Naslov (eng)

Nanoscopy and applications of two-dimensional and quasi-two-dimensional systems : doctoral dissertation

Autor

Ralević, Uroš

Doprinosi

Radovanović, jelena
Milanović, Vitomir
Isić, Goran
Tadić, Milan
Potrebić, Milka

Opis (eng)

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 excitations, 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...

Opis (eng)

Electrical and Computer Engineering-Nanoelectronics and Photonics Day of defence: 4. 9. 2017.

Opis (srp)

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 procep 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...

Jezik

engleski

Datum

2017-12-04T13:56:14.059Z

Licenca

Ovo delo je licencirano pod uslovima licence
Creative Commons CC BY-NC 2.0 AT - Creative Commons Autorstvo - Nekomercijalno 2.0 Austria License.

http://creativecommons.org/licenses/by-nc/2.0/at/legalcode

Predmet

OSNO - Opšta sistematizacija naučnih oblasti, Nanoelektronika

dvodimenzionalni sistem, kvazi dvodimenzionalni sistem, cerijum tritelurid, grafen, molibden disulfid

OSNO - Opšta sistematizacija naučnih oblasti, Nanoelektronika

two-dimensional system, quasi two-dimensional system, cerium tritelluride, graphene, molybdenium disulfide