bluuebunny/crossref_metadata_2025 huggingface dataset:
Microvia Filling By Using Insoluble Anodes in an Acidic Copper Planting Bath with a Novel Accelerator
Authors: Liu Chu-Chi , Dow Wei-Ping
Published: February 2020

To develop copper plating formula for high-speed via filling, a more stable insoluble anode, namely dimensionally stable anode (DSA), was used at high current density. We choose a novel accelerator, 3-(N,N-dimethylthiocarbamoyl)-thio propanesulfonic acid (DPS), which has better acceleration performance on copper superfilling than Bis(3-sulfopropyl) disulfide (SPS) in the DSA plating system. This work investigates the influence of experimental conditions on filling performance and also use numerical simulation method to quantify the filling performance.

According to the results, DPS can exhibit excellent acceleration on copper deposition in the DSA plating system only. NMR result shows that DPS is oxidized by the DSA to be more active products which bears -SH and -SO3
- groups, which can accelerate on copper deposition. Putting the DSA in a filter bag can block oxygen which was produced by water electrolysis at the anodes to enter the plating solution and reduce DPS oxidation on the surface of the DSA. As a result, via bottom and top deposition rate was different from that without the filter bag.

From the results of microvia filling and numerical simulation method, the inhibition of complex inhibitor (PEG-Cl-) and the filling performance was positive in correlation with convection in the blind via. In a plating system with a strong forced convection and a low temperature exhibited better filling performance. On the other hand, the filling performance was Cu(II) mass-transfer controlled in the weakly forced convection system, so that the filling performance is not good.
The Properties of a Three-Dimensional Porous Electrode Made from Cu Nanowires
Authors: Wiley Benjamin J. , Kim Myung Jun
Published: February 2020

The high surface area per unit volume and large mass-transfer rates offered by three-dimensional porous electrodes have resulted in their use in a wide variety of electrochemical processes, including organic electrosynthesis, water electrolysis, water treatment, fuel cells, and redox flow batteries.1-4 Many types of porous electrodes are commercially available, including carbon paper, graphite felt, reticulated vitreous carbon (RVC), metal mesh, and metal foam. Metal foam offers relatively high conductivity (1.5x10-5 ohm m) but low surface area (<4x104 m-1),5 whereas carbon paper has one of the highest surface areas (up to 1.6x105 m-1) but lower conductivity (4.7x10-5 ohm m).6

This presentation will describe the characteristics of a copper nanowire electrode (Fig. 1) that has 15 times more surface area (2.4x106 m­-1) and is 33 times more conductive (1.6x10-6ohm m) than carbon paper. The improvement in surface area is due to the small diameter of the nanowires relative to carbon fibers in carbon paper, whereas the high conductivity is due to intrinsically higher conductivity of Cu, and the fact that the metal nanowires can be sintered together, forming highly conductive inter-nanowire contacts. The porosity of the nanowire electrode is 0.94, and its permeability was only 4 times lower than carbon paper. This presentation will report the electrochemical performance of the Cu nanowire electrode relative to carbon paper for the reduction of Cu ions in a flow-through geometry. The high-conductivity, high surface area, and high porosity that can be achieved with Cu nanowire electrodes creates new opportunities for improving the performance of electrochemical systems for energy storage, hydrogen production, water treatment and the production of fine chemicals.

References:

1. J. Newman, and W. Tiedemann, AIche J., 21, 25 (1975).

2. R. Alkire, and P.K. Ng, J. Electrochem. Soc., 124, 1220 (1977).

3. J.M. Friedrich, C. Ponce-De-Leon, G.W. Reade, and F.C. Walsh, J. Electroanal. Chem., 561, 203 (2004).

4. S. Porada, L. Weinstein, R. Dash, A. van der Wal, M. Bryjak, Y. Gogotsi, and P. M. Biesheuvel, ACS Appl. Mater. Interfaces, 4, 1194 (2012).

5. S. Langlois, and F. Coeuret, J. Appl. Electrochem., 19, 43 (1989).

6. S.C. Barton, Y. Sun, B. Chandra, S. White, and J. Hone, Electrochem. Solid-State Lett., 10, B96 (2007).

Figure. 1.(A) Image of a porous Cu nanowire electrode. (B) SEM image of the nanowires in the electrode.

Figure 1
Fabrication of High-Stability Solid-State Receiver Electrodes in Exploration System for Detecting High-Resistive Gas Hydrates
Authors: Kuo Chu-Shan , Peng Hao-Ting , Lin Jeng-Yu
Published: February 2020

Generally, gas hydrate is nearly a prefect isolator with electrical resistivity of ca. 20,000 Ω·m. Therefore, the resistivity of seafloor sediments with brine-filled pores typically ranges from 0.5 – 1.0 Ω·m, whereas sediments containing hydrate within the pores can have resistivity of ca. 10 Ω·m. As for massive blocks of hydrate, it can have resistivity of 100 Ω·m or more. Up to date, electromagnetic (EM) and direct current resistivity (DCR) techniques are generally employed to explore gas hydrate by measuring electrical resistivity. Nevertheless, both of methods still require high-stability receiver electrodes for monitoring the variance of potential difference. 

In this study, the solid-state silver/silver chloride (Ag/AgCl) electrodes were successfully developed for using at high-pressure environment of deep sea. To evaluate the potential of solid-state Ag/AgCl electrodes as the receiver electrodes in EM and DCR systems, the effects of temperature, composition and flowing velocity of simulated seawater solution on the stability of the solid-state Ag/AgCl electrodes were investigated systemically. The solid state electrodes showed potential variance of ± 0.35mV at environment of room temperature or 5 ℃. Moreover, it revealed that the potential variance within ± 0.4mV when the simulated seawater solution containing 0.009 wt% bromide or 0.5wt% sulfate ion. Furthermore, it presented the potential variance within ± 0.45mV at flow rate of water in 1.5 m/s or vibration frequency at 100 Hz. Therefore, the fabricated solid-state Ag/AgCl electrode could be a promising receiver electrode candidate in EM or DCR exploration system for detecting the high resistive target, gas hydrate, under the shallow sea bead.
(Invited) PBI Membrane Development for Fuel Cells and Electrochemical Separations
Authors: Pingitore Andrew T , Qian Guoqing , Garrick Taylor R , Wilkins Cody H , Weidner John W. , Benicewicz Brian C
Published: February 2020

Polybenzimidazole (PBI) polymers are excellent candidates for PEM fuel cell membranes capable of operating up to 200˚C. Several years ago, we developed a sol-gel process to produce PBI membranes loaded with high levels of phosphoric acid. This process, termed the PPA process, uses polyphosphoric acid as the condensing agent for the polymerization and the membrane casting solvent. Membranes produced from this process showed the ability to maintain high levels of phosphoric acid (PA) and high proton conductivities while simultaneously exhibiting low levels of PA loss during operation. We have been exploring the effects of chemical structure on the basic membrane properties, as well as issues of membrane stability and durability. We will describe some of our recent results on the correlations between polymer structure and properties which provide valuable insights for designing membranes with extended durability tailored to fuel cells. Additionally, the synthetic variability in preparing many different PBI polymers has provided several opportunities to tailor the PBI chemistry to a growing number of devices related to energy and separations applications. PBI membranes have been prepared which were designed for hydrogen "pumping", the hybrid-sulfur cycle, and flow batteries. Recent results in these areas will be presented.
Innovative Separation Technology for Lithium-6 Enrichment Using Electrodialysis with Lithium Ionic Superconductor
Authors: Hoshino Tsuyoshi
Published: February 2020

Tritium needed as a fuel for fusion reactors is produced via neutron capture by lithium-6 (6Li). However, natural Li contains only about 7.8% 6Li, and enrichment of 6Li up to 90% is required for adequate tritium breeding in fusion reactors. The mercury amalgam method is superior to some of the lithium isotope enrichment methods. In Japan, lithium isotope enrichment methods have been developed to avoid the environmental hazards of using mercury. However, the isotope separation coefficient and efficiency is too low to meet the practical need of large mass production of 6Li.

Therefore, new Li isotope separation technique using a Li ionic superconductor functioning as a Li isotope separation membrane (LISM) have been developed [1]. Li ions move by electrodialysis through LISM between the cathode and the anode in lithium solutions. Because the mobility of 6Li ions is higher than that of 7Li ions, 6Li can be enriched on the cathode side of a cell.

It has been reported that the difference in the mobility between 6Li and 7Li become large in ionic superconductor. The isotope effect in ionic superconductor is expected to be applicable to isotope separation membrane. In this research, we numerically investigated the ionic mobility of Li isotopes in ionic superconductor. Combing the first principle and the kinetics Monte Calro simulation, we calculate the diffusion constant of 6Li and 7Li. I show the two important effects for the difference in the mobility between isotope of Li. The first is the quantum effect, which decrease the diffusion barrier for Li ion and increase the ratio of the diffusion constant of Li isotopes. The second is the correlation effect between 6Li, 7Li and vacancy.

Using Li0.29La0.57TiO3 (LLTO) as the Li ionic superconductor was prepared, and the relationship between the 6Li separation coefficient and the electrodialysis time was investigated. After electrodialysis, we obtained a maximum of 1.04 for the 6Li isotope separation coefficient. This result showed that the 6Li isotope separation coefficient of this method is the same as that of the amalgamation process using mercury (1.06). Thus, this method has the potential to be a superior 6Li enrichment method to produce 90% enriched tritium breeder for fusion reactors.

Figure 1
(Invited) Assessing Impacts of Material Chemistry and Operation Strategies on Capacitive Deionization Energy Consumption and Cost
Authors: Hand Steven M , Cusick Roland D
Published: February 2020

Based on the ability to couple energy storage with ion adsorption, capacitive deionization (CDI) systems have received increased attention as an alternative to reverse osmosis (RO) desalination. Preliminary modeling indicates that CDI must operate at a charge efficiency of 0.8 or greater to compete favorably with RO. In this presentation we will highlight how critical charge efficiency can be reached by incorporating complementary fixed charge groups or faradaic materials into the electrode to enhance both selectivity and capacitance. By replacing commonly employed hydrophobic polyvinylidene fluoride (PVDF) bound electrode ionically charged structural polysaccharides, chitosan (CS) and carboxymethyl cellulose (CMC) as composite electrodes binders, we observed charge efficiency values greater than 0.9 and salt adsorption increased by a factor of three. By incorporating MnO2 onto an aerogel through electroless deposition, we improved charge efficiency to 0.8 while also increasing sodium adsorption capacity by greater than one order of magnitude. These results indicate that model informed design of CDI electrodes could enable cost effective desalination with energy storage materials.
Kinetic Modeling of Bio-Oil Conversion By Electrocatalytic Hydrogenation and Deoxygenation
Authors: Das Sabyasachi , Saffron Christopher M.
Published: February 2020

Using renewable electricity, electrocatalytic hydrogenation can be used to stabilize biomass-derived pyrolysis oil. Stabilization occurs by electrochemically reducing highly reactive functional groups in bio-oil, such as aldehydes, ketones and aromatics, to more stable alcohols and cycloalkanes. This study develops a comprehensive kinetic model for the electrocatalytic hydrogenation of representative bio-oil compounds. The system under investigation is a two-compartment divided cell with a ruthenium impregnated activated carbon cloth cathode and a platinum anode using a Nafion membrane to separate the electrode compartments. The model, programmed in Matlab, includes mechanisms for all transient phenomena occurring in the electrolytic cell, such as bulk diffusion, intra-particle diffusion, adsorption, charge transfer reactions and surface reactions. The objective is to use this model to find rate constants and other model parameters, determine the rate-limiting steps, and identify the most sensitive variables to better understand the process and improve its performance. The development of this kinetic model is a crucial step towards scale-up of electrocatalytic hydrogenation as a keystone of novel pyrolysis-based bioenergy systems.
Electrochemical and Spectroscopic Studies of Oxidation of Biomass Mimics By Cobalt Complexes
Authors: Servedio Luke T. , Foister Shane , Zawodzinski Thomas A.
Published: February 2020

The reactivity of cobalt(II) complexes with molecular oxygen has long been a known and is a much-studied chemical mechanism. These interactions result in the formation of metal-dioxygen adducts that are responsible for numerous cobalt-catalyzed oxidations. In the case of 4-coordinate cobalt salen [Co(salen)] complexes, the formation of catalytically active, mononuclear, superoxo adducts in the presence of a secondary, N-donor ligands has been demonstrated [Co(salen)pyr-O2]. In batch reactions, these adducts are known to readily oxidize para-substituted phenolic compounds resulting in benzoquinone in high yield. Para-phenolic model compounds have been used to demonstrate the potential use of cobalt Schiff base complexes in the oxidation of lignin biomass.

This work investigates the redox behavior of the Co(salen)pyr-O2­­ adduct as a potential recyclable electrocatalyst. Using traditional electrochemical techniques, the activity of the Co(salen)pyr-O2 adduct is evaluated as it applies to the oxidation of the substrate syringyl alcohol (4-(hydroxymethyl)-2,6-dimethoxy-phenol) in acetonitrile. Typical EC’ electrochemical behavior is reported showing a near linear relationship between substrate concentration and peak current density (Jp) up to 200 mV s-1. Electrochemical titration of catalytic amounts of Co(salen) with pyridine in the presence of excess oxygen and substrate indicate that the one-electron oxidation of Co(salen)pyr-O2H is reversible up to 2:1 pyridine to cobalt. However, both FTIR and EPR characterization of electrolysis experiments with Co(salen)pyr-O2 in the presence of excess substrate show evidence for the deactivation and/or degradation of the catalyst system after the two-hour mark indicating possible poor ligand stability under reaction conditions.

Acknowledgements

We gratefully acknowledge the NSF EPSCoR program, TN-SCORE, for support of this work.
Understanding the Economic Feasibility of Valorizing Lignocellulosic Biomass through Electrochemical Hydrogenation
Authors: Orella Michael Julian , Brown Steven Michael , Roman Yuriy , Brushett Fikile R.
Published: February 2020

Lignocellulosic biomass presents a promising source of renewable carbon that can enable the sustainable generation of fuels, chemicals, and consumer goods that power our modern economy.1,2 While the feasibility of processing the cellulose and hemicellulose fractions of native biomass has been demonstrated, economical utilization of the lignin-containing fraction is more challenging3 due to it's chemical complexity, source-dependent structural variability, and recalcitrant nature.4,5 However, recent advances in reductive catalytic fractionation (RCF) processes have enabled clean separation of a small set of lignin monomers from the cellulose and hemicellulose fractions of native biomass, which, in turn, simplifies downstream approaches to converting these reaction products into more valuable chemicals.6,7

In this work, we investigate the potential economic feasibility of using electrocatalytic reactors, as compared to traditional thermochemical reactors, to upgrade lignin monomers to cycloalkyl and aromatic species, specifically targeting benzene, toluene, and xylene (BTX). To this end, we developed a process-based techno-economic model to quantify the viability of electrochemical upgrading, to benchmark materials and reactor performance requirements, and to identify potential technical hurdles. Furthermore, we investigate the model sensitivity to critical process parameters and key assumptions. This analysis enables a direct comparison between traditional thermochemical hydrogenation processes and proposed electrochemical hydrogenation processes across multiple installation scales as well as potentially favorable combinations of the two approaches. We hope that the results presented here inspire further research into electrochemical approaches to enable biomass upgrading.

References:

(1) Werpy, T.; Petersen, G. Top Value Added Chemicals from Biomass Volume I—Results of Screening for Potential Candidates from Sugars and Synthesis Gas; Department of Energy, 2004.

(2) Holladay, J. E.; Bozell, J. J.; White, J. F.; Johnson, D. Top value-added chemicals from biomass; Department of Energy: Pacific Northwest National Labs, 2007.

(3) Rinaldi, R.; Schüth, F. Energy Environ. Sci. 2009, 2 (6), 610.

(4) Vassilev, S. V.; Baxter, D.; Andersen, L. K.; Vassileva, C. G. Fuel 2010, 89 (5), 913.

(5) Zakzeski, J.; Bruijnincx, P. C. A.; Jongerius, A. L.; Weckhuysen, B. M. Chem. Rev. 2010, 110 (6), 3552.

(6) Bosch, S. V. den; Schutyser, W.; Vanholme, R.; Driessen, T.; Koelewijn, S.-F.; Renders, T.; Meester, B. D.; Huijgen, W. J. J.; Dehaen, W.; Courtin, C. M.; Lagrain, B.; Boerjan, W.; Sels, B. F. Energy Environ. Sci. 2015, 8 (6), 1748.

(7) Anderson, E. M.; Katahira, R.; Reed, M.; Resch, M. G.; Karp, E. M.; Beckham, G. T.; Román-Leshkov, Y. ACS Sustain. Chem. Eng. 2016, 4 (12), 6940.
Etching with Low Te Plasmas
Authors: Walton Scott G , Boris David R. , Hernandez Sandra Catalina , Rosenberg Samantha G , Miyazoe Hiroyuki , Jagtiani Ashish V , Engelmann Sebastian U , Joseph Eric A
Published: February 2020

Processing with atomic layer precision requires the ability to not only add, remove or modify one monolayer of material but to also leave adjacent layers unchanged. This requires fine control over the flux of species and energy deposition at the surface. The appropriate threshold and process windows are certainly material specific but it is reasonable to assume many applications require low energy ions. Electron beam-generated plasmas are generally characterized by high charged particle densities (1010- 1011 cm-3), low electron temperatures (0.3 - 1.0 eV), and in reactive gas backgrounds, a relatively low radical production rate compared to discharges. The flux at the surface will thus be characterized by a comparatively large amount of ions whose energies are < 5 eV, a value commensurate with the bond strength of most materials. As such, these sources are well-suited to explore processing space not commonly found in industrial tools. In this work, we discuss SiN etching using pulsed, electron beam generated plasmas produced in SF6 backgrounds. We pay particular attention to the etch rates, selectivity (vs. carbon films, Si and SiO2), and patterning as function of operating parameters such as relative gas concentration, operating pressure, and substrate bias. These results are compared with plasma diagnostics to gain a better understanding of the process requirements and windows for threshold etching of SiN. This work is partially supported by the Naval Research Laboratory base program.
Molecular Layer Deposition for Applications in Lithium-Ion Batteries
Authors: Van de Kerckhove Kevin , Mattelaer Felix , Dendooven Jolien , Detavernier Christophe
Published: February 2020

Molecular layer deposition (MLD) of hybrid organic-inorganic thin films called titanicones, vanadicones, tincones, and alucones was investigated for electrode and solid electrolyte applications in lithium-ion batteries.

The titanicone, vanadicone and tincone films were studied as electrode materials, both as anodes and cathodes. Novel MLD processes were developed for these materials and were based on an alkylamine metal precursor (TDMAT, TEMAV, TDMASn) and glycerol (GL) as the organic reactant. Linear and self-limited growth could be achieved for these metalcones in a broad temperature range with temperature-dependant growth rates ranging from 0.2 to 1.3 Å/cycle. Film growth was studied in situ with spectroscopic ellipsometry (SE) and infrared spectroscopy (FTIR). The as-deposited films appeared to be electrochemically inactive in all cases. A post-deposition heat treatment up to 500°C in either inert (helium) or oxidizing (air) atmosphere was able to electrochemically activate the films. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements showed that all carbon was removed during calcination in air and that the films crystallized. However, annealing in inert atmosphere conserved the carbon content of the film and thus the films remained amorphous. The performance with increasing charging and discharging rate, and cyclability of the heat-treated MLD electrodes was tested against their respective metal oxide references. The He-annealed metalcones emerged from these tests as the best performing electrodes at higher rates (left and middle figures) and with improved capacity retention and stability during repeated charging and discharging.

The transformation of alucone films, deposited with the TMA and ethylene glycol (EG) or GL process, into porous aluminium oxide was examined. Porous, non-conducting materials are interesting for lithium-ion battery research since they may serve as the matrix template for solid composite electrolytes. Calcination in air and water etching proved to be the most successful methods. For the calcination treatment, a clear relation was found between the ramp rate during both heating and cooling and the resulting porosity of the film (right figure). The aging behaviour of the films in ambient atmosphere was also investigated with FTIR and showed that the films deposited with EG decompose in a matter of only a few hours, as opposed to those deposited with GL.

Figure 1
(Invited) A Confined Phase Change Memory for M-Type Storage Class Memory
Authors: Kim Wanki , BrightSky Matt , Masuda Takeshi , Kim Sangbum , Bruce Robert , Carta Fabio , Fraczak Gloria , Ray Asit , Zhu Yu , Suu Koukou , Lam Chung
Published: February 2020

Phase Change Memory (PCM) is relatively mature emerging memory technology which shows promise for serving as a Storage Class Memory (SCM) which fills the gap between high speed DRAM and much slower NAND. However, most reported PCM cells show stuck-SET failure caused by elemental segregation or open failure (void formation) as their failure mechanisms. Because of these failure mechanisms, it has been challenging to achieve the endurance specifications needed for M-type SCM. In order to overcome these well-known failure mechanisms of PCM, we advanced the state of the art confined PCM cell with a thin metallic liner.

In this study, we present a robust high aspect ratio confined PCM cell which utilizes a dense nano-crystalline-as-deposited phase change material. The small pore structures were filled utilizing an in-situ metallic liner plus nano-crystalline ALD GST process. The tuned process for depositing and integrating the phase change material yields a void-free dense confined PCM inside the pore. This confined PCM with a metallic liner is found to be immune to classic endurance failure mechanisms. So, the highly reliable confined PCM yields a new record endurance (2x1012 cycles) and a fast programming speed of 80ns with 10x switching. In addition, we thoroughly investigate the excellent endurance of the novel confined PCM with a thin metallic liner. Experimental results confirm that both the proper metallic liner and the confined pore cell structure are required for a reliability advantage. This confined PCM cell has high potential of being incorporated as a M-type storage class memory with advanced memory technology node due to its outstanding endurance and fast set speed.
Thermoelectric Properties of Metal-Organic-Framework Thin Films
Authors: Chen Xin , Zhang Kai , Hassan Zeinab Mohamed , Wang Zhengbang , Lin Pengtao , Baumgart Helmut , Redel Engelbert
Published: February 2020

Bulk Metal-Organic-Framework (MOF) films are designed scaffold-like compounds which are composed by inorganic metal clusters connected with organic linker molecules, forming highly ordered, crystalline and porous structures. These bulk MOF frameworks were initially designed for gas storage due to their high storage capacity inside the pores of MOF bulk materials. However, the application for electrical devices were very limited resulting from their insulating character. Recently, it has been reported that the electrical properties of bulk host MOFs can be modulated by infiltrating guest molecules (metal clusters) inside the porous MOF framework. This renders MOF materials a novel and promising material for microelectronic devices, sensors, catalytically active materials and thermoelectrics.

In our work, oriented SURMOF films and random polycrystalline MOF films Cu3(BTC)2 (BTC: benzene tricarboxylate, known as HKUST-1 MOF, were synthesized by a liquid phase epitaxy (LPE) spray method grown on surface functionalized gold coated silicon substrates and regular non-functionalized silicon substrates covered with a thick 484 nm thermal SiO2 layer respectively. The tetracyano-quinodimethane (TCNQ) guest molecules were infiltrated into the MOFs to modulate the electrical properties of the film. The horizontal Seebeck coefficient parallel to the sample surface of both oriented SURMOF films and random polycrystalline MOF films were measured. The random oriented MOF films exhibit a high positive Seebeck coefficient of 422.32 µV/K at 350 K. However, the horizontal Seebeck coefficient of oriented SURMOF films fluctuates around 0 µV/K. This can be interpreted that these highly oriented SURMOF films exhibit a large anisotropy with no charge carrier transport in horizontal direction parallel to the sample surface, but only carrier transport in vertical direction. The anisotropic nature of SURMOF films were further proven by IV characterization. The electrical conductivity of polycrystalline MOF film in horizontal direction was observed in the temperature range of 260 K to 350 K to calculate power factor (S2δ) of MOF films. The maximum value of power factor was found at 350 K about 1.527 µW/(m2K), which is about one order of magnitude higher than reported one. The thermal conductivity measurement on polycrystalline MOF films indicated the TCNQ infiltration not only contributes to enhance electrical conductivity, but also results in a reduction of thermal conductivity of MOF films. The reduced thermal conductivity can be attributed to enhanced phonon scattering due to TCNQ infiltration. The results demonstrate that random polycrystalline MOF film has a promising application potential in future thermoelectric and electronic devices.
Synthesis of P-Type Fe3CoSnxSb12-X Skutterudite Single Phase By Designing Double Filled Compositions
Authors: Choi Soon-Mok , Son Geonsik
Published: February 2020

Double-filled Ce0.6Yb0.4Fe3CoSnxSb12-x (x=0.1 - 0.4) skutterudite compositions were designed for enhanced thermoelectric properties. We fabricated the skutterudite specimens by using a melt-spinning process with subsequent a spark plasma sintering (SPS). Effect of Sn doping amount on the thermoelectric characteristics of the Ce0.6Yb0.4Fe3CoSnxSb12-x system were investigated. Single phase formation was examined by a XRD (X-ray diffraction) method. The microstructure was investigated by SEM (scanning electron microscope). The carrier concentration and carrier mobility were also measured to analysis the Sn doping amount effects on formation of the single phase and their properties in detail.
(Invited) Volume Resistive Switching in Metallic Perovskite Oxides Driven By the Metal-Insulator Transition
Authors: Palau Anna , Gonzalez-Rosillo Juan Carlos , Ortega Rafael , Jareño Julia , Coll Mariona , Arndt B , Dittmann Regina , Maggio-Apprile Ivan , Suñé Jordi , Obradors Xavier , Puig Teresa
Published: February 2020

In recent years, huge efforts have been made in the research community to overcome the limitations in Flash and RAM memories, and consequently, new emerging technologies are competing in the race towards a new paradigm in information storage. In particular, nonvolatile memories based on the Resistive Switching (RS) effect, where two (or more) reversible resistance states can be induced upon application of an electric field, has emerged with excellent performance. This phenomenon has been observed in many oxide systems, in particular in perovskite oxides, which are materials showing outstanding properties giving rise to exotic physical phenomena due to the strong electronic correlation, such as metal-insulator transitions (MIT). This is the case of the metallic perovskite La1-xSrxMnO3 (LSMO), RENiO3 (RE=rare earth) and YBa2Cu3O7(YBCO) family compounds, which are able to display Volume RS effects induced by the MIT and therefore, small changes in carrier concentration can induce huge resistance changes. The mechanism underlying this phenomenon is still unclear although oxygen vacancies mobility plays an important role in the mechanism underneath this phenomenon.

In this presentation we will discuss our studies on bipolar resistive switching of the mentioned perovskite oxides. Switching characteristics have been evaluated by C-SPM and I(V) curves with metal electrodes. Scanning tunneling microscopy and spectroscopy (STM/S), transport and resistive measurements were performed to gain insight into the local density of states of the material for different resistance states. Large resistance rations (102-104), over 100 cycles experiments, multilevel switching and switching dynamics have been evaluated. In addition, we have confirmed the strong influence of different atmospheres on the resistive switching properties of bare LSMO thin films. Remarkably, this influence disappears when the LSMO layer is capped with a CeO2thin layer, which acts as an oxygen reservoir, making this bilayer a proper material choice for encapsulation. A 3-terminal proof of principle device based on Ag/CeO2/LSMO/CeO2/Ag will be presented.

We believe that these results contribute to a better understanding of the physical mechanism behind the robust RS effect of these metallic perovskite oxides films.
(Invited) Efficient MoS2 Catalyst Integrated on Si Heterojunction Cell for Photoelectrochemical Hydrogen Evolution
Authors: He Jr-Hau , Alarawi Abeer Ateeq , Varadhan Purushothaman
Published: February 2020

Hydrogen appears as a next-generation clean energy source to replace fossil fuels. One of the most promising ways to produce hydrogen is water splitting using the photoelectrochemical (PEC) cell. Silicon is widely used in this cell due to its viability to absorb light. However, its efficient catalysis and long-term stability remain key challenges due to the corrosion effect. Here we fabricate highly efficient and stable photocathode by integrating crystalline MoS2 as a catalyst with specially designed Si-based heterojunction cell (n+-p-Si) that exhibits ultra-high efficient water reduction in acidic media (0.5 M H2SO4) with excellent electrochemical stability. MoS2 is an efficient low-cost catalyst for hydrogen evolution reaction (HER) and it provides corrosion protection for the Silicon cell. Therefore, thermal decomposition process was used to synthesize few-layers MoS2 at different concentration, time and temperature. Detailed microscopic and spectroscopic characterizations and the corresponding electrolysis performance based on the synthesized MoS2 were systematically studied in this work. Based on the results, the best MoS2 catalyst was deposited on the (n+-p-Si) cell to carry out the photoelectrochemical process. The performance characteristics of the photocathode were investigated under 1-sun light illumination. The results showed efficient photocurrent of 38 mA/cm2 and onset potential of 0.4 V vs RHE. This study indicates that integration of MoS2 with heterojunction cell (n+-p-Si) is a promising pathway towards efficient and stable hydrogen production.
(Invited) Van Der Waals Heterojunctions for Energy-Efficient Electronics
Authors: Roy Tania
Published: February 2020

Van der Waals heterojunctions show immense potential in electronic and optoelectronic applications. In this talk, a vdW heterojunction-based all-two-dimensional transistor will be discussed. The all-2D transistor shows no surface roughness scattering, a property hitherto unforeseen in its three dimensional counterparts. A dual-gated MoS2/WSe2 vdW heterojunction diode can be tuned to operate in various diode operation regimes. The same device operates as a forward rectifying diode as well as a tunnel diode, merely by application of gate voltage. The first observation of gate controlled band to band tunneling in semiconducting 2D heterostructures was made here, enhancing the prospects of using vdW heterojunctions for low power electronic applications. A 2D/2D tunnel field effect transistor with WSe2 and SnSe2 will be discussed. VdW heterojunctions with graphene/h-BN/graphene show negative differential resistance, which can be used in analog applications, such as in oscillators and amplifiers. Also, a graphene/insulator/graphene heterostructure demonstrates resistive switching and can be used to make ultra-low power resistive memories. Thus, vdW heterojunctions display a new paradigm of materials innovation to sustain the aggressive improvement of electronics for the continued betterment of human lives.
(Invited) In Situ Electron Beam Driven Nano-Devices – a Route to New Materials Development for Energy Applications and Beyond
Authors: Rummeli Mark Hermann
Published: February 2020

A key feature of my research is to develop a transmission electron microscope (TEM) into an atomic-scale nano-chemistry laboratory to fabricate, modify and characterize samples so that crucial structure property studies and synthesis studies can be conducted in high spatial resolution and high temporal resolution. In this presentation I will show a variety of electron beam driven reactions and electron beam engineering techniques in which we can fabricate and manipulate nano-materials. I will also show how one can structure and look at structure-property relationship of graphene devices, both fabricated and examined in-situ in a TEM.
Bifacial Micropyramidal Surface for Achieving High Efficiency of Photoelectrochemical Water Splitting
Authors: Fu Hui-Chun , Varadhan Purushothaman , Tsai Meng-Lin , Li Wenjie , Ding Qi , Jin Song , He Jr-Hau
Published: February 2020

Photoelectrochemical splitting of water into hydrogen and oxygen are of great interest for the production of clean and storable form of chemical fuels. Silicon, the most investigated material as the photoelectrode has the potential for both the dual-absorber and tandem photoelectrochemical system. However, a major inadequacy in simultaneous achievement of efficiency, electrochemical stability, and the photon management hinders the practical prototype based on Si. Herein, we have successfully addressed the issues in band-structure engineering, light harvesting, and photon management in Si heterojunction (n+p-Si) photocathode for the concurrent improvement in the photon management, efficiency and stability. The resultant state-of-the-art Si heterojunction (n+p-Si) photocathode exhibits the current density of 61.2 mA/cm2 that yielded the solar-to-hydrogen conversion efficiency of 18.22% for the bifacial design, with the electrochemical stability over 370 h, the highest efficiency and stability reported so far on single junction Si-based photocathodes. Moreover, the surface structured photocathode demonstrates the excellent bifacial and omnidirectional light harvesting capability over a wide angle of about 180°, as compared to conventional single-sided devices that can absorb only <50° over an entire rotation. The high efficiency, chemically stable and bifacial photoelectrochemical cell demonstrated herein can provide a significant advance towards the development of next-generation renewable energy devices.
(Invited) Crystalline Electronic and Photonic Materials Grown on Non-Epitaxial Substrates
Authors: Kapadia Rehan , Sarkar Debarghya , Wang Wei
Published: February 2020

In this talk, we will discuss how single crystalline compound semiconductors may be grown on non-epitaxial substrates using liquid metals to define the geometry on both the nano- and micro-scale. Specifically, we will first talk about a general thermodynamic approach towards preventing dewetting of ultra-thin liquid metals with capping layers, defining the basic requirements for our growth substrates and capping layer. Next, we will talk about simple binary III-V semiconductors, and the general rules surrounding growth on non-epitaxial substrates. We will then discuss how this growth may be used to grow pure phases of more complex materials that have multiple stable phases, such as tin based compounds. Finally, we will discuss how this approach can be used to grow uniform ternary materials on non-lattice matched substrates. We discuss the quality and optoelectronic properties of each of these materials and will provide perspectives on the present challenges and paths forward.
(Invited) Requirements for Highly Accurate Multiphysics Modeling of SiC Power MOSFETs and Power Modules
Authors: Grossner Ulrike , Kakarla Bhagyalakshmi , Ziemann Thomas , Muting Johanna , Stark R. , Kovacevic-Badstuebner Ivana
Published: February 2020

With the current needs towards achieving significantly higher power density and energy efficiency of power conversion, the industry is highly interested in replacing mature Silicon devices with the emerging Silicon Carbide (SiC)-based technology in the new generation of power electronics systems. Multi-physics modelling represents a very important design step used to evaluate and confirm the potential of SiC devices in a wide-range of power electronics applications before any prototypes are constructed. It enables a detailed assessment of SiC technology with respect to different performance aspects including dynamics, thermal capabilities, and robustness against abnormal operating conditions. As a prototypical example, this paper presents a highly accurate modelling procedure for analyzing short-circuit (SC) capabilities of a commercial SiC power MOSFET (80mΩ, 1.2kV). First, the actual MOSFET structure is modeled in Synopsys Sentaurus TCAD tool suite and calibrated to match the I-V and C-V MOSFET characteristics, taking into account the mobility degrading effects and interface states at the SiC/SiO2 interface. In the next step, TCAD mix-mode simulations are performed using the developed physical model to gain a better understanding of the design parameters like cell pitch, channel length and p-base doping concentration and their impact on the MOSFET SC and dynamic characteristics considering temperature dependencies and design constraints. Accordingly, a trade-off analysis between improved SC capabilities and a good MOSFET dynamic performance will be discussed, which can be further used as a guideline for developing an optimized MOSFET structure. Moreover, a detailed three-dimensional electromagnetic model of the SC measurement setup will be presented in order to identify the influence of the circuit parameters on the current profile of the Device-Under-Test (DUT) during the SC events and to optimize the measurement setup. For a comparison between the measured and simulated MOSFET waveforms, coupling of electrical and electromagnetic domains will be performed in LTSpice, Saber and TCAD mix-mode tool. As a result, this paper will demonstrate the accuracy of three device models side-by-side: the compact device model implemented in LTSpice, the behavioral model of Saber, and the TCAD numerical model. Finally, the paper emphasizes the requirements for a very accurate and efficient multi-domain modelling procedure that can be integrated in the overall development process of SiC power MOSFETs.

Fig. 1 A comprehensive analysis of short-circuit (SC) capabilities of a commercial SiC power MOSFET (80mΩ, 1.2kV) based on a multi-physics modelling approach.

Figure 1
Investigation on Degradation of HT-PEM Membrane-Electrode-Assemblies for Fuel Cells Under Start-Stop-Cycling
Authors: Tullius Vietja , Rastedt Maren , Büsselmann Julian , Schonvogel Dana , Pilinski Nadine , Wagner Peter , Dyck Alexander
Published: February 2020

The emphasis of this study is the investigation of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFC) of various manufacturers with simulated start-stop cycles. This study is part of the national project QUALIFIX, which is funded by the German Ministry of Economy and Energy. Its purpose is to develop a framework to log, revise and improve the quality of fuel cells, its system components, as well as its manufacturing chain. Coherent test procedures enable the comparability of single fuel cells of various manufacturers. Furthermore, these framework conditions should enhance the lifetime of fuel cells, as well as minimize the production costs in an early stage.

In this study all tested membrane electrode assemblies (MEAs) have been investigated under identical test conditions using simulated Start-Stop (S/S) cycles. Consequently, the MEAs have been started up under defined conditions and operated for twelve hours at a constant current density of 0.3 A/cm². Following this, the MEAs have been shut down for another twelve hours and have been allowed to cool down to room temperature. Furthermore, all MEAs have been held under a nitrogen atmosphere at 30 °C during the stop phases before the next startup procedure has been performed. Figure one presents the fuel cell voltage at 0.3 A/cm² as function of time for one examinee after 500 h, correlating to 21 S/S cycles.

As a result, a continuous cell degradation rate of -33 µV/h could be observed. Next, degradation for HT-PEMFC MEAs have been evaluated by an extensive in situ electrochemical characterization, which has been executed before and after 21 S/S cycles. This characterization includes among the voltage curve, electrochemical impedance spectra, cyclic as well as linear sweep voltammetry. Additionally, all MEAs have been analyzed through ex situ characterizations, including, among others, micro computed tomography

(µ-CT), analysis of product water via ion chromatography (IC), as well as the determination of the phosphoric acid content, once S/S cycling has been stopped. Simultaneously, fresh MEAs of the same batch have been tested with the same ex situ methods. This allows to determine the ‘begin of life’ (BoL) condition in a pristine state.

As mentioned above, an unprecedented benchmarking of MEAs of various manufacturers has been performed with respect to HT-PEMFC degradation. Moreover, the results will be compared to the ex situ findings of the BoL-Analysis.

Figure 1: Voltage as function of time of one MEA under start stop cycles for 500 hours

Figure 1
Nanostructure of HT-PEFC Electrodes Investigated with Scattering Methods
Authors: Holderer Olaf , Khaneft Marina , Lin Yu , Liu Shuai , Feoktystov Artem , Kruteva Margarita , Zorn Reiner , Lehnert Werner
Published: February 2020

Small angle scattering with X-rays (SAXS) and neutrons (SANS) is used as a powerful tool to investigate different components of fuel cells or even groups such as membrane electrode assemblies (MEAs) (1,2). In particular, the structure of electrode layers and membrane electrode assemblies of High Temperature Polymer Electrolyte Fuel Cells (HT-PEFCs) is studied in this contribution with neutron and x-ray scattering (1). Electrode layers in different stages of preparation, pure and doped with different amounts of phosphoric acid have been studied with SAXS. Structural changes have been observed with the addition of phosphoric acid, which is used in this type of HT-PEFC as proton conducting electrolyte.

Details of the phosphoric acid distribution and possible void distribution in electrode layers have been obtained with contrast variation experiments in small angle neutron scattering, where the different parts of the sample can be highlighted by exchanging hydrogen with deuterium, here in the phosphoric acid.

An outlook will point at the strength of quasielastic neutron scattering experiments to shed light on the proton diffusion on different length scales in the range of 0.1-10 nm, as a microscopic equivalent to the macroscopic conductivity, and it will address the question of what can be retrieved from a multicomponent system such as the different parts of a fuel cell.

M. Khaneft, O. Holderer, O. Ivanova, W. Lüke, E. Kentzinger, M.S. Appavou, R. Zorn, W. Lehnert, Fuel Cells
16 (2016), 406 – 413

O. Holderer, O. Ivanova, B. Hopfenmüller, M. Zamponi, W. Maier, A. Majerus, W. Lehnert, M. Monkenbusch, R. Zorn, Int. J. Hydrogen Energy
39 (2014) 21657 – 21662
19F NMR Studies of 3M Ionomer Adsorption on Carbon Supports and Pt/C Catalysts
Authors: Cantillo Nelly M. , Li Luyue , Peng Jing , Goenaga Gabriel A. , Zawodzinski Thomas A.
Published: February 2020

In this study, the adsorption properties of water-dissolved 3M 825 equivalent-weight (EW) ionomer and carbon (C) supports or carbon-supported platinum (Pt/C) catalysts were studied with 400 MHz 19F Nuclear Magnetic Resonance Spectroscopy (NMR). The supports and catalyst materials (with and without ionomer addition) were also analyzed with Brunauer-Emmet-Teller (BET) nitrogen adsorption-desorption, transmission electron microscopy (TEM) and X-ray diffraction (XRD).

3M ionomer/carbon/Pt interactions were also explored through differential scanning calorimetry (DSC). Using these methods, a series of samples with and without ionomer addition were analyzed to explore the different interactions between components (Pt/Carbon, and Carbon/ionomer).

Preliminary DSC results are shown in Figure 1 for the 3M ionomer, ionomer/Pt, ionomer/Vulcan-carbon and the catalyst layer (CL) samples, where the CL is composed of ionomer/Vulcan-carbon/Pt. The 3M ionomer and ionomer/Vulcan-carbon samples, on the other hand, exhibit a weak and broad endothermic peak between 50 and 120°C. This process has been associated with the combination of structural changes in ionic cluster, and water volatilization in PFSA ionomers.1Both experiments with Pt present showed an exothermic feature around 95°C and 135°C for the ionomer/Pt and the CL samples, respectively.

The adsorption behavior of 3M ionomer on the carbon and catalyst samples was explored using 19F NMR. Figure 2 shows an NMR spectrum of the 3M PFSA ionomer in water solution after base correction. This figure also includes the chemical shifts and peak assignments. The strongest peak at -76.55 ppm corresponds to the internal reference (trifluoro acetic acid, CF3COOH) in solution. The ratio of the most prominent 3M ionomer peak (-124.13 ppm) associated with the CF2 group in the backbone and the internal reference peak was used for the analytical study, a similar approach to previous studies of Nafion.2–4

Figure 1