Elektronske i optičke osobine deformisanih grafitnih i helikalnih nanotuba

Abstract

Motivacija U ovoj tezi su prezentovani rezultati iscrpne analize elektronskih i optičkih osobina dva tipa ugljeničnih nanotuba. Prvi deo se odnosi na homogeno deformisane jednoslojne ugljenične nanotube (tj. grafitne nanotube), dok su u drugom delu rezultati za nedeformisane i podužno istegnute helikalne ugljenične nanotube. Konfiguracije nedeformisanih grafitnih nanotuba su dobro poznate: sa izuzetkom tuba jako malog dijametra, odgovara grafenskoj ravni urolovanoj na specifičan način. Sa druge strane, možemo smatrati da su helikalne nanotube rezultat periodičnog umetanja sedmougaonih i petougaonih defekata u grafensku rešetku, što prouzrokuje njihovu karakterističnu helikalnu morfologiju. Od svih nanomaterijala baziranih na ugljeniku ove nanotube imaju najsloženiju i najraznovrsniju strukturu. Pored tri ”globalna” geometrijska parametra, koje je moguće direktno meriti u ogledima, postoje i ”lokalni” parametari koji opisuju položaj defekata unutar monomera. Zbog toga se kod ovog tipa tuba očekuju i raznovrsnije elektronske osobine. U tezi je razmotren uticaj globalnih i lokalnih parametara, kao i moguće modifikacije elektronskih osobina pomoću mehaničkih napona. Kod nanotuba efekti deformacionog sprezanja na fizičke osobine nisu do sada sistematski analizirane. Za uspešnu primenu u različitim nano-elektromehaničkim uređajima detalno poznavanje efekata deformacionog sprezanja je od velike važnosti. Tendencija smanjivanja mehaničkih i elektronskih uređaja ka nanometarskoj skali, nameće potrebu za izradom efikasnih senzora za merenje i kontrolu ponašanja odgovaraju ćih nanouređaja. Postojeće mikrosenzore je nemoguće skalirati na nanodimenzije, a da ne dođe do drastičnog smanjenja dinamičkog opsega senzora. U cilju prevazilaženja prepreke nametnute skaliranjem 3D materijala, potrebno je razmotriti mogućnosti primene inherentnih 2D materijala, posebno onih baziranih na kompozitnim filmovima od grafitnih nanotuba kod kojih efekti skaliranja daleko manje utiču na promenu karakteristika...

Motivation Results of the comprehensive study of electronic and optical properties of two types of carbon nanotubes are presented in this thesis. First part considers homogenously deformed single-wall carbon nanotubes(i.e. graphitic nanotubes), while the second one contains results for non-deformed and uniaxially strained helically coiled carbon nanotubes. Configurations of non-deformed single-wall carbon nanotubes are well known: with exception of extremely narrow tubes, it corresponds to specifically rolled up graphene plane. On the other hand, helically coiled carbon nanotubes can be understand as the result of periodic insertion of heptagonal and pentagonal defects in graphene lattice which results in their characteristic helical morphology. Among all carbon based nanomaterials, these tubes have the most complex and most diverse structures. Besides three ”global” geometric parameters of helical coil, which can be directly measured in experiments, there are a number of ”local” parameters that describe position of defects within the monomer. Therefore, more diverse electronic properties are expected for these type of tubes. Influence of global and local parameters and possible modification of electronic properties by mechanical stress are addressed in this research study. For the nanotubes effects of strain coupling on its physical properties has not been systematically analyzed. For successful application in various nano-electromechanical devices, detailed knowledge of effects of strain coupling on electronic and optical properties are of the most importance. The tendency of decreasing mechanical and electronic devices to the nanometer scale, imposes need to develop effective sensors to measure and control the behavior of various nanodevices. However, without a drastic reduction of the basic characteristics of the existing micro-sensors it is impossible to scale them down to nanodimension. In order to overcome the barriers imposed by scaling of 3D materials, it is necessary to consider the possible application of inherent 2D materials, especially those based on composite films of carbon nanotubes where the change in characteristics are far less affected by scaling...