Ondrej Cernohorsky

Electrophoresis deposition of metal nanoparticles with reverse micelles onto InP

Abstract Nanolayers were deposited onto surfaces of n-type InP single crystal wafers by electrophoresis from reverse micelle colloid solutions containing palladium nanoparticles. Two types of nanolayers were deposited, by applying a positive potential or a negative potential on the InP wafer. Further, wafers with nanolayers were annealed in high vacuum at 400 °C. The nanolayers were studied using capacitance–voltage characteristics on a mercury probe, by atomic force microscopy and by secondary-ion mass spectroscopy. Two types of Schottky-like diodes were prepared on wafers with the two types of nanolayers and studied by current–voltage characteristics. The diodes with nanolayers deposited by applying the positive potential, which contained Pd nanolayers, showed characteristics with better rectifying properties than the other type of diodes. Correlations among measured characterizations were found.

Palladium nanoparticles on InP for hydrogen detection

Layers of palladium (Pd) nanoparticles on indium phosphide (InP) were prepared by electrophoretic deposition from the colloid solution of Pd nanoparticles. Layers prepared by an opposite polarity of deposition showed different physical and morphological properties. Particles in solution are separated and, after deposition onto the InP surface, they form small aggregates. The size of the aggregates is dependent on the time of deposition. If the aggregates are small, the layer has no lateral conductance. Forward and reverse I-V characteristics showed a high rectification ratio with a high Schottky barrier height. The response of the structure on the presence of hydrogen was monitored.

EPD of Reverse Micelle Pd and Pt Nanoparticles onto InP and GaN for High-Response Hydrogen Sensors

We investigated properties of nanolayers electrophoretically deposited (EPD) onto semiconductor indium phosphide (InP) or gallium nitride (GaN) single crystals from colloid solutions of metal palladium (Pd), platinum (Pt) or bimetallic Pd/Pt nanoparticles (NPs) in isooctane. Colloids with metal NPs were prepared by reaction of metal compounds with the reducing agent hydrazine in water confined to reverse micelles of surfactant AOT.. Chopped DC electric voltage was applied for the time period to deposit metal NPs, only partly covering surface of the wafer. The deposits were image-observed by scanning electron microscopy (SEM)..Diodes with porous Schottky contacts were made by printing colloidal graphite on the NPs deposited surface and making ohmic contact on the blank side of the wafer. The diodes showed current-voltage characteristics of excellent rectification ratio and barrier height values close to Schottky-Mott limit, which was an evidence of negligible Fermi level pinning. Large increase of current was observed after switching on a flow of gas blend hydrogen in nitrogen (H2/N2). The diodes were measured with various H2/N2 in the range from 1000 ppm to 1 ppm of H2. Current change ratios about 106 and about 10 were achieved with 1000 ppm and 1 ppm H2/N2.