Development of a method for highly localized growth of carbon nanotubes

Doktorsavhandling, 2008

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.