In situ fabrication and characterization of tungsten nanodots onSiO2/Si via field induced nanocontact with a scanning tunnelling microscope

Abstract

Tungsten nanodots were reproducibly fabricated on ultrathinSiO2/Si by a novel technique in which repeatedly large-scale voltage ramps were applied between a scanningtunnelling microscope (STM) tip and samples. These nanodots have a similar geometry with a height of1.0 ± 0.2 nm anddiameter of 4.0 ± 1.0 nm. Nanodot formation processes were inspected simultaneously during the fabrication bymeans of scanning tunnelling spectroscopy (STS). The appearance of high conductivityI–V curves indicates a nanocontact formed during the nanodot fabrication. The fabricationmechanism is believed to be the sequential process of the field induced tipelongation, nanocontact formation and nanocontact breaking. The behaviour ofthe electron transport through the nanocontact was scrutinized by fitting theI–V curves to a direct tunnelling model in the low bias range. A tunnelling barrier of1.2 ± 0.3 eV betweentungsten and SiO2 was deduced. We also present the feasibility of probing the STM tip apex by the nanodots,which could be applied in in situ monitoring of tip apex variation during STM operation.