INCONEL CARBON MULTILAYERS FOR X-RAY MIRRORS

The objective is to find new materials for the fabrication of X-ray mi rrors with high reflectance at 45 Angstrom wavelength at normal incide nce. We have examined multilayers of inconel and carbon, which have hi gh theoretical reflectivities. Planar magnetron sputtering was used to fabricate mirror samples (period = 22.5 Angstrom) on silicon substrat es. Our best 30-period inconel/carbon multilayers had a reflectivity o f 0.3%, which was about a factor of 20 below the theoretical maximum ( 5.5%). Experimental details presented here include our use of an in si tu ellipsometer to monitor the thickness of the layers and to provide information on the early stages of film growth and interdiffusion at t he interfaces. Interdiffusion was found to occur at the carbon-on-inco nel interface because of the rough underlying inconel layer, but not a t the inconel-on-carbon interface because of the smooth underlying car bon layer. Interdiffusion at the carbon-on-inconel layer was also foun d to increase with the number of layers. The accuracy of ellipsometry for monitoring film thickness during deposition was limited by the the oretical model used for the optical constants of the film. As a result , we were not able to improve on the standard technique of 'timing' fo r control of layer thicknesses. (C) 1997 Elsevier Science S.A.