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Identifier 000425154
Title Theoretical study of transition- metal dichalcogenides at low dimensions
Alternative Title Θεωρητική μελέτη διχαλκογενιδίων μεταβατικών μεττάλων σε χαμηλές διαστάσεις
Author Δαβέλου, Δάφνη
Thesis advisor Ρεμεδιάκης, Ιωάννης
Reviewer Κιοσέογλου, Γεώργιος
Κοπιδάκης, Γεώργιος
Αρματάς, Γεράσιμος
Κατσαράκης, Νικόλαος
Φρουδάκης, Γεώργιος
Χαρμανδάρης, Ευάγγελος
Abstract The isolation of graphene and other materials of atomic width caused intense interest in two – dimensional (2D) crystals. In the family of 2D materials, which is continuously growing, special place is held by the transition metal dichalcogenides MX2 where M=Mo or W and X= S, Se, Te, materials that are widely used in catalysis or as lubricants. Transition metal dichalcogenides, have been extensively studied due to the fact that they form a huge variety of structures, such as fullerenes, nanotubes, nanoribbons etc, while at the same time they present a huge field of applications from opto–electronics (for example in photovoltaics) to complex chemical reactions, such as water splitting, and biomedical applications such as drug delivery. In this PhD thesis we study the electronic properties of quasi one – dimensional nanostructures of TMDs. We begin by studying model S structures in the tight – binding approximation, in order to obtain insight into the electronic structure of S compounds. With Density Functional Theory as implemented by the open – source grid based projector augmented wave method (GPAW), we perform ab – initio calculations for the stability and electronic properties such as the edge energy, the density of states and the bandstructure. We find that MoS2, MoSe2, WS2 and WSe2 nanoribbons present metallic states localized at the edges, which present a 2D band gap crossing, similar to topological insulators. From the wavefunctions at the edge we examine the physics of the metallic states according to Shockley theory and we find that the broken periodicity due to the edge formation is responsible for the electron localization. Finally, with the introduction of defects such as oxygen atoms and hydroxyl radicals in our structures, we study a more realistic behavior of our materials when they interact with atmosphere and we find that the electronic properties of 1D TMDs are robust against environmental conditions, as opposed to the 2D semiconducting energy gap which undergoes a red shift.
Language English
Subject Electronic properties
First principle calculations
Two dimentional materials
Διδιάστατα υλικά
Ηλεκτρονικές ιδιότητες
Υπολογισμοί πρώτων αρχών
Issue date 2019-11-29
Collection   Faculty/Department--Faculty of Sciences and Engineering--Department of Materials Science and Technology--Doctoral theses
  Type of Work--Doctoral theses
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