Carbon nanotube material can now be produced in macroscopic quantities. However, the raw material has a disordered structure, which restricts investigations of both the properties and applications of the nanotubes. A method has been developed to produce thin films of aligned carbon nanotubes. The tubes can be aligned either parallel or perpendicular to the surface, as verified by scanning electron microscopy. The parallel aligned surfaces are birefringent, reflecting differences in the dielectric function along and normal to the tubes. The electrical resistivities are anisotropic as well, being smaller along the tubes than perpendicular to them, because of corresponding differences in the electronic transport properties.
International audienceA carbon nanotube specimen with a carbon content of 83 wt.% (95 vol.%) and a specific surface area equal to 790 m2/g (corresponding to 948 m2/g of carbon) is prepared by a catalytic chemical vapor deposition method. The nanotubes, 90% of which are single- and double-walled, are individual rather than in bundles. High-resolution electron microscopy shows a diameter distribution in the range 0.8-5 nm and Raman spectroscopy shows a high proportion of tubular carbon. Both techniques reveal a maximum in the inner wall diameter distribution close to 1.2 nm
The process of oxidation
of a copper surface coated by a layer
of graphene in water-saturated air at 50 °C was studied where
it was observed that oxidation started at the graphene edge and was
complete after 24 h. Isotope labeling of the oxygen gas and water
showed that the oxygen in the formed copper oxides originated from
water and not from the oxygen in air for both Cu and graphene-coated
Cu, and this has interesting potential implications for graphene as
a protective coating for Cu in dry air conditions. We propose a reaction
pathway where surface hydroxyl groups formed at graphene edges and
defects induce the oxidation of Cu. DFT simulation shows that the
binding energy between graphene and the oxidized Cu substrate is smaller
than that for the bare Cu substrate, which facilitates delamination
of the graphene. Using this process, dry transfer is demonstrated
using poly(bisphenol A carbonate) (PC) as the support layer. The high
quality of the transferred graphene is demonstrated from Raman maps,
XPS, STM, TEM, and sheet resistance measurements. The copper foil
substrate was reused without substantial weight loss to grow graphene
(up to 3 cycles) of equal quality to the first growth after each cycle.
It was found that dry transfer yielded graphene with less Cu impurities
as compared to methods using etching of the Cu substrate. Using PC
yielded graphene with less polymeric residue after transfer than the
use of poly(methyl methacrylate) (PMMA) as the supporting layer. Hence,
this dry and clean delamination technique for CVD graphene grown on
copper substrates is highly advantageous for the cost-effective large-scale
production of graphene, where the Cu substrate can be reused after
each growth.
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