Hexamethyldisiloxane polymer layers obtained at low frequency glow discharge were post-treated by ammonia vapours under the same plasma conditions. Infrared spectroscopic ellipsometry and atomic force microscopy studies were carried out with the aim to elucidate the structural and morphological changes accompanying this modification. The infrared ellipsometry combined with best-fit calculations was used to evaluate the optical constants of the polymer film before and after the treatment, and thus to provide data for the vibrational band analysis. No additional modified layer due to the plasma treatment was detected, but a newly emerged weak band at 1562 cm(-1) was observed in the ellipsometric spectra of the ammonia-treated sample, which was ascribed to N-H deformation in amines. The surface morphology was imaged by atomic force microscopy. The data revealed that the NH3 treatment had caused distinct microstructural modification on the top layer surface. The size of the nodule aggregates was largely reduced and this contributed to-a much better developed top surface. (c) 2004 Elsevier B.V. All rights reserved.