No 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.

Surface polymerization by ion-assisted deposition (SPIAD), the simultaneous dosing of hyperthermal ions while depositing an organic oligomer, was used to deposit titanyl phthalocyanine (TiOPc) thin films with 50 and 100 eV acetylene ions. The properties of the SPIAD TiOPc thin films are compared with films of the evaporated TiOPc monomer via examination of the electronic structure, ultraviolet-visible absorbance, and composition. Mass spectrometry, x-ray photoelectron spectroscopy, and other methods were used to determine the film composition, chemical bonding, and to examine the electronic structure. These results showed the formation of TiOPc dimers bound face to face. However, the overall phthalocyanine ring structure otherwise remained intact, except for small amounts of atmospheric oxidation at ion-induced radical sites.

Summary: Nanocomposite films were prepared by two methods in which lead sulfide (PbS) nanocrystals were contained in an organic matrix. One method used a wet chemical synthesis of the nanocrystals in the direct presence of a polymer, where the polymer controlled nanocrystal growth. The second method was gaseous deposition of nanocrystals into the organic phase. The two methods were similar in that the nanocrystals in the composites were free from surfactant capping layers that otherwise would add an interfacial region between the nanocrystal and the organic matrix. The gaseous deposition technique had several advantages over the wet chemical synthesis in that it allowed direct control over nanocrystal size and density, improved flexibility in the choice of organic phase, and was compatible with lithographic methods.

No abstract