Trapping Individual Carbon Nanotubes
A technique to deterministically manipulate individual Carbon Nanotubes (CNT) has been the brick-wall for the boom of CNT based devices. Here we demonstrate dielectrophoresis as an efficient technique to trap individual Single Walled Carbon Nanotubes (SWCNT) and Multi Walled Carbon Nanotubes (MWCNT). A coarse control on the number of nanotubes deposited was achieved by controlling the applied voltage and duration of deposition; additionally, a circuit that cuts off the electric field necessary for further CNT deposition after one single CNT deposition has been used. By using an external series resistance during dielectrophoresis, higher than the contact resistance of the carbon nanotube obtained after dielectrophoresis, we are able to limit the deposition to individual nanotubes. The contact resistance of a single SWCNT obtained by the coarse technique was found to be 80 MΩ. Hence we chose a limiting series resistance of 1 GΩ. P-type silicon substrate with resistivity of 0.1-0.5 Ωcm with thermal oxide of 200 nm was used as substrate. Cr/Pt (5nm/50nm) electrodes were patterned by conventional photolithography and lift-off process. SWCNT’s and MWCNT’s produced by CVD process were dispersed in DI water with 1wt% surfactant SDS. The solution was sonicated and centrifuged to remove impurities. An ac signal of 5 MHz with and without series resistance was used to perform dielectrophoresis. Around 20 µl of the solution was deposited and deposition time of 120 seconds and 300 seconds were used for SWCNT’s and MWCNT’s respectively. The yield is better in the case of SWCNT’s because they form better electrical contact with the electrodes than the MWCNT’s after dielectrophoresis. The proposed fabrication is based on materials compatible with CMOS process. This opens doors to easily study individual nanotubes and to integrate CNT based devices in CMOS technology.
Record created on 2009-07-15, modified on 2016-08-08