bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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
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
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.
On the Electrochemical Properties of New Materials in the Li2o-Fe2O3-V2O5 Ternary System
Authors: Benabed Yasmine , Pelé Vincent , Castro Laurent , Penin Nicolas , Carlier Dany , Wattiaux Alain , Duttine Mathieu , Darriet Jacques , Dollé Mickael 
Published: February 2020

In order to discover innovative electrode and electrolyte battery materials responding to specific needs in terms of capacity, working voltage, polarisation, alkali insertion mechanisms, it appears interesting to explore various insertion chemistries. With this in mind, our study was dedicated on the structural properties and electrochemical performances of iron vanadates positive electrode for Li batteries. More specifically, our groups focussed on the search for new stable phases in the Li2O - Fe2O3 - V2O5 ternary system with respect to several vanadates (FeVO4, NaCuFe2(VO4)3, β-Cu3Fe4(VO4)6, …), which structural and electrochemical properties upon Li insertion have been highlighted in previous work [1].
Among the Li2O - Fe2O3 - V2O5 system, this presentation is dedicated to two new compounds, which were not known from the literature. Both materials were obtained through solid synthesis routes, after optimising the annealing parameters to reach pure phases. After determination of the structure using single crystal X-Ray Diffraction, their physical and electrochemical properties were thoroughly characterized using SEM, Mossbauer spectroscopy, galvanostatic and potentiostatic cycling. Electrochemical characterizations in half cells resulted in finding the optimal voltage window to enhance the capacity retention of the material as compared to previously studied vanadates. The galvanostatic curves indicated complex mechanisms for both materials involving several monophasic and biphasic steps upon Li insertion (see figure for the structure of LiFeV2O7 viewed along the [-101] direction and its electrochemical curve in half cell). Mossbauer spectroscopy allows assessing the oxidation state of iron atoms in the structures before and upon the electrochemical processes.
[1] Patoux, S., Richardson, T.J. “Lithium insertion chemistry of some iron vanadates”, Electrochemistry Communications, 9 (3), pp. 485-491 (2007).
[2] Benabed, Y., Castro, L., Penin, N., Darriet, J., Dollé, M. “Synthesis, Structure, and Electrochemical Properties of LiFeV2O7”, Chemistry of Materials, 29 (21), pp. 9292-9299 (2017).

Figure 1