bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation into the Corrosion Mechanisms and Effective Inhibitor Additions for Zinc-Magnesium-Aluminium (ZMA) Alloys
Authors: Lewis Thomas , Sullivan James , Cooze Nathan , Gallagher Callum , Elvins Jonathon , Prosek Tomas , Thierry Dominique
Published: February 2020

The use of zinc-magnesium-aluminium (ZMA) alloys is increasing in popularity within the coated steel industry due to the potential advantages it can offer. As such, a collaboration of work involving three differing ZMA alloy coated steels were studied using the scanning vibrating electrode technique (SVET) and novel in situ time-lapse optical microscopy whilst immersed in a 1% NaCl electrolyte, facilitating the investigation of each microstructure. The collation of data demonstrated preferential corrosive attack of the eutectic phases amongst each of the alloy compositions, and more specifically the MgZn2 lamellae, succeeded by the corrosion of Zn-rich dendrites.

The use of SVET enabled an estimation of mass loss from each alloy, and when correlated with the time-lapse data, revealed a reduction in magnitude of corrosion with increasing content of Mg and Al alloy additions. The improvement in corrosion performance was likely a result of increased levels of both MgO and Al2O3 existing at the alloy surface, thereby restraining the corrosion event kinetics. A corrosion inhibitor in the form of Na3PO4 introduced to 1% NaCl electrolyte at varying concentrations exhibited marked effects on the corrosion of the selected ZMA alloy, as evidenced by both SVET and time-lapse microscopy data sets.

Approximations based on the measured SVET data showed that sodium phosphate additions diminished the corrosion activity, the extent of which was dependant on the chosen concentration. The time-lapse images establish suitable correlation with the estimated mass loss results at pH 7, whereby images indicated phosphate precipitation at anodic sites, and thus their passivation. Based on these observations, it can be realised that sodium phosphate inhibitor additions have an appreciable effect on corrosion behaviour within this particular alloy system.
Corrosion Properties of High-Corrosion-Resistance Galvanized Steel Sheet, Posmac(R)
Authors: Choi Changhoon , Cho Soo Hyoun , Oh Min-Suk
Published: February 2020

POSCO, one of the leading-edge steel makers in the world, recently launched a new high-corrosion-resistance galvanized steel product under the name of POSCO Magnesium Aluminum alloy Coating (POSMAC®). POSMAC® is considered to have superior corrosion resistance due to extra metal compositions in galvanic layer, which contains about 3% magnesium and 2.5% aluminum. POSMAC® with relatively thinner galvanic layer could replace heavy-galvanized steel thanks to excellent cut-edge corrosion properties. This new product is used for various applications and chromate or Cr-free coatings are applied to enhance corrosion resistance. Chromate coating is not favored nowadays for health and environmental issues. However, regulations regarding chromate usage are different for regions and trivalent chromate is still allowed even in some countries that prohibit hexavalent chromium. We tested several chromate coating compositions on POSMAC® and tried to determine best compositions for various applications. Darkening (blackening) as well as normal corrosion properties of chromated POSMAC® was tested according to chromate coating composition, especially hexavalent and trivalent chromium concentrations. Cr-free coating is mainly used for applications that require relatively better corrosion resistance against white rust formation such as electronic devices, where aesthetic property is also important. Corrosion resistance of Cr-free coating POSMAC® is enhanced by modifying coating compositions. Various techniques were used in this study to determine corrosion properties, i.e. salt spray test (SST), cyclic corrosion test (CCT), cut-edge corrosion test, etc. Several analytical techniques were used to investigate corrosion and anti-corrosion mechanism by chemical coatings.
Effects of Flow on Protective Scales Formation in a CO2 Saturated Brine Environment
Authors: Hassan SK Mobbassar , Abdullah Aboubakr Moustafa , Laycock Nicholas , Williams David E , Ingham Bridget
Published: February 2020

A significant amount of literature exists demonstrating the effect of CO2 on corrosion scale formation under non-flow conditions and its pH and temperature dependent protectivity. However, little information is available on the effects of flow on the nature and protectivity of corrosion scale. This work demonstrates the effects of flow on 4 different oil-field grade steels of varying chemistry (in terms of micro-alloying) and microstructures (ferritic /pearlitic and martensitic), in a CO2 saturated (1bar) brine (0.5 M NaCl) environment under conditions (pH = 6.3 and temperature = 80 oC) which generate a significantly compact and protective scale under non-flow conditions. Flow was introduced in the range of 0 - 3000 RPM via a rotating disk electrode (RDE) type arrangement which has been customized to comply with the needs of the experiment. The effect of flow was electrochemically characterized by potentiostatic current density (id
) vs time (t) measurement where Pt and Ag/AgCl were used as counter electrode and reference electrode respectively. Higher RPM (≥1000) indicated distinct characteristics compared to the lower RPMs (≤100) with a transition of i vs. t behavior observed around 500 RPM. Higher RPMs seemed to modulate the mechanism of the nucleation stage of scale formation and induce a relatively sluggish formation of protective scale by delaying the crystal growth process. Two plain carbon steels, J55 (ferritic /pearlitic) and L80 (Martensitic), did not show any qualitative difference in their i vs. t characteristics as function of flow. However, L80 steel required a longer time for crystal growth and achieving a similar degree of protection through scale formation compared to J55. 1 wt.% Cr micro-alloyed steels showed a lower current density compared to the plain carbon steels at the very early stage of scale formation; however the eventual protectivity of the scales formed on the plain carbon steels appeared to be much better on the basis of i vs t characteristics. Further characterizations of the scales in terms of phase identification, morphology and thickness by XRD, SEM and profilometry are in progress.

Figure 1
(Invited) Industrial High Efficiency Perc Solar Cells
Authors: Xing Guoqiang
Published: February 2020

While the first paper describing Passivated Emitter and Real Cell (PERC) appeared in 1989, the PERC cell structure was conceived several years earlier. After many years industrial development, world-wide PERC mass production capacity has gradually grown to about 2.5 GW by the end of 2014; thereafter the PERC installations experienced a rapid outburst to over 10 GW by Q1 2016. In this paper, we update the latest development of PERC technology and analyze the technical and economic reasons for PERC’s rapid growth in market shares, such as maturity in mass production equipment and materials, solution of light induced degradation (LID) of PERC cells. Furthermore we analyze different efficiency loss mechanisms of our current 21% mass production PERC cells, and establish roadmaps for PERC cells to reach 23% and beyond. PERC module performance and total cost of ownership of PERC technology will be discussed as well.
Improving Open-Circuit Voltage in Cu2ZnSnSe4 Thin Film Solar Cells Via Interface Passivation
Authors: Kim Jekyung , Park Sanghyun , Oh Jihun , Shin Byungha
Published: February 2020

The earth-abundant Cu2ZnSnSe4 (CZTS) thin film solar cells have demonstrated promising results with the record power conversion efficiency of 12.6%. However, they suffer from the high open-circuit voltage (Voc) deficit that hinders further improvement in the device performance. Ongoing studies regarding the origins behind this critical issue suggest that it stems from the fluctuation of band structures and non-radiative recombination centers in CZTS solar cells. Here, we focused on passivating the interfaces of CZTS solar cells – both a front CdS/CZTS interface and a back CZTS/Mo interface – to reduce the interfacial recombination that may greatly contribute to a large Voc deficit of CZTS solar cells. By applying a thin dielectric on top of the CZTS and a nano-patterned dielectric layer between the CZTS and the Mo, Voc is significantly enhanced; the Voc-deficit value is comparable to that of the world record CZTS solar cell. Structural and electrical properties of the CZTS devices with passivation layers were studied using scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, J-V and external quantum efficiency measurement, low-temperature photoluminescence, and time-resolved photoluminescence analysis. The effects of interface passivation in correlation with the device performance will be presented as well.
Theoretical Investigation of Unique Properties in Perovskite Solar Cell Materials
Authors: Yin Wan-Jian , Yan Yanfa , Wei Su-Huai
Published: February 2020

The emergence of perovskite (typically CH3NH3PbI3) solar cells revolutionized the field not only because of their rapidly increased efficiency, but also flexibility in material growth and architecture. The superior performance of the perovskite solar cell suggested that perovskite materials possess intrinsically unique properties.

In this talk, I will present our recent theoretical investigations into the structural, electrical, and optical properties of halide perovskite materials, especially CH3NH3PbI3, in relation to their applications in solar cells. (i) the optical transitions of CH3NH3PbI3 is direct p-to-p transition, which combines the advantage of the first- and second-generation solar cell materials, responsible for the strong optical absorption [1]; (ii) different from common p-type thin-film solar cell absorber, it exhibits flexible conductivity from good p-type, intrinsic to good n-type depending on the growth conditions; (iii) dominating intrinsic defects create only shallow defect levels, which partially explain the long carrier electron-hole diffusion length and high open-circuit voltage[2]; (iv) molecular dynamics simulations show that the structure of pristine CH3NH3PbI3 is much more distorted than the inorganic archetypal thin-film semiconductor CdTe. However, the structure disorders from both thermal fluctuation and grain boundaries (GBs) introduce no deep defect states within the band gaps, therefore, the polycrystalline show single-crystal-like properties; (v) although GBs introduce no gap states, they could act as hole trap state and increase the carrier effective mass. Cl and O can spontaneously segregate into GBs and passivate those defect levels and deactivate the trap state [3]. The unusual physical properties of perovskite are attributed to the unique electronic structures of halide perovskite: the strong coupling between cation lone-pair s orbital and anion p orbitals and the large atomic size of constitute cation atoms.

The correlation of experimental observations and the verification of our theoretical results, which may further guide experimental research will also be discussed [4].  

[1] W.-J. Yin, T. Shi and Y. Yan, Adv. Mater. 26, 4653 (2014).

[2] W.-J. Yin, T. Shi and Y. Yan, Appl. Phys. Lett. 104, 063903 (2014).

[3] W.-J. Yin, H. Y. Chen, T. Shi, S.-H. Wei, and Y. Yan, Adv. Elect. Mater. 1, 1400044 (2015).

[4] W.-J. Yin, J.-H. Yang, J. Kang, Y. Yan and S.-H. Wei, J. Mater. Chem. A 3, 8926 (2015).
Resistive Switching Nanodevices Based on Surmofs
Authors: Redel Engelbert , Baumgart Helmut , Wöll Christof , Wang Zhengbang , Nminibapiel David Malien , Shrestha Pragya
Published: February 2020

Bipolar switching was demonstrated in crystalline and monolithic SURMOF (surface-anchored metal–organic framework) thin films. By using conductive substrates as bottom and top electrodes, these metal-organic-hybrid materials act as novel nonvolatile RRAM memory devices. The huge flexibility of the SURMOF RRAM device was further enhanced by loading ferrocene into the free pores of the framework. This result demonstrates a huge potential of SURMOF thin films as scalable active materials for the next generation of digital processing and organic-based microelectronic devices.
Nanosecond Programming of SiOx Based Resistive RAM: Simplified Digital Programmers and Analog Neuromorphic Type Behavior
Authors: Montesi Luca , Buckwell Mark , Zarudnyi Konstantin , Garnett Leon , Hudziak Steven , Mehonic Adnan , Kenyon Anthony Joseph
Published: February 2020

Typical non-volatile flash memory technology has been approaching its scalability limit and showing slow access time, and high power dissipation. Meanwhile, filamentary resistive RAM (ReRAM) offers scalability, low-voltage nanosecond writing and therefore a low power profile; programming techniques also allow for beyond-binary applications. Here we stimulate our intrinsic switching TiN/SiOx/TiN (x<2) ReRAM devices using nanosecond pulses and look at aspects of their electrical response. Simplified programmers appear possible thanks to dynamic impedance mismatch between the programmer and the device under test; identical pulse sequences switch devices between two or more states. Such mismatch also allows us to track the electroforming process and confirm it occurs on the nanosecond timescale. Additionally, pulses of appropriate timing allow devices to enter temporary states. Behavior reminiscent of neuronal synapses (potentiation, depression and short-term memory) is therefore observed in our devices showing great potential for integration into novel parallel hardware neural networks.
Characteristic of Resistive Switching Device Using Mesoporous Carbon-Silica-Titania Nanocomposite
Authors: Jung Hunsang , Kim Yo-Han , Lee Hyun Ho
Published: February 2020

Resistive switching device using mesoporous carbon-silica-titania (m-CST) nanocomposite as active layer is demonstrated in simple structure of metal-mesoporous nanocomposite-metal. In this study, we try to fabrication method by soft-templating, which is simple technology to make mesostructure by reacting oligomeric resol, block copolymer surfactant and silicate source. Nanocomposite layer of mesostructure is formed by using sol-gel process with spin-coating. During the evaporation induced self-assembly (EISA) process, the solution of nanocomposite becomes more concentrated until the critical micelle concentration is reached. A well ordered mesostructure nanocomposite layer is formed through annealing process. For device structure, platinum (Pt) deposited silicon oxide wafer substrate was used as the bottom electrode. Top electrode of aluminium (Al) was deposited by thermal evaporation process. The current-voltage (I-V) characteristic showed analog-type resistive switching property, that the current is gradually changed depending on the sweep voltage and sweep directions, and threshold voltage shifts depending on the control voltage. Also, learning ability of potentiation and depression characteristic of the device is tested by Semiconductor Parameter Analyzer and pulse generator. The mesoporous nanocomposite property is analyzed with FT-IR and FE-SEM with EDS.
Graphene Oxide and ZnO/Al:ZnO Based Transparent Resistive Switching Devices for Memristor Applications
Authors: Pradhan Aswini K , Pradhan Sangram , Mundle Rajeh , Xiao Bo
Published: February 2020

Graphene Oxide (GO) based low cost flexible electronics and memory cell have recently attracted more attention for the fabrication of emerging electronic devices. As a suitable candidate for resistive random access memory technology, reduced GO (RGO) can be widely used for non-volatile switching memory applications because of its large surface area, excellent scalability, retention, and endurance properties. We demonstrated that the fabricated metal/RGO/metal memory device exhibited excellent switching characteristics, with on/off ratio of two orders of magnitude and operated threshold switching voltage of less than 1 V. We have also developed a high-temperature precursor vapor mask technique using Al2O3 to pattern the atomic layer deposition of ZnO and Al:ZnO layers on ZnO-based substrates. This technique was used to create a transparent memristor device based on Al:ZnO thin films having metallic and semiconducting and insulating transport properties ZnO. We demonstrated that adding combination of Al2O3 and TiO2 barrier layers improved the resistive switching behavior. The change in the resistance between the high and low-resistivity states of the memristor with a combination of Al2O3 and TiO2 was approximately 157 %.
(Invited) Challenges in Ultra-Small Device Manufacture
Authors: Morris Michael anthony
Published: February 2020

As semiconductor devices become smaller and approach the limits of conventional photolithography, achieving high quality pattern transfer becomes ever more challenging and expensive. Non-conventional lithographies may realize feature size below 10 nm but the etch challenges are not addressed. Here we examine how block copolymer lithography can be used to address both scaling and pattern transfer. In block copolymer (BCP) lithography, BCPs on a surface can self-assemble into regular arrangements for creation of ordered arrays on holes and line spacing. Recently we have extended these techniques to selectively include hard mask type materials into the polymer pattern. These then form an inorganic pattern of the same polymer structure and allow high contrast pattern transfer to a variety of substrates. Typical examples from the work are shown in Figure 1. We illustrate this work by hard masks based on NO, W and Zn and demonstrate device functionality using electrical characterization.

However, no matter how advanced this form of lithography becomes, grand challenges remain in scaling. The biggest of these is layer-to-layer registry or overlay of features. In this work, we extend our methodology to develop a form of selective area deposition. Selective deposition, if successful, could remove a number a key lithographic steps and lower fabrication costs. We use a methodology that combines etch techniques to enhance surface chemical contrast and so facilitate selective deposition. Recent results that allow direct deposition of dielectric deposition are provided.

Figure 1
(Invited) Microplasma Jet Deposition of Nanostructured Materials
Authors: Gordon Michael
Published: February 2020

The ability to synthesize functional nanoscale materials, as well as integrate them into larger systems, is fundamental to the development of next-generation micro- and optoelectronic devices, sensors, and energy harvesting and storage technologies. Toward this goal, we have developed a versatile, plasma spray-like deposition technique, based on flow-through micro-hollow cathode discharges at 10-100 Torr (microplasma jets), that can deposit nanoparticles, dense layers, and structured thin films of crystalline materials on virtually any surface. A supersonic DC microplasma jet is seeded with organometallic precursors under reducing or oxidizing conditions to create a directed flux of growth species (e.g., atoms, ions, clusters, and/or nanoparticles) that are subsequently 'spray-deposited' onto the surface of interest. A remote anode is used to complete the plasma circuit, allowing deposition on conductors, insulators, polymers, fibers, and lithographic patterns at room temperature in a conformal fashion. A diverse range of nanostructured materials, e.g., metals (Cu, Ni, Pd), oxides (CuO, ZnO, SnO2, NiO, Fe2O3, CoxOy), doped oxides (FexNi1-xO), spinels (NiFe2O4), and sulfides (CuS), with different morphologies (nanoparticles, dense columnar films, or hierarchical nanostructures, etc.) can be realized with the technique. The talk will specifically focus on microplasma jet operation, growth dynamics, and applications of microplasma-deposited films including solar cell, battery and supercap electrodes, photo(electro)catalysts, and biphasic nanogranular materials for magnetic exchange bias studies.
The Synergetic Catalytic Effect of Molten Gallium in the Presence of Hydrogen and Nitrogen Plasmas: Study and Applications
Authors: Jaramillo-Cabanzo Daniel Felipe , Carreon Maria , Chaudhuri Indira , Menon Madhu , Sunkara Mahendra Kumar
Published: February 2020

The synergetic effect of plasma and a metal catalyst is rising as an alternative to synthesize a great variety of materials - from gases to nanomaterials - that take place under highly energy consuming reactions. More specifically, this study will have an impact in the growth of silicon nanowires (Si NWs) as anodes for Li-ion batteries and the production of bulk gallium nitride. Our group has been able to synthesize Si NWs at temperatures as low as 200 C and in recent efforts we have been able to grow densely packed Si NWs (d∽20 nm) uniformly on stainless steel with areas as big as 1.5 x 5 cm. Highly oriented GaN flakes (as big as 1.25 cm x 1.25 cm) were also synthesized on quartz substrates using a plasma assisted catalytic method. The X-ray diffraction spectrum of the GaN film shows only (0002) and (0004) planes of wurtzite GaN, indicating good c-plane orientation. We have demonstrated a basic concept in which crystals self-orient with respect to each other if the growth takes place on molten gallium due to the enhanced rotational and translational mobility.

To gain insights into these mechanisms we have studied the interaction of hydrogen and nitrogen plasmas with low melting point metals, primarily with gallium. Absorption/desorption experiments as well as theoretical-computational calculations were performed. Experiments have shown an increment of adsorbed gaseous species into the molten metal in the presence of plasmas; furthermore, Density Functional Theory (DFT) calculations suggest a strong interaction between atomic hydrogen and molten gallium that is described as a high absorption on the surface, rapid diffusion and a steady state concentration of the gas inside the bulk.

Recent results suggest that the synergetic effect of molten gallium in the presence of hydrogen/nitrogen plasmas could have a transformational impact in the way energy-intensive processes are carried out. This presentation will highlight the novel aspects of molten metal plasma catalysis, future directions and applications.

Acknowledgments

The authors acknowledge the financial support from NSF EPSCoR Grant 1355438.

References

“Plasma Catalysis: Synergistic Effects at the Nanoscale.” E. C. Neyts, K. Ostrikov, M. K. Sunkara, and A. Bogaerts. Chemical Reviews 2015 115 (24), 13408-13446 DOI: 10.1021/acs.chemrev.5b00362

‘Low Temperature Synthesis of Silicon Nanowire Arrays” M.L. Carreon, J.B. Jasinski and M.K. Sunkara. 2014 Mater. Res. Express 1 045006 DOI: http://dx.doi.org/10.1088/2053-1591/1/4/045006
Galvanic Deposition of Copper, Silver and Gold on Silicon Surfaces from Fluoride Free Aqueous Solutions
Authors: Djokić Stojan S
Published: February 2020

Deposition of copper, silver and gold onto silicon surfaces is investigated in this work.  Traditionally, direct deposition of Cu, Ag and Au onto silicon surfaces is carried out using fluoride based solutions.  In the fluoride based solutions unavoidably present SiO2 at the surface of semiconductor is successfully removed and then deposition of metals such as Au or Ag proceeds via the galvanic displacement process.  The results of the present work demonstrate that the direct deposition of Cu, Ag or Au onto silicon surface is very successful from fluoride-free alkaline solutions containing Cu(II), Ag(I) or Au(III) ions at pH higher than 12.  The deposition of these metals does not require a reducing agent, i.e. process proceeds via galvanic displacement reactions.  The approach can further be applied on any metal with the standard electrode potential more positive than that of silicon, as long as the alkaline complexes of the targeted metals are reasonably stable in the strong alkaline electrolytes with pH more than 12.
Chemical Bath Deposition of Iridium Oxide Film for Implantable Neurostimulation Electrode Applications
Authors: Tso Kuang-Chih , Chung Tsai-Wei , Chen Yi-Cheng , Wu Pu-Wei , Chen Po-Chun
Published: February 2020

Iridium oxide is an attractive ceramic material for neurostimulation electrodes due to its desirable stability and biocompatibility. Electrostimulation medical devices for neural diseases require electroactive and biocompatible materials to transmit signals from electrodes to targeting tissues. In this study, we developed a cost effective and thickness controllable process to fabricate iridium oxide film by chemical bath deposition. The film thickness can be controlled by modifying solution recipe from 40 nm to 110 nm per batch. Surface morphology, crystallinity, and charge storage capacity of the iridium oxide with different thicknesses were analyzed. Accordingly, the iridium oxide films present rough and hydrophilic surfaces so that the films are expected to suitable for cell attachment and good biocompatibility for cell viability. In addition, the charge storage capacity (CSC) of the iridium oxide films with various thicknesses were significantly higher than platinum which is the conventional stimulation electrode material. Consequently, these results show advantages that make the iridium oxide film a promising neurostimulation electrode material for implantable medical devices in neural systems.
Shape Transition and Growth of CoxFe(1-x) Alloy Nanocrystals By Electrochemical Deposition
Authors: Park Kimoon , Yoon Sanghwa , Yoo Bongyoung
Published: February 2020

Nanocrystals were interesting materials for applications such as photocatalyst, biocatalyst, solar cells, sensors, lithium batteries, magnetic resonance imaging, water splitting, and etc. These properties were dependent on their shape and composition. Therefore, researches of the nanocrystal synthesis, shape and composition control have been significantly important.

Nanocrystals were prepared by chemical vapor deposition, hydrothermal methods, sol-gel techniques, spraying methods, and electrochemical synthesis methods. Among the these methods, electrochemical synthesis was great method since this method has advantages that simple process, low cost, low synthesis temperature, selective decoration on conductive substrates, various materials synthesis such as metal, semiconductor, and oxides. In addition to this, the nanocrystals were easily tuned by changing synthesis conditions, electrolyte concentration, pH, applied potential, and addictives.

The CoFe alloys were well known at magnetic materials due to their high magnetic saturation and show potential for the magnetic application. Despite the advantages of electrochemical synthesis methods, studies of the nanocrystal growth were restricted for mainly noble metals1 and oxides2. There were few studies of synthesis of the alloy nanocrystals, PtNi, PtFe, PtCo, and etc.3Therefore, studies of the alloy nanocrystal synthesis were still required.

In this research, The CoxFe1-x nanocrystals were synthesized by electrochemical synthesis method at various synthesis conditions such as applied potential, charge density, and electrolyte concentration. These nanocrystals were characterized by scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy. From the SEM images, there was shape transition from non-cube to cube shape when applied potential was increased. This shape transition was caused by composition change. The Co-rich CoxFe1-x nanocrystals show non-cube, which was nearly spherical, shape, while the 1:1 CoFe and the Fe-rich CoxFe1-xnanocrystals show cube shape. In addition to this, particle reduction phenomenon was observed as potential increased. This phenomenon was different with electrochemical deposition behavior that nucleation density was exponentially dependent on the potentials.

References

1. Y. Chen, S. Chen, Z. Zhou, N. Tian, Y. Jiang, S. Sun, Y. Ding, and Z. Wang, Science, 316, 732 (2007).

2. S. Yoon, S. Kim, S. Choi, J. Lim, and B. Yoo, Cryst. Growth Des., 15, 4969 (2015).

3. J. Wu, L. Qi, H. You, A. Gross, J. Li, and H. Yang, J. Am. Chem. Soc., 134, 11880 (2012).

Figure 1
(Invited) On-Wafer Microwave Devices Based on Magnetic Materials
Authors: Celinski Zbigniew , Camley Robert , Harward Ian , Goldman Sara
Published: February 2020

We present a review of theoretical and experimental results for on-wafer microwave devices. Specifically, we discuss construction of on-wafer inductors designed to operate in frequencies below 1-2 GHz. We also present recent progress in tunable microwave band-stop filters, band-pass filters, phase shifters, and a signal to noise enhancer, all based on a microstrip geometry and using a variety of magnetic thin films and layered structures. These devices are compatible in size and growth process with on-chip high-frequency electronics. For tunable devices based on metallic ferromagnetic films of Fe and Permalloy, the operational frequency ranges from 5 to 35 GHz for external fields below 5 kOe. For the band-stop filters, we observed power attenuation up to ∼100 dB/cm, and an insertion loss on the order of ∼2–3 dB, for both Permalloy and Fe-based structures. We also will discuss the use of thin films of hexagonal ferrites, and liquid crystals/magnetic nano-rods colloids, and show these materials can be used to make on-wafer microwave devices. The devices based on hexagonal ferrite operate in the frequency range 35-70 GHz while devices based on liquid crystal/magnetic nano-rods colloids operate in the frequency range 5 - 110 GHz.
Examining Electrical Properties of Solid Electrolyte Interface on Silicon Electrodes
Authors: Ban Chunmei , Son Seoung-Bum , Hurst Katherine , Jiang Chunsheng
Published: February 2020

The complex surface reactions contribute to the formation of solid-electrolyte interphases (SEI), and cause the irreversible capacity loss of silicon (Si) electrodes. The chemical and mechanical instability of the interphases finally leads to performance degradation. A microscopic characterization of the electrical properties at the interface is expected to gain information to understand the physical and chemical evolution caused by the formation of SEI, and provide the guidance for improvements in performance.

The microscopic electrical characterization techniques, including Kelvin probe force microscopy (KPFM) and scanning spreading resistance microscopy (SSRM), have been applied to silicon electrodes. The nanoelectrical probes have been developed in one atomic force microscopy (AFM)-based platform, and the complementary electrical characterizations can be performed on the same sample area in nm-scale. Based on the contact potential difference method, KPFM maps the work function (WF) on electrode surfaces, which is expected to largely change with lithiation and delithiation. WF is sensitive to Li-ion distribution and diffusion, which can be highly inhomogeneous in nm-scale and can be assessed and evaluated from the KPFM mapping. Local conductivity/resistivity of Li-ion electrodes has been studied by SSRM. Based on the contact mode of AFM, SSRM maps of local resistivity in 10-nm resolutions have been acquired by applying a voltage between the probe and a sample and measuring the current through the probe. Ex-situ measurements along the Lithiation/delithiation process have been performed to understand the formation of SEI and the impact of electrochemical reaction on the electrical properties of SEI. Figure 1 shows the SSRM resistance changes before and after lithiation of Si electrode. The inhomogeneity with grain and domain sizes of 200-500 nm is observed at the surface of Si electrode.

Surface modification by using atomic layer deposition and molecular layer deposition has also been used to modify the surface chemistry of silicon electrodes. This presentation will discuss the evolution in nm-scale resistance of SEI during electrochemical reactions, and the impact of surface coating materials on the electrical properties of SEI.

Figure 1
(Invited) Progress in High-Capacity Gradient Cathode Materials for Rechargeable Lithium Batteries
Authors: Sun Y.-K.
Published: February 2020

High-energy-density rechargeable batteries are needed to fulfill various demands such as portable electronic devices, energy storage systems, and (hybrid) electric vehicles. As a result, high-energy electrode materials enabling a long cycle life and reliable safety need to be developed. To ensure these requirements, new material chemistries can be derived from hybridization of at least two compounds in a secondary particle with varying chemical composition and primary particle morphologies having a core−shell structure and spherical cathode-active materials with rod-shaped primary particle. To this end, several layer gradient cathode materials were developed to ensure high capacity, reliability, and safety.
New Insight in Understanding the Evolution Mechanism of Li2o2 in Li-O2 Batteries: An operando Synchrotron X-Ray Diffraction Study
Authors: Liu Chenjuan , Brant William Robert , Younesi Reza , Edström Kristina , Gustafsson Torbjörn , Zhu Jiefang
Published: February 2020

Non-aqueous Li-air (Li-O2) batteries have been emerging as one of the most promising high-energy storage systems, e.g., to meet the requirements for electric vehicle applications, owing to their high theoretical energy density (3505 Wh kg-1 for Li/Li2O2 cells). One of the major challenges to develop high-performance Li-O2 battery is to understand the mechanism how Li2O2 is formed and decomposed during battery cycling. Although many cathode catalysts have proven to be effective to ORR/OER in Li-O2 batteries, little is known on such reversibility at fundamental level at present. Different from Li-ion batteries, the rechargebility cannot be easily determined by Coulombic efficiency in Li-O2 batteries because of extensive parasitic chemistry/electrochemistry. In most of the studies, the evaluations of Li-O2 battery rechargebility have been based on galvanostatic charge-discharge measurements, for which many Coulombic cycles are possible, and each cycle is possibly dominated by solvent decomposition1-3. Consequently, it is impossible to accurately judge the rechargeability of the system without any quantitative evidence to show which kind of and how much electrochemical reactions contribute to discharge or charge stage. Accurate quantification of the amount of Li2O2 that forms and decomposes in each cycle is a direct and simple way to determine the rechargebility of a Li-O2 battery. In this study, we have investigated this important fundamental issue by operando synchrotron X-ray diffraction. We modified the previous operando cell design, to achieve quantitative tracking of Li2O2 during both discharge (ORR) and charge (OER) in a binder-free CNT electrode. We present, for the first time, an approach that combines ex situ spectroscopic analysis and state-of-the-art operando X-ray diffraction with the ability of tracking real-time Li2O2 evaluation, as a means to better understanding of the mechanisms underlying electrochemical reactions. The evolutions of Li2O2 formation and decomposition related to its morphology and structure were observed under the actual electrochemical conditions in real time. Our operando X-ray diffraction results also reveal a two-step growth of Li2O2 on ORR and also a two-step oxidation of Li2O2 on OER, which can be associated with the different mechanisms on forming and decomposing Li2O2.

Reference

1. W. Xu, K. Xu, V. V. Viswanathan, S. A. Towne, J. S. Hardy, J. Xiao, Z. Nie, D. Hu, D. Wang and J.-G. Zhang, J Power Sources, 2011, 196, 9631-9639.

2. S. A. Freunberger, Y. Chen, Z. Peng, J. M. Griffin, L. J. Hardwick, F. Barde, P. Novak and P. G. Bruce, J Am Chem Soc, 2011, 133, 8040-8047.

3. F. Mizuno, S. Nakanishi, Y. Kotani, S. Yokoishi and H. Iba, Electrochem Commun, 2010, 78, 3.
Nanoscale (PEEM) Spectroscopy Combined with XPS to Elucidate the Surface Reaction Mechanism of Cycled Battery Electrodes
Authors: Leanza Daniela , A. F. Vaz Carlos , Novák Petr , El Kazzi Mario
Published: February 2020

For the first time we explore the potential and feasibility of X-ray PhotoEmission Electron Microscopy (PEEM) to investigate commercial-like battery electrodes and to study separately, at the nanoscale level, the surface layer chemistry evolution on the active materials and on the conductive carbon. Two types of electrodes are investigated, LiM (M=Mn, Ni, Co)O2-Li2MnO3 (NCM) and Li4Ti5O12 (LTO), as promising positive and negative electrodes, respectively, for Li-ion batteries. Thanks to the PEEM technique, we are able to overcome the limited spatial resolution and poor sensitivity to transition metals (TM) of conventional X-ray photoemission spectroscopy (XPS). Furthermore, both techniques probe the same range of depth (< 8 nm). The elemental contrast images in (Figure 1.I) attest the high lateral resolution of PEEM and its ability to distinguish single particles of the active materials, NCM or LTO, from the conductive carbon in typical commercial-like electrodes, without the need of using model systems. The local XAS spectra (Figure 1.II) at the Ni-, Co-, Mn-L edges and C-K edge acquired on NCM particles allow us to monitor their oxidation states as well as the chemical species present on the surface without interference from the signal arising from the conductive carbon. By combining PEEM with XPS (Figure 1.III) during the early stage of cycling together with long cycling, we can obtain a better insight on the mechanism behind the surface layer formation on the positive and negative electrodes. Moreover, the origin of the surface layer present on LTO as well as the oxidation states of the dissolved TM were elucidated, alongside the impact of the high potential on the NCM structure stability.

Figure 1
Microstructure Characteristics of Blend Cathodes Assessed By 3D-Tomography Methods
Authors: Costard Janina , Joos Jochen , Ivers-Tiffée Ellen
Published: February 2020

Electrode performance of lithium ion battery cathodes is strongly affected by its microstructure parameters. FIB (focused ion beam) / SEM (scanning electron microscopy) tomography is a powerful tool for determining microstructure parameters. The application of this method and processing of images has been optimized for battery electrodes [1], enabling an accurate detection of the three components (1) carbon black, (2) pore phase and (3) active material. A special challenge is to distinguish between different active materials which are combined in blend electrodes for optimizing their performance and energy density.

In this study, a dual beam modus is applied for analyzing the composition and microstructure of a blended battery cathode consisting of three active materials (NMC, NCA and LMO). By combining the information of InLens and Everhart-Thornley detector it was possible to reconstruct a volume of 35µm x 37µm x 20µm consisting of 1010 x 1070 x 570 voxel (isotropic voxelsize of 35 nm). The pore phase and the carbon black were segmented by evaluating images acquired using the Everhart-Thornley detector, due to lower falsification by local charging, whereas the active material was separated into its three components interpreting information of InLens detector which provides a better contrast of specific material. It was possible to clearly assign the three materials, confirmed by EDX analysis, and to calculate microstructure parameters for every specific component, as particle size distribution, active surface area, porosity and tortuosity.

Limiting factor for an application of this method is the representative volume element size which is dependent of the number of active materials as well as their maximum particle size, as reported in [2] for solid oxide fuel cells. For prospective studies, an increased reconstruction volume is necessary while maintaining high resolution of images, which is challenging with regard to FIB-procedure as well as processing of big data amount. Alternative tomography methods as X-ray tomography enable the reconstruction of larger volumes, but suffer from low contrast of carbon black and limited resolution.

Advantages and disadvantages of the different tomography methods are discussed and assed.

[1]           M. Ender, J. Joos, T. Carraro and E. Ivers-Tiffee, Journal of the Electrochemical Society, 159, A972-A980 (2012)

[2]           J. Joos, M. Ender, T. Carraro, A. Weber and E. Ivers-Tiffée, Electrochemica Acta,
82, 268-276 (2012)
Understanding Why Sodium Intercalated Graphite Is Unstable
Authors: Moriwake Hiroki , Kuwabara Akihide , Fisher Craig Andrew James , Nose Masafumi , Nakayama Hideki , Nakanishi Shinji , Iba Hideki , Ikuhara Yuichi
Published: February 2020

Sodium-ion batteries offer a potential solution to the problem of limited lithium resources, although developing compatible, high-performance cathode, anode, and electrolyte materials for such devices presents a more difficult challenge. In conventional lithium ion batteries, graphite is used as the anode, but it has been known for more than 40 years from experiment that, unlike the other alkali metals (Li, K, Rb, and Cs), intercalation of Na into graphite is thermodynamically unfavorable, so that modification of the anode material or addition of solvating species is needed if intercalation is to occur. First-principles calculations by Nobuhara et al. [2] and Wang et al. [3] showed that even at low Na densities NaC
x
compounds are energetically unstable. However, the underlying mechanisms responsible for the endothermic formation energies are still uncertain. To investigate this phenomenon in more detail we performed first-principles calculations of the intercalation behavior of alkali metals into graphite. A van der Waals correction was added to the standard density functional theory methods to better reproduce the laminated structures of graphite intercalated compounds. Calculated formation energies of intercalated systems XC6 (X = Li, Na, K, Rb, or Cs) are shown in Fig. 1(a). As the atomic number decreases from Cs to Na, the magnitude of the formation energy decreases, becoming positive (endothermic) in the case of Na. This tendency can be explained in terms of ionic bonding energies, which decrease as the atomic number of the alkali metal decreases because electronegativity increases as the alkali metal group is ascended. The reason for the negative formation energy in the case of LiC6 can be understood by examining the electron density and density of states, plotted in Fig. 1(b), which show greater covalent bonding between Li and C than the other alkali metals.

References

[1] K. Kim, et al., Energy Environ. Sci., 8, 2963 (2015).

[2] K. Nobuhara, H. Nakayama, M. Nose, S. Nakanishi, and H. Iba, J. Power Sources, 243, 585 (2013).

[3] Z. Wang, S. M. Selbach, and T. Grande, RSC Adv., 4, 4069 (2014).

Figure 1
Differential Thermal Voltammetry As a Low Cost in-Situ Diagnosis Tool for Lithium-Ion Batteries
Authors: Merla Yu , Wu Billy , Yufit Vladimir , Brandon Nigel P. , Martinez-Botas Ricardo , Offer Gregory James
Published: February 2020

Modern applications of batteries in portable electronics, electric vehicles and grid level energy storage, demands long lifetime in various operating conditions. Monitoring its state-of-health in real time and optimising its operation in a cost-effective manner presents a real challenge.

Differential thermal voltammetry (DTV) is a novel in-situ diagnosis technique for tracking degradation in lithium-ion batteries based on relatively simple cell surface temperature measurements. DTV only requires temperature and voltage measurements and is carried out by measuring the change in cell surface temperature during a constant current charge or discharge. It is a complimentary method to the incremental capacity or slow rate cyclic voltammetry analysis as it has additional information on the entropy characteristics as a result of temperature measurements.

Accelerated aging experiment was carried out on commercial lithium-ion cells where the cells were aged differently in a controlled environment. The cells were characterised regularly using the new technique. Each dT/dV peak in the resulting curve represents a combination of different contributions from positive and negative electrode phases (Figure 1). By decoupling these peaks and by monitoring the evolution of the peak parameters it is possible to quantitatively determine stoichiometric drift in the cell. Cell 1 which was stored at 55degC and held at 4.2V showed significant shift in electrode stoichiometry. On the other hand, cell 2 stored at 55degC and cycled at 1C showed little shift despite the similar capacity fade of approximately 10%.

This novel application of DTV presents an opportunity to estimate the state of health of a lithium-ion battery through tracking of decoupled dT/dV peaks. These results can then feed in to adaptively control the cell operation based on the diagnosis to optimise cell lifetime and available energy. Its low software and hardware requirements make it a practical solution to existing and future systems.

Figure 1. Decoupled dT/dV peaks for two aged cells at approximately 10% capacity fade. Cell 1 (left) was stored at 55degC and held at 4.2V. Cell 2 (right) was stored at 55degC and cycled at 1C. Schematics of combined phases are shown above each plot. Note the visible stoichiometric drift in cell 1.

[1] Y. Merla, B. Wu, V. Yufit, R.F. Martinez-botas, N.P. Brandon, G.J. Offer, Novel application of differential thermal voltammetry as an in-depth state of health diagnosis method for lithium-ion batteries, J. Power Sources. 307 (2016) 308–319. doi:10.1016/j.jpowsour.2015.12.122.

[2] B. Wu, V. Yufit, Y. Merla, R.F. Martinez-botas, N.P. Brandon, G.J. Offer, Differential thermal voltammetry for tracking of degradation in lithium-ion batteries, J. Power Sources. 273 (2015) 495–501. doi:10.1016/j.jpowsour.2014.09.127.

Figure 1