Langmuir-Blodgett films of C-60 and C60O on Silicon: Islands, rings and grains

We show that monolayer-high islands of C-60 and C60O can be transferred from Langmuir films on a water or phenol sub-phase to oxide-terminated Si(111) substrates. Faceted islands, in some cases incorporating a foam-like morphology reminscent of that previously observed for Langmuir films at the water-air interface using Brewster angle microscopy, are formed and transferred using small amounts (100-400 mu l) of low concentration (of order 10(-5)M) solutions of C-60 (or C60O) with low target pressures (similar to 10 mN/m). However, worm-like monolayer domains are also observed under identical experimental conditions, indicating the key role that inhomogeneous solvent evaporation plays in the formation of two-dimensional fullerene aggregates on the subphase surface. While Langmuir-Blodgett multilayers of C-60 and C60O are both granular, there are significant morphological differences observed between the molecular thin films. In particular, C60O multilayers contain a relatively high density of ring (or doughnut) features with diameters in the 100-300 nm range which are not observed for C-60. We attribute the origin of these features to dipolar or hydrogen bonding-mediated interactions between the C60O molecules at the water surface. (C) 2008 Elsevier B.V. All rights reserved.