Počet nalezených dokumentů: 626
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Effect of heat treatment on the properties of sol-gel deposited ZnO seed layers
Bašinová, Nikola; Černohorský, Ondřej; Grym, Jan; Maixner, J.
2018 - anglický
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 Klíčová slova: ZnO nanorods; Chemical bath deposition; Sol-gel Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Effect of heat treatment on the properties of sol-gel deposited ZnO seed layers

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 ...

Bašinová, Nikola; Černohorský, Ondřej; Grym, Jan; Maixner, J.
Ústav fotoniky a elektroniky, 2018

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
2018 - anglický
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 Klíčová slova: Scanning electron microscope; Hydrothermal growth; In-situ current-voltage measurements Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Electrical properties of nanoscale heterojunctions formed between GaN and ZnO nanorods

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 ...

Tiagulskyi, Stanislav; Yatskiv, Roman; Grym, Jan; Schenk, Antonín; Roesel, David; Vaniš, Jan; Hamplová, Marie
Ústav fotoniky a elektroniky, 2018

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
2018 - anglický
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 Klíčová slova: Photoluminescence spectroscopy; Conductive atomic force microscopy; Focused ion beam Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Optoelectrical characterization of well oriented n-type zno nanorod arrays on p-type GaN templates

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 ...

Yatskiv, Roman; Grym, Jan; Schenk, Antonín; Vaniš, Jan; Roesel, David; Chlupová, Šárka
Ústav fotoniky a elektroniky, 2018

Monolayers of platinum nanoparticles prepared by dip-coating
Černohorský, Ondřej; Grym, Jan; Yatskiv, Roman; Pham, V.H.; Hudry, D.; Dickerson, J.H.
2015 - anglický
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 Klíčová slova: Oleylamine; Pt nanoparticles; Self-assembly Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Monolayers of platinum nanoparticles prepared by dip-coating

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 ...

Černohorský, Ondřej; Grym, Jan; Yatskiv, Roman; Pham, V.H.; Hudry, D.; Dickerson, J.H.
Ústav fotoniky a elektroniky, 2015

Influence of H2O2 treatment on morphological and photoluminescence properties of hydrothermally grown ZnO nanorods
Yatskiv, Roman; Grym, Jan
2015 - anglický
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 Klíčová slova: ZnO nanorods; Photoluminescence; H2O2 treatment Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Influence of H2O2 treatment on morphological and photoluminescence properties of hydrothermally grown ZnO nanorods

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 ...

Yatskiv, Roman; Grym, Jan
Ústav fotoniky a elektroniky, 2015

DEPOSITION OF PVP-PROTECTED PLATINUM NANOPARTICLES ON SEMICONDUCTOR SUBSTRATES FOR HYDROGEN SENSING
Černohorský, Ondřej; Yatskiv, Roman; Grym, Jan
2015 - anglický
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 Klíčová slova: Graphite based Schottky junction; PVP - protected Pt nanoparticles; Hydrogen sensors Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
DEPOSITION OF PVP-PROTECTED PLATINUM NANOPARTICLES ON SEMICONDUCTOR SUBSTRATES FOR HYDROGEN SENSING

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 ...

Černohorský, Ondřej; Yatskiv, Roman; Grym, Jan
Ústav fotoniky a elektroniky, 2015

Optical infrastructure for time and frequency transfer
Smotlacha, V.; Vojtěch, J.; Kuna, Alexander
2013 - anglický
The paper describes optical infrastructure for time and frequency transfer in the Czech republic. The infrastructure is heterogeneous and utilises resources of the Czech academic optical network. It allows to interconnect Cesium standards in distant sites with the national time and frequency laboratory and to distribute accurate time and stable frequency. We also present results and compare them with other methods of time transfer Klíčová slova: Stable frequencies; Time transfer; Time and frequencies; čas; přenos Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Optical infrastructure for time and frequency transfer

The paper describes optical infrastructure for time and frequency transfer in the Czech republic. The infrastructure is heterogeneous and utilises resources of the Czech academic optical network. It ...

Smotlacha, V.; Vojtěch, J.; Kuna, Alexander
Ústav fotoniky a elektroniky, 2013

Evaluation of the accuracy of the method for measuring state-of-the-art ultra-high stability quartz crystal oscillators
Salzenstein, P.; Kuna, Alexander; Lefebvre, F.
2013 - anglický
The accuracy of the Three-Cornered Hat method is discussed when not simultaneously applied to the determination of the contribution on short term frequency stability performed on ultra-stable quartz oscillators Klíčová slova: oscillator; ultra-stable Quartz; non-simultaneity; oscilátory; křemen Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Evaluation of the accuracy of the method for measuring state-of-the-art ultra-high stability quartz crystal oscillators

The accuracy of the Three-Cornered Hat method is discussed when not simultaneously applied to the determination of the contribution on short term frequency stability performed on ultra-stable quartz ...

Salzenstein, P.; Kuna, Alexander; Lefebvre, F.
Ústav fotoniky a elektroniky, 2013

Local ties controlin application of laser time transfer
Kodet, J.; Schreiber, U.; Eckl, J.; Procházka, I.; Pánek, Petr
2013 - anglický
In many fundamental physical experiments time plays an important role. The standard way for the comparison of time and frequency is the application of GNSS signals and the Two-Way Satellite Time and Frequency Transfer - TWSTFT. This technique is based on radiofrequency signal transmission. Recently, there was a rapid increase of optical time comparison development, which uses the Satellite Laser Ranging network (SLR). Currently the French project T2L2 is in operation on board of Jason 2 and the European Space Agency project ELT in support of the Atomic Clock Ensemble in Space (ACES) is under development. The goal of both projects is the time synchronization with a precision below 40 ps rms and an absolute error well below 100 ps. Comparing the results of the optical time transfer with the GNSS time comparison requires unprecedented control of the local ties between the different observation techniques. One of the possible methods is the application of the Two Way Time Transfer (TWTT) on a single coaxial cable. Such a system can be implemented using two or more event timers, which are interconnected by a standard coaxial cable. Klíčová slova: time comparison; event timing; two way time transfer; čas; přenos Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Local ties controlin application of laser time transfer

In many fundamental physical experiments time plays an important role. The standard way for the comparison of time and frequency is the application of GNSS signals and the Two-Way Satellite Time and ...

Kodet, J.; Schreiber, U.; Eckl, J.; Procházka, I.; Pánek, Petr
Ústav fotoniky a elektroniky, 2013

Event Timing Device Providing Subpicosecond Precision
Pánek, Petr; Kodet, J.; Procházka, I.
2013 - anglický
We are reporting on the latest experimental results achieved with an event timing device using a surface acoustic wave filter as a time interpolator. During the tests of the first version of the device, the noise of the filter excitation was identified as the dominant source of the measurement error. Therefore a new concept of the excitation with very low level of the noise energy was designed. This new solution led to considerable improvement of the device performance. It results from the experimental measurements that the single shot precision is repeatedly lower than 500 fs RMS when time marks generated synchronously with the time base are measured. When asynchronous time marks are split into two event timers and the resulting time difference is measured, the single shot precision is below 700 fs RMS per channel. In this case the measurement is affected not only by random errors, but also by non-linearity of the time interpolation. The temperature dependence is below 0.1 ps/K. Operating the device in a common laboratory environment without temperature stabilization, the stability TDEV better than 3 fs has been routinely achieved for range of averaging intervals from 10 s to several hours Klíčová slova: surface acoustic wave filter; time interpolation; event timing; čas; teplota Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Event Timing Device Providing Subpicosecond Precision

We are reporting on the latest experimental results achieved with an event timing device using a surface acoustic wave filter as a time interpolator. During the tests of the first version of the ...

Pánek, Petr; Kodet, J.; Procházka, I.
Ústav fotoniky a elektroniky, 2013

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