Ota Salyk

Atomic force microscopy analysis of nanoparticles in non-ideal conditions

Nanoparticles are often measured using atomic force microscopy or other scanning probe microscopy methods. For isolated nanoparticles on flat substrates, this is a relatively easy task. However, in real situations, we often need to analyze nanoparticles on rough substrates or nanoparticles that are not isolated. In this article, we present a simple model for realistic simulations of nanoparticle deposition and we employ this model for modeling nanoparticles on rough substrates. Different modeling conditions (coverage, relaxation after deposition) and convolution with different tip shapes are used to obtain a wide spectrum of virtual AFM nanoparticle images similar to those known from practice. Statistical parameters of nanoparticles are then analyzed using different data processing algorithms in order to show their systematic errors and to estimate uncertainties for atomic force microscopy analysis of nanoparticles under non-ideal conditions. It is shown that the elimination of user influence on the data processing algorithm is a key step for obtaining accurate results while analyzing nanoparticles measured in non-ideal conditions.

Surface and bulk light scattering in microcrystalline silicon for solar cells

We present here an overview of the light scattering influence on the absorption coefficient spectra α(E) measured by constant photocurrent method (CPM) and/or by photothermal deflection spectroscopy (PDS). We compare results of numerical simulation with the measured CPM and PDS spectra and verify our theory by polishing the as-grown nanotextured layers. We show that the experimentally observed apparent absorption coefficient can overestimate the true α(E) by a factor of 10.

Reversible Formation of Charge Carrier Traps in Poly(Phenylenevinylene) Derivative due to the Phototransformation of a Photochromic Additive

ABSTRACT Kinetics of photochromic reaction of spiropyran dissolved in a poly(phenylenevinylene) derivative MEH-PPV was studied by optical and impedance spectroscopy. Spiropyran forms metastable, highly polar merocyanine under illumination with light of an appropriate wavelength. Due to charge-dipole interactions, charge carrier traps are formed and affect electrical properties of the polymer matrix, namely capacitance and photoconductivity.

A facility for characterization and testing of hydrogen sensors

Reliable and effective sensors for the accurate detection of hydrogen in air are essential for the safe operation of fuel cells, hydrogen fuelled systems and production, distribution and storage facilities. The paper presents a semi-automated facility designed and built for testing and validating the performance of such sensors under a range of conditions, representative of those to be encountered in service. Examples of characterization of some common sensor types are described as an example of the facilitys functioning and of test methodologies.

Wide Gap Hydrogenated Amorphous Silicon for Visible Light Emission

A series of samples of hydrogenated amorphous silicon (a-Si:H) was prepared from silane diluted highly with He by the microwave electron-cyclotron-resonance PE CVD. Such a wide gap (E≥2.0 eV) a-Si:H emits room temperature photoluminescence (PL) in the visible region. We attempt to reveal the microscopic origin of this PL by monitoring variations of PL intensity vs frequency of infrared vibrations in the vicinity of 2100 cm−1. We find that oligosilanes -(SiH2)n- act as one type of possible luminescence centres. We report also on room temperature electroluminescence (EL) from p-i-n junctions. Surprisingly, and unlike p-i-n structures from standard a-Si:H, weak EL radiation with external quantum efficiency of the order of 10−5% is emitted under reverse bias only. EL and PL emission spectra resemble strongly each other, except high energy wing of the EL spectrum. This high energy widening indicates the participation of hot electrons in the EL excitation mechanism.

Luminescence in plasma polysilylenes prepared from organosilanes

Abstract The photoluminescence in polysilanes (exemplified on poly(methylphenylsilylene) – PMPSi) during the change from linear 1D Si chain to amorphous 3D Si networks was studied. The excitonic absorption observed in 1D Si at 320 nm undergoes a blue shift on introducing branching and networking defects. With the transition to the 3D structure the redistribution of oscillator intensity along the absorption edge with the loss of the resolved σ–σ * band edge occurs. Further, the disappearance of main-chain exciton σ–σ * and appearance of the defect luminescence at 450 nm exhibiting red shift with increasing 3D networking are observed.

Template-Assisted Fabrication and Characterization of Nanostructured Copper Electrode for Adenine Detection

A nanostructured copper electrode (NSCuE) was prepared by copper electroplating in a porous membrane and characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and electrochemical impedance spectroscopy (EIS). Various parameters, which can influence the fabrication of copper nanostructures, were examined. After optimizing the fabrication process, electrochemical behaviour of the NSCuE in adenine solutions was investigated by differential pulse voltammetry (DPV) and the results were compared to those obtained using a flat electrode. The research of NSCuE contributes to the development of advanced biosensors which would be an environmentally safe alternative to mercury for the detection of adenine by voltammetric techniques.

Temperature dependent field effect in a-Si:H

The temperature dependent field effect (FE) was examined both computationally and experimentally. The regions of the validity of the surface approximation were determined, and the validity of the relation of the activation energy of FE and surface potential was discussed. The results of modelling were compared with the measurements of the temperature dependent FE using the method of TM-FE (temperature modulated field effect).

Organic Sensor for Cardiomyocytes Research

Organic electronic devices offer a convenient solution for bioelectronic sensor applications due to the biocompatibility of organic semiconductors and biologic tissues. So-called biosensors can convert electrochemical processes connected to cell membranes into electronic signals. A matrix of such biosensors can simultaneously scan a number of biological samples as well as living tissue in the body. The core of the device is a transistor, today mostly OECT (Organic Electro Chemical Transistor) fabricated by thin film or printing technique from semiconducting biocompatible polymer PEDOT:PSS (poly(3, 4-ethylenedioxythiophene) polystyrene sulfonate). Such transistors were printed both by inkjet and screen-printing technique and their main characteristics are presented.

Thickness measurement of thin soft organic films

This paper compares chromatic white light (CWL) and interference microscope measurements aiming to find a proper non-contact method for a thickness determination of thin soft organic films. Standard samples with vacuum deposited aluminum films of different thicknesses in the range of 50-1000 nm were prepared and measured by both methods. It was found that the CWL technique is proper for a measurement of thin soft organic films with higher than 40-50 nm film thicknesses. As a complementary feature of the method 2D and 3D surface morphology imaging of the films could be recorded and the surface film roughness could be calculated. In a case of optical inhomogeneity the method requires covering with a uniform high reflective coating. The interference microscopy method results in a relatively lower film thickness with a higher standard deviation and a higher standard relative error. It could be connected with the resolution of the interferograms measured.