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 C(61)(COO(-))(2) (FDCA) and poly(diallyldimethylammonium chloride) (PDDA) or a cationic fullerene C(60)C(2)H(4)N(CH(3))(2)(+) (FMAC) and poly(sodium 4-styrenesulfonate) (PSS). The dynamic light scattering and zeta-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 approximately 80 vol %. The conductivity of fullerene LbL films was comparable to that of a C(60)-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 x 10(-5) cm(2) V(-1) s(-1), which is comparable to the hole mobility of poly(p-phenylenevinylene) LbL films reported previously.