Surface Studies of C60 on Ferromagnetic Ni/Cu(100) and Co/Ru(OOOl) Thin Film Systems
Cummings, Marvin Lester
Barrera, Enrique V.
Doctor of Philosophy
This dissertation determined how the electronic and atomic structure of Ni/Cu(100) and Co/Ru(0001) thin films affect C6O-metal bonding and local magnetic properties at the surface. In-situ spin-averaged and spin-polarized scanning tunneling microscopy and spectroscopy techniques were used in this study. Homoepitaxial growth studies of Ni(100) and Co(0001) films investigated the influence of C60 on film growth. On 7.6 ML Ni films, C60 showed no obvious effect on the continued crystalline growth of Ni. The low mobility of C60 on the Ni surface and high Ni diffusion barrier limited the occurrence of Ni-C60 collisions during growth. On 1.84 ML Co films, crystalline growth with moire reconstructions continued with CGO present at the surface. However, Co islands were observed only nucleating and growing from step edges and around C60 suggesting the Co-C6O bond is stronger than the Co-Co bond on Co terraces. C60 mobility was also observed to vary across the Co film surface due to local variations in film reconstruction and dislocation networks. The results show that the nature of the C60-metallic bond at the surface can effect film growth and morphology. Scanning tunneling spectroscopy (STS) studies suggest that the spin-averaged and spinpolarized Co(0001) electronic structure is influenced by a number of factors: (i) sequential layer stacking (fcc/hcp), (ii) strain-induced reconstruction (moire), (iii) Co film thickness, and (iv) dislocations and defects at the surface. Spin-polarized STS measurements resolved spectral contributions from Co layer stacking and opposite perpendicular magnetic spin-orientations. The magnetic domain regions identified were fcctt/fcet..J, and hcptt/hcpt..J, stacked domains, respectively. No evidence of an in-plane magnetic spin-orientation or spin re-orientation transition was observed at the Co surface; however magnetic domain walls showed evidence of pinning at dislocation lines. Spin-polarized STM/STS measurements did not reveal any affect of C60 on the local magnetic properties of Co. However, an internal structure of C60 molecules adsorbed on the Co(0001) film surface was observed, corresponding to a 3-fold (symmetry) molecular-orientation; and in the near-region where CGO clusters were adsorbed, Co surface state peaks were observed to be absent, suggesting the local electronic structure of Co is perturbed by the presence of C60•
Mechanical engineering; Materials science