Fine structure and possible growth mechanisms of some electrodeposited CuCo granular films

Granular thin-films of the alloy Cu100-xCox within the composition range 6 < x < 35 have been grown by electrodeposition. The films have been investig ated both magnetically and structurally and a comparison made between both types of measurements. Low field susceptibility measurements have been made which, in principle, allow us to determine the distribution of blocking te mperatures and thus make an estimate of particle sizes. Before structural e xamination, the films were thinned either electrochemically or by ion-etchi ng; both standard electron diffraction and TEM techniques have been employe d. We believe that we are able to see Go-rich regions in the vicinity of su b-grain boundaries and that it is these regions that account for the magnet ic behaviour of the samples. Whereas electron diffraction patterns from thi n sections correspond to the FCC phase only, in thicker sections, additiona l reflections corresponding to interplanar spacings that cannot be indexed in terms of an FCC phase are observed. The possible origins of these extra reflections are discussed in terms of either double-diffraction at microtwi ns or, alternatively, in terms of extended, Go-rich HCP phases formed at ma trix/twin interfaces. A possible mechanism for the growth of the HCP phase, which is a consequence of the electrodeposition technique, is discussed. ( C) 2001 Published by Elsevier Science B.V.