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  • Author: Marián Marton x
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Marián Marton, Miroslav Mikolášek, Jaroslav Bruncko, Ivan Novotný, Tibor Ižák, Marian Vojs, Halyna Kozak, Marián Varga, Anna Artemenko and Alexander Kromka

Abstract

Diamond and ZnO are very promising wide-bandgap materials for electronic, photovoltaic and sensor applications because of their excellent electrical, optical, physical and electrochemical properties and biocompatibility. In this contribution we show that the combination of these two materials opens up the potential for fabrication of bipolar heterojunctions. Semiconducting boron doped diamond (BDD) thin films were grown on Si and UV grade silica glass substrates by HFCVD method with various boron concentration in the gas mixture. Doped zinc oxide (ZnO:Al, ZnO:Ge) thin layers were deposited by diode sputtering and pulsed lased deposition as the second semiconducting layer on the diamond films. The amount of dopants within the films was varied to obtain optimal semiconducting properties to form a bipolar p-n junction. Finally, different ZnO/BDD heterostructures were prepared and analyzed. Raman spectroscopy, SEM, Hall constant and I-V measurements were used to investigate the quality, structural and electrical properties of deposited heterostructures, respectively. I-V measurements of ZnO/BDD diodes show a rectifying ratio of 55 at ±4 V. We found that only very low dopant concentrations for both semiconducting materials enabled us to fabricate a functional p-n junction. Obtained results are promising for fabrication of optically transparent ZnO/BDD bipolar heterojunction.

Open access

Ivana Sálusová, Kristína Cinková, Barbora Brtková, Marian Vojs, Marián Marton and Ľubomír Švorc

Abstract

The electrochemical behavior and determination of ascorbic acid (AA) was investigated at a bare boron-doped diamond (BDD) electrode using cyclic and differential pulse voltammetry. The influence of pH of supporting electrolyte and scan rate on the current response of analyte was examined to select the suitable experimental conditions. It was found that AA provided one well-shaped irreversible and diffusioncontrolled oxidation peak at +0.87 V vs. Ag/AgCl in Britton-Robinson buffer pH 4.0. Applying differential pulse voltammetry, the peak current of AA was linearly proportional to its concentration from 5 × 10-6 to 2 × 10-4 mol L-1 (R2 = 0.999), with the limit of detection of 1.1 × 10-6 mol L-1 and the good repeatability (relative standard deviation of 2.3 %). The developed electroanalytical protocol was successfully applied to determine the content of AA in commercial pharmaceutical preparations, based on the standard additions method, with the obtained recovery of 122 %. The accomplished analytical performance indicates that BDD electrodes are promising electrochemical sensors for pharmaceutical analysis.

Open access

Kristína Cinková, Linda Dianová, Marian Vojs, Marián Marton and Ľubomír Švorc

Abstract

A novel protocol for the simple and rapid determination of nicotine using square-wave voltammetry at boron-doped diamond electrode was developed. The effect of pH of supporting electrolyte, scan rate and square-wave voltammetric parameters was examined. Behavior study revealed that nicotine provided two irreversible oxidation peaks, the first one well-shaped at +1.14 V and the second one poorly-defined at +1.61 V vs. Ag/AgCl electrode in the presence of phosphate buffer (pH 9.0). Under optimal experimental conditions (modulation amplitude of 40 mV, frequency of 50 Hz and scan rate of 0.225 V · s-1), the current response of nicotine was proportionally linear in the concentration range from 9.9 × 10-6 to 1.7 × 10-4 mol · L-1 (R2 = 0.996) with the detection limit of 6.1 × 10-6 mol · L-1 (0.989 mg · L-1) and the relative standard deviation of 8.8 % (number of measurements n = 10, 5.7 × 10-5 mol · L-1 nicotine). The proposed procedure was applied to the quantification of nicotine in cigarettes and chewing gums with the determined values in good agreement with those declared by producer. In this respect, the developed protocol could represent an effective and rapid alternative to chemically modified electrodes in analysis of alkaloids.

Open access

Jozef Liday, Peter Vogrinčič, Viliam Vretenár, Mário Kotlár, Marián Marton and Vlastimil Reháček

Abstract

We have designed and verified a new structure for ohmic contacts to p-GaN, mainly for applications in light emitting devices based on a layer of single-walled carbon nanotubes (SWCNT) and metallic layers of Cr and Au, namely in configuration Au/Cr/SWCNT/p-GaN. The layer of carbon nanotubes was deposited on p-GaN by spraying a solution of synthesized SWCNTs, while the layers of Cr and Au were vapour deposited. The effects of the annealing temperature and time upon the electrical properties of Au/Cr/SWCNT/p-GaN contacts have been studied. It has been found that the contact structure provides a low resistivity ohmic contact after subsequent annealing in N2 ambient at 700 °C for 1 minute.

Open access

C. Borz, D. Marian, T. Bara, O. Jimborean, T. Bara and D. Márton

Abstract

Liver transplantation is now a standard procedure for the treatment of end stage liver diseases. Since 1968 until 2012, a number of 113,627 liver transplantations were performed in Europe, in 28 countries and 153 institutions. Despite these impressive figures the waiting list is growing every year. Transplant surgeons were preoccupied to find new ways to increase the donor pool. Among them: reduced size liver transplantation, split liver technique and more recently living donor liver transplantation. At first in the early `90, living donor liver transplantation was used for pediatric patients because the left lateral hepatic segments were harvested. This graft is too small for the metabolic demands of an adult patient. So the next step was the harvesting of the right liver lobe from the donor and transplantation to adult patients. Living donor liver transplantation has gained fast a wide acceptance but there are a few issues to discuss. The main concern is about the donor safety which is a healthy person undergoing major surgery with potential risks. Also the surgical technique evolved due to a better understanding of the anatomy and physiology of the liver and the right liver graft. We discuss here the anatomical and surgical basis for living donor liver transplantation with the right liver lobe.

Open access

Jozef Liday, Peter Vogrinčič, Viliam Vretenár, Mário Kotlár, Marián Marton and Vlastimil Řeháček

Abstract

Due to their properties, carbon nanotubes and reduced graphene oxide are highly promising materials for obtaining low-resistance ohmic contacts to p-GaN with good optical transparency for visible light. In this contribution we designed a combination of these two materials, along with a cap layer, to be used as structures for ohmic contacts to p-GaN. Carbon nanotube (CNT) and graphene oxide (GO) layers were deposited by spray coating using an off-the-shelf airbrush on p-GaN layers. The metallic layers of Au/Pd were vapour deposited. The structures for ohmic contacts were prepared in two configurations, namely as Au/Pd/r-GO/CNT/p-GaN and Au/Pd/CNT/r-GO/CNT/p-GaN. The prepared structures provide a low resistivity ohmic contact after subsequent annealing in air ambient at 600 °C for 3 minutes. The contact containing the sandwich CNT/r-GO/CNT interstructure exhibits lower values of contact resistance in comparison with the r-GO/CNT interstructure.

Open access

Liday Jozef, Vogrinčič Peter, Vretenár Viliam, Kotlár Mário, Marton Marián, Mikolášek Miroslav and Řeháček Vlastimil

Abstract

We have designed and verified a new structure for ohmic contacts to p-GaN based on a layer of carbon nanotubes (CNT), reduced graphene oxide (r-GO) and metallic layers of Cr, Pd and Au, namely in configurations Au/Cr/r-GO/CNT/p-GaN and Au/Pd/r-GO/CNT/p-GaN. The effects have been studied of the annealing temperature and the gas ambient upon the electrical properties of the contacts. Annealing of the Au/Pd/r-GO/CNT/p-GaN structure in air at 500°C for 1 minute resulted in linear I - V curves measured between planar electrodes on the p-GaN. Hence, addition of r-GO to the CNT interlayer between p-GaN and the metallization layer is a highly promising procedure for further improvements of the ohmic contacts to p-GaN.

Open access

Jozef Liday, Peter Vogrinčič, Viliam Vretenár, Ivan Hotový, Mário Kotlár, Marián Marton and Vlastimil Řeháček

Abstract

We have examined electrical properties and concentration depth profiles of contact structures Au/Ni-Mg-(O)/SWCNT/p- GaN and Au/Ni-Mg-O/p-GaN, thus with and without an interlaying layer of single-walled carbon nanotubes (SWCNT). The metallization layers were deposited on p-GaN by DC reactive magnetron sputtering in an atmosphere with and without a low concentration of oxygen (cca 0.2 at%). The contacts were annealed in N2 . We have found that the structure containing the SWCNT interlayer exhibits lower values of contact resistivity in comparison with an otherwise identical contact without the SWCNT interlayer