Towards the Growth of 3D Forests of Carbon Nanotubes: Selective Height Control using Reservoirs and Overlayers

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Chemistry, Center for Nanotechnology, Bar-Ilan University, Ramat-Gan, Israel

Despite the massive progress achieved in growing carbon nanotube (CNT) forests on substrate, apart from lithographic patterning of the catalyst, little has been done to selectively (locally) control CNT height. Varying process parameters, gases, catalysts, or underlayer materials uniformly affects CNT height over the whole substrate surface. We will show here how, by using specific thin film reservoir materials placed below the alumina underlayer, we can locally control CNT height, from no CNTs (Cu-Ag alloy reservoir), to nominal height (no reservoir), up to 2X the nominal CNT height (Fe reservoir), up to 4X the nominal CNT height (Mo reservoir).

Additionally, we recently published two papers showing how a copper or nickel overlayer (stencil or bridge) placed above the catalyst surface during pre-annealing or during CNT growth deactivates the catalyst.3,4 We showed how we could pattern regions with CNTs and without CNTs by simply annealing the sample with a patterned overlayer positioned above its surface. We thus synthesized patterned CNT forests using a simple process, without the need for lithography.

We can now combine the overlayer technique with one of the above-mentioned reservoirs (no reservoir, Cu/Ag reservoir, Fe reservoir, or Mo reservoir) to further modulate CNT growth by offsetting some or all of the growth enhancements achieved using the reservoirs. We will show examples of growth with patterned regions of CNTs with different CNT heights (or without CNTs) that combine the reservoir and the overlayer techniques. This modulation of the CNT height is a significant improvement compared to the "CNTs (one height) / no CNTs" patterning that has been achieved using lithography of the catalyst, and moves us closer to building 3D architectures of CNTs.









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