New design of a cryostat-mounted scanning near-field optical microscope for single molecule spectroscopy

Due to the weakness of the fluorescence signal from a single fluorophore, a scanning near-field optical microscope for single molecule spectroscopy re quires a very efficient setup for the collection and detection of emitted p hotons. We have developed a home-built microscope for operation in a 1-He c ryostat which uses a solid parabolic mirror in order to optimize the fluore scence collection efficiency. This microscope works with Al-coated, tapered optical fibers in illumination mode. The tip-sample separation is probed b y an optical shear-force detection. First results demonstrate the capabilit y of the microscope to image single molecules and achieve a topographical r esolution of a few nanometers vertically and better than 50 nm laterally. ( C) 1999 American Institute of Physics. [S0034-6748(99)02102-4].