Slawomir Kulesza

Surface micromorphology and fractal geometry of Co/CP/X (X = Cu, Ti, SM and Ni) nanoflake electrocatalysts

This paper analyses the three-dimensional (3-D) surface texture of Co/CP/X (X = Cu, Ti, SM and Ni, CP: carbonaceous paste) nanoflakes prepared electrochemically using a conventional three electrode system. The surface chemical composition of the samples was investigated by X-ray photoelectron spectroscopy (XPS). Surface images were recorded using scanning electron microscopy (SEM) and analyzed by means of the fractal geometry. Statistical, fractal and functional surface properties of the prepared samples were computed. The statistical functions applied to the SEM data were employed in order to characterise the surfaces topographically (in amplitude, spatial distribution and pattern of surface characteristics). The analysis of the 3-D surface texture of Co/CP/X nanoflakes is essential to control the surface topography and for the correct interpretation of surface topographic features as well as its functional role. It also provides a compact representation of complex micromorphology information.

Fractal features and surface micromorphology of diamond nanocrystals.

This paper analyses the three‐dimensional (3‐D) surface texture of growing diamond nanocrystals on Au thin films as catalyst on p‐type Si substrate using hot filament chemical vapour deposition (HFCVD). Rutherford backscattering spectrometry (RBS), atomic force microscopy (AFM), Raman, X‐ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were applied also to characterize the 3‐D surface texture data in connection with the statistical, and fractal analyses. This type of 3‐D morphology allows a deeper understanding of structure/property relationships and surface defects in prepared samples. Our results indicate a promising way for preparing high‐quality diamond nanocrystals on Au thin films as catalyst on p‐type Si substrate via HFCVD method.

Effect of electric field direction and substrate roughness on three-dimensional self-assembly growth of copper oxide nanowires

This paper analyses the three-dimensional (3-D) surface texture of Copper oxide nanowires grown on different substrates and in an electric field. Atomic force microscopy, X-ray diffraction and field emission scanning electron microscopy analyses were applied also to characterize the 3-D surface texture data in connection with the statistical, and fractal analyses. This type of 3-D morphology allows a deeper understanding of structure/property relationships and studies the effect of micromorphology on CuO nanowires grown in electric field and the impact of growth direction on their properties. It also provides a compact representation of complex micromorphology information.

Fractal Analysis of AFM Data Characterizing Strongly Isotropic and Anisotropic Surface Topography

This study discusses changes in the value of fractal parameters determined based on functions of structure S(t), generated in different directions of anisotropy of the examined surfaces. The analyzed material consisted of AFM calibration standards TGT1, PG and TGZ1 which were used as models of strongly isotropic and anisotropic surfaces. The topography of the examined surfaces was imaged by atomic force microscopy. The obtained results indicate that all surfaces can be described mathematically to identify fractal parameters in any anisotropic direction.

Microstructure, morphology and electrochemical properties of Co nanoflake water oxidation electrocatalyst at micro- and nanoscale

Nowadays, fossil fuel limitations and environmental concerns push researchers to find clean and renewable energy resources. Solar hydrogen production via water splitting reactions in electrochemical and/or photo-electrochemical systems has been accepted as a promising route and efficient electrocatalysts are involved in both. Here, cobalt nanoflakes with an oxide/hydroxide surface and a conductive metallic core are grown on commercially available steel mesh modified with carbon based nanocomposites as a support layer. The portion of reduced graphene oxide sheets was changed from 0 to 100 wt% and the correlation of this concentration with the surface morphology and electro-catalytic activity of the final electrode was studied systematically for the first time. Obtained results revealed the least over potential (224.2 mV) for the sample with 50 wt% rGO in the water splitting reaction which is promising for use in alkaline electrolysis devices.

Microstructure and micromorphology of Cu/Co nanoparticles: Surface texture analysis

This paper analyses the three-dimensional (3-D) surface texture of Cu/Co thin films deposited by DC-Magnetron sputtering method on the silicon substrates. The prepared Cu/Co nanoparticles were used as research materials. Three groups of samples were deposited on silicon substrates in the argon atmosphere and gradually cooled down to room temperature. The crystalline structures and elemental compositions were analyzed by X-ray diffraction (XRD) spectrum with conventional Bragg-Brentano geometry. X-ray diffraction profile indicates that Co and Cu interpenetrating crystalline structures are formed in these films. The sample surface images were recorded using atomic force microscopy (AFM) and analyzed by means of the fractal geometry. Statistical, fractal and functional surface properties of prepared samples were computed to describe major characteristics of the spatial surface texture of Cu/Co nanoparticles. Presented deposition method is a versatile, costeffective, and simple method to synthesize nano- and microstructures of Cu/Co thin films. This type of 3-D morphology allows to understand the structure/property relationships and to investigate defect-related properties of Cu/Co nanoparticles. Presented results confirm the possibility of preparing high-quality Cu/Co nanoparticles via DC-Magnetron sputtering method on silicon substrates.

Fractal features of carbon–nickel composite thin films

This work analyses the three‐dimensional (3‐D) surface texture of carbon–nickel (C–Ni) films grown by radio frequency (RF) magnetron co‐sputtering on glass substrates. The C–Ni thin films were deposited under different deposition times, from 50 to 600 s, at room temperature. Atomic force microscopy was employed to characterize the 3‐D surface texture data in connection with the statistical, and fractal analyses. It has been found that up to 180 s the sputtering occurs in more metal content mode and in greater than 180 s it occurs in more non‐metal content mode. This behavior demonstrated a strong link between the structural and morphological properties of C–Ni composite films and facilitates a deeper understanding of structure/property relationships and surface defects in prepared samples. Furthermore, these findings can be applied to research on the mechanisms to prepare and control high‐quality C–Ni films.

Modeling the Real Estate Prices in Olsztyn under Instability Conditions

Abstract The paper deals with the description of the issues related to the dynamics of the real estate market in terms of sharp, unexpected changes in the housing prices which have been observed in the last decade in many European countries due to some macroeconomic circumstances. When such perturbations appear, the real estate market is said to be structurally unstable, since even a small variation in the control parameters might result in a large, structural change in the state of the whole system. The essential problem addressed in the paper is the need to define and discriminate between the intervals of stable and unstable real estate market development with special attention paid to the latter. The research aims at modeling hardly explored field of discontinuous changes in the real estate market in order to reveal the bifurcation edge. Assuming that the periods of sudden price changes reflect an intrinsic property of the real estate market, it is shown that the evolution path draws for most of the time a smooth curve onto the stability area of the equilibrium surface, and only briefly penetrates into the instability area to hop to another equilibrium state.

Influence of the artificial saliva storage on 3-D surface texture characteristics of contemporary dental nanocomposites

The aim of this study was to analyse the influence of the artificial saliva on a three‐dimensional (3‐D) surface texture of contemporary dental composites. The representatives of four composites types were tested: nanofilled (Filtek Ultimate Body, FUB), nanohybrid (Filtek Z550, FZ550), microfilled (Gradia Direct, GD) and microhybrid (Filtek Z250, FZ250). The specimens were polymerised and polished by the multistep protocol (SuperSnap, Shofu). Their surface was examined, before and after 3 weeks’ exposure to artificial saliva storage. The surface texture was analysed using the atomic force microscope (AFM). The obtained images were processed to calculate the areal autocorrelation function (AACF), anisotropy ratio Str (texture aspect ratio), and structure function (SF). The log–log plots of SF were used to calculate fractal properties, such as fractal dimension D, and pseudo‐topothesy K. The analysis showed changes in surface anisotropy ratio Str values, which became higher, whereas the Sq roughness (root‐mean‐square) reduced after the artificial saliva storage. All the samples exhibited bifractal structure before the saliva treatment, but only half of them remained bifractal afterwards (GD, FZ250), whereas the other half turned into a monofractal (FUB, FZ550). The cube‐count fractal dimension Dcc was found to be material‐ and treatment‐insensitive.

Similarities in Time-Series of Housing Prices on Local Markets in Poland

Abstract This study examined similarities between local real estate markets in Poland from 2006 - 2013 by analyzing changes in housing prices. The analyses covered five cities - all of which are major centers of their regions: Warsaw (Mazovia - the center of Poland), Bialystok (Podlasie - the east of Poland), Cracow (Malopolska - the south of Poland), Poznan (Wielkopolska - the west of Poland) and Gdansk (Pomerania - the north of Poland). The time period was chosen so that it covered an interval of rapid changes in real estate prices (a housing bubble) and their subsequent relaxation to the equilibrium state. Firstly, a multi-dimensional analysis which took into account the Chebyshev distance was employed. This helped to conduct an analysis of the correlation of price changes over time, which revealed their concurrence and, moreover, showed specific propagation delays to external stimuli, and hence could be a measure of the market’s inertia. The degree of integration of the local markets under study changed only slightly over time; therefore, a thesis can be put forth in regard to the interrelation of local real estate markets, imagined as a system of communicating vessels. In the second stage, the damped harmonic oscillator model was employed to describe the observed evolution of real estate prices. This study exhibited high inertia in real estate markets, manifested during rapid structural changes in the system’s state occurring in conditions far from equilibrium. In long-term evolution, the pace of change is slow enough for the systems to remain close to equilibrium