Structural and Morphological Characterization of PbS Nanocrystallites Synthesized in the Bicontinuous Cubic Phase of a Lipid

Abstract

We report the synthesis and characterization of monodispersed lead sulfide (PbS) particles with diameters in the range 4−14 nm, using bicontinuous cubic phase as a matrix. It was found, through polarized optical microscopy and small-angle X-ray scattering studies, that the viscous isotropic bicontinuous cubic phase continued to exist in the ternary sodium dioctyl sulfosuccinate (AOT)/water/sodium sulfide (Na 2 S) system as long as the concentration of aqueous Na 2 S solution was below 0.5 M. The exposure of this ternary mixture to aqueous 0.40 M lead nitrate (Pb(NO 3 ) 2 ) solution led to the formation of PbS nanocrystallites within the mesophase. A series of PbS particulate samples were synthesized, using different concentrations of aqueous Na 2 S solutions ranging between 0.025 and 0.30 M, extracted from the lipid matrix and capped by thiol molecules. The structure and diameter of the particles were determined from X-ray diffraction studies. The particle size was found to increase linearly with increase in Na 2 S concentration. Transmission electron microscopic (TEM) characterization of monoparticulate-layer samples, prepared by Langmuir−Blodgett technique showed PbS particles of uniform size when the concentration of Na 2 S solution was lower than 0.10 M. High-resolution TEM revealed the particles to be crystalline with no stacking fault. The monodispersity of the particles was lost for Na 2 S concentration >0.20 M and the larger particles showed cubic morphology. Absorption spectra showed blue shift with decreasing size, with no excitonic peaks.