1 February 2012
This method enables the introduction of carbon nanotubes onto all types of silicon-based devices and silicon surfaces.
The purpose of the invention is to covalently attach functionalized carbon nanotubes to silicon. This step allows for the introduction of carbon nanotubes onto all manner of silicon surfaces, and thereby introduction of carbon nanotubes covalently into silicon-based devices, onto silicon particles, and onto silicon surfaces.
Single-walled carbon nanotubes (SWNTs) dispersed as individuals in surfactant were functionalized. The nanotube was first treated with 4-t-butylbenzenediazonium tetrafluoroborate to give increased solubility to the carbon nanotube; the second group attached to the sidewall of the nanotube has a silyl-protected terminal alkyne that is de-protected in situ. This gives a soluble carbon nanotube that has functional groups appended to the sidewall that can be attached covalently to silicon. This reaction was monitored by UV/vis/NJR to assure direct covalent functionalization.
Once the reaction to form the appropriately functionalized carbon nanotube was complete, the nanotube solution was passed through a plug of glass wool to remove particulates. This filtered solution was then flocced by diluting with acetone, and filtered through a Teflon membrane. The collected solid was dispersed in dimethylformamide (DMF) with sonication and filtered once again through a Teflon membrane. The functionalized material was then dispersed in dry DMF and assembled onto silicon by hydrosilation. The assembly was conducted by treating the nanotube solution with a catalytic amount of triphenylcarbonium tetrafluoroborate and submersing a hydrogen-passivated silicon sample in the solution. The assembly mixture was agitated with warming for 12 hours. After that time, the silicon sample was rinsed with organic solvent and dried with a stream of nitrogen. The assembly was characterized by AFM (atomic force microscopy).
The most immediate and obvious use of this procedure is the covalent attachment of carbon nanotubes onto silicon. This method allows for the attachment of individual (not bundles) carbon nanotubes. With this methodology, the highest temperature required to regenerate the pristine carbon nanotube is 450 °C.
Although other methods exist to introduce carbon nanotubes into silicon- based devices, this methodology is selective for silicon and allows for the generation of working devices at a much lower temperature.
This work was done by James M. Tour, Christopher A. Dyke, Francisco Maya, Michael P. Stewart, Bo Chen, and Austen K. Flatt of Rice University for Johnson Space Center.