Dvodimenzionalni materijali nakon grafena

master's thesis

• Title (english): Two-dimensional materials beyond graphene
• Author: Borna Pielić
• Mentor: Marko Kralj (mentor)
• Mentor: Damir Bosnar (mentor)
• Committee member: Damir Pajić (predsjednik povjerenstva)
• Committee member: Vito Despoja (član povjerenstva)
• Committee member: Marko Kralj (član povjerenstva)
• Committee member: Damir Bosnar (član povjerenstva)
• Committee member: Goranka Bilalbegović (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2015-05-29, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

U ovom diplomskom radu proučen je rast dvodimenzionalnih WS_2 nanostruktura na površini Ir(111). Sva mjerenja obavljena su u uvjetima ultra-visokog vakuuma. Tehnike koje su pritom korištene su pretražna tunelirajuća mikroskopija (STM) te difrakcija elektronima niske energije (LEED). Najprije je karakteriziran rast volframovih otoka na površini Ir(111). Dobivene su razne pokrivenosti volframa na uzorku, a svaka od njih ima specifičnu morfologiju koja ovisi o parametrima naparivanja. Pri depoziciji volframa u atmosferi H_2S-a nije došlo do njegove sulfurizacije za primijenjeni raspon parametara. U nekim sintezama pri H_2S doziranju, podloga za rast bila je h-BN/Ir(111). Drugi izvor sumpora predstavljao je sulfidni mineral pirit, FeS_2. Njegovim grijanjem na površini uzorka došlo je do formiranja superstrukture 2 x √3 u odnosu na Ir(111). Ta superstruktura je rasla u domenama koje su međusobno bile zarotirane za 60°. Dodatno, njena geometrija je dimerizirana te sadrži dva atoma u bazi. Dani su i modeli koji oslikavaju moguće pridruženje superstrukture sa površinom Ir(111). Depozicijom volframa u pozadinskom tlaku ostvarenom grijanjem pirita uspješno je sintetiziran WS_2 na površini Ir(111). Njegov se rast najčešće javlja u jednoslojnim, dvoslojnim i troslojnim otocima trokutaste morfologije, a jednoslojni otoci sraštanjem mogu tvoriti puni sloj. Iz STM slika izmjerena je konstanta rešetke WS_2, aWS_2 = (3:01 ± 0:02)Å. LEED mjerenjima utvrđeno je postojanje heksagonalne strukture WS_2 čija se rotacija poklapa sa periodičnosti Ir(111). Analizirane su visine otoka, čije debljine jednosloja mogu varirati u skladu promjenom elektronske gustoće stanja na Fermijevom nivou. Uočeni su svijetli STM kontrasti rubova otoka, koji dolaze zbog hibridizacije elektronskih stanja kod otoka s nezanemarivim udijelom rubnih atoma.

Abstract (english)

In this thesis we have studied the growth of two-dimensional structures WS_2 structures at the Ir(111) surface. All measurements have been performed under the ultra high vacuum (UHV) conditions. Techniques that were used are scanning tunelling microscopy (STM) and low energy electron diraction (LEED). The former was used for characterizing the growth of tungsten islands on the surface of Ir(111). There were obtained various coverage of tungsten on sample, each of them has a specific morphology, which depends on the parameters of evaporation. Deposition of tungsten in H_2S atmosphere hasn't resulted by its sulphurisation. In some synthesis with H_2S dosing, the substrate was h-BN/Ir(111), but was equally unsuccessful. Another source of sulfur represented sulfid mineral pyrite, FeS_2. By it's heating the superstructure of 2 x √3 relative to the Ir(111) was formed. This superstructure grows in three equivalent domains, rotated by 60° with respect to each other. Additionally, the spatial arrangement is dimerized with the base comprising two atoms. We propose a model for this superstructure. By the deposition of the tungsten in the background pressure achieved by heating of the pyrite, WS_2 on Ir(111) has been succesfully synthesized. It's growth usually results by a single layer, bilayer and trilayer islands with triangular morphology, and single layer islands coarsening can form a full layer. The lattice constant of WS2 has been measured from the STM topographs, aWS_2 = (3:01 ± 0:02)Å. LEED measurements showed the presence of a hexagonal structure WS_2 with alignement fitting to that of Ir (111). The heights of the multilayered islands have been analyzed. It is revealed that each single layer STM heights may vary in accordance with the change of electronic density of states on the Fermi level. The edges of imaged WS_2 islands exhibit bright contrast indicating the hybridization of electronic states at the island rim involving edge atoms.

• Keywords: dvodimenzionalni materijali (2D); van der Waalsovi materijali (vdW); dihalkogenidi prijelaznih materijala (TMD)
• Keywords (english): two-dimensional materials; transition metal dichalcogenides (TMD)
• Language: croatian
• URN:NBN: urn:nbn:hr:217:439544
• Study programme: Title: Physics; specializations in: Research; Course: Research; Study programme type: university; Study level: integrated undergraduate and graduate; Academic / professional title: magistar/magistra fizike (magistar/magistra fizike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Access restricted to students and staff of home institution
• Created on: 2017-04-04 20:51:44