National Repository of Grey Literature 12 records found  1 - 10next  jump to record: Search took 0.00 seconds. 
Optoelectrical characterization of well oriented n-type zno nanorod arrays on p-type GaN templates
Yatskiv, Roman ; Grym, Jan ; Schenk, Antonín ; Vaniš, Jan ; Roesel, David ; Chlupová, Šárka
A heterojunction formed between a single n-type ZnO nanorod and p-type GaN template was successfully prepared by low cost chemical bath deposition technique. Periodic circular patterns were fabricated by focused ion beam etching through poly(methyl methacrylate) mask to control the size, position, and periodicity of the ZnO nanorods. A possible growth mechanism is introduced to explain the growth process of the nanorods. Optical and electrical properties of the heterojunctions were investigated by low temperature photoluminescence spectroscopy and by the measurement of current-voltage (I-V) characteristics. The I-V characteristics were measured by directly contacting single ZnO nanorods with the conductive atomic force microscopy tip. The diode-like rectifying behavior was observed with a turn-on voltage of 2.3 V and the reverse breakdown voltage was 5 V
Electrical properties of nanoscale heterojunctions formed between GaN and ZnO nanorods
Tiagulskyi, Stanislav ; Yatskiv, Roman ; Grym, Jan ; Schenk, Antonín ; Roesel, David ; Vaniš, Jan ; Hamplová, Marie
Vertical periodic arrays of ZnO nanorods are prepared by hydrothermal growth on GaN templates patterned by focused ion beam. Electro-physical properties of a single vertically-oriented ZnO nanorod are investigated by measuring the current-voltage characteristics using a nanoprobe in a scanning electron microscope. This technique enables to observe the surface morphology of ZnO nanorods simultaneously with their electrical characterization in vacuum. The vacuum chamber rejects the impact of gas adsorption and light irradiation, which both affect the properties of ZnO nanorods. Moreover, mechanical damage and strain induced during the nanorod transfer are eliminated. Nonlinear current-voltage characteristics under the forward bias are explained by the tunneling-recombination process and by the space charge limited current. The high reverse bias current in the p-n heterojunction is attributed to direct tunneling via a narrow tunnel barrier
Influence of H2O2 treatment on morphological and photoluminescence properties of hydrothermally grown ZnO nanorods
Yatskiv, Roman ; Grym, Jan
We report photoluminescence properties of hydrothermally grown ZnO nanorods (NRs) before and after hydrogen peroxide (H2O2) treatment. The H2O2 treatment introduces oxygen related defects and thus enhances chemisorption processes in ZnO NRs. These effects amplify interactions between the gas species and adsorbed oxygen and thus can influence sensing properties of ZnO NRs
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
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
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
Graphite Schottky barriers on n-InP and n-GaN with deposited Pd, Pt or bimetallic Pd/Pt nanoparticles for H2 sensing
Žďánský, Karel ; Muller, M. ; Černohorský, Ondřej ; Yatskiv, Roman
High Schottky barriers have been achieved by applying colloidal graphite on n-type InP and on n-type GaN semiconductor crystal wafers. The barrier heights were shown to be close to Schottky-Mott limit ad thermionic emission theory. Porous properties of the graphite Schottky contacts were demonstrated by scanning electron microscopy.
PD NANOLAYERS FOR HYDROGEN SENSORS
Yatskiv, Roman ; Žďánský, Karel ; Grym, Jan ; Piksová, K.
We presented study nanoparticle layers created by electrophoretic deposition. A possibility of using Pd nanolayers for the formation of Schottky barriers with a large Schottky barrier height (SBH) value on n-type tin doped InP is proposed together with its potential application in high-sensitive hydrogen sensors.
STUDY OF ELECTROPHORETIC DEPOSITION OF Pd METAL NANOPARTICLES ON InP AND GaN CRYSTAL SEMICONDUCTORS FOR H2 GAS SENSORS
Žďánský, Karel ; Yatskiv, Roman ; Grym, Jan ; Černohorský, O. ; Zavadil, Jiří ; Kostka, František
Deposition of Pd nanoparticles (NPs) on InP or GaN single crystal wafer was performed from isooctane colloid solution. Diodes were prepared by making Schottky contact with colloidal graphite on Pd NPs partly coated surface and ohmic contact on the blank side of the wafer. It was found that several ppb of hydrogen in nitrogen gas can be detected by monitoring the change of diode current at a constant bias voltage. Diodes made on GaN were about ten times more sensitive to hydrogen than those made on InP.
Growth of InP crystals for radiation detectors and other application
Pekárek, Ladislav ; Yatskiv, Roman
Bulk InP single crystals were grown by Czochralski method. Various dopants were added to the melt to obtain single crystals suitable for radiation detectors and other application. The intentionally doped of InP crystals were characterized by measurements of resistivity and Hall coefficient. Prototype detectors were prepared and evaluated by spectral detection of alpha particles and x-rays.

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