Yuri Petrov

Design Rules for Oxygen Evolution Catalysis at Porous Iron Oxide Electrodes: Thousand-Fold Current Density Increase

Nanotubular iron(III) oxide electrodes are optimized for catalytic efficiency in the water oxidation reaction at neutral pH. The nanostructured electrodes are prepared from anodic alumina templates, which are coated with Fe2 O3 by atomic layer deposition. Scanning helium ion microscopy, X-ray diffraction, and Raman spectroscopy are used to characterize the morphologies and phases of samples submitted to various treatments. These methods demonstrate the contrasting effects of thermal annealing and electrochemical treatment. The electrochemical performances of the corresponding electrodes under dark conditions are quantified by steady-state electrolysis and electrochemical impedance spectroscopy. A rough and amorphous Fe2 O3 with phosphate incorporation is critical for the optimization of the water oxidation reaction. For the ideal pore length of 17 μm, the maximum catalytic turnover is reached with an effective current density of 140 μA cm-2 at an applied overpotential of 0.49 V.

Scanning reflection ion microscopy in a helium ion microscope

Summary Reflection ion microscopy (RIM) is a technique that uses a low angle of incidence and scattered ions to form an image of the specimen surface. This paper reports on the development of the instrumentation and the analysis of the capabilities and limitations of the scanning RIM in a helium ion microscope (HIM). The reflected ions were detected by their “conversion” to secondary electrons on a platinum surface. An angle of incidence in the range 5–10° was used in the experimental setup. It was shown that the RIM image contrast was determined mostly by surface morphology but not by the atomic composition. A simple geometrical analysis of the reflection process was performed together with a Monte Carlo simulation of the angular dependence of the reflected ion yield. An interpretation of the RIM image formation and a quantification of the height of the surface steps were performed. The minimum detectable step height was found to be approximately 5 nm. RIM imaging of an insulator surface without the need for charge compensation was successfully demonstrated.

Waveguide fabrication in lithium-niobo-phosphate glasses by high repetition rate femtosecond laser: route to non-equilibrium material’s states

We study waveguide fabrication in lithium-niobo-phosphate glass, aiming at a practical method of single-stage fabrication of nonlinear integrated-optics devices. We observed chemical transformations or material redistribution during the course of high repetition rate femtosecond laser inscription. We believe that the laser-induced ultrafast heating and cooling followed by elements diffusion on a microscopic scale opens the way toward the engineering non-equilibrium sates of matter and thus can further enhance Refractive Index (RI) contrasts by virtue of changing glass composition in and around the fs tracks.

NEXAFS study of electronic and atomic structure of active layer in Al/indium tin oxide/TiO2 stack during resistive switching

Abstract We have studied the stability of the resistive switching process in the Al/(In2O3)0.9(SnO2)0.1/TiO2 assembly grown by atomic layer deposition. Besides electrical characterization the effect of electric field on the atomic electronic structure of the TiO2 layer was studied using near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The region of the current instability in the I-V characteristics was revealed. Presumably this current instability is supported by the amorphous structure of the TiO2 film but is initiated by the surface morphology of the Al substrate. A formation of the O2 molecules was established which occurs specifically in the region of the current instability that is a result of electrical Joule heating manifestation. Electrophysical and NEXAFS studies were implemented in the same point of Al/ITO/TiO2 assembly (left bottom corner). The region of the current instability in the I-V characteristics was revealed. The current instability resulted in transition to a new hysteresis loop (left upper corner). A formation of the O2 molecules in the volume of TiO2 active layer has been established specifically in the region of current instability (right upper and bottom corners).

Secondary Electron Generation in the Helium Ion Microscope: Basics and Imaging

The theories, modeling and experiments of the processes of secondary electron (SE) generation and SE usage in helium ion microscopy (HIM) are reviewed and discussed. Conventional and recently introduced SE imaging modes in HIM utilizing SE energy filtering and ion-to-SE conversion, such as scanning transmission ion microscopy and reflection ion microscopy, are described.

Electrical contact resistance and dynamic contact stiffness for a cluster of microcontacts: cross-property connection in the low-frequency range

An explicit cross-property connection for a rough interface between the electrical contact resistance and dynamic contact stiffness has been established in the low-frequency limit. The present analysis is based on the first-order asymptotic model of multiple dynamic contact between small flat-ended indenters on an elastic half-space, which is a dynamic analogue of the quasi-static Greenwood model. The obtained results can be used in developing a vibration method for measuring the interface contact stiffness in tribological systems, and in estimating the surface-roughness effect in oscillation indentation tests.

Multiscale Fracture Model for Quasi-Brittle Materials

Fracture of quasi-brittle heterogeneous materials is steered by processes at several different scale levels. These processes can progress independently or affect each other. In order to model fracture of such materials one should account for all rupture processes contributing to overall fracture process. This paper is presenting structural-temporal approach for analysis of multiscale nature of brittle fracture. Notion of spatial-temporal cell for different scale levels is introduced. Problem of experimental determination of a fixed scale level is discussed. Possible interconnections of this scale level with higher and lower scale levels are discussed. It is shown that this can give a possibility to predict fracture on a higher (real) scale level having experimental data obtained on a lower (laboratory) scale. This possibility is of extreme importance for many applications where the possibility to evaluate material strength properties on real structure scale level does not exist (ex. geological objects, big concrete structures, trunk pipelines, etc.).

The Effect of Grain Refinement on Solid Particle Erosion of Grade 5 Ti Alloy

In this work, the results on solid particle erosion of an ultrafine-grained Grade 5 titanium alloy, which was produced using high-pressure torsion (HPT) technique, are presented. In order to assess influence of the HPT treatment on material’s behavior in erosive conditions, special experimental procedures were developed. The ultrafine-grained (UFG) alloy was tested alongside with a conventional coarse-grained (CG) Grade 5 titanium alloy in equal conditions. The experiments were conducted in a small-scale wind tunnel with corundum particles as an abrasive material. Both particle dimensions and particle velocities were varied in course of the experiments. Erosion resistance of the samples was evaluated in two ways—mass reduction measurements with subsequent gravimetric erosion rate calculations and investigation of samples’ surface roughness after erosion tests. The UFG titanium alloy demonstrated considerable improvement of static mechanical properties (ultimate tensile strength, microhardness), whereas its CG counterpart appeared to be slightly more resistant to solid particle erosion, which might indicate the drop of dynamic strength properties for the HPT-processed material.

The Influence of Defects and Inclusions on Capacity for Work of Thin Plates

Some problems of strength and stability of thin constructions with defects and inclusions, which are of vital importance for nano- and microtechnology, are investigated. The attention is paid to the estimation of the number of defects influencing the capacity for work of nanosized plated and shells. The influence of surface effect is taken into account.

Interface-Assisted Synthesis of Single-Crystalline ScF3 Microtubes

Scandium fluoride (ScF3) microtubes with nanoscale wall thickness were for the first time successfully synthesized by an interface-assisted technique at the surface of a scandium nitrate aqueous solution without the addition of any surfactant as a result of interaction with hydrofluoric acid from the gaseous phase in only 30 min. X-ray diffraction analysis, scanning electron microscopy, helium ionic microscopy, transmission electron microscopy (TEM), and high-resolution TEM (HRTEM) were used to examine the morphology and crystal structure of ScF3 microtubes. The results show that the ScF3 microtube is single-crystalline and has a hexagonal structure. A hypothetical model of thin-walled microtube formation is proposed.