Stress development in Ni/C-multilayers on Si-substrates with increasing period number

For Ni/C X-ray optical multilayers, fabricated by pulsed laser deposition (PLD) at room temperature with typical period thickness d approximately=4.0 nm, stress is evaluated with growing period number up to the layer stack delamination. The amorphous/nano-crystalline structure of the Ni/C-layers does not allow to determine the stress state in the multilayers by X-ray diffraction directly. Therefore the stress state was only analyzed in a few micrometer thick surface region of the Si-substrate using a single crystal X-ray method. The obtained results were compared with the curvature of the Si-surface obtained by X- ray measurements, too. The found dependence of the substrate stresses on the total layer thickness points at low compressive stresses in the PLD- fabricated Ni/C-multilayers below-100 MPa and applies at least up to a total layer thickness of 1200 nm (300 periods). For larger period numbers the experimental data hint at an increase of the compressive stresses in the Ni/C-multilayer. A partial delamination of the layer stack was observed at 900 periods.