Thickness dependence of surface roughness and transport properties of La2/3Ca1/3MnO3 epitaxial thin films

In this work, we report on the impact of distinct growth parameters that affect the roughness and surface morphology of La2/3Ca1/3MnO3 epitaxial thin films grown by rf sputtering, namely, the film thickness and the deposition temperature. Data for films with thicknesses ranging from 2.4 to 108 nm will be presented. A correlation with transport measurements is also reported: whereas films thicker than 6 nm show the typical metal-to-insulator transition, the thinner film is insulating. The resistivity is strongly enhanced when decreasing film thickness. Nuclear magnetic resonance measurements have been used to monitor the relative concentration of the localized Mn4+ and delocalized Mn3+/4+ states. It is found that the relative intensity of the delocalized Mn3+/4+ configuration (I3+/4+) progressively lowers when reducing film thickness. Of significance could be the observation that I3+/4+ remains finite for the thicknesses corresponding to insulating films, thus suggesting that an electrically inhomogeneous state is formed in a region close to the interface with the substrate. (C) 2001 American Institute of Physics.