An efficient preparation method, which provides wedge-shaped cross-section transmission electron microscopy samples, has been developed. It was then used to investigate the structure of as-deposited cobalt multilayers on silicon substrates by rf plasma sputtering. It was found that an extended reaction takes place between Co and Si probably during the deposition. The cobalt atoms react with the silicon substrate to form an amorphous silicide layer. When the deposited layer is <3 nm thick, it entirely reacts with the substrate and can form an amorphous silicide as large as 5 nm. Above 4–5 nm thickness, growth of Co crystallites comes in competition with the formation of the amorphous silicide and limits it to 2 nm. The composition of this amorphous silicide is estimated to be Co2Si. In Co/C multilayers, the reactivity between the two materials is negligible, and the coalescence thickness of cobalt is 2–3 nm. At 2 nm, the cobalt layers are noncontinuous and very rough, whereas at 3 nm the critical thickness for crystalline nuclei coalescence has already been reached. The cobalt layers are then polycrystalline and have a reasonable roughness.
Sputtered Fe/Tb multilayers of various Fe and Tb thicknesses ͑0.22рt Fe р3.3 nm, 0.2рt Tb р1.9 nm͒ have been investigated by x-ray diffraction, Mössbauer spectrometry, and magnetic measurements in the 4.2-300 K temperature range. A compositionally modulated structure is shown with the appearance of pure amorphous iron in the center of the Fe layers thicker than 1.2 nm. When the Fe layers are thick enough ͑у2.2-2.4 nm͒, the Fe layers will crystallize. The magnetic properties ͑M ,T comp ,T c ,...͒ were analyzed in relation with Fe and Tb thicknesses and also with mean Tb composition. In agreement with the structure, the departure of magnetic properties from those of the corresponding amorphous alloys is observed when pure amorphous iron appears in the center of the layers. The dependence of the magnetic anisotropy axis on temperature and thicknesses is interpreted taking into account the composition modulation in the multilayers and the dominant magnetic subnetwork.
The hardness of Ti/TiN nanolaminated films is investigated in this study. Monolithic Ti and TiN films and Ti/TiN multilayers were deposited on silicon substrates by radio-frequency sputtering. The period thickness of multilayers was decreased from 20 to 2.5 nm. Grazing x-ray reflectometry showed that the modulation of composition of Ti/TiN multilayers exists for all the period thickness considered. From nanoindentation measurements, we determined the hardness and Young’s modulus of multilayers. Hardness increased with decreasing period thickness to go beyond the rule-of-mixture value for samples with period thickness of Λ⩽5 nm. The maximum hardness, 1.6 times higher than the value obtained by the rule of mixture, is obtained for Λ=2.5 nm. Our results are compared to a dislocation-based model previously introduced by Lehoczky.
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