Organic film formation investigated by atomic force microscopy on the nanometre scale

The formation of ultrathin, amorphous organic films on solids is studied for an application-oriented model system. A prepolymer or a copolymer of a cyanate-based high-temperature adhesive is spin cast or dip coated onto silicon wafers or aluminium coatings to produce films as thin as possible. The mean thickness ranges from 1 to 4 nm. After a thorough substrate characterisation by imaging and spectroscopic methods, the various films were investigated by atomic force microscopy (AFM). Besides imaging, for discontinuous films AFM was also utilised to measure the “borderline angle” introduced in this paper. The borderline angle characterises the slope of the surface of an isolated adsorbed organic object near the substrate. Thus, it is the geometric equivalent to the classical contact angle of a lying liquid drop. However, the phenomena leading to these angles are different. Nevertheless, the borderline angle is related to the affinity of the organic phase to the substrate and thus will play an important role in future investigations of film formation and adhesion on the nanometre scale.