Defect and nanocrystal cathodoluminescence of synthetic opals infilled with Si and Pt

Synthetic opals-composed of 250 nm amorphous silica spheres closed packed in a face centered cubic structure-have been infilled with silicon, platinum, and with Si and different Pt contents. The luminescent properties of these composites have been investigated by cathodoluminescence (CL) microscopy and spectroscopy. CL emission is influenced by the material used to infill the pores of the opal matrix. CL spectra of all the samples investigated show two well-known bands, associated with the defect structure of the silica spheres, centered at about 1.9 and 2.7 eV, respectively. Emission in the 2.15-2.45 eV range, particularly intense in opal-based composites with a high Pt content, is tentatively associated with SiO2 defects involving silicon clusters. A CL band peaked at about 3.4 eV as well as a band in the 1.50-1.75 eV range, whose peak position seems to be affected by the Pt content of the samples, are associated with the presence of Si nanocrystals. The behavior of these emissions suggests that both are related to defect states at the interface between Si nanocrystals and SiO2 forming the opal spheres

Scanning tunneling spectroscopy study of silicon and platinum assemblies in an opal matrix

Scanning tunneling microscopy and scanning tunneling spectroscopy (STS) are used to investigate the local electronic behavior of Pt-Si nanostructures fabricated in an opal matrix formed by silica spheres of 250 nm diameter. Si and Pt are regularly distributed inside the opal pores and form nanoscale metal-semiconductor-metal junctions. Normalized differential conductance curves enable us to study the distribution of Pt and Si and to detect the presence of regions showing a surface band gap in the range 0.5-0.8 eV, possibly associated with the formation of silicides. STS appears as a suitable technique for the electrical characterization of opal-based nanostructures