Fabrication and evaluation of nanometer-sized metal oxide structures on composite metal thin films using scanning near-field optical microscope

Nanometer-scale metal-oxide structures with optical transparency have been fabricated on metal films by anodic oxidation using a probe tip of a scanning near-field optical microscope (SNOM). We discuss the thickness and the optical transparency of the oxides depending on the bias voltage applied to samples for oxidation. For titanium (Ti) films, the thickness of the oxide increases up to 100 nm linearly with the bias voltage. For composite films consisting of titanium-aluminum (Ti-Al) and titanium-silver (Ti-Ag) layers, the bias-voltage dependence of the oxide thickness is altered at some bias voltages, which concur with those required for the oxidation of the upper Ti layers. Moreover, the oxides have been observed optically by the same SNOM as a transmission mode. The transmittance at the oxide increases with the growth of the oxides, because of the decrease of the thickness of the metal films due to the oxidation. The result also suggests that Ti-, Al- and Ag-oxides fabricated by this method are optically transparent.