bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dependency of Multi-Level-Cell Behavior on Thickness of Top MgO Tunneling Barrier in Double Pinned Structure Perpendicular Spin-Torque-Transfer Magnetic Random Access Memory
Authors: Jun Han-Sol , Park Miri , Jung Sunhwa , Choi Jin-Young , Ashiba Kei , Baek Jong-Ung , Shim Tae-Hun , Park Jea-Gun 
Published: February 2020

These days dynamic-random-access-memory (DRAM) fabrication to scale down under 10-nm is complex which leads to high cost [1]. On the other hand, perpendicular spin-transfer-torque magnetic random access memory (p-STT MRAM) cell has a possibility of high-density integration with feature size of 4F2. Therefore, p-STT MRAM is the most powerful candidate of new memory instead of DRAM. In hence, p-STT MRAM requires high tunneling magnetoresistance (TMR) ratio greater than 150%, enough 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 [2-4]. However, the thermal stability is hard to maintain when the cell size is scaled down to 10 nm because the small volume of free layer leads to the changes of direction of spin by thermal agitation [5].
In this study, we designed a p-MTJ spin-valve with a double pinned structure to realize two-bit operation to overcome a larger scaling limit. We calculated four resistance states using relationship between the two different TMR of each MTJs. In particular, if the TMR of MTJ1 is half of MTJ2 and ratio of parallel resistance(Rp2/Rp1) is 0.8-0.9, the difference of each resistance state is equal. (see Fig. 1(b)) The TMR is mainly dependent on thickness of MgO tunnel barrier; therefore, we fabricated the p-MTJ spin-valve with a different thickness of MgO tunnel barrier (0.90 nm-1.35 nm) of MTJ1. Finally, we confirmed that the R-H curves match the four resistance states of p-MTJ with double pinned structure with our predicted results, and interval of resistance state is uniform when the thickness of top and bottom MgO are 1.36 nm and 1.10 nm as shown in Fig. 1(c). 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.
In the end, we report dependency of MLC behavior on thickness of top MgO tunneling barrier in double pinned structure pSTT MRAM. In addition, we present the MLC behavior of pSTT-MRAM with double pinned structure and show the thickness of top MgO for uniform resistance state.

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] Y.Huai et.al., IEEE International Magnetics Conference, AB-07 (2015)
[4] H.-S. P. Wong et. al., “Stanford Memory Trends,” (2015)
[5] Shouzhong Peng, et al., IEEE MAGNETICS LETTERS,
volume 8 (2017).

Figure 1
Novel Degradation Model of Igzo TFT on High Drain Bias Stress
Authors: Kim Kihwan , Seo Miseon , Choi Byoung-deog 
Published: February 2020

In this paper, the TCAD degradation model of IGZO using spatial distribution (X, Y) of physical parameters is proposed for the first time and is confirmed according to various channel length, active thickness, and bias stress conditions that agree with actual measurements. Oxygen vacancy in the presence of 2+ ionized states (VO
2+) in IGZO is stable. However, when band bending is severe, the electrons are captured, and the structural transition occurs as a neutral VO in the meta-stable state. This process is assumed to be a mechanism of IGZO degradation at high drain bias stress, and the electric field (>0.5M V/cm) and electron concentration (>1x1010 cm-3) in the channel are considered as the main factors of degradation and are modeled using the mapping function provided by Silvaco. Fig.1 show that the flow of development of degradataion model using TCAD.
Based on the oxide degradation mechanism, the following mathematical model was proposed to determine the number of electrons captured by the electric field, Ɛ(X,Y) and the electron concentration n(X,Y) at each position in the oxide film according to equation 1. Here, ƐC and nc represent the critical electric field and electron concentration at which the deterioration starts, respectively, and 0.5 M V/cm and 1x1010 /cm3. ƐC represents the minimum energy required for metastable transition to the metastable state, and nc is a threshold value that rapidly increases the probability of occurrence of this event. These parameters can be very important physically, but they are now empirically derived from the measurement results.

Figure 1
Controlled Electrochemical Synthesis of Ag Nanoparticles and Their Morphology-Dependent Performances on Catalysing Hydrogen Evolution Reactions
Authors: Ma Yue , Rosillo-Lopez Martin , Cai Xiaosheng , Hadzifejzovic Emina , Foord John S. 
Published: February 2020

Hydrogen evolution reaction (HER) is one of the most critical reactions in fuel chemistry to produce clean and sustainable hydrogen gas as a renewable energy source. Nowadays, HER has always been catalysed with costly Pt or Pd metal1. To reduce the cost but still maintain a satisfactory performance, studies on Pt/Pd free catalysts for HER have never ceased. In the present work, we explore the electrodeposition of three morphologies (polyhedral, dendritic, and spherical) of Ag nanoparticles on boron-doped diamond electrodes (BDDEs) in various electrochemical conditions including deposition potential and deposition time. Specifically, by varying the deposition potentials of the single-stepped electrochemical deposition, a morphological change from polyhedral to homogeneous dendritic Ag was observed. The high deposition potential would drive the formation of dendritic Ag, which is a thermodynamically unfavourable structure with high surface energy. On the other hand, a two-stepped deposition mechanism was performed to synthesize spherical Ag nanoparticles. This two-stepped mechanism, which was used in synthesising small Au nanoparticles with high coverage by F. Bottari et al., contains a nucleation step at a more negative potential, and a growth step at a less negative potential.2 The sizes of each type of Ag nanoparticles were confirmed by Scanning Electron Microscopy (SEM), and the surface compositions were verified by X-Ray Photoelectron Spectroscopy (XPS). The current densities for HER catalysis were investigated using Linear Sweep Voltammetry (LSV), and a connection between morphologies and catalytic activities was drawn. All three types of Ag modified BDDEs showed better catalytic performance compared to that of drop-coated colloidal Ag-BDDE with comparable coverage and bare BDDE. Notably, spherical Ag-NP modified BDDE with an average particle diameter of 75nm has the highest percentage of pure elemental silver and showed the best performance as well as high stability in HER catalysis, which can be a less expensive yet efficient alternative for Pt/Pd containing catalysts.
References:

Walter, M.; Warren, E.; McKone, J.; Boettcher, S.; Mi, Q.; Santori, E.; Lewis, N. Chemical Reviews2010, 110, 6446-6473.

Bottari, F.; De Wael, K. Journal of Electroanalytical Chemistry 2017, 801, 521-526.
A Mathematical Model of Reduction Potentials of Lanthanide Alloys Correlation with Atomic Radius and Electronegativity Based on the Hume-Rothery Rules
Authors: Yan Yongde , Wang Chunqi , Wang Pu 
Published: February 2020

To achieve closed nuclear fuel cycle and sustainable development of nuclear energy, efficient pyroprocessing of spent fuel becomes one of the major concerns in Generation IV nuclear energy [1]. Molten salt based electrolysis is a promising method in future pyroprocessing technology. As neutron poison, lanthanides are the typical detrimental elements that encumber the realization of the so-called partitioning & transmutation (P&T) strategy, and thus must be separated from actinides [2]. Therefore, investigating the electrochemical properties of actinides and lanthanides is of pivotal importance. In fact, in light of the chemical similarity of trivalent actinides and lanthanides, the chemistry of actinides can be revealed somewhat through exploring the lanthanide elements which are more readily obtained [3, 4].
In this work, it was found that the reduction potentials of Cu(Ni, Al, Zn)-rich Cu(Ni, Al, Zn)-Ln alloys manifest an evident “Bimodal Effect”. Hume-Rothery rules pointed out that the main factors affecting the formation of alloy solid solution of two metal elements are: 1) the difference of the atomic radius of the solvent and the solute metals, and 2) the electronegativity difference between the solvent and the solute metals. By fitting the data of reduction potentials, differences of the atomic radii and electronegativity differences, a formula was built up, which provides a useful and reliable approach for predicting related important reduction potentials of actinide alloys. The result of multiple linear regression analysis (Fig. 1) indicated that the good reliability of forecast and goodness of fit.

Acknowledgments

This paper is funded by the International Exchange Program of Harbin Engineering University for Innovation-oriented Talents Cultivation.

References

[1] S. V. Perumal, B. P. Reddy, G. Ravisankar, K. Nagarajan, Actinides draw down process for pyrochemical reprocessing of spent metal fuel, Radiochim. Acta 103 (2015) 287–292.
[2] K. O. Kim, J. K. Kim, A study on artificial rare earth (RE2O3) based neutron absorber, Appl. Radiat. Isot. 105 (2015) 52–59.
[3] S. Vandarkuzhali, N. Gogoi, S. Ghosh, B. P. Reddy, K. Nagarajan, Electrochemical behaviour of LaCl3 at tungsten and aluminium cathodes in LiCl–KCl eutectic melt, Electrochim. Acta 59 (2012) 245–255.
[4] B. Y. Kim, D. H. Lee, J. Y. Lee, J. I. Yun, Electrochemical and spectroscopic investigations of Tb(III) in molten LiCl–KCl eutectic at high temperature, Electrochem. Commun. 12 (2010) 1005–1008.

Figure 1
Theory of Ionic Liquids in the Bulk and at the Interface
Authors: Schammer Max , Horstmann Birger , Latz Arnulf 
Published: February 2020

Theoretical studies and simulations are efficient means for the evaluation of materials and for improving the design of electrochemical devices [1]. Here, we present a thermodynamically consistent transport theory of ionic liquids. Our approach is based on a continuum framework and rigorous physical assumptions and we derive a set of coupled transport equations for the ions, charge and heat, based on modeling methodologies for lithium-ion batteries [2]. It describes the bulk phase of ionic liquid electrolytes. In addition, we incorporate microscopic interactions into our transport theory.
Upon this framework we model a zinc-ion battery with a mixture of ionic liquid and water as electrolyte, described experimentally in Ref. [3]. The battery is simulated along one dimension and good agreement with the experimental observations is found (see Figure, left). We integrate the particle nature of the medium into our transport theory. Near electrified interfaces, this leads to crowding and overscreening [4] for neat ionic liquids (see Figure, right). Recently, we have examined the influence of a minor additive species (Ag[TFSA]) on the interfacial structure of the neat ionic liquid Pyr[TFSA] in a joint experimental/theoretical study [5]. Our theory predicts the minimal minor salt concentration which is needed to destroy the layered structure. The theoretical predictions are in good agreement with experimental observations.
This work was supported by the Federal Ministry of Education and Research via the project “Zinc/Air Battery with Advanced Materials for Storage of Renewable Energies and Grid Balancing” (LUZI).
References:

Clark, A. Latz, B. Horstmann, Batteries, 4 (2018), 5. doi:10.3390/batteries4010005.

Latz et al., Beilstein Journal of Nanotechnology, 6 (2015), 987–1007. doi:10.3762/bjnano.6.102.

Endres et al., ACS Applied Materials and Interfaces, 8 (2016), 12158–12164. doi:10.1021/acsami.6b01592.

Bazant, et al., Physical Review Letters, 106 (2011), 046102. doi:10.1103/PhysRevLett.106.046102.

Hoffmann, M. Schammer, F. Endres et al., Physical Chemistry Chemical Physics, 20(2018),

Figure 1
In-Situ Seiras Observation of Co Electrodeposition in an Ionic Liquid: Correlation between the Reaction and Interfacial Restructuring
Authors: Motobayashi Kenta , Shibamura Yuhei , Ikeda Katsuyoshi 
Published: February 2020

Room temperature ionic liquids (RTILs), promising electrolyte materials for various electrochemical applications, requires molecular level description of their structures at the interface where electrochemical reactions occur. Recently, our studies using surface-enhanced infrared absorption spectroscopy (SEIRAS) that can selectively probe solid/liquid interfaces revealed that the first ionic layer is so rigid that a certain overpotential is required to change the adsorbed ions [1]. Therefore, the rigid first ionic layer possibly inhibits redox species from adsorption onto the electrode surface, which is the initial step of electrochemical reactions; however, no direct experimental evidence for such inhibition has been reported. For uncovering the correlation between electrochemical reactions and interfacial structures of RTILs, we measured electrochemical current and SEIRA spectra simultaneously during potential scans under reaction conditions of Co electrodeposition.
SEIRA spectra recorded for a polycrystalline Au electrode in neat [C3mpy][TFSA] (Fig.1) during potential scans showed hysteretic potential dependence, indicating the requirement of a certain overpotential for anion-cation exchange in the first ionic layer in analogy with the other RTILs [1]. SEIRA spectra for a Au electrode in [C3mpy][TFSA] containing 0.1 M Co(TFSA)2 indicated that the anion-cation exchange starts at -0.8 V vs Pt during a negative-going scan. Simultaneously observed CV shows the onset potential of Co electrodeposition at the same potential as shown in Fig. 1. It suggested that the anionic first layer prevent Co2+ from adsorption onto the electrode and thus electrodeposition did not start, and partial mixing of the first ionic layer triggered the adsorption and reduction of Co2+. This is the first direct observation of the correlation between electrochemical reactions and potential-induced interfacial restructuring of RTILs.
[1] K. Motobayashi et al., Electrochem. Commun. 100, 117 (2019).
Modeling of Industrial Electroplating Processes with Comsol Multiphysics in Order to Optimize Treatment of Complex Parts
Authors: Fedi Baptiste , Canals-riclot Jef , Hihn Jean-Yves 
Published: February 2020

Electroplating processes are widely used on several aeronautical applications to confer functional properties (electrical conductivity, tribological, anti-corrosion). In this industrial context, it is possible to keep the desired properties by respecting specifications such as thicknesses and coating composition for alloys. However, it is well-known that phenomena intrinsic to electrochemical processes create heterogeneities, especially on complex geometries like landing gears.
Industrially, the treatment of these disparities is part of the know-how of the workshops, and they are balanced by complex auxiliary tools in order to obtain a more uniform local current densities distribution, and therefore coating thickness. The development of these specific anode shapes is time-consuming and depends strongly of an empirical know-how. The numerical simulation of electrochemical processes is developed at Safran Tech in collaboration with Institute Utinam to optimize the development of plating tools at industrial scale with ComsolÒ Multiphysic software. The global objective is to improve the reliability of the existing systems, and moreover to enhance the innovation by facilitating new coatings integration. This is crucial in the context of tightening of environmental REACH regulations, such as the substitution of cadmium by zinc-nickel.
Modeling industrial electroplating processes by a secondary current distribution model is evaluated in terms of thickness prediction by a comparison with experimental results at a laboratory scale pilot. It has been emphasized that the main limitation are due to the failure to take full account of mass transport induced by convection.
The study also participate to the development of good practice for auxiliary tools design, and the simulation demonstrate invaluable assistance in industrial operations.

Figure 1
(Keynote) Beta Alumina – Prelude to a Revolution in Solid State Electrochemistry
Authors: Whittingham M. Stanley 
Published: February 2020

In 1971 Bob Huggins and I presented a paper at NBS, titled as above*. Little did we realize how prophetic our title would be. The remarkable ion transport properties of the beta alumina family not only led to searches for other ion conducting solids, but also to the use of mixed conducting materials as electrodes for electrochemical cells and shortly thereafter to the use of mixed conducting intercalation compounds for rechargeable lithium batteries.
The studies at Stanford identified several key parameters that control the ionic conductivity of such ions as Na+, Ag+, Cu+, Li+, K+, Tl+and NO+. These parameters include the ionic size, the lattice spacing (diffusion path size), the defect concentration, defect type and diffusion mechanism. Later, similar studies on the WO3, MoO3, TiO2and VOPO4materials, all of which exist in several different structures with varying molar volumes, show the criticality of matching the diffusion path size to the mobile cation. The learnings from these studies will be described.
*NBS Special Publication 364, Washington DC: U.S. Department of Commerce and National Bureau of Standards, 1972, 139-154
Understanding and Engineering Interfacial Transport in K-β′′-Alumina at Room Temperature
Authors: Baclig Antonio C , McConohy Geoff , Kong Nathan , Chueh William C 
Published: February 2020

Aided by Prof. Huggins’s contributions1, the research and development of sodium beta-alumina solid electrolytes led to the commercialization of the molten sodium-sulfur battery, used today for grid-scale energy storage. Sodium-sulfur and ZEBRA batteries typically operate above 300 °C, and recent efforts have explored lowering the operating temperature to 100-200 °C2–4. The melting point of sodium is 98 °C, but its alloy with potassium (Na-K) has a eutectic melting point of -13 °C and is a liquid metal at room temperature with a capacity in the liquid region of 580 mAh/g (using K). Na-K has seen recent attention for batteries with organic electrolytes5 as well as for flow batteries using K-β′′-alumina 6, since polycrystalline sodium beta-alumina is not compatible with Na-K.
A key challenge in using beta-alumina at low temperatures is transport through the interfaces. We discuss transport through the interfaces in a Na-K — K-β′′-alumina — aqueous potassium ferrocyanide (model posolyte) battery. On the Na-K — K-β′′-alumina interface, although Na-K does not wet K-β′′-alumina at room temperature, we find a form of reactive wetting, given certain conditions, that nearly eliminates the interfacial resistance between Na-K and K-β′′-alumina. On the aqueous posolyte — K-β′′-alumina interface, we find that ion exchange of hydrogen/hydronium species and K+ increases the interfacial resistance substantially over time, but this can be greatly decreased through modifying the solution chemistry.7 Understanding and engineering the interfaces of beta-alumina may enable novel applications of this amazing fast ionic conductor at low temperatures.

References

Whittingham, M. S. & Huggins, R. A. J. Chem. Phys.
54, 414 (1971).

Lu, X. et al.
Energy Environ. Sci.
6, 299–306 (2013).

Lu, X. et al.
Nat. Commun.
5, 4578 (2014).

Li, G. et al.
Nat. Commun.
7, 10683 (2016).

Xue, L. et al.
Adv. Mater.
28, 9608–9612 (2016).

Baclig, A. C. et al.
Joule
2, 1287–1296 (2018).

McConohy, G. et al.
Solid State Ionics
337, 82–90 (2019).
(Invited) “Decrepitation” and Mechanical Degradation: In Situ Investigation to Understand Chemo-Mechanical Stability in Batteries
Authors: McDowell Matthew T 
Published: February 2020

Mechanical degradation and fracture have long been recognized as challenges that have impeded development of large-volume-change electrode materials that exhibit stable cycling behavior. Bob Huggins (along with Bill Nix) was among the first to quantify mechanical fracture and “decrepitation” or fracture processes in alloying anode materials, predicting that fracture during electrochemical reaction should be dependent on particle size, among other variables [1]. In recent years, our understanding of how reaction processes relate to mechanical degradation in battery materials has advanced significantly, and in situ/operando experimental techniques have been key for this progress. Here, I discuss my group’s recent efforts in understanding chemo-mechanical degradation in battery materials. First, in situ transmission electron microscopy (TEM) experiments are presented in which individual nanocrystal electrode materials are observed to react with various alkali ions (Li+, Na+, and K+). For FeS2 nanocrystals, the reaction with all three ions involves conversion to form a mixture of phases, along with volume expansion. Despite larger volume changes during reaction with Na+ and K+, only reaction with Li+ was observed to cause fracture. This surprising result was found to be due to the shape of the reaction front as it evolves during reaction, with sharp corners during lithiation resulting in stress concentration and fracture. In addition to this work, other in situ TEM investigations of reaction processes in metal alloying anode nanocrystals have revealed the importance of the mechanical properties of the native oxide in determining transformation pathways during electrochemical cycling. Finally, our research on chemo-mechanical degradation at interfaces within solid-state batteries will be briefly discussed. This work points to the necessity of understanding and controlling chemo-mechanical phenomena in high-capacity battery materials for developing next-generation battery materials.
[1] R. A. Huggins, W. D. Nix “Decrepitation Model for Capacity Loss During Cycling of Alloys In Rechargeable Electrochemical Systems” Ionics, 2000, 6, 57.