Deposition and analytical characterization of fluoropolymer thin films modified by palladium nanoparticles.

Palladium-fluoropolymer nanostructured composites (Pd-CFx) are deposited by a separate and simultaneous sputtering of bulk Teflon and palladium targets in a vacuum chamber. Such nano-material can find application as active layer in sensing devices, as it swells when exposed to the vapors of organic solvents such as acetone, chloroform, 2-propanol. Ellipsometry shows that the swelling extent linearly depends on the solvent partial pressure in the measuring chamber. Moreover, Pd-CFx sensitivity and selectivity features are different to those of a parent gold-fluoropolymer (Au-CFx) nanocomposite, investigated in previous studies. In particular, Pd-CFx layers are generally more sensitive than Au-CFx ones, particularly in the case of chlorinated solvents, which are scarcely detectable by Au-CFx nanocomposites. The material morphological and chemical structure has been investigated by means of atomic force and transmission electron microscopies along with X-ray photoelectron (XPS) and Fourier transform infra-red spectroscopies. The analytical characterization demonstrates that morphological similarities exist between Pd-CFx films and Au-CFx ones having the same metal volume fraction f. XPS also reveals an almost identical surface structure for the dispersing polymer matrix of homologous Pd-CFx and Au-CFx films. Metal fluorides and oxides are identified as well and differences in the materials sensing performances are then ascribed to the presence of different amounts of these species that also have a different chemical reactivity and selectivity.