Effect of ion bombardment during the low-mobility growth of metallic superlattices

The structure of sputtered Mo/Fe superlattices of periodicities 9 to 30 A grown at a substrate temperature of 300 K at various pressures and levels of low-energy ion bombardment have been studied using x-ray diffraction. The samples show the growth of an amorphous phase below 17 A periodicity and a crystalline phase above 21 A, with mixed phases in between. Limited ion bombardment reduces the coherency in the growth direction in the crystalline phase, while heavy bombardment sufficient to promote significant mixing acts to improve the coherency, but not to the level observed in films with no bombardment. The relative intensities of the average lattice spacing reflection and its most intense satellite give the composition profile change due to the ion mixing. Some ion bombardment of the iron layer markedly improves the reflectance for x rays at both low and high angles near the Bragg peak due to the average lattice spacing