Electric Properties of the Co-nanodots using Kelvin Probe Force Microscopy
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1094-DD08-01
Electric Properties of the Co-nanodots using Kelvin Probe Force Microscopy Shin-ichi Yamamoto Department of Electrical Engineering, Kobe City College of Technology, 8-3, GakuenHigashi-machi, Nishi-ku, Kobe City, 651-2194, Japan Abstract We fabricated Co (cobalt metal) particles structures using a low-energy Ar+ ion beam. A monolayer of Co-ferritin molecules (CoO: cobalt oxide) was adsorbed on the native silicon oxide layer. The bombardment ion was optimized using Ar gas after the protein of the monolayer was eliminated with UV/O3. Athough it resulted in poor reduction when the irradiation time of the Ar+ ion beam was less than 30 sec, the Ar+ ion beam enabled the complete reduction, when the irradiation time of the ion beam was 60 sec. We reduced the core particles to conductive Co nano-particles. X-ray photoelectron spectroscopy (XPS) measurements confirmed the reduction of the cores. In addition, the Kelvin Probe Force microscopy (KPFM) profiles were not identical of the CoO and Co cores. It is relatively easy using conventional low Ar+ beam processes to fabricate such fine structure of Co cores. 1. Introduction The Utilization of a biomolecule is a promising option to obtain a uniform inorganic nanoparticle. Particularly, some proteins are very appropriate for this purpose. The cage-shaped protein, ferritin, is well known to bind iron ions and form the nanomeric uniform ferrihydrite
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(5Fe2O3 9H2O) nanoparticle core in its cavity in vivo. Efforts to synthesize the nanoparticle of various materials in a hollow cavity in vitro have made it possible for ferritin to accommodate a variety of transition metal oxide and semiconductor cores [1, 2]. Because the inner cavity size is restricted by the protein shell, the artificially biomineralized cores are uniform in size and shape. Moreover, ferritin can be placed on the desired area of the surface and the protein shell can be selectively eliminated by utilizing the excellent advantages of the protein, such as the chemical excitability of the protein surface and the vulnerability of the protein structure against heat/chemical treatment: we can produce a selectively deposited two-dimensional (2D) array of biomineralized nanodots. The results for CoO indicate the perfect reduction of oxides in agreement with previously reported results with high temperature [3]. The results for Fe2O3 ferritin indicate the perfect reduction of oxides in agreement with previously reported results [4]. In this paper, we present a comparative study of the compositional changes in CoO induced by 3 keV Ar+. In addition to the XPS study, we performed surface measurements by
Kelvin Probe Force Microscopy (KPFM) to determine the difference in the surface potential between CoO and Co ferritin, which might correspond to the particles of pure metal and metal oxidation.
2. Experiment
A large number of atomically identical protein molecules can be easily produced, because proteins are synthesized on the basis of information in DNA. The protein is an excellent candidate for making nano
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