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Description:
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A method offering precise control over the synthesis conditions to obtain carbon
nanotube (CNT ) samples of a single chirality (metallic or semi -conducting ) is presented .
Using this nanolithographic method of catalyst deposition , the location of CNT growth is
also precisely defined .
This technique obviates three significant hurdles that are preventing the exploitation
of CNT in micro - and nano -devices . Microelectronic applications (e .g . , interconnects ,
CNT gates , etc . ) require precisely defined locations and spatial density , as well as
precisely defined chirality for the synthesized CNT . Conventional CVD synthesis
techniques typically yield a mixture of CNT (semi -conducting and metallic types ) that
grow at random locations on a substrate in high number density , which leads to extreme
difficulty in application integration .
Dip Pen Nanolithography (DPN ) techniques were used to deposit the catalysts at
precisely defined locations on a substrate and to precisely control the catalyst
composition as well as the size of the patterned catalyst . After deposition of catalysts , a
low temperature Chemical Vapor Deposition (CVD ) process at atmospheric pressure
was used to synthesize CNT . Various types of catalysts (Ni , Co , Fe , Pd , Pt , and Rh ) were
deposited in the form of metal salt solutions or nano -particle solutions . Various characterization studies before and after CVD synthesis of CNT at the location of the
deposited catalysts showed that the CNT were of a single chirality (metallic or semiconducting )
as well as a single diameter (with a very narrow range of variability ) .
Additionally , X -ray photoelectron spectroscopy (XPS ) was used to characterize the
deposited samples before and after the CVD , as was lateral force microscopy (LFM ) for
determination of the successful deposition of the catalyst material immediately after
DPN as well as following the CVD synthesis of the samples . The diameter of the CNT
determines the chirality . The diameter of the CNT measured by TEM was found to be
consistent with the chirality measurements obtained from Raman Spectroscopy for the
different samples . Hence , the results showed that CNT samples of a single chirality can
be obtained by this technique . The results show that the chirality of the synthesized CNT
can be controlled by changing the synthesis conditions (e .g . , size of the catalyst patterns ,
composition of the catalysts , temperature of CVD , gas flow rates , etc . ) . |