Journal - PNAS

Abstract :

We report the controlled formation and characterization of heterojunctionsbetween carbon nanotubes and different metal nanocrystals (Fe,Co, Ni, and FeCo). The heterojunctions are formed from metal-filledmultiwall carbon nanotubes (MWNTs) via intense electron beamirradiation at temperatures in the range of 450–700 °Cand observed in situ in a transmission electron microscope.Under irradiation, the segregation of metal and carbon atomsoccurs, leading to the formation of heterojunctions betweenmetal and graphite. Metallic conductivity of the metal–nanotubejunctions was found by using in situ transport measurementsin an electron microscope. Density functional calculations showthat these structures are mechanically strong, the bonding atthe interface is covalent, and the electronic states at andaround the Fermi level are delocalized across the entire system.These properties are essential for the application of such heterojunctionsas contacts in electronic devices and vital for the fabricationof robust nanotube–metal composite materials. The authors declare no conflict of interest. This article contains supporting information online at www.pnas.org/cgi/content/full/0900960106/DCSupplemental.