Sept. 9, 2002

Nano-Welding Creates Tiny Junctions

Researchers have discovered how to weld together single-walled carbon nanotubes, pure carbon cylinders with remarkable electronic properties, which could pave the way for controlled fabrication of molecular circuits and nanotube networks.

Pulickel Ajayan, professor of materials science at Rensselaer, and his colleagues in Germany, Mexico, the U.K., and Belgium used irradiation and heat to form the welded junctions.

This is the first time single-walled nanotubes have been welded together, although multi-walled nanotubes with junctions previously have been created using growth techniques. The electrical properties of single-walled nanotubes surpass those of multi-walled tubes, which is why so many researchers have been anxious to try this experiment, said Ajayan.

"No one knew if junctions could be created," said Ajayan. "Single-walled carbon nanotubes are perfect cylinders without any defects, but in order to create junctions between them, inter-tube carbon-carbon bonds need to form. The irradiation and heating process we use creates just enough defects for these bonds to form without damaging their electrical properties."

The results were obtained after several years of ongoing experimentation. The difficulty was finding nanotubes that cross and touch, which are critical for the initiation of inter-tube links. "Unfortunately, we can't control this type of alignment just yet," Ajayan noted.

The researchers used a special electron microscope that has the capability to irradiate and produce the heat necessary for the experiment. The high-voltage microscope, located in Stuttgart, Germany, is one of only a few worldwide.