads from 50-year extreme wind and the 100-year extreme wave loading in Rhode Island Sound to determine the ultimate stresses in the structural members. Pile foundation weights were determined from an analysis of the axial capacity and the lateral capacity using commercially available pile design software. Jacket and foundation weights were calculated for water depth ranging from 30 m to 60 m and for three representative soil types. These analyses resulted in a Technology Type factor that varies with water depth according to a 2nd order polynomial, and also with soil type. The results were compared to the weights of two existing jacket structures in Europe and found to be in agreement with the upper bound estimate derived from this study. The Technology Type factor derived in this study was also in good agreement with the published actual cost (normalized) of jacket type foundations used in the United Kingdom.
Performance study of solar vacuum tubes type dryer
Authors: Mahesh A. , Sooriamoorthi C. E. , Kumaraguru A. K.
Published: November 2012

In the present work, a solar vacuum tubes type dryer is designed, fabricated, and tested for drying of different fruit and vegetable samples. The selected fruits and vegetables such as pineapple, apple, banana, guava, beans, brinjal, carrot, lady finger, and potato were dried separately by the open sun drying and by the solar dryer under consideration, and the drying efficiencies of the two methods were compared with each other. While conducting experiments on fruit samples, the solar air heater efficiency varied from 59% to 80% and the corresponding solar dryer efficiency and open sun drying efficiency were found to vary in the range of 55%–78% and 3.0%–5.0%, respectively. Similarly, while conducting experiments on vegetable samples, the solar air heater efficiency varied from 73%–84% and the corresponding solar dryer efficiency and open sun drying efficiency were found to vary in the range of 70%–79% and 3.0%–3.6%, respectively. The solar dryer reduces the average moisture content from 0.32 to 0.85 kg for drying fruits and from 0.36 to 0.71 kg for drying vegetables. The time taken by open sun drying is almost 1.5 times that taken by vacuum tubes type dryer under consideration and the final moisture content of the product in open sun drying is also higher. Therefore, in terms of utilisation of solar energy, solar vacuum tubes type collector dryer may be considered to be the best method for drying fruits and vegetables within a short period of time.
Flexible cobalt-phthalocyanine thin films with high charge carrier mobility
Authors: Singh Ajay , Kumar Arvind , Kumar Ashwini , Samanta Soumen , Debnath Anil K. , Jha Purushottam , Prasad Rajeshwar , Salmi Zakaria , Nowak Sophie , Chehimi Mohamed M. , Aswal Dinesh K. , Gupta Shiv K.
Published: November 2012

The structural and charge transport characteristics of cobalt phthalocyanine (CoPc) films deposited on flexible bi-axially oriented polyethylene terephthalate (BOPET) substrates are investigated. CoPc films exhibited a preferential (200) orientation with charge carrier mobility of ∼118 cm2 V−1 s−1 (at 300 K). These films exhibited a reversible resistance changes upon bending them to different radius of curvature. The charge transport in CoPc films is governed by a bias dependent crossover from ohmic (J–V) to trap-free space-charge limited conduction (J–V2). These results demonstrate that CoPc films on flexible BOPET having high mobility and high mechanical flexibility are a potential candidate for flexible electronic devices.
Coherent growth of GaGdN layers with high Gd concentration on GaN(0001)
Authors: Higashi K. , Hasegawa S. , Abe D. , Mitsuno Y. , Komori S. , Ishikawa F. , Ishimaru M. , Asahi H.
Published: November 2012

We report on the coherent growth of GaGdN with high Gd concentration on a GaN template using radio-frequency plasma-assisted molecular beam epitaxy under elevated growth conditions. X-ray diffraction and cross-sectional transmission electron microscopy observations revealed that at a growth temperature of 700 °C or below, GaGdN layers are coherently grown on the GaN templates without segregation of the secondary phases. As the GdN mole fraction x was increased to 0.08, the c-axis lattice parameter in Ga1−xGdxN increased linearly. Increasing the growth temperature to 750 °C causes lattice relaxation in GaGdN. All GaGdN samples exhibited photoluminescence emissions near the band-edge, a blue luminescence band emission, and a green luminescence band emission. The origin of the green luminescence band emission is discussed in relation to the compressive strain existing in the GaGdN layers coherently grown on GaN.
In situ X-ray diffraction study of deformation behavior in a Fe/NiTi composite
Authors: Hao Shijie , Cui Lishan , Shao Yang , Jiang Jiang , Jiang Daqiang , Wang Shan , Du Minshu , Wang Yandong , Brown Dennis E. , Ren Yang
Published: November 2012

A Fe/NiTi composite wire fabricated by simple mechanical processing exhibits a singular deformation feature of strain recovery ratio increase with increasing tensile strain, which is diametrically opposite to that of conventional metal materials. Furthermore, the composite possesses a recoverable strain of over 7% and a higher mechanical damping capability than that of the well-known high damping NiTi shape memory alloy. In-situ synchrotron X-ray diffraction reveals that these extraordinary features originate from the strong interaction between the soft Fe core and the superelastic NiTi tube during tensile cycling. This study offers in-depth understanding of the deformation behavior of the composites composed of soft metal and superelastic shape memory alloy.
Needle-like focus generation by radially polarized halo beams emitted by photonic-crystal ring-cavity laser
Authors: Kitamura Kyoko , Nishimoto Masaya , Sakai Kyosuke , Noda Susumu
Published: November 2012

Focused fields that possess a small spot size and long depth of focus (DOF) are expected to lead to the further development of optical applications. Here, we develop a photonic-crystal ring-cavity laser that emits a beam with a radially polarized halo shape (rinner/router > 0.9). This beam has a needle-like focus with a spot size of less than 0.4λ and a depth of focus longer than 10 λ for a 0.9 numerical aperture objective lens. We evaluate the focusing properties of the emitted beam and demonstrate that it has a longer depth of focus than conventional beams.
Continuous and scalable fabrication of flexible metamaterial films via roll-to-roll nanoimprint process for broadband plasmonic infrared filters
Authors: Ok Jong G. , Seok Youn Hong , Kyu Kwak Moon , Lee Kyu-Tae , Jae Shin Young , Jay Guo L. , Greenwald Anton , Liu Yisi
Published: November 2012

We demonstrate the continuous fabrication of large-area flexible metamaterial films via roll-to-roll (R2R) nanoimprint lithography (NIL) technique that can be conducted in an ambient environment at high speed. The plasmonic metal-insulator-metal structure is successfully fabricated by R2R NIL to continuously pattern the sub-wavelength scale metal disk array on flexible substrates. The patterned metal disks having varying diameters and sub-micron spacing with few defects lead to the desired broadband IR filtering performance at the designed dual-band, which correlates well with simulation analysis. Our method realizes a simple and high-throughput fabrication of plasmonic metamaterials for scalable and flexible optoelectronic and photonic applications.
Observation of threshold energy and hysteresis in high current ion beam guiding and transmission through a micro-glass-capillary
Authors: Paul Samit , Jayakiran A. , Bhattacharjee Sudeep
Published: November 2012

The energy dependent guiding of high current density (0.1–3 A/m2) argon ion beams through a micro-glass-capillary is studied. It is observed that ion transmission through the capillary takes place only if its energy is greater than the retarding potential barrier, which depends upon the amount of charge deposited on the capillary inner wall. Foremost evidence of the observation that the transmitted current exhibits hysteresis with ion energy is presented. Particle in cell simulations carried out by solving Poisson's and Newton's force equation self-consistently, agree reasonably well with the experimental results.
Experimental verification of field rotating with invisibility by full tensor transmission-line metamaterials
Authors: Liu Guochang , Li Chao , Chen Chao , Lu Zheng , Fang Guangyou
Published: November 2012

We demonstrate the experimental realization of a field rotator based on transmission line (TL) networks. The anisotropic and non-diagonal medium parameters of the field rotator are controlled by the coupling between the different branches of tensor TL metamaterials. Taking advantages of full parameters realization, the effect of field rotating companied with invisibility is verified. The non-resonant property of the TL structure also leads to a relatively broad bandwidth of the field rotation function, which is quantitatively evaluated based on our experimental results.
Vibrationally resolved photoelectron imaging of platinum carbonyl anion Pt(CO)n− (n = 1-3): Experiment and theory
Authors: Liu Zhiling , Xie Hua , Qin Zhengbo , Cong Ran , Wu Xia , Tang Zichao , Lu Xin , He Jian
Published: November 2012

Photodetachment of platinum carbonyl anions Pt(CO)n− (n = 1, 3) had been previously investigated using traditional photoelectron spectroscopy (PES) [G. S. Icking-Konert, H. Handschuh, G. Ganteför, and W. Eberhardt, Phys. Rev. Lett. 76, 1047 (1996)10.1103/PhysRevLett.76.1047; B. Chatterjee, F. A. Akin, C. C. Jarrold, and K. Raghavachari, J. Chem. Phys. 119, 10591 (2003)]10.1063/1.1619131. Here, we studied Pt(CO)n− (n = 1-3) using photoelectron velocity-map imaging method and extensive theoretical calculations. Vibrationally resolved spectra from photoelectron imaging experiments allow determination of the electron affinities of Pt(CO)n, which are 1.196 ± 0.034, 0.930 ± 0.042, and 1.253 ± 0.032 eV for n = 1, 2, and 3, respectively. Two vibrational progressions are resolved for the ground states of Pt(CO) and Pt(CO)3, while only one is resolved for that of Pt(CO)2. The frequencies are determined to be 2089 ± 91 and 581 ± 21 cm−1 for Pt(CO), 2173 ± 115 cm−1 for Pt(CO)2 and 2119 ± 88 and 444 ± 18 cm−1 for Pt(CO)3. Results from density functional theory and ab initio calculations agreed well with the experimental observations. The spectra were well reproduced by Franck-Condon fitting on the basis of the optimized geometries and the theoretical frequencies. The well-resolved PES also provided valuable benchmarks for various density functionals (B3LYP, BP86, and PW91PW91) for the platinum carbonyls.
Effect of high-pressure on the electronic and magnetic properties in double perovskite oxide Sr2FeMoO6
Authors: Qian Yan , Wu Haiping , Lu Ruifeng , Tan Weishi , Xiao Chuanyun , Deng Kaiming
Published: November 2012

The high-pressure effect on the physical properties in double perovskite Sr2FeMoO6 is explored theoretically. The structure of Sr2FeMoO6 exhibits I4/mmm symmetry in the whole external hydrostatic pressure applied. A spin crossover of Fe ion from high-spin to low-spin state is found at the pressure of about 33–36 GPa, accompanied by a transition from ferrimagnetic half-metallic to nonmagnetic semiconductor state. When the pressure is above 45 GPa, the nonmagnetic compound behaves as full metal. By the mean-field theory, the estimated Curie temperature of the ferrimagnetic Sr2FeMoO6 increases from 472 to 639 K when the pressure increases from 0 to 30 GPa.
Rare-earth free yellow-green emitting NaZnPO4:Mn phosphor for lighting applications
Authors: Haranath D. , Mishra S. , Yadav S. , Sharma R. K. , Kandpal L. M. , Vijayan N. , Dalai M. K. , Sehgal G. , Shanker V.
Published: November 2012

Manganese-doped sodium zinc phosphate (NaZnPO4:Mn) phosphor with exceptional features having ultra-violet (UV) to visible absorption (300–470 nm), yellow-green (∼543 nm) broad-band photoluminescence (PL), and appreciable color co-ordinates (x = 0.39, y = 0.58) is reported. It has a crystal structure consisting of discrete PO4 tetrahedra linked by ZnO4 and NaO4 distorted tetrahedral such that three tetrahedra, one of each kind, share one corner. The presence of UV sensitive Zn-O-Zn bonds and their efficient energy transfer to Mn2+ ions resulted in brightest PL and external quantum yield of 63% at 418 nm. Our experiment demonstrated the possibility of producing inexpensive white-light emitting devices for future.
Abundance of CuZn + SnZn and 2CuZn + SnZn defect clusters in kesterite solar cells
Authors: Chen Shiyou , Wang Lin-Wang , Walsh Aron , Gong X. G. , Wei Su-Huai
Published: November 2012

Kesterite solar cells show the highest efficiency when the absorber layers (Cu2ZnSnS4 [CZTS], Cu2ZnSnSe4 [CZTSe] and their alloys) are non-stoichiometric with Cu/(Zn+Sn)≈0.8 and Zn/Sn≈1.2. The fundamental cause is so far not understood. Using a first-principles theory, we show that passivated defect clusters such as CuZn+SnZn and 2CuZn+SnZn have high concentrations even in stoichiometric samples with Cu/(Zn+Sn) and Zn/Sn ratios near 1. The partially passivated CuZn+SnZn cluster produces a deep donor level in the band gap of CZTS, and the fully passivated 2CuZn+SnZn cluster causes a significant band gap decrease. Both effects are detrimental to photovoltaic performance, so Zn-rich and Cu, Sn-poor conditions are required to prevent their formation and increase the efficiency. The donor level is relatively shallower in CZTSe than in CZTS, which gives an explanation to the higher efficiency obtained in Cu2ZnSn(S,Se)4 (CZTSSe) cells with high Se content.
Field-effect transistors and intrinsic mobility in ultra-thin MoSe2 layers
Authors: Larentis Stefano , Fallahazad Babak , Tutuc Emanuel
Published: November 2012

We report the fabrication of back-gated field-effect transistors (FETs) using ultra-thin, mechanically exfoliated MoSe2 flakes. The MoSe2 FETs are n-type and possess a high gate modulation, with On/Off ratios larger than 106. The devices show asymmetric characteristics upon swapping the source and drain, a finding explained by the presence of Schottky barriers at the metal contact/MoSe2 interface. Using four-point, back-gated devices, we measure the intrinsic conductivity and mobility of MoSe2 as a function of gate bias, and temperature. Samples with a room temperature mobility of ∼ 50 cm2/V·s show a strong temperature dependence, suggesting phonons are a dominant scattering mechanism.
Tailoring the electronic properties of SrRuO3 films in SrRuO3/LaAlO3 superlattices
Authors: Liu Z. Q. , Ming Y. , Lü W. M. , Huang Z. , Wang X. , Zhang B. M. , Li C. J. , Gopinadhan K. , Zeng S. W. , Annadi A. , Feng Y. P. , Venkatesan T. , Ariando
Published: November 2012

The electronic properties of SrRuO3/LaAlO3 (SRO/LAO) superlattices with different interlayer thicknesses of SRO layers were studied. As the thickness of SRO layers is reduced, the superlattices exhibit a metal-insulator transition implying transformation into a more localized state from its original bulk metallic state. The strain effect on the metal-insulator transition was also examined. The origin of the metal-insulator transition in ultrathin SRO film is discussed. All the superlattices, even those with SRO layers as thin as 2 unit cells, are ferromagnetic at low temperatures. Moreover, we demonstrate field effect devices based on such multilayer superlattice structures.
Design in Ni–Mn–In magnetic shape-memory alloy using compositional maps
Authors: Huang Y. J. , Hu Q. D. , Li J. G.
Published: November 2012

Using empirical data, a map of composition versus magnetic properties was developed to design Ni-Mn-In magnetic shape-memory alloys. By the aid of this composition map, five alloys with desired properties were designed. A linear composition dependence of martensitic transformation temperature (Tm) and alloy was revealed. A transformation from austenite to martensite could be achieved at an electron concentration of ∼7.9. As such, a series of magnetic shape-memory alloys, which work at different conditions, can be designated under the guidance of a series of contour maps derived from Tm and thermal hysteresis.
Effects of hydrogen on the electronic properties of Ga(AsBi) alloys
Authors: Pettinari G. , Patanè A. , Polimeni A. , Capizzi M. , Lu Xianfeng , Tiedje T.
Published: November 2012

The effects of hydrogen incorporation on the electronic properties of Ga(AsBi) alloys are investigated in a wide range of Bi-concentration (0.6% ≤ x ≤ 10.6%) by Hall effect measurements in magnetic fields up to 14 T and by photoluminescence spectroscopy. For all the investigated Bi-concentrations, we report the passivation of Bi-induced shallow acceptor levels—responsible for the native p-type conductivity in Ga(AsBi)—and a tenfold increase of the hole mobility upon hydrogen incorporation in the host lattice. The emission energy is, instead, negligibly affected by hydrogenation, indicating that the narrowing of the band-gap energy with Bi and the native p-type conductivity are two uncorrelated effects arising from different Bi-induced electronic levels. Passivation by hydrogen of the shallow Bi-acceptor levels makes also possible to identify deep Bi-acceptor states.
Improved and orange emission from an n-ZnO/p-Si heterojunction light emitting device with NiO as the intermediate layer
Authors: Huang Huihui , Fang Guojia , Mo Xiaoming , Long Hao , Wang Haoning , Li Songzhan , Li Yuan , Zhang Yupeng , Pan Chunxu , Carroll David L.
Published: November 2012

n-ZnO/p-Si heterojunction light emitting devices with and without a NiO intermediate layer were fabricated using a radio frequency magnetron sputtering system. Electroluminescence measurements revealed that the device with the NiO intermediate layer exhibits a sharper and stronger orange emission peaks at ∼670 nm compared with that of the device without the NiO layer. And the light output-current characteristic of the n-ZnO/NiO/p-Si heterojunction device follows a nearly linear relationship (L ∝ I) rather than the superlinear relationship (L ∝ I1.5) for the n-ZnO/p-Si heterojunction device. This work indicates that the NiO intermediate layer could effectively improve the performance of the n-ZnO/p-Si heterojunction light emitting device.
Influence of the excitation area on the thresholds of organic second-order distributed feedback lasers
Authors: Calzado Eva M. , Villalvilla José M. , Boj Pedro G. , Quintana José A. , Navarro-Fuster Victor , Retolaza Aritz , Merino Santos , Díaz-García María A.
Published: November 2012

It is shown that the optical pump power (or energy) density thresholds required to obtain lasing from organic second-order distributed feedback lasers, increase when the excitation area (A) is smaller than a certain value (Acrit). So, in order to obtain the minimum possible thresholds and to ensure that they constitute adequate quantities for comparison purposes, the condition A > Acrit should be fulfilled. Results also indicate that when A < Acrit (Acrit ∼ 0.1 mm2 for the devices studied here), the operational device lifetime, which depends mainly on the pump power (or energy) density, becomes drastically reduced.
Polarization reversal and dynamic scaling of (Na0.5K0.5)NbO3 lead-free ferroelectric ceramics with double hysteresis-like loops
Authors: Fu Jian , Zuo Ruzhong
Published: November 2012

The polarization reversal and dynamic hysteresis of ferroelectrics specially with double hysteresis-like loops were investigated by using CuO-doped (Na0.5K0.5)NbO3 ceramics. The variation of the hysteresis area and current density clearly suggests three stages of the polarization reversal. It was found that the hysteresis behavior of the dynamics can be scaled as power law relationships apart from the second stage, where different numbers of domains can be rapidly activated. The main polarization mechanism was ascribed to the reversible domain wall motion (field amplitude Eo < 0.5Ec) and 180° domain switching (0.5Ec < Eo < Ec) for the first stage, and to the non-180° domain switching (Eo > 3.5 kV/mm) for the third stage.
An extremely low-noise heralded single-photon source: A breakthrough for quantum technologies
Authors: Brida G. , Degiovanni I. P. , Genovese M. , Piacentini F. , Traina P. , Della Frera A. , Tosi A. , Bahgat Shehata A. , Scarcella C. , Gulinatti A. , Ghioni M. , Polyakov S. V. , Migdall A. , Giudice A.
Published: November 2012

Low noise single-photon sources are a critical element for quantum technologies. We present a heralded single-photon source with an extremely low level of residual background photons, by implementing low-jitter detectors and electronics and a fast custom-made pulse generator controlling an optical shutter (a LiNbO3 waveguide optical switch) on the output of the source. This source has a second-order autocorrelation g(2)(0)=0.005(7), and an output noise factor (defined as the ratio of the number of noise photons to total photons at the source output channel) of 0.25(1)%. These are the best performance characteristics reported to date.
Impurity-limited lattice disorder recovery in ion-implanted ZnO
Authors: Azarov A. Yu. , Svensson B. G. , Kuznetsov A. Yu.
Published: November 2012

The presence of implanted impurities can affect intrinsic defect annihilation or, in macroscopic terms, so-called lattice recovery, specifically in high dose implantation experiments typically applied to radiation hard materials, e.g., ZnO. Correlating diffusion and lattice recovery data, we demonstrate that F bombardment of ZnO results in a unique situation when implantation induced disorder anneals at anomalously low temperatures, specifically due to the F outdiffusion from the disordered region. Control F + B implants resulted in the suppression of F diffusion and stabilization of the lattice disorder providing the evidence for impurity-limited lattice recovery.
Growth of In0.25Ga0.75As quantum dots on GaP utilizing a GaAs interlayer
Authors: Stracke G. , Glacki A. , Nowozin T. , Bonato L. , Rodt S. , Prohl C. , Lenz A. , Eisele H. , Schliwa A. , Strittmatter A. , Pohl U. W. , Bimberg D.
Published: November 2012

Coherent In0.25Ga0.75As quantum dots (QDs) are realized on GaP(001) substrates by metalorganic vapor phase epitaxy in the Stranski-Krastanow mode utilizing a thin GaAs interlayer prior to In0.25Ga0.75As deposition. Luminescence is observed between 2.0 eV and 1.83 eV, depending on the thickness of the In0.25Ga0.75As layer. The critical thickness for the two-dimensional to three-dimensional transition of the layer is determined to 0.75 to 1.0 monolayers. A mean activation energy of 489 meV for holes captured by In0.25Ga0.75As quantum dots is measured by deep-level transient spectroscopy, yielding a hole storage time of 3 µs at room temperature.
One-dimensional hybrid simulation of the dc/RF combined driven capacitively coupled CF4 plasmas
Authors: Wang Shuai , Xu Xiang , Wang Younian
Published: November 2012

We developed a one-dimensional hybrid model to simulate the dc/RF combined driven capacitively coupled plasma for CF4 discharges. The numerical results show the influence of the dc source on the plasma density distribution, ion energy distributions (IEDs), and ion angle distributions (IADs) on both RF and dc electrodes. The increase of dc voltage impels more ions with high energy to the electrode applied to the dc source, which makes the IEDs at the dc electrode shift toward higher energy and the peaks in IADs shift toward the small angle region. At the same time, it also decreases ion-energy at the RF electrode and enlarges the ion-angles which strike the RF electrode.
Stability analysis of a two-stage tapered gyrotron traveling-wave tube amplifier with distributed losses
Authors: Hung C. L. , Lian Y. H. , Yeh Y. S. , Chang T. H. , Cheng N. H.
Published: November 2012

The two-stage tapered gyrotron traveling-wave tube (gyro-TWT) amplifier has achieved wide bandwidth in the millimeter wave range. However, possible oscillations in each stage limit this amplifier's operating beam current and thus its output power. To further enhance the amplifier's stability, distributed losses are applied to the interaction circuit of the two-stage tapered gyro-TWT. A self-consistent particle-tracing code is used for analyzing the beam-wave interactions. The stability analysis includes the effects of the wall losses and the length of each stage on the possible oscillations. Simulation results reveal that the distributed-loss method effectively stabilizes all the oscillations in the two stages. Under stable operating conditions, the device is predicted to produce a peak power of 60 kW with an efficiency of 29% and a saturated gain of 52 dB in the Ka-band. The 3-dB bandwidth is 5.7 GHz, which is approximately 16% of the center frequency.
Observation of the generation of stacking faults and active degradation measurements on off-axis and on-axis 4H-SiC PiN diodes
Authors: Thierry-Jebali N. , Hassan J. , Lazar M. , Planson D. , Bano E. , Henry A. , Janzén E. , Brosselard P.
Published: November 2012

PiN diodes have been fabricated on nominally on-axis Si-face 4H-SiC material and their electrical characteristics are compared to PiN diodes processed with exactly the same device process recipe on 8°-off 4H-SiC material. Some diodes had an optical window on the top metal contact to observe the possible stacking faults generation and motion with photo emission microscopy. The diodes were electrically characterized in forward voltage to test their stability. Electrical characterizations demonstrate that there is no noticeable degradation for the diodes processed on on-axis 4H-SiC substrate and with optical characterization the formation of stacking faults was not observed.
InP-based 2.8–3.5 μm resonant-cavity light emitting diodes based on type-II transitions in GaInAs/GaAsSb heterostructures
Authors: Grasse Christian , Wiecha Peter , Gruendl Tobias , Sprengel Stephan , Meyer Ralf , Amann Markus-Christian
Published: November 2012

We present InP-based resonant-cavity light emitting diodes (LEDs), which are emitting at 2.8 μm, 3.3 μm, and 3.5 μm and were grown by metalorganic vapor phase epitaxy. This long wavelength electroluminescence is achieved by using highly strained GaInAs/GaAsSb type-II quantum wells. The performance of two different active region designs, superlattice (“SL”) and “W”-shaped quantum wells (“W”), is compared. Although continuous wave operation up to 80 °C could be proven, a spontaneous emission droop similar to nitride-based LEDs has been observed and is discussed.
Temperature and Bi-concentration dependence of the bandgap and spin-orbit splitting in InGaBiAs/InP semiconductors for mid-infrared applications
Authors: Marko I. P. , Batool Z. , Hild K. , Jin S. R. , Hossain N. , Hosea T. J. C. , Petropoulos J. P. , Zhong Y. , Dongmo P. B. , Zide J. M. O. , Sweeney S. J.
Published: November 2012

Replacing small amounts of As with Bi in InGaBiAs/InP induces large decreases and increases in the bandgap, Eg, and spin-orbit splitting, ΔSO, respectively. The possibility of achieving ΔSO > Eg and a reduced temperature (T) dependence for Eg are significant for suppressing recombination losses and improving performance in mid-infrared photonic devices. We measure Eg(x, T) and ΔSO (x, T) in In0.53Ga0.47BixAs1−x/InP samples for 0 ≤ x ≤ 0.039 by various complementary optical spectroscopic techniques. While we find no clear evidence of a decreased dEg/dT (≈0.34 ± 0.06 meV/K in all samples) we find ΔSO > Eg for x > 3.3–4.3%. The predictions of a valence band anti-crossing model agree well with the measurements.