Uniformity Of Current Density Research Articles

Uniformization of a large beam spot using sextupole magnets for a compact multiple-energy electron accelerator

We have commissioned a multiple-energy electron accelerator that illuminates an 800 mm × 800 mm target. The energy of the beam ranges from 0.5 to 5 MeV. A beamline following the accelerator has horizontal and vertical sections that include an alpha dipole and a “focus sextupole”. In the horizontal section, the alpha magnet, having a bend angle of 270° and a field index of 0.8, provides both vertical collimation and energy selection. In the vertical section, a focus sextupole converts the initial Gaussian beam distribution to a uniform distribution in one dimension without beam loss. We used a scanning magnet just ahead of the target to expand the beam in the orthogonal dimension. Using the French code TraceWin, we simulate the beam dynamics in this beamline by integrating electron trajectories through field maps of the magnets. We have determined experimentally that the focus sextupole creates a horizontal strip beam on target having a current density uniformity of better than 90 %. By scanning this strip beam vertically, we have achieved a two-dimensional current density uniformity of better than 90 %.

Effect of cooling surface temperature difference on the performance of high-temperature PEMFCs

Internal temperature distribution of the high-temperature proton exchange membrane fuel cell (HT-PEMFC) is affected by the cooling temperature, heat generation and reactant gas flow. Reasonable temperature control is helpful to improve the fuel cell performance and durability. In this work, a three-dimensional model that couples the reactant flows, species transport, heat transfer, charge transfer, and electrochemical reaction, was developed to simulate the HT-PEMFC operation. A solid mechanics model was established to analyze the stress distribution of the fuel cell. The polarization curves, distributions of temperature, membrane proton conductivity, current density and stress are investigated for different cooling surface temperature. Furthermore, the effect of assembly temperature on the stress of phosphoric acid-doped polybenzimidazole (PBI) membrane is discussed. Results reveals that the peak power density and uniformity of current density decrease with the increase of cooling surface temperature difference. The peak power density decreases by 9.14% when the temperature difference increases from 0 K to 40 K. The cooling surface temperature difference of less than 10 K and the voltage range in 0.5–0.7 V can achieve better current density uniformity and smaller current density change rate. In addition, the membrane in fuel cell has the highest stress, and increasing the assembly temperature is helpful to reduce the membrane stress. When the assembly temperature increases from 293.15 K to 343.15 K, the max and min compressive stresses in membrane in-plane decrease from 39.436 MPa to 31.416 MPa–24.934 MPa and 17.369 MPa at the temperature difference of 30 K, which decreases by 36.77% and 44.7%, respectively.

Elucidating non-uniform assembling effect in large-scale PEM fuel cell by coupling mechanics and performance models

The assembly of proton exchange membrane (PEM) fuel cell has a significant influence on contact pressure of BP and GDL, which affects key parameters of GDL including contact resistance, porosity, and permeability. In this study, a large-scale finite element method (FEM) PEM fuel cell model is developed considering realistic assembly, which is assembled by 14 bolts. The contact pressure at the interface of GDL and BP is converted into non-uniform contact resistance incorporated into a self-developed “3D + 1D” full PEM fuel cell multi-phase model with the active area of 108 cm2. The “3D + 1D” model simplifies part of components along through-plane direction into 1D model to improve calculation efficiency and stability. The results show that the performance reduces slightly when considering non-uniform contact resistance compared with that considering uniform contact resistance. The uniformity of current density and temperature distributions reduces evidently when considering non-uniform contact resistance affecting the performance and durability, which demonstrates the necessity of treatment of non-uniform contact resistance. Furthermore, the effects of porosity and permeability of deformed GDL under different preloading torques on performance are investigated. It is found that the contact resistance reduces first and then flats as the preloading torques increase, which results in the same trend of electronic ohmic loss, while the concentration loss nearly linearly increases. The simulation shows that the PEM fuel cell shows the best performance when the preloading torque is 3 Nm. This study provides some meaningful guidance for PEM fuel cell stack assembly.

An Investigation of Tin Electroless Deposition

Electroless metal/alloy deposition can be an efficient process in certain areas of microelectronic fabrication. In fact, it is often easier to obtain coatings of uniform thickness and composition using electroless deposition than with electrodeposition, since one does not have the current density uniformity problem of the latter. For example, we were able to develop a Ni(P) process as a replacement for the final aluminum interconnect level, significantly decreasing wafer processing cycle time, by selectively depositing a Ni(P) capping layer on the Cu bitline wiring level. In STTM MRAM, we successfully employed this Ni(P) capping process to enable the evaluation of memory state retention via functional testing in an air atmosphere at elevated temperatures (1).However, there is a need to explore materials + deposition methods for rapidly developing fields, such as Quantum computing, e.g., materials with superconducting properties. Conventional electroless metal deposition, utilizing a separate reducing agent, can deposit materials with unique and useful properties, such as phosphorus-containing alloys in the case of hypophosphite reducing agents. This talk discusses work we have carried out on electroless tin deposition, including aspects of electroless solution preparation and stability, copper substrate surface preparation and catalyzation, and the mechanisms of electroless deposition and solution decomposition.Electroless processes can deposit a limited number of materials, especially pure metals. This is in part due to conventional electroless processes requiring catalytically active surfaces both to initiate the deposition reaction and to sustain it, the heterogeneous oxidation of the reducing agent being a kinetically hindered process, often with multiple reaction pathways (2). Though not possessing good catalytic activity due to its Periodic Table related, p -block element status, pure Sn, an environmentally robust, superconducting metal, can be electrolessly deposited through a disproportionation reaction involving stannous ions (3) in an alkaline aqueous medium.We achieved electroless Sn deposition rates of up to 8 – 9 μm/hr for tartrate-citrate complexed electroless Sn solutions in the temperature range 80 – 85 ⁰C with sodium and potassium hydroxides to adjust alkalinity. We found that either in-house formulated, or commercially available, immersion Sn solutions deposited a uniform Sn catalyst layer (≤ 0.5 μm) to initiate the electroless Sn deposition reaction on copper; however, improperly formulated immersion Sn solutions rapidly developed precipitates due to tin ion hydrolysis.The biggest technical challenge was minimizing unwanted electroless deposition of tin in bulk solution, i.e., deposition not associated with the catalytically active substrate surface. Tin oxide (SnO) is known to be metastable at ambient conditions and to decompose at temperatures above 300 ⁰C with “noticeable rate” into Sn and SnO2 (4). Thus, removal of filterable hydrolysis products of Sn(II) following solution preparation was important, but not always sufficient, for obtaining solutions that were viable for several days of use. The reasons for, and mechanisms of, electroless Sn solution decomposition do not appear to have been adequately addressed in the literature.We will show SIMS analysis of both immersion and electroless Sn layers along with synchrotron X-Ray analysis results of immersion Sn catalyst films on Cu to determine the extent of Sn-Cu intermetallic formation following their formation. We will discuss the current understanding of the mechanism of electroless Sn deposition including that of concomitant H2 gas evolution. We will conclude with contrasting the Ni(P) and Sn electroless processes in terms of ease of operation and reliability for routine processing. † Present address: Solvay, 1937 West Main Street, Stamford 06902, CT. ‡ Quantum intern at the IBM TJ Watson Research Center, Summer 2019, 2020 and 2021.[1]. E. J. O'Sullivan, C. Camagong et al., 2019 Meet. Abstr. MA2019-02 916; https://doi.org/10.1149/MA2019-02/15/916.[2]. E. J. O'Sullivan, Ch 5, Advances in Electrochemical Science and Engineering, Volume 7, https://doi.org/10.1002/3527600264.ch5.[3]. A. Molenaar and J. W. G. de Bakker, 1989, J. Electrochem. Soc. 136, 378 and refs therein; H. Koyano, M. Kato, and M. Uchida, 1991, Plating and Surface Finishing, 78, 68-74 and refs therein.[4]. H. Giefers et al, 2005, Solid State Ionics, 176, 199-207; https://doi.org/10.1016/j.ssi.2004.06.006. Acknowledgements The authors gratefully acknowledge the efforts of the staff of the Microelectronics Research Laboratory (MRL) at the IBM T. J. Watson Research Center, where some of the fabrication work described in this talk was carried out.

Multi-objective optimization of graded catalyst layer to improve performance and current density uniformity of a PEMFC

The optimal use of compositions (platinum and ionomer) in cathode catalyst layers (CCLs) is essential to enhance the performance and improve the current density uniformity of proton exchange membrane fuel cells (PEMFCs). This paper presents a numerical study of graded CCL for a PEMFC. A one-dimensional, two-phase, non-isothermal model is developed, and the concept of the high power range (HPR) is defined. The effects of operating voltage and composition gradients across the catalyst layer thickness on output performance and current density distribution are investigated within the HPR. The results show an intense conflict between the output performance and current density uniformity, and only when biasing ionomer toward the membrane and operating in the higher spectrum of the HPR could improve them simultaneously. Otherwise, the improvement of one indicator means the deterioration of another. Finally, with the consideration of the interaction between the operating voltage and the gradients of platinum and ionomer, a multi-objective optimization is conducted to improve the aforementioned two indicators. Compared to the base case, the current density uniformity and the output performance were improved by 71.4% and 5.26%, respectively, which provides a solution to achieve higher performance and more uniform current density.

The design and evaluation of single-channel loopole coils at 7T MRI

Objective. Improving the local uniformity of field for awake monkey brain magnetic resonance imaging (MRI) at ultra-high fields while facilitating convenient placement and fixation of MRI-compatible multimodal devices for neuroscience study, can eventually advance our understanding of the primate’s brain organization. Approach. A group of single-channel RF coils including conventional loop coils and loopole coils sharing the same size and shape were designed for comparison; their performance as the transmit coil was quantitatively evaluated through a series of numerical electromagnetic (EM) simulations, and further verified by using 7T MRI over a saline phantom and a monkey in vivo. Main results. Compared to conventional loop coils, the optimized loopole coil brought up to 23.5% uniformity improvement for monkey brain imaging in EM simulations, and this performance was further verified over monkey brain imaging at 7T in vivo. Importantly, we have systematically explored the underlying mechanism regarding the relationship between loopole coils’ current density distribution and uniformity, observing that it can be approximated as a sinusoidal curve. Significance. The proposed loopole coil design can improve the imaging quality in awake and behaving monkeys, thus benefiting advanced brain research at UHF.

Effects of Cathode Gas Diffusion Layer Configuration on the Performance of Open Cathode Air-Cooled Polymer Electrolyte Membrane Fuel Cell

The design of a gas diffusion layer (GDL) is an effective way to manage water transport, thus improving the performance of air-cooled fuel cells. In the present study, three group designs of GDL with polytetrafluoroethylene (PTFE)—uniformly doped, in-planed sandwich doped and through-plane gradient doped—are proposed, and their effects on the performance of air-cooled fuel cells are explored by numerical simulation. The distribution of key physical quantities in the cathode catalyst layer (CCL), current density and the uniformity of current density distribution in the CCL were analyzed in detail. The results show that properly reducing the amount of PTFE in GDL is beneficial to promoting the water retaining capacity of air-cooled fuel cells, and then improving the performance of fuel cells. The performance of the in-plane sandwich GDL design cannot exceed the design with 10% PTFE uniformly doped, and this design will aggravate the uneven distribution of current density in CCL. Compared with the design of GDL with 40% PTFE uniformly doped, the current density can be improved by 22% when operating at 0.6 V by gradient increasing the PTFE content in GDL from the GDL/MPL interface to the gas channel. Furthermore, this design can maintain as good a current density uniformity as uniformly doping schemes.

Field emission properties of tetrapod-shaped ZnO/TiN point light source with semicircle reflecting anode

A novel point light source composed of tetrapod-shaped ZnO/TiN (T-ZnO/TiN) cathode and semi-circular groove reflective anode is demonstrated. The T-ZnO/TiN cathode is fabricated on nickel wire by spraying T-ZnO NRs powder and subsequent sputtering of TiN film. Semicircular reflective anodes with different opening sizes were prepared by wire electro-discharge machine. The field-emission properties of point light sources could be dramatically enhanced under semicircle reflecting anode by decreasing the threshold field from 2.61 to 2.10 V/μm. The point light source of D1500 has an extremely high emission current density of 132.73 mA/cm2 at 3.53 V/μm. The value of Jmax is about 2.7 times to that of D3000 (∼47.89 mA/m2 at 4.18 V/μm). Experiments and ANSYS electric field simulation show that the combination of low work function hybrid cathode and semicircular reflective anode structure leads to the increase of local field concentration and the enhancement of field emission characteristics. As far as we know, this point light source with semicircular reflective anode is prepared and applied for the first time. The results show that the point light source structure proposed here can not only effectively reduce the threshold field, but also improve the emission current density and luminescence uniformity.

Structure-improved current collector for performance enhancement of electrolyte membrane dehumidifiers: 3D simulations and in-situ measurements

Electro-dehumidification based on proton exchange membrane (PEM) is promising owing to its compact assembly and convenient operation. By numerically improving the effects of current collectors’ structure on the operation performance (moisture removal rate, current/temperature/humidity distribution and energy utilization rate), this research achieved a significant dehumidification enhancement (more than 40%) for electrolyte membrane dehumidifiers. 3D Multiphysics simulation and in-situ verification measurements were conducted. Compared with the original collectors, the dehumidification rate can be enhanced by 35% with the “口” collectors, and by more than 40% with “X”, “#” and “▪” collectors. The best performance occurred with the anode collector of “▪” structure (opening area: 9 × 10-4 m2), which the rate increased by 46%. The improvement effects were mainly due to the improvement of potential distribution (especially on the anode side) and the concentration of the reactant (water vapor) reaching the catalyst interface. Compared with the “口” type, the current density uniformity of membrane dehumidifier with the “▪” collector increased from 0.0033 to 0.032. The temperature and moisture distribution were also more uniform. The opening structure of anode collector resulted in a more significant effect than the opening area. Therefore, the system energy utilization rate and COP (coefficient of performance) can be doubled, up to 3.48 × 10−2 g·J−1·m−2 and 0.26, respectively. This research provides a theoretical basis and practical direction for improving current collectors of PEM dehumidifiers.

Numerical simulation analysis of the performance on the PEMFC with a new flow field designed based on constructal-theory

The design of the flow field structure has an important impact on the performance of PEMFC. An excellent design of the flow field will optimize the gas-liquid distribution inside the fuel cell, and enhance the diffusion of the reactant gases while reducing problems such as water flooding or uneven mass transfer of reactants, thus improving the overall performance of the cell. A new form of flow field based on the design ideas of Constructal-theory and Murray's Law was proposed in this paper. In this study, the PEMFC with the new and conventional flow fields were compared under the same conditions, and it is proved that the cell with the new flow field has a more balanced performance on output power and global pressure drop in contrast with conventional flow fields. In this study, the output power density of the PEMFC with the new flow field increased by an average of 1.35% compared to the PEMFC with Parallel flow field and Single Channel Serpentine flow field, and the pressure drop was reduced by 47.67% and 90.06% respectively compared to the PEMFC with the Single Channel Serpentine flow field and Double Channel Serpentine flow field. Meanwhile, the distribution of current density characteristics in a PEMFC with the new flow field was investigated and optimization of its structure size is analyzed. The reason for its non-uniform distribution of current density was revealed in this study, and an improvement scheme was proposed to improve the uniformity of current density, and the results of structural optimization research will have a certain guiding effect on practical applications.

Optimization of graded catalyst layer to enhance uniformity of current density and performance of high temperature-polymer electrolyte membrane fuel cell

The optimal use of catalyst materials is essential to improve the performance, durability and reduce the overall cost of the fuel cell. The present study is related to spatial distributions of current and overpotential for various graded catalyst structures in a high temperature-polymer electrolyte membrane fuel cell (HT-PEMFC). The effect of catalyst gradient across the catalytic layer (CL) thickness and along the channel and their combination on cell performance and catalyst utilization is investigated. The graded catalytic structure comprises two, three, or multiple layers of catalyst distribution. For a total cathode catalyst loading of 0.35 mg/cm2, higher loading near the membrane presents improved cell performance and catalyst utilization due to reduced limitations caused by oxygen and ion diffusions. However, non-uniformity in the current distribution is significantly increased. The increase in the catalyst loading along the reactant flow provides a substantially uniform current density but lower cell performance. The synergy of varying catalytic profiles across the CL thickness and along the cathode flow direction is investigated. The results emphasize the importance of a rational design of cathode structure and mathematical functions as a strategic tool for functional grading of a CL towards improved uniform current distribution and catalyst utilization.

Modeling Current Density Non-Uniformity to Detect Premature Failure in 3D Lithium-Ion Batteries

Conventional Lithium-ion (Li-ion) intercalation batteries that are composed of planar cathode, separator, and anode layers bear an intrinsic trade-off between energy density and power density. While thick electrodes allow for more active material loading and higher energy densities, thick electrodes lengthen ion transport pathways and limit power and fast charging performance. Conversely, thin electrodes have fast ion transport at the cost of reduced material loading which leads to lower energy densities. Due to the high weight and volume ratio of inactive components, stacking layers of thin planar batteries is inefficient for high capacity cells.1 Three-dimensional (3D) batteries decouple the power-energy trade-off in planar batteries by modifying electrode architecture on a micron to millimeter scale.2 3D batteries redistribute electrode material beyond planar geometry to controlled 3D spatial arrangements in pursuance of shorter ion-transport pathways and enhanced fast charging behavior in a battery cell. This enables high power performance without sacrificing the mass of active material in the cell, and ideally maintains high energy and power performance at high discharge and charge rates. However, a known issue in 3D batteries is the inhomogeneous transport distances between electrodes leading to nonuniform current density and local depletion of the electrode or electrolyte material.3,4 These nonuniformities can terminate a discharge or charge cycle prematurely. Although many 3D batteries have been proposed to date, few comparative modeling studies have been conducted for these architectures to understand their relative performance gains.In this work, we adapt a two-dimensional current density uniformity index (UI) measure from previous work5 and investigate its usage as a potential 3D metric for quantifying premature failure in 3D batteries. A series of 3D batteries are simulated using the software AMPERES that models a 3D electrochemical systems at the continuum level using volume-averaging techniques.6 Two material models – LiFePO4 (LFP) | Li4Ti5O12 (LTO) and LiNi0.5Mn0.3Co0.2O2 (NMC532) | Graphite – are investigated for each 3D battery architecture. We also visualize 3D Li-ion concentration profiles and Li-ion transport pathways to qualitatively analyze the transport behavior in each 3D battery. Our results show that 3D battery performance is material dependent, and 3D batteries with premature depletion demonstrate high UI metrics early in a discharge cycle. References C. L. Cobb and S. E. Solberg, J. Electrochem. Soc., 164, A1339–A1341 (2017).C. L. Cobb and M. Blanco, Journal of Power Sources, 249, 357–366 (2014).R. Hart, H. White, B. Dunn, and D. Rolison, Electrochemistry Communications, 5, 120–123 (2003).A. A. Talin, D. Ruzmetov, A. Kolmakov, K. McKelvey, N. Ware, F. El Gabaly, B. Dunn, and H. S. White, ACS Appl. Mater. Interfaces, 8, 32385–32391 (2016).D. Grazioli, V. Zadin, D. Brandell, and A. Simone, Electrochimica Acta, 296, 1142–1162 (2019).S. Allu, S. Kalnaus, S. Simunovic, J. Nanda, J.A. Turner, and S. Pannala, Journal of Power Sources, 325, 42–50 (2016). Acknowledgements This work was funded in part by a Defense Advanced Research Projects Agency (DARPA) Young Faculty Award under grant number D19AP00038. The views, opinions, and/or findings expressed are those of the authors and should not be interpreted as representing the official views or policies of the Department of Defense or the U.S. Government.

Performance of solid oxide fuel cell with chemical looping gasification products as fuel

Chemical looping gasification (CLG) can achieve the utilization of solid fuels for syngas production. The CLG system integrated with solid oxide fuel cell (SOFC) is a promising energy conversion way. In this work, an integration system of CLG and SOFC is evaluated via the implementation of a multi-field coupling modelling, where the products from the CLG are directly transported into the SOFC as the fuel and the coke deposition effect on the cell performance is evaluated. The results reveal that SOFC temperature using pure hydrogen as fuel has an increase of around 4 K compared to that with gas mixture as fuel owing to the inhibition of carbon deposition. It is found that the arrangement of anode and cathode in the countercurrent mode can promote the overall uniformity of current density compared to that in the cocurrent flow. Moreover, the impact of operating parameter of the CLG system on the SOFC performance is also examined. The results demonstrate that the increase of fuel reactor (FR) temperature and H2O/C molar ratio in the CLG system is beneficial to the inhibition of carbon deposition and the enhancement of the SOFC performance.

A pluggable current collector for in-operando current measurements in all-vanadium redox flow batteries with flow field

Understanding current distribution in operating Vanadium redox flow batteries (VRFBs) is vital for improving battery design and performance as the non-uniform current density distribution is known as a major cause of the corrosion and side reactions in VRFBs. However, the existing method for current density measurement in the VRFB with flow field is complex and the rib conductive structure of graphite plate is changed which reduces the measurement accuracy and reliability. In this study, we propose a novel pluggable current collector for in-operando current distribution measurements which greatly simplifies the current density distribution measurement process in VRFBs with flow field. The new method relies on eight pluggable graphite units in a flow plate frame to replicate the actual serpentine flow field structure, thereby providing higher measurement reliability compared to the existing methods which are mostly invasive. Using the new method, current density distributions at different electrode compression ratios (CR) and inflow electrolyte rates are investigated. It is found that insufficient supplemental reactant in electrode border region is the main reason for the uneven current density distribution and the current density non-uniformity is intensified in the initial and final stages of cycling process. Increasing CR can improve the current density in the electrode core region. The overall current density uniformity in a VRFB with serpentine flow field can be enhanced by increasing the inflow electrolyte rate. The developed method is believed to facilitate the understanding of the coupled local reactions and transport processes and guide on the future design of VRFBs.

Understanding Non-Uniformities in 3D Lithium-Ion Battery Electrode Architectures

Conventional Lithium-ion intercalation batteries that are composed of planar cathode, separator, and anode layers have an intrinsic trade-off between energy density and power density. While thick electrodes allow for more active material loading and higher energy densities, thick electrodes lengthen ion transport pathways and limit power performance. Conversely, thin electrodes have fast ion transport at the cost of reduced material loading which leads to lower energy densities. Three-dimensional (3D) batteries can potentially mitigate this power and energy trade-off through electrode architecture. Unlike planar electrodes, 3D batteries have unique and integrated electrode architectures that can modify ion transport pathways in three-dimensions on a micron to millimeter scale. These architectures may be locally imbalanced in material loading, leading to nonuniform current density and local depletion of the electrode or electrolyte material. These nonuniformities can terminate a discharge or charge cycle prematurely. Although many 3D battery architectures have been proposed to date, few comparative modeling studies have been conducted for these architectures to understand their relative performance gains.In this presentation, we will investigate the impact of 3D electrode architecture on current density uniformity and material lithiation at different discharge rates in several 3D batteries. Our batteries are simulated using the software CAEBAT: AMPERES 1 , which provides a 3D electrochemical model on the continuum level using volume-averaging techniques. 3D batteries with different parameterizations and geometries of interdigitated anode and cathode electrodes are studied. In addition, the effects of current collector placement, material loading, and electrode feature shapes are also presented.1. Allu, S., Kalnaus, S., Simunovic, S., Nanda, J., Turner, J. A., and Pannala, S., J. Power Sources, 325, 42 (2016)

Electroless Deposition for Nanoscale Applications: Challenges and Opportunities

We recently developed a maskless, electroless, high-P-content, Ni(P) process to protect the final Cu bitline wiring level in our STTM MRAM test vehicles to enable functional testing in an air atmosphere at elevated temperatures for evaluation of MRAM device memory state retention. The process was developed as a replacement for the final aluminum level, and drastically shortened wafer processing cycle time. We demonstrated an electroless Ni(P) that selectively deposited on Cu bit lines with effective spacing approaching 200 nm without shorting, for coating thicknesses up to ca. 50 - 60 nm, with excellent bitline coverage (no pinholes). This was achieved through optimization of Cu surface cleanliness, surface catalyzation using an acidic Pd solution, and finally electroless Ni(P) deposition (1).Testing (electrical resistance and magnetoresistance (R & MR)) of Ni(P)-coated wafers, showed virtually unchanged R & MR for MRAM 4Kb arrays encompassing a large range of device critical dimensions (CDs). Figure 1 shows a topdown SEM image of a region of electroless Ni(P)-coated Cu bitlines.While electroless deposition is capable of depositing only a limited number of metals and alloys compared to electrodeposition, it is often easier to obtain coatings of uniform thickness and composition, since one does not have the current density uniformity problem of electrodeposition. Although it is not always possible to obtain pure materials using electroless deposition, nevertheless, materials with unique properties, such as Ni(P) (corrosion resistance), and Co(P) (magnetic properties) and related alloys e.g., Co(W)(P), are readily obtained by electroless deposition methods. These materials may be crystalline or amorphous, and the crystallization kinetics of the latter type may be strongly dependent on film thickness, and have a two-dimensional character due to interfacial effects.It is important to understand how such materials transform upon heating, given that back-end-of-line (BEOL) processing may involve temperature excursions to 400 ⁰C. We will discuss in detail the kinetics of crystallization of our high-P-content, amorphous, electroless Ni(P) films on Cu thin films using synchrotron X-Ray diffraction analysis (2). For 1 um thick Ni-P films deposited on Cu/Ta/TaN underlayer, as we increase the rates at which the temperature is raised during ramp anneals, crystallization temperatures vary from about 360C to 400C from which we extract an activation energy of 3.4 eV for this crystallization. The in-situ data also shows a gradual reduction in lattice constant for the underlying Ta layer. We will complement the synchrotron X-Ray analysis study results with TEM, SIMS and X-ray fluorescence (XRF) results of Ni(P) film composition for unpatterned and patterned (sub-micron) features.In addition to the subtlety of its mechanisms and range of solution formulations, electroless deposition has much to offer in terms of niche applications, which explains why it is often turned to first by researchers seeking creative deposition methods in the still emerging field of nanofabrication. Given the wide range of materials involved in electroless deposition, whether it is the final product, or the choice of a reasonable reducing agent, the mechanism of electroless deposition tends to be complex. This talk will include a discussion of the mechanism of electroless deposition, and whether the sought after, one-mechanism-fits-all approach, is tenable.[1]. E. J. O'Sullivan et al 2019 Meet. Abstr. MA2019-02 916; https://doi.org/10.1149/MA2019-02/15/916 [2]. Canadian Light Source Inc., 44 Innovation Boulevard Saskatoon, SK S7N 2V3, Canada. Acknowledgements The authors gratefully acknowledge the efforts of the staff of the Microelectronics Research Laboratory (MRL) at the IBM T. J. Watson Research Center, where some of the fabrication work described in this talk was carried out. Part of the research described in this paper was performed at the Canadian Light Source, a national research facility of the University of Saskatchewan, which is supported by the Canada Foundation for Innovation (CFI), the Natural Sciences and Engineering Research Council (NSERC), the National Research Council (NRC), the Canadian Institutes of Health Research (CIHR), the Government of Saskatchewan, and the University of Saskatchewan.

Plasma electron source for generating a ribbon beam in the forevacuum pressure range.

We describe a plasma-cathode electron beam source based on a hollow cathode glow discharge and operating in the forevacuum pressure range that produces a steady-state ribbon beam. The electron beam is generated in the pressure range of 10-30 Pa. A multi-aperture electron extraction and beam formation system is used to provide beam stability and enhanced uniformity of beam current density, allowing the use of this kind of device for beam-plasma surface modification over relatively large areas.

Effects of reactants/coolant non-uniform inflow on the cold start performance of PEMFC stack

The failure at equally distributing reactants among different channels within the stack leads to uneven reaction and gas concentration distribution in the catalyst layers, which consequently impacts the performance and durability of proton exchange membrane fuel cell stacks (PEMFCs). A three-dimensional, transient, non-isothermal cold start model for PEMFCs with parallel flow-field configuration and coolant circulation is developed in this work to investigate the effects of non-uniform distribution of reactants/coolant inflow rates on the cold start process. The results show that the effect of non-uniform inflow on ice formation amount is obvious and that on the distribution uniformity of current density is apparent over the cold start survival time. Additionally, the simulation predictions show that the non-uniform initial membrane water content distribution due to the purge procedure can significantly increase the rate of ice growth and deteriorate the uniformity of current density distribution in the membrane. It is found that high stoichiometry operating condition is favorable to cold startup, but may result in drying in the membrane at regions close to the channel inlet side. As non-uniform inflow rates issue is inevitable in actual PEMFC stack operation conditions, our results demonstrate that the initial membrane water content and cathode stoichiometry ratio need to be identified to moderate the effects of reactants/coolant inflow maldistribution and to maintain a stable cold start performance for the PEMFC stack.

Factor analysis of the uniformity of the transfer current density in vanadium flow battery by an improved three-dimensional transient model

Vanadium flow battery has been regarded as one of the most promising candidates for large-scale energy storage, due to its attractive features of high safety, high performance-price ratio and environmental friendliness. The uniformity of transfer current density is one of the crucial factors affecting the performance of a vanadium flow battery. More uniform distribution of transfer current density will reduce the polarization and improve the battery reliability. In this work, a three-dimensional transient model in combination of the vanadium ions crossover through the separator has been developed. Based on the model, the effect of the applied current density, electrode porosity and electrolyte flow rate on the uniformity of transfer current density has been investigated. The result indicates that a lower applied current density, higher electrode porosity or higher electrolyte flow rate is beneficial to obtain a more uniform transfer current density and a reduced battery polarization. By comparison, the electrode porosity shows the most prominent effect on the uniformity of transfer current density, and a higher porosity is verified to be able to attain a better stability in several charge-discharge cycles. Finally, a preliminary study for an industrial scale battery designs has been performed based on an amplifying model.

Controlling structure of vertically grown graphene sheets on carbon fibers for hosting Li and Na metals as rechargeable battery anodes

Abstract Metallic Li/Na anodes are highly attractive for next-generation batteries due to their high capacity and low anode potential. But dendrite growth and huge volume change during long-term cycling hinder their practical application. Here, vertical graphene sheets grown on carbon fibers (VGSs/CFs) prepared by thermal chemical vapor deposition are used as 3D stable hosts for Li/Na metal anode. The results show that the structure of the VGSs has great influence on electrochemical performance of the anodes. The tightly interconnected VGSs provide numerous active sites for Li/Na adsorption and improve electrical conductivity of the anodes, increasing current density uniformity and decreasing energy barrier for the Li/Na nucleation on the composite electrode during cycling. The symmetrical cell based on VGSs/CFs composite Li anode (Li/VGSs/CFs) demonstrates a small overpotential of 76 mV for 1200 cycles at 5 mA cm−2 in carbonate-based electrolyte. The symmetrical cell using VGSs/CFs composite Na anode (Na/VGSs/CFs) shows a small overpotential of 98 mV for 2000 cycles at 10 mA cm−2. Furthermore, in full-cell configurations against Li4Ti5O12 or LiFePO4 cathodes, Li/VGSs/CFs anode displays ultrahigh cyclic stability and rate performance. The Li/VGSs/CFs and Na/VGSs/CFs anodes outperform the reported hosts for Li/Na anodes and are of high promise for practical application.