Mechanical and optical manipulation of porphyrin rings at the submicrometre scale

Scanning probe microscopes (SPMs) and especially the atomic force microscop e (AFM) can be used as tools for modifying surface structures on the submic rometre and even nanometre scale. For this purpose an advanced interface ha s been developed to facilitate these manipulations and greatly increase the number of possible applications. in this paper this interface (the nanoMan ipulator, developed at the University of North Carolina at Chapel Hill) is implemented on a combined AFM-confocal microscope. This setup allows AFM im aging, manipulations and fluorescence imaging of the same area on the sampl e. The new setup is tested on ringlike structures of a porphyrin derivative (B P6), A small amount of the fluorescent material could be displaced with the AFM tip. A special tool (sweep mode) allowed a modification of around 130 nm, which was afterwards detectable with the confocal microscope. The resol ution attainable in these kind of experiments could go down below 100 nm an d is primarily determined by the tip and sample geometry. Comparable with this experiment is the application of a near-held scanning optical microscope (NSOM) to make photochemical modifications. Using the ex citation power coming from the NSOM probe the fluorescence can be quenched by bleaching a selected area instead of displacing the material. Applicatio n on the BP6 rings led to a modification of 280 am wide. AFM can perform modifications on a smaller scale but is less selective than NSOM. Optical investigation of the changes after AFM manipulation can give more elaborate information on the modifications. This will extend the poss ible applications of the techniques and may ultimately go down to the singl e-molecule level.