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Compositional Changes in Co–Ferritin Nanoparticles Induced by Ion Bombardment as Determined by Kelvin Probe Force Microscopy in High Vacuum

We fabricated a Co (cobalt metal) core particle structure using a low-energy Ar+ ion beam. A monolayer of Co core ferritin molecules (CoO: cobalt oxide) was adsorbed on the silicon substrate. Bombardment energy was optimized using Ar gas after the protein of the monolayer was eliminated with UV/O3. The Ar+ ion beam enabled the complete reduction, when the irradiation time of ion beam was 60 s. We reduced the core particles to conductive Co nanoparticles. X-ray photoelectron spectroscopy (XPS) measurements confirmed the reduction of the cores. As a result, the diameter of the Co–ferritin nanostructure became 7 nm, which was not identical to that of the cobalt core in the ferritin after the ion beam bombardment. In addition, the Kelvin probe force microscopy (KFM) profiles of the CoO and Co cores obtained. It is relatively easy to fabricate such a fine structure of Co cores using conventional low energy Ar+ beam processes. The results obtained here will open a new field that combines semicoductor technology and biotechnology.