Tunneling and optical spectroscopy of InAs and InAs/ZnSe Core/Shell nanocrystalline quantum dots

We combine scanning tunneling spectroscopy and photoluminescence excitation spectroscopy (PLE) to study the electronic level structure and single elec tron charging effects of InAs and novel InAs/ZnSe core/shell nanocrystal qu antum dots. The two techniques provide complementary information on the ele ctronic structure of these systems. In the tunneling spectra of core InAs n anocrystals grown by colloidal chemistry, 2-7 nm in diameter, we directly i dentify atomic-like electronic quantum dot states with s and p character as two- and sixfold charging multiplets measurements are correlated with the low temperature PLE data and, surprisingly, excellent agree ment was observ ed between spacings of levels detected by the two techniques. yielding new information on the quantum dot level structure. The combined tunneling and optical spectroscopy approach was also applied to the study of InAs/ZnSe co re/shell nanocrystals, which have a high fluorescence quantum yield in the near IR range. The tunneling spectroscopy shows changes in their electronic structure compared to the cores with the s-p gap closing in thicker shells . This observation is supported by PLE spectroscopy, establishing the effec tiveness of the combined optical-tunneling spectroscopy approach in the stu dy of quantum dots.