NONEQUILIBRIUM PHASE MORPHOLOGY OF THIN POLY(STYRENE-BLOCK-METHYL METHACRYLATE) FILMS

The phase morphology of ultrathin (similar to 15 nm), nonequilibrium f ilms of a symmetrical block copolymer (poly(styrene-bloch-methyl metha crylate) is studied by atomic force microscopy (AFM) and X-ray photoel ectron spectroscopy(XPS). The films were spin-coated from a nonselecti ve solvent onto silicon at room temperature. The film is microphase se parated with the microphase stacking in the film plane; i.e., both mic rophases contact the film surface. Topographically elevated and depres sed surface areas consist of polystyrene and poly(methyl methacylate) microphases, respectively. The phase correlation length is in the rang e of the bulk equilibrium phase correlation length of the system. The poly(methyl methacrylate) phase extends down to the substrate. Reliabl e phase assignment to topographical features in AFM measurements is po ssible by topographical contrast enhancement through selective degrada tion of the poly(methyl methacrylate) microphases in a rf plasma. XPS results on the monomer composition at the film surface confirm the mor phological model.