Depth analysis of local conformation in poly(methyl methacrylate) adsorbed onto SiO x studied by soft X-ray absorption spectroscopy combined with an Ar gas cluster ion beam

Using X-ray absorption spectroscopy (XAS) with linearly polarized soft X-rays, we investigated the local conformation of poly(methyl methacrylate) (PMMA) adsorbed to a SiO x /Si(111) surface. The preedge intensity of the O K-edge XAS for PMMA, originating from the O 1s → π * transition at a C=O group in the side chain, was stronger for vertically polarized incident X-rays than for horizontally polarized ones. Conversely, the XAS intensity originating from the O 1s → σ * transition showed the opposite trend. These findings suggest that the C=O group in the side chain of PMMA exhibited preferential orientation rather than an amorphous arrangement. To gain further insights, we conducted a depth profile analysis of the local conformation of PMMA using XAS combined with an argon gas cluster ion beam (GCIB). GCIB-XAS analysis revealed that the orientation of the C=O group in the side chain of PMMA differs between the region from the SiO x interface to a distance on the order of 1 nanometer and the bulk PMMA region.