Function Follows Form: From Semiconducting to Metallic toward Superconducting PbS Nanowires by Faceting the Crystal

Abstract

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...

Surface Defines the Properties: Colloidal Bi2Se3 Nanosheets with High Electrical Conductivity

“…Surfaceinduced off-stoichiometry was already reported as a theoretical possibility for occurring midgap (surface) states at the Fermi level of PbS and the disappearance of the band gap at raising off-stoichiometry. 35,36 However, an effective passivation with surface cations reopens the band gap, 37 returning the sample its semiconducting properties. The surface bismuth in our case is linked to the PVP ligands and obviously to oxygen (Bi−O bond from XPS), and the possible dangling bonds producing metallic states are thus (at least partially) saturated.…”

The Promise of Soft‐Matter‐Enabled Quantum Materials

“…[356] The application of soft matter for the synthesis of quantum materials in the thin film regime has already begun paying dividends, shown in earlier sections on superconductors, [114,115] topological materials, [155,165] multiferroics, [187,190] or spintronics. [79,[198][199][200]210] However, future work in this area may seek to take full advantage of the established techniques and capabilities present in soft matter thin film formation for the creation of new quantum metamaterials or devices. To begin, soft matter is already ubiquitous in nanofabrication in the form of photoresists, liftoff layers, packaging materials, and many other forms.…”

“…In the quasi-0D regime, much work has been performed to create nanoscale superconducting objects. In many studies, quantum dot synthetic techniques have been used to create isolated nano-objects or weakly Josephson coupled arrays of superconducting lead nanocrystals, [68,[75][76][77][78] Pb/PbSe core shell particles, [79] gallium nanoclusters, [80] or palladium bismuth chalcogenide nanoparticles. [81] In much of this work, it has been found that critical field strength and critical temperature typically increase with decreasing material size until a certain material-dependent point, at which critical field, H c , and T c decrease until superconductivity is lost.…”

“…[82] By tuning the ligand composition during growth, Moayed et al synthesized superconducting "zigzag" lead sulfide (PbS) nanowires. [79] Bezryadin and co-workers used DNA molecules as templates for superconducting wires (Figure 3d). [72,84,85] Electrodeposition into track etched polycarbonate membranes has also very often been used to create nanowires [86] (Figure 3b) of ruthenium, [87] gold, [88] bismuth, [89][90][91][92] zinc, [69,[93][94][95][96] tin, [97][98][99][100][101][102][103][104][105] lead, [97,99,[105][106][107][108][109] or composites and alloys thereof.…”

Anomalous behavior induced by water insertion in molybdenum disulfide nanoflowers

“…For instance, alkali metal intercalation, substitutional doping, strain effect, and structural transformation induced metallike behavior in semiconductors but increased the scattering rate and reduced the mobility of charge carriers [6][7][8][9]. It was only recently demonstrated that metallic and superconducting phases in a semiconductor can be achieved through surface reconstruction [10]. Notwithstanding this development, realizing metal-like behavior in conventional semiconductors is still elusive.…”