1. Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA
2. Department of Chemistry, University of California, Santa Barbara, California 93106, USA
3. Division of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts 02138, USA
4. These authors contributed equally to this work.

Correspondence to: Correspondence and requests for materials should be addressed to C.M.L. (e-mail: Email: cml@cmliris.harvard.edu).

Abstract

Nanometre-scale electronic structures are of both fundamental and technological interest: they provide a link between molecular and solid state physics, and have the potential to reach far higher device densities than is possible with conventional semiconductor technology¹,². Examples of such structures include quantum dots,which can function as single-electron transistors³,⁴ (although theirsensitivity to individual stray charges might make them unsuitable for large-scale devices) and semiconducting carbon nanotubes several hundred nanometres in length, which have been used to create a field-effect transistor⁵. Much smaller devices could be made by joining two nanotubes or nanowires to create, for example, metal–semiconductor junctions, in which the junction area would be about 1 nm² for single-walled carbon nanotubes. Electrical measurements of nanotube 'mats' have shown the behaviour expected for a metal–semiconductor junction⁶. However, proposed nanotube junction structures⁷ have not been explicitly observed, nor have methods been developed to prepare them. Here we report controlled, catalytic growth of metal–semiconductor junctions between carbon nanotubes and silicon nanowires, and show that these junctions exhibit reproducible rectifying behaviour.