21 Jan 2005
A US team that has devised a way to make semiconducting aerogels with optical properties.
Scientists at Wayne State University, US, have assembled metal chalcogenide nanoparticles into an aerogel. The team says the combination of high surface area, quantum confinement effects and photoluminescence make metal chalcogenide aerogels attractive candidates for photocatalytic, photovoltaic and sensing applications. (Science 307 397)
Aerogels, which are highly porous structures, are typically made from metal oxides and carbon, and are electrically insulating. Metal chalcogenides are commonly used to make quantum dots. Crucially, the team’s chalcogenide aerogels retain their semiconducting properties opening up many applications.
The researchers have made aerogels from cadmium sulphide, cadmium selenide, zinc sulphide and lead sulphide nanoparticles. What's more, they believe they will be able to extend the fabrication method to other materials.
“These aerogels cover the optical spectrum from the infrared through the ultraviolet,” explains Stephanie Brock and her colleagues. “The optical features of each material can be effectively “tuned” over a substantial range by adjusting the heating profile employed.”
To prepare the aerogels, the team made nanoparticles capped with thiolates. Then they oxidized the thiolate capping groups, causing the nanoparticles to form a gel. Finally, the researchers dried the gel with supercritical carbon dioxide to maintain the pore architecture. The resulting structures contained pores 2-50 nm in diameter.
According to Brock, the materials displayed sharp, band edge photoluminescence at energies significantly blue shifted from single crystals. "Post-annealing permits the absorption energy of the material to be tuned to the red as the framework coarsens and the average crystallite size grows," she added.
The team plans to study the electrical and surface characteristics of the materials and generate them as thin-films to evaluate their potential for photovoltaic and sensing applications.
Liz Kalaugher is editor of Nanotechweb.