Carbon structures have a big role in nanoscience today because of their rich and
promising electrical, mechanical and optical properties. However, advancing these
properties requires understanding the underlying structure and its behavior. In addition
to ideal systems, defects are frequently unavoidable in experiments; hence their
e ects, along with their possibilities to enrich the functionalities of carbon nanostructures,
should be investigated.
This thesis concentrates on computational studies of various defects in graphene and
carbon nanotubes. It combines investigations of changes in Raman-active modes of
single-walled carbon nanotubes due to vacancies and bending, reconstructions for
graphene edges, and adsorption and di usion mechanism of single gold atoms in
graphene. Most of the results can be understood in terms of simple physical principles
and relations to experiments are discussed in detail.
E ects of carbon atom vacancies on Raman-active phonons are understoo
d via their
symmetry properties and structural weakening. However, the e ect of tube bending
on Raman-active modes is complicated to understand. Bending proved to be computationally
challenging, but our so-called wedge boundary conditions o ered a way to
practical modeling. Wedge boundary conditions are free from constraints and nitesize
e ects, and really make bending the only disturbance in the system. This kind of
approach will be useful for other physical problems as well.
In this thesis we found a new ground state for graphene edges a new edge beyond
armchair and zigzag. We show that this speci c reconstruction of zigzag selfpassivates
the edge against molecular hydrogen adsorption and increases the rigidity
of the graphene edge. We discuss about the possibilities to identify the edge structure
from scanning tunneling microscope (STM) images, Raman-active modes and
vibrational properties relating the di erences to physical properties.
This thesis also shows that gold atoms are thermally stable in-plane with graphene
opening possibilities to tune the properties of carbon nanostructures. Our results
con rm that, in addition to imaging, transmission electron microscope (TEM) has a
great potential as a preparation tool for samples of carbon nanomaterials containing
metals. Because contacts may dominate behaviour in nanosize systems, understanding
the metal-carbon interface through defects like vacancies is important. With the help
of TEM-beam there can be a way to selectively make direct contacts with metals and
carbon nanostructures at any point of the lattice, not only at the edges.
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