bluuebunny/crossref_metadata_2025 huggingface dataset:
An Optimization Study of Nafion-1,2,3-Triazole - H3PO4 Composite Membrane for High Temperature- Non Humidity Condition of PEMFC
Authors: Jun Mun-Suk , Ghil Lee-Jin , KIM Je-Deok
Published: February 2020

The proton exchange membrane fuel cells (PEMFCs) are receiving increasing attention as one of the clean energy and suitable primary power sources for transportation and stationary applications. The proton exchange membrane of recent PEMFCs is commonly used perfluorosulfonic acid polymer membranes (e.g., Nafion). This polymeric membrane is depend on the presence of water to solvate the protons from the sulfonic acid groups. Consequently, the operational cell temperature is limited to below 100oC. However, the PEMFC when operating at high temperature (above 120oC) is having numerous advantages because include increased reaction kinetics, easier water management and a better tolerance to CO.

In this study, we examined Nafion-based composite membrane that can be used at high temperature and non-humidity condition. A novel Nafion-based composite membrane with 1,2,3-triazole and phosphoric acid was prepared by autoclave solution processing [1-3]. Nafion-1,2,3-triazole-H3PO4 (Na-Tri-PA) composite membranes were used as an electrolyte membrane for PEMFC at non-humidity condition of 150oC. Here, we obtained homogeneous membrane as adding 1,2,3-triazole in the Na-PA membrane, and from an optimization process for MEA, Na-Tri-PA composite membrane showed the power density of about 70mW/cm2.

Acknowledgements

This work was partially supported by MEXT program for development of environmental technology using nanotechnology.

[1] J. –D. Kim, M. –S. Jun, C. Nishimura, Y. –W. Choi, ECS transactions, 35, 241 (2011).

[2] J.-D. Kim, A. Suzuki, M.-S. Jun, ECS transactions, 58, 1185 (2013).

[3] M.-S. Jun, J.-D. Kim, ECS transactions, 58, 1195 (2013).
Cross-Linked Anion Exchange Membranes for AEMFC
Authors: Amel Alina , Hickner Michael , Ein Eli Yair
Published: February 2020

Anion-exchange membranes (AEMs) have attracted great interest for their operation in alkaline platinum-free fuel cells .However the use of AEMs in a wide range of devices has been limited due to various challenges. Two major obstacles are the membranes' low conductivity and poor stability in the highly alkaline environment required for fuel cells that necessitates generation of hydroxide anions and transport through the solid polymer membrane.

The effect of cross-linker and its apparent impact on AEM properties will be the focus of this study. Two different cross-linkers were chosen, one has an amino-ether group and the other, has a trymethylhexadecyl amine group. These two crosslinkers have a fundamental difference, where the amino-ether is more hydrophilic and therefore would improve membrane's conductivity and may prevent membrane’s drying out. The properties and stability of the membrane with these two cross-linkers were investigated. Conductivity and swelling measurments were examined at various temperatures for both types of samples. Indeed, water uptake and conductivity were found to be higher for the amino-ether crosslinker. However, degradation measurements analyzed by FTIR and XPS, indicated that the membrane cross-linked by amino-ether group degraded faster at high temperature and pH conditions. Thus, the ether linkage in the cross-linker has a negative influence on the thermal and alkaline stability of the membrane.
Effect of Immobilization Method in the Electrocatalytic Properties of Alcohol-Dehydrogenase Enzyme
Authors: Galindo de la Rosa Juan de Dios , Arjona Noé , Ledesma-García Janet , Guerra-Balcázar Minerva , Arriaga Luis Gerardo
Published: February 2020

Alcohol dehydrogenase enzyme (ADH) from Saccharomyces cerevisiae is immobilized on glassy carbon surface by two methods: physical adsorption and covalent-bonding in order to compare the electrocatalytic properties as a function of the immobilization method. Physical adsorption was carried out by deposition of a mixture composed with nicotinamide-adenine dinucleotide (NAD) as coenzyme, Nafion® (5 wt%) as a binder and ADH onto a graphite surface. Physical adsorption was carried out by deposition of a mixture composed with nicotinamide-adenine dinucleotide (NAD) as coenzyme, Nafion® (5 wt%) as a binder and ADH onto a graphite surface. The covalent-bonding immobilization consisted of a polyaniline film (previously synthesized by cyclic voltammetry on graphite surface) which naturally bonds with NAD and tetra-butylammonium bromide (TBAB) in the presence of ADH. Cyclic voltammetry was used to evaluate the redox behavior and confirm the presence of ADH. Furthermore, the electrocatalytic activity of both bio-electrode arrays was evaluated in terms of the ethanol oxidation reaction showing excellent performance. These interesting bio-electrode arrays offer potential possibilities of application as electrocatysts in direct ethanol biofuel cells.
Gas-Diffusion and Direct Electron Transfer-Type Bioanode for Hydrogen Oxidation with Oxygen-Tolerant [Nife]-Hydrogenase As an Electrocatalyst
Authors: Kano Kenji
Published: February 2020

In order to realize the promising hydrogen energy conversion system, a superior catalyst to oxidize hydrogen is needed.Nowadays, the power devices such as an H2/O2 fuel cell rely on platinum as a catalyst, which is a rare metal and thus too expensive. Many researchers have explored alternative catalysts. From the aspect of bioelectrochemistry, hydrogenase that catalyzes the redox reaction between hydrogen and proton have received a lot of attention, and the bioelectrocatalytic properties has extensively been characterized all over the world.

The discovery of O2- and CO-tolerant [NiFe]-hydrogenase is one of the breakthroughs essential for the construction of the aforementioned biofuel cell, and the unique properties have been investigated from several viewpoints. One critical problem in utilization of [NiFe]-hydrogenase is reversible inactivation caused by the anaerobic oxidation at high electrode potential or high solution potential. Several spectroscopic studies have revealed that the catalytic cycle proceeds in three states: Ni-SI (active silent form), Ni-R (H2-reduced form), Ni-C (one-electron oxidized form of Ni-R), and that the inactivation generates a Ni(III) state form known as Ni-B by one-electron oxidation of Ni-SI, in which a hydroxide ligand is coordinated to the Ni atom in a bridging position with respect to the Fe(II).

A membrane-bound [NiFe]-hydrogenase (MBH) from Hydrogenoviblio marinus allows a direct electron transfer (DET)-type bioelectrocatalysis for the H2 oxidation and is an O2-tolerant promising enzyme for the construction of enzymatic H2/O2 biofuel cells.

From the practical viewpoint of the electricity production, the H2 depletion near the electrode surface and the oxidative and reversible inactivation (as a competitive inhibition) of [NiFe]-hydrogenases limit the H2 oxidation, and consequently causes the power decline. In this research, the Michaelis constant has been evaluated as 0.57 mM under steady-state conditions for the DET-type H2 oxidation by MBH chemically immobilized on Ketjien black mesoporous carbon electrode. In order to spontaneously supply H2 from the gas phase and to avoid the inactivation, an MBH-adsorbed gas-diffusion-type electrode has been constructed. The maximum current density of H2 oxidation has reached about 6 mA cm-
2 at 0 V (vs. Ag|AgCl|sat. KCl electrode) under quiescent (passive) and H2 atmospheric conditions.
Characterization of the Electron Transport Chain Metabolon Bioelectrocatalysis
Authors: Pelster Lindsey , Minteer Shelley D.
Published: February 2020

The electron transport chain is a group of membrane redox enzymes that are the driving force for the production of energy in mitochondria. Several theories and models have circulated different structures of the enzymes in the inner membrane.1 The three enzyme complexes form a supercomplex or respirasome, where Complex I, dimer Complex III, and various copies of Complex IV are electrostatically, hydrophobically and catalytically connected. While structural, kinetic, and genetic evidence prove the formation of the supercomplex, characterization of the bioelectrocatalysis has never been attempted of the three enzymes together on an electrode.2 The supercomplex contains multiple redox cofactors of the individual complex that span the lipid membrane and can come in contact with the electrode surface. By purifying the electron transport chain supercomplex, we have been able to reconstruct the inner membrane and immobilizing it onto a gold electrode. A polymer tethered lipid bilayer allows for the study of the natural bioelectrocatalysis of the large transmembrane proteins. With the addition of oxidized cytochrome c, Complex IV gives a catalytic response indicating that Complex III and Complex IV are active. With the addition of NADH and oxidized cytochrome c, the catalytic peaks increase. This indicates that all three enzymes are working together increasing their redox activities at the surface of the electrode. The supercomplex is further confirmed by inhibition of CIII and CIV, eliminating all activity of the enzymes at the electrode surface. This evidence shows how dependent the enzymes are on each other for efficient catalytic activity. The characterization of the supercomplex of these transmembrane redox enzymes and their bioelectrocatalysis on the electrode is the first for studying a natural metabolon electrochemically.

References

1. Hackenbrock, C. R.; Chazotte, B.; Gupte, S. S., The random collision model and a critical assessment of diffusion and collision in mitochondrial electron transport. J Bioenerg Biomembr
1986,
18 (5), 331-368.

2. (a) Genova, M. L.; Lenaz, G., Functional role of mitochondrial respiratory supercomplexes. Biochimica et Biophysica Acta (BBA) - Bioenergetics
2014,
1837 (4), 427-443; (b) Genova, M. L.; Baracca, A.; Biondi, A.; Casalena, G.; Faccioli, M.; Falasca, A. I.; Formiggini, G.; Sgarbi, G.; Solaini, G.; Lenaz, G., Is supercomplex organization of the respiratory chain required for optimal electron transfer activity? Biochimica et Biophysica Acta (BBA) - Bioenergetics
2008,
1777 (7-8), 740-746.
Effect of Humic Acid on the Electrochemical Performance of Microbial Fuel Cells (MFCs)
Authors: Rodriguez Valadez Francisco Javier , Gonzalez Nava Catalina
Published: February 2020

Microbial fuel cell (MFC) are bioelectrochemical system using exoelectrogenic microorganisms to produce electricity, electrons are transferred through a biofilm growth on the anode surface (Sund et al., 2007), the humic acid had optimal biofilm formation, reducing the lag-time and improve the performance of the MFCs. The aim of this work was to evaluate the effect of humic acid addition on the performance of MFC. The biofilm growth with and without humic acid was evaluated by cyclic voltammetry (CV), chronopotentiometry at open circuit potential and scanning electron microscopy (SEM), the performance of MFC was evaluated by polarization curves and values of voltage, current density and power density achieved with data acquisition system. Triplicate measurements made in a MFC with two chambers of 375 mL, carbon cloth electrodes and proton exchange membrane. From the 5th day, the MFC without humic acid showed a voltage of 0.1 V in response to biofilm wrowth and a steady voltage of 0.34 V after 40 days, cyclic voltammetry showed reduction signs in -0.284 to 0.259 V Vs SHE and oxidation signs in -0.643 to 0.060 V Vs SHE, showing electroactivity biofilms. Optimal biofilm formed reduce the internal resistance from 50 to 4.5 kµÙ, also the anode potential changed from -0.251 to -0.512 V Vs SHE for better performance of MFC. The MFC showed a maximum power density of 1.78E-03 W/m2, current density of 3.6 mA/m2 and power density of 1.4 W/m2. The optimal biofilm formation is important for the performance of MFCs (Martin et al., 2013) and humic acid had effect on the electrode surface supported the growth of biofilm due to functional groups with redox properties (Wandruszka Palmer, 2010).

References

Sund et al., 2007. Appl Microbiol Biotechnol. 76, 561-568.

Palmer y Wandruszka, 2010. Environmental Science & Pollution Research. 17, 1362-1370.

Martin et al., 2013. J. Appl. Electrochem. DOI 10.1007/510800-013-0537-2.
Theoretical Analysis of Surface Waves: Revisited
Authors: Yamamoto Masahiro , Kano Kenji
Published: February 2020

The surface wave for the strongly adsorbed redox spices on electrode is one of the fundamental electrochemical issues, because we don’t need considering the mass transfer of redox species and can calculate voltammogram easily. The ideal voltammogram of the surface wave is symmetric for the forward and the backward scan and it is well known the full-width-at-the-half-maximum (FWHM) is 91 mV.

Recently Nieh et al. proposed the potentiometric coulometry based on charge accumulation with a peroxidase/osmium polymer-immobilized electrode for sensitive determination of hydrogen peroxide [1]. In this potentiometric coulometry the peak shape and width of the surface wave is the key point to get the amount of the hydrogen peroxide in the polymer film. Kakutati and Senda [2] and Laviron [3] showed that the interaction between the adsorbed redox species change the FWHM of the surface wave, i.e. the FWHM is decreased (increased) when e(O-O) + e(R-R) – 2e(O-R) < 0 (> 0).

In this study we have reformulated the chemical potential of the interacting redox species based on Bragg-Williams and Bethe-Guggenheim approximation, and the surface wave voltammogram is evaluated. For the attractive interaction we have found the limiting case that the FWHM become almost zero and the current diverges.　In the Monte Carlo simulation for Kawasaki dynamics system we have confirmed chemical potential obtained by the Bethe-Guggenheim approximation is good enough approximation for the nearest-neighbor interaction model.

We also proposed that the asymmetry of surface wave voltammogram is due to the counter-ion binding interaction for the redox species.

References

[1] C.-H. Nieh et al. Electrochemistry Communications 33 (2013) 135-137.　

[2] T. Kakutani and M. Senda, Bull. Chem. Soc. Japan 52 (1979) 3236-3241.

[3] E. Laviron, J. Electroanal. Chem. 100 (1979) 263-270.
Voltammetric Reduction of Organics at Poly-Para-Aminophenol Modified Graphite Electrodes
Authors: Haque Inam ul , Bano Kiran , Tariq Muqaddas
Published: February 2020

Polymer coated graphite electrodes were obtained by reductive electro-polymerization of para-aminophenol in 1.0 M nitric acid. Linear sweep voltammetry was employed to investigate electrolytic reduction of nitrobenzene and acetone at these electrodes, Figures 1 and 2. Suitability of the electrodes for analytical determination of these compounds is demonstrated.

References

L. I. Halaoui, H. Sharifian, and A. J. Bard, J. Electrochem. Soc., 148, E386-E393 (2001).

I. U. Haque, K. Bano and S. Iqbal, J. Chem. Soc. Pak., 32, 717-723 (2010).

I. U. Haque and K. Bano, Sci. Int. (Lahore), 24, 415-419 (2012).

1IUH Presently at J-263 Phase-I Defence Housing Authority Lahore 54792 Pakistan

2KB Presently at School of Chemistry Monash University Clayton Victoria 3800 Australia
Study on Horn-Shaped Polypyrrole Electrodes Prepared By Pulse Potential
Authors: Li Li , Wang Jingping
Published: February 2020

Recently, many research in alternative biopotential sensor technologies for electrocardiograms (ECG) and electroencephalograms (EEG) applications was carried out due to skin irritation or inflammations often caused by the conventional Ag/AgCl electrode. The electrode material is a key to development of new biopotential sensor. Polypyrrole (PPy) is considered as one of most potential electrode material for biopotential sensor and artificial muscles due to its high electronic conductivity, long-term environmental stability, environmental friendliness and the relatively easy synthesis process. The preparation of PPy electrode by electrochemical method offers several advantages including high conductivity, easy controllability of its thickness and morphology However, this method does not provide horn with high distribution density on the surface of PPy film. Thus, further development of this method is needed.

Polypyrrole (PPy) films were prepared by direct current (DC), pulse current (PC) and pulse potential (PP) in aqueous solutions. The scanning electron microscope (SEM) images of PPy films indicated that a lot of horn-shaped PPy was formed during PP-PPy polymerization process. The top-end of horn-shaped PPy exhibits both open and closed structures. The body of horn-shaped PPy has a hollow structure with a thin wall. The micelles composed by PPy monomer and p-toluenesulfonate anions (PTS-) was formed when pyrrole monomer was dispersed in aqueous solution containing PTS- anions by mechanical stirring. In PP polymerization, the micelles with negative charge were repelled and hence leave the surface of PPy films at switch off time. As a result, the PTS- anions on the surface of micelles were effectively supplied, and thus stabilized the micelles. This process results in the continuous growth of horn-shaped PPy. The hollow horn-shaped PPy films showed big specific capacitance, high charging/discharging rate and better stability.
Controlled CVD Growth of Carbon Nanotubes on Monolayer Graphene Substrates
Authors: Kim Younsu , Kumar Kitu , Fisher Frank T , Yang Eui-Hyeok
Published: February 2020

Graphene and carbon nanotubes exhibit exceptional electrical and material properties. Full utilization of these properties in three dimensional nano-architectures towards envisioned applications necessitates that the integrity of the graphene layer during the CNT growth step is maintained. Recent efforts in fabricating 3D composite nanostructures consisting of 2D graphene and 1D nanomaterials of carbon and conducting polymer are of interest for a number of applications, including next-generation, high capacity, fast-discharge supercapacitors. For these types of energy storage applications, the advantages of graphene arising from the nature of its dimensionality, such as large surface area-to-volume ratio and excellent conductivity, may be compromised due to self-aggregation and charge transfer between the graphene flakes, 1D nanomaterials, and current collector during fabrication. The direct growth of 1D nanostructures such as carbon nanotubes directly on graphene to yield hybrid 3D nano-architectures would, by design, circumvent this self-aggregation, while maintaining low contact resistance to enable effective electron transfer. In our previous work, CNTs were directly grown by chemical vapor deposition (CVD) on graphene using CH4 gas as a carbon source, and the performance of the resultant 3D nanoarchitecture as an advanced electrical double layer capacitor was characterized. However, during this earlier CNT growth, the graphene layer was often found to be etched away at so-called “etched tracks”. We attribute the formation of these etched tracks to hydrogenation by the catalyst nanoparticles (Nickel (Ni)nanoparticle + Cgraphene + 2H2 → Ni + CH4) and their subsequent expansion to carbothermal reduction (SiO2 + Cgraphene → SiO(g) +CO(g)) and hydrogen etching at the tracks’ defect points. This graphene etching process during CNT growth has thus far not been extensively studied in the literature. Therefore, in this work, we grow CNTs atop graphene substrates using C2H4 to demonstrate that the high hydrocarbon conversion rate of this gas, at relatively lower temperature than the more stable CH4 used in our previous study, allows optimization of CNT growth through fine tuning the process parameters including growth temperature, gas flow rate and gas ratio. Further, we optimize the supersaturation state of the catalyst nanoparticles by adjusting the seed density, temperature and carbon source concentration. We also confirm that the controlled use of C2H4is essential for balancing the competing processes of carbon deposition and carbon removal, which ultimately blocks undesired etching of the graphene substrate during the CNT growth process.
Graphene-Based Hybrid Materials Incorporating Multichromophores
Authors: Economopoulos Solon P. , Tagmatarchis Nikos
Published: February 2020

Hybrid materials based on graphene have the potential to drive a variety of nanotechnological applications ranging from optoelectronics, to biomedical, as well as, industrial. Herein, we present an array of novel graphene-based materials incorporating one or more chromophore systems, anchored onto graphene through covalent or non-covalent interactions, targeted for energy conversion schemes.

Graphene single- and/or few-layered graphene sheets have been prepared through ultrasonication processes, introducing minimal defects onto the graphitic backbone while affording comparatively large quantities to allow for chemical modification.1 The chromophores selected to form hybrid graphene nanoensembles, through covalent bond formation, range from pyrene, porphyrin and oligo-thiophene adducts.2 The resulting hybrids afforded stable suspensions in a variety of common organic solvents and allowed for detailed characterization in liquid phase. In addition, non-covalently formed graphene-based nanoensembles were also prepared and the various systems comprised of thiophene chromophores, but also pyrene-porphyrin and dual porphyrin systems.2

All synthesized hybrids have been extensively characterized with thermogravimetric analysis, microRAMAN, and optical techniques (absorption, steady state and time-resolved photoluminescence spectroscopy) among others to verify, the structural and optoelectronic properties of the nanoensembles. Also due to the increased solubility of the hybrids and the ability to form stable suspensions, electrochemistry was used to elucidate the energy levels of the chromophores, as well as the resulting hybrids, affording insight on the thermodynamically favored mechanisms in the system. Finally, time-resolved photoluminescence experiments verify the promotion of electronic communication of the chromophores with the graphene substrate.

Financial support from GSRT/NSRF 2007-2013 through action “Supporting Postdoctoral Researchers” project GRAPHCELL PE5(2126) is acknowledged.

References

S. P. Economopoulos, N. Tagmatarchis, Chem. Eur. J. 2013, 19, 12930.

S. P. Economopoulos, N. Tagmatarchis, Manuscript in preparation, 2014.
Improved Resistive Memory Switching Characteristics of Gold Nanoparticles Embedded Graphene Oxide
Authors: Khurana Geetika , Misra Pankaj , Katiyar Ram S.
Published: February 2020

Resistive random access memory (ReRAM) has recently attracted great attention due to its potential for replacement of flash memory in next-generation nonvolatile memory applications. However, ReRAM devices are facing the problem of stability and repeatability which can be ascribed to the randomness of the conducting filaments formation. Nanoparticles are found to enhance electric field in their vicinity, which is anticipated to define the conductive filament precisely and favorable for the improved switching characteristics if embedded in devices. We have fabricated thin films of graphene oxide with embedded gold nanoparticles through spin coating on ITO/Glass substrates. Top electrodes of Aluminum were deposited using thermal evaporation through a shadow mask. Current-Voltage measurements were carried out using Keithley 2401 in top-bottom configuration at room temperature. The switching characteristics of the device with gold nanoparticles performed well in regard to stable and repeatable switching between low resistance and high resistance states along with low switching voltages with narrow window for switching voltages. These devices showed improved and stable resistance ratio over the period of 104 sec and hence it had good retention and endurance properties. These devices can be seen as potential candidates for memory applications in regard to repeatability and stability.
Synthesis and Characterization of Graphene-Polyaniline Composites Preparated in Site for Fuel Cell Applications
Authors: Pereyra Elsa , Menchaca Carmina , Cano Ulises , Albañil Loyda , Guardian René , Uruchurtu Jorge
Published: February 2020

Keywords: graphene, polyaniline, fuel cells.

Fuel cells have been attracting increasing attention in recent decades due to the high energy demands, fossil fuel depletion and environmental pollution throughout world. However there are still challenges to implement sources and alternative fuels, as in the case of fuel cells: raise increase production cell voltage and reduce material costs and corrosion.

This work focuses on the study of a graphene / polyaniline composite that can be used to improve the efficiency of the electrode in a fuel cell. Graphene alone is a good conductor material with high surface area, however to create a polyaniline intrinsic polymer composite, improvement is expected in their charge-transfer properties.

Two different synthesized graphene as a conductive material, were formed by electrochemical synthesis or modified Hummer method in different particle sizes, and were characterized to study their behavior.The experimental development was carried out by depositing graphene oxide films on a brass plate. The synthesis of polyaniline (PANI) was in situprepared through polymerization of aniline in the presence of graphene or grapheme oxide

The morphology and structure of the material were characterized by scanning electron microscopy (SEM), infrared spectroscopy (IR) and X-ray diffraction (XRD). The electrochemical properties of the resulting materials were systematically studied using cyclic voltammetry (CV), as well as evaluation by electrochemical impedance spectroscopy. Good behavior was observed. The conductivity was also influenced by the particle size of graphene and the improvement is attributed to the fact that graphene not only serves as a highly conductive support material, but also provides large surface for PANI. High conductivity and large specific surface area greatly improve the charge transfer efficiency, providing good corrosion protection to the metal substrate.
SOI and Bulk FinFET Alternatives from the Perspective of Strain Engineering
Authors: Peidous Igor V , Lottes Charles , Jost Christopher
Published: February 2020

Fabrication of MOSFETs with mechanically strained channels has been an effective means for enhancing transistor drive currents and improving performance of CMOS circuits. FinFET devices appear to suit best for leading-edge ULSI and may be scaled to satisfy the requirements of 10 nm technology generations and beyond. There are two generic options for FinFET implementation – SOI and Bulk. The effectiveness of FinFET strain engineering is one of the decisive factors for selecting a preferred FinFET option.

The purpose of the present work is to provide an insight into the stress states of strain-engineered SOI and Bulk FinFETs. The results of computer simulations quantifying the stress effects on carrier mobility in FinFETs of different geometries and channel orientations are presented. The modeling was performed using a specially developed 2D FEM algorithm that enabled fast turnaround in conducting numerous iterative simulation experiments.

The obtained results show that embedded SiGe stressors (eSiGe) formed in Source/Drain areas of FinFETs are the key element for enhancing drive currents of PFETs to the level comparable with NFETs. However, due to the differences in transistor architectures, the stress induced by eSiGe in SOI FinFET channels and the corresponding change of the carrier mobility is about 2 times lower than that in bulk FinFETs. On the other hand, SOI offers a higher degree of freedom for stress engineering to compensate eSiGe deficiency. SOI FinFET designers may consider alternative crystal orientations for Fins, strained SOI, and low-defect Ge or III-V semiconductors on insulator.
The Dual-Heterojunction Ge on Si Photodetector
Authors: Sahni Subal , Hon N. K. , Masini Gianlorenzo
Published: February 2020

Metal contact plugs are today commonly used to establish electrical connection to the anode and cathode electrodes of Ge on Si integrated photodetectors. While large progress has been made in optimizing these contacts, scattering loss at the metal regions still remains the most important efficiency-limiting factor. In addition, the process used to form the contacts is challenging because of the relatively high attack rate of Ge in aqueous solutions. In this paper an alternative way of building and contacting a Ge diode is presented: leveraging the presence of the Si substrate, highly doped n- and p-type regions are formed on the sides of the Ge region. These both serve establishing the built in potential in the diode as well as offering a low resistance path for the photocurrent extraction. Devices built using this approach match and sometime exceed the performance of the classic “PIN” homojunction ones.

In this paper experimental results from a number of dual heterojunction Ge on Si devices based on the LuxG process (Luxtera’s integrated sislicon photonic process) will be presented and discussed.
Surface Charge Properties of Nanoparticle: Size Dependency and Boundary Effect
Authors: Atalay Selcuk , Beskok Ali , Qian Shizhi
Published: February 2020

Surface charge properties of nanoparticles play an important role in many applications, such as drug delivery, cellular uptake and their separation. Surface charge properties of silica nanoparticles are investigated as functions of particle’s size, solution properties including pH and background salt concentration, and separation distance from a flat silica surface using a multi-ion charge-regulation model. In contrast to most previous studies utilizing constant surface charges regardless of the local solution properties, surface chemical reactions in the presence of multiple ionic species are considered in this study. The obtained results agree with experimental data available from the literature. Results show that the magnitude of nanoparticle’s surface charge density increases with its size due to the curvature effect and the presence of the nearby boundary induces spatially non-uniform surface charge around the nanoparticle as while decreasing the k
h, the degree of nonhomogeneous distribution increases. Due to the surface chemical reactions, both pH and background salt concentration significantly affect the charge properties of silica nanoparticles.
Electroformation of Guvs on Microchip with Coplanar Microelectrodes
Authors: Wang Qiong , Yang Jun , Liao Yan-jian , Hu Ning , Luo Hong-yan
Published: February 2020

Recently, microfluidic chip with coplanar microelectrodes is generally used in cell electrofusion and electroporation, it is also more and more popular in the electroformation of giant unilamellar vesicles (GUVs). Higher yield and more uniform size distribution of GUVs can be formed between coplanar microelectrodes than those on conventional devices.

In this study, microchips with planar-comb teeth (PCT), symmetrical comb teeth (SCT), and interdigital comb teeth (ICT) coplanar microelectrodes are used to carry out electroformation of GUVs to compare the impact of different configurations. COMSOL Multiphysics software is used to simulate distributions of the electric field and electroosmotic flow (EOF). Horizontal and vertical electroformation chamber are also simulated. Simulation results show that the electric field and EOF distribution of coplanar microelectrodes are quite different from the traditional 3D chips. In addition, ICT gets better EOF distribution than PCT and SCT.

On-chip experiments show that high yield and uniform size distribution of GUVs can be achieved on these new chips as existing devices based on coplanar microelectrodes. Moreover, the size distribution of GUVs is narrowed from several to hundreds of microns (in traditional methods) to several to several ten of microns. As the simulation results proved, lipid vesicles on a microchip with ICT get a more uniform size distribution.
Study on Processing Technique of 3-D PDMS-Ag Composite Microelectrodes Integrated in Microfluidic Systems
Authors: Jiang Fan , Zheng Xiao-lin , Chen Li , Zhang De-yan , Hu Ning , Liao Yan-jian , Luo Hong-yan
Published: February 2020

Benefited from the development of soft lithography technology, the material polydimethylsiloxane (PDMS) has been widely used serving as a unique material in chip fabrication owing to its properties such as transparency, biocompatibility, and good flexibility. However, PDMS itself is a non-conducting polymer, and the adhesion between metal and PDMS is really weak. Hence, integrating metallic microelectrodes with PDMS-based microchips structures has become an urgent technical issue.

To overcome this problem, we present a method of patterning 3-D microelectrode structures by using a new kind of conductive composite, synthesized by mixing Ag powders with pure PDMS gel. The advantage of this material is the ease of patterning and embedding these microstructures into PDMS-based channels. Compared with other conventional 3-D microelectrode preparations, the technological process was greatly simplified and the cost was effectively reduced.

In this paper, first, the dimensional electric field distributions induced by sidewall electrodes was simulated. Furthermore, we designed a dentate electrode array based on PDMS-Ag conductive composites for cell electrokinetic operations. Integrating 3D-electrode structures into microchips, chip package and fabrication were accomplished by multiple exposures, developments and plasma bonding. The feasibility of electrodes was validated on cell alignment driven by dielectrophoresis force. The results obtained demonstrate that the method seems to be a valuable solution for 3-D microelectrode processing. It is also compatible with existing micro-processing technology with much simpler operations. Thus, we aim at highlighting the promising prospects of this conductive composite material in microfluidic devices.
Interface Investigations and Bulk Behaviors of an All-Solid-State Lithium Microbattery By Means of Electrochemical Impedance Spectroscopy
Authors: Larfaillou Séverin , Guy-Bouyssou Delphine , Le Cras Frédéric , Franger Sylvain
Published: February 2020

Constant miniaturization of electronic devices leads nowadays to the conception of smaller batteries. In this domain, using an all solid state thin film technology has many advantages over conventional lithium cells. These microbatteries are thin, bendable, with a long service lifetime and can also be produced with customizable shapes for better integration in electronic devices. Moreover, without liquid electrolyte, they are safe and comply well with environmental standards. Unfortunately their design and relative small dimensions imply some difficulties to accurately characterize them (from a physico-chemical point of view) without damages.

This paper will present the use of Electrochemical Impedance Spectroscopy to understand the behavior of thin film batteries built by stacking several active layers thanks to physical vapor deposition technics (with LiCoO2 as positive electrode, lithium phosphorus oxynitride vitreous glass as electrolyte (LiPON) and lithium metal as negative electrode). The first step of this study was to distinguish the impedance response between each individual active layer and interface by testing different systems. Metal-insulator-metal stack let us access to the ionic transport properties in LiPON [1]. Half-cells composed with electrolyte and LiCoO2 or lithium, give us information about the electrolyte/active material interfacial behavior. At last, the insertion electrode bulk electronic conductivity can be obtained with a Pt/LiCoO2/Pt symmetrical cell. Thanks to all these results it is thus possible to determine an electrical equivalent model for the complete battery. The model is composed of serial contact and collector resistivity (A), bulk electrolyte (B), capacitance and resistance interfaces (C, D), semi-infinite diffusion in LiCoO2 (E) and charges accumulation phenomena (F).

The Second step was to explain the reasons for spectrum evolutions in function of state of charge, aging or other external conditions. EIS was systematically performed after battery manufacturing and after aging, from 1 MHz to 50 mHz and between 3V and 4.2V. The most obvious observation is the evolution of the “D” contribution with cell potential. Iriyama et al. already attributed it to the charge transfer process at the LiCoO2/LiPON interface [2]. But after aging a new potential dependent R//C contribution appears and could correspond to bulk phenomena in the insertion electrode created by crystalline evolution during aging.

To conclude, thanks to electrochemical impedance spectroscopy, we will propose an electrical equivalent model of the operating microbattery to predict its evolution, failure and aging.

[1] X.Yu, J. Bates, G. Jellison anf F. X. Hart, J. Electrochem Soc., 144, 524 (1997)

[2] Y. Iriyama, T. Kako, C. Yada, T. Abe and Z. Ogumi, Solid State Ionics, 176, 2371 (2005).
Live-Formation of Interphases in Li Ion Batteries
Authors: Russell Selena M. , Cresce Arthur v. , Xu Kang
Published: February 2020

The chemical composition and morphology of interphases dictate not only the reversibility (cycle or calendar life), but also the kinetics of the cell chemistry (power density), and it has been well-recognized that the complicated interplay among electrolyte components (solvent, salt anion, additive) and electrode surfaces affect interphasial properties. While there is general agreement on the formation of the interphase on graphitic anodes from electrolyte component decomposition, the roles of anions and additives is not well characterized and the existence and nature of an analogous interphase on cathode surfaces remains debatable. This presentation summarizes our efforts in investigating the live-formation of interphases in Li ion batteries on both cathodes and anodes under various chemical and electrochemical environments, and the identified key factors that affect the key interphasial properties.
Design and Performance of Compact Air-Cooled SiC Mosfet Inverters for Low-Power Variable Speed Drive Applications
Authors: Bellur Dakshina-Murthy , Kunin Sergey , Ayana Elias , Palmer Brad , Leonarski Jaroslaw , Varigonda Subbarao , Shenai Krishna
Published: February 2020

Design and experimental results of scalable and modular air-cooled power inverters using commercial SiC power MOSFETs are reported. Compared to the well-established silicon IGBT power inverter, the new SiC power MOSFET inverter offers 40% more output power and 4% higher efficiency for a 12 kW, 20 kHz air-cooled design. A detailed design and performance tradeoff will be presented from a system-level perspective in terms of cost/kW for WBG inverter applications for vehicle electrification and power generation applications. The design is based on a simple circuit simulation model developed from measurements made on commercial packaged SiC power MOSFETs.
Innovative Solutions to Materials Challenges for High-Voltage SiC Power Devices
Authors: Gaskill D. Kurt , Myers-Ward R.L. , Klein P.B. , Mahadik N.a. , Stahlbush R.E. , Eddy C.R.
Published: February 2020

Silicon carbide (SiC) is a material of interest for high-temperature, high-voltage and high-power switching device applications. Key materials challenges inhibiting such devices include elimination of basal plane dislocations (BPDs) and enhancement of minority carrier lifetimes in the drift or blocking regions of the device. Recent progress in addressing both of these issues is presented.

BPDs are a major concern for the SiC bipolar devices required for high-voltage applications as they source Shockley-type stacking faults in the presence of an electron-hole plasma and reduce minority carrier lifetimes. Many methods have been investigated to reduce the BPD density including pre-growth treatments, substrate orientation, growth parameters and growth interrupts. It has been shown that the conversion of BPDs to threading edge dislocations (TEDs) continues throughout the epitaxial growth process in 4° off-axis SiC material and that a minimum thickness of ~16 µm is required to convert all BPDs to TEDs. Here we show that optimizing a hydrogen etch of the substrate prior to epitaxial growth significantly enhances conversion efficiency in a thin highly doped n+ buffer layer (BL). IN this work, epitaxial layers were grown on 4° off-axis substrates in an Aixtron/Epigress VP508 horizontal hot-wall reactor using the standard chemistry of silane (2% in H2) and propane.

In addition, using various growth approaches, low-doped epitaxial layers of only 20 µm in thickness on a 5 µm highly doped buffer layer have demonstrated minority carrier lifetimes up to 4 µs, as measured by time resolved photoluminescence, without any pre- or post- processing treatment. Interface recombination likely dominates these measurements. We extend this approach by presenting new data investigating the non-uniformity of lifetime found on as-grown material under various conditions.

This work is supported by the Office of Naval Research
Comparison of the Forward Voltage Drop of Si and SiC High Voltage Diodes
Authors: Gachovska Tanya , Hudgins Jerry L
Published: February 2020

To obtain a high coefficient of efficiency of a converter, the components used to build it should be well chosen. Significant part of the losses is due to the power semiconductor switches. For the same break down voltage, SiC bipolar device have significantly thinner lightly doped drift region (n- base) and therefore low switching losses and also low voltage drop in the drift region. The forward voltage drop of a bipolar device is sum of the drift region voltage drop and the junction voltages. The junction voltages of Si device are significantly smaller as compared to the SiC devices since their bandgap is smaller. Therefore, for not so high voltage devices (< 4 kV), the forward voltage drop will be smaller for Si compared to the SiC devices, while for high voltage devices it is opposite. In this work, physics-based models of Si and SiC diodes are used to calculate their forward voltage drop for different breaking voltage and the simulation results are compare to determine a border between Si and SiC devices.
Workforce Development at PEIC – Power Electronics Industry Collaborative
Authors: Hryn John N.
Published: February 2020

The Power Electronics Industry Collaborative is a national, industry driven membership-based consortium comprised of OEMs, suppliers, researchers, and other stakeholders working to accelerate the development and growth of power electronics in the US. As support grows for domestic energy storage and electric vehicle industries, the US has a promising opportunity to accelerate the power electronics industry. The US has the skills, markets, and technologies to meet the emerging demand for power electronics. As one of its key objectives, PEIC will work to develop a highly skilled, competitive workforce to support design and manufacturing needs of the power electronics industry. This presentation will cover workforce development activities at PEIC.
Study of Ti-Rich and Al-Rich Contact Metallization for AlGaN/GaN HEMT Power Devices
Authors: Bertrand Dimitri , Fayolle Murielle , Blanquet Elisabeth , Torres Alphonse , Volpi Fabien
Published: February 2020

AlGaN/GaN heterostructures have great potential for high-power applications due to their material properties: wide band-gap, high electron mobility in a 2D electron gas and high breakdown field. Low resistance ohmic contacts are required to benefit from the full advantages of the high-electron-mobility-transistor (HEMT) structure. A choice of metallization in agreement with the CMOS-industry standards (i.e. without Au) is required to facilitate the industrialization of such devices. Hence, a Ti/Al stack is a viable solution. Realization of low resistive ohmic contacts is very sensitive to Ti/Al composition and annealing temperatures [1-2]. Understanding metallurgical mechanisms is crucial to optimize the contact.

This work is focused on the study of the Ti/Al metallization and the reactions occurring during a two-steps annealing (300s at 600°C then 60s at 900°C in N2 ambient) in both Ti-rich and Al-rich cases. Two Ti/Al stacks, Al-rich (75/225 nm) and Ti-rich (95/200 nm) have been studied first on Si3N4/Si substrates in order to observe only the Ti+Al reactions and eventual nitridation. Then, the best promising stack (the Ti-rich one) has been transferred on AlGaN substrate. Characterizations consist in AFM, sheet resistance (R), XRD (Fig.1) and cross-section SEM (Fig.2.a) & STEM-EDX measurements (Fig.3). Thermodynamics study has been performed to follow the material behavior.

Regarding the Al-rich stack, XRD peaks (Fig.1.a) prove the formation of TiAl3 at 600°C. This is confirmed by the R value (570 mW) corresponding to a resistivity close to the TiAl3 one (respectively ~20 and 17 µW.cm). At 900°C, R reaches a very resistive value (>8 W) and voids can be identified on SEM images above the remaining TiAl3 (Fig.2.a). XRD reveals the presence of AlN (Fig.1.b) probably formed by the nitridation of Al in excess during the annealing by the N2. This is consistent with the ternary diagram of the Ti-Al-N system (Fig.2.b).

Regarding the Ti-rich stack, XRD graph (Fig.1.c) demonstrates the formation of TiAl3 and a Ti-rich phase at 600°C. At 900°C, XRD reveals the presence of a titanium nitride phase in the contact. This probably results from the reaction of Ti-Al stack with the Si3N4substrate.

The Al-rich metallization creates a thick and resistive layer on top of the stack which is not suitable for achieving low resistive contacts. At the opposite, the Ti-rich metallization allows formation of a titanium nitride layer involving the substrate, a key-reaction for achieving ohmic contacts. Hence, we transferred on AlGaN substrate the Ti/Al 95/200nm stack. Same methodology using also cross-section STEM+EDX (Fig.3) has been applied to complete the scenario of reactions between the Ti/Al stack and AlGaN substrate.

References

[1] B. Jacobs et al., J. Cryst. Growth 241, 15 (2002)

[2] H-S. Lee et al., IEEE Electron Device Lett. 32, 623 (2011)

[3] Q. Chen, B. Sundman, J. Phase Equil. 19, 146 (1998)
Accurate Estimation of Switching Losses in SiC Power MOSFET’s
Authors: Pozo Arribas Alejandro , Krishnamurthy Mahesh , Shenai Krishna
Published: February 2020

The increasing reduction of the manufacturing costs of SiC devices and in particular SiC Power MOSFETs will soon make them cost competitive with other Si devices such as Si IGBTs. For the same voltage and current ratings, SiC Power MOSFETs offer better switching characteristics. Therefore, it is a matter of time that these new devices overtake the role of Si IGBTs in several applications.

Before that moment comes, there is still a lack of uniformity among SiC Power MOSFET manufacturers, especially in terms of the information related to the switching losses that is given in the Datasheet. If we take a look at the Datasheet information for Si Power MOSFETs, most of the manufacturers provide the transition times but not the switching losses. Besides those transition times are typically referred to resistive switching conditions.

Nevertheless, Si Power MOSFETs do not have the same voltage and current ratings as their SiC counterparts. Hence, they are typically used in different applications. Therefore, it makes more sense to compare SiC Power MOSFETs with their competence. These are Si IGBTs.

After analyzing Si IGBTs and their Datasheets we can notice that more information is given for the switching losses. In fact, many manufacturers choose to provide not only the switching times but also the switching losses. Besides, the switching losses are given under inductive switching conditions. For that purpose a freewheeling diode is required to provide a current path when the switch is turned on. This implies that the diode can affect switching performance of the device under test (MOSFETs or IGBT), especially during the turn on, due to the reverse recovery. To prevent from this, Schottky barrier diodes, with zero reverse recovery, are used as freewheeling diodes.

The question then is, is it correct to give the switching losses under inductive conditions? What is the impact of the freewheeling diode on the switching losses? Would a resistive switching test provide more accurate information.