Growth of Aligned MWNT Arrays Using a Micrometer Scale Local-Heater at Low Ambient Temperature

Abstract

Ambient room temperature growth of aligned multi-walled carbon nanotube arrays on micrometer scale local heaters is demonstrated. High growth rates of up to 8.8 microm per second have been achieved and the growth has been monitored in situ using optical microscopy. The growth starts and ends abruptly over the length of the local heater. The terminal length of the nanotubes shows a clear dependence on growth temperature and small inhomogeneities in temperature across the heater are seen to lead to interesting microstructure of the arrays. The activation energy for growth was seen to be consistent with earlier reports for acetylene growth of nanotubes on iron catalysts.

Origin of periodic rippling during chemical vapor deposition growth of carbon nanotube forests

“…Thus, the rippling is not evenly distributed across the forest, unlike the random distributions in several previous reports [2,3]. The distribution observed here is different than a previously observed nonrandom distribution [8].…”

“…Dittmer et al [8] see a non-random distribution of ripples in their forests, though their distribution is essentially the opposite of the present report (straight nanotubes on the edges). They explain their ripples as a result of mechanical interaction between nanotubes and a non-uniform growth rate across their small forests that is in turn a result of a non-uniform temperature across their sample due to their local heating process.…”

“…In some previous reports, the ripples were observed to form only at the base of the forest [6,7]. Here, the ripples extend for a significant portion of the forest height, as seen in an earlier report [8]. Furthermore, all nanotubes on the forests' sidewalls participate in the rippling; no straight nanotubes are visible, in contrast to several other previous studies [2,3].…”

“…Under certain growth conditions, the meandering becomes highly ordered, coherent, and synchronized over lengths of hundreds of lm such that the sidewalls of the forest have a rippling pattern on them. Previous reports of ripples on as-grown forests, such as in the present report, include ripples on forests grown with externally applied forces in situ [1], wandering nanotubes in forests due to specific catalyst pretreatment and preparation methods [2][3][4][5], ripples near the base of tall forests [6,7], and ripples due to a temperature non-uniformity in micrometer scale local heating [8]. A similar rippling pattern can also occur on forests (composed of initially straight nanotubes) that are intentionally subjected to externally applied mechanical compression ex situ [9][10][11].…”

“…A similar rippling pattern can also occur on forests (composed of initially straight nanotubes) that are intentionally subjected to externally applied mechanical compression ex situ [9][10][11]. The interactions between nanotubes have previously been shown to be important for forest morphology [6][7][8][12][13][14][15][16][17][18][19], and will be considered here.…”