Influence of annealing on magnetic, relaxation and structural properties of composite and multilayer films

This work is devoted to the research of influence of annealing to ferromagnetic resonance (FMR) properties of films of the A, B series with the compositions of (Co45-Fe45-Zr10)x(Al2O3)y, multilayer films of the D series with compositions {[(Co45-Fe45-Zr10)x(Al2O3)y]-[alpha-Si]}120 and revealing their relationship with the nanostructure characteristics. The films were obtained in an argon atmosphere (the A, D series) and with addition of oxygen (the B series). All samples were deposited on substrates by the ion-beam sputtering method and were annealed. The resonant fields and width of ferromagnetic resonance (FMR) line were measured before and after annealing. The changes in the FMR field and width of the line at varying temperatures of annealing for the composite and multilayer films are analyzed in the work. The character of changes in the structural characteristics of films at different annealing temperatures is determined.     

Multifrequency imaging in the intermittent contact mode of atomic force microscopy: beyond phase imaging

The cantilever dynamics in single-frequency scanning probe microscopy (SPM) are undefined due to having only two output variables, which leads to poorly understood image contrast. To address this shortcoming, generalized phase imaging scanning probe microscopy (GP-SPM), based on broad band detection and multi-eigenmode operation, is developed and demonstrated on diamond nanoparticles with different functionalization layers. It is shown that rich information on tip-surface interactions can be acquired by separating the response amplitude, instant resonance frequency, and quality factor. The obtained data allow high-resolution imaging even in the ambient environment. By tuning the strength of tip-surface interaction, different surface functionalizations can be discerned.     

Open-loop band excitation Kelvin probe force microscopy

A multidimensional scanning probe microscopy approach for quantitative, cross-talk free mapping of surface electrostatic properties is demonstrated. Open-loop band excitation Kelvin probe force microscopy (OL BE KPFM) probes the full response-frequency-potential surface at each pixel at standard imaging rates. The subsequent analysis reconstructs work function, tip-surface capacitance gradient and resonant frequency maps, obviating feedback-related artifacts. OL BE KPFM imaging is demonstrated for several materials systems with topographic, potential and combined contrast. This approach combines the features of both frequency and amplitude KPFM and allows complete decoupling of topographic and voltage contributions to the KPFM signal.     

Symmetry relationship and strain-induced transitions between insulating M1 and M2 and metallic R phases of vanadium dioxide

The ability to synthesize VO2 in the form of single-crystalline nanobeams and nano- and microcrystals uncovered a number of previously unknown aspects of the metal-insulator transition (MIT) in this oxide. In particular, several reports demonstrated that the MIT can proceed through competition between two monoclinic (insulating) phases M1 and M2 and the tetragonal (metallic) R phase under influence of strain. The nature of such phase behavior has been not identified. Here we show that the competition between M1 and M2 phases is purely lattice-symmetry-driven. Within the framework of the Ginzburg-Landau formalism, both M phases correspond to different directions of the same four-component structural order parameter, and as a consequence, the M2 phase can appear under a small perturbation of the M1 structure such as doping or stress. We analyze the strain-controlled phase diagram of VO2 in the vicinity of the R-M2-M1 triple point using the Ginzburg-Landau formalism and identify and experimentally verify the pathways for strain-control of the transition. These insights open the door toward more systematic approaches to synthesis of VO2 nanostructures in desired phase states and to use of external fields in the control of the VO2 phase states. Additionally, we report observation of the triclinic T phase at the heterophase domain boundaries in strained quasi-two-dimensional VO2 nanoplatelets, and theoretically predict phases that have not been previously observed.     

Kinematic characteristics of pulsed speed regulators

Experimental kinematic characteristics are presented for pulsed speed regulators with eccentric free-wheel clutch mechanisms of different designs. Formulas have been obtained for the change in transmission ratios of pulsed speed regulators under load.     

Nanoscale Ferroelectricity in Crystalline γ‐Glycine

Ferroelectrics are multifunctional materials that reversibly change their polarization under an electric field. Recently, the search for new ferroelectrics has focused on organic and bio‐organic materials, where polarization switching is used to record/retrieve information in the form of ferroelectric domains. This progress has opened a new avenue for data storage, molecular recognition, and new self‐assembly routes. Crystalline glycine is the simplest amino acid and is widely used by living organisms to build proteins. Here, it is reported for the first time that γ‐glycine, which has been known to be piezoelectric since 1954, is also a ferroelectric, as evidenced by local electromechanical measurements and by the existence of as‐grown and switchable ferroelectric domains in microcrystals grown from the solution. The experimental results are rationalized by molecular simulations that establish that the polarization vector in γ‐glycine can be switched on the nanoscale level, opening a pathway to novel classes of bioelectronic logic and memory devices.     

Mapping irreversible electrochemical processes on the nanoscale: ionic phenomena in li ion conductive glass ceramics

A scanning probe microscopy approach for mapping local irreversible electrochemical processes based on detection of bias-induced frequency shifts of cantilevers in contact with the electrochemically active surface is demonstrated. Using Li ion conductive glass ceramic as a model, we demonstrate near unity transference numbers for ionic transport and establish detection limits for current-based and strain-based detection. The tip-induced electrochemical process is shown to be a first-order transformation and nucleation potential is close to the Li-metal reduction potential. Spatial variability of the nucleation bias is explored and linked to the local phase composition. These studies both provide insight into nanoscale ionic phenomena in practical Li-ion electrolyte and also open pathways for probing irreversible electrochemical, bias-induced, and thermal transformations in nanoscale systems.     

Experimental investigation of the kinetics of hydrolysis of sodium borohydride aqueous-alkaline solutions

Distinctive features of an experimental procedure for determination of the conversion of sodium borohydride in hydrolysis in an aqueous-alkaline medium are described; the procedure is based on measuring the amount of the released hydrogen. Technical and methodological features of implementation of this procedure and measurement errors are discussed; a technique for calculation of the conversion of sodium borohydride in hydrolysis is presented. Experimental data in the form of the constants of a quasistationary hydrolysis regime are given for different isothermal conditions. The range of experiments covers temperatures from 20 to 95°C and alkali concentrations from 10⁻² to 5 M.     

Decomposition of radioactive methyl iodide in an electric discharge field

The possibility of using electric discharge for removing radioactive iodine in the form of volatile organic compounds from air-gas streams was examined. In an electric discharge field, at the methyl iodide concentration in the range from 0.9 to 19 mg l^?1, relative humidity within 48–90%, and linear flow velocity of 0.5–3.5 cm s^?1, the decontamination factor characterizing the methyl iodide decomposition is ≥1.4 × 10⁵.     

Long-term stability of sodium borohydrides for hydrogen generation

As a source of the high purity hydrogen, sodium and potassium borohydrides are investigated in terms of long-term stability in the form of the concentrated solutions, heterogeneous mixtures and in the solid state corresponding to NaBH₄ or KBH₄ crystal hydrates. In order to improve their stability during the long-term storage sodium and potassium hydroxides were added to the initial borohydride compositions. The effect of temperature, concentration of the borohydride and the alkaline solution, and the nature of the cation in the alkaline solution on the rate of borohydride hydrolysis was investigated. The differential technique developed for evaluation of the rate of borohydride hydrolysis was successfully applied for the determination of the long-term stability of the water-alkaline solutions containing NaBH₄(KBH₄)·5H₂O with 1–10 wt.% of NaOH or KOH at 30 °C and 50 °C.