Solventless synthesis of copper sulfide nanorods by thermolysis of a single source thiolate-derived precursor

Organic monolayer protected Cu2S nanorods, 4 nm in diameter and 12 nm long, were synthesized using a novel solventless synthetic approach. Thermolytic degradation of a copper thiolate precursor at temperatures ranging from 140 to 200 degrees C produces Cu2S nanorods. Higher temperatures promote isotropic growth of spherical nanocrystals. X-ray diffraction and high-resolution TEM reveal that the nanorods exhibit a hexagonal Cu2S crystal structure, which in the bulk is ferroelectric. The appropriate reaction conditions produce nanorods that are size and shape monodisperse and organize into smectic superlattices. The extent of superlattice ordering and the appearance of extended strands of nanorods provide evidence for strong dipole-dipole coupling between Cu2S nanorods.     

Synthesis of hybrid CdS-Au colloidal nanostructures

We explore the growth mechanism of gold nanocrystals onto preformed cadmium sulfide nanorods to form hybrid metal nanocrystal/semiconductor nanorod colloids. By manipulating the growth conditions, it is possible to obtain nanostructures exhibiting Au nanocrystal growth at only one nanorod tip, at both tips, or at multiple locations along the nanorod surface. Under anaerobic conditions, Au growth occurs only at one tip of the nanorods, producing asymmetric structures. In contrast, the presence of oxygen and trace amounts of water during the reaction promotes etching of the nanorod surface, providing additional sites for metal deposition. Three growth stages are observed when Au growth is performed under air: (1) Au nanocrystal formation at both nanorod tips, (2) growth onto defect sites on the nanorod surface, and finally (3) a ripening process in which one nanocrystal tip grows at the expense of the other particles present on the nanorod. Analysis of the hybrid nanostructures by high-resolution TEM shows that there is no preferred orientation between the Au nanocrystal and the CdS nanorod, indicating that growth is nonepitaxial. The optical signatures of the nanocrystals and the nanorods (i.e., the surface plasmon and first exciton transition peaks, respectively) are spectrally distinct, allowing the different stages of the growth process to be easily monitored. The initial CdS nanorods exhibit band gap and trap state emission, both of which are quenched during Au growth.     

Cu(1.94)S nanocrystal seed mediated solution-phase growth of unique Cu(2)S-PbS heteronanostructures

Unique Cu(2)S-PbS heteronanostructures with good photothermal conversion effect have been synthesized for the first time by a Cu(1.94)S nanocrystal seed mediated colloidal solution-phase growth method. The present nanocrystal seed mediated growth method may be extended for the growth of other unique semiconductor heteronanostructures.     

Nickel sulfide and copper sulfide nanocrystal synthesis and polymorphism

Nickel sulfide and copper sulfide nanocrystals were synthesized by adding elemental sulfur to either dichlorobenzene-solvated (copper sulfide) or oleylamine-solvated metal(II) precursors (nickel sulfide) at relatively high temperature to produce the metal sulfide. Nickel sulfide nanocrystals are cubic Ni(3)S(4) (polydymite) with irregular prismatic shapes, forming by a two-step reduction-sulfidation mechanism where Ni(II) reduces to Ni metal before sulfidation to Ni(3)S(4). Despite extensive efforts to optimize the Ni(3)S(4) nanocrystal size and shape distributions, polydisperse nanocrystals are produced. In contrast, copper sulfide nanocrystals can be obtained with narrow size and shape distributions. The copper sulfide stoichiometry depended on the Cu:S mole ratio used in the reaction: Cu:S mole ratios of 1:2 and 2:1 gave CuS (covellite) and Cu(1.8)S (digenite), respectively. CuS nanocrystals formed as hexagonal disks that assemble into stacked ribbons when cast from solution onto a substrate. CuS, Cu(1.8)S, and Ni(3)S(4) differ from the Cu(2)S and NiS nanocrystals obtained by solventless decomposition of metal thiolate single source precursors, in terms of stoichiometry for copper sulfide, and both stoichiometry and morphology for nickel sulfide [Ghezelbash, A.; Sigman, M. B., Jr.; Korgel, B. A. Nano Lett. 2004, 4, 537-542. Sigman, M. B. Ghezelbash, A.; Hanrath, T.; Saunders, A. E.; Lee, F.; Korgel, B. A. J. Am. Chem. Soc. 2003, 125, 16050-16057].     

A facile chemical route to semiconductor metal sulfide nanocrystal superlattices

We report a facile chemical route for the synthesis of monodisperse nanocrystals of various metal sulfides (PbS, Cu(2)S, and Ag(2)S) and their assemblies into nanocrystal superlattices (NCSs); the sulfides NCSs were precipitated by adding ethanol to nanocrystal colloids, which were obtained directly by a reaction between metal thiolate and thioacetamide in a pure dodecanethiol solvent.     

A facile "dispersion-decomposition" route to metal sulfide nanocrystals

In this paper, we demonstrate a simple and general "dispersion-decomposition" approach to the synthesis of metal sulfide nanocrystals with the assistance of alkylthiol. This is a direct heating process without precursor injection. By using inorganic metal salts and alkylthiol as the raw materials, high-quality Ag(2)S, Cu(2)S, PbS, Ni(3)S(4), CdS, and ZnS nanocrystals were successfully synthesized. The mechanism study shows that the reaction undergoes two steps. A key intermediate compound, metal thiolate, is generated first. It melts and disperses into the solvent at a relatively low temperature, and then it decomposes into metal sulfide as a single precursor upon heating. This method avoids using toxic phosphine agent and injection during the reaction process. The size and shape of the nanocrystal can be also controlled by the concentration of the reactant and ligands. Furthermore, the optical properties and assembly of the nanocrystals have also been studied. This report provides a facile, direct-heating "dispersion-decomposition" approach to synthesize metal sulfides nanocrystals that has potential for future large-scale synthesis.     

Laser-induced silver nanocrystal formation in polyvinylpyrrolidone solutions

We report unusual laser-induced shape conversions of silver nanoparticles dispersed in polyvinylpyrrolidone (PVP) aqueous solutions. Silver nanocrystals such as nanoplates and nanorods were formed using laser irradiation for colloidal silver nanoparticles prepared using laser ablation in aqueous solutions of PVP. Differing from the nanocrystal formation observed in neat water and halide solutions, which were induced by weak laser or fluorescent-light irradiation, the nanocrystal formation in PVP solutions was induced by strong laser irradiation. On the other hand, nanocrystal formation was not observed in polyvinylalcohol (PVA) solutions, in which fusion of nanoparticles were prominent. It is proposed that the nanocrystals were formed from fragmented nanoparticles protected by PVP via a ripening process.     

Synthesis and shape control of CuInS(2) nanoparticles

Cu(2)S-CuInS(2) hybrid nanostructures as well as pure CuInS(2) (CIS) nanocrystals were synthesized by methods of colloidal chemistry. The structure, the shape and the composition of these nanomaterials were investigated with transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX). By changing the reaction conditions, CuInS(2) nanorods with different aspect ratio, dimeric nanorods as well as hexagonal discs and P-shaped particles could be synthesized. Under our reaction conditions, CIS nanoparticles crystallize in the hexagonal wurtzite structure, as confirmed by Rietveld analysis of the X-ray diffraction patterns. The formation of Cu(2)S-CuInS(2) hybrid nanostructures turned out to be an essential intermediate step in the growth of CIS nanoparticles, the copper sulphide part of the hybrid material playing an important role in the shape control of the CIS nanocrystals. By a treatment of Cu(2)S-CuInS(2) with 1,10-phenanthroline, Cu(2)S parts of the hybrid nanostructures could be removed, and pure CIS nanoparticles with shapes not accessible with other methods can be obtained. Our synthetic procedure turned out to be suitable to synthesize also other compounds, like CuInS(2)-ZnS alloys, and to modify, in this way, the optical properties of the nanocrystals.     

Metal-cation-mediated nanocrystal arrays of sandwich-type (phthalocyaninato) [tetrakis(4-pyridyl)porphyrinato] cerium complex formed at the water-chloroform interface

Regular square, wirelike, quadrate, and rodlike nanocrystal arrays of Cd2+, Hg2+, or Ag+ metal-cation-mediated sandwich-type mixed (phthalocyaninato) [5,10,15,20-tetrakis(4-pyridyl)poprhyrinato] cerium(III) double-decker complex Ce(Pc)(TPyP) have been successfully prepared at the water-chloroform interface. The nanocrystal growth processes were monitored by transmission electron microscopy (TEM), which reveals that different morphologies of nanocrystals have been fabricated from double-decker molecules connected by different kinds of metal cations, forming coordination polymers. These nanoscaled coordination polymers were characterized by FT-IR spectra and energy-dispersive X-ray spectra (EDS). EDS results clearly revealed the elements of the nanocrystals and the FT-IR spectra give evidence for the coordination interaction between the double-decker molecules and metal cations. The UV-vis absorption spectrum indicates the formation of J-aggregates of the double-decker molecules in the nanocrystals formed.     

One-pot controlled synthesis of hexagonal-prismatic Cu1.94S-ZnS, Cu1.94S-ZnS-Cu1.94S, and Cu1.94S-ZnS-Cu1.94S-ZnS-Cu1.94S heteronanostructures

Playing six-a-side: Complex hexagonal prism Cu(1.94)S-ZnS heteronanostructures were synthesized by a colloidal route. Cu(1.94)S-ZnS, Cu(1.94)S-ZnS-Cu(1.94)S, and Cu(1.94)S-ZnS-Cu(1.94)S-ZnS-Cu(1.94)S structures are formed with screw-, dumbbell-, and sandwich-like shapes by using CuI and [Zn(S(2)CNEt(2))(2)] as precursors in oleylamine.     

Controlled synthesis, growth mechanism, and properties of monodisperse CdS colloidal spheres

Highly monodisperse submicrometer CdS colloidal spheres (CSCS) with a controllable and tunable size (between 80 and 500 nm) have been synthesized through a facile solvothermal technique. Owing to the controllability of the reaction process, the growth mechanism of the colloidal spheres has been elucidated in detail. The whole growth process can be summarized as homogenous and slow nucleation of nanocrystals, formation of "cores" through 3D-oriented attachment of nanocrystals, and further surface-induced growth to monodisperse colloidal spheres through in situ formation and random attachment of additional nanocrystals. It has been demonstrated that the obtained CSCS colloidal particles are able to be assembled into films which show characteristic stop band gaps of photonic crystals. By using the CSCS as a template, Ag2S, Bi2S3, Cu2S, HgS, and Sb2S3 colloidal spheres, which are difficult to obtain directly, have also been prepared successfully through ion exchange.     

Study of Interactions in the CuInS2-FeS System

Russian Journal of General Chemistry - The CuInS2-FeS section of the ternary Cu2S-In2S3-FeS system has been studied by means of differential thermal, X-ray diffraction, and microstructural...     

Morphological control and luminescent properties of YVO4:Eu nanocrystals

Rodlike, olivelike, pineapplelike, and particlelike nanocrystals of theYVO4:Eu (5 at. % Eu) were synthesized by a hydrothermal reaction with different conditions, respectively. The rodlike nanocrystal has a rectangular cross-section with about 35 x 60 nm2 and a length of about 220 nm. The olivelike nanocrystal has an equatorial diameter of approximately 40 nm and a length of approximately 200 nm. The pineapplelike nanocrystal with an equatorial diameter of approximately 200 nm and a length of approximately 300 nm, is a superstructure consisting of self-organized nanorods with a diameter of approximately 20 nm and a length of approximately 50 nm. The particlelike nanocrystals show globular and polyhedral shape with a diameter of approximately 50 nm. Their UV-vis absorption peaks are at 305, 308, 285, and 280 nm, respectively, and there is such a trend that the absorption peaks shift to higher energy as the size of the particles decreases. Compared with other-shape nanocrystals, the luminescence intensity of the olivelike nanocrystals is obviously enhanced. It suggests that we could obtain the function-improved materials by tailoring the size and shape of theYVO4:Eu nanostructures.     

Formation of different gold nanocrystal core-resin shell structures through the control of the core assembly and shell polymerization

The formation of different Au nanocrystal core-resin shell structures through the control of the nanocrystal assembly and shell polymerization is investigated. 4-Mercaptophenol is employed together with formaldehyde as the resin monomers. 4-Mercaptophenol molecules bond to the surface of Au nanocrystals so that the resultant phenolic resin can intimately encapsulate Au nanocrystals. The morphologies of the obtained structures are determined by the nanocrystal assembly and the monomer polymerization behaviors, which are controlled by the solution pH as well as the monomer amounts. At pH = 8-9, Au nanorods are assembled and fused together under hydrothermal conditions in a preferential end-to-end manner. The fused structures are coated with a layer of resin, with the thickness controlled by the supplied amounts of the monomers. At pH = ～10, Au nanorods are coated with resin of controllable thicknesses and separated from each other. The resin-coated Au nanorods are stable in both aqueous and nonaqueous solutions. At pH = ～12, Au nanorods are coated with a thin layer of resin and assembled together in a side-by-side manner. A similar assembly and resin coating behavior is also observed with Au nanopolyhedrons. Moreover, plasmonic-fluorescent bifunctional structures are readily produced by incorporating CdTe nanocrystals in the resin shell that is coated on Au nanocrystals, owing to the presence of a number of thiol groups in the resin shell.     

Synthesis and characterization of Cu(In(x)B(1-x))Se2 nanocrystals for low-cost thin film photovoltaics

Chalcopyrite quaternary semiconductor Cu(In(x)B(1-x))Se(2) nanocrystals have been successfully prepared via a relatively simple and convenient solvothermal route. The effect of different solvents on the formation of the product also indicates that diethylenetriamine is the optimal solvent for this reaction. The device parameters for a single junction Cu(In(x)B(1-x))Se(2) solar cell under AM1.5G are as follows: an open circuit voltage of 265 mV, a short-circuit current of 25.90 mA/cm(2), a fill factor of 34%, and a power conversion efficiency of 2.34%. Based on a series of comparative experiments under different reaction conditions, the probable formation mechanism of crystal Cu(In(x)B(1-x))Se(2) nanorods is proposed.     

Shape evolution of Cu2O nanostructures via kinetic and thermodynamic controlled growth

We report the shape evolution process of Cu(2)O nanocrystals upon slow oxidation of Cu under ambient conditions, yielding novel hexagonal and triangular platelike morphologies. The shape of the obtained nanocrystals evolves from hexagonal to triangular to octahedral; the growth patterns are governed by kinetically and thermodynamically controlled growth. Preferential adsorption of I(-) on {111} planes of Cu(2)O nanoparticles induced the selective crystal growth of metastable platelike structures with {111} faces as the basal planes. On aging, the growth process appeared to shift into the thermodynamic regime and the thermodynamically stable octahedral shape is obtained. The possible growth mechanisms were investigated by varying the synthetic conditions. The band gap of Cu(2)O nanooctahedrons was determined by the classical Tauc approach to be 2.24 eV, which is blue shifted with respect to the bulk Cu(2)O value (2.17 eV). Results suggest that the slow oxidation process and use of crystallographic selective surfactants are essential for the appearance of anisotropic metastable shapes. In general, surface energy control by surfactant molecules might provide a convenient channel for tailoring nanocrystal shapes of metal oxides.     

Synthesis of organic monolayer-stabilized copper nanocrystals in supercritical water

When water is heated and pressurized above the critical point, it becomes a suitable solvent to employ organic capping ligands to control and stabilize the synthesis of nanocrystals. Without alkanethiol ligands, Cu(NO(3))(2) hydrolyzes to form polydisperse copper(II) oxide particles with diameters from 10 to 35 nm. However, in the presence of 1-hexanethiol, X-ray photoelectron spectroscopy, selected area electron diffraction, and transmission electron microscopy reveal the formation of copper nanocrystals approximately 7 nm in diameter. The use of a different precursor, Cu(CH(3)COO)(2), leads to particles with significantly different morphologies. A mechanism is proposed for sterically stabilized nanocrystal growth in supercritical water that describes competing pathways of hydrolysis to large oxidized copper particles versus ligand exchange and arrested growth by thiols to produce small monodisperse Cu nanoparticles.     

Formation pathway of CuInSe2 nanocrystals for solar cells

Copper, indium, and gallium chalcogenide nanocrystals (binary, ternary, and quaternary) have been used to fabricate high-efficiency thin-film solar cells. These solution-based methods are being scaled-up and may serve as the basis for the next generation of low-cost solar cells. However, the formation pathway to reach stoichiometric ternary CuInSe(2) or any chalcopyrite phase ternary or quaternary nanocrystal in the system has not been investigated but may be of significant importance to improving nanocrystal growth and discovering new methods of synthesis. Here, we present the results of X-ray diffraction, electron microscopy, compositional analysis, IR absorption, and mass spectrometry that reveal insights into the formation pathway of CuInSe(2) nanocrystals. Starting with CuCl, InCl(3), and elemental Se all dissolved in oleylamine, the overall reaction that yields CuInSe(2) involves the chlorination of the hydrocarbon groups of the solvent. Further, we show that the amine and alkene functional groups in oleylamine are not necessary for the formation of CuInSe(2) nanocrystals by conducting successful syntheses in 1-octadecene and octadecane. Hence, the role of oleylamine is not limited to nanocrystal size and morphology control; it also acts as a reactant in the formation pathway. Typically, the formation of copper selenide (CuSe) and indium selenide (InSe) nanocrystals precedes the formation of CuInSe(2) nanocrystals in oleylamine. But it was also found that Cu(2-x)Se (0 < x < 0.5) and In(2)Se(3) were the primary intermediates involved in the formation of CISe in a purely non-coordinating solvent such as 1-octadecene, which points to the surface-stabilization effect of the coordinating solvent on the less thermodynamically stable indium selenide (InSe) nanocrystals. We also show that the yield of the chalcopyrite phase of CuInSe(2) (as opposed to the sphalerite phase) can be increased by reacting CuSe nanocrystals with InCl(3).     

Homogeneously alloyed CdSxSe1-x nanocrystals: synthesis, characterization, and composition/size-dependent band gap

Alloy nanocrystals provide an additional degree of freedom in selecting desirable properties for nanoscale engineering because their physical and optical properties depend on both size and composition. We report the pyrolytic synthesis of homogeneously alloyed CdS(x)Se(1-x) nanocrystals in all proportions. The nanocrystals are characterized using UV-visible absorption spectroscopy, transmission electron microscopy, X-ray diffractrometry, and Rutherford backscattering spectrometry to determine precisely structure, size, and composition. The dependence of band gap on nanocrystal size and composition is elucidated, yielding a bowing constant of 0.29, in agreement with bulk values. In addition, the morphology of the resultant nanocrystals can be altered by changing the reaction conditions, generating structures ranging from homogeneous, spherical nanocrystals to one-dimensional gradient nanorods.     

Alloyed ZnS–CuInS2 Semiconductor Nanorods and Their Nanoscale Heterostructures for Visible‐Light‐Driven Photocatalytic Hydrogen Generation

A promising photocatalytic system in the form of heterostructured nanocrystals (HNCs) is presented wherein alloyed ZnS–CuInS₂ (ZCIS) semiconductor nanorods are decorated with Pt and Pd₄S nanoparticles. This is apparently the first report on the colloidal preparation and photocatalytic behavior of ZCIS–Pt and ZCIS–Pd₄S nanoscale heterostructures. Incorporation of Pt and Pd₄S cocatalysts leads to considerable enhancement of the photocatalytic activity of ZCIS for visible‐light‐driven hydrogen production.