Optical characteristics of nanostructured aluminium/diamond composite systems in the visible range

The inclusion of aluminium (Al) nanoparticles (NPs) in chemical vapor deposition (CVD) diamond structures was achieved by depositing Al thin films on commercial CVD single-crystal diamond plates, and then covering them by a CVD diamond thin film to encapsulate the metal NPs formed by the dewetting occurring during the CVD process. Morphology and composition are investigated, showing a peculiar structure formed by an Al/diamond composite with both Al NPs and Al2O3 islands included and surrounded in the diamond matrix, respectively. A mosaic-patterned homoepitaxial growth occurs for the capping diamond layer. The experimentally measured reflectivity matches the simulation of a system where the thickness of the Al/diamond composite layer is 1.80 +/- 0.05 mu m and the composition is 95 +/- 2 % diamond and 5 +/- 2 % Al. Simulations of the plasmonic response of Al NPs embedded in the diamond layer suggest that the decrease in transmission of the sample in the blue region of the spectrum is unlikely to be due to plasmonic absorption by the NPs. It is concluded that the shape of the transmission spectrum follows a Rayleigh-like scattering induced by the nanoporous diamond film. Ultrafast transient absorption measurements allow us to identify a sharp feature at 700 nm which can be associated with a modification of an interband transition in Al due to heating after photon absorption at 380 nm.