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First-Principle Study of Electronic Properties of Ultrathin Layers
Nezval, David ; Vázquéz, Hector (oponent) ; Friák, Martin (oponent) ; Bartošík, Miroslav (vedoucí práce)
This work characterizes the structural properties of adsorbed gallium atoms and water molecules on graphene. It also investigates the changes in the electronic properties of graphene caused by the adsorption of each adsorbent. The density functional theory (DFT) calculations are the perfect tool to investigate and explain the physical and chemical processes that occur during adsorption. The electronic properties are studied using band structure calculations and the Bader charge analysis. Recent experimental findings have revealed that in low concentration the Ga atoms negatively dope (n-doping) graphene. This doping effect is reduced at higher Ga concentrations when the clustering of Ga atoms occurs. This work presents the adsorption of individual Ga atoms and the Ga clusters. While single atoms n-dopes graphene with 0.64 electrons, atoms bound in clusters interact with each other and thus weaken the doping of graphene. Cluster formation is fundamentally affected by the diffusion of Ga atoms over graphene. Therefore, a section is devoted here to calculations of the diffusion barrier energy and how this barrier can be affected by the charging of graphene. The experimental observations indicate positive doping (p-doping) of graphene exposed to water molecules. However, these observations were not supported by DFT calculations. This thesis investigates the effect of multilayer water on the electronic properties of graphene. Attention has been paid to the influence of the water molecule orientation in the first layer toward graphene on its doping properties. The presented results show p-doping of graphene when 6 or more layers of water are oriented by oxygen to graphene.
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Ab initio studium elektronové struktury 2D materiálů
Pekár, Zdenko ; Nezval, David (oponent) ; Černý, Miroslav (vedoucí práce)
V tejto bakalárskej práci sú najprv zhrnuté základné pojmy a princípy súvisiace s dichalkogenidmi tranzitívnych kovov a teóriou funkcionálu hustoty. Ďalej je v teoretickej časti uvedených niekoľko príkladov konfigurácií atómov mriežky takýchto materiálov a aproximácií výmenno-korelačného funkcionálu. Praktická časť je zameraná na výpočtovú simuláciu a optimalizáciu buniek rôznych fáz dichalkogenidov tranzitívnych kovov a porovnávanie ich vlastností s údajmi v odbornej literatúre, takisto ako získanie nových, doposiaľ neoverených údajov o týchto materiáloch.
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