Abstract

Atomic Layer Deposition (ALD) of Al2O3 on tall multiwalled carbon nanotube forests shows concentration variation with the depth in the form of discrete steps. While ALD is capable of extremely conformal deposition in high aspect ratio structures, decreasing penetration depth has been observed over multiple thermal ALD cycles on 1.3 mm tall multiwalled carbon nanotube forests. SEM imaging with Energy Dispersive X-ray Spectroscopy elemental analysis shows steps of decreasing intensity corresponding to decreasing concentrations of Al2O3. A study of these steps suggests that they are produced by a combination of diffusion limited delivery of precursors with increasing precursor adsorption site density as discrete nuclei grow during the ALD process. This conceptual model has been applied to modify literature models for ALD penetration on high aspect ratio structures, allowing several parameters to be extracted from the experimental data. The Knudsen diffusion constant for trimethylaluminum (TMA) in these carbon nanotube forests has been found to be 0.3 cm2s-1. From the profile of the Al2O3 concentration at the steps, the sticking coefficient of TMA on Al2O3 was found to be 0.003.

Degree

College and Department

Physical and Mathematical Sciences; Physics and Astronomy

Rights

http://lib.byu.edu/about/copyright/