Fabrication and Conductive Properties of Multilayered Ultrathin Films Designed by Layer-by-Layer Assembly of Water-Soluble Fullerenes

Fullerene ultrathin films were fabricated by layer-by-layer (LbL) assembly of an anionic fullerene C₆₁(COO⁻)₂ (FDCA) and poly(diallyldimethylammonium chloride) (PDDA) or a cationic fullerene C₆₀C₂H₄N(CH₃)₂⁺ (FMAC) and poly(sodium 4-styrenesulfonate) (PSS). The dynamic light scattering and ζ-potential measurements revealed that both water-soluble fullerenes are stably dispersed as polyelectrolytes with a diameter of 20−70 nm for FDCA and 60−180 nm for FMAC in aqueous solutions. In spite of such large fullerene aggregates, the thickness of fullerene LbL films increased regularly by a few nanometers with each deposition, and the resultant LbL films were homogeneous. For FMAC/PSS LbL films, the monolayer thickness was evaluated to be 4 nm for FMAC and 0.5 nm for the PSS layer. In other words, the volume fraction of the fullerene moiety is as high as ∼80 vol %. The conductivity of fullerene LbL films was comparable to that of a C₆₀-dispersed polystyrene film with a similar fullerene fraction, suggesting that there exist effective percolating networks due to the high fullerene fraction in the LbL films. The electron mobility of FMAC/PSS LbL films was as high as 3 × 10⁻⁵ cm² V⁻¹ s⁻¹, which is comparable to the hole mobility of poly(p-phenylenevinylene) LbL films reported previously.