Ion beam sputtering system under ultra high vacuum was used to deposit two-layer C/a-Si thin films on the Si(100) substrates at room temperature (RT). Carbon (C) layer thickness was fixed at 100 nm and amorphous silicon (a-Si) was varied at 5 nm and 50 nm. Rapid thermal annealing was performed to investigate the formation of SiC nanoparticles (np-SiCs) at 750-900 degrees C for 0.5 min. Field emission scanning electron microscope (FESEM), Raman spectroscopy and X-ray diffraction were used for the characterization of nanoparticle formation, evolution of bonding between Si and C reaction and phase formation, respectively. No particle appears on the surface of two-layer C/a-Si films deposited at RT and post annealed at 750 degrees C. Many np-SiCs were formed at 900 degrees C on the surface of films with thin underlying a-Si of 5 nm but not in the two-layer film with thick a-Si of 50 nm. The sample with thinner a-Si film on bulk Si(100) has lower activation energy for the diffusion of Si atoms in the film and bulk to react with C to form np-SiC at 900 degrees C compared to the sample with thicker a-Si film. A mechanism of np-SiCs formation on the Surface of two-layer C/a-Si films using thermal annealing was proposed and discussed. (C) 2008 Elsevier B.V. All rights reserved.