Summary form only given. A fast deposition method, utilizing a thermal plasma which expands into a vacuum vessel, has been used to deposit amorphous hydrogenated silicon and carbon layers (a-Si:H and a-C:H, respectively). The deposited layers are produced by admixing silane and methane (or acetylene) to the argon carrier plasma. In contrast to the conventional plasma enhanced chemical vapour deposition where the deposition is diffusion limited, in this deposition device the deposition mechanism is flow determined. As a result, the deposition rates are large, typically 100 nm/s for a-C:H and 10 nm/s for a-Si:H. The a-Si:H layers are deposited on crystaline silicon and Corning glass substrates, and the a-C:H layers are deposited on either ste...