Browsing by Author "Yilmaz, D. E."

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    Analysis of strain fields in silicon nanocrystals
    (American Institute of Physics, 2009) Yilmaz, D. E.; Bulutay, C.; Çaǧın, T.
    Strain has a crucial effect on the optical and electronic properties of nanostructures. We calculate the atomistic strain distribution in silicon nanocrystals up to a diameter of 3.2 nm embedded in an amorphous silicon dioxide matrix. A seemingly conflicting picture arises when the strain field is expressed in terms of bond lengths versus volumetric strain. The strain profile in either case shows uniform behavior in the core, however, it becomes nonuniform within 2-3 Å distance to the nanocrystal surface: tensile for bond lengths whereas compressive for volumetric strain. We reconcile their coexistence by an atomistic strain analysis.
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    Pathways of bond topology transitions at the interface of silicon nanocrystals and amorphous silica matrix
    (The American Physical Society, 2008) Yilmaz, D. E.; Bulutay, C.; Çaǧin, T.
    The interface chemistry of silicon nanocrystals (NCs) embedded in an amorphous oxide matrix is studied through molecular dynamics simulations with the chemical environment described by the reactive force field model. Our results indicate that the Si NC-oxide interface is more involved than the previously proposed schemes, which were based on solely simple bridge or double bonds. We identify different types of three-coordinated oxygen complexes that are previously not noted. The abundance and the charge distribution of each oxygen complex is determined as a function of the NC size as well as the transitions among them. The oxidation at the surface of NC induces tensile strain to Si Si bonds, which become significant only around the interface, while the inner core remains unstrained. Unlike many earlier reports on the interface structure, we do not observe any double bonds. Furthermore, our simulations and analysis reveal that the interface bond topology evolves among different oxygen bridges through these three-coordinated oxygen complexes.