Communication: ''Ultra-monomolecular'' films of block copolymers, i.e., films whose surface concentration is so low that the substrate cannot be covered homogeneously without affecting the structure of the macromolecules very strongly, have been studied using tapping- and friction-mode SFM. Two-dimensional phase separation yielding an ordered pattern of polystyrene and poly-2-vinylpyridine surface domains is observed. SFM is shown to distinguish topological features and also to discriminate between chemically different components. The surface features generated and the formation mechanisms involved are discussed.