Browsing by Author "Kotakoski, J."

Filter results by typing the first few letters
Now showing 1 - 3 of 3
  • B and N ion implantation into carbon nanotubes: Insight from atomistic simulations
    (2005) Kotakoski, J.; Krasheninnikov, A. V.; Ma, Yuchen; Foster, Adam S.; Nordlund, K.; Nieminen, Risto M.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    By employing atomistic computer simulations with empirical potential and density functional force models, we study B/N ion implantation onto carbon nanotubes. We simulate irradiation of single-walled nanotubes with B and N ions and show that up to 40% of the impinging ions can occupy directly the sp2 positions in the nanotube atomic network. We further estimate the optimum ion energies for direct substitution. Ab initio simulations are used to get more insight into the structure of the typical atomic configurations which appear under the impacts of the ions. As annealing should further increase the number of sp2 impurities due to dopant atom migration and annihilation with vacancies, we also study migration of impurity atoms over the tube surface. Our results indicate that irradiation-mediated doping of nanotubes is a promising way to control the nanotube electronic and even mechanical properties due to impurity-stimulated crosslinking of nanotubes.
  • Defects in bilayer silica and graphene: common trends in diverse hexagonal two-dimensional systems
    (2013) Björkman, T.; Kurasch, S.; Lehtinen, O.; Kotakoski, J.; Yazyev, O.V.; Srivastava, A.; Skakalova, V.; Smet, J.H.; Kaiser, U.; Krasheninnikov, A.V.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    By combining first-principles and classical force field calculations with aberration-corrected high-resolution transmission electron microscopy experiments, we study the morphology and energetics of point and extended defects in hexagonal bilayer silica and make comparison to graphene, another two-dimensional (2D) system with hexagonal symmetry. We show that the motifs of isolated point defects in these 2D structures with otherwise very different properties are similar, and include Stone-Wales-type defects formed by structural unit rotations, flower defects and reconstructed double vacancies. The morphology and energetics of extended defects, such as grain boundaries have much in common as well. As both sp2-hybridised carbon and bilayer silica can also form amorphous structures, our results indicate that the morphology of imperfect 2D honeycomb lattices is largely governed by the underlying symmetry of the lattice.
  • Structural manipulation of the graphene/metal-interface with Ar+ irradiation
    (2013) Åhlgren, E.H.; Hämäläinen, Sampsa; Lehtinen, O.; Liljeroth, P.; Kotakoski, J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Controlled defect creation is a prerequisite for the detailed study of disorder effects in materials. Here, we irradiate a graphene/Ir(111) interface with low-energy Ar+ to study the induced structural changes. Combining computer simulations and scanning-probe microscopy, we show that the resulting disorder manifests mainly in the forms of intercalated metal adatoms and vacancy-type defects in graphene. One prominent feature at higher irradiation energies (from 1 keV up) is the formation of linelike depressions, which consist of sequential graphene defects created by the ion channeling within the interface, much like a stone skipping on water. Lower energies result in simpler defects, down to 100 eV, where more than one defect in every three is a graphene single vacancy.