OBSERVATION OF TEMPERATURE-DEPENDENT THICKNESSES IN ULTRATHIN POLYSTYRENE FILMS ON SILICON

The temperature dependent thicknesses of ultrathin polystyrene films u nder vacuum on Si(111) substrates were investigated via x-ray reflecti vity in situ. The contraction of ultrathin polymer films was directly observed for the first time to the authors' knowledge. The degree of c ontraction depends on the initial thickness of the ultrathin polystyre ne film, with the magnitude of contraction increasing with decreasing initial film thickness. This contraction ranged from 0%-17% and occurr ed at temperatures well below the reported bulk polystyrene glass tran sition temperature.