bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetic Conductive Filament Formed in the Reram Device with Ferromagnetic Electrode
Authors: Yoshida Hayato , Shimizu Tomohiro , Ito Takeshi , Shingubara Shoso 
Published: February 2020

We have studied electrical transport properties of the ReRAM device with ferromagnetic electrode, in order to understand origin of the nano-conductive filament (NCF) which was formed in the low resistance state (LRS). We observed anisotropic magnetoresistance (AMR) in the device having ferromagnetic electrode at one or both sides of electrodes. [1, 2] The device structure is Ni(40 nm)/HfO2(3.8 nm)/FeNi(40 nm). The size of the cross-point device area is 1×1 μm2. The HfO2 layer was deposited by reactive sputtering using Ar and O2mixture gases.
Figure 1 shows the resistance switching characteristics of the ReRAM device with two ferromagnetic electrodes. The bipolar operation was observed. We measured magnetic conduction property of the LRS, as shown in Figure 2. Direction of the magnetic field is in-plane and parallel to the Ni top electrode. The structures of the devices in Figure 2-a and 2-b are same, but the shapes of magnetoresistance were quite different. Negative magnetoresistance appeared in the sample #1 (Fig.2-a), however, positive magnetoresistance appeared in the sample #2 (Fig.2-b). Both cases showed hysteresis property against change in the magnetic field, and there are abrupt changes in MR ratio around 200 mT. These magnetoresistance properties are considered to be anisotropic magnetoresistance. Positive MR appears when magnetic field is parallel to current, and negative MR appears when the magnetic field is perpendicular to the current. It is suggested that NCF is parallel to the field for #2, and perpendicular to the field for #1. In our samples, dielectric layer of HfO2surrounds the bottom Ni electrode, and NCF formation occur either at the top or at the sidewall of the bottom electrode. The abrupt MR jump may be related to single domain switching in the narrow magnetic NCF, and detailed discussion based on micro-magnetic simulation is in progress.
References
[1] S. Otsuka, D.Ito, Y.Hamada, T.Shimizu, and S.Shingubara, Jpn. J. Appl. Phys. 54, (2015) 05ED02.
[2] S.Otsuka, Y.Hamada, T.Shimizu, and S.Shingubara, Applied Physics A, 118 (2015) 613-619.

Figure 1
Reversible Phase Transition in Gete through Resonance Bond Swiching
Authors: Cho Mannho , Yang Wonjun , Kim Dasol , Park Seungjong , Ahn Min , Han JeongHwa , Jung Hoon 
Published: February 2020

Phase change materials, especially those along the GeTe-Sb2Te3 tie-line (GST), have been widely used in applications of memory devices. Using these materials, information can be stored as optical and electrical change contrast arising from thermally induced structural transitions between the crystalline and amorphous phases. Amorphous phase is obtained by heating the material of crystalline phase upon melting temperature and cooling it fast enough so that it solidify in the amorphous phase. On the other hand, crystalline phase is obtained by heating the material of amorphous phase during relative longer time (a few ns) than amorphization time within appropriate temperature range between crystallization temperature and melting temperature. Contrary to this relatively small difference of heating condition, their physical properties are extremely different from each other. Besides, their fast switching properties and rather good reversibility show promising characteristics for phase change materials as a candidate material for universal memory as well as a most intriguing topic in material society. Despite of these specific material properties, the fundamental reasons for this reversible and fast transition are still in a debate and needs to be understood more considerably as a view point of local structure and orbital environment. Many of the previous studies for understanding phase change mechanism concentrated in comparison of orbital structure between the crystalline phase and amorphous phase. However, the investigation on the modified crystalline phases which is weakly perturbed by thermal variation or external stress could show possible phase transition path.
In this study, using uni-axial stress (bending stress), the crystalline GeTe is modulated to have reversible structure deformation which gives rise to drastic change on optical property with resonance bond breaking. Modulated GeTe also shows reversible electrical change caused by orbital rearrangement and irreversible electrical change caused by defect formation. A stress which is relatively smaller thermodynamic perturbation than heat also can be an important variable in phase change mechanism and it might support the reason why both of set and reset state in phase change memory contain various of chemical states.
Hopping Conduction in Intermediate Resistance State of Tantalum Oxide Resistive Switching Memory
Authors: Huang Jiu-Xing , Chen Jen-Sue 
Published: February 2020

Resistive switching memory with a simple MIM (metal-insulator-metal) structure has the characteristics of high operation speed, high retention time, low operation voltage. Generally, the resistance switching mechanism is strongly related to defect states in oxide and the electrode/oxide interface. Based on I-V sweeping curves, Ta/TaOx/Pt device can be operated in bipolar mode, with writing at positive bias and erasing at negative bias. Different resistance states are achieved in the device by controlling the reset stop voltage under bipolar mode operation. According to the I-V measurement at various temperatures, it is observed that conduction mechanisms are different in three resistance states of the device. The low resistance state (LRS) shows ohmic conduction with a semiconductor-like behavior. This situation can be interpreted by the existence of the oxygen vacancy filament connecting the top and bottom electrodes. The high resistance state (HRS) is governed by Schottky emission conduction. The intermediate resistance state (IRS) shows hopping conduction. It can be regarded as changing of interior state of the active layer between HRS and IRS.
To characterize separate contribution to the total resistance from individual component, complex impedance spectroscopy is used to study three resistance states of the device. It is shown that HRS and IRS can be described with an equivalent circuit consisting of the major components R
1, R
2, R3, C1and C
2, and LRS can be characterized with an equivalent circuit consisting of the major components R
1, R
2, R3, C1. These components show a strong dependence on the reset stop voltage, which can be explained in the framework of oxygen vacancy model and conductive filament concept.
According to results of temperature-dependent I-V measurement and complex impedance analysis, different current conduction mechanisms and values of major components in equivalent circuit in three resistance states can be attributed to changing of the filament structure and the oxygen vacancy distribution.
(Invited) Electrostatic Field and Non-Thermal Plasma for Handling and Processing Bio-Molecules and Cells
Authors: Mizuno Akira 
Published: February 2020

Electrostatic field is an important tool for handling fine objects such as biological molecules and cells. Non-thermal plasma generates reactive radicals. Long life-time radicals can migrate in liquids to penetrate membranes of cells and tissues. Electrophoresis, or Coulombic force has been widely used in biology for separation of cells and molecules. Dielectrophoresis in non-uniform AC-field uses gradient force. Since AC voltage can be applied to conductive liquid with minimum generation of bubbles, dielectrophoresis is an important tool for handling living cells and micro-organisms. Due to polarization, gradient force appears on particles of neutral charge, and magnitude and direction of the gradient force depend on the frequency response of the objects. Gradient force can be generated using a focused laser without using fixed electrodes. Biological cells are pulled into the laser focus where E-field is high, and they are trapped. This is called laser tweezers, and is a convenient tool for handling microbes and fine objects with diameter range between 0.2 – 5 micro-meter. Laser tweezers cannot hold DNA molecules of random-coiled shape, because they are too thin (2 nm diameter). The globule transition of DNA molecules can be used to fold random-coiled DNA into a solid globule DNA. This transition is reversible, controlled by concentration of counter ions in medium. Globule DNAs, therefore, can be stretched again. Globule DNAs are manipulated by laser tweezers. Droplet-in-oil emulsion is a suitable container to be manipulated using electrostatic force or laser tweezers. This emulsion system can be used to conduct PCR amplification starting from single fragment of DNA. High electric field causes reversible or irreversible puncture of membrane of cells. This phenomenon can be used for cell fusion, infection of genes and chemicals, cell fusion, or sterilization. To punctuate cell membranes, reactive radicals are also effective. Radicals are generated in NTP and injected into liquid. Certain long-lived radicals migrate in the liquid and penetrate into cells through membrane or protein shell.
E.coli or B. subtilis spore in liquid was exposed to NTP, either DBD(dielectric barrier discharge) or a plasma jet with Ar or He. Analysis using decay of GFP (green fluorescent protein) fluorescence proved that oxidative radicals are penetrating through the membrane into cells. Exposure of NTP to Bacteriophages indicated that protein shells are damaged at first, and that double stranded DNA is stronger than that of single stranded genes of the phages. In conclusion, electrostatic force and NTP are effective tools for handling and for processing biological particles including cells, viruses and molecules. Wide range of applications are still to be developed. Several examples will be reported of the application of electrostatic field and NTP in handling and processing of cells and single DNA molecules.
(Invited) Plasma Assisted Preparation of Low Pt Content Proton Exchange Membrane Fuel Cell Anode Catalysts
Authors: Matolin Vladimir , Dubau Martin , Ostroverkh Anna , Lavkova Jaroslava , Matolinova Iva 
Published: February 2020

Pt doped cerium oxide thin films with a nano-porous structure was prepared by reactive rf magnetron deposition on a fuel cell gas diffusion layer (GDL) coated with nitrogenated amorphous carbon films (CNx) as an interlayer. We show that the structure and morphology of the cerium oxide-CNx composites depend on the oxygen and nitrogen concentration in working gas used for catalyst deposition. Considerable plasma erosion of the carbonaceous interlayer accompanied by the formation of highly porous carbon/cerium oxide bilayer systems is reported. Oxygen plasma etching of the carbon interlayer occurring simultaneously with cerium oxide film growth is considered to be the driving force for the formation of cerium oxide film nanoporosity with large active surface.
Thin film techniques permits to grow the catalyst film characterized by highly dispersed platinum showing high hydrogen oxidation activity and stability. These new materials may help to substantially reduce the demand for expensive noble-metals in proton exchange membrane fuel cell (PEMFC) catalytic applications.
We measured Pt-CeOx thin film anode catalyst activity in hydrogen PEMFC and compared it with performance of a standard reference cell. We showed that membrane electrode assembly (MEA) made by assembling Pt-CeOx/CNx anode, containing 2-4 μg per cm2 only, and a reference standard cathode can deliver 1.2 W/cm2 power density.
IR Laser Modifications of Anodic Tantalum Pentoxide for Photonic Applications
Authors: Kulpa Alina 
Published: February 2020

Making waveguides requires modification of material along a waveguide path in such a way that conditions for light propagation are advantageous along the waveguide but not so much in surrounding material. Usually, waveguides are produced with micro or nano photolitographic techniques that later require some wet chemistry, and wet or dry etching processes, or in-diffusion processes. Here we are presenting our experiments on non photolitographic modification of electrochemically prepared tantalum pentoxide, Ta2O5, for possible photonic applications. The e-beam evaporated thin tantalum layers on glass were anodized at 23◦C in the 0.5% H2SO4 electrolyte. After anodization samples were rinsed with deionized water and blow dried with nitrogen gas. Laser material modifications were performed in an OPTOMEC, Inc. Aerosol Jet Printer, Model AJ300CE that was equipped not only with a pneumatic and an ultrasonic jet printing set ups, but also with a UV source and with a IR laser. The laser was static over a platen where a sample was located. The laser beam was perpendicular to the platen. Laser writing was done by moving the platen. The platen motion (+/- 1um) was computer controlled and that practically allowed any design. Any *.dxf design files were transformed into the program files that run the system. Straight lines were tested for various laser powers. The width of lines was laser power depended. The circular designs and random designs were generated at the constant laser power and at the constant platen speed. Zeiss optical microscope images of samples were collected without a filter. The microscope light was perpendicular to the surface of the samples. All laser inscribed patterns were very bright compared to the rest of the samples - Figure 1. Figure 1. The IR laser inscribed pattern in anodic Ta2O5 sample. The line with is ~115um. * Electrochemical Society Active Member

Figure 1
Influence of Cooling Rate on Coercivity and Microstructures in Hot-Deformed Nd-Fe-B Magnets By Nd-Cu Electrochemical/Electroless Deposition
Authors: Kwon Jeehye , Yoo Dayoung , Park Jieun , Lee Dongyun 
Published: February 2020

In order to produce a high performing Dy free NdFeB permanent magnet for use at high temperature, control of grain size and interfaces is a significant factor: fabrication of magnetic domain-sized grains aligned in a specific direction and well-separated interfaces by non-magnetic materials. In this study, we used a melt spun powder of several tens of nanometer to produce domain-sized grains and then hot-pressing and dye-upsetting processes were performed to form anisotropic-grained NdFeB magnets. Now, we focused on to coat thin layers in between grains to produce well-separated interfaces by non-magnetic species. For that purpose, we used a well-known grain boundary diffusion process, GBDP. Nd-Cu system was chosen because of making lower melting eutectic alloys, and electrochemical and electroless deposition methods were adopted for mass production.
Nd and Cu were deposited by electrochemical and electroless methods, respectively followed by heat treatment in vacuum at 600°C for 25 min. And then they were cooled down in three different ways; furnace cooling, oil cooling at room temperature, and frozen oil cooling. By controlling the microstructures of the interfaces, we can restrict the reverse of magnetic domain mostly generated by defects and grain growth of the NdFeB raw materials. Interfacial microstructures could be controlled by heat treatment especially on cooling rate after GBDP. As a result, it was found that the Nd-rich phases were well distributed in the grain boundaries with the cooling rate. It was confirmed that the change of interfacial microstructure influenced on the magnetic properties, e.g. coercivity, remanence. In case of room temperature oil cooling, coercivity was increased 15.65kOe to16.37kOe, while the coercivity was reduced by frozen oil cooling. Presumably, α-Fe phase decreased with increasing cooling rate which induced increase of coercivity. On the other hand, main phase of NdFeB might be transformed to amorphous phase with further increase of cooling rate that caused decrease of coercivity. In order to identify the phases during GBDP and cooling process, an intensive TEM work will be presented in this presentation.
(Invited) From Solid State Chemistry to Battery Materials Electrochemistry: A Tool for Solid State Chemistry
Authors: Delmas Claude 
Published: February 2020

Researches on battery materials has considerably increased during the last 30 years due to the huge development of lithium-ion batteries for portable devices (laptops, cellular phones, …) and more recently with the need to store energy in order to optimize its consumption. The next goal is the development of batteries for electric vehicles and their use into the grid. Nevertheless, the aqueous batteries (Ni-Cd, Ni-MH and Lead Acid) are always used in numerous applications thanks to their low price. In most of the batteries, the intercalation (deintercalation) of monovalent cations (H+, Li+, Na+) and electrons is the basic electrochemical reaction. The cell voltage is equal to the difference in Fermi level between the two electrodes. If one electrode exhibits a constant voltage it can act as reference and therefore, the cell voltage reflects all structure modifications which occurs on the material upon intercalation. The change is cell voltage depends on: (i) the electronic band filling, (ii) the change in the band structure due to change in composition, (iii) the modification of the Magdelung energy. In some cases the monotonous decreases of the voltage during the intercalation reaction indicates that the reaction occurs through a monophasic domain. In numerous cases, the reaction mechanism is more complicated and involves biphasic domains and/or formation of materials with a specific composition. The voltage vs composition curve is much more complicated and gives directly the phase diagram of the studied system.
For the solid state chemist, the studies of the electrochemical reaction using a battery opens new possibilities to determine phase diagram at RT, but also to synthesize new metastable phases from a precursor made by classical solid state chemistry. The in situ or in operando experiments allow to follow directly the structural modifications occurring during the electrochemical reaction. Using synchrotron experiments it is possible to make experiments at high rate and therefore evidence intermediate states and understand the reactions mechanism. In the recent years, XRD diffraction and XAS analysis were intensively used.
On the opposite way, very sophisticated Solid State Chemistry techniques like solid state MAS NMR, Mossbauer spectroscopy and high resolution electron microscopy in aberration corrected microscope allowed to characterize battery materials at the atomic level.
In this presentation, some typical results obtained in Bordeaux concerning lithium and sodium layered oxides will be presented to emphasize the dual approach:
batteries to solid state chemistry and solid state chemistry to batteries.
Energy Dispersive X-Ray Diffraction (EDXRD): An Effective in-Situ Approach for Spatial Resolution of Electrode Reactions
Authors: Takeuchi Esther S , Marschilok Amy C , Takeuchi Kenneth J 
Published: February 2020

Energy dispersive x-ray diffraction (EDXRD) presents a special opportunity to achieve spatial resolution of an electrochemical process within the electrode inside a functioning electrochemical cell, providing the opportunity for tomographic-like data analysis. White beam radiation coupled with a synchrotron “wiggler” insertion device emits high energy radiation which can penetrate bulk engineering materials such as steel, enabling in-situ measurement of conventionally designed prototype and production level batteries. Unlike other in-situ methods, EDXRD does not require the use of a modified or special cell design. Rather, the method enables a direct probe of electrode reactions in cells fully encased in their steel housings. These studies used a family of AgxVOy(PO4)z materials as model systems to provide insights into the electrochemical reduction process for inherently poorly conducting phosphate and diphosphate based cathode materials. The systems proved to be particularly well suited for EDXRD in-situ studies as the Ag0metal product formed on reduction could be detected in small amounts.
In-situ EDXRD was measured at several x-direction locations in several stainless steel coin cells with AgxVOy(PO4)z cathodes discharged to different depths of discharge under several rates. At each location spectra were collected in increments through the thickness of the electrode. The presence of Ag0 as a reduction product in silver vanadium phosphate cathodes had been verified ex situ using x-ray diffraction and scanning electron microscopy experiments. However, in situ measurements of the Ag0 provided the opportunity for further insight into the electrochemical reduction mechanism, regarding the location and distribution of the reduction products.
Charge Transfer Parameters (rCT, j0 and k) Determined By Combining Tomography Analysis with Impedance Modelling
Authors: Costard Janina , Joos Jochen , Weiss Michael , Ivers-Tiffée Ellen 
Published: February 2020

Lithium-ion batteries allow for a broad range of power to energy ratio, i.e., originating from their flexibility in terms of (positive) electrode material, blend ratio, and microstructure design. Electrode models, which consider the required functionality in an appropriate way, are mandatory for optimization. Among them, electrochemical models are based on fundamental equations describing migration, diffusion and intercalation kinetics.
A crucial and challenging part of the model development is its parameterization. Material parameters, especially for (positive) intercalation electrodes, are hardly available from literature and/or the variance of the available values is (too) large, as discussed in [1].
The present work investigates the charge transfer process taking place at the interface between a (positive) electrode material and the liquid electrolyte. The model parameters (i) area specific charge transfer resistance rCT (ii) exchange current density j0 and (iii) rate exchange coefficient k are determined using a combination of focused ion beam milling (FIB) and electrochemical impedance spectroscopy (EIS). The microstructure parameters tortuosity, porosity and active surface area are determined from a 3-dimensional reconstruction of the electrode and the measured impedance spectra are fitted with an appropriate transmission line model (TLM). These methods have already been applied by our group for the investigation of battery electrodes [2, 3] but a combination of both methods has not been performed so far. By correlating the microstructure parameters (obtained by FIB) with the loss processes (obtained by EIS), the required material parameters for modelling the charge transfer process became accessible.
For validating the reliability of the presented approach, 4 cathodes of the (NixMnyCo1-x-y) solid solution system with varying microstructure are examined and compared yielding very low variance compared to values from literature.

References

[1] M. Ecker, T.K.D. Tran, P. Dechent, S. Käbitz, A. Warnecke and D.U Sauer, J. Electrochem.
Soc.
162, A1836-A1848 (2015)
[2] M. Ender, J. Joos, T. Carraro and E. Ivers-Tiffée, J. Electrochem. Soc.
159, A972-A980 (2012)
[3] J. Illig, M. Ender, A. Weber, E. Ivers-Tiffée, J. of Power Sources
282, 335-347 (2015)

Figure 1