István Endre Lukács

Nano-hydroxyapatite preparation from biogenic raw materials

Hydroxyapatite (HAp) was successfully produced from recycled eggshell, seashell and phosphoric acid. The phases obtained depended on the ratio of calcined eggshell/ seashell to phosphoric acid, the calcination temperature and the mechanochemical activation method (ball milling or attrition milling). The HAp structures were characterized by X-ray diffraction, scanning electron microsopy and infrared spectroscopy. Attrition milling was more effective than ball milling, yielding nanosize, homogenous and pure Hap.

Determination of deformation induced by thin film residual stress in structures of millimeter size

The deformation of Si/SiN x based square membrane structures are measured by Makyoh topography. The results are compared to finite-element modelling of the structure, and the thermal expansion coefficient of SiN x is extracted.

Realisation of quantitative Makyoh topography using a digital micromirror device

Makyoh topography (MT) is an optical characterisation tool for flatness testing of mirror-like surfaces. In MT, the surface is illuminated by a collimated light beam, and the reflected image is detected on a screen placed some distance away from the sample. Because of the focussing/defocussing action of the surface undulaations, the image shows intensity variations related to the sample morphology. In its original form, MT is qualitative only. By inserting a structured mask (e.g., a grid) into the path of the illuminating beam, the surface topography can be calculated by the integration of the gradients obtained by the determination of the displacements of the grid node positions, compared to a reference flat, similarly to a wavefront sensor. A DMD provides an easy and verstile way of realisation of such a structured mask. In this paper, we report on a quantitative MT set-up using a programmed DMD. Possibilities of the realisation of different mask patterns are analysed. The results are compared to interferometry.

Makyoh-topography assessment of etch and polish removal of processed circuits for substrate re-use

A Makyoh-topography study of the removal of processed Si circuits by etching and lapping/polishing for substrate re-use is reported. Removal of the individual circuit layers (oxide, metal) causes a uniform change in the overall wafer curvature, corresponding to strain release. Lapping/polishing removes the undulation that is originally present but introduces a new one that is characteristic of the imperfection of the polishing process.

Electrospinning – A Candidate for Fabrication of Semiconducting Tungsten Oxide Nanofibers

The excellent gas sensing properties of the tungsten oxides have been manifested first of all in nanostructure and 1D, and 2D open structured forms. For optimal performance the sensing layer substrates should be of large specific surface. In this paper we report on electrospinning – a candidate for fabrication of large specific surface tungsten oxide nanofibers. Fibrous tissues doped with tungstic acid hydrate (H2WO4.H2O) and tungsten oxide one third hydrate (WO3.1/3H2O) has been created and characterized by X-ray diffraction, scanning electron microscope and energy dispersive spectroscopy in order to learn about the changes the materials suffer during the process.

Production of Polymer Nanofibers Containing Hydroxyapatite by Electrospinning

Hydroxyapatite (HAP) is the main inorganic component of mammal bone and teeth. It is one of the few bioactive materials, which helps cell growing. The objective of this study was to fabricate hydroxyapatite-biopolimer nanofiber mats. To achieve this goal, two different suspensions were used. Approximately 1 μm diameter size fibers with large HAP agglomerates were fabricated using acetone and acetic acid. Fibers with a larger diameter size and homogenous distributed HAP particles were produced applying acetone and isopropanol. During the experiment the effect of the processing parameters: applied voltage, diameter of needle, the distance of the needle tip and the collector, flow rate was analyzed.

Photocatalytic properties of h-WO3 nanoparticles obtained by annealing and h-WO3 nanorods prepared by hydrothermal method

In the present study, two different methods for preparing hexagonal WO3 (h-WO3) photocatalysts were used - controlled thermal decomposition and hydrothermal synthesis. WO3 nanoparticles with hexagonal structure were obtained by annealing (NH4)xWO3-y at 500 °C in air. WO3 nanorods were prepared by a hydrothermal method using sodium tungstate Na2WO4, HCl, (COOH)2 and NaSO4 precursors at 200 °C. The formation, morphology, structure and composition of the as-prepared nanoparticles and nanorods were studied by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDX). The photocatalytic activity of the h-WO3 nanoparticles and nanorods was studied by decomposing methyl orange in aqueous solution under UV light irradiation.

Effect of Different Anions Upon the WO3 Morphology and Structure

In this study the effects of various anions (SO2-₄, ClO-₄ and PO3-₄) were investigated on the hydrothermal treatment of WO₃ from Na₂WO₄ and HCl at 180 and 200 °C. The products were analyzed by XRD and SEM. With the usage of SO2-₄ the obtained product was hexagonal (h-) WO₃ in the form of nanorods at both temperatures. Applying ClO-₄ resulted in a mixture of WO₃·0.33H₂O and small amount of m-WO₃ at 180 °C and pure WO₃·0.33H₂O at 200 °C. The morphology was consisted of cuboid shapes arranged into spherical structures at 180 °C and longitudinal ones at 200 °C. By the application of PO3-₄ no product formed at either temperature. Using the combination of SO2-₄, and ClO-₄ the product was h-WO₃ at both 180 and 200 °C with rod-like crystals; thus, the effect of ClO-₄ was overdominated by the SO2-₄ions. Utilization of PO3-₄ together with SO2-₄, and/or ClO-₄ resulted again in no product, meaning that adding PO3-₄ to the reaction mixture completely blocks the hydrothermal formation of solid products by forming water soluble phosphotungstic acids.

Chemical Sensors Based on Nano-hexagonal Tungsten Oxide: Synthesis and Characterization

Tungsten oxide based materials have received a great attention in the fabrication of semiconducting oxide based gas sensor devices. In the present work the preparation of nanocrystalline hexagonal WO3 (hex-WO3) from sodium tungstate solution by acidic precipitation as a nanocrystalline processing route is presented. Metal decorated carbon nanotubes (CNTs) were added to hex-WO3 nanopowder with the aim to further lower the operating temperature of sensors. Hex-WO3/Au-decorated MWCNTs composites were able to detect as low as 100 ppb of NO2, with no need to heat the sensors substrates during operation, which demonstrates the high potential of our new gas sensors. The developed porous tungsten oxide nanofibers might be find application on a special chip designed for gas sensorics.

Imaging-limiting effects of apertures in Makyoh-topography instruments

The effects of apertures on the imaging in Makyoh-topography instruments are analysed. It is shown that, depending on the actual settings and the type of the instruments, an aperture can limit the size of the image, the size of the sample being studied or the maximum surface slope that can be detected. The model is corroborated by experiments.