Spectroscopic studies of semiconducting single-walled carbon nanotubes
The unique nature of optical properties of single-walled carbon nanotubes
(SWCNT), together with their promising potential applications, have created
enormous interest towards the photophysics of SWCNT. Many aspects of
carbon nanotubes originate from the electronic structure of carbon honeycomb
lattice and one-dimensionality. SWCNTs exist in various chiral structures and
diameters, which the optical and electrical properties are dependent on. It has
been discovered that SWCNT excited states are excitonic with strong Coulomb
interaction between the electron and the hole. However, many features of
excitons are not yet well defined, such as absorption cross-sections, fluorescence
quantum yields, exciton lifetimes, and the nature of exciton mobility. The
cylindrical shape with all atoms on the surface makes SWCNTs highly sensitive
to environment which is a significant factor affecting the optical properties.
First part of this thesis concentrates on the temperature dependence
of excitonic absorption transitions. The importance of this study lies in the
complexity of environmentally induced mechanisms to alter the energy gap and
shift the electronic absorption transitions as a function of temperature. The
results revealed abrupt shift in the energy gap interpreted to originate from
interactions with water. The second part discusses the processes occurring after
absorption: exciton mobility and dynamics. By analyzing reactions between
single-molecule diazonium salt and individual nanotubes, the distance
travelled by exciton during its lifetime, in different surfactants and for different
chiral structures was determined. The results indicate that localized excitons
have diffusional motion along the nanotube axis. The large diffusion ranges
obtained (160 - 340 nm) explain the sensitivity of SWCNT emission to changes
in local environment. The dynamics of excitons were studied with excitation
dependence measurements. Results revealed the existence of long lived states
that act as quenchers of emission even at relatively low excitation intensities.
...


Publisher
University of JyväskyläISBN
978-951-39-4063-8ISSN Search the Publication Forum
0357-346XKeywords
eksitonin diffuusio hiilinanoputket Fourier transform infrared (FTIR) spectroscopy exciton diffusion exciton dynamics fluorescence spectroscopy fluorescence microscopy carbon nanotubes spectroscopy fysikaalinen kemia optiset laitteet spektroskopia fluoresenssi absorbtio lämpötila liuottimet kemialliset reaktiot
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- Väitöskirjat [3295]
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