Atomic structure of ion-sputtered Fe/Ti multilayers studied by HREM

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Abstract
The atomic structure of ion-sputtered Fe/Ti multilayers (average composition FeTi2) is studied by high-resolution electron microscopy (HREM). Special attention is given to the influence of the multilayer period, Λ For 4 nm < Λ < 8 nm the Ti-rich layer is crystalline and b.c.c. For 8 nm < Λ the Fe-rich layer is also crystalline and the Ti-rich layer is mainly h.c.p. Whatever the period a chemical gradient at the interfaces is evidenced by d spacing measurements. A marked asymmetry between the two sides of a given layer is measured. These observations are interpreted in the frame of a growth model for ion-sputtered deposited layers. This model assumes that down to a constant depth a mixing of arriving atoms occurs. The calculated concentration profiles explain the different phase transitions as well as the asymmetry. An estimate of the mixing depth, 1·8 nm, is deduced from a comparison with the experimental d spacing profiles.