Particle growth and the behavior of particle clouds in hydrogen-methane capacitively coupled rf plasmas are investigated. At room temperature, most for different wall temperatures and gas compositions of these particles are due to flakes of layers delaminated from the electrode surfaces. Heating of the electrodes up to 800 K and dilution by hydrogen (up to H-2:CH4=20:1) suppresses the production of the particles from the electrode surfaces. The electron temperature in the particle levitation region is controlled by introducing an additional electrode made from a grid (=gridded electrode) in between the levitation electrode and the driven electrode. If we introduce diamond seed particles (similar to 2.8 mu m in diameter) into the plasma with the gridded electrode in place, we observe nucleation of new grains (similar to 100 nm) on the surfaces of the diamond particles. On the other hand, without the gridded electrode, we do not observe nucleation but growth of amorphous carbon films on them. (c) 2005 Elsevier B.V. All rights reserved.