bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a Machine Learning Model for Quantifying SEM Images of Electrode Materials Based on AFM Topography Image
Authors: Choi Youngwoo , Hong Seungbum
Published: December 2024

Scanning electron microscopy (SEM) is a tool that allows for easy visualization of surface morphology of materials, but it has the drawback of difficulty in quantitative shape analysis. On the other hand, atomic force microscopy (AFM) enables quantitative analysis of material surface morphology with very high precision; however, it suffers from long analysis times and difficulties in analyzing a wide area. In particular, materials like graphite, used in electrode materials for batteries, possess high roughness, which poses additional challenges for AFM analysis.

To extend the spatial precision of AFM across a wide range of material surfaces, we developed a machine learning model to quantify SEM images. Based on the dependency of SEM image brightness on the quantity of scattered electrons, we devised an algorithm to generate corresponding topography. By utilizing SEM and AFM images from the same area of a single sample, we trained the machine learning model to produce a unique topography image. With this model, it becomes feasible to reliably quantify SEM images of the material using only pairs of AFM-SEM images.

In this study, we utilized a graphite anode electrode and acquired AFM and SEM images from an 80 x 80 μm area. To obtain AFM images over a wide area, we divided the entire region into 16 sections of 20 x 20 μm each for analysis. Subsequently, we further divided each section into four parts, resulting in a total of 256 pairs of images for training the machine learning model. Through the machine learning process, we inversely calculated the contributions of height and gradient of the topography in graphite material to SEM brightness. Simultaneously, we derived the boundary conditions necessary for the algorithm to calculate topography from SEM images. By applying this trained model, we were able to quantify SEM images in areas where AFM image analysis previously had not been conducted.

Quantifying SEM images has long been considered a significant drawback in SEM analysis due to its complexity. However, applying such methodologies makes SEM image quantification remarkably straightforward. This approach is not limited to electrode materials but can be widely applicable in various material fields such as nano-materials and thin films where quantification is essential. Furthermore, by extending the utilization of AFM data in model training, it is anticipated that combining various AFM modes such as Lateral Force Microscopy (LFM), Piezoelectric Force Microscopy (PFM), and Conductivity AFM (C-AFM) with SEM surface images will enable even higher-dimensional material surface analysis.
Rapid Experimental Optimization of Liquid Electrolytes Compositions for Safe Li-Ion Battery with Outstanding Long-Term Performance: Multi-Objective Constrained Bayesian Optimization Approach
Authors: Roh Kosan , Park Jaehyun , Appiah Pius , Song Seung-Wan , Oh Taekeon
Published: December 2024

Li-ion batteries have received significant attention from academia and industry to fulfill the steadily growing demand for electric vehicles. The urgency to develop safe and efficient energy storage solutions has prompted extensive research efforts in optimizing battery materials and technologies. However, optimizing the compositions of battery materials via repetitive experiments to achieve high performance can be exceedingly time-consuming and resource-intensive. This challenge is made worse by the lengthy battery cycle life tests, which often span several weeks to months. To address this critical issue, we have employed multi-objective constrained batch Bayesian optimization (BO) for the highly efficient design of experiments (DoE) of a nonflammable liquid electrolyte for a Li-ion battery. As an objective function, we propose a combination of multiple performance indicators that effectively lead to an excellent long-term performance of the battery despite relatively short cycle life tests (100 cycles at 1C). This method allows for planning the most efficient experiments (i.e., requiring only a few battery cycle tests) with a probabilistic approach to achieve high battery performance while ensuring safe operation. Using our in-house BO-DoE toolkit, we demonstrated that less than 20 experimental datasets were required to discover the optimal compositions of the liquid electrolyte with outstanding long-term performance while meeting the safety constraint.

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Effect of Gate-Electrode/Gate-Dielectric Interlayer on Gate Screening of Remote Phonon Scattering in InGaZnO Thin-Film Transistor with High-k Gate Dielectric
Authors: Sun Hao , Lai PuiTo
Published: December 2024

InGaZnO thin-film transistors with various SiO2 thicknesses (0, 3.5, 8.5, 18.8 nm) in double-layered gate dielectric (NdHfO/SiO2) and different gate doping concentrations (2.4×1015, 1.5×1018, 2.1×1019 /cm3) are fabricated to systematically study the influence of the SiO2 low-k interlayer on the remote phonon scattering (RPS) in the conduction channel originated from the NdHfO high-k layer. The performances of the TFTs show critical dependence on the SiO2 thickness and the gate doping concentration. On the one hand, the channel-carrier mobility increases with the rise of gate doping concentration because more plasmons formed by more gate-electrode holes produce a stronger gate screening effect to suppress the RPS on the channel carriers. On the other hand, the SiO2 interlayer between the gate electrode and the NdHfO layer separates the gate-electrode plasmons and the gate-dielectric phonons, thus weakening the gate screening effect, which is supported by decreasing carrier mobility with increasing SiO2 thickness. Furthermore, through comparison with counterparts without the SiO2 interlayer, the carrier-mobility increment with increasing gate doping concentration is found to decrease from 9.67 cm2V-1s-1/decade to 6.33 cm2V-1s-1/decade due to weakened gate screening effect caused by the insertion of a 19-nm SiO2 interlayer. In summary, the gate screening effect and the RPS-limited channel-carrier mobility can be enhanced by higher gate doping concentration, but reduced by thicker gate-electrode/gate-dielectric interlayer.
(Invited) TFT-Based Neuromorphic Circuits for Computer Haptics
Authors: Wang Kai
Published: December 2024

Computer haptics is an emerging field that addresses haptic sensation and feedback especially for Metaverse applications. In physical world, human haptic system is used to establish tactile sensation and feedback between human skin and physical object. In Metaverse, computer haptics is used to build tactile sensation and haptic rendering when interacting with a virtual object (Figure 1). In another word, computer haptics is to realize and render a“true”feeling of touch when interacting with a virtual object.

Inspired by human haptics, both tactile sensors and interface circuits must be redesigned to tackle key challenges that modern electronics face such as high power consumption and high computing cost.

This paper presents TFT-based neuromorphic circuits including artificial synapse and neurons to convert tactile stimuli of artificial sensory neuron to discrete spike signals, enabling signal encoding. In addition, a TFT-based artificial neural network matrix multiplication circuit with ReLU activation function circuit will be given for neuromorphic computing.

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(Invited) The Synthesis and Optical Properties of 2D Janus Quantum Layers
Authors: Tongay Sefaattin , Povilus Blake
Published: December 2024

Named after the two faced Roman God Janus, 2D Janus layers contain two different atomic types on its top and bottom faces. Previous theoretical studies have shown that broken mirror symmetry together with large change transfer across the top and bottom face opens up completely new quantum properties including Rashba effect, colossal Janus field, dipolar excitons, and Skyrmion formation. Despite the theoretical advances in the field, experimental results are still limited due to limitations in high quality 2D Janus layer synthesis. In this talk, I will introduce recent discoveries made at Arizona State University towards different types of Janus layers. The growth process relies on Plasma enhanced low pressure chemical vapor deposition (PE-LPCVD). With this all room temperature technique, our team can synthesize different Janus layers as well as their vertical / lateral heterojunctions, and Janus nanoscrolls. Further studies from our team will introduce on-demand fabrication of 2D Janus layers with unique in-situ growth capabilities that allows us to collect spectroscopy data during the course of Janus material growth. Results are presented along with microscopy, spectroscopy, high -pressure studies, and electronic transport datasets for complete understanding of these systems1-5.

References

Petrić, M. M.; Kremser, M.; Barbone, M.; Qin, Y.; Sayyad, Y.; Shen, Y.; Tongay, S.; Finley, J. J.; Botello-Méndez, A. R.; Müller, K., Raman spectrum of Janus transition metal dichalcogenide monolayers WSSe and MoSSe. Physical Review B
2021,
103 (3), 035414.

Hajra, D.; Sailus, R.; Blei, M.; Yumigeta, K.; Shen, Y.; Tongay, S., Epitaxial Synthesis of Highly Oriented 2D Janus Rashba Semiconductor BiTeCl and BiTeBr Layers. ACS Nano
2020,
14 (11), 15626–15632.

Trivedi, D. B.; Turgut, G.; Qin, Y.; Sayyad, M. Y.; Hajra, D.; Howell, M.; Liu, L.; Yang, S.; Patoary, N. H.; Li, H.; Petrić, M. M.; Meyer, M.; Kremser, M.; Barbone, M.; Soavi, G.; Stier, A. V.; Müller, K.; Yang, S.; Esqueda, I. S.; Zhuang, H.; Finley, J. J.; Tongay, S., Room Temperature Synthesis of 2D Janus Crystals and Their Heterostructures. Advanced Materials
2020, 2006320.

Li, H.; Qin, Y.; Ko, B.; Trivedi, D. B.; Hajra, D.; Sayyad, M. Y.; Liu, L.; Shim, S.-H.; Zhuang, H.; Tongay, S., Anomalous Behavior of 2D Janus Excitonic Layers under Extreme Pressures. Advanced Materials
2020, (32), 2002401.

Yagmurcukardes, M.; Qin, Y.; Ozen, S.; Sayyad, M.; Peeters, F. M.; Tongay, S.; Sahin, H., Quantum properties and applications of 2D Janus crystals and their superlattices. Applied Physics Reviews
2020,
7 (1).

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(Invited) Bilayer Molybdenum Disulfide Strain Controlled Field Effect Transistor
Authors: Ozkan Cengiz Sinan
Published: December 2024

Silicon nitride stress capping layers are pivotal in the semiconductor industry for their role in enhancing electron mobility and driving currents in n-channel silicon MOSFETs. This research delves into the effects of silicon nitride-induced strain on the electronic properties of bilayer Molybdenum Disulfide (MoS2), a promising two-dimensional semiconductor. We first examine the modifications in the photoluminescence and Raman spectra of bare bilayer MoS2 under strain. By depositing a silicon nitride stress liner on a bilayer MoS2 field effect transistor (FET), which impacts both the gate and the source-drain regions, we replicate the stress conditions akin to those experienced in silicon MOSFETs. This methodical approach enables us to comprehensively study the evolution from back-gated to top-gated, and ultimately, to strain-gated FET configurations. Our findings indicate that tensile strain crucially modifies the electronic structure of MoS2, primarily reducing the indirect band gap by lowering the conduction band at the K point. Performance evaluations of the FETs demonstrate a marked increase in electron mobility and on-current in the strain-gated configurations compared to top-gated setups, highlighting the positive effects of tensile strain on carrier transport within MoS2. This study not only furthers our understanding of strain effects on MoS2 but also underscores the potential of strain engineering in optimizing semiconductor devices.
High Quality Carbon Nanotube Thin Films for Transistor Application
Authors: Li Yi , Xi Meiqi , Zhu Xuehao , Bai Lan , Cao Yu , Liang Xuelei
Published: December 2024

Semiconducting carbon nanotubes (s-CNTs) are promising channel materials for both high-performance ultra-scaled field-effect transistors (FETs) and thin film transistors (TFTs) due to their excellent electronic properties. Many research groups have demonstrated the application of s-CNTs in either logical computing circuits or large area electronics. However, before the CNT-based electronics technology takes real impact, many challenges should be overcome, such as achieving high purity of s-CNTs, reliable methods for their deposition and alignment, development of scalable and cost-effective production techniques, and corresponding quality characterization metrology. In this presentation, we will report our progress on the s-CNT materials and their application for FETs and TFTs.

Conjugated polymer wrapping method was used to extract s-CNTs from the raw CNT materials. We have developed a closed-loop recycling strategy, in which raw materials (CNTs and polymers) and solvents were all recycled and reused for multiple separation cycles, thus high-purity (99.9999%) and high structural quality s-CNTs were mass produced. The cost was reduced to ~ 1% in comparison with commercially available products, and total yield was increased to 36% in comparison with 2%–5% of usual separation methods.

Highly unform and density-controllable thin films of random-oriented CNTs (R-CNTs) were fabricated by a dip-coating method on 4-inch/8-inch Si wafers and 2.5th generation (G2.5) backplane glasses (370 mm × 470 mm). Ultra-clean wafer-scale aligned s-CNTs (A-CNTs) were fabricated by a modified dimension-limited self-alignment (m-DLSA) method. To quantify the overall quality of both R-CNT and A-CNT films, we proposed a four-parameter metrology which includes the local tube density (DL), global density uniformity (Cv), local degree of order (OL), and the relative tube proportion in a certain orientation (Pθ) at a location. The four-parameter metrology is not only powerful for overall quality evaluation of CNT films, but also able to predict the performance fluctuation of fabricated devices.

TFTs fabricated using the R-CNTs show mobility of 45-55 cm2/Vs with a high-performance uniformity (Cv ≈ 11%–13%) on a 4-inch wafer. A micro-LED display with 32×32 pixels were driven successfully by 2T1C AMTFT back plane based on R-CNT TFTs. Top-gated FETs based on A-CNTs exhibit excellent electronic performance with an on-state current (Ion) of 2.2 mA/μm, peak transconductance (gm) of 1.1 mS/μm, low contact resistance (Rc) of 191 Ω•μm and negligible hysteresis, among the best reported performance of CNT FETs. We believe our progress in the s-CNT materials will greatly push the CNT-based electronics technology into practical applications.
(Invited) 2-Dimensional Halide Perovskite Memristors for Data Storage and Neuromorphic Computing
Authors: Jang Ho Won
Published: December 2024

Halide perovskites, fascinating memristive materials owing to mixed ionic-electronic conductivity, have been attracting great attention as nonvolatile data storage and artificial synapses recently. However, polycrystalline nature in thin film form and instability under ambient air hamper them to be implemented in demonstrating reliable electronic devices. We successfully fabricated vertically aligned 2D halide perovskite films (V-HPs) for active layers of ReRAM and artificial synapses, showing moisture stability. Unlike random-oriented HPs, which exhibit negligible current hysteresis, V-HPs with Ag top electrodes exhibited highly stable and reliable binary memory performance. We built a flexible crossbar array to verify data storage capability, achieving a high (~100 %) device yield, robust endurance (5 × 106 cycles), long retention (2 × 105 s), reliability to operate under bending conditions, and moisture stability over a year. V-HPs with Au top electrodes showed multilevel analog memristive characteristics, programmable potentiation and depression with distinguished multi-states, long-short-term plasticity, paired-pulse facilitation, and even spike-timing-dependent plasticity. Our findings provide material design strategy that can be extended to the development of new semiconductor materials for next-generation memory devices.
(Invited) Active Matrix Organic/Perovskite Light Emitting Diodes Based on MoS2 Thin Film Transistors
Authors: Kim Soo Young
Published: December 2024

Electronic applications are continuously developing and taking new forms, including foldable, rollable and wearable displays. These wearable displays are applicable in human healthcare monitoring and robotics, and their operation relies on organic light emitting diodes (OLEDs). The development of semiconducting materials with high mechanical flexibility has remained a challenge and has restricted application to unusual format electronics. This talk presents a wearable full color OLED display using a two-dimensional (2D) material-based backplane transistor.[1,2] The 18x18 thin-film transistor array was fabricated on a thin MoS2 film that was transferred to Al2O3 (30 nm)/polyethylene terephthalate (6 m). Red, green, and blue OLED pixels were deposited on the device surface. This 2D material offered excellent mechanical and electrical properties and proved to be capable of driving circuits for the control of OLED pixels. Furthermore, the uniform deposition of perovskite light-emitting diodes (PeLEDs) and their integration with backplane thin-film transistors (TFTs) remain challenging for large-area display applications. Herein, an active-matrix PeLED display fabricated via the heterogeneous integration of cesium lead bromide (CsPbBr3) LEDs and MoS2-based TFTs is presented.[3] The single-source evaporation method enables the deposition of highly uniform perovskite thin films over large areas. PeLEDs are integrated with MoS2 TFTs to fabricate an active-matrix PeLED display with an 8×8 array, which exhibits excellent brightness control capability and high switching speeds. This study demonstrates the potential of PeLEDs as candidates for next generation displays and presents a novel approach for fabricating optoelectronic devices via the heterogeneous integration of 2D materials and perovskites, thereby paving the way toward the fabrication of practical future optoelectronic systems.

References

[1] “Flexible active-matrix organic light-emitting diode display enabled by MoS2 thin-film transistor”, Science Advances, vol. 4, eaas8721 (2018)

[2] “Full-color active-matrix organic light-emitting diode display on human skin based on a large-area MoS2 backplane”, Science Advances, vol. 6, eabb5898 (2020)

[3] “Perovskite light-emitting diode display based on MoS2 backplane TFT”, Advanced Materials, , vol. 36, p.2309531 (2024)
All Inkjet-Printed Electronics from Electrochemically Exfoliated Two-Dimensional Nanomaterials
Authors: Song Okin , Kang Joohoon
Published: December 2024

Inkjet printing is in the spotlight as a cost-effective and scalable method to assemble colloidal materials into desired patterns in a vacuum- and lithography-free manner. Two-dimensional (2D) nanosheets represent a promising class of nanomaterials for the fabrication of printed electronics due to their excellent adaptability to solution- based processing which facilitates the creation of stable ink formulations, accommodating a diverse array of electronic properties from metals, semiconductors, to insulators. Additionally, their dangling bond-free surface enables atomically thin, electronically-active thin films with van der Waals contacts which significantly reduce the junction resistance. This research presents a demonstration of fully inkjet- printed thin-film electronics consisting of electrochemically exfoliated graphene, MoS2, and HfO2 as metallic electrodes, a semiconducting channel, and a high-k dielectric layer, respectively. In particular, the high-k dielectric layer is prepared via two-step; electrochemical exfoliation of semiconducting HfS2 followed by thermal oxidation process to overcome incompatibility of electrochemical exfoliation with insulating crystals. Consequently, all inkjet-printed 2D nanosheets with various electronic types enable the fabrication of high-performance thin-film transistors, which exhibit enhanced field-effect mobilities and current on/off ratios of ~10 cm2 V-1s-1 and >105, respectively, at low operating voltage.

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Van Der Waals Heterostructures Based on Two-Dimensional Semiconductors with Built-in Potential for Improved Electrochemical Water Splitting
Authors: Cho Yun Seong , Kang Joohoon
Published: December 2024

In our pursuit of carbon neutrality, we have focused on advancing the efficiency of green hydrogen production through electrochemical water splitting. This process typically necessitates lowering the activation energy of the evolution reaction to optimize energy conversion. To enhance this, we have innovatively utilized two-dimensional (2D) materials to construct heterojunction structures that effectively facilitate charge transfer, a key aspect often overlooked in catalyst development. Specifically, we have synthesized a novel heterogeneous thin-film electrode by depositing p-type black phosphorus and n-type molybdenum disulfide nanosheets in a layered arrangement, thereby forming a large-area p-n junction directly within the film. This structure not only significantly reduces the overpotential but also achieves a higher reaction rate and superior stability in both hydrogen and oxygen evolution reactions. The strategic configuration of the 2D nanosheets in a film format ensures an efficient charge pathway, markedly enhancing the long-term stability of the catalytic process, even when combined with commercial catalysts such as Pt for hydrogen evolution and Ir for oxygen evolution. Through this method, we demonstrate a robust, scalable approach to improving catalytic performance and energy efficiency in hydrogen production systems.
Interfacial Engineering to Decouple Electrical and Thermal Conductivities in an Energy Efficient Low Thermal Budget Additive Manufacturing Technique for Flexible Thermoelectric Generators
Authors: Huang Jiyuan , Ambade Rohan B. , Lombardo Jacob , Brooks Ben , Poosapati Aswani , Banerjee Priyanshu , Saeidi-Javash Mortaza , Zhang Yanliang , Madan Deepa
Published: December 2024

The global focus on renewable and consistently available energy sources has given rise to research into alternative sources of energy harvesting, such as thermoelectric generators (TEG). TEG devices provide the solid-state conversion of waste heat into electrical power by utilizing the Seebeck effect. Thermoelectric (TE) performances can be measured by a dimensionless figure of merit (ZT). To increase the ZT value of a TE material, it is necessary to increase both the electric conductivity (EC) and Seebeck coefficient (SC) while minimizing the total thermal conductivity (TC) of the material. These values are highly interdependent and difficult to independently control.

The scalability of traditional thermoelectric generators (TEGs) has been held back by the inclusion of a high-temperature, long-duration curing process to produce high-performance thermoelectric (TE) films. Additive manufacturing has been investigated as a more time, energy, and cost-efficient method compared to traditional manufacturing techniques. Importantly, additive manufacturing allows for design freedoms including the addition of flexibility in the fabrication of TEGs. With a growing interest in the widespread adoption of TEGs to capture low waste heat energy from non-planar surfaces like the human body, the need for flexible, high performance, and energy-efficient TE manufacturing techniques is increasing.

This work investigates the synergistic effect of a small amount of chitosan binder (0.05wt%), a micron and nanosized particle size distribution, the application of mechanical pressure (20 MPa), thickness variation (170µm vs 300µm) – on the performance of p-Bi0.5Sb1.5Te3 (p-BST) and n-Bi2Te2.7Se0.3 (n-BTS) TE composite films manufactured using a low thermal budget manufacturing technique. The combination of these four factors controls the micro and nanostructure of the films to decouple their electrical and thermal conductivity effectively. This resulted in figures of merit (ZTs) of 0.89 and 0.5 for p-BST and n-BTS, respectively - comparable to other additive manufacturing methods despite eliminating the high-temperature, long-duration curing process. The process was also used to fabricate a 6-couple f-TEG device which could generate 357.6 µW with a power density of 5.0 mW/cm 2 at a ∆T of 40 K. The device demonstrated air stability and flexibility for 1000 cycles of bending. Finally, the device was integrated with a voltage step-up converter to power a LED and charge and discharge capacitor at a ∆T of 17 K, demonstrating its applicability as a self- sufficient power source.
(Invited) Structure and Function Tuning of Nanostructured Titania for Photochemical and Electrochemical Applications
Authors: Nishida Hisataka , Han Do Hyung , Park Hyunsu , Kondo Yoshifumi , Cho Sunghun , Seo Yeongjun , Goto Tomoyo , Sekino Tohru
Published: December 2024

Titania nanotubes (TNTs) [1], that essentially has ultraviolet light responsibility, have been modified by various chemical protocols such as peroxo functional groups modification and transition metal doping via facile solution chemical routes. When peroxo functional groups (-O-O-) were introduced to the lattice of TNT by hydrogen peroxide solution treatment of pristine TNTs or by bottom-up chemical synthesis from peroxo titanium complex precursor [2,3], yellowish powders were obtained. Optical band gap energy of titania nanostructures was decreased to 2.6 eV that was lower than that of pure TNTs of typically around 3.4 eV. This large red-shift of optical absorption edge might be due to the addition of electron states owing to excess oxygen to titanium oxide lattice and followed variation of energy level of conduction band for the peroxo-modified TNTs (hereafter as PTNTs).

Further materials tuning could also be possible by cation doping such as copper ions to the pristine TNT as well as PTNT by Cu2+ ion adsorption and followd UV-light irradiation to control oxidation state of copper ions. These Cu-modified nanotubes exhibited additional optical absorption band among visible light regions, provably due to the formation of d-d transition level in TNT and/or PTNT crystals. Such modifications of nanostructure titania allowed to show the photocatalytic performance enhanced under the visible light irradiating.

Photo-irradiation induced active species during light irradiation of photocatalytic performance investigations were identified by using various radical trap agencies. It was found that the photo-exited electron played a major role for visible-light driven photocatalytic degradation of organic molecules via the formation of superoxide anion radicals. Addition of cupper species made enhancement of hydrogen formation under the visible light irradiation and followed water splitting.

Such photo-induced functions might be expected to contribute not only to environmental cleaning but also to application as photochemical hydrogen generation. Detailed synthesis processes, formation mechanisms, chemical and photochemical properties will be discussed.

References:

[1] T. Kasuga, M. Hiramatsu, A. Hoson, T. Sekino, K. Niihara, Langmuir, 14, 3160-63 (1998).

[2] H. Park, T. Goto, D. H. Han, S. Cho, H. Nishida, T. Sekino, ACS Applied Nano Materials, 3, 7795–7803(2020).

[3] H. Park, D. H. Han, T. Goto, S. Cho, Y. Morimoto, T. Sekino, Nanoscale Advances, 4, 3573-3584 (2022).
(Invited) A Brief Overview and Outlook on the Progress of III-Nitride Semiconductor Materials
Authors: Freitas Jaime A.
Published: December 2024

In the last three decades, III-Nitride (GaN, AlN, InN, and its alloys) semiconductors have revolutionized both the optoelectronic and electronic device industries. Despite a previous lack of native substrates, a number of devices exceeding the performance of those fabricated from well-developed semiconductors were realized. More recently, bulk GaN (ammonothermal) and AlN (physical vapor transport) substrates were developed and commercialized. Both substrates are characterized by low dislocation density, a single crystal nature, and high flatness; but they lack full control of the electrical properties. Films deposited by vapor transport techniques (HVPE and CVD) and molecular beam epitaxy allowed the growth of device layers with high crystalline quality and improved electrical properties. These films have intrinsic free carrier concentrations that are several orders of magnitude lower than that of the substrates. This demonstrates the usefulness of this new type of substrate to fabricate highly efficient optoelectronic and electronic devices. Despite that, low acceptor solubility limit and the high activation of energy of the p-type dopants leads to low free hole concertation at room temperature.

Many relevant figures of merit related to electronic device performance scale superlinearly with the band gap; hence, ultra-wide band gap (UWBG) materials (Eg > 3.4 eV) have the potential for far superior performance than conventional WBG materials such as GaN and SiC [1]. UWBG materials will be critical enablers of future electronic components and systems, and a fundamental understanding of their synthesis and properties is critical to exploiting their advantages. In particular, cubic boron nitride, among the semiconductor materials in the UWBG group (c-BN, AlN, Ga2O3, and diamond), with a band gap of ~6 eV and thermal conductivity of 13 W/mK (second only to diamond, 20 W/mK) offers the best combination of breakdown voltage and specific on-resistance [2,3]. Another advantage of c-BN over other UWBG semiconductors is that it can be doped with donors and acceptors, enabling the fabrication of bipolar devices.

The development of WBG and UWBG substrates will be reviewed and a brief overview of the intrinsic properties of selected semiconductors will be presented.

[1] J.Y. Tsao et al., Adv. Electron. Mater. 4, 1600501 (2018)

[2] N. Miyata et al., Phys. Rev. B 40, 12028 (1989)

[3] L. Vel et al., Mat. Sci. Engineer. B 10, 149 (1991)

This work supported by the Office of Naval Research
(Invited) Heterointegration of Wide and Ultrawide Bandgap Semiconductors
Authors: Goorsky Mark S. , Liao Michael Evan , Huynh Kenny , Carson Brandon
Published: December 2024

Combinations of layers involving wide and ultra-wide bandgap materials for electronic benefits, thermal management, and other aspects can be achieved using heterointegration techniques that include but also go beyond epitaxial deposition. Here, we describe some important wide bandgap combinations achieved through wafer bonding / fusion / layer transfer / as well as deposition to demonstrate how control of interfaces can lead to better multi-layer performance and also how thermal transport models can be applied to these novel systems to lead to improvements in combined electronic and thermal management performance. Examples will include bonding using diamond, GaN-AlN bonding across N-face and metal face interfaces, and b-Ga2O3 structures. The importance of understanding interface preparation for both bonding and deposition applications as well as judicious introduction of thin interfacial layers will be described for such wide bandgap materials.
(Invited) review of Broadband Dielectric Spectroscopic Detection of Volatile Organic Compounds with Surface Anchored Organic Frameworks As Solid-State Sensor Materials
Authors: Amoah Papa Kojo , Baumgart Helmut , Redel Engelbert , Hassan Zeinab , Franklin Rhonda R , Obeng Yaw
Published: December 2024

Volatile Organic Compounds (VOCs) encompass a very wide range of organic compounds characterized by high vapor pressure at lower temperatures, which gives them significant volatility already at room temperatures. They are present in the living and work environments. Long-term indoor exposure to VOCs can cause fatigue, headache, nausea, eye, nose, and throat irritation in sensitive persons, but also damage the central nervous system and other organs. Because of their widespread occurrence in our environment, there is a need for good detectors and sensors for VOCs. We have investigated the perturbation of the physico-chemical the properties of Zinc Oxide (ZnO) and Metal-Organic Frameworks (MOFs) in the presence of VOCs, and developed a novel approach for the detection of such VOCs utilizing Broadband Dielectric Spectroscopy (BDS) techniques.

In this talk, we will review the current state-of-the-art in MOF sensing research to provide a context for the novel BDS metrology we have developed, discuss our effort to elucidate the sensing mechanisms of HKUST-1 MOF films with BDS, and showcase the capabilities of BDS for metal-oxide sensing research advancement. Specifically, we will focus on the use of surface anchored MOF (SURMOF)– as opposed to free running powdery MOFs, as sensing agents. Our results show that the SURMOF sensing agent is stable, more robust, and more sensitive in detecting VOCs, than traditional metal oxide (MOS) agents even at temperatures well below 100 °C.
Luminescence Color Control Based on Inter Molecular Excited Energy Transfer Induced by Electrochromic Reaction
Authors: Nakamura Kazuki , Kobayashi Norihisa
Published: December 2024

Electrochemical switching of luminescence color, i.e., electrofluorochromism, has received increasing attention because of its extensive applications. We have reported photo- and electrochemical- functional materials enabling dual reflective and emissive function by combining EC materials and luminescent lanthanide(III) complex. This modulation of emission is caused by control of photoexcitation energy transfer from the luminescent lanthanide(III) complex to EC material. In this study, we investigate the combination of a luminescent EC molecule and a blue luminescent molecule to achieve electrochemical control of luminescence color by controlling the energy transfer through an electrochromic reaction. We employed a functional leuco dye (Yellow-1), which shows yellow coloration and green emission by electrochemical oxidation, and 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene (BBT), which shows strong blue luminescence upon photoexcitation. Using this combination, the blue photoluminescence of the BBT molecule can be electrochemically modulated by the EC reaction of the Yellow-1 molecule, allowing the control of the luminescence color between blue and green emissions through electrochemical reactions.
Electrochromism of Redox-Active Ionic Liquids and the Kinetics of the Colorations
Authors: Tahara Hironobu , Murakami Hiroto
Published: December 2024

Electrochromic (EC) devices have been gaining attention for display, electronic paper, and smart windows because of the low-power consumption, low-voltage drive, and memory effect of the colored state holding sharp contrast. They could be useful for the intended usage, which organic light emitting diode and liquid crystal display do not cover.

The minimum components of EC devices are (i) redox-active EC material for a transparent electrode of interest, (ii) supporting electrolyte, (iii) medium (solvent), and (iv) charge-compensating (charge-balancing) redox material for another electrode. The medium (solvent) is required for electrolytes, which provide electric conductivity to the device. However, it is difficult to solve the problems of solvent evaporation and leakage of the electrolyte solution from the device. Recently, ionic liquids (ILs) are the focus of extensive investigations for electrochemical devices due to their non-volatility, moderate viscosity, and chemical stability. ILs can play roles of both solvent and supporting electrolytes. We have been focused on ILs as a designable liquid material with the above useful properties and developed electrochromic redox-active ionic liquids (RAILs).

In RAILs, either or both constituent ions are redox-active. RAILs are a new class of ILs, which are non-volatile, electro-conductive, and viscous liquid materials. In addition, RAILs consist of concentrated redox-active ions, resulting in large redox density. In the case of RAILs with electrochromic ions, which are electrochromic RAILs (EC-RAILs), the concentrated electrochromic species give a large light absorption resulting in a very thin device thickness. The non-volatility and chemical stability provide the long-term durability of the EC devices. EC-RAILs play the roles of (i)-(iv) required in EC devices. In this study, we developed EC-RAILs, the coloration process by the voltage control, and their application to the EC devices without using solvents and supporting electrolytes. Because of the concentrated redox species and absence of the supporting electrolyte, the resistance of the EC cells could be dominant for the coloration kinetics.

In this study, we have analyzed the electrode kinetics of the EC device composed of pure EC-RAILs.
Electrochromism of Redox-Active Ionic Liquids Based on Pyridinium Derivatives
Authors: Murakami Hiroto , Tahara Hironobu
Published: December 2024

Electrochromism is a phenomenon in which reversible color change occurs by redox reaction and devices with such characteristics are called electrochromic (EC) devices. The EC devices are often composed of EC materials, compensators for the reaction charge, electrolytes, solvents, and electrodes. Such EC devices, however, contain potential issues such as solvent volatilization and damage caused by physical cracks.

By the way, ionic liquids (IL) are non-volatile, flame retardant, chemically stable, and possess high ionic conductivity. In addition, ILs play double roles as electrolytes and solvents. Therefore, fabricating all components of the EC device using IL leads to not only clearing up the issues at once but also the development of the eco-friendly one.

In this work, we have fabricated two types of EC devices. In this work, we have fabricated two types of EC devices. One is an all-in-one type that consists of only ferrocene (Fc)-viologen (V)-linked IL.1 The other is a composite type that is composed of an Fc IL and V IL without any additives: solvent, supporting, and electrolyte.2 As a result, both EC devices showed good EC performance. The efficiency of the former and later devices were 70 and 91.4 cm2 C-1 at 1.0 V, respectively; the EC process was stable even after over 10 000 potential cycles for the former device and 13 000 ones for the latter device.

In this presentation, we also describe the synthesis of ILs and their electrochemistry in detail.
(Invited) Large-Area Flexible and Stretchable Electrochromic Devices with Viologen Derivatives
Authors: Park Jong Seung
Published: December 2024

Electrochromic devices (ECDs) demonstrate reversible color switchings through electron and ion exchanges during redox reactions. Viologen derivatives are commonly utilized in ECD fabrication due to their electron-accepting properties and straightforward synthesis pathways. However, viologens often present issues like slow switching speeds, limited long-term stability, and low coloration efficiency. Indium tin oxide (ITO), among various transparent conducting oxide electrodes, plays a crucial role in ECD performance. Nevertheless, ECDs, particularly those employing ITO-PET films, frequently encounter low conductivity and poor uniformity. This study focuses on the development and performance evaluation of large-area flexible and stretchable ECDs incorporating viologen derivatives. The versatility of viologen derivatives in synthesis was utilized, and the active layer, formed using ion gels through various solution processing methods, exhibited high ionic mobility and good long-term stability. Electrochromic behaviors were examined and compared with traditional viologen-based ECDs. Additionally, highly stretchable ECDs were fabricated utilizing self-healing and self-adhesive polymer electrolytes, showcasing significant transmittance contrast at extended states and stable switching throughout stretching cycles. These findings present viable strategies for producing large-area flexible and stretchable ECDs at cost-effective rates, leveraging viologen derivatives, modified electrodes, and solution coating techniques.
Modulation of Coloration Properties for Silver Deposition-Based Electrochromic Device Using Organic Capping Agents
Authors: Uji Shun , Nakamura Kazuki , Kobayashi Norihisa
Published: December 2024

The electrochromic (EC) device is capable of reversible color change with the electrochemical reaction of redox-active materials. EC technology is expected to be applied for light-modulating devices such as digital signages, e-papers, and smart windows. For practical applications, an EC device that enables full-color representation is desired. Considering a novel multicolor EC system, we focused on the superior colorability of Ag nanoparticles (AgNPs). Based on this concept, we have reported multicolor Ag deposition-based EC devices, achieving various optical states: transparent, mirror, black, cyan, magenta, and yellow by modulating of morphology of AgNPs. In chemical synthesis, various capping agents of metal nanoparticles have been reported to control the morphology of metal nanoparticles. In this study, an organic capping agent was introduced into an Ag deposition-based EC device as a capping agent for electrodeposited AgNPs to improve the coloration characteristics of EC devices and to precisely control the size and shape of the AgNPs. Through the coordination of capping agent molecules with Ag+ ions in the EC electrolyte, the critical voltage for the deposition of AgNPs decreased, resulting in a lower operating voltage of the EC device in comparison with the conventional one. Since particle growth and AgNP aggregation were suppressed by the capping effect of capping agents, achieving uniform electrodeposition of AgNPs. Aggregation suppression enabled vivid cyan, yellow, and red coloration using a simple driving procedure. The suppression of AgNP aggregation by capping agents was demonstrated even in an electrochemical system. Furthermore, the capping effect of capping agents also improved image retention. Better color retention properties were achieved even without the use of any counter-modified electrode cells.
Organic Synthesis Using Piezoelectric Materials
Authors: Kubota Koji
Published: December 2024

Visible-light-mediated photoredox catalysis has gained momentum over the past decades as an indispensable tool for selective small-molecule activation. We postulated that a complementary method for the redox-activation in response to applied mechanical energy could be developed through the piezoelectric effect. Based on our experience of organic synthesis using ball milling, we designed a new redox-activation platform, mechanoredox. In this approach, the agitation of piezoelectric materials such as BaTiO3 via ball milling could generate temporarily highly polarized particles. These particles can act as charge transfer catalysis, thereby inducing the selective formation of bonds in a manner analogous to photoredox catalysis. In this lecture, some key advances in mechanoredox reactions will be highlighted and discussed.

Figure 1
Defect Engineering Centrosymmetric 2D Material Flexocatalysts
Authors: Chen Yu-Ching , Wu Jyh-Ming
Published: December 2024

In this study, we examined the flexoelectric characteristics of two-dimensional TiO2 nanosheets. Our theoretical calculations and experimental results reveal an excellent strain-induced flexoelectric potential (flexopotential) by an effective defect engineering strategy, which suppresses the recombination of electron–hole pairs, thus substantially improving the catalytic activity of the TiO2 nanosheets in the degradation of Rhodamine B dye and the hydrogen evolution reaction in a dark environment. Our results indicated that strain-induced bandgap reduction enhances the catalytic activity of the TiO2 nanosheets. In addition, the TiO2 nanosheets degraded Rhodamine B, with being approximately 1.5 × 10−2 min−1 in dark, while TiO2 nanoparticles show only an adsorption effect. 2D TiO2 nanosheets achieved a hydrogen production rate of 137.9 µmol g−
1 h−
1 under a dark environment, 197% higher than those of TiO2 nanoparticles (70.1 µmol g−
1 h−
1). The flexopotential of the TiO2 nanosheets was enhanced by increasing the bending moment, with excellent flexopotential along the y-axis. Density functional theory was used to identify the stress-induced bandgap reduction and oxygen vacancy formation, which resulted in the self-dissociation of H2O on the surface of the TiO2 in the dark. The present findings provide novel insights into the role of TiO2 flexocatalysis in electrochemical reactions.

Figure 1
Toward a Fundamental Understanding of Solid-Solid Interfaces in Hydrogen Fuel Cells and Water Electrolysis through First-Principles Based Modeling
Authors: Zeng Zhenhua
Published: December 2024

To achieve Net-Zero Emissions by 2050, hydrogen and hydrogen fuel cells will play a significant role in powering vehicles. In this talk, I will show, through first-principles-based modeling, how to achieve rigorous modeling and a fundamental understanding of the solid-solid interface for the oxygen reduction reaction in hydrogen fuel cells and the hydrogen evolution and oxygen evolution reactions in water electrolysis. I will further show how the fundamental understanding paves the way toward developing both model and industrial electrocatalysts with significantly improved performance. Specifically, I will introduce the following three topics.

[1] metal-metal interfaces: strain generation and strain tuning of epitaxial, stepped and free-standing platinum group metals for the oxygen reduction reaction in hydrogen fuel cells. (1, 2)

[2] metal-oxide interfaces: stability and activity of monolayer oxide/Pt interface toward improving the hydrogen evolution reaction in the alkaline electrolysis.(3)

[3] oxide-oxide interfaces: self-consistent modeling of active phases, reaction centers, and catalytic mechanisms of Ni- and Co-based layered double hydroxides for the oxygen evolution reaction in the alkaline electrolysis.(4-6)

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