Effect of the Anionic Component of Cadmium Salt on the Morphology, Composition, and Topological Features of CdS–PbS Nanocrystalline Films

CdS–PbS nanocrystalline films with a thickness of 0.5 to 1.2 µm are obtained by Chemical Bath Deposition (CBD) from an ammonium-citrate reaction mixture by varying the concentrations of different cadmium salts CdAn n ( An is CH 3 COO − , , ) within 0.01–0.08 mol/L. The morphology and surface topography of the films are studied by scanning electron and atomic-force microscopy. The film’s composition is determined by energy-dispersive analysis. A nonlinear change in the content of the main CdS–PbS film elements and their morphological characteristics is shown. The influence of the anionic component of the salt CdAn n on the cadmium content in thin film layers is established. This effect correlates with the lyotropic series of anions: > > CH 3 COO − . A mechanism for the anion nucleophilic addition to the thiocarbonyl atom of thiourea is proposed. As a result, a nucleophilic attack promotes thiourea activation by weakening the carbon–sulfur bond. Based on the results of comprehensive study of the morphology and the fractal analysis of the surface of the CdS–PbS semiconductor layers, we conclude that the studied films are predominantly formed by particle–cluster diffusion-limited aggregation (DLA).