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Monolayers of platinum nanoparticles prepared by dip-coating
Černohorský, Ondřej ; Grym, Jan ; Yatskiv, Roman ; Pham, V.H. ; Hudry, D. ; Dickerson, J.H.
Platinum is a transition metal known for its catalytic properties, which are further enhanced when employed in a nanoparticle form. We have recently shown that a monolayer of Pt nanoparticles deposited on semiconductor substrates forms high quality Schottky diodes, which were used in sensitive hydrogen sensors with a detection limit of 1 ppm of H-2 in N-2. Preparation of ordered monolayers of Pt nanoparticles is essential for the understanding of the behaviour of such an interface. To obtain a hexagonal closed-packed nanoparticle array, we prepared Pt nanoparticles stabilized by oleylamine and oleic acid with a narrow size distribution and uniform shapes. A monolayer prepared by dip-coating of Si substrate in the suspension containing Pt nanoparticles showed hexagonal arrangement within separate domains with the surface coverage up to 90%. The increase of the surface coverage with increasing withdrawal speed of the dip-coating process was observed
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Characterization of semiconducting nanowires
Novotný, Karel ; Grym, Jan (referee) ; Kolíbal, Miroslav (advisor)
This diploma thesis is focused on characterization of semiconductive nanowires. Theoretical part of thesis deals with basic physical properties of TiO2 and a search of selected properties of titanium dioxide nanostructures is preseted. The experimental part describes several spectroscopic measurements carried out with complex of TiO2 nanowires. The influence of gold nanoparticles (deposited on the nanowire surface) on sample properties is also tested. The final part of thesis is devoted to methodology for measurement of electrical properties. These experiments are carried out only with one nanowire. Focused electron beam induced deposition (resp. Focused ion beam induced deposition) and electron lithography are utilized.
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Modification of semiconductor nanowire growth
Pejchal, Tomáš ; Grym, Jan (referee) ; Kolíbal, Miroslav (advisor)
This diploma thesis deals with the growth of semiconductor nanowires on Ge(111) surface. The nanowires were prepared by means of PVD (physical vapor deposition). The growth was calatyzed by Au colloidal nanoparticles. An impact of different growth conditions on nanowire morfology is presented. It is demonstrated that Ge nanowires grow preferentially along axis. Ge wires with orientation were observed as well.
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DEPOSITION OF PVP-PROTECTED PLATINUM NANOPARTICLES ON SEMICONDUCTOR SUBSTRATES FOR HYDROGEN SENSING
Černohorský, Ondřej ; Yatskiv, Roman ; Grym, Jan
High quality Schottky diode hydrogen sensors were prepared by the deposition of colloidal graphite on n-type InP substrates partly covered with PVP-protected Pt nanoparticles (NPs). A sub-monolayer of the Pt NPs was created by simple evaporation of the solvent in which Pt NPs were dispersed. The Pt NPs serve to dissociate hydrogen molecules into atomic hydrogen, which is absorbed at the metal-semiconductor interface. Hydrogen absorption leads to the formation of the dipole layer, which changes the Schottky barrier height and results in the increase of both forward and reverse current. The proposed hydrogen sensor showed high sensitivity response of similar to 10(6) to 1000 ppm H-2 in N-2 at room temperature
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LAYERS OF METALS NANOPARTICLES ON VARIOUS SEMICONDUCTORS FOR HYDROGEN DETECTION
Černohorský, Ondřej ; Žďánský, Karel ; Yatskiv, Roman ; Grym, Jan
Metal nanoparticles have many interesting properties which is given by their space restriction. Their large active surface is very well exploited during catalysis. Pd and Pt are metals know for their ability to dissociate molecular hydrogen on single atoms. We prepared Schottky diodes on semiconductors InP, GaN, GaAs, and InGaAs to obtain hydrogen sensor. Method of preparation such diodes is electrophoretic deposition of Pd or Pt nanoparticles from their colloid solution onto semiconductor substrate. Over the layer of nanoparticles, porous metal contact was prepared. Hydrogen molecules are dissociated on these metal nanoparticles and single atom which settles on the interface between metal and semiconductor and they increase or decrease Schottky barrier height. By this method we can measure from 1 ppm H2 in the air, where the current change is over one order of magnitude
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