Challenges of reliable AFM-tip shape reconstruction and approximation.

Reliable reconstruction of AFM tip geometry is not an easy task. The shape of the tip can be (partially) reconstructed from the AFM image of a calibration sample using a blind reconstruction method. The result is a range of the tip shapes (from unrealistically sharp to blunt). A criterion for selecting the true shape is proposed. It is based on reconstruction of the calibration relief. Further refining the probe geometry by indenting an elastic polymer is discussed. The choice of the test sample is another problem. In practice, the researcher has a small number of commercially available test gratings. Their limitations are highlighted. An approximation of tip geometry by a body of revolution is required in indentation experiments. A hyperboloid was found to be the closest approximation to the conventional probes. The contact area was obtained for the hyperboloids with different parameters indenting an elastic material. RESEARCH HIGHLIGHTS: Criteria for blind reconstruction algorithm of AFM tip shape. Pros and cons of tip shape calibration samples. Contact area of the elastic indentation by hyperbolic indenter.

Elastic Modulus of a Carbonized Layer on Polyurethane Treated by Ion-Plasma.

Nanocoatings formed by various plasma and chemical methods on the surface of polymeric materials have unique properties. However, the applicability of polymeric materials with nanocoatings under specific temperature and mechanical conditions depends on the physical and mechanical properties of the coating. The determination of Young's modulus is a task of paramount importance since it is widely used in calculations of the stress-strain state of structural elements and structures in general. Small thicknesses of nanocoatings limit the choice of methods for determining the modulus of elasticity. In this paper, we propose a method for determining the Young's modulus for a carbonized layer formed on a polyurethane substrate. For its implementation, the results of uniaxial tensile tests were used. This approach made it possible to obtain patterns of change in the Young's modulus of the carbonized layer depending on the intensity of ion-plasma treatment. These regularities were compared with regularities of changes in the molecular structure of the surface layer caused by plasma treatment of different intensity. The comparison was made on the basis of correlation analysis. Changes in the molecular structure of the coating were determined from the results of infrared Fourier spectroscopy (FTIR) and spectral ellipsometry.

Evaluating structural, morphological, and multifractal aspects of n-ZnO/p-ZnO homojunctions and n-ZnO/p-NiO heterojunctions.

We have investigated the evolution of the structure and surface morphology of n-ZnO/p-ZnO homojunctions and n-ZnO/p-NiO heterojunctions transparent structures deposited by radio frequency-sputtering on quartz (Q)/ITO substrates. X-ray diffraction (XRD) analysis of the as-deposited and annealed ZnO, n-ZnO/p-NiO/Q/ITO, and n-ZnO/p-ZnO/Q/ITO thin films showed that ZnO had a wurtzite hexagonal structure and (002) preferred growth direction. The annealing temperature played a key role in improving the crystalline structure of the films, as evidenced by the changes in the intensity and position of the XRD (002) peak. Morphological analysis revealed that the roughness of the film varies with increasing annealing temperature. Particle size dictates the vertical growth of p-ZnO homojunctions, while particle shape dictated the p-NiO heterojunctions growth. Fractal analysis showed that p-ZnO homojunctions have similar spatial complexity, surface percolation, and topographical uniformity and are dominated by low dominant frequencies. Moreover, a robust multifractal character was observed, where n-ZnO/p-ZnO homojunctions follow similar vertical growth dynamics, which differed from the n-ZnO/p-NiO heterojunctions growth dynamics. These results prove that annealing temperature plays a key role in the n-ZnO/p-ZnO homojunctions and n-ZnO/p-NiO heterojunctions structure, surface morphology, and vertical growth dynamics.

Mechanical Properties of the Carbonized Layer Formed by Ion Flow Orientated at Different Angles to the Polyurethane Surface.

Polymer materials are widely used in medicine due to their mechanical properties and biological inertness. When ion-plasma treatment is used on a polymer material, a carbonization process occurs in the surface nanolayer of the polymer sample. As a result, a surface carbonized nanolayer is formed, which has mechanical properties different from those of the substrate. This layer has good biocompatibility. The formation of a carbonized nanolayer on the surface of polymer implants makes it possible to reduce the body's reaction to a foreign body. Typically, to study the properties of a carbonized layer, flat polymer samples are used, which are treated with an ion flow perpendicular to the surface. But medical endoprostheses often have a curved surface, so ion-plasma treatment can occur at different angles to the surface. This paper presents the results of a study of the morphological and mechanical properties of a carbonized layer formed on a polyurethane surface. The dependence of these properties on the directional angle of the ion flow and its fluence has been established. To study the surface morphology and elastic properties, methods of atomic force microscopy and methods of elasticity theory were used. The strength properties of the carbonized layer were studied using a stretching device combined with a digital optical microscope.

Atomic force microscopy nanoindentation kinetics and subsurface visualization of soft inhomogeneous polymer.

Modern techniques of nanoindentation by atomic force microscopy (AFM) produce maps of topography and physical-mechanical properties of the material. Analysis of the interaction rate of the AFM tip with the soft surface reveals the surface and subsurface structure and expands standard analysis of the material behavior. Phase-separated polymer (polyurethane, elastic modulus-6 MPa) is studied. Reversible inelastic changes of the surface at different stages of indentation were established in dependence on peculiarities of velocity and position of the AFM-tip in the material: uniform soft nanofilm covering the outer surface gradually passes into fibrillar heterogeneous structure of the polymer. The point of stable mechanical contact is defined, and the elastic moduli of soft and hard blocks of the polymer are estimated using certain intervals of the indentation. The presented methods of surface analysis are useful in the study of a wide class of soft heterogeneous materials.

Atomic force microscopy studies of enamel, inner enamel, dentin, and cementum in canine teeth.

The main goal of the present work is to explore the three dimensional (3-D) atomic force microscopy (AFM) images of human teeth and investigating their micromorphology. For this purpose, 10 fresh and permanent canine teeth were selected from a group of 40-year-old men who were candidate for the experimental processes. Afterward, they were all applied for studying the morphology of their hard tissues. The tapping mode of AFM was used to characterize the surface micromorphology on the square areas of 1 µm × 1 µm (512 × 512 pts). AFM results and surface stereometric analysis indicate the relationships between the micromorphology of the surface and the structural properties of these tissues across the length scales. As can be seen, the surface of cementum has the most irregular topography (D = 2.87 ± 0.01) while the most regular topography (D = 2.43 ± 0.01) is found in dentin. Furthermore, the more and less regularity of the surface have been found in inner enamel (Sq = 26.26 nm) and dentin (Sq = 41.28 nm), respectively. Stereometric and fractal analyses give valuable information about human canine teeth via 3-D micromorphology.

Multifractal investigation of Ag/DLC nanocomposite thin films.

The objective of this study is the experimental investigation of the silver in diamond-like carbon (Ag/DLC) nanocomposite prepared by the co-deposition of radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) and RF-sputtering. Atomic force microscopy (AFM), X-ray diffraction analyses, ultraviolet-visible (UV-visible) spectroscopy measurements were applied to describe the three-dimensional surface texture data in connection with the statistical, and multifractal analyses. Additional information about structure-property relationships in prepared Ag/DLC nanocomposite was studied in detail to allow a better understanding of the surface micromorphology. The performed analysis revealed the studied samples have multifractal properties and can be included in novel algorithms for graphical representation of complex geometrical shapes and implemented in computer simulation algorithms.

Multifractal Characterization of Butterfly Wings Scales.

A lot of insect families have physical structures created by evolution for coloration. These structures are a source of ideas for new bio-inspired materials. The aim of this study was to quantitatively characterize the micromorphology of butterfly wings scales using atomic force microscopy and multifractal analysis. Two types of butterflies, Euploea mulciber ("striped blue crow") and Morpho didius ("giant blue morpho"), were studied. The three-dimensional (3D) surface texture of the butterfly wings scales was investigated focusing on two areas: where the perceived colors strongly depend on and where they do not depend on the viewing angle. The results highlight a correlation between the surface coloration and 3D surface microtexture of butterfly wings scales.

Structural-mechanical and antibacterial properties of a soft elastic polyurethane surface after plasma immersion N2(+) implantation.

The surface of elastic polyurethane treated by plasma immersion N2(+) ion implantation at different fluences has been investigated. A folded surface structure is observed in all cases. Analysis has been performed to study the structural (roughness, steepness and fraction of folds, fractal characteristics), mechanical (stiffness, adhesion force between the AFM probe and the material) and wetting properties of surfaces. Under uniaxial stretching the cracks orthogonal to the axis of deformation and longitudinal folds are formed on the examined surfaces. After unloading the initial structure of the surface of deformed materials exposed to low fluences becomes smoother and does not recover, i.e. it has plastic properties. By contrast, the structure of the surfaces of materials subjected to high-fluence treatment recovers without visible changes and the cracks are fully closed. The study of Staphylococcus colonies grown on these materials has demonstrated significant reduction (from 3 to 5 times) in the vitality of bacteria on treated surfaces. This result was repeated on samples after 11 months of storage. Such antibacterial properties are primarily related to the structural changes of the surfaces accompanied by the increased hydrophilicity.