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February 27, 2006

Self assembly advance: self assembled nanofold network

Efforts to link nanotubes have usually begun with the most familiar kind, cylinders whose structure is equivalent to one or more rolled-up sheets of a layered crystal like graphite. Now researchers at Lawrence Berkeley National Laboratory's National Center for Electron Microscopy (NCEM) and the Christian Albrechts University of Kiel, Germany, have found a completely new way to form complex networks of nanotubes. The researchers describe their results in the March 3, 2006 issue of Physical Review Letters, now available online. The new method causes extensive hexagonal networks of tubes, intricately branched and connected, to form in less than a second on the surface of a layered crystal. The tubes themselves are prismatic folds, having the cross section of a pitched roof.

A multilayered crystal of vanadium selenide, seen in a field of view roughly as wide as a red blood cell: after enough copper atoms penetrate the uppermost layers of the crystal, a hexagonal network of nanofold tubes appears spontaneously, each tube 30 nanometers across and enclosing an empty space 4 nanometers high.

There are many practical questions as well. Surface nanotube networks suggest numerous applications, including networks of pipes for the storage and transport of minute quantities of materials, or templates for the fabrication of nanowire networks.

"There are many exciting follow-ups to investigate in these systems," says Dahmen, "ranging from whether and how the tubes can be filled with liquids or with metal atoms to form wires, to controlling the sizes and patterns of the networks, to understanding the atomic structure of their junctions."

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In previous self-assembly research..there was progress made on targeted self-assembly. Possibly these capabilities could be combined.

Success in nanoscale self-assembly could make the transition to MNT easier by allowing more complex structures to be self assembled and less mechanochemistry to be required to "finish" a MNT product. More capability could be available sooner. If there was a progression in the number of mechanochemistry operations per second that are performed by a particular system or device, then by shifting more operations to more capable self-assembly the threshold for useful mechanochemisty would be reduced and the sooner MNT would be useful.

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