Surface Properties of Nanocrystalline PbS Films Deposited at the Water-Oil Interface: A Study of Atmospheric Aging
Journal Article - Open Access
University of Manchester Manchester United Kingdom
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Nanocrystalline thin films of PbS are obtained in a straightforward reaction by precipitation at the interface between toluene containing a Pb precursor and water containing Na2S. Lead thiobiuret PbSONCNiPr222 and lead diethyldithiocarbamate PbS2CNEt22 precursors are used. The films are characterized by X-ray diffraction and electron microscopy, revealing typical particle sizes of 1040 nm and preferred 200 orientation. Synchrotron-exciteddepth-profiling X-ray photoelectron spectroscopy XPS is used to determine the depth-dependent chemical composition as a function of surface aging in air for periods of up to 9 months. The as-synthesized films show a 11 PbS composition. Initial degradation occurs to form lead hydroxide and small quantities of surface-adsorbed SH species. A lead-deficient Pb1xS phase is produced as the aging proceeds. Oxidation of the sulfur occurs later to form sulfite and sulfate products that are highly localized at the surface layers of the nanocrystals.These species show logarithmic growth kinetics, demonstrating that the sulfitesulfate layer acts to passivate the nanocrystals. Our results demonstrate that the initial reaction of the PbS nanocrystals forming lead hydroxide is incongruent. The results are discussed in the context of the use of PbS nanocrystals as light-harvesting elements in next-generation solar technology.