Ing. Alexandr Pošta

Epitaxial growth of diamond is critically important for the fabrication of diamond-based electronic devices. The emerging study of the epitaxial diamond growth on the (113) vicinal surfaces evidences highly needed high growth rates and low structural defects concentrations with both p- and n-type doping. In this work, we compare the morphology and dopant concentration incorporation of heavily boron-doped (113) epitaxial diamond layers with conventionally studied (100) and (111) epitaxial layers. Epitaxial layers were grown using resonance cavity Microwave Plasma Enhanced Chemical Vapor Deposition (MWPECVD) system. The surface morphology of epitaxial layers was studied by optical microscopy and atomic force microscopy, whereas the boron incorporation homogeneity was determined by Raman spectroscopy mapping. Heavily boron-doped (113) epitaxial diamond layers can be grown at a high growth rate with a smooth surface, without pyramidal hillocks or non-epitaxial crystallite defects, and with homogeneous boron concentration. These results confirm that epitaxial diamond growth on (113) vicinal surfaces is a promising solution for the development and fabrication of diamond-based electronic devices. (9) (PDF) Effect of the substrate crystalline orientation on the surface morphology and boron incorporation into epitaxial diamond layers. Available from: https://www.researchgate.net/publication/349892789_Effect_of_the_substrate_crystalline_orientation_on_the_surface_morphology_and_boron_incorporation_into_epitaxial_diamond_layers [accessed Aug 25 2021].

Although significant efforts have been dedicated to optimize the quality of epitaxial diamond layers, reported properties of diamond based electronic devices do not yet approach expected theoretical values. Recent works indicate that boron-doped and phosphorous-doped diamond can be grown on atomically stepped (113) surfaces (A. Tallaire et al., 2016; M.-A. Pinault-Thaury et al., 2019), however the electrical properties of these layers have not been studied in detail. In this work, we report on structural and electrical properties of boron-doped epitaxial diamond layers grown on (113) substrates. Properties of the diamond layers have been investigated by means of scanning electron microscopy, atomic force microscopy, Hall effect, secondary ion mass spectrometry and Raman spectroscopy. Our results show that boron-doped diamond layers can be grown on (113) substrates at high deposition rates with atomically flat surfaces, excellent electrical properties and high boron incorporation efficiency.

In this paper we prepared flexible ammonia (NH3) gas sensor based on polyaniline (PAni) as an active sensing thin film layer. The sensors function was based on chemiresistive principle with thin film deposited on top of interdigitated electrodes. We measured the change in resistance of the thin film under gas exposure. The PET based foil has been used as the sensors substrate. The Interdigitated electrodes (IDE) has been printed with Fujifilm Dimatix DMP 2831 inkjet printer by nanocoloid silver ink. The active thin film has been prepared by drop casting method from polyaniline nanoparticle dispersion. The morphology of thin films surface was characterized by atomic force microscopy (AFM). The sensors response was investigated in a gas chamber and the gas flow was controlled by mass flow meters. The sensitivity towards various gases under different concentration in synthetic air has been tested. The tested gases were NH3, NO2, CO2 and CO. The measurement of the sensors response to the different levels of humidity was also conducted. All the measurements were performed at room temperature, which is important feature for the sensor to be able to operate in hazardous environment and it facilitates low-power operation of the sensor as well. We also observed the long-term stability of the sensors response, as well as the effect of bending of the sensing platform on the sensors response and stability.

The SU-8 is commonly used epoxy-based photoresist in manufacturing microfluidics and microelectromechanical systems (MEMS). In this paper, we investigated temperature dependent polymerization process of SU-8 by means of Raman spectroscopy. The Raman spectrum were recorded in-situ during the heating of the sample from 25 to 160 degrees of Celsius. From the collected spectrum we can observe increase in the intensity of 1183 cm-1 and 1108 cm-1 peaks corresponding to the asymmetric vibrations of C-O-C bond in polymer and decrease in the intensity of 930 cm-1 peak attributed to symmetric vibration of C-O-C bond in the polymer.

Polyaniline as a conducting polymer is proposed to react with gas molecules and thus change its electrical conductivity. In this paper, a polyaniline molecule, in the form of emeraldine salt, and its electrical conductivity in or without the presence of NH3 were studied using numerical modelling. From the I-V characteristic of emeraldine salt molecule in the presence and without the presence of ammonia molecule, the effective resistance (R−R0)/R0 was computed and compared with experimental data. Because of only one molecule computation, I-V characteristics come to saturation (limited amount of charge carriers). The resistance is computed for pure polyaniline (PANI) and PANI with adsorbed ammonia molecule corresponding to approximative ammonia gas concentration of 3 ppm. The relative resistance increase was compared with experimental data and it was shown to be consistent with the measured values. From the results, PANI in the form of emeraldine salt is suitable as a sensing element in NH3 gas sensors.