bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intrinsic Channel Mobility Associated with Extended State Transport in IGZO TFTs
Authors: Kabir Muhammad Salahuddin , Powell Eli , Manley Robert G. , Hirschman Karl D. 
Published: November 2022

There is wide variation in the understanding of the interaction and/or independence of channel mobility and charge trapping in IGZO TFTs. A new interpretation of transport behavior proposes an intrinsic channel mobility with distinctive temperature dependence. Bottom-gate TFTs were fabricated with a 50 nm IGZO film sandwiched between a 50 nm gate oxide and a 50 nm passivation oxide layer. The working metal was molybdenum for the gate electrode and source/drain contacts. A passivation anneal was done and a capping layer was added to promote electrical stability; full process details are provided in a previous report. Devices were tested using a Lakeshore cryogenic probe station, with transfer characteristic measurements taken from room temperature to below 100 K.
Electrical measurements made on long-channel devices (L = 12 µm) has revealed temperature-dependent behavior that is not explained by existing TCAD models employed for defect states and carrier mobility. An IGZO TFT device model has been recently developed using Silvaco Atlas, which accounts for the role of donor-like oxygen vacancy defects, acceptor-like BTS, acceptor-like interface traps, and a temperature-dependent intrinsic channel mobility. The model demonstrates a remarkable match to transfer characteristics measured at T = 150 K to room temperature. The temperature-dependent mobility follows a power-law relationship resembling behavior consistent with ionized defect scattering; the source of which is proposed. Details of the material and device model, and associated defect distribution parameters will be presented.

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(Invited) Oxide TFT Applications: Principles and Challenges
Authors: Kuo Yue 
Published: November 2022

The main advantage of the thin film transistor (TFT) is that it can be fabricated on non-wafer substrate independent of the size, flexibility, and morphology. All composing films of the TFT are deposited at the low temperature. Therefore, TFTs can be applied to a broad range of consumer, biological, chemical, and optical products that are difficult to fabricate with the wafer based MOSFETs.
There are many reports on a-Si:H and poly-Si TFT applications in displays, imagers, sensors, drivers, flexible electronics, and circuits (1,2). In principle, oxide TFTs can be applied to similar products. However, since the device characteristics and compositing materials of the oxide TFT are different from those of the a-Si:H and poly- Si TFTs, as shown in Figure 1 and Table 1, there are advantages and disadvantages in former’s applications. In this presentation, oxide TFT applications in the following three areas will be discussed.

Control of the attached device, such as pixel-driving in displays,

Integrated circuits, such as drivers or inverters, and

Changing of characteristics with environment, such as pH, optical, and temperature sensors.

L. Antonuk, Chapt. 10, and Y. Kuo, Chapt. 11, Amorphous Silicon Thin Film Transistors, pp. 395-505, Kluwer Academic Publishers, 2004.

B.-D. Choi, et al., Chapt. 11-13, Polycrystalline Silicon Thin Film Transistors, Y. Kuo Editor, pp. 360-495, Kluwer Academic Publishers, 2004.

Kuo and G. W. Chang, ECS Trans, 64(10), 145-153 (2014).

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(Invited) Progress in Elucidating the Growth Process for Basic Ammonothermal GaN
Authors: Pimputkar Siddha 
Published: November 2022

Gallium nitride (GaN) is an attractive materials platform for the pursuit of high-power, high-efficiency (opto-)electronic devices. Key to allowing this wide band gap material system to achieve its full potential is the availability of low-cost, large-area, high-crystal-quality native substrates. While important advances have been made to this effect, continued progress and breakthroughs are required to truly meet this objective.
The ammonothermal method, which utilizes supercritical ammonia to preferentially dissolve and crystalize GaN on a native seed, offers a true bulk crystal growth process to yield large, inexpensive GaN substrates. To further enhance the growth rate and quality of GaN, much still needs to be learned and gained from an improved understanding of the chemical processes and growth mechanisms occurring in the ammonothermal environment. A key challenge to achieving this, is the difficulty in obtaining in-situ information during growth of GaN due to the use of thick-walled autoclaves containing the corrosive environment at temperatures up to ~ 650 °C and pressures up to ~ 2500 atm.
This talk will present the progress made in our understanding of the underpinnings of the basic ammonothermal growth of GaN. Specifically, it will discuss advances made to allow us to understand the thermodynamic foundation of the solvent, for the first time. This is achieved by the creation and application of a new, simple equation of state for supercritical ammonia under ammonothermal conditions. Additionally, by combining this solvent knowledge with in-situ temperature, total system measurements, and GaN single crystal growth, various aspects of the crystal growth process and solute behaviors are elucidated and will be presented. Consequences towards our ability to enhance the growth rate of basic ammonothermal GaN will then be discussed.
Investigation of the Area Defects in Ammonothermal Grown Gallium Nitride Substrate Wafers
Authors: Liu Yafei , Peng Hongyu , Chen Zeyu , Cheng Qianyu , Hu Shanshan , Raghothamachar Balaji , Dudley Michael 
Published: November 2022

Gallium Nitride (GaN) is one of the most promising wide band gap semiconductor materials that are replacing silicon (Si) in power electronic applications. However, the quality of the material is limiting its application in high performance power electronic materials. Apart from the threading dislocations reported in our previous studies [1, 2], some area defects are observed in both ammonothermal GaN substrates by synchrotron X-ray topography (XRT) (Figure 1). Information on the nature of these defects is important to prevent the formation of such defects and improve the crystal quality.
In this study, synchrotron X-ray rocking curve topography (SXRCT), Nomarski optical microscopy (NOM), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) are adopted to investigate the nature of the area defects. Apart from XRT images, these domain features are visible in the NOM images (Figure 2). SXRCT results show that these areas have a different strain level from the rest of the wafer area. SEM images in RBSD mode show that the area defects are observed as a diffraction contrast. To investigate the atomic configuration of these domains, HRTEM of specimens sliced from the domains are being compared with those from outside the domains. The characterization results from SXRCT, SEM and TEM analysis in conjunction with observations from other techniques like XRT and NOM will be discussed to determine the nature of the area defects and their formation mechanisms will be deduced.
[1] Y. Liu, B. Raghothamachar, H. Peng, T. Ailihumaer, M. Dudley, R. Collazo, J. Tweedie, Z. Sitar, F.S. Shahedipour-Sandvik, K.A. Jones, Journal of Crystal Growth 551 (2020) 125903.
[2] Y. Liu, H. Peng, T. Ailihumaer, B. Raghothamachar, M. Dudley, Journal of Electronic Materials 50 (2021) 2981-2989.

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(Digital Presentation) Liquid-Metal-Printed Ultra-Thin ITO-Thin-Film Transistor
Authors: Tang Yalun , Nomura Kenji 
Published: November 2022

Indium oxide is one of the promising materials for the n-channel layer for high-mobility oxide-TFT because of its high electron mobility characteristics due to the nature of spatially spread-In 5s orbital. However, excess carrier electrons in In-based channels cancel field-effect gate modulation and causes the formation of a short depletion layer. Moreover, it is challenging to reduce the electron density without the degradation of electron transport. Therefore, developing fully-depletion operated TFT using an ultra-thin channel is a straightforward strategy to demonstrate the high potential of In-based materials for TFT applications.
In this work, we developed an ultra-thin tin-doped Indium oxide (ITO) channel (~ 1.9 nm-thick.) and demonstrated a fully-depleted ITO-TFT exhibiting high mobility of 27 cm2/Vs. The ITO channel was grown by a cost-effective vacuum-free liquid-metal-printing route at the maximum process temperature of ~ 200 oC in an ambient atmosphere. Post-thermal annealing in air made significant improvement of device characteristics originating from the reduction of shallow acceptor-like in-gap defects in the ITO channels, and high-performance n-channel ITO-TFT with a large on/off-current ratio of 109 and a sharp threshold slope was achieved. By controlling air-annealing temperature, we also successfully fabricated both enhancement and depletion-mode devices and developed a full signal swinged-oxide-NMOS inverter composed of a depletion-load structure.
One-Step Synthesis of Selective Nife-Layered Double Hydroxide Anode Catalyst for Highly Efficient and Stable Anion Exchange Membrane Water Electrolyzers, Operating with Seawater
Authors: Xing Jiale , Zeng Zhiqiao , Koni Arkid , Mirshekari Gholamreza , Best Wesley , Kumar Vikas , Sammes Lauren , Bonville Leonard J. , Maric Radenka , Bliznakov Stoyan 
Published: November 2022

Seawater electrolysis faces unique and fundamental chemical challenges, such as the suppression of highly detrimental halogen chemistries [1], that poison the current state-of-the-art anode catalyst and accelerate the degradation of the membrane [2]. The technically favored solution path is to address these issues by developing a new selective catalyst and possibly by limiting operating conditions [3]. Therefore, developing a facile and cost-effective way to design highly active, selective, and and stable seawater-splitting catalysts is of great importance for research and industry [4]. In this work, hexagonal NiFe-layered double hydroxide (LDH) nanosheets were synthesized by one-step solvothermal reactions. As synthesized NiFe-LDH catalyst exhibits high activity, selectivity, and stability towards the oxygen evolution reaction (OER) in alkaline electrolyte, delivering current densities of 10 mA/cm2 at low overpotentials of 359 mV, with no significant degradation observed during RDE testing at constant voltage of 1.57 V for 72 hours in 1.0 M KOH electrolyte. In addition, in order to fabricate catalyst coated electrode (CCE), the nanostructured NiFe-LDH catalyst was homogeneously sprayed onto a platinized titanium porous transport layer (PTL) using an ultrasonic spray coating system. As prepared CCE is used as an anode and commercially available Raney nickel catalyst deposited on a nickel fiber frit is used as a cathode to assemble a MEA with Sustainion® X37-50 grade T anion exchange membrane (AEM) that was tested in alkaline seawater. Employing local seawater, the AEM electrolyzer cell demonstrated stable performance for over 1000 hours at a constant current density of 300 mA cm -2.

Reference:

[1] S.-C. Ke, R. Chen, G.-H. Chen, X.-L. Ma, Energy Fuels 2021, 35, 12948.
[2] S. Dresp, F. Luo, R. Schmack, S. Kühl, M. Gliech, P. Strasser, Energy Environ. Sci. 2016, 9, 2020.
[3] S. Dresp, F. Dionigi, S. Loos, J. Ferreira de Araujo, C. Spöri, M. Gliech, H. Dau, P. Strasser, Advanced Energy Materials 2018, 8, 1800338.
[4] H. Koshikawa, H. Murase, T. Hayashi, K. Nakajima, H. Mashiko, S. Shiraishi, Y. Tsuji, ACS Catal. 2020, 10, 1886.
Reverse Monte Carlo Modeling for Catalyst Nanoparticles in Polymer Electrolyte Fuel Cells By High-Energy X-Ray Diffraction Measurement
Authors: Mizuno Yuki , Tsuji Hirokazu , Uruga Tomoya , Kaneko Takuma , Ohara Koji , Uchimoto Yoshiharu , Imai Hideto , Tsuji Yoichiro , Sakurai Yoshiharu 
Published: November 2022

Polymer electrolyte fuel cells (PEFCs) consist of a gas diffusion layer (GDL) and an electrode on each side, and a polymer electrolyte membrane (MEA) between the electrodes. The main components of the MEA are catalysts, electrolyte membranes and electrodes. In this study, the local atomic structures of catalytic nanoparticles in MEA were investigated by high-energy X-ray diffraction measurement and reverse Monte Carlo (RMC) modeling. The purpose of this study is to show guidelines for improving the performance of the PEFCs that contribute to industry by clarifying the differences in each catalyst structure and linking them with catalyst performance such as catalytic activity and catalyst durability.
In this conference, we report the structural work on the platinum nanoparticles-supported carbon catalyst TEC10V30E (manufactured by TANAKA KIKINZOKU KOGYO K.K.). Although this sample is a commercial product, it is important to investigate its structure because it can be used as a standard sample for evaluating various catalyst samples in the future.
RMC modeling based on the structure factor S(Q) obtained from high-energy X-ray diffraction measurement is suitable to determine the 3-dimensional (3D) atomic structures of nanoparticles. High-energy X-ray diffraction measurements were performed using a two-axis diffractometer at the beamline BL04B2 in SPring-8; the energy was used 61.4 keV corresponding to 0.202 Å in wavelength. RMC simulations were performed to obtain structure information from RMC-generated 3D configuration models using RMC_POT software in the case of non-periodic boundary conditions for experimental structure factor data. Figure 1 shows the experimental structure factor of the Pt nanoparticles in TEC10V30E and the RMC-simulated structure factor. For the Pt nanoparticle studied here, the initial configuration of the RMC simulations is a spherical shape with 3.8 nm in diameter based on the fcc bulk crystal structure. The agreement between the experiment and the RMC-simulated S(Q) is satisfactory. The 3D structure model of the Pt nanoparticle obtained by RMC simulations is shown in Fig. 1. It was found that the deviation from the lattice position was larger on the surface than on the inside in the obtained structure model.
This research approach is expected to accelerate the creation of new catalysts for fuel cells by providing local atomic-scale structural information. It is also important to create the database of atomic arrangement structure data that is the basis of material design and material research.
In the meeting, data recorded from actual catalyst samples will also be presented, including those from the MIRAI fuel cell (manufactured by Toyota Motor Corp.).
This work was performed under the NEDO FC-Platform project.

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3D Visualization of Liquid Water in Catalyst Layer Using X-Ray CT
Authors: Sugahara Takaya , Sasabe Takashi , Naito Hiroshi , Kodama Manabu , Hirai Shuichiro 
Published: November 2022

Polymer electrolyte fuel cells (PEFCs) play an important role in solving environmental and energy problems, and are required to perform at higher current density to achieve the cost reduction. Under a certain operating condition, however, water condenses and accumulates in the cathode catalyst layers (CLs) and the gas diffusion layers (GDLs). In such cases, the oxygen transport is prevented by liquid water accumulation, and therefore more precise water management methods are required to perform at higher current density. In this study, we perform 3D visualization of liquid water not only in GDLs but also in CLs in order to study the mechanism of generation-discharge mechanism of liquid water in the membrane electrode assembly (MEA) in more detail.
In this study, X-ray measurements were performed using laboratory-based X-ray imaging equipment Rigaku nano3DX. The fuel cell with an active area 1.0 × 1.0 mm2 was used. The GDLs used were Toray TGP-H-060 coated with micro porous layer (MPL). Considering X-ray transparency, CLs with relatively lower Pt loading (10wt%) was applied to the membrane. The images modification, which corrects displacements of membrane due to swelling, were performed to compare the wet case and the dry case. The present operation was performed under room temperature.
The figure shows liquid water of cathode CL integrated in the thickness direction at current density of 1.0 A/cm2. It is observed that liquid water in CL accumulates above the Rib. In addition, it was found that liquid water in CL accumulates in the regions close to the liquid water accumulating in the cracks of MPL.

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Visualizing 4D Pore-Scale Gas Transport in Operating PEM Electrolyzers Using X-Ray Computed Tomography
Authors: Ham Chaeyoung Tina , Shrestha Pranay , Kober Leya Roshani , Bazylak Aimy 
Published: November 2022

Mass transport losses in polymer electrolyte membrane (PEM) electrolyzers are predominantly caused by the accumulation of oxygen gas within the pores of the porous transport layer (PTL), hindering reactant water delivery to reaction sites (1). To enhance mass transport and optimize electrolyzer performance, a comprehensive understanding of the mechanisms driving oxygen gas transport in the PTL is required. Numerous studies have utilized various imaging techniques - including optical, neutron, and X-ray radiography to elucidate the evolution and transport of oxygen gas in the multiphase flow regime during PEM electrolyzer operation (2). However, these techniques only capture two-dimensional (2D) images, resolving average gas distributions rather than a holistic pore-scale quantification. Few studies have used three-dimensional (3D) imaging to resolve the dynamic microscale distributions of oxygen gas in the PTL. Understanding the impact of key parameters affecting 3D oxygen gas transport, such as PTL morphology, will allow for tailored pore-scale material optimization for enhanced gas transport and improved performance of PEM electrolyzers.
This study presents a non-destructive operando imaging approach using X-ray computed tomography (CT), enabling the visualization of transient 3D oxygen gas evolution and transport in the PTL of a PEM electrolyzer. Using state-of-the-art synchrotron X-rays, high temporal and spatial resolutions were achieved to capture the pore-scale formation and growth of oxygen gas pathways within the PTL at various operating conditions. Electrochemical performance of an in-house designed electrolyzer cell was also characterized while acquiring tomographic images to investigate the impact of observed transport mechanisms on performance. The methodology presented in this work showcases the capability of using X-ray CT to visualize the complex interfacial multiphase flow in PTLs. Findings from this study will provide valuable insight towards pore-scale material optimization of clean energy porous materials aimed at curtailing the costs of green hydrogen production.
References
1. M. Suermann, T. J. Schmidt, and F.N. Büchi, ECS Trans., 69(17), 1141-1148 (2015).
2. M. Maier, K. Smith, J. Dodwell, G. Hinds, P. R. Shearing, and D. J. L. Brett, Int. J. Hydrog. Energy.,
47(1), 30-56 (2022).
(Digital Presentation) Characterization of Molecular Aggregation State in Deteriorated Nafion Membrane on the Basis of X-Ray Diffraction Measurement
Authors: Hirai Tomoyasu , Seko Tamio , Higashiguchi Wataru , Fujii Syuji , Nakamura Yoshinobu 
Published: November 2022

Nafion is widely utilized as key polymer for proton electrolyte fuel cells owing to their high chemical, mechanical, and proton-conducting properties. The molecular aggregation state in Nafion films strongly affects the performance in the fuel cells. During operation process in fuel cells, peroxide derivatives such as H2O2 is generated and the chemical species deteriorates Nafion membrane, leading to a decreasing of performance of the fuel cells. The detail deterioration process including local structure, however, does not well-understand. In this work, we evaluate the local molecular aggregation state in deteriorated Nafion using microbeam wide X-ray diffraction (WAXD) measurements.
Figure 1a shows WAXD line profile of before and after deterioration of Nafion membranes. The diffraction peaks were observed in ranging from 11 to 12 nm-1, which could be assigned to crystalline and amorphous structure in Nafion. The ratio of crystalline peak in deteriorated Nafion was more striking than that of initial Nafion membrane. This phenomenon might be explained following two mechanism. ① Polymer chains in amorphous domain were disconnected and were removed from the membrane. ② Polymer chains were disconnected and molecular motion of lower molecular weight is activated, leading to a formation of new crystalline domain caused by aggregation of lower molecular weight polymer chains. It is anticipated that above mechanisms occurs individually or at the same time. Though the dominant mechanism is still not clear, we can conclude that deterioration in Nafion starts from amorphous domain.
To evaluate local molecular aggregation state in deteriorated Nafion, microbeams with size of 50 μm and 7 μm were utilized for WAXD measurements. Figure 1b and c show variation of ratio in crystalline domain as function of strain. The ratio of the crystalline domain in deteriorated Nafion was more striking than that of untreated Nafion. The ratio was constant when 50 μm beam was used, but not the case in 7 μm beam. This indicates that deterioration of Nafion membrane occurs 7 to 50 μm scale. The detail will be discussed in my presentation.

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Operando Measurement of Hydrogen Crossover in Proton Exchange Membrane Electrolysis Cells at Differential Pressures
Authors: Wrubel Jacob A , Zack Jason , Park Andrew M , Bender Guido 
Published: November 2022

Low temperature water electrolysis (LTE) using proton exchange membrane electrolysis cells (PEMECs) is a promising approach for producing green H2 that can use electricity from renewable sources. In practice, H2 is stored and dispensed at high pressures. To alleviate efficiency losses associated with pressurizing the product hydrogen, PEMECs can be operated at high differential pressures, e.g., >30bar on the cathode side. However, high differential pressure operation can result in undesirable H2 crossover to the anode (O2) side. This not only reduces the Faradaic efficiency of the cell, but also can result in flammability hazards.
H2 crossover in PEMECs is a function of both materials properties such as membrane thickness, water uptake, and permeability, and operating conditions such as temperature, differential pressure, and current density. Example data are shown in Figure 1. While thinner membranes are susceptible to higher H2 crossover rates, they are a desirable material to use because they can result in significantly improved cell performance and lower material and production costs. To mitigate safety concerns related to H2 crossover, gas recombination catalyst (GRC) layers can be introduced into the membrane electrode assembly. The GRCs will react the crossover H2 with O2 to produce water, thereby minimizing the amount of H2 entering the O2 stream.
In this talk we will present data from operando crossover measurements of PEMECs employing a variety of membrane materials, both with and without GRCs. The experiments are complimented by modeling results that allow further insights into the processes at hand. Multiple temperatures, differential pressures, and current densities are studied. The results will investigate the tradeoff between performance and capturable H2 production that occurs when thinner membranes are used, and how this effect responds to differential pressure operation.

Figure 1