bluuebunny/crossref_metadata_2025_split huggingface dataset:
Revisiting Band Tails and Localized States in Amorphous Semiconductors
Authors: Luo Yuezhou , Flewitt Andrew J. John 
Published: December 2024

Amorphous semiconductors, such as hydrogenated amorphous silicon (a-Si:H) and amorphous indium gallium zinc oxide (a-IGZO) have been central to the development of thin film transistors (TFTs) for large-area electronic applications such as displays. This is a result of the exceptional material uniformity that can be achieved when depositing over very large areas (~10 m2). This means that all TFTs are essentially identical over an entire large display panel. However, there is a technological price to pay – the carrier mobility is generally less in amorphous semiconductors compared to their crystalline equivalent.
The origin of this reduced carrier mobility is a result of a key difference in the density of states between crystalline semiconductors and their amorphous counterparts. The long-range order of a crystalline lattice means that all carrier states in the conduction and valence bands exist over long distances. These ‘extended states’ are associated with generally high mobility carriers. However, there is no long-range order in amorphous semiconductors, but only short-range order over one to two bond lengths associated with local atomic coordination requirements (and to some degree a medium-range order over a few bond lengths). The result is that the bottom of the conduction band and top of the valence band gain ‘tail’ states which are localized in nature.
Not only do these localized states frequently dominate (or at least significantly affect) conduction in amorphous semiconductors and hence the switching characteristics of TFTs, but they also have a role to play in other important processes such as hysteresis and bias stress instability. But what are these localized band tail states, how should we think about them in the context of conduction and how do they relate to extended states?
These questions are revisited from the starting point that there is a perturbation in the delocalized charge concentration with position in an amorphous semiconductor compared to its crystalline counterpart, and this can be quantified as a spatially varying excess charge concentration (where a deficit is just a negative excess). The rate of spatial variation is long relative to the rate of change in the electron wavefunction, and reflects the short- and medium-range order distances. Charge conservation means that that this excess charge concentration will have a mean of zero and a Gaussian probability distribution is assumed. A model using this as a starting point has been created which reproduces band tails and which provides new insights into their physics which are discussed.
Enhanced Electromagnetic Wave Absorption Properties of Layer-By-Layer Films Comprising MXene@Fe3O4/Thermoplastic Polyurethane Fabricated via Spray Coating
Authors: Jeon JongYun , Kim Young-Seok 
Published: December 2024

Electromagnetic interference (EMI) poses significant challenges in various fields, including automotive, military, and maritime applications, as well as concerns regarding its impact on human health. Consequently, research efforts have been directed towards developing effective electromagnetic shielding materials. While metals have traditionally been utilized for their excellent conductivity, recent focus has shifted towards 2D materials due to their lightweight and deformability. Among these materials, MXene has emerged as a promising candidate owing to its remarkable electrical conductivity. However, its application in absorption-based shielding, crucial for stealth operations, is hindered by reflection-based characteristics stemming from impedance mismatching.
In this study, we synthesized iron oxide (Fe3O4) nanoparticles, known for their magnetic properties, in conjunction with MXene via a hydrothermal synthesis method to enhance absorption properties and mitigate impedance mismatching. We employed a simple spray-coating technique to fabricate layer-by-layer films comprising Thermoplastic polyurethane (TPU) and MXene@Fe3O4 composites. This facilitated the creation of interlayer spacing, promoting multiple reflections and thereby augmenting absorption shielding properties. Our study presents a synergistic approach to enhancing electromagnetic absorption shielding through the integration of MXene and Fe3O4 nanoparticles, offering potential applications in diverse electromagnetic interference mitigation scenarios.
Effect of Pt Catalyst Instead of Pd on Switchable Ag Mirror Devices
Authors: Kageyama Yui , Aoki Atsushi 
Published: December 2024

Electrochromic devices can control the transmittance of incident light between transparent state and color state under electrical bias, and has already been put into practical use in airplane windows and other applications. However, it has some drawback that the temperature rises due to absorption of light in the color state, and the heat is radiated inside. Meanwhile, the Ag mirror device that reversibly switches between transparent state and mirror state has attractive attention due to suppressing heat radiation. Since specular reflection is used in the mirror state, the Ag mirror device has an advantage over electrochromic device in that it does not emit heat and can suppress increases in room temperature.
In the previous study, Ag mirror device based on reversible silver plating on Pd-modified ITO electrodes has been reported. The Pd-modified ITO electrode is prepared by electrochemical reduction of palladium ion to get highly dispersed Pd nanoparticles on ITO surface. Pd becomes a nucleation site for Ag plating, resulting in formation of a smooth mirror surface. The Ag plating bath consists of silver nitrate, and citric acid in the mixture of acetonitrile and ionic liquid. When a negative voltage is applied in this plating liquid, the Ag⁺ is reduced to Ag metal on the ITO electrode, forming a mirror surface of Ag. Conversely, when a positive voltage is applied, the plated Ag is oxidized and dissolved in the Ag plating bath, resulting in return to a transparent state. A problem with the Pd catalyst used in this device is that Pd gradually dissolves as the number of cycles increases. In this study, in order to solve this problem and to improve cycle durability, we will consider change of the catalyst from Pd to Pt, which is a noble metal with catalytic property and electrochemical stability.
We prepared a new Pt plating bath consisting of hexachloroplatinic acid(IV) hexahydrate and hydrochloric acid in pure water. Pt modification on the ITO electrode was performed by applying a constant current of -10 mA/cm2 for 1.0 sec. Although the Pt-modified ITO electrode succeeded in switching between the mirror state and the transparent state, the switching characteristics degraded with increasing number of cycles. We assume that the degradation was caused by that the amount of modification of the Pt catalyst could not be controlled because the reducing current for Pt metal formation was also used for hydrogen generation in the acid solution. Thus we changed from acidic condition to basic condition in the Pt plating bath. We will conduct SEM image analysis and transmittance measurements to clarify the amount and form of Pt modification. After that, we will search for suitable Pt modification conditions for application to the silver mirror device, and examine whether it is possible to switch between a mirror state and a transparent state, and to improve the number of cycles.
Modified Prussian Blue Nanoparticles with Salicylate for Electrochromic Devices
Authors: Han Jisu , Kim Tae-Youb , Ah Chil Seong , Song Juhee 
Published: December 2024

Prussian blue is an important material for electrochromic devices which can act in small range of applying voltage and its various color from blue to yellow. The color changes are displayed within narrow voltage range, therefore, the specific voltage should be selected to operate the selected color. Hence, it is hard to obtain both large transition and electrochemical reaction. Modification of Prussian blue needs to be considered because of the future electrochromic devices are required either colorable or fast response.
Improving coloration efficiency of electrochromic devices is achieved in two different ways; one is to increase the optical density and the other is to lower the reacted charge. It is known that enhancing the optical properties were being researched by adding or modifying iron atom of Prussian blue structures by other metal atoms. Those are good approaches, and it effectively enhanced the optical properties. However, lowering the reacted charge is considered a property that cannot easily controlled.
In this study, we focused on lowering the reacted charges with modify the Prussian blue nanoparticles by additives as salicylate derivatives. Synthesis was done with four-type of additives, and its nanoparticle characteristics were investigated. Thin films for electrochromic measurements were deposited on the ITO electrodes. Evaluation of reacted charges was carried out by measuring electrochemical properties. Furthermore, the electrochromic properties were confirmed by its optical characteristics and calculation of coloration efficiency. The addition of salicylate into Prussian blue was achieved higher coloration efficiency compared with the regular Prussian blue by decreasing the reacted charges.

Keywords

: Prussian blue, Salicylate additives, electrochromic devices, high coloration efficiency
Fabrication of PbS QD-Mediated Organic-Inorganic Hybrid Swir Opds Using Azide Functional Ligand (FPA-S) and Study of Polymer Morphology Control
Authors: Park KyoBin , Chung Dae Sung 
Published: December 2024

The efficiency of exciton dissociation and electron mobility in organic photodetectors (OPDs) is critically dependent on the microscale morphology of the interpenetrating network structures between electron donor and acceptor materials. Therefore, understanding the impact of phase separation within the active layer and the interactions between components is crucial for OPD performance.
In this study, we propose a hybrid Short Wavelength Infrared (SWIR) photodiode that utilizes PbS quantum dots (QDs) minimally, leveraging their exceptional SWIR absorption properties, alongside an organic semiconductor matrix to counterbalance their poor charge transport characteristics. While similar concepts of organic-inorganic hybrid photodiodes have been suggested previously, the straightforward blending of organic semiconductors and QDs has been constrained by poor miscibility due to differences in surface energy between organic and inorganic phases. This results in reduced phase stability post-film fabrication and significant phase separation. Therefore, we introduce an azide-functional ligand (FPA-S) capable of coordinating with QDs and bonding with polymers via azide groups, to induce photo-crosslinking and suppress phase separation between polymers and QDs.
Effectively separating excitons while minimizing the amount of PbS QDs, which are toxic and exhibit low charge mobility, necessitates controlling the morphology of the active layer. We optimized conditions such as solvent type, evaporation rate, volume ratio, and external humidity based on a quaternary phase diagram derived from Flory-Huggins interaction parameters. Additionally, we sought to identify the optimal condition by calculating the equilibrium state of the phase-separated structure of polymers using a phase-field model with the Ising machine.
Using Operando NMR to Elucidate Degradation Mechanisms in Silicon Anodes
Authors: Wang Evelyna , Rodrigues Marco-Tulio , Park Sohyun , Dogan Fulya , Key Baris 
Published: December 2024

Replacing graphite anodes with Si anodes can greatly increase the energy of current Li-ion batteries. Detailed characterization of Si lithiation reactions, SEI formation, and reversibility are therefore active areas of research. Solid-state 7Li nuclear magnetic resonance (NMR) spectroscopy is a useful for characterizing different lithium local environments within Si anodes. Here, we developed an operando NMR methodology to characterize cycle and calendar aging of Si anodes in pouch cells paired with Ni-rich cathodes in a non-destructive manner. The developed pouch cells mimic long term performance of larger scale pouch cells. We observed a new lithiation mechanism for small Si nanoparticles: direct formation of over-lithiated Li15+xSi4 (x < 0.6) phase. Furthermore, our novel operando cells maintained good performance with long-term cycle and calendar aging allowing direct identification of Li-loss and degradation mechanisms in full cells with NMR. To this end, we identified trapped lithium silicides as a major contributor to capacity fade with aging in a number of different silicon electrodes. We will discuss the new capability and the quantitative information and insights gained from full cells such as Li-inventory losses. We envision a plethora of future operando NMR work with long term aged cells, comparing the effects of cycle aging with calendar aging as well as standardized comparison of aging mechanisms in various Si anode materials and other advanced materials with new electrolytes, additives, binders etc.
Related publication: Evelyna Wang, Marco Rodrigues, Sohyun Park, Fulya Dogan and Baris Key, Journal of Power Sources, Volume 604, 2024, 234477

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Spatially-Resolved Characterisation of Large-Format PEMFC Electrodes: Electrochemical Impedance, ECSA and O2 Concentration
Authors: Curnick Oliver , Afra Mehran , Thirkell Alexander , Meyer Quentin , Özyalcin Can , Fleming Joe , Foster Simon 
Published: December 2024

Fuel cell stacks are growing: both in numbers deployed in the field but also in terms of active electrode areas. The pursuit of higher-power applications and power densities means that cell active areas upwards of 400cm² are now commonplace. With larger electrodes comes an increased risk of non-uniform distributions of current density, temperature and reactant concentrations, which may lead in turn to locally-accelerated degradation and premature failure. Whilst detailed CFD/FEA modelling and simulation can help to refine designs, direct observations via in-situ and in-operando measurements are vital to verify model outputs and identify complex phenomena that models can fail to capture.
Our group has developed three spatially-resolved diagnostic techniques along with instrumentation, measurement systems and software tools designed to make their application as straightforward as possible for the characterisation of large-format PEMFC MEAs.
Spatially-resolved electrochemical impedance spectroscopy (SR-EIS) has been demonstrated using a commercially-available, segmented current sensor plate. A new software tool integrates a multiplexer for automated SR-EIS measurements, along with automatic equivalent circuit fitting and visualisation of spatially-resolved Ohmic, charge transfer and mass transport-related losses.
A novel technique has been developed for the measurement of distributed electrochemical surface area (dECSA), allowing localised changes in ECSA resulting from non-uniform ageing to be determined for the first time.
Finally, a chronoamperometric sensor array is demonstrated for the spatially-resolved measurement of in-plane oxygen concentration at the PEMFC cathode.
In combination, these characterisation techniques offer a significant advance in PEMFC diagnostics, providing a deeper insight into non-uniform conditions and degradation in large-format PEMFCs.
Direct Use of Ammonia in Solid Oxide Fuel Cells
Authors: Bae Kiho , Park Jinsoek , Lee Kyung Min 
Published: December 2024

With the global movement to suppress carbon use, hydrogen is emerging as an effective alternative to fossil fuels. However, there are difficulties in entering the energy market due to the lack of infrastructure and difficulties in storage/transportation when using hydrogen. Ammonia attracts attention as a promising solution to the hydrogen problem through well-established infrastructure around the world.
Direct use of ammonia in solid oxide fuel cells (SOFCs) offers more attractive aspects such as high efficiency and compact system size. However, instability in long-term operation has been reported in many literatures, which is mostly attributed to Ni nitridation. To overcome Ni nitridation, the current study proposes an alloy-based fuel electrode and its facile fabrication process. In this study, we intend to improve ammonia cracking in anode layer in SOFCs, contributing to improvement both fuel cell performance and long-term stability. The details on the current work will be presented.
Simulating CO2 Capture with Synthetic Microstructures in High-Temperature Mixed Conducting Membranes
Authors: Jin Xinfang , Shoukry Yasser 
Published: December 2024

Composite solid oxide/molten carbonate (SO/MC) membranes [1] are gaining attention for CO2 capture due to their superior selectivity and efficiency at high temperatures, which allows them to outperform conventional methods such as wet scrubbing and pressure swing adsorption [2]. The topological characteristics of the composite material’s microstructure exert a substantial influence on the overall effective conductivity of the membrane. This influence arises from the interplay of volume fraction and tortuosity within each phase, which in turn affects the pathways of charge carrier. Quantifying the precise impact of various microstructure features is challenging through homogeneous simulations or experimental techniques alone. Consequently, the adoption of heterogeneous simulations [3] becomes imperative to gain deeper insights into how distinct microstructural attributes shape the overall macroscopic performance.
This study has developed a numerical simulation utilizing heterogeneous microstructures to optimize the performance of these membranes, capturing complex multi-phase and multi-species conducting behaviors. To enhance the simulation process, we have developed proprietary MATLAB code that imports microstructure data from Dream3D into COMSOL. This code is designed to effectively manage unconnected material segments, streamline the selection of simulation entities, and simplify the application of governing equations and boundary conditions within COMSOL. Additionally, the simulation integrates an in-situ generated Li1-xNi1+xO2 (LNO) layer within Sm0.2Ce0.8O3-δ/MC/NiO (SDC/MC/NiO) membranes. Our findings indicate that reducing the molten carbonate phase's volume fraction significantly increases the CO2 flux density across the membrane. Furthermore, this computational approach has successfully replicated experimental CO2 permeation fluxes for SDC/MC/NiO membranes, quantitatively demonstrating the advantageous impact of the in-situ generated LNO phase.

References:

[1] J. L. Wade, K. S. Lackner and A. C. West, "Transport model for a high temperature, mixed conducting CO2 separation membrane," Solid State Ionics, 2007.
[2] D. Shekhawat, D. R. Luebke and H. W. Pennline, "A Review of Carbon Dioxide Selective Membranes," US Department of Energy (US), 2003.
[3] T. W. Heo, A. Grieder, B. Wang and M. Wood, "Microstructural impacts on ionic conductivity of oxide solid electrolytes from a combined atomistic-mesoscale approach," Computational Materials, 2021.
Enhancing Oxygen Catalytic Performance in Zinc-Air Batteries through Localized Micro-Interface Reconstruction of Cobalt-Manganese Spinel
Authors: Xu Nengneng , Adjah-Tetteh Christabel , Wang Yudong , He Zizhou , Zhou Xiao-Dong 
Published: December 2024

Reversible zinc-air batteries are widely regarded as one of the most promising candidates for clean energy conversion and storage technology owing to their cost-effectiveness, inherent safety, wide operating temperature window and high theoretical energy density.(1) In general, the performance of zinc-air batteries is heavily dependent on highly active bifunctional electrocatalysts, which effectively accelerate oxygen reduction/evolution reaction (ORR/OER) kinetics. Among various electrocatalysts for advanced air cathodes, multivalent Co3-xMnxO4±δ oxides, as the representative mixed transition metal spinel, have attracted widespread interest because of their O2 catalytic potential and diverse properties.(2) In comparison to the state-of-the-art Pt- and Ir-based catalysts, the catalytic performances of Co3-xMnxO4±
δ remains constrained by its low electrical conductivity and inadequate ability to adsorb and activate O2.(3) Herein, we develop a unique pathway to achieve the self-reconstruction of the local micro-interface and electronic structure of Co3-xMnxO4±δ via a combustion reaction coupled with a high-temperature reduction process. The Co particles derived from the self-reconstructed Cox@Co1.5-xMn1.5O4-δ catalyst not only facilitate the formation of a metal/oxide heterojunction active interface but also improve the electrical conductivity. More importantly, Co metal precipitated from the tetrahedral site with high spin electronic configuration induces the transformation of lattice oxygen into oxygen vacancies, thereby effectively accelerating reactant adsorption. As expected, the Cox@Co1.5-xMn1.5O4-δ catalyst shows good ORR/OER activity with low overpotential. Furthermore, the zinc-air battery assembled by Cox@Co1.5-xMn1.5O4-δ catalyst demonstrates an extended charge-discharge lifespan exceeding 1000 hours, significantly surpassing that of the Pt/C+Ir/C catalyst (100 hours). The primary factor contributing to its high stability is the dimensional growth following catalyst reconstitution. This work offers novel insights into enhancing the small molecule electrocatalytic performance of typical mixed transition metal oxides, including spinel and perovskite catalysts.
References

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C. Li, X. Han, F. Cheng, Y. Hu, C. Chen and J. Chen, Nature Communications, 6, 7345 (2015).