Daniel J. Asunskis

Cluster beam deposition of lead sulfide nanocrystals into organic matrices.

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.

Shape-controlled colloidal synthesis of rock-salt lead selenide nanocrystals.

Developing simple synthetic methods to control the size and morphology of nanocrystals is an active area of research as these parameters control the materials electronic and optical properties. For a semiconductor with a symmetrical crystal structure such as lead selenide, anisotropic colloidal growth has been previously accomplished via the use of templates, seeds, or by block assembly of smaller, symmetrical subunits. Here, we present a simple method to create monodisperse lead selenide nanorods and multipods at low temperatures. The size distribution and the observed morphologies are consistent with a continuous, anisotropic growth of material. The syntheses of these anisotropic shapes are due to the nature of the nuclei that form upon injection of precursors into partially oxidized alkene solvents that may contain lactone and carbonate-functional derivatives.