2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

Coupling of CdSe/ZnS quantum dots: among themselves and with matrices

K. Liu and R. Tsu
University of North Carolina at Charlotte, US

Keywords:
photoluminescence, peak shift, quantum dots

Abstract:
We investigate the photoluminescence (PL) properties of CdSe/ZnS QDs deposited on Si, fused silica, Au film, and silica nanospheres. The red shifts of the PL peak were observed with increasing density of QDs on various matrices: Si, fused silica, and Au film. This red shift is attributed to interaction between QDs forming bonding and anti-bonding states with PL emerging from the lower bonding states. We found strong blue shift whenever a second peak at a lower energy is detected. The second lower peak on fused silica and Au film is tentatively assigned to the molecular complexes on the interface of the QD/matrices. Increasing the substrate surface roughness results in enhanced interaction due in part to both surface areas increase and increase of effective surface electric field. We have not observed the second peak on Si with ~3nm of native oxide having RMS roughness of ~0.4nm, whereas strong second peak appears whenever RMS roughness is ~1nm or greater. For the case of QDs on the silica spheres, a blue-shift of ~8.5% was observed, with higher up-shifts for higher packing density. Our results demonstrated the enhanced bonding of QDs to the surface of the spheres with the thiolation process.

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