Cluster Beam Deposition of Lead Sulfide Nanocrystals into Organic Matrices

Abstract

Lead sulfide nanocrystals (PbS NCs) were codeposited into two organic films, titanyl phthalocyanine (TiOPc) and alpha-sexithiophene, using cluster beam deposition (CBD). NCs of average diameters of approximately 3-4 nm were evenly distributed in these organic films with average particle spacings of approximately 4 nm, as determined by transmission electron microscopy. The film composition and NC surface chemistry were monitored by X-ray photoelectron spectroscopy (XPS) and other methods. Pb:S stoichiometry in the NC/TiOPc film was determined by XPS to correspond to the PbS cubic rock salt structure. Soft-XPS using 200 eV energy photons determined the NC-organic surface chemistry by resolving the S 2p core level into four distinct components for sulfur. The soft-XPS results found that the PbS NC surface chemistry could be tuned by varying the H(2)S/Ar gas ratio within the CBD source.

Photoresponse of PbS nanoparticles–quaterthiophene films prepared by gaseous deposition as probed by XPS

“…PbS clusters were formed in a magnetron condensation source by reactively sputtering a Pb metal target in an Ar/H 2 S gas mixture, as previously described. 8,9 The gaseous PbS clusters were simultaneously deposited onto the Si substrate with oligothiophene (sexithiophene, CAS 88493-55-4, Sigma-Aldrich, St. Louis, MO) evaporated from a heated ceramic crucible (LTE 11 000 K, 1 cc, Kurt J. Lesker, Pittsburgh, PA). The oligothiophene sublimation temperature was varied from 413 to 513 K to maintain a 1:1 fluence with the PbS clusters, as monitored with a quartz crystal microbalance.…”

“…These four components were assigned as S 4T arising from 4T at binding energy of 164.3 eV, S 4T-PbS arising from 4T interacting with the PbS nanoparticle at 163.7 eV, S PbS-Surf , which is the surface component of PbS at 162.2 eV, and S PbS-Core , which is the core component of PbS at 161.3 eV. 8 Comparison of core level spectra on samples with and without C 2 H þ x ion modification indicates enhanced bonding within the nanocomposite film. The ratio of S 4T-PbS /Pb for the 4T þ PbS samples was 0.7 6 0.4, but this ratio increased to 1.1 6 0.3 for the 4T þ PbS þ ion samples, indicating that ion modification increased the coupling between the nanoparticles and 4T.…”

“…Prior work showed that well-separated, 3.5 6 0.9 nm diameter PbS nanoparticles with some degree of crystallinity were formed under conditions similar to those used to prepare the 4T þ PbS films. 8 Those experiments were performed by depositing nanoparticles and organic oligomer onto copper grids for subsequent analysis by dark field scanning transmission electron microscopy. However, more recent attempts to examine changes in film morphology by transmission electron microscopy were hindered by the erosion of the copper grids by acetylene ion bombardment.…”

“…Cluster beam deposition (CBD) allows direct control of nanoparticle properties, including surface chemistry and matrix environment. 8,9 CBD can also be used to prepare films with predetermined thicknesses and additionally allows indirect control of film morphology. CBD is performed under vacuum, reducing oxidation effects on the deposited films and nanoparticles therein.…”

<em>In Situ</em> SIMS and IR Spectroscopy of Well-defined Surfaces Prepared by Soft Landing of Mass-selected Ions

“…Recent efforts have indicated potential future applications of soft landing of mass-selected ions in the preparation of peptide and protein arrays for use in high-throughput biological screening 7,8 , separation of proteins and conformational enrichment of peptides [9][10][11][12] , covalent attachment of peptides to surfaces 9,10,13,14 , chiral enrichment of organic compounds 15 , electrochemical characterization of specific redox-active proteins [16][17][18] , production of thin molecular films 19,20 , processing of macromolecules such as graphene 21 and preparation of model catalyst systems through soft landing of ionic clusters [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] , nanoparticles [40][41][42][43][44][45][46][47][48] and organometallic complexes onto support materials 19,…”