The Valuation of Callable Russian Options for Double Exponential Jump Diffusion Processes (Financial Modeling and Analysis)

There is a strong interest to attach nanoparticles noncovalently to one-dimensional systems like boron nitride nanotubes to form composites. The combination of those materials might be used for catalysis, in solar cells, or for water splitting. Additionally, the fundamental aspect of charge transfer between the components can be studied in such systems. We report on the synthesis and characterization of nanocomposites based on semiconductor nanoparticles attached directly and noncovalently to boron nitride nanotubes. Boron nitride nanotubes were simply integrated into the colloidal synthesis of the corresponding nanoparticles. With PbSe, CdSe, and ZnO nanoparticles, a wide range of semiconductor band gaps from the near-infrared to the ultraviolet range was covered. A high surface coverage of the boron nitride nanotubes with these semiconducting nanoparticles was achieved, while it was found that a similar <i>in situ</i> approach with metallic nanoparticles does not lead to proper attachment. In addition, possible models for the underlying attachment mechanisms of all investigated nanoparticles are presented. To emphasize the new possibilities that boron nitride nanotubes offer as a support material for semiconductor nanoparticles, we investigated the fluorescence of BN-CdSe composites. In contrast to CdSe nanoparticles attached to carbon nanotubes, where the fluorescence is quenched, particles attached to boron nitride nanotubes remain fluorescent. With our versatile approaches, we expand the library of BN-nanoparticle composites that present an interesting, electronically noninteracting complement to the widely applied carbon nanotube-nanoparticle composite materials

A New Synthesis Approach for Carbon Nitrides: Poly(triazine imide) and Its Photocatalytic Properties

Poly­(triazine imide) (PTI) is a material belonging to the group of carbon nitrides and has shown to have competitive properties compared to melon or g-C₃N₄, especially in photocatalysis. As most of the carbon nitrides, PTI is usually synthesized by thermal or hydrothermal approaches. We present and discuss an alternative synthesis for PTI which exhibits a pH-dependent solubility in aqueous solutions. This synthesis is based on the formation of radicals during electrolysis of an aqueous melamine solution, coupling of resulting melamine radicals and the final formation of PTI. We applied different characterization techniques to identify PTI as the product of this reaction and report the first liquid state NMR experiments on a triazine-based carbon nitride. We show that PTI has a relatively high specific surface area and a pH-dependent adsorption of charged molecules. This tunable adsorption has a significant influence on the photocatalytic properties of PTI, which we investigated in dye degradation experiments

From Dots to Stripes to Sheets: Shape Control of Lead Sulfide Nanostructures

Controlling anisotropy in nanostructures is a challenging but rewarding task because confinement in one or more dimensions influences the physical and chemical properties of the items decisively. In particular, semiconducting nanostructures can be tailored to gain optimized properties to work as transistors or absorber material in solar cells. We demonstrate that the shape of colloidal lead sulfide nanostructures can be tuned from spheres to stripes to sheets by means of the precursor concentrations, the concentration of a chloroalkane coligand and the synthesis temperature. All final structures still possess at least one dimension in confinement. The structures cover all dimensionalities from 0D to 3D. Additionally, the effect of temperature on the shape and thickness of PbS nanosheets is shown and electrical transport measurements complement the findings

Synthesis and Characterization of Monodisperse Metallodielectric SiO₂@Pt@SiO₂ Core–Shell–Shell Particles

Metallodielectric nanostructured core–shell–shell particles are particularly desirable for enabling novel types of optical components, including narrow-band absorbers, narrow-band photodetectors, and thermal emitters, as well as new types of sensors and catalysts. Here, we present a facile approach for the preparation of submicron SiO₂@Pt@SiO₂ core–shell–shell particles. As shown by transmission and scanning electron microscopy, the first steps of this approach allow for the deposition of closed and almost perfectly smooth platinum shells onto silica cores via a seeded growth mechanism. By choosing appropriate conditions, the shell thickness could be adjusted precisely, ranging from ∼3 to ∼32 nm. As determined by X-ray diffraction, the crystalline domain sizes of the polycrystalline metal shells were ∼4 nm, regardless of the shell thickness. The platinum content of the particles was determined by atomic absorption spectroscopy and for thin shells consistent with a dense metal layer of the TEM-measured thickness. In addition, we show that the roughness of the platinum shell strongly depends on the storage time of the gold seeds used to initiate reductive platinum deposition. Further, using polyvinylpyrrolidone as adhesion layer, it was possible to coat the metallic shells with very homogeneous and smooth insulating silica shells of well-controlled thicknesses between ∼2 and ∼43 nm. After depositing the particles onto silicon substrates equipped with interdigitated electrode structures, the metallic character of the SiO₂@Pt particles and the insulating character of the SiO₂ shells of the SiO₂@Pt@SiO₂ particles were successfully demonstrated by charge transport measurements at variable temperatures

Template-Mediated Formation of Colloidal Two-Dimensional Tin Telluride Nanosheets and the Role of the Ligands

We report the colloidal synthesis of 2D SnTe nanosheets through precursor hot injection in a nonpolar solvent. During the reaction, an important intermediateSn-templateis formed which defines the confined growth of SnTe. This “flake-like” structure gives the first evidence for the possible 2D morphology formation prior to the anion precursor injection (TOP-Te). Additionally, we explore the role of each ligand in the reaction process. Thus, we explain the formation and morphology evolution of 2D SnTe nanostructures from a mechanism perspective as well as the role of each ligand on the molecular scale. The interplay of ligands provides the necessary conditions for the realization of stable low-dimensional SnTe nanomaterials with tunable size and shape

Supramolecular Interaction of Single-Walled Carbon Nanotubes with a Functional TTF-Based Mediator Probed by Field-Effect Transistor Devices

The supramolecular interaction between individual single-walled carbon nanotubes and a functional organic material based on tetrathiafulvalene is investigated by means of electric transport measurements in a field-effect transistor configuration as well as by NIR absorption spectroscopy. The results clearly point to a charge-transfer interaction in which the adsorbed molecule serves as an electron acceptor for the nanotubes through its pyrene units. Exposure to iodine vapors enhances this effect. The comparison with pristine carbon nanotube field-effect transistor devices demonstrates the possibility to exploit charge-transfer interactions taking place in supramolecular assemblies in which a mediator unit is used to transduce and enhance an external signal

Correlating Superlattice Polymorphs to Internanoparticle Distance, Packing Density, and Surface Lattice in Assemblies of PbS Nanoparticles

Assemblies of 3.5 nm PbS nanoparticles (NPs) nucleate in three dominant superlattice polymorphs: amorphous, body-centered-cubic (bcc) and face-centered-cubic (fcc) phase. This superlattice relationship can be controlled by the inter-NP distance without changing the NP size. Upon increase of inter-NP distance, the packing density decreases, and the capping molecules at NP surfaces change in structure and accordingly modify the surface energy. The driving force for NP assembly develops from an entropic maximization to a reduction of total free energy through multiple interactions between surface molecules and NPs and resulting variation of surface molecules. Upon long-term aging and additional thermal treatment, fcc undergoes a tetragonal distortion and subsequently transforms to bcc phase, and simultaneously, the NPs embedded in supercrystals reduce surface energy primarily in {200} facets. Linking molecule-NP interactions with a series of changes of packing density and surface lattice spacings of NPs allows for an interpretation of principles governing the nucleation, structure stability, and transformation of PbS NP-assembled supercrystals

Competing Interactions between Various Entropic Forces toward Assembly of Pt₃Ni Octahedra into a Body-Centered Cubic Superlattice

Anisotropic nanocrystal assembled supercrystals with open superlattices (SLs) manifest novel and unique properties, but poor understanding of the nucleation/growth mechanisms limits their design and fabrication for practical applications. Using highly anisotropic Pt₃Ni octahedral nanocrystals, we have grown large single supercrystals with an open body-centered cubic (bcc) superlattice that has a low filling factor of 26.8%. Synchrotron-based X-ray structural reconstruction fully revealed the coherence of translational and orientational orderings and determined that the constituent octahedra arrange themselves with the vertex-to-vertex and face-to-face configurations along the SL[100] and SL[111] directions, respectively. The large face-to-face separation and flexible vertex-to-vertex elastic contact provided the rattle space and supporting axis for local rotations of Pt₃Ni octahedra within the bcc superlattice. Development of orientational disordering along with robust preservation of translational ordering during the heating process of a supercrystal in the oleic acid wetting environment confirmed the dominance of rotational entropy of hard octahedra in the formation of the open bcc superlattice. Ultimate achievement of dynamic equilibrium between the vertex-oriented elastic repulsions and the face-oriented attractions of surface-coating ligands governs the structural and mechanical stability of the supercrystal. This discovery provides significant insights into the design and control of geometrical shapes for the fabrication of highly anisotropic nanocrystals into desired open superlattices with tailored optical and electronic properties

Shell or Dots − Precursor Controlled Morphology of Au–Se Deposits on CdSe Nanoparticles

The most prevalent image of the morphology of Au–CdSe hybrid nanoparticles (HNPs) is that of dumbbells or matchsticks with CdSe nanoparticles (NPs) acting as seed material onto which spherical Au dots are deposited. On the basis of a system with only three reaction components, CdSe seeds, <i>n</i>-dodecyltrimethylammonium bromide-complexed AuCl₃, and dodecanethiol, we demonstrate how the morphology of the Au deposits on the semiconductor NPs, either in the form of dots on the vertices or in the form of a shell around the NP surface, can be determined by controlling the oxidation state of the metal precursor. Furthermore, we apply X-ray photoelectron spectroscopy to show that the resultant deposits are composed of partially oxidized Au, corresponding to a Au–Se compound regardless the deposit morphology. To obtain a detailed characterization of the HNPs with different morphologies and to gain mechanistic insights into the deposition process, (cryogenic) high-resolution transmission electron microscopy, mass spectrometry, cyclic voltammetry, and computational simulations have been performed. Our results emphasize that the knowledge of the surface chemistry of the seed particles as well as a defined picture of the metal precursors is necessary to understand heterodeposition processes

QSAR Models for P-450 (2D6) Substrate Activity

Halogen compounds are capable of playing an important role in the manipulation of nanoparticle shapes and properties. In a new approach, we examined the shape evolution of CdSe nanorods to hexagonal pyramids in a hot-injection synthesis under the influence of halogenated additives in the form of organic chlorine, bromine and iodine compounds. Supported by density functional theory calculations, this shape evolution is explained as a result of X-type ligand coordination to sloped and flat Cd-rich facets and an equilibrium shape strongly influenced by halides. Synchrotron XPS measurements and TXRF results show that the shape evolution is accompanied by a modification in the chemical composition of the ligand sphere. Our experimental results suggest that the molecular structure of the halogenated compound is related to the degree of the effect on both rod growth and further shape evolution. This presents a new degree of freedom in nanoparticle shape control and highlights the role of additives in nanoparticle synthesis and their possible in situ formation of ligands