Characterization of 12-8-diacetylene Langmuir-Blodgett films by scanning-force microscopy

Multilayers of 12-8-diacetylene (10,12-pentacosadiynoic acid) films prepared by the Langmuir-Blodgett technique on ordinary microscope and indium tin oxide coated glass were characterized by scanning-force microscopy (SFM) before and after polymerization. Well-resolved molecular images were obtained in monomeric diacetylene films over areas as large as 60×60 ${\mathrm{nm}}^2$. After exposing the films to uv radiation for polymerization it was found that the layer thickness decreased by approximately 10% while lattice parameters changed nearly by 5%. Also it was found that the roughness increased upon polymerization and the molecular scale images were better resolved in one lattice direction than in the other. The better resolved direction may be the polymer backbone of the film suggesting that the force between the SFM tip and the sample is strong enough to penetrate through the ${\mathrm{C}}_{12}$-alkyl chains without seriously damaging the film.