We report on fluorescence experiments by apertureless near-field optical microscopy. We develop a simple model that demonstrates the importance of non-radiative transfer and that takes into account the dependence of non-radiative transfer on tip geometry. This process is in competition with field enhancement and it is a key process to understand the observed fluorescence enhancement factors. The analysis of the different factors involved in the global fluorescence enhancement or quenching leads to new strategies to reach resolution down to a few nanometers by apertureless fluorescence microscopy.
We report on fluorescence enhancement in near field optical spectroscopy by apertureless microscopy. Our apertureless microscope is designed around a confocal fluorescence microscope associated with an AFM head. First, we show that the confocal microscope alone allows single molecule imaging and single molecule fluorescence analysis. When associated with the AFM head, we demonstrate, for the first time to our knowledge, that single molecule fluorescence is enhanced under the silicon tip. We tentatively attribute this effect to field enhancement under the tip.
We report on optical image contrast for a specific apertureless near-field optical microscope. We demonstrate that the main part of the optical image's contrast results from the sample's topography. The coupling mechanism is analyzed, and we show that the microscope can be regarded as an interferometer that sensitively detects near-field components. However, in the basic configuration the reference field of the interferometer is coupled to the topography. Finally, it is demonstrated that, by controlling the phase of the reference field, one can largely decorrelate the optical image from the topography.
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