Langmuir–Blodgett films of C60 and C60O on Silicon: Islands, rings and grains

We show that monolayer-high islands of C60 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 μl) of low concentration (of order 10− 5M) solutions of C60 (or C60O) with low target pressures (~ 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 C60 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 C60. We attribute the origin of these features to dipolar or hydrogen bonding-mediated interactions between the C60O molecules at the water surface.