Sehun Kim

Enhanced Magnetic Transition of Core-Shell Cobalt-Platinum Nanoalloys

Synthesis of ‘solid solution’ and ‘core-shell’ types of well defined Co-Pt based nanoalloys smaller than 10nm have been achieved by redox transmetalation reactions. This redox transmetalation are selectively observed only if the redox potential between two metals is favorable. The composition of the magnetic alloys can also be tuned by adjusting the ratio of reactants. Annealed core-shell nanoparticles transformed into mixed nanoalloys with face centered tetragonal (fct) structures, which show large coercivity and ferromagnetism at room temperature. These nanoparticles can potentially be used as an independent single magnetic bit of tera-bit information storage. Also, this kind of redox transmetalation reaction can be utilized as a general process to synthesize various types of nanoalloys with controlled composition in a selective fashion.

1‐D Molecular Chains of Thiophene on Ge(100)

The adsorption geometry of thiophene on Ge(100) have been studied by high‐resolution core‐level photoemission spectroscopy (HRPES) using synchrotron radiation and scanning tunneling microscopy (STM). From the analysis of the Ge 3d, S 2p, and C 1s core‐level photoemission spectra, we found three different adsorption geometries, which were assigned to a dative bonding feature, a [4+2] cycloaddition reaction product, and a desulfurization reaction product. Furthermore, we investigated that the ratio of the components induced by three adsorption geometries changed depending on the molecular coverage and the annealing temperature. At low coverage, the kinetically favorable dative bonding features favorably form 1‐D molecular chains. Increasing the molecular coverage, the energetically more stable [4+2] cycloaddition reaction products are additionally created.