Colloidal materials of tin(II) sulfide (SnS), as a layered semiconductor with a narrow band gap, are emerging as a potential alternative to the more toxic metal chalcogenides (PbS, PbSe, CdS, CdSe) for various applications such as electronic and optoelectronic devices. We describe a new and simple pathway to produce colloidal SnS nanosheets with large lateral sizes and controllable thickness, as well as single-crystallinity. The synthesis of the nanosheets is achieved by employing tin(II) acetate as tin precursor instead of harmful precursors such as bis[bis(trimethylsilyl)amino] tin(II) and halogen-involved precursors like tin chloride, which limits the large-scale production. We successfully tuned the morphology between squared nanosheets with lateral dimensions from 150 to about 500 nm and a thickness from 24 to 29 nm, and hexagonal nanosheets with lateral sizes from 230 to 1680 nm and heights ranging from 16 to 50 nm by varying the ligands oleic acid and trioctylphosphine.The formation mechanism of both shapes has been investigated in depth, which is also supported by DFT simulations. The optoelectronic measurements show their relatively high conductivity with a pronounced sensitivity to light, which is promising in terms of photoswitching, photo-sensing, and photovoltaic applications also due to their reduced toxicity.

Tin telluride is a narrow gap semiconductor with promising properties for IR optical applications and topological insulators. We report a convenient colloidal synthesis of quasi-two-dimensional SnTe nanocrystals through the hot-injection method in a nonpolar solvent. By introducing the halide alkane 1-bromotetradecane as well as oleic acid and trioctylphosphine, the thickness of two dimensional SnTe nanostripes can be tuned down to 30 nm, while the lateral dimensional can reach 6 μm. The obtained SnTe nanostripes are single-crystalline with a rock-salt crystal structure. The absorption spectra demonstrate pronounced absorption features in the IR range revealing the effect of quantum confinement in such structures.

We present a colloidal synthesis strategy to obtain single-crystalline PbS nanorings. By controlling the ripening process in the presence of halide ions, a transformation of initial PbS nanosheets to frame-like structures and finally to nanorings was achieved. We found that the competing ligands oleic acid, oleate and halide ions play an important role in the formation of these nanostructures. Therefore, we propose a formation mechanism based on a thermally induced ripening of crystal facets dependent on the surface passivation. With this method, it became possible to synthesize colloidal nanorings of cubic crystal phase galena PbS. The synthesis was followed via TEM and the products are characterized by XRD, AFM and STEM tomography. Control of the initial nanoframe morphology allows adjusting the later nanoring dimensions.

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...