Preparation of mica surfaces for enhanced resolution and cleanliness in the surface forces apparatus

We describe a simple technique for preparing arbitrarily thin mica substrates of unparalleled purity for use in the surface forces apparatus (SFA). Relatively thick mica samples (4-8 mu m) are prepared in the conventional way, coated with a sputter deposited layer of silver, and attached (silver side down) to cylindrical lenses with a thick coat of thermosetting epoxy. These surfaces are then placed in a glovebox with the cell of the SFA where they are cleaved once again with a piece of tape, and then mounted and sealed in the SFA for immediate use. With this technique, the surfaces are never exposed to laboratory air, they are insensitive to asperities in the glue/silica support, and may be made arbitrarily thin by removing more mica until the desired thickness is achieved. We find that adhesion between two surfaces cleaved in this manner (similar to 300 mJ/m(2)) is significantly larger than for mica prepared in the conventional way (similar to 200 mJ/m(2)), and consistent with the adhesion measured in direct cleavage experiments. This suggests a cause for discrepancies in the measured adhesion which have appeared in the literature.