Applied voltage dependence of nano-oxidation of ferromagnetic thin films using atomic force microscope

Abstract

Nanodots of Ni, CoFe, and Cr oxide were fabricated by the nano-oxidation technique using atomic force microscope. The dot size was controlled from 40 to 200 nm by changing the pulse voltage applied to the cantilever from 2 to 10 V. In order to evaluate the size of the nanostructures quantitatively, the electric field emitted from the cantilever was calculated. The threshold electric field strength was defined as the minimum strength to promote the oxidation. The threshold field strength of the order of 107 V/m was derived by fitting the experimental results. The voltage dependence of the size of fabricated Cr-oxide dots was fitted well by the calculation. The dot size of the ferromagnet-based oxide was fluctuating and did not agree with the calculation. From the theoretical analysis, it was suggested that the size of the nanostructures did not depend on the distance between the cantilever and film surface, but significantly depended on the curvature radius of the cantilever.