bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Cyclic Hygrothermal Loading on the Mechanical Fatigue Durability of PEM Fuel Cells
Authors: M.H. Khorasany Ramin , Singh Yadvinder , Alavijeh Alireza Sadeghi , Kjeang Erik , Wang Gary , Rajapakse Nimal
Published: February 2020

The membrane electrode assembly (MEA) in polymer electrolyte membrane (PEM) fuel cells undergoes hygrothermal cyclic loading during normal operating conditions. These cyclic loadings create in plane and through plane cyclic stresses being distributed in the membrane. To understand the mechanical fatigue behavior, samples in dogbone shapes (Figure 1) are prepared and placed under the application of cyclic mechanical loadings in controlled ambient conditions [1]. Both pure PFSA membrane and catalyst coated membrane samples are used in the experiments. The tests are conducted ex-situ and the environmental conditions selected in this study cover the temperature and relative humidity levels from those of room conditions to fuel cell conditions. The experimental results are used to benchmark the effect of environmental and loading conditions on the fatigue lifetime of the membrane. Our previous studies [2,3] show that the catalyst layers play a significant role in the mechanical behavior of catalyst coated membranes. Hence, in this study the effect of catalyst layers on the mechanical durability and final elongation of the membrane before the mechanical failure is also investigated.

A strain based fatigue model is then used to develop a finite element numerical scheme for simulating the membrane fatigue lifetime under hygrothermal mechanical loadings. Using the experimental results, the accuracy of the finite element simulations results are verified (Figure 1). The effects of temperature and relative humidity swings on the mechanical longevity of the pure membrane are explored. It is seen that hydration swings have a more profound effect on the fatigue lifetime of the membrane than the temperature swings. Then, using the ex-situ results for the catalyst coated membrane, the impact of the catalyst layers on the membrane/CCM fatigue lifetime is investigated. The finite element model is then used to study the in-situ mechanical stability of pure membranes and catalyst coated membranes under hygrothermal cyclic conditions.

Acknowledgements:

This research was supported by Ballard Power Systems and the Natural Sciences and Engineering Research Council of Canada through an Automotive Partnership Canada (APC) grant.

References

[1] R.M.H. Khorasany, A.S. Alavijeh, E. Kjeang, G.G. Wang, R.K.N.D. Rajapakse, J. Power Sources (2014) under review.

[2] M.A. Goulet, R.M.H. Khorasany, C. De Torres, M. Lauritzen, E. Kjeang, G.G. Wang, N. Rajapakse, J. Power Sources 234 (2013) 38-47.

[3] R.M.H. Khorasany, M.-A. Goulet, A.S. Alavijeh, E. Kjeang, G.G. Wang, R.K.N.D. Rajapakse, J. Power Sources 252 (2014) 176-188.

Figure 1: (a) Dogbone sample used in simulations (with dimensions given in mm), membrane fatigue lifetime at room conditions (23oC, 50% RH) under cyclic mechanical loadings with a maximum force of (b) 1.16 N and (c) 0.95
A Combined Microstructure Characterization of Moisture Permeation Barriers Layers by Means of Electrochemical Impedance Spectroscopy and Ellipsometric Porosimetry
Authors: Perrotta Alberto , Michels Jasper J , García Santiago J , Creatore Mariadriana
Published: February 2020

In engineering and manufacturing organic electronic devices, encapsulation layers are mandatory due to the sensitivity of active layers and low work function cathodes to moisture. The quality of the barrier is generally validated by means of water vapor transmission rate (WVTR, gm-2day-1) measurements as well as in terms of conformal control on the density of local defects (e.g. pinholes) that act as pathways for the water molecules. Furthermore, it has been demonstrated that the water permeation through the barrier nanoporosity (i.e. the intrinsic barrier), responsible for the homogeneous water permeation through the bulk of the barrier, can be 15-20 times higher than through large defects [1]. While several methods allow the identification of pinholes/defects, novel techniques able to characterize the barrier microstructure in the broad range of nano- and meso-porosity are sought. In this work, electrochemical impedance spectroscopy (EIS) and ellipsometric porosimetry (EP) have been adopted to study the residual (open) porosity and water permeation in PE-CVD and (PE-) ALD single inorganic barrier layers and the results have been correlated to the intrinsic barrier performances as well as to their opto-chemical properties. Trivinyltrimethyl cyclotrisiloxane (dV3D3 = 1 nm) and water (dH2O = 0.3 nm) have been adopted as adsorptives in EP and the barrier microstructure has been studied. The pore size range of 0.3–1 nm and its relative content have been found to control the intrinsic WVTR transition towards the 10-4-10-6 gm-2day-1 regime, highlighting the role of residual nanoporosity in controlling the intrinsic barrier properties [ref]. Furthermore, EIS has been employed for the first time to study the water uptake (φ, the volume fraction of water) and diffusivity coefficient (D) of different moisture barrier layers. The layer capacitance has been determined by modelling the impedance data with the proper equivalent circuit and the change of the capacitance upon water permeation has been followed. The Brasher-Kingsbury equation has been successfully applied and φ and D values in the range of 0.8-4% and 10-13-10-15 cm2sec-1 have been found, respectively. In addition, the diffusion of cations having different hydrated shell sizes, i.e. Na+, Li+, K+ and Cs+, through the barriers has been studied. Changes in the resistance of the layer have been attributed to the formation of conductive pathways due to the ion diffusion. With this method, the relative pore size distribution in the range 0.3-1 nm has been characterized in detail.

[1] J. Affinito, D. Hilliard, in: 47th Annual Technical Conference Proceedings (2004) 563.

[2] A. Perrotta, E.R.J. van Beekum, G. Aresta, A. Jagia, W. Keuning, M.C.M. van de Sanden, W.M.M. Kessels, M. Creatore, Microporous and Mesoporous Materials, 188 (2014), 163-171.
Understanding the Meat Color Attributes by Direct Electrochemistry of Myoglobin Films on Electrodes
Authors: Krishnan Sadagopan , Nerimetla Rajasekhara , Walgama Charuksha , Ramanathan Ranjith
Published: February 2020

Protein film electrochemistry (PFE) is a unique method with high simplicity to obtain mechanistic information about complex biological electron transfer and catalytic processes. The emerging applications of PFE are in the development of selective biosensors, biofuel production, renewable energy processes, green biocatalytic systems, and biomedical tools.[i],[ii],[iii] Along this line, we are exploring the novel utilization of heme-protein electrochemistry to understand the meat color qualities. Myoglobin (Mb) is a muscle protein predominantly responsible for meat color. Mb can exist in three different forms namely deoxy-, oxy-, and metmyoglobin. The extent of oxymyoglobin (Mb-FeII-O2) state mainly influences the characteristic red color of meat. On the other hand, the oxidation of oxy- or deoxymyoglobin leads to discoloration of meat or metmyoglobin (Mb-FeIII) accumulation.

Our objective was to investigate the kinetics of metmyoglobin reduction and oxymyoglobin formation using myoglobin model and examine its relevance to meat color properties. For our initial electrochemical analysis, we have chosen three meat related pH conditions such as pH 7.4 (physiological muscle), pH 6.4 (stress-out animal muscle), and pH 5.6 (typical postmortem muscle) and investigated the rates of Mb-FeIII reduction and Mb-FeII-O2 formation using Mb-films adsorbed on graphite electrodes. We observed that under the physiological muscle pH condition, the rates of Mb-FeIII reduction and the subsequent formation of Mb-FeII-O2 were highly favored in comparison to the low acidic pH conditions. Our electrochemical results correlated well with the prior biochemical and redox-titration studies that reported the faster discoloration of meat with lowering pH conditions.[iv],[v] Our investigation suggests that myoglobin-PFE is simple, inexpensive, rapid, and powerful in probing atomic level redox-properties, and thus a valuable tool to predict meat color.

Acknowledgements. This work was supported by the Oklahoma State University.

[i]. (a) M. Meredith and S.D. Minteer, Annu. Rev. Anal. Chem., 2012, 5, 157-179; (b) S. Xu and S.D. Minteer, ACS Catalysis, 2013, 3, 1756-1763.

[ii]. L. Halamkova, J. Halamek, V. Bocharova, A. Szczupak, L. Alfonta and E. Katz, J
.
Am
.
Chem
.
Soc
., 2012,4
, 5040.

[iii]. (a) S. Krishnan and F. A. Armstrong, Chem
.
Sci
., 2012, 3, 1015-1023; (b) S. Krishnan and J. F. Rusling, Thin Iron Heme Enzyme Films on Electrodes and Nanoparticles for Biocatalysis, Chapter 5, p.125, in New and Future Developments in Catalysis, S. Suib (Ed.), Elsevier Publishers, 2013; (c) C. Walgama and S. Krishnan,J. Electrochem. Soc., 2014, 161, H1-H6; (d) S. Krishnan and C. Walgama, Anal. Chem.,
2013, 85, 11420−11426.

[iv]. A. L. Alderton, C. Faustman, D. C. Liebler, D. W. Hill, Biochemistry
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, 42, 4398.

[v]. R. Ramanathan, R. A. Mancini, G. A. Dady, C. B. Van Buiten, Meat Science
2013, 93, 888.
The Influence of the Interaction between Silicon and Hydroxyl Radicals before the Copper Electrodeposition. Activity Changes of the Silicon Surface
Authors: Muñoz Eduardo Carlo , Navarrete Emilio Alonso , Heyser Cristopher Alejandro , Henríquez Rodrigo Gonzalo , Schrebler Ricardo Silvio , Córdova Ricardo Alejandro
Published: February 2020

Several studies have emerged in an attempt to explain the aging process which occurs in the human body, where free radicals (FR) are species involved in these alterations. Considering this subject, there is a great interest in being able to detect, quantify and control the amount of FR that human body produces at certain periods, and especially the hydroxyl radical (OH) [[i],[ii]].

In this study we examined the changes in the surface activity of n-Si after its exposition to a solution containing hydroxyl radicals. Changes in the surface activity caused by the interaction between silicon and OH radicals were characterized by analyzing the nucleation and growth mechanism (NGM) of copper on silicon electrodes. For this aim, we studied the copper deposition on: i) n-Si without exposure to hydroxyl radicals and ii) n-Si exposes at different periods of time to hydroxyl radical. It was observed a change in the copper NGM on n-Si, from 3D progressive nucleation diffusion-controlled growth (PN3DDIFF), for the system without exposure to the OH radical, toward 3D instantaneous nucleation diffusion-controlled growth (IN3DDIFF), when the semiconductor substrate was exposed to the OH radicals. In both cases analysis by the Atomic Force Microscopy (AFM) technique was performed confirming these mechanisms.

[[i]] Tomasz Rapecki, Anna M. Nowicka, Mikolaj Donten, Fritz Scholz, Zbigniew Stojek, Electrochem. Commun. 12, (2010), 1531-1534.

[[ii]] Anna Maria Nowicka, Ulrich Hasse, Mikolaj Donten, Michael Hermes, Zbigniew Jan Stojek, Fritz Scholz, J Solid State Electrochem., 15, (2011), 2141–2147.
Monolayer Catalyst Design Using Slrr of UPD Monolayers – Fundamental Aspects and Interplay of UPD, Reaction Kinetics, and Nucleation Kinetics
Authors: Brankovic Stanko
Published: February 2020

The deposition protocol based on surface limited Redox replacement reaction (SLRR) of UPD monolayers [[i]] has gained a lot of attention in recent years. It has been extensively used for preparation of highly active catalysts [[ii],[iii],[iv],[v],[vi],[vii]], and for growth of homo/heteroepitaxial 2D films with arbitrary thickness [[viii],[ix]]. The concept behind this deposition protocol has potential for a wide range of applications, yet very little is known about the governing phenomena determining morphology of deposited catalyst monolayers.

In this talk we will review fundamental relations controlling the catalyst monolayer nucleation as a prelude for its morphology design. The analytical model describing the nucleation density as a function on reaction stoichiometry, rate constant, reaction order, and fundamental parameters describing surface transport will be presented and discussed with reflection to experimental data. We will show the practical relevance of SLRR reaction kinetics on deposition flux and nucleation kinetics of metal/catalyst monolayers. The different approaches for manipulation of the reaction kinetics and thermodynamics will be discussed within the frame of experimental design/protocols to control the morphology of deposited catalyst monolayers. The emphasis will be made on some convenient and yet allowed approximation relevant to the real systems.

In the second part of the talk the spectroscopic data will be presented emphasizing that catalyst morphology i.e. nanocluster size is an important design parameter directly affecting the monolayer catalyst performance. Examples of Pt/Pd(hkl) and Pt/Au(hkl) will be discussed with in the light of the Pt monolayer morphology.

In the last part of the talk we will show the examples of Pb UPD on Pt and Ru modified Au(111) as a prelude to design of the novel 2D catalyst monolayers and nanoclusters configurations.

The authors acknowledge the support from NSF Chemistry division under the contract # 0955922.

[1] SRBrankovic@uh.edu

References:

[i]) S. R. Brankovic, J. X. Wang and R.R. Adzic, Surface Science, 474, L173 (2001).

[ii]) V. M. Brussel, G. Kokkinidis, A. Hubin, C. Buess-Herman, Electrochim. Acta
48, 3909 (2003).

[iii]) J. L. Znahg, M.B. Vukmirovic, Y. Xu, M. Marvikakis, R. R. Adzic, Angewandte Chemie-International Edition,
44, 2132 (2005).

[iv]) J. L. Znahg, M.B. Vukmirovic, K. Sasaki, A. U. Nilekar, M. Marvikakis, R. R. Adzic, J. Am. Chem. Soc.,
127, 12480 (2005).

[v]) A. Kongkanand, and S. Kuwabata, J. Phys. Chem. B, 109, 2319 (2005).

[vi]) Y. D. Jin, Y. Shen, and S. J. Dong, J. Phys. Chem.
B, 108, 8142, (2004).

[vii]) K. Sasaki, Y. Mo, J. X. Wang, M. Balasubramanian, F. Uribe, J. McBreen, R.R. Adzic, Electrochim. Acta, 48, 3841, (2003).

[viii]) R. Vasilic, L.T. Viyannalage and N. Dimitrov J. Electrochem. Soc.,
153, C648, (2006).

[ix]) Y.G. Kim , J.Y. Kim, D. Vairavapandian, J.L. Stickney, J. Phys. Chem.
B
110, 17998 (2006)
O2 Reduction at Se Modified Surfaces: Characterization by SPM and DEMS
Authors: Baltruschat Helmut , Iqbal Shahid , Bondü Christoph
Published: February 2020

Metal chalcogenides have been extensively studied as catalysts for oxygen reduction reactions, due to their tolerance for small organic molecules especially in relation to fuel cell applications. We have recently reported that also adsorption of Se on polycristalline Ru leads to an increased activity as compared to Ru.[1]. A theoretical study also showed that intermediate surface contents of Ru or Rh by Se or S lead to an increased activity.[2] However, fundamental studies on well-defined rhodium (Rh) single-crystal surfaces modified with chalcogenides (Se) are very rare.

Here, irreversible adsorption of Se on Rh(111) was examined by voltammetric technique. Surface structure characterization of Se modified Rh(111) substrate was achieved using cyclic voltammetry and in situ STM and AFM. STM images also show a roughening starting at step edges for Se adsorption at certain potentials, similar to the roughening transition observed on Au(111) surface for S and Se adsorption [3][4] or As on Pt(111)[5], suggesting the formation of an. Se–Rh intermetallic compound. Results on the effect on oxygen reduction activity will be presented.

It was observed that chalcogenides usually stripped off under fuel cell operating conditions [6] and also electrochemical hydrogen selenide formation at lower potentials [7].Here, we used differential electrochemical mass spectrometery (DEMS) for an additional quantitative characterisation of Se adlayers via reductive desorption on model fcc metal surfaces like [Rh(111), Pt(111) and Au(111)]

References

[1] N. Bogolowski, T. Nagel, B. Lanova, S. Ernst, H. Baltruschat, K. Nagabhushana and H. Boennemann, J. Appl. Electrochem., 37 (2007) 1485

[2] Tritsaris, G. A.; Nørskov, J. K.; Rossmeisl, J.; Electrochim. Acta 56 (2011) 9783.

[3] C. Wei, N. Myung, K. Rajeshwar, J. Electroanal. Chem. 375 (1994) 109.

[4] T.A. Sorenson, K. Varazo, D.W. Suggs and J.L. Stickney, Surf. Sci., 470 (2001) 197.

[5] X.Y. Xiao and H. Baltruschat, Langmuir, 19 (2003) 7436.

[6] D. C. Papageorgopoulos, F. Liu and O. Conrad, Electrochimica Acta 52 (2007) 4982.

[7] M. O. Solaliendres, A. Manzoli, G. R. Salazar-Banda, K. I. B. Eguiluz, S. T. Tanimoto and S. A. S. Machado, J. Solid State Electrochem. 12 (2008) 679.
Absorption of Flue-Gas Components by Ionic Liquids
Authors: Kolding Helene , Thomassen Peter , Mossin Susanne , Kegnæs Søren , Riisager Anders , Rogez Jacques , Mikaelian G , Fehrmann Rasmus
Published: February 2020

Gas separation by ionic liquids is a promising new research field with several applications of industrial interest. Thus cleaning of industrial off gases seems to be attractive by use of ionic liquids and Supported Ionic Liquid Phase (SILP) materials. The potential of selected ionic liquids for absorption of NOx, COx and SOx will be demonstrated and the possible mechanism of absortion will be described on the molecular level. Our vision of application of these ionic liquids to flue gas cleaning in power plants, waste incineration plants, cement and glass factories as well as unborad ships will be adressed.
Electrodeposition of Zn - Ni Alloys from Protic Ionic Liquids
Authors: Ortega Borges Raul Martin , Garcia Ramos Tania , Trejo Córdova Gabriel , Meas Vong Yunny
Published: February 2020

Electrodeposition of metals and alloys is currently carried out from aqueous solutions despite the environmental problems associated to the complex baths needed to obtain electrodeposits with controlled properties (composition, roughness, etc). In this context, ionic Liquids (IL) are studied as an option to be used as new green solvents for electrodepositon due to their interesting properties : non volatility, low fusion temperature, conductivity, viscosity, etc. However, commercial LIs are generally toxic and highly reactive in the presence of water which limits their application in many chemical and electrochemical processes. In this work, we study the use of environmentally friendly and stable protic ionic liquids (PILs) as solvents in the electrochemical deposition of nanostructured metals (Ni and Zn) and their alloys.

The studied PILs synthetized by using well-known amounts of a linear aliphatic amine and a single-chain carboxylic acid as precursors in order to get mixtures of controlled composition (e.g., pure PIL or mixture of a pure PIL and its pure acidic or basic precursor as a co-solvent) to be applied directly as the depositon bath in the electrochemical deposition of nanostructured nickel, zinc and their alloys.

The electrodeposition process was studied by electrochemical techniques and the obtained deposits were characterized by optical microscopy and also by SEM and AFM techniques. For the electrodeposition of the studied single metals (Ni and Zn), results shown that nanostructured nickel and zinc deposits can be electrodeposited from these protic ILs with faradic efficiencies dependent on the composition of the IL and on the temperature; the influence of the physicochemical properties of the studied PILs and of the temperature on the morphological characteristics of the obtained deposits were also evaluated. The major effects were attributed to the influence of composition on mass and charge transfer properties of the PILs.

In the case of the electrodeposited Ni-Zn alloys, results allow to evaluate the influence of the composition of the ionic liquid on the composition of the electrodeposited alloys. In these media, it is observed that Zn-rich alloys are commonly formed. The morphology of the obtained electrodeposits are strongly dependent on the temperature.

These results allow conclude that the studied PILs are good as new reaction media with tunable properties for electrochemical applications, allowing to propose them as new systems for electrodeposition processes, as new single solvents without the use of organic additives.

Acknowledgements: Authors gratefully acknowledge financial support from SEP–CONACyT Program (Project CB 2011-1-168032). TBGR is indebted to CONACYT for the fellowship.
Cellulose-Chitosan-Keratin Composite Materials: Synthesis, Immunological and Antibacterial Properties
Authors: Rosewald Meghann , Hou Fang Yao Stephen , Mututuvari Tamutsiwa m , Harkins April , Tran Chieu d
Published: February 2020

We have developed a simple and recyclable method to synthesize novel biocompatible composites from cellulose (CEL), chitosan (CS) and keratin (KER). Butylmethylimidazolium chloride [BMIm+Cl-], an ionic liquid (IL), was used as a sole solvent for dissolution and preparation of the composites. Since majority of [BMIm+Cl-] used (>88%) was recovered for reuse, the method is recyclable. Various spectroscopic and imaging techniques including powder X-ray diffraction (XRD), FT-IR, near-IR, 13C CP MAS –NMR, and scanning electron microscope were used to monitor the dissolution process, to characterize the composites and to confirm that CEL, CS and KER were successfully regenerated by the method. The [CEL-CS+KER] composites obtained retain properties of their components, namely superior mechanical strength (from CEL), excellent antimicrobial activity (from CS), superior adsorption capability for organic pollutants (from CS) and ability to controlled delivery of drug (from KER). For example, the composites can effectively adsorb various endocrine disruptors including polychlorophenols and bisphenol A, and toxin such as microcystins. The composites were found to substantially reduce growth of Escherichia coli (ATCC 8739), Staphylococcus aureus (ATCC 25923), methicillin resistant S. aureus (ATCC 33591) and vancomycin resistant Enterococcus faecalis (ATCC 51299). The composites are non-toxic to fibroblasts; i.e., fibroblasts were found to grow and proliferate in the presence of the composites. Antibiotic such as ciproprofloxacin can be encapsulated into the composite and kinetic its release can be controlled by judiciously adjusting composition of the composites.
Ion Intercalation into 2D Titanium Carbide Based MXenes: Applications for Electrochemical Capacitors
Authors: Lukatskaya Maria R. , Ren Chang E. , Mashtalir Olha , Dall'Agnese Yohan , Barsoum Michel W. , Simon Patrice , Gogotsi Yury
Published: February 2020

We recently produced a new 2-D material, viz. Ti3C2, by selectively etching aluminium from a MAX phase Ti3AlC2 and labelled it MXene. MXenes represents a large family of transition metal carbides and carbonitrides, not just a single phase. Unlike graphene, whose chemistry is restricted to carbon, MXenes allow a variety of chemical compositions and are establishing themselves as a new class of two-dimensional materials. MXenes possess good in-plane conductivity, which in combination with the rich surface chemistry makes them attractive for electrical energy storage applications. However while potential of MXenes as anode materials for Li-ion batteries has already been shown, their use in electrochemical capacitors has not been explored.

Herein, we report on the intercalation of Li+, Na+, Mg2+, K+, NH4
+, and Al3+ ions between the 2D Ti3C2Tx layers. In most cases, the cations intercalated spontaneously. The intercalation of some ions, notably Al3+, can be promoted electrochemically. We also report on intercalation-induced high volumetric capacitance of flexible Ti3C2Tx paper electrodes. This study provides a basis for exploring a large family of 2D carbides and carbonitrides in electrochemical energy storage applications using single- and multivalent ions.

References.

Lukatskaya, M.R., et al., Cation Intercalation and High Volumetric Capacitance of Two-Dimensional Titanium Carbide. Science, 2013. 341(6153): p. 1502-1505.
Separator Materials Influence on Supercapacitors Performance in Viscous Electrolytes
Authors: Tõnurist Kerli , Thomberg Thomas , Jänes Alar , Lust Enn
Published: February 2020

It is well known that a high internal resistance limits the power capability of the supercapacitor (SC) and ultimately its application. In SCs a number of sources contribute to the internal resistance and are collectively measured and referred to as the equivalent series resistance. These are resistance of the electrode material, the interfacial resistance between the electrode and the current-collector, the ionic resistance of ions moving in small pores, the ionic resistance of ions moving through the separator and the electrolyte resistance. Separator has an effect on the ionic charge compensation rate between the positively and negatively charged microporous carbon electrodes soaked into the electrolyte solution. Therefore the molar conductivity of ions in the porous separator matrix is extremely important.

The aim of this paper was to study the influence of the separator material characteristics (chemical composition, morphology, thickness, porosity) on the performance of SCs at lower temperatures and viscous electrolytes. For that two different electrolytes were used: 1 M triethylmethylammonium tetrafluoroborate solution in dimethyl carbonate, ethylene carbonate and propylene carbonate mixture (TEMABF4 + DMC:EC:PC) with 1:1:1 volume ratio and 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid. Temperature dependence study was performed with TEMABF4 + DMC:EC:PC electrolyte at the temperature range from +24 to -30 °C. To study the influence of the separator material characteristics different separator materials were used: commercially available separators prepared from cellulose (TF4425) and polypropylene (Celgard2400), and self-made separators, prepared by electrospinning method from poly(vinylidene fluoride) with different surface morphologies. Carbide-derived carbon electrodes, prepared from TiC at chlorination temperature T=950°C, were used. Our SCs were tested by cyclic voltammetry, constant power discharge and electrochemical impedance spectroscopy methods.

In given paper it will be discussed how high-frequency series resistance, phase angle, characteristic relaxation time constant and specific power values of SC depends on the separator parameters used. Also it will be shown that for the high power pulse generation systems, the properties of the separator material have to be carefully optimized and separator materials effect is highly important for the viscous electrolyte solutions based SCs and for systems working at lower temperatures.
Atomic Layer Deposition of Nanostructured Tunable Resistance Coatings: Growth, Characterization, and Electrical Properties
Authors: Mane Anil U. , Tong William M. , Brodie Alan D. , McCord Mark A. , Elam Jeffrey W.
Published: February 2020

We have developed ALD method to synthesize nanocomposite coatings comprised of conducting, metallic nanoparticles embedded in an amorphous dielectric matrix. These films are nominally composed of M:Al2O3 where M= W or Mo, and are prepared using alternating exposures to trimethyl aluminum (TMA) and H2O for the Al2O3 ALD and alternating MF6/Si2H6 exposures for the metal ALD. By varying the ratio of ALD cycles for the metal and the Al2O3 components in the film, we can tune precisely the resistance of these coatings over a very broad range (e.g. 1011-104 Ohm-cm). These films exhibit Ohmic behavior and resist breakdown even at high electric fields of 107V/m. Moreover, the self-limiting nature of ALD allows us to grow these films inside of high aspect ratio substrates and on complex, 3D surfaces.

To investigate the ALD growth mechanism for the nanostructure composite films we employed in-situ quartz crystal microbalance (QCM), quadrupole mass spectrometry, and Fourier transform infrared (FTIR) absorption spectroscopy studies. For M:Al2O3 films, QCM showed that the metal ALD inhibits the Al2O3 ALD and vice versa. Despite this inhibition, the relationship between metal content and metal ALD cycle percentage was close to expectations. Depth profiling X-ray photoelectron spectroscopy showed that the M:Al2O3 films are uniform in composition and contained Al, O, and metallic Mo or W as expected, but also presence of moderate F and C. Attempts were also made to investigate the TMA as reducing precursor for MF6 and resulted in similar kind of resistive coatings but very significant F and C which shows influence on microstructure of the layers. Cross-sectional transmission electron microscopy (XTEM) revealed the film microstructure to be metallic nanoparticles (~1-2 nm) embedded in an amorphous matrix. The transport properties of these M:Al2O3 were studied as function of ratio of metal to Al2O3ALD cycles.

We have utilized these nanocomposite coatings to functionalize capillary glass array plates to fabricate large-area MCPs suitable for application in large-area photodetectors. In addition, we have applied these films to serve as charge drain coatings in MEMS devices for a prototype maskless electron beam lithography tool, permitting high resolution electron beam patterns without charging artifacts. Here we will discuss the ALD growth, characterizations, and applications of ALD tunable resistive coatings.
Merits of Batch ALD
Authors: Dingemans Gijs , Jongbloed Bert , Knaepen Werner , Pierreux Dieter , Jdira Lucian , Terhorst Herbert
Published: February 2020

In this presentation, we provide an overview of the merits and applications of batch ALD in a vertical furnace. In addition, a number of common perceptions related to cycle time, films specs and batch processing in industry will be examined more closely.

Batch ALD offers a significant cost-per-wafer reduction compared to clustered single-wafer tools for a range of existing and emerging materials and applications. We present results on cycle time reduction to 20 s and below for ALD Al2O3 and TiN processes without significantly impacting uniformity, resistivity and step coverage. How purge and precursor flows influence the deposition process will be shown by combining experiment and simulation. The influence of deposition temperature and growth inhibition will be covered by presenting a thermal process for the deposition of AlN. A throughput of >50 wafers per hour was achieved for 10 nm films. For Si solar cells, the throughput and costs requirements are the most stringent. We will show that a platform of 4 reactors with automated handling for square solar wafers can reach 4800 wafers/hour (5 nm Al2O3) with remarkably low TMA consumption.

With the workhorse materials being TiN and Al2O3 and applications as diverse as metal gates in logic, trench capacitor electrodes, capacitor dielectrics, barrier layers and passivation films, batch ALD has firmly established itself at device manufacturers and foundry sites. Prospects for emerging markets such as MEMS, solar and LED will be discussed.
Challenges with Industrialization of Atomic Layer Deposition of Silicon Nitride
Authors: Hausmann Dennis , Henri Jon , Sims Jim , Kelchner Kathryn , Janjam Sathish , Tang Shane
Published: February 2020

Scaling of next generation logic and memory semiconductor devices requires conformal thin films on high aspect ratio features at low deposition temperatures (<500ºC). Atomic layer deposition (ALD) is an ideal method for depositing these films and is currently being used in high volume manufacturing (HVM) to deposit high-k dielectric materials (HfO2, ZrO2, etc.) as well as the more traditional dielectrics silicon oxide (SiO2) and silicon nitride (SiNx). With the notable exception of silicon nitride, all of these films can be deposited at sufficiently low temperatures to satisfy the integration requirements while maintaining reasonable throughput and cost. In the HVM environment, silicon nitride ALD has historically been deposited in large furnaces operating at high temperatures, and although both plasma and thermal deposition of silicon nitride have been reported at low temperatures1-2, translation of these low temperature R&D films into HVM films has been challenging.

In this presentation, we discuss some of the challenges faced with addressing the requirements associated with bringing low temperature ALD SiNx into HVM, which include achieving high wafer throughput and low per wafer cost, while simultaneously keeping the resistance of the film to multiple downstream etches and cleans, which may include exposure to hydrofluoric acid (HF). Generic to all ALD processes is the high cost of the precursors relative to traditional chemical vapor deposition (CVD); in the case of SiNx, this is exacerbated by the relative low “reactivity to cost ratio” of available silicon precursors. Cost can partially be addressed with chlorosilane precursors, but the chlorine byproducts create challenges with deposition chamber materials and effluent management. Low reactivity of the silicon precursors poses challenges with respect to process design; the choice of spatial ALD vs. temporal ALD and isobaric vs. non-isobaric deposition sequences affects the final cost and throughput. Lastly, the use of plasmas in ALD poses challenges for achieving isotropic film properties over the complex topography on today’s semiconductor substrates.

References:

1. H. Goto, K. Shibahara and S. Yokoyama, Applied Physics Letters,
68, 3257 (1996).

2. J. Klaus, A. Ott, A. Dillon and S. George, Surface Science Letters,
418, L14 (1998).
Selective-Area Atomic Layer Deposition of Copper Nanostructures for Direct Electro-Optical Solar Energy Conversion
Authors: Willis Brian G. , Qi Jie , Jiang Xiaoqiang , Chen James , Weisel Gary J. , Zimmerman Darin T.
Published: February 2020

Nanoantennas combined with rectifying diodes have been proposed as new devices for light harvesting in the visible and infrared. Metallic nanostructures act as antennae to concentrate electric fields at nanogaps and enable the conversion of light into an electrical signal through asymmetric tunneling across metal-vacuum-metal junctions. Electro-optical conversion occurs when surface-plasmon induced charge oscillations are converted into unidirectional electrical current flow. The proposed devices would accomplish the electro-optical conversion without the need for semiconductor materials. The nanofabrication of antenna-coupled tunnel diodes is extremely challenging, and requires sub-nm precision for tuning tunnel junction resistance. Atomic layer deposition is one of the few methods available with the necessary precision to accomplish this. In this work, we investigate selective-area atomic layer deposition of copper to modify lithographically-defined antenna structures and form arrays of geometrically-asymmetric tunnel diodes. Finite-difference time-domain simulations and optical characterization measurements are used to guide antenna design, including shape, polarization dependence, and wavelength response. Simulations show the electric-field enhancement in the gap to increase significantly with decreasing gap distance; moreover, antenna size and morphology allows for tuning of the peak wavelength response over the infrared to visible range. Nucleation is found to be a critical factor for tuning the electrical and geometric properties of the tunnel junctions. Whereas conformal, epitaxial growth is desired, actual growth is sensitive to surface preparation and seed-layer properties. Analysis of copper growth on palladium seed layers using in-situ spectroscopic ellipsometry reveals a surface chemistry mechanism different than previously understood. Contrary to expectations, palladium-hydrogen complexes are found to be the stable intermediates during growth cycles, and their sensitivity to surface structure may explain non-epitaxial growth. The discussion underscores the link between fundamental surface chemistry and advanced applications of atomic layer deposition.
Self Assembled Metamaterials Formed via Plasma Enhanced ALD of Ag Thin Films
Authors: Prokes S. M. , Glembocki Orest J.
Published: February 2020

Plasma enhanced atomic layer deposition (PEALD) of Ag thin films using Ag(fod)(PEt3) as the precursor has been investigated. Although a regular film of Ag does not have any plasmonic activity, when silver is grown by PEALD, it exhibits unexpected plasmonic behavior, shown in Fig.1 characterized by the Surface Enhanced Raman (SERS) intensity. We show that these films consist of a mosaic structure (inset, Fig. 1) characterized by 2D Ag islands separated by very narrow air gaps (<8nm), which are parallel and extend down to the substrate. These parallel air gaps are an inherent property of the PEALD film, and the source of the plasmonic behavior. We have modeled the ALD-Ag film using FDTD E-M simulations, representing the film as a ring shaped air gap in Ag. The result of the model is shown in figure 2 where we display spatial maps of the electric fields at the resonance wavelength above the film and in cross section. The maps show a very strong confinement of optical fields in the gaps with an enhancement >10x. When PEALD Ag is combined with an active SERS material, such as dielectric core nanowires, the SERS enhancement can be enhanced by > 100x. We have also calculated the time evolution of these fields and have found that the confined plasmonic fields persist long after the excitation pulse. These results indicate that the ALD-Ag is a metamaterial with unique optical constants.

Since the air gaps are critical to the plasmonic behavior of this material, we will also discuss the effect of surface modification of the Ag PEALD. This was achieved by examining the effect of Ag oxide removal by H2 plasma as well as by ALD deposition of Al2O3, where the conformal nature of the coverage is critical. Ellipsometry data indicate a blue shift of the plasmonic resonance with the widening of the air gap (achieved by oxide removal) and with the addition of 2 cycles of Al2O3, which result in the lowering of the refractive index with the addition of the Al2O3. We will discuss the source of this blue shift and show how ellipsometry combined with electric field simulations can be used to obtain detailed chemical information on the surface and in the air gaps of this material, which would not be possible by experiment alone.
5minutes TSV Filling
Authors: Funaahashi Chikara , Kondo Kazuo , Yokoi Masayuki , Okamoto Naoki , Saito Takeyasu
Published: February 2020

1.
Introduction

TSV(Through Silicon Via) is promising interconnection for the next generation smartphone, driving assistance and medical care system because of its ability of high speed image processing and low energy consumption. Conventional TSV filling requires several 10min. to hour because of applying small current of less than 10mA/cm2. This long time electrodeposition prevents TSV realization. We have achieved TSV filling within 5min. and the details will be presented.

2.Results

1.We have used via of diameter of 6μm and 25μm.

2.High current density of 90mA/cm2 is possible to apply without void formation by adopting the PR-current wave form.

3.Di-allyl amine type additive has been used.

4.Fig.1 shows the via filled witnin 5min.. We are further seeking for 1min. TSV filling in order to spread the low cost TSV process world wide.

References

K.Kondo, J. Electrochem. Soc. 2009 156(12): D548-D552

K.Kondo, J. Electrochem. Soc. 2005 152(11): H173-H177
Plating through Hole with High Throwing Power Using Dual Levelers
Authors: Hsu Chia-Fu , Dow Wei-Ping , Huang Su-Mei
Published: February 2020

In recent year, the technology evolution of wireless networks promoted the development of multifunctional pad, computers and mobile phones. The circuit density of density electron product increased as function increased. As a result, the reliability of electron products was more and more important for high density interconnect (HDI) tendency. The copper electroplating process for high throwing power of plating through holes and the thin surface layer with filling via technology were key process for HID. In this paper, copper electroplating formulas that were composed of dual levelers were studied for plating through holes with high throwing power (TP). The base plating solution contained CuSO4, H2SO4, chloride ions, polyethylene glycol (PEG), bis (3-sulfopropyl) disulfide (SPS). When leveler A was added in the base plating solution, it resulted in a smooth surface, which looked like a mirror, but its TP was not good. When leveler B was added to the base plating solution, it enhanced the TP of the plated through hole. However, the board surface was rougher than that adding leveler A. Both leveler A and leveler B could not lead to smooth surface and good TP simultaneously. Interestingly, when both leveler A and leveler B were simultaneously added in the base plating solution, they not only enhanced the TP of the plated through hole but also made the board surface smooth and bright. These results show that chemical interaction can achieve unexpected functional plating.

Key words： High throwing power, high density interconnection, plating through hole and dual levelers.
Development of Glyoxylic Acid Based Electroless Copper Deposition on Ruthenium
Authors: Inoue Fumihiro , Philipsen Harold , van der Veen Marleen , Armini Silvia , Van Huylenbroeck Stefaan , Struyf Herbert , Shingubara Shoso , Tanaka Tetsu
Published: February 2020

High aspect ratio through Si via (TSV) has received much attention as a process integration route to reduce stress build up around the TSV, leading to a small keep-out zone where device performance is impacted. High aspect ratio TSV requires alternative barrier and seed process, because physical vapor deposition (PVD) is facing difficulties yielding continuous layer in such structures. Combining the excellent conformality of ELD in high aspect ratio TSV and atomic layer deposition of barrier and liner, is seen as a potential process route [1]. Glyoxylic acid is a non-toxic reducing agent for ELD-Cu on Ru [2]. In previous work, we found that the nucleation mechanism is catalyst reaction [2]. In this paper, the different anodic reaction of formaldehyde and glyoxylic acid on Ru was compared by polarization analysis. Furthermore, the purity was evaluated after adding stabilizer in the ELD bath. The demonstration of deposition in TSV was performed using 3 × 50 µm TSV.

Figure 1 shows polarization analysis of glyoxylic acid and formaldehyde on Ru and PVD-Cu as a reference. All the measurements showed anodic oxidation. It indicates that the driving force of anodic oxidation of glyoxylic acid and formaldehyde is catalysis of Ru and Cu. Although the anodic oxidation of glyoxylic acid on Ru was weaker than formaldehyde, glyoxylic acid showed similar potential on Ru (-0.63 V) and Cu surface (-0.68 V) at -0.01 mA/cm2. They were -0.63 V on Ru and -0.83 V on Cu for the case of formaldehyde.

Furthermore, we found that 2,2’-bipyridyl worked as stabilizer, brightener and suppressor in the glyoxylic acid based bath. Figure 2 shows surface morphology, roughness and purity of ELD Cu using various concentrations of 2,2’- bipyridyl. The roughness and the purity of copper films improved by adding 2,2’-bipyridyl in the bath. The high purity of Cu might help to reduce void generation during the annealing process after filling. Figure 3 shows cross sectional TEM images of TSV after ELD on Ru. The ELD layer was defect free and worked as a seed layer for electrodeposition of copper. The advantage of depositing a conformal seed layer is that it also reduces the total Cu overburden, which is to be removed by CMP.

Reference

[1] F. Inoue, H. Philipsen, A. Radisic, S. Armini, Y.Civale, S. Shingubara, and P. Leunissen Journal of The Electrochemical Society, 159 (7) D437-D441 (2012)

[2] F. Inoue, H. Philipsen, A. Radisic, S. Armini, Y. Civale, P. Leunissen, M. Kondo, E. Webb, and S. Shingubaraba, Electrochimica Acta
100 (2013) 203– 211
Medium Voltage Hybrid Si IGBT/SiC JBS Diode Module Development
Authors: Hobart Karl D , Imhoff Eugene A , Ray Biswajit
Published: February 2020

Wide bandgap semiconductors are an obvious choice for high voltage applications due to their large critical electric field. While both SiC and GaN will support large electric fields, approximately 10x that of the dominant power semiconductor Si, the wide availability of SiC substrates up to 150 mm diameter provides a cost effective platform over GaN for which even 50 mm substrates are in high demand. Besides substrate technology, high growth rate epitaxy, ion implantation and anneal technologies are well established for SiC. The typical insertion path begins with majority carrier devices such as Schottky diodes which are robust and relatively simple to manufacture. Junction barrier Schottky diodes have been shown to be stable at 10kV [1] and are commercially available up to 1.7 kV. The obvious application for JBS diodes is as a substitute for Si PiN diode freewheeling diodes. The key advantage is the transition from the minority carrier Si bipolar device to the majority carrier unipolar SiC device. This transition to the SiC Schottky virtually eliminates the reverse recovery effects typical of Si PiN diodes. Further, the adoption of the junction barrier Schottky structure results in low reverse leakage current and stable blocking voltages.

In this work medium voltage, 4.5 kV SiC JBS diodes matched to commercially available 4.5 kV IGBTs are joined to form efficient hybrid modules. Dynamic and static characteristics as well as reliability phenomena are evaluated. Compared to the all-Si module, the hybrid module shows up to a factor of six reduced turn-on loss as is demonstrated in Fig. 1 where 4.5 kV Si PiN diode compared to a SiC JBS diode. The recovery current is shown on the left and the impact on the IGBT turn-on characteristics is shown on the right. Through simulations and hardware testing the modules have been optimized for the IGBT/JBS die are ratio in terms of total power dissipation. Other considerations include surge capability which is limited by the JBS diode and the reverse blocking voltage of the IGBT. An external circuit that clamps the voltage across the diode is developed and demonstrated greatly increasing the surge rating. Reliability considerations such as high temperature dV/dt and HTRB are assessed and will be presented.

Overall, the hybrid modules are extremely efficient and robust. Total power losses are reduced by one-half by replacing only the freewheeling Si PiN diode with a SiC JBS diode. The optimized solution reduces the needed SiC die area and thus module costs. Reliability assessments show that the modules are robust.

References:[1] Brett A. Hull, Joseph J. Sumakeris, Michael J. O’Loughlin, Qingchun Zhang, Jim Richmond, Adrian R. Powell, Eugene A. Imhoff, Karl D. Hobart, Angel Rivera-López, and Allen R. Heffner, “Performance and Stability of Large-Area 4H- SiC 10-kV Junction Barrier Schottky Rectifiers”, IEEE Transactions on Electron Devices, vol. 55, no. 8, pp.1864-1870 (2008). Figure 1
Characterization of Defects in SiC Substrates and Epilayers
Authors: Dudley Michael , Wang Huanhuan , Wu Fangzhen , Yang Yu , Guo Jianqiu , Chung Gil , Thomas Berndt , Sanchez Edward K , Mueller Stephan , Hansen Darren , Loboda Mark , Zhang Jie
Published: February 2020

A review will be presented of recent monochromatic and white beam synchrotron topography based studies of defects in SiC substrates, epilayers and devices. The methodologies used in applying these techniques to gain understanding of the origins and evolution of the defect structures in PVT grown boules and CVD grown epilayers will be elucidated. In particular, criteria used in distinguishing grown-in defects from deformation induced defects will be discussed. Contrast observed from the various dislocations present in the crystals will be explained, and it will be shown how contrast simulation can be used to identify the detailed characteristics of the dislocations (for example, both Burgers vector sign and magnitude). Application of the various techniques to the complete analysis of the distribution, character and origins of grown-in c-axis screw dislocations (both hollow and closed-core), deformation induced basal plane dislocations, and grown-in threading edge dislocations will be discussed.