bluuebunny/crossref_metadata_2025 huggingface dataset:
Strained p-Channel MOSFET Fabrication Challenge and Perspective for the 28-Nm Technology Node and Beyond
Authors: Zheng Zhe , Xiao Fangyuan , Zhang Haiyang
Published: October 2015

The embedded epitaxial silicon germanium (eSi1-xGex) in the recessed source/drain (S/D) area modulates the lattice constant and band structure of silicon at the channel region then enhances the hole/electron mobility of MOSFETs. For the 28nm node planar devices, the strict control of recessed profile could be achieved by plasma-based one-step or two-step silicon dry etch process combined with the post wet chemical treatments. Here we analyzed the process loading correlated to the pitch of gate electrodes and the tunable capability on final sigma-shaped trench profile for these two types of processes. The strain/stress induced mobility enhancement technique of fin structure FETs should be significantly different from that of traditional planar FETs. We successfully decoupled the trade-off between the gate capping layer protection and the silicon nitride spacer pull-back before the p-channel fin recess step. Additionally, by balancing the isotropic and anisotropic spacer open parts in the whole etch process, we also demonstrated the fin structures with flat and smooth recessed surface on their top area, which would benefit for future good crystalline and well controlled Pi-shaped eSi1-xGex growth.
(Keynote) Heterogeneous Integration of MEMS by Adhesive Bonding
Authors: Esashi Masayoshi , Tanaka Shuji
Published: October 2015

Wafer-level adhesive bonding has been applied for the fabrication of microsystems which have heterogeneous components on LSI (large scale integrated circuit). Devices or functional materials formed on a carrier wafer are transferred to a LSI wafer, which enables versatile heterogeneous integration, overcoming process incompatibility. Based on the developed process technology, RF resonators, a piezoelectric microswitch, tactile sensors, a parallel electron beam source etc. have been demonstrated.
CMOS and NEMS Hybrid Architectures
Authors: Ernst Thomas , Ouerghi Issam , Ludurczak Willy , Arcamone Julien , Duraffourg Laurent , Ollier Eric , Philippe Julien , Hentz Sébastien
Published: October 2015

This paper reviews various realizations in the field of monolithic integration of Nano-Electro-Mechanical-Systems (NEMS) with CMOS. Such integrated solutions are of great interest in emerging domains as chemical analysis and life science. Co-integration enables to address a large number of sensors or to achieve enhaned sensitivity thanks to a high signal to noise ratio.
(Invited) Innovative Embedded Non-Volatile Memories: Flexibility and Reliability
Authors: Navarro Gabriele , Vianello Elisa , Molas Gabriel , Sousa Véronique , Perniola Luca
Published: October 2015

Innovative non-volatile memory technologies promise high performance and low integration cost with respect to conventional Flash memory, in a market context where the demand of data storage is constantly increasing and the portfolio of possible applications is rapidly widening. Non-Volatile Resistive Memory NVRM (e.g. Phase-Change Memory, Oxide-based Memory and Conductive Bridging Memory) is rapidly increasing in maturity, and it can represent a real breakthrough in terms of performances, power consumption lowering and cost reduction. Since flexibility and reliability are among the key words of the actual and future semiconductor memory scenario, we present some of the features of the main NVRM technologies and how target specifications can be satisfied by materials tuning, architecture engineering and specific programming techniques.
(Invited) Wide Bandgap (WBG) Power Switching Devices for Distributed Clean Energy Systems
Authors: Shenai Krishna
Published: October 2015

Important criteria for the widespread usage of DC electricity are the overall energy efficiency and cost of delivering electricity from the point of generation to the point of usage. Wide bandgap (WBG) semiconductor power switching devices, including those made from Silicon Carbide (SiC) and Gallium Nitride (GaN) semiconductors, offer unprecedented advantages over conventional silicon devices in terms of significantly increased energy efficiency and superior thermal performance. For example, for power conversion applications requiring power switches rated below 900V, commercial GaN lateral power transistors offer more than 5% higher energy efficiency with superior load regulation, especially for point-of-load (PoL) converters and wireless energy transfer devices. For higher voltage applications, commercially available vertical SiC power diodes and MOSFETs provide increased energy efficiency than feasible with silicon power MOSFETs and IGBTs, especially for certain low- and medium-power inverters and DC-DC converters.
(Invited) High Power SiC Power Processing Unit Development
Authors: Scheidegger Robert , Santiago Walter , Bozak Karin E , Piñero Luis R , Birchenough Arthur
Published: October 2015

NASA GRC successfully designed, built and tested a technology-push power processing unit for electric propulsion applications that utilizes high voltage silicon carbide (SiC) technology. The development specifically addresses the need for high power electronics to enable electric propulsion systems in the 100s of kilowatts. This unit demonstrated how high voltage combined with superior semiconductor components resulted in exceptional converter performance.
Vertical Buffer Leakage and Temperature Effects on the Breakdown Performance of GaN/AlGaN HEMTs on Si Substrate
Authors: Benkhelifa Fouad , Müller Stefan , Polyakov Vladimir M. , Breuer Steffen , Czap Heiko , Manz Christian , Mikulla Michael , Ambacher Oliver
Published: October 2015

The epitaxial growth of a GaN/AlGaN HEMTs epi-structure based on a carbon doped superlattice buffer has been optimized for achieving a highly isolated buffer, and transistors with high breakdown voltages and low leakage currents. The 10 mm gate periphery normally-on HEMTs demonstrate a drain-source leakage current lower than 0.4 µA/mm at 600 V drain bias. Furthermore, the breakdown voltage performance of the HEMT is not altered at 600 V bias when the measurement is performed with the substrate being grounded. The isolation blocking voltage of the epi-structure reaches 840 V for a corresponding leakage current density of 10 µA/mm2. We highlight low buffer vertical isolation degradation at high temperature (150°C) and that the decrease in HEMT’s breakdown voltage performance is not due to the vertical buffer leakage when increasing the substrate temperature.
(Invited) Epitaxial III-Nitride Film Growth in a Single Wafer Rotating Disk MOCVD Reactor
Authors: Papasouliotis George D , Su Jie , Krishnan Balakrishnan , Arif Ronald
Published: October 2015

We are reporting on the epitaxial growth of Al/Ga/N films on 200 mm Si substrates carried out in Veeco’s Propelä rotating disk, single wafer, vertical MOCVD reactor. The TurbodiscÒ reactor is designed for uniform alkyl and hydride flow distribution, and temperature profile, resulting in uniform and concentrically symmetric epilayer thickness and chemical composition. Results are presented on film stress and wafer curvature control facilitated by adjusting the thickness and growth conditions of individual layers in AlN/GaN superlattices. The growth of highly resistive, intrinsically carbon-doped GaN layers is studied, and the influence of growth conditions, growth temperature, pressure, and V/III ratio, on carbon incorporation rate, crystal quality, and surface morphology will be discussed in this paper. Carbon incorporation is enhanced at lower growth temperature, lower pressure, and lower V/III ratios; we have obtained concentrations as high as 3E19/cm3 at a growth pressure of 35 Torr and growth temperature of 960 °C.
(Invited) Vertical GaN p-i-n Diodes Formed by Mg Ion Implantation
Authors: Anderson Travis J , Greenlee Jordan D , Feigelson Boris , Hite Jennifer K , Hobart Karl D , Kub Francis J
Published: October 2015

An ion implanted p-i-n diode was demonstrated for the first time using the multicycle rapid thermal annealing technique and a capping structure that was re-optimized for device structures on bulk GaN. Electrical characterization exhibited rectifying behavior with low reverse leakage current and forward characteristics consistent with a p-n junction. Electroluminescence suggests recombination in the anode region under forward bias, and reverse leakage paths through crystalline defects. The ability to integrate p-type GaN layers in device structures by ion implantation represents a significant step for next-generation power devices.
(Invited) Ion Implantation into GaN and Implanted GaN Power Transistors
Authors: Nomoto Kazuki , Takahashi Kengo , Takuya Oikawa , Ogawa Hiroki , Nishimura Tomoaki , Mishima Tomoyoshi , Xing Huili Grace , Nakamura Tohru
Published: October 2015

We report great possibilities of ion implantation technology for applying to high-power GaN electron devices. We demonstrated high-performance normally-off self-aligned metal gate GaN MISFETs with Si ion implantation to reduce the contact resistances for ohmic contacts and N ion implantation for the device isolation. We formed p-type GaN in n-type GaN using Mg ion implantation and observed p-n junction diode behavior on forward I-V characteristics and EL measurements.
(Invited) Characteristics of a Wire-Bonding-Less SiC Power Module Operating in a Wide Temperature Range
Authors: Sato Shinji , Tanisawa Hidekazu , Anzai Takeshi , Takahashi Hiroki , Murakami Yoshinori , Kato Fumiki , Watanabe Kinuyo , Sato Hiroshi
Published: October 2015

Using high-speed switching, SiC power devices can reduce on-resistance in the on-state to realize low power converter losses. In addition, SiC power devices can be operated in high temperatures; thus, their cooling systems can be reduced in size or removed altogether, thereby increasing the power density of the power converter. The authors have studied a power module and power converter using properties of SiC power devices, and have previously proposed a power converter having high power density with a power module that is capable of high temperature operation , a gate driving technique for SiC power devices to prevent false turn-on with high-speed switching, and development of a noise filter for high-speed switching or high-frequency switching. In this study, we designed and fabricated a SiC power module with a built-in snubber circuit. This power module is operable in high temperatures over 200 °C.
Post Deposition Annealing Atmosphere Effect on SSI-LEDs Made of Zr-Doped HfO2 High-k Gate Dielectric
Authors: Zhang Shumao , Kuo Yue , Verkhoturov Stanislav
Published: October 2015

The phenomenon of white light emission from solid state incandescent light emitting devices made of Zr-doped HfO2 high-k dielectric stacks under the O2 or N2 post deposition annealing condition has been investigated. Compared with the N2 annealed sample, the O2 annealed sample had different properties: 1) a SiOx-like interface layer, 2) lower defect densities in bulk and interface layers, 3) a larger dielectric breakdown voltage, 4) a low leakage current, 5) fewer light emission dots, and 6) stronger emitted light. The shape of the emitted light and other optical properties were little influenced by the annealing gas. The high temperature of the conductive path during the operation enhanced the diffusion of Si to the gate electrode and Zr to the high-k/Si interface. This kind of device is applicable to a wide range of areas.
(Invited) Strain and Phonon-Carrier Interactions in Ge-Si0.5Ge0.5 Core-Shell Nanowires Probed Using Tip-Enhanced Raman Spectroscopy
Authors: Yu Edward T. , Zhang Zhongjian , Dillen David , Brasile Bryan W. , Tutuc Emanuel
Published: October 2015

Tip-enhanced Raman spectroscopy (TERS) is used to characterize nanoscale correlations between strain and nanowire dimensions in Ge-Si0.5Ge0.5 core-shell nanowires, and to elucidate phonon-carrier interactions that are manifested via shifts in Raman peaks originating from Ge-Ge vibrational modes within the quantum-confined hole gas formed at the Ge-Si0.5Ge0.5 interface. Two distinct peaks associated with Ge-Ge vibrational modes are observed – one arising from Ge-Ge vibrations in the nanowire Ge core region, and the other from Ge-Ge vibrations occurring within the quantum-confined hole gas at the Ge-Si0.5Ge0.5 interface. Both peaks exhibit a dependence of Raman shift on local nanowire diameter consistent with coherent strain in the nanowire, demonstrating that the TERS measurements provide the ability to probe strain at the nanoscale. The separation between these peaks is a consequence of coupling between intervalence band transitions and the Ge-Ge phonon mode leading to Fano resonance behavior and a shift in the phonon self-energy.
(Invited) Microscopic Studies of Black Phosphorus and Its Field-Effect Transistors
Authors: Pan Minghu , Yuan Hui , Xu Ya-Qiong , Zhou Zhixian , Meunier Vincent
Published: October 2015

In this manuscript, we report atomic scale studies of electronic direct bandgap measurement of the puckered honeycomb structure of freshly cleaved black phosphorus using a high-resolution scanning tunneling spectroscopy (STS) survey. Through a combination of STM/S measurements and first-principles calculations, a model for edge reconstruction and the related edge states are also determined. Besides, we also investigate electrical transport and optoelectronic properties of field effect transistors (FETs) made from few-layer black phosphorus (BP) crystals down to a few nanometers. In particular, we explore the anisotropic nature and photocurrent generation mechanisms in BP FETs through spatial- and polarization-dependent photocurrent measurements. Our results reveal that the anisotropic feature primarily results from the directional-dependent absorption of BP crystals.
AlGaN/GaN High Electron Mobility Transistors for Cardiovascular Disease (CVD) Marker Detection
Authors: Chu Chia-Ho , Sarangadharan Indu , Regmi Abiral , Chen Yi-Ting , Wang Yu-Lin
Published: October 2015

According to the statistics published by the World Health Organization (WHO) in 2011, cardiovascular disease (CVD) is the leading cause of death globally. Recent studies suggest that the level of C-reactive protein can be an important indicator of a person’s risk for cardiovascular disease. In this study, we detect low concentration of C-reactive protein (1 fM) electronically by immobilizing CRP-specific aptamer on the AlGaN/GaN HEMT based biosensor, showing that this technique is promising for biosensor applications.
Aptamer Immobilized Field Effect Transistor for Early Diagnostic of Human Immunodeficiency Virus Type 1 (HIV-1)
Authors: Chu Chia-Ho , Sarangadharan Indu , Regmi Abiral , Chen Yi-Ting , Wang Yu-Lin
Published: October 2015

In recent years, aptamer-based biosensors have aroused great interest in detecting different targets, such as proteins, peptides and whole cells. In contrast to antibodies-based biosensors, the selected aptamer can be synthesized with high reproducibility. Also, aptamers are usually chemically stable. In this study, we demonstrated HIV-1 RT-specific aptamers-immobilized AlGaN/GaN high electron mobility transistors (HEMTs) for detecting different concentrations of HIV-1 RT protein ranging from 1 fM to 10 pM in physiological salt concentrations.
(Invited) Piezotronics in 1D/2D Nanomaterials for Active and Adaptive Nano-Electronics/Optoelectronics
Authors: Wu Wen Zhuo
Published: October 2015

New technologies for developing smart electronics/optoelectronics with tunable/adaptive functionalities are critical to emerging applications in wearable devices, renewable energy, personal healthcare and environmental monitoring. Non-electrical stimuli, such as mechanical agitation, are ubiquitous and abundant in the environment for controlling and powering these devices. It is however not facile to directly interface them using the state-of-the-art silicon technology, in which the intelligent-bearing operations are implemented by electrically-gated transistors. Piezoelectric effect has been widely used in sensing, actuation and energy harvesting. However, the fundamental effect of piezoelectric polarization on charge carrier processes has been long overlooked. I will discuss recent advances in the emerging field of piezotronics, which is the modulation of carrier process by dynamic-strain-induced polarization. This provides the novel approach for modulating device characteristics without modifying the interface structure or chemistry, and may open up opportunities in enabling technology advances in energy harvesting, sensing, human-machine interfacing, robotics, healthcare and more.
(Invited) A Spontaneously Generated Electrical Charge of an Aqueous Droplet by Pipetting and Its Use of a Self-Powered Sensor
Authors: Choi Dongwhi , Kim Dong Sung
Published: October 2015

We report that pipetting dispenses an electrically charged aqueous droplet by a spontaneous electrical charging process. This electrification originated from the electrical charge separation between the droplet and the inner surface of the tip of the pipet. Methods to suppress and control the electrical charge of a droplet should be developed because such unexpected phenomenon is mostly undesirable in many experiments. Two different methods for controlling the electrical charge, i.e., passive and active methods, have been developed and reported. Utilizing these methods, it is possible to intentionally control the behavior of droplets in oil environment. Furthermore, since this spontaneous generation of the net electrical charge is equivalent with the generation of the electrical power, the potential use of the electrification as a self-powered sensor is briefly discussed.
Development of Fiber-Based Devices as Energy Harvesters and Self-Powered Sensors
Authors: Chang Ting-Wei , Ke Yi-Yun , Lin Zong-Hong
Published: October 2015

Harvesting Energy from human motions to power portable electronic devices and sensors has been recognized as a new approach to solve the energy problem. In this study, we start to realize the concept by using commercial carbon fibers as the substrates to fabricate nanogenerators. Those fiber-based nanogenerators not only strongly show the potential do develop energy clothes in the near future but also provide an effective way to harvest energy from all directions. Nanowire arrays are designed to grow on carbon fibers first in order to enhance the electric outputs from nanogenerators. By further coating biocompatible polymers on the nanowire arrays, the fiber-based nanogenerators have been successfully demonstrated to harvest mechanical energy from walking. The nanogenerators have also been demonstrated as self-powered force sensors.
Investigation of the Dynamic Relaxation Behavior of Biomolecules Immobilized on Metal Electrode in Time Domain
Authors: Hsu Chen-Pin , Wang Yu-Lin
Published: October 2015

Biomolecules such as DNA immobilized on metal electrodes and non-Faradaic current was measured in buffered solution. The metal-biomolecules-liquid-metal structure can be regarded as a liquid type of capacitor. The measurement of the capacitive current, which is affected by the ions, biomolecules, and liquid in the solutions. It is interesting to investigate the charging and discharging process in time domain, which brings important information of the dynamic behavior of the whole system. In this study, double-stranded DNA (dsDNA) was immobilized on gold electrodes and the capacitive current was measured in buffer solution with a pulse stimulus. Different relation time constants were revealed for various surface modifications. The transient current of the sensor was measured in de-ionized water, TE buffer before and after dsDNA immobilized, different concentrations of HIV-1 RT protein. This technique shows ultra-high sensitivity of the protein detection (1 fM), indicating that this technique is promising for biosensor applications.
CMOS Compatible in-Situ
N-Type Doping of Ge Using New Generation Doping Agents P(MH3)3 and As(MH3)3 (M=Si, Ge)
Authors: Xu Chi , Gallagher James Dennis , Senaratne Charutha , Sims Patrick , Kouvetakis John , Menendez Jose
Published: October 2015

New in-situ methods have been developed to dope Ge-on-Si films with P and As using reactions of novel compounds P(MH3)3 and As(MH3)3 (M=Si, Ge) and UHV-CVD and molecular source epitaxy methods. In these experiments Ge3H8, Ge4H10 hydrides were used to deposit intrinsic Ge layers on Si(100) to produce i-Ge/Si(100) platforms upon which the n-Ge layers were grown at ultra-low temperatures of 300-330°C. The resultant n-Ge/i-Ge/Si(100) samples exhibited device quality crystallinity and defect-free microstructures as evidenced by XTEM. Infrared spectroscopic ellipsometry (IRSE) and Hall revealed carrier concentrations, mobilities and resistivities that are on par with values observed in bulk Ge. SIMS gave flat dopant profiles and abrupt transitions at the n/i interfaces. The highest carrier concentration was achieved in As doped samples at 8.44×1019 cm-3 and the lowest resistivity was observed in P doped samples at 4.2×10-4 Ω∙cm. Comparison between IRSE and SIMS data revealed near full activation (>80%) of the absolute dopant concentrations in the range of 1×1020 cm-3. The methods reported here have the potential for applications in group-IV semiconductor technologies that require high doping levels, low resistivities and shallow junction depths.
Towards Electrochemical Fabrication of Free-Standing Indium Phosphide Nanofilms
Authors: Quill Nathan , O'Dwyer Colm , Buckley D. Noel , Lynch Robert P
Published: October 2015

The formation of sub-surface truncated tetrahedral voids beneath suspended ~40 nm thick dense InP shelves is achievable via a two-step etching method. The first step involves the electrochemical anodisation of n-type InP in aqueous KOH electrolyte resulting in the formation of truncated tetrahedral domains of pores beneath an ~40 nm thick dense surface layer with an individual pit that penetrates the dense surface layer of each domain. The second step involves the preferential chemical etching of these porous domains with only limited etching of the surrounding bulk InP and dense surface layer. The resulting structure of each domain is a truncated tetrahedral void with a dense InP layer suspended above it. This new technique may be a very useful tool in the fabrication of devices based on III-V semiconductors and it may be possible to extend the technique to the fabrication of free-standing InP nanofilms.
Recent Developments in Mercury Cadmium Telluride IR Detector Technology
Authors: Antoszewski Jarek , Akhavan Nima Dehdashti , Umana-Membreno Gilberto , Gu Renjie , Lei Wen , Faraone Lorenzo
Published: October 2015

In spite of many attempts to find better material for infrared detectors, HgCdTe still dominates the high performance end of the market. At present, the research in this field is directed towards high pixel density, high yield, reduced cooling and hyperspectral operation. Long lasting issue of availability of high quality, large area substrates for epitaxial growth of HgCdTe seems to be easing recently with development of 4” CdZnTe lattice matching substrates reported recently. The quality of HgCdTe grown on alternative substrates like silicon, GaAs or recently investigated GaSb still falls behind that achievable on CdZnTe due to large lattice mismatch leading to high defect density. Recent effort to scale down the pixel size and pitch resulted in development of diffraction limited high definition focal plane arrays. Implementation of unipolar n-type/barrier/n-type detector structure in HgCdTe material system has been recently proposed and studied intensively. Due to superior transport and optical properties of HgCdTe it is expected that, when optimized, these structures will allow for background limited performance at significantly higher operating temperatures.
Flexible Graphene Electrode-Based Organic Photovoltaics with Record-High Efficiency
Authors: Park Hyesung , Chang Sehoon , Zhou Xiang , Kong Jing , Palacios Tomas , Gradecak Silvija
Published: October 2015

Advancements in the field of flexible high-efficiency solar cells and other optoelectronic devices will strongly depend on the development of electrode materials with good conductivity and flexibility. To address chemical and mechanical instability of currently used indium tin oxide (ITO), graphene has been suggested as a promising flexible transparent electrode, but challenges remain in achieving high efficiency of grahene-based polymer solar cells (PSCs) compared to their ITO-based counterparts. Here we demonstrate graphene anode- and cathode-based flexible PSCs with record-high power conversion efficiencies of 6.1% and 7.1%, respectively. The high efficiencies were achieved via thermal treatment of MoO3 electron blocking layer and direct deposition of ZnO electron transporting layer on graphene. We also demonstrate graphene-based flexible PSCs on polyethylene naphthalate substrates and show the device stability under different bending conditions. Our work paves a way to fully graphene electrode-based flexible solar cells using a simple and reproducible process
(Invited) From MRTA to SMRTA: Improvements in Activating Implanted Dopants in GaN
Authors: Greenlee Jordan D , Feigelson Boris , Anderson Travis J , Hite Jennifer K , Hobart Karl D , Kub Francis J
Published: October 2015

The implantation and activation of dopants in GaN is a key enabling step for future devices requiring selective area doping. High temperatures (over 1300 ˚C) are required to activate p-type dopants in GaN. These high temperatures are above the decomposition temperature of GaN, which necessitates advanced annealing processes. One such process, the multicycle rapid thermal annealing (MRTA) process, has enabled the implantation and activation of p-type dopants in GaN. In this research, we demonstrate the symmetrical multicycle rapid thermal annealing (SMRTA) annealing process. The SMRTA annealing process includes an extra conventional annealing step after the rapid heating and cooling cycles and is shown to improve the crystalline structure of annealed GaN compared to the MRTA process.
Study on Effect of Proton Irradiation Energy in AlGaN/GaN Metal-Oxide Semiconductor High Electron Mobility Transistors
Authors: Ahn Shihyun , Dong Chen , Zhu Weidi , Kim Byung-Jae , Hwang Ya-Hsi , Ren Fan , Pearton Stephen J. , Yang Gwangseok , Kim Jihyun , Kravchenko Ivan
Published: October 2015

The effects of proton irradiation energy on Al2O3/AlGaN/GaN metal oxide semiconductor high electron mobility transistors (MOSHEMT) were studied. MOSHEMTs were irradiated at different irradiation energies of 5 MeV, 10 MeV, or 15 MeV with a fixed proton dose of 5 × 1015 cm-2. After the 5 MeV, 10 MeV and 15 MeV proton irradiation, MOSHEMTs’ saturation current at gate voltage of 1V were reduced by 95.3, 68.3 and 59.8% and maximum transconductance were reduced by 88, 54.4, and 40.7% respectively. The carrier removal rate of the irradiation energy employed in this study was in the range of 127-289 cm-1, having lower energy with the highest removal rate.
Cathodoluminescence Studies of Gamma-Irradiation Effects on AlGaN/GaN High Electron Mobility Transistors (HEMTs)
Authors: Yadav Anupama , Antia Michael , Flitsiyan Elena , Chernyak Leonid , Lubomirsky Igor , Salzman Joseph
Published: October 2015

The effects of 60Co gamma-irradiation on AlGaN/GaN High Electron Mobility Transistors (HEMTs) were studied by means of temperature dependent Cathodoluminescence (CL). The CL spectra were examined for several devices with radiation exposures of gamma-ray doses up to 1000 Gy, and for temperature ranging from 25°C to 125°C. Gamma-irradiation causes the CL intensity of HEMTs to decrease by creating defects that act as non-radiative recombination centers. The activation energy was observed to decrease as dosage was incremented to 200 Gy. The decrease in activation energy is related to Compton electron induced increase in carrier lifetime. However for doses above 200 Gy, the activation energy increases as the dose increases. This behavior could be explained by the formation of large electrically active defect complexes through the addition of new radiation defects to the defects formed at low doses.
A Laboratory Study of Partial Anode Effects during Aluminium Electrowinning
Authors: Asheim Henrik , Aarhaug Thor , Sandnes Espen , Kjos Ole Sigmund , Solheim Asbjørn , Haarberg Geir Martin
Published: October 2015

The behaviour of graphitic anodes during electrolysis in low-alumina cryolite melts was investigated. The experimental setup consisted of two anodes in separate electrolyte compartments connected in parallel with a single combined cathode. The results show that the anodes to some extent will vary their current uptake based on their resistance towards reaction. The results also indicate that PFC production at normal industrial electrolysis potentials will give a cooling of the anode surface, even with slight elevation of the voltage as the PFC producing reactions have a much higher isothermal potential.
Mass Transport in Oxide Thin Films - Visualization and Control
Authors: Kim Jae Jin , Chen Di , Bishop Sean R. , Cook Stuart N. , Tuller Harry L.
Published: October 2015

Experimental results obtained on electrochemical cells of the form PCO/YSZ/Ag by a novel experimental technique capable of simultaneously performing in situ optical absorption and electrochemical impedance spectroscopy (EIS) measurements under bias were used to demonstrate the ability to extract and control nonstoichiometry in thin film oxides. We showed, that when applied to model materials systems such as PrxCe1-xO2-δ
(PCO), these techniques are capable of deriving a detailed picture of the defect equilibria and transport properties of such materials and determining whether, and to what degree, they differ from bulk properties. Key studies of chemical capacitance, optical absorption and color front motion kinetics are used to extract key thermodynamic and kinetic (kex, DO) parameters in PCO.
Ion Transport and Surface Kinetics in Oxygen Ion Conducting Nanocrystalline Oxide Thin Films
Authors: Bae Jiwoong , An Jihwan , Kim Young Beom , Gur Turgut M , Prinz Fritz B.
Published: October 2015

Nanocrystalline materials often exhibit extraordinary electrical and electrochemical properties related to high density of grain boundaries. In this regard, we have investigated grain boundary structure and grain boundary’s role for ionic transport and surface kinetics using atomic simulations, electrochemical analysis and spectroscopic/spectrometric experiments. Thereby, it was found that the segregation of dopants and vacancies near grain boundaries facilitates oxygen exchange while impeding cross-boundary ionic transport.
Effect of Water Adsorption on Conductivity in Epitaxial Sm0.1Ce0.9O2
-δ Thin Film for Micro Solid Oxide Fuel Cells Applications
Authors: Yang Nan , Strelcov Evgheni , Belianinov Alex , Tebano Antonello , Foglietti Vittorio , Schlueter Christoph , Lee Tien-Lin , Jesse Stephen , Kalinin Sergei V. , Balestrino Giuseppe , Aruta Carmela
Published: October 2015

Water adsorption, splitting, and proton liberation were investigated on Sm0.1Ce0.9O2-δ thin films by scanning probe microscopy. An irreversible volume expansion was observed by applying a positive bias with increased temperature. The volume expansion is also linearly dependent on the relative humidity. A reversible water adsorption process and its effect on the conductivity were also investigated by electrochemical strain microscopy and first order reversal curve under a number of experiment conditions. The presence of a Ce3+ along with OH groups, detected by hard x-ray photoemission spectroscopy established a clear correlation between the water incorporation and the valence state of Ce.
Development of Ceria-Based Microtubular Solid Oxide Fuel Cells
Authors: Sumi Hirofumi , Yamaguchi Toshiaki , Shimada Hiroyuki , Hamamoto Koichi , Suzuki Toshio
Published: October 2015

It is well known that gadolinia-doped ceria (GDC) has high oxide-ion conductivity for electrolyte, and it improves electrochemical activities for fuel oxidation and oxygen reduction for electrodes of solid oxide fuel cell (SOFC). In this work, we investigated the usage of ceria for cathode, anode and electrolyte of microtubular SOFCs for low temperature operation and direct hydrocarbon utilization.
Study of the Effect of Calcination Temperature on the Morphology and Activity of Iridium Oxide Electrocatalyst Supported on Antimony Tin Oxide (ATO) for PEM Electrolyser Technology
Authors: Karimi Fatemeh , Peppley Brant A. , Bazylak Aimy
Published: October 2015

Iridium oxide nanoparticles supported on Antimony Tin oxide (ATO) have been widely used for the oxygen evolution reaction in polymer electrolyte membrane (PEM) electrolysis. In this paper the morphology, crystallinity, catalyst-support interaction and performance for the oxygen evolution reaction (OER) activity of the catalyst iridium oxide supported on ATO at various calcination temperatures will be reported. The supported catalyst was synthesized using a modified Polyol method and calcined at temperatures of 200, 350, 500 and 700ºC. The electrocatalysts were physically characterized by Differential Scanning Calorimetry, Thermogravimetric Analysis, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Brunauer, Emmett and Teller (BET) surface area measurements. The catalysts were also electrochemically characterized by cyclic voltammetry in a typical three electrode system. The main focus of this work is to study the effect of calcination temperatures on the morphology of the iridium oxide nano particles as a function of temperature and degree of crystallization. We find that iridium oxide nano particles synthesized with Polyol method has amorphous structure and calcining at temperatures higher than 400ºC increases the particle size and changes its structure from amorphous to crystalline. It also was found that the amorphous iridium nano particles are highly active and efficient catalyst toward OER, while calcining the catalyst decreases the electrochemically active surface area and its activity.
In-Situ through-Plane Measurements of Ionic Potential Distributions in Non-Precious Metal Catalyst Electrode for PEFC
Authors: Komini Babu Siddharth , Chung Hoon T , Zelenay Piotr , Litster Shawn
Published: October 2015

This manuscript presents micro-scale experimental diagnostics and nano-scale resolution X-ray imaging applied to the study of proton conduction in non-precious metal catalyst (NPMC) fuel cell cathodes. NPMC’s have the potential to reduce the cost of the fuel cell for multiple applications. However, NPMC electrodes are inherently thick compared to the convention Pt/C electrode due to the lower volumetric activity. Thus, the electric potential drop through the Nafion across the electrode thickness can yield significant performance loss. Ionomer distributions in the NPMC electrodes with different ionomer loading are extracted from morphological data using nanoscale X-ray computed tomography (nano-XCT) imaging of the cathode. Microstructured electrode scaffold (MES) diagnostics are used to measure the electrolyte potential at discrete points across the thickness of the catalyst layer. Using that apparatus, the electrolyte potential drop, the through-thickness reaction distribution, and the proton conductivity are measured and correlated with the corresponding Nafion morphology and cell performance.
The Effect of Carbon-Based Substrates onto Non-Precious and Precious Electrocatalytic Centers
Authors: Sreekuttan M. Unni , Campos-Roldan Carlos A. , Mora-Hernandez Juan M. , Luo Yun , Estudillo-Wong Luis A. , Alonso-Vante Nicolas
Published: October 2015

Here, we report the effect of substrate for tuning the active reaction center of precious and non-precious electrocalysts for efficient oxygen reduction reaction (ORR) activity. We have selected surface modified carbon morphologies to study the substrate effect on Pt and CoSe2 catalytic center. Pt supported on surface modified carbon nanotube (CNT) substrates shows, defective sites is important for effective dispersion of Pt on it. CO stripping process probes the effect of Pt interaction with defective and graphitic domains of carbon support. Improved mass activity and specific activity is observed for Pt supported on pyridine functionalized CNT compared to Pt on other CNT substrate. Similarly, CoSe2 supported on nitrogen doped carbon nanohorn (NCNH) shows improved ORR activity in alkaline and acid conditions compared to other carbon based substrates. Enhanced mass activity and specific activity of CoSe2/NCNH is observed in both alkaline and acidic media compared to CoSe2 supported on other modified substrates.
Selective Hydrogen Oxidation Catalyst for Reduced Startup/Shutdown Degradation in Low Temperature Fuel Cells
Authors: Durst Julien , Orfanidi Alin , Rheinländer Philipp J. , Hasché Frédéric , Eickes Christian , Suchsland Peter , Binder Matthias , Gasteiger Hubert A.
Published: October 2015

In this study, we are reporting for the first time clear evidence that Ir-based electrocatalysts are feasible alternatives to state-of-the-art Pt/C anode catalysts for PEMFC applications. While Ir/C has almost the same hydrogen oxidation activity as Pt/C, so that only minor voltage penalties are observed in H2/air performance curves (<20 mV at 1.5 A/cmgeo
2 at 0.1 mgmetal/cm2), its oxygen reduction activity is substantially lower. Therefore, a replacement of Pt/C with Ir/C anodes would be expected to result in lower startup/shutdown (SUSD) damages. It will be shown that indeed 3-fold lower SUSD degradation rates are obtained with Ir/C compared to Pt/C anodes.
Surface Characterization and Platinum-like Electrocatalytic Activity of Nano-Scale Platinum Deposited on Transition Metal Carbide Nanotubes via Atomic Layer Deposition
Authors: Saha Shibely R. , Witters Zachary Everett , Leonard Brian M. , Li Dongmei
Published: October 2015

This work focuses on a new class of electrocatalyst fabrication in which phase pure β-molybdenum carbide (referred to as Mo2C hereafter) was synthesized into hollow nanotubes and subsequently modified with nanoscale platinum (Pt) particles (1-5 nm) deposited via rotary Atomic Layer Deposition (ALD) (referred to as Pt/Mo2C). Pt has been deposited on Mo2C with 15, 50 and 100 ALD cycles. Strong interaction between Pt and Mo2C was observed by XPS and HRTEM. In this paper, we focus on presenting comparison of eletrochemical and surface characterization data among three ALD cycles (100, 50 and 15) to elucidate how performance of the resulting co-catalyst can be tuned by the easily tunable ALD process parameter, number of ALD cycles.
Three Dimensional, High Resolution MPL Generation for Thermal and Mass Transport Modeling of PEM Fuel Cells
Authors: Banerjee Rupak , Bazylak Aimy
Published: October 2015

A stochastically generated microporous layer (MPL) model has been numerically simulated for studying their thermal and mass transport properties. In this work, the MPLs have been generated with a particle diameter of 50 nm and a filling radius of 15 nm. The resulting structure has a bulk porosity of 0.6, a PTFE content of 31 wt. %, and has been generated at a resolution of 2.5 nm/voxel. The high resolution structure allows the particle to particle contact region to be studied, which is critically important for heat transfer studies. Both the thermal conductivity and effective diffusion coefficient were calculated. Thermal conductivity has been calculated to 17.6 W/m-K using an iterative form of the Fourier heat conduction equation. The effective diffusion coefficient of oxygen has been found to be 7.6 mm2/s using OpenPNM, which is an open source pore network modeling platform.
PEM Electrolysis: Ready for Impact
Authors: Mittelsteadt Cortney K
Published: October 2015

The need for energy storage has never been so pressing; due to the increased proliferation and intermittent nature of wind and solar power sources, many regional grids can no longer accept more of these sources. Electrolysis of water using polymer electrolyte membranes (PEMs) has long held the promise of large-scale energy storage, needing only the simplest of reactants, water. The adoption of PEM electrolyzers has been impeded due to the headwinds of high capital cost, poor efficiency, and unknown reliability. Numerous incremental improvements, and increasing economies of scale over the past 10 years have led to very large decreases in the cost of PEM electrolysis. Increasing operating temperature has had the largest impact on efficiency and output. Subsequently, whereas only a few years ago there were no commercial PEM electrolyzer stacks in the 1 MW range, today at least five companies are at or near launch of MW electrolyzer systems.
Current Status and Future Outlook of Fuel Cell Vehicle Development in Toyota
Authors: Kojima Koichi , Fukazawa Kazuhiro
Published: October 2015

Fuel Cell Vehicle (FCV) can be one of the solutions to energy issues andclimate change. FCV has both environmentally-friendly and userfriendlyfeatures such as cruising range of more than 500km, coldstartability and about 3 minutes’ refueling time. In December 2014,Toyota started selling the FCV called “MIRAI” in Japan. The FC systemis composed of Toyota-self-developed components like FC stack, FCboost converter and high pressure hydrogen tanks. The FC stack achievesthe maximum output of 114 kW and the volume power density of 3.1kW/L. Moreover, the FC stack doesn’t require any external humidifier.The FC boost converter can boost the power generated in the FC stack to650 volts. The high pressure hydrogen tanks with three layers includingthe carbon fiber-reinforced plastic layer can store hydrogen at the veryhigh working pressure of 70 MPa to achieve the storage density of 5.7wt%.
Design of Supported PtCo Electrocatalysts for Pemfcs
Authors: Stassi Alessandro , Gatto Irene , Saccà Ada , Patti Assunta , Monforte Giuseppe , Baglio Vincenzo , Aricò Antonino S.
Published: October 2015

Pt-alloy electrocatalysts have been investigated for operation in both hydrogen and methanol-fed polymer electrolyte membrane (PEM) fuel cells with the aim of evaluating their performance. Nanosized PtCo catalysts with particle size of about 3 nm were prepared by using a sulphite complex route. To achieve a high degree of alloying a carbothermal reduction was used. This caused the occurrence of a primitive cubic ordered structure. The surface properties were investigated by X-ray photoelectron spectroscopy (XPS) and low-energy ion scattering spectroscopy (LE-ISS, 3He+ at 1kV). The formation of a Pt skin layer on the surface of the alloy electro-catalyst was studied. The structural and surface characteristics of the samples as well as the type of catalyst support appear to strongly influence the PtCo catalyst performance.
Activity, Stability and Degradation of Carbon Supported Palladium (Pd/C) Fuel Cell Electrocatalysts for the Oxygen Reduction
Authors: Mittermeier Thomas , Weiß Alexandra , Hasché Frédéric , Gasteiger Hubert A.
Published: October 2015

In this experimental study, we determine the size dependent activity as well as accelerated voltage cycling stability of various carbon supported palladium electrocatalysts for the oxygen reduction in acidic medium. Furthermore, ex-situ transmission electron microscopy studies before and after accelerated voltage cycles provide a deeper understanding regarding particle stability during operating conditions. Regarding oxygen reduction, a particle size effect on the specific activity is observed, with bulky Pd-black (≈4 m2/gPd) exhibiting ≈x6 times higher activity than Pd supported on Vulcan carbon (≈190 m2/gPd). Mass activities, however exhibit a strong correlation with catalyst surface area at small values, but are observed to be weakly dependent only between ≈50-200 m2/gPd. As stability tests during voltage cycling reveal a benefit for smaller surface areas, i.e. bigger particles, a limited gain in stability can be achieved by increasing catalyst particle size at a negligible cost of electrocatalytic mass-based activity.
Effects of Core-Shell Interface Structures on ORR Activities: a Model Catalyst Study of Pt/Pd(111)
Authors: Todoroki Naoto , Bando Yohe , Watanabe Hirofumi , Wadayama Toshimasa
Published: October 2015

We investigated surface structures and oxygen-reduction reactions (ORR) of Pt–Pd(111) model bimetallic surfaces fabricated by molecular beam epitaxy. The Pt/Pd(111) surfaces were prepared by depositing 0.6-nm-thick Pt on Pd(111) at substrate temperatures of 573 and 673 (xK-Pt0.6nm–Pd(111), where x = 573 or 673). Reflection high-energy electron diffraction patterns and ultra-high-vacuum scanning tunneling microscopy images revealed that Pt grew epitaxially on the Pd(111) substrate under the deposition conditions selected for the study. However, analysis of low-energy ion scattering results suggested that the Pt and Pd atomic compositions of the topmost surfaces were different for 573K-Pt0.6nm/Pd(111) and 673K-Pt0.6nm/Pd(111). The ORR activities of the 573K-Pt0.6nm/Pd(111) and 673K-Pt0.6nm/Pd(111) surfaces were 6.3 and 3.6 higher than that for Pt(111), respectively. The results indicate that alloy structures near the surface determine the ORR activity of practical Pd@Pt core–shell catalysts.
Investigation of Phosphoric Acid Distribution in PBI Based HT-PEM Fuel Cells
Authors: Pilinski Nadine , Rastedt Maren , Wagner Peter
Published: October 2015

Phosphoric acid is utilized as electrolyte in high temperature polymer electrolyte (HT-PEM) fuel cells to guarantee proton conduction. Loss of electrolyte may be identified as one of the main degradation aspects. The data presented in this paper focus on a better understanding of the degradation paths caused by acid loss from the membrane-electrode-assembly. Therefore this investigation examined the phosphoric acid distribution in an experimental fuel cell setup. Two operational strategies with long term tests under constant load conditions at 0.3 A/cm² and load cycling tests between high current densities of 0.6 A/cm² and 1.0 A/cm² have been performed. The detection of acid content in the various fuel cell components in combination with imaging methods for the identification of changes in surface structure on the bipolar plates provide good instruments to investigate the influences of acid loss during fuel cell operation.
Advancements in Anion Exchange Membrane Cations
Authors: Sturgeon Matthew R , Long Hai , Park A M , Pivovar Bryan S
Published: October 2015

Anion-exchange membrane fuel cells (AME-FCs) are of increasingly popular interest as they enable the use of non-Pt fuel cell catalysts, the primary cost limitation of proton exchange membrane fuel cells. Benzyltrimethyl ammonium (BTMA) is the standard cation that has historically been utilized as the hydroxide conductor in AEMs. Herein we approach AEMs from two directions. First and foremost we study the stability of several different cations in a hydroxide solution at elevated temperatures. We specifically targeted BTMA and methoxy and nitro substituted BTMA. We've also studied the effects of adding an akyl spacer units between the ammonium cation and the phenyl group. In the second approach we use computational studies to predict stable ammonium cations, which are then synthesized and tested for stability. Our unique method to study cation stability in caustic conditions at elevated temperatures utilizes Teflon Parr reactors suitable for use under various temperatures and cation concentrations. NMR analysis was used to determine remaining cation concentrations at specific time points with GCMS analysis verifying product distribution. We then compare the experimental results with calculated modeling stabilities. Our studies show that the electron donating methoxy groups slightly increase stability (compared to that of BTMA), while the electron withdrawing nitro groups greatly decrease stability in base. These results give insight into possible linking strategies to be employed when tethering a BTMA like ammonium cation to a polymeric backbone; thus synthesizing an anion exchange membrane.