XPS study of carbon/inconel bilayers as a function of substrate bias

X-ray photoelectron spectroscopy (XPS) was used to study the chemical content of sputter deposited carbon/inconel bilayers as a function of substrate bias voltage. The thickness of the layers was 10 Å for inconel and 12.5 Å for carbon; they have been used as the low and high index materials in X-ray multilayers that operate at 45 Å wavelength, at normal incidence. The objective was to investigate the most favourable growth conditions. The carbon layer formed a continuous film only for samples grown with a bias voltage of −40 V. Single layers of carbon and inconel were also studied as a function of substrate bias using grazing X-ray reflection (GXR) to investigate the effect of ion bombardment on the surface quality of the layers. The smoothest inconel single layers were obtained with a moderate substrate bias (−40 to −60 V) while the roughness of single carbon layers was not affected by the substrate bias. We conclude that the open structure observed in bilayers grown with substrate bias voltages other than −40 V is due to the rougher underlying inconel layer, which in turn ‘roughens’ the thin carbon layer.