NPGS  : Carbon Nanotubes

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This atomic force microscope image shows a pair of crossed single-walled carbon nanotubes. The image field is 1.5 microns square and the nanotube diameters are ~1 nm. Note that the 1 nm diameters were measured in the z direction of the AFM which gives considerably better height resolution than the lateral resolution seen in the image.

This crossed-tube device was fabricated at Rice University using a novel lithographic technique utilizing self-assembled monolayers (SAMs). First, electron-beam lithography (EBL) is used to fabricate a set of gold alignment marks on a silicon substrate covered with a thermal oxide. A SAM with a chemically inert termination is prepared the substrate. EBL is then used to expose a grid of crosses in the SAM, exposing the bare substrate. A second SAM with a chemically active termination is deposited in the exposed regions. The sample is then placed in a carbon nanotube suspension and tubes are attracted to the SAM with the active termination. After removal from the suspension, a pair of crossed tubes is located using atomic force microscopy. A final EBL step in which gold leads are aligned to the nanotubes completes the process. A full description of the lithographic technique can be found in Liu et. al, Chem. Phys. Lett. 303, 125 (1999).