bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and Optimization of 3DSi Electrode for Li-Ion Battery Applications
Authors: Ababtain Khalid Abdullitife , Arava Leela mohana reddy , Ganguli Babu
Published: February 2020

Abstract

Lithium ion batteries are revolutionized today's information-rich e-society due to their light weight and high energy density. Despite their great success in portable electronic devices at the present time, interest is continued in advancing new and improved electrode materials for lithium ion batteries with higher energy capacity and longer cycle life. Silicon is one of the most promising anode materials for lithium batteries, as it appeals with highest theoretical specific capacity (4200 mAh/g) among known materials, relatively low cost, and environmental benignity. However, silicon anodes suffering from huge volume change associated with the insertion and extraction of lithium during charge-discharge process. Such an unavoidable volume changes result to cracking and pulverization of the anode, which leads to a loss of electrical contact and eventual fading of capacity upon cycling. Herein, we report a porous three-dimensional framework of current collectors to form 3DSi nanostructure to provide continuous electron transport network and accommodate the volume expansion of Si particles.

3D porous Ni current collectors are prepared by galvanostatic electrodeposition with tuning its experimental parameters such as deposition current and pH of bath solution etc. Silicon is deposited conformally by plasma enhanced chemical vapor deposition (PECVD) technique. During PECVD process, parameters such as time, flow rate of the silane gas (SiH4), pressure and power are optimized to ensure uniform conformal coating of Si to form desired three-dimensional silicon structure.  X-ray diffraction and Microscopy analysis revealed the formation of 3DNi current collectors by electrodeposition and conformal coating of Si by PECVD. Electrochemical studies such as cyclic voltammetry, electrochemical impedance spectroscopy and charge-discharge studies have been carried out to understand the influence of 3D structure on silicon capacity and cycle life properties. Such a 3D Si electrodes exhibit capacity of 2600 mAh/g with an excellent columbic efficiency at 0.2 C rate for 100 cycles. Further, full cell configuration has been fabricated using LiFePO4/C cathode to demonstrate feasibility of presently designed 3D Si electrode for high capacity Li-ion battery applications.

# - Corresponding Author - leela.arava@wayne.edu
Metal Oxide Anode Materials for Lithium-Ion Batteries
Authors: Mustain William E , Liu Ying , He Junkai , Meng Yongtao , Suib Steven
Published: February 2020

Lithium-ion batteries have become the most popular power source for portable electronics, offering very good energy density, along with favorable stability and efficiency [1]. At the Li-ion anode, graphitic carbons have been ubiquitous [2], though these materials may lack sufficient energy density to enable grid or home-scale energy storage or the realization of fully electric vehicles with sufficient driving range.  Therefore, recent years have seen a shift in focus to the development of materials with higher capacity than graphite. 

Metal oxides are a promising family of materials that could potentially replace graphite as the anode in lithium-ion batteries. Metal oxides typically do not intercalate lithium during charging process, but rely on chemical transformations with more than one electron transfer to store and deliver energy, which results in much higher capacities.  In addition, they also have a safer lithiation potential that eliminates the problematic lithium plating process during charging.  However, the use of metal oxides has been limited mainly by their low electrical conductivity, and inferior cycling stability [3-5]. To circumvent these challenges, nanostructured metal oxides and their composites with advanced carbon materials, such as graphene, can be used to improve their capacity retention by suppressing phase segregation during charge/discharge and volumetric expansion, as well as enhancing ionic and electronic transport.

In this work, the interaction between metal oxides (Co3O4, SnO2, NiO, MnO2) and several carbon substrates was explored using a combination of electrochemical and physical characterization.  Increased interfacial interaction between carbon and metal oxide, while minimizing the carbon loading, is critical to improve battery performance. Excellent capacity retention and rate capability can be realized through a combination of material chemistry and structure, and promising approaches to achieve this will be the focus of this presentation. 

[1] Tarascon. J, Armand. M, Nature, 414 (2001) 359.

[2] Sawai. K, Ohzuku. T, J. Electrochem. Soc., 150 (2003) A674.

[3] Lee, S. H.; Kim, Y. H.; Deshpande, R.; Parilla, P. A.; Whitney, E.; Gillaspie, D. T.; Jones, K. M.; Mahan, A. H.; Zhang, S. B.; Dillon, A. C., Adv. Mater., 20 (2008) 3627.

[4] N.S. Spinner, A. Palmieri, N. Beauregard, L. Zhang, J. Campanella and W.E. Mustain, J. Power Sources, Accepted.

[5] N. Spinner, L. Zhang and W.E. Mustain, J. Mat. Chem. A, 2(6) (2014) 1627-1630.
A Novel U-Shaped Finfet with Vertical Channels
Authors: Liu Yunfei , Yin Haizhou , Li Rui , Zhu Huilong , Zhao Chao , Wang Pengfei , Mei Shaoning , Ye Tianchun
Published: February 2020

A novel U-shaped FinFET (UFET) with vertical channels is introduced in this work. A main feature of this device is that it consists of two fins with vertical channels. A top portion of one fin serves as the transistor source, and the top portion of another fin serves as the drain. Unlike traditional FinFETs, gate length (Lg) of the UFET depends on the fin height, whereas gate width (Wg) depends on the fin length. With vertical channels, device footprint scaling would not necessarily need to reduce the gate length. The source and drain is on the same plane and naturally isolated from each other which help to reduce the coupling between them in the subthreshold region. Therefore, the UFET structure has excellent short channel effect (SCE) control, and its effective gate width is significantly increased when compared to traditional FinFETs at the same device footprint, thus considerably increasing drive current and achieving low leakage current at the same time. TCAD simulation of an n-type UFET with Lg = 30 nm shows that the device drive current can achieve 3.46 mA/um at 26 nA/um Ioff and 0.75V. An outstanding subthreshold slope (S.S.) of 64 mV/dec. and 9 mV/V DIBL are achieved. A 78% effective gate width increase is achieved when compared with conventional logic FinFETs at the same device footprint. Moreover, 3D NOR flash can be easily built by this UFET.

Figure 1
Improved Structural and Electric Characterstics of Al/ALD-HfO2/Ge MOS Capacitor by Germanium Dioxide and Germanium Oxynitride as Interfacial Layer
Authors: Prasher Rakesh , Dass Devi , Vaid Rakesh
Published: February 2020

In this work HfO2 thin films has been deposited on Ge substrate by ALD with thickness of 9.77 nm. Thickness evaluation of film was done by Spectroscopic Ellipsometer (SE) and Filmetrics Reflectometer whereas chemical compositions and the states of the elements of the films were investigated by X-ray Photoelectron Spectroscopy (XPS). High-frequency Capacitance-Voltage (C-V), Conductance-Voltage (G-V) techniques and Current-Voltage (I-V) measurement were used to obtain the electrical properties of the high-k MOS capacitor. Different Ge surface cleaning methods preceding high-k ALD have been used for reducing oxide traps. Rapid Thermal Oxidation (RTO) and Rapid Thermal Nitridation (RTN) have been used to form the gate interlayer (IL) of GeO2 and GeON for the gate stack of P-MOS capacitor. By assimilating a thin GeON interlayer, excellent MOS capacitors with very small capacitance–voltage hysteresis and low gate leakage have been demonstrated. Physical and Electrical characterization investigates the quality of the oxynitride interlayer and low interface trap density (Dit ≈ 0.63×1012eV-1cm-2) in case of GeON/Ge which is improved as compared to the GeO2/Ge interface (Dit ≈ 2.53×1013 eV-1cm-2). Further electrical characterizations of HfO2 gate dielectric MOS capacitors deposited by the ALD using RTO & RTN as IL were investigated for the measurement of EOT and Qeff. The calculated EOT and Qeff values for GeON/Ge are 3.23 nm and 16.92×1012 cm-2 respectively which is better in comparison with GeO2 and as deposited samples.
(Invited) Preparation of GaSb Surface for Low Interfacial Trap Density MOS Capacitors
Authors: Chen Chen-Yu , Hsueh Wei-Jen , Chang Chao-Min , Hsu Hsien-Ming , Chyi Jen-Inn
Published: February 2020

High mobility III-V compound semiconductors have been extensively investigated recently for future complementary metal-oxide-semiconductor (CMOS) applications. GaSb, which has high electron and hole mobilities as well as a narrow bandgap is an attractive material for future high-speed and low-power integrated circuits. Due to the easy formation of native oxides, i.e. SbOx, GaOx, and elemental Sb clusters on GaSb surface, Fermi-level pinning and high interfacial trap density (Dit) has been a major obstacle to high quality MOS devices. In this talk, we will present both in-situ and ex-situ techniques to prepare GaSb surface and realize metal-oxide-semiconductor capacitors (MOSCAPs) with low interfacial trap density.

The i
n-situ approach is conducted in a system equipped with a high vacuum sample transfer tube that connects a molecular beam epitaxy (MBE) tool and an atomic layer deposition (ALD) chamber. A native oxide-free surface can thus be preserved for high-κ dielectrics deposition. HfO2/Al2O3/GaSb MOSCAPs fabricated on Sb-stabilized surface exhibit clear inversion behavior at low frequency and good modulation of the Fermi level across the whole GaSb band gap. Modulation of the inversion capacitance at 100 kHz reaches 30 %, suggesting low Dit as well as low bulk trap density at the interface. The Dit extracted by the conductance method is about 7.6×1011 cm-2eV-1 near the valence band. As to the ex-situ process, air-exposed GaSb samples are treated by hydrogen plasma at room temperature prior to ALD dielectrics. Under optimized plasma treatment conditions, similar C-V characteristics and gate leakage current of HfO2/Al2O3/GaSb MOSCAPs to those of the in-situ ones are observed. Modulation of the inversion capacitance at 100 kHz even reaches 36 % and the Dit near the valence band is as low as 6.0×1011 cm-2eV-1.

Structural and chemical analyses of the dielectric/semiconductor interface by high-resolution transmission electron microscopy (HRTEM) and x-ray photoelectron spectroscopy (XPS) show that the in-situ MOSCAPs have a native oxide-free interface, while hydrogen plasma treatment results in the formation of GaOx, which may serve to passivate defects and dangling bonds at the GaSb surface
Invited: Ohmic Contacts to Semiconductor Compounds: From III-V Semiconductors to Layered Transition Metal Dichalcogenides
Authors: Mohney Suzanne E.
Published: February 2020

In this presentation, I will review work on low-resistance ohmic contacts to III-V semiconductors, particularly our group’s most recent work on contacts to InGaAs. Then I will discuss contacts to layered transition metal dichalcogenide semiconductors and how some of the lessons learned from III-V semiconductors may apply to contacts to the transition metal dichalcogenides. I will also highlight important differences between the families of materials and their ramifications for forming low-resistance ohmic contacts to layered semiconductor compounds.

To realize low-resistance ohmic contacts to semiconductors, it is necessary to understand and control many factors. The Schottky barrier between the metal and semiconductor should be minimized but is not always strongly affected by the choice of metal due to Fermi level pinning. The Schottky barrier can also be affected by the preparation of the semiconductor surface prior to metallization and the presence of intentional or unintentional interfacial oxide layers. I will discuss this effect in contacts to heavily doped n-type InGaAs, particularly Ni contacts of interest for self-aligned “salicide-like” processes. I will also discuss a possible explanation for the vastly different values of specific contact resistance reported by different groups that have studied these Ni contacts.

The interfacial reactions between a metal and semiconductor can be used in many ways to engineer current transport through contacts, so it is beneficial to understand the contact metallurgy­–both phase equilibria and reaction kinetics. This topic has been studied extensively for contacts III-V semiconductors. As a recent application, I will highlight the introduction of co-dopants (Si and S) through solid-state reactions to form a shallow ohmic contact to n-type InGaAs, which resulted in an exceptionally low contact resistance on lightly doped n-type InGaAs.

Finally, I will discuss our newest studies on contacts to transition metal dichalcogenide semiconductors. I will present information on phase equilibria and reaction kinetics in metal-Mo-S systems and their implications for contacts to MoS2. Then I will compare these systems to the metal-III-V systems and predict how reactions and surface preparation will be important for engineering contacts to layered transition metal dichalcogenide semiconductors.
The Effect of Interfacial Contamination on Antiphase Domain Boundary Formation in GaAs on Si(100)
Authors: Barrett Caleb Shuan Chia , Lind Aaron Gregg , Bao Xinyu , Ye Zhiyuan , Ban Keun-Yong , Martin Patrick , Sanchez Errol , Jones Kevin Scott
Published: February 2020

As integrated circuits continue to shrink, there is growing interest in the use of III-V compound semiconductors to increase performance at lower operating power. Some III-V semiconductors offer beneficial electrical properties over Si, but industry tools are based on large Si wafers. Thus, III-Vs will have to be integrated onto Si. A major hindrance to integration is the formation of defects such as antiphase domains in the III-V layer due to the nature of growing a polar material on a nonpolar substrate. It is well known that annealing Si(100) substrates at temperatures near 1000 °C can induce the formation of double steps on the surface which can inhibit the formation of antiphase domain boundaries (APBs). However, this process requires a large thermal budget, which may not be compatible with other existing devices on the chip. Thus, the relationship between APB behavior and process conditions must be better understood in order to realize meaningful reduction in APB density with lower thermal budgets. One major factor associated with increased defect density is the presence of interfacial impurities between the epitaxial III-V layer and Si. In this study, 450 nm thick GaAs films were grown on 300 mm Si(100) substrates (exact cut) by an Applied Materials III-V MOCVD (metal-organic chemical vapor deposition) system. The substrates were cleaned with a dry remote fluorinated plasma prior to growth. Samples were characterized using a chemical etch and scanning electron microscopy to quantify APB density, transmission electron microscopy to study the depth evolution, and secondary ion mass spectrometry to quantify the carbon and oxygen doses at the interface. It was found that for an approximately 10x range of interfacial carbon and oxygen dose, the APB density increased logarithmically from a value of 0.14 μm-1 to a maximum of 3.2 μm-1. This is believed to be the first quantitative correlation between carbon/oxygen contamination and APB density, of particular relevance to reduced thermal budget processing.
Epitaxial Growth of High Quality GaN Films on Lattice Matched Metallic Layers
Authors: Dabiran Amir M , Machuca Francisco , De Indranil , Weiss Robert
Published: February 2020

In recent years there have been great advances in wide bandgap electronic and optoelectronic devices based on GaN materials.  However, problems arising from growth on non-native substrates, such as sapphire or Si, continue to present major hurdles for development of higher performance and lower cost devices.  For example, complex layer structures and processes have been developed to successfully mitigate some of the problems arising from mismatch in both lattice constant (LC) and coefficient of thermal expansion (CTE) between GaN and foreign substrates.  However, the added complexity and costs reduce the utility of these techniques for many applications.  In the past, GaN growth on metallic substrates, buffer layers and interlayers have been studied by few groups for a number of applications including thermal management in high power devices, back contact for vertical-transport devices, backside mirror for light emitters and detector, and as threading dislocation filters.   The major obstacles for the growth of high quality GaN films in these studies have been 1) deposition of single crystal metal film with proper orientation on foreign substrates, 2) avoiding strong chemical reactions and interface mixing during the nucleation of GaN on the metal surface, 3) minimizing mismatch in LC and CTE to avoid high dislocation density, stress cracks or sever wafer bowing, and 4) achieving adequate thermal and chemical stability of the GaN/metal/substrate structure for the demanding growth conditions encountered in deposition of III-nitride films for example by hydride vapor phase epitaxy.  

 In this work we have studied high quality growth of GaN by RF-plasma assisted molecular beam epitaxy (PA-MBE) and metal organic chemical vapor deposition (MOCVD) on high-quality, single crystal refractory metals deposited by plasma sputtering on c-plane sapphire and Si(111) substrates.  We will first discuss the deposition and optimization of fully relaxed high quality metal layer structures that are properly oriented and lattice matched for the growth of low defect GaN films on c-plane sapphire and Si(111).  We will then compare the nucleation and growth of GaN by PA-MBE and MOCVD on these metal layers. Some initial results such as x-ray diffraction scans for GaN grown on these lattice-matched metal alloys are quite comparable to high quality GaN grown on c-plane sapphire.   Finally, we present some examples of improved wide bandgap devices based on GaN films grown on metal layers.

Figure 1
(Invited) Unraveling the Efficiency Limits of GaN-Based Emitters and the Surprising Connection to Electron Devices
Authors: Speck James
Published: February 2020

In this talk, we review our recent experiments designed to reveal the fundamental efficiency limits of GaN-based LEDs:  (i) electroemission spectroscopy studies of InGaN-based LEDs with cesiated surfaces provide the first direct measurement of Auger electrons that result from an electron-electron-hole (eeh) Auger process.  Auger-generated electrons survive transit through the p-GaN by transfer to a low lying side valley.  The relationship between the observation of Auger electrons and the onset of droop provides compelling evidence that the internal Auger process is the dominant droop mechanisms [1]; (ii) related above gap photoemission studies on p-GaN with cesiated surfaces demonstrate a low level side conduction band valley (nominally referred to as “L”) ~0.9 eV above Γ [2]; (iii) atom probe tomography studies on InGaN-based LEDs demonstrate that the indium alloy follows a binomial distribution, as expected for a random alloy.  2D drift-diffusion simulations show that the alloy fluctuations are essential to explain the low turn-on voltages of InGaN-based LEDs [3];  (iv)  vertical carrier transport studies on majority carrier analogs to LEDs, namely all n-type InGaN/GaN MQWs  and GaN/AlGaN/GaN structures confirm the importance of natural alloy fluctuations in vertical transport [4,5].

[1]  J. Iveland et al., Phys Rev. Lett. 110, 177406 (2013)

[2]  M. Piccardo et al., Phys. Rev. B, in press (2014)

[3]  Y.-R. Wu et al., Appl. Phys. Lett. 101, 083505 (2012)

[4]  D. Browne et al., in preparation (2014)

[5]  M. Fireman et al., in preparation (2014)
(Invited) Fully Porous GaN p-n Junctions Fabricated by Chemical Vapor Deposition: A Green Technology towards More Efficient LEDs
Authors: Carvajal Joan J. , Mena Josue , Bilousov Oleksandr , Martínez Oscar , Jiménez Juan , Zubialevich V.Z. , Parbrook Peter J. , Geaney Hugh , O'Dwyer Colm , Díaz Francesc , Aguiló Magdalena
Published: February 2020

GaN is an important wide band-gap semiconductor in electronics and optoelectronics. In its porous form is particularly interesting for developing optoelectronic devices with improved efficiency, such as LEDs with enhanced efficiency and sensors with enhanced sensitivity.

Through chemical vapour deposition (CVD) [1], we have shown that it was possible to produce nanoporous GaN without any secondary etching or chemical post-growth treatment in order to generate the porosity, present only on the (0001) face of the material, providing a green approach for the production of porous GaN. These nanoporous GaN particles can be deposited on different substrates, including boron nitride, silicon, sapphire and SiC, obtaining porous particles with a low density of defects, as revealed by the emission arising only from the band-edge of the particles obtained in the cathodoluminescence studies [2]. By using this methodology of growth, we demonstrated the fabrication of low resistivity ohmic Pt and Au metallic contacts on porous n-type GaN by the formation of intermetallic seed layers through the vapour-solid-solid (VSS) mechanism [3]. Also, we have been able to develop p-type porous GaN by doping with Mg, with a charge carrier concentration of the order of 1018 cm-3 [4].

Through the careful selection of the substrate it is possible to produce porous GaN epitaxial layers [5] that allow for the fabrication of high quality partially and fully porous GaN rectifying p-n junctions, through a 2 step CVD process, and show their behaviour as diodes with effective uniform conduction [6]. These porous junctions have potential applications in high brightness unencapsulated LEDs with enhanced light emitting properties and high surface area sensors with improved sensitivity.

[1] Carvajal & Rojo, Crystal Growth Des. 9 (2009) 320

[2] Carvajal et al., Microsc. Microanal. 18 (2012) 905

[3] Bilousov et al., ACS Appl. Mater. Interfaces 4 (2012) 6927

[4] Bilousov et al., Appl. Phys. Lett. 103 (2013) 112103

[5] Bilousov et al., CrystEngComm  16 (2014) 10255

[6] Bilousov et al., ACS Appl. Mater. Interfaces 6 (2014) 17954
Durability Evaluation of PEFC Catalyst Layers through in-Situ SEM/STEM Techniques
Authors: Hayashi Akari , Kitamura Masahiko , Noda Zhiyun , Sasaki Kazunari
Published: February 2020

Electrocatalysts for PEFC, made of platinum deposited carbon materials, have an import role to govern PEFC performance. Although the initial activity is high enough to be commercialized, their long-term durability should still be improved. Especially, carbon oxidation under stop/start cycles of fuel cell vehicles, where the potential at the cathode becomes as high as 1.5 V vs RHE. In order to check long-term durability of electrocatalysts against carbon oxidation, we need to perform accelerating degradation tests. Potential cycling up to high potential is usually used to accelerate degradation.

  In this study, we introduce our method to accelerate degradation of electrocatalysts using Environmental TEM (Hitachi HF-3300). For carbon oxidation, the air is introduced into the specimen chamber, and the specimen holder is heated up to 200 oC to accelerate degradation instead of cycling to high potential many times. In this method, it is possible to observe degradation of electrocatalysts in real-time. In addition, our method makes it possible that both surface and transmitted images are available at the same time through simultaneous SEM and STEM observation.

  So far, we have observed a catalyst composed of platinum nanoparticles on Vulcan carbon, and we have found a new phenomenon of platinum particles embedded into Vulcan carbon with almost no agglomeration. However, on graphitized Vulcan carbon surface, agglomeration more occurs, and embedding of platinum is rather suppressed. Since platinum on graphitized carbon have shown much improved durability on a separate experiment using potential cycling, embedding is believed to be a more predominate factor than agglomeration.

  We have further tried similar experiments with a sample directly picked up from the cathode catalyst layer of PEFC, which includes Nafion ionomer. Similar to the case without Nafion, platinum is embedded after the acceleration test as shown in Figure 1, even though agglomeration is slightly increased. However, the surface image is somewhat different. We believe that this is due to the existence of Nafion ionmer on the carbon surface.

  We have also controlled the atmosphere of observation using hydrogen or humidified air. We will discuss possible degradation mechanisms through the comparison to accelerated degradation derived by potential cycling.

Figure 1
(Invited) Fuel Cell Catalyst Development and Prospects of Refining Business in Tkk
Authors: Matsutani Koichi
Published: February 2020

For a full-scale spread of FCs, the necessity of reducing Pt on the stack is increasing. I will introduce effort of TKK for reducing Pt loading, it means that how we tried to improve the catalytic activity.  In addition, need of precious metal recycling is growing upon commercializing. I will introduce the prospects for the future of the recycling business.
Elimination of Surface Adsorbates on Gadolinium Doped Ceria for Electrochemical Strain Microscopy
Authors: Xu Jie , Li Jiangyu , Adler Stuart B.
Published: February 2020

Use of solid oxide fuel cells for the conversion of electrochemical energy has a number of advantages over current technologies.  These systems offer high efficiencies for energy conversion, a choice of inexpensive hydrocarbon fuels, and environmentally friendly operation.  The mechanisms which govern the functionality of these materials may be elucidated using scanning probe microscopy based techniques.  However, the formation of surface adsorbates complicates their use.  One such technique, electrochemical strain microscopy, quantifies the mechanical response of a surface resulting from the application of an AC bias through a cantilever.  We have used this methodology in conjunction with a number of strategies to understand the behavior of gadolinium doped ceria, a widely used electrolyte material, while circumventing the issues that arise at the material surface.  Sections of the ceria sample were ablated using a focused ion beam to expose a surface previously shielded from the ambient environment, then subsequently studied with electrochemical strain microscopy.  We find that the ablation process produced a surface morphology exhibiting an enhanced electromechanical response similar to polycrystalline ceria at the grain boundaries that has previously been attributed to the space-charge effect.  Thermogravimetric analysis, between 20°C and 400°C, revealed a plateau in weight around 200°C and 350°C, suggesting these are points that surface adsorbates may be removed from the electrolyte.  We are currently studying the ablated regions at 250°C in a controlled environment to analyze the strain response under these conditions.
(Invited) Platinum Electrochemial Dissolution and Its Consequences for Platinum Electrocatalysis
Authors: Cherevko Serhiy , Geiger Simon , Keeley Gareth , Topalov Angel A. , Zeradjanin Aleksandar R. , Mayrhofer Karl J.J.
Published: February 2020

While the fact that platinum dissolves has been known for more than a century, its nature is still obscure. Platinum dissolution as a result of an anodic treatment of a platinum electrode was documented as early as at the beginning of the twentieth century in the works of the founder of electrochemical kinetics, Julius Tafel.1
,
2 In the second half of the twentieth century several groups reported on the quantification of platinum dissolved from platinum electrodes during potentio- or galvano-static or potentiodynamic conditions.3-5 Later, platinum dissolution was mainly discussed in relation to  platinum catalyst degradation in proton exchange membrane fuel cell (PEMFC) cathodes.6 Recently, we applied a novel setup composed of a scanning flow cell and inductively coupled plasma mass-spectrometer (SFC-ICP-MS) for precise time- and potential-resolved investigation of platinum dissolution under acidic conditions.7 In the current work we are going to show and discuss these and new results obtained using SFC-ICP-MS. Inter alia an effect of pH, potential, temperature, presence of chloride ions or reactive gases on the process of platinum dissolution will be communicated. Besides dissolution of polycrystalline platinum electrode new data on the stability of nanoparticulated carbon-supported platinum catalysts will be shown and a comparison with the bulk material will be made. Based on the obtained experimental results consequences of platinum dissolution on the application of platinum in electrocatalysis of oxygen reduction and other important reaction of platinum electrocatalysis will be discussed.     

References

1.         K. Müller, Journal of the Research Institute for Catalysis, Hokkaido University, 17, 54 (1969).

2.         G. T. Burstein, Corros. Sci., 47, 2858 (2005).

3.         A. N. Chemodanov, Ya. M. Kolotyrkin, M. A. Dem'rovskii and T. V. Kudryavina, Doklady. Akad. Nauk. SSSR, 171, 1384 (1966).

4.         D. A. J. Rand and R. Woods, J. Electroanal. Chem., 35, 209 (1972).

5.         D. C. Johnson, D. T. Napp and S. Bruckenstein, Electrochim. Acta, 15, 1493 (1970).

6.         R. M. Darling and J. P. Meyers, J. Electrochem. Soc., 150, A1523 (2003).

7.         A. A. Topalov, S. Cherevko, A. Zeradjanin, J. Meier, I. Katsounaros and K. J. J. Mayrhofer, Chemical Science, 5, 631 (2014).
Plasmonic Metal Oxide Nanocrystals and Their Near Infrared Electrochromism
Authors: Milliron Delia J. , Runnerstrom Evan , Llordes Anna , Wang Yang , Dahlman Clayton
Published: February 2020

Degenerately doped metal oxide semiconductors, like ITO, exhibit plasmonic resonance at near and mid-infrared wavelengths tunable by varying their composition. Nanocrystals of many such materials have now been synthesized and applications are emerging that leverage the responsiveness of their localized surface plasmon resonance (LSPR) to electronic charging and discharging. One such application is electrochromic glass that can dynamically control heat loads in buildings as the plasmonic absorption of the nanocrystals is electrochemically modulated. I will discuss the principles of electrochromic switching in such materials and describe our efforts to integrate plasmonic nanocrystals into full electrochromic devices. Fundamental understanding of the nature of the electronic states giving rise to infrared absorption is also being pursued.  For example, near-edge x-ray absorption spectroscopy is illuminating the charge state of the metal cations in as-prepared doped nanocrystals and in electrochemically-charged materials. Localization of charge upon lithium insertion gives rise to visible tinting, useful for controlling daylight intensity in smart windows. Finally, fabrication strategies compatible with flexible substrates are explored, opening the door to low cost manufacturing.
Ultrathin and Nanostructured Organic Layers with on/Off Switching Properties Based on Covalently Grafted Olidothiophenes
Authors: Lacroix jean Christophe
Published: February 2020

Conducting surface modification by covalent attachment of organic molecules is needed in research fields such as molecular electronics. or smart surfaces. Among several methods leading to immobilisation of organic molecules onto a surface, one of the most frequent reactions is the electrochemical reduction of an aryl diazonium salt. We have used this method with several diazonium salts containing thiophene units. The resulting surfaces were characterized employing electrochemical measurements and X-ray photoelectron (XPS) analysis. The layers have thicknesses between 3 and 20 nm and are strongly attached to the surface as a result of covalent grafting. Unusual electrochemical responses towards several outer-sphere redox couples have been observed. In case of redox couples bearing a redox potential below a threshold potential, a diode-like behaviour was observed whereas for redox potentials superior to this threshold potential, the film becomes conducting and no modification of the electrochemical signal of the redox probes were observed when compared to bare electrodes. The threshold can be easily tuned by the molecular structure of the grafted oligomers. Ultrathin layer junctions based on conjugated oligomers with reversible on/off switching capabilities controled by the redox state of the oligomer have thus been obtained. 1, 2

Such diazonium salts can be easily included in cyclodextrine. We have shown that the electroreduction of the encapsulated diazonium salts in water solution leads to modified surfaces consisting of grafted oligothiophenes and cyclodextrins which can be removed from the surface.  Electroreduction of a second diazonium in the generated holes is possible and leads to mixed layers. 3, 4 Finally such films can be nanostructured using Nanosphere lithography and several nanostructured multifunctional layers can be generated using this inexpensive technique. 5

The use of such ultrathin, nanostructured and multifunctional organic layers will be discussed. 6

1 Fave C.; Noel V.; Ghilane J.; Trippe-Allard G.; Randriamahazaka, H., Lacroix J. C.   J. Phys. Chem. C (2008), 112(47), 18638

2 Stockhausen V.; Ghilane J.; Martin P., Trippe-Allard, G.; Randriamahazaka, H.; Lacroix J. C. JACS  (2009), 131(41), 14920.

3. Santos L.; Ghilane J.; Martin P.; Lacaze, P.-C.; Randriamahazaka, H.; Lacroix J. C. JACS, (2010) 132(5), 1690.

4. Santos L., Ghilane, J.; Lacroix J. C. JACS  (2012) 134 , 12, 5476-5479

5. Santos L.,  Ghilane, J.; Lacroix J. CElectrochemistry Communications (2012) 18, 20-23

6. Martin P.; Della Rocca, M. L. ; Anthore, A. ; Lafarge, P. ; Lacroix J. C. JACS  (2012) 134(1), 154-157. Yan, H.; Bergren, A. J.; McCreery, R.; Della Rocca, M. L.; Martin, P.; Lafarge, P.; Lacroix, J.C. PNAS, (2013) 110, 14, 5326-5330.
An Electrochromic Device Based on Prussian Blue, Polymer Matrix Immobilized Viologen, and Ferrocene
Authors: Lu Hsin-Che , Kao Sheng-Yuan , Chang Ting-Hsiang , Kung Chung-Wei , Ho Kuo-Chuan
Published: February 2020

Viologens attracted much attention on electrochromic applications for its dramatic optical contrast between its dication state (bleached) and cation-radical state (colored). For the stability concern of eletrochromic device (ECD), solution-type viologen based ECD is necessary to avoid instability. Thus, gel-type electrolytes or immobilized viologens are preferred for solving the long-term instability. In this study, viologen was immobilized on the counter electrode of the ECD by a 3D polymer matrix based gel electrolyte. The polymer matrix with immobilized viologen was fabricated by UV-curing method. Prussian blue (PB) was used as the working electrode of this ECD for its good stability and high contrast ratio. A redox mediator ferrocene (Fc) was added into the ECD to balance the charge between the two electrodes. By doing so, the longer bleaching time of the PB/viologen based ECD (~10 s) was significantly shortened. The working principle of this ECD is sketched in Fig. 1. The PB/Fc/Immobilized viologen based ECD was operated between 1.2 V and -0.8 V. Under this potential bias, the ECD exhibited 61.6% transmittance change (DT%) at 615 nm, and a relatively fast bleaching time of 1.86 s compared to other known PB/viologen based ECD1, is shown in Fig. 2. The proposed ECD also shows a tunable multi-electrochromism among bleached (-0.8 V), open-circuit voltage (OCV, no potential bias) and colored states (1.2 V).

REFERENCES

(1) Kuo, T. H.; Hsu, C. Y.; Lee, K. M.; Ho, K. C. Sol. Energy Mater.  Sol. Cells 2009, 93, 1755.

Figure 1
Electrochromic Devices Using Prussian Blue Electrochromic Layer and HPC-Based Electrolyte
Authors: de Assis Lucas Marinho Nóbrega , dos Santos Leandra Pereira , Sabadini Rodrigo César , Pawlicka Agnieszka
Published: February 2020

Electrochromic devices (ECDs) have been studied for technological application. The ECDs with Prussian blue (PB)/hydroxypropyl cellulose (HPC) electrolyte/CeO2-TiO2 configuration were assembled and characterized. The films of PB were obtained by galvanostatic electrodeposition applying -0.45 μA for 300 s on ITO glass immersed in a solution of 0.05 M K3Fe(CN)6, 0.05 M FeCl3×6H2O and 0.05 M HCl. The electrolyte was prepared by mixing 0.3 g of HPC with 30 mL of acetone and addition of 10 % m/m of LiClO4. To this mixture, polyethyleneglycol (PEG) also was added. The ECDs were assembled by combining the HPC membrane between the counter-electrode consisting of CeO2-TiO2 and the Prussian Blue electrochromic layer. The devices were characterized by chronocoulometry coupled with UV-Vis transmittance, open circuit properties, and voltammetric cycling. The ECD was switched transparent and blue states applying -2.6 and 2.0 V, respectively. The charge density measurements showed an increase from ~-10 to -14 mC/cm2 when the potentials where applied for 15 s and 60 s, respectively. While this potential is applied, we observe a variation of transmittance in the UV-Vis spectra region, revealing that switching the ECD between -2.6 and 2.0 V for 15 s/15 s and 60 s/60 s resulted in 27 % and 42 % of difference between both states. Changes of transmittance in open circuit after applying a potential of -2.6 V for 15 s revealed a decrease from 50% to 27 % in 24 h. The cyclic voltammetry measurements performed at 100 and 200 mV/s showed better resolutions of the oxidation and reduction peaks for higher scan rates. Moreover, it was observed that after 1,000 cycles, the charge density decreased from -10 to -6.9 mC/cm2 and the difference of transmittance between colored and bleached state decreased from 41 to 30 %. The obtained results revealed that Prussian blue with HPC electrolyte are very promising materials for ECD applications. …
AA-CVD and ALD of Vanadium Pentoxide Thin Films for Electrochromic Applications
Authors: Kazadojev I I , O'Brien S , Louloudakis D , Katsarakis N , Koudoumas E , Vernardou D , Pemble M E , Povey I. M
Published: February 2020

Despite the high potential impact of vanadium based electrochromic devices, there are still many issues to be resolved before widespread market implementation can be realised. The current limitations arise from cost, the slow electrochemical kinetics and the poor cycling stability of vanadium pentoxide.

  In this work we initially employed aerosol assisted chemical vapor deposition (AACVD)  at 400°C in combination with a 600°C  anneal in air to grow films on fluorine doped tin dioxide (FTO) coated glass. The aerosol was generated from a methanolic solution of vanadyl (IV) acetlyacetonate using an ultrasonic humidifier and a nitrogen carrier gas. All annealed films were found to be monoclinic vanadium pentoxide but only the thicker films demonstrated a viable electrochemical response. The lack of response from the thinner films was proposed to be due to either the formation of an unstable interfacial oxide or non-uniform growth due to the aerosol method.  To determine the reasons for this limitation two experiments were performed, firstly the addition of a sub-nm alumina barrier layer by atomic layer deposition between the FTO and the V2O5 to inhibit the formation of any interfacial mixed oxide; Secondly, the low temperature growth of V2O5via atomic layer deposition using vanadyl triisopropoxide and oxygen as reagents.

  Initial indications are that the inclusion of an alumina barrier layer does not improve the uniformity of the thinner AACVD films. The ALD grown V2O5 films however demonstrated significant improvements in uniformity even at very high optical transparencies. These observations are discussed with reference to electron microscopy, UV-visible spectroscopy, XRD and the samples’ electrochemical responses.
Charge Transport and Structural Dynamics in Polymerized Ionic Liquids
Authors: Sangoro Joshua R , Paddison Stephen J.
Published: February 2020

Polymerized ionic liquids (PolyILs) are a novel class of functional polymers that combine the unique physicochemical properties of molecular ionic liquids with the outstanding mechanical characteristics of polymers [1-2]. This special mix of features might help to circumvent the key limitations of low molecular weight ionic liquids, namely, leakage and poor mechanical properties while utilizing their outstanding characteristics such as low vapor pressures, wide liquidus ranges, high thermal stability, high ionic conductivity, and wide electrochemical windows. PolyILs have shown remarkable advantages when employed in electrochemical devices such as dye-sensitized solar cells, lithium batteries, actuators, field-effect transistors, light emitting electrochemical cells, and electrochromic devices, among others. Despite their promising prospects as ideal polymer electrolytes, the role of molecular structure, morphology, and polymer dynamics on charge transport in PolyILs remains poorly understood.

According to classical theories, the self-diffusion and ion transport in electrolytes are controlled by structural relaxation. These approaches predict similar temperature dependence for the dc conductivity and structural dynamics. Although this prediction has been shown to hold reasonably well for low molecular weight aprotic ionic liquids [3], it fails for PolyILs [2]. In addition, the impact of morphology charge transport is not considered within the framework of these theories.

            In this talk, new insights obtained from both experimental studies employing broadband dielectric spectroscopy, temperature-modulated differential scanning calorimetry, and scattering techniques along with multiscale modeling investigations to elucidate charge transport and structural dynamics in a systematic series of polymerized ammonium- and imidazolium- based ionic liquids will be presented. Detailed analyses reveal strong decoupling of these processes in the PolyILs, implying failure of the classical theories in describing charge transport and molecular dynamics in these materials. In addition, the strong correlation observed between ionic conductivity from dielectric experiments and morphologies from scattering studies will be discussed.

References

1)      Mecerreyes, D. Progress in Polymer Science 2011, 36, 1629.

2)      Sangoro, J. R. et al., Soft Matter 2014, 10, 3536.

3)      Sangoro, J. R.; Kremer, F. Accounts of Chemical Research 2012, 45, 525; J. R. Sangoro, C. Iacob, A. Serghei, C. Friedrich, F. Kremer, Phys. Chem. Chem. Phys. 11, 913, (2009)
Rapid Detection of Fluoride in Potable Water
Authors: Chavali Ravi , Gunda Naga Siva , Naicker Selvaraj , Mitra Sushanta
Published: February 2020

The development of rapid, efficient and inexpensive methods for the detection of fluoride in potable water, has been gaining significant attention in the recent years, particularly in the developing countries. Fluoride, which is known to have antimicrobial properties, plays a significant role in human health. Fluoride helps in treating Osteoporosis and also has many beneficial effects in the maintenance of dental health. Fluoride is an additive in most of the toothpastes that are commercially available. Fluoride is also added to drinking water in limited concentrations owing to its properties in preventing and controlling dental Caries. The recommended level of fluoride in drinking water is 1.5 mg/L as directed by the World Health Organization (WHO). However, an increase in fluoride concentration above this level leads to dental and skeletal fluorosis. Excess exposure to fluoride is also known to induce many endocrine effects such as decreased thyroid function and Type II diabetes. Hence, fluoride levels in drinking water have to be regularly monitored and precautions need to be taken to control the increased levels of fluoride in drinking water. In view of the need for a simple cost effective method for the detection of fluoride ion, we considered the unique chemistry of fluoride ion towards the silyl ethers. The highly electronegative fluoride ion has been widely used to remove the silyl protective group from silyl ethers. In order to use this unique character of the reaction, we have synthesized a new water soluble colorless chemical sensor 7-O-tert.Butyldiphenylsilyl-4-methylcoumarin (SiC), which upon interaction with fluoride ions in water, releases fluorescent molecules that impart blue fluorescence to the solution. The blue fluorescence can be observed using simple hand held ultraviolet (UV) lamps. For quantification, the resultant fluorescence can be measured using simple and portable battery operated optical readers. SiC is extremely sensitive to fluoride and our results indicate that fluoride concentrations as low as 1 mmol/L can be accurately detected within a few seconds. This method is quite simple and rapid compared to the conventional methodologies. This method doesn’t warrant any special training and can be used by any unskilled person on site at the source of water and can also be easily incorporated into any multiplexed detection system.

Figure 1
(Keynote) Dielectrophoresis: Exploring the â€˜2nd Frontierâ€™ of Its Application in the Biomedical Sciences
Authors: Pethig Ronald
Published: February 2020

Dielectrophoresis (DEP) has been widely studied for its potential as a biomarker-free method of sorting cells based on their intrinsic dielectric properties [1-4]. Under appropriate experimental conditions the DEP frequency spectrum typically exhibited by a viable mammalian cell in suspension is characterized by two frequencies, f
xo1 and f
xo2. At these two characteristic frequencies the effective conductance and capacitance values of the cell exactly match those of the fluid it has displaced, and are commonly known as the DEP cross-over frequencies.

At low frequencies (<10 kHz) viable cells typically exhibit negative DEP and move away from electrodes, with the transition to positive DEP occurring at f
xo1 - where the cells move towards high field regions at the electrodes. The investigation, understanding (in terms of cell biology) and biomedical exploitation of this phenomenon can be considered to represent exploration of the ‘1st frontier of dielectrophoresis’. The results of this work, extending over more than 25 years, are now exploited in the form of various commercial devices for clinical and biomedical applications.  The status of this activity will be reviewed.

A transition back to negative DEP occurs at f
xo2 (~150 MHz). The factors that control the high frequency DEP cross-over at f
xo2 have only recently been explored, and the status and implications of this ‘2nd frontier of dielectrophoresis’ will also be reviewed in this presentation.

1. Pethig, R. Review Article - Dielectrophoresis: Status of the theory, technology, and applications. Biomicrofluidics  4, 022811 (2010).

2. Gagnon, Z.R. Cellular dielectrophoresis: Applications to the characterization, manipulation, separation and patterning of cells. Electrophoresis
32: 2466-2487 (2011).

3. Pethig, R. Dielectrophoresis: An assessment of its potential to aid the research and practice of drug discovery and delivery. Adv. Drug Deliv. Rev.
65: 1589-1599 (2013).

4. Gascoyne, P.R.C. and Shim, S. Isolation of circulating tumor cells by dielectrophoresis, Cancers
6: 545-579 (2014).

5. Chung, C., et al. Dielectrophoretic characterisation of mammalian cells above 100 MHz, J. Elec. Bioimpedance 2: 64-71 (2011)