Can charged quantum dots emit? Does a change in the surface charge occur when a dot switches from bright to dark in a blinking event? While theorists have been wrangling with these difficult questions for some time now, we hope to throw some additional hard evidence into the debate by using two imaging techniques simultaneously to observe fluorescing quantum dots. Electrostatic Force Microscopy (EFM) provides an image of the topography of quantum dots on a surface as well as a color-scaled rendering of their charges with nanometer and sub-electron resolution. Additionally, we use an inverted confocal microscope connected to a CCD detector to acquire images of the fluorescence produced by laser excitation of the same dots. This tandem method will be used to study both monolayer ensembles and single dots.
Fluorescence image of micrometer-scale spots of CdSe quantum dots deposited by the Bioforce Nanoenabler. These thin, isolated spots make good candidates for monolayer studies.
