bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comprehensive Structure-Function Studies of Photoactive Ionic π-Conjugated Supermolecular Assemblies
Authors: Mazur Ursula , Hipps K W 
Published: February 2020

Organic semiconductors possess unique photon absorption characteristics that result from their highly polarizable π-electronic structures. Although organic semiconductors have become viable alternatives to their well-established inorganic counterparts there is still a continuing need for research in controlling their composition and structure since those factors determine how they function. Consequently, a good fundamental understanding of structure–property relationships is essential in designing and building high performance, stable, and durable molecular materials and is one of the main scientific challenges for advancing organic optoelectronic technology.
The work that we will present is a detailed structure–property study of ionic porphyrin based semiconductors using both experiment and theory. Nano to millimeter size crystalline binary porphyrin structures were synthesized reproducibly from oppositely charged synthons and characterized using XRD, AFM, SEM, DRS, UV-visible, and photoconductivity measurements. The photoconductive properties of the porphyrin materials are linked with their molecular organization and morphology. Electronic band calculations help explain the experimental photoconductivity measurements and provide guidelines for future structure modification to optimize charge transport properties in these π-conjugated systems. These studies are the first to combine structure determination, electronic band calculations, and experiment in a unified approach for these materials.
Coordination to Supported Metalloporphyrins at the Solid-Solution Interface
Authors: Hipps K W , Mazur Ursula 
Published: February 2020

Metalloporphyrins play a starring role in the chemistry and physics of biology, photo-electricity, sensing, catalysis, electrochemistry, and other important areas. Because of this, they have been widely studied (both experimentally and theoretically) in the solid state and in solution. Very recently it has become possible to experimentally probe their chemistry at the single molecule level. Of even more relavence to applications, it is now possible to do single molecule studies at the solution-solid interface. Scanning tunneling microscopy (STM) provides images, at the single molecule level, of reactions between surface supported metal porphyrins and molecular species like oxygen, imidazole, and other reactive species. These scanning probe studies clearly demonstrated that the chemistry of the supported porphyrin can be very different than in solution. Density functional theory has allowed us to more fully understand the nature of the substrate-porphyrin-ligand interaction relative to the substrate free case. We find that whenever the porphyrin is supported on a conducting substrate, there is a complex charge exchange process that can significantly modify the axial binding relative to what is observed in solution. In some cases, the interaction is such that even the spin state of the surface supported metal ion differs from that of the same chemical system in solution or gas phase. We will present examples of experimental and computational studies of this new chemistry.
Tailoring the Corrosion Behavior of Biodegradable Mg Alloys By Surface Modification
Authors: Virtanen Sannakaisa 
Published: February 2020

The possible use Mg alloys in biodegradable biomedical devices has found tremendously increasing research interest in recent years. However, the corrosion rate should be controlled for the specific applications. There is still need for optimization and further development of biocompatible, biofunctional and biodegradable coatings for Mg alloys. The presentation discusses some recent developments on various surface modification and coating approaches on Mg alloys, including coatings based on natural and synthetic biopolymers. Fabrication routes of coatings will be presented and discussed. Corrosion protection effects, degradation behavior of the coatings, and biocompatibility of the treated surfaces will be discussed.
Deposition of Ultrathin Cellulose Nanofibers Films As Bio-Implant Corrosion Coatings
Authors: Wilson Benjamin Paul , Paukkonen Niina , Yliniemi Kirsi , Hakalahti Minna , Tammelin Tekla , Kontturi Eero , Lundström Mari 
Published: February 2020

The wide use of magnesium and magnesium-based alloys for bio-implant materials has so far been restricted due to the rapid corrosion rate of such materials under in-vivo conditions 1,2. Cellulose based coatings have previously been examined as coatings for magnesium materials although the use of TEMPO-oxidised nano-fibrillated cellulose (CNF-TEMPO) coatings has yet to be explored 3,4. The work outlines details of an investigation in to the effect that deposition method has on the coating characteristics. Three different methods were used to deposit CNF-TEMPO coatings including adsorption, spin coating and anodic electrophoretic deposition. The coatings were subsequent analysed using atomic force microscopy (AFM), ellipsometry and quartz crystal microbalance (QCM) to determine differences in nanotopographic surface roughness and hydrophilicity in particular. The ability of the EPD technique to deposit films from relative dilute solutions (0.01 to 0.1 wt-%) was demonstrated. Finally, samples of magnesium were coated and the corrosion properties of the ultrathin films were determined using a number of electrochemical techniques including linear sweep voltammetry, polarization and free corrosion measurements. Overall, the results show that CNF-TEMPO coatings produced using the EPD method offer a potential starting point for the next generation of biobased coatings for implant materials.

References

[1] S. Virtanen, Mater. Sci. Eng. B, 2011, 176, 1600-1608
[2] F. Witte, N. Hort, C. Vogt, S. Cohen, K. U. Kainer, R. Willumeit, F. Feyerabend, Current Opinion in Solid State and Materials Science, 2008, 12, 63-72.
[3] S. Heise, S. Virtanen, A. R. Boccaccini, Journal of Biomedical Materials Research A, 2016 104A, 2628-2641.
[4] K. Yliniemi, B. P. Wilson, F. Singer, S. Höhn, E. Kontturi S. Virtanen, ACS Applied Materials and Interfaces, 2014, 6, 22393-22399.

Figure 1
In-Situ Determination of Hydrogen Evolution Rate on Mg and Mg Alloy during Anodic Dissolution By Gas-Chromatographic Analysis
Authors: Hoshi Yoshinao , Takemiya Rie , Shitanda Isao , Itagaki Masayuki 
Published: February 2020

Mg and Mg alloys are expected to be an active material for the negative electrode of air batteries 1) because they dissolve actively in the aqueous solution at less noble potential. However, the hydrogen evolution is occurred on the Mg and Mg alloys during the anodic dissolution in the aqueous solution, which calls the negative difference effect, NDE 2, 3). It may lead to the self-discharge and loss of discharge capacity of air batteries in operation.
In the present study, we determined the hydrogen evolution rate on Mg and Mg alloys during anodic dissolution by gas-chromatographic analysis. Song et al. 4) reported the hydrogen evolution behavior of Mg and Mg alloys. They 4) carried out the gas collection by using a burette vertically mounted over the funnel to estimate the volume of hydrogen gas generated on Mg alloys at different applied current density. Comparing to this, we previously developed an electrochemical cell combined with a gas chromatograph 5) to perform an in-situ determination of hydrogen evolution rate on Mg during anodic dissolution. In this system, the gas generated on the working electrode is directly delivered to a gas chromatograph by a stream of carrier gas 5), namely, the qualitative and quantitative analysis of the gas generated on the working electrode can be carried out. It enables us the analysis of gases involving nitrogen and oxygen during anodic dissolution of Mg and Mg alloys. The details of the developed system and measurement conditions are described in our previous work 5). In the present study, hydrogen evolution rate on various kinds of Mg alloys during anodic dissolution were determined by developed system and the gases evolved on Mg alloys during anodic dissolution were discriminated.
References:
1. R. P. Hamlen, E. C. Jerabek, J. C. Ruzzo and E. G. Siwek, J. Electrochem. Soc., 116, 1588 (1969).
2. G. Song, A. Atrens, D. St John, X. Wu and J. Nairn, Corros. Sci., 39, 1981 (1997).
3. G. S. Frankel, A. Samaniego and N. Birbilis, Corros. Sci., 70, 104 (2013).
4. G. Song, A. Atrens, D. Stjohn, J. Nairn and Y. Li, Corros. Sci., 39, 855 (1997).
5. Y. Hoshi, R. Takemiya, I. Shitanda and M. Itagaki, J. Electrochem. Soc., 163, C303 (2016).
Impedance Measurements to Monitor Concrete Degradation and Rebar Corrosion
Authors: Itagaki Masayuki , Okamoto Tatsuki , Tokieda Hiroyuki , Hoshi Yoshinao , Shitanda Isao , Kato Yoshitaka 
Published: February 2020

The degradation of steel-reinforced concrete is serious problem in infrastructures. It is well known that the rebar corrosion in concrete is strongly influenced by the conditions of cover concrete. Figure 1 shows schemes of interface between steel rebar and concrete. Thin water layer is formed at this interface due to water absorption in the concrete which covers the steel rebar. And this water layer is called “transition zone” in the field of civil engineering. The pH of water at transition zone is high when the concrete is good health status, and the passive film is formed on steel rebar. The breakdown of passive film occurs by neutralization and chloride concentration in the water layer with the degradation of concrete. Corrosion resistance of steel rebar is influenced by the water quality in the transition zone. Thus, we can conclude that rebar corrosion in concrete is electrochemical process at metal/water interface. Electrochemical measurements are useful to investigate the corrosion mechanisms. There are some literatures regarding the electrochemical tests, which are mainly measurements of corrosion potential [1] and polarization curves, to evaluate the stability of passive film formed on rebar in concrete. Dawson et al. [2] applied an electrochemical impedance spectroscopy (EIS) to the investigation of rebar corrosion in concrete because the charge transfer resistance at rebar/concrete interface can be determined from the impedance spectrum.
The authors developed an electrode as a sensor probe to monitor concrete degradation and rebar corrosion. A couple of electrodes, which were made of same material as rebar, can be embedded in concrete structure and complex impedance can be measured continuously on the basis of two-electrode method. In this presentation, the authors report the results of three impedance measurements as follows.
(1) Impedance between two electrodes in aqueous solution that simulates the water quality of transition zone (laboratory test).
(2) Impedance between two electrodes embedded in the concrete which was fabricated in the laboratory.
(3) Field test at bridge pier of the highway in coastal marine environment.
References:
[1] ASTM C 876-91 (Reapproved 1999): Standard Test Method for Half-Cell Potentials of Uncoated Reinforcing Steel in Concrete, Annual Book of ASTM standards, Vol. 03.02, pp. 457-462, 1999.
[2] J. L. Dawson, L. M. Callow, K. Hladky and J. A. Richardson, Corrosion/78, No-125 (1978).

Figure 1
A New Reactive-Transport Modeling Framework for Simulating Pore Solution Chemistry at Localized Imperfections Along Steel-Concrete Interface
Authors: Isgor Burkan , Jafari Azad Vahid 
Published: February 2020

The variability and uncertainty associated with chloride thresholds for corrosion initiation in reinforced concrete structures can be partly explained by the presence of localized defects and imperfections along steel-concrete interface such as elongated cracks, pores, gaps, crevices, and mill scale. It has been demonstrated in prior research that pore solution in these imperfections might be different from that of the bulk pore solution, and this difference may create the necessary conditions for the breakdown of the passive film. These studies showed that the chemistry of the pore solution, in particular pH and Cl-/OH-, within localized defects provide more favorable conditions for depassivation than the bulk concrete pore solution. Local acidification and increase in Cl-/OH- within these defects were observed, albeit to different degrees. Defect geometry has been found to be a critical parameter affecting local acidification and the increase in Cl-/OH-. However, chemical composition of the pore solution, reactions between corrosion products and the ionic species in the pore solution and changes in transport properties within the defect due to accumulation of solid corrosion product have also been shown to affect the process. Due to these complications, it is challenging to study these effects experimentally, hence numerical investigation techniques are required.
In order to better understand the processes that take place within local defects along the steel-concrete interface a reactive-transport modeling framework is developed. The model incorporates finite element analysis (FEM) with thermodynamic/kinetic modeling of cementitious systems. The FEM module is responsible for modeling multiphysics phenomena such as corrosion, mass transport, heat transfer, phase flow and kinetics, while thermodynamic module is used to model chemically complex reaction computations based on Gibbs Energy Minimization (GEM) theory. A non-iterative operator splitting technique in a time marching scheme is used for uncoupling the multiphysics phenomena from reaction equations. The framework is able to analyze complex chemical systems including processes that take place in cementitious materials and as a result of corrosion reactions.
The presentation will highlight the main components of developed framework and demonstrate its functionality though case studies and hypothetical simulations.
Anodic Oxidation of Bismuth in Halide Containing Electrolytes
Authors: Macak Jan M. , Sopha Hanna 
Published: February 2020

The synthesis of highly-ordered nanostructures of valve metal oxides has recently attracted huge scientific and technological interest motivated by their possible use in many applications. The two most established members of this group of materials are nanoporous Al2O3 and TiO2 nanotubes [1,2]. While Al2O3 membranes have been since than widely used as template material of choice for a range of materials [2-4] due to the flexibility of the pore diameter/length and the relative ease of the Al2O3 dissolution, TiO2 nanotubes received high attention because of their applications in e.g. photocatalysis, water splitting, solar cells and biomedical uses [5].
Bismuth oxide is another interesting material and its nanostructures show an enhanced photoelectrochemical performance [6,7]. However, the formation of bismuth nanostructures, such as bismuth oxide nanopores [6,7] or bismuth phosphate nanorods [8], by anodization is not well explored by now. Similar to the formation of nanoporous Al2O3 nanoporous Bi2O3 was produced in acidic, F--free electrolytes.
In this presentation, we demonstrate the anodization of bismuth in halide containing electrolytes similar to the electrolytes classically used for the formation of TiO2 nanotubes.
References
1. H. Masuda, K. Fukuda, Science, 268 (1995) 1466.
2. J.M. Macak et al., Curr. Opin. Solid State Mater. Sci. 1-2 (2007) 3.
2. K. Nielsch, F. Müller, A.-P. Li, U. Gösele, Adv. Mater. 12 (2000) 582.
3. H. Asoh et al., J. Electrochem. Soc. 148 (2001) B152.
4. J. Kolar, J. M. Macak, K. Terabe, T. Wagner, J. Mater. Chem. C, 2 (2014) 349.
5. K. Lee, A. Mazare, P. Schmuki, Chem. Rev. 114 (2014) 9385.
6. X. Lv, J. Zhao, X. Wang, X. Xu, L. Bai, B. Wang, J. Solid. Stat Electrochem. 17 (2013) 1215.
7. K.C. Chitrada, K. S. Raja, R. Gakhar, D. Chidambaram, J. Electrochem. Soc. 162 (2015) H380.
8. M. Yang, N. K. Shrestha, R. Hahn, P. Schmuki, Electrochem. Solid-State Lett. 13 (2010) C5.
Influence of CVD Growth Parameters on the Corrosion Resistance of the Resultant Graphene Coating
Authors: R. Anisur M. , Banerjee Parama Chakraborty , Singh Raman R K 
Published: February 2020

Graphene coatings have been reported to suppress corrosion of various metal substrates due to their chemical inertness. However, the extent of protection offered depends on the uniformity and defect density of the graphene layers developed on the metallic substrates. Among the various synthesis methods, chemical vapour deposition (CVD) is one of the most promising ones to produce graphene coating on a variety of metal substrates. However, achieving controlled CVD growth of large area, uniform and less defective graphene coating is still challenging. This study investigates the influence of various CVD growth parameters during the graphene synthesis, such as hydrogen flow, carbon precursor flow, growth temperature and cooling rate used on the uniformity of the resultant graphene coating and its corrosion resistance. The barrier properties of graphene-coated Cu substrates were evaluated using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) in 0.1 M NaCl for 1008 h. High graphene growth temperature (1060 ºC) and low hydrocarbon flow rate (1 sccm) in the absence of H2 flow were identified to synthesize a uniform graphene coating, which showed durable barrier performance. During the initial hours of immersion, the graphene coated copper (Cu) specimens showed about one and half order of magnitude improvement in corrosion resistance in 0.1 M NaCl and even after 1008 h, the corrosion resistance provided by the graphene coating was almost five times more than that of bare Cu. The optimized CVD graphene parameters reported here can provide a new direction to achieve long-term durable graphene coating.
Electrochemical Behavior of Steels in CO2-H2o Systems for Direct Supercritical CO2 Power Cycle Applications
Authors: Repukaiti Richard , Teeter Lucas , Ziomek-Moroz Margaret , Dogan Omer , Tucker Julie 
Published: February 2020

In experiments simulating direct supercritical CO2 power cycle conditions, a change in the corrosion behavior of 316 and 347H stainless steels has been observed during the startup and shut down periods. In these exposure tests, the steels experienced environments which are CO2-saturated water systems at elevated temperature and pressure. Due to the electrochemical nature of corrosion processes occurring in these systems, corrosion behavior of ferritic-martensitic P91 steel and austenitic 347H stainless steel was studied in CO2-saturated H2O using potentiodynamic and potentiostatic experiments. The solution was prepared by bubbling CO2 through H2O at constant temperature. The solution preparation and the experiments were carried out at 25 and 50°C.
Potentiodynamic experiments, including cyclic voltammetry, were performed to determine the corrosion behavior of selected materials. Corrosion rates were determined from linear polarization resistance experiments. Optical and scanning electron microscopy of the corroded surfaces were performed after the potentiostatic experiments.
(Invited) Switchable White Graphene: Electrochemistry of the Boron Nitride Nanomesh
Authors: Mertens Stijn F. L. 
Published: February 2020

On Rh(111), a monolayer of hexagonal boron nitride (h-BN, isoelectronic with graphene) forms a so-called nanomesh superstructure [1], characterized by a 3.2-nm lattice constant and strong electronic corrugation, which can be used for trapping atoms and molecules [2,3]. Here, we show that hydrogen underpotential deposition (H upd) is easier on h-BN/Rh(111) than on the naked substrate [4], and leads to submonolayer quantities of hydrogen intercalated between the h-BN overlayer and Rh(111), as demonstrated by electrolyte-to-vacuum transfer experiments and thermal desorption spectroscopy. In situ STM measurements reveal that the intercalation lifts the corrugation of the nanomesh, and that this process is fully reversible under potential control. Copper upd is used to quantify the defect density in the nanomesh, and to increase the understanding of the electrochemical window where the nanomesh is stable. By measuring dynamic contact angles of an electrolyte drop (see Figure), we show that the microscopic change within the 2-dimensional material leads to a macroscopic effect related to a 10% change in adsorption energy [4]. The static friction on the other hand, which can be extracted by extending the Young equation for non-equilibrium effects, remains unchanged for the surface in the two states.
[1] M. Corso, W. Auwärter, M. Muntwiler, A. Tamai, T. Greber, J. Osterwalder, Science 303 (2004) 217–220.
[2] S. Berner, M. Corso, R. Widmer, O. Groening, R. Laskowski, et al. Angew. Chem., Int. Ed. 46 (2007) 5115–5119.
[3] H. Dil, J. Lobo-Checa, R. Laskowski, P. Blaha, S. Berner, J. Osterwalder, T. Greber, Science 319 (2008) 1824–1826.
[4] S.F.L. Mertens, A. Hemmi, S. Muff, O. Gröning, S. De Feyter, J. Osterwalder, T. Greber, Nature 534 (2016) 676–679.

Figure 1
Nanoscale Spin-Transfer Torque MRAM Etching Using Various Gases
Authors: Yang Kyung Chae , Park Sung Woo , Lee Ho Seok , Yeom Geun Young 
Published: February 2020

As the volatile dynamic random access memory (DRAM) device faces a physical limitation, new memory devices are actively investigated to solve this problem. Among them, spin transfer torque magnetic random access memory (STT-MRAM) has received a lot of attention because of its very high speed of device, endurance, low power consumption of device, and high density memory cell in addition to the non-volatility of information. Especially, the MTJ memory elements which consist of CoxFeyBz/MgO/CoxFeyBz multilayer structure are the critical building blocks for high density magnetic random access memory with high tunneling magnetoresistance(TMR). However, the dry etching of MTJ stack with sub 70 nm is a challenging step in the fabrication of STT-MRAM. The etching of nanoscale MTJ induces oxidation in magnetic layer, pattern degradation and damage or sidewall redeposition at patterned MTJ sidewall especially.
In this study, for successful etching of MTJ and MTJ related materials, RIB (reactive ion beam) etching using NF3, CH3OH, and CO/NH3 gas mixture and ICP etching using Ar, He, CO/NH3 and so on were conducted. Etch characteristics of magnetic tunnel junction (MTJ) stacks masked with W were investigated precisely using field emission scanning electron microscopy (FE-SEM) and TEM (Transmission electron microscopy). Simulation of MTJ material and hardmask material was conducted with SRIM simulation to observe tendency with etch process of blank unit thin film samples. In addition, the magnetic hysteresis curves were analyzed by a vibrating sample magnetometer (VSM). The results showed that, among the various gas combinations, the use of He gas improved etch selectivity of MTJ materials over W and also improved the etch profile of MTJ features. Also the He etch gas could be beneficial in reducing damage. The detailed etch mechanism and results on the etching of MTJ materials will be presented.