Date : 2014. 4. 10, 4:30 PM Place : Int"l conf. room, Bldg.25-1 -Abstract- Colloidal quantum dots (QDs) have been successfully developed into nanoscale light sources with variable wavelength. However, fluorescence intermittency (FI), also known as photoluminescence blinking, remains a major problem. FI was first observed seventeen years ago in a QD1. It is now thought that trap states in the QD play a major role in the origin of FI. However, proposed microscopic models still give contradictory predictions, mainly due to the lack of information on the spatial and energetic distribution of traps. We observed internal and surface trap states for the first time using scanning tunneling microscopy and spectroscopy. Internal defects induce tens to hundreds of midgap electronic states within every QD. Surface traps appear as charged quantum islands at some ligand molecules. We found that trapping and detrapping dynamics among internal and surfaces traps are important for understanding FI statistics. By performing a Monte Carlo simulation that includes the measured spatial and energetic distribution of the internal and the surface traps, we demonstrate the characteristic power-law statistics of FI. Two types of FI dynamics observed in a recent spectroelectrochemistry experiment2 can also be successfully explained with our internal-surface trap-distribution model. We anticipate this observation to become a corner stone for the complete elimination of FI.