Nanotubes Stay in Step


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Carbon nanotube on sapphire substrate


Sometimes a rough start makes for a smooth finish. Carbon nanotubes are excellent candidates for components of tiny nanoelectronic circuits, but their organization into ordered arrays on surfaces remains a major obstacle.




In an effort to manipulate their growth, the research group of Dr. Ernesto Joselevich of the Institute’s Materials and Interfaces Department experimented with the application of electrical fields to control the direction of nanotube formation on various surfaces. When a sapphire surface was chosen, the group was surprised to observe a beautiful parallel arrangement of nanotubes formed in an orientation completely independent of the electrical field. Closer examination of the sapphire revealed that it had not been cut precisely along the crystal plane, so the surface consisted of a series of terraces separated by steps of atomic dimensions. The iron nanoparticles used as a catalyst to produce nanotubes proved to be a lazy partner that didn't like to “climb stairs” but instead preferred to “glide” along the edge of the step. In its wake lay an organized trail of nanotubes formed snugly along this edge.  The nanotubes even followed kinks in the steps caused by defects in the crystal. This resulted in either straight or zigzag-shaped tubes, which are expected to have particularly interesting electronic properties.
“The direction and shape of the atomic steps can be controlled simply by the cut of the crystal,” says Joselevich. “This could lead to intriguing nanotube architectures.” Exploiting these small steps could mean a big step toward large-scale nano-fabrication to produce different nanowire arrangements in a controlled fashion.
Full details of the study appear in the cover story of the prestigious journal Angewandte Chemie
Dr. Ernesto Joselevich’s research is supported by the Ilse Katz Institute for Material Sciences and Magnetic Resonance Research; the Asher and Jeannette Alhadeff Research Award; Sir Harry A.S. Djanogly, CBE, UK; the Philip M. Klutznick Fund for Research; and Sylvia and Henry Legrain, Spain. Dr. Joselevich is the incumbent of the Dr. Victor L. Ehrlich Career Develop-ment Chair.