Development of a method for highly localized growth of carbon nanotubes
A method for growing carbon nanotubes on chip using highly localized
resistive heating is developed. By deliberately designing molybdenum
electrodes to be highly resistive in a very small region we create a
micrometer sized hot-zone where carbon nanotubes can be grown.
Due to the limited size of the hot-zone we are able to control the
growth time very accurately since cooling below growth temperature
is almost instant. The small size of the chamber further helps in
efficiently stopping growth by evacuation.
Effects of using different catalysts -- Fe and Ni, supported on
Al2O3 of different thicknesses or directly in contact with the
electrode and carbon feedstocks are studied using in situ
Raman spectroscopy and SEM. We find that the choice of catalyst is
crucial in this process - even more so than in similar CVD methods.
Using acetylene, C2H2, as carbon feedstock, with 1 nm iron,
Fe, supported on 5 nm aluminium oxide, Al2O3, as catalyst, we
are able to grow multi-wall nanotubes with diameters of 5-10 nm
directly on molybdenum electrodes.
With ethylene, C2H4, using the same catalyst, we grow
single-wall nanotubes with diameters in the range of 0.7-1.8 nm.
Thin multi-wall tubes are also grown using ethylene.
Using the resistive growth method we perform sequential growth of
crossed nanotubes using electric field alignment. We also develop a
process for making a RF resonator based on low temperature grown
arrays of aligned nanotubes.
Being able to keep the sample temperature down during growth
benefits the integration of carbon nanotubes with CMOS-technology as
well as bioelectronics, and also permits using low temperature
materials as building blocks for nanoelectromechanical
structures on chip. The mean temperature of our samples is 60C during growth.
chemical vapour deposition
low temperature CVD