Abstract by David Kane
Physics and Astronomy
Richard Vanfleet, Robert Davis
Varying Penetration Depths in Atomic Layer Deposition on High Aspect Ratio Carbon Nanotube Forests
Atomic Layer Deposition (ALD) which uses alternating pulses of at least two precursors to deposit single atomic layers, provides a method for thin film deposition on high aspect ratio structures. Carbon Nanotube (CNT) forests are a high aspect ratio structures which could be used to make a number of devices. We have observed steps in the penetration depth during ALD on tall CNT forests. The deposition thickness at the top of the forest is greater than that at the bottom and varies in distinct steps. Existing ALD models cannot explain these steps. We propose a modification to the models that can explain the step formation. In this modification, the low density of nucleation sites on nanotubes means each site grows as an isolated island of deposited material. Each new layer increases the number of places for the next pulse of precursor to absorb, increasing the consumption of the available precursor, and limiting the penetration of the subsequent pulses. We have measured the steps for our Al2O3 ALD process and good fits to our model are observed.