Facet-controlled facilitation of PbS nanoarchitectures by understanding nanocrystal growth.

Nanostructured lead sulphide is a significant component in a number of energy-related sustainable applications such as photovoltaic cells and thermoelectric components. In many micro-packaging processes, dimensionality-controlled nano-architectures as building blocks with unique properties are required. This study investigates different facet-merging growth behaviors through a wet-chemical synthetic strategy to produce high-quality controlled nanostructures of lead sulphide in various dimensionalities. It was found that 1D nanowires or 2D nanosheets can be obtained by the merging of reactive {111}- or {110}-facets, respectively, while promoting {100} facets in the early stages after nucleation leads to the growth of 0D nanocubes. The influence of temperature, capping ligands and co-solvent in facilitating the crystal facet growth of each intermediate seed is also demonstrated. The novelty of this work is characterized by the delicate manipulation of various PbS nanoarchitectures based on the comprehension of the facet-merging evolution. The synthesis of facet-controlled PbS nanostructures could provide novel building blocks with desired properties for use in many applications.

Tilted face-centered-cubic supercrystals of PbS nanocubes.

We demonstrate a direct fabrication of PbS nanocube supercrystals without size-selection pretreatment on the building blocks. Electron microscopic and synchrotron small angle X-ray scattering analyses confirm that nanocubes pack through a tilted face-centered-cubic (fcc) arrangement, that is, face-to-face along the <110>(super) direction, resulting in a real packing efficiency of as high as ∼83%. This new type of superstructure consisting of nanocubes as building blocks, reported here for the first time, is considered the most stable surfactant-capped nanocube superstructure determined by far.

Intercalating oleylamines in graphite oxide.

Graphite oxide has been synthesized from raw graphite particles and been treated with various mass amounts of oleylamine as intercalants to form intercalation compounds. X-ray diffraction patterns reveal that the inter-sheet distances strongly depend on the graphite oxide to oleylamine mass ratios. The equilibrium-like behavior implies diffusion-dominated oleylamine adsorption on graphite oxide in solution and excluded volume intercalations among oleylamine-adsorbed graphite oxide during restacking. The intercalation compounds are soluble in organic solvents, and their applications in the fabrication of transparent and conductive coatings have been demonstrated.

Synthesis of PbSeTe single ternary alloy and core/shell heterostructured nanocubes.

We report a robust method for synthesis of monodisperse PbSeTe single ternary alloy and core/shell heterostructured nanocubes, respectively. The key synthetic strategy to produce such different classes of nanocubes is to precisely control the time of reaction and successive growth. The crystallinity, shape/size distributions, structural characteristics, and compositions of as-prepared nanocubes, both ternary alloy and core/shell, were carefully studied. A plausible growth mechanism for developing each type of lead chalcogenide nanocubes is proposed. These delicately designed PbSeTe nanoscale architectures offer tunable compositions in PbSeTe ternary alloy and nano-interfaces in core/shell nanocubes, which are the critical factors in controlling thermal conductivity for applications in thermoelectrics.

Hybrid nanostructure heterojunction solar cells fabricated using vertically aligned ZnO nanotubes grown on reduced graphene oxide.

Using reduced graphene oxide (rGO) films as the transparent conductive coating, inorganic/organic hybrid nanostructure heterojunction photovoltaic devices have been fabricated through hydrothermal synthesis of vertically aligned ZnO nanorods (ZnO-NRs) and nanotubes (ZnO-NTs) on rGO films followed by the spin casting of a poly(3-hexylthiophene) (P3HT) film. The data show that larger interfacial area in ZnO-NT/P3HT composites improves the exciton dissociation and the higher electrode conductance of rGO films helps the power output. This study offers an alternative to manufacturing nanostructure heterojunction solar cells at low temperatures using potentially low cost materials.

Quantitative characterization of vertically aligned multi-walled carbon nanotube arrays using small angle X-ray scattering.

We have used small angle X-ray scattering (SAXS) to quantitatively characterize the morphology of vertically aligned (VA) multiwall carbon nanotube (MWCNT) arrays. We examined the extent of alignment of MWCNTs in terms of order parameter by analyzing SAXS intensity as a function of azimuthal angle. The SAXS measurements at different heights of CNT arrays from the substrate reveal two distinct morphologies and increasing alignment. We are able to quantitatively characterize a real variation in CNT diameters of the VA-MWCNTs through model fitting of the SAXS spectra. It found that the average CNT diameter increases with increasing distance from the substrate.

Cu-doping induced ferromagnetism in ZnO nanowires.

Cu-doped and undoped ZnO nanowires have been successfully fabricated at 600 degrees C using a vapor transport approach. Comprehensive structural analyses on as-fabricated nanowires reveal highly crystalline ZnO nanowires with 0.5 at. % of substitutional Cu doping. Ferromagnetism has been observed in Cu-doped ZnO nanowires but not in undoped ones, which is probably associated with defects involving both Cu dopants and Zn interstitials.

Simple cubic super crystals containing PbTe nanocubes and their core-shell building blocks.

We report a preparation of high-quality cubic PbTe nanocrystals and their assembly into both square-array, two-dimensional patterns and three-dimensional simple cubic super crystals. The influence of oleylamine in the nanocrystal synthesis and core-shell formation through an anion-exchange mechanism was also studied. The simple cubic super crystals together with two-dimensional assembly patterns containing PbTe nanocubes and their core-shell building blocks were examined using TEM, SEM, AFM, XRD, SAXS, and FTIR. Such super crystals consisting of cubic structural building blocks may allow engineering of more complex materials from which novel properties may emerge.