rule, roughness acts to reduce the strength of adhesion be-We introduce a technique to characterize, in situ, the solidtween two solids (3-5), but in ways that have made quantisolid interface formed when a rough metal surface is placed in tative characterization formidable (4,6). One of the key contact with a smooth mica surface. The technique is based on difficulties in this regard is that the structure of the interface the use of extended spectral analysis of multiple beam interferomecan change as a function of loading or unloading, as a result try in conjunction with the surface forces apparatus (SFA). The of elastic and plastic deformations of surface asperities (7).
intensity versus wavelength spectra of light transmitted through
Although a variety of techniques are available for characthe rough metal/mica interface is measured and compared to that terizing the topography of free solid surfaces-such as scantransmitted through a smooth metal/mica interface. Interference ning-tunneling and atomic force microscopy (8-10)theory is used to characterize the rough interface based on differences in the measured spectra. Roughness on the order of nanome-none of these can be used if a surface is close to, or in ters can be resolved. The key to our technique is the creation of contact with, another solid surface. One technique, however, a perfectly smooth metal/mica interface that is in all respects, that offers the potential to characterize the structure of a except for roughness, identical to the metal/mica interface created solid/solid interface is multiple beam interferometry (MBI) in the SFA. We accomplish this by thermal evaporation of a metal (11). This well-established technique is typically used to film directly onto mica. We demonstrate the effectiveness of the measure film thicknesses of either fluid or solid materials. technique by characterizing the structure of silver/mica and gold/ This is basically accomplished by incorporating the film of mica interfaces. We also show how the technique can be used to unknown thickness into an interference filter; under ideal investigate the exchange of fluids within the contact region.
conditions, film thicknesses as small as angstroms can be แญง 1997 Academic Press resolved (12). When two rough solids are placed in contact,