National Repository of Grey Literature 26 records found  1 - 10nextend  jump to record: Search took 0.02 seconds. 
Effect of EU doping on the optical properties of ZnO nanorods prepared by chemical bath deposition
Yatskiv, Roman ; Bašinová, Nikola ; Grym, Jan ; Vaniš, Jan
We report on the properties of Eu-doped ZnO nanorods prepared by chemical bath deposition from aqueous solutions in an autoclave. The autoclave enables to grow the nanorods above the boiling point of water. The nanorods were characterized by scanning electron microscopy, secondary ion mass spectroscopy, and low temperature photoluminescence spectroscopy. Under the UV light excitation, the nanorods show a strong blue emission at 450 nm, which is associated with the 4f(6)5d - 4f(4) transitions of Eu2+ ions. We discuss the mechanisms responsible for the blue luminescence. We further clarify how the growth parameters affect the morphology and the optical properties of the nanorods. Growth temperatures above the boiling point of water significantly influence the intensity ratio of the near band edge emission to the deep level emission and greatly enhance optical quality of the nanorods.
Charge transport in halide perovskites affected by the surface treatment and metalization.
Šlechta, Miroslav ; Belas, Eduard (advisor) ; Grym, Jan (referee)
In this thesis, I study charge transport in halide perovskites. This is done using the characterization method, which here is the I-V characteristics. It studies the effect of current and voltage on the prepared sample, also at different temperatures. A significant sensitivity of the material to the measurement history was found. Derived evaluations of this measurement technique further provide possibilities for the detection of hysteresis behavior as well as the evaluation of measurements over time to determine the temporal stability of carrier collection. This also proved the phenomenon of electromigration of defects. Furthermore, transport parameters were calculated from the time measurements, which point to their non-monotonic development in increasing temperatures. A theoretical model explaining such behavior was proposed as a possibility for further research on perovskites and development of this topic.
Preparation of nanowires for photonics
Mikula, Martin ; Grym, Jan (referee) ; Kolíbal, Miroslav (advisor)
This thesis is dealing with nanowires of zinc oxide and of cesium lead bromide. Main goal was a preparation of ZnO nanowires using MBE. This goal was partially achieved and growth of needle-like structures was observed. Another goal was characterization of already prepared ZnO nanowires. We successfully determined polarity of their surfaces, examined the influence of lattice defects and assessed the result of their doping. Side goal of this work was characterization of nanostructures of cesium lead bromide. However, preparation of cesium lead bromide nanowires remains an open issue.
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
Effect of heat treatment on the properties of sol-gel deposited ZnO seed layers
Bašinová, Nikola ; Černohorský, Ondřej ; Grym, Jan ; Maixner, J.
Zinc oxide nanorods as a potential material for nanoscale devices are prepared by chemical bath deposition (CBD). The effect of the quality of the sol-gel deposited seed layer on the vertical alignment of the nanorods to a silicon substrate is discussed. Emphasis is put on the investigation of the impact of the heat treatment on the properties of the seed layer deposited by dip-coating. The sol-gel method is a multi-stage process consisting of three principal steps: (i) preparation of a solution with suitable precursors, (ii) deposition of the precursor solution, and (iii) the heat treatment. The preheating needs to be performed to thermally decompose the zinc acetate precursor into zinc oxide seeds. Three different temperatures of preheating are compared (300 degrees C, 350 degrees C, 400 degrees C) followed by annealing in argon at 800 degrees C and the influence on the quality of the seed layers and vertical alignment of nanorods are discussed. When the preheating temperature is higher than 350 degrees C, the seed layer comprises smaller and denser crystallites with a preferential orientation along the c-axis. CBD growth of ZnO nanorods on these seed layers results in their good vertical alignment
Study of deposition of catalytic materials into fuel channels of micro-fuel cells on a chip
Chlupová, Šárka ; Matolínová, Iva (advisor) ; Grym, Jan (referee)
This diploma thesis is interested in usage of Electron Beam lithography process as an instrument of transport of contacts and catalytic layers to micro-channels of the micro monolithic planar fuel cell. Experimental part includes optimization of the PMMA resist deposition method on the 3D topography - spray coating - is performed with alternative spray coating system. The optimal spin speed resist, molecular weight and concentration is chosen during the optimization. Parameters of the exposition, developing and lift-off are also modified and three EBL processes are performed. The first ensures deposition of Au contacts to the channels; the second is for application of Pt layer to the cathode channel and the last aimed to cover the anode channel with CeO/CNx layer. All layers are deposited by magnetron sputtering.
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
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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