bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of Large Area Graphene Flakes with Low Defect Density Using the Electrochemical Exfoliation Technique
Authors: Mir Afkham , Shukla Anupam
Published: February 2020

Ever since the discovery of graphene in 2004 by Novoselov and Geim, the researchers across the globe have been in search for a cheap scalable method for bulk production of good quality graphene films. Electrochemical exfoliation has lately emerged as one of the strongest contenders for large scale production of graphene with focus being on the production of uniformly distributed monolayer graphene flakes preferably covering a larger area [Max reported flake size of 10 µm (Parvez et al, JACS, 2014)]. In this work, we demonstrate a method for synthesis of monolayer graphene films with flake sizes as large as 30 × 30 µm2. This can be achieved by making a proper choice of solvent for dispersing the graphene flakes. Over 25 solvents have been studied to determine the factors affecting the greater dispersibility of electrochemically exfolaited graphene flakes and hence achieving a larger flake size. UV-vis spectroscopy was performed to find the concentration of dispersed graphene flakes. Raman spectroscopy was done to determine the defects present in the sample as well as to rule out any oxidation of graphene layers in the presence of strong oxidants during the electrochemical exfoliation. In order to further reduce the defects in the graphene films, ultrasonication times for dispersing graphene flakes in the solvent have been reduced to as low as 2 min. Using this technique the best results were obtained for Propylene Carbonate in which single layer graphene flakes with 20 × 20 µm2 area with low defect ratio (ID/IG = 0.16) was synthesized as shown in the figure. Graphene produced via his route finds huge applications in various fields like synthesis of highly conductive electrodes.

Figure 1
The P- and N- Doping of Graphene through Specific Plasma Processing
Authors: Narayanan Rajaram , Zaretski Aliaksandr , Lipomi Darren , Bandaru Prabhakar R
Published: February 2020

The interfacial capacitance of graphene, the fundamental building block of carbon based high surface area electrodes, is limited by its quantum capacitance (CQ
).1,2 We will show that the CQ
of single-layer and few-layer graphene can be increased, e.g., through doping using specific plasma processing techniques. We will first show that the density of states and consequently the carrier concentration of graphene can be increased via argon based plasma processing.3 Subsequently, we will suggest ways to modulate the effective doping (both, p- and /n- type) through subjecting the graphenes to plasmas consisting of differently charged ions (Argon and Nitrogen).  We will indicate extensive Raman spectroscopy and electrochemical characterization, to clearly elucidate the nature of plasma doping and its effect on the quantum capacitance.4 The implications of plasma processing to the resistance change and the power density of graphene based electrochemical capacitors will be indicated. The work is of considerable scientific and technological interest.5, in terms of evaluating the underlying charge storage mechanisms of graphene for potential use in energy storage devices.

References:

1. J. Xia, F. Chen, J. Li, and N. Tao, Nat. Nanotechnol., 4, 505–509 (2009).

2. H. Yamada and P. R. Bandaru, Appl. Phys. Lett., 102, 173113 (2013)

3. R. Narayanan et al., Nano Lett., 15, 3067–3072 (2015).

4.  A.Das et al., Nat. Nanotechnol., 3, 210–215 (2008).

5. L. L. Zhang et al., Energy Environ. Sci., 5, 9618 (2012).
(Invited) Control of Film Morphology, Crystal Structure and Band Energy for Perovskite Solar Cells
Authors: Diau Eric Wei-Guang , Tsai Cheng-Min , Wu Hui-Ping
Published: February 2020

The development of all solid-state thin-film solar cells has reached a new milestone when the devices made of organometallic lead halide perovskite materials were reported with power conversion efficiency (PCE) exceeding 20 %. The key issue to make a device with a great photovoltaic performance for this kind of solar cells is to control the film morphology of perovskite under different experimental conditions. Varied mesoporous TiO2 nanostructures were applied to show the morphological effect of the scaffold on the device performance with a mesoscopic heterojuction. Anti-solvent method was applied to improve the morphology and crystallinity of the perovskite films to obtain device performance exceeding PCE 16 %. Varied additives were applied to control the formation morphology of the perovskite nanocrystals with a planar heterojunction. Moreover, we developed a simple drop-casting method via solvent-solvent extraction to grow dense and uniform perovskite nanocrystals at room temperature for carbon-based mesoscopic solar cells free of an organic hole-transport layer. The CH3NH3PbI3/ N-methyl-2-pyrrolidone (NMP) precursor solution (40 %) was first dripped onto a substrate with film configuration TiO2/Al2O3/C and infiltrated at 70 °C for 10 min. The perovskite substrate was next immersed in a bath of diethyl ether at 25 °C for 30 min. Third, the solvent-extracted substrate was stored in a dry box (humidity 50 %) at 25 °C for at least 100 h to complete the crystal growth. The device performance attained an efficiency 12.3 % of power conversion (PCE), which is significantly greater than that of DMF (6.3 %) and NMP (8.3 %) devices using traditional thermal annealing. For tin-rich perovskite, we designed and synthesized alloyed Sn-Pb mixed halide perovskites by dipping the precursor solutions on the mesoporous films with the TiO2/Al2O3/C configuration to form solar cells free of organic HTM. When 30 mol% of SnF2 additive was added in the tin-rich mix halide precursor solution, the device performance was improved from PCE 2.2 % (without SnF2) to PCE 4.3 % (with SnF2) with little effect of hysteresis; the short-circuit current density J
SC has reached a remarkable level with 23.33±0.73 mA cm-2.
(Invited) Photovoltaic Aspects of Organic Lead Halide Perovskites
Authors: Kamat Prashant V , Manser Joseph S , Yoon Seogjoon
Published: February 2020

Organic lead halide perovskites have gained a lot of attention in recent months because of their photovoltaic property. Varying the composition of Br- and Cl- in such perovskites allows us to tune the bandgap of these materials. Crystallization kinetics can be tailored to yield improved thin film homogeneity by simply tuning the composition of halides in the precursor solution. Formation of methyl ammonium lead halide in films prepared from mixed halide systems is dictated by the complexation equilibrium between Pb2+ and Br-, and Pb2+ and I-. The excited state characterization offers a convenient way to probe the evolution of perovskite structure from lead halide complex. Spectroscopic and structural characterization techniques shed light on the thermally-driven evolution of the perovskite structure in mixed halide systems.
(Invited) Hybrid Organic/Inorganic Bismuth-Based Materials for Solution-Processed Thin-Film Photovoltaics
Authors: Fabian David M , Ardo Shane
Published: February 2020

The lead–halide-based hybrid organic–inorganic perovskite material, methylammonium lead iodide (MAPbI3), has recently garnered increased attention among researchers worldwide as a promising photovoltaic material. As of 2015, perovskite photovoltaic devices have achieved laboratory efficiencies in excess of 20%. Many challenges regarding the stability and toxicity of the MAPbI3 material, however, remain at the forefront of current research. Due to the toxicity of lead and a purely fundamental interest in dicationic organic groups in place of monocationic MA+, less toxic dicationic bismuth–halide materials are the object of my research. The bismuth–iodide networks of the materials under investigation were hypothesized to form chains that extend in one dimension, whereas in MAPbI3 the lead–iodide network forms a lattice in three dimensions. If a small dicationic organic group is incorporated into the structure, however, it was hypothesized that the bismuth–iodide chains are in close enough proximity to each other to provide for long-range charge transport in three dimensions, similar to that observed in MAPbI3.

A library of dicationic bismuth–halide materials has been investigated to determine optimal dicationic groups based on film quality, optical band gap, and current density versus potential (J–E) characteristics. XRD data of dicationic bismuth–halide thin films have suggested larger average crystal grain size than MAPbI3 thin films and SEM images of dicationic bismuth–halide thin films have indicated greater surface coverage than MAPbI3 thin films. UV–Vis absorption spectra of dicationic bismuth–halide thin films have revealed onsets of light absorption in the range of 565 nm to 620 nm, which correspond to optical band gaps between 2.2 and 2.0 eV. J–E measurements have indicated that dicationic bismuth–halide photovoltaic devices exhibit a photovoltage of almost 400 mV (Fig. 1). Thermal stability tests suggest that dicationic bismuth–halide thin films are significantly more robust than MAPbI3 thin films. Large single crystals have been obtained for a dicationic bismuth–halide material, and single-crystal XRD data have indicated that the material formed binuclear clusters of Bi2I10
4-, with two dicationic organic groups and two H2O molecules associated with each binuclear cluster. To my knowledge, this represents the first report of a crystal structure of this material. Efficient photovoltaic devices featuring a dicationic bismuth–halide material may offer a more environmentally friendly, stable alternative to MAPbI3 photovoltaic devices that currently dominate emerging photovoltaic technology research.

Figure 1
(Invited) Cost-Effective Anthryl Dyes for Dye-Sensitized Cells Under Dim Light
Authors: Lin Ching-Yao
Published: February 2020

A series of anthracene-based organic dyes were prepared via cost-effective synthetic procedures for dye-sensitized cell application. UV-visible and fluorescent spectra, electrochemical properties as well as photovoltaic performance of the dyes were studied. Under one sun (100 mW/cm2), the AN-3 small cell (area = 0.16 cm2) outperforms others in the series. Under a dim light condition, the AN-3 modules (area = 36 cm2, manufactured by TDP, Taiwan) showed PCE comparable to that of the Z907 modules. After optimizing the synthetic procedure, we found that AN-3 can be manufactured at a fairly low price.

Reference: J. Phys. Chem. C 2015, 119, 24282−24289

Figure 1
(Invited) Linear and Star-Shaped Phthalocyanine-Acceptor Systems
Authors: Sastre-Santos Angela , Follana Jorge , Molina Desiré , Blas-Ferrando Vicente M. , Ortiz Javier , León Martín M. , Fernández-Lázaro Fernando
Published: February 2020

Linear and star-shaped molecules based on p-conjugated chromophores containing a polycyclic aromatic core, with the adequate HOMO LUMO energy orbitals, have generated significant interest for use in optoelectronic devies due to their properties of isotropic absorption and strong tendency to stack into quasi-1D columns, thus generating a preferred charge transporting pathway.[1]

The majority of organic semiconductors display hole-transporting properties (p-type), with the phthalocyanines (Pcs)[2] as one of the most representative families. Donor-acceptor systems formed by electron-rich groups conjugated with electron-poor moieties that can organize themselves into columns are good candidates to show ambipolar behavior. For this reason, the fussion of p-type phthalocyanines with some other n-transporting materials might give rise to different grade of conjugation between both systems affording potential candidates for ambipolar character. The synthesis of this type of systems has been scarcely described to date due to the difficulties to synthetize phthalocyanines with the adequate substituents for the condensation with acceptor moieties.

Herein, we will emphasize the progress in the chemistry of donor-acceptor conjugated Pcs-acceptor arrays (Figure 1)[3] with particular attention being focused on systems that exhibit attractive electronic, optical and electrochemical properties, thus allowing them to be considered as promising candidates for future applications such as NIR dyes, photovoltaic dyes, nonlinear optical materials and nano-electronic devices.

Acknowledgements. This work has been supported by the Spanish Ministerio de Economía y Competitividad, Generalitat Valenciana and the European FEDER funds (grants CTQ2011-26455, CTQ2014-55798-R, PROMETEO 2012/010 and ISIC/2012/008)

References:

(1)    (a) Forrest, S. R. Nature, 2004, 428, 911. (b) Shirota, Y.; Kageyama. H. Chem. Rev. 2007, 107, 953.

(2)    (a) de la Torre, G.; Claessens, C. G.; Torres, T. Chem. Commun. 2007, 2000. (b) Martin-Gomis, L.; Fernández-Lázaro, F.; Sastre-Santos, A. J. Mater. Chem. A 2014, 2 15672.

(3)    (a) Blas-Ferrando, V. M.; Ortiz, J.; Campos, V.M.; Mas-Torrent, M.; Fernandez-Lázaro, F.; Sastre-Santos, Á.; submitted. (b) Follana-Berná, J, Inan, D.; Blas-Ferrando, V. M.; Gorczak, N.; Fernández-Lázaro, F.; Grozema, F.; Sastre-Santos, Á. in preparation.

Figure 1. Chemical structure of different conjugated phthalocyanine-acceptors arrays

Figure 1
(Invited) Self-Organization and Cross-Linking of Tetraazaporphyrin Derivatives
Authors: Eichhorn S. Holger , Abdulhamied Elmahdy , Ahmida Mohamed M , Kayal Himadri
Published: February 2020

Despite the many advances in the design of porphyrin derivatives for Langmuir Blodgett (LB) films, the formation of compressible monolayers with a flat-on orientation of the macrocycle has remained elusive. Presented here is the synthesis of tetraazaporphyrins (TAPs) that contain different types of functional groups to enhance their amphiphilic properties and stabilize their face-on orientation at the air-water interface. Some of these compounds also display self-organization in their bulk phase. The new design of these TAPs combines several structural features of TAPs we previously reported, which contain eight identical side-chains with terminal carboxylic acid, azide, and acetylene groups.1,2 Attachement of both carboxylic acid and azide or acetylene groups generated TAPs that form stable Langmuir and LB monolayers with flat-on orientation of the macrocycle. We also succeeded in cross-linking these Langmuir and LB monolayers via cycloaddition of azide and acetylene groups (click chemistry) in the presence Cu catalyst and thermally.

1. M. M. Ahmida, S. Dufour, Hui–Sheng Li, H. Kayal, R. Schmidt, C. E. DeWolf and S. H. Eichhorn, 2013, Soft Matter (9,3) 811-9, DOI:10.1039/c2sm27064a.

2. Himadri Kayal, M. M. Ahmida, S. Dufour, H. Taing, and S. H. Eichhorn, 2013, J. Mater. Chem. C, (1,42) 7064-7072, DOI: 10.1039/C3TC31588F.
(Invited) New Cyclic Porphyrin Arrays ~ Preparation and Specific Elution Behavior on Modified Silica-Gel Columns
Authors: Satake Akiharu
Published: February 2020

Functionalized nanorings are expected to provide unique reaction fields in which specific and selective molecular transformation occurs. Here, we designed new cyclic porphyrin trimers (CP3s) in which three porphyrin moieties were connected through 2,2’-bipyridyl groups at their 3,3’-positions. CP3s were synthesized by nickel-mediated reductive coupling reaction of bis(2-chloro-4-methoxycarbonyl-6-pyridyl)porphyrinatozinc derivatives (1).(ref. 1) In a CP3, three bipyridyl parts are directed toward the center of the ring. Unlike metal-organized porphyrin cages formed from tetrapyridyl substituted porphyrins and metal ions, the three bisnitrogen pairs on the three bipyridyl moieties in CP3 are not used to construct the macrocyclic structures. Therefore, active metal species, such as coordinatively unsaturated complexes can be generated inside the rings, whereas generation of such active species in metal-oraganized nanocages is generally difficult because of destabilization of the skeletons. As well as the three bidentate 2,2’-bipyridyl ligands, three tetradentate porphyrinato parts gives metal ligands. The two kinds of metal ligands connected in a circular manner to provide a macrocyclic ligand for multicofacial and multinuclear complexes within a one-nanometer cavity. In fact, three π-allyl palladium complexes were incorporated into a zincporphyrin nanoring to give a hexametallic complex.

During the synthesis of CP3s, an efficient separation method by using modified silica-gel columns was discovered. Reductive coupling of bis(chloropyridyl)porphyrin 1 gave mixtures of acyclic and cyclic porphyrin oligomers. They were eluted in the order of hydrodynamic volume of the oligomers on gel permeation chromatography (GPC), and repeated GPC processes were necessary to obtain pure material of CP3. To reduce the time- and solvent-consuming processes, several modified silica-gel columns, COSMOSIL series supplied from Nacalai Tesque, PYE (pyrene-modified), π-NAP (naphtalene-modified), PBB (pentabromobenzene-modified), NBE (nitrobenzene-modified), and CN-MS (cyanopropyl), were tested. When a mixture of pyridine and toluene was used as an eluent, extremely specific retention behavior of CP3 was observed on the modified silica-gel columns. Under the conditions, other acyclic oligomers were eluted without retention. Therefore, the target CP3s can be much easily isolated from reaction mixtures compared with GPC separation. The observed specificity is probably related to molecular recognition between CP3s and substituents on the used modified silica-gel columns.

Reference

1) Ohkoda, Y., Asaishi, A., Namiki, T., Hashimoto, T., Yamada, M., Shirai, K., Katagami, Y., Sugaya, T., Tadokoro, M. and Satake, A., Chem. Eur. J., 2015, 21, 11745–11756. doi:10.1002/chem.201501854.
(Invited) Multi-Chromophore Containing Nanostructures Prepared Using Host-Guest Interactions
Authors: Jayawickramarajah Janarthanan , Zhu Mengyuan , Battle Cooper , Zhou Xiao
Published: February 2020

This seminar will discuss our recent efforts on self-assembling multi-chromophore containing nanoarchitectures. The emphasis will be on the supramolecular chemistry and photophysical properties of porphyrin-containing host-guest assemblies and materials wherein the porphyrin units are (a) assembled in competitive aqueous media and (b) do not undergo pi-pi aggregation. The first portion of the talk will discuss the construction and photonic properties of multi-porphyrin containing wires, spheres, and films that are assembled through cyclodextrin-driven host-guest chemistry. The second portion of the talk will discuss our recent efforts to expand the scope of multi-chromophore architectures by utilizing cucurbituril derived encapsulation as well as using the self-assembly properties of synthetic oligonucleotides.
Renewable Carbon Sources and Novel Technologies for the Manufacturing of Carbide Parts
Authors: Martinez-Duarte Rodrigo
Published: February 2020

Carbides are a class of high performance materials used in a variety of applications ranging from cutting tools to rocket nozzles. Examples of common carbides include Tungsten, Titanium and Boron Carbides. The synthesis of carbide is based on the reaction between carbon and metal or metal oxide powders at high temperatures. Current technology heavily relies on the use of carbon powders from the petrochemical industry. The reactant powders, or the already reacted carbide powder, are then pressed into specific shapes. Here, I will briefly detail current research on the use of renewable resources as the carbon source and on novel technologies to shape precursors to carbide parts.

The premise regarding the use of renewable resources is that a biopolymer-metal oxide nanoparticle composite can act as a carbide precursor. The biopolymer carbonizes below 1000 C leading to a carbon matrix decorated with metal nanoparticles. As the temperature is increased, these react to yield carbide. In my group we are exploring common biopolymers such as carrageenan, an extract from seaweed; chitin, from shrimp shells; konjac gum from the plant with the same name. We also actively exploring cellulose, from plants and bacteria, in the shape of powder, paper or individual fibers. The environmental cost of extracting these biopolymers is expected to be far less than petroleum-based ones while the colloidal proximity between the polymer and the metal nanopowders is expected to allow for the use of lower temperatures to complete the carbide-forming reaction. Thus, the process can be more energetically efficient than current ones.

Regarding manufacturing of precursor shapes, we are actively studying 1) the extrusion of composite pastes towards additive manufacturing of carbide precursors; 2) an origami-inspired technology by using cellulosic paper as the carbon source; and 3) a nanomanufacturing platform featuring the physical manipulation of bacterial cells capable of extruding cellulose nanofibers under optimized culture conditions.
In-Vivo Characterization of Glassy Carbon µ-Electrodes and Histological Analysis of Brain Tissue after Chronic Implants
Authors: Vomero Maria , Dryg Ian , Maxfield Tyler , Shain William , Perlmutter Steve , Kassegne Sam
Published: February 2020

For neural applications, materials that combine excellent electromechanical properties with long-term (> 5 years) and high fidelity performance capabilities have not yet been reported. Good electrodes should not only be able to adapt to eventual physiological changes in the body (e.g. inflammatory responses), but also able to perform without damaging the host tissue. The combination of these two characteristics is difficult to accomplish, because the ability of a material to undergo changes is often accompanied by the formation of reaction products that might interact with the surrounding tissue, and eventually harm it. Glassy carbon is a biocompatible and electrochemically inert material with tunable mechanical and electrical properties, high charge injection capacity and great resistance to corrosion. These merits motivate the use of glassy carbon for neural applications, and in particular for the realization of electrocorticography (ECoG) microelectrodes that can sense and stimulate brain activity.  Thus we propose to replace the commonly used noble metals like platinum, gold and iridium, with glassy carbon to improve the performances of traditional neural prostheses, thanks to better charge transfer capabilities and higher electrochemical stability. This investigation specifically reports characterization of glassy carbon microelectrode arrays (MEAs) used to sense and stimulate neural activity. Further, we report on key findings in long-term effects based on histological analysis of the brain tissue after chronic implants. Significant focus is given in this work to the investigation of tissue responses of motor cortex after 6 weeks of implantation, and to materials degradation of chronic in-vivo implants. In-vivo long-term impedance measurements and brain activity recordings are also performed to test the functionality of the neural devices and reported here.
Study of Pulling Effect on the Electrical Conductivity of Suspended Carbon Microfibers Due to Electromechanical Spinning (EMS)
Authors: Salazar Arnoldo , Bauer Maria , Holmberg Sunshine , Madou Marc J
Published: February 2020

Electromechanical Spinning (EMS) of fibers from the negative photoresist SU-8, in combination with photolithography and pyrolysis is used for the fabrication of monolithic carbon devices based on suspended carbon micro/nanofibers. During pyrolysis, the SU-8 fibers experience an elongation due to the shrinkage that the walls undergo in this process. Elongation or stretching of the fibers can be associated with increased graphitization. This is observed as an increased electrical conductivity and Young's modulus in the obtained fibers. Besides pyrolysis, the fibers experience a pulling effect during EMS deposition due to: 1) electrical pulling during jet formation and 2) mechanical pulling from the collecting movable substrate. Few information exists on the effect that the pulling of the polymer jet during EMS has over the final carbon fibers. This work quantifies this effect by observing the change in the carbon fiber's electrical conductivity.
Effects of a Magnetic Field on Anodic Dissolution and Surface Morphology of Iron in a Chloride Solution with Nitrite Ions
Authors: Chen Zhen , Li Hongjuan , Xiao Qian , Lu Zhanpeng
Published: February 2020

The corrosion of metallic materials in industrial and natural environments,especially localized corrosions such as pitting corrosion, crevice corrosion and stress corrosion cracking, caused huge damage. Some metallic components servicing in corrosive environments can be affected by magnetic fields produced by the special electrical equipment nearby. To analyze and evaluate the corrosion behavior under magnetic field, it is necessary to understand the effect of magnetic field on uniform and localized corrosion.

In this study, the effects of a 0.4T magnetic field on the electrochemical behavior and corrosion morphologies of iron in chloride solutions with sodium nitrite ions were studied by optical microscope (OM), scanning electron microscope (SEM) and several electrochemical methods such as potentiodynamic polarization curve, potentiostatic polarization and electrochemical impedance spectroscopy,

Potentials in different regions of the anodic polarization curves were chosen to for potentiostatic polarization by applying or removing a 0.4T magnetic field. The current density vs. time curves were measured, as shown in Fig. 1. The impact of magnetic field on the surface morphology of the electrodes after potentiostatic polarization were observed.

The anodic current density increased with increasing polarization potential with or without a 0.4T magnetic field. The current density was very low in the passivation regions during potentiostatic polarization, which was reduced by the applied magnetic field, as shown in Fig. 1 a. The effect of the applied magnetic field on the the current density in near the passivation-transpassive transition potential was complex. The applied magnetic field increased the anodic current density under high potentials such as 0.4 V(SCE), as shown in Fig. 1 b.

The changing of pit number and area for iron in chloride solutions with sodium nitrite with polarization potential exhibited differences with or without 0.4 T magnetic field. The impact of magnetic field on the pitting corrosion is closely related to the polarization potentials, polarization time and the initial state of the electrode surface.

Figure 1
The Effects of Hydrogen on Corrosion Products Formed on Iron in Chloride Solutions
Authors: Ejaz Ahsan , Chen Junjie , Xiao Qian , Han Guangdong , Lu Zhanpeng
Published: February 2020

The effects of charged hydrogen on the properties of the surface films formed on iron in pure water and 10-4 to 0.5 mol/L NaCl solutions at 25°Cwere investigated by open circuit potential (OCP) measurements, optical microscope, scanning electron microscope and X-ray diffraction (XRD). After 21h immersion in pure water, the surface of non-charged iron did not significantly and showed only local corrosion sites, while the surface of hydrogen-charged iron was covered with dark film with many yellow corrosion sites on it. After 21h immersion in 10-4 mol/L NaCl solution,  the non-charged iron was partly covered by surface film, while the hydrogen-charged iron was fully covered by surface film, as shown in Fig. 1. After 21h immersion in 0.5 mol/L NaCl solution, the surface of the non-charged iron was partly dark and partly covered with yellow rusts, and the surface of the hydrogen-charged iron had a larger area covered with more yellow rusts than that on the non-charged iron, as shown in Fig. 2. Results of OCP monitoring showed that OCP values for hydrogen-charged iron in pure water, 10-3 and 10-4 mol/L NaCl solutions were lower than those for non-charged iron, as partly shown in Fig. 3a. In 0.5 mol/L NaCl solution, the OCP differences between non-charged iron and hydrogen-charged iron was at first big but gradually became smaller with increasing immersion time, as shown in Fig. 3b. Raman spectra showed the presence of magnetite in the film on hydrogen-charged iron after immersion in 10-4 mol/L NaCl solution, as shown in Fig. 4a, which was supported by XRD results. Yellow rust and the XRD peak for hematite in the films on non-charged and hydrogen iron specimens (Fig. 4) indicated that the mechanism for the effect of hydrogen on the corrosion products of iron in dilute NaCl solutions could be different from that in concentrated NaCl solutions. In solutions with a high chloride concentration, hydrogen in iron might be able to promote the formation of high valence iron oxide, while in many other cases it was found that the formation of magnetite was promoted by hydrogen in iron.

Figure 1
Inhibition Effect of Some Cationic Surfactants on Carbon Steel in 1M H2so4 and 1M HCl Medium
Authors: Branzoi Florina , Pacuretu Catalina , Branzoi Roxana
Published: February 2020

The inhibition effect of some cationic surfactants (bromide hexadecylpyridiunium, bromide haxadecyltrimethylammnonium and chloride dodecyltrimethylammonium) on the corrosion of two carbon steels (OL 37 and OLC 45) in 1M H2SO4 and 1M HCl was studied weight loss method, potentiostatic and potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and metallurgical microscopy techniques.

The inhibition activity analysis of these organic inhibitors was made by assuming that the mechanism of inhibition by organic molecules is chemisorptions. We presume that, these organic inhibitors inhibit corrosion of carbon steel by a protective mechanism, forming insoluble iron complexes and repairing the porous oxide layers. The addition of the organic inhibitors led in all the cases to inhibition of the corrosion process in acidic solution at different temperatures. At concentrations lower than critical micelle concentration (CMC), the inhibition of these three surfactants is negligible and at concentrations higher than the CMC, the inhibiting action of these inhibitors increases rapidly. Polarization curves indicate that they are mixed type of inhibitors. The inhibition efficiency was high in all the studied cases. The corrosion parameters obtained from polarization curves and from EIS spectra are in good concordance and point out the inhibitory action of cationic surfactants. The adsorptions of the organic compounds on the carbon steels surface obeyed Langmuir’s isotherm. The thermodynamic parameters of adsorption enthalpy (ΔH0), adsorption free energy (ΔG0) and adsorption entropy (ΔS0) were calculated. Further characterization using Fourier transform infrared spectroscopy (FT-IR) demonstrates the adsorption of organic inhibitors and the formation of corrosion products on the carbon steels surface. The inhibition process was attributed to the formation of the adsorbed film on the metal surface that protects the metal against corrosive agents. The EIS measurements have confirmed this protection and pointed out the formation of adsorption layers on the electrode surface.
Comparative Corrosion Behavior of Austenitic Stainless Steels in Carbonate Melt at 650 °C Under Controlled CO2-O2 Environment
Authors: Sah Santosh Prasad , Tada Eiji , Nishikata Atsushi
Published: February 2020

Concentrated solar power (CSP) has recently attracted much attention as clean energy mainly for base load applications. High temperature CSP technology has high efficiency and it can attract wide commercial applications. Corrosion of metallic materials is a key problem for high temperature CSP systems. Careful selection of molten medium and metallic material can slow down the corrosion processes and hence extend the overall life span of CSP plants. High temperature oils and nitrate-based salts are commonly used for commercial CSP plants. These materials are not stable at temperature higher than 600 °C. However, alkali metal carbonates are stable beyond 800 °C and have working temperature of ~ 400-800 °C. These carbonates are less expensive and more environment friendly than the state-of-art high temperature oils [1]. Employing high corrosion resistance of cheaper alloys, like stainless steels, could significantly promote the popularity of CSP plants. In this study, corrosion behavior of austenitic stainless steels (SS) is observed in ternary alkali carbonate melt at 650 °C under defined CO2-O2 gas environment.   

Weight loss, electrochemical characterization and morphological and microstructural examination were carried out to understand the corrosion behavior of Type 304 SS, Type 316L SS and Type 310S SS in 43Li2CO3-31.5Na2CO3-25K2CO3 (mol%) melt at 650 °C under flowing 0.98 atm CO2-0.02 atm O2 mixed gas.

Weight loss observed due to 24 hours corrosion is 7.7 mg cm-2 for Type 304 SS, 6.5 mg cm-2 for Type 316L SS and 1 mg cm-2 for Type 310S SS. Potentiodynamic polarization showed that corrosion of SS is a cathodic-controlled process. Corrosion potential of Type 310S SS is nobler than that of Type 316L and Type 304 SS. Reduced weight loss of Type 310S SS due to corrosion should be due to high potential of anode reaction. Cathodic limiting current is not significantly different for all the SS; however, it is slightly higher for Type 304 SS than that of Type 316L and should be responsible for slightly higher weight loss of Type 304 SS. Anodic polarization behavior well agrees with the weight loss observed for all the examined SS. SEM and EDS analysis showed that a very thin Cr-rich uniform corrosion layer is formed on Type 310S; however, thicker corrosion layer formed on Type 304 is composed of a heterogeneous mixture of Cr- and Fe-rich phases. Corrosion layer formed on Type 316L is Cr-rich but locally contains Fe-rich phases. Corrosion resistance of SS in carbonate melt in decreasing order is as: Type 310S>Type 316L>Type 304.

This work was supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “energy carrier” (Funding agency: JST).

Reference

K. Vignarooban, X. Xu, A. Arvay, K. Hsu, A. M. Kannan, Applied Energy, 146 (2015) 383-396
Polarization Behavior of Iron Under Artificial Zinc Corrosion Products Formed from Aqueous MgCl2 Solutions Containing Zn2+
Authors: Tada Eiji , Nishikata Atsushi
Published: February 2020

Galvanized steels are widely used in various industrial fields such as automobiles and construction since they have excellent corrosion protection in atmospheric corrosion environments.  The corrosion protection property of Zn coating has been improved by addition of another elements such as Mg and Al.  However, the effect of Mg on corrosion protection of the galvanized coating is still unclear.  In this study, we investigated polarization behavior of iron under artificial zinc corrosion products formed in an aqueous solution containing Mg2+.

A pure iron bar (purity: 99.9%) was annealed at 850 oC for 2 h and sliced into disks of 12 mm in diameter and several millimeter in thickness.  The surface of the iron disk was abraded with SiC papers up to JIS #2000 grit and then the disk was etched chemically to get a mirror-like surface finish.  To form artificial zinc corrosion products on an iron disk, it was polarized cathodically at various potential for 1.8 ks in an aqueous solution of 1 M MgCl2 containing ZnCl2.  The zinc corrosion products formed on the iron disk was investigated by SEM and other analytical instruments.  Polarization behavior of iron covered with the artificial zinc corrosion products was investigated by the measurements of cathodic and anodic polarization curves in 0.1 M NaCl.

Artificial zinc corrosion products were successfully formed on an iron disk during cathodic polarization in 1 M MgCl2 containing ZnCl2.  It was found from surface analysis that the amount of the artificial zinc corrosion products formed on the disk changes depending on polarization potential.  At around -0.85 V (SSE), the whole surface of the iron disk was covered homogeneously with zinc corrosion products.  Cathodic polarization curves for iron covered with artificial zinc corrosion products showed that oxygen reduction reaction (ORR) is slightly inhibited in comparison with ORR on bare iron.  On the other hand, anodic polarization curves for iron covered with artificial zinc corrosion products showed that anodic dissolution of iron under the zinc corrosion products also tends to be suppressed.  The effect of Mg on polarization behavior of iron covered with artificial zinc corrosion products is going to be discussed in detail.
(Invited) Tuning the Strain and Physical Properties of Highly Epitaxial Perovskite Thin Films on Vicinal Substrates
Authors: Lin Yuan , Yao Guang , Gao Min , Chen Chonglin
Published: February 2020

Controllable interfacial strain can manipulate the physical properties of epitaxial films and help understand the physical nature of the correlation between the properties and the atomic microstructures. In this presentation, we demonstrated that the interface strain in epitaxial thin films can be well controlled by adjusting the miscutting angle of a vicinal single-crystal substrate via a surface-step-terrace matching growth mode. Epitaxial perovskite or perovskite-like oxide thin films such as CaCu3Ti4O12 (CCTO) and (Ba,Sr)TiO3 were grown on vicinal (001) single-crystal LaAlO3 (LAO) substrates with various miscutting angles of 1.0°, 2.5°, and 5.0° by a polymer assisted deposition (PAD) technique. High-resolution X-ray diffraction were employed to study the epitaxial nature and interface strains induced by the substrate step terrace dimensions. It is found that the strain is determined by the mismatch between the lattice of the thin film and the substrate step terrace dimensions. A model is proposed that both compressive and tensile strained domains would form in the film to fit the size of each step terrace whereas the ratio of the two kinds of domains can be tuned by the miscutting angle. Based on this growth mode, a proper design of the substrate step terrace dimension can tune the properties of the thin films. For example, an optimized design of a CCTO thin film on a 5o-miscutting (001) LaAlO3 substrate can maintain a similar dielectric constant and reduce the dielectric loss by half an order of magnitude compared with the films grown on the regular (001) LaAlO3 substrates, briefly by releasing a large part of the interfacial stress through the complementary strained domains instead of dislocations.

This work is supported by the National Basic Research Program of China (973 Program) under Grant No. 2015CB351905, the National Natural Science Foundation of China (Nos. 51172036, 11329402, and 51372034), and the Technology Innovative Research Team of Sichuan Province of China (No.2015TD0005).
Low Dielectric Constant, Air-Cavities Created By the Use of Low-Ceiling Temperature Polymers
Authors: Schwartz Jared , Phillips Oluwadamilola , Pan Zhaoqun , Sutlief Alexandra , Kohl Paul A
Published: February 2020

Low decomposition temperature (<200oC) template polymers that decompose into gaseous products have been used as templating materials in the formation of air-cavities and porous dielectrics. It is especially important for the sacrificial, templating polymer to decompose cleanly to gaseous products at a specific temperature, which is compatible with the other materials present, especially the dielectric superstructure surrounding the sacrificial material. It is also important for the sacrificial polymer to leave little or no residue so that undesirable materials are not formed during the process.  One method of producing a low-temperature sacrificial material is the use of a low ceiling temperature polymer. Above the ceiling temperature, the polymer reverts back to monomers.  A polymer with a low ceiling temperature can rapidly depolymerization back to monomer and vaporize, if the monomer vapor pressure is suitably high at room temperature (>10 Torr).  This work focuses on the synthesis and decomposition of low ceiling temperature polyaldehydes using high vapor pressure monomers.  Polyphthalaldehyde could be used as the template polymer for creating air-gaps and porous dielectrics. Polyphthalaldehyde has a moderate decomposition temperature of 125oC and a moderate vapor pressure.  Copolymers of aldehydes are of interest because the vapor pressure of the sacrificial polymer decomposition products can be increased. Polyaldehyde copolymers were synthesized with the goal of increasing the thermal decomposition temperature and increase the evaporation rate of the decomposition products.  A random copolymer of phthalaldehyde and butyraldehyde raised the 50 percent decomposition temperature of the polyaldehyde by 25oC when compared to the phthalaldehyde.  homopolymer.  Even a small amount of the higher vapor pressure monomer, butyraldehyde, increased the evaporation rate substantially.
(Invited) The Defects of ZnO Nanorods Passivated By Ultra-Thin Al2O3 Film
Authors: Li Shibin , Liu Detao , Zhang Peng , Wang Yafei , Sarvari Hojjatollah , Xuan Yaoyu , Chen Zhi David
Published: February 2020

In recent years, perovskite solar cells have attracted many researchers’ interest because of the rapid increment of the efficiency of perovskite solar cells. Titanium dioxide is used widely as the electron transportation layer (ETL), but it needs high temperature process. Owing to the preparation at low temperature, Zinc oxide is regarded as the promising materials for the ETL of the flexible perovskite solar cells. ZnO nanorods is grown to improve the efficiency of charges transportation. As shown in Fig.1 (a), a dense of ZnO nanorods arrays have been prepared on conductive glass (SnO2: F) (FTO) substrate by hydrothermal growth. The compact seed ZnO layer between the ZnO nanorods and FTO is prepared by the spin-coating method. The defects on the nanorods may induce the degeneration of the performance of ZnO based perovskite solar cells. Ultra-thin Al2O3 film is deposited by atomic layer deposition (ALD) on the ZnO nanorods with 5 cycles to passivate the defects. The perovskite layer is afterwards spin-coated on passiviated ZnO nanorods, and holes transportation material (HTM) is prepared on the top of perovskite subsequently as shown in Fig.1 (b). ZnO based perovskite solar cell is fabricated after the evaporation of gold electrode on HTM layer. Because the thickness of Al2O3 coating layer is less than 1nm, the photogenerated electrons can easily tunnel to the ZnO layer and realize the separation of charges. The average photoelectric conversion efficiency of Al2O3 coated perovskite solar cells based on ZnO nanorods has been improved by10% .

Figure 1
(Invited) Photocurrents in Topological Insulators Based on Hgte
Authors: Dantscher Kathrin-Maria , Ganichev Sergey D.
Published: February 2020

The paper overviews experimental and theoretical studies of photocurrents induced in various Dirac fermions systems by polarized electromagnetic radiation. We consider second order opto-electronic phenomena [1,2] excited by terahertz radiation in topological insulators (TIs). In focus of our discussion are two- (2D) and three- (3D) dimensional HgTe-based topological TIs [3,4]. We present the state-of-the-art of the experiments, discuss the phenomenological and microscopic theory, and show that nonlinear transport excited by laser radiation opens up new opportunities for the probing of Dirac electrons. A particular attention is paid to the helicity sensitive edge photogalvanic currents in 2D TIs [5] and cyclotron resonance assisted spin polarized currents in 3D TIs [6] and HgTe/HgCdTe quantum wells of a critical thickness [7,8]. We demonstrate that cyclotron resonance induced photocurrents in the surface states of 3D TIs provides a sensitive method to probe the cyclotron masses of Dirac fermions, which can be applied even for micrometer sized structures, to measure Fermi velocity, and to study tiny details of the spin orientation in TIs, in particular, to explore the role of bulk and structure inversion asymmetry in the band structure.

[1] S.D. Ganichev and W. Prettl, Intense Terahertz Excitation of Semiconductors, Oxford University Press (2006)

[2] M.M. Glazov and S.D. Ganichev, Physics Reports 535 101-138 (2014)

[3] B.A. Bernevig, et al., Science 314, 1757 (2006)

[4] M.S. König, et al., Science 318, 766 (2007)

[5] Z.D. Kvon, et al., JETP Letters 99, 290-294 (2014)

[6] K.-M. Dantscher, et al., Phys. Rev. B 92, 165314 (2015)

[7] P. Olbrich, et al., Phys. Rev. B 87, 235439 (2013)

[8] C. Zoth, et al., Phys. Rev. B 90, 205415 (2014)
(Invited) Control of Thermally-Grown SiO2/4H-SiC Mos Interface Properties and Its Impact on Mosfet Performances
Authors: Kita Koji , Hirai Hirohisa , Fujino Yuki , Kajifusa Hiroyuki
Published: February 2020

4H-SiC MOSFETs is extensively studied for high-voltage power device applications, however, the control of MOS interface properties have been one of the most challenging issues to meet the requirements of low on-resistivity and high-reliability. It is a challenging issue to reduce interface defect density at thermally oxidized SiO2/SiC interfaces since the thermal oxidation is inevitably accompanied with by a carbon-related product generation. We recently demonstrated that selective use of a high-temperature oxidation on 4H-SiC (0001) resulted in a significant improvement of MOS properties by a formation of a MOS capacitor with nearly-ideal CV characteristics and less interface state density (Dit) [1], even without introduction of nitrogen by NO annealing process. We consider high-temperature oxidation works to reduce the remaining carbon byproduct significantly [2].

  We also investigated the impact of the post-deposition annealing (POA) conditions on interface state density. It was found that the POA at a relatively low temperature in O2 is quite effective to reduce Dit, probably due to the reduction of oxygen-deficiency induced defects. Employing sufficiently low temperature is so important to suppress further oxidation of the interface during POA. Thus appropriate selection of both POA time and temperature is inevitable to optimize the POA effects. We also found a significant decrease of near-interface oxide traps (NITs), which are the most possible origin of the slow responses of the electrical characteristics to the applied bias. After an optimization of the post-oxidation annealing processes in oxygen ambient at low temperature, the estimated density of NITs decreased by several times.

  Finally, a lateral-MOSFET on 4H-SiC (0001) was fabricated based on those process techniques. A relatively high effective mobility ~30 cm2/Vs, as a SiC MOSFET without nitridation of the interface, was obtained with the gate stack prepared simply by the combination of high-temperature thermal oxidation and post-oxidation annealing processes, while we can expecte a further improvement by applying the additional passivation techniques. The process design of thermal oxidation of SiC would be one of the promising ways to improve the MOSFET performance from the viewpoint of both the reduction of channel resistance and the improvement of device reliability.

This work was partly supported by CSTI Cros-ministerial Strategic Innovation Promotion Program"Nex-generation power electrnonics" (funding agency: NEDO) and JSPS KAKENHI.

[1] R. H. Kikuchi and K. Kita, Appl. Phys. Lett. 105, 032106 (2014).

[2] H. Hirai and K. Kita, Appl. Phys. Express 8, 021401 (2015).