bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystal Lattice Rearrangement Occurred at Au/Ag Bonded Interface in Atomic Diffusion Bonding in Vacuum
Authors: Goto Fuki , Iemura Hikaru , Uomoto Miyuki , Shimatsu Takehito
Published: February 2024

Atomic diffusion bonding (ADB) processing of wafers using thin metal films is a promising route to achieving room-temperature wafer bonding [1,2]. When two film surfaces mutually contact at room temperature during ADB, crystal lattice rearrangement occurs, thereby enhancing the bonding performance. Generally, films of the same material used for bonding are fabricated on two flat wafer surfaces. Therefore, methods for examining the crystal lattice rearrangement mechanism are few. Two representative material films used for bonding, those of the metals Au and Ag, have fcc crystal structure and show a solid solution in the whole Au–Ag composition range. Moreover, lattice mismatch of these materials is very slight: less than 0.2%. For this study, Au film and Ag film were bonded in vacuum using ADB. The crystallographic structure of Au/Ag bonded films and depth profiles of Au and Ag atoms were examined.

Au and Ag films were fabricated respectively on two flat wafer surfaces using sputter deposition, followed by bonding of the two films on the wafers in vacuum. Figure 1 portrays cross-section STEM images of Au(20 nm)/Ag(20 nm) bonded films: (A) a bright field image, and (B) an HAADF image corresponding to (A). Films were deposited on Si wafers, with 5-nm-thick Ta films underneath. Figure 1(A) shows that no interface corresponding to the original Au/Ag interface is visible; no vacancy is observed. Grains were formed continuously across the original interface over the entire thickness of the bonded films, indicating that crystal lattice rearrangement occurred at room temperature when the films mutually contacted in vacuum. Although the crystallographic structures of Au and Ag layers are identical because of the crystal lattice rearrangement, the contrast between the upper and lower half areas in Figure 1(B) is expected to be attributable mainly to the different atomic weights of Au and Ag. Figure 2 presents the depth profiles of Au, Ag, and Ta evaluated using EELS analysis along line (a) in Figure 1(B). Results supported that interdiffusion at the Au/Ag bonded interface is not remarkable. This report presents discussion of the relation between crystal lattice rearrangement and interdiffusion of atoms based on results of analyses of Au/Ag bonded films with various layer structures.

T. Shimatsu and M. Uomoto, J. Vac. Sci. Technol., B 28, 706 (2010).

T. Shimatsu and M. Uomoto, ECS Trans., 33 (4), 61 (2010).

Figure 1
(Invited) Exciton Transport in Strained 2D Semiconductors
Authors: Michaelis de Vasconcellos Steffen , Schmidt Robert , Rosati Roberto , Brem Samuel , Perea-Causín Raul , Niehues Iris , Kern Johannes , Preuß Johann , Schneider Robert , Malic Ermin , Bratschitsch Rudolf
Published: February 2024

Being atomically thin, flexible, and exhibiting considerable light emission and ultrafast non-equilibrium dynamics, semiconducting transition metal dichalcogenides (TMDs) have been considered as promising candidates for next-generation optoelectronic devices. The optical and electronic properties of TMDs are governed by a rich landscape of tightly bound excitons, including regular bright excitons, as well as optically inaccessible dark exciton states. Recently, strain engineering of monolayer TMDs has been introduced to tune their optical properties, such as the exciton transition energy, exciton-phonon coupling, or the Stokes shift [1-3].

Transport of charge carriers is crucial for nanoelectronics. In conventional materials, electronic transport can be conveniently controlled by external electric fields. However, the tightly bound excitons, being neutral particles, are only weakly affected by electrical fields. We demonstrate that mechanical strain can also be used to manipulate the transport of excitons in TMDs. To this end, we apply homogeneous tensile strain to a WS2 monolayer by bending the substrate [1], which causes a redshift of the X0 exciton photoluminescence. By measuring the spatiotemporal photoluminescence after near-resonant excitation with femtosecond laser pulses, we map the spread of excitons and extract the strain-dependent diffusion coefficient [4].

Furthermore, we demonstrate the propagation of excitons in an inhomogeneous strain landscape. We create inhomogeneous tensile strain in TMD monolayers by transferring them onto patterned substrates with nanopillars or by a nanoimprint technique [5]. Due to the redshift of the exciton resonances with applied strain, excitons are expected to move towards high-strain regions in an inhomogeneous strain field - the so-called "funneling" effect. We verify this behavior for the "bright" TMD material monolayer MoSe2. In the case of the "dark" monolayer WS2, we observe exactly the opposite effect. Here, the excitons are expelled from the high-strain regions ("anti-funneling") [6]. By comparing our experimental results with a microscopic theory, we explain this observation by the drift of momentum-dark KΛ excitons, which, in contrast to bright excitons, shift to higher energies with strain.

Our joint experiment-theory study highlights the dominant role of momentum-dark excitons for the dynamics in monolayer TMDs and provides crucial design guidelines for TMD devices based on exciton transport. References [1] J. Roldan et al., Journal of Physics: Condensed Matter 27, 313201 (2015) [2] I. Niehues et al., Nano Letters 18, 1751 (2018) [3] I. Niehues et al., Nanoscale 12, 20786 (2020) [4] R. Rosati et al., 2D Materials 8, 015030 (2021) [5] J. Bensmann et al., arXiv:2212.11873 (2022) [6] R. Rosati et al., Nature Communications 12, 7221 (2021)
Simultaneous Piezoelectrocatalytic Hydrogen-Evolution and Degradation of Water Pollutants By Quartz Microrods@Few-Layered MoS2 Hierarchical Heterostructures
Authors: Lai Sz-Nian , Lin Yu-Ting , Wu Jyh Ming
Published: February 2024

Intense light attenuation in water/wastewater results in photocatalysts exhibiting a low quantum efficiency. This study develops a novel piezoelectrocatalysis system, which involves quartz microrods (MRs) abundantly decorated with active edge-sites MoS2 nanosheets to form quartz microrods@few-layered MoS2 hierarchical heterostructure (QMSH). Through theoretical calculations, quartz MR serves as a parallel-plate capacitor, which is self-powered to provide an internal electric field to the few-layered MoS2 nanosheets surrounding the quartz MR surfaces, and the piezoelectric potential (piezopotential) effectively facilitates redox reactions with the free carrier in MoS2. The self-powered quartz MRs in QMSH present an internal bias to the MoS2 nanosheets, thus yielding a piezoelectrocatalysis system. An efficient piezoelectrocatalytic hydrogen evolution reaction (HER) and decomposition of wastewater without light irradiation could achieve simultaneously. The second-order rate constant of QMSH is approximately 0.631 L mg-1min-1, which was 650-fold that of quartz MRs, indicating that the piezoelectric heterostructural catalysts display exceptionally high efficiency on piezo-electrocatalytic redox reactions rather than in the peizocatalytic process. The H2-production rate of QMSH catalysts approached approximately 6456 μmo1·g−1 h−1 and peaked at approximately 16.8 mmol g−1 in 8 h. The piezoelectrocatalytic process may be a promising method for treating industrial wastewater and producing clean energy.
(Invited) Metal Halide Perovskite Heterostructures: Synthesis and Fundamental Charge Transfer Studies
Authors: Jin Song
Published: February 2024

Metal halide perovskites are inexpensive semiconductor materials promising for high performance solar cells and light emitting diodes (LEDs) because they are easy to synthesize and tolerant of defects. Fundamental understanding of the factors controlling the carrier transfer mechanisms in heterostructures of halide perovskites is crucial for guiding the synthetic strategies to improve properties and device applications. We developed new methods for synthesizing nanostructures of both three-dimensional (3D) perovskites and two-dimensional (2D) Ruddlesden–Popper (RP) layered perovskites, and using them to create novel and arbitrary heterostructures, such as 2D/3D perovskite, vertical and lateral 2D heterostructures, with high quality interface and tunable band alignments. Various structural characterization and time-resolved spectroscopic methods have been employed to collaboratively study the carrier transfer mechanisms between these well-defined heterostructures of 2D and 3D perovskites. These diverse families of perovskite materials and their nanostructures and heterostructures can enable high performance solar cells, lasers, LEDs, and spintronic applications.
(Invited) Nanoscale Devices for Accelerating AI Algorithms
Authors: Kapadia Rehan , Ahsan Ragib , Chae Hyun Uk , Tao Jun
Published: February 2024

The energy consumption of training and deploying state-of-the-art artificial intelligence (AI) models has experienced exponential growth, driven by increasing model parameters and the necessary training data. Recent models demand over 1 billion PetaFLOPs of total computation for training, potentially taking weeks to complete. With current GPU performance at approximately 1-3 TOPS/W, GPU training energy consumption alone can exceed 100,000 kWh, equivalent to the monthly energy expenditure of 100 US households. Over the next decade, these models are expected to scale up further, driving total computing energy to constitute a significant portion of global consumption. In this talk, we describe both synaptic and neuronal devices that can accelerate AI algorithms with potentially multiple orders of magnitude improvement in power efficiency.

First, we describe an oscillatory retinal neuron (ORN) that directly converts incident DC light into voltage spikes. Coupled arrays of this device result in an imager that carries out in-sensor processing while capturing an image. Uniquely, the conversion from input light to output voltage spikes occurs without external power. When coupled in arrays, the neighboring neurons interact with each other to influence the spiking frequency spectrum. This allows the arrays to carry out frequency multiplexed computation on an input image. It is shown that this approach can achieve>20,000 TOPS/W, multiple orders of magnitude greater than the current approaches. Theory and simulation is used to elucidate how coupled ORNs carry out computation on an input image. When coupled, each output frequency band encodes a unique computation on the input image. By tuning the coupling impedances and the frequency bands, user defined computations can be carried out on the input. We experimentally show that this can be carried out with a 3x3 array that demonstrates simultaneous edge detection, intensity filtering, image segmentation and other functions. This hardware is then used to demonstrate improvement in MNIST handwritten digit classification accuracy over a traditional imager connected to a fully connected network.

Next, we describe spiking synaptic devices that can be directly fabricated in the back-end of line of CMOS devices. These devices consist of an InP transistor channel with an engineered gate stack. Using a uniform gate insulator, we can demonstrate behaviors of biological synapses, such as potentiation, depression, spike number dependent plasticity, and spike timing dependent plasticity. By introducing a heterostructured gate insulator, it is shown that short-term to long-term memory transitions can be designed into the device. Finally, by using a transparent gate, an in-sensor synaptic phototransistor is demonstrated and the performance of these devices at a system level is demonstrated.
(Invited) Three-Dimensional Filter of Polyvinylidene Difluoride (PVDF) Implanted Rice Husk-Derived Silicon Dioxide of Porous Solid-State Electrolytes
Authors: Liang Tzu Yun
Published: February 2024

Lithium-ion batteries are the most promising energy storage devices in the battery technology field. They are widely used for numerous advantages, such as high energy density, fast charging, and being environmentally friendly. Lithium metal as an anode is highly attractive among different electrode materials because of its extraordinarily high specific capacity. However, lithium metal is prone to form dendrites during the battery charging process. Unfortunately, the conventional battery composed of flammable organic liquid electrolytes fails to suppress the lithium dendrite formation. The lithium dendrite thus penetrates the separator, causing battery short and bringing about explosions and catastrophes. Solid-state electrolytes (SSEs) have recently attracted much attention due to their higher energy density, wide electrochemical stability window, and longer cycle life. In addition, SSEs are mechanically more robust, suppressing the lithium dendrites formation. Therefore, replacing liquid electrolytes with solid-state electrolytes is an effective strategy to resolve safety concerns. To increase the mechanical strength of the SSEs, in this work, we report a three-dimensional filter-network-reinforced SSEs with a porous polyvinylidene difluoride (PVDF) filter host, polyethylene glycol (PEG) matrix with bistriﬂuoromethanesulfonimide lithium salt (LiTFSI) and rice husk-derived silicon dioxide (RHSiO2) as a passive filler. Rice husk-derived silicon dioxide possesses many superiorities, such as low-cost, easy processing, and non-toxicity. The mechanically robust PVDF filter helps to improve the mechanical property (tensile strength > 5 MPa) and prevents dendrite penetration, which raises thermal and mechanical stability. At room temperature, the ionic conductivity of the 5wt% SSE reach 1.110-4 S cm-1. The battery with 5wt% RHSiO2 SSE enabled stable cycling for over 300 hr during the Li plating and stripping process, demonstrating that the PVDF filter host SSEs with RHSiO2 is promising for the high-safety energy storage systems.
(Poster Award - 3rd Place) Photocatalysis of TiO2 Nanosheets Prepared by the Cellulose Nanofiber Template
Authors: Chen Yu-Ching , Wu Jyh Ming
Published: February 2024

Two-dimensional material inspired tremendous research interest by its unique structure and specific property different from bulk material, which could benefit various applications such as optics, electronics, and chemistry. However, most documented processes for 2D materials are complicated with a lengthy process. We introduced the cellulose nanofiber (CNF) extracted from agricultural waste rice straws, which inherently possesses many functional groups, e.g., hydroxyl group, and carboxylate group, making it a terrific template method candidate. Besides, aerogel composed of cellulose nanofiber provides many surface and layered structures that facilitate the adhesion of titanium isopropoxide to form a uniform coating layer, which hydrolyzed to TiO2. The cellulose nanofiber serves as a template and could be removed entirely in an easy thermal process by thermogravimetric analysis; meanwhile, we can transform the original amorphous TiO2 nanosheet into an anatase phase which is flavored in the photocatalyst field. Atomic force microscopy (AFM) results spotted a stacked ultrathin TiO2 nanosheet with a thickness of less than 5 nm for each layer, and the lateral size could reach micron size. For the RhB dye degradation test, TiO2 nanosheets could decompose the 10 ppm RhB solution within 30 mins with a reaction rate of 0.065 min-1. In conclusion, we combine the CNF template and hydrolysis process, proposing a simple 2D TiO2 nanosheets
(Invited) Transparent Conductive Films of PEDOT:PSS-Amino Acid Composite
Authors: Adhikari Ramesh Y. , Chamria Div , Kutlubas Ege
Published: February 2024

Transparent conductive electrode is an important component of optoelectronic devices such as light emitting diodes, photodiodes, and photovoltaic cells as well touchscreen technology. Growing demand for these technologies, as well as need for functionalities such as cost-effectiveness and flexibility, has resulted in various research on developing organic polymer-based transparent electrodes as an alternative to indium tin oxide (ITO) which is the current industry standard. One of the organic conducting polymers most commonly studied for their potential to be used as ITO-free transparent electrodes is PEDOT:PSS due to its high transmittance as a thin film, solution processability, flexibility, environmental stability, and commercial availability. There have been various works carried out to improve the conductivity of the PEDOT:PSS-based thin films by introducing dopants to improve the charge transport. We present our results demonstrating that not only the conductivity but also the transmittance of PEDOT-PSS-based films can be significantly improved by the introduction of amino acids such as phenylalanine in the film. We have observed that this enhancement in conductivity and optical transmittance of PEDOT:PSS-phenylalanine composite film is retained even when the amount of amino acid in the composite films is larger than the amount of PEDOT:PSS. We will present our study on the charge transport mechanism on these films based on electrochemical impedance spectroscopy (EIS) measurements. We will also further present our studies based on Scanning Electron Microscopy (SEM) as well as Scanning Probe Microscopy techniques such as topography imaging and conducting probe atomic force microscopy (CP-AFM) to elucidate the relationship between film morphology and charge transport in these composite films. The use of bioderived materials such as amino acids to create transparent composite films could open up avenues for developing and integrating bio-based materials in future electronics, help improve the environmental footprint of the electronics, and potentially also allow for the development of materials with a higher degree of biocompatibility for their application in bioelectronics.
(Invited) Safety of Li-Ion Batteries: Current Challenges in a Policy Context
Authors: Pfrang Andreas , Adanouj Ibtissam , Bruchhausen Matthias , Da Costa Barata Ricardo , Hildebrand Stephan , Lazareanu Mircea , Leite Patrão Rafael , Lebedeva Natalia
Published: February 2024

Batteries are a key technology required to meet our objective for climate neutrality, to reduce dependency on fuel imports as well as to ensure maximum use of renewable electricity. Over 80 GW / 160 GWh of stationary batteries and over 50 million electric vehicles are expected in the EU by 2030. Lithium-ion batteries are expected to dominate the market well beyond 2030, while developments in other technologies will continue in parallel. Battery-related policies are currently of high interest and have to evolve quickly in order to facilitate and accommodate technological progress.

With increasing numbers of electric vehicles and batteries in operation and the parallel rise of energy density in lithium-ion batteries, risks related to battery safety e.g., through battery fires, increase. The Joint Research Centre (JRC) carries out research on battery safety to support policymaking and develop fit-for-purpose testing methodologies: the recently proposed Batteries Regulation, aiming at a sustainable battery value chain, foresees new safety requirements for stationary batteries. Another example is the Global Technical Regulation on Electric Vehicle Safety, where a thermal propagation test procedure is being developed with international partners.

In this context, thermal runaway initiation methods and criteria for thermal runaway events had been analysed. A rapid heating method and suitable criteria for thermal runaway were applied in a thermal propagation test campaign on full electric vehicles and corresponding battery packs. While a high degree of reproducibility was observed, a difference in severity between pack and vehicle-level tests was found, and gas emissions from the tests are currently being analysed.

Figure 1
Modeling and Analysis of Coupled Thermal and Mechanical Capacity Degradation in Silicon-Based Lithium-Ion Batteries
Authors: Mishra Lubhani , Subramaniam Akshay , Garrick Taylor R. , Subramanian Venkat R.
Published: February 2024

Large-format cells are gaining popularity for battery electric vehicles (BEVs) to maximize volumetric and gravimetric energy densities but are associated with challenges in ensuring adequate thermal management. Spatial current density and temperature variations negatively affect overall cell utilization and lifetime.In addition, the mechanical stresses generated within the silicon-based battery electrodes also cause aging and resultant capacity loss. The coupled effects of the thermal and mechanical factors could thus particularly exacerbate cell capacity degradation. Rigorous mechano-thermo-electrochemical models for battery degradation can be a powerful complementary tool to understand these phenomena better. Simulating performance scenarios can significantly improve cell design and experimentation while reducing time and cost commitments. Model-based design approaches thus have the potential to yield substantial economic benefits.

This work shall serve as an extension to the previously developed thermal degradation model for non-uniform aging in lithium-ion batteries by coupling with mechanical models predicting the effects of volume change within the batteries over cycling. The observed capacity fade trend for a given battery is ultimately the result of an interplay between multiple degradation mechanisms, which depend on a range of design and operating parameters. The errors between the model predictions and experimental data can provide information on the suitability of a given model and the relative prevalence of a given degradation mechanism, with functional and practical benefits, as there exists significant variation in the parameters, mechanisms, and predictive capability of models in the literature. In addition, a rigorous model of volume changes increases the accuracy of predictions of dynamic stress-strain profiles, which in turn helps improve predictions of associated mechanical degradation phenomena. As a first step towards including mechanical effects, the current model builds on the previously reported studies for modeling volume change in porous electrodes due to intercalation (deintercalation) during lithiation (delithiation). This volume change leads to dimensional and porosity changes in the porous electrodes. Furthermore, these mechanical models will help predict generated stresses and strain profiles within the battery and will be related to models of resultant degradation, especially in the case of silicon/graphite electrodes characterized by substantial volume changes.
Swelling of Polypropylene Separators and Its Effect on the Lithium-Ion Battery Performance
Authors: Gor Gennady , Maksimov Andrei V , Maksimova Olga , Molina Marcos
Published: February 2024

The safety of lithium-ion batteries (LIBs) depends on separators -- porous materials providing ionic transport between the electrodes while preventing them from direct contact. Many commercial separator materials are polymers, e.g., polypropylene. Polypropylene has a non-polar structure, so it tends to interact favorably with non-polar solvents, such as carbonates used in LIBs as electrolyte solvents. These favorable interactions result in two effects: separator plasticization (softening) [1] and swelling [2]. Both swelling and plasticization affect the battery performance and cause safety concerns.

Here we present a model which predicts the swelling of a porous polymer separator based on the molecular structures of the polymer and the solvent. The model is based on Flory's theory of polymer solutions and the Flory–Huggins parameter for polymer–solvent interactions. We introduced two additional parameters to Flory's theory, taking into account the complex structure of the porous polymers. These two parameters can be obtained from experimental data on two solvents. The Flory–Huggins parameter is calculated based on the UNIFAC-FV group contribution method for a given polymer–solvent pair. Our model predicts swelling of polypropylene separators in various solvents, matching the experimental data [3] quite well. By relating the swelling of the separator to the change in its porosity and tortuosity, we estimated the increase of cell impedance as a result of the swelling.

Finally, the plasticization of the separator makes it less persistent to mechanical impacts, increasing the chances of failure. Since the solvent-induced plasticization of the separator is correlated with its swelling [3], our model can also be utilized to assess this effect. Therefore, our model can be used to quickly evaluate various polymer–solvent pairs for application in lithium-ion batteries.

1. Sheidaei, A.; Xiao, X.; Huang, X.; Hitt, J. Mechanical behavior of a battery separator in electrolyte solutions. J. Power Sources 2011, 196, 8728−8734.

2. Cannarella, J.; Liu, X. Y.; Leng, C.; Sinko, P.; Gor, G. Y.; Arnold, C. B. Mechanical properties of a battery separator under compression and tension. J. Electrochem. Soc. 2014, 161, F3117−F3122.

3. Gor, G. Y.; Cannarella, J.; Leng, C. Z.; Vishnyakov, A.; Arnold, C. B. Swelling and softening of lithium-ion battery separators in electrolyte solvents. J. Power Sources 2015, 294, 167−172.

4. Maksimov, A. V.; Molina, M.; Maksimova, O. G.; Gor, G. Y. Prediction of Swelling of Polypropylene Separators and Its Effect on the Lithium-Ion Battery Performance. ACS Appl. Polym. Mater. 2023, 5(3), 2026-2031.
Understanding Internal Short Circuit Caused Thermal Runaway of Li-Ion Cells through in-Situ Diagnosis
Authors: Liu Siyi , Long Mary K , Zhang Guangsheng
Published: February 2024

Internal short circuit (ISC) caused thermal runaway of Li-ion batteries has been a challenge for decades due to difficulties in prevention and early detection of ISC. This challenge becomes increasingly urgent in recent years with the rapid growth of electric transportation industries which demand large-format, high-energy-density and fast-charging Li-ion batteries. Various ISC triggering methods have been developed to evaluate failure behaviors and advance safety designs of Li-ion cells and batteries. However, in-situ diagnosis is often overlooked in many ISC triggering methods and tests. Considering that ISC is a highly localized and transient phenomenon, in-situ diagnosis is important in understanding if and how an ISC triggers thermal runaway. In this presentation, our work on triggering ISC while simultaneously monitoring critical ISC parameters, such as ISC current, ISC resistance and ISC temperature, will be discussed to demonstrate the importance of in-situ diagnosis in understanding ISC and thermal runaway of Li-ion cells.
Operando Ultrasonic Characterization of Lithium Metal Batteries
Authors: Chang Wesley
Published: February 2024

Significant progress has been made in understanding and engineering rechargeable lithium metal batteries. Here, I discuss ultrasound as a technique to probe cell-level dynamics for lithium metal batteries in liquid and solid electrolytes. Multiple imaging modalities provide information on physical properties of lithium metal cells, including electrode wetting and consumption, lithium microstructural change and gas evolution. In a first case study, I discuss correlations between ultrasonic transmission signals and lithium microstructure size in liquid electrolytes, as a function of stack pressure and temperature. Anode and cathode effects can be decoupled. In a second case, acoustic amplitude is used to detect void formation in solid-state electrolytes. Third, ultrasound is used to characterize the formation process for various anode-free cells, where the improved chemical and electrochemical stability of localized ether electrolytes is correlated with decreased rates of cell swelling and minimal gas formation. Ultrasonic characterization and imaging is a portable and non-invasive means of probing commercial lithium metal cells after manufacturing, during use, or at the end-of-service.
All-Solid-State Battery Safety Investigation in Calorimeter Coupled with Fast X-Ray Radiography
Authors: Charbonnel Juliette , Darmet Natacha , Deilhes Claire , Broche Ludovic , Reytier Magali , Thivel Pierre Xavier , Vincent Remi
Published: February 2024

All-solid-state battery (ASSB) are expected to be a solution to increase energy density in Li-ion technology. However, high-energy storage capacities make the safety a crucial issue. The main reactions leading to thermal runaway in conventional LiB are anode/electrolyte at 110 °C, electrolyte decomposition at 150 °C and cathode/electrolyte at 300 °C. Therefore, without liquid electrolyte, it can be expected that ASSB are less likely to have a thermal runaway.

To assess safety of such non-fully mature battery technologies, a new methodology is proposed and a closed calorimeter was designed to perform operando experiments in abuse conditions with high-speed synchrotron X-ray radiography and measurement of temperature, pressure and energy. The data and image of thermal runaway of all-solid-state batteries are presented and compared to the result of Li-ion batteries with liquid electrolyte. An 11 % decrease of heat release was measured for cell with solid electrolyte. Gas volume, amount of matter that reacts in the cell and reaction kinetics have also been compared.

Such a methodology allows deepening hypotheses on associated material degradation and that can assist in development of new battery technologies, by evaluating battery safety from the start of the design from battery composition to cell shape.
Linking Microstructure Modeling of Lithium-Ion Batteries during Rapid Charging to System Performance
Authors: Teel Hunter , Lopata Joseph Steven , Garrick Taylor R. , Wang Fengkun , Zhang Han , Zeng Yangbing , Shimpalee Sirivatch
Published: February 2024

Battery models can be used to predict conditions ripe for lithium metal plating in the anode during rapid charging. One common procedure is to simulate a rapid charge using a pseudo-two-dimensional (P2D) model and determine if and when the minimum local potential reaches 0.0 V with respect to metallic lithium in the anode. This normally occurs at higher states of charge during a DC fast charging or rapid regenerative charging event. However, we have recently determined that three-dimensional (3D) models, while broadly agreeing with P2D results, demonstrate much variation in the in-plane and through plane direction, which P2D models cannot resolve. Because P2D models employ effective medium approximations, any “local” value in the P2D space along the through-plane coordinate represents an average across a slice of the domain. Therefore, it may be insufficient to use minimum anode potentials from P2D models as indicators of local plating and may only be representative of global lithium plating onset.

The results of rapid-charge 3D microstructure simulations are compared to P2D results [1,2]. This allows us to verify whether rapid charging induces negative local potentials at the anode active material surface that are left undetected in a P2D model. The expected result implies that the 3D microstructure model is necessary to predict the onset of lithium plating. We then extend our previous study to look at the impact of design changes on the microstructure performance, and then link the microstructure performance changes to performance metrics at the battery cell, module, pack, and vehicle level.

References

J. S. Lopata, T. R. Garrick, F. Wang, H. Zhang, Y. Zeng and S. Shimpalee, ECSarXiv (2022).

J. S. Lopata, T. R. Garrick, F. Wang, H. Zhang, Y. Zeng and S. Shimpalee, J Electrochem Soc, 170, 020530 (2023).
Comprehensive Analysis of Performance Evolution and Failure Mechanisms for Commercial Large-Format NMC-Gr Lithium-Ion Pouch Cells
Authors: Gasper Paul , Thakkar Foram , Sunderlin Nathaniel , Saxon Aron , Schiek Andrew , Finegan Donal P. , Smith Kandler
Published: February 2024

With the accelerating adoption of lithium-ion battery systems, careful analysis of the performance evolution and failure mechanisms of commercially produced batteries is crucial for predicting the lifetime of battery systems, estimating operating and maintenance costs, and ensuring safe operation. Here, we present the results of a 2-year aging study conducted on large-format NMC-Gr pouch cells from a large battery manufacturer. Calendar and cycle aging tests were conducted on 23 cells, with calendar aging conducted at varying temperature and state-of-charge, and cycle aging conducted at varying temperatures, average voltage, voltage window, charge-discharge rates, using both constant-current cycling and drive cycles.

The evolution of cell performance throughout aging was observed using electrochemical characterization tests. DC pulses show a general trend of decreasing then increasing resistance, while EIS measurements are used to deconvolute resistance evolution modes. Capacity checks show decreasing capacity throughout life for all cells. Fitting of C/20 charge and discharge curves using half-cell voltage data is used to quantify loss of lithium inventory and loss of active material degradation modes, as well as reveal the de/lithiation window experienced by electrodes throughout aging.

While cell performance evolution is often neatly explained by a few key degradation modes, cell failures observed during testing were often the result of several interacting degradation mechanisms. Degradation mechanisms were identified by a variety of physical, electrochemical, and microstructural characterizations. Key degradation mechanisms observed were SEI growth at graphite/electrolyte interfaces, electrolyte decomposition and gassing leading, NMC particle cracking, Li plating, and electrode dry-out. Degradation mechanisms observable in early life often initiate new failure mechanism that lead to cell failure or safety concerns through physical or electrochemical interactions. The findings demonstrate the multi-faceted challenge of cell lifetime and failure prediction in real-world systems.
(Invited) Challenges in Fabricating and Scaling up Silicon Carbide Wafers and Devices
Authors: Das Hrishikesh , Kostelnik Petr , Kocian Karel , Novak Tomas , Domeij Martin , Sunkari Swapna , Justice Joshua
Published: February 2024

Silicon Carbide is rapidly growing in the power electronics industry. This is fueled to a great degree by the adoption of electric cars and power electronics needed both inside the vehicle and to support the charging infrastructure. This attention from automotive industry comes with a clear spotlight on the cost, quality, and efficiency of SiC power devices. This in turn results in intense pressure and scrutiny to improve yields and reduce defects in every part of the manufacturing chain. There is a wide release and proliferation of Diode and MOSFET devices from various companies in the marketplace. Several companies are investing billions of dollars in capacity expansions driving exponential growth of wafers and devices.

In this review, we will discuss the steps and processes of fabricating a SiC wafer including crystal growth, wafering, epitaxy and device fabrication. The process challenges associated with the steps unique to SiC will be highlighted with a perspective on scaling up volumes and the transition to 200mm wafers. New innovations at some of the steps are enabling higher efficiency and output. The impact of these innovations will be presented. In addition, defects at each step of the process will be reviewed along with how they interact with the following steps [1]. Finally, the effect of various processes and defects on devices and reliability will be presented [2,3].

References:

H. Das, et. al., Mater. Sci. Forum, Vol. 1004, pp 458-463, (2020)

T. Neyer et. al., 2021 IEEE International Reliability Physics Symposium (IRPS), pp. 1-6, (2021)

S. Kochoska et. al., Mater. Sci. Forum, Vol. 1062, pp 554-559, (2022)
(Invited) Effect of Seed Crystal Orientation on Ammonothermal Growth of GaN
Authors: Valenzuela Jonny , Pimputkar Siddha
Published: February 2024

Gallium nitride (GaN) is a wide bandgap semiconductor which has received widespread attention as it has enabled the development of short wavelength (UV, blue) optical emitters and promises a new generation of high efficiency power electronic devices. To enable widespread use of high power, high efficiency devices, the availability of large-area, inexpensive, low-defect-density GaN substrates is necessary.

The ammonothermal method is a bulk, single crystal growth method which has demonstrated growth of high structural quality GaN boules greater than 2 inches in diameter. Despite these demonstrations, challenges remain with regards to improving growth rates to reduce cost of boules and understanding the growth behavior of GaN in these environments to further improve upon crystal quality. In particular, the general trend and affect of the GaN seed crystal on growth rates and crystal quality has not been studied in detail.

This talk will discuss our current understanding of how the initial seed crystal orientation affects the resulting ammonothermal GaN growth, surface morphology, crystal quality, and impurity incorporation. Seed crystals were sourced from hydride vapor phase epitaxial (HVPE) grown GaN boules that were sliced and polished to atomically smooth crystallographic facets of varying orientations. Three series were created resulting in incrementally changing orientations ranging from +c-plane to m-plane to -c-plane, from +c-plane to a-plane to -c-plane and from m-plane to a-plane.
(Invited) Application of 3D in-Situ X-Ray Visualization to Track the Formation of Dislocation Clusters during PVT Growth of SiC
Authors: Wellmann Peter , Strüber Sven , Steiner Johannes , Ihle Jonas , Schultheiss Jana , Nguyen Binh Duong , Sandfeld Stefan , Salamon Michael , Uhlmann Norman
Published: February 2024

SiC has become the key player among wide bandgap semiconductors for power electronic applications. Since the first description of the physical vapour transport (PVT) growth process of SiC by Tairov and Tsvetkov (J. Crystal Growth, 43, 209(1978)), there has been steady progress in SiC-based crystal growth, epitaxy and device processing. The success of SiC compared to Si is related to its superior material properties such as extremely high electrical breakdown field and high thermal conductivity compared to the standard silicon counterpart. In addition, SiC device processing utilises much of the standard Si processing equipment. A major reason for the success of SiC in power electronic applications compared to other wide bandgap counterparts such as GaN, Ga2O3 and diamond is related to the availability of large diameter SiC wafer materials (150mm = standard, 200mm = developped). Bulk SiC growth is now a very well developed process with comparatively high yields. The extraordinary physical properties also include obstacles related to the strong chemical bonding and complex phase diagram of the material, which pose challenges to the growth process. Therefore, there are still a number of open questions related to the nucleation, progression and termination of the bulk growth process that require fundamental research in materials science and technology.

The aim of this presentation is (i) to give an overview of the state-of-the-art PVT growth process and (ii) to discuss a current research topic dealing with the early stage of the growth process and the defect formation that can occur during the initial nucleation of SiC. We have applied 3D in-situ visualisation of the growth process using X-ray computed tomography to visualise island formation on the large seeding area. These data are related to growth process instabilities such as temperature variations during the seeding process and axial doping level changes from the seed to the newly grown crystal. Both process instabilities induce mechanical stress on the SiC lattice and act as sources for dislocation generation and multiplication. We will show a series of growth processes with varying growth parameters that shed light on the initial growth stage of SiC.

As the crystal diameter of SiC increases from 150 mm to 200 mm, the results of this study become increasingly important.
The Correlation between the Microstructure and the Characteristic Luminescence in the High Crystalline α-Ga2O3 Grown on the Thin-Wall Single Crystal Al2O3
Authors: Lee Yong-Hee , Yang Duyoung , Gil Byeongjun , Sheen Mi-Hyang , Yoon Euijoon , Park Yongjo , Jang Ho Won , Yoon Sangmoon , Kim Miyoung , Kim Young-Woon
Published: February 2024

A high-quality alpha-Ga2O3 thin film was grown on an Al2O3 single-crystal thin-wall channel structure. Alpha-Ga2O3 crystals are grown with a 3-fold symmetry template provided by the Al2O3 surface, which forms domain boundaries from the small rotation of the mosaic structure. The anti-phase domain (APD) was confirmed by convergent-beam electron diffraction (CBED), and it is believed to be developed at the stage of nucleation based on the unstable, or uneven Al-O bonding on the Al2O3 surface. The in-phase domain and the APD boundaries exhibit bright contrast in ADF, which originates from a local strain of crystallographic rotation and not from the local elemental fluctuations of gallium. As confirmed by CL measurement in TEM, the bandgap energy of alpha-Ga2O3 is inferred to be 5.56 eV with a near band edge transition of ~ 223 nm. Even though the heights and positions of peaks vary slightly from area to area, 4 distinct luminescence peaks and a long tail of wavelength are commonly observed throughout the crystal. 2-dimensional mapping with the specific wavelength window reveals a clear difference between the inside domain, in-phase domain boundary, and APD boundary. A luminescence peak of distinct 350 nm was observed at the APD boundary. Misorientation between domains was found, which leads to an in-plane mismatch in crystallographic lattices at the boundary when the two misoriented domains grow and the growth front merges. The imperfect lattice structure at the boundary is believed to create strain and intermediate states.
High Reliability Tungsten-Doped Indium Zinc Oxide Thin Film Transistors for Display Applications
Authors: Deng Jing-Zhong , Chiang Tsung-Che , Li Zhen-Hao , Liu Po-Tsun , Kuo Yue
Published: February 2024

Abstract

Recently, flat panel display technologies are based on amorphous silicon (a-Si), polycrystalline silicon (poly-Si) or amorphous oxide semiconductor (AOS) thin film transistors (TFTs) technology. In order to reach higher performance for ultra-high resolution display applications, the material selection for the channel layer is vital. AOS TFTs drawn lots of attention because of its advantages such as low leakage current, high driving current and high uniformity [1,3]. In this work, we presented a novel amorphous oxide semiconductor (AOS) material of gallium-free a-InWZnO thin film transistors (IWZO TFTs) which is very promising to be applied for ultra-high resolution display technology.

Experiment

In this work, we demonstrated the structure of a-IWZO TFTs processes. Figure 1 shows the schematic of the TFT cross-section. After growing a 550 nm thermal oxide layer as buffer layer, a 25-nm-thick of molybdenum was deposited by DC-sputter as the bottom gate electrode. A 10-nm-HfO2 was deposited by plasma-enhanced atomic layer deposition (PEALD) system as high-κ gate dielectric (GI). Then, post deposition annealing (PDA) was carried out to enhance the quality of the insulator layer. Next, an ultra-thin body a-IWZO was deposited by RF-sputter as channel layer. Finally, source and drain were defined by lift-off process and the gate contact via was etched by dry etching to finish the device fabrication.

Result and Discussion

Figure 1(b) shows the negative gate bias stress (NGBS) transfer curve (ID-VG) of a-IWZO TFTs with passivation layer. The experimental results have shown that passivation layer could keep the back channel of IWZO channel from exposing to oxygen and hydrogen from the atmosphere. Without the passivation layer, the back channel would contact moisture leading the diffused hydrogen atoms to fill oxygen vacancy sites and de-trap free carriers, causing the VTH shifts negatively. The ultra-thin a-IWZO TFTs with passivation layer exhibited a low subthreshold swing (S.S.) of 89.7 mV/dec, high on/off current ratio (ION/IOFF) of 2.1×107 and small threshold voltage shift (ΔVth) of -0.097 V during NGBS of -2MV/cm with 2000s. To sum up, the passivation layer could enhance the a-IWZO TFTs reliability.

Reference

[1] Kamiya, H. Hosono, NPG Asia Mater., vol. 2, pp. 15, 2010.

[2] Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano, and H. Hosono, nature, vol. 432, no. 7016, pp. 488-492, 2004.

[3] Y. Kuo, C. M. Chang, I. H. Liu, and P. T. Liu, Scientific reports, vol. 9, no. 1, pp. 1-7, 2019.

Figure 1
Integration of Machine Learning Models into Three-Dimensional Numerical Simulation of Polymer Electrolyte Membrane Fuel Cells
Authors: Matsumoto Ryuki , Takayama Tsutomu , Tsukamoto Takayuki , Tsujimura Ippei
Published: February 2024

Numerical simulations are powerful tools for understanding phenomena in Polymer Electrolyte Membrane Fuel Cells (PEMFCs) and developing PEMFCs with high performance and durability. We have been developing a three-dimensional (3D) PEMFC simulator P-Stack [1]. P-Stack can perform 3D cell/stack simulations for long-time operation about 10 ~ 100 hours at most. However, fuel cell degradation occurs on longer time scales. To simulate such very long time scales within acceptable computational time, the computational speed need to be improved innovatively. As one of the approaches, we have integrated machine learning models into the simulation.

In the power generation calculation of P-Stack, an in-plane current density distribution is determined by calculating a one-dimensional (1D) electrochemical reaction model at each point. In the present study, the 1D electrochemical reaction model is replaced with a machine learning model. The learning data is the result of “pseudo-1D” power generation calculation of 500 cases generated by P-Stack. Here, “pseudo-1D” means the power generation calculation for sampling is performed for small cell geometry, guaranteeing that in-plane distribution is almost homogeneous. It also suitable for sampling calculation because computational cost is very low. In the data generation by P-Stack, the input parameters of P-Stack were determined by Latin hypercube sampling. The input parameters for the machine learning model are the potential, the concentration of each gas species in the anode and cathode catalyst layers, and the temperature. The prediction parameters are current density, cell resistance, overvoltages, molar flux of each gas species and heat flux.

As shown in Figure 1, the machine learning model well predicts the target parameters, and the coefficient of determination was about 0.9 for various prediction targets of the verification data. As a result, machine learning could be used to predict power generation. We have implemented this machine learning model into P-Stack. We will also discuss the stability and accuracy of computation coupled with machine learning model and P-Stack, and how much the calculation can be accelerated by our approach.

Reference

[1] T. Tsukamoto, T. Aoki, H. Kanesaka, T. Taniguchi, T. Takayama, H. Motegi, R. Takayama, S. Tanaka, K. Komiyama, M. Yoneda, J. Power Sources 488 (2021) 229412

Figure 1