Dinara Sobola

Micromorphology investigation of GaAs solar cells: case study on statistical surface roughness parameters

The purpose of this work is surface characterization of GaAs solar cell using atomic force microscopy. The surface appearance influences the optical properties of the cells. It impacts light trapping and consequently affect the efficiency of the solar cells. In case of nano-structural surface, the properties are strongly depends on its geometrical characteristics. Surface appearance was studied by atomic force microscopy (AFM). Fractal analysis was done by the triangulation method and evaluation of statistical metrics was carrying out on the basis of AFM-data, before and after heating. The results of fractal analysis show the correlation of fractal dimension and statistical characteristics of surface topography. Characterization technique and data processing methodology are essential for description of the surface condition.

Influence of scanning rate on quality of AFM image: Study of surface statistical metrics

The purpose of this work is to study the dependence of AFM‐data reliability on scanning rate. The three‐dimensional (3D) surface topography of the samples with different micro‐motifs is investigated. The analysis of surface metrics for estimation of artifacts from inappropriate scanning rate is presented. Fractal analysis was done by cube counting method and evaluation of statistical metrics was carrying out on the basis of AFM‐data. Combination of quantitate parameters is also presented in graphs for every measurement. The results indicate that the sensitivity to scanning rate growths with fractal dimension of the sample. This approach allows describing the distortion of the images against scanning rate and could be applied for dependences on the other measurement parameters. The article explains the relevance and comparison of fractal and statistical surface parameters for characterization of data distortion caused by inappropriate choice of scanning rate.

Thermal stability of gallium arsenide solar cells

This article summarizes a measurement of gallium arsenide (GaAs) solar cells during their thermal processing. These solar cells compared to standard silicon cells have better efficiency and high thermal stability. However, their use is partly limited due to high acquisition costs. For these reasons, GaAs cells are deployed only in the most demanding applications where their features are needed, such as space applications. In this work, GaAs solar cells were studied in a high temperature range within 30-650 °C where their functionality and changes in surface topology were monitored. These changes were recorded using an electron microscope which determined the position of the defects; using an atomic force microscope we determined the roughness of the surface and an infrared camera that showed us the thermal radiated places of the defected parts of the cell. The electrical characteristics of the cells during processing were determined by its current-voltage characteristics. Despite the occurrence of subtle changes on the solar cell with newly created surface features after 300 °C thermal processing, its current-voltage characteristic remained without a significant change.

Stereometric Parameters of Butterfly Wings

This paper analyses the data stereometric of three samples obtained using the atomic force microscope. The data concern the two butterfly species: Euploea mulciber (known as “Striped Blue Crow”) and Morpho didius (also named as “Giant Blue Morpho”). These species have a strong correlation color wings of the angle of incidence of light. This is structural coloration and it depends on the surface topography. Here we present a method for the topography evaluation. A script created in Matlab software version R2012 by MathWorks® was used for segmentation data stereometric and analysis of localized motifs occurring on the surface of the samples. An analysis of the data using stereometric software MountainsMap® Premium version 7.3.7746 by Digital Surf was made to compare the results obtained using the script developed in Matlab, for identification of all sorts of motifs, such as peaks, pits, or irregular shapes in correlation with the surface statistical parameters. The analysis of motifs is essential when choosing the appropriate technique for imaging the 3-D (three-dimensional) microtextured features of butterfly wings surfaces. This stereometric analysis proves to be an effective method that can be successfully used for estimation of micro- and nano- topography by processing of AFM data

Multiscale experimental characterization of solar cell defects

The search for alternative sources of renewable energy, including novel photovoltaics structures, is one of the principal tasks of 21th century development. In the field of photovoltaics there are three generations of solar cells of different structures going from monocrystalline silicon through thin-films to hybrid and organic cells, moreover using nanostructure details. Due to the diversity of these structures, their complex study requires the multiscale interpretations which common core includes an integrated approach bridging not only the length scales from macroscale to the atomistic, but also multispectral investigation under different working temperatures. The multiscale study is generally applied to theoretical aspects, but is also applied to experimental characterization. We investigate multiscale aspects of electrical, optical and thermal properties of solar cells under illumination and in dark conditions when an external bias is applied. We present the results of a research of the micron and sub-micron defects in a crystalline solar cell structure utilizing scanning probe microscopy and electric noise measurement.

Fractal Analysis of the 3-D surface Topography of GaAs Solar Cells

This article is devoted to study of Atomic Force Microscopy (AFM) images of solar cells based on gallium arsenide (GaAs). Mathematical processing of data involves obtaining additional information about topography. The analysis was carried out using AFM data for GaAs solar cells, before and after temperature treatment. The state of the surface affects the reflectivity, so the structuring of the surface is of particular interest. Optimized textures are needed to improve the optical properties of surfaces. Fractal analysis allows quantifying the condition of the morphology of the surface on the basis of AFM data.

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.

Noise behaviour of field emission cathode based on lead pencil graphite

The paper describes electrical noise of experimental field emission cathodes based on “polymer” pencil leads which have a high content of hybridized carbon with a low degree of surface oxidation and silicon monoxide (SiO). Charge transport within experimental samples is evaluated based on results provided by the noise spectroscopy method. The paper also briefly describes the experimental preparation method of graphite tips based on ion milling which allow obtaining ultrasharp tips of a diameter lower than 100 nm.

Multifractal characterization of epitaxial silicon carbide on silicon

Abstract The purpose of this study was to investigate the topography of silicon carbide films at two steps of growth. The topography was measured by atomic force microscopy. The data were processed for extraction of information about surface condition and changes in topography during the films growth. Multifractal geometry was used to characterize three-dimensional micro- and nano-size features of the surface. X-ray measurements and Raman spectroscopy were performed for analysis of the films composition. Two steps of morphology evolution during the growth were analyzed by multifractal analysis. The results contribute to the fabrication of silicon carbide large area substrates for micro- and nanoelectronic applications.

Analysis and Recommendations for Education Process of Experts in the Field of Scanning Probe Microscopy

This paper describes the mandatory conditions for training specialists in the widespread and still continuously developing microscopic technique for studying of materials surface. Traditional methods of education are not sufficient for teaching of the multidisciplinary subjects. Available information technologies and resources alone do not ensure learning success. There is need for a conceptual review and analysis of the cases in the sphere of specialists training. Scanning probe microscopy is based on the fundamental concepts of quantum mechanics, physics, chemistry, etc. In this regard, the specialist has to achieve knowledges in the field of science (physical and chemical laws), and at the same time there is necessity to be educated in approaches for the study and description of surface quality. Introduction The relevance of this work is based on the need to modernize the educational process, taking into account the rapid dynamics of the development of such areas as scanning probe microscopy (SPM). Important conditions for training specialists in the field of scanning probe microscopy are: strong background in the field of science (which laid the foundations in principles of measurement techniques), continuous study of information technologies, research of modern trends in the development of electronics, practical training in their professional activities. Scanning probe microscopy is one of the powerful modern methods of studying morphology and local surface properties with high spatial resolution. It is not an exotic methodology of a small group of scientists. It is the widely used tool in many areas where surface quality is crucial. The development of SPM caused the development of new methods in nanotechnology and nano-engineering. In addition to teaching theoretical knowledge, it is necessary to offer practical training in working with nanotechnology equipment. A well-equipped research center focused on research, modification and creation of structures with high accuracy is a beneficial component in the training of specialists in the field of SPM [1]. Factors for ensuring competitiveness of specialists and success at the national and world levels: equipping with specialized tools for teaching practical skills, supply of special educational and methodical materials, training of teachers. The subject of the study is professional competence of specialists in the field of SPM and growth of their comprehension in this field to a higher level. Metrological bases of SPM should be also implemented into study process and become a part of complex investigation of the materials’ surface. Interdisciplinary technologies that teach the work in nanometer range of object sizes and high accuracy of controlled impacts have great importance [2-9]. Based on the basic principles, concepts and technology, we describe all aspects from the perspective of practical considerations.