Al2O3 growth in PMMA thin films by sequential infiltration synthesis: in situ thickness evolution and mass uptake investigation

Abstract

Sequential infiltration synthesis (SIS) represents a simple and straightforward approach to grow inorganic materials in polymeric films. In this work a combination of in situ and ex situ spectroscopic ellipsometry (SE) analysis is used to provide a comprehensive picture of polymer film evolution and Al₂O₃ incorporation as a function of the number of SIS cycles. Two different growth regimes can be clearly distinguished. Initially, Al₂O₃ incorporation determines a marked swelling of polymer films during each SIS cycle. Subsequently, no significant variation of the polymer film thickness is observed by means of in situ SE, despite Al₂O₃ mass uptake at each SIS cycle being clearly highlighted by the gradual increase of the refractive index observed by in situ SE as well as by the regular increment of Al₂O₃ film thickness detected by ex situ SE. The experimental data suggest that after a few SIS cycles, Al₂O₃ growth in the polymer film results in a rigid inorganic–organic template. Precursor penetration determines further incorporation of Al₂O₃ within its volume during subsequent SIS cycles, without any significant swelling of the template. This picture is supported by ex situ X-ray reflectivity (XRR) analysis of the infiltrated polymer films and the residual Al₂O₃ film upon removal of the organic matrix.