bluuebunny/crossref_metadata_2025 huggingface dataset:
Synaptic Weight Modulation By Controlling Metal Oxide Rram Switching
Authors: Veksler Dmitry , Bersuker Gennadi , Shrestha Pragya Rasmi , Cheung Kin P. , Ayvazian Talin , Bushmaker Adam
Published: February 2020

Device technologies developed to address specific needs for neuromorphic systems include non-volatile memory (NVM), which can serve as microelectronic "synapses" for low-power mobile computing applications. Desirable memory stack characteristics include, among others, scalability, fast programming, low voltage and power operations, high retention and endurance, multi-state operation and 3D integration capability. Metal-oxide RRAM meets most of these requirements [1]; however, the critical capabilities such as symmetric and gradual conductance update, and potentiation and depression in spike-timing-dependent-plasticity scheme have not been demonstrated. In this study, we show that hafnia-based filamental RRAM devices are capable of gradual multi-level switching at ultra-fast (ps) time scale at low operation voltages (< 1V). This enables high frequency/bandwidth operations with extremely low energy switching.

RRAM devices are formed by crossbar 50x50 nm MIM capacitors fabricated with an ALD polycrystalline 5nm HfO2 film and TiN electrodes. An ultra-fast pulse setup (Fig. 1) provides precise control over the power delivered to the cell and removes the need for a current compliance control (1R configuration). Resistance is shown to stepwise increase or decrease depending on voltage value and polarity (Fig. 2).

To evaluate how synaptic weight can be modulated by the time between the incoming signals, we investigated dependency of the RRAM resistance on time between the consequent pulses (Fig. 3). Reducing the time interval between pulses below 2 ns results in significant amplification of their effect on resistance. It’s consistent with theoretical expectations that, by briefly increasing local temperature [2], the first pulse magnifies the structural changes inducing by the subsequent pulse.

To emulate the effect of time window between the pulses from pre- and post- synaptic neurons, a pair of pulses of positive (pre-synaptic) and negative (post-synaptic) polarity was applied to the same electrode (Fig. 4). In bi-polar switching, a negative polarity pulse induces resistance change in the same direction as a positive pulse applied to the opposite electrode. Potentiation or depression were observed depending on a positive pulse preceding or following the negative one, consistent with the reported brain-inspired operations. A very short time interval between incoming signals enabling potentiation/depression processes implies extremely fast neuromorphic system operations capabilities.

G. Bersuker et al., J. Comput. Electron. 16, 1085, 2017

D. M. Nminibapiel et al., EDL 38, 326, 2017

Figure 1
(Invited) The Non-Volatile Redox Memory for Neuromorphic Computing
Authors: Talin Albert Alec
Published: February 2020

Inspired by the efficiency of the brain, CMOS-based neural architectures and memristors are being developed for pattern recognition and machine learning. However, the volatility, design complexity and high supply voltages for CMOS architectures, and the stochastic and energy-costly switching of memristors complicate the path to achieve the interconnectivity, information density, and energy efficiency of the brain using either approach. In my talk, I will review the latest advances in neuromorphic computing architectures based on deep neural networks implemented using CMOS and memristors and describe the challenges in achieving both high accuracy and energy efficiency using these devices. I will then discuss an alternative approach based on the non-volatile redox memory (NVRM): a device with a resistance switching mechanism fundamentally different from existing memristors, involving the reversible, electrochemical reduction/oxidation of a material to tune its electronic conductivity. The first type of NVRM that I will describe is based upon the intercalation of Li-ion dopants into a channel of Li1−xCoO2. This Li-ion synaptic transistor for analog computing (LISTA) switches at low voltage (mVs) and energy, displays hundreds of distinct, non-volatile conductance states within a 1V range, and achieves high classification accuracy when implemented in neural network simulations1. The second type of NVRM I will describe operates on a similar principle but is based on the polymer system PEDOT:PSS, and which we call the electrochemical neuromorphic organic device (ENODe) 2. Plastic ENODes are fabricated on flexible substrates enabling the integration of neuromorphic functionality in stretchable electronic systems. Mechanical flexibility makes ENODes compatible with three-dimensional architectures, opening a path towards extreme interconnectivity comparable to the human brain.

(1) E. J. Fuller, F. El Gabaly, F. Léonard, S. Agarwal, S. J. Plimpton, R. B. Jacobs-Gedrim, C. D. James, M. J. Marinella and A. A. Talin, Advanced Materials 29, 1604310 2017.

(2) Y. B. van de Burgt, E. Lubberman, E. J. Fuller, S.T. Keene, G. C. Faria, S. Agarwal, M. J. Marinella, A. A. Talin* and A. Salleo*, Nature Materials 16, 414 2017.
Resistance Switching Properties of Silicon Nitride Material with Heavily Doped Si As Bottom Electrode
Authors: Karakolis Panagiotis , Speliotis Athanasios , Ioannou-Sougleridis Vassilios , Normand Pascal , Skarlatos Dimitrios , Dimitrakis Panagiotis
Published: February 2020

RRAMs are considered as the most promising devices for NVM and storage class memory applications at technology nodes below 20nm. In addition, due to their memristive properties pave the way for the realization of neuromorphic prototype circuits. The majority of these devices are two-terminal MIM structures and use as insulator (active material) metal oxides in combination with proper metals. The present models assuming the oxide and metal physical and chemical properties seem that can explain the observed resistive phenomena. Nevertheless, the effect of humidity seems to play a crucial role in the reliability of RRAMs.

In this context, nitride based insulators are of special importance because of their immunity in humidity and oxygen related parasitic effects. The present contribution reports on the preliminary results related to our research on MIM devices where LPCVD Si3N4 is used as insulating material, sputtered Cu as active (top) electrode and heavily doped Si (<0.003 Ω.cm) bottom electrode (BE). Both conductivity types of Si n and p have been tested (Figure). The devices have been characterized in terms of static I-V, resistance variability, impedance spectroscopy (IS) and retention measurements. Room temperature I-V measurements suggest that a space charge limited conduction (SCLC) is dominating through the nitride layer. According to our results the MIM diodes with p+ Si as BE present higher variability in VSET and VRESET compare to those diodes with n+ Si BE. IS measurements are in progress to investigate the mechanism for resistance switching. Upon the current results, his mechanism may be attributed to the presence of diffusion process. Temperature variable measurements are currently contacted in order to identify the electronic or ionic nature of the diffusion mechanism. The fabricated devices exhibit attractive multi-state operation under different current compliance values. In addition, retention measurements at room temperature indicated that the LRS is retained for 10 yrs.

Figure 1
(Invited) Energy Alignment at the Molecule – Electrode Interface: An Electrochemical-Potential / Hardness View
Authors: Vilan Ayelet
Published: February 2020

A major aspect of hetero-interfaces is the relative position the energy levels / bands of two adjacent phases, known as the ‘injection barrier’. From inorganic semiconductors to thin organic films, interfacial energy alignment is accompanied by charge redistribution and therefore, creation of a built-in potential. Seemingly, adsorbed molecules (isolated or within a monolayer) follow similar principles: the injection barrier is equivalent to the tunneling barrier in molecular junctions (ε, all quantities are illustrated below) while charging is expressed as an adsorption-induced molecular dipole (Δ). However, molecules have no free carriers and their nearest energy level is way-off the electrode’s Fermi-level. This explains why the electrode-molecule interface is widely assumed to be ‘inert’: adsorption induces no long-range charge rearrangement beyond the mere chemical bond (Δ=0; left-side illustration). This scenario is equivalent to ‘vacuum level alignment’ (Schottky limit) in bulk semiconductors where the injection (tunneling) barrier is predicted from the work-function of the clean electrode (WF) and the frontier-level of the isolated molecule (IP in the illustration). However, evidence is growing for the opposite: electrodes of largely different work-function hardly affect the tunneling barrier (constant ε) while the molecular dipole varies drastically (Δ ≠ 0; right-side illustration). It is as if the molecules are “Fermi-level-pinned”, but molecules have no Fermi level! Instead the electrochemical potential (μ) of the molecule is a well-defined thermodynamic quantity. I will describe how electrochemical balance combined with the notion of chemical “hardness / softness” (electronic polarizability) provide qualitative guidelines for predicting the energy alignment of adsorbed molecules. This concept will be demonstrated on our own results with molecular monolayers on Si(111) and by reference to literature works on thiol-bonded monolayers on Au.

Figure 1
(Invited) Towards a Perfect Junction: Effect of Smoothening Electrodes on Tunneling Behaviors across Large Area Molecular Junctions
Authors: Chen Jiahao , Kundu Souvik , Du Chuasen , Kadoma Atte , Giroux Thomas , Thuo Martin
Published: February 2020

Large area self-assembled monolayers (SAMs) based tunneling junctions have recently received heightened attentions, in part, due to high yield of working junctions, ease of fabrication, and data reproducibility. Eutectic gallium indium (EGaIn) and ultra-flat metal substrate are used to form these molecular junctions. Despite the advances, effect of sub-nanometer roughness inhibits delineation of second-order effects on tunneling characteristics. These effects, like intra-molecular keesom interactions, can lead to new approaches to tuning charge transport behavior – a fete that is yet to be harnessed. To address this challenge, we deployed a three-pronged approach entailing; i) polishing of the top-electrode, ii) tuning roughness of the bottom electrode and the angstrom scale, and iii) deploying statistical analysis to uncover these effects. In this talk, effect of these modifications on SAM and associated charge transport behavior will be discussed.
(Invited) Interface Engineering of Silicon-Based Molecular Devices
Authors: Hacker Christina A. , Bruce Robert C , Takeuchi Saya
Published: February 2020

Incorporation of novel materials, such as molecular layers or 2D layers, into electronic paradigms enables transformative potential in applications ranging from memory, batteries, catalysts, flexible devices, and alternate computing paradigms. In order to take advantage of the promising properties of these components, holistic study of the fundamental components as well as their impact on the final device properties are important. As interfaces continue to dominate the electrical performance, the ability to adjust the interface for desired properties becomes more critical. Molecular layers offer a versatile means of tuning interfacial electronic, chemical, physical, and magnetic properties.

This talk will focus on our work with engineering silicon interfaces and the impact that molecules have on the electrical properties. We will describe the impact surface functionalization conditions have on the resulting electrical properties where the monoloayers are characterized by using vibrational spectroscopy, photoelectron spectroscopy, contact angle, and e-GaIn based electrical measurements.
Morphology-Dependent Performance of NiO Via Facile and Controllable Synthesis for Electrochemical Methane Activation
Authors: Peng Luwei , Qiao Jinli
Published: February 2020

Nickel oxide（NiO）as a semiconductor using as active catalysts for electrochemical CH4 activation at room temperature has attracted considerable attention. In this study, series of NiO with diverse morphologies including nanoparticle(NP),nanoflower(NF),nanoslice(NS) have been successfully synthesized to inquire their electrocatalysic performance in CH4 oxidation. Physicochemical properties of these materials were characterized by several techniques, like BET,XRD,TEM,CV,LSV,EIS. The NF and NS of samples possess much better low-temperature reducibility and higher CH4 conversion comparing with other samples. This proposal of low temperature electrochemical oxidation of methane may provide a method for the complex organic compounds of carbon and syngas.
An Experimental Strategy with Zwitterionic Pendants Groups on Poly (poly (ethylene glycol) Methacrylate) to Know the Role of Ion Clusters in the Fast Ionic Conductivity of on Ppegma / LiPF6
Authors: Nava Dora Patricia
Published: February 2020

In this work propose an experimental strategy to explain the fast ion transport of pPEGMA /LiPF6 electrolytes at high salt concentration with the presence of ion clusters. In this study it has demonstrate the ability to functionalize the lateral chains of pPEGMA with zwitterionic groups without altering the morphology of pPEGMA. This work show a successful functionalization of pPEGMA (pMPS8-co-PEGDMA) able to dissociate salt completely. The analysis of TG, DSC, XRD and IES show that in pPEGMA/LiPF6 at low salt concentration the ionic conductivity is coupled with the mobility of chains, the transport mechanism occur through dynamic percolation theory where the translational dynamics of the ions depends of segmental dynamics and by renewal of hopping probabilities. The monotonic increase of ionic conductions with increasing of ion clusters, is due that the ion motion is complete decoupled of relaxation chains. Tg values increase from -49 to -32 oC, enough to obtain a rigid polymer electrolyte in which the cation transport occur through a static ion clusters way by percolation theory. The ion conduction of the polyether pPEGMA show that it morphology reach a certain rigidity as a rubbery electrolyte when the system change to polymer in salt. Therefore pPEGMA is an ideal polymer to use in the next generation of advanced polymer electrolyte.

Figure 1
Analysis of Oxide Film on Aluminum Electrode in Aluminum-Air Battery
Authors: Mohammad adbul Kaleem , Hosmane Narayan S , Cho Kyu Taek
Published: February 2020

In this research, aluminum air battery system was revisited to investigate key issues which have challenged its full application as a rechargeable battery. The Al-air battery had received intense attention once due to the excellent benefits such as low cost and high energy density, but due to the challenging issues such as hydrogen evolution, and inactive oxide film formed on the Al surface, it could not be fully applied. Recently, ionic liquid which is a salt in liquid form at room temperature started to be applied in the battery system to overcome the issues in aqueous electrolyte [1,2], but the inactive oxide film on Al surface is still dominant in decreasing cell performance and detailed research to understand how to control the oxide film was not conducted. In this study, 1-Ethyl 3-Methyl Imidazolium Chloride ([EmIm]Cl) and Aluminum Chloride (AlCl3) was applied in the Al-air battery, and its effect on oxide film on the surface aluminum electrode was analyzed through cell-base test, and SEM image analysis. It was found that the inert oxide film on aluminum, which is one of the most challenging issues, could be controlled and removed by using of proper ratio of [EmIm]Cl and AlCl3, and the growth/breakdown mechanism of the oxide film was theoretically considered. This research results are expected to suggest a new direction to control the surface of aluminum electrode to make it the most promising system.

References

[1] D. Gelman, B. Shvartsev, Y. Ein-Eli, Journal of Materials Chemistry A, 2 (2014) 20237-20242.

[2] R. Revel, T. Audichon, S. Gonzalez, J. Power Sources, 272 (2014) 415-421.
(Keynote) To Honor Michel Armand: Developments on New Electrode and Electrolyte Materials for Batteries at the IMN
Authors: Guyomard Dominique , Boucher Florent , Brousse Thierry , Crosnier Olivier , Dupré Nicolas , Gaubicher Joël , Le Bideau Jean , Lestriez Bernard , Moreau Philippe , Poizot Philippe , Soudan Patrick
Published: February 2020

A selection of recent developments at IMN will be reviewed on several research directions dealing with new electrode and electrolyte materials for batteries. We focus on innovative surface modifications of electrode components, new electrode materials, compositions and architectures, and failure mechanism upon cycling by in-depth characterization through coupled advanced techniques. We cover the topics of silicon electrodes for Li-ion batteries, positive and negatives for Na batteries, renewable organic aqueous batteries, and all-solid-state ionogel Li-metal batteries.

Surface derivatization of powder oxide materials by molecular grafting modifies their interfacial chemical reactivity, thus increasing cycle life and decreasing self-discharge. Molecular junctions through double-side grafting between non-carbon-coated LFP and multiwall carbon nanotubes (MWCNT) enables original electrode architecture, leading to higher specific capacity and better capacity retention. Our recently synthesized lithium-doped PANI shows excellent performance both as bulk material and as thin layer coating of bare LFP particles.

We are also developing organic materials for bulk application in the new generation of renewable organic batteries. New results in the area of organic aqueous batteries for renewable energy storage will be disclosed.

In the Na-FePO4 system, we identified the intermediate phase as a fully ordered Na2/3FePO4 composition showing a vacancy ordering along the channels coupled with a Fe(II)/Fe(III) charge ordering. Ab initio DFT total energy and molecular dynamics calculations lead to the optimized structure of the Li2/3FePO4 phase, and show the Na2/3FePO4 phase is thermodynamically stable while the Li2/3FePO4 phase is metastable. In the domain of negatives for non-aqueous Na-ion batteries, we found GaV4S8 is a new material with high cycled capacity of 500 mAh/g and an atypical reaction mechanism.

In the field of silicon negative electrodes, we show some examples of nanoscale STEM-EELS imaging of the reaction mechanism upon cycling, and we describe an electrode maturation process that improves the performance whatever the type of silicon, binder and conductive agent. We also identify the end-of-life mechanism that is different in half cell and in full cell.

Ionogels, which are confined ionic liquids within various host networks, are developed in order to fabricate self-standing solid-state membranes, all-solid-state Li metal batteries, and all-solid-state supercapacitors with good performance. We analyze as well what are the needed criteria to obtain good cycling efficiency and durability of the Li metal electrode in contact with these ionogel solid electrolytes.
(Invited) Do Hybrid Electrolytes Offer the Best Option for Lithium Metal Rechargeable Batteries?
Authors: Blomgren George E
Published: February 2020

Research and development on the technology of solid state batteries has become an important field of enquiry in recent years. The history of the field goes back to the 1980’s when thin layers of positive active material, solid electrolyte and evaporated lithium were developed into the so-called micro-battery. These micro batteries were capable of very high cycle life and reasonable current densities, but the capacity is always low and the cost of production is high. The vacuum methods, however, resulted in thin, dense layers which had excellent interfacial contact with the layer above and below, which resulted in the good performance as well as the high cycle life. The discovery of much high conductivity solid electrolytes, some with good stability against lithium metal, has resulted in the renewal of interest in the field.

Research into these new, high conductivity materials has led to attempts to form thicker layers in more conventional methodology with the hopes of lower cost and obviating the interfacial problems of earlier work with thick layers. Eliminating porosity with such methods as well as eliminating ion blocking interfacial layers has proved to be a problem. Also, the original idea that lithium metal would be blocked from access to the positive electrode because of the non-porous solid electrolyte has also proven to difficult to attain. These aspects of the conventional approach will be explained.

More recent attempts have been made with the use of liquid electrolytes to contact the dense solid electrolyte layer as well as fill the porosity in the inherently porous pressed powder positive electrode and sometimes to serve as an intermediate layer between the solid separator and lithium foil. The results of such tests on “hybrid” electrolyte cells will be discussed and an attempt to predict the likelihood of success of such batteries will be made. The approach will also be compared to the more conventional all solid electrolyte systems that have been studied to date.
(Keynote) All-Solid-State Rechargeable Batteries
Authors: Goodenough John B. , Braga Maria Helena
Published: February 2020

In 2004, the group of Michel Armand reported a cation conductivity σi ≤ 3 × 10-3 S cm-1 at 25°C with a salt in the plasticizer N ≡ C – CH2 – CH2 –C ≡ N. We have investigated the use of this plasticizer as the contact with the cathode in an all-solid-state rechargeable cell containing a solid dielectric amorphous-oxide electrolyte contacting the anode. With this configuration, we obtain a rechargeable-battery cell that stores electric power as both chemical and electrostatic energy.
(Keynote) Tribute to Michel Armand: Lithium Metal Solid State Batteries from 1979 to 2019
Authors: Zaghib Karim , Julien Christian M , Mauger Alain
Published: February 2020

Research on lithium metal combined with polymer electrolyte in lithium rechargeable batteries was started in 1979 by Michel Armand. Since that time, lithium battery research has expanded worldwide. Several new polymers, solid electrolytes and ionic liquids with improved conductivity were identified. These advances resulted from a better understanding of the major parameters controlling ion migration, such as favorable polymer structure, phase diagrams between solvating polymers and lithium salts, and the development of new lithium counter-anions. In spite of the progress so far, the quest for a highly conductive dry polymer at room temperature is still not available. However, effort is continuing, and all-lithium polymer battery (LPB) developers presently face the challenge of whether to heat the polymer electrolyte to enable high-power performance, as required for electric vehicles and energy storage. LPB developers have explored both the high-temperature and low-temperature options.

The commercial use of lithium metal/polymer batteries has been delayed because of the adverse effects of dendrites on the surface of the lithium electrodes, and the difficulty in finding a polymer that has both the mechanical strength and ionic conductivity required in a solid electrolyte. However, recent strategies have emerged to overcome these difficulties, and now these batteries are currently an option for different applications, including electric cars.

In this presentation, we review these strategies and discuss the different promising routes that should result in further progress on lithium metal/polymer batteries in the near future. This presentation also discusses the challenges and opportunities in developing thin lithium negative electrodes with stable SEI layers for three battery technologies using:

All solid-state Li- batteries

Rechargeable lithium batteries containing dry polymer and ionic liquid-polymer électrolytes

Li-Sulfur batteries.

In addition, we will discuss the safety of lithium, dendrite mechanism, interface phenomena, side reactions, protection of lithium metal, and lithium alloys that are relevant to lithium batteries.

Acknowledgement: The author thanks the CETEES groups in Varennes Shawinigan teams for helpful discussion.
Polymer Gel Electrolytes for Magnesium Batteries: Ion Transport and Electrochemical Characterization
Authors: Merrill Laura C. , Ford Hunter O. , Brankin Colin , Schaefer Jennifer L.
Published: February 2020

The development of new rechargeable battery systems employing novel chemistries is imperative to meet the increasing energy storage demands of emerging technologies. Magnesium metal batteries are one attractive type of beyond lithium-ion system, due to the widespread abundance, gravimetric and volumetric charge capacity, and electrodeposition potential of magnesium. However, the electrolyte formulations that enable magnesium deposition and dissolution are few in comparison with lithium. Here we report on the ion transport and electrochemical properties of magnesium polymer gel electrolytes based crosslinked, ionomeric networks that are swelled. The nature of the solvent(s) and salt(s) of the liquid medium, and the charge density of the ionomer network, are all found to heavily influence the properties of the gel electrolyte.

Magnesium polymer gel electrolytes are created by swelling the ionic networks in electrolytes containing AlCl3, MgCl2, and/or Mg(HMDS)2. Interestingly, higher ionic conductivities and higher current densities for magnesium deposition/dissolution are observed for some gel electrolytes compared to the properties of the pure liquid component. This is hypothesized to be due to the speciation of the free complex ions, which is altered by the presence of the ionic polymer network. These gels are further applied to the Mg-S system, and it is shown that the structure and charge density of the gels influence anionic polysulfide transport. Gel formulations are identified where polysulfides are preferentially rejected while complex magnesium cations are facilely transported across the gel. Structure-property correlations will be presented as found from the combination of SAXS/WAXS, diffusion, elemental analysis, and conductivity measurements.

Single-ion conducting magnesium polymer electrolytes are also created by swelling the ionomeric networks in pure solvents. High ionic conductivities are achievable (> 10^-4 S/cm). However, even when these electrolytes have high magnesium conductivity and are electrochemical stable (non-passivating) against magnesium metal, no magnesium electrodeposition is induced at reasonable potentials. This is suspected to be due to the difficulty of the desolvation of Mg+2.
Nano-Enabled Microinductors for Power Electronics Microfabricated By Advanced Heterogeneous Integration
Authors: Langlois Eric D. , Watt John , Pillars Jamin R. , Kaehr Bryan J. , Abere Michael J. , Huber Dale L. , Monson Todd C.
Published: February 2020

Novel nano-enabled microinductors for power electronics using advanced heterogeneous integration have been developed. These toroidal microinductors employ a first-of-its-kind nanocomposite magnetic core material employing superparamagnetic iron nanoparticles that are covalently cross-linked. This nanocomposite has high resistivity, is mold injectable, and can be cured at low temperature (63 °C) making it better suited for microfabrication than current, state-of-the-art ferrite core materials. The coil is micromachined out of electroformed copper consisting of top, inner/outer, and bottom winding layers. Two unique methods are used to form the electroplating molds for the inner/outer windings to accommodate thick core layers demonstrating two different ways these microinductors can be made. The first method employs high-aspect-ratio 3D printed resin molds instead of standard photoresist. The second method uses the non-conducting nanocomposite core itself as the plating mold and patterning is performed via femtosecond laser micromachining. These Sandia developed technologies enable new, low-cost, advanced heterogeneous integration schemes for creating high performance, nano-enabled microinductors that are radically different than previous attempts using LIGA or other costly, non-optimal microfabrication techniques. 2 μH output and 500 nH input microinductors for use in a high performance buck converter are showcased. Both inductors have 50 wire turns and less than 1 cm3 form factors. A process flow outlining the steps needed to realize these devices is provided. This flow takes advantage of the molding capabilities of our iron nanocomposite core material, the high electrical conductivity of electroformed copper, and the high-aspect-ratio capabilities of 3D printing and femtosecond laser micromachining. Initial characterization results over frequency are presented for this unique set of power inductors.
(Invited) Lanthanide Magnetoelectrocatalysis: Studying Electrocatalytic Effects of Various Lanthanide Triflates As Related to Their Magnetic Properties
Authors: Knoche Krysti L. , Parr Daniel , Rathuwadu Nadeesha , Leddy Johna
Published: February 2020

Electron transfer events are commonly considered in light of the transfer of charge. But, electrons also have properties of spin. Electron spins interact with magnetic fields. In the presence of a localized magnetic field, electron transfer rates of electrochemical reactions change. Correlations between a redox species’ number of unpaired electrons and the change in electron transfer rate have been found.

Many important reactions that include the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), and carbon dioxide reduction have been shown to be kinetically limited. ORR limits performance of many fuel cell and air batteries. Increased rates of HER facilitate energy generation. The presence of lanthanides at electrode surfaces can mediate the rates of such important reactions. For example, Ytterbium triflate extracted into Nafion on an electrode in acetonitrile increases oxygen reduction currents by 15%.

Despite largely similar properties, lanthanide magnetic properties are diverse because the number of unpaired electrons in the d orbitals ranges from 0 to 7. Voltammetry for lanthanides extracted into Nafion films on electrodes undertaken in the presence of some of these species will be presented. Correlations between lanthanides (and their spin and magnetic properties) and the type and magnitude of effects on important reactions will be discussed.
(Invited) Magnetic Gradient-Assisted Physical and Chemical Structuring of Electrodeposits
Authors: Blanc Niclas , Tschulik Kristina
Published: February 2020

Magnetic thin films, micro and nano structures are key features in magnetic sensors and for data storage in hard drives. To date often physical deposition methods are more frequently employed than electrodeposition to produce these magnetic structures. This is due to the fact that the usually inexpensive alternative production by electrodeposition requires sophisticated masking or templating if structured deposits are desired. Magnetic-field assisted electrodeposition has been demonstrated as a method to produce structured deposits by employing reusable magnetic gradient templates. [1] The working principle is based on a locally enhanced mass transports thanks to a magnetic gradient force induced local convection in the electrolyte during electrodeposition. In regions of high magnetic gradients, typically film thickness and roughness are increased for paramagnetic ions like Cu2+, Co2+ or Fe2+. Here, we demonstrate that not only single component metals, but also bimetallic alloy electrodeposits can be deposited in a desired structure by this approach. By suitably selecting the electrolyte composition and deposition parameters, we demonstrate that the current efficiency can be increased for the electrodeposition of transition metal-based alloys. This is evidenced by electrochemical quartz crystal microbalance studies during electrodeposition of CoFe in the presence of varied magnetic gradients. [2] In addition, we show that also chemical structuring of bimetallic deposits can be achieved by means of magnetic gradient-assisted electrodeposition, which is shown or CuNi electrodeposits. For both systems the observed local morphological and compositional changes are characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. The experimental findings are then discussed in terms of magneto-hydrodynamic effects, which are attributed to the magnetic field gradient force. Thus, magnetic-gradient assisted electrodeposition is suggested as a new route to magnetic patterning of surfaces.

[1] Tschulik, Kristina; Koza, Jakub Adam; Uhlemann, Margitta; Gebert, Annett; Schultz, Ludwig

Electrochemistry Communications, 2009, 11(11), 2241–2244

[2] Karnbach, F.; Uhlemann, M.; Gebert, A.; Eckert, J.; Tschulik, K.

Electrochimica Acta, 2014, 123, 477–484
Galvanic Replacement of Chiral Hosts for Generating Helical Nanoparticles with Engineerable Compositions and Optical Activity
Authors: Liu Junjun , Huang Zhifeng
Published: February 2020

Metallic helices with a characteristic helical pitch (P) in the micro- or nano-scale have been proposed to develop diverse chirality-related primary applications. However, limit development of nanofabrication techniques leads to P > 20 nm; molecules are too small in size to effectively perceive the helical chirality, and such the dimensional mismatch will substantially prohibit the development of those applications.

Currently, we devise glancing angle deposition (GLAD) with fast substrate rotation to successfully generate metallic helical nanoparticles (HNPs) with a sub-10-nm P. The sub-10-nm P is compatible with the molecular scale, such that we use the sub-10-nm-P HNPs to amplify optical activity of enantiomers that are grafted on the HNPs in roughly one order of magnitude, and to effectively mediate the enantioselective photocyclodimerization of 2-Anthracenecarboxylic acid.

However, GLAD is operated at an extremely oblique deposition angle of > 85° with respect to the direction of substrate normal, resulting in an evidently low deposition yield given that most of evaporated atoms will not condense on the substrate. From the production cost point of view, low deposition yield tends to severely limit the application of such the technique to generate HNPs made of noble metals, which typically function as heterogeneous asymmetric catalysts. It is of practical demand on developing an economic method to produce noble metal HNPs with high production yield.

In this talk, we will present a two-step fabrication of noble metal HNPs, composed of fast-substrate-rotation GLAD of HNPs made of low-cost metals (such as Cu, denoted as chiral host) and galvanic replacement of chiral hosts with noble metals (such as Ag, Au, Pt, and so on). Limit, controllable usage of noble metal salts in the galvanic replacement reaction not only reduces the production cost of noble metals, but also leads to generating alloy HNPs with tunable alloy composition. Systematic characterizations of nanostructure, material and optical activity are operated to study the galvanic replacement processes and dynamics. This work paves the way to generating novel asymmetric catalysts to operate heterogeneous asymmetric catalysis with high enantioselectivity, and to dramatically enhancing enantiodifferentiation by amplifying optical activity of enantiomers.
Influence of Pretreatment on the Electroless Metallization of Stereolithography Resins
Authors: Bernasconi Roberto , Alagna Leone , Magagnin Luca
Published: February 2020

One of the most attractive techniques currently under development in the sector of additive manufacturing is the 3D printing of metallic objects. Parts realized with pure metals or alloys present many useful functional and aesthetic properties: electrical and thermal conductivity, metallic luster, high mechanical properties. Many techniques, including selective laser sintering (SLS) or electron beam melting (EBM), are able to yield good quality results [1]. All metal 3D printing techniques are however characterized by common drawbacks that limit their applicability: poor surface quality, residual porosity and inability to reach extremely low feature sizes (useful in the so called additive microfabrication).

Another approach that can be followed to obtain parts presenting metallic properties is the surface metallization of polymeric 3D printed objects. Polymers are easier to print than metals and some techniques, like stereolithography, are able to reach micrometric feature sizes. Metallic layers can be in principle applied using many different techniques, but electroless plating in particular presents important advantages in terms of cost per unit and flexibility.

Methods to electroless metallize stereolithography printed parts are available in literature [2], but the influence of different pretreatment routes on the quality of the final metallic layer was never fully investigated. In the present work, three stereolithography resins were pretreated following three different methods. The first one was based on the use of an acidic etching solution, the second was based on an alkaline etching, while the latter saw the application of atmospheric plasma to the pretreatment of the resins. Evolution of surface properties for the different pretreatment routes was investigated employing SEM, contact angle measurements, compositional analysis and FT-IR. Following surface preparation, resins were metallized with electroless copper. By doing this, the influence of the pretreatment on coating quality and adherence was evaluated.

[1] I. Gibson, D. W. Rosen, B. Stucker, Additive manufacturing technologies, Springer (2010)

[2] R. Bernasconi, C. Credi, M. Tironi, M. Levi, L. Magagnin, Electroless Metallization of Stereolithographic Photocurable Resins for 3D Printing of Functional Microdevices. J. Electrochem. Soc. 164, B3059–B3066 (2017)
Influence of Temperature on Peculiarities of Electroless Copper Deposition
Authors: Norkus Eugenijus , Stalnioniene Irena , Stalnionis Giedrius , Tamašauskaitė-Tamašiūnaitė Loreta
Published: February 2020

The industrial electroless copper plating solutions containing formaldehyde as reducing agent are known from the middle of the last century and are widespread in the practice up to now. They are widely used in electronics for deposition of metallic copper layers on semiconductors or dielectrics (silicon wafers, resins etc.). Since such kind solutions are alkaline (formaldehyde is strong enough reducing agent for Cu(II) only in alkaline solutions), ligands are needed for preventimg of formation of Cu(OH)2 precipitate and binding Cu(II) into complexes

Ethylenediaminetetraacetic acid (EDTA) is one of the most widely used ligand in alkaline electroless copper plating baths due to its perfect chelating properties. The possible solution equilibria in alkaline Cu(II)-EDTA-formaldehyde solutions are discussed in details.

The data on use of EDTA in electroless copper plating as a Cu(II) ligand are enough wide-ranging, but, it is worth noting that practically all data are obtained at room or higher temperature. Therefore in this work copper coatings were deposited from alkaline formaldehyde-containing solutions, using EDTA as Cu(II) ligand at temperatures, mainly lower than room temperature.

The experiments were carried out in electroless plating solutions at pH 12.0 - 13.0 and 5 - 30 °C temperature during 0.5 and 1h (Fig. 1). The thickness of the compact copper coatings obtained under optimal operating conditions in 1 h can reach ca. 4 μm, depending on the pH and temperature. The maximum values of plating rate are reaching at pH 12.5 at all investigated temperatures. The real surface areas (R
f) of deposited copper coatings vary widely, i. e. from ca. 3.1 up to 39.3. The maximum R
f values were obtained at pH 12.0 for investigated temperatures.

The anodic formaldehyde oxidation measurements were carried out in formaldehyde solution at pH 12.5. It was found, that the rate of formaldehyde anodic oxidation depends on conditions of the formation of copper coatings – the highest rate of HCHO oxidation was determined on the surface’s electrolessly obtained at 5 °C and pH 13.0.

Acknowledgment

This research was funded by a Grant (No. LAT-12/2016) from the Research Council of Lithuania.
The Synthesis and Characterization of Atomically-Thin Pt Monolayer to Multilayer Pt Films on Graphene and MoS2 and Their Application for ORR and HER
Authors: Alamgir Faisal M , Arnold Christopher , McDowell Matthew T , Kacher Josh , Warner Jamie H
Published: February 2020

This work explores the deposition of Pt monolayers on 3D graphene and 2D MoS2 as catalyst architectures for electrocatalysis. Ni foam was utilized as a starting substrate for the 3D graphene growth before Pt was deposited layer-by-layer in a surface-limited electrochemical scheme to achieve highly wetted and atomically thin growth. A similar surface-limited technique was utilized for the deposition of Pt on both vertically and horizontally aligned MoS2. High resolution TEM, XPS, SEM/EDX, and electroanalytical techniques were used to characterize these samples and reveal the evolution of the atomic/electronic structure as a function of the number of Pt monolayers. Specifically, the ORR and the HER reactions were used to characterize the catalytic activities of the graphene- and the MoS2-templated catalysts, respectively. It is demonstrated that the synthesis scheme outlined here allows for the design of dimensionally-controlled and ligand-flexible catalyst architectures that can have a wide range of chemical applications.
Co-Mn Oxide Electrodeposition for High Temperature Solar-to-Thermal Energy Conversion Systems
Authors: Cetina Dorantes Marco , Lizama Tzec Francisco Ivan , Oskam Gerko
Published: February 2020

Solar concentration systems use solar collectors consisting of a metal tube with a selective coating, and an evacuated, glass vacuum tube to minimize losses by convection, conduction and thermal emission. The glass tubes eventually loose the vacuum, and the exposure to air results in degradation of the selective coating. Manganese cobalt oxides are alternative air-stable selective coatings, related to the spinel structure they form, which is stable up to high temperatures. The optical properties of the selective coating are expected to depend on the proportions of Co, Mn and O in the material; hence, the electrodeposited film needs to be optimized by tailoring the composition.

In this work we report on the combinatorial electrodeposition of Co-Mn oxides employing a Hull cell, in order to prepare a compositional materials library and to relate the composition with the solar absorptance and thermal emittance. The Co-Mn oxide material library was deposited in galvanostatic mode using a two-electrode setup, with a stable anode and stainless steel cathode (AISI 304). The electrodeposited cathodes were treated at 600 oC for a short time in order to complete the oxidation of the material. The solar absorptance and thermal emittance in the 200 nm - 15 µm range were obtained from reflectance measurements. From the best optical values, the current density corresponding to the optimal position on the cathode was selected for further characterization of the deposited material. Co-Mn oxide films were then deposited on 6 cm x 4 cm stainless steel substrates for thermal tests at 252 oC for 600 hours in order to evaluate the performance criteria. The film composition was obtained from energy-dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), and X-ray diffraction (XRD).
Electrochemical 3D Printing with Nanopipettes
Authors: Momotenko Dmitry , Zambelli Tomaso , Vörös János
Published: February 2020

Nanopipette-based electrochemical methods rapidly develop into highly versatile and powerful tools in nanoscience for a variety of applications from imaging and sensing to nanoscale fabrication. Herein, we present advanced three-dimensional printing approaches for the fabrication of complex features using state-of-the-art nanopipette-based scanning probe techniques. Hollow cantilevers for atomic force microscope (AFM), known also as FluidFM probes,1 and pulled double-barrel glass capillaries are employed for precise local delivery of precursor species using pressure-controlled fluid flow and fluxes given by electrophoretic migration of ions. The intrinsic advantage of these concepts is the automated feedback mechanism, based either on the detection of mechanical forces (FluidFM) or on variation of ionic current through the nanopipette, that allows to maintain a constant distance (typically, from a few to several tens of nanometers) between the probe and a growing printed feature. This ensures precise control of the electrodeposition process and enables rapid fabrication of high-aspect ratio features at rates approaching hundreds of nm s-1. These new techniques open avenues for the architecture of a variety of features using continuous deposition and voxel-by-voxel printing strategy,2 and also enable in situ read-out of the printed patterns thanks to the primary functionality of nanopipette methods as scanning probe microscopy tools.3

References

1. Hirt et al., RSC Adv., 5, 84517 (2015)

2. Hirt et al., Adv. Mater., 28, 2311 (2016)

3. Momotenko et al., ACS Nano, 10, 8871 (2016)
Influence of Interfacial Properties on the Capacitive Deionization Performance of TiO2 Thin-Film
Authors: Wang Yang , Anderson Marc Arlen , Tejedor-Tejedor M. Isabel , Tan Wei
Published: February 2020

Naturally, the solid liquid interface interaction widely exists. The study of electrode and aqueous solution interface is significant to the application of capacitive deionization as the principal reaction takes place at the interface. This paper focuses on the pure oxide thin-film, TiO2, in an aqueous solution concerning the response to solution chemistry including protons and specific adsorbing ions, phosphate for instance. Through the measurement of zeta potential and open circuit potential, the mechanism that the interfacial properties can be influenced by solution chemistry is illustrated. With the results of capacitance at different state of solution chemistry, the relationship between the interfacial properties, especially the surface potential, and the capacitance is obtained. The electrochemical capacitance is related to the surface potential of TiO2 porous thin-film and can be changed with the addition of protons and specific adsorbing ions. The capacitance increases away from isoelectric point in absence of phosphate, and phosphate addition displays an optimal effect over the neutral range of pH from 5 to 9, where many oxides are highly stable with quite low dissolution. Based on the results above, capacitive deionization system with phosphate modified TiO2 porous thin-film is designed, which possesses better deionization performance compared to the one without specific adsorption. It is believed that these TiO2 porous thin-film could be used as electrodes or coatings for electrodes due to their high surface area, good wettability of the pore walls and controllable surface potential. Further study of the interface is important in the development of capacitive deionization.