We report on a method for detectingC60and otherC2nmolecules in the vapor phase during their initial growth stage. The technique, which utilizes a Langmuir probe, was originally proposed by Fukuzawa &etal; [T. Fukuzawa, M. Shiratani, and Y. Watanabe, Appl. Phys. Lett.64, 3098 (1994)] for the detection of dust particles in silane plasmas. By measuring the positive and negative saturation currents in the afterglow plasma, the mass ratio of negative and positive ions can be determined. We found that aM−/M+=56±10occurs only for discharge times greater than 0.5 s. As most of the positively charged species are expected to be singly charged carbon, a mass ratio of 56 is close enough to be attributed to theC60molecule, in agreement with mass spectroscopy results. ©1997 American Institute of Physics.