Reduction of intercalation in the thin film of cadmium sulfide (CdS) and zinc sulfide (ZnS) nanoparticles by adding the second surfactant mercapto ethanol

This article reports on the formation and characterization of extremely small CdS and ZnS semiconductor nanoparticles (NPs) using a mixture of surfactants, mercaptoethane sulfonate, and mercaptoethanol in different concentrations (from 0.1 mM to 1.4 mM) to control the particles’ sizes. UV-visible spectroscopy study of the solution of CdS NPs showed significant blue spectral shifts from 512 nm (bulk CdS) to about 409 nm. While for ZnS NPs colloid, the shifts is from 335 nm (bulk ZnS) to about 290 nm. The spectral shift are caused by the quantum confinement of carriers in NPs, which allowed us to determine the radii of CdS and ZnS nanoparticles of about 1.86 and 1.68 nm. These results were confirmed by small angle neutron scattering (SANS) measurements on CdS and ZnS NPs which yielded 1.6 and 1.2 nm in radius. The introduction of mercaptoethanol as a second surfactant did not significantly change the NPs’ sizes of about 1.9 nm for CdS and ZnS. Still, it reduces the ion interaction in the electrostatic layer-by-layer (LbL) deposition of CdS and ZnS NPs. X-ray diffraction (XRD) measurements of such thin films confirmed the wurzite structure of CdS and ZnS nanoparticles. The lattice parameters obtained are a = 4.160 Ǻ and c = 6.756 Ǻ for CdS. While ZnS lattice parameters are a = 3.820 Ǻ and c = 6.260 Ǻ. The size of lattice crystals of CdS and ZnS nanoparticles was found to decrease as mercaptoethanol concentration increased from 0.1to 1.4 mM.