Optička svojstva dihalkogenida prijelaznih metala

master's thesis

• Title (english): Optical properties of Transition Metal Dichalcogenides
• Author: Valentino Jadriško
• Mentor: Nataša Vujičić (mentor)
• Mentor: Ivo Batistić (mentor)
• Committee member: Nataša Vujičić (predsjednik povjerenstva)
• Committee member: Mario Novak (član povjerenstva)
• Committee member: Ivo Batistić (član povjerenstva)
• Committee member: Hrvoje Buljan (član povjerenstva)
• Committee member: Emil Tafra (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2017-07-13, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

Nakon otkrića prvog dvodimenzionalnog materijala grafena 2004. godine uslijedio je rast zanimanja fizikalne zajednici o 2D materijala. Ubrzo nakon izolirani su i drugi 2D materijali sa sličnom van der Waals slojevitom strukturom. Neki od njih su i intrinzični poluvodiči poput MoS2 te u svom jednoslojnom obliku predstavlja jednu od mogućih opcija kao zamjena za silicijske tranzistore koji dostižu teorije granice tehnološkog razvoja. Jednosloj MoS2 je poluvodič s direktnim energetskim procjepom, dok je u višeslojnom i cjelovitom obliku poluvodič indirektnog energetskog procjepa. Zbog efekata zasjenjenja i kvantnog zatočenja u jednosloju MoS2 energije vezanja kvazičestica (ekscitona i triona) je puno veća nego u cjelovitom obliku, što nam omogućava njihovo opažanje na sobnoj temperaturi u spektrima fotoluminiscencije i apsorpcije. Eksciton se sastoji od jako vezanog para elektron- šupljina, dok trion može biti pozitivan (vezano stanje ekscitona i šupljine) i negativan (vezano stanje ekscitona i elektrona). U ovom diplomskom radu sam koristio eksperimentalni postav Raman spektrometar na Institutu za fiziku u Zagrebu te eksperimentalni postav vremenski razlučive fotoluminiscencije na Italian Institute of Technology u Milanu. Uzorci MoS2 su naraštani CVD metodom na Institutu za fiziku u Zagrebu, te su dobiveni jednosloji i dvosloji na SiO2/Si podlozi, dodatno su karakterizani jednosloji MoS2 transferirani na čistu SiO2/Si podlogu. U spektru fotoluminiscencije 2D MoS2 opažamo ekscitone A i B te pri dopiranim uzorcima pojavljuju se i trioni. U ovom radu ispituje se ovisnost spektra fotoluminiscencije o fotoinduciranom dopiranju koje smo postizali povećanjem snage lasera valne duljine 532 nm u rasponu od 1 μW do 500 μW. Primijetili smo pri velikim snagama lasera odnosno jakom fotodopiranju dominaciju triona u spektru fotoluminiscencije te pri niskim snagama lasera i slabom dopiranju uzorka MoS2 slabljenje trionskog potpisa u spektru i veću zastupljenost eksictona. Opaženi rezultati i ovisnost ekscitona i triona u spektru fotoluminiscencije o fotodopiranju su u skladu sa rezultatima električnog i kemijskog dopiranja. Kako bi ispitali dinamiku fotodopiranja i ovisnost populacija ekscitona A i triona A− u vremenu koristili smo vremenski razlučivu fotoluminiscenciju.

Abstract (english)

After the discovery of first two dimensional material graphene in 2004., interest of scientific community about 2D materials started to grow. Soon after other 2D materials have been isolated with similar van der Waarls layered structure. Some of them are intrinsic semiconductors, for instance Mo S2 which in his monolayer form is one of suitable replacement for silicon based transistors which are coming to their theoretical limits of technological development. Monolayer MoS2 is a semiconductor with direct band gap, but in the form of multilayers and bulk it is indirect band gap semiconductor. Because of the effects of screening and quantum confinement in monolayer Mo S2 binding energy of quasiparticles as excitons and trions is much bigger than in bulk form, which enables us to observe them in photoluminescence and absorption spectra at room temperature. Excitons are made of tightly bound electron hole pairs, whereas trions can be positive (bound exciton hole pair) and negative (bound exciton electron pair). In this diploma thesis I have used experimental setup Raman spectrometer on the Institute of Physics in Zagreb and time resolved photoluminescence on Italian Institute of Technology in Milan. Samples of monolayer and bilayer MoS2 were grown by method of chemical vapor deposition, additionally we characterized transferred Mo S2 monolayers on SiO2/Si substrate. In the photoluminescence spectrum of 2D MoS2 we observe excitons A and B, under increased doping new features emerges in spectrum which we identified as trions. In this thesis we investigated dependence of photoluminescence spectrum on photo doping which we accomplished by tuning the laser power from 1 μW to 500 μW with 532 nm wavelength. Under high laser powers and photo doping we observed domination of trions in photoluminescence spectra and under low laser powers and phot doping excitons are dominant in photoluminescence spectra. Observed results and dependence of exciton and trion population on photo doping are in correspondence with the published results of electrical and chemical doping. In order to investigate dynamics of photo doping and dependence of exciton and trion populations in time we used time resolved photoluminescence.

• Keywords: dihalkogenidi prijelaznih materijala
• Keywords (english): transition metal dichalcogenides
• Language: croatian
• URN:NBN: urn:nbn:hr:217:516694
• 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: Open access; Embargo expiration date: 2018-04-01
• Created on: 2017-08-01 10:50:55