AVS 64th International Symposium & Exhibition
    Thin Films Division Thursday Sessions
       Session TF+MI+NS-ThA

Paper TF+MI+NS-ThA3
Varying Penetration Depths in ALD on High Aspect Ratio Carbon Nanotube Forests

Thursday, November 2, 2017, 3:00 pm, Room 21

Session: ALD and Nanostructures
Presenter: David Kane, Brigham Young University
Authors: D. Kane, Brigham Young University
RC. Kane, Brigham Young University
R.R. Vanfleet, Brigham Young University
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We have observed steps in the penetration depth in atomic layer deposition on tall vertically aligned multiwall carbon nanotube (MWCNT) forests. The deposition thickness at the top of the forest is greater than that at the bottom and varies in distinct steps. The MWCNT forests used were 200 μm tall with an aspect ratio of about 2000. In the thermal TMA/water process on MWCNTs, precursor pulse times ranged from 0.5s to 2s. We propose a model for banding where Al2O3 nuclei grow in each cycle, thus the number of TMA adsorption sites increases. Due to the confined geometry, Knudsen diffusion and adsorption site density determine the relationship between precursor penetration depth and exposure time. The penetration depth is inversely proportional to the square root of the precursor adsorption site density and proportional to the square root of the exposure time. We have measured the penetration depth for different bands and a good fit to our model is shown.