In situ quantification of electrical isolation in STM-fabricated TiOx nanostructures
In this Letter, a combination of conductive atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) with a compliant cantilever is used to electrically probe oxidised TiO2−x nanostructures in situ. In STM mode, both the written width and the effective resistivity of material in the written line increase with write bias. At low writing voltages (∼3.5 V), the STM written lines are narrow (30 nm), but they are not resistive enough to allow patterns with a 1–2 µm perimeter to provide electrical isolation above 10 MΩ. Raising the bias to 8.5 V during writing allows similar structures to provide isolation of better than 250 MΩ. The resistivity in the lines written at the latter with high bias is 28 Ω m. From electrical estimates, the oxidation appears to go through the thickness at all voltages, but is more chemically incomplete (larger value of x) at low voltage. The data are not consistent, with a small amount of metallic Ti remaining under the written mark, that is, partial penetration of the oxidation. The thickness of this Ti layer would have to be unphysically small (1 million times smaller than an atomic layer thickness) to allow this interpretation.
