Synthesis and characterizations of quaternary Cu2FeSnS4 nanocrystals

Quaternary tetragonal Cu(2)FeSnS(4) nanocrystals have been synthesized by a simple hot-injection method. Detailed characterizations have been made. A suitable optical band gap of 1.28 ± 0.02 eV and a notable and stable photoelectrochemical response indicate their potential for application in solar cells.     

Cu2ZnGeSe4 nanocrystals: synthesis and thermoelectric properties

A synthetic route for producing Cu(2)ZnGeSe(4) nanocrystals with narrow size distributions and controlled composition is presented. These nanocrystals were used to produce densely packed nanomaterials by hot-pressing. From the characterization of the thermoelectric properties of these nanomaterials, Cu(2)ZnGeSe(4) is demonstrated to show excellent thermoelectric properties. A very preliminary adjustment of the nanocrystal composition has already resulted in a figure of merit of up to 0.55 at 450 °C.     

Fluoride-assisted synthesis of anatase TiO2 nanocrystals with tunable shape and band gap via a solvothermal approach

A simple solvothermal approach employing oleic acid has been developed to prepare anatase TiO₂ nanocrystals with different shapes, which were tuned from nanorods to nano-ellipsoids by increasing the amount of NaF from 0 to 0.5 mmol, and the optical band gap decreased from 3.47 eV to 3.29 eV accordingly. However, when the fluoride was changed to NH₄F, the resultant TiO₂ nanocrystals possessed an anatase phase but weremade up of smaller-sized nanocrystals and nanorods, and the band gap was increased to 3.53 eV. The X-ray photoelectron spectroscopy (XPS) results illustrated an increase of fluorine content with an increasing amount of NaF could account for the variation of the shape and optical band gap of TiO₂ nanocrystals. Moreover, the absence of fluorine content brought about less change of shape and increase of optical band gap of the product synthesized in the presence of NH₄F. This result may offer another way to alter the shape and band gap of metal oxide nanocrystals with the assistance of fluoride.     

Wurtzite Cu2ZnSnS4 nanocrystals: a novel quaternary semiconductor

A new wurtzite phase Cu(2)ZnSnS(4) was discovered and the corresponding nanocrystals have been successfully synthesized. They have been characterized in detail and showed the photoelectric response, which demonstrated their potential in the application of photovoltaic devices.     

Colloidal synthesis of Cu2CdSnSe4 nanocrystals and hot-pressing to enhance the thermoelectric figure-of-merit

We report a solution-based synthesis of monodispersed Cu(2)CdSnSe(4) nanocrystals and a study on the thermoelectric properties of these wide-band-gap dense materials compacted from nanocrystals for the first time. With the help of copper dopants and selenium vacancies generated during wet-chemistry synthesis, a large increment in the power factor is observed, and the dimensionless figure-of-merit ZT reaches a peak value of 0.65 at 450 °C.     

Controllable synthesis of Cu2S nanocrystals and their assembly into a superlattice

Highly uniform Cu2S nanocrystals with controllable sizes and shapes (circular and elongated) have been synthesized through a novel water-oil interface confined reaction. They can self-assemble into highly ordered multilayer superlattices. By controlling the size and shape of building block nanocrystals, the packing symmetry of the superlattice can be engineered. For circular nanocrystals, both fcc and hcp multilayer superlattices are found in the sample. For elongated nanocrystals, they can also generate a close-packed layer and further stack into a multilayer superlattice. The dipole moment of the inner nanocrystals is useful for their stacking. This work provides a simple bottom-up approach to integrate nanocrystals, as well as to adjust the packing symmetry of the final superlattice, which may have potential applications for nanomaterials and nanodevices in the future.     

Continuous production of Cu2ZnSnS4 nanocrystals in a flow reactor

A procedure for the continuous production of Cu(2)ZnSnS(4) (CZTS) nanoparticles with controlled composition is presented. CZTS nanoparticles were prepared through the reaction of the metals' amino complexes with elemental sulfur in a continuous-flow reactor at moderate temperatures (300-330 °C). High-resolution transmission electron microscopy and X-ray diffraction analysis showed the nanocrystals to have a crystallographic structure compatible with that of the kesterite. Chemical characterization of the materials showed the presence of the four elements in each individual nanocrystal. Composition control was achieved by adjusting the solution flow rate through the reactor and the proper choice of the nominal precursor concentration within the flowing solution. Single-particle analysis revealed a composition distribution within each sample, which was optimized at the highest synthesis temperatures used.     

Ultraviolet-emitting conjugated polymer poly(9,9'-alkyl-3,6-silafluorene) with a wide band gap of 4.0 eV

An ultraviolet-emitting conjugated polymer, poly(9,9'-alkyl-3,6-silafluorene) with a wide band gap of 4.0 eV, has been synthesized and characterized.     

Alloyed Cu2Fe1-xBaxSnS4 for photoelectrochemical applications: band gap tailoring and structural transition

Journal of Solid State Electrochemistry - Cu2Fe1-xBaxSnS4 (CFBTS) thin films have been fabricated by the low-cost successive ionic layer and adsorption reaction (SILAR) method. The bandgap energies...     

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.     

Cu(2+)-assisted synthesis of hexoctahedral Au-Pd alloy nanocrystals with high-index facets

Controlled syntheses of multicomponent metal nanocrystals (NCs) and high-index surfaces have attracted increasing attention due to the specific physical and chemical properties of such NCs. Taking advantage of copper underpotential deposition as a bridge, hexoctahedral Au-Pd alloy NCs with {hkl} facets exposed were successfully synthesized, while phase separation occurred in the absence of Cu(2+) ions. The as-prepared hexoctahedral Au-Pd alloy NCs exhibited very excellent performance in terms of both formic acid electro-oxidation and methanol tolerance due to synergism between the high-index facets and the alloy.     

Electrical bistability and memory switching phenomenon in Cu2FeSnS4 thin films: role of p-n junction

Journal of Solid State Electrochemistry - Electrical bistability of Cu2FeSnS4 (CFTS) thin films fabricated via successive ionic layer adsorption and reaction (SILAR) method was studied here. The...     

Size control and quantum confinement in Cu2ZnSnS4 nanocrystals

Starting with metal dithiocarbamate complexes, we synthesize colloidal Cu(2)ZnSnS(4) (CZTS) nanocrystals with diameters ranging from 2 to 7 nm. Structural and Raman scattering data confirm that CZTS is obtained rather than other possible material phases. The optical absorption spectra of nanocrystals with diameters less than 3 nm show a shift to higher energy due to quantum confinement.     

Solution-based synthesis of quaternary Cu-In-Zn-S nanobelts with tunable composition and band gap

We have demonstrated that quaternary Cu(x)In(x)Zn(2(1-x))S(2) nanobelts could be synthesized through a facile solution-based method. The composition and band gap of quaternary nanobelts can be tuned within the broad range by changing the relative ratio of precursors. The growth mechanism of quaternary nanobelts was deduced to be catalyst-assisted growth.     

Colloidal HgTe nanocrystals with widely tunable narrow band gap energies: from telecommunications to molecular vibrations

A convenient, aqueous-based synthesis of stable HgTe nanocrystals with widely size-tunable room temperature emission between wavelengths of 1.2 to 3.7 mum is demonstrated. By the choice of the thiols, applied as stabilizers, we optimized the growth dynamics, the luminescence quantum yields (up to 40%), and a ligand-exchange procedure, required to transfer the nanocrystals from water to nonpolar organic solvents. The latter is greatly improved and facilitated by the use of mercaptoethylamine as initial stabilizer. The possibility to tune the HgTe nanocrystal sizes from 3 to 12 nm and to control their surface functionalities (hydrophobic and hydrophilic) makes them very promising for the development of infrared optical devices, emitting in the wavelength region between the telecommunications and the molecular vibrations.     

Colloidal synthesis of magnetic CuCr2S4 nanocrystals and nanoclusters

Nanocrystals and nanoclusters of the room-temperature magnetic spinel CuCr(2)S(4) have been synthesized using a facile solution-based method. The synthesis involves hot injection of an excess of 1-dodecanethiol (1-DDT) into a boiling coordinating solvent containing CuCl(2) and CrCl(3)·6H(2)O. Using octadecylamine (ODA) as a solvent yields cube-shaped nanocrystals with an average size of 20 ± 2 nm, while with oleylamine (OLA), nanoclusters with an average size of 31 ± 2.5 nm are obtained. In both cases, powder X-ray diffraction patterns confirmed the formation of the pure spinel phase without any impurities. While the synthesized powders are superparamagnetic near room temperature, they exhibit ferromagnetic behavior at lower temperatures, with magnetization (M(S)) values of 30 emu/g (1.63 μ(B)/f.u.) and 33 emu/g (1.79 μ(B)/f.u.) for the ODA- and OLA-capped nanocrystals and nanoclusters, respectively, at 5 K.     

Reversible tunability of the near-infrared valence band plasmon resonance in Cu(2-x)Se nanocrystals

We demonstrate that colloidal Cu(2-x)Se nanocrystals exhibit a well-defined infrared absorption band due to the excitation of positive charge carrier oscillations (i.e., a valence band plasmon mode), which can be tuned reversibly in width and position by varying the copper stoichiometry. The value of x could be incrementally varied from 0 (no plasmon absorption, then a broad peak at 1700 nm) to 0.4 (narrow plasmon band at 1100 nm) by oxidizing Cu(2)Se nanocrystals (upon exposure either to oxygen or to a Ce(IV) complex), and it could be incrementally restored back to zero by the addition of a Cu(I) complex. The experimentally observed plasmonic behavior is in good agreement with calculations based on the electrostatic approximation.