Number of found documents: 621
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DEPOSITION OF PVP-PROTECTED PLATINUM NANOPARTICLES ON SEMICONDUCTOR SUBSTRATES FOR HYDROGEN SENSING
Černohorský, Ondřej; Yatskiv, Roman; Grym, Jan
2015 - English
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 Keywords: Graphite based Schottky junction; PVP - protected Pt nanoparticles; Hydrogen sensors Available on request at various institutes of the ASCR
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 - English
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 Keywords: Stable frequencies; Time transfer; Time and frequencies; čas; přenos Available at various institutes of the ASCR
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 - English
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 Keywords: oscillator; ultra-stable Quartz; non-simultaneity; oscilátory; křemen Available at various institutes of the ASCR
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 - English
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. Keywords: time comparison; event timing; two way time transfer; čas; přenos Available at various institutes of the ASCR
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 - English
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 Keywords: surface acoustic wave filter; time interpolation; event timing; čas; teplota Available at various institutes of the ASCR
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

VLBI receiver chain monitoring
Michálek, V.; Kodet, J.; Schreiber, U.; Ploetz, Ch.; Procházka, I.; Pánek, Petr
2013 - English
he most demanding goal of the Global Geodetic Observing System initiative is the definition of station positions to an accuracy of 1mm and the corresponding velocities to 0.1 mm/year. The main remaining sources of error are caused by systematics, leading to intra- and inter- technique biases. In this work, we have focused on Very Long Base Interferometry (VLBI) and phase calibration generator currently in operation. This unit is injecting calibration tones into the detection chain through an input coupler located near the input of the antenna. The tones propagate further through entire detection chain and are recorded with the observed signal. Then they are extracted in post processing. These tones are generated out of an atomic frequency standard. The supplied frequency is significantly influenced by temperature and mechanical changes since usually a long cable is employed to bring the frequency to the calibration unit. To monitor the electrical length of the cable, calibration with a picosecond precision is essential. We have redesigned a phase calibration unit so that it enables the implementation of the Two Way Time Transfer (TWTT) method on single coaxial cable using two event timers to monitor the electrical length of the critical cable. Such a system has been installed in parallel to the unit currently in operation. The comparison of the TWTT method with previous measurement method is presented Keywords: Frequency standards; Calibration; Two-way time transfers; kalibrace; kmitočet Available at various institutes of the ASCR
VLBI receiver chain monitoring

he most demanding goal of the Global Geodetic Observing System initiative is the definition of station positions to an accuracy of 1mm and the corresponding velocities to 0.1 mm/year. The main ...

Michálek, V.; Kodet, J.; Schreiber, U.; Ploetz, Ch.; Procházka, I.; Pánek, Petr
Ústav fotoniky a elektroniky, 2013

Single Photons Optical TwoWay Time Transfer Providing Picosecond Accuracy
Procházka, I.; Blažej, J.; Kodet, J.; Pánek, Petr
2013 - English
We are reporting on a new approach to an optical two-way time transfer based on signals of individual photons. This approach enables to reach extreme timing stabilities and minimal systematic errors using existing electro-optic technologies. In our indoor experiment we have achieved sub-picosecond precison and 3 ps accuracy of a two-way time transfer via free space optical channel. The entire system is compact and simple. It is a perspective technique for space application, where it might provide picosecond accuracies over space distances Keywords: two-way time transfer; photon counting; picosecond stability; čas; přenos Available at various institutes of the ASCR
Single Photons Optical TwoWay Time Transfer Providing Picosecond Accuracy

We are reporting on a new approach to an optical two-way time transfer based on signals of individual photons. This approach enables to reach extreme timing stabilities and minimal systematic errors ...

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

Time and Frequency Transfer Using Satellite Based Augmentation System GAGAN
Pánek, Petr; Kuna, Alexander
2013 - English
Aided Geo Augmented Navigation) is an Indian SBAS (Satellite Based Augmentation Systems). In contrast to the European EGNOS, this system already supports the navigation function and it transmits signals both in L1 and L5 frequency channels. We used the GAGAN signals for an experimental common-view time transfer between IPE Prague and PTB Braunschweig which is a distance of 370 km and we also tested the time transfer properties using a single clock common-view. The L1 and ionosphere-free code measurements have markedly lower accuracy compared to a GPS common-view because of rather narrow bandwidth of the SBAS signal in L1 frequency channel. L5 code measurement provides much better precision. It results from the single clock common-view that the observed fluctuations can be described as white noise with standard deviations of 6 ns, 1.3 ns and 14 ns for L1, L5 and ionosphere-free combination. The results obtained from the carrier phase measurements are promising. The single clock common-view precision was approximately 30 ps RMS even for the ionosphere-free combination. Keywords: Frequency channels; Navigation functions; GAGAN; kmitočet; letecká navigace Available at various institutes of the ASCR
Time and Frequency Transfer Using Satellite Based Augmentation System GAGAN

Aided Geo Augmented Navigation) is an Indian SBAS (Satellite Based Augmentation Systems). In contrast to the European EGNOS, this system already supports the navigation function and it transmits ...

Pánek, Petr; Kuna, Alexander
Ústav fotoniky a elektroniky, 2013

LOW SUPERSATURATION OVERGROWTH OF NANOPOROUS GaAs SUBSTRATES
Nohavica, Dušan; Grym, Jan; Gladkov, Petar; Hamplová, Marie
2012 - English
Oriented pore networks in GaAs were created by electrochemical dissolution. Low supersaturation overgrowth of the porous substrates by InxGa1-xAs (x<4%) was realized by Liquid Phase Epitaxy (LPE) Keywords: Porous III-V semiconductors; Electrochemical etching; Pores conversion Available at various institutes of the ASCR
LOW SUPERSATURATION OVERGROWTH OF NANOPOROUS GaAs SUBSTRATES

Oriented pore networks in GaAs were created by electrochemical dissolution. Low supersaturation overgrowth of the porous substrates by InxGa1-xAs (x<4%) was realized by Liquid Phase Epitaxy (LPE)

Nohavica, Dušan; Grym, Jan; Gladkov, Petar; Hamplová, Marie
Ústav fotoniky a elektroniky, 2012

Graphite/n-InP Schottky barrier with electrophoretically deposited Pt nanoparticles for hydrogen and nitrogen-monoxide detection
Žďánský, Karel; Vaniš, Jan; Černohorský, Ondřej; Kacerovský, Pavel; Fojtík, A.
2012 - English
N-type InP was deposited with Pt nanoparticles (NPs) by electrophoresis. The Pt NPs density was varied from a tenth of monolayer to several monolayers. Schottky contacts were made by colloidal graphite on the InP wafer site covered with Pt NPs. It was observed that H2 was detected by an increase of the current while NO was detected by its decrease. For explanation, we discuss mechanism which involves negative charging of adsorbed H atoms with electrons by increasing affinity level due to correlation efects Keywords: semiconductor devices; nanostructures; sensors Available in a digital repository NRGL
Graphite/n-InP Schottky barrier with electrophoretically deposited Pt nanoparticles for hydrogen and nitrogen-monoxide detection

N-type InP was deposited with Pt nanoparticles (NPs) by electrophoresis. The Pt NPs density was varied from a tenth of monolayer to several monolayers. Schottky contacts were made by colloidal ...

Žďánský, Karel; Vaniš, Jan; Černohorský, Ondřej; Kacerovský, Pavel; Fojtík, A.
Ústav fotoniky a elektroniky, 2012

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