Journal
JOURNAL OF CHEMICAL PHYSICS
Volume 114, Issue 19, Pages 8596-8609Publisher
AMER INST PHYSICS
DOI: 10.1063/1.1365931
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The dramatic modifications of molecular fluorescence in the proximity of a sharp nanoscopic probe is investigated by an apertureless or antenna-based near-field scanning optical microscope, which exploits the interactions between a fluorescent sample and a laser illuminated Si atomic force microscope probe. Specifically, luminescence is monitored from evanescently excited, dye-doped polystyrene nanospheres (R-S=20-80 nm) on a fused silica prism surface as a function of probe-sample geometry. The incident laser field is enhanced in the near-field of the probe tip, resulting in images with high sensitivity (sigma (min)approximate to2 Angstrom (2) in a 1 Hz detection bandwidth) and strongly subdiffraction-limited spatial resolution. At probe-sample distances greater than approximate to lambda /2, the images are dominated by far-field interference between (i) direct fluorescence from the molecular sample and (ii) indirect fluorescence from image dipoles induced in the atomic force microscope probe. Near-field shadowing of the molecular fluorescence by the probe also occurs and is studied as a function of probe-sample-detector geometry. Finally, effects of probe-sample proximity on the fluorescence emission spectrum are investigated. In summary, the data elucidate several novel near- and far-field molecular fluorescence enhancement effects relevant to further development of molecular and nanostructural spectroscopic methods with spatial resolution well below the diffraction limit. (C) 2001 American Institute of Physics.
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