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Transport of Electric Charge in Tantalum Capacitor
Pelčák, Jaromír ; Koktavý, Bohumil (referee) ; Hájek, Karel (referee) ; Grmela, Lubomír (advisor)
The task of the thesis was studding of tantalum capacitors with solid electrolytes properties. Ta – Ta2O5 – MnO2 capacitor by its construction represents MIS structure, where tantalum anode has metal conductivity and MnO2 cathode is semiconductor. Isolation layer consists of tantalum pentoxide Ta2O5 with relative permitivity r = 27. Dielectric thickness is typically in range from 30 to 150nm. The capacitor charge is not only stored and accumulated on electrodes but also in localised states (oxide vacancies) in isolation layer. The capacitor connected in normal mode represents MIS structure polarized in reveres direction when the applied voltage higher potential barrier between semiconductor - MnO2 cathode and isolation of Ta2O5. The transport of charge carriers via isolation layer is determined by Poole-Frenkel mechanisms and tunnelling. Poole-Frenkel mechanism of charge transport is dominant in low intensity of electric field. Tunnelling determines current at higher electric field intensity. During low intensity of electric field ohmic component is also presented which is determined by volume of resistance of impurities in isolation layer due to donor states of oxygen vacancies. Based on the modelling of measured VA characteristics is possible to estimate determine dielectric thickness of Ta2O5 and determine share of Poole-Frenkelov and tunnel current and charge transportation. The thesis is described charge transport and charge concentration on tantalum capacitor in low frequency area and analysis of capacitor behaviour at frequency band. The first impulse for the thesis was an effort to create equivalent circuit diagram of tantalum capacitor in respect of its physical and electrical behaviour. There is an opportunity to study and determine electric charge transport and its accumulation based on the equivalent circuit diagram structure. There is also a chance to define and trace potential barriers and charge distribution in the capacitor structure based on an measurement and carried out experiments. This methodology and analysis consists of electrical characteristic determination to create physical model of the capacitor describing it function, properties and behaviour.
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Separation of chiral compounds
Šrolerová, Tereza ; Kubíčková, Anna (advisor) ; Křížek, Tomáš (referee)
This bachelor thesis deals with the chiral separation of newly synthesized orthoconic antiferroelectric liquid crystals using ultra-high performance liquid chromatography. These studied compounds differ in the alkyloxy-spacer length, in the presence and/or position of the fluorine atom on the phenyl ring and in the chiral center. The separation took place in a reverse separation mode using a chiral stationary phase based on derivatized amylose. First, the effect of mobile phase flow rate and column temperature on separation efficiency was exanimated. The effect of the composition of the mobile phase on the enantioseparation were studied at the optimum temperature and flow rate. The mobile phase was based on acetonitril, while deionized water was added gradually using isocratic elution. Furthermore, the effect of chromatographic conditions and the structure of the studied analytes on resolution and enantioselectivity was investigated, concretely the presence and position of fluorine atom on pfenyl ring, the length of alkyloxy-spacer and the effect of divergent chiral center. Under optimized chromatography conditions we succeeded to separate all examined substances on the base line. Key words: ultra-high performance chromatography, liquid crystals, enantioseparation, chiral stationary phase, reverse mode
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Optimization of HPLC method for separation of tetracyclines
Kučerová, Gabriela ; Kalíková, Květa (advisor) ; Janečková, Lucie (referee)
The aim of this work is to develop and to optimize HPLC method for separation of a set of four tetracycline antibiotics - tetracycline, chlortetracycline, oxytetracycline, and doxycycline. Four different reversed octadecyl-silica stationary phases in various mobile phase compositions were examined in isocratic elution. The baseline resolution of all the analytes was obtained by using two columns - Astec C18 and Atlantis C18 I. The optimized separation system consisted of Atlantis C18 I. column, ACN/0.1% formic acid 15/85 (v/v) as the mobile phase and flow rate of 2 ml/min. The baseline resolution was achieved and the analysis time did not exceed 27.5 minutes.
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Transport of Electric Charge in Tantalum Capacitor
Pelčák, Jaromír ; Koktavý, Bohumil (referee) ; Hájek, Karel (referee) ; Grmela, Lubomír (advisor)
The task of the thesis was studding of tantalum capacitors with solid electrolytes properties. Ta – Ta2O5 – MnO2 capacitor by its construction represents MIS structure, where tantalum anode has metal conductivity and MnO2 cathode is semiconductor. Isolation layer consists of tantalum pentoxide Ta2O5 with relative permitivity r = 27. Dielectric thickness is typically in range from 30 to 150nm. The capacitor charge is not only stored and accumulated on electrodes but also in localised states (oxide vacancies) in isolation layer. The capacitor connected in normal mode represents MIS structure polarized in reveres direction when the applied voltage higher potential barrier between semiconductor - MnO2 cathode and isolation of Ta2O5. The transport of charge carriers via isolation layer is determined by Poole-Frenkel mechanisms and tunnelling. Poole-Frenkel mechanism of charge transport is dominant in low intensity of electric field. Tunnelling determines current at higher electric field intensity. During low intensity of electric field ohmic component is also presented which is determined by volume of resistance of impurities in isolation layer due to donor states of oxygen vacancies. Based on the modelling of measured VA characteristics is possible to estimate determine dielectric thickness of Ta2O5 and determine share of Poole-Frenkelov and tunnel current and charge transportation. The thesis is described charge transport and charge concentration on tantalum capacitor in low frequency area and analysis of capacitor behaviour at frequency band. The first impulse for the thesis was an effort to create equivalent circuit diagram of tantalum capacitor in respect of its physical and electrical behaviour. There is an opportunity to study and determine electric charge transport and its accumulation based on the equivalent circuit diagram structure. There is also a chance to define and trace potential barriers and charge distribution in the capacitor structure based on an measurement and carried out experiments. This methodology and analysis consists of electrical characteristic determination to create physical model of the capacitor describing it function, properties and behaviour.
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