bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma Oxidation of Liquid Precursors
Authors: Sunkara Mahendra Kumar , Ajayi Babajide , Jaramillo-Cabanzo Daniel Felipe
Published: February 2020

Several grand challenges in energy storage and conversion involve the discovery functional materials which many agree will be multi-element solid solution of metal oxides. The conventional wet chemical methods for synthesis of multi-metal oxide often require time-consuming high pressure and temperature processes, and so the challenge is to develop rapid and scalable techniques with precise compositional control.

This presentation will discuss the concept of plasma oxidation of liquid precursors for making mixed metal oxides with compositional control and rapid time scales. The concept is demonstrated with binary, ternary and quaternary metal oxide with control over entire composition range using metal precursor solutions.1 For the ternary system, the results show the selective formation of metastable spinel solid solution phases with compositions over the entire range by tuning the metal precursor composition.

The concept of plasma oxidation of liquid precursors is investigated to produce a number of materials systems for electrocatalysts, lithium ion batteries and heterogeneous catalysts. For example, in terms of oxygen evolution reaction, ternary alloys involving manganese doped nickel ferrite nanoparticles, NiMnzFe2-zO4 (01), exhibited considerable electrocatalytic activity achieving an overpotential of 0.39V at a benchmarking current density of 10 mAcm-2 for low manganese content at z = 0.2.1 Lithiated NMC compounds exhibit about 220 mAh/g capacity after 50 cycles.

Acknowledgements

 The authors acknowledge support from NSF EPSCoR (1355438) and access to facilities at the Conn Center for Renewable Energy Research.

Reference

B.P. Ajayi, S. Kumari, D. Jaramillo-Cabanzo, J. Spurgeon, J. Jasinski and M.K. Sunkara, “A rapid and scalable method for making mixed metal oxide alloys for enabling accelerated materials discovery”, J. of Materials Research, DOI: http://dx.doi.org/10.1557/jmr.2016.9231 (11), 1596-1607(2016)
(Invited) Nanotip-Defined High Local Electric Fields Accelerate CO2 Reduction Heterogeneous Catalysts
Authors: Liu Min , Sargent Edward H.
Published: February 2020

The electrochemical reduction of carbon dioxide (CO2) provides a promising path towards the storage of renewable energy and to the sustainable synthesis of carbon-based chemical feedstocks. A key challenge for such a process is the low activity and selectivity of the CO2 reduction reaction (CO2RR). It is intensely desired to reduce CO2 at low overpotentials, generating desired products at high current densities over extended periods, and reacting selectively without the formation of undesired byproducts. However, CO2RR today is hindered by the low local concentration of CO2 in aqueous electrolytes, in which more kinetically favorable reduction of protons to H2 often outcompetes CO2RR, eroding reaction selectivity. We developed a field-induced reagent concentration (FIRC) method to enhance the CO2RR process. Through shaping electrodes into arrays of nanoneedles, we generated a high local electric field even when using low applied overpotentials. The high field concentrates electrolyte cations, and the cations bring with these a high local concentration of CO2 to the active CO2RR surface. Simulations revealed that 10-fold higher electric fields can be achieved on nanometrically sharp tips compared to that of quasi-planar regions. Utilizing bottom-up synthesized gold nanoneedle electrodes, record-low onset potential and record-high geometric current density at the low potential of −0.35 V with nearly quantitative (>95%) Faradaic efficiency (FE) for CO2 reduction to CO conversion were achieved (1). This current density surpasses by an order of magnitude the performance of the best previously-reporeted gold nanorods, nanoparticles, and oxide-derived noble metal catalysts. The nanoneedle electrodes exhibited robust continuous reactions over 8 hours in an inorganic aqueous electrolyte. The FIRC concept has also be leveraged to build other metal nanoneedles and metal or metal sulfide covered gold nanoneedles. These electrodes exhibit much enhanced CO2to hydrocarbon conversion efficiencies, proving the wider application of the FIRC concept.

References:

(1) M. Liu, Y. Pang, B. Zhang, P. D. Luna, O. Voznyy, J. Xu, X. Zheng, C. T. Dinh, F. Fan, C. Cao, F. P. Arquer, T. S. Safaei, A. Mepham, A. Klinkova, E. Kumacheva, T. Filleter, D. Sinton, S. O. Kelley, E. H. Sargent, Nature, 2016, 537, 382.
Understanding of Transition from Gas-Phase to Material-Kinetic Limitations for Nonstoichiometric Oxides
Authors: Ji Ho-Il , Davenport Tim , Haile Sossina M
Published: February 2020

Oxygen nonstoichiometric oxides are important materials in technologies such as fuel cells, permeation membranes, and solar-driven thermochemical fuel production owing to their reversible redox characteristics. The material kinetic properties of the oxides, the surface reaction rate constant at the solid/gas interface and the chemical diffusion in the bulk, have been widely investigated for the understanding of chemical redox kinetics. However, under certain conditions, insufficient oxidant/reductant supply hinders the overall redox kinetics in which the oxides accompany relatively large nonstoichiometry (δ) deviations during the reaction. Furthermore, since the oxides are usually structured as mesoporous or microporous forms to enhance the effective surface reaction rate and thereby enhance kinetics, understanding the correlation among the material kinetic properties, the morphology of the oxides, and the oxidant/reductant gas supply is essential for establishing the strategy for maximizing global reaction rates.

 We will present the effects of morphology, temperature and gas flow rate on the global redox kinetics of porous undoped ceria (CeO2-δ) as a model system. Using the reticulated porous ceramic (RPC) approach, and the morphology of the samples was controlled by modifying the starting ceria slurry with/without pore-formers. Kinetic behavior was examined as a function of temperature and gas flow rate by the electrical conductance relaxation technique, which is attractive due to its ease for extracting the kinetic parameters. The validity of the electrical conductance relaxation technique for assessing the kinetic behavior of the porous oxides in the limits of the gas-phase supply and the surface reaction of material will be discussed, and the theoretically anticipated transition behavior from the gas-phase to the material kinetic limits will be shown in comparison to the experimental result.
A Reduced-Order Battery Degradation Model for Battery Management Systems
Authors: Li Jie , Lotfi Nima , Landers Robert G , Park Jonghyun
Published: February 2020

An accurate and prompt prediction of the State of Health (SOH) of lithium ion batteries is a critical process for a Battery Management System (BMS). In this work, a single particle-based degradation model is developed by focusing on Solid Electrolyte Interface (SEI) layer formation and its evolution, which is coupled with the crack propagation due to the developed stress inside particles. The lithium ion loss estimated from the SEI layer evolution is incorporated with an advanced single particle model, where the electrolyte physics is included, for prompt calculation that is critical for online estimation. This model well predicts the measured capacity fade and voltage change as a function of cycle number and temperature. The lithium ion loss due to SEI layer formation, resistance rise, and operating voltage window are examined to explain the capacity fade. Besides its lower-order implementation in a single particle, the results provide quantitative information about the role of SEI layer growth and crack propagation, and corresponding capacity fade and power loss, which are critical for SOH and BMS.
Mechanistic Studies of Hydrogen Evolution during Electroless Nickel-Phosphorus Deposition
Authors: Liu Xinyu , Akolkar Rohan
Published: February 2020

In the present talk, mechanistic aspects of the electroless nickel-phosphorus (Ni-P) deposition process using sodium hypophosphite as reducing agent will be discussed. We will focus primarily on the mechanism of hydrogen evolution during electroless Ni-P deposition. The role of pH and reducing agent concentration on the kinetics of hydrogen evolution will be discussed. A combination of volumetric analysis of the hydrogen evolved, titration analysis of the hypophosphite consumed and compositional gas analysis when using D2O and H2O as solvents shows that hydrogen evolution proceeds primarily via hydrolysis of the reducing agent rather than electrolysis of water. Mechanistic aspects of the reductant hydrolysis reaction will be investigated using a rotating disc electrode to unravel the role of surface kinetics and mass transport on the hydrogen generation process. Findings will be incorporated into a simple mathematical process model. Implications of the present study to improved process design for electroless deposition of amorphous alloys will be discussed.
Integration of Upscaled Microbial Fuel Cells in Real Municipal Sewage Plants
Authors: Muddemann Thorben , Jiang Bolong , Kunz Ulrich , Bormann Hinnerk , Haupt Dennis René , Niedermeiser Michael , Schlaefer Ottmar , Sievers Michael
Published: February 2020

In search for appropriate processes to enhance the efficiency of municipal sewage plants, microbial fuel cells (MFC) have moved into research focus. Due to the MFC characteristic, which is able to treat wastewater while generating power simultaneously, it is also a promising approach to change the energy balance of sewage plants – switching from the biggest municipal energy consumer to an energy producer.

Owing to the small power density of MFCs in comparison to chemical fuel cells, large active surface areas and therefore low-cost cell constructions, electrodes and catalysts are necessary.

Challenges in MFC upscaling have been overcome and a functional and less price intensive cell design for integration in existing aeration tanks of municipal wastewater treatment plants has been developed (figure left). The new cell design integrates a double-sided graphite/polymer composite anode between two cathodes, to enlarge the surface area. It allows online half-cell potential measurement and biofilm flushing by nitrogen (figure right), among other options. High performance catalytic active cathodes are used, which are produced in-house by a semi-automatic production line.

A fuel cell stack of up to fifty MFCs, each with an active area of 6000 square centimeters respectively, has successfully started operation with real municipal wastewater at the wastewater treatment plant in Goslar, Germany.

In addition to the technical cell design, the wastewater parameters strongly affect the electrochemical performance of microbial fuel cells. Therefore the influences of process parameters (temperature, pH, O2, TOC etc.) were measured to determine optimized operating points when fed by real wastewater.

Additionally cathodic catalysts influence the MFC performance considerably, so the electrode-performance of the scaled up microbial fuel cells were investigated by half-cell measurements.

Figure 1
Quantitative Microstructure Characterization of a NMC Electrode
Authors: Usseglio-Viretta François Laurent Emilien , Smith Kandler
Published: February 2020

Performance of lithium-ion batteries (LIBs) is strongly influenced by the porous microstructure of their electrodes. In this work, the microstructure of a non-calendared LiNi1/3Mn1/3Co1/3O2 (NMC) electrode has been investigated in order to extract relevant properties useful for battery modeling. At first, the image level of detail has been evaluated (using original criteria based upon edge detection) to assess the overall data quality available for the study. Then, transport properties (volume fraction, connectivity, particle size and tortuosity) and electrochemical property (specific surface area) have been calculated for the pore and the active material. Figure 1 shows concentration field calculated within the pore (used to determine the effective diffusion coefficient) and the active material particle size.

Special attention has been paid to determine (i) the size of the so-called representative volume element (RVE) required to be statistically representative of the heterogeneous medium and (ii) the voxel size dependence for each properties. Both analyses are essential since they allow checking the relevance of the calculated values, before actually using them in macroscopic models. It has been found that the investigated properties exhibit different RVE sizes and image resolution dependences. Several properties have been calculated using a panel of different numerical methods in order to compare their results. Indeed, some of these methods rely on different assumptions and exhibit intrinsic bias, leading as a consequence to different outcomes as established in this work.

Properties have been calculated on the whole domain and have been then plotted along the electrode thickness to evaluate their overall heterogeneity and assess the presence of edge effects, if any. It is then possible to introduce subsequently these spatially-dependent properties into 1D macroscopic battery model in order to take into consideration the heterogeneity, between each slice, of the electrode material while retaining the advantage of an inexpensive CPU time macroscopic model. This approach is particularly relevant for graded electrode materials that exhibit microstructure gradients. Edge effects, as well as property gradients, are shown for the investigated electrode material.

An additional microstructure analysis has been performed on a calendared NMC electrode. Indeed, in industrial LIB electrode manufacturing, the cast electrode undergoes a compression step (calendaring) in order to improve particle connectivity and reduce the electrode’s porosity which increases battery capacity. The effect of this compression step on the material properties have been quantified in this work and significant microstructure properties change are shown.

Figure 1
The Limitations of the Application of Darcy Law in Serpentine Flow Field
Authors: Zhang Xuyang , Liu Hongtan
Published: February 2020

One of most common flow fields used in proton exchange membrane (PEM) fuel cells is the serpentine flow field. Diffusion (which is caused by concentration gradient) and convection (which is caused by pressure gradient) are two major transport mechanisms in the serpentine flow field. In the serpentine flow field, there is a pressure difference between two adjacent channels that leads to an under-land cross-flow through the porous media of the gas diffusion layer (GDL) from the higher pressure channel to the lower pressure channel. High under-land cross-flow rate leads to a high oxygen concentration under the land area and a high water removal capability, but it causes a high pressure drop at the same time. Most researchers use Darcy law in their modeling to predict the under-land cross-flow rate, and the inertial effect is neglected. At low velocity, the inertial force can be neglected, so the relation between pressure gradient and velocity inside the GDL is linear. However, the inertial force becomes important at high velocity, and the relation between pressure drop and velocity inside the GDL is no longer linear, so Darcy law is not applicable. Thereby, the modified Darcy Law which includes the inertial effect is developed. Non-Darcy effect is defined as the ratio of the inertial effect to the sum of the inertial effect and the viscous effect, and it is used as a benchmark for accounting the importance of the inertial effect. In this study, our numerical modeling applied Darcy law and modified Darcy law in the single serpentine flow field, respectively. When non-Darcy effect is no less than 5%, Darcy law over-predicts the cross-flow rate by more than 10% compared to the modified Darcy law. Criterions of the application range of Darcy law in the single serpentine flow field are found with the dimensional analysis as well. From the experimental results, Darcy law significantly under-estimates the pressure drop in the single serpentine flow field, which has narrow land, high permeability and high inertial coefficient.
Structural and Electrochemical Characterization of Activated Carbon for Supercapacitors
Authors: Köse Kadir Özgün , Aydinol Mehmet Kadri
Published: February 2020

Electrochemical double layer capacitors (EDLC) are energy storage devices that utilize ion adsorption at the double layer. Their typical electrodes are porous, conductive materials, such as activated carbon. In the present study, activated carbon is derived from pine cone (pinus pinea). The activation process is carried out with the aid of ZnCl2 activating agent. High temperature vacuum treatment is conducted to increase the conductivity of activated carbon. The effects of impregnation ratio (mass of activating agents/mass of precursor), on the resulting porosity, pore size distribution and texture of the activated carbon are examined. Surface area and pore volume are measured by N2 adsorption at 77 K. Raman spectroscopy is used for characterizing the order of the resulting carbon. To achieve high energy density, organic electrolyte (acetonitrile) is used with TEABF4 dissolved in it. Galvanostatic charge-discharge, cyclic voltammetry and electrochemical impedance spectroscopy are applied to assess electrochemical behavior. The effect of porous structure and conductivity on the energy and power characteristics of the EDLC is determined and by manipulating the activation process of AC, the properties of EDLC are optimized.
Hybrid Vehicle Battery Pack Useful Life Simulation
Authors: Duan Xiaohong Nina
Published: February 2020

This paper describes the development of a computational model of a traction battery system for hybrid vehicle application. The battery model simulates the electrical and thermal performance of the entire battery system, including series and/or parallel cell design configuration in the pack, cell energy/power performance, thermal and electrical controls, and interfaces to the vehicle and external environment. The battery model is capable of estimating the battery performance and predicting the battery life under a variety of use cases in different environmental conditions. The model enables rapid optimization of battery pack size, electrical and thermal controls design to maximize battery usage and/or minimize battery cooling needs while still meeting the battery’s life targets. A systematic approach has been developed in which this vehicle-level information is quantified and ranked to be able to identify and simulate the battery usage for varieties of customer. Simulation results are verified with variety of laboratory and vehicle test data. The availability of this battery pack model enables minimizing of costly and time-consuming pack-level performance and life testing, allowing the majority of the life cycle analyses to be conducted before battery packs and vehicles are actually assembled. The model aims to ensure that when the battery pack model is utilized for life simulations, compliance with the battery pack warranty and fuel economy targets, as well as other vehicle standards, may be quickly and reliably assessed. The accuracy of the model predicted battery life performances is further validated with real field application vehicle data from customer return pack.
Computational Design and Sensitivity Analysis of Non-Aqueous Lithium O2 Batteries
Authors: Raoufi Arman , Torayev Amangeldi , Thangavel Vigneshwaran , Franco Alejandro A.
Published: February 2020

In this study, a gradient-based optimization algorithm is used for the computational design and optimization of a non-aqueous lithium-O2 battery. The sensitivity analysis and numerical optimization capabilities are appended to the multiscale framework previously developed at LRCS for the discharge behavior of this type of batteries. The transport of oxygen in the porous cathode is modeled using Fick’s law at the continuum scale, by assuming isothermal conditions. A micro-scale model predicting the discharge product morphology is coupled to the continuum one. The final discharge product is assumed to form, through both the surface limited thin film growth mechanism and the solution phase reaction mechanism. The cathode microstructure in the model is based on experimentally measured PSD (pore size distribution). A detailed reaction mechanism considering the microstructural properties of the cathode, the surface limited reaction, surface thin film growth and solution phase reaction is used. The sensitivity analysis for the Lithium-O2 cell is performed using the finite difference approach. Sensitivity derivatives are used to identify the variables that have the most significant impact on design performance of the battery. This information is helpful prior to an optimization study as it can be used to remove design parameters that do not strongly influence. Design variables investigated are the O2diffusion coefficient, the cathode porosity, temperature, separator porosity and the cathode thickness. The cell performance is optimized and improved using a quasi-Newton algorithm. In the quasi-Newton algorithm, sensitivity derivatives are utilized in determining a search direction that maximizes a cost function representing the cell capacity. This work provides a comprehensive receipt on the implementation of efficient algorithms devoted to the predictions of optimized cell designs. Design guidelines arising from the computational results are discussed from an engineering perspective.

References:

[1] Kan-Hao Xue, Trong-Khoa Nguyen, and Alejandro A. Franco, “Impact of the Cathode Microstructure on the Discharge Performance of Lithium Air Batteries: A Multiscale Model”, J. Electrochem. Soc. 2014 volume 161, issue 8, E3028-E3035.

[2] Kan-Hao Xue, Euan McTurk, Lee Johnson, Peter G. Bruce, and Alejandro A. Franco, “A Comprehensive Model for Non-Aqueous Lithium Air Batteries Involving Different Reaction Mechanisms”, J. Electrochem. Soc. 2015 volume 162, issue 4, A614-A621.
A Multi-Physics Model of Low-Voltage Dual-Electrolyte Water Electrolyzers
Authors: Mora Joy Marie , Cervera Rinlee Butch , Ocon Joey Duran , Matuba Jan Samuel C.
Published: February 2020

Traditional water electrolyzers usually require large overvoltages for splitting water into hydrogen and oxygen due to ohmic resistances, electrode overpotentials, and thermodynamic requirements. One of the most promising concepts in electrolyzer design is the hybrid dual-electrolyte water electrolyzer. This type of system takes advantage of the pH gradient between electrodes whereby a theoretical potential of around 0.4 V vs. SHE is possible. While the traditional electrolyzer operates at 1.23 V, the hybrid electrolyzer operates at voltages as low as 0.8 V, as shown in a recent work by Chen et al. In order to fully understand the mechanisms of this type of system, it is important to perform a multi-physics model that would predict the behavior of a hybrid dual-electrolyte water system across a specified set of parameters. The modelling approach done in this study allows describing a range of dual-electrolyte water systems. The study takes into account the dependence of the electrical performance on structural parameters and operating conditions of the electrolyzer. The developed multi-physics model was solved using COMSOL MultiphysicsⓇ simulation software. The simulation tool was also used to compare the performance of a single- (both acidic and alkaline) and dual-electrolyte system. The analysis of the results showed dual-electrolyte systems having superior performance over their traditional counterparts and that improved electrolyzer operating strategies can be identified with the developed simulation study.
(Invited) Chemically Modified Semiconductor Photoelectrodes
Authors: Maldonado Stephen
Published: February 2020

This presentation will describe our cumulative advancements in the design of semiconductor/electrolyte interfaces. The emphases will be on the chemical functionalization of Groups IV (Si) and III-V (GaP, GaAs) semiconductors and their support of heterogeneous charge transfer processes when in contact with liquid electrolytes. Additionally, new advancements on the measurement of charge-transfer rate constants using ultramicroelectrodes will be presented.
Electrochemical Deposition of Tin Selenide (SnSex) Thin Films
Authors: Howell Pauline , Stickney John Lewellen
Published: February 2020

Tin selenide belongs to group IV-VI chalcogenide. Its electrical, optical, and structural properties are attractive for having both direct and indirect bandgaps, and its potential for being a 2D material. Tin selenide is also a component of Cu2ZnSn(S,Se)4 and can be combined with other binary compounds to form absorber materials for photovoltaic applications 1. In this study, tin selenide thin films (SnSex) were grown on gold substrates using electrochemical atomic layer deposition (E-ALD) 2. E-ALD works by depositing one component followed by the other, keeping the condition simple at room temperature using a three electrode flow cell. A monolayer (ML) of the compound completes one cycle. This type of deposition process adds control to the compound growth by limiting the amount of deposit to less than a ML per cycle. Potentials for deposition were selected based off of cyclic voltammetry of Sn and Se. The Sn deposition potential was varied to see the effect on the thin films. Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), and x-ray diffraction (XRD) were used to characterize the composition and structure of the deposits. Results from XRD and Raman suggest that the tin selenide films contain both SnSe and SnSe2. Particle shapes of the deposit vary as a function of Sn deposition potential. Changing the deposition potential of Sn also alters the ratios of Sn and Se. Future studies will include quantification of the SnSe and SnSe2 present, as well as optimization of the homogeneity thin films.

References

1. Czerniawski, J. M.; Perdue, B. R.; Stickney, J. L., Potential Pulse Atomic Layer Deposition of Cu2Se. Chem Mater
2016,
28 (2), 583-591.

2. Stickney, J. L.; Villegas, I.; Suggs, D. W.; Gregory, B. W., Electrochemical Atomic Layer Epitaxy (ECALE). Abstr Pap Am Chem S
1991,
201, 289-Coll.
The Role of Surface States in the Electrochemical Behavior of Semiconductor-Electrolyte Interfaces from First Principles
Authors: Campbell Quinn , Dabo Ismaila
Published: February 2020

Solar energy is the most abundant energy source available to humankind; however, this energy cannot be harnessed on demand due to the variability of sunlight. Artificial photosynthesis offers a sustainable way to overcome that variability through the photocatalytic conversion of solar power into chemical fuels at a semiconductor–electrolyte interface. Although considerable progress has been made in simulating the bulk properties of semiconductors from first principles, much less has been done to address the electrochemical response of electrified semiconductor–electrolyte interfaces under realistic environmental conditions. In particular, band bending and surface states are two important contributors to the photogeneration of electrical current at semiconductor–electrolyte interface. We present a broadly applicable and highly transferable computational techniques to simulate semiconductor–electrolyte interfaces. By introducing a continuum model of the semiconductor and electrolyte regions surrounding the quantum-mechanical interfacial layer, the model enables for the self-consistent determination of the surface states and of the Schottky barriers that subsequently form within the space charge of the semiconductor electrodes. Validation of these simulations is provided by the analysis of experimental charge-voltage measurements, focusing on the photovoltage region close to the onset of the photocurrent, which depends strongly on the properties of surface states. Our model provides a detailed understanding of the electrochemical stability and intrinsic current–voltage response of semiconductor electrodes taking into account the surface states that arise from the adsorption of oxygen and hydrogen species towards optimizing photocatalytic performance.
(Invited) Photoelectrocatalysis: Solar-Assisted Hydrogen Production in Microgravity Environments
Authors: Brinkert Katharina , Richter Matthias Hermann , Liedtke Janine , Mitrovic Slobodan , Akay Ömer , Giersig Michael , Matsushima Hisayoshi , Fukunaka Yasuhiro , Lewerenz Hans Joachim
Published: February 2020

Artificial photosynthesis systems, which follow the concept of the Z-scheme of natural photosynthesis, are presently being realized as catalyst-functionalized photovoltaic tandem devices for the photoelectrochemical oxidation of water and the simultaneous generation of hydrogen as a so-called “solar fuel”. The successful implementation of an efficient photoelectrochemical (PEC) water splitting cell is not only a highly desirable approach to solving the energy challenge on earth: an effective air revitalization system generating a constant flux of O2 while simultaneously recycling CO2 and providing a sustainable fuel supply is also essential for the International Space Station and long-term space missions, where a regular resupply from earth is not possible.

Here, we present the photoelectrochemical production of hydrogen in microgravity environments on p-type indium phosphide electrodes with deposited rhodium electrocatalysts. Our findings indicate that microgravity has a significant impact on the gas bubble evolution behaviour and the mass transfer rate of the evolved hydrogen gas on the electrode surface. Furthermore, microgravity influences the current-voltage characteristics and the overall solar-to-hydrogen efficiency of the catalyst functionalized semiconductor-based half-cell. Further experiments with nanostructured rhodium catalysts fabricated by shadow nanosphere lithography on the InP surface suggest that the structure of the electrode surface plays a significant role for the gas bubble evolution behaviour and for the further the development of efficient prototypes for solar-assisted water splitting and hydrogen production that operate in micro- and hypergravity environments.
Electrodeposition of Germanene from Aqueous Solution, pH 9.0
Authors: Bui Nhi , Ledina Maria , Jung Jin , Reber Theodore James , Stickney John Lewellen
Published: February 2020

The group IV elements including C, Si, Ge and Sn have all shown to form 2D allotropes that have drastically different properties from their bulk component. Following the discovery of graphene and silicene, the study of germanene has garnered increasing interest and has raised many questions pertaining to its exact structure, properties and formation. A number of theoretical calculations have proposed structures for germanene with varying bond distances and degree of buckling. Some experimental works suggest that germanene could be deposited via molecular beam epitaxy (MBE) using germanium wafer as source. This study proposes an alternative route of forming germanene via electrodeposition 1. Electrochemical scanning tunneling microscopy (EC-STM), and in situ surface-enhanced micro Raman (SERS) are used as means to gather information on the deposition process of Ge on Au(111). The optimal condition to grow a single atomic layer of Ge was selected based on atomic resolution images from EC-STM. Various phases of Ge were observed, detailing the transition from a precursor stage to complete honeycomb rings of germanene. The nucleation process started with growth of some small Ge domains, followed by a lateral expansion through the edges. After forming the second layer, the surface became passivated as expected for an insulating gap of a 2D bulk material. Current efforts are being directed toward forming a thicker germanene film using our previously developed methodology called Ge-Te bait-and-switch electrochemical ALD cycle 2-4. The approach involves using Te as a capping layer and as a basal support to allow Ge to form new layer.

This work is supported by the National Science Foundation.

References

1. Ledina, M. A., Liang, X., G. Kim, Y., Jung, J., Perdue, B., Tsang, C., Soriaga, M.P., Stickney, J. L., Investigations into the Formation of Germanene using Electrochemical Atomic Layer Deposition (E-ALD). ECS Transaction
2015,
66(6), 129-140.

2. Liang, X. H.; Jayaraju, N.; Thambidurai, C.; Zhang, Q. H.; Stickney, J. L., Controlled Electrochemical Formation of GexSbyTez using Atomic Layer Deposition (ALD). Chem Mater
2011,
23(7), 1742-1752.

3. Liang, X. H.; Kim, Y. G.; Gebergziabiher, D. K.; Stickney, J. L., Aqueous Electrodeposition of Ge Monolayers. Langmuir
2010,
26(4), 2877-2884.

4. Liang, X. H.; Zhang, Q. H.; Lay, M. D.; Stickney, J. L., Growth of Ge Nanofilms Using Electrochemical Atomic Layer Deposition, with a "Bait and Switch" Surface-Limited Reaction. J Am Chem Soc
2011,
133 (21), 8199-8204.
Simulation of the Interfaces of Anatase TiO2 (001), (100), (101) with KOH Solution By Molecular Dynamics
Authors: Sang LiXia , Lei Lei
Published: February 2020

Hydrogen can be produced by the photoelectrochemical water splitting system with KOH solution as electrolyte and TiO2 as photoanode. In this work, the interaction between anatase TiO2 (001), (100), (101) surfaces and KOH solution is studied by molecular dynamics simulations at room temperature. The dynamic interfacial structures and properties of K+ on anatase TiO2 surfaces are obtained by analyzing the radial distribution function, the diffusion coefficient, the surface charge distribution, electric field and electrostatic potential distribution. The results have revealed that the coordination number of K+ is reduced because it adsorbed on the anatase TiO2 surface, resulting in the weakening of hydration. And there are three kinds of K+ adsorption sites on (001) and (101) surfaces and two adsorption sites on (100) surface. To obtain more information about the effect of KOH on the interface, the electrostatic properties of KOH solution and aqueous solution were qualitatively compared and analyzed. The maxima of the charge density and electric field profiles are increased in KOH solution but remains more or less at the same position as for the aqueous solution. There is a significant difference in electrostatic potential comparison. While the electrostatic potential of aqueous solution are smooth and well converged, that of KOH solution are rather noisy. This can be explained by the asymmetrical distribution of K+ and OH-. Therefore, the KOH solvent contributes substantially to the electrostatic behavior of the liquid near the interface. Based on Grahame double layer model, the zeta potential of the three surfaces (001), (100), (101) in inner Helmholtz layer is observed as 6.42V, 4.76V and 5.18V, respectively, corresponding to the width of Stern layer 3.99Å, 4.40 Å, 3.72 Å. The thickness is in full agreement with already mentioned compact layer (3.4 Å). We also approximately estimate that the surface depletion layer width of anatase (001), (100), (101) is about 7.16Å, 10.23Å and 8.23Å, respectively. All above results clearly illustrate the enormous improvement in our quantitative understanding of the molecular-scale structure and diffusional dynamics of K+ at semiconductor-electrolyte interfaces, as compared with continuum-based Grahame model of the electrical double layer. And the differences between aqueous solution and KOH solution qualitatively explain the effect of KOH solution on the electrolyte, which can increase the conductivity of the solution and provide a chemical reaction bias. Investigations of the double layer structure, which are presently under way in our group, are expected to provide further insight into semiconductor/electrolyte interface.

Figure 1
The Effect of Defects on Time Dependent Dielectric Breakdown Acceleration in TiN/ZrO2/Al2O3/p-Ge Gate Stacks
Authors: Ding Yiming , Misra Durgamadhab , Tapily Kandabara , Clark Robert D. , Consiglio Steven , Wajda Cory S. , Leusink Gert J.
Published: February 2020

Introduction of a thin GeO2 as the interfacial layer (IL) seems to be beneficial for formation of high-k gate stacks on germanium substrate. The thickness of GeO2/GeOx impacts the overall equivalent oxide thickness (EOT) because of its low dielectric constant compared to high-k layer. Current trends indicate that the formation of appropriate thickness of GeOx or GeO2 between high-k and Ge substrate seems to have low interface state density (D
it). Since ZrO2 showed lower leakage current than HfO2 with similar dielectric high-k stack, ZrO2/Al2O3 bilayer as gate dielectric is becoming popular. Even though excellent gate stacks on germanium substrate has been demonstrated the reliability and the impact of interfacial layer is still unknown.

This work investigates the p-Ge/Al2O3/ZrO2/TiN gate stacks with thin GeO2 or GeOx layer, formed when the gate stack was exposed to pre- or post-deposition slot plane antenna plasma oxidation (SPAO). The post Al2O3/ZrO2 deposition SPAO forms relatively thicker GeO2 and post Al2O3 deposition SPAO forms thinner GeO2 whereas pre-deposition SPAO forms thin fragmented GeOx layer at the interface. We have observed that the relatively thicker GeO2 interfacial layer formed after the post Al2O3/ZrO2 deposition SPAO degraded faster during time dependent dielectric breakdown (TDDB) measurements on substrate injection mode compared to the thin GeO2 or GeOx interfacial layers (Fig. 1). The improvement in TDDB degradation for thinner interfacial layer thickness suggests that electrons tunnel through the thinner GeOx IL, and TDDB measured the quality of Al2O3 rather than IL.

The TDDB characteristics in gate injection mode suggests that the SPAO can significantly affect the TDDB characteristics GEI mode (Fig. 1). The SPAO treatment effectively removes the trap centers in ZrO2 and Al2O3 layers when SPAO was performed after the gate stack deposition. By employing carrier transport mechanisms as a function of temperature in both gate and substrate injection mode we were able to identify the traps that contributes to the TDDB degradation. The trap center (f
t1 = 0.13 eV) observed in the ZrO2 when ZrO2 is not subjected to the SPAO, i.e. pre-deposition SPAO. This trap f
t1 (0.13 eV) was eliminated for post Al2O3/ZrO2 deposition SPAO. While defects in the ZrO2 layer determines the TDDB characteristics in gate injection mode the GeO2 or GeOx interfacial layer thickness determines the TDDB degradation in substrate injection mode.

Figure 1
Multi-Wavelength Raman Characterization of Epitaxial Silicon Wafers for In-Line Process Characterization and Monitoring Applications
Authors: Yoo Woo Sik , Ishigaki Toshikazu , Kang Kitaek
Published: February 2020

Epitaxial Si wafers are widely used for high performance advanced memory devices and CMOS image sensor (CIS) device manufacturing. Surface morphology observation and resistivity measurements are frequently done as quick in-line quality monitoring of epitaxial Si layers. High resolution X-ray diffraction (HRXRD) and etch pit characterizations are done for randomly selected wafers. However, these conventional characterization techniques are not sensitive enough to detect small quality variations in epitaxial Si wafers.

For Si wafers with multiple epitaxial layers and different dopant concentrations, the conventional characterization techniques are even less useful. Introduction of new epitaxial characterization techniques is strongly desired for effective in-line process monitoring. A non-contact, in-line characterization technique, with virtual depth profiling capability, would be beneficial for proper characterization of Si wafers with multiple epitaxial layers.

In this study, we have characterized 200 mm and 300 mm Si wafers with triple epitaxial layers using multiwavelength, high resolution Raman spectroscopy. Ninety three (93)-point wafer mapping measurements were performed on all wafers, Statistics of Raman signal intensity, shift and full-width-at-half-maximum (FWHM) values, under different excitation wavelengths, were extracted and compared with two types of reference Si wafers (prime Si wafers and reclaimed Si wafers). Significant variations in Raman signal intensity, shift and FWHM were measured between reference wafers and epitaxial wafers, indicating potential Si lattice stress and crystallinity. Excitation wavelength dependence of Raman signal intensity, shift and FWHM also indicated variations in Si lattice stress and crystallinity of epitaxial layers in the depth direction. Non-contact multiwavelength Raman measurements are very sensitive to the quality of epitaxial Si layers and are effective as a complimentary in-line process characterization and monitoring technique.

Figure 1
(Invited) Wide Bandgap Analog and Mixed-Signal IC Design for Advanced Power Electronics
Authors: Mantooth H. Alan
Published: February 2020

Economy and performance are benefits that come with high power density power electronics, just as in the case of VLSI electronics. High density power electronics require the heterogeneous integration of disparate technologies including power semiconductor devices, driver, protection and control circuitry, passives and voltage isolation techniques into single modules. Such integration activity was central to the Google Little Box Challenge competition conducted last year. One of the keys to advancing power electronic integration has been the commercial reality of wide bandgap power semiconductor devices made from silicon carbide and gallium nitride. The ability to design and manufacture wide bandgap integrated circuits as drivers, controllers, and protection circuitry allows them to be packaged in close proximity to the power device die to minimize parasitics that would adversely impact system performance. These impacts include excessive ringing, noise generation, power loss, and, potentially, self-destruction. The state of the art in wide bandgap analog and mixed-signal IC design will be described including example circuits such as amplifiers, data converters, controllers, and protection circuits and their integration into power electronic platforms. A synthesis tool under development for heterogeneous power circuit layout will be briefly described as a capstone to the application space descriptions. Advances in semiconductor device modeling of low-voltage SiC MOSFETs will be described as well.
(Invited) Effect of Temperature and 5 Mev Proton Irradiation Damage on Performance of b-Ga2O3 Photodetectors
Authors: Ren Fan , Pearton Stephen J. , Ahn Shihyun , Kim JiHyun , Jung Younghun , Oh Sooyeoun , Mastro Michael A , Hite Jennifer K , Eddy Charles R.
Published: February 2020

Effect of temperature and MeV protons at doses from 1013 -1015 cm-2 on photo-response to 254 nm wavelength, and blindness to 365 nm light, of planar photodetectors fabricated on β-Ga2O3 films grown on Al2O3 by metalorganic chemical vapor deposition. Ohmic contacts were formed by Si-implantation and annealing at 900ºC, followed by deposition of Ti/Au metallization. The photocurrent induced by 254 nm illumination increased monotonically with temperature, from ~2.5 x10-7 A at 25 ºC to ~2.2 x10-6 A at 350 ºC at a fixed 254 nm light intensity of 760 µW/cm2. The temperature dependent photo-to-dark current ratio (PDCR) for this wavelength was 328 at room temperature and decreased to ~9 at 350ºC. The responsivity increased from 5 to 36 A/W over this temperature range, with corresponding external quantum efficiencies of 2.5 x103 % at 25ºC and 1.75 x104 % at 350ºC. Similarly large numbers reported for Ga2O3 photodetectors have previously been ascribed to carrier multiplication effects.

For the effect of 5 MeV protons irradiations, the photocurrent increased with dose due to the introduction of damage from non-ionizing energy loss by the protons. The total calculated vacancy concentration increased from 5x1015-5x1017 cm-3 over the dose range investigated. The dark current increased in proportion with the implant dose, leading to a decrease in the ratio of photocurrent to dark current. The photocurrent induced by 254 nm illumination increased with dose, from ~0.3 x10-7 A at 25 ºC for a dose of 1013 cm-2 to ~10-6 A at a dose of 1015 cm-2 at a fixed light intensity of 760 µW/cm2. The photo-to-dark current ratio decreased from ~60 in the control samples to ~9 after proton doses of 1015 cm-2, with corresponding external quantum efficiencies of ~103 % in control samples, ~2 x103 %  for a dose of 1013 cm-2 and 104 % for a dose of 1015 cm-2. The mechanism for the increase in photocurrent is introduction of gap states, since the dark current of the photodetectors was increased by illuminating with sub-bandgap (red or green laser light) for the proton irradiated samples.
Characterization of Electrochemically Gated Graphene Field-Effect Transistor for Bioelectronic Applications
Authors: Asgarifar Sanaz , Inácio Pedro Carrilho , Mestre Ana , Hubbard Peter , Borme Jérôme , Machado George , Alpuim Pedro , Gomes Henrique Leonel
Published: February 2020

Abstract

This work provides an experimental characterization and equivalent circuit modelling of electrochemically gated field effect transistors (EGFETs) using a graphene layer. The aim is to demonstrate the detection limit of these sensing devices for bioelectronics applications. Towards that, we present a detail study of the; (i) sources of intrinsic noise, (ii) the effect of ionic density in charge transfer resistance and (iii) the existence of parasitic conducting paths in the surrounding electrolyte.

To investigate the liquid-based applications of graphene based EGFETs, quantifying the basic physical properties of graphene/solution interface is crucial. Towards that, we present a detail study of zero bias charge transfer resistance by using different type of ionic solutions and cell culture mediums. Measurements of the electrical noise were also performed to determine the EGFET detection limit.

The performance of the EGFET to record the electrophysiological signals was evaluated using adult zebra fish heart and electrogenic cell cultures. The electrocardiogram of the zebrafish heart was monitored with signal-to-noise-ratio higher than 7.

This contribution also discusses the application of graphene based EGFETS to measure electrophysiological signals in cell cultures. For instance, ultra-week extracellular signals resulting from cell metabolic activity or low frequency calcium waves.

Keywords.
Graphene, electrochemically gated field effect transistor, charge transport, intrinsic noise, extracellular signals.

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(Invited) Mechanically Flexible Integrated Photonic Systems for Sensing and Communications
Authors: Li Lan , Lin Hongtao , Michon Jerome , Geiger Sarah , Li Junying , Zheng Hanyu , Huang Yizhong , Yadav Anupama , Richardson Kathleen A , Gu Tian , Hu Juejun
Published: February 2020

Conventional integrated photonic devices are fabricated on rigid semiconductor or dielectric substrates and are therefore inherently incompatible with soft biological tissues. Over the past few years, we have developed a suite of active and passive photonic devices and systems integrated on plastic substrates which can be bent, twisted, and stretched without compromising their optical performance. In this talk, we will review the latest progress in multi-material photonic integration on unconventional flexible substrates, and discuss emerging applications of flexible photonics in biological sensing and high-bandwidth data communications.