Elena Prokopyeva

AFM imaging of natural optical structures

The colors of some living organisms assosiated with the surface structure. Irridesence butterfly wings is an example of such coloration. Optical effects such as interference, diffraction, polarization are responsible for physical colors appearance. Alongside with amazing beauty this structure represent interest for design of optical devices. Here we report the results of morphology investigation by atomic force microscopy. The difference in surface structure of black and blue wings areas is clearly observed. It explains the angle dependence of the wing blue color, since these micrometer and sub-micrometer quasiperiodical structures could control the light propagation, absorption and reflection.

Angular absorption of light used for evaluation of structural damage to porcine meat caused by aging, drying and freezing

Meat as a rich source of protein is sought after by people from all over the world. It is also very susceptible to decay because of many internal and external processes affecting it. In this work an easy and quick method of detection of structural damage caused by decay or mishandling the meat is attempted by the method of angular absorption of light. The difference between structural changes due to aging, drying and freezing is explored and the resulting changes in light absorption in meat samples are presented. This work demonstrates that the measurement of optical angular dependency of absorption in relation to the muscle fibers in muscle tissue has the potential of detecting structural damage to the sample for meat quality control purposes.

Comparison of optical and electrical investigations of meat ageing

Different ultrasonic, electromagnetic, electrical and optical methods are used for meat ageing detection. Muscles are turbid anisotropic media, they exhibit changes in electrical and optical properties according to the direction of the electrical and optical fields in the sample. The work assesses the feasibility of impedance measurements for meat ageing detection and their comparison with optical measurement of scattered light. The pork chop slices were used for their relative homogeneity. An investigation was carried out for the detection of the ageing of unpacked slices exposed directly to the air, and other packed in polyethylene bags. The electrical method is a promising method due to the possibility of getting much information and realizing cheap and fast enough measurement systems. The optical method allows measure the rotation of polarization plane in the range of 95 degrees within considered period. Nevertheless, further work has to be provided to determine closer relationships between optical scattering characteristics, electrical anisotropy in ageing-related tissue structural properties.

Changes in optical properties of biological tissue: experiment and Monte Carlo simulation

Biological tissue is a very complex, yet important material to describe and analyze. Its properties are affected by chemical processes too numerous to easily understand and describe. By simplifying and grouping some aspects together we are able to create a model for simulating behavior of a photon inside of a biological sample. Using the Monte Carlo method an algorithm for calculating photon propagation through the tissue based on several optical parameters, like absorption and scattering coefficients, refractive indices and optical anisotropy, can be created. Based on some of the results of the simulation a comparative measurement on a muscle sample was performed to prove the usefulness of such model and to describe changes in the tissue sample based on the aforementioned optical parameters in both real life and the simulation.

Optical scattering in muscle tissue and its utilisation

This paper describes optical scattering properties of muscle t issue, special traits, and the difficulties its composition causes. The pH of tissue and angle of the myofibrils relative to the incident light used as a probe changes the results of measurements. Distribution of colagen, as well as other substances that can be found in muscle tissue, also affect the outcome of any attempt to examine the sample via the means of optical analysis. Measurement results and scattering models are compared in effectiveness of characterization of the non-linear optical system that is muscle tissue for both medical use and food quality control, depending on the properties and composition of the tested sample.

Optical properties of metal nanoparticles used in biosensors

Metal and semiconductor nanoparticles have excellent optical and electrochemical properties that strongly depend on their size and shape. Local biosensors are advanced devices, whose basic working principle is to analyze spectra of noble metal nanoparticles. Here a model of a local biosensor is described. It takes into account the interaction of the particle with a glass prism and the viewing angle of lens. The results for the layered particle made of a polystyrene latex core with a golden outer shell and for nanorods are presented. The influence of the metal shell thickness, particle diameter and the nanoscale rod form on the location of dissipation spectrum maximum is analyzed.

Local topography of optoelectronic substrates prepared by dry plasma etching process

In this work, the etch rate of silicon carbide and aluminum oxide were studied as a function of the angle etching material and flow of plasma. Al2O3 and SiC are important materials in the design of optical and electronic devices and the topography of the wafers has a large influence on the device quality. Argon was applied for the dry etching of Al2O3 and SiC wafers. The wafer slope for highest obtained etch is defined. Atomic force microscopy was used to good morphology control of etched wafers. Statistical and correlation analysis was applied to estimate the surface perfection. Interferometry allowed to control etching rate.

Interferometry and Atomic Force Microscopy of Substrates for Optoelectronics Proceeded by Dry Plasma Etching

The paper describes the process of sapphire and silicon carbide substrates preparation by dry plasma etching and its characterization. The study confirms the possibility of using dry plasma etching processes for wide band gap materials treatment, since the condition of the substrate surface is an important parameter for electronic and optoelectronic devices manufacturing. Processed substrates were studied by interferometry to define the etch depth, and by atomic force microscopy to study the topography and statistical analysis of surface roughness before and after etching. The interferometry reveals the dependence of etch rate on the angle between the substrates and defocused beam of argon ions. It is also shown in low scale image that the surface damage occurs after the substrate treatment. But the common large area surface topography indicates the decreasing of roughness. In order to have purely physical etching the argon plasma was used. Thus this combination of methods allows determine optimal conditions of the substrate preparation.

Optical and electrical detection and localization of solar cell defects on microscale

Monocrystalline silicon wafer is up-to-date most used material for the fabrication of solar cells. The recent investigation shows that the quality of cells is often degraded by structural defects emerging during processing steps. Hence the paper gives first an overview of solar cell efficiency investigation on macroscale. Then a detection and microscale localization of tiny local defects in solar cell structures which evidently affect electrical and photoelectrical properties of the cells is targeted. The local defects can be classified as microfractures, precipitates and other material structure inhomogeneities. Detection and localization of the defects in the structure and the assigning of particular defects to corresponding degradation of photoelectrical parameters are key points for solar cell lifetime and efficiency improvement. Although the breakdown can be evident in current-voltage plot, the localization of defects on the sample has to be provided by microscopic investigations as well as by defects light emission measurement under electrical bias conditions. The experimental results obtained from samples where the defects were microscopically repaired by focused ion beam are presented. Electrical and photoelectrical properties of sample before and after milling processing are also discussed.