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Optimization of devices for deposition GaN nanostructures
Šimek, Daniel ; Voborný, Stanislav (referee) ; Mach, Jindřich (advisor)
This bachelor thesis deals with the automation of sources for the deposition of GaN nanocrystals used at the Institute of Physical Engineering. For the purpose of the thesis, the mechanism of automatic control of the gallium effusion cell shutter was designed and constructed and the control electronics containing components enabling automatic switching of the ion atomic source of nitrogen ions. In addition, samples of GaN nanocrystals on four different substrates that were studied for cold electron emission were prepared by the method of ion beam assisted molecular beam epitaxy IBA-MBE. The results of the measurement are discussed in the conclusion.
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GaN deposition on a tungsten substrate
Pikna, Štěpán ; Piastek, Jakub (referee) ; Čalkovský, Vojtěch (advisor)
This bachelor thesis is focused on deposition of GaN nanocrystals on the etched tungsten tips. Motivation was to prepare these GaN structures on the Schottky cathode made by company ThermoFisher Scientific and measure its field emission. In the theoretical part of the thesis GaN and tungsten field emission properties are introduced. The experimental part begins with tungsten tip etching optimalization, where the right values for best tips are temperature 20 °C, depth of the tip 2,5 mm and solution NaOH used. Further the gallium structures were prepared on these tips using molecular beam epitaxy (MBE). The right temperature to prepare GaN nanocrystals was determined as 200 °C. The deposition of gallium was set to 2 hours and following nitridation was 3 hours. Finally, the field emission from GaN prepared on copper foil with graphene was measured and compared with other experiments.
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GaN deposition on a tungsten substrate
Pikna, Štěpán ; Piastek, Jakub (referee) ; Čalkovský, Vojtěch (advisor)
This bachelor thesis is focused on deposition of GaN nanocrystals on the etched tungsten tips. Motivation was to prepare these GaN structures on the Schottky cathode made by company ThermoFisher Scientific and measure its field emission. In the theoretical part of the thesis GaN and tungsten field emission properties are introduced. The experimental part begins with tungsten tip etching optimalization, where the right values for best tips are temperature 20 °C, depth of the tip 2,5 mm and solution NaOH used. Further the gallium structures were prepared on these tips using molecular beam epitaxy (MBE). The right temperature to prepare GaN nanocrystals was determined as 200 °C. The deposition of gallium was set to 2 hours and following nitridation was 3 hours. Finally, the field emission from GaN prepared on copper foil with graphene was measured and compared with other experiments.
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Optimization of devices for deposition GaN nanostructures
Šimek, Daniel ; Voborný, Stanislav (referee) ; Mach, Jindřich (advisor)
This bachelor thesis deals with the automation of sources for the deposition of GaN nanocrystals used at the Institute of Physical Engineering. For the purpose of the thesis, the mechanism of automatic control of the gallium effusion cell shutter was designed and constructed and the control electronics containing components enabling automatic switching of the ion atomic source of nitrogen ions. In addition, samples of GaN nanocrystals on four different substrates that were studied for cold electron emission were prepared by the method of ion beam assisted molecular beam epitaxy IBA-MBE. The results of the measurement are discussed in the conclusion.
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Nano modification of the W(100)/ZrO electron emitter tip using reactive ion etching
Horáček, Miroslav ; Matějka, František ; Kolařík, Vladimír ; Matějka, Milan ; Urbánek, Michal
The W(100)/ZrO electron emitter tip is typically prepared from a tungsten single-crystal shaft of a diameter of 125 μm using electrochemical anodic etching. In order to prepare an emitter for e-beam writer with a shaped beam it is desirable to etch the tip with a radius around 100 nm. Despite the anodic etching is precisely controlled using dedicated software, the desired final form shape of the emitter tip is not achieved in every case. The correcting anodic etching is not possible due to the technology principle of the etching itself. We present in this contribution the procedure that modifies/repairs the tungsten tip shape in a nanoscale region using a reactive ion etching (RIE) in CF4 + O2 gaseous mix in a barrel type reactor at the radio frequency of 13,56 MHz and the working pressure of 1000 Pa. The change of the geometry after the RIE process is checked using a high resolution scanning electron microscope. The influence of the tip modification of the activated thermal-field W(100)/ZrO electron emitter on its emission characteristics is also presented.
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Thermal-field electron emission W(100)/ZrO cathode: facets versus edges
Matějka, František ; Horáček, Miroslav ; Kolařík, Vladimír ; Matějka, Milan
The tungsten cathode in the thermal-field emission (TFE) regime can achieve significantly higher angular current density in comparison with the Schottky cathode. The Schottky emission regime is located between the thermal emission regime and the cold field emission regime. The typical operation electric field is 0,1 - I V/nm and tip radius varies from 0.3 to 1.0 im . The thermal-field regime is located between the Schottky regime and the cold field emission regime. In the cold field emission regime the electron tunnelling is a dominant mechanism due to the electric field higher than 1 V/nm. The TFE is a combination of the field supported thermal emission and the field emission under the higher electric field. The radius of the thermal-field emitter should be lower in comparison with the Schottky emitter.
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