bluuebunny/crossref_metadata_2025 huggingface dataset:
Mucosal and systemic immune responses induced by a single time vaccination strategy in mice
Authors: González Aznar Elizabeth , Romeu Belkis , Lastre Miriam , Zayas Caridad , Cuello Maribel , Cabrera Osmir , Valdez Yolanda , Fariñas Mildrey , Pérez Oliver
Published: May 2015

Vaccination is considered by the World Health Organization as the most cost-effective strategy for controlling infectious diseases. In spite of great successes with vaccines, many infectious diseases are still leading killers, because of the inadequate coverage of many vaccines. Several factors have been responsible: number of doses, high vaccine reactogenicity, vaccine costs, vaccination policy, among others. Contradictorily, few vaccines are of single dose and even less of mucosal administration. However, more common infections occur via mucosa, where secretory immunoglobulin A plays an essential role. As an alternative, we proposed a novel protocol of vaccination called Single Time Vaccination Strategy (SinTimVaS) by immunizing 2 priming doses at the same time: one by mucosal route and the other by parenteral route. Here, the mucosal and systemic responses induced by Finlay adjuvants (AF Proteoliposome 1 and AF Cochleate 1) implementing SinTimVaS in BALB/c mice were evaluated. One intranasal dose of AF Cochleate 1 and an intramuscular dose of AF Proteoliposome 1 adsorbed onto aluminum hydroxide, with bovine serum albumin or tetanus toxoid as model antigens, administrated at the same time, induced potent specific mucosal and systemic immune responses. Also, we demonstrated that SinTimVaS using other mucosal routes like oral and sublingual, in combination with the subcutaneous route elicits immune responses. SinTimVaS, as a new immunization strategy, could increase vaccination coverage and reduce time–cost vaccines campaigns, adding the benefits of immune response in mucosa.
On the Effect of Exploiting GPUs for a More Eco-Sustainable Lease of Life
Authors: Scanniello Giuseppe , Erra Ugo , Caggianese Giuseppe , Gravino Camine
Published: May 2015

It has been estimated that about 2% of global carbon dioxide emissions can be attributed to IT systems. Green (or sustainable) computing refers to supporting business critical computing needs with the least possible amount of power. This phenomenon changes the priorities in the design of new software systems and in the way companies handle existing ones. In this paper, we present the results of a research project aimed to develop a migration strategy to give an existing software system a new and more eco-sustainable lease of life. We applied a strategy for migrating a subject system that performs intensive and massive computation to a target architecture based on a Graphics Processing Unit (GPU). We validated our solution on a system for path finding robot simulations. An analysis on execution time and energy consumption indicated that: (i) the execution time of the migrated system is less than the execution time of the original system; and (ii) the migrated system reduces energy waste, so suggesting that it is more eco-sustainable than its original version. Our findings improve the body of knowledge on the effect of using the GPU in green computing.
Evaluation of Stipulated Conditions Imposed at the Time of Grant of Environment Clearance from the Perspective of Implementation of Compliance-A Case Study for Construction Projects in India
Authors: GUPTA Sunil , SHARMA Sanjay , SAINI Randeep Singh
Published: May 2015

The purpose of the paper is to discuss the stipulated conditions imposed at the time of grant of environment clearance from the perspective of implementation of compliance in case of construction projects in India. Conditions as imposed on 40 different building and construction projects in India from 2008 to 2013 are studied and evaluated and for a ready reference a sample of 14 representative project types is given in the paper. Based on the evaluation, we conclude that the laid down conditions are general in nature and more or less same irrespective of the location or type of the project may be an educational institute, hospital, office, hotel, group housing, bus terminus, or multiplex and whether it graded platinum or bronze in rating or ungraded. The impacts of the project nowhere find a mention in the stipulated conditions and thus there is no correlation between the conditions imposed and the baseline environment parameters. There is a dire need to rework the stipulated conditions itself on the lines of environment management plan proposed by the project proponent including setting apart the cost of implementation, if an effective compliance as envisaged by Ministry of Environment and Forests, Government of India is to be achieved.
(Invited) Radiation Effects in AlGaN/GaN and InAlN/GaN High Electron Mobility Transistors
Authors: Pearton Stephen J. , Hwang Ya-Hsi , Ren Fan
Published: May 2015

GaN HEMTs are more radiation hard than their Si and GaAs counterparts due to the high bond strength in III-nitride materials. We review data on the radiation resistance of GaN-based transistors such as AlGaN/GaN and InAlN/GaN High Electron Mobility Transistors (HEMTs) to different types of ionizin gradiation. The primary energy levels introduced by different forms of radiation, carrier removal rates and role of existing defects are discussed. The carrier removal rates are a function of initial carrier concentration, dose and dose rate but not of hydrogen concentration in the nitride material grown by Metal Organic Chemical Vapor Deposition. Proton and electron irradiation damage in HEMTs creates positive threshold voltage shifts due to a decrease in the two dimensional electron gas concentration resulting from electron trapping at defect sites, as well as a decrease in carrier mobility and degradation of drain current and transconductance. Neutron irradiation created more extended damage regions and at high doses leads to Fermi level pinning while 60Co γ-ray irradiation leads to much smaller changes in HEMT drain current relative to the other forms of radiation.
(Invited) Failure Mechanisms in AlGaN/GaN HEMTs Irradiated with 2MeV Protons
Authors: Anderson Travis J , Koehler Andrew D. , Specht Petra , Weaver Brad D , Greenlee Jordan D , Tadjer Marko J , Hite Jennifer K , Mastro Michael A , Porter Matthew , Wade Michael , Dubon Oscar , Luysberg Martina , Hobart Karl D , Weatherford Todd R , Kub Fritz J
Published: May 2015

GaN high electron mobility transistors (HEMTs) have shown the potential to be extremely tolerant of the space radiation environment. AlGaN/GaN HEMT structures on three different substrates were exposed to proton irradiation at fluences up to 6x1014 cm-2, which resulted in a 30% reduction in mobility and saturation current density. Dynamic ON-resistance measurements demonstrated increased degradation by a factor of 10 under off-state quiescent voltage stress conditions. High resolution transmission electron microscopy revealed a radiation-induced void under the gate metallization, indicative of a Kirkendall effect.
(Invited) Simulation of Radiation Effects in AlGaN/GaN HEMTs
Authors: Patrick Erin , Choudhury Mohua , Ren Fan , Pearton Stephen J. , Law Mark E
Published: May 2015

Physics-based models accounting for radiation-induced degradation are incomplete for AlGaN/GaN high electron mobility transistors (HEMTs). In this work, we show that a partially ionized impurity scattering mobility model can explain the observed reduction in mobility. Electrostatic changes can be explained by confinement of negative charge near the 2DEG in the GaN buffer layer. Simulation results from FLOODS (a TCAD simulator) demonstrate that partial ionization of donor traps is responsible for this phenomenon. Compensation of the acceptor traps by the ionized donors in the GaN confine the acceptor traps to a thin layer near the AlGaN/GaN interface. Our results imply that device performance can be accurately simulated by simultaneously accounting for mobility and electrostatic degradation in TCAD solvers using the presented approach.
(Invited) Neutron Irradiation Effect on GaN-Based Materials
Authors: Zhang Ming-lan , Yang R X , Wang X L , Liu S F
Published: May 2015

Effects of neutron irradiation on GaN-based materials were investigated. Temperature dependent Hall measurements were used to study the electrical property of two dimensional electron gases (2DEG). The mobility of 2DEG was sensitive to neutron, while sheet carrier density (ns) showed nearly no decrease until a fluence of 3.66×1015cm-2. Raman measurement was used to examine the strain in AlGaN/GaN heterostructure, and no peak shift was observed in the spectrum. In order to investigate the influence of neutron irradiation on the optical properties of GaN, persistent photo conductivity (PPC) and low temperature photoluminescence (PL) were measured. Pronounced PPC was observed, but no yellow luminescence (YL) band appeared in PL spectrum measured at 5K, suggesting that PPC and YL were not related. Thermal stimulated current (TSC) and low temperature photoluminescence (PL) techniques were used to determine the position of deep levels in GaN with high resistance. Four traps are identified in neutron irradiated GaN.
(Invited) Thermal Limitations in Wide Bandgap (WBG) Semiconductor Power Switching Devices
Authors: Shenai Krishna
Published: May 2015

Power switching devices made using wide bandgap (WBG) semiconductors such as Silicon Carbide (SiC) and Gallium Nitride (GaN) have the potential to make transformative impact on electrical energy generation, transmission, distribution and conditioning. Although SiC power diodes and power MOSFETs are commercially available for voltage ratings up to 1,700 volts, a careful review of the published data suggests that reliability of WBG power devices may be severely compromised compared to identically rated silicon power devices. For example, dv/dt, avalanche, and safe-operating area (SOA) of SiC power diodes and MOSFETs are inferior to silicon power devices with identical ratings. This paper will present a simple physics-based thermal analysis of the power handling capability of WBG power devices and explain the possible causes of lower reliability ratings.
(Invited) Synchrotron White-Beam X-Ray Topography Analysis of the Defect Structure of HVPE-GaN Substrates
Authors: Kirste Lutz , Danilewsky Andreas N. , Sochacki Tomasz , Köhler Klaus , Zajac Marcin , Kucharski Robert , Boćkowski Michal , McNally Patrick J.
Published: May 2015

The defect structure of HVPE-GaN crystals are examined using synchrotron white-beam X-ray topography (SWXRT) and topography results are interpreted and discussed in comparison to reciprocal lattice point broadening from high resolution X-ray diffraction (HRXRD) measurements. Two as-received commercial HVPE-GaN wafers from two different vendors and one HVPE-GaN which was grown on an ammonothermal GaN-seed are investigated in this study. From large-area topography the formation of a cellular defect network is identified for the commercial HVPE-GaN. Large differences in the crystal lattice misorientation deformation (mosaicity) are determined for the different samples by transmission section topography. For the HVPE-GaN grown on an ammonothermal GaN-seed a very low defect density was ascertained. From the contrasts of the topography threading screw-type dislocations and threading mixed-type dislocations were identified. The structure analyses show that the outstanding structural properties of the ammonothermal GaN-seed are adopted by the HVPE-GaN.
(Invited) Developing Periodically Oriented Gallium Nitride for Frequency Conversion
Authors: Hite Jennifer K , Freitas Jaime A. , Mastro Michael A , Vurgaftman Igor , Meyer Jerry R. , Brown Christopher G. , Kub Francis J , Bowman Steven R. , Eddy Charles R.
Published: May 2015

The development of GaN as a quasi-phase matched material for high power frequency conversion by periodically orienting the crystal orientation is presented. For high power applications, thick material on native substrates is required. Recent work has produced periodically oriented (PO) GaN with thicknesses reaching 500μm on N-polar GaN substrates. Work on Ga-polar substrates has progressed, with demonstrations of PO structures. The ability to create PO structures on both polar faces of GaN substrates offers the promise of engineered materials with custom lateral and vertical polarity variations for applications in novel electronic and optoelectronic devices, a subset of which are expected to be suitable for non-linear optics.
Epitaxial Growth of High Quality GaN Films on Lattice Matched Metallic Layers
Authors: Dabiran Amir M , Machuca Francisco , De Indranil , Weiss Robert
Published: May 2015

We discuss the development of high-quality ZrTi metal layers that are epitaxially deposited by sputtering on sapphire and Si, and which are c-axis oriented and lattice matched for growth of low-defect hexagonal GaN films. We also explain and discuss the nucleation and growth of thick GaN layers by molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) on these metal layers. Finally, we present the results of thin-film measurements to demonstrate the high crystal qualities and very smooth surface morphologies of highly specular GaN layers grown on ZrTi buffers in this work.
Oil-Immersion Raman Spectroscopy for c-Plane GaN on Si and Al2O3 Substrates
Authors: Imai Ryosuke , Kosemura Daisuke , Ogura Atsushi
Published: May 2015

An E1(TO) branch was excited even under the backscattering geometry from c-plane GaN layers on Si and Al2O3 substrates by oil-immersion Raman spectroscopy. The frequencies of the excited E1(TO) were lower than those obtained in the dry Raman measurements. This behavior was able to be understood as the result of the mixing of optical phonon frequencies.
(Invited) InGaN/GaN Multiple Quantum Well Solar Cells for Energy and Hydrogen Generation
Authors: Jiang Hongxing , Lin Jingyu
Published: May 2015

InGaN alloys are promising for solar cells and solar water splitting because they have direct bandgaps that cover almost the whole solar spectrum. This paper provides a brief overview on recent advances made by our group in the area of III-nitrides for energy and hydrogen generation. Solar cells based on InxGa1-xN/GaN (x∼0.35) multiple quantum well (MQW) structures have been fabricated and were shown exhibit an open circuit voltage (Voc) of 1.80 V, short circuit current density (Jsc) of 2.5 mA/cm2 and a solar-energy-to-electricity conversion efficiency (η) of 2.95% under the irradiation by a simulated sunlight (AM 1.5 G, 1-sun,100 mW/cm2). Under the irradiation of concentrated sunlight, Voc, Jsc and η were found to increase with solar concentration. Furthermore, InGaN/GaN MQW solar cells were effectively monolithic solar-photoelectrochemical cells which are capable to directly generate hydrogen gas under zero bias via solar watersplitting. Under the irradiation of 1 sun (AM 1.5 G), a 1.5% solar to-fuel conversion efficiency has been achieved under zero bias with an excellent chemical stability.
(Invited) Nitride Photocatalyst to Produce Clean Hydrogen from Water without Extra Bias
Authors: Ohkawa Kazuhiro
Published: May 2015

Nitrides are attractive materials not only for energy saving devices such as LEDs and LDs but also clean energy devices. Nitride photocatalysts are possible to produce “clean hydrogen” from water splitting using light energy. Furthermore nitride photocatalysts can reduce CO2 which causes the global warming. In nitride photocatalysis, CO2 has changed into hydrocarbons as “renewable energy”.
(Invited) High Efficiency Green-Yellow Emission from InGaN/GaN Quantum Well Structures Grown on Overgrown Semi-Polar (11-22) GaN on Regularly Arrayed Micro-Rod Templates
Authors: Gong Y , Xing K , Xu B , Yu X , Li Z , Bai J , Wang Tao
Published: May 2015

A simple but cost-effective overgrowth technique has been developed for the growth of semi-polar (11-22) GaN on mask-patterned micro-rod array templates fabricated on thin (11-22) GaN layers on sapphire. As a result, a fast coalescence with a thickness of ~1 μm has been obtained. Massively improved crystalline quality has been achieved, confirmed by detailed X-ray rocking curve measurements, which show that the full width at half maximum (FWHM) has been reduced to 0.096° and 0.097° at both 0° and 90° azimuth angle measured on an overgrown sample with a total thickness of 4.5 μm. The root mean square (RMS) roughness measured by atomic force microscopy is 1.47 nm. A number of InGaN/GaN multiple quantum well (MQW) structures with high In composition have been grown on the overgrown semi-polar GaN templates, showing strong photoluminescence (PL) emission with a wavelength from 495 to 590 nm at room temperature. Temperature dependent PL measurements have been performed to estimate their internal quantum efficiency (IQE), demonstrating ~ 8% of IQE for the sample with an emission wavelength of 590 nm. Power dependent PL measurements indicate weak quantum confined Stark effects (QCSE).
Hydrothermally Grown Nonpolar a-Plane ZnO and Its Applications
Authors: Kim Jimin , Baik Kwang Hyeon , Jang Soohwan
Published: May 2015

Nonpolar a-plane ZnO and CdZnO were successfully grown on a-plane GaN templates by simple, low-cost, and mass producible hydrothermal method at the low temperature of 90□. Unlike hydrothermal growth on c-plane GaN, film type ZnO and CdZnO with high crystalline quality were obtained due to the anisotropic growth rates along the specific crystallographic directions. A-plane n-type ZnO/p-type GaN hybrid structure LED was fabricated, and the device shows sharp ultra-violet electroluminescence without any significant green and yellow emissions.
(Invited) Power Loss Reduction in Perforated-Channel HFET Switches
Authors: Shur Michael , Gaevski Mikhail , Gaska Remis , Simin Grigory , Wong Hugh Yung , Braga Nelson , Mickevicius Rimvydas
Published: May 2015

The work presents a novel perforated channel field-effect transistor (PC-FET) design that reduces the power losses and significantly improves the efficiency of power electronics systems. The improvement is achieved by making use of a strong current spreading effect in the source-gate and gate-drain spacing and by lateral/vertical profiling of the channel under the gate. The reduction of the switch on-resistance and output capacitance reduces the conversion loss in the power switch by more than a factor of 2.
A Novel Backside Gate Structure to Improve Device Performance
Authors: Hwang Ya-Hsi , Zhu Weidi , Dong Chen , Ahn Shihyun , Ren Fan , Kravchenko Ivan , Smith David , Pearton Stephen J.
Published: May 2015

A novel structure with backside gate was proposed in this study. The effect of backside gate to the device performance including DC performance and breakdown voltage was investigated. When the back-side gate was biased at -25V, the leakage current could be suppressed to one order lower. As a result, the subthreshold swing (SS) could be improved from 240 to 137 mV/dec. Most important of all, the off-state drain breakdown voltage could be increased by 40%. If the back-side gate is connected to the front-side gate, which could be viewed as a back-side gate field plate structure, the off-state drain breakdown voltage could be improved by 7%
(Invited) High-Power AlGaN/GaN Heterostructure Field-Effect Transistors on 200mm Si Substrates
Authors: Lo C.-F. , Laboutin O. , Kao C.-K. , O'Connor K. , Hill D. , Johnson W.
Published: May 2015

Crack-free AlGaN/GaN heterostructure field-effect transistors on a 200 mm silicon substrate were demonstrated to enable large-volume, low-cost manufacturing technology for GaN power electronics. Low normalized buffer leakage of around 3 × 10-9 A/mm and low normalized three-terminal subthreshold leakage of around 2 × 10-7 A/mm were obtained using highly carbon-doped buffer epilayers. A high three-terminal off-state breakdown voltage of 1.35 kV and a low specific on-resistance of 1.3 mohm-cm2 were achieved on the 4.5-µm-thick device with a 10 µm gate-to-drain spacing. The figure of merit of our device is calculated as 1.4×109 V2ohm-1cm-2
In-Situ Characterization of Defect Dynamics in 4H-SiC Power Diodes under High-Voltage Stressing
Authors: Shenai Krishna , Raghothamachar Balaji , Dudley Michael , Christou Aris
Published: May 2015

Wide bandgap (WBG) semiconductor power switching devices, especially those made on silicon carbide (SiC) and gallium nitride (GaN), promise transformative advances in electrical power switching systems because of superior electrical and thermal properties of these materials compared to the semiconductor silicon. However, the progress has been slow despite intense scientific and industrial development. Both SiC and GaN semiconductors contain a high density of crystal defects and the role of defects on the performance and reliability of electrical power switching devices under extreme operating environment is not clear. Using synchrotron white beam X-ray topography (SWBXT), it is shown that the breakdown mechanism in 4H-SiC is initiated at the threading screw dislocations present in the high field regions of a power diode. To avoid this phenomenon from occurring, commercial 4H-SiC high-voltage diodes are rated for punch-through leakage currents rather than for avalanche breakdown condition. Thus, crystal defects in 4H-SiC present a major roadblock for performance and reliability optimization of power switching devices.
(Invited) Investigations and Improvements of AlInN/GaN HEMTs Grown on Si
Authors: Chyi Jen-Inn , Hsin Yue-Ming , Lee Geng-Yen , Chiu Hsien-Chin
Published: May 2015

This paper reports our continuous efforts and achievements in understanding and improving AlInN/AlN/GaN heterostructure for high performance field-effect transistors and switching devices. AlInN/AlN/GaN high electron mobility transistors (HEMTs) with high electron mobility and low sheet resistance have been demonstrated on 6” Si(111) substrates. It is found that electron mobility of AlInN/AlN/GaN HEMTs is closely related to the presence and quality of the AlN spacer layer, which determines the dominant carrier scattering mechanism. A comparative study on the electrical characteristics of AlInN/AlN/GaN and AlGaN/GaN metal-insulator-semiconductor (MIS)-HEMTs shows that both devices exhibit similar low-frequency noise behavior and no obvious generation–recombination (g–r) noise component, implying carrier number fluctuation is the dominant noise mechanism in both structures.
Optically Transparent Flexible IGZO TFTs Fabricated with a Selective Wet-Etch Process
Authors: Tari Alireza , Lee Czang-Ho , Wong William S.
Published: May 2015

Given the relatively poor selectivity to common semiconductor etchants, IGZO (InGaZnO) thin film transistors (TFTs) are typically fabricated using lift-off processes to define the electrical contacts. However, the success of the emerging transition-metal oxide materials system for flexible electronics requires compatibility with conventional TFT fabrication processes. In this research, flexible IGZO TFTs having 85% optical transparency in the visible regime were fabricated on polyethylene napthalate (PEN) substrates using a selective wet etching process to eliminate the need for lift-off processing. The devices were processed directly onto the plastic platform at the maximum temperature of 150°C. The fabricated TFTs exhibited a field-effect mobility of ~12.5 cm2/V.sec, threshold voltage of ~5.0 V, and an Ion/Ioff ratio of <106. No current crowding behavior was observed for the TFTs at the low drain-source voltage (VD) regime. The highly selective etching process provides a means to fabricate IGZO based circuits with low processing complexity that will enable system-on-“plastic” integration of flexible transparent flexible displays.
Effects of Annealing Pressure and Ambient on Thermally Robust RuOx Schottky Contacts on InAlN/AlN/GaN-on-Si(111) Heterostructure
Authors: Kyaw Lwin Min , Liu Yi , Lai Mei Ying , Bhat Thirumaleshwara N. , Tan Hui Ru , Lim Poh Chong , Tripathy Sudhiranjan , Chor Eng Fong
Published: May 2015

We study the effects of annealing ambient and pressure (vacuum at the pressure of 6.67×10-3 Pa, N2 and Ar at the pressure of 101.3 kPa) on the electrical and material characteristics of RuOx Schottky diodes. With annealing in vacuum at 800 oC for 1 minute, the effective SBH of RuOx Schottky contacts decreases by ~0.208 eV and the reverse leakage current increases by about one order of magnitude with respect to those of contacts without annealing. In contrast, with annealing in Ar, the SBH increases by ~0.207 eV and the reverse leakage current decreases by about 100 times. Annealing in N2 yields the same results as annealing in Ar, and this indicates that N2 is unlikely to react with RuOx and the annealing pressure plays a critical role for the changes in the electrical and material characteristics of RuOx Schottky diodes.
Weak Quantum Confinement and Polaritons in ZnO and ZnO Cu Nanocrystals Prepared by Electrochemical Method
Authors: Torchynska Tetyana V. , El Filali Brahim , Díaz Cano Aaron Israel , Shcherbyna Lyudmula V.
Published: May 2015

Photoluminescence, X-ray diffraction, Scanning electron microscopy and Raman scattering have been used for the optical and structural characterization of ZnO and ZnO Cu nanocrystals (NCs) of various sizes. The samples prepared by an electrochemical method have a size from the range 60 to 600 nm after a heat treatment for 2 hours at 400 oC in ambient air. X-ray diffraction diagrams present a small shift of peaks that testifies on a change in the lattice parameters of NCs with decreasing the NC size. The Raman scattering technique presents the several active modes including the surface phonon mode. The Raman intensity increases with decreasing the NC size is attributed to the surface enhanced Raman scattering (SERS) effect in ZnO Cu NCs. Photoluminescence spectra show a free exciton and defect-related emission. The intensity stimulation of exciton-related PL bands with NC size decreasing up to 60 nm is attributed to the realization of the week confinement and the exciton-light coupling with the formation of polariton in small size ZnO NCs.
A New Capacitance-Voltage Model for Hydrogen-Terminated Diamond Mosfet
Authors: Zhou XI , Albin Sacharia
Published: May 2015

A new device model that takes into account of a surface adsorbate layer (ADL) is generated to study the C-V characteristics of the hydrogen-terminated diamond (HTD) MOSFET. In this model, the ADL acts like a reservoir of hole carriers and forms a hetero-structure with the hydrogen-terminated diamond surface. Our device model is applied to the C-V characteristics of a practical device and the results match well. This work is helpful in computer-aided design and optimization of future HDT devices.
Blue Emission Stimulation in Mixture of ZnO and Carbon Nanocrystals at Mechanical Processing
Authors: Torchynska Tetyana V. , Perez Millan Brenda , Velazquez Lozada Erick , Kakazey Mukola , Vlasova Marina
Published: May 2015

The photoluminescence and X ray diffraction of the mixture of ZnO + 1.0% C nanocrystals (NCs) have been studied before and after intensive mechanical processing (MP) with the aim to identify the nature of emission bands and radiative defects. The study reflects the diversity of physical processes occurring during MP: the destruction of primary ZnO NC aggregates, crushing individual ZnO NCs from the size of 250 nm down to 14 nm, the interaction of carbon atoms with oxygen in a treatment chamber and with the surface of ZnO nanoparticles etc. The new PL band peaked at 2.84-2.95 eV has been revealed in PL spectra after 9 min of MP. The origin of this emission in ZnO has not been conclusively established. The new PL band peaked at 2.84-2.95 eV has been studded and its nature is discussed.
Photocurrent Enhancement of TiO2 Nanotubes Decorated with PbS Quantum Dots
Authors: Du Kang , Liu Guohua , Chen Xuyuan , Wang Kaiying
Published: May 2015

In this paper, ordered TiO2 nanotubes (TNTs) were fabricated by electrochemical anodization in a fluoride-containing electrolyte solution. In order to extent absorption spectrum to visible light band, annealed TNTs with different PbS QDs contents, acting as light sensitizer, was loaded by ultrasonic-assisted dip coating approach. The QDs sensitized TNTs were characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and UV-vis spectroscopy analysis. The average diameter of nanotube and PbS QD were approximately ~150nm and ~30nm, respectively. The TNTs decorated with PbS QDs present strong visible-light absorption.
Effect of Rare-Earth Doping on Structural and Luminescent Properties of Screen-Printed ZnO Films
Authors: Khomenkova L. , Kushnirenko V.I. , Osipyonok N.M. , Singaevsky A.F. , Pekar G.S. , Avramenko K. , Strelchuk V.V. , Borkovska L.V.
Published: May 2015

The effect of Sm3+ and/or Ho3+ doping on structural and luminescent properties of screen-printed ZnO films sintered at 1000°C was investigated by photoluminescence (PL), PL excitation and Raman scattering methods. For all the films, ultraviolet excitonic and visible defect-related PL bands of ZnO were detected. The doping with Ho3+ ions produced an enhancement of PL in ZnO films, the excitonic PL intensity being increased prominently, while the co-doping with Sm3+ and Ho3+ ions resulted in PL decrease in ZnO films. Only for (Sm,Ho)- co-doped ZnO films, the rare-earth PL bands were detected. The reduction of Sm3+ to Sm2+ was observed demonstrating 5D0→7FJ radiative transitions. The mechanism of PL and PL excitation is discussed in terms of the formation of rare-earth complexes as well as energy transfer towards them from ZnO host.
Need for In Operando Characterization of Electrochemical Interface Features
Authors: Traulsen Marie Lund , Chatzichristodoulou Christodoulos , Hansen Karin Vels , Kuhn Luise Theil , Holtappels Peter , Mogensen Mogens Bjerg
Published: May 2015

The problems of understanding the electrode reaction kinetics and in particular the degradation of the kinetics destroying the electrode performance, is briefly described. This is followed by an analysis of information that is needed and which knowledge may be acquired by available in operando and in situ techniques. The latter is illustrated by some examples. Further, it is discussed how research may be improved by refining and combining the available methods. Finally, possible research strategies are discussed.
Activation of Platinum-Based Centers through Modification with Metal Oxo Species toward Electrocatalytic Oxidation of Dimethyl Ether and Methanol
Authors: Rutkowska Iwona Agnieszka , Sek Jakub P. , Marks Ewelina , Zelenay Piotr , Kulesza Pawel J
Published: May 2015

We studied electrooxidation of dimethyl ether on Pt and PtRu nanoparticles: bare and deposited on ZrO2 film. When compared to the behavior of bare Pt and PtRu nanoparticles (deposited on glassy carbon at the same loading of 100 μg cm-2), the enhancement effect in the presence of ZrO2 was demonstrated in terms of increases of electrocatalytic (voltammetric) currents recorded at room temperature (22oC) in 0.5 mol dm-3 H2SO4 containing 1.05 mol dm-3 DME. Introduction of the metal oxide (zirconia) nanostructures at the electrocatalytic interface should produce high population of reactive –OH groups favoring mobility of protons and inducing the oxidative removal of poisoning (CO-type) intermediates, at platinum and ruthenium sites of the deposited bimetallic PtRu nanoparticles.
Surface Segregation in Solid Oxide Electrode Materials Occurring at Intermediate Temperatures
Authors: Druce John , Téllez Helena , Ishihara Tatsumi , Kilner John A.
Published: May 2015

The segregation of constituent elements and impurities affects the surface composition of solid oxide electrode materials, and hence, the rate of the surface exchange reaction. In this work, we compare segregation occurring at 400 °C in Pr0.5Sr0.5CoO3-δ (PSCO) and PrBaCo2O5-δ (PBCO). The surface composition changes rapidly on annealing at low temperature, with segregation of the divalent cation evident after just 15 minutes. The PBCO contained a Na impurity which undergoes similar segregation behavior to the Ba, becoming the dominant surface cation after 2 hours of annealing. Although cation mobility in these materials is slow compared to oxygen, it is sufficient to cause significant changes in surface composition on timescales of the order of hours.
Surface Segregation and Inter-Diffusion of Cations and Impurities in Microelectrodes for Solid Oxide Fuel Cells and Electrolyzers
Authors: Téllez Helena , Druce John , Shi Yanuo , Kubicek Markus , Simrick Neil J. , Rupp Jennifer L. M. , Ishihara Tatsumi , Kilner John A.
Published: May 2015

The surface segregation and inter-diffusion of cations and impurities in La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF) electrode structures micro-patterned on a Zr0.84Y0.16O1.92 (YSZ) single crystal was investigated by high-resolution Time-of-Flight Secondary Ion Mass Spectrometry and Low-Energy Ion Scattering. The outermost and near surface of the microelectrodes showed significant changes after patterning and electrochemical testing of the cell. As occurring in bulk LSCF ceramics, Sr segregation towards the surface is observed after annealing at 500°C. Furthermore, the electrode showed that impurities (i.e. Na, Si and Ca) originating from the YSZ electrolyte bulk migrate actively to the LSCF electrode during electrochemical testing. The impurity migration has implications for oxygen surface exchange at the cathode-electrolyte and air interface for solid oxide fuel cells: the electrolyte YSZ surface becomes cleaner whereas the segregation of Sr to the LSCF outer surface seems to be suppressed with respect to the operation time of the device.
Nature and Functionality of Oxygen/Cathode/Electrolyte-Interfaces in SOFCs
Authors: Szász Julian , Wankmüller Florian , Wilde Virginia , Störmer Heike , Gerthsen Dagmar , Menzler Norbert H. , Ivers-Tiffée Ellen
Published: May 2015

The functionality of oxygen electrodes for solid oxide fuel cells (SOFC) is mainly determined by intrinsic material properties and fabrication controlled microstructure parameters for an enhanced oxygen reduction reaction at the solid/gas interface. La1-xSrx Co1-yFeyO3-δ (LSCF) delivers high oxygen-exchange kinetics and is widely used as a cathode material for high performing anode-supported fuel cells. LSCF is however chemically instable against Zr-based electrolytes (f.e. Y stabilized ZrO2 - YSZ) and is therefore separated by a 5-8 µm thick diffusion barrier interlayer, consisting of rare earth doped Cerium oxide (f.e. doped with Gd - GDC). This study shows that variations in GDC manufacturing conditions tremendously influence the cathode performance. The LSCF-GDC-YSZ layer sequence reveals a complex interacting nature during fabrication that needs to be understood for further optimization and reproducible performance of the oxygen/cathode /electrolyte interface in SOFCs.
(Invited) Structure and Stability of Pt-Y Alloy Particles for Oxygen Reduction Studied by Electron Microscopy
Authors: Deiana Davide , Wagner Jakob Birkedal , Hansen Thomas Willum
Published: May 2015

Platinum-yttrium alloy nanoparticles show both a high activity and stability for the oxygen reduction reaction. The catalysts were prepared by magnetron sputter aggregation and mass filtration providing a model catalyst system with a narrow size distribution. The structure and stability of nanostructured Pt-Y alloy catalysts were studied using transmission electron microscopy techniques. Using elemental X-ray mapping and high-resolution electron microscopy, the specific compositional structure and distribution of the individual nanoparticles was unraveled and the stability assessed. Studying the catalyst after reaction and after aging tests shows the development of a core-shell type structure after being exposed to reaction conditions.
Investigation of Infiltration via Multi-Physics Simulation Tool with Realistic Microstructure Properties
Authors: Yang Tao , Celik Ismail Bektas , Sezer Hayri , Lee Shiwoo , Gerdes Kirk
Published: May 2015

Infiltration is a potential method to improve the performance of SOFCs. The purpose of this study is to investigate the effects of infiltration via multi-physics simulation tools with realistic microstructure properties. The physics-based simulation tool is developed to extract the properties of fuel cells based on the measured polarization curves and impedance behavior for different fuel/air utilization cases, which has been verified in our previous work. Furthermore, we incorporate the microstructure properties distribution within the electrodes of realistic SOFC. These structural properties are either obtained from experiments (e.g. volume fraction) or calculated based on percolation theory (e.g. interface area, length of triple phase boundary, etc.). In this study, we apply the previously developed simulation tool to analyze both the baseline button cell and the one with infiltrated cathode. The performances of both cells are predicted with the multi-physics numerical simulation and compared against experimental data. In addition, the performances of baseline cell and cathode-infiltrated cell with working loads are predicted. Finally, the properties of both cells are extracted and compared to show the effects of infiltration. The results will help us better understand and improve the infiltration processes.
Modification of Oxygen/(Ba0.5Sr0.5)(Co0.8Fe0.2)O3-δ Interfaces Derived by Metal-Organic Deposition
Authors: Asano Koichi , Niedrig Christian , Menesklou Wolfgang , Wagner Stefan F. , Ivers-Tiffée Ellen
Published: May 2015

In this study, nanoscaled (Ba0.5Sr0.5)(Co0.8Fe0.2)O3-δ (BSCF) thin films (with thicknesses below 100 nm) have been successfully deposited onto NdGaO3 single crystal substrates using a metal-organic deposition (MOD) method. In contrast to physical vapor deposition techniques, e.g. pulsed-laser deposition or magnetron sputtering, BSCF thin films formed by an MOD method provide the possibility to custom-tailor the surface morphology by subsequent annealing treatments. Changes of surface area or phase composition (cubic, hexagonal BSCF, others) are expected to affect the catalytic activity of oxygen-transport membranes. A study of surface morphologies achieved by a variation of the post-deposition thermal treatment is presented. The electrical properties of selected MOD thin films were determined and compared to data for epitaxial BSCF thin films and bulk samples. Lastly, oxygen exchange kinetics were investigated by electrical conductivity relaxation measurements analyzed in the frequency domain, yielding oxygen surface exchange coefficients k
δ(T).
Surface Modification of LaNi0.6Fe0.4O3-δ Film Electrode by Ce0.9Gd0.1O1.95 Porous Layer
Authors: Budiman Riyan Achmad , Miyazaki Takamichi , Hashimoto Shin-ichi , Yashiro Keiji , Amezawa Koji , Kawada Tatsuya
Published: May 2015

The Ce0.9Gd0.1O1.95 porous layer was deposited into the top of LaNi0.6Fe0.4O3-δ film electrode and compared to the bare LaNi0.6Fe0.4O3-δ film electrode to determine the surface oxygen exchange rate. The measurement has been done by electrochemical impedance spectroscopy and isotope exchange experiment under various temperatures and oxygen partial pressures. The surface oxygen exchange rate of LaNi0.6Fe0.4O3-δ film - Ce0.9Gd0.1O1.95 porous layer was enhanced compared to the bare LaNi0.6Fe0.4O3-δ film electrode. The role of Ce0.9Gd0.1O1.95 was the promotion of incorporation step on the oxygen reduction process in the electrode as the reason of the enhancement of surface oxygen exchange rate. An Auger electron spectroscopy measurement has been done to investigate the compositional change at the LaNi0.6Fe0.4O3-δ film surface. No compositional change was observed on the LaNi0.6Fe0.4O3-δ film surface which can be associated to the enhancement of surface oxygen exchange rate.
Study of Electrode Performance for Nanosized La0.4Sr0.6Co0.8Fe0.2O3-Î” IT-SOFC Cathode
Authors: Mogni Liliana Veronica , Yakal-Kremski Kyle , Chanquía Corina Mercedes , Gao Zhan , Wang Hongqian , Caneiro Alberto , Barnett Scott A
Published: May 2015

La0.4Sr0.6Co0.8Fe0.2O3-δ (LSCF4682) perovskites were successfully synthesized by an assisted ammonium nitrate combustion method. The sample shows a sponge-like structure with meso and macro-pores channels distributed between interconnected nanosized particles (~45 nm) with a high specific surface area. Cathode performance of LSCF4682 was investigated in the intermediate temperature range of 400°C-700°C by using symmetrical cell configuration on La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte. The cathode polarization resistances Rc,p are 0.067 and 0.035 Ω·cm2 at 600°C and 700 °C, respectively. The long-term behavior of Rc,p was studied by applying an accelerate aging at 800 °C and testing the polarization resistance at 700°C as a function of time. After 500 h of aging, a degradation rate of (1/RC,P)(dRC,P/dt)= 0.002 h-1 raises the Rc,p to 0.1 Ω·cm2 at 700°C. A maximum power density of 1.23 Wcm-2 was achieved at 650 °C testing the LSCF cathode deposited on a porous SLT-LSGM supported multilayer cell. The results demonstrate that this material is a competitive SOFC cathodes for the intermediate temperature operation.
Oxygen Nonstoichiometry and Electrochemical Properties of LaNiO3-δ
Authors: Budiman Riyan Achmad , Hashimoto Shin-ichi , Nakamura Takashi , Yashiro Keiji , Amezawa Koji , Kawada Tatsuya
Published: May 2015

The chemical stability and electrochemical properties of LaNiO3-δ was measured by various temperature and oxygen partial pressure p(O2). The chemical stability of LaNiO3-δ has been determined by coloumetric titration and high temperature X-ray diffraction (XRD). The LaNiO3-δ has a short range of chemical stability over the p(O2). At the high temperature and low p(O2) (10-4 bar) the XRD patterns shows the NiO peaks, where the Ni3+ reduce into Ni2+. On the other side, the study on the electrochemical impedance spectroscopy indicates that it has relatively high area specific conductivity, although it has short range chemical stability over the p(O2).
GDC-Infiltrated La0.3Ca0.7Fe0.7Cr0.3O3-
δ Symmetrical Oxygen Electrodes for Reversible SOFCs
Authors: Molero-Sánchez Beatriz , Addo Paul Kwesi , Buyukaksoy Aligul , Birss Viola
Published: May 2015

Our recent studies have shown that La0.3Ca0.7Fe0.7Cr0.3O3-
δ (LCFCr) is a promising material as an air electrode for use in reversible solid oxide cells, due to its excellent activity towards the oxygen reduction and oxygen evolution reactions, along with its good thermal expansion coefficient match with common electrolytes, such as gadolinium-doped ceria (GDC). In the present work, GDC was infiltrated into a pre-sintered, porous, LCFCr scaffold, forming a porous layer on the LCFCr surface. This resulted in further improvements in the electrochemical performance, due to the enhanced ionic conductivity introduced by the GDC phase. The impedance spectroscopy results showed that GDC addition lowered the resistance specifically of the high frequency process.
(Invited) High Temperature CO2 Electrolysis on La(Sr)Fe(Mn)O3 Oxide Cathode by Using LaGaO3 Based Electrolyte
Authors: Ishihara Tatsumi , Wu Kuan-Ting , Wang Shijing
Published: May 2015

Electrochemical conversion of carbon dioxide to carbon monoxide (CO2→CO) is a potential useful step in the desirable transformation of the greenhouse gas to fuels or useful chemicals. In this study, the electrochemical conversion of CO2 to CO on oxide cathode was studied in a solid oxide electrolysis cell (SOEC) by using a LaGaO3-based electrolyte (La0.9Sr0.1Ga0.8Mg0.2O3, LSGM) at elevated temperature (i.e. 973 - 1173 K), which is a good candidate as electrolyte for electrolysis cell because of the high oxide ion conductivity at intermediate temperatures. It was found that a LaFeO3-δ–based perovskite material as cathode (La0.6Sr0.4Fe0.8Mn0.2O3-δ, LSFM6482) shows much higher activity for CO2 electrolysis among the examined oxide and a current density of CO2 electrolysis is achieved with a value of 0.52 A/cm2 at 1.6 V and 1173 K. Doping Sr and Mn to LaFeO3 is highly effective for increasing the cathode activity for CO2 electrolysis under the feed gas condition, which is consisted of 50%CO2, 1%CO, and 49%Ar. Porous structure with fine particle (0.5 μm) and main phase stability of LSFM6482 cathode can be sustained under CO2 electrolysis condition.
Phase Field Simulation Coupling Microstructural Evolution and Crack Propagation during Performance Degradation of Solid Oxide Fuel Cells
Authors: Abdullah Taufiq , Liu Lin
Published: May 2015

Microstructural evolution and crack propagation occur in Solid Oxide Fuel Cells (SOFCs) at elevated operation temperatures (above 600°C). These phenomena cause performance degradation in electrochemical activity and compromise of structural integrity of SOFCs as well. Nickel (Ni) coarsening of Ni-yttria stabilized zirconia (YSZ) in the anode of a SOFC is believed to lead to microstructural evolution. Meanwhile, stress concentration and pore aggregation causes crack propagation in the anode. Both microstructural evolution and crack propagation have a significant impact on the performance of SOFCs. Based on theories of diffuse-interface and Ginzburg-Landau, an integrated phase field model is developed to couple electrode microstructural evolution and crack propagation in the anode. Interfacial diffusion of the phases is observed to lead to Ni particle coarsening. The triple phase boundary (TPB) is found to be affected by microstructural evolution and the crack propagation.
Sulfur Tolerance of La0.3M0.7Fe0.7Cr0.3O3
-δ (M= Sr, Ca) Solid Oxide Fuel Cell Anodes
Authors: Addo Paul Kwesi , Molero-Sanchez Beatriz , Buyukaksoy Aligul , Paulson Scott , Birss Viola
Published: May 2015

Symmetrical full cells, based on La0.3M0.7Fe0.7Cr0.3O3-
δ (M = Sr, Ca) perovskite oxide electrodes, were constructed, using a Yttria-stabilized zirconia (YSZ) electrolyte with a Samaria-doped ceria (SDC) buffer layer, and then tested in a range of fuel environments at 800 oC. It is demonstrated that the Ca analog (La0.3Ca0.7Fe0.7Cr0.3O3-δ -LCFCr) is an equally good fuel electrode (anode) and air electrode (cathode) as the Sr member of this family (LSFCr), exhibiting very good electrochemical performance in H2, CO and H2+CO atmospheres. LCFCr and LSFCr anodes were also evaluated in the presence of 9 ppm H2S exposures, showing a small, but reproducible and reversible, decrease in polarization resistance (Rp). Studies at cell polarizations of -100 and -300 mV from the open circuit full cell voltage showed a ca. 2-4 % increase in current density in the presence of 9 ppm H2S + 30 % H2, with the cell recovering fully when H2S was removed.
(Invited) Electrochemical Upgrading of Bio-Oil
Authors: Elangovan S , Larsen Dennis , Hartvigsen Joseph J , Mosby James M , Staley Jacob , Elwell Jessica , Karanjikar Mukund
Published: May 2015

Biomass is a potential renewable source for liquid fuels and most commodity chemicals. Lignocellulosic biomass residue such as agricultural and forestry residue can be converted to liquid fuels via bio-oil production by fast pyrolysis. The high oxygen content of bio-oil poses a challenge for its practical use. The conventional approach to deoxygenate is the hydro-deoxygenation process. Typical bio-oil is biphasic and only the organic phase is processed in subsequent upgrading steps, leaving behind valuable carbon-containing material in the aqueous phase. Deoxygenation of model compounds and aqueous phase of pine wood bio-oil have been tested using an oxygen ion conducting ceramic membrane based electrochemical cells operated in the temperature range of 500 – 600 °C. The product from the electrochemical cell contained a suite of compounds with significantly lower oxygen content.