We review our recent developments of near-field scanning optical microscopy (NSOM) that uses an active tip made of a single fluorescent nanodiamond (ND) grafted onto the apex of a substrate fiber tip. The ND hosting a limited number of nitrogen-vacancy (NV) color centers, such a tip is a scanning quantum source of light. The method for preparing the ND-based tips and their basic properties are summarized. Then we discuss theoretically the concept of spatial resolution that is achievable in this special NSOM configuration and find it to be only limited by the scan height over the imaged system, in contrast with the standard aperture-tip NSOM whose resolution depends critically on both the scan height and aperture diameter. Finally, we describe a scheme we have introduced recently for high-resolution imaging of nanoplasmonic structures with ND-based tips that is capable of approaching the ultimate resolution anticipated by theory.
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