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Fluorescence of Single ZnS Overcoated CdSe Quantum Dots Studied by Apertureless Near-Field Scanning Optical Microscopy



V V. Protasenko, M Kuno, Alan Gallagher, David Nesbitt


The fluorescence of single ZnS overcoated CdSe quantum dots (Qds) embedded in the evanescent optical field above a prism surface has been studied using an Apertureless Near-field Scanning Optical Microscope (ANSOM). Optical and topographic ANSOM images reveal far-field and near-field components in the optical interaction between a non-contact silicon (SI) atomic force microscope probe and an isolated QD. We demonstrate that the fluorescence intensity of an individual QD can be enhanced 5 times when the Si probe is located over the QD. Furthermore, we show that the fluorescence contrast in ANSOM images is typically 5 times greater than the above enhancement coefficient. The manimum observed full width at half maximum of the fluorescence images (FWHMfluorencence), using etch-cleaned probes with a 2.8 nm QD, is difference} 15 nm. Most of this additional optical width is attributed to the relatively large probe-taper angle, which spreads the field enghancement near the probe tip. A fluorescence width below the topographic width is observed for crash blunted probes, consistent with this interpretation. The fluorescence of single QDs exhibits the familiar blinking, but also variations in fluorescence intensity over long periods with many blinking events.
Optics Communications
No. 1-2


ANSOM, fluorescence enhancement, quantum dots


Protasenko, V. , Kuno, M. , Gallagher, A. and Nesbitt, D. (2002), Fluorescence of Single ZnS Overcoated CdSe Quantum Dots Studied by Apertureless Near-Field Scanning Optical Microscopy, Optics Communications (Accessed July 18, 2024)


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Created August 31, 2002, Updated October 12, 2021