Nucleation and growth of lead sulfide nano- and microcrystallites in supramolecular polymer assemblies

Multilayer thin film assemblies fabricated by the sequential adsorption of polyelectrolytes on a quartz substrate were used as a supramolecular reacti on template to study the in situ nucleation and growth of PbS nano- and mic roparticles. Chemical reaction within the polymer film was initiated by abs orbing pb(2+) from an aqueous solution of Pb(NO3)(2) followed by exposing t he film to H2S gas. Electron microscopic examination of the films revealed that while nanoparticles are formed in films that were subject to one or tw o reaction cycles, large crystallites were formed when these films were exp osed to a large number (10) of reaction cycles. In the latter case, a broad distribution of particle sizes is observed and may be attributed to Ostwal d ripening. Detailed studies show the nucleation and growth of the PbS part icles into crystallites of different shapes. UV-vis absorption studies reve al that the absorption spectral profiles of the films are dependent on the size of the PbS crystallites. The broadened absorption spectral profile obs erved for films subject to a large number of reaction cycles may be attribu ted to the superposition of the spectral profiles of the small clusters tha t tend to be blueshifted due to quantum confinement effects and the large c lusters that are redshifted.