Browsing by Subject "Spectra"
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Item Open Access Formation of silicon nanocrystals in sapphire by ion implantation and the origin of visible photoluminescence(AIP Publishing, 2006) Yerli, S.; Serincan, U.; Dogan, I.; Tokay, S.; Genisel, M.; Aydınlı, Atilla; Turan, R.Silicon nanocrystals, average sizes ranging between 3 and 7 nm, were formed in sapphire matrix by ion implantation and subsequent annealing. Evolution of the nanocrystals was detected by Raman spectroscopy and x-ray diffraction (XRD). Raman spectra display that clusters in the matrix start to form nanocrystalline structures at annealing temperatures as low as 800 degrees C in samples with high dose Si implantation. The onset temperature of crystallization increases with decreasing dose. Raman spectroscopy and XRD reveal gradual transformation of Si clusters into crystalline form. Visible photoluminescence band appears following implantation and its intensity increases with subsequent annealing process. While the center of the peak does not shift, the intensity of the peak decreases with increasing dose. The origin of the observed photoluminescence is discussed in terms of radiation induced defects in the sapphire matrix.Item Open Access Vibrations of the cubane molecule: inelastic neutron scattering study and theory(Elsevier, 1999-08-13) Yildirim, T.; Kiliç, Ç.; Çıracı, Salim; Gehring, P. M.; Neumann, D. A.; Eaton, P. E.; Emrick, T.Cubane (C8H8) is an immensely strained molecule whose C-C-C bond angle is 90 degrees rather than 109.5 degrees as expected for sp(3) bonding of carbon. We have measured the intramolecular vibrational spectrum of cubane using inelastic neutron scattering. The neutron data are used to test the transferability of various phenomenological potentials and tight-binding models to this highly strained molecule. Unlike these models, first-principles calculations of the INS spectrum (both energy and intensity) agree well with the experimental data.