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Characterisation of TCNQ and 5A heteromolecular layers on Ag(100)
Cohl, Alexandr ; Jakub, Zdeněk (referee) ; Stará, Veronika (advisor)
This bachelor thesis deals with the formation and subsequent characterization of mixed phases of pentacene (5A) and tetracyanoquinodimethane (TCNQ) on the surface of a Ag(100) monocrystal. The preparation of these mixed phases was carried out by deposition from an effusion cell in ultra-high vacuum (UHV) conditions. The quality and arrangement of the formed layers were then characterized by low-energy electron microscopy (LEEM) and scanning tunneling microscopy (STM). The behaviour and arrangement of monomolecule layers of both TCNQ and 5A on the surface is also described. Mixed phases with different ratios of 5A and TCNQ and the effect initial coverage and deposition order have on the formation of the final structure are discussed as well. Ultraviolet photoelectron spectroscopy (UPS) measurements are used to compare the electronic properties of the 5A and TCNQ monomolecule layers with the 1:1 mixed phase.
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Growth of organic heterostructures on metal surfaces
Kugler, David ; Novák,, Jiří (referee) ; Procházka, Pavel (advisor)
Během depozice organických molekul na kovové substráty často dochází k spontánnímu uspořádání molekul vlivem mezimolekulárních a molekulárně-substrátových interakcí. Tento jev se nazývá samouspořádání a může být využit k vytváření atomárně přesných funkčních struktur. Vzrůstající zájem vzbuzují zejména tenké vrstvy organických polovodičů pro jejich potenciální využití v polovodičovém průmyslu. Efektivita takovýchto zařízení je však nevyhnutelně spojena s přechodovým odporem na rozhraní polovodiče a kovové elektrody. Studium typu růstu organických polovodičů na kovových substrátech je tak zcela zásadní pro jejich budoucí využití. Tato diplomová práce se nejprve zabývá vytvořením krycí monovrstvy substrátu Ag(111) z dobře uspořádaných molekul kyseliny 1,3,5-benzen-trikarboxylové (BTB). Hlavním cílem práce je pak použití této vrstvy jako substrátu pro růst dalších vrstvev tvořených molekulami pentacenu, což je jeden z intenzivně zkoumaných organických polovodičů. Bylo dosaženo pokrytí povrchu uspořádanou vrstvou pentacenu o rozloze vhodné pro praktické využití. Pro studium růstu molekulárních vrstev a jejich vlastností byla použita nízkoenergiová elektronová mikroskopie, skenovací tunelovací mikroskopie, rentgenová fotoelektronová spektroskopie a ultrafialová fotoelektronová spektroskopie.
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On the Hardness of General Caching
Folwarczný, Lukáš ; Sgall, Jiří (advisor) ; Koutecký, Martin (referee)
Caching (also known as paging) is a classical problem concerning page re- placement policies in two-level memory systems. General caching is its vari- ant with pages of different sizes and fault costs. We aim at a better charac- terization of the computational complexity of general caching in the offline version. General caching in the offline version was recently shown to be strongly NP- hard, but the proof needed instances of caching with pages larger than half of the cache size. The primary result of this work addresses this problem as we prove: General caching is strongly NP-hard even when page sizes are limited to {1, 2, 3}. In the structural part of this work, a new simpler proof for the full characterization of work functions by layers for classical caching is given and then extended to caching with variable cache size. We invent two algorithms for restricted instances of general caching building on results around caching with variable cache size.
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On the Hardness of General Caching
Folwarczný, Lukáš ; Sgall, Jiří (advisor) ; Koutecký, Martin (referee)
Caching (also known as paging) is a classical problem concerning page re- placement policies in two-level memory systems. General caching is its vari- ant with pages of different sizes and fault costs. We aim at a better charac- terization of the computational complexity of general caching in the offline version. General caching in the offline version was recently shown to be strongly NP- hard, but the proof needed instances of caching with pages larger than half of the cache size. The primary result of this work addresses this problem as we prove: General caching is strongly NP-hard even when page sizes are limited to {1, 2, 3}. In the structural part of this work, a new simpler proof for the full characterization of work functions by layers for classical caching is given and then extended to caching with variable cache size. We invent two algorithms for restricted instances of general caching building on results around caching with variable cache size.
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Some electrical and photoelectrical properties of organic semiconductors
Chomutová, Radka ; Toušek, Jiří (advisor) ; Křivka, Ivo (referee)
Title: Some electrical and photoelectrical properties of organics semiconductors Author: Radka Chomutová Department: Department of Macromolecular Physics Supervisor: doc. RNDr. Jiří Toušek, CSc., Department of Macromolecular Physics Abstract: The object of this study is to determine some electrical and photoelectrical properties of polymer materials and their importance considering their usage as a solar cell. Especially, thin layers of polythiophene (PT1,PT2) and poly-3-hexylthiophene (P3HT) are measured and determined. Studied parameters are Fermi level by Kelvin method, the concentration of free charge carriers, conductivity, exciton diffusion length and thickness of the space charge region by surface photovoltage method (SPV). Obtained values were then added to older measurements with similar focus for polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4- phenylenevinylene] (MEH-PPV). Keywords: sollar cell, diffusion lenght, surface photovoltage method, Kelvin probe, organic layer
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