bluuebunny/crossref_metadata_2025 huggingface dataset:
Resistance Switching Phenomenon Associated with Anisotropic Magnetoresistance of the ReRAM Device with Ferromagnetic Electrodes
Authors: Ito Daisuke , Yoshida Hayato , Shimizu Tomohiro , Shingubara Shoso
Published: February 2020

A resistive random access memory (ReRAM) is expected to be a next-generation nonvolatile memory substituting NAND Flash because of good scalability against downsizing, fast switching speed and low power consumption. ReRAM operation relies on the ability of the metal oxide to reversely change its resistance from high resistance to low resistance and vice versa by SET or RESET operation. The device structure is composed of a metal oxide layer sandwiched between two metal electrodes. In general, it is considered that resistive switching is caused by the formation and rupture of conductive filament (CF) such as metallic filaments or an oxygen vacancy filaments formed in the oxide layer. It is widely accepted that the type of filaments formed in the ReRAM devices depends on the combination of materials used as the electrodes and the oxide layer. The metallic filament is considered to be formed by metal ions migrated from the oxidizable electrode when a positive bias is applied to the oxidizable electrode. In the previous study, we found that ferromagnetic filament was formed at the on-state of the Ni/TiO2/Pt device [1]. Actually we observed a weak anisotropic magnetoresistance (MR)  at room temperature. This study suggested that the conductive filament was formed with migration of Ni atoms from Ni electrode.

In this study, we fabricated ReRAM device having two ferromagnetic electrodes; Ni and Fe-Ni. Both electrodes may be active under the voltage stress. Figure 1 shows the MR characteristics measured for the Ni/HfOx/Fe-Ni device at the room temperature. MR ratio is defined as α = [R(H)-R(H0)/R(H0)]×100. The ferromagnetism of filament was confirmed because the resistance of filament changed against magnetic field. It is most likely that this behavior is categorized as anistropic magnetoresistance. From the results, it is suggested that the conductive filament of Ni/HfOx/Fe-Ni device is formed by ferromagnetic materials. Further discussions and analysis will be presented in the symposium.

References

[1] S. Otsuka, Y. Hamada, T.Shimizu, and S. Shingubara, Appl. Phys. A, 118 (2015) 613.

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Structural Investigation of Sodium Layered Oxides Via in Situ Synchrotron X-Ray Diffraction
Authors: Jung Young Hwa , Christiansen Ane Sælland , Johnsen Rune E. , Norby Poul , Kim Do Kyung
Published: February 2020

Sodium layered oxides with mixed transition metals have received significant attention as positive electrode candidates for sodium-ion batteries due to high reversible capacity. Sodium layered oxides would be more promising candidates than lithium-compounds in terms of high stability of MO2 slabs after extraction of Na induced from larger ionic size of Na. In addition, rich crystal chemistry for sodium layered compounds is available since larger Na+ ion is stable in more spacious prismatic site as compared to Li+ ion. In view of this, the phase transformation of layered compounds during electrochemical reaction is generally considered to be a pivotal feature for understanding the relationship between layered structures and electrochemical properties. Here the structure, phase stability, and electrochemical properties of two kinds of layered oxides, P2 and O3, are investigated through in-situ synchrotron XRD experiments. A capillary Na-based cell is designed to minimize interference in other substances such as a separator or external battery parts. This approach could give us to obtain clear diffraction patterns with high intensity during electrochemical reaction in a short period of time without further relaxation step. We carefully scrutinized reversible structural phase transformations during electrochemical reaction of P2 and O3-layered compounds based on in situ analysis, and detailed results will be discussed.
Cathode Design for a Molten Salt Lithium-Oxygen Battery
Authors: Tozier Dylan , Giordani Vincent , Gallant Betar Maurkah , Burke Colin , McCloskey Bryan D , Greer Julia R , Chase Gregory V , Addison Dan
Published: February 2020

The rechargeable lithium-oxygen battery has attracted attention due to its large theoretical energy density compared to modern lithium-ion batteries. This large energy density is attributed to the reaction of lithium with molecular oxygen to form lithium peroxide, which grows on the surface of the cathode. While this is a promising chemistry, there are many practical challenges that remain to be solved, such as the decomposition of organic electrolyte in the presence of superoxide anions and large overpotentials on charge. Additionally, the mechanism of lithium peroxide growth and its resulting morphologies is not fully understood.

Here we propose a system which inherently avoids many of the issues associated with organic electrolyte decomposition, while also forming lithium peroxide with a unique morphology. By using a molten salt (Li/K nitrate) in place of a conventional solvent/salt electrolyte, solvent decomposition is obviated. In addition, the elevated temperature of the molten salt as well as the large concentration of lithium ions encourage faster diffusion and kinetics.

In literature, the three commonly observed morphologies of electrochemically grown lithium peroxide are thin films, platelets, and “toroids” which are small stacks of platelets. While we do observe the platelet style growth of lithium peroxide, we also see much larger structures which appear to be stacks of hexagonal layers (see attached figure). We believe these stacks to be a new morphology of lithium peroxide growth. To substantiate this claim, we note that the Wulff construction for lithium peroxide is a short hexagonal prism, while also confirming the reaction product using XRD. This new morphology could be attributed to the fact that our cell operates with elevated temperature and large concentration of lithium and superoxide ions, making it easier to achieve an equilibrium (Wulff) structure.

We have shown a lithium-oxygen battery chemistry that produces a new morphology of lithium peroxide, and begun to develop a mechanism for why it forms. In addition, we have explored the effect of various cell parameters such as discharge rate on the morphology of the resulting lithium peroxide.

Figure 1
Phase Field Modeling of Lithium-Ion Diffusion and Crack Formation in the Solid Electrolyte Interphase of Silicon-Based Lithium-Ion Battery
Authors: Guan Pengjian , Liu Lin
Published: February 2020

Lithium-ion batteries (LIBs) play a key role in portable equipment, electric vehicles, and other energy storage modules. Solid electrolyte interface (SEI) layer cause a significant degradation for lithium-ion batteries’ electrochemical performance. Recently, silicon or Si-based anodes becomes an attractive candidate for the electrode of LIBs due to the low cost and high theoretical specific capacity. However, the mechanism of lithium-ion transport through the SEI layer is not fully understood as well as the crack formation of SEI layer due to silicon severe volume change. A phase field model is employed and developed to simulate the SEI structure and lithium-ion diffusion inside SEI layer including the thermodynamic chemical potential and elastic energy. SEI layer is believed to have multilayered structure; And SEI formation can be regarded as a solidification process. The phase field model is a powerful tool to investigate solidification problems without explicitly tracking the interfaces between the SEI species and electrolyte solution. Two sets of phase field variables are used to describe the microstructure of SEI layer and Lithium-ion transport in SEI layer. One is associated with the volume fraction of the interface. And the other is associated with the concentrations of SEI species. Lithium-ion transport will cause the elastic energy change. Therefore, elastic field needs to be considered in the developed model. And the elastic energy can be applied to investigate the crack initiation and propagation. Most importantly, the present developed model has great potential to be extended to three dimensional spaces for SEI layer spatial growth investigation.
High Capacity Magnesium Metal Rechargeable Battery Enabled By Dual Ion Chemistry
Authors: Gao Tao , Noked Malachi , Suo Liumin , Han Fudong , Zhu Yujie , Luo Chao , Xu Kang , Wang Chunsheng
Published: February 2020

Electrochemical energy storage is the core technology for the success of green transportation and renewable energy. Among existing energy storage chemistries, magnesium metal rechargeable batteries (MRB) are receiving growing attention due to the abundance of magnesium and its highly reversible and dendrite-free deposition/dissolution in Grignard–based complex electrolyte, which enables the exploit of the high capacity magnesium anode(2233 mAh/g).These merits have made MRB a promising candidate system to store electrochemical energy. However, the strong coulombic interaction between an intercalation host and the bivalent Mg2+ makes the solid state diffusion of the latter rather sluggish, resulting in low Mg2+intercalation level, large polarization during charge/discharge and/or rapid capacity decay for common cathode materials.

To solve the problem, we developed a high capacity MRB by coupling TiS2 with magnesium foil in a dual-ion chemistry(Mg2+/Li+). The battery operates by Li+ insertion/extraction at cathode and Mg deposition/dissolution at anode. The battery simultaneously combines high-capacity/high-voltage, fast Li+ intercalation of TiS2 and the high-capacity/dendrite-free deposition of Mg anode.

Compared to other MRBs, the theoretical specific capacity and specific energy of the dual-ion battery is 161.0 mAh/g and 209.3 Wh/kg even when the weight of lithium salt was taken into account, which are 32.2% and 56.2% higher than 121.8 mAh/g and 134 Wh/kg of the state-of-the-art MRB(with Mo6X8 cathode). Noteworthily, there is still a huge potential to be exploited for this dual-ion battery concept. If a high voltage/capacity cathode compatible to electrolyte can be found, the specific energy could be increased largely. This could make it an alternative even competitive to the mainstream LIB technology, not mentioning the advantages of a dendrite-free Mg anode that is free of inert masses (current collector, binder, and conductive additives) and first cycle irreversible reaction associated with SEI formation.

Figure 1
Novel Organic Positive Electrode Materials for a New Generation of Greener Batteries : Design and Electrochemical Properties
Authors: Guyomard Dominique , Deunf Elise , Moreau Philippe , Quarez Eric , Dolhem Franck , Poizot Philippe
Published: February 2020

The necessity to integrate renewable electricity both on and off-the-grid, coupled with eagerness of the electric automotive industry and electronic manufacturers, have markedly increased the need for high-performance and affordable electrochemical generators, particularly the rechargeable ones. Consequently, the world production of secondary batteries is expected to keep on growing. However, most common electrode materials are based on inorganic materials obtained from non-renewable resources and synthesized by ceramic route. To fulfil the actual market demands as well as the emerging environmental concerns, there is a need to design better but also “greener” battery technologies. Along that line, the implementation of Organic Electroactive Materials (OEMs) could be perceived as one of the possible alternatives. Switching from metal-based compounds to organic structures may offer several potentialities and environmental benefits including first the possibility to alleviate the pressure on scarce metals currently used by the battery industry. Indeed, organic molecules are composed of quite naturally abundant chemical elements (e.g., C, H, N, O). From an electrochemical point of view, the multiplicity of chemical combinations at the molecular level gives rise to an incomparable tool for adjusting the redox potential of conjugated systems. Over the past 5 years, beyond redox-active polymers, different interesting organic host structures have been identified by several groups notably based on carbonyl-containing cyclic structures. However the development of efficient and reliable organic batteries is clearly in its early stage. One significant issue of organic electrode materials is their tendency to dissolve in common liquid electrolytes used in batteries. Another limitation lies in the difficulty in finding robust positive electrode materials. This communication will be an opportunity to present recent advances in the field especially in terms of poorly soluble organic cathode materials capable of being reversibly charged at a high enough potential.
(Invited) Physical, Chemical and Biological Sensors Based on Nanomaterials for Wearable and Smart Electronics
Authors: Lee Nae-Eung , Trung Tran Quang , Roh Eun , Hwang Byeong-Ung , Kim Doil , Shrivastava Sajal , Duy Le Thai , Dang Vinh Quang , Son Yeong-Min , Lee Wonil , Sohn Il-Yung , Lee Ju-Hyuck , Kim Bo Young , Siddiqui Saqib , Kim Sang-Woo
Published: February 2020

For realization of wearable and smart electronics, developments of physical, chemical and biological sensors and sensor-integrated platforms are essentially required. For various applications such as smart health, cars, buildings or environments in the future, highly sensitive and reliable sensors with new functionalities such as flexibility, stretchability and/or optical transparency are to be integrated in various platforms including watch, glasses, smart phones, textiles, shoes, band, patch and etc. In this presentation, we demonstrate ultrasensitive flexible, stretchable and/or transparent physical (strain, pressure, temperature, IR, UV and visible light), chemical (gases, ions) and biological (protein, DNA, enzyme and small molecule) sensing devices based on low-dimensional nanoscale materials (0D, 1D and 2D), nanocomposites and hierarchical nanohybrids in FET, resistor and optical transducers. Some examples of patchable integrated platforms with multiple sensors or sensor-energy harvester-supercapacitor are presented for monitoring of physiological parameters, emotional expressions, body motions, daily activities of human.
(Invited) Efficient Perovskite Thin Film Solar Cells on Nanostructrue
Authors: Fan Zhiyong , Tavakoli Mohammad Mahdi , Leung Siu-Fung , Kwong-Hoi Tsui
Published: February 2020

Lead halide perovskite materials, such as CH3NH3PbI3 and CH3NH3PbI3-xClx, have emerged as attractive candidates for low-cost and efficient solar cells due to their appealing optical and electrical properties. They can be readily synthesized at low temperature from earth-abundant elements thus greatly lowering the requirement on fabrication facilities. More importantly, these materials hold promise for high performance photovoltaics devices, i. e. solar cells, due to higher charge carrier mobilities and longer diffusion lengths than many organic semiconductors. In addition, their band-gap can be conveniently and widely tuned via doping process. Over the past few years, interest on perovskite photovoltaics has surged, triggered by the fast development of low-cost and efficient lead halide perovskite thin film solar cells. However, further improve performance of perovskite solar cell still remains as a challenge. Here we report fabrication of high efficiency thin film perovskite solar cells on nanostructures which demonstrate excellent flexibility and improved performance. Our systematic investigations have revealed that improved light absorption leads to device performance enhancement. Meanwhile, nanostructures also help to maintain device structure integrity, which is especially important for flexible devices.
Characterization of InN - In0.25Ga0.75N Quantum Well Laser Structure for 1330 nm Wavelength
Authors: Polash Md. Mobarak Hossain , Alam M. Shah
Published: February 2020

In this work, a nitride based wurtzite-strained single quantum well laser has been designed and characterized at 1330 nm wavelength. Here, 12Å InN layer has been used as well material and 15Å In0.25Ga0.75N layer has been used as barrier material along with GaN as separate confinement heterostructure for better carrier and optical confinement. To determine the electronic properties of the designed structure, a developed self-consistent method has been solved. Conduction subband calculation has been performed with the solution of Schrodinger equation formed by single band Hamiltonian followed by Poisson's equation. 6-bands k . p Hamiltonian for wurtzite semiconductor has been solved for valence band Schrodinger's equation with Poisson's equation considering band mixing effect, strain due to lattice mismatch and spontaneous and piezoelectric polarization. The interband momentum matrix elements, optical gain, spontaneous emission rate, spontaneous radiative recombination rate and radiative current density have been calculated to analyze the optical properties of the designed laser and a good agreement with previously published works is obtained. All analysis has been performed using injection carrier density of 6×10-19 cm-3 at T = 300 K. Due to the strain effect, the wave-function overlap integral has been obtained as 43.27%. From the electronic properties analysis, it has been found that, the designed structure is TE polarized with C1-HH1 and C1-LH1 dominating transitions. From the analysis of optical properties, the obtained spontaneous emission rate is 5945.2 s-1 at 1329.55 nm and spontaneous emission rate per energy interval per unit volume is 7.21×1027 s-1cm-3eV-1 at same wavelength. The obtained radiative recombination rate is 7.77×1029 s-1cm-3 and radiative current density is 149.19 Acm-2. The optical gain for TE polarization of the designed QW structure is 5261.52cm-1 at 1336.7 nm.

Figure 1
Fast and Patternable Synthesis of Graphene and Transition Metal Dichalcogenide Materials Via Laser Annealing on Insulating Substrates
Authors: Medina Henry , Chen Yu-Ze , Huang Chih-Chi , Chueh Yu-Lun
Published: February 2020

The two-dimensional layered materials such as graphene and transition metal dichalcogenides (TMDs) have recently attracted much interest due to their astonishing properties under reduced dimensionality. Exceptional physical properties including ultra high mobility with high electrical conductivity for graphene and transition from indirect to direct bandgap showing excellent field effect behavior in TMD’s; open up a wide range of potential applications in optoelectronics, energy harvesting, Li-ion batteries and supercapacitors. However, the synthesis approach by CVD does not allow pattern and requires the use of high temperature processes restricting the use of substrates that can sustain such temperatures. Furthermore, the films have to be transferred to an additional substrate due to the damage caused to the original substrate used for synthesis. Therefore, further improvement of the synthesis methods is an important step to pursue. Here, we use a laser approach to induce simultaneously grow and pattern of graphene, WSe2 and MoSe2 directly on insulating substrates ready for device fabrication without the necessity of additional transfer processes. Raman and X-ray Photoelectron Spectroscopies supported by TEM observations to confirm the synthesis and crystallinity of the synthesized films. The process can be tuned to achieve a controllable number of atomic layers of the synthesized material. Moreover, this approach can be extended to the synthesis of other materials. This laser annealing assisted method develops a new approach that is fast, cheap and patternable giving a step forward on the technology development for practical applications.
(Invited) Triboelectric Nanogenerators for Self-Powering Small Electronics
Authors: Kim Sang-Woo
Published: February 2020

Recently autonomous smart systems met a large success. Especially, the internet of things is a key driving force for the development of wireless, sustainable and independent smart systems. Therefore, their autonomy is critical and despite the progresses in low power electronics and battery, it is not enough and energy harvesters are becoming increasingly important. For this, harvesting mechanical energy is essential as it is widespread and abundant in our daily life environment. Among harvesters, flexible triboelectric nanogenerators (TENG) have good performances and are easy to integrate which make it the perfect candidate for many applications, and so crucial to develop. In this presentation, I first briefly introduce the fundamentals of TENGs, including the four basic operation modes. Then I discuss the different improvement parameters. I will also address some progresses made in terms of performances and integration which have been realized through the understanding of each operation mode and the development of innovative structures. Finally I present the last trends, structures and materials in view of better performances and applications.
Aptamer Immobilized Field Effect Transistor for Early Diagnostic of Human Immunodeficiency Virus Type 1 (HIV-1)
Authors: Chu Chia-Ho , Sarangadharan Indu , Regmi Abiral , Chen Yi-Ting , Wang Yu-Lin
Published: February 2020

The acquired immunodeﬁciency syndrome (AIDS) caused by human immunodeficiency virus type 1 (HIV-1) has been a worldwide health problem. Currently, typical diagnositic of HIV is to detect the antibody that generated from human immune system after HIV infection. However, it takes several weeks for human immune system to generate the antibody against the HIV. The enzyme-linked immunosorbent assay (ELISA) is frequently used for antibody detection. On the other hand, nucleic acid amplification by PCR can detect the HIV in early stage. However, the cost for PCR is quite expensive and require specific reagents, and sophisticated. In this study, high electron mobility transistors (HEMTs) immobilized with HIV-1-specific aptamer, which is sigle-stranded DNA, have been shown to detect the HIV-RT enzyme directly with a extremely low concentration as 1fM. The highly sensitive sensor allows the diagnostic of HIV-1 in early stage, which may prevent the spreading of the disease and facilitate early therapy. The principle and the design of the sensor will be discussed.

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Thin-Film Vapor-Liquid-Solid Growth of Compound Semiconductors on Heteroepitaxial and Amorphous Substrates
Authors: Kapadia Rehan
Published: February 2020

We demonstrate the versatility of a previously developed low-cost thin-film vapor-liquid-solid (TF-VLS) compound semiconductor growth technique. Specifically, we show that the quality of compound semiconductors grown via this technique enables a variety of optoelectronic and energy devices with geometries and material combinations unavailable to traditional vapor-phase growth techniques. Critically, this is enabled by the confinement of a liquid metal solvent layer, enabling precise control over the position and shape of nuclei on non-epitaxial and hetero-epitaxial substrates simply by controlling the shape of the solvent. Unlike vapor-phase processes, in which control over the shape of a growing nuclei is extremely challenging and primarily defined by the growth rates of various crystal facets, the TF-VLS process enables full control over nuclei, enabling fabrication of single crystal and ultra-large grain polycrystalline compound semiconductors regardless of substrate microstructure. This control over the material is then utilized to demonstrate compound semiconductor devices for energy harvesting, photon generation, and photon detection.
Measurement of Optical Emission from Gesn Waveguides
Authors: Zhao Yun , Gallagher James , Li Zairui , Agha Imad , Menendez Jose , Kouvetakis John , Mathews Jay
Published: February 2020

The development of Si-based lasers has been a goal of the photonics industry for many years. A number of methods have been explored for achieving lasers on Si platforms, and a few attempts, such as the Si Raman laser, have achieved marginal success, but typically suffer from low efficiency. The silicon photonics problem requires the realization of high-efficiency lasers on CMOS-compatible platforms.

One possible solution to this problem is to employ the use of direct band gap materials that can be grown on Si. Of course, the epitaxial growth of such materials has been extremely difficult, and the efforts have mostly concentrated on the use of III-V materials like InGaAs. These materials typically suffer from high defect densities when grown directly on silicon, making them unsuitable for use in lasers. Additionally, the introduction of Group III and Group V materials into a CMOS fabrication facility can cause severe problems in device production due the electronic properties of these atoms, which are typically used as dopants in Si.

GeSn alloys present a possible path forward for the realization of Si-based lasers, as these materials are grown directly on Si or Ge-buffered Si and have a band structure that is more suited for efficient optical emission. A laser based on tensile strained Ge grown directly on Si has been demonstrated at room temperature, but the efficiency is limited by the indirect nature of the Ge band gap. More recently, demonstration of lasing at low temperature in GeSn (12.6% Sn) was achieved using optical pumping of a GeSn waveguide. While this represents a first step to the actualization of GeSn lasers, room temperature operation is a necessary condition for widespread adoption and incorporation into everyday devices.

The approach for demonstration of lasing in GeSn and Ge-on-Si has typically relied on measuring the optical emission spectrum at very high resolution to see the narrowing of the emission linewidth and the presence of cavity modes while optically-pumping a waveguide with a pulsed laser via topside illumination. We have designed a new system for optically pumping waveguides by coupling into the waveguide edge, which increases the absorption length by orders of magnitude, thereby increasing optical emission intensity and relaxing the constraints under which lasing is achieved. We employ a CW laser and erbium-doped fiber amplifier at 1550 nm as the pump source, which serves to decrease the cost of the experiment and increase the pump power. The edge emission from the waveguide is sent into a Fabry-Perot cavity with an InGaAs detector, and the optical pump power is increased until coherence is achieved, which results in the observance of modes in the Fabry-Perot cavity. This measurement can be performed with much lower pump power than a measurement using a high-resolution spectrometer. In this work, we demonstrate the use of this method for measuring the optical emission from GeSn waveguides with Sn concentrations of 4-7%.
TEMPO-Modified Linear Poly(ethylenimine) for Immobilization-Enhanced Electrocatalytic Oxidation of Alcohol
Authors: Hickey David P , Milton Ross D , Chen Dayi , Sigman Matthew S , Minteer Shelley D.
Published: February 2020

Small molecule electrooxidation catalysts such as (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) are capable of electrochemically oxidizing short chain alcohols and various sugars to the corresponding aldehydes and carboxylic acids under physiological aqueous conditions. This makes them ideal alternatives to enzymatic catalysts when deeper oxidation of a fuel is desired in the anodic compartment of a biofuel cell. While enzymes are capable of very fast rates of electrochemical alcohol oxidation (when compared to that of either transition metal catalysts or small organic catalysts), their activity is often limited to a small range of substrates. Therefore multiple oxidative reactions with a single molecule of fuel requires that several redox enzymes be immobilized at an electrode surface simultaneously, which results in additional complexity as well as diffusional limitations as substrate travel between a specific sequence of active sites.

Alternatively, TEMPO has been recently shown to catalyze multiple sequential oxidations in situ of the biofuel glycerol thereby allowing for the collection of up to 12 electrons per molecule of fuel. However, in order to utilize TEMPO in a fuel cell application, the catalyst must be immobilized at the electrode surface, and previous methods for TEMPO immobilization have resulted in a dramatic loss of catalytic activity due to diffusional restrictions. Thus there is still a need for immobilization techniques that do not result in activity loss.

We have developed a method to immobilize a TEMPO catalyst in a cross-linked hydrogel film at the surface of a carbon electrode that allows for a dramatic increase in the rate of electrocatalytic oxidation of several sugars and short-chain alcohols. A TEMPO derivative was covalently attached to a linear poly(ethylenimine) backbone, and the modified polymer was cross-linked onto the surface of a glassy carbon electrode. The use of a hydrogel film allows for a porous network through which substrate can freely diffuse and the use of a polyamine provides a high localized concentration of base necessary for the catalytic cycle of TEMPO.
In-Situ Reduction/Carburization of WO3 in the Presence of Hydrocarbon
Authors: Singla Gourav , Singh K. , Pandey O. P.
Published: February 2020

Among transition metal carbides, tungsten carbide (WC) with a wide range of particle size is used in industrial applications as cemented carbide. This work deals with the synthesis of nano crystalline tungsten carbide powders using solvothermal route. A mixture of WO3+Mg+C (hydrocarbon) was heated in a sealed autoclave. Possibility of different reactions to obtain nanocrystalline WC has been studied. As compared with the conventional methods, the present preparation method is remarkably simplified one and involves low cost. To facilitate the reactions excess amount of hydrocarbon (C3H6O, C6H14) were taken to compensate the loss of C in the form of CO and CO2. The synthesized powders were characterized by XRD, FESEM and TEM/HRTEM to analyze the purity, morphological features and particles size of obtained product and analyze further electrochemical stability in the presence of acidic medium.
Oxidation Characteristics with Various Fuels in a Molten Carbonate Fuel Cell
Authors: Kim Tae-Kyun , Kim Yoo-Jeong , Lee Sang-Woo , Lee Choong-Gon
Published: February 2020

This work has been focused on the effect of CO2 and H2O on the overpotential at the cell performance. A reference of Ang and Sammells, the reaction of hydrogen oxidation in molten carbonate has positive orders with the partial pressures of H2, CO2, and H2O. Therefore, the anode requires three gases for H2 oxidation. When the conventional H2 gas (H2:CO2:H2O=0.69:0.17:0.14atm) is used, then the overpotential is expected due to a lack of the CO2 and H2O. Ash free coal (AFC) was employed which was produced by a microwave method with a polar solvent of NMP. Adding CO2 to the AFC fuel in a coin type molten carbonate fuel cell (MCFC), the cell performance was analyzed with electrochemical method of steady state polarization and step chronopotentiometry. It was found that lack of CO2 and H2O induced significant overpotential in the MCFC and generation of them at polarization state mitigated the overpotential.
Effect of Water Adsorption on Conductivity in Epitaxial Sm0.1Ce0.9O2
-δ Thin Film for Micro Solid Oxide Fuel Cells Applications
Authors: Yang Nan , Strelcov Evgheni , Belianinov Alex , Tebano Antonello , Foglietti Vittorio , Schlueter Christoph , Lee Tien-Lin , Jesse Stephen , Kalinin Sergei V. , Balestrino Giuseppe , Aruta Carmela
Published: February 2020

The growing demand for miniaturized systems for energy conversion and storage has prompted extensive research aimed at fabricating electrochemical devices, such as solid oxide fuel cells for portable applications (μ-SOFCs). This goal requires reducing the operating temperature by producing components as thin films. Nowadays, there is a huge gap between macroscopic device-level electrochemical techniques and microscopic electrochemical techniques to study atomic-level diffusion and transport process.

Recently, a new scanning probe microscopy technique, named electrochemical strain microscopy (ESM) has been developed in order to study the structure and physical properties on the microscopic level. After applying the dc bias to the tip, the oxygen vacancies and protons injection or annihilation can occur, depending on the working conditions and the material properties. The subsequent oxygen ion or proton movement results in localized strain under the tip, which can be detected through dynamic surface displacement.[1] This technique can be very useful to investigate the electrochemical activity at the nano-scale in ionic or proton conductors.

In this presentation, I will discuss several examples of high-resolution studies of pure and Sm-doped CeO2 epitaxial thin films surfaces which allowed to understand water interaction and conductivity mechanisms on the nanoscale. In particular I will show:

(1) The effect of the different doping concentrations on Sm1-xCexO2-a in terms of different transport mechanism and  different type of charge carriers [2].

(2) The role of granularity and porosity on the oxygen ion or proton conduction 20% Sm doped CeO2 nanocrystalline films [3].

(3) The bias dependent mechanisms of irreversible cathodic and anodic processes on a pure CeO2 film.[4]

 [1] A. Kumar et al. Nature Chemistry, 2011, 3,707.

[2] Nan Yang et al. ACS Nano DOI: 10.1021/nn505345c (2014)

[3] S. Doria, Nan Yang, et al. Appl. Phys. Lett. 103, 171605 (2013)

[4] Nan Yang et al. Nanotechnology 25, 075701 (2014).
Highly Confined Electronic and Ionic Conduction in Oxide Heterostructures
Authors: Pryds Nini
Published: February 2020

The conductance confined at the interface of complex oxide heterostructures provides new opportunities to explore nanoelectronic as well as nanoionic devices. In this talk I will present our recent results both on ionic and electronic conductivity at different heterostructures systems.

In the first part of my talk I will show some of our resent results that we demonstrated the possibility of stabilizing δ-Bi2O3 using highly coherent interfaces of alternating layers. Remarkably, an exceptionally high chemical stability in reducing conditions and redox cycles at high temperature, usually unattainable for Bi2O3-based materials, is achieved[1]. These confined heterostructures provide a playground not only for new high ionic conductivity phenomena that are sufficiently stable but also uncover a large variety of possible technological perspectives.

At the second part, I will discuss and show our recent results of high mobile samples realized by, interface confined redox reactions
[2]
, strain induced polarization
[3]
and modulation doping at complex oxide interfaces. This collection of samples offers unique opportunities for a wide range of rich world of mesoscopic physics.

[1] S. Sanne et al. “Enhancement of the chemical stability in confined δ-Bi2O3”. Nature Materials (2015) doi:10.1038/nmat4266

[2] Y. Z. Chen et al. “A high-mobility two-dimensional electron gas at the spinel/perovskite interface of γ-Al2O3/SrTiO3”. Nature Commun. 4, 1371 (2013)

[3] Y. Z. Chen et al. “Creation of High Mobility Two-Dimensional Electron Gases via Strain Induced Polarization at an Otherwise Nonpolar Complex Oxide Interface” Nano Letters. 3774-3778 (2015) 10.1021/nl504622w
Lattice Boltzmann Simulation on Water Transport in Gdl of PEMFC
Authors: Jeon Dong Hyup
Published: February 2020

This study presents the effect of compression ratio on the dynamic behavior of liquid water transport in GDL. The experimental study investigates the emergence and growth of liquid droplet in the channel at various compression ratios by adopting direct visualization device. The results of the experiment show that water breakthrough occurs at the channel for low compression ratio, whereas it is observed at the channel/rib interface for high compression ratio. To determine the mechanism of water transport dynamics in GDL, multiphase lattice Boltzmann method (LBM) is developed with simplified porous structure of GDL. The observation of LB simulation shows that the compression ratio significantly affects the water transport in GDL. The results indicate that the lower compression ratio is favorable for the fuel cell performance by reducing the water saturation in GDL. Both simulation and experiment present similar result.
Hydroxide Transport in Next Generation Anion Exchange Membranes
Authors: Sarode Himanshu N , Pandey Tara P , Yang Yuan , Knauss Daniel M , Coughlin E. Bryan , Liberatore Matthew W , Herring Andrew M
Published: February 2020

The potential of anion exchange membrane (AEM) fuel cells/electrolyzers and other devices to provide inexpensive compact power from a wider variety of fuels than is possible with a proton exchange membrane (PEM) fuel cell, has continued to drive the research interest in this area.  Alkaline catalysis in fuel cells has been demonstrated with non-precious metal catalysts, and with a variety of fuels beyond H2and methanol. Alkaline fuel cells (AFCs), based on aqueous solutions of KOH, have serious drawbacks associated with system complexity and carbonate formation. AEM fuel cells have a number of advantages over both PEM fuel cells and traditional AFCs; however, although anionic conductivity in AEMs can be comparable to PEMs the chemical stability of membrane attached cations in hydroxide is still not always sufficient for practical applications.  The real issue though, is water transport; water is both a product and a reactant in these systems, and wet cations are much more stable than dry. So an understanding of water in these membranes is essential.

Recenetly we have fabricated a  series of membrnes with sufficent stability that we are able to measure the hydroxide conductivity in them at elevted temperatures while being humidified.  Here we discuss water and hydroxide transport in a series of thin mechanically robust state of the art experimental AEMs.  The membranes are generally constructed from an isoprene or ethylene block and a vinyl benzyl bromide block, either randomly or in di-, tri- or penta- block configurations.  Post quaternization leads to functionalized AEMs.  We use electrochemical impedance spectroscopy to measure anion conductivity, multi-nuclear pulse field gradient spin echo NMR to measure self-diffusion, and broadband electric spectroscopy to measure the relaxation processes in these polymers.  This information is coupled with microscopy and SAXS to explore the polymer morphology.  Putting transport and morphology together allows us to describe a complete picture of water and anion transport in these systems.
Molecular Simulation of Oxygen Solubility and Diffusivity in Ionomer on Pt Surface
Authors: Kurihara Yuya , Mabuchi Takuya , Tokumasu Takashi
Published: February 2020

Polymer electrolyte fuel cell (PEFC) is focused as a next-generation energy conversion system because of a high efficiency and a low environmental load. In the cathodic catalyst layer, there are Pt catalysts on supported carbon microparticles, and those particles are covered with ionomer films composed of polymer electrolytes, hydronium ions and water molecules. The ionomer has two properties for the water-generating reactions in the cathodic catalyst layer: the proton conductivity and the oxygen permeability. In particular, the dependence of the oxygen permeability on water content has not been clear.

In this study, we analyzed the oxygen permeability in the ionomer on the Pt surface using molecular dynamics simulations. At first, we constructed the system of the ionomer on the Pt surface, and then we set the gas oxygen molecules above the ionomer, and let the molecules permeate through the ionomer by the pressure gradient as shown in Fig. 1. Using this system, we calculated the oxygen solubility and the oxygen pathways in each region: the ionomer/gas interface, the bulk region, the ionomer/Pt interface. In general, the oxygen permeability is evaluated by the product of the oxygen solubility and the oxygen diffusivity. Thus, we calculated the oxygen solubility of each region in the ionomer at different water contents. As a result, the solubilities of all regions tend to decrease as water content increases. Moreover, we evaluated the oxygen pathways in the ionomer to evaluate the oxygen diffusivity, and the result shows that oxygen prefers the surface of hydrophilic regions to the hydrophobic regions. In experimental data, the diffusion coefficient of oxygen in a dry membrane is smaller than that of oxygen in bulk water. Therefore, the dependence of oxygen diffusivity on water content was estimated by calculating the ratio of the number of oxygen molecules in the hydrophilic region to that in the hydrophobic region.

Figure 1
Effects of Water Structure on Proton Transport in Nafion Thin Films with Molecular Dynamics Simulations
Authors: Aochi Joji , Mabuchi Takuya , Tokumasu Takashi
Published: February 2020

Polymer electrolyte fuel cell (PEFC) is expected to play important roles for next generation power systems in terms of high efficiency and low environmental burden and capability for emergency use, but there are still many hurdles to be largely commercialized. One of them results from problems in catalyst layers (CL). What required for CL is, for example, reducing the amount of Pt particles with keeping high current density. To accomplish this, knowledge about optimum structures of CL based on material transport properties is needed because there is a strong correlation between current density and transport properties. Although there are many reports about material transport properties in the polymer electrolyte membrane (PEM), it is predicted that material transport properties in CL show some unique characteristics because of effects of interfaces in CL. It means that the knowledge obtained from PEM should not be applied to CL. In addition, the researches about CL have been tried by means of experiments and simulations, but especially the transport properties have not been clarified yet. There are nanoscopic structures in Nafion thin films and it is hard to capture the transport phenomena in such a small area by experiments and macroscopic simulations.

 

In this study, we analyze proton transport properties in the cathode CL using molecular dynamics simulations, focusing on the dependences of the diffusion coefficient on water content. We consider the proton transport mechanism as a combination of the Vehicular mechanism and the Grotthuss mechanism. The Grotthuss mechanism is represented using empirical valence bond methods. It has been shown by previous researches in PEM that the Grotthuss mechanism is a dominant factor for proton diffusion in relatively high water contents. Thus, it is essential to consider the Grotthuss mechanism for analysis of proton transport in CL as well. The system consists of graphite surface and Nafion thin films. Pt particles are neglected because of a restriction of calculation cost. In PEM analysis, the diffusion coefficient of protons increases with increasing water contents. First, we report whether the same trend as observed in PEM can be seen in CL and the correlation between diffusibility and structures. Next, unique characteristics of proton transport properties in CL compared to the PEM analysis are reported. They are evaluated in terms of mass distribution of the thin films and solvent molecules. From this analysis, it is found that the diffusibility is not much affected by surface because of a lack of solvent molecules on surface, which is attributed to the hydrophobic properties of graphite.
Design and Luminescent Properties of Ce3+-Activated Oxide Phosphor
Authors: Kim Sun Woog , Hasegawa Takuya , Muto Masaru , Kawano Yukari , Uematsu Kazuyoshi , Toda Kenji , Takaba Hiromitsu , Ishigaki Tadashi , Sato Mineo
Published: February 2020

Ce3+ ion has been usually used as an activator in the white LEDs phosphor because Ce3+-activated phosphors have a strong optical absorption at wide light region from UV to blue light and exhibit broad emission band owing to the 5d-4f transition of Ce3+. Because 5d orbital electrons are not shielded by outer 6s and 6p orbital electrons, the excitation and emission band position of Ce3+-activated phosphors is strongly affected by the crystal structure of host materials.1) According to the crystal field theory, the energy splitting of 5d excited level generally increases when Ce3+ occupied in the compact site with short bonding length in host lattice.2) The larger energy splitting will contribute to shift the excitation and emission band of Ce3+-activated phosphors to longer wavelength side. From the viewpoint of the crystal field theory, we have been selected the oxide materials including 5, 6 or 7 coordination site with short bonding distance in the lattice of host materials to develop novel white LEDs phosphor that show excitation and emission spectra at longer wavelength region. As a result, we could successfully synthesize the novel red emission phosphors,3,4) and in this study, we presents the luminescence properties of the novel oxide phosphors developed. In this study, we present our design concept for development of novel white LEDs phosphors and luminescence properties of Ce3+-activated phosphors designed by our original materials design concept.

This work was supported by a project from NEDO, New Energy and Industrial Technology Development Organization (Rare Metal Substitute Materials Development Project Development of Technology for Reducing Tb and Eu Usage in Phosphors for Fluorescent Lamp by High-speed Material Synthesis and Evaluation).

References

W. M. Yen, S. Shionoya, and H. Yamamoto, Phosphor Handbook 2nd ed., CRC Press, Boca Raton, FL (2007)

B. Henderson and G. G. Imbush, Optical Spectroscopy of Inorganic Solids, Clarendon, Oxford (1989).

Y. Kawano, S. W. Kim, T. Ishigaki, K. Uematsu, K. Toda, H. Takaba, and M. Sato, Opt. Mater. Express, 4, 1770 (2014).

T. Hasegawa, S. W. Kim, T. Ishigaki, K. Uematsu, T. Takaba, K. Toda, and M. Sato, Chem. Lett., 40, 828 (2014).
Luminescent Properties of Al2O3:Tb3+ Powders Embedded in Polyethylene Terephthalate Films
Authors: Mariscal B. L. , Carmona-Tellez Salvador , Falcony Ciro , Murrieta Sánchez Héctor
Published: February 2020

The luminescent properties of Al2O3:Tb3+ powders embedded in polyethylene therephtalate (PET) films have been studied. Luminescent Al2O3:Tb3+ polycrystalline powders were synthesized by a simple evaporation method. X-ray diffraction (XRD) spectrum of powders of Al2O3:Tb3+ have the α-Al2O3 crystalline phase with peaks located at 2Θ = 25.78, 35.34, 37.96, 43.56, 45.8, 52.74, 57.7, 61.5, 66.74, 68.44, 77.12 and 80.94, which are associated with the planes (012), (104), (110), (113), (202), (024), (116), (018), (214), (300), (119) and (220), and the δ-Al2O3 phase is also present as identified  by peaks in 2Θ = 32.82, 45.8, 61.36 and 66.74, associated with the planes (220), (400), (511) and (440). The powder embedded films were obtained by the spray pyrolysis technique. The photoluminescence and cathodoluminescence emission spectra from these samples show, in both cases, luminescence peaks associated with transitions within the electronic energy levels of Tb3+ ions. The dominant peak is at 544nm corresponding to the 5D4→7F5 transition and present 5D4→7F6,
5D4→7F4 y 5D4→7F3 transitions in 494, 587 y 622nm, when excited with λexc = 299 nm at room temperature. The CIE coordinates for non-doped PET films are (x = 0.2045,  y = 0.3636), when excited with 270nm, this emission falls in the blue region. CIE diagram for powder embedded PET films excited with 299 nm have coordinates (x = 0.31, y = 0.5111); in this case, the emission is a combination of Al2O3:Tb3+ green light and PET blue light emissions. UV-Vis % transmission measurements on these films show that they are transparent (~ 80 and 95 %T).