Structural and chemical characterisation of Ni/Ti multilayers with TEM

Ni/Ti multilayers were prepared by argon sputtering. We observe changes of lattice parameter, strain, grain size and texture depending on the single layer thickness and the pressure of the sputter gas. Moreover the quality of the layers can be improved by including impurities during the growth of the Ni and the Ti layers. Generally the results show that such additions lead to more planar layers and to structural changes within the individual layers. Although we observe hexagonal Titanium in the as-deposited films, some of the specimens which were prepared for TEM observation reveal an fcc-Ti structure. The chemical composition of the layers has been investigated in a field emission microscope using a probe diameter of 1nm. Composition profiles were determined by evaluating EELS spectra taken at each point in an automated scan. In this way it was possible to determine residual concentrations of Ni in Ti layers lower than 0.5%. In the samples studied the interface width appears to be of the order of 4-5nm and the concentration profiles of Ni-Ti interfaces appear to be different from those of the Ti-Ni interfaces.