Synthesis of highly non-stoichiometric Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> nanoparticles with tunable bandgaps

Non-stoichiometric Cu₂ZnSnS₄ nanoparticles with average diameters of 4–15 nm and quasi-polyhedral shape were successfully synthesized by a colloidal method. We found that a non-stoichiometric composition of Zn to Cu in Cu₂ZnSnS₄ nanoparticles yielded a correlation where Zn content increased with a decrease in Cu content, suggesting formation of lattice defects relating to Cu and Zn, such as a Cu vacancy (V_Cu), antisite with Zn replacing Cu (Zn_Cu), and/or defect cluster of V_Cu and Zn_Cu. The bandgap energy of Cu₂ZnSnS₄ nanoparticles systematically varies between 1.56 and 1.83 eV depending on the composition ratios of Cu and Zn, resulting in a wider bandgap for Cu-deficient Cu₂ZnSnS₄ nanoparticles. These characteristics can be ascribed to the modification in electronic band structures due to formation of V_Cu and Zn_Cu on the analogy of ternary copper chalcogenide, chalcopyrite CuInSe₂, in which the top of the valence band shifts downward with decreasing Cu contents, because much like the structure of CuInSe₂, the top of the valence band is composed of a Cu 3d orbital in Cu₂ZnSnS₄.     

Doctor-bladed Cu2ZnSnS4 light absorption layer for low-cost solar cell application

The doctor-blade method is investigated for the preparation of Cu₂ZnSnS₄ films for low-cost solar cell application. Cu₂ZnSnS₄ precursor powder, the main raw material for the doctor-blade paste, is synthesized by a simple ball-milling process. The doctor-bladed Cu₂ZnSnS₄ films are annealed in N₂ ambient under various conditions and characterized by X-ray diffraction, ultraviolent/vis spectrophotometry, scanning electron microscopy, and current-voltage (J-V) meansurement. Our experimental results indicate that (i) the X-ray diffraction peaks of the Cu₂ZnSnS₄ precursor powder each show a red shift of about 0.4°; (ii) the high-temperature annealing process can effectively improve the crystallinity of the doctor-bladed Cu₂ZnSnS₄, whereas an overlong annealing introduces defects; (iii) the band gap value of the doctor-bladed Cu₂ZnSnS₄ is around 1.41 eV; (iv) the short-circuit current density, the open-circuit voltage, the fill factor, and the efficiency of the best Cu₂ZnSnS₄ solar cell obtained with the superstrate structure of fluorine-doped tin oxide glass/TiO₂/In₂S₃/Cu₂ZnSnS₄/Mo are 7.82 mA/cm², 240 mV, 0.29, and 0.55%, respectively.     

Three‐Dimensional Multilayer Assemblies of MoS2/Reduced Graphene Oxide for High‐Performance Lithium Ion Batteries

Three‐dimensional (3D) multilayer molybdenum disulfide (MoS₂)/reduced graphene oxide (RGO) nanocomposites are prepared by a solution‐processed self‐assembly based on the interaction using different sizes of MoS₂ and GO nanosheets followed by in situ chemical reduction. 3D multilayer assemblies with MoS₂ wrapped by large RGO nanosheets and good interface are observed by transmission electron microscopy. The interaction of Na⁺ ions with oxygen‐containing groups of GO is also investigated. The measurement of lithium ion batteries (LIBs) shows that MoS₂/RGO anode nanocomposite with a weight ratio of MoS₂ to GO of 3:1 exhibits an excellent rate performance of 750 mAh g^?1 at 3 A g^?1 outperforming many previous studies and a high reversible capacity up to ≈1180 mAh g^?1 after 80 cycles at 100 mA g^?1. Good rate performance and high capacity of MoS₂/RGO with 3D unique layered‐structures are attributed to the combined effects of continuous conductive networks of RGO, good interface facilitating charge transfer, and strong RGO sheets preventing the volume expansion. Results indicate that 3D multilayer MoS₂/RGO prepared by a facile solution‐processed assembly can be developed to be an excellent nanoarchitecture for high‐performance LIBs.     

Tailoring MoS2 Ultrathin Sheets Anchored on Graphene Flexible Supports for Superstable Lithium‐Ion Battery Anodes

2D MoS₂ has a significant capacity decay due to the stack of layers during the charge/discharge process, which has seriously restricted its practical application in lithium‐ion batteries. Herein, a simple preform‐in situ process to fabricate vertically grown MoS₂ nanosheets with 8–12 layers anchored on reduced graphene oxide (rGO) flexible supports is presented. As an anode in MoS₂/rGO//Li half‐cell, the MoS₂/rGO electrode shows a high initial coulomb efficiency (84.1%) and excellent capacity retention (84.7% after 100 cycles) at a current density of 100 mA g^?1. Moreover, the MoS₂/rGO electrode keeps capacity as high as 786 mAh g^?1 after 1000 cycles with minimum degradation of 54 µAh g^?1 cycle^?1 after being further tested at a high current density of 1000 mA g^?1. When evaluated in a MoS₂/rGO//LiCoO₂ full‐cell, it delivers an initial charge capacity of 153 mAh g^?1 at a current density of 100 mA g^?1 and achieves an energy density of 208 Wh kg^?1 under the power density of 220 W kg^?1.     

Structural and optical properties of Cu2ZnSn(S,Se)4 films obtained by magnetron sputtering of a Cu2ZnSn alloy target

Results of the study of structural and optical properties of Cu₂ZnSn(S,Se)₄ thin films obtained by sulfitation (selenization) of Cu₂ZnSn films which were sputtered by target direct current magnetron sputtering using a stoichiometric Cu₂ZnSn (99.99%) target are presented. It has been found that Cu₂ZnSn(S,Se)₄ thin films are polycrystalline with a grain size of ~60 nm. The optical bandgap of Cu₂ZnSnS₄ (E ^op _g = 1.65 eV) and Cu₂ZnSnSe₄ (R ^op _g = 1.2 eV) thin films have been determined.

     

Morphological effect of MoS2 nanoparticles on catalytic oxidation and vacuum lubrication

The closed layered MoS₂ nano-balls and the opened layered MoS₂ nano-slices were prepared by decomposing MoS₃ in hydrogen atmosphere. The obtained MoS₂ nanoparticles were respectively used as catalysts for S²⁻ oxidation into SO₄²⁻ and lubricating fillers in polyoxymethylene (POM) plastic. Only basal surface could be found in the closed layered MoS₂ nano-balls, which represented very low catalytic efficiency for S²⁻ oxidation into SO₄²⁻. However, the opened layered MoS₂ nano-slices were of both basal surface and rim-edge surface and showed excellent catalytic properties. Moreover, it was shown that MoS₂ nano-balls could improve the self-lubrication of POM plastic in vacuum. However, MoS₂ nano-slices led to the obvious degradation of POM, implying it is not a proper additive for POM. The high activity of MoS₂ nano-slices for catalyzing S²⁻oxidation and degrading POM was ascribed to their small sizes and partly wedge-like shapes, which led to a considerable increase in the rim sites. The weak catalysis and excellent lubrication of MoS₂ nano-balls were resulted from its closed structure and chemical inertness.     

Theoretical investigation of the optical spectra and g factors for Cu2+ in dioptase

The optical spectra of Cu²⁺ in dioptase are calculated using crystal-field theory. Good agreement between measured and calculated energy values is obtained under D _4h point-symmetry approximation. The electron paramagnetic resonance g factors, g _// and g _⊥, are also investigated from high-order perturbation formulae. The local structure of Cu²⁺ in dioptase is obtained using these formulae. Theoretical results are in perfect agreement with experimental findings.     

Nanostructured solar cell based on solution processed Cu2ZnSnS4 nanoparticles and vertically aligned ZnO nanorod array

Cu₂ZnSnS₄ (CZTS) has attracted intensive interest for application in photovoltaic technology due to its excellent semiconductor properties. We report a nanostructured CZTS solar cell which was fabricated by infiltrating of CZTS nanoparticles into CdS coated ZnO nanorod arrays. The well aligned ZnO nanorods facilitate the efficient infiltration of CZTS nanoparticles. A hole transport layer was deposited to facilitate the transport of holes. The nanostructured CZTS solar cell demonstrated a remarkably high short‐circuit current density (11.0 mA/cm²). As a result, a power conversion efficiency of 2.8% was obtained. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Thermally-enhanced sono-photo-catalysis by defect and facet modulation of Pt-TiO2 catalyst for high-efficient hydrogen evolution

Sono-photo-catalysis (SPC) has been regarded as a promising route for hydrogen evolution from water splitting due to the sono-photo-synergism, whereas its current performance (∼μmol g⁻¹ h⁻¹) is yet far from expectation. Herein, we give the first demonstration that the intrinsically coupled thermal effects of light and ultrasound, which is normally underestimated or neglected, can simultaneously reshape the photo- and sono-catalytic activities for hydrogen evolution and establish a higher degree of synergy between light and ultrasound in SPC even on the traditional Pt-TiO₂ catalyst. A high-efficient hydrogen evolution rate of 225.04 mmol g⁻¹ h⁻¹ with light-to‑hydrogen efficiency of 0.89% has been achieved in thermally-enhanced SPC, which is an order of magnitude higher than that without thermal effects. More impressively, the increase of synergy index up to 53% has been achieved. Through experiments and theoretical calculations, the thermally-enhanced sono-photo-synergism is attributed to the sono-photo-thermo-modulated structural optimization of defect-rich TiO₂ support and deaggregated Pt species with functional complementary lattice facets, which optimizes not only the thermodynamic properties by enhancing light harvesting and the charge redox power, but also the kinetic properties by accelerating the net efficiency of charge separation and the whole processes of water splitting, including the dissociation of water molecules on high-index (200) Pt facets and production of H¹ intermediates on defect-rich TiO_2-x support and low-index (111) Pt facets. This study exemplifies that coupling light- and ultrasonic-induced thermal effects in SPC system could enhance the synergy between light and ultrasound by modulating catalyst structure to achieve double optimization of thermodynamic and kinetic properties of SPC hydrogen evolution.     

Mesoporous CdS-pillared H2Ti3O7 nanohybrids with efficient photocatalytic activity

Heterostructured CdS-pillared H₂Ti₃O₇ nanohybrids were prepared by the self-assembly of exfoliated trititanate nanosheets and CdS nanosol particles under the electrostatic interactions. It was revealed that the present nanohybrids were mesoporous with specific surface areas of about 90 m² g⁻¹. The nanohybrids exhibited high photocatalytic activity and good recurrence stability in the H₂ evolution from water splitting. When the preparation molar ratio of H₂Ti₃O₇/CdS was 2:1, the nanohybrid reached a high H₂-evolution rate of 1523 μmol h⁻¹ g⁻¹ under a 300 W Xe lamp irradiation, which was 13 times higher than the bare CdS. Apart from the wider spectral responsive range, the superior photocatalytic performance of the nanohybrids was predominantly attributed to the efficient photogenerated charge separation between the trititanate nanosheets and the encapsulated CdS nanoparticles.     

Optically induced structural transformation in disordered kesterite Cu2ZnSnS4

The kesterite-structured semiconductor Cu₂ZnSnS₄ is one of the most promising compound for earth-abundant low-cost solar cells. One of the complex problem on this way deals with its stoichiometry. In this work Raman spectra of Cu-rich Cu₂ZnSnS₄ crystals are discussed in connection with the non-stoichiometric composition and disordering within the cation sublattice of the kesterite. The shift of the main A-peak from 338 to 331 cm^?1 and its broadening are attributed here to transition from the kesterite (I $\bar 4$ symmetry) to the disordered kesterite structure (I $\bar 4$ 2m symmetry). It is shown that this transition may also be driven by an intense light, which could stimulate transformation of Cu⁺-ion to Cu²⁺-ions and facilitates generation of Cu_Zn-defects on 2d-crystalographic positions.     

Wintersweet Branch‐Like C/C@SnO2/MoS2 Nanofibers as High‐Performance Li and Na‐Ion Battery Anodes

Structure and morphology of molybdenum disulfide (MoS₂) play an important role in improving its reversible lithium storage and sodium storage as anodes. In this study, a facile method is developed to prepare C/C@SnO₂/MoS₂ nanofibers with MoS₂ nanoflakes anchoring on the core–shell C/C@SnO₂ nanofibers through hydrothermal reaction. By adjusting the concentration of MoS₂ precursors, the synthesized MoS₂ with different slabs dimensions, size, and morphologies are obtained, constituting budding and blooming wintersweet branch‐like composite structure, respectively. Owing to scattered MoS₂ nanoparticles and sporadic MoS₂ nanoflakes, the budding wintersweet branch‐like composite nanofibers processes less slabs of staking in number and large specific surface area. Benefiting from the exposed C@SnO₂ shell layer, the synergistic effect among SnO₂, carbon, and MoS₂ is strengthened, which maximizes the advantage of each material to exhibit stable specific capacities of 650 and 230 mAh g^?1 for Li‐ion batteries and Na‐ion batteries after 200 cycles.     

Effect of nanostructured MoS2 morphology on the glucose sensing of electrochemical biosensors

In this study, the effects of the morphological characteristics of MoS₂ nanomaterials on the glucose sensing of electrochemical biosensors were explored. Nanostructured MoS₂ materials, including nanoparticles (NPs), nanoflowers (NFs), and nanoplatelets (NPLs), were prepared via a simple hydrothermal method. The structure and morphological characteristics of MoS₂ nanomaterials were examined through X-ray diffraction, field emission scanning electron microscopy, and Raman spectroscopy. Electrochemical properties were analyzed through cyclic voltammetry. Results showed that the obtained sensitivity was 64, 68.7, and 77.6 μAmM⁻¹ cm⁻² for MoS₂ NP-, MoS₂ NF-, and MoS₂ NPL-based biosensors, respectively. The limit of detection (LOD) of all MoS₂-based glucose biosensors was 0.081 mM. In addition, the pH, temperature, glucose oxidase (GOx) concentration, reproducibility, specificity, and stability of glucose biosensors with different MoS₂ morphologies were also investigated and indicated the oxidation current response of the MoS₂ NPL-based glucose biosensor was higher than that of MoS₂ NF- and NP-based biosensors.     

Preparation of Cu2ZnSnS4 thin films by hybrid sputtering

In order to fabricate Cu₂ZnSnS₄ thin films, hybrid sputtering system with two sputter sources and two effusion cells is used. The Cu₂ZnSnS₄ films are fabricated by the sequential deposition of metal elements and annealing in S flux, varying the substrate temperature. The Cu₂ZnSnS₄ films with stoichiometric composition are obtained at the substrate temperature up to 400 °C, whereas the film composition becomes quite Zn-pool at the substrate temperature above 450 °C. The Cu₂ZnSnS₄ film shows p-type conductivity, and the optical absorption coefficient and the band gap of the Cu₂ZnSnS₄ film prepared in this experiment are suitable for fabricating a thin film solar cell.     

Layer‐dependent resonant Raman scattering of a few layer MoS2

We report resonant Raman scattering of MoS₂ layers comprising of single, bi, four and seven layers, showing a strong dependence on the layer thickness. Indirect band gap MoS₂ in bulk becomes a direct band gap semiconductor in the monolayer form. New Raman modes are seen in the spectra of single‐ and few‐layer MoS₂ samples which are absent in the bulk. The Raman mode at ~230 cm⁻¹ appears for two, four and seven layers. This mode has been attributed to the longitudinal acoustic phonon branch at the M point (LA(M)) of the Brillouin zone. The mode at ~179 cm⁻¹ shows asymmetric character for a few‐layer sample. The asymmetry is explained by the dispersion of the LA(M) branch along the Γ‐M direction. The most intense spectral region near 455 cm⁻¹ shows a layer‐dependent variation of peak positions and relative intensities. The high energy region between 510 and 645 cm⁻¹ is marked by the appearance of prominent new Raman bands, varying in intensity with layer numbers. Resonant Raman spectroscopy thus serves as a promising non invasive technique to accurately estimate the thickness of MoS₂ layers down to a few atoms thick. Copyright © 2012 John Wiley & Sons, Ltd.     

Optical properties and mechanisms of current flow in Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> films prepared by spray pyrolysis

Thin films Cu₂ZnSnS₄ (up to 0.9 μm thick) with p-type conductivity and band gap E_g = 1.54 eV have been prepared by the spray pyrolysis of 0.1 M aqueous solutions of the salts CuCl₂ · 2H₂O, ZnCl₂ · 2H₂O, SnCl₄ · 5H₂O, and (NH₂)₂CS at a temperature T_S = 290°C. The electrophysical properties of the films have been analyzed using the model for polycrystalline materials with electrically active grain boundaries. The energy and geometric parameters of the grain boundaries have been determined as follows: the height of the barriers is E_b ≈ 0.045–0.048 eV, and the thickness of the depletion region is δ ≈ 3.25 nm. The effective concentrations of charge carriers p₀ = 3.16 × 10¹⁸ cm^–3 and their mobilities in crystallites μ_p = 85 cm²/(V s) have been found using the technique for determining the kinetic parameters from the absorption spectra of thin films at a photon energy hν ≈ E_g. The density of states at grain boundaries N_t = 9.57 × 10¹¹ cm^–2 has been estimated.     

Formation of lithium-like boron and nitrogen ions in the <Superscript>4</Superscript><Emphasis Type="Italic">P</Emphasis><Subscript>5/2</Subscript> state in gaseous media

We experimentally determined the fraction of α_v of lithium-like boron B²⁺ and nitrogen N⁴⁺ ions in the ⁴ P _5/2 state having a velocity of 3.6 au that are formed upon capture of two (α₂) electrons by hydrogen-like B⁴⁺ and N⁶⁺ ions and upon capture of one (α₁) electron by helium-like (1s2s)^1,3 S metastable B³⁺ and N⁵⁺ ions in gaseous media (H₂, He, N₂, Ar), as well as upon passage through a celluloid film. In light-element media (H₂, He), α₂ increases proportional to the target thickness T _g and reaches a maximum at T _g ≈ 10¹⁶ atom/cm² (for B ions, α₂ ≈ 0.2 in H₂ and α₂ ≈ 0.4 in He). For boron and nitrogen ions passing through thin layers of heavier gases (N₂, Ne), α₂ depends considerably more weakly on T _g , and, in Ar, becomes practically constant. It is assumed that, since hydrogen and helium do not contain electrons with parallel spins, autoionizing lithium-like ions are formed as a result of successive (one by one) capture of electrons, whereas, in the heavier gases, simultaneous capture of two electrons predominates. At T _g ～ 10¹⁵ atom/cm², the fraction α₁ of boron ions is the highest in He, ～0.15, and the lowest in Ar, ～0.07, being in qualitative agreement with calculations.     

Flower-like MoS<Subscript>2</Subscript> supported on three-dimensional graphene aerogels as high-performance anode materials for sodium-ion batteries

Flower-like MoS₂ supported on three-dimensional graphene aerogel (MoS₂/GA) composite has been prepared by a facile hydrothermal method followed by subsequent heat-treatment process. Each of MoS₂ microflowers is surrounded by the three-dimensional graphene nanosheets. The MoS₂/GA composite is applied as an anode material of sodium-ion batteries (SIBs) and it exhibits high initial discharge/charge capacities of 562.7 and 460 mAh g^?1 at a current density of 0.1 A g^?1 and good cycling performance (348.6 mAh g^?1 after 30 cycles at 0.1 A g^?1). The good Na⁺ storage properties of the MoS₂/GA composite could be attributed to the unique structure which flower-like MoS₂ are homogeneously and tightly decorated on the surface of three-dimensional graphene aerogel. Our results demonstrate that as-prepared MoS₂/GA composite has a great potential prospect as anodes for SIBs.     

MoO2@MoS2 Nanoarchitectures for High‐Loading Advanced Lithium‐Ion Battery Anodes

The capacity loading per unit area is of importance as specific capacity while evaluating the lithium‐ion battery anode. However, the low conductivity of several advanced anode materials (such as molybdenum sulfide, MoS₂) prohibits the wide application of materials. Nanostructural engineering becomes a key to overcome the obstacles. A one‐step in situ conversion reaction is employed to synthesize molybdenum oxide (MoO₂)–MoS₂ core–shell nanoarchitectures (MoO₂@MoS₂) by partially sulfiding MoO₂ into MoS₂ using sulfur. The MoO₂@MoS₂ displays a 3D architecture constructed by hundreds of MoS₂ ultrathin sheets with several layers arranged and fixed to an MoO₂ particle vertically with the size in the range of 200–500 nm. MoO₂ acts as the molybdenum source for the synthesis of MoS₂, as well as the conductive substrate. The designed 3D architectures with empty space between MoS₂ layers can prevent the damage originated from volume change of MoS₂ undergoing charge/discharge process. The lithium storage capacities of the MoO₂@MoS₂ 3D architectures are higher and the stability has been significantly improved compared to pure MoS₂. 4 mAh cm^?2 capacity loading of MoO₂@MoS₂ has been achieved with a specific capacity of more than 1000 mAh g^?1.     

Neutronh 11/2 alignments in the triaxial nucleus133La

High spin states have been studied in¹³³La via the¹²²Sn (¹⁵N, 4ny) fusion evaporation reaction. Bands build on low lying h_11/2,g_7/2 and d_5/2 proton states have been identified. At higher spin a h_11/2 neutron alignment is observed. The softness with respect to the triaxial deformation makes the nuclear shape sensitive to the quasiparticle configurations and coexistence between states withy ≈ + 30°,y ≈ ? 30° andy ≦ ? 60° was found. The results have been interpreted using total routhian surface (TRS) model calculations.