Imaging and spectroscopy of individual CdSe nanocrystals on atomically resolved surfaces

Abstract

Imaging and spectroscopy of individual CdSe nanocrystals have been performed with the scanning tunneling microscope (STM) on atomically resolved hydrogenated Si(100) surfaces. The CdSe nanocrystals have been deposited under vacuum onto the surface by using the pulse valve method. Two different types of CdSe nanocrystals, capped either with trioctylphosphine oxide ligands or with cadmium stearate ligands, have been studied to optimize their anchoring to the surface. The I(V) spectroscopy shows a characteristic resonant excitation spectrum through the unoccupied levels of the nanocrystals with no significant charging effect. This suggests that the nanocrystals are weakly coupled to the surface, thus requiring a stronger coupling with the STM tip to achieve a measurable tunnel current. These results demonstrate the importance of depositing nanocrystals on clean and atomically well-defined surfaces for reliable measurement of their properties.