bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Cage Skeletal Transformation of Fullerene Via Chlorination
Authors: Yang Shangfeng
Published: February 2020

A classical fullerene is composed of hexagons and pentagons only, and its stability is generally determined by the Isolated-Pentagon-Rule (IPR). In 2005 Taylor et al. reported the first cage skeletal transformation of fullerene C60 via fluorination at 550 0C, affording two stable non-classical fullerene derivatives containing heptagons. It is then intriguing to investigate whether cage skeletal transformation of fullerene can be fulfilled under less harsh conditions. Herein, we present our recent studies on cage skeletal transformations of classical higher fullerenes in the course of high-temperature chlorination. Chlorination-promoted cage skeletal transformations occur by Stone-Wales rearrangements (SWRs, i.e., a rotation of a C−C bond by ca. 90°) and/or losses of C2 units (C2Ls). In particular, the C2L realized by the removal of a 5:6 C-C bond from the cage generates a cage heptagon, thus resulting in the formation of a non-classical cage. We show several examples of chlorination-promoted one-, two-, and multi-step cage transformations in different higher fullerenes.
(Invited) Paramagnetic Endohedral Fullerenes for Biomedical Applications
Authors: Cornes Stuart , Zhou Shen , Barendt Timothy , Zheng Xiaoyu , Eaton Sandra , Eaton Gareth , Davis Jason , Beer Paul , Porfyrakis Kyriakos
Published: February 2020

N@C60 is a paramagnetic endohedral fullerene species comprised of a single nitrogen atom incarcerated within a C60 carbon cage. Shielding of the nitrogen from the external environment results in extremely long relaxation times of its electron spin (T1 = 0.375 ms, T2 = 0.25 ms). This provides the molecule with a very sharp EPR signal,1 which undergoes observable dipolar broadening in the presence of other paramagnetic species, suggesting that N@C60 derivatives would be ideal candidates as spin probes for biological applications.2–4 In order for this to be realised functionalisation of the inherently hydrophobic fullerene cage must be undertaken to render it compatible with aqueous environments.

Several methodologies for the solubilisation of empty cage and other endohedral fullerene species have been demonstrated,5–7 however many of these are unsuitable for use with N@C60 due to its instability at elevated temperatures.8 Herein we report the first examples of water-soluble derivatives of N@C60, prepared using an adaptation of the widely used Bingel reaction.9 Preliminary investigations towards the use of these materials as electron paramagnetic resonance imaging (EPRI) agents is also discussed.10

1 J. J. L. Morton, A. M. Tyryshkin, A. Ardavan, K. Porfyrakis, S. A. Lyon and G. Andrew D. Briggs, J. Chem. Phys., 2006, 124, 014508.

2 K.-P. Dinse, H. Käß, C. Knapp and N. Weiden, Carbon, 2000, 38, 1635–1640.

3 G. Liu, A. N. Khlobystov, G. Charalambidis, A. G. Coutsolelos, G. A. D. Briggs and K. Porfyrakis, J. Am. Chem. Soc., 2012, 134, 1938–1941.

4 S. Zhou, M. Yamamoto, G. A. D. Briggs, H. Imahori and K. Porfyrakis, J. Am. Chem. Soc., 2016, 138, 1313–1319.

5 J. Li, A. Takeuchi, M. Ozawa, X. Li, K. Saigo and K. Kitazawa, J. Chem. Soc. Chem. Commun., 1993, 0, 1784–1785.

6 M. Brettreich and A. Hirsch, Tetrahedron Lett., 1998, 39, 2731–2734.

7 I. Rašović, Mater. Sci. Technol., 2016, 0, 1–18.

8 A. Iwasiewicz-Wabnig, K. Porfyrakis, G. A. D. Briggs and B. Sundqvist, Phys. Status Solidi B, 2009, 246, 2767–2770.

9 S. Zhou, I. Rašović, G. A. D. Briggs and K. Porfyrakis, Chem. Commun., 2015, 51, 7096–7099.

10 S. P. Cornes, S. Zhou and K. Porfyrakis, Chem. Commun., 2017, DOI:10.1039/C7CC07106J.

Figure 1
Highly Selective Silicon Dry Chemical Etch Technique for Advanced FinFET Technology
Authors: Bi Zhenxing , Loubet Nicolas J , Greene Andrew , Yeung Chunwing , Zhang Jingyun , Devarajan Thamarai , Sankarapandian Muthumanickam , Zhou Huimei , Wang Miaomiao , Conti Richard , Saulnier Nicole , Stolfi Michael , Bhatnagar Ajay , Cogorno Matt , Zhang Jingchun
Published: February 2020

With transistor scaling in 7nm technology and beyond, sacrificial silicon materials etches (e.g. dummy poly silicon gate removal) are considered to be among the most challenging hurdle in FinFET process development. In this paper, we present a dry chemical etch technique for selective etching of single crystal, poly-crystal and amorphous silicon on various FinFET device process steps. It was demonstrated that this technique could completely remove poly silicon in vertically high aspect ratio (AR>5) FinFET gates with a large process window (over-etch budget ~200%) while achieving the lowest gate leakage current and best short channel FET yield. Proper surface preparation, queue time control and etch by-product removal strategies are discussed. The residue free etch and etch by-product sublimation mechanisms are also investigated by High Resolution Electron Microscopy (HREM) and Fourier Transform Infrared Spectroscopy (FTIR) surface analysis.

This work was performed by the IBM Research at various IBM Research and Development Facilities.
Simulations of Correlative Defect Forming in Hafnia
Authors: Pil'nik Andrey A. , Chernov Andrey A. , Perevalov Timofey V. , Islamov Damir R.
Published: February 2020

High-κ hafnium oxide is widely used in different electronic devices. The electronic properties of HfO2 (e.g. leakage currents, optics) are defined by defects and traps, namely by oxygen vacancies (VO). Generation of new defects leads to breakdown, increasing the leakage, that leads to the FET and FRAM degradation. On the other hand, active layers in RRAM devices use traps as precursors for HRS/LRS switch. The aim of the work is predicting the defect forming in dielectrics in strong electric fields using analytical, numerical and ab initio simulations. Despite the advances in computational performance, the ab initio simulations still require large time and efforts. Analytical and half-analytical solutions of the problem can be helpful in a way of predicting conditions for defect formation.

The rate of new defect generation in the hafnium oxide with only one VO was calculated using the heat transfer equation with a strong positive loopback. The analytical and half-analytical solutions were found and compared with numerical ones. The most probable positions of new defect at specific electric field were found. These results were compared with ab initio (DFT) calculations of oxygen polyvacancy structure in monoclinic HfO2. It was found that the most favorable spatial configuration of an oxygen polyvacancy is a chain, where the next vacancy is formed near the already existing one, and no more than 2 removed O atoms are related to a Hf atom. Found distances between neighboring VO are (4.05-4.21) Å.

The work was supported by the Russian Science Foundation, grant #16-19-00002.
(Invited) Surface Free Energy and Interfacial Strain in HfO2 and Hzo Ferroelectric Formation
Authors: Chagarov Evgueni , Kavrik Mahmut , Katz Michael , Stanford Norman , Davydov Albert , Lee Min-Hung , Kummel Andrew C
Published: February 2020

The mechanism of stability of the phases of HfO2, ZrO2, and HZO (HfxZr1-xO2) were systematically investigated with density functional theory molecular dynamics (DFT-MD) to determine the mechanism for HZO having a much larger process window for formation the ferroelectric phase as compared to doped HfO2 or ZrO2. For the bulk states, the monoclinic phase (“m”) is about 80 mV per formula unit more stable than either the orthorhombic ferroelectric (“f”) phase or tetragonal (t-phase) for all three oxides. The surface free energies of the (001), (110), and (111) surfaces of all three oxides were calculated using an identical DFT technique. For all three oxides, the (111) face has the lowest surface free energies consistent with experimental data on columnar HZO grains showing [111] is the preferred growth direction. However, the surface free energy for all direction are nearly degenerate between HfO2, ZrO2, and HZO; therefore, even for nanocrystal formation the surface free energy does not favor f-phase formation. The effect of stress/strain was calculated by determining the free energy of formation as a function of the volume of the unit cell. When the oxides are grown in the low density amorphous phase but a post deposition anneal is perform for crystallization. The crystalline forms are more dense than the amorphous forms and the DFT calculation show that a higher surface area per unit cells will greatly favor f-phase formation. However, the effect is nearly identical for HfO2, ZrO2, and HZO; this is consistent with experiments showing the molar volumes of HfO2 and ZrO2 being within 2%. Instead, formation of nanocrystalites is hypothesized to be the source of the enhanced processing window for HZO. Experimental data is consistent with partial phase separation in HZO. Atom probe tomography imaging of the chemical composition of TiN/5 nm HZO/Si(001) ferroelectric films show an asymmetric distribution of the Hf and Zr within the HZO layer with the Zr being concentrated near the TiN/HZO interface; this is consistent with ZrO2 having a 100C lower crystallization temperature than HfO2 and therefore initiate the crystallization starting on the TiN(111) surface. It is hypothesized that the nanocrystals which template on TiN(111) can produce the interfacial stress/strain needed to stabilize f-phase formation; high resolution TEM shows regions of epitaxial alignment between HZO and TiN consistent with this mechanism. In addition atom probe tomography (APT) was performed on TiN/HZO/Si structures to determine the film composition of the interfaces for indication of possible phase separation of HZO since phase separation could promote nanocrystal formation.

Funding by LAM Research is gratefully acknowledged.
Eco-Friendly All-Inorganic Perovskite Memristors and Artificial Synapses
Authors: Kim Sun Gil , Jang Ho Won
Published: February 2020

Artificial Synapse has been an emerging research field as emulating the functions of biological synapse. It is regarded as a basic building block for neuromorphic computing. Organic lead-based perovskites including CH3NH3PbI3 and CH3NH3PbBr3 have been researched as materials for synaptic devices based on Resistive Random Access Memory(RRAM). They have shown gradual increase and decrease of conductivity that represent the synaptic plasticity such as STP (Short Term Potentiation), LTP (Long Term Potentiation), and LTD (Long Term Depression) which imitate learning and forgetting in human brain. However, there have been some environmental concerns about using lead-based materials in large-scale applications because of the possibility of lead contamination. Also, it is still required to increase perovskites’ air-stability. All-inorganic halide perovskites are considered as promising alternatives for RRAM and synaptic devices because of their remarkable stability. Therefore, this study focused on fully inorganic CsPb(1-x)BixI3 perovskite to achieve lower lead content and better stability. Optimized bismuth content was discovered according to their morphology, grain size, and synaptic performances. CsPb(1-x)BixI3 emulates synapse by showing similar functions such as STP and LTP by different current change rate depending on the intensities and frequencies of pulses. Also, STD and LTD can be obtained by applying opposite pulses. Therefore, based on these synaptic functions that optimized CsPb(1-x)BixI3 achieves, it can be applied as a single synapse with low energy consumption for neuromorphic computing which works by parallel operation to connect and store information.
(Invited) Voltage-Controlled Magnetic Memory: Recent Progress and Opportunities
Authors: Khalili Pedram
Published: February 2020

We review the recent progress and perspectives of voltage-controlled spintronic memory devices with ultralow dynamic energy dissipation, for applications in high-performance computing. We first discuss progress in the development of magnetic tunnel junctions using voltage-controlled magnetic anisotropy (VCMA) for switching, which exhibit the lowest power consumption MRAM cells to date (single-digit fJ/bit with precessional switching times < 1 ns). The current device and materials-level challenges and opportunities are discussed next, including biasing, VCMA coefficients, reduced read disturbance, and write error rates. We then evaluate array-level performance of this memory considering different use models within the memory hierarchy and different workloads. Recent results, device proposals and material requirements are then discussed for further reduction of write time, error rates, energy, and bit cell size.
(Invited) Self-Terminated Electrodeposition Reactions
Authors: Moffat Thomas P. , Liu Yihua , Ahn Sang Hyun , Ritzert Nicole L. , Wang Rongyue , Gillette Eleanor , Gokcen Dincer , Tan Haiyan , Hangarter Carlos , Bendersky Leonid , Bertocci Ugo , You Hoydoo
Published: February 2020

Recently, an inexpensive “wet form” of ALD based on self-terminated electrodeposition reactions was uncovered that enables controlled formation of ultrathin films of Pt, Ir and iron group metals and alloys thereof. Common to all these systems is the role of reaction intermediates, namely adsorbed H or OH-, in the quenching of metal deposition reactions. Further details on the mechanisms of self-terminated deposition reactions will be discussed. Likewise, the utility and relevance of the process to the synthesis of nanoparticles and thin films, and the study of bimetallic electrocatalysts will be detailed.
In Situ stress Measurements during Strained-Layer Electrodeposition
Authors: Stafford Gery R. , Ambrozik Stephen , Bertocci Ugo , Liu Yihua , Lafouresse Manon C. , Moffat Thomas P.
Published: February 2020

Enhanced catalytic activity has been demonstrated in elastically strained thin films, pseudomorphically grown on substrates with an appropriate lattice mismatch. The enhancement in catalytic activity is typically attributed to both electronic interactions and the epitaxial mismatch strain in the overlayer. The magnitude of the strain is often estimated from lattice-constant measurements using x-ray diffraction. An additional probe gaining popularity in electrochemistry involves the measurement of surface and growth stress using cantilever curvature. Cantilever curvature offers a nice complement to the direct strain measurementand can provide an in situ measurement while the strained layer is being formed. This talk will focus on the biaxial growth stress that develops during the self-terminated electrodeposition of ultrathin Pt films onto a variety of cantilever substrates that introduce different levels of misfit strain into the Pt. The cantilever was a borosilicate glass strip measuring 60 mm × 3 mm × 0.108 mm and was metallized on one side by electron beam evaporation, resulting in substrates with strong (111) crystallographic orientation. The electrolyte was 0.5 mol/L NaCl containing 3 mmol/L K2PtCl4. Deposition consisted of stepping the potential from the open circuit potential (~ -0.1V vs SSE) down to -1.2V for 10s and then back to -0.1V for another 30s, following the procedure established by Liu et al.1Figure 1 shows the stress response for Au, Pt and Ir substrates. Pt grown on Au exhibits considerable tensile stress, which is consistent with the +3.9% lattice mismatch between Au and Pt. In contrast, Pt deposition onto a Pt cantilever deposits homoepitaxially as an unstrained continuation of the substrate. The slight increase in stress with continued deposition is likely microstructural. Pt grown on Ir, with its -2.1% lattice misfit, initially exhibits compressive stress, before leveling off and turning tensile, similar to the growth of Pt on Pt. Although it is tempting to focus on lattice misfit as the primary source of stress, one must consider other contributions, such as step line tension associated with the growth of small islands, possible intermixing, and surface roughness.

References

Y. Liu, D. Gokcen, U. Bertocci and T. P. Moffat, Science 338, 1327 (2012).

Figure 1
Electrodeposition of Mo/Zn/Cu/Sn Unconventional Stack for CZTS Thin Films Synthesis
Authors: Panzeri Gabriele , Dell'Oro Ruben , Müller Dominic , Magagnin Luca
Published: February 2020

The interest towards Cu2ZnSnS4 (CZTS) photoactive material relies into the abundancy and non-toxicity of the elements considered [1, 2]. Among the fabrication routes investigated in literature, the single layer approach, consisting in the electrodeposition of Cu, Sn, Zn layers followed by reactive annealing, is the most promising showing higher efficiency devices than coelectrodeposition-based ones. The typical stack order is Mo/Cu/Sn/Zn, where the electrodeposition of the most noble metal is followed by intermediate and subsequently by the least noble one [2, 3]. This layer sequence is strongly connected to water-based electrolytes where pH dependence limits the possible stack combinations. However, it was reported that the ideal layer stacking, fabricated by means of sputtering, would consider to have Zn as first layer to avoid its loss during the annealing treatments (high vapor pressure) and to promote a good interface with Mo [4]. In the present work, a traditional electrodeposition-annealing route of an unconventional stack order (Mo/Zn/Cu/Sn) is proposed by employing an organic solution based on ethylene glycol for the copper electrodeposition while an aqueous one for zinc and tin depositions. The electrochemical behaviour of the copper solution was investigated by means of cyclic voltammetry (CV) and linear sweep voltammetry. Galvanostatic approach was investigated, employing of Hull cell as preliminary test. Soft and reactive (sulfur atmosphere) annealing were performed; the formation of kesterite were verified by means of Raman spectroscopy. CZTS thin films were characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD); photoelectrochemical characterization was performed to evaluate the photoactivity.

References

[1] Kumar, Mukesh, et al. "Strategic review of secondary phases, defects and defect-complexes in kesterite CZTS–Se solar cells." Energy & Environmental Science 8.11 (2015): 3134-3159.

[2] Colombara, Diego, et al. "Electrodeposition of kesterite thin films for photovoltaic applications: Quo vadis?." physica status solidi (a) 212.1 (2015): 88-102.

[3] Ahmed, Shafaat, et al. "A high efficiency electrodeposited Cu2ZnSnS4 solar cell." Advanced Energy Materials 2.2 (2012): 253-259.

[4] Araki, Hideaki, et al. "Preparation of Cu2ZnSnS4 thin films by sulfurization of stacked metallic layers." Thin Solid Films 517.4 (2008): 1457-1460.
A Mathematical Model and Experimental Examination of the Electrodeposition of Nanocatalysts on Various Substrates for Energy Conversion and Storage Applications
Authors: Karimi Shahram
Published: February 2020

Pulsed electrodeposition of nanocatalysts from aqueous electrolyte solutions has received considerable attention on account of its ease of use, relative low cost, reproducibility, and access to several process parameters, compared with other widely used techniques. It is, therefore, desirable to determine the influence of different operating parameters to optimize the electrodeposition process. A detailed mathematical model, which includes the effects of ionic migration, was developed to accurately predict the influence of various electrodeposition parameters on the resulting electrodeposited layers in terms of size, distribution and catalytic activity. Most of the available models for pulsed electrodeposition are restricted to conventional square pulses and ignore contributions from the growth current during nucleation. The model presented here is based on progressive nucleation and takes into account contributions from both nucleation and growth currents. Furthermore, the model considers all contributing factors towards growth current, including diffusion, ohmic and charge transfer phenomena. Lastly, unlike many models that are restricted to a constant diffusion coefficient for a given species, the presented model is based on a system with varying diffusion coefficients for all active species in the electrolyte.

Nanocatalysts, including platinum, nickel, copper, and cobalt, were electrodeposited on different substrates employing a pulsed current electrodeposition (PCE) technique. Pulses with low duty cycle, high peak deposition current densities, and delivered in milli- and nano-second range utilizing square, triangular, and ramp-down waveforms were used. The presence of nanocatalysts, ranging from 2-50 nm in diameter, was confirmed by SEM and XRD. Additional electrochemical characterization techniques were also employed. According to the model, at high peak deposition current densities and low duty cycles, ramp-down waveform yields the highest nucleation rate, confirming the experimental findings in which nanoparticles generated with the above waveform produces the smallest average grain size, ranging from 2 to 10 nanometer in diameter for platinum nanocatalysts on carbon cloths and 5 to 50 nm in diameter for nickel and copper nanoparticles deposited on titania nanotubes.
(Invited) Electrochemical Design of Materials for Energy Applications
Authors: Innocenti Massimo , Passaponti Maurizio , Salvietti Emanuele , Giaccherini Andrea , Giurlani Walter , De Luca Antonio , Di Benedetto Francesco
Published: February 2020

The global environmental concerns and the escalating demand for energy, coupled with a steady progress in renewable energy technologies, are opening up new opportunities for the utilization of renewable energy resources. Electrodeposition is well known for depositing metals and metallic alloys at the industrial level, with a wide range of applications from large area surface treatments to most advanced electronic industries. Electrodeposition of semiconducting materials represents a new challenge, not only from the academic point of view, but also from the economic point of view, since this method presents interesting characteristics for large area, low cost and generally low temperature and soft processing of materials. In this presentation, we exploited alternated electrodeposition of some metals by E-ALD (Electrochemical Atomic Layer Deposition) to obtain thin films, controlling the growth of the structures at the nanometric level. In this presentation we will report the results for the electrodeposition of an entire p-n junction of semiconductors deposited by E-ALD technique. In this communication we present a structural study of these composite ultra-thin films by means of electrochemical operando SXRD experiment performed at ID03 in Grenoble. We also present the results of modified surfaces obtained by electrodeposition or new catalysts obtained from microwave assisted pyrolysis (MAP) of waste tires for direct alcohol fuel cells. A fundamental aim of material sciences is to reckon the relationship between the properties of a device, and the morphological and structural characteristics of the surface. Combining basic electrochemical techniques with spectroscopic, microscopic and structural techniques is crucial for characterizing the structure-activity relationship for many different Materials for Energy Applications.
Fabrication and Characteristics of Ni Doped Titania Nanotubes By Electrochemical Anodization
Authors: Tirano Joaquin , Zea Hugo , Bredol Michael
Published: February 2020

The semiconductor properties of titanium dioxide (TiO2) offer an interesting alternative to convert sunlight into electrical energy by water splitting. This is because of its band gap, a high photogenerated charges mobility and the possibility to be doped both n-type and p-type. However, it has been found that charge recombination and low visible radiation sensitivity are the bottlenecks in the efficient solar energy conversion. Although in the last decade important advances in the synthesis of nanostructured morphologies with high interaction area like nanotubes have been achieved, the conversion efficiency growth has decreased. This is a logical result because there are intrinsic limitations imposed by the electronic properties of TiO2.

One of the alternatives to modifying the TiO2’s band gap and improving its photoactivity under visible light irradiation is to dope the nanotubes with transition metals. This option requires fabricating efficient nanostructured photoelectrodes with controlled morphology and specific properties able to offer a suitable surface area for metallic doping. Also, transition-metal oxides and hydroxides are frequently applied as low-cost water-splitting catalysts because they reduce the needed activation energy to overcome the kinetic barrier and increase the electrochemical reaction rate. There are thus important challenges and opportunities from the material science point of view that require a substantial effort for developing new knowledge and advancing in the controlled synthesis of this type of nanostructures. This research focuses on the synthesis and characterization of Ni doped titanium dioxide nanotubes (TNTs) for improving its photocatalytic activity in solar energy conversion applications. Initially, TNTs with controlled morphology were synthesized by two-step potentiostatic anodization of titanium foil. The anodization was carried out at room temperature in an electrolyte composed of ammonium fluoride, deionized water and ethylene glycol. Consequent thermal annealing of as-prepared TNTs was conducted in the air between 450 °C - 550 °C. Afterwards, the nanotubes were superficially modified by nickel deposition.

Studies of the morphology and crystalline phase of the samples, before and after nickel deposition, were carried out by SEM, EDS and XRD analysis. Determining the photoelectrochemical performance of photoelectrodes is based on typical electrochemical characterization techniques (OCP, EIS, LSV). Also, the morphological characterization associated electrochemical behavior analysis were discussed to establish the effect of nickel nanoparticles modification on the TNTs. The methodology proposed in this research allows using other transition metal for nanotube surface modification and studying new routes for improving the performance of low cost water-splitting catalysts.
Effect of Additives on the Process of Cobalt-Based Alloys Electrodeposition from Citrate Bath
Authors: Kwiecińska Anna , Plucik Monika , Kolczyk Karolina , Kutyla Dawid , Żabiński Piotr , Kowalik Remigiusz
Published: February 2020

The electrochemical deposition of cobalt binary alloys with transition metals has received recently much attention due to some characteristic properties and possible practical applications of the coatings. These alloys, besides high electrocatalytical properties, exhibit useful properties such as high corrosion resistance and premium hardness. Additionally, these alloys are also seen as environmentally safe substitutes for hard chromium plating and a new materials for microelectronic and microelectromechanical systems and ultralarge-scale integrated systems.

The present work aims to deposit of active cobalt alloys as catalytic coatings for hydrogen evolution. Electrodeposition mechanism and kinetics of cobalt-based alloys deposition was studied by the electrochemical methods. Chronoamperometry and cyclic voltammetry techniques were combined with electrochemical quartz crystal microbalance to analyze this process in details. The proper adjustment of the process of electrolysis has a crucial role on the composition, and therefore structure and morphology of the deposited coatings, which decide about their electrocatalytic properties. In the present investigations, the composition of the citrate electrolyte with different additives, potential and current density were changed systematically in ranges within which they significantly effect on the composition and structure of the resulting cobalt alloys. The morphology, structure and the composition of the deposited alloys was identified by SEM, XRD, XRF and EDS techniques. Also we try to clarify the effect of the additives in enhancing the high activity for hydrogen evolution. The electroactivity of the coatings were analyzed by different electrochemical techniques.

This work was supported by the Polish National Center of Science under grants 2016/21/B/ST8/00431 and the research was carried out in the frames of COST Action MP1407 (e-MINDS).
(Electrodeposition Division Research Award) Old Stagnant Technology Becoming Hot Technology:Electroplating Advanced Functional Materials
Authors: Myung Nosang Vincent
Published: February 2020

The ever-increasing demands for faster, smaller and less expensive systems have resulted in the development of a novel, cost-effective processes. Electrochemical processes including electrodeposition, and anodizing meet the needs of emerging technology. It is one of the easiest and most versatile solution-based synthesis techniques that can be used in a cost-effective and scalable manner. It typically operated near ambient conditions and able to synthesize various materials including metals, metal oxides, conductive polymers and semiconductors. Precise control over the dimensions, composition, morphology, and degree of crystallinity can be achieved by varying electrodeposition parameters, such as the applied potential, electrolyte concentration, temperature, agitation, and additives. Additionally, the non-equilibrium reaction makes it possible to synthesize stoichiometric or non-stoichiometric materials easily without changing other aspects of the material properties. In this presentation, applications of electroplated materials including thermoelectrics, biological and chemical sensor arrays will be discussed.
Reversible Ag Electroplating Onto ITO Electrode for Smart Window
Authors: Aoki Atsushi , Ito Akira , Watanabe Shigeki
Published: February 2020

Reversible electrochromic mirror by electroplating and electrodissolution of Ag film has been investigated onto transparent ITO electrode. It’s applicable to smart window and thermal management for house and vehicle. In order to form mirror surface of Ag film, Pd nanoparticles were firstly deposited onto ITO electrode by chronopotentiometry at the constant current of -10 mA/cm2 for 0.5 s, resulting in the diameter of Pd nanoparticles of 63 nm and good dispersion from SEM observation and visible light transmittance of around 80 % from UV–vis absorption spectroscopy. Pd nanoparticles are electrochemically stable for electroplating and electrodissolution of Ag film and behave as catalyst for forming Ag film. Without Pd nanoparticles on ITO electrode, the deposited Ag film becomes white surface because of light scattering from less dispersive and quite large Ag semi sphere crystals on the ITO electrode. However, Ag mirror surface was not formed even on the Pd nanoparticle deposited ITO electrode. So, several additive regents were investigated to form Ag mirror surface. At first, as 2-hydroxypyridine (2-HP) is employed as additive, yellow color smooth Ag mirror surface was achieved at the electroplating condition of the constant current of -4 mA/cm2 for 100 s. The SEM observation indicates that Ag crystal grew up anisotropically to form planar crystal. On the other hand, eletrodissolution of Ag film at the constant current of +1 mA/cm2 for 400 s was imperfect to remain residue onto ITO electrode and the color of the Ag plating solution changed from transparent to brown due to the oxidation of 2-HP. Next, as citric acid was used as additive, smooth Ag mirror surface was created by the electroplating condition of the constant current of -4 mA/cm2 for 20 s. The SEM observation shows anisotropical Ag crystal growth as similar as that in the 2-HP additive. The time taking to form Ag mirror state becomes shorter than that in the 2-HP additive because the anisotropy ratio of citric acid would be larger than that of 2-HP. The electrodissolution of Ag film at the constant current of +4mA/cm2 for 20 s shows that it’s almost back to the transparent ITO electrode at the transmittance of ca. 70 %. Repeating property has been tried to be several times so far. We will determine the repeating limit in this system.
Cobalt Electrodeposition at Different Substrates from a Deep Eutectic Solvent
Authors: Landa-Castro Midori , Gómez Valentín Elvira , Montes de Oca-Yemha María Guadalupe
Published: February 2020

The global demand for materials that are possessing high yields in the energy conversion, storage and use, has led to new research. These materials with a high surface-volume ratio allow an increase in the contact area between the electrode and electrolyte. Nanometric materials, such as nanoparticles, nanowires, nanorods, and nanosheets, generally have a greater reversible capacity and long-term useful life. Developing alternative materials, where their structure, porosity and morphology are mainly adapted. The Co (II) evaluation process was carried out onto three different substrates: glassy carbon, Au/Ti/Si and platinum. The Co deposits were obtained from a Deep Eutectic Solvent (1ChCl: 2Urea), and characterized by Scanning Electron Microscopy (SEM). The SEM images show that the Co morphology at glassy carbon is similar to the desert roses (Figure 1), and a reticular structure for metallic substrates. X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) confirm that the deposits obtained correspond to the metallic cobalt. The potentiostatic experiments at low overpotentials show 3D nucleation and growth process on the glassy carbon substrate [1].

[1] L. Manh y M. Palomar Pardave, On Wetting Angles and Nucleation Energies during the Electrochemical Nucleation of Cobalt onto GC from a DES, Journal of The Electrochemical Society, 164, 12, pp. D694-D699, 2017.

Figure 1
Electrodeposition of Indium from a Phosphonium-Based Ionic Liquid
Authors: Fransaer Jan , Binnemans Koen , Deferm Clio , Oosterhof Harald , Luyten Jan
Published: February 2020

Electrochemical deposition of indium metal from aqueous electrolytes is challenging as it occurs simultaneously with hydrogen evolution. The evolution of hydrogen can compromise cathodic current efficiency and can cause porosity of the deposited metal, but it can be avoided by using ionic liquid electrolytes. The high thermal stability of ionic liquids allows for high-temperature electrodeposition on a liquid cathode, offering several advantages over a solid electrode, such as easier separation of electrolysis products and the possibility to design a continuous electrowinning process. In this paper, the electrochemical behavior of indium in the ionic liquid trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101) was studied at 120 °C and 180 °C. Indium metal was electrodeposited on platinum and molybdenum substrates and on a liquid indium cathode at 180 °C. Impurities present in commercial Cyphos IL 101 interfered with the measurement of the electrochemical window, so that it had to be carefully purified. The electrochemistry of indium in Cyphos IL 101 was studied by cyclic voltammetry, QMCB, rotating disk and rotating ring disk voltammetry. InCl3 concentration between 10 and 400 mM in Cyphos IL 101 were used in this study. Therefore, the major indium(III) species in solution corresponds to the [InCl6]3– complex. Using the Levich equation, a diffusion coefficient of (7.5 ± 0.1) 10–12 m2 s–1 at 120 °C was calculated for [InCl6]3–. It was found that indium(III) is the most stable oxidation state in the ionic liquid. This ion is reduced via a two-step process, going from indium(III) to indium(I) and subsequently to indium(0). The disproportionation of indium(I) to indium(III) and indium(0) was clearly illustrated. During cyclic voltammograms, the anodic and cathodic peak potentials was found to depend on the scan rate. As the scan rate increases, the separation between the anodic and cathodic peaks becomes greater, indicating that the deposition of indium is irreversible or quasi-reversible. The indium electrodeposits were characterized by SEM-EDS. When depositing indium on molybdenum substrates, the deposition of spherical indium droplets was observed, even at temperatures substantially below the melting point of indium (see figure). The probable mechanism behind this deposition morphology will be explained.

Figure 1
Initial Zinc Electrodeposition on Copper Studied By in-Situ AFM
Authors: Neupane Shova , Oezaslan Mehtap , Renner Frank Uwe
Published: February 2020

Zinc deposition on copper surfaces is being studied before, mostly as a model system to understand film formation but more recently also in the context of catalysis or Zn batteries [1]. Electrochemical deposition of zinc on copper enables to obtain different ratios of Cu and Zn in the deposit alloy layers [2]. Zn electrodeposition on Cu surfaces can be monitored by in-situ Atomic Force Microscopy (AFM) and allows to follow the initial growth of Zn on different copper surfaces [3,4]. In this work, we pretreated different textured polycrystalline Cu surfaces by chemical etching and electropolishing to modify and improve the surface quality. Surfaces are then pre-characterized by AFM, Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD). The local surface morphology is changed after the different surface pretreatments. In-situ AFM measurements of Zn electrodeposition were performed on as-received as well as pretreated Cu surfaces and monitored the initiation of Zn deposition in real time (Figure 1). Deposition of Zn on Cu surfaces critically depends on the Cu surface morphology and specific surface orientations. For applications, the surface morphology of the Zn deposition may play a critical role in controlling the performance of the films.

References:

[1] T. Otani et al Electrochem. Acta 242 (2017) 364-372

[2] F.Jia et al, J. Phys. Chem. 111 (2007) 8424-8431

[3] L. N. Poloni et al Chem.Matter . 29 (2017) 331−345

[4] S. Xu et al, J. Phys. Chem. 121 (2017) 3938−3946

Figure 1
(Invited) Patterned Printing of Ceramics By Electrodeposition, and Applications in Micro-Robotics
Authors: Ngan Alfonso H.W. , Wang Pingyu , Kwan Kenneth K.W.
Published: February 2020

Developing cost-effective capabilities to fabricate materials into desired shapes and sizes has always been a prime focus of materials research. Selective-laser sintering, which is based on sintering of tiny particles, is currently limited to polymers and metals, and is generally not directly applicable to ceramic powders because of their high melting temperatures. Electrodeposition has the advantages of low costs, availability at room temperature and easy scalability. In this paper, an efficient technique for writing 2D oxide patterns on conductive substrates is demonstrated. In this method, a minimum quantity of liquid electrolyte is delivered through an extrusion nozzle and manipulated into the desired shape on the substrate, meanwhile being electrodeposited into the product by an applied voltage across the nozzle and substrate. Using this method, patterns of primarily Cu2O were successfully fabricated on stainless steel substrates. This is intriguing because, according to the Pourbaix diagram, the equilibrium deposited product at the low voltage used should be metallic Cu. A key factor that allows the product to be primarily oxide Cu2O is the non-equilibrium condition involved in the process due to the short deposition time; hence the nature of the product is shown to be tunable by printing conditions. A second material printed using this method was nickel hydroxide/oxyhydroxide which exhibits an interesting electrochemical actuation effect in alkaline media. Applications in printing micro-robots involving this material will also be discussed.
3D Printing of Nanotwinned Metals
Authors: Minary Majid
Published: February 2020

Microstructure of a metal determines its properties. A major effort in the field of additive manufacturing (AM) of metals is

controlling and predicting the microstructure. Nanotwinned (nt)-metals exhibit superior mechanical and electrical properties compared to their coarse-grained and nano-grained counterparts. nt-metals have a unique microstructure with grains that contain a high density of layered nanoscale twins divided by coherent twin boundaries (TBs). These metals often show higher strength and ductility compared to their nanocrystalline counterpart, since TBs can effectively block dislocation motion. These metals show more resistance to electromigration, which is a common problem for metals at the nano/ microscale. nt-metals in film and bulk forms are obtained using physical and chemical processes including pulsed electrodeposition (PED), plastic deformation, recrystallization, phase transformation, and sputter deposition. However, currently, there is no process for 3D printing (AM) of nt-metals. Given their unique properties, it is desirable to establish an AM process for nt-metals. We developed a new process for 3D printing of nt-metals, termed localized PED (L-PED). We demonstrate microscale 3D printing of nt-Cu with high density of coherent TBs using this process. This cost-effective process, which is performed at ambient environment, enables direct printing of 3D microscale structures of pure metals with nanoscale twins. The 3D printed nt-Cu is fully dense, with low to none impurities, and low microstructural defects, and without obvious interface between printed layers, which overall result in good mechanical and electrical properties, without any postprocessing steps.
Coupling Additive Manufacturing and Wet Metallization for Advanced Microfabrication
Authors: Bernasconi Roberto , Magagnin Luca
Published: February 2020

Nano and microfabrication are general terms to indicate a broad selection of techniques suitable to produce functional structures at the nano or microscale. This ability is at the base of many advanced applications in the main fields of engineering. However, many techniques typically used in microfabrication, like lithography or thin film deposition, are characterized by a limited tridimensionality of the final product. These manufacturing methods are commonly said to operate in 2.5 dimensions, due to the limited envelope achievable in the vertical direction.

To overcome said limitations, 3D printing techniques able to work at the microscale have been introduced in the last few years. The application of such techniques, based on direct writing of the different layers that compose the object by mean of a laser beam, to microfabrication gave origin to a new concept of production: additive microfabrication [1]. The main disadvantage of methodologies like stereolithography (SLA) or two photons lithography (2PL) is the material used for printing: a mixture of photocurable polymers. The need to use resins implies significant limitations on the final properties of the object: relatively low mechanical properties and total or partial lack of conductivity. A possible approach to impart metallic properties to SLA or 2PL printed parts is the deposition of metal thin films on the surface of the 3D printed part.

In the present work, a possible hybrid production route that combines SLA and wet metallization is described in general and applied to real microfabrication. Electroless deposition on SLA resins has already been attempted in the past [2], as well as deposition of multilayers. Starting from these propaedeutic work, the hybrid SLA/wet metallization approach is here applied to the micromanufacturing of two prototypical devices belonging to two distinct classes: MEMS and magnetically steerable microdevices. These two selected applications demonstrate the applicability of the manufacturing methodology but does not limit the range of possible uses, which span from bioengineering to microelectronics or to microfluidics.

[1] Misawa, Hiroaki, ed. (2006). 3D Laser Microfabrication: Principles and Applications, Germany: Wiley

[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)
Flexible Free-Standing and Binder-Free Porous Carbon Cloth (C-Felt) for Lithium-Ion Battery Anodes
Authors: Kalu Egwu Eric , Watson Venroy George , Yeboah Yaw D. , Weatherspoon Mark H.
Published: February 2020

Interest in the development of flexible free-standing electrodes for wearable batteries is on the rise 1-3. Carbon nanotube (CNT) and graphene films have severally been evaluated to serve as active materials for lithium-ion batteries (LIBs). However, CNTs and graphene nano-sized carbon materials are made into a sheet as free standing electrodes through vacuum filtration of a solution of the nano-sized particles. This is a limitation to the mechanical deformation strength of the dispersed particles and thus limits possible applications of the flexible CNT/graphene electrodes. In the present work, un-doped, untreated, flexible freestanding mesh-like carbon cloth (C-Felt) was examined as a potential anode to replace the commonly used powdered graphite composite anodes (GRA) in a full cell Li-ion battery. We compared the discharged capacity performances of LiFePO4/GRA versus LiFePO4/C-Felt full cells of different cathode to anode ratios. Our results show that C-Felt anode presents itself as a potential cost effective, ready to use, lightweight, free-standing and flexible anode material that can be used in a practical full cell.

References

Janicek, A., Gao, N., Fan, Y., Liu, H., 2015 “High Performance Activated Carbon/Carbon Cloth Cathodes for Microbial Fuel Cells,”, Fuel Cells, 15( 6), pp. 855–861.

Hu, L. B., Wu, H., Mantia F. L., Yang, Y., Cui, Y., 2010, “Thin, flexible secondary Li-ion paper batteries,” ACS Nano., 4, pp. 5843-5451.

Liu, B., Zhang, J., Wang, X., Chen, G., Chen, D., Zhou, C., Shen, G., 2012, “Hierarchical Three-Dimensional ZnCo2O4 Nanowire Arrays/Carbon Cloth Anodes for a Novel Class of High-Performance Flexible Lithium-Ion Batteries,” Nano Lett., 12, pp. 3005-3011