Technique Creates Bent Nanotubes by Manipulating Electric Field

Researchers at the University of California, San Diego (UCSD) have made carbon nanotubes bent in sharp predetermined angles. This technical advance could lead to use of the long, thin cylinders of carbon as tiny springs, tips for atomic force microscopes, smaller electrical connectors in integrated circuits, and in many other nanotechnology applications

Nanotubes can be made almost perfectly straight in special chambers of gas plasma. However, the creation of sharp bends is difficult because once a growth phase of nanotubes is interrupted, the catalyst particles at the tips of the growing nanotubes become encased with carbon, blocking future growth. A key to the researchers successful growth of bent nanotubes involved the discovery of a technique to prevent the unwanted carbon from encasing the catalyst between growth steps.

The strong alignment of nanotube growth was exploited with the direction of electric field lines. After growing an aligned array of straight nanotubes, the orientation of electric field lines was switched 90° to make L-shaped tubes. More orientation changes were made which created “zigzags.”

Carbon nanotubes hold great promise because of their exceptionally strong mechanical properties, their ability to efficiently carry high densities of electric current, and other unique electrical and chemical properties. A plasma enhanced chemical vapor deposition technique was used to grow about 2 billion nanotubes per square centimeter on silicon wafers seeded with nickel catalyst nanoparticles.

One possible use for the bent nanotubes could be to improve the performance of atomic force microscopy – the use of a mechanical probe to magnify rigid materials at the atomic scale to produce 3-D images of the surface.

The bent nanotubes also could be used as replacements for conventional electrical connectors made of metal wires in ever-smaller integrated circuits. Such wires are roughly 70-nm wide, but nanotube connectors as thin as 1.2 nm are theoretically capable of supplying sufficiently large electric currents to integrated circuits.

Using a modification of the approach to make zigzag nanotubes, the researchers also produced parallel arrays of T- and Y-shaped nanotubes that could be used to make fuel cells more efficient. These arrays of parallel, branched nanotubes could act as 3-D scaffolding for platinum catalyst particles. High densities of platinum catalyst-tipped nanotubes could enable fuel cells produce electricity more efficiently.


Fig. 1. UCSD researchers exploited the strong alignment of nanotube growth with the direction of electric field lines to create tailor-made bends.

Fig 2. Nanotube connectors as thin as 1.2 nm are theoretically capable of supplying sufficiently large electric currents to integrated circuits.

Visit http://ucsdnews.ucsd.edu/newsrel/general/JPC_AuBuchon.asp