Imaging energy flow and excited states

Interaction and energy transfer between QDs and other molecules are important for applications in biological imaging, solar cell and photocatalysis. We use optically assisted STM to study absorption and intermolecular energy transfer between single quantum dots (QDs) and carbon nanotubes (CNTs). Single PbS, CdSe, CdSe/ZnS QDs and CNTs are deposited onto gold, silicon, crystalline silicon carbide (c-SiC), amorphous silicon carbide (a-SiC) and epitaxial graphene on SiC surfaces by matrix-assisted dry contact transfer. Adsorbed molecules are excited with modulated 532 nm light and the modulated tunneling current proportional to the optical absorption signal is detected by STM with a lock-in amplifier. Using the STM, we can move the QDs and CNTs to investigate energy transfer in real space.

Recently, we have added a tunable and femtosecond MaiTai laser (690-1100 nm) to extend our spectral and temporal range.

L. Nienhaus, J.J. Goings, D. Nguyen, S. Wieghold, J. Lyding, X. Li and M. Gruebele, “Imaging excited orbitals of quantum dots: experiment and electronic structure theory”, J. Am. Chem. Soc., 137 (46), 14743-14750 (2015).