"We are very interested in the fabrication of nano devices such as a single electron/hole tunnelling device by scanning probe microscopy [SPM] nanotechnology," Daisuke Fujita told nanotechweb.org. "Up to now we have demonstrated that gold nanodots can be transferred onto Si(111) 7x7 surfaces from a gold STM tip by the application of voltage pulses. However, the gold transfer yield - about 50% - is not enough to make continuous nanowires."

Using a silver-coated STM tip, the researchers achieved deposition reliabilities of almost 100% - that is, nearly every single voltage pulse they applied resulted in the formation of a nanodot. "Owing to this high reproducibility, it's much easier to fabricate continuous nanowires than with a gold tip," added Fujita.

Fujita and colleagues reckon the dots are made by the field-enhanced diffusion of silver atoms to the apex of the tip so that a point contact formed between the tip and the silicon surface. When the tip is removed, some of the silver atoms remain on the silicon surface because they have formed a chemical bond. Typically, the dots had a full-width half-maximum (FWHM) dimension of about 25 nm and were 2.5 nm high.

"This nanofabrication method can be applied in principle for most conductive substrates, such as the industrially important Si(100) wafer," added Fujita. "By this method we can produce nanocircuits for single electron devices and various other quantum-effect devices." Now the researchers will continue to investigate the model of tip-material transfer. Then the plan is to make a nano single electron transistor (SET) device. "Our nano SET device is aiming to achieve tunnelling of electrons and holes into the centre island, which will realize the smallest light-emitting device in the world," said Fujita.

The researchers reported their work in Applied Physics Letters.