Physisorbed and covalently bound Langmuir-Blodgett (LB) monolayers of sulfur-bearing lipids on mica and on gold substrates, respectively, have been studied. Scanning force microscopy, in topography and friction modes as well as in contact and noncontact modes have been used to investigate these films in the region of coexisting phases. For the first time, a detailed and complex internal structure of solid-analogous monolayer domains, reflecting their symmetric morphology, has been observed. Comparisons of physisorbed monolayers on mica with chemisorbed monolayers on gold show distinct differences in the structure and stability of the films caused by the different substrate/film interactions. It is found that the use of a substrate to which the film can bind covalently does not result in changes to the morphology of solid-analogous domains in the films. The structure of covalently bound monolayers is well-preserved over long time periods and is stable at solid/fluid interfaces. However, the covalently bound LB monolayers are more susceptible to damage by the SFM tip than the physisorbed films on mica.