bluuebunny/crossref_metadata_2025 huggingface dataset:
Orthogonal Collocation on Finite Element Method for Lid-Driven Cavity Flow
Authors: Jang Taejin , Pathak Chintan , Subramanian Venkat R.
Published: February 2020

Among the candidates for the Electrical Energy Storage (EES), Redox Flow Batteries (RFBs) are drawing attention towards a feasible solution. They are advantageous in flexibility and long-term stability of capacity and are therefore expected to play a critical role in the renewable energy and microgrid system. Meanwhile, the performance of the RFBs greatly depends on the motion of the electrolyte. And the problem becomes more complicated when we consider the edge effect in 2-dimensional modeling. Up to date, there is no analytical solution for the fluid dynamics of electrolyte flow in RFBs. To maximize the performance and enable optimum real-time battery management, fast and robust algorithm for the flow model and numerical simulation in multi-dimension is essential.

In this presentation, we introduce Orthogonal Collocation on Finite Element (OCFE) approach in the successive domain for the classical 2-D lid-driven cavity flow problem. The Navier-Stokes equation is mathematically reformulated as Partial Differential Equations (PDE) of stream function and vorticity. To get the vorticity boundary condition, imaginary points, which are located at the outside of the cavity boundary, are introduced. The result shows good agreements with precedential values while using minimum computational time and memory.
Microstructural Principles for Porous Li-Ion Battery Electrode Designs
Authors: Deva Abhas , García R. Edwin
Published: February 2020

During battery cycling, lithium ions follow a tortuous, reactive diffusion path around a densely packed distribution of particles of active material in a porous battery electrode, which defines its instantaneous response and long term degradation. The associated microstructural properties that control the electrochemical battery response are particle morphology, spatial orientation, size and size distribution, and is a direct function of electrode fabrication. While traditional microstructure optimization approaches are made through fabrication trial and error, the impact on performance of currently used porous electrode microstructures remains unclear. In this paper, we present an alternative approach to evaluate the impact of several existing, possible (and a few impossible) battery microstructure architectures on their corresponding macroscopic properties. Based on published 2D and 3D microstructural data for traditionally and non-traditionally used battery fabrication approaches, we discuss the microstructural characteristics of these architectures by defining a theoretical framework where they can be compared on the same footing.
(Invited) Multiscale Modeling of Transport Phenomena in Ion-Conducting Membranes and Aqueous CO2 Reduction Cells
Authors: Weber Adam Z. , Crothers Andrew Robert , Singh Meenesh , Radke Clayton J. , Bell Alexis T.
Published: February 2020

Transport phenomena is a critical component of electrochemical engineering of energy-conversion devices including fuel cells and solar-fuel generators. In fuel cells, ion-conducting polymers, such as perflurosulfonic-acid (PFSA) membranes, typically nanophase separate into conducting and nonconducting or structural domains that arrange together on the mesoscale and result in macroscopically observable properties. To examine these interactions, a multiscale model has been developed that includes a mean-field local-density theory at the nanoscale, a physically derived resistor-network for the mesoscale that leads up to macroscale. The nanoscale includes cation and water chemical potentials to model transport in the aqueous domains including cation-polymer electrostatic interactions, solvation energy, and a concentrated-solution transport theory to model transport and account for dielectric friction induced by the strong electrostatic fields of charged polymer groups. For the mesoscale, the model accounts for transport along the segments of the mesoscale network of the aqueous domains where mass and charge are conserved at each node (i.e. branching point) of the network. The difference in ionic potential and species chemical potentials between connected network nodes are driving forces for transport. The resistance of each segment of the network is determined from the nanoscale model. The results reveal nonlinear and nonintuitive transport pathways, where the overall properties agree with experimental property measurements.

In solar-fuel generators, including CO2 reduction cells, transport phenomena play a critical, yet not fully realized, role in controlling the overall reaction rate. To understand this interplay, multiscale modeling is used to examine the reaction mechanism of CO2 reduction to CO over a planar silver catalyst. Traditional Nernst-Planck expressions for ion and gas transport are coupled to a microkinetics model, where the reaction rates and barriers for the various reaction steps are taken from DFT calculations. The modeling approach helps to resolve the reaction mechanism and demonstrates good agreement with experimental data and trends without fitting parameters.

Acknowledgements

The fuel-cell work was funded under the Fuel Cell Performance and Durability Consortium (FC PAD) funded by the Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy under contract DE-AC02-05CH11231. The CO2 reduction was funded under the Joint Center for Artificial Photosynthesis (JCAP), a BES Energy Innovation Hub.
Water Phenomena in PEFCs As the Origin of the Pt Loading Effect: A Comprehensive Modelling Study
Authors: Muzaffar Tasleem Ahmad , Eikerling Michael Hermann
Published: February 2020

The highly prioritized objective of research on polymer electrolyte fuel cells is to make highly performing and stable catalyst layers with drastically reduced platinum loading. Achieving this objective demands an understanding of the impact of composition and porous structure of the electrode layers on the water balance in the cell. Experimental studies
1-3
have shown a marked increase in the resistance to oxygen diffusion when the Pt content of the cathode catalyst layer was lowered
4
. We present a water balance model to explain these trends. Figure 1 illustrates modeling domain and processes considered. The set of 1D continuity and flux equations is formulated and solved for water distribution and fluxes in catalyst layers, diffusion media and flow fields. Model solutions reveal the impact of structure, composition, and operating conditions on the water transport phenomena and performance. Reducing the Pt loading induces a drastic shift of the balance between rates of water production and vaporization. This leads to a build-up of the liquid water pressure in catalyst layer and gas diffusion layer on the cathode side that raises the liquid water accumulation and thereby drastically diminishes the effective oxygen diffusivity. Our model unravels the fine details of this interplay and it helps identify strategies for minimizing the Pt loading without running into this water trap

References:

[1] A. Kongkanand et al., ACS Catal., 6, 1578-1583, (2016)

[2] J. Owejan et al. J. Electrochem. Soc. 160, F824-F833, (2013)

[3] M. Wilson, J. Electrochem. Soc., 139. L28-L39, (1992)

[4] T. Muzaffar et al., “Advanced Energy Materials”,
in Review

Figure 1
(Invited) Laser Annealing in CMOS Manufacturing
Authors: Gluschenkov Oleg , Jagannathan Hemanth
Published: February 2020

Laser Annealing was introduced into mainstream CMOS manufacturing nearly a decade ago and since then has been capturing new applications and expanding into new process regimes. This talk reviews applications of millisecond-scale laser annealing in CMOS technologies from dopant activation to gate dielectric reliability effects to creating metastable alloys to forming silicides. Mitigation of thermal pattern effects and laser-induced substrate distortions are discussed in the context of different device architectures built on both bulk and SOI substrates. Nanosecond-scale laser annealing greatly expands the annealing process space enabling synthesis of highly metastable alloys, spatially selective thermal processing, and targeted thermal treatments with virtually zero impact on the overall thermal budget. Building on the presented historical perspective, we discuss and compare applications of nanosecond-scale laser annealing in future CMOS technologies with 3-dimensional transistors and advanced BEOL interconnects.
(Invited) Enabling on-Device Learning with Deep Spiking Neural Networks for Video Classification
Authors: Soures Nicholas , Zyarah Abdullah , Kudithipudi Dhireesha
Published: February 2020

Spiking recurrent neural networks are gaining traction in solving complex temporal tasks. In general, spiking neural networks are resilient and computationally powerful. These intrinsic properties make them attractive for learning on the edge of the devices. In this work, we propose a semi-supervised deep spiking neural network that can be deployed on embedded devices. We present memristor synapse and neuron circuits integrated in a neuromemristive system to implement a deep spiking neural network. For optimal performance on-device, the synaptic crossbar array is trained using a modified gradient descent rule in conjunction with an unsupervised rule. The proposed deep spiking neural network is validated for on-device video classification tasks.
(Invited) Development of Plasma Atomic Layer Etching in Close-To-Conventional Etch Tools
Authors: Cooke Mike , Goodyear Andy
Published: February 2020

Plasma-based atomic layer etching is a cyclical etching process of gas dosing and surface bombardment that removes material layer by layer, and has the potential to remove single atomic layers with low damage. The authors consider how a conventional plasma etcher can be modiﬁed to perform this style of recipe and give results for a range of materials: Si, MoS2, GaN/AlGaN. The need for precise control of ion bombardment energy and gas dose is highlighted, requiring specialised hardware.
Selfrectifying Memristor Device Based on Polarization Switching and Space Charge Distribution Via External Electric Field
Authors: Lee Ho Jin , Lee Joonbong , Choi Taekjib
Published: February 2020

Strong interest in resistive switching phenomena is driven by a possibility to develop electronic devices with novel functional properties not available in conventional systems. Bistable resistive devices are characterized by two resistance states that can be switched by an external voltage. Recently, ferroelectric memristors divices with tunable resistive behavior—have emerged as a new paradigm for nonvolatile memories and adaptive electronic circuit elements. In this work, we fabricated the tunable ferroelectric tunnel junction memristor device as future memory device. Ca doped BiFeO3/BiFeO3 thin films grown on Nb doped SrTiO3 substrate (conductive electrode) by pulsed laser deposition are studied by X-ray diffraction and I-V measurement to characterize their structure and memristive properties. These are simultaneously realized that the change of the resistance of the semiconductor substrate due to the remanent polarization of the ferroelectric thin film and the change of the anisotropic resistance due to the distribution of the space charge in the thin film were simultaneously realized. The results indicate that the self-rectifying resistive switching properties, and this device can be applied as memory device integrating the function of a selector in 3D cross point array.
Effect of Copper Diffusion in Low Dielectric Constant Dielectrics Under Thermal Stress on Electrical and Reliability Characteristics
Authors: Lee Chih-Yen , Chang Wei-Yuan , Cheng Yi-Lung
Published: February 2020

Low dielectric constant materials (low-k) as interlayer dielectrics in back-end-of-line (BEOL) interconnects of integrated circuits can provide lower parasitic capacitance between the metal lines. However, the interaction between copper (Cu) conductors and low-k dielectrics is a critical issue. In this study, effects of Cu diffusion on the electrical and reliability characteristics of low-k dielectrics were investigated using Cu/low-k/Si capacitors. Low-k dielectrics with the porosities ranging from 0 to 35 % were used. The thermal annealing with different temperatures and times was applied to drive Cu diffusion. The experimental result showed that the Cu diffusion depth increased with the annealing temperature and annealing time in all low-k films and is dominated by the annealing temperature. Moreover, in the low-k film with a higher porosity, the Cu diffusion rate is faster. The Cu diffusion in the low-k film induced an increase in the leakage current density and a degradation in the dielectric breakdown field and exhibited a positive correlation. Furthermore, it was found that the dielectric breakdown failure time are proportional to the Cu diffusion depth for all low-k films. Therefore, this study points out an important conclusion that a fast reliability evaluation on the Cu/low-k interconnects can be done by measuring the Cu diffusion depth.
Influence of Size and Current Density on the Optoelectrical Properties of Green III-Nitride Micro-Light-Emitting Diodes
Authors: Kim Dae-Hyun , Seong Tae-Yeon
Published: February 2020

High efficiency III-nitride light-emitting diodes (LEDs) have been applied to solid-state lighting. A luminous efficacy (about 150 lm/W) of InGaN/GaN-based LEDs is much higher than those of other self-emissive devices such as organic LEDs (OLEDs). As mobile electronics scale down, display technologies must also move to smaller form factors and ultra-high resolutions while maintaining high efficiencies to extend battery lifetime. III-nitride LEDs are an ideal candidate for achieving these goals. Current technologies including liquid crystal displays (LCDs) and organic light emitting diode (OLED) suffer from low efficiencies and brightness. For the realization of ultrahigh resolutions, around 10 μm or smaller light-emitting pixel sizes are required. In this regard, the InGaN/GaN μLED-based displays have emerged as a promising technology in terms of high brightness, contrast, luminous efficacies, resolution, compactness, operation under harsh conditions, and long lifetime, which cannot be satisfied by conventional LCD and OLED-based display technologies. Several groups have fabricated single-color μLED-based arrays with pixel dimensions as small as 12 μm. This self-emissive technology can be used in applications where high resolution, brightness, and efficiency are necessary such as smartphones, smartwatches, head-mounted and near-eye displays. In addition, μLEDs have exhibited improved thermal management, enhanced light extraction, and operation at higher current densities over their broad-area counterparts. Despite these benefits, surface recombination at small dimensions has been noted as a potential source for reducing device efficiencies.

We have investigated the effect of chip size on the forward voltage, light output, emission image and spectral shift of InGaN based green LEDs (518 nm) as a function of current density. The size of the chips was varied from 10 to 100 μm. The smaller chips exhibited higher light output power although the lower output powers were obtained at the higher current densities. Furthermore, the smallest devices showed the better current spreading at higher current densities. It was observed that green μLEDs underwent spectral shift more pronouncedly when dc drive current increased than when chip size increased. It was observed that variation of dc drive current more pronouncedly affected the spectral shift of green μLEDs compared with change of chip size. The relation between the electroluminescence characteristics and current density of different-size devices exhibited that the devices experienced more dominantly blue shift than red shift. However, at the same current density, the peak of the devices was not shifted when the device size changed. Dependence of size and current density on the spectral shift of green μLEDs will be described and discussed in terms of band-filling and stress relaxation effects.
(Invited) Gallium Nitride Device Technology for Commercial RF Applications
Authors: Green Bruce
Published: February 2020

Advances in gallium nitride (GaN) device technology over the last 25 years have enabled commercial radio frequency (RF) applications to benefit from its high-power handling capability and speed. Because of these advances, GaN has emerged as a leading technology for future 4G and 5G communications systems. This presentation will cover GaN device technology starting with the basics of GaN materials and device structures. It will show how the step-function improvement in materials and device capability with GaN translates to step-function advances in system capability. It will then give examples of GaN power amplifier applications for present day 4G wireless communications applications. Along the way, the presentation will address industry progress that has enabled GaN technology to become commercially viable. Finally, the presentation will preview opportunities for GaN technology in future 5G communications applications.
(Invited) Current-Induced Degradation in Bulk GaN Vertical Schottky Diodes
Authors: Porter Matthew , Kaplar Robert J. , Pickrell Greg W. , Allerman Andrew A. , Specht Petra , Weatherford Todd
Published: February 2020

The recent availability of high quality bulk GaN substrates with low threading dislocation density has made vertical power device structures an attractive possibility. Due to the low probability of a threading dislocation occurring within the active area of devices grown upon bulk GaN, reliability is driven by bulk or surface effects. Past work upon the reliability of Ni-GaN Schottky interfaces has suggested that interdiffusion of the Ni into the GaN can occur under thermal stress, adversely affecting the effective energy height of the barrier and increasing the ohmic nature of the interface. Conditions similar to such thermal stressing can be found at typical operating points in high current power devices used in power electronic applications. Our work examines the influence of high current density stress upon the reliability of vertical bulk GaN Schottky diodes. The vertical diodes studied were fabricated with Pd Schottky metallization with an Au ohmic overlayer. To study the effects of surface chemistry, reliability is compared between devices fabricated with different acidic and basic surface preparations, using HCl and KOH respectively. The fabricated devices were subject to life testing under varying levels of constant current density, up to 10 kA/cm^2. The lifetesting system was designed as a stress-measure-stress system, allowing for the evaluation of device parameters in-situ during testing. Electrical parameters indicating the state of the Schottky barrier were evaluated continuously during the measurement points of testing. In addition, a measurement of barrier inhomogeneity, evaluated using the Tung model, was also used as an indication of the condition of the Schottky interface. The microstructure of the interface before and after stress was examined using S/TEM imaging of representative lamellae samples of the stressed and unstressed devices. EDS imaging was used to determine the degree of diffusion between the Schottky metallization and the GaN substrate. Results of microstructure imaging are correlated with the electrical measurements taken to determine the responsible mechanisms for device degradation.
Electrical Properties of Silicon Doped GaN Activated By Ion Implantation
Authors: Gallagher James C , Anderson Travis J , Luna Lunet E , Koehler Andrew D , Hobart Karl D. , Kub Francis J
Published: February 2020

One major goal of GaN based technology studies is the fabrication of rugged power switching devices. While this is best achieved through vertical GaN technology, the process development of GaN substrates is not yet mature, and the substrates for lateral power switch are more cost effect than GaN. A common way of doping lateral GaN devices is through ion implantation followed by rapid thermal annealing for ion activation. Activation of most p-type dopants requires temperatures above 1300 °C; however, silicon will activate as an n-type dopant at lower temperatures. This research reports on the electrical properties of devices such as junction field effect transistors and Van der Pauw structures containing silicon doped GaN activated by ion implantation.
(Invited) High Al-Content AlGaN for Power Electronics: A Fabrication Perspective
Authors: Douglas Erica A. , Klein Brianna , Allerman Andrew A. , Armstrong Andrew M. , Kaplar Robert J. , Baca Albert G. , Neely Jason C.
Published: February 2020

Wide bandgap materials, such as GaN and SiC, have been rapidly maturing for use in power electronic applications. Recently, there has been a push to investigate materials with ultra-wide bandgaps (Eg > 3.4eV), such as Ga2O3 and AlGaN, in an attempt to achieve higher critical electric field, as it scales with the bandgap to the >2 power. Increasing the Al-content of AlGaN has been pursued for several applications, including both power electronics and UV optoelectronics, as the bandgap, and thus critical electric field, of the material increases with increasing Al-content. Though decades have been spent maturing GaN and low Al-content AlGaN for power, RF, and optoelectronic applications, the path for fabricating devices utilizing Al-rich AlGaN is not as straightforward as one may hope.

An overview of Sandia National Laboratories’ device development with Al-rich AlGaN will be presented. In addition, this talk will report on the intricacies faced during fabrication of Al-rich AlGaN devices, including both the challenges and advancements that AlGaN can present such as the effects of Al content on dry etch characteristics (e.g. surface morphology and etch rates), effects of surface cleaning and preparation, as well as metallization schemes and characteristics for both Schottky and Ohmic contacts.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
Reliability of SiC Schottky Diodes with Mo2C Electrode
Authors: Saito Daiki , Muneta Iriya , Hoshii Takuya , Wakabayashi Hitoshi , Tsutsui Kazuo , Iwai Hiroshi , Kakushima Kuniyuki
Published: February 2020

Abstract

High current density electrical test was performed on SiC Schottky diodes. The shift in the Schottky barrier height was suppressed by adopting Mo2C as an electrode. Physical analysis revealed an epitaxial growth of Mo2C on SiC surface, which may be the origin of the stability.

Introduction

SiC Schottky barrier diodes (SBD) are used for high efficiency power conversion circuit owing to its high breakdown voltage, low ON-resistance and fast operation speed. However, pure metal and SiC surface reacts during high temperature annealing, forming an inhomogeneous interface [1]. Therefore, there is a concern in the diode characteristics change with time. We have shown diode characteristics with high temperature stability by using Mo2C as Schottky electrodes [2]. In this report, electric characteristics of SiC-SBD with Mo or Mo2C electrode when this devices is applied current of high current density and TEM analysis of Mo2C/SiC interface with high temperature stability are reported.

Experiments

A SiC wafer used in this study is an epitaxially grown 4°-off n-type 4H-SiC (0001) with a donor concentration of 1015cm-3 on a SiC substrate. Mo or Mo2C electrodes were sputter-deposited and patterned by reactive ion etching. The Mo and Mo2C samples were annealed in 500 or 850oC, respectively. Diode characteristics were measured before and after flowing a current density of 100A/cm2 for 500 s.

Results and discussions

The diode characteristics before and after the electrical current test are shown in fig. 1. Although increase in the Schottky barrier height was observed in both diodes, the amount of shift was suppressed with the Mo2C diode. This fact suggests that local interface reaction due to inhomogeneous current flow was suppressed. Moreover, only a slight degradation in the ideality factor was suppressed with the Mo2C electrode. Transmission electron microscope image of the diode, shown in fig. 2, revealed an epitaxial growth of a Mo2C layer on the SiC surface. The reliable diode characteristics might be originated from the sharp and uniform interface.

Conclusion

An electrical current test was performed on SiC Schottky diodes with Mo2C electrodes. A stable Schottky barrier height with a robust ideality factor was observed.

TEM analysis revealed an epitaxial growth of Mo2C on the SiC surface with a sharp and uniform interface.

References

[1] L. Kolaklieva, et al., ISBN 978-953-307-027-8, (2009) [2] T. Suzuki, et al., IEEE Electron Dev. Lett., 37, 618 (2016)

Figure 1
In Situ Studies of Zinc Oxide Nucleation and Growth
Authors: Yu Dian , Yu Yixuan , Kodambaka Suneel , Orme Christine A.
Published: February 2020

There has been recent interest in the growth of zinc oxide (ZnO) from solution phase because it is a low cost and versatile method to integrate thin films onto substrates. The prevailing mechanistic models for ZnO growth describe two different crystallization scenarios. The first scenario proposes that initially metastable phases such as Zn(OH)2 forms. These metastable phases create reservoir rich in zinc and oxygen from which ZnO nucleate driven by dehydration. The second scenario proposes that growth occurs via solution precipitation of ZnO; ZnO colloids nucleate in the solution and then attach to the substrate. More generally, while it is appreciated that nucleation and growth behaviors impact electrical and optical performance there have not been systematic studies of ZnO growth kinetics using tools that are indicative at the nanometer scale as needed to measure island formation and atomic step propagation. To address this gap, we have employed three in situ tools to track ZnO growth: in situ atomic force microscopy to image nucleation and growth dynamics; in situ WAXS to verify material phase; and in situ quartz crystal microbalance to measure film growth rates.
(Invited) Pixel-Parallel 3-D Integrated CMOS Image Sensors for Next-Generation Video Systems
Authors: Goto Masahide , Honda Yuki , Watabe Toshihisa , Hagiwara Kei , Nanba Masakazu , Iguchi Yoshinori , Saraya Takuya , Kobayashi Masaharu , Higurashi Eiji , Toshiyoshi Hiroshi , Hiramoto Toshiro
Published: February 2020

Performances of image sensors including pixel counts, capturing speed, and dynamic range continue improving to meet the demands for high-reality video systems such as 8K/4K television and three-dimensional (3-D) imaging. Recent 3-D integration technology of silicon device has boosted sensor performances by using through-silicon vias (TSVs) and micro-bumps [1-2]. However, fully parallel signal processing has not been possible yet because the size of TSVs or micro-bumps is larger than the imaging pixel.

We have proposed a new 3-D integration technology without using TSV or micro-bumps but by using direct bonding of silicon-on-insulator (SOI) wafers, in which gold electrodes are embedded in the SiO2 intermediate layer. The gold electrodes formed by the damascene process with chemical mechanical polishing (CMP) can be reduced to 1 μm or less in diameter. This 3-D integration technology enables us to develop pixel-parallel 3-D integrated CMOS image sensors [3-5] as illustrated in Fig. 1. Two SOI wafers are stacked and directly connected by the embedded gold electrodes within every pixel. We have also developed novel in-pixel A/D converters (ADCs) with pulse frequency output, where signal charges generated in photodiodes (PDs) are converted into pulse signals at a frequency corresponding to the input illuminance. The ADC has an advantage of wide dynamic range of illuminance because the signal charge accumulated in the PD is never saturated in principle.

Prototype sensors of 128 × 96 resolution were developed with 80-μm square pixel each and 10-μm diameter gold electrodes. The upper layer was assigned for the PDs and ADCs, and the lower was for the 16-bit pulse counters. The two wafers were bonded by an image recognition of infra-red camera, where we achieved alignment accuracy as high as 1 μm or better. We evaluated the sensor and confirmed an excellent linear output with a wide dynamic range of 96 dB, which corresponds to the 16-bit output of the pulse counter. Fig. 2 shows an example image captured by the developed sensor. We successfully demonstrated the operation of the pixel-parallel sensor without any pixel defects.

In summary, a pixel-parallel 3-D integrated CMOS image sensor with pulse-frequency-output A/D converters was developed by using direct bonding of SOI wafers and embedded gold electrodes. The developed process is promising for image sensors with ultimate performances and various More-than-Moore type devices.

References

[1] T. Haruta et al., ISSCC, p. 76, 2017.

[2] T. Kondo et al., Symp. VLSI Tech. Dig., p. 90, 2015.

[3] M. Goto et al., IEEE Trans. Electron Devices, 62 (11), pp. 3530, 2015.

[4] M. Goto et al., ECS trans., 61 (6), p. 87, 2014.

[5] M. Goto et al., IEDM, 4.2, 2014.

Figure 1
(Invited) a Strategic Approach for Co-Production of Ethylene and Hydrogen Via Electrochemical Non-Oxidative Deprotonation of Ethane
Authors: Ding Dong , Zhang Yunya , Wu Wei , He Ting
Published: February 2020

The shale gas revolution in the United States in recent years has resulted in an oversupply of methane and ethane, the major components of natural gas and natural gas liquids, respectively, and this trend will continue for the foreseeable future. Due largely to these cheap resources, e.g., the current price of ethane is less than 20 cents/gal, the chemical industry has moved manufacturing plants back to the United States, creating thousands of jobs, while enjoying healthy margins compared to international rivals that typically use more expensive oil-based naphtha as feedstock. However, the ethylene production from ethane or naphtha is energy intensive and represents the single most energy consuming process in the chemical industry. To fully exploit the potential of ethane as a feedstock, low-thermal-budget and low-carbon footprint processes are required. We demonstrated, for the first time, co-production of ethylene and hydrogen through an electrochemical non-oxidative deprotonation process (NDP) at 400oC, with an ethylene selectivity close to 100% and a hydrogen generation rate of 0.448 mol cm-2 per day. Compared to the commercial ethane steam cracking process, the NDP can achieve a 65% in process energy saving and reduce the carbon footprint by as much as 72% or even more (> 90%) if renewable electricity and heat are used. If the heating value of produced hydrogen is taken into account, the electrochemical deprotonation process actually has a net gain in processing energy.
(Invited) Flexible and Transparent Thermally Conductive Materials for Heat Dissipation of Electronics
Authors: Mehra Nitin , Ji Tuo , Zhu Jiahua
Published: February 2020

Heat dissipation problem is becoming a crucial barrier in the continuous process of electronic devices and systems miniaturization. Thermal management of devices and systems directly determines their efficiency and life time. In recent years, the rise of mobile device and touch screen applications has driven new research and development efforts into materials compatible with transparent and flexible design requirements. Existing research to develop thermally conductive polymer composite are based on traditional fillers (metal/ceramic/carbon) and matrix system which requires high loading of fillers and in turn suffers with various fabrication and property issues. In this talk, a new approach of engineering thermal transport channels via intermolecular interaction will be introduced. Thermal conductivity enhancement of around 2-3 times the neat polymer can be achieved without using any traditional fillers. The critical factor responsible for thermal conductivity enhancement was found to be the “thermal bridges” formed by hydrogen bonding between molecular species. These thermal bridges lead to the formation of continuous thermal highways for the efficient phonon transport. This talk presents a unique approach to engineer material interaction at molecular level and achieves macro-scale function as desired.
(Invited) 3D Printing Functional Materials & Devices
Authors: McAlpine Michael C.
Published: February 2020

The ability to three-dimensionally interweave biological and functional materials could enable the creation of bioelectronic devices possessing unique and compelling geometries, properties, and functionalities. Indeed, interfacing high performance active devices with biology could impact a variety of fields, including regenerative bioelectronics, smart prosthetics, medical robotics, and human-machine interfaces. Biology, from the molecular scale of DNA and proteins, to the macroscopic scale of tissues and organs, is three-dimensional, often soft and stretchable, and temperature sensitive. This renders most biological platforms incompatible with the fabrication and materials processing methods that have been developed and optimized for functional electronics, which are typically planar, rigid and brittle. A number of strategies have been developed to overcome these dichotomies. One particularly novel approach is the use of extrusion-based multi-material 3D printing, which is an additive manufacturing technology that offers a freeform fabrication strategy. This approach addresses the dichotomies presented above by (1) using 3D printing and imaging for personalized, hierarchical, and interwoven device architectures; (2) employing nanotechnology as an enabling route for introducing high performance materials; and (3) 3D printing a range of soft and nanoscale materials to enable the integration of a diverse palette of high quality functional materials with biology. Moreover, 3D printing is a multi-scale platform, allowing for the incorporation of functional nanoscale inks, the printing of microscale features, and ultimately the creation of macroscale devices. This blending of 3D printing, functional materials, and ‘living’ platforms may enable next-generation 3D printed devices.

Figure 1
(Invited) Micatronics: A New Platform for Flexible X-Tronics
Authors: Chu Ying-Hao
Published: February 2020

In the present era of ‘‘Internet-of-Things”, the demand for flexible, light-weight, low-cost, low-power consumption, multifunctional, and environmentally friendly electronics has moved to the forefront of materials science research. Numerous compounds with unique material properties in epitaxial thin film form hold key to future technologies. van der Waals epitaxy (vdWE) involving two-dimensional layered materials can play a crucial role in the expansion of thin film epitaxy by overcoming the bottleneck of material combinations due to lattice/thermal matching conditions inherent to conventional epitaxy. Among the layered materials, mica is a well-known phyllosilicate mineral that can have a remarkable impact on flexible electronics. We confine ourselves to the validity of vdWE of functional oxides on muscovite mica throughout this treatise. These heterostructures with excellent properties are flexible and exhibit high-temperature stability. With such demonstrations, it is anticipated that MICAtronics, vdWE on mica, can reveal unusual properties and emergent phenomena in the realm of high-performance flexible device applications.
SrTiO3/ZnO Heterostructure for Transparent and Flexible Photoelectrochemical Water Splitting
Authors: Wang Pei-Chun , Hsu Yung Jung , Chu Ying-Hao
Published: February 2020

Transparent and flexible applications have captured extensive attention recently due to the intriguing functionalities and great potential influencing our daily life. In addition, with the increasing demand for green energy, photoelectrochemical (PEC) water splitting, which is a clean process directly converting solar energy to chemical energy in the form of hydrogen, becomes much emphasized worldwide. In this work, we combine these two popular trends to develop a transparent and flexible PEC photoelectrode. We use pulsed laser deposition process to fabricate heterostructural SrTiO3/ZnO bilayer on flexible muscovite substrate. ZnO is a well-known material for PEC water splitting due to its good photoactivity and suitable band gap across the redox potential of water. SrTiO3 also has photocatalytic ability and highly photochemical stability as the surface protection oxide to enhance the retention of PEC performance. This combination not only shows good transmittance in visible light region but also exhibits superior performance on PEC activity. Furthermore, the photocurrent of SrTiO3/ZnO heterostructure under different bending condition is investigated. This study first demonstrates a pathway to flexible and transparent photoelectrode for developing innovative PEC devices on water splitting.
Design of Nanostructured Materials for Flexible Photothermal Energy Generation Functionalities
Authors: Ho Ghim Wei
Published: February 2020

Intensive efforts have been devoted to develop high-performance light-to-heat converting materials through delicate tuning of solar absorbing materials composition, design of multilayer coating, and engineering of surface structure to achieve high solar absorptance with low thermal emittance and optical reflectance. Here, an overview of materials (metallic and hybrid combination of organic-inorganic and metallic-semiconductor) designs with distinct photothermal conversion mechanisms will be presented. Essentially, these heat generating nanomaterials can be tailored with desirable photothermal actuation and energy generation functionalities through structural engineering and system design. Metamaterial coupled pyroelectric material, that performs synergistic waste heat rejection and photothermal heat-to-electric conversion will also be presented. Unlike any other pyroelectric configuration, this new conceptual design deviates from the conventional by deliberately employing back-reflecting NIR to enable waste heat re-utilization/recuperation to enhance pyroelectric generation, avoiding excessive solar heat uptake and also retaining high visual transparency of the device. Passive solar reflective cooling is realized and in the meanwhile enhanced photothermal pyroelectric performance capitalizing on the back-reflecting effect is validated. Finally, proof-of-concept for concurrent photothermal management and enhanced solar pyroelectric energy generation under a real outdoor environment is demonstrated.
Inertia Based in-Vivo Triboelectric Nanogenerator for Self-Powering Implantable Electronic Devices
Authors: Ryu Hanjun , Kim Sang-Woo
Published: February 2020

Huge amount of mechanical energy generated by continuous human motion usually is abandoned. Among technologies that convert such abandoned mechanical energy into reusable electrical energy, the triboelectric nanogenerators (TENGs) has many advantages. These TENGs can be used in electronics for human body implants, but the amount of mechanical energy (heartbeat, blood flow, muscle movement) generated inside the human body is very small and the amount of energy converted might be negligible. While, since TENGs are a power generation device using mechanical energy, research on application to the human body is still intensively ongoing worldwide. The highest mechanical energy potential of a person's movement is the mechanical energy due to the upward and downward movement that occurs when a person walks, and cannot be ignored if one adult walks more than 5,000 times a day. If devices capable of harvesting mechanical energy by up-and-down movements are developed, they can be operated as wearable, e-skin, and various sensors and device power supplies for implanted electronics and battery charging supporters. We have developed a device that is optimized based on inertial principle of mechanical energy generated when a person is walking. Assuming a displacement of about 6.3 cm when a person walked, the inertial-based TENG produced a voltage of about 220 V and a current of 45 µA in a single-layer device. Since the developed inertial-based TENG is very easy to be stacked, it can be stacked up to multiple layers, and the voltage characteristics of about 380 V and the current characteristics of 85 µA are reached in the three - layer stacked inertial-based TENG. To verify the feasibility of this level of inertial-based TENG as an energy source at a usable level, the output characteristics were verified by implanting live animals (dogs). In addition, the conversion of mechanical energy generated by the movement of the animal into electrical energy was verified in real time through the integrated Bluetooth. Our approach is expected to have a significant impact on a wide range of applications in biomedical biomedicine as a simple, cost-effective and high energy density output.
(Invited) Free-Standing Two-Dimensional Nanomaterials from Functional Oxides
Authors: Wang Xudong
Published: February 2020

Two-dimensional (2D) nanomaterials, particularly when their thickness is just one or a few atomic layers, exhibit physical properties dissimilar to those of their bulk counterparts and other forms of nanostructures. Nonetheless, 2D nanostructures so far have been largely limited to naturally layered materials, i.e. the van der Waals solids, synthesized either from top-down or bottom-up. A much larger and diverse portfolio of 2D materials including non-layered compounds are desirable to meet the specific requirements of individual components in various devices. We demonstrate that surfactant monolayers could serve as a soft template supporting the nucleation and growth of 2D nanomaterials in large area beyond the limitation of van der Waals solids. Through this approach, 1 to 2 nm thick, single-crystalline free-standing ZnO nanosheets with sizes up to tens of microns were synthesized at the water-air interface. This technique was denoted as the Adaptive Ionic Layer Epitaxy (AILE) – the first solution-based technique for growing large-area ultrathin nanosheets without the support of crystalline substrates. The nanosheet thickness was controlled by the initial ion concentrated zone (the Stern layer) formed underneath the negatively charged surfactant monolayer. While ZnO crystals are always an n-type semiconductor, the as-synthesized ZnO nanosheets exhibited a p-type semiconductor behavior with the highest hole mobility up to 10 cm2/Vs. Density functional theory (DFT) calculations revealed that absorption of the surfactant induces a p-type doping to the ZnO nanosheet and changes it to a direct bandgap p-type semiconductor. AILE is a major breakthrough in materials science. It vastly broadens the range of 2D nanomaterials from layered van der Waals solids to oxides, ceramics, and metals, opening up opportunities for discoveries of exciting transport, photonic, and catalytic properties. So far, in addition to ZnO, we have showed successful synthesis results from NiO, and CoO, MnO2. The new 2D nanomaterials enabled by AILE will lead to extraordinary performance gain or new functionalities in many scientific and technology disciplines, such as energy harvesting and storage, information systems, sensing, and optics.
Introduction to Performance Issues with Low Pt-Loaded Fuel-Cell Electrodes
Authors: Weber Adam Z.
Published: February 2020

To commercialize successfully polymer-electrolyte fuel cells (PEFCs), the cost must be reduced. Such cost reductions come about through simplification of balance of plant, increasing cell and stack durability and lifetime, improving cell performance, and, decreasing the cost of the cell components without sacrificing performance and lifetime. Of particular importance is this latter issue, where cell developers are trying to reduce the cost of the relatively expensive platinum-group-metal (PGM) catalysts [1]. As discussed previously, it is thought that current architectures and materials reach a limit, below which unacceptable performance losses are realized as the PGM loading is decreased [2]. To understand the genesis of these limitations, one must understand the key processes that occur during PEFC operation and measure the local resistances. In this talk, performance issues with low Pt-loaded PEFC catalyst layers will be introduced and possibly ways to mitigate them discussed. This talk will serve to explore some of the relevant issues and set the stage for following, more specific talks.

Acknowledgements

This work was funded under the Fuel Cell Performance and Durability Consortium (FC PAD) funded by the Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy.

References

[1] Fuel Cell Technologies Office Multi-Year Research, Development and Demonstration Plan, U.S. Department of Energy, 2013.

[2] A.Z. Weber and A. Kusoglu, ‘Unexplained transport resistances for

low-loaded fuel-cell catalyst layers,’ J. Materials Chemistry A, 2 (42), 17207-17211 (2014).
Identifying the Major Source of Oxygen Transport Resistance By Modeling Studies
Authors: Suzuki Takahisa , Yamada Haruhiko , Kudo Kenji , Jinnouchi Ryosuke , Morimoto Yu
Published: February 2020

The interface between a perfluorosufonic acid ionomer like Nafion and platinum, the electrocatalyst, has been attracting more and more attention in the studies on PEFCs recently because experimental and theoretical studies have been revealing that the interface has the dominant impact on the PEFC performance in both the high and low current density regions.

This tutorial lecture reviews those studies especially focusing on the theoretical and modeling studies and suggests key areas for further improvement.
Controlled Selectivity of CO2 Reduction on Metal Electrodes By Pulsing the Electrochemical Potential
Authors: Kimura Kevin Wayne , Suntivich Jin , Hanrath Tobias
Published: February 2020

We demonstrate a simple strategy to enhance the CO2 reduction reaction (CO2RR) selectivity by applying a pulsed electrochemical potential to a flat polycrystalline Cu electrode. By controlling the duration and magnitude of the cathodic and anodic pulses, we show that the selectivity for the CO2RR dramatically improves above 97% faradaic efficiency (FE) and consequently suppresses the competing hydrogen evolution reaction. Selectivity toward methane was found to be up to 83% FE – an unprecedented level of selectivity for a flat polycrystalline Cu electrode. The product output was also found to be tunable toward C2H4 and CO depending on the pulse profile applied. Here we investigate three alternate hypotheses and present evidence to disentangle the complex interplay of mass transport, surface coverage, and facet reconfiguration. We conducted CO reduction, rotating disk electrode tests, and in-situ XAS experiments, as well as coupled transport modelling to discern the exact mechanism. Additionally, to further understand the role of dynamic changes in the surface structure we tested CuO, Au, and Mo2C, which were found to also improve selectivity of products. These results show that pulsing dependence is not unique to Cu, but a more general phenomenon. Our findings provide new insights into the timescales of competing pathways. It also enables an opportunity to further improve the performance of next generation electrocatalyst materials.