Nitrogen-doped multiwalled carbon nanotubes (CN
x
MWNTs) have been cut to an average length of ∼1 μm
by room-temperature acid treatment. Imaging of the surface morphology of the CN
x
MWNTs (x = 2−5%)
after sonication in acid or in ethanol (as a control) allowed the relationship between surface structure and
acid cutting to be characterized. The effect of the acid treatment on the electrical conductance of the CN
x
MWNTs was also determined. The conductance of acid-treated CN
x
MWNTs was found to vary significantly
within the sample and to be lower than the value of 1.0 G
0 observed for as-produced CN
x
MWNTs. The
G
−
V curves reported for acid-treated CN
x
MWNTs had an average slope of 0.19 G
0/V, which is significantly
smaller than the average of 0.70 G
0/V measured for as-produced CN
x
MWNTs. Acid-treated CN
x
MWNTs
exhibited a more rapid electrical breakdown with larger current steps, indicating the breakdown of several
MWNT layers simultaneously.
Biomolecule-functionalized carbon nanotubes (CNTs) combine the molecular recognition properties of biomaterials with the electrical properties of nanoscale solid state transducers. Application of this hybrid material in bioelectronic devices requires the development of methods for the reproducible self-assembly of CNTs into higher-order structures in an aqueous environment. To this end, we have studied pattern formation of lipid-coated Fe-filled CNTs, with lengths in the 1-5 mm range, by controlled evaporation of aqueous CNT-lipid suspensions. Novel diffusion limited aggregation structures composed of endto-end oriented nanotubes were observed by optical and atomic force microscopy. Significantly, the lateral dimension of assemblies of magnetized Fe-filled CNTs was in the millimeter range. Control experiments in the absence of lipids and without magnetization indicated that the formation of these long linear nanotube patterns is driven by a subtle interplay between radial flow forces in the evaporating droplet, lipid-modulated van der Waals forces, and magnetic dipole-dipole interactions.
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