Nanoscopy and applications of two-dimensional and quasi-two-dimensional systems
Nanoskopija i primene dvodimenzionalnih i kvazi dvodimenzionalnih sistema
Докторанд
Ralević, UrošМентор
Radovanović, JelenaЧланови комисије
Milanović, VitomirIsić, Goran
Tadić, Milan
Potrebić, Milka
Метаподаци
Приказ свих података о дисертацијиСажетак
This thesis addresses some of the fundamental and technological aspects of two- or
quasi-two-dimensional systems realised within novel materials or metallic nanoparticle
clusters. In particular, charge density modulations of the quasi-two-dimensional
electron system in CeTe3, the two-dimensional electron system in graphene, twodimensional
excitons in MoS2, and surface plasmons in metallic nanoparticle clusters
were probed by a number of scanning probe microscopy and optical spectroscopy
techniques. The optical properties, spectroscopic data and some potential applications
of two-dimensional systems were investigated by numerically solving the
macroscopic Maxwell equations by the nite element or re
ection pole methods.
The charge density waves in CeTe3 were investigated at room temperature by
scanning tunneling microscopy, scanning tunneling spectroscopy and Raman spectroscopy.
The modulation wavevector and the induced energy gap, which are crucial
for describing these exci...tations, were assessed. The mixing of the modulation's
wavevector with the wavevectors of the underlaying lattice was also observed. The
charge density modulation was found to be followed by periodic rearrangement of
tellurium atoms in planar layers hosting the modulation.
The in
uence of the environment on the two-dimensional charge carriers in
graphene was investigated by Kelvin probe force microcopy and electrostatic force
microscopy. This study was done for bare and isolated electrically gated graphene
samples in which the concentration of charge carriers can be tuned via the electric
eld eect. The results of this study, based on the analysis of the measured contact
potential dierence, showed that the environment induces instabilities in doping
levels of graphene even upon application of the gate voltage. The stability of gateinduced
changes of the doping level in graphene is crucial for graphene based devices.
Therefore this result indicates that improved performance of graphene based devices
can be expected if graphene is isolated from the environment.
Interaction between graphene and guided modes of optical waveguides was studied
by means of exact numerical simulations and a convenient perturbation theory.
The conclusion reached in this study is that graphene modies the modal propagation
constants and that this eect can be used in construction of graphene based
optical modulators.
Investigation of the in
uence of metallic nanoparticle clusters on two- dimensional
excitons in MoS2 has showed that these nanoobjects do not alter the spectral
position or width of the exciton photoluminescence but rather induce a small enhancement
of the A excitonic peak. The reason for the weak interaction was found
in the misalignment of the MoS2 plane and the dominant cluster's electric eld component,
as well as in the fact that the electric elds are weak near the MoS2 plane.
The electric elds were found to be the strongest within nano-gaps between the adjacent
nanoparticles. This was utilized for the surface enhanced Raman spectroscopy
study of the adsorption of thin aggregated dye layers on the cluster surface...
U ovoj tezi razmatrani su neki od fundamentalnih i tehnoloskih aspekata dvodimenzionalnih
ili kvazi dvodimenzionalnih sistema, koji su realizovani u novim materijalima
ili klasterima metalnih nanocestica. Tehnikama skenirajuce mikroskopije
i opticke spektroskopije proucavani su modulacija gustine naelektrisanja u kvazi
dvodimenzionalnom elektronskom sistemu u CeTe3, dvodimenzionalni elektronski
sistem u grafenu, dvodimenzionalni ekscitoni u MoS2 i povrsinski plazmoni u klasterima
metalnih nanocestica. Opticke osobine, spektroskopski podaci i potencijalne
primene dvodimenzionalnih sistema proucavani su numerickim resavanjem
makroskopskih Maksvelovih jednacina pomocu metoda re
eksije polova i konacnih
elemenata.
Pomocu skenirajuce mikroskopije, skenirajuce spektroskopije i Ramanove spektroskopije
proucavan je talas gustine naelektrisanja u CeTe3 na sobnoj temperaturi.
Kao rezultat ove studije odredeni su talasni vektor modulacije elektronske gustine
stanja i energetski proc...ep kojima se talas gustine naelektrisanja moze opisati.
Uocena je i pojava mesanja talasnog vektora modulacije sa talasnim vektorima atomske
resetke u ravni u kojoj se formira talas gustine naelektrisanja. Utvrdeno je da
modulacija elektronske gustine stanja postoji zajedno sa periodicnom modulacijom
atomske resetke telurovih atoma u kojima se talas gustine naelektrisanja formira.
Uticaj faktora iz spoljasnje sredine na dvodimenzionalne nosioce naelektrisanja
u grafenu proucavan je pomocu skenirajuce Kelvinove mikroskopije i mikroskopije
elektrostatickih sila. Ova studija je realizovana u slucajevima kada je grafen izlozen
odnosno izolovan od uticaja iz okolne sredine. Proucavani su uzorci pripremljeni
u takozvanoj gejt konguraciji koja omogucava promenu koncentarcije nosilaca u
grafenu primenom napona gejta. Na osnovu analize izmerene kontaktne potencijalne
razlike nadeno je da faktori iz spoljasnje sredine dovode do nestabilnosti
koncentracije elektrona u grafenu, cak i kada je napon gejta primenjen. Posto je
stabilnost nivoa dopiranja neophodna za rad naprava na bazi grafena, ova studija
pokazuje da se bolje performanse mogu ocekivati kada je grafen izolovan od uticaja
iz spoljasnje sredine.
Razmatrana je i interakcija grafena sa vodenim modovima optickih talasovoda.
Za analizu ovog problema upotrebljeni su razliciti numericki alati. Zakljuceno je da
grafen dovodi do modikacije propagacione konstante vodenih modova i da se ova
pojava moze iskoristiti u konstrukciji optickih modulatora.
Ispitivanjem uticaja klastera metalnih nanocestica na fotoluminescenciju ekscitona
u MoS2 nadeno je da metalni nanosistemi ne uticu na poziciju i spektralnu
sirinu fotoluminescencije, ali da ipak dovode do slabog pojacanja ekscitonskog A
pika. Razlozi su slabo sprezanje elektricnog polja metalnih klastera i MoS2 kao i
slab intenzitet ovih polja u blizini MoS2. Cinjenica da je elektricno polje u okviru
metalnih klastera jako u supljinama izmedu nanocestica iskoriscena je za proucavanje
mehanizma adsorpcije tankih slojeva organske boje na povrsinu klastera, pomocu
povrsinom podstaknute Ramanove spektroskopije...