Polyparaxylylene-CdS nanocomposite films: Optical spectra, photoluminescence, and surface topography

For polyparaxylylene-CdS nanocomposite films prepared by solid-phase cryochemical synthesis, the dependences of the optical absorption spectra, photoluminescence intensity, and surface topography on the CdS concentration were examined. It was revealed that the most significant changes, such as the shift of the position of the exciton absorption band by ～1 eV and the increase of the surface roughness (the magnitude of variation of heights h _max ? h _min along a surface profile) occur within a CdS concentration range of from ～5 to ～8 vol %. The average size of the nanoparticles was determined from the position of the exciton absorption maximum: 2R _np ? ? 3 nm at c ≤ 5 vol % and 2R _np ≥ 5?7 nm at c ≥ 10 vol %. The formation of 3-nm particles at low CdS concentrations was confirmed by the existence of exciton photoluminescence with maximum at 370 nm. Exciton luminescence was not observed at c ≥ 10 vol %. By contrast, at all c values, photoluminescence with maxima at ～520 and ～570 nm, which is usually assigned to interstitial S and Cd atoms, correspondingly, and a the weak emission of unknown nature with a maximum at 545 nm were observed.