Surface Properties of Nanocrystalline PbS Films Deposited at the Water鈥揙il Interface: A Study of Atmospheric Aging

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• 作者：David J. H. Cant ; Karen L. Syres ; Patrick J. B. Lunt ; Hanna Radtke ; Jon Treacy ; P. John Thomas ; Edward A. Lewis ; Sarah J. Haigh ; Paul O鈥橞rien ; Karina Schulte ; Federica Bondino ; Elena Magnano ; Wendy R. Flavell
• 刊名：Langmuir
• 出版年：2015
• 出版时间：February 3, 2015
• 年：2015
• 卷：31
• 期：4
• 页码：1445-1453
• 全文大小：561K
• ISSN：1520-5827

文摘

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 [Pb(SON(CNp>ip>Pr₂)₂)₂] and lead diethyldithiocarbamate [Pb(S₂CNEt₂)₂] precursors are used. The films are characterized by X-ray diffraction and electron microscopy, revealing typical particle sizes of 10鈥?0 nm and preferred (200) orientation. Synchrotron-excited depth-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 1:1 Pb/S composition. Initial degradation occurs to form lead hydroxide and small quantities of surface-adsorbed 鈭扴H species. A lead-deficient Pb_1鈥?i>xS 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 sulfite/sulfate 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.