Highly Conductive Single-Walled Carbon Nanotube Thin
Film Preparation by Direct Alignment on Substrates from Water Dispersions
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Abstract
A safe,
scalable method for producing highly conductive aligned
films of single-walled carbon nanotubes (SWNTs) from water suspensions
is presented. While microfluidic assembly of SWNTs has received significant
attention, achieving desirable SWNT dispersion and morphology in fluids
without an insulating surfactant or toxic superacid is challenging.
We present a method that uniquely produces a noncorrosive ink that
can be directly applied to a device <i>in situ</i>, which
is different from previous fabrication techniques. Functionalized
SWNTs (f-SWNTs) are dispersed in an aqueous urea solution to leverage
binding between the amine group of urea and the carboxylic acid group
of f-SWNTs and obtain urea-SWNT. Compared with SWNTs dispersed using
conventional methods (e.g., superacid and surfactants), the dispersed
urea-SWNT aggregates have
a higher aspect ratio with a rodlike morphology as measured by light
scattering. The Mayer rod technique is used to prepare urea-SWNT,
highly aligned films (two-dimensional nematic order parameter of 0.6,
5 μm spot size, via polarized Raman) with resistance values
as low as 15–1700 Ω/sq in a transmittance range of 2–80%
at 550 nm. These values compete with the best literature values for
conductivity of SWNT-enabled thin films. The findings offer promising
opportunities for industrial applications relying on highly conductive
thin SWNT films