X-Ray Optical Properties of C/C-Multilayers Prepared by Pulsed Laser Deposition (PLD)

Abstract

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.