[en] Ferromagnetic resonance in an array of Co nanowires electrolytically deposited into nanoporous alumina template is investigated at four microwave frequencies in the range from 9.3 to 69.7 GHz. The array consists of highly textured hcp Co with hexagonal axes perpendicular to the nanowires. The spectra measured at higher frequencies can be decomposed into four wide resonances peaks. Different mechanisms, which can lead to the multi-peak resonance, are discussed.

[en] The influence of surface magnetic anisotropy on ferromagnetic resonance (FMR) in submicron wires is investigated both theoretically and experimentally. An analytical formula for resonance fields of radial spin waves in a long axially magnetized circular cylinder is obtained. Three types of surface anisotropy with the easy direction along one of the cylindrical coordinates are considered. For sufficiently strong surface anisotropy with hard direction parallel to the cylinder axis the surface spin wave mode is observed. The theoretical results are verified by FMR measurements at six microwave frequencies from 9 to 69 GHz on glass-covered amorphous FeCrSiB wires with diameters from 541 to 1032 nm. From the bulk spin wave resonances the exchange stiffness constant about 6.5 10⁻⁷ erg/cm is obtained. The frequency dependence of the surface mode resonance field indicates that a perpendicular surface anisotropy with anisotropy constant K_s = 6.2 erg/cm² is present at the metal/glass interface.

[en] Silicene, a monolayer of silicon atoms arranged in a honeycomb lattice, is excellently compatible with the materials used in today’s semiconductor manufacturing. In this paper, silicene-terminated CaSi₂ is cleaved inside a transmission electron microscope using an in situ manipulator. HRTEM studies on a standard lift-out lamella performed from several crystallographic orientations confirm the cell parameters of a = 3.7 Å and c = 30.60 Å, and allow to determine its exact orientation in the SEM/FIB system. A FIB procedure with corrected tilting and rotating angles has been developed to ensure that the tensile force applied by the manipulator is perpendicular to the (0 0 1) plane, and that the [1 0 0] pole axis could be used for HRTEM imaging. A sharp and flat cleavage interface with a length of more than 1 μm was observed in one in situ experiment. HRTEM images from multiple regions confirm that the flat cleavage follows the (0 0 3) plane of the CaSi₂ crystal. The current in situ study demonstrates that a surface sheet with silicene-like atomic arrangement can be mechanically exfoliated from silicide compounds. (paper)

[en] The evolution of elastic properties with temperature and magnetic field was studied in two differently heat-treated single crystals of the Ni–Mn–Ga magnetic shape memory alloy using resonant ultrasound spectroscopy. Quenching and slow furnace cooling were used to obtain different densities of antiphase boundaries. We found that the crystals exhibited pronounced differences in the c′ elastic coefficient and related shear damping in high-temperature ferromagnetic phases (austenite and premartensite). The difference can be ascribed to the formation of fine magnetic domain patterns and pinning of the magnetic domain walls on antiphase boundaries in the material with a high density of antiphase boundaries due to quenching. The fine domain pattern arising from mutual interactions between antiphase boundaries and ferromagnetic domain walls effectively reduces the magnetocrystalline anisotropy and amplifies the contribution of magnetostriction to the elastic response of the material. As a result, the anomalous elastic softening prior to martensite transformation is significantly enhanced in the quenched sample. Thus, for any comparison of experimental data and theoretical calculations the microstructural changes induced by specific heat treatment must be taken into account. (paper)

[en] Tessellation models have proven to be useful for the geometric description of grain microstructures in polycrystalline materials. With the use of a suitable tessellation model, the complex morphology of grains can be represented by a small number of parameters assigned to each grain, which not only entails a significant reduction in complexity, but also facilitates the investigation of certain geometric features of the microstructure. However, for a given set of microstructural data, the choice of a particular geometric model is traditionally based on researcher intuition. The model should provide a sufficiently good approximation to the data, while keeping the number of parameters small. In this paper, we discuss general aspects of the process of model selection and suggest several criteria for selecting an appropriate candidate from a certain set of tessellation models. The choice of candidate represents a trade-off between accuracy and complexity of the model. Here, the selected model is used solely to approximate given data samples, but it also provides guidance for developing stochastic tessellation models and generating virtual microstructures. Model fitting is carried out by simulated annealing, applied in a consistent manner to twelve different tessellation models.

[en] Highlights: • Light-weight ferromagnetic Co-Ni-Al:Ti composites were successfully compacted to full density by spark plasma sintering. • During the sintering, new intermetallic phases at Co-Ni-Al/Ti interfaces were formed. • The composites exhibit low density (around 6 g⋅cm^{− 3}), high flexural strength (up to 860 MPa) and detectable ferromagnetic response. • The composites are structurally stable at least from – 120 °C to 400 °C. Light-weight ferromagnetic Co-Ni-Al:Ti composites were consolidated by spark plasma sintering. Powders of ball-milled Co-Ni-Al and gas atomized α-Ti were mixed together in three different ratios and spark plasma sintered at 950 °C, using two sintering times, i.e. dwell times at the maximal temperatures: 1 and 5 min. The composites were successfully compacted and new intermetallic phases were formed at the Co-Ni-Al/Ti interfaces. The composites exhibit favourable flexural strength, excellent high-temperature stability, and relatively high saturation magnetization. On the other hand, the newly emerged intermetallic phases are non-ferromagnetic, which slightly deteriorates the magnetic properties.

[en] The objective of this work was to develop an accurate method for automatic determination of the size of elliptical nanoparticles from atomic force microscopy (AFM) images that would yield results consistent with results of manual measurements by experts. The proposed method was applied on phenylpyridyldiketopyrrolopyrrole (PPDP), a granular organic material with a wide scale of application and highly sensitive particle-size properties. A PPDP layer consists of similarly sized elliptical particles (c. 100 nm × 50 nm) and its properties can be estimated from the average length and width of the particles. The developed method is based on segmentation of salient particles by the watershed transform and approximation of their shapes by ellipses computed by image moments; it estimates the lengths and widths of the particles by the major and minor axes, respectively, of the corresponding ellipses. Its results proved to be consistent with results of manual measurements by a trained expert. The comparison showed that the developed method could be used in practice for precise automatic measurement of PPDP particles in AFM images

[en] Highlights: • Planar and porous BDD films deposited at B/C ratios of 500–8000 ppm characterised. • Electrochemical behaviour of porous BDD is affected by the presence of sp² carbon. • Following increased growth time of porous layers (“thicker” BDD), behaviour resembles planar electrodes. • For dopamine, the lowest detection limit of 0.21 μmol L⁻¹ achieved on 4000 ppm “thicker” porous electrodes. • Selectivity of “thicker” porous BDD enhanced for dopamine detection in excess of AA, UA, and paracetamol. -- Abstract: Complex characterization of as-deposited conventional planar and newly available porous boron doped diamond (BDD) films with various boron doping levels (B/C ratio in the gas phase: 500 ppm, 1000 ppm, 2000 ppm, 4000 ppm, and 8000 ppm) was carried out by scanning electron microscopy, Raman spectroscopy and electrochemistry by performing cyclic voltammetric (CV) experiments with outer- and inner-sphere redox probes [Ru(NH₃)₆]^3+/2+, [Fe(CN)₆]^3−/4−, and dopamine. The double layer capacitance was estimated from CV and electrochemical impedance spectroscopic measurements. For planar BDD films, a roughly 80% increase in the double layer capacitance, a 100 mV narrower potential window and a 51 mV negative shift of the peak potential of dopamine were observed when the boron doping level increased from 500 ppm to 8000 ppm. Conversely, higher sp² carbon content confirmed by Raman spectra affects the electrochemical performance of porous samples more significantly than the doping level. For the set of porous BDD electrodes, the double layer capacitance decreased by ca 95% with increasing boron content, peak-to-peak separation values of the studied inorganic redox markers were lower than 59 mV, suggesting their partial adsorption in the bulk of the material, and lower potentials for dopamine oxidation approaching values obtained for other sp² carbon-based materials were recorded, but no dependency of potential values on boron concentration was revealed. Enhanced electron transfer rate on porous BDD materials resulted in increased sensitivity for dopamine detection using square-wave voltammetry in contrast to the planar set of electrodes. The lowest detection limit of 2 × 10⁻⁷ mol L⁻¹ was estimated in a medium of 0.1 mol L⁻¹ phosphate buffer pH 7.4 on B/C 4000 ppm porous electrodes with increased BDD growth time, without any activation applied between the individual scans. Moreover, for selected porous electrodes, improved selectivity for dopamine sensing in excess of common interfering compounds such as uric acid, ascorbic acid and paracetamol was achieved.

[en] Accurate crystal structure of single nanocrystals as small as tens of nanometers can be obtained by the recently published full dynamical structure refinement of precession electron diffraction tomography (PEDT) data. Here we apply the method to the structure redetermination of the nickel silicide ε-Ni_3Si_2 from a nanowire with the diameter of 35 nm. The structure was determined as centrosymmetric Cmcm, in disagreement with the published structure, which was determined by single crystal X-ray diffraction in 1961 in the noncentrosymmetric space group Cmc2_1. The structure was also determined by single crystal X-ray diffraction (SCXRD), giving the same results as PEDT. The average difference of the atomic positions between the models obtained by PEDT and SCXRD was smaller than 0.007 Å. - Highlights: • Crystal structure of ε-Ni_3Si_2 was redetermined on a nanowire with d = 35 nm. • The structure is centrosymmetric Cmcm, not Cmc2_1 as previously published. • Single nanocrystal was measured using precession electron diffraction tomography. • The dynamical theory was used for the refinement of the structure parameters. • Atomic positions accuracy is approaching that of single crystal X-ray diffraction.

[en] Highlights: • Number of porous layers is a crucial factor influencing final BDD_porous properties. • Faster electron transfer kinetics observed with increased porous layer number. • The highest sensitivity and the lowest LOD for dopamine obtained on 5L-BDD_porous. • Enhanced selectivity demonstrated for 3L- and 5L-BDD_porous electrodes. • Stability of PLL layer differs depending on the electrode surface morphology. Novel porous boron-doped diamond (BDD_porous)-based materials have attracted lots of research interest due to their enhanced detection ability and biocompatibility, favouring them for use in neuroscience. This study reports on morphological, spectral, and electrochemical characterisation of three BDD_porous electrodes of different thickness given by a number of deposited layers (2, 3 and 5). These were prepared using microwave plasma-enhanced chemical vapour deposition on SiO₂ nanofiber-based scaffolds. Further, the effect of number of layers and poly-l-lysine coating, commonly employed in neuron cultivation experiments, on sensing properties of the neurotransmitter dopamine in a pH 7.4 phosphate buffer media was investigated. The boron doping level of ∼2 × 10²¹ atoms cm⁻³ and increased content of non-diamond (sp²) carbon in electrodes with more layers was evaluated by Raman spectroscopy. Cyclic voltammetric experiments revealed reduced working potential windows (from 2.4 V to 2.2 V), higher double-layer capacitance values (from 405 μF cm⁻² to 1060 μF cm⁻²), enhanced rates of electron transfer kinetics and larger effective surface areas (from 5.04 mm² to 7.72 mm²), when the number of porous layers increases. For dopamine, a significant boost in analytical performance was recognized with increasing number of layers using square-wave voltammetry: the highest sensitivity of 574.1 μA μmol⁻¹ L was achieved on a BDD_porous electrode with five layers and dropped to 35.9 μA μmol⁻¹ L when the number of layers decreased to two. Consequently, the lowest detection limit of 0.20 μmol L⁻¹ was obtained on a BDD_porous electrode with five layers. Moreover, on porous electrodes, enhanced selectivity for dopamine detection in the presence of ascorbic acid and uric acid was demonstrated. The application of poly-l-lysine coating on porous electrode surface resulted in a decrease in dopamine peak currents by 17% and 60% for modification times of 1 h and 15 h, respectively. Hence, both examined parameters, the number of deposited porous layers and the presence of poly-l-lysine coating, were proved to considerably affect the characteristics and performance of BDD_porous electrodes.