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Rapid and scalable method for direct and indirect microstructuring of vertical aligned carbon nanotubes

 
: Langheinrich, D.; Dörfler, S.; Althues, H.; Kaskel, S.; Lasagni, A.

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Surface and coatings technology 206 (2012), No.23, pp.4808-4813
ISSN: 0257-8972
English
Journal Article
Fraunhofer IWS ()
carbon nanotubes; chemical vapor deposition; laser interference patterning; surface modification

Abstract
Multi-walled carbon nanotube (MWCNT) films are grown by chemical vapor deposition (CVD) on silicon substrates using an alumina buffer and a Fe/Co layer as catalyst with different Fe/Co ratios. For both coatings, a scalable wet-chemical technique is applied. The highest CNT forests (100-125 μm) are obtained with Fe content between 60 and 80 wt.%. After deposition of the films, direct laser interference patterning (DLIP) method is used for fabricating micro patterns of the CNTs, using a frequency tripled Nd:YAG laser emitting 10 ns pulses. Two different approaches for fabricating periodic MWCNT arrays are presented. The first approach is the direct patterning of the CNT layer itself (CNT-DLIP) obtaining well defined line-like structures with 10 μm spatial period. By adjusting the l aser fluence (from 150 to 250 mJ cm - 2) and the number of laser pulses (from 1 to 20), the morphology (structure depth and line width) of the fabricated arrays can be varied. Thermal simulations of the CNT ablation process validate the experimental observations. The second approach involves indirect patterning of the CNTs, by fabricating line-like structures on the iron/cobalt catalyst layer (CAT-DLIP). In the last case, moderate energy densities (100 mJ cm - 2) permitted to remove the catalyst layer locally at the interference maxima positions. By altering the number of laser pulses from 1 to 20 the line width can be tuned. The CNT forests are subsequently grown on the patterned catalyst. Using Raman spectroscopy, we demonstrate that in the case of direct patterning of the CNTs (CNT-DLIP ) the chemical structure is preserved if a low number of laser pulses as well as moderate laser fluences are utilized. In the case of CAT-DLIP, the chemical structure of the grown CNTs on the patterned CAT-layer show a similar quality compared to the CNTs grown on the non-patterned CAT layer.

: http://publica.fraunhofer.de/documents/N-207004.html