Optical properties of electrostatically assembled films of CdS and ZnS colloid nanoparticles

This work presents a cost-effective alternative technology for the formation of nanostructured semiconductor materials for tunable light emitting devices. CdS and ZnS semiconducting colloid nanoparticles coated with organic shell, containing either SO3- or NH3+ groups, were deposited as thin films using the technique of electrostatic self-assembly. The films produced were characterized with UV-vis spectroscopy, spectroscopic ellipsometry and AFM. UV-vis spectra show a substantial blue shift of the main absorption band of both CdS and ZnS with respect to the bulk materials due to the phenomenon of quantum confinement. The nanoparticles' radius of 1.8 nm, evaluated from the spectral shift, corresponds well to the film thickness obtained by ellipsometry. AFM shows the formation of larger aggregates of nanoparticles on solid surfaces. Keywords: CdS, ZnS, colloid nanoparticles, electrostatic self-assembly, quantum confinement, ellipsometry, AFM