Credit: © 2007 ACS

Covalently attaching semiconductor quantum dots (QD) on carbon nanotubes (CNTs) can oxidize the CNT surface and generate structural defects, which can affect the electronic and mechanical properties of the nanotube. Researchers at the University of Hamburg in Germany have now shown that they can, in one step, non-covalently attach QDs to CNTs and control the shape into which they grow.

Horst Weller and colleagues1 made cadmium selenide QDs using a slightly modified procedure in which there was an additional step of adding a nanotube suspension to the cadmium solution before the selenium was introduced. Using this approach, pyramid-shaped CdSe QDs were formed at high densities, and attached very closely to the CNTs. Raman spectroscopy confirmed the nanotubes were not oxidized, and that the QD–CNT interaction was a non-covalent one. Control experiments suggest that the shape of the QDs results from selective etching, followed by Ostwald ripening over time. Although other carbon allotrope surfaces were able to transform the shape of the nanoparticles, non-covalent attachment was only observed in the case of CNTs, suggesting the importance of the pi-electron system for stable attachment.

This QD–CNT material combines the outstanding electrical properties of CNTs with the unique optical characteristics of QDs, and may prove useful for various optoelectronic and photovoltaic applications in the future.