Progress Toward Carbon-Nanotube Arrays for Probing Cells

Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio

Friday, February 01 2008

A process for deposition of presynthesized SWNTs holds great promise.

Progress has been reported in research oriented toward the goal of fabricating arrays of interconnected single-walled carbon nanotubes (SWNTs) that could serve as probes for measuring localized events within living cells. As used here, “interconnected” signifies mechanically and electrically connected to patterned metal films (interconnections) that lead to contact pads, which, in turn, enable electrical connection to external electronic instrumentation. This research poses a high economic risk because it entails pushing several technological disciplines beyond their present limits. There is no previously reported combination of fabrication techniques and processes for producing carbon nanotubes that have the required properties at the required positions and orientations on patterned metal films.

This research follows three parallel tracks: (1) photolithography and other processing to pattern interconnection metals on quartz substrates and seed metals (catalysts for growth of carbon nanotubes) on the interconnections, (2) fabrication of SWNTs and integration of the SWNT-fabrication process with the interconnection-fabrication process, and (3) for SWNTs that are in place in an array, developing strategies for chemically functionalizing the nanotubes for specific applications.

A process for fabricating the interconnections (see figure) was developed under the original assumption that vertically aligned SWNTs would be grown by chemical vapor deposition (CVD) in nanoscale holes (vias) formed at desired locations (by use of either electron beam lithography and reactive ion etching or focussed-ionbeam drilling) through a layer of silicon nitride (SiNx) covering the metal layers. It was found that the SiNx layer could not withstand the thermal cycles involved in CVD, making it necessary to abandon CVD.