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Optoelectronic Properties of Organic Semiconductors
Navrátil, Jiří ; Boušek, Jaroslav (referee) ; Kratochvílová, Irena (referee) ; Weiter, Martin (advisor)
The main objective of this thesis is the study of the optical and optoelectronic properties of organic semiconducting materials. At the beginning of this thesis is shown the growing interest in these materials and their practical application. The theoretical part presents the current state of knowledge of studied problematic related to optical phenomena and the transport of charge carriers in organic semiconductors, photochormic phenomena of reversible molecular switch and charge transfer in DNA biopolymeric matrix. Experimental section, which consists of selected author’s publications, includes study of the charge transport, photochromic reversible switching and the role of dopant in pi-conjugated organic polymer system. Conductive and semiconductive characteristics of the DNA biopolymer have been aslo studied. Conductive and photoconductive techniques together with measurement of the optical characteristics have been used for organic semiconductors characterization.
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Transport and Noise Characteristics of MOSFET Transistors
Chvátal, Miloš ; Hudec, Lubomír (referee) ; Koktavý, Bohumil (referee) ; Pavelka, Jan (advisor)
This doctoral thesis is focused on the analysis of transport characteristics of submicron and micron transistors MOSFET. The assumption is a constant gradient of concentration, which leads to the fact that the diffusion current density is independent of the distance from the source. Active energy was determined from temperature dependence. The proposed physical model made it possible to determine the value of access resistance between drain and source their temperature dependence. Based on the assumption that the divergence of the gradient of the current density in the channel is zero. IV characteristics of the transistor MOSFET are derived and conducted experimental monitoring current channel depending on the collector voltage for the series of samples with different channel lengths in a wide temperature range from 10 to 350 K. Information on the concentration of charge transport in the channel and the position of the Fermi level at the point of active trap, which is the source of RTS noise, is obtained from the analysis of the transport characteristics. Determining the concentration of charge transport and the position of the Fermi level is important because these variables determine the intensity of quantum transitions and their values are not the same throughout the length of the channel. It was experimentally proved from the analysis of the characteristics of RTS noise that concentration at the local channel decreases with increasing current at a constant voltage on the gate and a variable voltage at the collector. Further, the position of active traps of RTS noise was intended and it was found that this is located near the collector. Active trap is located at the point where the Fermi level coincides with energy level of the traps.
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Study of Optical and Electrical Properties of Biomaterials
Flimelová, Miroslava ; Táborský, Petr (referee) ; Drbohlavová, Jana (referee) ; Weiter, Martin (advisor)
Studium nových materiálů potenciálně využitelných pro organickou elektroniku a fotoniku získává velmi důležitý význam z hlediska ekologie. Tato práce je zaměřena na studium vlastností biologických materiálů, které by našly uplatnění v aplikační sféře. Zájem o znalosti v oblasti základních a pokročilých vlastností organických a biologických materiálů, které mohou být potenciálně využity v oblasti organické elektroniky a fotoniky přináší nové otázky, které mohou přispět k rozvoji této oblasti. Ke studiu základních procesů souvisejících s optickými a elektrickými vlastnostmi materiálů, jako je například přenos náboje, jsme využili různé techniky a metody charakterizace. První část práce je zaměřena na souhrn vlastností anorganických a organických materiálů umožňující jejich možné využití v organické elektronice a fotonice, druhá část práce poskytuje nejnovější přehled z oblasti pokročilých biologických materiálů a jejich vlastností související se záměrem této práce. Třetí část práce pak shrnuje experimentální metody a shrnuje získané výsledky. Nakonec je diskutován vztah mezi pozorovanými jevy a strukturou studovaných materiálů na molekulární úrovni.
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Analysis of Fluctuation Processes of Solar Cells
Macků, Robert ; Chobola, Zdeněk (referee) ; Franc,, Jan (referee) ; Koktavý, Pavel (advisor)
The thesis deals issue of the silicon solar cells non-destructive testing. The manufacturing technology of solar cells currently features a very high level of perfection. Its further development appears to be limited by amongst other issues imperfect diagnostic methods. The objective of presented research consists in non-destructive studies of processes that influence specimen life and reliability. To this end, I will employ mainly noise based analytical methods in connection with observation of defect optical activities, capacitance measurement etc. These methods are closely related to some specimen bulk imperfections, crystal-lattice defect induced traps, local-stress-subjected regions and, finally, breakdowns, which might bring about specimen destruction. Based on a detailed study and understanding of transport processes, regions in which noise is generated can be identified and appropriate technological measures can be proposed and adopted. Presented research focuses, first of all, on the real solar cell structures, which are inhomogeneous in their nature and are difficult to diagnose. The significant part of this study is attend to the random n-level (in most case just two-level) impulse noise, usually referred to as microplasma noise. This noise is a consequence of local breakdowns in micro-sized regions and brings about reduction of lifetime or destruction of the pn junction. The micro-sized regions have been studied separately by electrical and optical methods and defect properties have been put forward. Nevertheless, no less significant part of the thesis is devoted to the fluctuation modeling of the bulk imperfections in the semi-analytical form.
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Detection of DNA/RNA fragments using graphene sensor and influence of upper electrolytic gate
Herzánová, Kristína ; Konečný, Martin (referee) ; Bartošík, Miroslav (advisor)
Jedinečné vlastnosti grafenu, jako je biokompatibilita, vysoká mobilita nosičů náboje a povrchová citlivost, z něj činí vhodný materiál pro biosenzory. Cílem této práce je popsat a představit takové senzory a měření provedená za účelem detekce fragmentů DNA, konkrétně látek na bázi cytosinu. Grafen je v polem řízených tranzistorech zapojen jako vodivý snímající kanál. Dopování grafenu vyvolané adsorpcí molekul na vodivém kanálu způsobuje změny transportních vlastností grafenu. Tyto změny se odrážejí v měření elektronických odezev: měření odporu grafenové vrstvy reagujícího v reálném čase na přidávání různých roztoků a závislost odporu na průběžné změně hradlového napětí. Druhou metodu měření lze provádět FET senzorem zapojeným v konfiguraci se spodním nebo elektrolytickým horním hradlem. Je sledován rozdíl mezi oběma konfiguracemi a také vliv vzdálenosti mezi grafenem a horní hradlovou elektrodou na odezvu senzoru. Výsledkem těchto měření jsou transferové křivky vykazující typické píky označující bod neutrality (Diracův bod) grafenu. Různé koncentrace roztoku analytu vedou k různým hodnotám napětí Diracova bodu, což slouží ke kvantifikaci úrovně dopování grafenu.
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Chemical and Physical Properties of Single Molecules and Their Assemblies Adsorbed on Solid Surfaces
Houska, Václav ; Starý, Ivo (advisor) ; Mazal, Ctibor (referee) ; Církva, Vladimír (referee)
Interaction of organic molecules with solid surfaces represents a key area of physical-chemistry research. From heterogenous catalysis to OLED displays, in numerous such systems molecules interact on interfaces, and understanding their behavior is crucial for the correct operation of such applications. In this work, I focused on the study of large π-conjugated macrocycles based on dibenzo[5]helicenes with emphasis on their behavior on graphite surface. The chemical synthesis of the investigated macrocycles was initially impeded by a number of obstacles, particularly by their extremely low solubility. In this work, an efficient solubilization strategy based on the modification of the macrocycles with trityl groups was discovered, which effectively diminishes the intense intermolecular π-π interactions. This opened a path towards a subsequent study of the compound's properties. The attention was focused mainly on a trimer, which was successfully fully characterized, enabling further experiments. Since only a few tens of milligrams of the trimer was prepared, and some stereoisomers were isolated in only microscopic amounts, it was important to develop a suitable experimental methodology. These methods were successfully employed in the measurement of the isomerization kinetics, which allowed us to map...
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Detection of DNA/RNA fragments using graphene sensor and influence of upper electrolytic gate
Herzánová, Kristína ; Konečný, Martin (referee) ; Bartošík, Miroslav (advisor)
Jedinečné vlastnosti grafenu, jako je biokompatibilita, vysoká mobilita nosičů náboje a povrchová citlivost, z něj činí vhodný materiál pro biosenzory. Cílem této práce je popsat a představit takové senzory a měření provedená za účelem detekce fragmentů DNA, konkrétně látek na bázi cytosinu. Grafen je v polem řízených tranzistorech zapojen jako vodivý snímající kanál. Dopování grafenu vyvolané adsorpcí molekul na vodivém kanálu způsobuje změny transportních vlastností grafenu. Tyto změny se odrážejí v měření elektronických odezev: měření odporu grafenové vrstvy reagujícího v reálném čase na přidávání různých roztoků a závislost odporu na průběžné změně hradlového napětí. Druhou metodu měření lze provádět FET senzorem zapojeným v konfiguraci se spodním nebo elektrolytickým horním hradlem. Je sledován rozdíl mezi oběma konfiguracemi a také vliv vzdálenosti mezi grafenem a horní hradlovou elektrodou na odezvu senzoru. Výsledkem těchto měření jsou transferové křivky vykazující typické píky označující bod neutrality (Diracův bod) grafenu. Různé koncentrace roztoku analytu vedou k různým hodnotám napětí Diracova bodu, což slouží ke kvantifikaci úrovně dopování grafenu.
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Study of transport properties of some polymer layers
Růžička, Aleš
This work studies various properties of polymer layers and hybrid layers containing inorganic nanoparticles. MEH-PPV and Polythiophene films are characterized by different experimental techniques. Dark J-V characteristics were measured at different temperatures and the mobility of holes was evaluated in a few cases. Photovoltage spectra are used for a determination of the exciton diffusion length and the SPV method is discussed. The influence of the inorganic nanoparticles CdS and ZnO incorporated into the polymer layers is studied by various experimental methods and the applications of these layers in the inorganic-organic hybrid solar cells are discussed. The inorganic nanoparticle size distributions are obtained by several experimental techniques and the results correspond with the assumptions.
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Study of electrical and dielectric properties of conducting polymers
Varga, Martin ; Prokeš, Jan (advisor) ; Petzelt, Jan (referee) ; Pfleger, Jiří (referee)
Title: Study of electrical and dielectric properties of conducting polymers Author: Mgr. Martin Varga Department: Department of Macromolecular Physics Supervisor: RNDr. Jan Prokeš, CSc., Department of Macromolecular Physics Abstract: Charge transport in polyaniline (PANI) and polypyrrole (PPy) was studied in respect to various oxidants, dopants, morphology, and other modifica- tions in their synthesis. The mechanism of transport was discussed in the frame- work of combination of several models characteristic for disordered solids due to inherent heterogeneous structure of conducting polymers. Effect of drying on conductivity was studied and the long-time limit was explained with the diffusion- based model for bulk materials. For PPy nanotubes stability in strong alkaline media and aging were studied by AC and DC techniques. While conductivity of naturally aged samples after two years remained in the same order of magni- tude, after exposure to alkaline media or accelerated aging at high temperatures, conductivity decreased several orders of magnitude. Degraded material exhibited strong disorder and the transport model was completely changed. Despite severe treatment electrical properties were still comparable to other as-prepared mate- rials. Finally, an application example as ammonia sensor, the response of...
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