Photoinduced Film Formation of Colloidal CdSe Quantum Dots

Tri-n-octylphosphine oxide (TOPO)-capped colloidal cadmium selenide (CdSe) quantum dots (QDs) in octane formed a QD film under laser irradiation. The film was formed at a constant rate of deposition after an incubation period. The deposition rate increased linearly with increasing laser intensity and QD concentration. Addition of TOPO molecules into the suspension significantly retarded film formation. The TOPO molecules are thought to desorb from the QD surface under laser irradiation because well-capped QDs with TOPO molecules did not form a film. We propose that absorbed photons induce desorption of TOPO molecules from QDs and destabilized QDs are formed in the suspension. The formed unstable QDs attach to the substrate, resulting in the formation of a QD film. A model is proposed to analyze the kinetics of film formation. It consists of three steps: the diffusion of QDs from the bulk suspension, the photoinduced desorption reaction of TOPO molecules, and the mass transport of unstable QDs onto the sub...