bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Graphite Lithiation Behaviour in Li-Ion Full Cells Using a Novel Cross-Sectional in Situ Optical Microscopy Method
Authors: Hogrefe Christin , Waldmann Thomas , Benavente Molinero Miguel , Wildner Ludwig , Axmann Peter , Wohlfahrt-Mehrens Margret
Published: November 2022

In Li-Ion batteries, the graphite anode undergoes chromatic changes from grey (unlithiated graphite) to blue (LiC18) to red (LiC12) to gold (LiC6) during lithiation.1 When charged with high current rates, lithiation gradients are observable due to mass transport limitations within the anode.2 Due to high lithiation degrees at the surface, the anode potential decreases locally and the possibility of Li deposition is increased.3

We introduce a new in situ optical microscopy set-up, which allows a direct observation of the cross-section of Li-ion full cells in combination with simultaneous recording of electrochemical data (Figure 1). Extensive analysis of the chromatic changes from the graphite electrode surface to the current collector gives insights into the lithiation processes on electrode and particle level. The set-up was validated by comparing the electrochemical results with data from coin full cells. The propagation of lithiation fronts for LiC12 (~ 3300 µm2 min-1) and LiC6 (~1260 µm2 min-1) at 1C through the graphite electrode coating were determined as well as the estimation of apparent solid-state diffusion coefficients in the order of 10-10 cm2 s-1 from analyzing the phase propagation within single particles at C/10. Additionally, the expansion of all components of the whole cell can be observed individually. We found that the graphite contributes mainly to the cell expansion, both irreversibly (4%) and reversibly (4-13%). Directly observing the described phenomena in the full cell can give insights into aging mechanisms of the materials.

Figure 1 Exemplary image from the video at the end of charge of an in situ measurement (cycling at C/10) of a graphite-NMC 622 full cell cross-sections.

References

P. Maire, A. Evans, H. Kaiser, W. Scheifele and P. Novák, J. Power Sources,
155(11), A862 (2008).

M. Weiss, R. Ruess, J. Kasnatscheew, Y. Levartovsky, N. R. Levy, P. Minnmann, L. Stolz, T. Waldmann, M. Wohlfahrt-Mehrens, D. Aurbach, M. Winter, Y. Ein-Eli and J. Janek, Adv.
Energy Mater.,
11(n/a), 2101126 (2021).

T. Gao, Y. Han, D. Fraggedakis, S. Das, T. Zhou, C.-N. Yeh, S. Xu, W. C. Chueh, J. Li and M. Z. Bazant, Joule (2021).

Figure 1
Stabilization of Silicon Anode By Advanced Localized High Concentration Electrolytes
Authors: Cao Xia , Li Qiuyan , Yi Ran , Xu Wu , Zhang Ji-Guang
Published: November 2022

The rapid market penetration of EVs requires batteries with higher energy densities. However, graphite-based lithium-ion batteries (LIBs) has eventually reached their practical limit and an anode with higher specific capacities is required to further improve energy density of LIBs. In this regard, silicon (Si) anode has been pursued as one of the most promising anodes because it exhibits a capacity ten times as high as those of graphite. However, fast capacity fade during cycling and calendar aging limits the practical application of Si-based anodes due to its severe volume changes and continuous side reactions with electrolyte. Therefore, development of electrolytes that are stable with an electrode with large volume expansion is critical to stabilize the Si anode and enable the full potential of the Si based LIBs. In the case of graphite, a stable solid electrolyte interphase (SEI) can be formed on graphite surface because it does not experience large volume change (< 10%), so the SEI can prevent further reactions between graphite and electrolyte once it is formed. In contrast, the SEI layer formed on Si anode must be mechanically strong and withhold large volume changes (>300%). This work reports the design and performance of advanced localized high concentration electrolytes (LHCEs) for Si anode, in which robust SEI forms on the surface of Si anode and protects the Si anode from the pulverization caused by the large volume changes. As a result, the overall performance of the Si based LIBs are greatly improved by using the optimized LHCEs. The electrolytes have been tailored for different applications, including high voltage (4.45 V), high temperature (45°C) and high rate (> 2C) applications. The fundamental understandings of LHCEs and corresponding SEIs developed in this work can guide the design of new electrolytes for other anodes with large volume expansion.
Revealing Hidden Structural Anisotropy in Cation-Disordered Rock Salts
Authors: Chen Dongchang , Wang You
Published: November 2022

Cation disordered rock salts (DRX), a new class of cathode materials for Li ion batteries, have attracted lots of attention in recent years, due to their fascinatingly simple cubic structure, highly diverse composition, and great electrochemical performance. As cations in DRX are randomly distributed in a long-range, how the cations (Li and transition metal) are arranged in a shorter range is an intriguing question for the community of cathode materials research. In this work, we study the vibrational structure of a series of DRXs with well controlled compositions and revealed significant anisotropy of cation arrangements. Based on the results, we propose a scheme that describes how the structural anisotropy could exist in rock salt structures but shows an overall cubic Fm-3m diffraction pattern. Furthermore, we raise a model of Li transport based on the scheme we proposed, which complements the theory of Li percolation in DRX. The electrochemical behavior of the cathodes used in the study supports the model.
(Digital Presentation) Elucidation of Active Oxygen Sites upon Delithiation of Li3IrO4
Authors: Li Haifeng , Perez Arnaud , Boyko Teak , Freeland John , Doublet Marie-Liesse , Cabana Jordi
Published: November 2022

Transformational increases in the storage capacity of battery cathodes could be achieved by tapping into the redox activity at oxide ligands in addition to conventional transition metal couples. Yet the key signatures that govern such lattice oxygen redox (LOR) have not been ascertained. Li3IrO4 has the largest reversible LOR, rendering it a unique model system. Here, X-ray spectroscopy and computational simulations reveal that LOR in Li3IrO4 is selectively compensated via O sites with 3 lone pairs, which are activated by Li/Ir disorder. The 2-electron LOR can be reversed to regenerate the initial state without unlocking competing bulk reactions observed in many other compounds. We uncover an intricate interplay between stoichiometry, O coordination and non-bonding states in LOR and pinpoint spectroscopic signatures. This interplay is indispensable to design materials with 3d metals that fulfill the promise of LOR to overcome the bottlenecks of current cathodes for future implementation in practical batteries.
Effect of Metal Cation Selection on Phase Properties and Electrochemical Performance of Co-Free High Entropy Spinel Oxide Anodes
Authors: Patra Jagabandhu , Nguyen Thi Xuyen , Ting Jyh-Ming , Chang Jeng-Kuei
Published: November 2022

Recently, high entropy oxide (HEO) materials received compelling research consideration for lithium-ion batteries (LIBs) owing to their exceptional cycling stability, high specific capacity, and exclusive tailorable properties. This unique tailorable aspect of HEO enables the use of infinite metal cation combinations to develop new electrode materials with exciting and unexplored properties. In this study, we developed a series of Co-free spinel-type HEO (HESO) anodes via a facile hydrothermal method. The effects of various elemental combination on phase purity, morphology, crystallinity, microstructures, valence states, and electrochemical charge-discharge properties of the HESO electrodes are systematically studied. For the first time, we demonstrate that the chemical composition of HESOs is crucial to the phase purity, morphology, and oxygen vacancy concentration. The oxygen vacancy concentration seems to have a substantial impact on the rate capability and reversibility of the HEO electrodes. This study demonstrates that an electrochemically inactive spectator element is not necessary for achieving high cyclability, given that the phase purity of the HEO is wisely controlled. The single-phase (CrNiMnFeCu)3O4 shows a great high-rate capability and no capacity fading after 400 cycles. In addition, the charge/discharge behavior was examined using operando X-ray diffraction. According to the operando XRD analysis, a spinel-to-rock salt phase transition is observed for (CrNiMnFeCu)3O4 before the formation of short-range ordered nano-crystals during the first lithiation. The nano-crystalline nature is preserved upon cycling. The the practical feasibility of HEO anode is evaluated by constructing a 4MCu||LiNi0.8Co0.1Mn0.1O2 full cell.
High-Performance LiNiO2: A New Baseline for State-of-the-Art Ni-Rich Cathodes
Authors: Lee Eungje , Gim Jihyeon , Han Jinhyup , Kahvecioglu Ozgenur , Wang Chongmin , Zuo Peng , Dogan Fulya , Garcia Juan , Iddir Hakim , Croy Jason R.
Published: November 2022

With the rapidly increasing market penetration of electric vehicles, more stringent energy density and cost targets are being required for advanced cathode materials. The current development of Li(Ni1-x-yMnxCoy)O2 cathodes (NMCs) has focused on increasing Ni content while decreasing expensive Co to maximize the energy density per cathode cost. Now, with the Ni content reaching over 80% in some commercially available NMCs, a fundamental understanding of a true state-of-the-art LiNiO2 material is essential for the development of next-generation, Ni-based, Co-free cathodes. In a collaborative project supported by the U.S. Department of Energy (DOE), a consortium team of multiple DOE national labs has conducted a deep-dive into the process-structure-electrochemical properties associated with realizing a true LiNiO2 cathode and its derivatives. In this presentation, high-performance LiNiO2 cathodes, developed by the consortium team, will be introduced and the critical factors that control their structures and properties will be discussed.

Figure 1
Performance Optimization of High Ni (≥90%) Cathode Materials: Synthesis & Modification
Authors: Gim Jihyeon , Han Jinhyup , Kahvecioglu Ozgenur , Zuo Peng , Zou Lianfeng , Dogan Fulya , Mane Anil U. , Darapaneni Pragathi , Wang Chongmin , Elam Jeffrey W. , Lee Eungje , Amine Khalil , Croy Jason R.
Published: November 2022

The significant growth rate of the electric vehicles (EVs) market, powered by rechargeable lithium-ion batteries (LIBs), in favor over of the internal combustion engine (ICE), represents an opportunity to massively reduce CO2 emissions and help limit global warming issues. EVs should have a similar performance to that of ICE-powered vehicles in terms of fulfilling driving range as well as lifetime of the battery to appeal the potential consumers. However, the driving range of EV’s is limited by the battery performance, which is related to the properties of the cathode material. Therefore, the development of advanced cathodes is needed.

Current state-of-the-art, Li-ion cathodes for EV batteries are derived from layered LiNiO2 (LNO) by substitution of Ni with other elements such as Mn, Co, and Al – so called LiNixMnyCozAl1-x-y-zO2 (NMCA). Substitutions are used to offset the inferior structural stability and poor cycle-life performance of typically-produced, high-capacity NMCAs. In this regard, pure LNO has been reported as a baseline material for gauging the improvements, via doping/coating strategies, for the NMCA-class of cathodes. However, for the purposes of a fully understanding the roles of Mn, Co, Al, and other dopants in NMCAs, the development of a truly state-of-the-art, LNO cathode should be accomplished. This presentation will discuss the various parameters affecting the synthesis and performance of LNO and LNO-based oxides, from precursors to final products, and the strategies that have been pursued at Argonne National Laboratory towards the realization of high-performance LNO baselines and derivatives thereof. Their potential applicability to battery applications will be also reviewed.
High-Performance Ni-Rich Cathodes through Precision Control for Electric Vehicle Batteries
Authors: Sun Yang-Kook
Published: November 2022

Li-ion batteries (LIBs) become the main portable energy source for electric vehicles (EVs) owing to their high energy and power densities as compared to those of other forms of secondary batteries. As the overall performance and cost of LIBs are largely determined by the cathode material, recent research has heavily focused on developing high-capacity cathode materials. However, chasing high-energy-density without compromising service life is very challenging. Among the available cathode materials for LIBs, layered Li[Ni1-x-yCox(Mn or Al)y]O2 (NCM or NCA) is the material of choice owing to its high theoretical capacity of 275 mAh g−1. The demand for higher energy density at a lower cost has pushed the Ni content to approach 90% because Ni is in charge of energy density in NCM and NCA cathode. The inclusion of more Ni in the NCM and NCA cathodes has significant benefits in LIB energy density and cost, as it concomitantly reduces the content of expensive Co. However, the increase in Ni content sacrifices cycling and thermal stability due to the high reactivity of Ni. Such a trade-off between energy density and stability becomes increasingly severe with increasing Ni content. Capacity fading of Ni-rich NCM and NCA cathodes, especially above Ni 80%, largely originates from microcracking which exposes a large portion of the cathode interior to deleterious electrolyte attack. To suppress the development of microcracks on cathode materials, Ni-rich cathode materials should guarantee mechanical stability even in highly charged states. In this presentation, Ni-rich layered cathodes through precision control are presented. One approach is an optimization of both the crystal structure and primary particle morphology by introducing high valence ions. Another strategy is to develop concentration gradient (CG) cathodes with rod-shaped primary particles that are elongated along the radial direction. The CG cathodes are further optimized via high-valence ion doping thereby preserving the microstructure until the cathode attains optimal crystal structure via the reduction of cation mixing. These cathodes exhibit outstanding performance in long-term cycling tests.
Tailoring Redox Reactions for Stable Cycling of High-Capacity Li-Ion Cathodes
Authors: Tong Wei
Published: November 2022

Development of new cathode materials with even better performance and lower cost is needed to meet the ever-increasing global demand on lithium-ion batteries. As such, extensive efforts have been devoted to developing next-generation cathodes for high-energy Li-ion batteries, e.g., Li-rich transition metal oxides. As a counterpart to the conventional cation-ordered layered oxides, cation-disordered rocksalts (DRXs) have emerged as a new class of high-capacity cathode materials. One unique advantage of the DRX chemistry is the structural flexibility that substantially lessens the elemental constraints and enables the incorporation of a wide variety of TMs and fluorine anion at a decent amount in the crystal lattice. As a result, the dominant TMs have been extended from redox-active Ni and Co in layered cathodes to cost-effective and earth-abundant Mn and Fe as well as redox-inactive TM (e.g., Nb, Ti, Zr, Mo) to facilitate the DRX phase formation. This exceptional chemical diversity largely opens up the opportunity to tune the material compositions for optimal performance through the control of redox reactions.

In this talk, I will present our recent work on several high-capacity cathodes based on Mn and Ni redox centers. We specifically focused on understanding the redox chemistry, including cationic and anionic redox, using combined electrochemical, soft X-ray absorption (XAS), and resonant inelastic X-ray spectroscopy (RIXS) techniques. This presentation summarizes the different TM and O redox behaviors and their roles in the electrochemical processes of these high-capacity cathodes. I will then show some examples on how this understanding leads to improved cathodes with enhanced performance by tailoring the redox reactions.
(Invited) Novel Van Der Waals Compounds and Their Potential for Optical Biosensing
Authors: Huang Shengxi
Published: November 2022

Emerging 2D van der Waals compounds have gained increasing attention due to their unique electronic and optical properties, and have shown promise in sensing applications. The realization of sensing devices using these materials still faces several challenges. For example, it is critical to gain clear understandings of (1) the fundamental light-matter interactions and their relations to the atomic structures, which govern many key material properties and device performances; and (2) the coupling with other nanostructures and molecules, which is a required structure for sensing devices and systems. This talk introduces new discoveries and pioneering works on these critical challenges, and novel applications of these materials in biochemical sensing. The first part of this talk presents light-matter interactions and techniques to augment material performance, such as 2D Janus transition metal dichalcogenides. The second part of this talk focuses on the interaction of 2D materials with organic molecules and related sensing applications. In particular, a novel enhancement effect of molecular Raman signals on 2D surface was discovered, which offers a new paradigm of biochemical sensing with high specificity, high multiplexity, and low noise. The selection rule for the 2D material substrates has been revealed, which is critical for device design. Two sensing applications for Alzheimer’s disease and respiratory viruses will also be discussed. Overall, the works presented in this talk are significant in fundamental quantum science, and offer important guidelines for practical applications in sensing and quantum technologies. The methodologies used here also provide a framework for the future study of many emerging materials and sensing scenarios.
Characterization of ALD Ta2O5, Al2O3, and Ta2O5/Al2O3 Nanolaminate as Metal-Insulator-Metal Capacitor Dielectric for GaAs HBT Technology
Authors: Yota Jiro
Published: November 2022

In order to reduce die size and increase capacity, the metal-insulator-metal (MIM) capacitor area in circuit designs fabricated using GaAs hetero-junction bipolar transistor (HBT) technology has to be reduced. This can be achieved by using a capacitor dielectric material that has a high dielectric constant or high capacitance density. In GaAs HBT technology, the MIM capacitor dielectric film is typically also required to have a high breakdown voltage (>20 V) and low leakage current. Furthermore, the deposited dielectric film has to be compatible with GaAs processing and has to be deposited at a temperature of < 300oC, due to the limited process thermal budget in the HBT technology. As a result of these requirements, there are only a few materials available for MIM capacitor dielectric application in GaAs HBT technology.

In this study, 60 nm tantalum pentoxide (Ta2O5), aluminum oxide (Al2O3), and Ta2O5/Al2O3 nanolaminate deposited using atomic layer deposition (ALD) have been characterized and evaluated as MIM capacitor dielectric for GaAs HBT technology. The results show that the capacitor with 60 nm of ALD Ta2O5 has the highest capacitance density (3.84x10-15 F/μm2), followed by the capacitor with 60 nm Ta2O5/Al2O3 nanolaminate, and the capacitor with 60 nm Al2O3 capacitor dielectric film with a capacitance density of 2.40x10-15 F/µm2 and 1.37x10-15 F/μm2, respectively. The calculated dielectric constant of ALD Ta2O5 and Ta2O5/Al2O3 nanolaminate is 26.1 and 16.3, respectively, while that of ALD Al2O3 is 9.3, as shown in Figure 1.

Figure 2 shows the I-V characteristics of MIM capacitors with 4055 μm2 area and with 60 nm of ALD Ta2O5, Ta2O5/Al2O3 nanolaminate, and Al2O3 capacitor dielectric. As can be seen, the capacitor with Al2O3 capacitor dielectric has significantly lower leakage and higher breakdown voltage (46 V), while the capacitor with Ta2O5/Al2O3 and Ta2O5 capacitor dielectric has higher leakage current and lower breakdown voltage of 32.7 V and 22.4 V, respectively. Figure 3 shows the C-V characteristics of capacitors with the 3 ALD capacitor dielectric films. The results show that the capacitance of MIM capacitor using these three films increased marginally by 2.2% to 4.3%, when the temperature was increased from 25oC to 125oC. No significant change in capacitance density of these ALD capacitor dielectric films was observed, when the applied voltage was varied from -5 V to +5 V.

Figure 1
(Invited) Thin-Film Transistor Accumulation-Mode Modeling
Authors: Wager John F
Published: November 2022

Analytical equations are developed for electrostatic assessment of accumulation-mode thin-film transistors (TFTs) so that potential, electric field, and accumulation layer free electron concentration profiles may be generated. Additionally, equations are derived for plotting TFT trap density versus surface potential, based on accurate extraction of the channel mobility as a function of gate voltage. A key factor in formulating these device physics equations is distinguishing between a ‘long-base’ or ‘short-base’ channel thickness. A ‘long-base’ (‘short-base’) channel thickness is defined to occur when the accumulation layer thickness (as calculated in the normal manner) is less than (greater than) the physical thickness of the channel layer. The electrostatic equations derived herein are applied to the analysis of two amorphous oxide semiconductor (AOS) TFTs with differing channel layers, i.e., a 40 nm amorphous indium gallium zinc oxide (a-IGZO) or a 7 nm amorphous indium zinc oxide (a-IZO). Application of these equations suggests that optimal TFT performance is obtained when the channel layer thickness is chosen to be similar to its Debye length. Estimated trap densities of these two AOS TFTs are found to be quite similar. Therefore, the superior mobility performance of the a-IZO TFT compared to the a-IGZO TFT is ascribed to the smaller effective mass of a-IZO, assuming that the maximum (no trapping) drift mobility in the channel is established by the thermally-limited diffusive mobility.
(Digital Presentation) The Effect of a Copolymer Interfacial Layer on the Performance of Organic Thin-Film Transistors
Authors: Tarekegn Eyob Negussie , Seyedi Mastooreh , Luzinov Igor , Harrell William R.
Published: November 2022

The effects of adding a copolymer interfacial layer on the performance of Poly (3-hexylthiophene-2, 5-diyl) (P3HT) based organic thin film transistors (OTFT) were investigated. Poly (oligo (ethylene glycol) methyl ether methacrylate- glycidyl methacrylate- lauryl methacrylate), which is referred to as POGL, was used as an interfacial layer between P3HT and the dielectric. OTFTs with and without a POGL interfacial layer were fabricated. The devices were based on the bottom gate bottom contact structure. Current–Voltage (I-V) measurements were performed to characterize the performance of the OTFTs, and atomic force microscopy (AFM) measurements were used to analyze the morphology of the POGL and P3HT surfaces. The field effect mobility and the threshold voltage were extracted for all the devices. The OTFTs with a POGL interfacial layer were observed to have a smaller threshold voltage than the OTFTs without an interfacial layer, which makes the POGL devices attractive for low power applications. The POGL OTFTs were also observed to have much more ideal drain current saturation characteristics with very small I-V curve slope. This is explained by the deep trap states on the POGL surface. However, the POGL OTFTs were observed to have a smaller drain current and mobility than the non-POGL OTFTs. This is explained by the surface roughness of the POGL, which affects the charge transport in the channel of the device. The morphology of the P3HT on POGL surface also showed a higher density of voids and non-uniform coverage than P3HT on the SiO2 surface, contributing to the smaller drain current and mobility of the POGL devices.
(Invited) Metal Oxide Thin-Film Transistors with Deep Submicron Channel Enabled By Self-Aligned Nano Gap Patterning
Authors: Cho Sung Haeng , Sung Chihun , Nam Sooji
Published: November 2022

We demonstrate the fabrication technology of metal oxide semiconductor thin-film transistors (TFTs) with deep submicron channel length and their electrical characterization. We call the method as self-aligned nano gap patterning (SANP), where the pattern resolution is limited not by optical diffraction in photolithography, but by the details in etching and deposition process. Therefore, this makes it enable to overcome the obstacle in the scale down of large area electronic devices, for which high resolution photolithography tools such as VUV or XUV used in semiconductor industry are almost useless due to the extremely low throughput and high cost. In this work, we employ the contact aligner with line and space resolution of 3 μm, and the oxides TFTs with 0.1μm channel length was successfully fabricated with field-effect mobility of 12 cm2/Vs, subthreshold swing of 100 mV/dec, Ion/Ioff of 1010, and turn-on voltage of -0.88 V.
(Invited) Short Channel Coplanar Amorphous-Indium-Gallium-Zinc-Oxide Thin-Film Transistors on Polyimide Substrate for High Resolution Displays
Authors: Lee Jiseob , Jang Jin
Published: November 2022

High-resolution active-matrix organic light-emitting diode (AMOLED) thin-film transistor (TFT) backplane with lower power consumption is needed for augmented reality (AR) applications. The near-to-eye format of AR terminals needs facing several technical challenges, such as higher optical efficiency, wider field of view, lighter weight, and smaller size to accelerate widespread applications. For these reasons, downscaling of TFTs with amorphous-indium-gallium-zinc-oxide (a-IGZO) or LTPS is required. The channel length should be less than 1 μm and the flexible substrate is better than glass because of light weight and very thin structure. TFT technologies on polyimide (PI) substrate can support the applications for foldable and rollable displays. For flexible AMOLED, PI layer of 10 to 20 um is widely used for foldable displays. The PI layer is coated by slot coating on the top of a carrier glass with a buffer layer of carbon nanotubes (CNTs) and graphene oxide (GO) mixture coated by spray. This layer can reduce the adhesion force between PI and glass and thus mechanical detachment can be possible. The CNTs are conducting so that it can release the electrostatic discharge (ESD) damage because CNTs/GO layer exists on the bottom side of the PI substrate. The PI substrate is covered by SiO2 and ZrAlOx layers (five layers in total starting with SiO2) by plasma enhanced chemical vapor deposition and spray pyrolysis, respectively, which acts as a gas barrier. The amorphous ZrAlOx film by spray coating can be used as a high-k gate insulator and also a gas barrier. The threshold voltage of a-IGZO TFTs tends to shift toward negative gate voltage with decreasing the channel length. In this work, a ZrAlOx passivation layer is introduced for the short channel, coplanar a-IGZO TFT. A very thin ZrAlOx layer is deposited by spray pyrolysis on the top of a-IGZO TFT at the substrate temperature of 350 ℃ before interlayer deposition. The a-IGZO TFT with a very thin ZrAlOx layer exhibits the stable threshold voltage dependence with decreasing the channel length. The 0.8 μm channel length a-IGZO TFT with ZrAlOx layer by spray pyrolysis at the substrate temperature of 350 ℃ exhibits the field-effect mobility of 7.09 cm2 V-1 s-1, the threshold voltage of -0.6 V, and on/off current ratio of 3.3 × 107. The formation of Zr-O bonds on the a-IGZO surface region reduces the carrier concentration in the a-IGZO TFT offset region, between source/drain contact and the channel, and blocks the carrier diffusion into the channel. This is the first reported self-aligned coplanar a-IGZO TFT under 1 μm channel length on a flexible substrate.

Figure 1
Micro LED Display Pixel Circuit Using Amorphous Indium-Gallium-Zinc Oxide Thin-Film Transistor
Authors: Kang Seo Jin , Yu Eun Seong , Lee Hyuk Su , Bae Byung Seong
Published: November 2022

Micro LED (μ-LED) refers to a micro-light emitting diode with a chip size of 5 to 100 μm. Since micro-LED displays use individual LED chips as a light source of the pixel, they do not need backlight and color filters, which are suitable for implementing flexible displays. In addition, micro-led displays have many advantages over OLED displays, such as excellent color gamut, power consumption, lifetime, and response time. With these advantages, micro-LED displays are attracting attention as next-generation displays, and accordingly, interest in micro-LED driving technology is increasing. While existing OLED displays express grayscale by controlling the amount of current flowing through the light-emitting device, micro-LED can have a problem of color change depending on the grayscale because the light-emitting wavelength shifts when the amount of current changes. Therefore, in order to express a certain color, it is necessary to express the grayscale by adjusting the emission time at the same current density. That is, it is more suitable to use the PWM(pulse width modulation) for each pixel than to use the PAM(pulse amplitude modulation) for the grayscale representation of the OLED display. Therefore, unlike OLED, the micro-LED display requires a new pixel circuit because it must use a PWM driving. In addition, unlike LCDs, micro-led displays are sensitive to changes in electrical characteristics of TFTs depending on the location of each pixel or external stress. Thus, threshold voltage compensation is essential because changes and degradation of the characteristics of the thin film transistor backplane, such as threshold voltage shift, cause non uniform brighteness. Therefore, we propose a PWM compensation pixel circuit based on a-IGZO TFT that can be fabricated on a flexible substrate and has a lower process cost than LTPS and greater mobility than a-Si TFT.

The operation of proposed pixel is divided into (1) reset 1, (2) PWM data compensation, (3) reset 2, (4) CCG (constant current generation)compensation, and (5) emission. The circuit is divided into a CCG unit that generates a constant current and a PWM unit that adjusts emission time by a ramping signal. Figure 1 (a) shows the output current simulation result according to PWM data voltage variation. When the PWM data voltages vary from -1 to ~ - 5V, the currents were constant at 70.9 μA, and the smaller the PWM data voltage, the longer the emission time was. In addition, Figure 1 (b) shows the effect of the threshold voltage compensation. The current and emission time are constant for various threshold voltages such as 1, 2, and 3 V.

Figure 1
(Invited, Digital Presentation) Aqueous Zinc Battery for Safe Energy Storage
Authors: Zhi Chunyi
Published: November 2022

Development of energy storage system in the past year focus on improvement of energy density. While the progress is remarkable, safety problems of lithium-ion batteries (LIB) have been intensively exposed. On one hand, LIB is not intrinsically safe with very active anode, flammable electrolyte and oxygen-releasing cathode; on the other hand, many application scenarios actually don’t require very high energy density.

We work on aqueous electrolyte batteries to achieve both high energy density and superior safety performance. We developed a few approaches to improve stability of Zn anode and figured out potential problems of the current Zn anode studies. We tackled the challenge of stability of Zn anode at high areal capacity and high current density by developing artificial SEI film, electrolyte regulation and organic anode development. In addition, we develop Zn powder based anode and improve their stability for more practical applications.

In terms of cathode of cathode materials, we develop various Mn, PBA, organic materials and MXenes based materials, targeting on a stable and high-capacity ones. We also develop a few cathode materials based on conversion mechanism, providing extraordinary capacity and decent voltage output. We also developed a few approaches to regulate conventional cathode materials for better stability.

Our research purpose is to develop aqueous Zn batteries for large scale energy storage with ultimate safety performance and integrate them with renewable energy systems. We hope our research can contribute to sustainable society development.
(Invited) Quantum Well Architecture to Realize High Optical Gain Lasing Media
Authors: Zamkov Mikhail , Harankahage Dulanjan
Published: November 2022

Photonic applications of semiconductor quantum dots (QDs) had significant drawbacks due to their ultrafast Auger decay of multiple excitons. These nonradiative processes have hindered the performance of electroluminescent and lasing devices. The emergence of the colloidal quantum well (QW) architecture where semiconductor quantum shell with an inverted QD geometry has led to suppressed Auger recombination. Ultra long biexciton lifetime (>10 ns) and large biexciton quantum yields has been achieved through spatial separation promoted by the QW geometry. Moreover, architecture induced exciton-exciton repulsions have led to the splitting of exciton and biexciton optical transitions which resulted in the single exciton gain mode along with the biexciton gain mode. High biexciton lifetime and the longest reported single exciton gain lifetime (>6 ns) has rendered this geometry a worthy candidate for the development of optically and electrically pumped gain media
(Invited, Digital Presentation) Ternary III-Sb Nanowires: Synthesis and Their Electronic and Optoelectronics Applications
Authors: Yip Sen Po , Wang Wei , Ho Johnny C
Published: November 2022

Nowadays, the increasing demand for low power and highly efficient electronics and optoelectronics has driven the semiconductor industry to look for the alternatives of Si which is approaching its physical limit. Materials like graphene, carbon nanotube, III-V materials and so on, are the most promising candidates as the replacement of silicon. Among them, III-Sb materials, a sub-group of III-V materials, have been extensively researched due to their narrow and direct bandgap, high charge carrier mobility and high g-factor which makes them suitable for transistor, infra red detection and so on. Their nanowire counterparts have also been explored as the geometry of nanowire provide unique advantages.

One of the research directions of III-Sb nanowire is to study their ternary counterpart (III-V-Sb or III-III’-Sb) like InAsSb, GaAsSb and InGaSb. Compares with binary compounds, ternary compound provides more room for engineering freedom like lattice parameter engineering and bandgap tuning. In this presentation, the synthesis and the electronic and optoelectronic applications of ternary III-Sb nanowires will be introduced. The high-crystal quality and high-aspect ratio ternary III-Sb nanowires were synthesized by using solid-source chemical vapor deposition method. Composition tunability was demonstrated successfully by adjusting the precursor ratio which allowed us to control the physical properties. We further integrated these nanowires into transistors and photodetectors which exhibit good performance like high carrier mobility and good photoresponse.
(Invited) From Bulk to Nanostructured Perovskites
Authors: Ho Johnny C
Published: November 2022

The dimensionality of semiconductors has a crucial role in determining their properties. Recently, metal halide perovskites have been demonstrated with many exciting applications, attracting wide attention to further their development for advanced optoelectronics, such as photovoltaics, photodetectors, light-emitting diodes, and lasers. At length scales down to nanoscale regimes, surface features as well as quantum confinement effects become dominant in regulating the material properties of perovskite materials. In past years, our group focus on the synthesis and characterization of metal halide perovskites with different configurations, ranging from bulk films, microplates, nanosheets, to nanowires. The corresponding physical properties and device applications were also systematically studied based on their widely tunable dimensionality, morphologies, and compositions.

Specifically, for perovskite bulk films, surface defects and bulk structural order significantly affect their device performance. Through optimizing processing techniques, self-assembled quasi-2D perovskite films with graded phase distribution were successfully prepared. Gradient type-II band alignments along the out-of-plane direction of perovskites with spontaneous separation of photo-generated electrons and holes are obtained, which is later employed to construct self-powered vertical-structure photodetectors for the first time. Without any driving voltage, the device exhibited impressive performance with the responsivity up to 444 mA/W and ultrashort response time down to 52 µs. In addition, to assess the intrinsic material properties of crystalline perovskites, freestanding MAPbI3 nanosheets and lead-free Cs3Sb2I9 microplates were fabricated by two-step chemical vapor deposition method, in which excellent optoelectronic performance (e.g., responsively of MAPbI3 nanosheet is measured to be 40 A/W) together with ultra-fast response speed (down to 58 µs) and superior thermal stability were obtained.

For nanostructured perovskites, understanding the dimensional features and their impact on the materials and devices is becoming increasingly important. Lately, we reported the direct vapor-liquid-solid growth of single-crystalline all-inorganic lead halide perovskite (i.e., CsPbX3; X = Cl, Br, or I) NWs. These NWs exhibited high-performance photodetection with the responsivity exceeding 4489 A/W and detectivity over 7.9 × 1012 Jones toward the visible light regime. Field-effect transistors based on individual CsPbX3 NWs were also fabricated to show the impressive carrier mobility of 3.05 cm2/Vs, being higher than other all-inorganic perovskite devices. Besides, the realization of high-mobility CsPbBr3 NW devices is reported via a simple surface charge transfer doping strategy. After MoO3 decoration and device fabrication, the hole mobility of CsPbBr3/MoO3 core-shell NW device is significantly enhanced to 23.3 cm2/Vs. All these results provide important guidelines for the further improvement of these perovskite nanostructures for practical utilization.
(Invited) Miniature Image Sensor Based on Van Der Waals Semiconductors
Authors: Lei Sidong
Published: November 2022

Miniature electronics are highly demanded by implantable and prosthetic devices, minimally invasive techniques, medical microrobotics, and many emerging applications. In line with this trend, power sources, communication transceivers, and actuators have been miniaturized successively. In contrast, the downscaling of image sensors is significantly delayed, due to the bottleneck of current device architectures. In this talk, we report our recent progress in addressing this challenge, leveraging van der Waals semiconductors (vdW-Ss). Our vdW-S image sensor replaces the widely used lateral Bayer configuration with a vertical color sensing structure, as such, only occupies a quarter of the original space. By properly arranging the position of red, green, and blue sensing channels in this vertical structure, we can also deliver an image sensor with the capability of chromatic aberration correction, which is rarely achieved by its counterparts. The correction of aberration, in turn, facilitates the lens system simplification and accelerates the downscaling of cameras. In order to implement the genuine integration of our image sensor architecture, a vdW-Ss doping level control strategy is also being developed and will be discussed in this talk.
(Digital Presentation) Enhancement on Degradation of Organic Dye through Piezophototronic Activities by High Entropy Oxide-(CaZrYCeCr)O2 / Bi4Ti3O12 Nanocomposite
Authors: Chang Shun Cheng , Wu Jyh-Ming
Published: November 2022

High entropy material demonstrates several effects from multi-component composition, which is potential in the catalytical field. During this decade, combining the mechanical force-driven piezoelectric/ferroelectric catalysts with photocatalysts has attracted much attention due to the separation of photogenerated carriers, leading to synergistic catalytic activities. This study reports a novel composite of high entropy oxide (CaZrYCeCr)O2 with unique ferroelectric properties mixing with bismuth titanate (Bi4Ti3O12) microplates, improving the piezo-phototronic catalytic activities. The results show that high entropy oxide catalyst (CaZrYCeCr)O2 mainly consists of the porous structure with multivalent transition metal substitution, contributing to severe lattice distortion. Consequently, the precipitation of disordered phase Ca(Zr1-xCrx)O3(x=0.05~0.1) caused by lattice distortion was decorated on the porous framework. In addition, Ca(Zr1-xCrx)O3 with a non-centrosymmetric structure exhibits ferroelectric property and plays a vital role in separating the electron-hole pairs, which performs higher degradation efficiency around 588 % compared to pristine ZrYCeO2. Additionally, the ferroelectric Bi4Ti3O12 was considered to construct a Z-scheme catalytic activity and form a heterojunction high entropy oxide. Furthermore, we demonstrated that morphotropic phase boundaries between Bi4Ti3O12 and CaZr1-xCrxO3 could dramatically enhance the ferroelectric property and promote the performance of the piezo-phototronic activities, revealing that CaZrYCeCrO2/ Bi4Ti3O12 could be an innovative catalyst in the future.
Quantitative Analysis of Dislocations in 4H-SiC Wafers Using Synchrotron X-Ray Topography with Ultra-High Angular Resolution
Authors: Peng Hongyu , Chen Zeyu , Liu Yafei , Cheng Qianyu , Hu Shanshan , Raghothamachar Balaji , Huang Xianrong , Assoufid Lahsen , Dudley Michael
Published: November 2022

The wide band gap semiconductor, 4H-SiC, is a promising material for high-power and high-temperature devices due to its outstanding physical properties. Unlike Silicon, defects in 4H-SiC still cannot be completely eliminated even using the latest crystal growth techniques. These defects can be detrimental to the devices and it is important to investigate their properties. The non-destructive characterization technique, X-ray topography (XRT), has been developed over several decades and widely applied to study the crystallographic features of various materials. The utilization of a Si (331) beam conditioner together with a Si (111) double-crystal monochromator (DCM) enables the angular resolution of XRT to be increased by an order of magnitude compared to grazing incidence topography (GIT) or back reflection topography conducted with the DCM alone. This improved technique with extremely small beam divergence is referred to as synchrotron X-ray plane-wave topography (SXPWT). In this study, we will show that the rocking curve width of 4H-SiC 0008 in PWT is only 2.5ʹʹ and thus the lattice distortion at the scale of 1ʹʹ will significantly affect the diffracted intensity. Herein, we report the ultra-high angular resolution in SXPWT enables the detailed probe of the lattice distortion outside the dislocation core in 4H-SiC where the sign of the Burgers vector can be readily determined (Fig. 1). Additionally, dynamical theory of X-ray diffraction was applied to calculate the rocking curve (reflectivity) in SXPWT, and the ray tracing simulation was modified accordingly to calculate the dislocation images under any diffraction conditions.

Figure 1
Modeling the Environment-Dependent Kinetics of Oxygen Reduction Reaction – Effect of Relative Humidity
Authors: Shibata Masao Suzuki , Anderson Grace , Morimoto Yu , Zenyuk Iryna V. , Weber Adam Z.
Published: November 2022

For proton exchange membrane fuel cells (PEMFCs) to achieve broad commercialization, the kinetics of oxygen reduction reaction (ORR) need to be better understood to improve the efficiency with minimized use of expensive Pt-based electrocatalyst(1). The increasing demands of PEMFC-powered heavy-duty vehicles make this issue critical, especially to meet the efficiency target (ultimately 72%)(2). Previous first principle-based theoretical analyses reasonably explained catalyst-dependent activity in ideal conditions (on single crystal catalysts in HClO4 solution under room temperature)(3). To design a practical catalyst, further analysis is required to bridge the gap between the ideal and actual PEMFC conditions (typically, covered with perfluorosulfonic acids under 60 to 90 °C, and 30 to 100% RH). In this talk, we examine the effect of relative humidity (RH) on ORR activity on a platinum surface. The effect of RH on ORR activity has been a controversial topic: an experimental study suggested lower RH increases the ORR activity(4), while another study showed the opposite trend(5). By using a multiscale continuum model, we validate our hypothesis that the controversial experimental results stem from the difference in the properties of the electrode/electrolyte interface. In the mathematical calculation, we assume that the polycrystalline platinum catalysts consist of multiple single crystalline surfaces(6) and that their activity is described by the summation of the activities on the single crystalline surfaces. Based on transition state theory, the reaction rate of each elementary step is calculated from the reaction free energy, reactant concentration, and activation energy with explicit accounting of the double-layer structure and interactions. In the presentation, the calculation results will be compared with experimental solid-state data using microelectrodes, and the mechanism of RH-dependent ORR activity will be discussed.

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