The development of interface roughness in reactively sputtered Ni/Ti multilayers is investigated by neutron re#ectivity measurements. The re#ectivity data of supermirrors show that the interface roughness of the layers is considerably reduced by reactive sputtering. But the degree of interdi!usion appears to remain the same. Samples prepared at various partial pressures of air clearly demonstrate that a minimum partial pressure of air is su\$cient to obtain smooth interfaces. A drastic decrease of the re#ectivity with increasing substrate roughness is observed indicating that the reactive sputtering is not su\$cient to smoothen the layers that are grown on rough substrates. 2000 Elsevier Science B.V. All rights reserved.
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