bluuebunny/crossref_metadata_2025_split huggingface dataset:
Оxygen Vacancy Influence on the Stabilization Properties of Ferroelectric Hf0.5Zr0.5O2: First Principle Study
Authors: Perevalov Timofey V. , Islamov Damir R. , Gritsenko Vladimir A. 
Published: February 2020

The aim of the study is the investigation of the oxygen vacancy (VO) role for the stabilization of orthorhombic noncentrosymmetric (Pbc21) phase in Hf0.5Zr0.5O2 films. The simulations carried out in terms of the hybrid DFT using Quantum-ESPRESSO code for the four low temperatures Hf0.5Zr0.5O2 crystalline phases: orthorhombic ferroelectric (of-), monoclinic (P21c), orthorhombic oI (Pbca) and orthorhombic oII (Pnma).
It is shown that the VO concentration increasing leads to the fact that the pressure range under which the of-Hf0.5Zr0.5O2 structure can exist is narrowed. It is concluded that high VO concentration has a negative impact on the ferroelectric phase stabilization even for thin Hf0.5Zr0.5O2 films. It is established that of-Hf0.5Zr0.5O2 with O vacancies in any concentration is not stable for bulk crystal at any value of external pressure in which the structure is able to exist. However, it is shown that VO have a positive impact on the stabilization of the centrosymmetric oII phase of Hf0.5Zr0.5O2. Thus, the presence of oxygen vacancies and polyvacancies not only does not contribute to the Hf0.5Zr0.5O2 ferroelectric phase stabilization, but also leads to the destruction of the ferroelectric structure. This is consistent with the hypothesis that the degradation ferroelectric response of FeRAM elements during repeated reprogramming, is caused by the oxygen vacancies generation.
The work is supported by the Russian Science Foundation grant #14-19-00192.
Design of Perpendicular Magnetic-Tunneling-Junction Spin-Valve Including [Co/Pt]n Free Layer As Bulk Perpendicular Magnetic Anisotropy
Authors: Baek Jong Ung , Kondo Kei , Jung SunWha , Park Jea-Gun 
Published: February 2020

Recently, dynamic random access memory (DRAM) has scaling limit because of its capacitor area. To replace DRAM, the next generation memory devices are being studied. Among them, perpendicular spin transfer torque magnetic random access memory (p-STT MRAM) is considered as a promising candidate because of easy scaling down, low power consumption, high read and write speed and non-volatility.
p-STT MRAM has several challenges for commercialization. To keep a high retention time (~10 years), STT-MRAM should have thermal stability greater than 74. Although the thickness of free layer is increased with thermal stability, the thickness of free layer is limited to maintain perpendicular magnetic anisotropy (PMA). One of studies, double MgO based p-MTJ spin-valve structure is issued for its large volume because in case of double MgO based p-MTJ spin-valve, PMA of the free layer is originated from two i-PMA between the CoFeB free layer / MgO tunneling barrier and CoFeB free layer / MgO capping layer. The i-PMA induced from the two interfaces increases the total volume of the magnetic free layer which increases the thermal stability, but it is still limited by the thickness of the individual CoFeB free layers. In our study, therefore, we propose a new structure using interfacial Co2Fe6B2 and [Co/Pt]n multi-layer as bulk PMA to achieve higher thermal stability than that of double MgO based p-MTJ spin-valve structure.
The dependence of the magnetic moment and thermal stability on the number of [Co/Pt]n multi-layers was estimated by using vibrating sampling magnetometer (VSM) as shown in Fig.1 b. Magnetic moment t~180μemu/cm2) of i-PMA+[Co/Pt]2 multi-layers is similar to that(~180μemu/cm2) of double MgO based p-MTJ spin-valve structure. Also, magnetic moment (t~366μemu/cm2) of i-PMA+ [Co/Pt]5 multi-layers is about two times more than that of double MgO based p-MTJ spin-valve structure and thermal stability (~181) is two times higher than that (~74) of the double MgO based p-MTJ spin-valve structure. The thermal stability can be modulated by simply changing the number of [Co/Pt]n multi-layers. Obviously, these results show that i-PMA + [Co/Pt]n multilayer as bulk PMA based p-MTJ spin-valve can achieve a high thermal stability.
In our presentation, we report the different characteristics of the p-MTJ spin-valve with [Co/Pt]n multi-layers by examining the static magnetization behavior, TMR ratio and MgO crystallinity. In addition, we present how these properties influence mechanism of p-MTJ spin-valve.

Acknowledgements

This work was supported by a Basic Science Research Program grant from the National Research Foundation of Korea (NRF) funded by the Korean government (MSIP) (No. 2017R1A2A1A05001285) and the Brain Korea 21 PLUS Program in 2014.

Figure 1
Design of Double Pinned Perpendicular Magnetic-Tunnel-Junction Spin-Valve Exhibiting Multiple Resistance States
Authors: Choi Jin-Young , Kondo Kei , Baek Jong-Ung , Shim Tae-Hun , Park Jea-Gun 
Published: February 2020

Perpendicular spin-transfer-torque magnetic random access memory (p-STT MRAM) cells consist of a perpendicular magnetic tunnel junction and a selective device has been researched intensively because of the possibility of overcoming the scaling limitations of the current dynamic random access memory (DRAM) below the 10-nm design rule [1]. p-STT-MRAM requires high tunneling magnetoresistance (TMR) ratio greater than 150%, sufficient thermal stability (Δ=KuV/kBT) above 75 for a ten-year retention-time, and low switching current (J
C0 ~ 1 MA/cm2) must be achieved for low power consumption [2-3]. However, the thermal stability is hard to maintain when scaling down in 10-nm scale of the p-STT MRAM cells for terabit integration. It requires high interfacial anisotropy K
i
to maintain the thermal stability requirement for 10-year retention time [4].
In this study, we designed a p-MTJ spin-valve with a double pinned structure to realize two-bit operation to secure a larger scaling limit (see Fig. 1(a)). We investigated the dependency of the number of [Co/Pt]n multilayers on the coupling strength to the pinned layers in order to control the spin-electron direction of the pinned layers. The total number of [Co/Pt]n SyAF multilayers ferro-coupled to the bottom pinned layer was reduced from 9 to 3 layers to reduce the roughness of the MgO tunneling barrier to increase the TMR ratio. Also, the number of [Co/Pt]n of the top upper SyAF multilayers was modulated so that the coercive field (H
c) required to switch the spin-electron direction of the top pinned layer increased from about 0.3 kOe to 1 kOe which is sufficient to ensure the memory margin for two-bit operation, as shown in Fig. 1(b). Then, we investigated the multiple resistance states with the R-H loop of the double pinned p-MTJ spin-valve, as shown in Fig. 1(c). It showed four different resistance states depending on the spin-electron direction of the free layers and pinned layers as shown in Fig. 1(d) with a maximum TMR ratio of 166%. This implies that the double pinned p-MTJ spin-valve may be suitable for terabit integration compared to that of the single-bit operating p-STT MRAM memory cells.

Acknowledgements

This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No.2017R1A2A1A05001285) and Brain Korea 21 PLUS Program in 2014.

References

[1] K. C. Chun et al., IEEE J. Solid-st. Circ. 48, 598 (2013)
[2] J. G. Park et al., IEEE Int. Electron Devices Meeting, IEDM 2015–February, 19.2.1-19.2.4 (2015).
[3] Amiri, P.K., et al., App. Phys. Lett. 98, 112507 (2011)
[4] Shouzhong Peng, et al., IEEE MAGNETICS LETTERS,
volume 8 (2017).

Figure 1
Magnetic Field Assisted Electrodeposition of Co-Ru Nanorods for Water Splitting Reaction
Authors: Dobosz Iwona , Kutyla Dawid , Kolczyk Karolina , Kowalik Remigiusz , Zabinski Piotr 
Published: February 2020

The article presents results of tests on potentiostatic electrodeposition of ruthenium and Co-Ru alloys. The tests applying the method of cyclic voltammetry with the use of gold disk electrode (RDE) allowed to define a potentials range in which it is possible to obtain ruthenium and its alloys with cobalt from acid chloride electrolytes.
The influence of electrodeposition parameters and the electrolyte composition on the composition, morphology and structure of the obtained deposits was determined. Co-Ru alloys underwent XRD tests, an analysis with the XRF method and observations using scanning electron microscopy (SEM). Hydrogen evolution tests have been also performed.
Then, cobalt-ruthenium nanorods have been successfully synthesized by electrochemical deposition using an aluminum oxide membrane template with superimposed external magnetic field. The length and average diameter of cobalt alloy nanorods arrays are 4,5 - 9 μm and 100 nm, respectively. For nanorods deposited in applied external magnetic field of 0.6T we observe higher saturation magnetization and slightly higher coercivity field. This method offers a convenient and efficient path to synthesize metal array nanostructures with designed composition.
An Entropic Approach for Controlled Testing of Electrochemical Components
Authors: Bruce David Robert 
Published: February 2020

Custom-designed electrochemical test systems allow for specific measurements to be generated for isolated variables in advanced materials testing. A well designed first-principle system can give insight into more complex interactions often found in real-world devices. Often, such isolated test systems utilize sub-systems that draw upon external reactants for sustained testing and exhaust reaction products as a result. Practical limitations on delivery of purified feed streams and mediation of exhaust require system operation that can fail unexpectedly, often as a result of failure of the system itself rather than of the materials under investigation.
A novel system for testing of zinc-air fuel cell cathodes is presented as an example system that allows for total internal flows of reactant and product chemical flows. Such systems allow for cyclic purification and analysis of reaction products and establishment of a device in which the only output of the testing is heat and reliable data.
Examination of test system control of state properties and elimination of suspected system contaminants highlight the benefits of the developed self-contained flow systems. Insight into general design characteristics for robust electrochemical test systems are developed in light of the limitations of the presented entropy machines.
Electrochemical Generation of Sulfur Vacancies in the Basal Plane of MoS2 for Hydrogen Evolution
Authors: PARK Sangwook , Tsai Charlie , Li Hong , Nørskov Jens , Abild-Pedersen Frank , Zheng Xiaolin 
Published: February 2020

Molybdenum disulfide (MoS2) based catalysts for the electrochemical hydrogen evolution reaction (HER) have been widely studied as alternatives to platinum based catalysts due to the earth-abundance and great catalytic activity. Since the edge sites of 2H phase MoS2 were shown to be the active sites for HER, a great number of studies have focused on maximally exposing catalytically active edge-sites through diverse engineering process. Recently, we demonstrated that active sites could be created on the basal plane of 2H-MoS2 by generating sulfur (S)-vacancies. At the S-vacancy sites, the under coordinated Mo atoms introduce gap states that allow for favorable hydrogen binding, introducing the highest per site turnover frequency (TOF) reported for any MoS2-based catalyst for HER. However, the S-vacancies in the basal plane have so far only been generated using controlled argon (Ar) plasma exposure and H2 annealing. A more industrially viable alternative to the argon plasma desulfurization process is needed. To effectively utilize S-vacancies in MoS2 catalysts for industrial applications, a facile, general, and scalable route for generating S-vacancies in MoS2 of any morphology is needed.
Electrochemical desulfurization is one of the possible methods for generating S-vacancies by removing sulfur atoms from the basal plane of MoS2. This method removes the sulfur atoms in the basal plane of 2H-MoS2 to form hydrogen sulfide (H2S) gas through a desulfurizing activation cycle. In this work, we show an electrochemical (EC) desulfurization method for generating S-vacancies in monolayer as well as polycrystalline multilayer MoS2 supported on diverse electrodes. Density functional theory (DFT) calculations show that S-vacancies are expected to be thermodynamically favorable relative to the pristine basal plane at a sufficient negative potential. The concentration of S-vacancies can be controlled by changing the applied desulfurization voltage. These theoretical predictions are experimentally verified with the continuously grown MoS2 monolayers on gold (Au) showing that electrochemically generated S-vacancies are comparable to the recent work about Ar-plasma treated ones. In addition, we demonstrate the generality of the electrochemical desulfurization approach by generating S-vacancies on MoS2 multilayers supported on flat carbon rods and porous carbon foams leading to a significant HER activity enhancement. Finally, we experimentally show that the HER activity is stable under extended desulfurization durations as well as operating durations and that the concentration of S-vacancies and activity can be varied using the applied potential in polycrystalline multilayer MoS2 on carbon foam electrode.
Nanostructured Cu-Sn Alloy for Actively and Selectively Converting CO2 to CO
Authors: Ju Wenbo , Zeng Juqin , Rentsch Daniel , Ma Huan , Castellino Micaela , Bejtka Katarzyna , Pirri Candido F. , Vogt Ulrich F. , Battaglia Corsin 
Published: February 2020

Many strategies have been proposed for carbon dioxide (CO2) reduction aiming to close the carbon cycle and compensate anthropogenic CO2 emissions. Electrochemical CO2 reduction has several advantages that it can be carried out under ambient conditions with water as the only additional feedstock, and electricity generated from renewable sources can be employed to achieve a fully sustainable route [1].
Copper (Cu) has unique features for electrochemically converting CO2 to a range of chemicals including hydrocarbons [2], but its selectivity for specific products is low. Especially, at a low or intermediate overpotential, the hydrogen evolution reaction (HER) dominates the overall process on polycrystalline Cu in aqueous solutions [3]. However, the selectivity of Cu can be tuned by introducing a secondary metal. Tin-modified nanostructured Cu (CuSn) electrocatalysts have been developed for electrochemically converting CO2 to carbon monoxide (CO). The doped Sn atoms in the topmost layer alloy with Cu, form a CuSn shell, and efficiently suppress the HER. By optimizing the Sn content in the CuSn layer and the nanostructure, the faradaic efficiency for CO reaches > 90 % at -0.7 V vs. RHE, and remains above 85 % in a wide potential range from -0.7 to -1.0 V [4]. However, the excellent selectivity for CO can be only observed at CuSn dendrites. When the CuSn catalyst has a particulate morphology, the selectivity for CO becomes much worse, even though the surface composition has the optimal Cu/Sn ratio. The CuSn particles are active for the HER at a low overpotential. Although the HER can be efficiently suppressed to a faradaic efficiency of less than 15 % at a high overpotential, the major products for CO2 reduction are both CO and formate (COOH-) [5]. This work highlights the importance of nanostructure and surface composition of CuSn catalysts for active and selective CO2 reduction.
Electrodes consisting of a three-dimensional porous architecture are prepared for a large active surface per unit geometric area. The CO production achieves a high partial current density of 4.9 mA·cm-2 at -0.8 V [4].
[1] Centi, G., et al. Energy Environ. Sci. 2013, 6, 1711-1731 [2] Qiao, J., et al., Chem. Soc.
Rev.
2014, 43, 631-675 [3] Li, C., et al., J. Am. Chem. Soc.
2012, 134, 7231-4 [4] Zeng, J., et al., submitted [5] Ju, W., et al., in preparation
Electrochemicaly Assisted Separation of REE Magnetic Ions in the Microchannel
Authors: Kolczyk Karolina , Kutyla Dawid , Wojnicki Marek , Kowalik Remigiusz , Luty-Blocho Magdalena , Zabinski Piotr 
Published: February 2020

Rare earth elements (REE) are interesting due to their magnetic, luminescence properties. They found an application in high technology e.g.: a radar, a sonar, a telescope, hybrid cars, as catalytic converters, television and computers screens, computer hard drives, wind turbines, etc. REE are produced both from primary and secondary sources. In hydrometallurgical processes, the most problematic step of those metals production is their separation. For this reason, it is desirable to improve the current processes via application of High Magnetic Gradient. It utilizes the different magnetic properties of rare earth metal ions to achieve separation by attraction or repulsion in an inhomogeneous magnetic field.
In this study, the using of elcectrochemical method combined with an inhomogeneous magnetic field allows for an enrichment of Ho3+ ions and then their separation from depleted aqueous solutions. The experiments were carried out in a microreactor produced by a 3D printing technology. The ions movement was carried out on a circular path due to the spiral arrangement of the microchannel. The inhomogeneous magnetic field in the channel was created by the placement of the microreactor in a laboratory electromagnet. During the flow conditions, the metal ions were exposed on the force coming from the gradient magnetic field and their separation into two streams was observed. First one consisting of the enrichment solution in magnetic ions and second one containing depleted solution. These solutions were collected and analyzed using UV/Vis spectrophotometry and MP-AES (Microwave Plasma-Atomic Emission Spectrometer).
In this work the influence of the applied current, direction of current field lines, residence time of the magnetic ions in the microchannel and their concentration on the efficiency of separation enrichment and depleted solution were examined.
Acknowledgment
The authors would like to thank Polish National Science Centre for the financial support provided by the grant: No UMO-2014/15/B/ST8/01528.
Biowaste-Derived Carbon Electrodes for Capacitive Deionization
Authors: Lado Julio , Ruotolo Luis Augusto Martins , L. Zornitta Rafael 
Published: February 2020

Capacitive Deionization (CDI) is one of the most relevant emerging desalination technologies. CDI is based on the electrosorption of salts using a pair of electrically charged porous electrodes. In this way the CDI process consists on charging (ion removal)/discharging (ion desorption) cycles using the same operational principles of the supercapacitors. Therefore, CDI cells might potentially allow to recover part of the energy consumed in the desalination process while delivering drinking water.
One of the key elements in this technology are, as in the supercapacitor field, the electrodes. In accordance with this, intensive research has been conducted in order to find the best electrode candidates in terms of specific surface area (SSA), porosity, electrical conductivity, surface chemistry and optimized chemical surface charge of the electrode. The combination of these properties are expected to provide higher values of salt adsorption capacity (SAC) and average salt adsorption rate (ASAR). Moreover, it should be also remarked that one of the critical requirements in order to make CDI competitive with current desalination technologies (such as reverse osmosis or electrodialysis) is the cost of the electrode materials. In order to address this challenge, the preparation of carbon electrodes from abundant biowaste precursors was studied as a low cost and green alternative to more innovative carbon composite complex materials.
In this work the authors decided to evaluate different activation treatments of a biowaste precursor in order to obtain suitable activated carbons for capacitive deionization. The different structural properties (BET SSA, pore size distribution, chemical surface groups) of the synthesized AC’s were correlated not only with their electrochemical response (specific capacitance) but also with the CDI performance (SAC, electrosorption kinetics, charge efficiency and the energy consumption).
(Invited) Visible Light Driven Photoelectrocatalytic Degradation of Acid Yellow 17 Dye Using Thin Film Sn3O4 Flowers-like Nanostructurred Supporting Onto Ti
Authors: Zanoni Maria VALNICE BOLDRIN , Huda Adri , Suman Pedro H , Orlandi Marcelo Ornaghi , Torquato Lilian D. M. 
Published: February 2020

Photoelectrocatalysis is a technique with consolidated principles that has gained prominence and has been successfully applied in organic compound oxidation, microorganism inactivation, CO2 reduction energy[1]. Their application on wastewater treatment is based on the use of a semiconductor that generates charge carriers (e-/h+) when irradiated by light energy equal or greater than its band gap and simultaneously biased by a gradient potential. The recent progress of photoelectrocatalysis is intimately related to the advances in materials science, especially in nanomaterials. Other challenges are the development of stable semiconductor materials able to be activated by solar irradiation.
Among the numerous types of semiconductors used as photocatalysts, tin oxides with diﬀerent forms (SnO, SnO2 and Sn3O4), present wide-spread applications, because of its abundant availability and non-toxicity. The aim of this work was to perform the synthesis of a Sn3O4 ordered structure under mild operational conditions to further apply it in the photoelectrocatalytic degradation of a dye, taken Acid Yellow 17 as a model of textile dye treatment. The hierarchical form of Sn3O4, with the flower-like nanostructure with triclinic Sn3O4/Ti, was successfully prepared using microwave-assisted hydrothermal method at pH 6, in 150 oC. The as-prepared Sn3O4 was deposited in the titanium substrate using spin coating methods. The Sn3O4 /Ti nanostructure demonstrated high photocatalytic activity in the visible wavelength (λ>390 nm), calculated band gap of energy 2.4 eV by diffuse reflectance. The electrode was successfully applied on degradation of 10 ppm solution of AY17 (pH 4) at low bias potential (0.5 V) and visible light irradiation reached complete discoloration after only 30 min of treatment. The TOC removal reached 83% after 4000 s-1 of light irradiation time. Therefore, the flower-like nanostructured Sn3O4 proved to be efficient in the visible light driven photoelectrocatalytic degradation of AY17 dye, which represents an energy-saving option for its future treatment and removal of the environment.

Acknowledgments

We acknowledge the financial support from INCT-DATREM, process FAPESP 14/50945-4 and CNPq 465571/2014-0.

References

[1] G. G. Bessegato, T. T. Guaraldo, J. F. de Brito,M. F. Brugnera, M. V. B. Zanoni, Electrocatal. 2015 6, 415–441.