Noble Metal Nanocluster Formation in Epitaxial Perovskite Thin Films.

We studied the synthesis of nanocomposite materials consisting of noble metal clusters embedded in an oxide semiconductor matrix. The embedded nanostructures form in a simple self-organized single-step growth process. The primary interest is in developing materials for photo-electrochemical energy conversion where spatially inhomogeneous band structures can enhance photogenerated charge separation and carrier extraction from a semiconductor. We show that spontaneous segregation of metallic Ir occurs during the initial growth of an Ir:SrTiO thin film. Cross-sectional transmission electron microscopy suggests that the nanoscale Ir clusters are epitaxial with the host lattice, and their presence is not detectable by surface morphology measurements.