bluuebunny/crossref_metadata_2025 huggingface dataset:
Micro-Scale Study of Redox Flow Battery Using Pore Network Modelling
Authors: Shokriafra Mohammadjavad , J. Niasar Vahid
Published: May 2020

Producing energy from intermittent renewable energy sources has been extensively developed over the past decades. One of the goals at the grid scale is to provide sustainable energy output to the end-users. To this end, efforts must be done to store huge amount of energy in robust batteries to provide stable and flexible electricity to the costumers during peak hours. Redox flow batteries have been attracted attention to be one of the best candidates amongst electrochemical technologies. Many researchers have focused on these batteries to find the best electrolyte pairs, optimise the electrode structure and efficiently manufacture membrane which prohibits cross-flow while transfer charges.

Despite efforts has been made in RFB area, these batteries are not economical in large scales. The main problem is losses related to charge and mass transport in electrodes. Focusing on the modelling the electrode design, seems to be a reasonable solution mostly because of time consuming nature of experiments and difficulties arising in experimental procedures. As an example, electrode is only a few hundred microns thick and measuring concentration, electric field or pressure inside that is impossible. Many researchers have developed several control-oriented and continuum macroscopic models. However, those models have investigated macroscopic features, but are deficient in considering microscopic characteristics of electrodes like pore structure.

Alternatively, pore-scale studies pave the way to investigate several processes in the electrodes. The complex porous electrode transformed to a network of connected pores and throats, and transport processes are directly applied for that network. This method can take into account electrolyte flow, electrochemical reactions, charge transport and ion transport, those are simultaneously occurring in RFB. Several paper works show the result of using pore network modelling in RFB, but these works neglect complex concepts like interaction between channels and pores. Additionally, they are not able to manage large scale simulations and consume considerable time that is not costly effective. In this work, electrode pore network is reconstructed from X-ray computed tomography image of carbon cloth. This work focuses on hydrogen bromine RFBs that hydrogen gas is oxidised in the anode and the produced protons goes to the cathode to reduce bromine in the cathode as the following equation.

Stokes flow equation for electrolyte, convection, diffusion and reaction equations for bromine and electro-migration equation for electron are considered as governing equations in the pore network. All resulted equations are solved with C++ code and the results are going to be validated with experimental results.

Figure 1
(Invited) Self-Assembly Synthesis and Interfacial Control of Electrode Architectures
Authors: Dai Sheng
Published: May 2020

Enhancement in electrochemical energy storage resides in tailored nanotextures resulting from making electrode materials with controlled compositions and structures. The complex interplay of solvent and solute structure and dynamics at the charged interface, the transport of electrolyte ions into and out of the pores, the solvation/desolvation processes occurring in pores approaching bare-ion dimensions, and formation of interfaces via chemical reactions are all important parameters. Herein, several self-assembly synthesis methods for carbon and oxide composites as electrode materials for energy storage will be discussed. The objective of this talk is to demonstrate that nanostructured carbons and oxides derived from soft-template synthesis not only entail a high storage capacity but also, most importantly, can be made to have a significantly enhanced electronic conductivity and storage capacity. This enhanced transport property in these electrode architectures is the key to providing high rate capability for the corresponding energy storage systems.
Computational Modelling Studies of Structural Transition in Li1+XMn2O4 (0≤x≤1) Nanoparticles
Authors: Hlungwani Donald , Ledwaba Raesibe Sylvia , Ngoepe Phuti E
Published: May 2020

Lithium-ion batteries, comprising nanoparticulate Ni-Mn-Co (NMC) cathodes that have been used to power electric vehicles, can be improved by blending NMC with LiMn2O4 (LMO). However, LMO undergoes a cubic to tetragonal phase change during charge cycling, which cracks and pulverises the material resulting in capacity fading [1]. Structural characterisation during the phase transition is the first step in mitigating capacity fading and can be challenging experimentally and computationally. The simulated amorphisation and recrystallisation method, based on empirical interatomic potentials were utilised to generate Li-Mn-O composite nanoparticles, with approximately 3000 atoms, and are amnenable to linear scaling DFT methods. The techniques was previously successfully used to study nanostructures of MnO2 [2], with composite structures. A wealth of microstructural features such as heterostructures, point defects and grain boundaries were observed. The discharge process of the nanoparticle was simulated by lithiating the Li-Mn-O composite nanoparticle. The nanoparticle was characterized by radial distribution functions and simulated X-ray diffraction patterns (XRDs). Furthermore, the structural changes with lithiation were visualised and details of various defects, including grain boundaries could be observed from microstructures. The presence of layered and spinel components were also noted and validated by XRDs. Linear scaling density functional theory methods were used to determine voltage profiles of simulated structures.

References

1. Okumura T., Yamaguchi Y., Shikano M. and Kobayashi H., J. Mater. Chem. A, 2, 8017, (2014).

2. Sayle, T.X.T, Kgatwane K., Ngoepe P.E. and Sayle D.C., J. Mater. Chem. A
4, 6456 (2016).
(Invited) Optical Characterization of Nanomaterial By Means of Hyperspectral Global Imaging
Authors: Dion-Bertrand Laura-Isabelle , Martel Richard , Heller Daniel A.
Published: May 2020

Fluorescence and Raman spectroscopy are powerful techniques to probe the intrinsic properties of low dimensional materials such as carbon nanotubes and graphene. In this study, we present how a hyperspectral imaging platform based on Bragg gratings designed for global imaging can help improve the fabrication methods of various nanomaterials. Spectrally and spatially resolved maps were acquired on different samples over a million points. The intrinsic specificity of Raman scattering combined with the analysis performed by the global imaging modality makes it a useful method to assess large maps (hundreds of microns) of the spatial distribution of defects, number of layers and stacking order. On the other hand, hyperspectral photoluminescence provides straightforward information on photostability and allows multiplexing. This presentation will highlight how hyperspectral microscopy can be used to study carbon nanotubes based fluorophores, CVD graphene and MoS2.
Carbon Nanotube Metal Polymer Composites for Flexible Active Interconnects
Authors: Park Junsung , Liu Xueqing , Ytterdal Trond , Kim Jin Ho , Xu Jimmy , Shur Michael
Published: May 2020

We report on the fabrication of metal polymer carbon nanotube (MPCNT) composites for flexible active interconnects. Our experiments demonstrated that such CNTs-reinforced polymer-metal composites have several times higher tolerance to bending strains than the metal-polymer composites without the CNTs layer. Since CNT-polymer layer electrically separated from the metal layer until destructive breakdown, it is feasible to fabricate electronic components isolated from the metal layer in MPCNT composites. Thus, the MPCNT composites-based interconnects could be utilized as a platform for CNTs-based environment monitoring sensors and CNT Thin Film Transistors (TFTs) with applications in Internet of Things (IoT), autonomous vehicle systems, and wearable electronics. To estimate the electrical characteristics of the CNT-polymer based electronic devices, we developed the compact Unified Charge Control Models (UCCM) for single CNT field effect transistors (FETs) and CNT mat TFTs. The UCCM models were validated by comparison of the simulated results with different experimental data reported by other groups. The models could be widely used for device simulation and circuit design for developing flexible active interconnects and electronic components based on the single CNTs, CNT mats, and MPCNT composites.
Use of Superparamagnetic Nanoparticles to Remove Arsenite from Contaminated Water
Authors: Bandara Shashika Nadishani , Burriss Daniel , Atwood David A
Published: May 2020

The arsenite removal from the water was attributed using thiol (S-H) coupled magnetic nanoparticles (MNPs). The composite Fe3O4-SiO2-linker-AB9 (AB-MNP) was made using MNPs coated with the amine-functionalized silica surface, which is then coupled to AB9= 2,2’-(isophthaloybis(azanaediyl))bis-3-mercaptopropanoic acid; (a sulfhydryl compound with pendant carboxylate groups). Complete arsenic removal was achieved with As(III) solutions of 200, 500, and 1000 ppb resulting in detectable arsenic dropped to below 10 ppb. This single solid-composite immobilize As(III) by forming strong covalent As-S bonds producing “proposed” structure As(III)-AB9@MNP (Figure 1). The components of this new composite material are made from non-toxic, earth-abundant elements, and rapid magnetic separation allows them to be used as an effective, affordable means of providing arsenic-free drinking water to at-risk populations around the world.

Figure 1
Enhanced Corrosion Performance By Micro Arc Oxidation Coating with the Addition of 2-Aminobenzimidazole Loaded Halloysite Nanotubes on AZ31 Alloy
Authors: Wu Wen-Xin , Lee Howard , Lin Hsin-Chih
Published: May 2020

The application of Magnesium alloys has drawn great attention in recent years. As the lightest structure metal on earth, the usage of Mg is attractive to the automotive, aerospace and electronics industries owing to its high weight-to strength ratio. Unfortunately, the poor corrosion resistance impedes the development of Mg alloys. To date, several methods have been proposed to improve the anti-corrosion ability, such as conventional anodizing, sol-gel coating, and micro arc oxidation (MAO). MAO is an innovative technique for generating surface oxide coatings on valve metals and alloys, which exhibits strong adhesion to the substrate, high thickness, hardness, corrosion and wear resistance, and provides an environmentally-friendly alternative to acid-based anodizing treatment.

Despite all these advantages, the intrinsic structural imperfection of MAO coatings, including a loose structure featured by micro-pores and micro-cracks, facilitate quicker penetration of the corrosive ions into the base magnesium, and thus, increase the rate of corrosion. To overcome the problem of porous MAO film, composite coatings with self-healing ability that are capable to repair themselves when damage occurs have been utilized. In this study, the concept of self-healing is carried out by incorporating corrosion inhibitors, 2-aminobenzimidazole (2-ABI), loaded nanocontainers, halloysite nanotubes (HNT), to silicate-based electrolyte to obtain MAO coatings on AZ31 alloy in single step. The coatings are evaluated by SEM, EDX, and XRD. Corrosion performance is studied with EIS, PDP and salt spray test. The effects of various electrical parameters, including current density, frequency and working time, on the coating are also investigated. Experimental results indicate that the corrosion resistance of MAO films with the addition of 2-ABI loaded HNT is significantly improved, and thus confirms the feasibility of 2-ABI as corrosion inhibitor to Mg alloys.
Inhibition of Acid Corrosion of Mild Steel By Selected Quinoxalinyl-Pyrazolyl-Propanones: Electrochemical and Computational Studies
Authors: Olasunkanmi Lukman Olawale , Ebenso Eno E
Published: May 2020

Acid corrosion of mild steel was studied in the presence of two propanone derivatives of quinoxalin-6-yl-4,5-dihydro-1H-pyrazol-1-one, namely 1-[3-(3-methoxyphenyl)-5-(quinoxalin-6-yl)-4,5-dihydropyrazol-1-yl]propan-1-one (Mt-3-PQPP) and 1-(3-(4-chlorophenyl)-5-(quinoxalin-6-yl)-4,5-dihydro-1H-pyrazol-1-yl)propan-1-one (Cl-4-PQPP). The inhibitive potentials of the compounds were assessed by measuring the corrosion rate of mild steel in the electrolyte admixture using electrochemical techniques. Both compounds were found to repress steel corrosion in HCl. Tafel polarization experiments suggested that the compounds are mixed-type inhibitors as they reduce both the anodic and cathodic corrosion reactions. Electrochemical impedance spectroscopy (EIS) measurements revealed that Mt-3-PQPP and Cl-4-PQPP molecules adsorbed on mild steel surface to form pseudo-capacitive film. Surface coverage data was fitted into the Langmuir adsorption isotherm and the evaluated thermodynamic parameters suggested chemisorption for Mt-3-PQPP and competitive physisorption and chemisorption for Cl-4-PQPP. Scanning electron microscopy (SEM) analyses further revealed that adsorbed film of the inhibitor molecules protected the steel from direct exposure to acidic ions. Quantum chemical calculations suggested that higher corrosion inhibition efficiency of Mt-3-PQPP compared to Cl-4-PQPP molecule is due to the higher electron donating tendency of the former. Mt-3-PQPP molecule also showed higher protonation tendency in the acid than Cl-4-PQPP and its protonated form is more reactive than that of Cl-4-PQPP. Monte Carlo simulation of the adsorption of Mt-3-PQPP and Cl-4-PQPP molecules on Fe(110) surface also confirmed higher adsorption energy for the former.
Transient Potential Induced Dissolution of Metal Biporlar Plates Used in Proton Exchange Membrane Fuel Cell
Authors: Hong Yuan-Yuan , Wang Xian-Zong , Muneshwar Triratna , Cadien Ken , Luo Jing-Li
Published: May 2020

Corrosion of metallic bipolar plates (BPPs) under the aggressive working conditions is the major issue that impedes its application in proton exchange membrane fuel cells (PEMFCs). Transient potential is generated during the different operating conditions of PEMFCs such as start-up/shut-down(SU/SD), and dynamic loading stages. Transient potential-induced corrosion is a serious problem encountered by BPPs. To investigate the influence of transient potentials on corrosion of BPPs, potential pulses with different amplitudes are applied to specimens. Also, a novel zirconium oxynitride coating is prepared via atomic layer deposition to improve the stability of BPPs.

Results show that transient potentials generated at passive and transpassive potential regions are both detrimental to the stability of BPPs. For the uncoated samples, a larger potential fluctuation in the passive region could induce a much higher frequency of passive film breakdown than that generated by a smaller potential fluctuation during the cyclic pulse tests. In the transpassive region, upon increasing transient potentials, the passive film formed on surface enters the potential dependent dissolution region, leading to severe intergranular corrosion after a certain cycles of pulse tests.

The zirconium oxynitride coated samples present improved performance in both normal potentiostatic polarization and transient potential conditions. The enhanced corrosion resistance of coated samples is attributed to the continuous formation of protective oxide layer which has a wider band gap than passive films formed on uncoated samples. Therefore, the coated sample enters the transpassive potential region at a more positive potential and thus exhibits much lower dissolution rate. Moreover, the Mott-Schottky plots suggests that the defect density of the coated samples is much lower than the uncoated counterpart, and the deterioration of uncoated sample performance under different transient potentials is related to the passive film disorder degree.

From our study, transient potentials would accelerate the degradation of BPPs, and the development of bipolar plates coated with dense protective surface films could help mitigate the dissolution induced by the transient potentials, thus improving stability and durability of BPPs. Specially, a layer of coating with a wider band gap between Fermi level and valance band is beneficial to reduce the dissolution in the transpassive potential region.
A Phase-Field Model Study of Microstructural Effects on the Corrosion of Mg Alloys
Authors: Montiel David , DeWitt Stephen , Chadwick Alexander F. , Thornton Katsuyo
Published: May 2020

Understanding how alloy composition and thermal history determine the corrosion behavior is crucial to designing alloys with lower corrosion rates. We employ a model that combines the phase-field and smoothed boundary methods [1] to investigate the effect of second phases and particles on the corrosion behavior of Mg alloys. In this model, the dissolution rate at the metal/electrolyte interface is determined by the coupling of mass transport within the electrolyte and the Butler-Volmer electrochemical kinetics at the interface. The model is implemented in the PRISMS-PF framework [2,3], an open-source framework for phase-field modeling that employs a matrix-free finite element method. Simulations of corrosion are conducted with varying microstructure and compositions with associated corrosion parameters representative of Mg alloys. Specifically, we show how our approach can describe the experimentally observed microgalvanic effects due to the presence of impurities and second phases. Finally, we show the results of a parametric study of the dependence of the rate for various combination of the corrosion parameters for each phase.

This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering as part of the Center for PRedictive Integrated Structural Materials Science (PRISMS Center) at University of Michigan.

[1] A.F. Chadwick, J.A. Stewart, R.A. Enrique, S. Du, K. Thornton, Numerical Modeling of Localized Corrosion Using Phase-Field and Smoothed Boundary Methods, J. Electrochem. Soc. 165 (2018) C633–C646.

[2] S. DeWitt, S. Rudraraju, D. Montiel, W. B. Andrews, K. Thornton, PRISMS-PF: A General Framework for Phase-Field Modeling with a Matrix-Free Finite Element Method. Submitted to npj Comput. Mater.

[3] http://prisms-center.github.io/phaseField/
Synergism in Tribocorrosion: From Theoretical Approach to Lab Test Outcome on Hard Chromium Replacement
Authors: Georgiou Emmanuel , Celis Jean-Pierre
Published: May 2020

Tribocorrosion is defined as the study of chemical, electrochemical and mechanical factors on the material degradation in mechanical systems undergoing a relative displacement of the mechanical contacts. The combination of knowledge about corrosion processes and tribological processes does not provide yet sufficiently knowledge on the tribocorrosion mechanisms that can be used industrially. By using various electrochemical methods like open-circuit potential measurements, polarization curves, and EIS measurements, important information are nowadays obtained,on the kinetics of reactions taking place in sliding contacts, as well as on the depassivation/repassivation of protective surface films, and on the interactions between electrochemical reactions and friction.

In this presentation, at first a brief review of the existing modelling of the coupling of tribology and corrosion will be presented, as well as the development of a standard test for the determination of synergism under tribocorrosion.

Then the outcome of following R&D-work initiated as a result of the EU legislation to replace hard chromium, will be presented:

• establishing a methodology to evaluate tribological properties of Ni-P coatings under tribo-corrosive conditions,

• correlating structural characteristics of coatings (grain size, phase distribution, intermetallic formation, particle strengthening) with tribo-corrosive behaviour,

• comparing Ni-P coatings with benchmarks and hard chrome coatings under tribo-corrosive conditions.

In the discussion, a major focus will be given on the aspect of synergism linked to the galvanic coupling generated along sliding tracks immersed in electrolytes.
Controllable Corrosion and Electrochemical Nanoimprint
Authors: Zhan Dongping
Published: May 2020

When the contact potential field between the metal catalyst and semiconductor were exposure to the electrolyte environment, a primary corrosion cell would be formed. The corrosion processes are controllble and going strictly along the metal/semiconductor/electroyte three-phase boundaries. Once the metal were seperated from the semiconductor with the corrosion going on, the corrosion would be ceased. In this way, the corrosion processes are well controlled in the scale of Debye-length of the space charge at the metal/semiconductor boundaries. Baseed on this corrosion principle, electrochemical nanoimprint was developed as a very competitive nanoimprint method to fabricate the functional micro-/nano-structures on semiconductor wafers such as Si, GaAs and other III-V semiconductors. Electrochemical nanoinprint are free of thermalplastic or photocuring resists, mold-filling and demolding processes. It can make micro-/nano-structures directly on semiconductor wafers with high efficiency and low cost. Furthermore, the machining processes can be accelerated by the external physical fields, such as electric filed, light field and force field. In this talk, we will give a comphrehensive report on our recent advances in electrochemical nanoimprint.
Pushing the Boundaries of Conversion Coatings with an Unconventional Approach
Authors: Kumar Kuldeep , Bezer Silvia
Published: May 2020

In the 20th century, the use of steel as the primary construction material for applications such as vehicles, bridges, and buildings led to the development of surface protection by phosphate based conversion coatings. The discovery of anti-corrosion property of phosphatized surfaces can be dated back to 1906 when iron and steel were phosphatized using a phosphoric acid solution. Over time, numerous technical enhancements were achieved in the performance of phosphate coatings such as reduction in process time and temperature and the use of oxidizing agents such as nitrates for accelerated kinetics. However, zinc phosphate is not a universally suitable system; with the current market growth of aluminum alloys and their suitability for lightweight applications, automotive industries are utilizing aluminum alloys (e.g. AA6022) to reduce the vehicle weight to improve fuel efficiency. Interestingly, running aluminum alloys in zinc phosphate baths leads to excessive sludge formation and faster depletion of pretreatment bath. The frequent bath replenishments, increased sludge disposal costs, and new environmental constraints on the usage of phosphorous, nitrates, and nickel compounds in the pretreatment solution, drive the investigation of new technologies based on titanium and zirconium compounds. Zirconium and titanium based coatings offer several advantages over conventional zinc phosphate coatings, e.g. a very thin film thickness (~100 nm), a simpler process, and an environmentally friendly pretreatment solution.

During the formation of conversion coatings, the very top surface of metal alloys undergoes an oxidation reaction (e.g. M → Mn+ + ne‒). This reaction is coupled with the reduction of hydrogen ion in the pretreatment bath (e.g. H+ + e‒ → ½ H2) which leads to a slightly higher pH in the vicinity of metal substrate. If adjusted to suitable conditions, the passivating species are hydrolyzed on the substrate and determines the corrosion and adhesion properties of the alloy surface. The research at PPG Industries focuses on tuning the chemistry of pretreatment solutions, chemical modifications of subsequent layers, and engineering processing conditions which can favor the thermodynamic stability and kinetic growth of coating systems. Besides that, the utility of several analytical tools such as SEM, XPS, XRF and various modes of corrosion testing – cabinet tests, electrochemical tests, and immersion tests – are instrumental in the ongoing research. This presentation will focus on the historical development of conversion coatings, shortcomings in the phosphatized surfaces, processing and mechanism of thin film coatings, and ongoing research at PPG Industries.
(Invited) Wafer-Scale Integration of 2D TMD Heterostructures of Controlled Layer Orientation on Arbitrary Substrates Towards Mechanically-Reconfigurable Electronic Devices
Authors: Jung Yeonwoong
Published: May 2020

Advancements of modern electronics have demanded to incorporate a diverse set of additional functionalities into device platforms such as high mechanical deformability and improved material/process sustainability. Traditional silicon (Si) wafers-based device manufacturing is intrinsically limited in realizing such novel aspects owing to their rigid/bulky nature as well as complex and unsustainable process schemes. Two-dimensional (2D) transition metal dichalcogenide (TMD) semiconductors are highly promising owing to their extremely large mechanical flexibility and near atom thickness coupled with van der Waals (vdW) attraction-enabled relaxed assembly requirement. Major challenges for realizing such opportunities for emerging electronics have been associated with a lack of reliable manufacturing methods to precisely separate 2D TMD layers from original growth wafers and integrate them on desired functional substrates in a controllable, scalable, and sustainable manner. In this talk, I will discuss recent efforts in my group on exploring viable manufacturing strategies to assemble wafer-scale 2D TMD layers of heterogeneously tailored components on arbitrary substrates. We grew various 2D TMD layers of controlled layer orientation on specially-treated growth substrates with high hydrophilicity or water solubility via a chemical vapor deposition (CVD) process. By taking advantage of the large surface energy contrast between growth substrates vs. grown 2D TMDs, we precisely peel off wafer-scale 2D TMD layers from their original substrates using water preserving their intrinsic structural/chemical integrity. We then integrate them on substrates of virtually unrestricted kinds and shapes in a layer-by-layer fashion, realizing heterogeneously-assembled wafer-scale 2D TMDs layers on a variety of exotic substrates impossible with any conventional approaches. The achieved material quality has been characterized via extensive microscopy/spectroscopy techniques, and the original substrates have been sustainably recycled for sequential growth and integration. Several demonstrations of 2D TMDs-enabled mechanically reconfigurable electronic devices will be presented, which will be impossible with any other traditional materials. This novel manufacturing strategy is believed to greatly broaden the applicability of 2D TMDs in emerging areas of electronics such as three-dimensionally conformal electronic devices of unconventional forms factors.
(Invited) Development of New High-Dielectric Constant Thin Films By Combinatorial Synthesis
Authors: Nagata Takahiro
Published: May 2020

The development of high-dielectric constant film materials is essential for future active and passive nanoelectronics devices. By using combinatorial synthesis, high throwput material development, we developed high-dielectric constant film materials for film capacitor and gate dielectrics.In the case of the passive devices, we focused on the power device application. Power devices such as SiC require high-temperature operational passive devices, which are capable of operating over 250°C. For module and system level advancement, the high-temperature operational passive should be developed urgently. By employing combinatorial method and the thermal diffusion theory, we found some candedates based on ferroelectric materials. For the relaxor feroelectric, the permitivity of 400 and the stability <8% from room temperature to 400°C has been obtained, which are promising as a high-temperature dielectric medium. In the presentation, we also introduce the development of new high-k gate materials for GaN and Ge channels. For a Ge channel, which has been attracting a lot of attention as a replacement for the Si channel used in current Si-based metal-oxide-semiconductor (CMOS) devices. This is because the Ge channel has high electron and hole mobility, which lead to a higher drive current, and Ge has a narrower band gap than Si thus allowing supply voltage scaling. However, Ge has the same issue as Si, namely an unintentionally oxidized layer with a low dielectric constant (~5.6) can form at an oxide/Ge interface. Furthermore, in contrast with SiO2, which is a good insulating layer for MOS devices, GeOx is thermodynamically unstable and water soluble. These properties cause high defect densities at the interface between high-k and Ge and a large hysteresis in the capacitance-voltage characteristic. To overcome these issues, we have proposed the direct growth of (110) rutile TiO2 or non-oxide materials on (100) Ge substrates.
Bandgap Engineering of Ge Nanocrystals by Size Controlled Deposition and Doping
Authors: Honeit Florian , Beyer Jan , Heitmann Johannes
Published: May 2020

Germanium nanocrystals (nc) offer promising properties for different applications in electronics and photonics, like non-volatile memories [1] or photodiodes for the visible or infrared wavelength region [2, 3]. For those applications, a spatially and size controlled synthesis is necessary to enable for example electrical isolation between the nanocrystals or the proper adjustment of the optical bandgap.

Recent work has shown that the material systems Ge/TaZrOx, Ge/SiO2 and Ge/TaZrOx/SiO2 fulfil these requirements. To form size controlled nc, a Ge rich oxide layer like SiO2 or TaZrOx and pure oxide layer are deposited alternatingly via co-sputtering. Subsequent rapid thermal annealing forms the Ge nc by phase separation and crystallization. During the annealing process the pure TaZrOx interlayers act as a diffusion barrier for Ge, so these nc are confined to the thickness of the deposited mixed layer. The addition of a pure SiO2 interlayer leads to enlarged nc size by growth of the nc into the SiO2 layer. The use of an additional SiO2 layer has the further advantage of improved lateral nc separation in comparison to structures without the SiO2 interlayers. This leads to an improved electrical isolation of each nc. Still the bandgap of these nc can be adjusted easily by their size due to the quantum confinement effect.

Another advantage of Ge is the full compatibility to Si based processes. However, both Si and Ge has an indirect band gap, so the efficiency of e.g. light emitting diodes is low. The fabrication of Sn containing Ge can lead to a direct bandgap [4]. In our work we show the formation of Sn doped Ge nc in TaZrOx and SiO2, to create nc of controlled size. Our focus is the crystallization process of the nc, to avoid formation of pure Sn crystals, but still achieve a complete separation of the Ge-Sn alloy from the oxides. Samples with different Sn concentrations are annealed in a range of 500 °C to 800 °C and checked by Raman scattering and TEM. Furthermore, the influence of the used oxide on the nc crystallization temperature is investigated.

[1] Tiwari, S. Appl. Phys. Lett. 1996, 69, 1232

[2] Haas, S. J. Appl. Phys. 2013, 113, 44303

[3] Lehninger et al. Phys
.
Stat. Sol. (a), 2018, 155, 1701028

[4] Slav, A. et al. ACS Appl.NanoMater. 2019, 2, 3626−3635
Single Nanocrystals Studies of Upconverting Nanoparticles
Authors: Krajnik Bartosz , Holodnik Katarzyna , Noculak Agnieszka , Golacki Lukasz , Kostiv Uliana , Horak Daniel , Podhorodecki Artur
Published: May 2020

Upconverting nanocrystals (UCNC) such as NaYF4:Er3+, Yb3+ have been recently a subject of intensive investigation due to their unique optical properties and high potential in applications in biology and medicine as multifunctional diagnostic probes. Despite the level of attention paid to this material, their very low emission quantum yield is still an important problem excluding them from clinical applications. Thus, understanding of UCNC emission intensity limitation together with a development in growth protocols are crucial challenges to bring these materials to clinical practice. One of the main obstacles, which slowdown the progress in this field, is the complicity of the emission quantum yield measurements. Moreover, even the relative emission intensity measurements (from sample to sample), became a very challenging experiment in case of UCNC. These two difficulties make the optimization of growth process and understanding of experimental data very challenging tasks.

In this paper, we will discuss the influence of relative ions concentration, size and the shape of UCNC on their optical properties. We will also show our results obtained for a single UCNC, measured however in the wide field mode giving also the possibility of statistical analysis of UCNC properties. These results will include both the optical imaging as well spectroscopic data. With these results we will show, that this type of experiment enables to measure the relative UCNC emission intensity from sample to sample, what allows for optimization of nanocrystals growth as well as enables to understand the physical limitation of UCNC emission intensity. In particular, we will investigate the effects of Yb3+ ions clustering and its impact on NaYF4:Yb3+, Er3+ UCNC emission intensity. We will also support our conclusions with numerical data.

Based on our results we will explain the influence of Yb3+ concentration on optical properties of UCNC in details. Moreover, based on obtained experimental and numerical results we will explain the existence of optimal Yb3+ concentration in UCNC often reported in the literature.
(Invited) Realizing Narrow Bandwidth Visible Photoluminescence from Colloidal Silicon Quantum Dots
Authors: Veinot Jonathan
Published: May 2020

Quantum dot light-emitting diodes (QD-LEDs) are an attractive alternative to organic light-emitting diodes (OLEDs) that have attracted attention for next generation optoelectronic devices due to their high colour-saturated photoluminescence, processability, and stability. Existing QD-LEDs often employ toxic or rare metals (e.g., Cd, Pb, In, etc.). Although colloidal silicon quantum dots (SiQDs) are an attractive alternative because of their abundance, biocompatibility and tailorable surface chemistry, tuning their luminescence throughout the visible spectrum can be challenging. Furthermore, SiQD emission shows a comparatively wide bandwidth that is a consequence of the inherent properties of the Si band structure. As a result the narrowing SiQD luminescence is not readily achieved by straightforward size selection methods used for other quantum dots. One alternative approach is to prepare optical cavities that preferentially select specific emission wavelengths using optical structures. This presentation will outline our investigations targeted on realizing bright, high quantum yield, narrow bandwidth luminescence from SiQD-polymer hybrids.
Thermally Stimulated Evolution of Optical and Structural Properties of Germanium-Doped Alumina Films
Authors: Khomenkova Larysa , Makasheva Kremena , Petrik Peter , Bonafos Caroline , Ratel-Ramond Nicolas , Melnichuk Oleksandr , Melnichuk Lyudmyla , Balberg I. , Gourbilleau Fabrice , Korsunska N.
Published: May 2020

Group IV semiconductor nanoclusters/nanocrystals attract a great interest because of substantial transformation of their optical, electrical and luminescent properties due to quantum confinement effects. During last decades significant attention was paid to the Si nanocrystals (ncs) embedded in Si oxide or nitride, and later, to the Ge-ncs embedded in these matrices. The mechanism of these 'ncs' formation was investigated in details.

Recently we have reported on the Si-ncs formation in hafnia and alumina thin films. This work will present the results obtained for the Ge-rich Al2O3 films. The effect of Ge content and annealing conditions on the evolution of optical and structural properties of these materials and formation of Ge-ncs will be addressed.

The films with different Ge content were grown on quarts substrates by magnetron co-sputtering of Ge and Al2O3 targets in argon plasma. After deposition, they were annealed in nitrogen atmosphere and analyzed by means of spectroscopic ellipsometry, FTIR, Raman scattering, XRD and photoluminescence methods. It is observed that suitable thermal treatment leads to the decomposition of nonstoichiometric films and results in the Ge-ncs formation. The formation of Ge-ncs via phase separantion requires lower temperatures (600-700°C) than that for Si-ncs production in alumina host (1050-1100ºC). An annealing at 800-950ºC results in the Ge out-diffusion from the films via formation of volatile GeO. This process results in the significant depletion of the near-surface regions in germanium that was confirmed by an appearance of gradient in the refractive index via film volume.

Decomposition process stimulates also an appearance of visible and near-infrared photoluminescence. The shape of luminescent spectrum depends significantly on both Ge content and the excitation wavelength. It is observed that exciton recombination inside nanocrystals dominates at longer wavelength excitation, whereas the UV-blue excitation results in the radiative recombination via interface or host defects in the materials. This result was found to be caused by the competition of different radiative channels in the films. The evolution of optical and luminescent properties will be discussed in details.
Plasma-Assisted Catalyst Active Phase Regeneration in Formate-Selective Carbon Dioxide Electroreduction
Authors: Hu Jie , Lin Guanzhou , Liu Fuqiang
Published: May 2020

Electrochemical carbon dioxide conversion to more valuable products such as formate (its protonation leads to formic acid, a versatile liquid fuel) is an appealing approach to mitigating the greenhouse gas emission and storing a surplus of renewable energy, but the catalysts developed to date are typically plagued by rapid deactivation. Catalyst deactivation often results in a very low selectivity, in the form of a multitude of products, including H2, formate, methanol, CO, and hydrocarbons instead of more preferably a single product, which normally originates from CO-induced phase transformation of hydride catalyst active phases (e.g., Pd hydride). This phase transformation is typically manifested by a high sensitivity of Faradaic Efficiency (FE) and catalyst active phase to small changes of potentials, pH, and temperature. Despite recent developments in catalysts for electrochemical CO2 conversion, least effort has been devoted to regenerating catalyst active phases, especially for Pd-based catalysts when they are targeted for converting CO2 to formate. Effective regeneration of the catalyst active phase would allow enhanced efficiency and catalytic activity in CO2 conversion, greater supply of formate as a fuel, and reduced greenhouse effect. To address the above issues, non-thermal plasma has been utilized to regenerate the hydride catalyst active phase by exacting H from water and assisting in H sorption, and thus eliminate the CO-induced phase transformation through the repulsive interaction between CO and H. This work intends to establish a new framework of multi-electron/proton and heterogeneous electrochemical kinetics driven/mediated by free charged species in plasma.
Extreme Fast Charging: The Current State of Understanding
Authors: Tanim Tanvir R , Dufek Eric J. , Kim Sangwook , Evans Michael C , Dickerson Charles C
Published: May 2020

Enabling fast charging between 10 to 15 minutes has been identified as one of the key challenges to facilitate rapid penetration of battery electric vehicles in the mass market. 1,2 Fast charging in 10 to 15-minute, however, could create multiple performance and safety consequences for the conventional graphite-based lithium ion batteries. Our earlier studies have identified the key bottlenecks of enabling extreme fast charging for a low loading (⁓2 mAhcm-2) cell (high power design).3–5

This presentation will discuss the effects of extreme fast charging on moderate loading cells (⁓3 mAhcm-2). The key cell limitations during such high rate charging will be revisited for moderately loaded graphite/NMC532 single layer pouch cells. The long-term performance and aging issues for 4C to 6C charging rates will be shown with experimental data. The identified dominating aging mechanisms will also be presented for the two different fast charging rates.

The benefits of using different charging protocols, e.g., constant current- constant voltage and several multistep charging protocols will also be shown. Lastly, the opportunities and challenges of Li plating detection via electrochemical means will also be discussed.

References

1. Howell et al., D. Enabling Extreme Fast Charging: A Technology Gap Assessment.

2. Ahmed, S. et al. Enabling fast charging – A battery technology gap assessment. J. Power Sources
367, 250–262 (2017).

3. Tanim, T. R. Extreme Fast Charging of Lithium-Ion Battery: Understanding Bottlenecks and Safety Issues. (2019).

4. Tanim, T. et al. Extreme Fast Charge Challenges for Lthium-Ion Battery: Variability and Positive Electrode Issues. J. Electrochem. Soc.
166, A1926–A1938 (2019).

5. Colclasure, A. et al. Electrode scale and eletrolyte effects on extreme fast charging of lithium-ion cells. J. Electrochem. Soc.
submitted, (2019).
Direct Write Additive Manufacturing and Characterization of Battery Electrodes with Engineered Architecture and Porosity
Authors: Almansour Amjad S , Gorven Alastair , Singh Mrityunjay , Dornbusch Donald A.
Published: May 2020

The development of batteries with high specific power and energy densities will enable the next generation of smart devices, and allow for more efficient implementation of all-electric aircraft and urban air mobility (UAM) technologies. Additive manufacturing technologies can be leveraged to produce engineered 3-dimensional cell structures with increased electrolyte/electrode interfacial area, yielding increased power density and reducing weight through the implementation of ceramic electrodes. Direct-write additive manufacturing (DWAM) technology allows for the deposition of solid-bearing inks with a high degree of dimensional accuracy. Ink rheology was adjusted in order to optimize material characteristics of the final object. Engineered LiFePO4 (LFP) cell structures were manufactured, sintered, and characterized by leveraging the sub-micron accuracy of direct write printing. The sintered electrodes were shown to exhibit favorable porosity and dimensional tolerances. The direct write additive manufacturing process, ink rheology, and sintering properties will also be discussed
Adsorbate-Driven Electrode Processes, Part 1: Faceting and Anisotropic Dissolution
Authors: Groenenboom Mitchell C. , Moffat Thomas P. , Schwarz Kathleen
Published: May 2020

Monolayers of adsorbates on metal surfaces under electrochemical conditions can promote faceting of the underlying electrode surfaces, and facilitate anisotropic dissolution. Here we use density functional theory (DFT) to model these metal-adsorbate interactions. We train Behler-Parrinello neural networks to approximate the DFT potential energy surfaces of stepped surfaces. We use these neural networks to identify adsorbate structures near step edges and demonstrate that the long-range order of the adsorbate adlattice drives anisotropic dissolution.
(Invited) Operando Optical Monitoring of Nanoparticle Electrodeposition
Authors: Lemineur Jean-François , Noël Jean-Marc , Combellas Catherine , Kanoufi Frederic
Published: May 2020

Electrodes, made of nanoparticles (NPs), are key components in electrochemistry to store and convert energy. The nanometer scale allows exalting surface properties and revealing, in addition to the composition, the importance of size, shape and NP organization on the kinetic and thermodynamic performance of devices. Therefore, the use of ultra-small objects and the study of their formation and reactivity appear as one of the best ways to meet the current energy challenges.

Herein, electrodeposition, one of the most popular electrochemical methods for producing nanostructured electrodes, is coupled to an ultra-sensitive interferometric microscopy technique to probe operando the heterogeneity of electrochemical processes at the single NP level. The strategy is illustrated through the monitoring of the electrochemical growth of individual silver NPs, whose sizes can be tracked dynamically down to 10 nm in diameter. Optical images are further used to quantify the presence of metal nanoclusters at the early stages of the electrodeposition and to highlight galvanic reactions occurring between NPs with distinct surface free energies.

As interferometric microscopy relies on refractive index changes, the technique can be applied to many kinds of nanomaterials and electrochemical experiments. For example, the optical coupling has proved to be useful for studying NP transformation.

Figure. Schematic representation of the coupling and same location microscopy experiment with a scanning electron microscope.

J.-F. Lemineur, J.-M. Noël, C. Combellas, D. Ausserré, F. Kanoufi. Angew. Chem. Int. Ed., 2018, 57,11998-12002.

J.-F. Lemineur, J.-M. Noël, C. Combellas, D. Ausserré, F. Kanoufi. Faraday. Discuss., 2018, 210, 381-395.

Figure 1
(Invited) Molecular Models for Electrodeposition Inhibitors, Suppressors, and Anti-Suppressors
Authors: Gewirth Andrew A. , Schmitt Kevin Gary , Rooney Ryan , Schmidt Ralf , Bandas-Rivera Christopher
Published: May 2020

We evaluate the effect of chain length for a series of alkyl sulfonic acid additives on Cu electrodeposition by using a combination of electrochemical and Raman spectroscopic methods. The combination of these methods suggests that effective Cu electrodeposition acceleration processes require: 1) direct tethering of mercaptoalkylsulfonate species to the electrode, 2) partial desolvation of Cu2+ by the sulfonate group to minimize its solvent reorganization energy, and 3) stabilization of Cu+ adjacent to the electrode surface by addition of halide. Finally, we use the cis-trans ratio idea developed for SPS to examine the effect of inhibitors on SPS activity.

We also investigate the behavior of Cu plating bath suppressor additives poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) using normal Raman spectroscopy, surface-enhanced Raman spectroscopy (SERS), and electrochemical quartz crystal microbalance (QCM) measurements. Raman and SERS show a clear spectroscopic trend of increased intensity in higher wavenumber modes in the CH stretching region as the environment is changed from pure material to solution to surface for both PEG and PPG. The spectral changes associated with PEG are larger than those associated with PPG, suggesting that the relatively more hydrophilic PEG undergoes more conformational changes upon surface association relative to the more hydrophobic PPG. In the presence of Cl-, PPG forms a denser surface layer compared to PEG on a Cu underpotential deposition (UPD) layer on Au. These differences are consistent with the increased hydrophobicity of PPG relative to PEG.