Electrical Characterisitics of ferritin cores Investegated by Kelvin Probe Force Microscopy

We fabricated Fe (iron metal) cores structure by using a low energy Ar+ ion beam. A monolayer of ferritin molecule (Fe2O3 : iron oxide) was adsorbed on the thermal silicon oxide layer. The bombardment energy was optimized using Ar gas by changing the input power after the protein of the monolayer was eliminated with UV/O-3. Though it was resulted in a poor reduction when the time of ion beam was less than 30 sec, Ar+ ion beam enabled completely reduction when the time of ion beam was in 60 sec. We reduced the core particles to conductive Fe nanodots. X-ray photoelectron spectroscopy (XPS) measurements confirmed the reduction of the cores. As a result, the diameter of the ferritin nano-structure was 7 nm, which was not identical to that of the iron core in the ferritin after ion beam. Additionally, the Kelvin Probe Force microscopy (KFM) profile was not almost identical between Fe2O3 and Fe cores. It is very difficult for conventional Ar+ beam processes to fabricate such fine structure of Fe cores, because the high energy ions enhanced the bombardment damage of the iron core in the conventional reduction processes. The results that the change of lattice constant from 0.25 to 0.2 nm corresponds from ferrihydrite (110) to alpha-Fe(111), respectively, which suggests the ferrihydrite cores reduced to Fe nanodots after ion beam process. Furthurmore, the diameter of the ferritin core decreased from 7 nm to 5 nm after the ion beam process.