Surface Studies of C60 on Ferromagnetic Ni/Cu(100) and Co/Ru(OOOl)Thin Film Systems

[摘要] This dissertation determined how the electronic and atomic structure of Ni/Cu(100) andCo/Ru(0001) thin films affect C6O-metal bonding and local magnetic properties at thesurface. In-situ spin-averaged and spin-polarized scanning tunneling microscopy andspectroscopy techniques were used in this study. Homoepitaxial growth studies ofNi(100) and Co(0001) films investigated the influence of C60 on film growth. On 7.6 MLNi films, C60 showed no obvious effect on the continued crystalline growth of Ni. The lowmobility of C60 on the Ni surface and high Ni diffusion barrier limited the occurrence ofNi-C60 collisions during growth. On 1.84 ML Co films, crystalline growth with moirereconstructions continued with CGO present at the surface. However, Co islands wereobserved only nucleating and growing from step edges and around C60 suggesting theCo-C6O bond is stronger than the Co-Co bond on Co terraces. C60 mobility was alsoobserved to vary across the Co film surface due to local variations in film reconstructionand dislocation networks. The results show that the nature of the C60-metallic bond atthe surface can effect film growth and morphology.Scanning tunneling spectroscopy (STS) studies suggest that the spin-averaged and spinpolarizedCo(0001) electronic structure is influenced by a number of factors: (i)sequential layer stacking (fcc/hcp), (ii) strain-induced reconstruction (moire), (iii) Co filmthickness, and (iv) dislocations and defects at the surface. Spin-polarized STSmeasurements resolved spectral contributions from Co layer stacking and oppositeperpendicular magnetic spin-orientations. The magnetic domain regions identified werefcctt/fcet..J, and hcptt/hcpt..J, stacked domains, respectively. No evidence of an in-planemagnetic spin-orientation or spin re-orientation transition was observed at the Cosurface; however magnetic domain walls showed evidence of pinning at dislocationlines. Spin-polarized STM/STS measurements did not reveal any affect of C60 on thelocal magnetic properties of Co. However, an internal structure of C60 moleculesadsorbed on the Co(0001) film surface was observed, corresponding to a 3-fold(symmetry) molecular-orientation; and in the near-region where CGO clusters wereadsorbed, Co surface state peaks were observed to be absent, suggesting the localelectronic structure of Co is perturbed by the presence of C60•

[发布机构] Rice University

[效力级别] engineering