Imaging and Spectroscopy of Artificial-Atom States in Core/Shell Nanocrystal Quantum Dots

Current imaging scanning tunneling microscopy is used to observe the electronic wave functions in $\mathrm{InAs}/\mathrm{ZnSe}$ core/shell nanocrystals. Images taken at a bias corresponding to the $s$ conduction band state show that it is localized in the central core region, while images at higher bias probing the $p$ state reveal that it extends to the shell. This is supported by optical and tunneling spectroscopy data demonstrating that the $s-p$ gap closes upon shell growth. Shapes of the current images resemble atomlike envelope wave functions of the quantum dot calculated within a particle in a box model.