"This is the first time that single-walled carbon nanotubes have been joined to form a molecular junction," Florian Banhart of the University of Ulm told nanotechweb.org. "Normally, crossing tubes would never join even if they were pressed together mechanically - in the electron beam we create vacancies (missing carbon atoms) in the tubes that promote joining when two tubes cross each other."

The scientists created "X"-shaped molecular junctions between single-walled carbon nanotubes by irradiating crossing tubes heated to 800°C. They also formed "Y" and "T" junctions by using further irradiation to remove one of the arms of an X-junction.

"Molecular junctions of single-walled nanotubes would be the key elements of electronic devices based on nanotubes," added Banhart. "For example, a three-terminal device could act as a transistor if the semiconducting properties of the tubes were appropriate. A way to connect nanotubes with each other is therefore essential in the development of molecular nanoelectronics."

Now the scientists want to optimize parameters such as the temperature of the system and the electron energy. "We are trying to carry out these experiments with higher selectivity between the tubes," said Banhart. "However, the controlled arrangements of tubes such as to constitute a real network is still an open problem."

The scientists reported their work in Physical Review Letters.