Victor Kaidas

Localized Synthesis of Iron Oxide Nanowires and Fabrication of High Performance Nanosensors Based on a Single Fe2O3 Nanowire

A composed morphology of iron oxide microstructures covered with very thin nanowires (NWs) with diameter of 15-50 nm has been presented. By oxidizing metallic Fe microparticles at 255 °C for 12 and 24 h, dense iron oxide NW networks bridging prepatterned Au/Cr pads are obtained. X-ray photoelectron spectroscopy studies reveal formation of α-Fe2 O3 and Fe3 O4 on the surface and it is confirmed by detailed high-resolution transmission electron microscopy and selected area electron diffraction (SAED) investigations that NWs are single phase α-Fe2 O3 and some domains of single phase Fe3 O4 . Localized synthesis of such nano- and microparticles directly on sensor platform/structure at 255 °C for 24 h and reoxidation at 650 °C for 0.2-2 h, yield in highly performance and reliable detection of acetone vapor with fast response and recovery times. First nanosensors on a single α-Fe2 O3 nanowire are fabricated and studied showing excellent performances and an increase in acetone response by decrease of their diameter was developed. The facile technological approach enables this nanomaterial as candidate for a range of applications in the field of nanoelectronics such as nanosensors and biomedicine devices, especially for breath analysis in the treatment of diabetes patients.

Low temperature degradation of single layers of multilayered zirconia in comparison to conventional unshaded zirconia: Phase transformation and flexural strength

OBJECTIVES The aim of this study was to evaluate the transformation of yttrium stabilized tetragonal zirconia (Y-TZP) to monoclinic phase and its change in flexural strength of the various layers of multilayered zirconia (enamel layer, transition layer 1, transition layer 2 and body layer) in comparison to two conventional zirconia ceramics. Additionally, the ball-on-three-balls test was compared with a conventional biaxial flexural strength test. METHODS The crystallographic structure of the four layers of Katana Zirconia ML (Kuraray), e.max ZirCAD (Ivoclar Vivadent) and Lava Plus (3M ESPE) was investigated by x-ray-diffraction before and after hydrothermal aging in an autoclave for 5, 10, 15 and 20h. The biaxial flexural strength was examined with a piston-on-three-ball test and a ball-on-three-balls test. RESULTS There was a significant difference of the ratio of transformation with respect to the tested materials, also between the four different layers of multilayered zirconia. After 20h of hydrothermal aging the mean ratio of monoclinic phase ranged from 9.9vol% (LAVA Plus) to 44.2vol% (Katana Zirconia ML, enamel layer). However, hydrothermal aging had no significant influence on the flexural strength of any material. Furthermore, the flexural strength measured by the ball-on-three-balls test was higher than that measured by the piston-on-three-ball test. CONCLUSION A ratio of 40% monoclinic phase at the surface did not significantly influence the biaxial flexural strength. Both test methods provide reliable results. However, as the ball-on-three balls test is less dependent on surface roughness, it might be preferred for investigations adapted to clinical reality.

Sensing Properties of Ultra-Thin TiO2 Nanostructured Films Based Sensors

In this work, ultra-thin TiO2 nanostructured films, synthesized by atomic layer deposition method (ALD), were integrated in sensor structures. The effect of post-growth annealing and thickness of TiO2 samples on UV and hydrogen gas sensing properties is investigated. An increase in current value of more than one order of magnitude (I UVON /I UVOFF ~38) has been detected under exposure to UV light (365 nm) of sample with 45 nm thickness and annealed in furnace at 650°C for 2 hours. Samples with 15 nm thickness and rapid thermal annealed at 450°C for 3 min, have shown hydrogen gas response ( 3.75).