* Patterned Growth:
Focused ion beam milling
as a universal template technique for patterned growth of carbon nanotubes
Ying Chen, Hua Chen, Jun Yu, James S. Williams and Vince Craig
APPLIED PHYSICS LETTERS 90, 093126
(2007)
Abstract Focused ion beam (FIB)
milling system has been used to create nanosized patterns as the template
for patterned growth of carbon nanotubes on Si substrate surface without
predeposition of metal catalysts. Carbon nanotubes only nucleate and grow
on the template under controlled pyrolysis of iron phthalocyanine at 1000
°C. The size, growth direction, and density of the patterned nanotubes
can be controlled under different growth conditions and template sizes.
Atomic force microscopy and electron microscopy analyses reveal that the
selective growth on the FIB template is due to its
special surface morphology and crystalline structure.
Patterned growth of
carbon nanotubes on Si substrates without predeposition of metal catalysts
Y. Chen and J. Yu
APPLIED PHYSICS LETTERS 87, 033103 (2005)
Abstract:Aligned carbon nanotubes (CNTs)
can be readily synthesized on quartz or silicon-oxide-coated Si substrates
using a chemical vapor deposition method, but it is difficult to grow them
on pure Si substrates without predeposition of metal catalysts. We report
that aligned CNTs were grown by pyrolysis of iron phthalocyanine at 1000
°C on the templates created on Si substrates with simple mechanical
scratching. Scanning electron microscopy and x-ray energy spectroscopy analysis
revealed that the trenches and patterns created on the surface of Si substrates
were preferred nucleation sites for nanotube growth due to a high surface
energy, metastable surface structure, and possible capillarity effect. A
two-step pyrolysis process maintained Fe as an active catalyst.
* Controlled Growth:
Improved growth of aligned carbon
nanotubes by mechanical activation
Y. Chen and L.T. Chadderton
Journal of Materials Research, Vol. 19, No. 10, Oct 2004
Abstract: Straight aligned carbon nanotubes with multiwalled
cylindrical structure have been produced by pyrolysis of iron phthalocyanine
(FePc) after ball milling treatment. The pre-ball milling treatment prevented
the formation of curved nanotubes with bamboo or conelike structures. X-ray
diffraction analysis revealed that the milled FePc has an activated and
disordered structure, which contributes a lower vaporization temperature
determined by thermal gravimetric analysis. The low formation temperature
and an increased nanotube growth rate are favorable to the formation of
cylindrical structure than bamboo tubes.
* Solid-state Formation:
The nucleation and growth of carbon nanotubes in a mechano-thermal process
Y. Chen, M.J. Conway, J.D. FitzGerald, J.S. Williams,
L.T. Chadderton
Carbon, 42 (2004) 1543
Abstract:
Separate nucleation and growth processes of carbon nanotubes were found in a mechano-thermal method in which carbon nanotubes are produced by first mechanical milling of graphite powder at room temperature and subsequent thermal annealing up to 1400 C. The ball-milled graphite contains nucleation structures (nanosized metal particles and deformed (0 0 2) layers containing pentagons), and disordered carbon as a free carbon atom source. The subsequent annealing activates the growth of two types of multi-walled nanotubes in the absence of carbon vapor. Thin nanotubes (diameter <20 nm) are formed via crystallization of the disordered carbon with the preferred formation of the (0 0 2) basal planes. Thick nanotubes (diameter >20 nm) are formed through a metal catalytic solution–precipitation process (solid–liquid–solid). In both cases, carbon nanotubes grew out from disordered carbon particles with closed tips.
