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.

Surface and Interface Chemistry in Colloidal Quantum Dots for Solar Applications Studied by X‐Ray Photoelectron Spectroscopy

“…Similar experiments using colloidal QDs are more challenging, because of the presence of large amounts of organic ligand. However, the basic features of the PbS oxidation reaction determined by Cant et al . are confirmed in our studies on PbS CQDs …”

“…The question of whether or not the reaction proceeds congruently (with dissolution of Pb and S in equivalent amounts) has been extensively debated . We have been able to resolve this in studies of nanocrystalline thin films of PbS obtained in a straightforward reaction by precipitation at the interface between toluene (containing a Pb precursor, such as lead diethyldithiocarbamate (Pb(S 2 CNEt 2 ) 2 ) and water (containing Na 2 S) . This preparation produces high quality material that is largely free of the organic material that attenuates XPS signals from the inorganic nanocrystals.…”

In Situ Synthesis of PbS Nanocrystals in Polymer Thin Films from Lead(II) Xanthate and Dithiocarbamate Complexes: Evidence for Size and Morphology Control

“…16,17,30 To date, the only metal sulphides to have been synthesised by the decomposition of single source precursors in a polymer film are CdS, 4,5,32,33 , CuInS 2 , 29 ZnS, 34,35 Bi 2 S 3 , 36 and Sb 2 S 3 . 31 Despite an extensive family of single source precursor molecules used for chemical vapour deposition and nanoparticle synthesis, [37][38][39][40][41][42] relatively few have been investigated within a polymer matrix. Of particular note, metal dithiocarbamate complexes have been widely used as precursors for the synthesis of metal sulfide nanocrystals and thin films but have not been tested with the in situ approach.…”

Versailles Project on Advanced Materials and Standards Interlaboratory Study on Measuring the Thickness and Chemistry of Nanoparticle Coatings Using XPS and LEIS

“…This method has been employed routinely for many decades to study the surfaces of nanoparticles used in supported heterogeneous catalysis, and is increasingly being used to measure the properties of nanoparticles used for medical and optoelectronic applications. 13-17 Recent reports have indicated that ion scattering methods, such as low and medium energy ion scattering (LEIS and MEIS) may be employed as a sensitive method for measuring the coating thickness of nanoparticles. 18,19 There are a number of challenges that analysts face when they employ ultra-high vacuum techniques to characterize nanoparticles.…”