AVS 53rd International Symposium
    Advanced Surface Engineering Wednesday Sessions
       Session SE-WeM

Paper SE-WeM6
Ta Nanocolumns Grown by Glancing Angle Deposition: Effect of Surface Diffusion on Column Branching, Merging, and Growth Competition

Wednesday, November 15, 2006, 9:40 am, Room 2007

Session: Glancing Angle Deposition
Presenter: C. Zhou, Rensselaer Polytechnic Institute
Authors: C. Zhou, Rensselaer Polytechnic Institute
D. Gall, Rensselaer Polytechnic Institute
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Periodic arrays of Ta nanocolumns were grown by glancing angle sputter deposition onto patterned substrates at growth temperatures T@sub s@ ranging from 200 to 900 @super o@C. The substrates were patterned using colloidal self-assembly of 260-nm-diameter SiO@sub 2@ nanospheres that form a close-packed monolayer. At low growth temperatures, T@sub s@ @<=@ 500 @super o@C, the 200-nm-wide and 500-nm-tall Ta columns replicate the hexagonal arrangement of the initial pattern. However, the arrays randomize with increasing T@sub s@ and completely degrade at T@sub s@ = 900 @super o@C, due to strong inter-pillar competition caused by the increasing adatom diffusion length with increasing T@sub s@. The competitive growth mode results in a decrease in the pillar separation and pillar number density, an increase in the average pillar width, the accelerated growth of some pillars at the cost of others which die out, and an increased probability for the merging of neighboring pillars. In addition, kinetic roughening at pillar tops leads to the branching of some pillars. The fraction of branched pillars decreases with increasing T@sub s@, due to an increased lateral diffusion length, from 30% at 200 @super o@C to 4% at 700 @super o@C. The branching at high T@sub s@ @>=@ 500 @super o@C occurs during the nucleation stage where multiple nuclei on a single SiO@sub 2@ sphere develop into subpillars during a competitive growth mode which, in turn, leads to intercolumnar competition and the extinction of some nanopillars.