bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrathin Pd Films on PBI-HFA Membranes for Selective Hydrogen Separation
Authors: Choi Sun Hee , Kim Da Hye , Yoon Chang Won , Ham Hyung Chul , Kim Hyoung-Juhn , Nam Suk Woo , Lim Tae Hoon , Han Jonghee
Published: February 2020

A polymeric gas separation membrane utilizing polybenzimidazole (PBI) based on 4,4'-(hexafluoroisopropylidene)bis(benzoic acid) (HFA) with an effective permeating area of 8.3 cm2 and a thickness of 30(± 2) mm was prepared and its gas permeation properties were investigated using H2, CO2, CO, and N2 at various temperatures ranging from 24 to 200 oC.  The PBI-HFA membrane not only exhibited excellent H2 permeability, but it also displayed superior gas separation performance particularly for H2/N2 and H2/CO2.  The permeation parameters for both permeability and selectivity ( PH2 and α(H2/N2); PH2 and α(H2/CO2)) obtained for the new material were found to surpass those reported by Robeson in 2008.  The gas permeation properties of the prepared membrane were found to be dependent on trans-membrane pressure difference as well as temperature.

A gas-tight palladium (Pd) membrane was fabricated on a PBI-HFA membrane by a vacuum electroless plating technique (VELP).  The thickness and effective permeating area of the Pd/PBI-HFA membrane were estimated in the range of 228–261 nm, and 8.3 cm2, respectively.  The Pd membrane prepared using the VELP technique had a more uniform microstructure than those manufactured by a conventional electroless plating method (CELP), with no delamination or agglomerated Pd particles observed.  The gas permeation properties of the prepared Pd membranes were evaluated using H2, N2, CO2, and CO as functions of:35 to 200 °C temperature, 0.4 to 0.8 MPa pressure difference, and membrane preparation methods including CELP, VELP, and VELP following a H2O2 surface treatment (H-VELP).  The Pd film fabricated by the H-VELP method showed superior performance, and proved to be impermeable to nitrogen as well as carbon monoxide.  Additionally, the Pd membranes prepared by H-VELP with a 228 nm thickness also demonstrated an excellent gas tightness with an infinite H2/N2 permselectivity, and its separation performance was above the Robeson’s 2008 upper bound.
Investigation of Zinc Whisker Growth from Electrodeposits Produced Using an Alkaline Non-Cyanide Electroplating Bath
Authors: Wu Liang
Published: February 2020

Metal whiskers are spontaneous growths protruding from metal surfaces. It has been observed that tin, zinc and cadmium surfaces, especially their electroplated coatings are prone to develop whiskers. Many electrical and electronic failures have been attributed to the presence of these small metallic filaments. During the past 70 years, researchers have been striving to address the problems induced by metal whisker growth. However, most research effort has been focused on tin whiskers, whilst very little attention was paid to reliability issues associated with zinc whiskers. Only a few previous studies have been carried out to investigate the growth mechanisms of zinc whiskers, but the results of such studies are often conflicting and there is, at present, no widely accepted growth mechanism in place.

The current study focuses on whisker growth from zinc coatings on mild steel substrates electrodeposited from a commercial alkaline non-cyanide electroplating bath. Experimental work has been undertaken to investigate the effect of deposition parameters and storage conditions on whisker growth, and also to understand the formation and growth mechanism. Scanning electron microscope (SEM), focused ion beam (FIB), energy dispersive x-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) have been used to characterise the as-deposited structure of the zinc coatings and to evaluate whisker growth.

Analysis showed that, for samples stored at room temperature, whiskers were present on samples deposited at current densities in the range of 20 – 50 mA cm-2 within 4 weeks of electroplating. However, electroplating at low current densities significantly reduced whisker growth and no whiskers were observed on samples deposited at 5 mA cm-2 after 12 months. Also, it was found that short period of post-electroplating heat treatment at high temperatures markedly reduces zinc whisker growth. In terms of the mechanisms for zinc whisker growth, our experimental data indicated that hydrogen evolution reaction that occurs on the steel, due to the low overpotential, was closely associated with zinc whisker growth. In addition, recrystallisation of the as-deposited columnar structure occurred at the whisker root.

Figure 1
Structural and Optical Characterization of Electrodeposited Black Chrome-Graphite Encapsulated FeCo Nanoparticles Composite Solar Selective Coatings
Authors: Harinipriya S , Usmani Belal
Published: February 2020

Abstract

      Black Chrome-graphite encapsulated FeCo nanoparticles (BC-GE FeCo NPs) composite based solar selective coatings were prepared on substrates such as stainless–steel, Cu and Ni-coated Cu employing electrodeposition technique. Electrodeposition was done by addition of three different weight proportions of GE FeCo NPs (0.025, 0.05, and 0.1) in the electrolyte bath. X-ray diffraction, Atomic Force Microscopy, UV-Visible and FTIR spectroscopy were used to characterize the structural and optical properties of these coatings. The major content of the deposited film is contributed by Cr (ICDD 74-7045), Fe-Cr (ICDD 34-0396), Fe2AlCr (ICDD 54-0387) and FeCr0.29Ni0.16C0.06 (ICDD 33-0397) as deduced from XRD. Spectral reflectance of the selective surface is observed to be low in UV-Visible region even after the addition of GE FeCo NPs. The low surface reflectance in the near infrared region due to the addition of GE FeCo NPs indicates increase in the absorptance of the selective surface in near infrared region. Atomic Force Microscopy indicated that film smoothness increases and grain size decreases with decrease in the weight percentage of GE FeCo NPs. Hardness and Young’s modulus were found to decrease with decreasing weight percentage of GE FeCo NPs.

Keywords:

Electrodeposition; Black Chrome; Graphite encapsulated FeCo NPs, solar selective coatings
Novel Titanium Electrowinning Process Using Specialized Segmented Diaphragms
Authors: Hsueh Chang-Jung , Antloga Mirko , Virnelson Craig , Landau Uziel , DeGuire Mark , Akolkar Rohan
Published: February 2020

Titanium metal, with high strength-to-weight ratio, is an important structural metal for aerospace and defense applications. However, titanium is expensive largely due to the energy-intensive nature of the Kroll process conventionally used for titanium extraction from ore. At Case Western Reserve University, we are developing an alternative low-cost titanium extraction process based on electrolysis of titanium salts from halide melts. The key innovation in our titanium electrowinning process is a specialized diaphragm stack, which separates the catholyte and anolyte compartments of the cell. The diaphragm stack eliminates extraneous reactions in the electrowinning cell, enabling stable and energy-efficient electrolytic extraction of high-purity titanium sponge. In this talk, we will outline the fundamental electrochemical principles governing the operation of this novel electrowinning process. We will also present proof-of-concept results collected on a prototype electrowinning reactor, which show feasibility of this revolutionary electrolytic titanium extraction approach. Broader impacts of our electrowinning approach to other multivalent metal systems will be discussed.

Figure 1. Schematic of our titanium electrowinning cell, showing a stack of thin diaphragm separators, each with thickness L. Diaphragm thickness is selected so that the potential drop across the diaphragm is lower than the thermodynamic onset potential for bipolar reactions. This design eliminates extraneous bipolar reactions in the cell, enabling stable cell voltage [as shown in (a)] and efficient titanium electrowinning [as shown in (b)].

Figure 1
Recovery of Rare Earth Metals By Electrodeposition from Ionic Liquids
Authors: Stevenson Keith J. , Redman Daniel
Published: February 2020

Rare earth elements have become increasingly important to modern life as they are used in nickel-hydride batteries in current hybrid vehicles, as phosphors in fluorescent and LED lighting, and magnets used in computer hard disks and various automotive subsystems.1 In recent years the prices of the many of these elements have increased drastically due to reduced exports.2 Developing recycling methods for these elements is becoming a necessity for meeting future demands. Electrodeposition is a low-cost technique that could prove exceedingly useful to recover these elements from various sources. Traditional aqueous electrolytes are unsuitable for the electrodeposition of rare earth elements because they lie outside the electrochemical window of stability. This requires alternative electrolytes. Ionic liquids have received considerable attention as alternative electrolytes for electrodeposition due to several of their interesting chemical and physical properties. The large electrochemical windows of ionic liquids allow for the electrodeposition of electropositive elements, such as rare earth metals. In addition, the low volatility and high thermal stability of these solvents allows higher temperatures to be used in electrochemical processes.

Recently, our group has used ionic liquids to electrodeposit various elements and compounds, including Ge, Se, GeSx, and MoSx.
3,4,5 This was done by finding and synthesizing appropriate elemental precursors and ionic liquids for electrochemical deposition. This same strategy has been employed for the electrodeposition on rare earth metals. A number of precursors have been synthesized and investigated for electrodeposition. The effect of temperature on the electrodeposition was investigated. In addition, several ionic liquids were employed to investigate the effect of the cation and anion on the deposits.

References

1.) Van Gosen, B.S.; Verplanck, P.L.; Long, K.R.; Gambogi, J.; Seal II, R.R. The Rare-Earth Elements – Vital to Modern Technologies and Lifestyles. United States Geological Survey, USGS Mineral Resources Program. Reston, VA. November 2014.

2.) Rare Earth Elements: A Review of Production, Processing, Recycling, and Associated Environmental Issues. Environmental Protection Agency, National Risk Management Research Laboratory. Cincinnati, OH. December 2012.

3.) Murugesan, S.; Kearns, P.; Stevenson, K.J. Langmuir. 2012, 28(13), 5513-5517.

4.) Murugesan, S.; Akkineni, A.; Chou, B.P.; Glaz, M.S.; Vanden Bout, D.A.; Stevenson, K.J. ACS Nano. 2013, 7(9), 8199-8205.

5.) Redman, D.W.; Murugesan, S.; Stevenson, K.J. Langmuir. 2014, 30, 418-425.
In-Situ Nanoscale Investigation of Calcium Sulfate Nanoparticles Immersed in Deionized Water
Authors: He Kun , Nie Anmin , Megaridis Constantine , Tolou Shokuhfar Tolou , Lu Yu-Peng , Shahbzian-Yassar Reza
Published: February 2020

It is very common to synthesize and use nanomaterials nowadays. Because most nanomaterials are prepared in the laboratory, especially for those synthesized using chemical methods in aqueous environments, it is difficult to observe and understand the reaction process accurately. Herein, employing transmission electron microscopy (TEM), aberration-corrected scanning transmission electron microscopy (STEM) and liquid holder techniques, we investigate the reaction of calcium sulfate with water. Using TEM, we obtained clear evidence that the morphology and microstructure of calcium sulfate hemihydrate (Bassanite, CaSO4•0.5H2O) and calcium sulfate dihydrate (Gypsum, CaSO4•2H2O) are both changed when encountering deionized (DI) water. Bassanite reacts with water to form gypsum, with the microstructure changing from powder to nanowires with needle or rod shape. When gypsum reacts with DI water, the microstructure changes to nanowires without any compositional or crystallographic variation, as confirmed by electron diffraction. Using a liquid holder, the structure transformation of the gypsum is tracked and recorded in real time. Some of the gypsum powders are observed to dissolve in DI water. The dissolution of nanowires that formed during reaction of gypsum powder and water starts when the particles are exposed to the electron beam.
Mechanically Stable Poly(aryl ether) Anion Exchange Membranes for Alkaline Applications
Authors: Wang Lihui , Arges Christopher George , Jung Min-suk , Ramani Vijay K
Published: February 2020

The alkaline stability of poly(aryl ether) backbones in anion exchange polymer electrolyte membranes (AEMs) featuring quaternary benzyl N, N- dimethylhexylammmonium (DMH+) and trimethylammonium (TMA+) groups were investigated in poly(2,6-dimethyl 1,4-phenylene) oxide (PPO) and Udel® polysulfone (PSF) polymers. Previous works have demonstrated that quaternary ammonium and phosphonium groups trigger polymer backbone degradation in commercially available poly(aryl ethers) despite the non-cation functionalized polymers being resilient in alkaline media. Recently, DMH+ cations in PPO was shown to eliminate cation triggered backbone degradation, but it was unknown whether or not implementation of this cation would also eliminate cation triggered backbone degradation in PSF. Herein, we demonstrate that the electron withdrawing or donating character in the poly(aryl ether) backbone, ultimately decides whether or not the prepared AEMs will become brittle in alkaline media. For instance, DMH+ at the benzyl position in Udel® PSF does not mitigate cation triggered backbone degradation. PPO backbones functionalized with bromine at the aryl position in addition to having DMH+ cations did not prevent cation triggered backbone degradation either. Mitigation of cation triggered backbone degradation was only achieved when electron withdrawing substituents (not including the cation), such as sulfone or bromine, were not incorporated in the polymer backbone. PPO AEMs prepared through chloromethylation, rather than free radical bromination, were resistant to backbone hydrolysis in alkaline media because each cation functionalized repeat unit had two electron donating methyl groups rather than a single methyl group. In closing, some design rules will be presented for preparing mechanically stable poly(aryl ether) AEMs from low cost, commercially available polymers for alkaline applications.
Production of Hydrogen and Chemicals from the Electroreforming of Renewable Alcohols
Authors: Miller Hamish Andrew , Vizza Francesco , Bevilacqua Manuela , Lavacchi Alessandro , Bellini Marco , Chen Yanxin , Wang Lianqin
Published: February 2020

The exploitation of hydrogen in fuel cells has been widely advocated as the ideal solution for an energetically and environmentally sustainable future for transportation. An essential part of such a solution will be the use of renewable energy resources (photovoltaics, wind, wave power etc.) in conjunction with water electrolysis to provide a “zero emission” source of hydrogen. Water electrolysis is a well-established commercial technology; nevertheless its practical application for the mass production of hydrogen is still limited. Costly electrical energy consumption is certainly one of the major factors hampering the diffusion of electrolysis.

Both Alkaline and PEM electrolyzers exploit water splitting, evolving hydrogen at the cathode and oxygen at the anode. The standard reaction potential for this process is 1.23 V, meaning that water splitting is a strongly uphill reaction. In practice to get current densities in the range of 1 A cm-2 the cell potential usually ranges between 1.6 and 2 V. Considering 1.8 V as a reasonable average, we conclude that 68.3% of the energy input is consumed by thermodynamics, while kinetic factors account for only 31.7%.

Replacing anodic oxygen evolution with the oxidation of much more readily oxidizable species leads to a significant reduction of the potential required to produce hydrogen. Following this strategy compounds such as ammonia, methanol, ethanol, glycerol and urea have been recently tested. These electrolytic processes that lead also to the concomitant generation of chemicals at the anode and hydrogen at the cathode are often indicated as “Electrochemical Reforming”.

While undoubtedly promising, these approaches suffer the limitation of delivering current densities well below 1 A cm-2, and as such are unpractical for technological exploitation.

Here we propose to overcome such limitations using a range of nanostructured anode electrocatalysts which combine fast electrode kinetics for alcohol electrooxidation with tunable selectivity for the formation of partially oxidised intermediates of industrial interest.

We demonstrate that electrochemical reforming can occur at current densities comparable to that of state of the art PEM water electrolysis. Furthermore we report a net energy analysis of hydrogen production by bio-ethanol electrochemical reforming. Particularly, we define the energy cost break-even point, expressed in terms of the Energy Return of the Invested Energy of bio-ethanol production, at which electrochemical reforming becomes more energy efficient than water electrolysis.

Figure.
Electrochemical reforming and water electrolysis comparison. Schematic of (A) PEM water electrolysis and (B) anion exchange membrane electrochemical reforming.

Figure 1
The P2D Model of a Lithium Cell with Vacancy Effect in Solid-State Diffusion
Authors: Lin Chyun-Yaw , Yen Shi-Chern
Published: February 2020

The modeling of lithium ion battery considers transport phenomenon and porous electrode kinetics such as solid or liquid state diffusion, migration, and kinetics of electrode reaction. The intercalation/deintercalation process of lithium ion at particle surface is the key to understand the charge-discharge phenomenon of lithium battery. The solid state diffusion model with a two-component diffusion term can be reduced to a simple nonlinear diffusion form and applied to the behavior of single electrode particle. The nonlinear diffusion equation shows the vacancy effect in the solid-state diffusion of the particles inside the cell is illustrated in the nonlinear diffusion equation. The simulated results of voltage versus capacity obtained at discharge rate below 0.6C agree well with the experimental data.
Electropolishing of Nb for Superconducting Radio-Frequency (SRF) Cavities
Authors: Tian Hui , Reece Charlie E
Published: February 2020

Niobium superconducting radio-frequency (SRF) cavities are widely used in modern particle accelerators, because of higher operating efficiency than normal-conducting cavities made of copper. Since the superconducting RF current flows in a surface layer about 40 nm deep, a set of preparation techniques have been developed over the years to assure good superconducting properties of the surface layer.  Electropolishing (EP) is the technique of choice being developed for high–field SRF cavities, which result in a typical surface roughness of about 0.1 μm.  Currently, the 1:10 volume ratio HF (49%) and H2SO4 (96%) electrolyte was widely used for high field SRF cavity production. Electrochemical impedance spectroscopy (EIS) and related techniques point to the electropolishing mechanism of Nb in a sulfuric and hydrofluoric acid electrolyte of controlled by a compact surface salt film under F- diffusion-limited mass transport control. In addition, data indicates that above 25oC electrode kinetics become competitive with the mass transfer current limitation and increase dramatically with temperature. These findings are guiding the optimization of EP process parameters for achieving controlled, reproducible and uniform nano-smoothes surface finishing for SRF cavities.  The problem with using HF is that it is dangerous both to people and to the environment. Alternative approaches recently were developed, such pulse reverse EP which catholic pulse is used to remove the oxide layer rather than HF, and results are promising.  Also ionic solution such as acid-free vitamin B4 electrolyte has been introduced and has shown promising results. Those results will be briefly introduced here.
20 Years of Corrosion Sensing and Microvisualization of Corrosion Processes
Authors: Smyrl William H
Published: February 2020

Localized corrosion processes continue to be a major cause for degradation failure in damaging fluids.  Initiation stages of response remain difficult to characterize, arising in part because of the difficulty in being able to predict the location and onset of the attack.  Propagation stages are seldom constant but change with time due to competing processes of dissolution and product deposition at the corrosion sites.  The progress of the attack changes the local environmental concentrations which are especially important at buried interfaces that are isolated from bulk conditions.  The present paper will describe some of the recent advances in optical, electrochemical, and microscopy that are directed at providing local information on “precursor sites” and vulnerable areas on metal and covering oxide surfaces.  Previous studies of coupled reactions on reactive surfaces provide a general basis for the work to be described here.

The objectives of the experimental techniques are: (1) to measure the local corrosion rate; (2) to locate breakdown sites, and; (3) to study the fundamental properties of passive films and how they are related to the stability of the films and damaging environments.  The latter is of particular interest since it will allow one to predict why a particular precursor site is more vulnerable to breakdown as compared to neighboring areas.

In locating precursor sites, entire regions of the corroding surface can be imaged concurrently or point-by-point using scanned probe or beam.  Both classes will be discussed with their capabilities.  The techniques used in our laboratory are: (1) the Quartz Crystal Microbalance (QCM); (2) Optical Fiber Micromirrors (FOP); (3) Confocal Laser Scanning Microscopy (CLSM); (4) Photoelectrochemical Microscopy (PEM); (5) Scanning Electrochemical Microscopy (SECM); (6) Scanning Photoelectrochemical and Electrochemical Microscopy (SPECM); (7) Near Field Scanning Optical and Spectroscopic Microscopy (NSOSM).  The experimental setup for each and the capability help to reveal the advantages that are offered by them.

Optical sensing by the QCM and optical fiber micromirrors have been used to measure corrosion rates, with sensitivity of fractions of an atomic layer.  Similar to them but with the capability to image a larger reactive surface is the CLSM to determine local attack rates at various surface sites.  The NSOSM is valuable to obtain both vertical and lateral super resolution images of reacting surfaces of about 60 nanometers. The techniques support the development of miniature corrosion sensors devoted to monitoring reactive surfaces in remote and occluded regions, coupled with wireless transmission.
Enhanced Surface Finishing of Tungsten Carbide By Using Organic Additives
Authors: Schneider Michael , Schubert Nora , Simunkova Lenka , Michaelis Alexander
Published: February 2020

The mechanical machining and finishing of cemented carbides is associated with high abrasive wear of cutting tools. Electrochemical Machining (ECM) is the technical application of high rate metal dissolution and well established for steels and several non –ferrous metals. ECM is a priory free of mechanical tool wear. Recently the authors investigated the high rate dissolution of cemented carbides in ammonia containing alkaline electrolytes [1]. The electrolyte system is suitable for ECM of tungsten carbide as well as cobalt. A homogenous dissolution of the compound material was achieved. In industrial practice, Electrochemical Machining is used to realize high surface quality of work pieces. The existence of anodic films during the machining step is important in controlling the texture of the machined surface obtained [2]. If the dissolution process is controlled by material transport through a film of compact dissolution intermediate, precipitated products [3] or viscous product layer [4] the surface will occurs bright and shiny. The formation of viscous surface layers can be enhanced by surface active organic additives of the electrolyte [5]. In the present work the authors investigated the effect of different solvents on the surface roughness during ECM of tungsten carbide. The electrochemical experiments were carried out in a channel flow cell. Firstly, an aqueous solution containing 2M ammonia and 1.5M sodium nitrate was used as reference electrolyte. In a second step ethanol and glycol, respectively, were added. Both additives change the conductivity as well as the viscosity of the electrolyte. All samples were investigated by SEM after the ECM experiments. A decreasing surface roughness in the order of water, water/ethanol and water/glycol was achieved. A quantitative evaluation will be given by using laser scanning microscopy.

References

[1] N. Schubert, M. Schneider, A. Michaelis, Electrochemical Machining of cemented carbides, Int. J. Refractory Metals and Hard Materials 47 (2014) 54-60

[2]  J. Bannard, Electrochemical Machining, J. Appl. Electrochem. 7 (1977) 1-29.

[3]  T.P. Hoar, T.W. Farthing, Solid Films on Electropolishing Anodes, Nature 169 (1952) 324–325.

[4]  P. A. Jacquet, The Electrolytic Polishing of Metallic Surfaces, Metal Finishing Vol. 47 (1949) 83.

[5]  J. Bannard, The effect of a surface-active additive on the dissolution efficiency and surface finish in ECM, J. Appl. Electrochem. 7 (1977) 189–195.
(Invited) Design of Polymeric Semiconductors for Transistor Applications
Authors: Heeney Martin
Published: February 2020

In this presentation I will discuss a number of strategies to control backbone planarity in conjugated polymers. I will show how the control of backbone planarity influences solid state microstructure, as well as the optoelectronic properties. The influence of backbone planarity of transistor performance in a number of different device geometries will be reported.
(Invited) Routes to Stabilization of Linearly-Fused Aromatics
Authors: Anthony John , Liyanage Thilanga
Published: February 2020

Linearly-fused aromatic hydrocarbons have remarkable electronic properties that change substantially as the length of the fused ring chain is increased. Unfortunately, this increased length brings with it worsened solubility and dramatically decreased environmental stability. A number of strategies have been explored to combat these issues. In the case of simple functionalization, the decrease in stability and solubility upon increased chromophore length can be mitigated slightly, but as the materials grow beyond 6 or 7 linearly fused rings, the substituents become so numerous and bulky that intermolecular aromatic-aromatic contacts are eliminated entirely, precluding semiconductor applications for these materials. An alternative approach substitutes strategic carbocyclic rings with heterocycles; these hetero-acenes do show improved stability up to a point, but again once the ~7-ringed systems have been attained, the same problems of solubility and stability again become an issue. Further complicating matters in these systems, issues of isomerism due to the limited synthetic routes to these compounds become an issue. It is becoming clear that while isomeric mixtures yield excellent semiconductor performance, the pure isomers exhibit fewer destructive phase transitions along with slight increases in performance. An alternative strategy involves the off-linear fusion of aromatic rings. In these carbocyclic systems, off-linear fusion allows the construction of linearly-fused aromatic systems of unprecedented length, while maintaining excellent stability and tunable solubility. The off-linear ring fusions allow for additional functionalization to tune the chromophore's optical and electronic properties, and yield the potential to substantially increase intermolecular overlap. The synthesis, structural, and electronic characterization of these new fused-ring chromophores will be discussed.
(Invited) Thin Films of Eumelanin Pigment: Charge Carrier Transport, Ion Storage, and Interaction with Metal Electrodes
Authors: Kumar Prajwal , Di Mauro Eduardo , Wuensche Julia , Santato Clara
Published: February 2020

The ubiquitous natural pigment eumelanin is widely studied for its photoprotective, thermoregulating, free-radical scavenging, and anti-oxidant functions in the human body. Recently, eumelanin received increased attention for potential applications in organic bioelectronics due to its unique set of physicochemical properties including strong broad-band UV-Vis absorption, metal chelation properties, and potentially mixed electronic-ionic conduction in a hydrated state [1,2]. To further explore the use of eumelanin in organic bioelectronic devices, the properties of eumelanin thin films interfaced with device components such as metal electrodes need to be investigated in presence of water and ionic species. A good understanding of the interaction of eumelanin with different metal electrodes is also essential to study the intrinsic charge transport properties of eumelanin films, which are still largely undiscovered.

We characterized eumelanin films grown on substrates patterned with gold, platinum, and palladium hydride electrodes using hydration-dependent transient electrical current and atomic force microscopy measurements. We discovered an electrochemical interaction among metal-chelating catechol groups of hydrated eumelanin, Cl- traces in the eumelanin material and Au electrodes, assumed to be electrochemically stable in previously published works on the electrical properties of eumelanin. This interaction leads to the growth of highly conductive Au-eumelanin dendrites between the electrodes, ultimately leading to sudden resistive changes of the sample. This phenomenon suggests new possibilities for biocompatible memory devices and has to be taken into account when integrating eumelanin-like materials in electronic devices [3].

Electrical characterization of eumelanin films interfaced with ion-blocking Pt and proton-transparent electrodes [4] complemented by cyclic voltammetry and  impedance spectroscopy measurements give new insights into the charge transport properties of eumelanin films. Our results indicate the presence of protonic currents in eumelanin thin films, increasing with sample hydration, and cannot exclude the presence of electronic currents. These results support recently published data obtained by spectroscopic measurements on eumelanin pellets [2] and underline the attractiveness of eumelanin films for applications at the interface of electronics and biology.

[1] M. D’Ischia et al., Angew. Chem. Int. Edit. 48, 3914 (2009).

[2] A. B. Mostert et al., Proc. Natl. Acad. Sci. 109, 8943 (2012).

[3] J. Wünsche et al., Adv. Funct. Mater. 23, 5569 (2013).

[4] C. Zhong, Y. Deng, A. F. Roudsari, A. Kapetanovic, M. P. Anantram, M. Rolandi, Nat. Commun. 2, 476 (2011).
(Invited) Importance of Interface Engineering in Organic Spintronics
Authors: Jang Hyuk-Jae , Pookpanratana Sujitra , Lee Jun-Sik , Kline R. Joseph , Basham James I. , Gundlach David J. , Hacker Christina A. , Kirillov Oleg A. , Jurchescu Oana D , Richter Curt A.
Published: February 2020

Organic semiconductors provide a route to revolutionary changes in many areas of device technology with their unique electronic properties and functionalities, which can be easily tailored by chemical synthesis and molecular engineering.[1] In particular, an emerging research area referred to as organic spintronics has initiated a range of device concepts by exploiting spin-related properties in organic semiconductors.[2]

Currently, there are two major interests in organic spintronics technology.[3] One of them is to realize a system enabling the injection/transport/detection of spin polarized charge carriers in organic semiconductors.[3] The other one is to understand and explore the magnetic field effects (MFEs) of organic semiconductors for the development and improvement of organic-based devices such as organic light emitting diodes and magnetic sensors.[3]

It has been known that in organic-based devices, the interfaces between active materials play a critical role in their performance and functionality because the interfaces greatly affect the injection/transport/extraction of charge carriers in organic semiconductors.[4] Recent findings suggest that the interface engineering is also very crucial in organic spintronics technology such as enabling efficient spin-polarized charge carrier injection and tuning of organic MFEs.[5-7] 

In this presentation, we will discuss our efforts towards the realization of efficient spin injection and transport in organic semiconductors as well as the modification of organic MFEs by interface engineering. We experimentally show the importance of band alignment between a metal electrode and an organic semiconductor at their interface for efficient spin injection/detection.[6] We will also show how one can utilize a molecular self-assembled monolayer by inserting it between a metal electrode and an organic semiconductor in order to change the characteristics of spin injection into an organic semiconductor from a ferromagnetic metal as well as in order to tune the organic MFEs.[7]

 

1.    Editorial, Nat. Mater.
12, 591 (2013).

2.    C. Boehme and J. M. Lupton, Nat. Nano.
8, 612 (2013).

3.    W. Wagemans, et al., SPIN, 1, 93 (2011).

4.    H. Ma, et al., Adv. Funct. Mater. 20, 1371 (2010).

5.    S. Sanvito, Nat. Phys. 6, 562 (2010).

6.    H.-J. Jang, et al., Appl. Phys. Lett. 101, 102412 (2012).

7.    H.-J. Jang, et al., ACS Nano
8, 7192 (2014).
(Invited) Ionic Liquid-Gated PCBM Transistors: Pushing the Limit of the Doping in Organic Transistors
Authors: Sayago Jonathan , Patel Mitesh , Cicoira Fabio , Soavi Francesca , Santato Clara
Published: February 2020

Electrolyte-gated (EG) organic transistors are interesting for their low voltage operation and versatile cost-effective fabrication and printability.1 Room temperature ionic liquids (RTILs) are attractive as gating media for their chemico-physical properties, such as ionic conductivity up to 10 mS·cm-1, negligible volatility, and electrochemical stability windows up to ca 5 V.2 The availability of RTILs with different molecular structures gives the possibility to control specifically the interactions between the ions constituting the RTIL and the channel material in view of an optimized doping. Clear guidelines to establish an effective doping as a function of the ions constituting the electrolyte, are yet to be established. In this work we report on EG transistors with phenyl-C61-butyric acid methyl ester (PCBM), as the channel material, and room temperature ionic liquids based on bis(trifluoromethylsulfonyl)imide ([TFSI]) anion, as the gating medium. The cations constituting the ionic liquids were 1-ethyl-3-methylimidazolium ([EMIM]), 1-butyl-3-methylimidazolium ([BMIM]) or 1-butyl-1-methylpyrrolidinium ([PYR14]). Electrical measurements show that the cation strongly affects the behavior of n-type EG PCBM transistors. The higher charge carrier mobility, lower on/off ratio and faster response time obtained with [PYR14][TFSI]-gated transistors, suggests lower cation incorporation into the PCBM channel material. [EMIM][TFSI]- and [BMIM][TFSI]-gated PCBM transistors featured similar electric behavior, coherent with the similar molecular structure of the cations.

1. S. H. Kim et al., Adv.
Mater. Weinheim, 25, 1822–1846 (2013).

2. M. Galiński, A. Lewandowski, and I. Stępniak, Electrochim. Acta, 51, 5567 (2006).
Pvdf Based Gel Polymer Electrolyte for Applications in Flexible Devices
Authors: Oriani Andrea Vittorio , Cojocaru Paula , Spreafico Marco Alberto , Apostolo Marco , Triulzi Francesco , Magagnin Luca
Published: February 2020

In the last years growing interest is being focused on the production of flexible devices including electronics, organic solar cells and displays. Considering specific applications where electrochemical processes take place, e.g. Die Sensitized Solar Cells (DSSC), an electrolyte is needed between the electrodes to allow ion diffusion and redox reactions.  In this case, relevant issues are related to the fluid, namely liquid, nature of traditional electrolytes. Considering this characteristic, the limitation is twofold: on one hand, considering large area devices, for example DSSC integrated in the façade of buildings, electrolyte flow from the top to the bottom of the system can occur. On the other hand electrolyte leakage may occur in the presence of defects or damage, with significant environmental safety concerns. Finally, considering flexible devices, issues are relative to electrolyte flow during bending, due to pressure gradients inside the device. It’s therefore clear that most of these limitations could be overcome using electrolytes with good ion transport properties but also higher resistance to flow with respect to traditional systems, i.e. electrolytes behaving as much as solids when subjected to external loads/strains. For this reason a process is proposed that allows producing a PVdF network by sol-gel method, this is soaked with electrolyte and allows maintaining good ion conductivity and excellent transparency while highly reducing issues related to leakage and electrolyte flow inside between the electrodes of the device.
(Invited) The Effect of Molecular Dynamics on Charge Transport in Organic Semiconductors
Authors: Jurchescu Oana D
Published: February 2020

Organic semiconductors are studied extensively for their incorporation in next generation large-area, low-weight flexible optoelectronic applications. Librational motion is ubiquitous in such materials; this motion, however, has been difficult to connect with experimental observations of a material’s electronic properties. Here we present the effect of libration on charge transport in monomolecular compounds and binary charge-transfer (CT) complexes through a combined experimental and theoretical approach. The case study of trans-stilbene (STB) and its CTs with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (STB:F4TCNQ) and 7,7,8,8-tetracyanoquinodimethane (STB:TCNQ) will be discussed. It will be shown that the change in amplitude of the torsional oscillation (libration) of the double bond connecting the C7 and C7a carbons in the stilbene molecule results in a crossover from thermally activated to a temperature-independent charge transport. This pedal-like (crankshaft) motion, is responsible for inter-conversion between the two possible conformers. At low temperature the libration amplitude is not sufficiently large to mediate this rotation, generating thermodynamic non-equilibrium states and resulting in freezing in of orientational disorder. The transport can take place only via tunneling, therefore being temperature-independent. At higher temperatures, when inter-conversion motion is fast, a transition to temperature-activated hopping transport occurs.

The following people contributed to this work: K. P. Goetz, A. Fonari, D. Vermeulen, P. Hu, H. Jiang, P. J. Diemer, J. W. Ward, M. E. Payne, C. S. Day, C. Kloc, V. Coropceanu, L.E. McNeil, and O. D. Jurchescu.
Chemical Nature and Control of High-k Dielectric/III-V Interfaces
Authors: Cabrera Wilfredo J , Halls Mathew D. , Chabal Yves J
Published: February 2020

III-V semiconductor surfaces are notoriously difficult to control as their native oxides are not stable. For the growth of high-k dielectric, interface passivation layers have recently been incorporated into InP/high-k dielectric stacks using different approaches, including atomic layer deposition (ALD) to grow thin aluminum silicate layers and deposition of a buffer silicon layer prior to aluminum oxide growth. While beneficial effects have been observed on the interface electrical properties, little is known about the chemical composition and formation mechanisms of these interfacial layers. Futhermore, there is growing evidence that elemental diffusion from the substrate or its oxide may impair electrical properties. There is therefore a need for chemical characterization of surfaces and interfaces under typical processing conditions.

Combined in-situ IR measurements and ab initio calculations of InP(100) surfaces reveal that a mild annealing (~300oC) typically needed for atomic layer deposition leads to marked chemical changes at the surface, with the formation of surface InPO4-species (P=O and P-OH species). The initial interaction of trimethylaluminum with this hydrophosphonated surface is characterized by the formation of P-O-Al and dative bonding between Al and the oxygen atom of neighboring P=O moiety, requiring several cycles to complete this interfacial layer. This chemical interface transformation and subsequent impact on the quality of an ALD-grown Al2O3 layer can be substantially altered by silicon deposition using trisilane exposure. Comparison of several silicon precursors [SiCl4, Si(OCH3)4 and Si3H6] by in-situ spectroscopy reveals that Si3H6 best reacts with the hydrophosphonate-terminated surface and reduces the native oxide by forming a SiOx layer that prevents interaction of TMA with the native oxide, leading to a denser Al2O3  layer. Deposition of a thin aluminum silicate barrier layer by ALD is also investigated, and Al from TMA found to play a key role in activating silicon precursors. However, TMA reaction with Si-modified surfaces leads to efficient methyl transfer to Si, a source of interfacial carbon contamination.

Finally, mass transport is examined in HfO2/In0.53Ga0.47As stacks.  Diffusion of indium through HfO2 is observed after post deposition annealing in N2 or forming gas environments by low energy ion scattering and X-ray photo electron spectroscopy, and found to be consistent with changes in interface layer thickness observed by transmission electron microscopy. Prior to post processing, elemental arsenic is detected in the form of arsenic oxide at the surface of ALD-grown HfO2 and is desorbed upon annealing at 350oC. Indium diffusion occurring upon annealing, resulting in a reduction of the interfacial layer thickness and a potential densification of HfO2, is confirmed by an increase in capacitance.
(Invited) Fabrication and Characterization of Silicon Microwire Anodes by Electrochemical Etching Techniques
Authors: Nöhren Sandra , Quiroga-González Enrique , Carstensen Jürgen , Föll Helmut
Published: February 2020

Silicon with a gravimetrical capacity of 4200 mAh/g for Li storage is optimal for Li ion battery anodes. Unfortunately neither bulk silicon nor silicon micro particles (mixed in pastes together with e.g. carbon black, CNT's) up to now allowed for stable battery anodes. In contrast highly ordered silicon microwire arrays galvanically connected to a Cu electrode shows good cycling stability, combined with nearly optimal gravimetric capacity taking into account the strong expansion of silicon when loaded with Li. In this paper several aspects of the completely (electro-) chemical process sequence of the Si microwire anode will be discussed including macropore ethching with sophisticated pore diameter modulation (cf. Fig. 1), post etching for wire formation and galvanic Cu deposition for optimal embedding of the Si microwires into a Cu foil electrode [1, 2].

FFT impedance (FFT-IS) analysis has been used for the in-situ characterization and optimization as well of the electrochemical process steps as for the performance of the battery anode. Several examples will be presented. Optimal cycling stability has been found for a Li charging up to 75% of the full capacitance while the wire length can be tuned to capacitance per area of the cathode, e.g. microwires with a length of 70 µm ,with an active loading of 1.35 mg/cm2show a stable capacity of 3150 mAh/g for more than 100 cycles [1].

Especially the comparison of FFT-IS data for standard paste electrodes containing silicon particles and for the silicon microwire anodes clearly indicates that the highly symmetric (closed packed) arrangement of the microwires increases the cycling stability: when charging the anode the expansion of hexagonally closed packed silicon wires leads to a mechanical stabilization between the wires. In addition no passive material is forced to move and the electrical contact to the Cu electrode is not affected while the silicon wires enlarge in size. Further improvements for silicon containing anodes will be discussed.

[1]      E. Quiroga-González, J. Carstensen, and H. Föll, Electrochim. Acta 101, 93 (2013).

[2]      E. Quiroga-González, J. Carstensen, and H. Föll, Materials 6, 626 (2013).

Figure 1
(Invited) Investigation of the Si/TiO2/Electrolyte Interface Using Operando Tender X-ray Photoelectron Spectroscopy
Authors: Lichterman Michael Frankston , Richter Matthias Hermann , Hu Shu , Crumlin Ethan J , Axnanda S , Favaro Marco , Drisdell Walter , Hussain Z , Mayer Thomas , Brunschwig Bruce , Lewis Nathan S. , Lewerenz Hans Joachim , Liu Z
Published: February 2020

Photoelectrochemical (PEC) cells based on semiconductor-liquid interfaces provide a method of converting solar energy to electricity or fuels 1-3. Recently, we have demonstrated operational systems that involved stabilized semiconductor-liquid junctions 4,5.

We have employed operando ambient-pressure X-Ray photoelectron spectroscopy (AP-XPS) on these highly stable semiconductor-liquids junctions to directly characterize the semiconductor-liquid junction at room temperature under real-time electrochemical control 6,7. The escape depth of photoelectrons that originate from tender X-ray synchrotron radiation — 2.3 to 5.2 keV — allows for sampling of the sample simultaneously near the sample surface but through an electrolyte layer as the inelastic mean free path of such photoelectrons is on the order of 5 to 10 nanometers. Accordingly, tender X-ray AP-XPS has enabled simultaneous monitoring of the semiconductor surface, the semiconductor-electrolyte interface, and the bulk electrolyte of a PEC cell as a function of the applied potential, E. Accumulation, depletion and Fermi level pinning were observed. The observed shifts in the core level emission binding energies with respect to the applied potential directly revealed ohmic and rectifying junction behavior on metallized and semiconducting samples, respectively.

1. H. J. Lewerenz et al., Energ. Environ. Sci., 3, 748–760 (2010).

2. H. J. Lewerenz, in Photoelectrochemical Materials and Energy Conversion Processes, R. C. Alkire, D. M. Kolb, J. Lipkowski, and P. N. Ross, Editors, vol. 12, p. 61–181, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany (2010).

3. Z. Huang, C. Xiang, H. J. Lewerenz, and N. S. Lewis, Energ. Environ. Sci., 7, 1207–1211 (2014).

4. S. Hu et al., Science, 344, 1005–1009 (2014).

5. M. F. Lichterman et al., Energy Environ. Sci., 7, 3334–3337 (2014).

6. S. Axnanda et al., Meet. Abstr., MA2013-02, 921–921 (2013).

7. S. Axnanda et al., (2014), submitted.