Controlling anisotropy in nanostructures is

In the realm of colloidal nanostructures, with their immense capacity for shape and dimensionality control, the form is undoubtedly a driving factor for the tunability of optical and electrical properties in semiconducting or metallic materials. However, influencing the fundamental properties is still challenging and requires sophisticated surface or dimensionality manipulation. Such a modification is presented for the example of colloidal leadsulfide nanowires. It is shown that the electrical properties of lead sulfide nanostructures can be altered from semiconducting to metallic with indications of superconductivity, by exploiting the flexibility of the colloidal synthesis to sculpt the crystal and to form different surface facets. A particular morphology of lead sulfide nanowires is prepared through the formation of {111} surface facets, which shows metallic and superconducting properties in contrast to other forms of this semiconducting crystal, which contain other surface facets ({100} and {110}). This effect, which is investigated with several experimental and theoretical approaches, is attributed to the presence of lead-rich {111} facets. The insights promote new strategies for tuning the properties of crystals and new applications for lead sulfide nanostructures.of materials with different properties. [6,8] One example for the successful implementation of this approach is the synthesis of lead sulfide, which has been produced with a broad spectrum of shapes, sizes, and properties. [10][11][12] This material has been already used for many applications such as photodetectors, [13] field-effect transistors, [14] spintronic components, [2] and solar cells. [15,16] Regarding all of these applications, a certain statement is valid: PbS exhibits semiconducting properties, which is not a surprising fact considering the electronic structure of this material. [2,6,8,[10][11][12][14][15][16][17][18][19][20][21][22] However, violating this statement could be of great scientific and practical importance, since it establishes new strategies to tune the properties of crystalline materials based on their target applications.Here, we introduce a method to change the electrical properties of colloidal lead sulfide nanowires from normal semiconducting to metallic with indications of superconductivity. This could be achieved by faceting the crystal, or in other words, by altering the surface facets of the crystal to the {111} ones, which are single element facets. This Pb-rich surface provides delocalized surface states at room temperature or presumably Cooper pairs at low temperatures, causing metallic and supposedly superconducting properties, in contrast to other forms of PbS nanocrystals, which are all semiconducting. Altering the surface facet is done by ligand-mediated growth in the presence of oleic acid (OA), lithium chloride, and trioctylphosphine, with expressed {111} facets giving a zigzag shape.Such zigzag wires are synthesized together with nanostripes, which have a flat shape, containing Pb and S atoms on their...

Highly crystalline vertically aligned Ag2S/CdS heterostructured nanosheets with lateral sizes of several micrometers and thicknesses of a few nanometers are prepared directly on silver surfaces by a two-step process. Firstly, Ag2S sheets were prepared by direct reaction of partially dissolved elementary sulfur in methanol with a solid silver surface in methanol at room temperature. The second step involves a self-limited cation exchange of Ag+ vs. Cd2+ to achieve the formation of large-area Ag2S/CdS heteronanosheets on the solid substrate. The cation exchange was proven and investigated over time via several analytical methods, e.g. X-ray diffraction, Raman spectroscopy and three-dimensional photoluminescence mapping.