Impact of Negative Line Tension on the Shape of Nanometer-Size Sessile Droplets

The sign and value of the line tension has been measured from the size dependence of the contact angle of nanometer-size sessile fullerene (C(60)) droplets on the planar SiO(2) interface, measured with atomic force microscopy (AFM). Analysis according to the modified Young's equation indicates a negative line tension, with a magnitude between -10(-11) and -10(-10) N/m, in good agreement with theoretical predictions. The experiments also indicate that droplets with contact area radii below 10 nm are in fact two-dimensional round terraces.