The mass density of thin a-C films prepared by PLD is determined by the parameters of the ablation process. This fact results from various concentrations of sp3 and sp2 bounded atoms in the films, that are created for different laser power densities. Thus more diamondlike or more graphite-like layers are obtained. The alternate deposition of layers with different mass densities enables the preparation of C/C- multilayers that show X-ray optical activity. In the present investigations C/C-multilayers were deposited on silicon substrates at room temperature under UHV-conditions.
The double layer thickness d was changed in the range from 74Å through 18Å. High quality interfaces and very reproducible average d-spacing resulted in an energy resolution of 0.7% for 120 period stacks. Due to chemically almost equivalent layers the chemical driving forces of atomic transport in these multilayers vanish. Thus e.g. thermal stability is observed up to 700°C for an appropriate heat treatment. The limiting factor of thermal stability is caused by SiC-formation from reactions between layer stack and silicon substrate.
In-situ ellipsometry, grazing incidence x-ray diffraction, high resolution electron microscopy (HREM) and image processing were applied for specimen characterization.