bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study of Anticorrosion Coatings for Surface Modification of Biodegradable Magnesium Alloy
Authors: Wang Jing
Published: February 2020

Magnesium alloys material would dissolve easily in body fluid which contains chloride ion, and the corrosion products are necessary to the human body. Due to the suitable mechanical property, biocompatibility and biodegradability, magnesium alloys are promising in the development of bio-absorbable orthopedic implants for interventional therapy and bone tissue engineering. However, a rapid corrosion rate resulted form the intrinsically active response of magnesium alloys to chloride-containing blood plasma and human body fluid remains the problem. Subsequently, a better understanding of the interaction between magnesium alloys and human body environment is the prerequisite to lower the corrosion rate. The surface modification technique could change the surface composition and the degradation rate of magnesium alloys. In this study, Diamond-like carbon films (DLC) are deposited on AZ31 magnesium alloy by combining plasma enhanced unbalance magnetron sputtering physical vapor deposition (PEUMS-PVD) and microwave electron cyclotron resonance plasma enhanced chemical vapor deposition (MW-ECR PECVD) techniques. In these techniques, the SiC interlayer is introduced between metallic substrates and DLC films by using methane (CH4) and silicon target in order to increase the coating’s adherence. The corrosion behavior of the DLC films in simulated body fluid and biocompatibility have been measured and evaluated synthetically by the surface analysis technique, electrochemical measurement and hemocompatibility experiments.The present study demonstrated that DLC films were successfully formed by PECVD on Mg alloy substrate. Both films are composed of graphite that had a disorderedgraphite-like structure. Silicon component of Si/SiC intermediate layers suppresses the formation of sp2 graphitic clusters and increases the sp3 bonding and the hydrogen content in the DLC films. Based on these observations, it might be concludedthat DLC films on the Mg alloy substrate leads to a moderate increase in degradation resistance. As a hard DLC film was formed on the Mg alloy substrate, further study is worthwhile to check biocompatibility of these coatings and improve the quality of the film.
The Photogenerated Cathodic Protection of Steel Using the Thin Layers of Photoactive Nanocomposite Fabricated By Electrophoretic Deposition
Authors: Park Ji Hoon
Published: February 2020

The photogenerated cathodic protection of steel can be achieved by a photoactive coating layer. It is recently attracting attention because it can overcome the limitations of the sacrificial cathodic protection method. In theory, it can provide permanent cathodic protection because it used energy from solar light rather than to consume itself to protect against corrosion of steel. In the present work, a novel nano-structured layer for the photogenerated cathodic protection was coated on steel using electrophoretic deposition (EPD). Through EPD, thin photoactive composite films can effectively be fabricated on conductive substrates using the colloidal suspension of functional nanoparticles with the simple application of an electrical field. Firstly, crystalline TiO2 nanoparticles were deposited on a steel substrate by the EPD process for the photo-generated cathodic protection. To improve the cathodic protection ability of the photo-stimulated layer, graphene nanoplatelets were incorporated into the TiO2 composite layer by the simultaneous co-deposition of graphene and TiO2 nanoparticles using EPD. Despite the superior cathodic protection afforded by a photo-stimulated TiO2 EPD layer, the coating only works when exposed to solar irradiation during the daytime. However, steel suffers from corrosion at all times. There have been many attempts to overcome this drawback. The incorporation of various photo-electron storing materials into the coating layer is the most promising strategy for maintaining the efficacy of the cathodic protection that is provided by TiO2 in the absence of sunlight. WO3 nanoparticles were used in this study to impart photo-generated cathodic protection to the EPD layer at all times. Moreover, the graphene was exploited as a barrier to protect steel from corrosion because it forms a better barrier to molecules. A graphene film was prepared on steel using EPD with a suspension of graphene oxide in water. When graphene was used as an underlying film for the organic coating, the corrosion resistance of the coated steel improved significantly.
Reaction Mechanism of Lanthanide Zirconate Thermal Barrier Materials in Exposure to CMAS
Authors: Wang Honglong , Zhang Xingxing , Tarwater Emily , Agubra Victor , Fergus Jeff W.
Published: February 2020

The working temperature in gas turbine engines could reach as high as 1200°C. Thus, a ceramic coating is applied to protect the blade from high temperature. Additionally, molten dust from the air could cause the degradation and make the coatings fail to work. Lanthanide zirconia material is a new promising materials in thermal barrier coatings due to its high phase stability and corrosion resistance from CMAS (CaO-MgO-Al2O3-SiO2). This research would demonstrate the corrosion resistance is due to the dense reaction layer which can prevent further corrosion.
Gravimetric Measurement of Hydrogen Evolution on Magnesium
Authors: Fajardo Santiago , Frankel Gerald
Published: February 2020

The aim of this work is to study the suitability and limitations of a new gravimetric hydrogen evolution (HE) collection method for corrosion rate determination on pure Mg. This method, originally developed by Curioni [1], is based on the real-time weight measurement of the H2 produced during dissolution and exhibits a higher accuracy level as well as better collection efficiency than the traditional volumetric method. The gravimetric HE collection method overcomes some of the limitations exhibited by the traditional volumetric HE method, where hydrogen gas tends to accumulate at the walls of the funnel and the burette, leading to a lower determination of the amount of H2 produced and thus, an underestimation of the HE rate. The gravimetric HE collection method also exhibits good suitability for the study of Mg alloys with high corrosion resistance and for short experimental times, where the low levels of H2 produced prevents reliable measurements of the amount of gas evolved by the volumetric HE collection method. The gravimetric HE collection method is also applicable for dynamic measurements, i.e. potentiodynamic and galvanodynamic polarizations. The gravimetric method was evaluated for the study of anodic HE on pure Mg (also termed Negative Difference Effect (NDE)), which is characteristic of Mg and its alloys when they are forced to dissolve at anodic potentials from the E
corr. Possible artifacts and experimental limitations of the gravimetric experimental method will be discussed.

[1] M. Curioni, The behaviour of magnesium during free corrosion and potentiodynamic polarization investigated by real-time hydrogen measurement and optical imaging, Electrochim. Acta 120 (2014) 284-292.
Cathodic Activation of Magnesium
Authors: Birbilis Nick
Published: February 2020

The cathodic activation of magnesium has been studied in a wide range of conditions using electrochemical cycling.

The are several key characteristics of cathodic activation, including pH dependence, and its manifestation in several metals (other than magnesium).

Cathodic activation implies an enhanced ability to support water reduction (i.e. the cathodic reaction) on surfaces that have undergone anodic exposure or some dissolution. This activation is capable of leading to superfluous hydrogen, which is then also a key contributor to the so-called ‘negative difference effect’, or, persistent hydrogen evolution.

A number of experiments are combined in order to provide a holistic description of the cathodic activation effect, and its physical origins – which is of key significance to understanding electrochemistry of reactive metals.
Effect of Al Content on the Microstructure and Corrosion Resistance of Plasma Electrolytic Oxidation (PEO) Coatings on Mg-Al Alloys
Authors: Zhang Tao
Published: February 2020

Effect of Al on the microstructure and corrosion resistance of plasma electrolytic oxidation (PEO) coating of Mg-Al alloys was investigated by means of microscopy observation and electrochemical measurement. The outer layer of PEO coating was composed of MgO and Mg2SiO4. While, the inner layer on α phase, eutectic phase and β phase was mainly consisted of MgO and MgF2, Mg2SiO4, Mg2SiO4 and MgF2, respectively. Al content had two influences on the corrosion resistance of PEO coating of Mg-Al alloys, on one hand, the MgF2 composition of the inner layer with the volume fraction of β phase, indicating the enhancement of corrosion resistance. On the other hand, the interface of inner layer above the eutectic phase and β phase increased with Al content, on which corrosion preferentially initiated on it due to high misfit degree and difference of Femi level, leading to the decrease of the corrosion resistance. In brief, with the increase of Al content, the corrosion resistance of PEO coating of Mg-Al alloys increased and then decreased.

Figure 1
Mg Corrosion Control By Biopolymer-Polyelectrolyte Membranes
Authors: Wilson Benjamin Paul , Yliniemi Kirsi , Singer Ferdinand , Höhn Sarah , Kontturi Eero , Murtomäki Lasse , Virtanen Sannakaisa
Published: February 2020

Mg and Mg alloys offer a great potential for use as a biomedical material for temporary implant applications: its lack of toxicity, ability to easily dissolve in aqueous environments, and its bone-like bulk properties. One of the key drawbacks however, that prevents the more widespread use of magnesium-based materials is their fast and often uncontrollable corrosion within the human body that impedes its utilisation in a wide range of orthopaedic components1,2. The possibility to control this dissolution is vital if Mg alloys are to be considered as a practical, temporary biomedical implant materials. In this study we detail how this aim can be attained by the use of biocompatible polymeric membrane materials. For example, by using a polyelectrolyte like poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) to modify cellulose acetate (CA) membranes it is possible to achieve Mg dissolution control.

Commercially pure magnesium surfaces were spin-coated with differing concentrations of PDMAEMA to create a number of cellulose based surfaces that were subsequently exposed to an aqueous solution. On immersion it was observed that the CA film distends and begins to function like a membrane that can control both ion flow and H2 gas evolution. Electrochemical measurements (open circuit potential, polarisation and linear sweep voltammograms) demonstrate that by varying the CA:PDMAEMA ratio, the rate of Mg corrosion can be controlled. Additional measurements of pH and with ICP-OES clearly demonstrate that the accumulation of corrosion products between the membrane and the sample also reduces the undesirable effects of H2 formation and high local pH that takes place during the corrosion process3.

Furthermore, SECM studies (with ferrocenemethanol as a redox mediator and using a custom-made cell set-up) were performed in order to determine membrane permeability: knowledge over the permeability of the membrane is crucial when designing the membrane for dissolution control.

Overall, these findings demonstrate that the presence of polyelectrolyte modified cellulose membranes have the potential to control Mg corrosion in physiological environments and that the permeability of the membrane can be controlled by additions of a cationic polyelectrolyte like PDMAEMA.   

(1) 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.

(2) S. Virtanen, Mater. Sci. Eng. B, 2011, 176, 1600-1608.

(3) K. Yliniemi, B. P. Wilson, F. Singer, S. Höhn, E. Kontturi S. Virtanen, ACS Applied Materials and Interfaces, 2014, 6, 22393-22399.
Investigation of Pitting on Stainless Steel Using Scanning Electrochemical Microscopy
Authors: Souto Ricardo M.
Published: February 2020

Metallic materials are usually employed in a state of passivation with an oxide layer formed on their surface acting as a barrier to ionic migration effectively separating the underlying metal from its environment. As a result, the release of metal ions from the substrate into the electrolytic phase is greatly hindered, and the material is regarded to be stable for sufficiently long service periods. Unfortunately, passivity breakdown and localized pitting corrosion are common phenomena to many materials in chloride solutions. In that event, though most of the material remains passive, effectively experiencing very slow corrosion rates, pits propagate very rapidly penetrating into the bulk of the material. Failure and even catastrophic destruction of the material often occurs as result of such penetration, which is the motivation for the significant research efforts investigating the causes and mechanisms of pitting. Though pit nucleation can often be correlated to heterogeneities in the material, pits can also be nucleated on homogeneous metallic surfaces, producing random distributions as a result. Significant progress in the knowledge of the origins of corrosion has been gathered from electrochemical measurements in the micrometer range, in order to greatly reduce the number of pitting events simultaneously occurring on the investigated section of the substrate. In this way, the electrochemical signal obtained from the sample could eventually arise from individual pits.

The inherently localized nature of the pitting process requires methods capable to gain information about the generation and evolution of the pit formation in the micrometer range with high spatial resolution, preferably in real time. In situ measurements during the corrosion process performed in the actual corroding media under study are mandatory, especially for the analysis of the initial stages of the process. In this regard, scanning electrochemical microscopy (SECM) is highly attractive for corrosion studies, and various experimental procedures have been developed for studying corrosion phenomena.
Diffusion-Limited 1D Pit Growth of S13Cr in Brine at Elevated Temperature
Authors: Jun Jiheon , Frankel Gerald , Sridhar Narasi
Published: February 2020

Diffusion-limited pit growth of Super 13Cr stainless steel (S13Cr) was studied using one-dimensional (1D) pit electrodes in 0.1 – 3 M NaCl solutions at 85 °C. Applied potential (Eapp) was controlled in four different steps to achieve a target pit depth and measure the anodic current density for S13Cr dissolution under potentiostatic polarization and during a backward scan. For pits with similar depths, the diffusion-limited current density (ilim) of anodic dissolution decreased with increasing NaCl concentration. A characteristic potential, below which the current density started to decay from steady ilim, was found during the backward scan. This potential is associated with dissolution of a salt film at the pit bottom and was defined as the potential of salt film dissolution (Esfd). Esfdalso decreased with increasing NaCl concentration.

To explain the dependence of ilim and Esfd on NaCl concentration, the diffusion coefficient of metal ions (D) and saturation concentration of FeCl2 (Csat), which are directly associated with the product of pit depth and ilim, were calculated using model concentration profiles in a pit and a thermodynamic database software. Both D and Csat were predicted to decrease as NaCl concentration increased, indicating slower diffusion and easier precipitation of salt film, which both increase the stability of a salt film. The product of the calculated D and Csat values was used to predict ilim for certain pit depths, and the predicted ilim values were in the range of experimentally-measured ilim in different NaCl concentrations, which validated the model.
Pitting and Hydrogen Evolution on Aluminum in Concentrated HCl Solutions
Authors: Lynch Brandon , Fajardo Santiago , Frankel Gerald
Published: February 2020

According to the Pourbaix diagram, Al is amphoteric, exhibiting passivity in the mid-pH region and dissolving to form aluminate and Al3+ ions at high and low pH, respectively. This prediction, which is based on thermodynamics, would indicate that pitting corrosion should occur only in neutral solutions because a passive film is required for the establishment of pitting. Furthermore, the pH of pit environments in Al is considered to be on the order of 3. This study investigates the behavior of Al in concentrated HCl solutions, not because it is a material of construction for such environments, but because of the insight it might shed on Al pit stability. Some retained passivity and pit formation can be observed on surfaces of pure Al samples polarized to high potentials in solutions with as much as 4 M HCl. In very concentrated HCl solutions, the surface is roughened, with more attack at grain boundaries, but no evidence of pitting. The rate of hydrogen evolution (HE), which has previously been observed to occur to about 20% of the total anodic current density in pits formed in neutral solutions, was measured during anodic polarization. Similar to the situation found on anodically polarized Mg, the rate of HE increases with increasing applied anodic current density. However, unlike Mg, a prepolarized Al surface does not exhibit enhanced cathodic reactivity during a subsequent cathodic polarization measurement. The implications of these observations on the Al pitting mechanism will be addressed.
Susceptibility of 5xxx Aluminum Alloys to Localized Corrosion in Natural Waters
Authors: Lee Jason S , Little Brenda J.
Published: February 2020

Future ship designs and modernization of existing platforms rely on lightweight Al, particularly 5xxx series Al-Mg alloys. Fatigue damage, stress corrosion cracking and microstructure instability are the major degradation mechanisms for ship structures. It is our hypothesis that microorganisms can control the rate and mechanism of degradation for 5xxx Al. Field and laboratory testing will be designed to answer the following questions related to aqueous corrosion: 1) Can naturally occurring microorganisms influence pitting and/or crevice corrosion in 5xxx Al? 2) Are microorganisms attracted to anodic sites and does their presence stabilize localized corrosion propagation?  3) Does degree of sensitization influence biofouling and its effect on open circuit potential?
Comparison of Fractographic Behaviors of Electrochemically Hydrogenated and Liquid N2 Treated 4340 Steel of Various Microstructures
Authors: Hassan SK Mobbassar , Overfelt Ruel , Abdullah Aboubakr Moustafa
Published: February 2020

Fractographic behaviors of electrochemically hydrogenated low alloy 4340 steel samples were compared with low temperature (liquid N2) treated samples of same grain sizes and hardnesses. 4340 samples of grain size range of 10-100 μm and hardness range of 41-52 HRC were electrochemically charged with hydrogen in 0.5 M H2SO4 + 5 mg/l As2O3 solution over 0-40 min charging time. Liquid N2 treatment of the samples of same microstructural range was conducted by encapsulating the sample inside an insulating container (thermos) while the temperature (-136oC) of the sample was tracked in-situ during the tensile test. Fracture surfaces of liquid N2 treated samples showed exactly same fractographic characteristics (quasi cleavage) irrespective of the grain sizes and hardnesses while electrochemically hydrogenated samples showed range of fractographic features depending on the grain sizes and hardnesses.
Vibrio neocaledonicus Sp., a Novel Marine Bacterium with the High Corrosion Inhibition Efficiency
Authors: Moradi Masoumeh , Song Zhenlun , Xiao Tao
Published: February 2020

Many marine steel structures, such as harbor and oil exploration facilities become corroded over time and need to be renovated or modified, which is expensive. Therefore, it is essential to extend the service life of the existing structures using appropriate methods. Current corrosion protection techniques usually involve toxic or expensive applications, such as volatile organic compounds, which are considered to be a major human health issue or expensive elements incorporated for a stainless steel effect. These limitations have prompted a greater interest in developing alternative methods for corrosion protection. The most promising approaches to achieve effective environmentally friendly corrosion control are to avoid the use of biocides or other traditional strategies. The inhibitory effects of bacteria were shown for the first time in 1988 in that bacteria could reduce corrosion rate of carbon steel. In this study, from a marine environment, we isolated a new inhibitory bacterium namely Vibrio
neocaledonicus sp.  which increased the corrosion resistance by more than 60-fold. This is the highest corrosion inhibitory effect that has been reported by bacteria. This inhibitory effect is stable as long as the growth medium is refreshed. This capacity was comparable with some industrial coatings such as electroless Ni-P or Ni-P-PTFE. FTIR analysis confirmed the formation of iron-EPS complexes on a metal surface as EPS is adsorbed on the surface as an inhibitory layer and provides the first inhibitory effect. EPS adhered to metal surfaces by the functional groups of an exopolymer substance. FTIR spectra detected the presence of carbohydrates and amide groups in the EPS structure which enable EPS adhere irreversibly to metal surfaces.

Figure 1
(Invited) Electrodeposition in Microporous Silicon from the Viewpoint of Hydration Property: Effect of Coexisting Ions in Zinc Electrodeposition
Authors: Fukami Kazuhiro , Koda Ryo , Koyama Akira , Sakka Tetsuo , Abe Takeshi , Kitada Atsushi , Murase Kuniaki
Published: February 2020

A chemical reaction in a nanospace is decelerated once a diffusion-limited condition is reached due to the difficulty in supply of reactants from the bulk. We illustrate how to overcome this problem for platinum electrodeposition within nanoporous silicon electrodes. The surface-induced hydration structure of reactants is essential. We make nanopore surfaces hydrophobic by covering them with organic molecules and adopt platinum complex ions with sufficiently large sizes as reactants. Such ions, which are only weakly hydrated, are excluded from the bulk aqueous electrolyte solution to the surface, and thus they are hydrophobic in this sense. When the ion concentration in the bulk was gradually increased, at a threshold the deposition behavior exhibited a sudden change, leading to drastic acceleration of the electrochemical deposition. Using statistical-mechanical theory for confined molecular liquids, we show that this change originates from a surface-induced phase transition. When the affinity of the surface with water was gradually reduced with fixing the ion concentration, qualitatively the same transition phenomenon was observed. We examine how the platinum electrodeposition behavior is affected by the cation species coexisting with the anions. We compare the experimental results obtained using three different cation species: K+, (CH3)4N+, and (C2H5)4N+. It is shown that the threshold concentration, beyond which the electrochemical deposition within nanopores is drastically accelerated, is considerably dependent on the cation species. The threshold concentration becomes lower as the cation size increases. Finally, we extend the concept to electrodeposition of other metals such as zinc. Zinc is normally deposited as dendritic crystals under a high current density. However, the dendritic deposition is suppressed by using microporous silicon electrodes. In addition, by choosing the coexisting ions, the dendritic growth of zinc is strongly suppressed. This strategy is crucial for the development of next-generation rechargeable batteries using a metal anode.
(Invited) Pore Filling of Porous Silicon with Ferromagnetic Nanostructures
Authors: Rumpf Klemens , Granitzer Petra , Poelt Peter , Michor Herwig
Published: February 2020

Metal deposition within porous silicon is under investigation for more than 2 decades whereat the incorporation of metals has been examined with respect to the influence of the light emission or to the modification of the conductivity of porous silicon but also to the growth of different metals inside macropores has been studied in detail. In the frame of this work the deposition of different metals, especially ferromagnetic ones within high aspect ratio mesopores will be elucidated with respect to the specific nucleation and growth of the deposited nanostructures under various conditions. To ensure that the nanostructure growth starts at the pore bottom pulsed electrodeposition has been used. Since mesoporous morphologies offer dendritic pore walls these structural inhomogeneities of the matrices are critical for the deposition process. From experiments one can see that the nucleation preferentially starts at the “tops” of the rough surface. The electrochemical parameters offer the opportunity, but have to be chosen exactly, to obtain desired results. A further key point of the presentation is the magnetic characterization of the various nanocomposites. Magnetic characterization of the three dimensional nanowire/nanoparticle arrays shows that not only the morphology of the deposited metal structures (size, shape, distribution) determines the magnetic properties but also the morphology of the template, e.g. side-pores of different length. In this sense magnetic coupling between the nanostructures plays a crucial role and is strongly influenced by morphological parameters. From all these findings it is possible to prepare samples with specific magnetic properties which could be of interest for on-the-chip devices.
Magnetic Studies of Iron Oxide Nanoparticles Encapsulated within Nanostructured Silicon
Authors: Granitzer Petra , Rumpf Klemens , Gonzalez-Rodriguez Roberto , Coffer Jeffery , Poelt Peter , Reissner Michael
Published: February 2020

In the frame of this work the structural and magnetic characterization of encapsulated iron oxide nanoparticles within a nanostructured silicon host is discussed. Two approaches are depicted, one to infiltrate readily synthesized Fe3O4 particles into the pores and second to grow iron oxide inside the pores out of an ethanolic iron salt solution. Beside the particle size dependent investigations, a key point of the presentation is the optimization of the system with respect to the desired magnetic properties (magnetic moment as high as possible, blocking temperature below room temperature) which are controlled by the filling parameters as well as by the morphology of the host. The readily synthesized particles are coated with oleic acid for stabilization and to avoid agglomeration and it also prevents magnetic exchange coupling. Dipolar coupling takes place dependent on the particle size and their distance among each other. The chemical growth of iron oxide strongly depends on the electrolyte composition as well as on the applied potentiostatic conditions. Results gained from SEM show that the grown iron oxide forms elongated structures instead of small nanoparticles. But temperature dependent magnetization measurements exhibit a blocking temperature around 35 K which indicates superparamagnetic behavior. An explanation can be given by deposits consisting of weakly interacting grains. All investigated composite systems exhibit a blocking temperature far below room temperature and due to the fact that all utilized materials are biocompatible the presented systems are promising for using as vehicle in biomedicine.
(Invited) Bright Light Emitting Silicon/Germanium Nanostructures
Authors: Lockwood David J
Published: February 2020

Light emission from Si and Ge nanostructures has been of great interest for some time now owing to the need for silicon-based light sources for applications in silicon opto-electronics and photonics.  Optical interconnects are required now for on-chip technology as an alternative to metal wires, because of data transmission bottlenecks introduced by their unavoidable delay times, significant signal degradation, problems with power dissipation, and electromagnetic interference. Two major avenues toward optical interconnects on a chip include a hybrid approach with III-V densely packaged optoelectronic components and the all-group-IV approach (mainly Si, Ge and SiGe), where the all major components, e.g., light emitters, modulators, waveguides and photodetectors, are monolithically integrated into the CMOS environment. Both Si and Ge possess indirect band gaps, which makes them very inefficient light emitters. Band gap engineering employing quantum wells, quantum wires or quantum dots has been proposed as one way to overcome this limitation and Si/Ge or Si/SiGe-alloy thin-multilayer quantum well structures grown on Si have been produced on this principle, and although light emission with greatly improved efficiency has been obtained at low temperatures the emission at room temperature is still very weak, because of exciton dissociation. Recently, through employing novel band-gap engineering strategies, we have prepared several different entirely new bright light-emitting Si/Ge nanostructures including one possessing a direct gap. The latter structure is based on constructing a new super unit cell comprised of multiple planar epitaxial layers of Si and Ge grown on (001) Si0.4Ge0.6. Others are based on silicon-germanium layers grown epitaxially on silicon in in such a way as to form multiple layer three-dimensional nanostructures (quantum dots). Lastly, we have developed a simple and efficient electrochemical process that combines galvanic reaction and focused-ion-beam lithography to selectively synthesize gold nanoparticles that are consequently used for the growth of ordered SiGe nanowire arrays with predefined diameter (200 nm) and position. Here we report on the optical properties of such Si/Ge nanostructures, which are found to luminesce efficiently at wavelengths in the important spectral range of 1.1–1.6 μm.

This work has been carried out in collaboration with J.-M. Baribeau and N.L. Rowell, National Research Council, Ottawa, Canada; L. Tsybeskov, New Jersey Institute of Technology, Newark, USA; and I. Berbezier, Institut Matériaux  Microélectronique Nanosciences de Provence, Marseille, France.
Plasmonic Mesostructures Prepared by Oriented Mesoporous Materials as a Template
Authors: Murai Shunsuke , Uno Shiguma , Kamakura Ryosuke , Fujita Koji , Tanaka Katsuhisa
Published: February 2020

Recent progress in top-down nanolithography now allows to fabricate plasmonic metallic structures on the scale comparable to the lightwaves.  However, it is still a challenge to fabricate structures one-order smaller than the lightwaves in a large scale.  On the other hand, bottom-up strategies, such as self-assemblies and electrochemical etching, have been studied to fabricate smaller structures as a complementary to top-down techniques.

In this study, mesoporous silica was used as a template to fabricate metallic meso-structures.  Highly-oriented mesoporous silica thin films with hexagonally-packed meso-cylinders aligned parallel to the surface were prepared on rubbing-treated silicon and silica substrates following ref.[1].  The meso-cylinders are exposed on the surface by the wet-etching treatment[2].  Oblique angle deposition of metals on the substrates results in the discrete metallic mesostructures with rod-like islands aligning along the meso-cylinders.  Figure shows the top-view image of Pt meso-grating.  We have measured optical transmission for the gold meso-gratings.  The transmission is highly polarization-sensitive, reflecting its anisotropic morphology.

Acknowledgement

We gratefully acknowledge Dr. Hirokatsu Miyata (Canon inc.) for the supply of rubbing-treated substrates.

References

S. Hayase et al.,
Langmuir
29, 7096 (2013). 2. M. Kobayashi et al., Chem. Lett.
43, 846 (2014).

Figure 1
Effects of Substrate Composition on Morphology and Growth of Porous Oxide Layers
Authors: Tsuchiya Hiroaki , Kim Min-Su , Erami Toshiaki , Otani Yuki , Fujimoto Shinji
Published: February 2020

Nanostructured materials have attracted much attention in various application fields due to their unique size-dependent properties. In addition to characterize their structures and to evaluate their properties, therefore, research efforts have targeted the fabrication process of nanostructured materials. Electrochemical anodization is one of the most straightforward approaches to fabricate nanostructured materials and, leads to the formation of highly ordered nanoporous or nanotubular oxide layers on various metallic substrates in self-organized manner under optimized condition. For examples, nanoporous oxide layers are formed on aluminum in suitable acidic electrolytes while on the other valve metals such as titanium and zirconium nanotubular oxide layers are obtained. So far a variety of electrochemical conditions such as electrolyte composition, pH and applied potential have been extensively studied. The present work focus on substrate composition, that is, we examine the growth and morphology of oxide layers formed on various alloy substrates.
Semi-Metallic TiO2 Nanotubes: Growth, Properties and Applications
Authors: Hahn Robert , Schmuki Patrik
Published: February 2020

Self organized nanotubular structures of transition metal oxides grown on their metallic substrates, especially titanium, have attracted great scientific and technological interest due to the possibility to exploit their functional properties (such in photo-catalysis, electro-catalysis, solar energy conversion, DSSCs and as host for Li storage) in nanotubular morphology. In contrast to the conventional way to grow anodic TiO2 nanotubes, which is an optimized electrochemical treatment of Ti in fluoride containing electrolyte (for an overview see [1]) this work reports on the growth of nanotubes by so-called RBA (rapid breakdown anodization).[2] This nanotube growth-process is in comparison extremely fast (seconds instead of hours) and seems to be initiated by a pit. This leads to surface coatings consisting of dense packed bundles of nanotubes with very high aspect ratios (tube length up to 50 micrometer, tube diameter of ~40 nanometer). In addition, this method provides a new route for an insitu electrochemical doping during the growth of TiO2 nanotubular layers with various transition metals to adjust the electronic levels in the material which is important for charge transfer reactions through the semiconductor/electrolyte interface [3]. The second part of the presentation will demonstrate that alternatively the electronic and optical properties [4] of these TiO2 nanotubes can be significantly modified, showing semi-metallic behavior by a high temperature reduction treatment in acethylene or ammonia creating a suitable platform for highly conductive surface area electrodes which is important i.e. sensing, methanol oxidation or supercap applications [5]

References:

[1] S. Berger, R. Hahn, P. Roy, P. Schmuki Phys. Status Solidi B247, 10,2424 (2010).

[2] R. Hahn, J. M. Macak, P. Schmuki, Electrochem. Commun.,9, 947 (2007).

[3] M. Stark, R. Hahn, M.S. Killian, P. Schmuki Catal. Sci. Technol., 3, 1765 (2013).

[4] R. Hahn, F. Schmidt-Stein, J. Salonen, S. Thiemann, Y.Y. Song, J. Kunze, V.-P. Lehto, P Schmuki, Angewandte Chemie - International Edition 48(39), 7236 (2009).

[5] S. A. Al-Thabaiti, R. Hahn, N. Liu, R. Kirchgeorg, S. So, P. Schmuki, S. N. Basahel, S. M. Chemistry Communication 50, 7960 (2014).
Dealloying of Few Coating: From Disorder to Order
Authors: Ling Yunhan , Zhang Jun , Yu Siqi , Liu Weifeng
Published: February 2020

Oxide semiconductors are widely used as photocatalysts in environmental purification as well as energy harvesting and transformation. Thanks to its narrow energy band gap, WO3 (2.7eV) and Fe2O3 (2.2eV)  is recognized as one of the most promising n-type semiconductors resistant to photocorrosion in acidic and alkaline aqueous solution respectively, and shows interesting properties both in visible light absorption and its good charge transport abilities. To pursue higher quantum efficiency, nanostructures are a favorable choice, many WO3 and Fe2O3 nanostructures in the form of powders, nanowires, nanorods, nanobelts and nanochannels have been synthesized and reported.

Precisely controlled conditions and complicated fabrication methods have been needed in the preparation of WO3 and Fe2O3-based photocatalysts for water decomposition. Dealloying was considered to be a simple, mild and economical method to fabricate nanostructures, such as nanoporous structures, nanowires, nanocages, etc. As determined by their chemical potentials, the more active (less noble) component is selectively dissolved, while the other phase represents simultaneously a self-assembling action, which is controlled by atom diffusion and the materials’ intrinsic properties.

In this work, we propose a more facile and efficient way to nanostructures by dealloying the as-electrodeposited FeW amorphous alloy coating  in an acidic and alkaline environments. It was found that highly ordered WO3 and Fe2O3nanoflake arrays were successfully synthesized and remarkable photoelectrochemical performance in water splitting of the novel nanostructure photoanode can be achieved by this disorder to order transformation.

References

[1] J. Zhang, Y. H. Ling, W. B. Gao, S. Wang and J. T. Li,  J. Mater. Chem. A, 2013, 1, 10677–10685

[2] Z. F. Liu, T. Yamazaki, Y. B. Shen, D. Meng, T. Kikuta, N. Nakatani and T. Kawabata, J. Phys. Chem. C, 2008, 112,1391.

[3] J. Su, X. Feng, J. D. Sloppy, L. Guo and C. A. Grimes, Nano Lett., 2011, 11, 203.
Switching from Homogeneous to Localized Corrosion in Stainless-Type Amorphous and Nano-Crystalline Steels
Authors: Renner Frank Uwe , Duarte Maria Jazmin
Published: February 2020

Amorphous stainless-type steels with high Cr content provide next to some applications as corrosion protective coatings an interesting playground for fundamental studies of electrochemical corrosion behavior (1-4). Starting from an ultimately homogeneous glassy version, partially and fully nanocrystalline states with large elemental heterogeneity depending on the crystallization can be derived by simple heat treatments (1,2). The amorphous materials Fe65-xCrxMo14C15B6show relative low passive currents which significantly increase after partial crystallization owing in part to a related nano-scaled roughness of the passive films (Fig.1). For low-Cr contents we have as well observed  a clear switch from the typical homogeneous corrosion of these alloys to a clearly localized attack. We will discuss this phenomenon in the light of atom probe tomography (Fig.2), microscopy, and electrochemical measurements.

1. M. J. Duarte, A. Kostka, J. A. Jimenez, P. Choi, J. Klemm, D. Crespo, D. Raabe, F. U. Renner, Crystallization, phase evolution, and corrosion of Fe-based metallic glasses: an atomic-scale structural and chemical characterization study, 2014, Acta Materialia 71 (2014), 20-30.

2. M.J. Duarte, J. Klemm, S. O. Klemm, S. Borodin, K. Mayrhofer, M. Stratmann, A.H. Romero, D. Crespo, J. Serrano, P. Choi, D. Raabe, F. U. Renner, Element-Resolved Corrosion Analysis of Stainless-Type Glass-Forming Steels, Science 341 (2013), 372-376.

3. M. Madinehei, P. Bruna, M.J. Duarte, S. J. A. Figueroa, E. J. Lede, J. Lengsfeld, F. U. Renner, E.Pineda, Glass-formation and corrosion properties of Fe-Cr-Mo-C-B glassy ribbons with low Cr content, J. Alloy. Comp. 615 (2014), 128 -  131.

4. J. Klemm, M.J. Duarte, S. O. Klemm, P.Choi, K.J.J. Mayrhofer, F.U. Renner, Multi-element-resolved electrochemical corrosion analysis. I. Dissolution behavior and passivity of amorphous Fe50Cr15Mo14C15B6, Corrosion Science 89 (2014), 59-68.

Figure 1
Corrosion Product Structures of Steel Samples Exposed to Amine Solutions Used for H2s Removal.
Authors: Alpuche-Aviles Mario A , Waite Scott , Malkiewich Ryan , Parajuli Suman , Muñoz Maria , Chhetri Pushpa
Published: February 2020

We present our results on the corrosion effects of heat stable salts (HSS), i.e., amine salts and amino acids that occur during removal of H2S from petroleum and natural gas with alkanolamines. The salts include heat stable salts and amine degradation products. Corrosion was measured using coupon weight loss in liquid and vapor phases in stirred solutions that model amine plant environment (e.g., in refinery systems). We have developed a chamber that enables exposure of samples to the gas and liquid phases of amine solutions. At increasing concentration of HSS the corrosion products show well defined structures in the nanometer scale in the solutions exposed to the liquid phase. However, this was not observed in the vapor phase. Overall, the corrosion products include amorphous, columnar and disk-shaped structures depending on the exposure conditions. We discuss the implication of the products formed on the corrosion mechanism under this environment and we propose that the substrates become passivated and that localized corrosion takes place under the conditions of our study that mimic the HSS buildup in a plant.

The corrosion products were characterized by scanning electron microscopy and X-ray powder diffraction. We report our findings for the corrosion rate measured in amine solutions with progressive additions of H2S and additional amine salts. In summary, we found the weight loss to be significantly different for samples exposed to the liquid phase and to the vapor phase: all of our liquid samples had corrosion rates < 10 mils per year (mpy), while the samples in the head space corroded at ³ 10 mpy. Our measurements were carried out in a closed environment with the liquid composition under control. For all of our experiments, the solution was purged with N2 and then H2S was dosed to achieve a concentration of 0.01 M/M of H2S/MDEA . The corrosion rates in the head space do follow a trend with respect to the composition in the liquid. Most notably, the corrosion rates in both liquid and gas increase when bicine is added.  In addition the corrosion rate in both liquid and gas phases increased when the HSS level increased from 1.4 to 5%. This suggests that some of the heat stable salts are present in the head space, possibly from partitioning via vaporization or splashing into the head space.
Modulating the Anionic-Electronic Transport Kinetics to Trigger Memristance for Resistive Switching Non-Volatile Memories: New Materials, Structering and Methods
Authors: Rupp Jennifer L. M. , Messerschmitt Felix , Schweiger Sebastian , Schmitt Rafael , Kubicek Markus
Published: February 2020

Bipolar resistive switches were recently proposed as a new class of non-volatile switches capable of reading, writing and erasing memory information by switching non-linearly between low- and high-resistance values by application of mV voltage pulses in the ns range. In the last years, resistive switching has been reported for various classes of materials ranging from sulfides to oxides. Despite their promises oxide-based resistive switches are rarely connected in their diffusion kinetics and constants to the memristive device performance characteristics under bias. In particular, models to describe the mixed anionic-electronic defect contributions for two-carrier systems are missing; this difficults the material selection criteria for best performing devices beyond classic gate oxide selection. Firstly, we report on how to probe carrier diffusion characteristics and memristance for mixed anionic-electronic resistive switches and their oxide materials for the newly proposed Memristor-based Cotrell analysis.  For this, we fabricated 2-terminal Pt|SrTiO3-δ|Pt cross-bar array structures as a model system in terms of its mixed defects which show stable and reproducible resistive switching. Secondly, new material engineering of oxides are discussed to control resistive switching device properties like retention, Ron/Roff ratios and power consumption by "interfacial strain engineering of mixed conducting oxide" is reported. Lattice strain engineering using heterostructures at internal interfaces can be used to tune material properties in micro-dots as new resistive switching archiectures far beyond the change accessible by doping. We exemplify the switching characteristics based on either comprsively or tensily strained Gd0.1Ce0.9O2-x heterolayers by Er2O3 or Sm2O3 monolayer modulation, respectively. Thirdly, the role of grain boundaries is discussed for epitaxially and nm-roughness grown LaFeO3 thin film resistive switches with controlled defect levels. We compliment classic resistive switching tests characterizing the near order Raman vibrational (ionic bonding), direct and non-linear optic spectroscopy techniques (electronic contributions).
(Keynote) Nanoscale Memories: What Does Physics Have to Say?
Authors: Zhirnov Victor V. , Meade R , Pandey S. C. , Sandhu G
Published: February 2020

Device scaling and energy consumption during computation has become a matter of strategic importance for future information technologies. The central question addressed in this talk is: What is the smallest volume of matter needed for a memory element? A generic physics-based abstraction for memory devices will be introduced and applied to several baseline memory technologies. The scaling limit of electron-based devices is~5-7 nm due to quantum-mechanical tunneling. Smaller devices can be made, if information-bearing particles are used whose mass is greater than the mass of an electron. Therefore the new principles for devices, scalable to ~1 nm, could be ‘moving atoms’ instead of ‘moving electrons’.

Theoretical feasibility of the 1-nm devices will be justified based on electrical properties of the few-atom systems. Next, thermal properties of atomic contacts and devices such as nanoionic switch/ReRAM memory cell will be discussed to provide an insight whether such small structure could have sufficient thermal stability for reliable operation.

An important task for sub-10 nm nanodevices is recognition of the fundamental role of ‘defects’ that should not be treated as imperfections but instead as controllable entities. The materials nonstoichiometry due to point defects plays a key role in the electronic properties of many materials, for example in metal oxides. Due to these nonstoichiometric defects, the materials often behave as doped semiconductors. In fact, these materials form a special class, sometimes called ‘chemiconductors’.

In addition to solid-state nanoionic devices such as ReRAM) concepts of ‘fluid nanoelectronics’ are proposed that utilize liquid media, which may offer a new promising path to replace the foundation of today’s computing technologies. Examples include nanoionic devices based on electrolyte-filled nanochannels. In principle, such structures might be used to make devices scalable to ~1 nm or below.

Recently there have been suggestions from research that the physical limits of semiconductor technology may in fact be overcome by borrowing from synthetic biology principles. For example, it has recently been shown that DNA can be used to achieve storage densities that cannot be approached by any known solid-state technology. This lecture will examine how one might develop a technology in the semiconductor context that would open up DNA memory to widespread applications.