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 af fect 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 wi ll be presented. A correlation with transport measurements is also reported : whereas films thicker than 6 nm show the typical metal-to-insulator trans ition, the thinner film is insulating. The resistivity is strongly enhanced when decreasing film thickness. Nuclear magnetic resonance measurements ha ve been used to monitor the relative concentration of the localized Mn4+ an d delocalized Mn3+/4+ states. It is found that the relative intensity of th e delocalized Mn3+/4+ configuration (I3+/4+) progressively lowers when redu cing film thickness. Of significance could be the observation that I3+/4+ r emains finite for the thicknesses corresponding to insulating films, thus s uggesting that an electrically inhomogeneous state is formed in a region cl ose to the interface with the substrate. (C) 2001 American Institute of Phy sics.