title: Surface properties of nanocrystalline PbS films deposited at the water-oil interface: a study of atmospheric aging.
abstract: 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(CN(i)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 10-40 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 -SH species. A lead-deficient Pb1-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.
authors.affiliation: School of Physics and Astronomy and the Photon Science Institute, and ‡School of Materials, The University of Manchester , Manchester M13 9PL, United Kingdom.
authors.forename: David J H
authors.initials: DJ
authors.lastname: Cant
authors.forename: Karen L
authors.initials: KL
authors.lastname: Syres
authors.forename: Patrick J B
authors.initials: PJ
authors.lastname: Lunt
authors.forename: Hanna
authors.initials: H
authors.lastname: Radtke
authors.forename: Jon
authors.initials: J
authors.lastname: Treacy
authors.forename: P John
authors.initials: PJ
authors.lastname: Thomas
authors.forename: Edward A
authors.initials: EA
authors.lastname: Lewis
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Haigh
authors.forename: Paul
authors.initials: P
authors.lastname: O'Brien
authors.forename: Karina
authors.initials: K
authors.lastname: Schulte
authors.forename: Federica
authors.initials: F
authors.lastname: Bondino
authors.forename: Elena
authors.initials: E
authors.lastname: Magnano
authors.forename: Wendy R
authors.initials: WR
authors.lastname: Flavell