bluuebunny/crossref_metadata_2025 huggingface dataset:
Bi-Metal Deposits within Nanostructured Silicon with Respect to Permanent Nanomagnets
Authors: Rumpf Klemens , Granitzer Petra , Gonzalez-Rodriguez Roberto , Coffer Jeffery , Poelt Peter , Michor Herwig
Published: February 2020

The purpose of this work is to fabricate nanostructured silicon with two different materials of embedded magnetic nanostructures to exploit the magnetic properties of both metals and gain control of the exchange coupling between the two metals especially with respect to their volume ratio. Furthermore a variation of the structure size and the proximity of the metal deposits modifies the exchange coupling and thus the energy product. Finally nanocomposits with an energy product as high as possible are achieved to give rise to on-chip applications using permanent nanomagnets, especially arranged in arrays.

In this work magnetic nanostructures of two different metals are deposited within nanostructured silicon to control the magnetic switching behavior of the silicon/metal nanocomposite. Two different templates, porous silicon and porous silicon nanotubes are utilized to achieve such nanocomposites. The morphology (pore diameter, tube diameter) of the two systems is comparable. In the case of the utilization of porous silicon templates a mesoporous morphology with average pore diameters of 50 nm are used and these oriented and separated pores are filled with two different metals, namely Ni and Co. The two metals are deposited alternatingly by electrodeposition. A further approach is the chemical growth of Co nanoparticles within porous silicon nanotubes (SiNTs) and the additional deposition of a Ni layer on the outer surface of the tubes. The inner diameter of the silicon tubes is around 50 nm and the wall thickness is about 10 nm. Since the silicon wall of the tubes offers a porous structure the Co particles, which are localized near the pore surface on the wall of a given nanotube, can touch the Ni layer. An alternative structure involves the deposition of an additional Si layer (after the growth of Co particles inside the tubes) as a spacer before the Ni deposition.

The morphology of the deposited bi-metal Ni/Co structures is figured out by SEM and EDX. Figure 1 shows an EDX-map of a cross-section of a porous silicon sample filled with Ni and Co.

In the presented work the dependence of the magnetic properties of a nanostructured silicon/bi-metal nanocomposite on the volume ratio of the metals, on the proximity of the nanostructures and also on the size of the metal deposits has been figured out. If the distance between the deposited bi-metal structures is small enough magnetic exchange coupling between them is present which could be observed. By tuning the bi-metal deposition an optimized energy product is achieved which gives rise to self-assembled nanocomposite systems containing permanent nanomagnets and arrays of them, respectively for on-chip applications.

Figure 1: EDX mapping of a cross-section of a porous silicon sample with deposited Ni-Co structures showing the ratio between Ni and Co (Ni …yellow, Co … Red).

Figure 1
Highly Sensitive Acetylcholinesterase Biosensor Based on Shaped Controlled ZnO Nanostructure for Paraoxon Pesticide Detection
Authors: Fallatah Ahmad , Kuperus Nicolas , Almomtan Mohammed , Padalkar Sonal
Published: February 2020

Zinc oxide (ZnO) is an attractive material that finds applications in areas ranging from transistors, varistors, solar cells, photocatalysts and biosensors. Here we report the electrodeposition of ZnO nanostructured thin films in the presence of various capping agents like potassium chloride, ammonium fluoride and ethylenediamine to form different morphologies of ZnO. These ZnO nanostructures were used as biosensing platforms for the immobilization of acetylcholinesterase (AChE) and detection of the pesticide paraoxon. The electrodeposition of ZnO nanostructures was performed on carbon paper and carbon fabric substrate by using a zinc nitrate (Zn(NO3)2) precursor at 70 °C temperature with an applied potential of -1.0 V and 30 min reaction time. Many different morphologies of ZnO such as nanorods, nanoneedles, nanoplatelets, nanoflowers were successfully synthesized and characterized using scanning electron microscopy (SEM). Further the ZnO nanostructures were characterized by X-ray diffraction (XRD), UV-Vis spectroscopy, Raman spectroscopy and electrochemical impedance spectroscopy (EIS). An amperometric current response for the detection of paraoxon was recorded. The biosensor shows a detection limit to paraoxon in the range of 1nM–5µM . The developed biosensor shows high sensitivity, stability and low cost.

[PS[E1]Detection limit should be 1 nM. Let us not write a range. It can be confusing.

[PS[E2]You have written the abstract very well. Good job!
A Cell-Imprinted Polymer Capacitive Biosensor for the Detection of Escherichia coli
Authors: Lu Weihao , Mugo Samuel
Published: February 2020

Food-borne bacteria contamination in food and water has become an important topic for food industries as well as common people. Escherichia coli is one of the common infectious bacteria and the maximum acceptance of E. coli in drinking water in Canada is 0/100 mL. Current traditional detection techniques such as ELISA and PCR are time-consuming, tedious and expensive. To develop more rapid and effective detection methods, several studies had reported the preference of cell imprinting technique in the biosensor applications (2,4). However, the sensitivity and the accessibility of the biosensors remain a challenge. In this regard, we have developed a capacitive biosensor based on a layer by layer, boronic acid doped polyaniline methacrylic based molecular imprinted polymers (MIPs) on a carbon nanotube conductive film. The tailor-made MIPs have been found to be highly selective affinity to E. coli. Highly miniaturized (the size of 1.5 x 1.5 cm2) and inexpensive, the fabricated sensor schematically depicted below is currently being hyphenated to cellular phones through a blue tooth, can be deployed for on site remote analysis of pathogens in drinking water and food analysis. The sensor performance was impressive with a wide dynamic range of four orders of magnitude and low limit of detection of 36 CFU/mL for E. coli detection. Moreover, by simply tailoring the molecular receptors, the sensor can be employed in the detection of other pathogenic bacteria such as Staphylococcus spp. and Salmonella spp. in food and water.
Defect Engineering: Polycrystalline TiO2 Nanofibers with H2 Plasma Treatment Tuning Grain to Grain Boundary Potential for Photochemical Antibacterial Agents
Authors: Pan Pin-Chun , Lai Po-Hao , Yeh Ping-Hung , Chen Lih-Juann
Published: February 2020

Light to electric conversion photochemical effect can be achieved by using biocompatible material, polycrystalline TiO2 nano-fibers (poly-TiO2 NFs). With versatility and low cost advantages, electrospinning process had been explored recently as means for preparing a wide variety of polycrystalline nanofiber materials for potential applications, for example, in tissue engineering, membranes, solar cells, and chemical and biological sensors. Cell division and antibacterial issues were widely explored in recent research. However, as a large bandgap n type semiconductor, single crystalline TiO2 materials has the attribute of responding UV light (400 nm). Due to the defect-rich structure, polycrystalline TiO2 NFs can respond not only to UV light but also to visible light (wavelength between 400~550 nm). The photochemical effect hugely can be hugely enhanced by using specific power hydrogen plasma treatment because plasma treatment can tune the barrier height between grains, surface potential and defect level. The soft energy light (long wavelength light, such as the red light (region wavelength between 620~730 nm)) can also be used in bio research (such as stimulating the cell growth or antibacterial growth). Antibacterial observation or the cell growth process always incubates in solution. The photo responses of our device are different between low and high humidity environment.

Recently, there are considerable interests in electrospun-titanium dioxide nanofibers (TiO2 NFs) as antibacterial agents owing to their large grain to grain surface and the formation of reactive hydroxyl radicals (which can react with bacteria, cell membranes, and cellular proteins, leading to cell death). However, the photocatalytic effects of TiO2 NFs are relatively low due to the rich defect states. With H2 plasma treatment passivation, the surface potential of polycrystalline TiO2 nanofibers were in was smoothened for electrons to transport. Consequently, the H2 plasma treated TiO2 nanofibers remained showed greater numbers of hydroxyl radicals and significantly enhanced visible light photocatalytic antibacterial activity. Based on these defect and interface engineering, poly-TiO2 NFs with hydrogen plasma treatment is a potential candidate for bio application.
Using Impedance Spectroscopy to Detect the Selective Sorption of Iodine By MOF ZIF-8
Authors: Small Leo J. , Nenoff Tina M
Published: February 2020

Detection of iodine species is important for the safety of the population in cases of nuclear accidents or advanced nuclear fuel reprocessing. Here we leverage the selective sorption of I2 by metal organic framework (MOF) ZIF-8 to create an impedance spectroscopy-based sensor for the real-time detection of gaseous I2. Methanolic ZIF-8 suspensions were cast onto interdigitated electrodes, dried, and exposed to gaseous I2 at 25, 40, or 70 °C. Equivalent circuit models were developed to separate the response of the extremely resistive ZIF-8 from that of the underlying glass substrate. While high fidelity measurements enable electrical characterization of pure ZIF-8, such precision is woefully unnecessary to detect I2; a >105× decrease in ZIF-8 resistance was observed upon sorption of 116 wt% I2 by ZIF-8 at 70 °C. Such large changes in impedance open the door for I2 detection schemes using inexpensive electronics. Tests for interfering gases such as air, argon, methanol, and water revealed minimal changes in impedance and equivalent circuit response. Using an unoptimized sensor geometry, I2 was readily detected at 25 °C in air. Further optimization of sensor geometry, decreasing MOF film thicknesses and maximizing sensor capacitance, will enable faster detection of trace I2, providing a rapid, robust, and reliable iodine sensor for the safety of the populace.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
In-Situ Electrical Characterization of Low Temperature Getter Thin Films Activation
Authors: Lemettre Sylvain , Bessouet Clément , Coste Philippe , Bosseboeuf Alain , Moulin Johan
Published: February 2020

Thanks to their reactivity to gases, getter materials are involved in vacuum packaging to compensate leaks and permeation through the package. After deposition, the material is passivated due to the contact with the air, and must be thermally activated to force the diffusion of the passivation layer inside the film. However, new MEMS technologies imply more fragile devices thus processes with a limited temperature. In this frame, we investigate getter materials presenting a low activation temperature, such as Zr-based alloys.

Moreover, in most investigations of getter films, activation and sorption are characterized separately by room temperature surface analysis techniques in UHV and by sorption experiments under specific gases, respectively. In this work, we have studied the behavior of getter thin films in vacuum as a function of the temperature and the pressure to be as close as possible to the conditions of integration, i.e. wafer bonding. This consisted in following the sheet resistance measured by using the 4-probes technique and comparing electro-thermal properties (resistivity, Temperature Coefficient of Resistance TCR) to pre- and post- characterization (composition, structure).

Thin films of Zr, V, Ti, Zr-Ti, Zr-V and Zr-Co with thicknesses of 300-400 nm have been deposited by co-evaporation in UHV. Their sheet resistance was measured as a function of the temperature under vacuum. The control of the pressure, from 10-6 to 10-3 mbar, allowed to activate the films in different conditions. For as-deposited films, results show that the resistivity and TCR are linked and follow the Mooij rule: the TCR decreases with the resistivity and becomes negative for resistivities higher than 150 µW.cm. The values globally depend on the composition, but separated groups are also linked to the disorder of the structure, from the lowest to the highest: pure metals, Zr-Ti, Zr-V then Zr-Co. In case of Zr-Ti, the grain size directly impacts the evolution of the coupled TCR and resistivity.

The activation in vacuum involves simultaneous and continuous diffusion inside the films and sorption at the surface. The latter cannot be avoided, even at 10-6 mbar, and the resistivity increases with the square root of the time. However, differences of behavior as a function of the pressure can be linked to the gettering efficiency and the diffusion length of oxygen in the material, which depends on both the composition and the microstructure. Crystalline Zr-Ti films behave as Zr and Ti and the grain size directly impacts the diffusion, thus the quantity of oxygen sorbed in the film. The structure of Zr-V or Zr-Co is more complex, which can be either crystalline or amorphous depending on the composition. Large variations in the sheet resistance can be obtained and the high disorder of the structure allow them to sorb more gaseous species than Zr-Ti.
(Keynote) Integrated Microfluidic Bioanalytical Systems: Growing and Monitoring Microbial Cultures in Outer Space
Authors: Ricco Antonio
Published: February 2020

We develop miniaturized bio/analytical instruments and platforms that integrate microfluidics and sensors to conduct economical, frequent, autonomous life-science experiments in outer space. The technologies represented by several of our recent 5-kg “free-flyer” small-satellite missions are the basis of a growing suite of miniaturized biologically- and chemically-oriented instrumentation now enabling a new generation of in-situ space science experiments. Over the past decade, our missions have included studies of space-environment-related changes in gene expression, drug dose response, microbial longevity, the degradation of biomarker molecules, the effects of microgravity on antibiotic resistance, and the "biosentinel" application of microbes to record rates of radiation-induced DNA damage in interplanetary space. The science and technology of several of these missions will be highlighted in the context of conducting biological and chemical experiments in outer space using miniaturized integrated systems.
Immobilization of the Alcohol Dehydrogenase Enzyme on TiO2 Nanotubes for Application in Microfluidic Fuel Cell
Authors: Arriaga Luis G. , Real Jesús Díaz , Ledesma-García Janet , Galindo de la Rosa Juan de Dios , Alvarez Alejandra , Gonzalez Solano Geraldine
Published: February 2020

Microfluidic fuel cells are a low-power demand fuel cells which work without the need of a physical membrane and have a wide range of potential applications. Biological catalysts such as immobilized enzymes can be used in electrodes to carry out the oxidation processes of different organic fuels using the immobilization technology of enzymes; they are carried out under moderate conditions of pH and temperature, and the specificity of the catalytic reactions. The alcohol dehydrogenase enzyme has been used for the development of bioanodes for the oxidation of different alcohols such as ethanol and methanol. In this work, the immobilization of this enzyme was carried out using nanotubes of titanium dioxide for the development of electrodes for an air-breathing microfluidic fuel cell. TiO2 nanotubes has excellent properties such as pH resistance, superior mechanical strength, good biocompatibility making it a great candidate for the process of immobilization of the enzyme alcohol dehydrogenase. TiO2 nanotubes were fabricated by electrochemical anodic oxidation on Ti foils. The foils were pre-treated with sand-paper, thereafter immersed in ethanol, placed in ultrasonic bath, dried under N2 flow. An ethylene glycol-based solution with a concentration of 0.1M NH4F (96% purity, Alfa-Aesar) and 2% w/w deionized water was used as electrolyte. The anodization times used was 1 h with a voltage step of 60 V via a power source. Using this nanostructure, the enzymatic electrode was constructed using a catalityc ink with enzyme, tetrabutylammonium bromide and Nafion to carry out the immobilization process. We carried out the characterization of the electrode developed by means of different electrochemical and kinetic techniques, where it was demonstrated that the enzyme is present and active in the electrode, as well as its capacity to oxidize ethanol. Then the bioanode was evaluated in the microfluidic device also using an inorganic cathode of Pt / C, obtaining a good performance over an open circuit potential greater than 0.93V.
A Microfluidic Platform for Electrochemical Detection and Mechanism Studies
Authors: Molina Daniel E. , Medina Adan , Beyenal Haluk , Ivory Cornelius F.
Published: February 2020

A poly(methyl methacrylate) (PMMA) microfluidic platform with a hot-embossed microchannel, 150 mm wide by 20 mm deep, was developed for multiple purpose electrochemical detection and mechanistic studies. The platform was tested using a redox couple consisting of Fe(CN)6
−3 and Fe(CN)6
−4 with 100 mM KCl supporting electrolyte. The device includes microelectrodes installed in the microchannel. It accommodates a three-electrode system, with each electrode encased in 1/16” diameter PEEK tubing. These electrodes are removable so they can be re-used after cleaning, polishing and can be calibrated before and after experimental runs. The working microelectrode is a micro-disc made of platinum, and a platinum wire is the counter electrode. Other types of working and counter electrodes can be used and their surfaces can be modified depending on the target analyte under consideration. A commercial, true "leak-less" reference electrode was employed, which is stable, durable and which avoids cross-contamination.

Characterization of the microchip was performed using electrochemical impedance spectroscopy, cyclic voltammetry and chronoamperometry. Hydrodynamic tests were performed at flow rates between 0.1 and 10 mL/min, and analyte concentrations between 5 and 20 mM. The effect of scan rates in the range 20-100 mV/s during cyclic voltammetry was also studied. It was found that application of convection greatly enhances the current density at the micro electrode surface. At sufficiently high flow rates the voltammetric response exhibits the expected steady-state curve, at any of the studied scan rates. The limiting current increased in direct proportion to the concentration, and a cube root proportionality between limiting current and average fluid velocity was found. This is in agreement with 3D numerical modeling done in COMSOL Multiphysics® v5.3, using Butler-Volmer electrode kinetics, the Nernst-Planck equations for ion transport and Navier-Stokes equations for the hydrodynamic flow. Our model is used to simulate cyclic voltammetry and chronoamperometry at different flow rates, concentrations, and scan rates as well as for data regression and parameter estimation.

Figure 1
Multiplexed Electrochemical Immunosensor for Label-Free Detection of Cardiac Markers Using Carbon Nanofiber Array Device
Authors: Kumar Rakesh , Meyyappan M. , Koehne Jessica E.
Published: February 2020

A sensor platform based on vertically aligned carbon nanofiber (CNF) electrode arrays was developed. CNF’s inherent nanometer scale, high conductivity, wide potential window, good biocompatibility and well-defined surface chemistry make them ideal candidates as biosensor electrodes. Here we present a 3x3 electrode device, with each electrode containing 40,000 carbon nanofiber nanoelectrodes. The device was demonstrated as a multiplexed immunosensor for simultaneous, label-free detection of cardiac troponin-I, C-reactive protein and myoglobin. A hydrophobic photoresist layer was used to generate wells for discretely printing antibody probes on each electrode pad. Antibodies specific to cardiac troponin-I, C-reactive protein and myoglobin were covalently bound to the CNF surface and non-specific binding is controlled through a milk protein backfill. Antibody probe immobilization and subsequent protein binding were characterized using electrochemical impedance spectroscopy and differential pulse voltammetry. Each step of the modification process resulted in changes in resistance to charge transfer due to the changes at the electrode surface upon antibody immobilization and binding to the specific cardiac protein. The real-time label free detection of the three cardiac markers from pure components and mixtures was demonstrated with high sensitivity, down to 0.2 ng/mL, and good selectivity. Detection in human blood serum did not present false positives from non-specific protein adsorption. The results demonstrate that the present sensor can serve a miniaturized, low cost device for detection of proteins in complex mixtures making this platform a good candidate for early stage diagnosis of myocardial infarction.
TbYxOy Electrolyte-Insulator-Semiconductor Glucose Biosensor
Authors: Chan Chi-Lin , Huang Yen-Hsiang , Lou Bih Show , Pan Tung Ming
Published: February 2020

We report a glucose biosensor based on glucose oxidase (GOD) immobilized on TbYxOy sensing film deposited on the Si substrate through reactive cosputtering in this study. The structural properties of TbYxOy sensing films annealed at different temperatures (600, 700, 800, and 900 °C) were carried out using X-ray photoelectron spectroscopy and atomic force microscopy to obtain the optimal annealing condition. The TbYxOy electrolyte-insulator-semiconductor (EIS) sensor annealed at 900°C exhibited a higher sensitivity of 59.79 mV/pH, a lower drift rate of 0.26 mV/h, and a smaller hysteresis voltage of 1 mV in comparison with the other annealing temperatures. We attribute this behavior to the formation of a honeycomb-like structure and the reduction of lattice defects to improve the TbYxOy stoichiometry. Moreover, we compared two surface modification techniques with 3-aminopropyltriethoxysilane (APTES) and APTES+glutaraldehyde (GA) to immobilize the TbYxOy film surface and thus the enzymatic GOD was covalently bounded to the functionalized surface of a TbYxOy EIS sensor. The TbYxOy glucose biosensor prepared with APTES+GA has a high sensitivity (19.85 mV/mM) in solutions containing glucose at concentrations in the range 2–8 mM. This TbYxOy EIS biosensor is very promising sensing membrane materials for general clinical examination of blood glucose.
Advanced Nuclear Magnetic Resonance Techniques for Characterizing Ionic Liquids for Lithium Ion Battery Applications; High Presssure NMR and Fast Field Cycling Relaxometry
Authors: Mallia Christopher , Pilar Kartik , Rua Armando , Suarez Sophia , Lai Shen , Jayakody Jayakody , Hatcher Jasmine , Wishart James F. , Greenbaum Steven
Published: February 2020

Ionic liquids (ILs) have received widespread acclaim for their potential use as a safe and effective alternative to unstable and flammable organic solvents used in electrolytes for lithium-ion secondary batteries. The thermal and chemical stability of ILs, as well as the tunable properties of ILs by altering cation and anion species, have made them promising materials for use in multiple applications: such as textile dyeing, nuclear waste recycling, and solar cells. A limiting characteristic for IL use in secondary lithium-ion batteries is a notable lower ionic conductivity in most known species. Characterizing the effect of cation and anion structure on ionic diffusion in ILs, as well as studying molecular dynamics in IL species is of great importance for increasing their potential utility in battery chemistries. To this end, the techniques of Fast Field Cycling Nuclear Magnetic Resonance (FFCNMR) and pressure dependent NMR diffusometry are used to study ionic liquid species of interest. Fast field cycling measurements of spin-lattice relaxation times (T1) allow for access to time dependent molecular dynamics in ionic systems, as functions of both magnetic field strength and temperature. FFC measurements are complementary to high-pressure NMR experiments, which reveal pressure dependence of reorientation and tumbling processes, as well as the effects of alkyl chain length on ionic mobility in specific species. Presented here is the application of these two techniques to 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (CnMIM TFSA) ILs. Specifically, a selectively deuterated species of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (BMIM TFSA) is observed and characterized. FFC results were used to extract cation self-diffusion coefficients, showing good agreement with Pulse Field Gradient (PFG) NMR measurements. High pressure T1 data on selectively deuterated cation isotopologues revealed site dependent interactions on the cation alkyl chain. The work at BNL (JFW and JH) was supported by the US-DOE Office of Science, Division of Chemical Sciences, Geosciences and Biosciences under contract DE-SC0012704.
Selection of Electrolytes for Optimal Reverse Electroactuation Energy Harvesting
Authors: Adhikari Pashupati R. , Reid Russell C.
Published: February 2020

A number of new developments have taken place over the years with respect to mechanical energy harvesting. However, significant progress is yet to be made to improve the energy density to sufficiently and reliably power our everyday mobile devices and other applications. Recently, a new approach in energy harvesting based on the principles of reverse electroactuation has been reported and is drawing much interest. Reverse electroactuation can be considered the opposite of electrowetting-on-dielectric, which is the manipulation of liquid droplets on dielectric with applied voltage. The reverse electroactuation approach of energy harvesting adopts a fundamental principle that the movements of liquid droplets on a dielectric film generate power by dynamically modulating the liquid-solid interfacial dielectric capacitance. The amount of power generated using this approach depends on various factors such as the type of conducting liquid used, dielectric coating type and thickness, and droplet pinning. Power densities up to 103 W/m2 have been reported using reverse electroactuation with Mercury as electrolyte, but using Mercury for real applications is not feasible due to its toxicity. In this study, we test a number of alternative conducting liquids as well as dielectric coatings in reverse electroactuation. The main objective is to observe and analyze the effect electrolyte and dielectric coatings have on power density and to compare the experimental results to previously published theoretical models. In addition to improving energy harvesting, this research contributes to fundamental understanding of how liquid movement under the combined influence of pressure, surface tension, and electric fields affect charge density. This may impact the design and development of porous materials for applications such as supercapacitors, electrodialysis, and reverse osmosis.

Figure 1. In reverse electroactuation, a conducting liquid droplet is placed between two electrodes, one of which is insulated (A). A dynamic mechanical loading deflects the droplet, resulting in a modulating capacitance and therefore an electrical current (B).

Figure 1
High Temperature Electrooxidation of Glycerol on Nickel
Authors: Borsboom Tory , Holm Thomas , Bao Han , Escobar Alberto , Harrington David A.
Published: February 2020

This work involves the long term electrooxidation of glycerol in a custom autoclave setup. Experiments are usually performed over approximately 48 hours. The custom autoclave setup was adapted from work done by Thomas Holm [1,2]. Within the autoclave a typical three electrode cell is built, wherein all glass pieces have been replaced with alkaline stable counterparts. This is largely done with Teflon, however a Nafion membrane is used to separate the working and reference electrode volumes from the bulk volume at the counter electrode to avoid contamination at the reference, and to keep the oxidation volume small. A small oxidation volume leads to higher concentrations of products, allowing them to be more easily detected using HPLC.

Analysis of the oxidized products is performed via HPLC using an Aminex HPX-87H column. Using these techniques we have been able to show that the temperature at which electrooxidation occurs significantly alters the selectivity of products, as well as causing some new products to form (See Figure 1). Calibration curves have been made up for each of these products using known standards, and so we are able to quantitatively determine how much of each product is formed. However, the carbonate peak is not quantitative, and so carbonate was separately analysed by gravimetric or titrimetric methods.

With this information we have been attempting to carry out a carbon balance between products and reactants to ensure all products has been accounted for. Though some reasonable values have been attained for this, problems arise when an electron balance is attempted. Much more oxidation is carried out than is expected from the number of electrons used during the experiment, and so we can conclude that some chemical interactions are occurring in solution. It is likely that some products are reacting with the alkaline solution, perhaps through chemical disproproportionation reactions. The existance of such reactions can be confirmed for glyceraldehyde, which has been shown to exist on a short time scale using PM-IRRAS [3] even though no glyceraldehyde is detected by HPLC. We find that HPLC glyceraldehyde standards decompose into other compounds that we see here. Work is ongoing to establish the identity and distribution of products as a function of the reaction conditions.

This research was conducted as part of the Engineered Nickel Catalysts for Electrochemical Clean Energy project administered from Queen’s University and supported by Grant No. RGPNM 477963-2015 under the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Frontiers Program.

1. T. Holm, P.K. Dahlstrøm, S. Sunde, D. A. Harrington, F. Seland, ECS
Trans,
75, 1055, (2016).

2. T. Holm, P.K. Dahlstrøm, O.S. Burheim, S. Sunde, D.A. Harrington, and F. Seland, Electrochim. Acta., 222, 1792 (2016).

3. M.S.E. Houache, E. Cossar, S. Ntais, E.A. Baranova, J. Power Sources, on the web, doi:10.1016/j.jpowsour.2017.08.089.

Figure 1
Synthetic Design of a Supramolecular Complexing Agent for Advanced Cu Chemical Mechanical Planarization Applications
Authors: Mistry Neera , Hill Madison , Kilmer Lucas , Shuchi Halima , Kissel Daniel S. , Keleher Jason J.
Published: February 2020

As the complexity of three-dimensional large-scale integration (3D-LSI) circuits increases, copper (Cu) Chemical Mechanical planarization (CMP) has emerged as a critical step in the fabrication of semiconductor wafers attaining global planarization. Through-silicon Via (TSV) CMP incorporates elimination of deposited excess trench overburden above a silicon wafer at a high removal rate, thus allowing additional layers to be added for substantial 3D-LSI circuit architecture. Enhancing the planarity of the substrate as a result of undesired topography removal is controlled through optimization of slurry composition. In traditional slurries, a synergistic chemical interaction between a corrosion inhibitor and a complexing agent removes irregularities from the surface while at high downforce. To optimize slurry interaction and promote film formation at the interface, a suite of additives incorporating both properties of the slurry are being developed. More specifically, the functionalization of a supramolecular structure enables removal rate to rely heavily on surface chemistry due to its polymeric nature while simultaneously preserving surface uniformity. The introduction of substituents with high-binding affinity for Cu into the slurry such as heterocyclic pyridines, amino, and carboxyl groups directly correlate to a higher removal rate. Preliminary results have shown a correlation between the molecular structure of the complexing and inhibiting agents and their effect on film formation. Adding a system that integrates simultaneous chelation and passivation to the slurry via the supramolecular complex will directly impact the planarity and therefore alter the removal mechanism. This work employs electrochemical surface analysis such as open-circuit potential (OCP) to monitor film formation kinetics and results have shown a direct correlation to CMP parameters.
Bayesian Statistical Framework for Deconvolving the Distribution of Relaxation Times from Electrochemical Impedance Spectroscopy Data
Authors: Effat Mohammed B. , Ciucci Francesco
Published: February 2020

Electrochemical impedance spectroscopy (EIS) is a powerful electrochemical characterization technique used in scientific research and industry. Interpreting the EIS data correctly is the essential step to unravel the nature of the underlying physical processes happening inside the electrochemical system (e.g. Li-ion battery) and to obtain the quantitative values of the corresponding parameters (i.e. diffusion coefficients, reaction rate constants, etc.). The most common approach to interpret impedance data is by fitting to an equivalent circuit model (ECM). The problem of this approach is that many (ECMs) can fit the data well. In the past decade, the distribution of relaxation times (DRT) has appeared as a complementary methodology that enables better interpretation to the impedance data. In this method, the time scales of the underlying processes can be directly accessed, enabling the construction of the most relevant ECM. However, obtaining the DRT requires solving an ill-posed inverse problem that is sensitive to the noise level in the data and number of data points available. We tackled this issue by framing the DRT problem in a Bayesian statistical framework. Within this framework, we can introduce our experience regarding the EIS in the form of prior models and define the DRT as probability distribution function (pdf). We employed two prior models. The first one is implemented on the regularization parameter and we become able to detect the discontinuities in the DRT. This allows the recovery of various discontinuous elements including the Gerischer impedance. The second prior model focuses on the weights which we can assign to each individual data point. This allows the detection of outliers in the EIS data. We can also sample the DRT from its pdf given the data and the hypotheses on the regularization parameter and weights. By applying this framework to synthetic experiments and real EIS data of Li-ion battery, we show that we can obtain far more insight about the analysis of the EIS data, typically needed by the EIS practitioner.
A Dynamic Impedance Study of the Initial Stages of Nickel Oxidation
Authors: Alikarami Mohammad , Holm Thomas , Harrington David A.
Published: February 2020

The nature of the species that form on oxidizing Ni electrode in alkaline solution has been studied for a long time. Bode summarized the formation and interconversion of these hydroxide and oxyhydroxide phases in terms of time and potential [1], but their structure and kinetics remain an active area of study [2]. The initially formed oxide is believed to be a hydrated hydroxide, α-Ni(OH)2, which irreversibly interconverts to a less hydrated β-Ni(OH)2 at higher potentials.

The formation and interconversion of these hydroxide phases is studied here by dynamic electrochemical impedance spectroscopy (dEIS) [3,4], which applies a multi-frequency waveform during a cyclic voltammetry sweep or during a chronoamperometry experiment. It enables the study of non-steady states of the surface that cannot be accessed by conventional potentiostatic EIS. It is particularly suited to study the irreversible α-Ni(OH)2 to β-Ni(OH)2 interconversion.

An electrochemical polishing procedure was used to remove the oxide layer in order to have a clean and oxide-free surface before doing the experiment. This step consisted of galvanostatic holding in phosphoric acid solution. Impedance data were collected during voltammograms at different slow sweep rates, with selected hold periods before, during, or after the peaks, and were correlated to charges under the voltammograms. The impedance data were fitted to equivalent circuits. In most cases the faradaic impedance approximated a charge-transfer resistance, but the use of complex capacitance plots showed evidence for additional structure at low frequencies. Comparison of the the polarization resistance determined from the slope of the voltammograms with the estimated low-frequency intercept of the impedance showed a discrepancy in the peak region, which also suggests that a slow process exists that whose kinetics is not determinable by dEIS.

The sweep-hold experiments followed the conversion of the α phase to the β phase, and found that the oxidation is not complete in the potential range of 0.2-0.3 V. Voltammograms of the admittance at selected frequencies were found to be sensitive to the surface condition, and showed that the surface condition did not return to the same value after cycling.

This research was conducted as part of the Engineered Nickel Catalysts for Electrochemical Clean Energy project administered from Queen’s University and supported by Grant No. RGPNM 477963-2015 under the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Frontiers Program.

[1] H. Bode, K. Dehmelt and J. Witte. Electrochim. Acta.,
11, 8 (1966).

[2] M. Alsabet, M. Grden and G. Jerkiewicz, Electrocatalysis,
2, 4 (2011).

[3] R.L. Sacci, F. Seland and D.A. Harrington, Electrochim. Acta., 131, 13 (2014).

[4] R.L. Sacci and D.A. Harrington, ECS Transactions, 19, 31 (2009).
Structure and Electrical Properties of ZrO2/Al2O3/TiO2 Films Grown Via Atomic Layer Deposition on TiN Electrodes
Authors: Cha Soon Hyung , An Cheol Hyun , Kim Sang Hyeon , Kim Dong Gun , Kwon Dae Seon , Cho Seong Tak , Hwang C. S.
Published: February 2020

As the design rule becomes smaller, it becomes increasingly difficult to ensure the storage capacitance of DRAM. At present, ZrO2/Al2O3/ZrO2 (ZAZ) is being used for dielectric film of DRAM capacitor. When the design rule of device becomes < 20nm, the ZAZ film thickness should be too thin to crystalize it. As a result, the dielectric constant of a ZAZ thin film is lower than the expected value, particularly the upper ZrO2 layer [1]. In this regard, TiO2, which has a higher dielectric constant than that of ZrO2 and lower crystallization temperature, could be an alternative to the ZrO2 layer. However, the small band gap of TiO2 (3.4eV) makes it challenging to be used as a single dielectric layer in the structure. Therefore, in this study, the upper ZrO2 layer of the conventional ZAZ structure is replaced by a TiO2 layer, which may result in the lower equivalent oxide thickness (EOT) than that of the original structure without a significant increase in the leakage current.

In this study, the electrical and physical properties of ZrO2/Al2O3/TiO2 (ZAT) and ZAZ deposited on TiN substrate using ALD method were evaluated. A traveling-wave-type ALD reactor was used for in-situ ZAT and ZAZ and the oxygen source of O3 and the precursors of TEMAZr, TMA and TTIP were used to deposit ZrO2, Al2O3 and TiO2. Various ratios between upper and lower dielectric layers were evaluated in order to observe any changes in their properties. The capacitance density of ZAT dielectric was higher (Figure 1) even without the rapid thermal annealing (RTA) process, and there was no significant difference in the I-V properties. The capacitance of ZAT device was improved by 50% after the N2 ambient RTA performed at 600oC for 30 seconds, but the higher leakage current was observed. The EOT decreases due to the crystallization of TiO2 and the extent of crystallization was analyzed. A tetragonal phase was observed in ZrO2 after the annealing. With the use of thinner ZAT films, EOT was improved by ~0.5 nm at a given physical thickness of 7nm which is a significant merit over ZAZ.

References [1] D. Zhou, Appl. Phys. 108 (2010) 124104. [2] S. K. Kim, Appl. Phys. Lett., 85, 4112 (2004)

Figure 1
Liquid-Feed Flame Spray Pyrolysis Derived Nanopowders As a Route to Electrically Conducting Calcium Aluminate (12CaO.7Al2O3) Thin Films
Authors: Temeche Eleni , Yi Eongyu , Laine Richard
Published: February 2020

Transparent conductive oxides (TCOs) have extensive applications in the diverse optoelectronics applications. However, it is often difficult to identify transparent oxides with high electrical conductivity due to their intrinsically wide band gaps. Furthermore, those that have been identified as offering useful properties often contain high cost and/or toxic components (e.g. In2O3) or are difficult to process (e.g. CuAlO2) or both; leading to challenging commercialization issues.

In comparison, CaO and Al2O3, traditional cement components, have long been studied and found to form multiple phases at different stoichiometric ratios. Among these, 12CaO.7Al2O3 (C12A7) in particular has received considerable recent attention because it is a novel type of TCO. C12A7 is a light metal oxide with a unique set of cage structures that can be processed to give transparent, dense films that are typically insulating but that can be easily transformed into a transparent semiconducting films. As formed, C12A7 consists of a set of cage structures wherein charge balance is maintained through incorporation of O2- ions in these cages. Hosono et al among other groups has discovered that these O2- ions can be replaced through H2 treatment with OH- and H- ions (C12A7:H). Most important is their finding that UV treatment of (C12A7:H) can be used to generate transparent electrides, (C12A7:e-) providing materials with conductivities as high as 1 S cm-1 in pellets or sputtered films. These materials thus offer the potential to process low cost TCOs at commercial scales providing simple processing routes to such materials can be developed.

Traditionally, C12A7 materials have been processed using solid-state reactions followed by pulsed laser deposition (PLD) or floating zone (Fz) crystallization methods as high temperature, high cost approaches to single-phase films. These techniques require a significant number of process steps to generate C12A7:e. We demonstrate here an effective mass production method by producing C12A7 nanopowders (NPs) via liquid-feed flame spray pyrolysis (LF-FSP). Nearly fully dense, single phase, dense, flexible and transparent C12A7 thin films (< 30 m) can be produced by processing these NPs into green films by tape-casting, thermo-compression and then sintering to 1300/3 h/O2. Subsequent heat treatments in 20% H2/80% N2 to replace O2- ions forming C12A7:H- followed by UV irradiation provide C12A7:e- with electrical conductivities of 75 mS cm-1. C12A7:e- is expected to belong to a new class of TCOs due to its low materials and processing costs, environmental affinity, and natural abundance when processed efficiently.
Synthesizing Core-Shell Heterostructures for SOFCs Using a Solution Precipitation Method
Authors: Levitas Benjamin , Zhu Yuexing , Gopalan Srikanth
Published: February 2020

In the last three decades, solid oxide fuel cells (SOFCs) have garnered significant interest for viable distributed power generation systems. In this work, we focus on the cathode in SOFCs, where oxygen reduction occurs in two steps—adsorption and electronation, and surface/bulk diffusion to incorporation sites. Transition metal oxides such as strontium-doped lanthanum manganite (LSM) and strontium-doped cobalt iron oxide (LSCF) have been used as cathode materials, however both individually lack the key characteristics to successfully complete oxygen reduction. Furthermore, the accumulation of chromium (chromium poisoning) on SOFC cathodes is known to significantly hinder the performance of the cells. Incorporating core-shell hetero-structures as the cathode material could alleviate this problem: effectively combining the functionalities of both materials, and providing a nanoscale protection from Cr poisoning with a shell such as Cr-doped LSM (LSCM). However, synthesizing core-shell cathode structures previously has proved difficult requiring multiple steps, resulting in non-uniform core-shell structures. In this work we propose utilizing a molten salt synthesis process to create core-shell structures with precise composition with relative ease. The core is synthesized using high-temperature calcination and ball milled with the precursors of the target shell material. The milled powder mixtures are added to a LiCl-KCl eutectic melt to form core-shell hetero-structures via heterogeneous nucleation. Prior results have shown the successful formation of LSM and LSCF using the molten salt synthesis, along with the formation of core-shell LSCF-LSM hetero-structures. Synthesis temperatures dropped from the conventional 1000 ºC to 500 ºC, with dwell times as low as 10 minutes. Furthermore, SOFC cathodes consisting of LSCM were found to have stable polarization resistances, whereas the polarization resistance in LSM cathodes steadily increased. This result provides a strong motivation to further explore LSCM as a shell for core-shell cathodes to ensure protection from chromium poisoning. In essence, this work demonstrates an inexpensive method to synthesize core-shell cathodes that can simultaneously provide high power densities and low rates of degradation arising from Cr-poisoning.

Figure 1
A Nonlinear Model for Analyzing the Electrical Conductivity Relaxation Data of Mixed Ionic Electronic Conductors
Authors: Effat Mohammed B. , Quattrocchi Emanuele , Wan Ting Hei , Saccoccio Mattia , Belotti Alessio , Ciucci Francesco
Published: February 2020

Mixed ionic electronic conductors (MIECs) are materials able to conduct both ions and electrons and are used in many applications including solid oxide fuel cells, electrolyzers, and oxygen sensors. The performance of these materials can be assessed using electrical conductivity relaxation (ECR) technique. This technique is used to obtain two physical parameters related to the diffusivity and activity of the MIEC namely, 𝐷chem and 𝑘chem. The analytical model usually used to fit the ECR data is obtained from a linear partial differential equation for the oxygen transport with a linearized surface reaction rate as the boundary condition. In this work, we extend the linear approach and develop a nonlinear ECR simulation framework. The latter is based on a nonlinear partial differential equation that models the transport of oxygen defects and nonlinear surface reaction rates. Our approach also considers the influence of extrinsic factors, namely the impact of testing-chamber’s size and the gas-feed flow-rates on the ECR response. We show that the nonlinear model is able to model ECR well beyond the limits of the typical linear analytical models, i.e., when the final partial pressures inside the testing chamber are low. Further, we also show that, under certain conditions, the exchange of oxygen between the MIEC and the testing chamber can significantly affect the ECR response.