Synthesis of large-scale atomic-layer SnS<Subscript>2</Subscript> through chemical vapor deposition

Two-dimensional layers of metal dichalcogenides have attracted much attention because of their ultrathin thickness and potential applications in electronics and optoelectronics.Monolayer SnS2,with a band gap of ～2.6 eV,has an octahedral lattice made of two atomic layers of sulfur and one atomic layer of tin.Till date,there have been limited reports on the growth of large-scale and high quality SnS2 atomic layers and the investigation of their properties as a semiconductor.Here,we report the chemical vapor deposition (CVD) growth of atomic-layer SnS2 with a large crystal size and uniformity.In addition,the number of layers can be changed from a monolayer to few layers and to bulk by changing the growth time.Scanning transmission electron microscopy was used to analyze the atomic structure and demonstrate the 2H stacking poly-type of different layers.The resultant SnS2 crystals is used as a photodetector with external quantum efficiency as high as 150％,suggesting promise for optoelectronic applications.     

Active-layer evolution and efficiency improvement of (CH<Subscript>3</Subscript>NH<Subscript>3</Subscript><Subscript>3</Subscript>Bi<Subscript>2</Subscript>I<Subscript>9</Subscript>-based solar cell on TiO<Subscript>2</Subscript>-deposited ITO substrate

We systematically investigated the development of film morphology and crystallinity of methyl-ammonium bismuth (III) iodide (MA₃Bi₂I₉) through onestep spin-coating on TiO₂-deposited indium tin oxide (ITO)/glass. The precursor solution concentration and substrate structure have been demonstrated to be critically important in the active-layer evolution of the MA₃Bi₂I₉-based solar cell. This work successfully improved the cell efficiency to 0.42% (average: 0.38%) with the mesoscopic architecture of ITO/compact-TiO₂/mesoscopic-TiO₂ (meso-TiO₂)/MA₃Bi₂I₉/2,2′,7,7′-tetrakis(N,N-di-4-methoxyphenylamino)-9,9′spiro-bifluorene (spiro-MeOTAD)/MoO₃/Ag under a precursor concentration of 0.45 M, which provided the probability of further improving the efficiency of the Bi³⁺-based lead-free organic–inorganic hybrid solar cells.

Open image in new window

     

Thermal Conductivity of Chalcogenide As<Subscript>2</Subscript>S<Subscript>3</Subscript> Thin Films

In order to investigate the photo-induced thermal property changes in chalcogenide thin films, amorphous As ₂ S ₃ thin film samples, whose thicknesses are 0.5, 1.0, 2.0, and 4.0 m, were prepared on silicon wafers by thermal evaporation. Their thermal conductivity was measured by the 3 method between room temperature and 100 °C. These measurements were repeated after the illumination of an Ar⁺ laser beam whose photon energy is consistent with the bandgap energy of As ₂ S ₃, and repeated again for annealed films at 180 °C for 1 h. The result shows that the thermal conductivities of fresh films were 0.14 to 0.27 W·m ^–1·K ^–1; however, the values increase to 0.28–0.47 W·m ^–1·K ^–1 after illumination of the sample and decrease to 0.19–0.42 W·m ^–1·K ^–1 after annealing of the sample. These changes can be explained by the change in microstructure produced from the photo-darkening and thermal annealing.     

Multidimensional CdS nanowire/CdIn<Subscript>2</Subscript>S<Subscript>4</Subscript> nanosheet heterostructure for photocatalytic and photoelectrochemical applications

Nanomaterial shapes can have profound effects on material properties,and therefore offer an efficient way to improve the performances of designed materials and devices.The rational fabrication of multidimensional architectures such as one dimensional (1D)-two dimensional (2D) hybrid nanomaterials can integrate the merits of individual components and provide enhanced functionality.However,it is still very challenging to fabricate 1D/2D architectures because of the different growth mechanisms of the nanostructures.Here,we present a new solventmediated,surface reaction-driven growth route for synthesis of CdS nanowire (NW)/CdIn2S4 nanosheet (NS) 1D/2D architectures.The as-obtained CdS NW/CdIn2S4 NS structures exhibit much higher visible-light-responsive photocatalytic activities for water splitting than the individual components.The CdS NW/CdIn2S4 NS heterostructure was further fabricated into photoelectrodes,which achieved a considerable photocurrent density of 2.85 mA.cm-2 at 0 V vs.the reversible hydrogen electrode (RHE) without use of any co-catalysts.This represents one of the best results from a CdS-based photoelectrochemical (PEC) cell.Both the multidimensional nature and type Ⅱ band alignment of the 1D/2D CdS/CdIn2S4 heterostructure contribute to the enhanced photocatalytic and photoelectrochemical activity.The present work not only provides a new strategy for designing multidimensional 1D/2D heterostructures,but also documents the development of highly efficient energy conversion catalysts.     

Photoluminescence of Si<Subscript>0.9</Subscript>Ge<Subscript>0.1</Subscript>O<Subscript>2</Subscript> and GeO<Subscript>2</Subscript> films irradiated with silicon ions

We have studied the photoluminescence (PL) of GeO₂ and 90 mol % SiO₂-10 mol % GeO₂ films synthesized by method of RF magnetron sputtering and then irradiated with silicon ions and annealed. The PL of silicon-implanted GeO₂ films, related to the presence of Si nanocrystals (nc-Si), was observed for the first time. It is established that the transformation of the defect centers responsible for the PL in the spectral range 350–600 nm, as well as the formation of nc-Si emitting in the region of 700–800 nm, significantly depend on the matrix type. In particular, the PL intensity at 700–800 nm in 90 mol % SiO₂-10 mol % GeO₂ films is weak. The role of the isovalent substitution of Si and Ge atoms in the transformation of defect centers and the formation of nc-Si is discussed.     

Ba<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>TiO<Subscript>3</Subscript> ferroelectric nanofilms on silicon buffered with a TiO<Subscript>2</Subscript> layer

Polycrystalline, 50- to 70-nm-thick barium strontium titanate films of composition Ba_0.8Sr_0.2TiO₃ have been grown on single-crystal silicon substrates by rf ion-beam sputtering. We have determined their structure and composition and detected impurities at the film/substrate interface in the form of titanium silicide islands. The deposition of a 4- to 6-nm-thick TiO₂ buffer layer onto Si by ion-beam sputtering before ferroelectric film growth is shown to prevent uncontrolled formation of impurities near the interface. The buffered heterostructures possess high thermal stability.     

Rambutan-like hierarchically heterostructured CeO<Subscript>2</Subscript>-CuO hollow microspheres: Facile hydrothermal synthesis and applications

Hierarchically heterostructured hollow spheres are of great interest for a wide range of applications owing to their unique structural features and properties.However,the fabrication of well-defined hollow spheres with highly specific morphology for mixed transition metal oxides on a large scale remains challenging.In this work,uniform rambutan-like heterostructured CeO2-CuO hollow microspheres with numerous copper-ceria interfacial sites and nanorods and nanoparticles as building blocks are prepared via a facile hydrothermal method followed by calcination.Importantly,this approach can be readily scaled up and is applicable to the synthesis of various CuO-based mixed metal oxide complex hollow spheres.The as-prepared CeO2-CuO hollow rambutans exhibit superior performance both as electrode materials for supercapacitors and as Cu-based catalysts for the Rochow reaction,mainly due to the small primary nanopartide constituents,high surface area,and formation of numerous interior heterostructures.     

Methylammonium cation deficient surface for enhanced binding stability at TiO<Subscript>2</Subscript>/CH<Subscript>3</Subscript>NH<Subscript>3</Subscript>PbI<Subscript>3</Subscript> interface

Heterojunction interfaces in perovskite solar cells play an important role in enhancing their photoelectric properties and stability.Till date,the precise lattice arrangement at TiO2/CH3NH3PbI3 heterojunction interfaces has not been investigated clearly.Here,we examined a TiO2/CH3NH3PbI3 interface and found that a heavy atomic layer exists in such interfaces,which is attributed to the vacancies of methylammonium (MA) cation groups.Further,first-principles calculation results suggested that an MA cation-deficient surface structure is beneficial for a strong heterogeneous binding between TiO2 and CH3NH3PbI3 to enhance the interface stability.Our research is helpful for further understanding the detailed interface atom arrangements and provides references for interfacial modification in perovskite solar cells.     

Ballistic transport in single-layer MoS<Subscript>2</Subscript> piezotronic transistors

Because of the coupling between semiconducting and piezoelectric properties in wurtzite materials, strain-induced piezo-charges can tune the charge transport across the interface or junction, which is referred to as the piezotronic effect. For devices whose dimension is much smaller than the mean free path of carriers (such as a single atomic layer of MoS₂), ballistic transport occurs. In this study, transport in the monolayer MoS₂ piezotronic transistor is studied by presenting analytical solutions for two-dimensional (2D) MoS₂. Furthermore, a numerical simulation for guiding future 2D piezotronic nanodevice design is presented.

Open image in new window

     

Synthesis and characterization of new glasses based on Li<Subscript>2</Subscript>S-P<Subscript>2</Subscript>S<Subscript>5</Subscript>-Sb<Subscript>2</Subscript>S<Subscript>3</Subscript> system

There is great interest in sulfide glasses because of their high lithium ion conductivity. New sulfide glasses based on Li₂S-P₂S₅-Sb₂S₃ system have been synthesized by a classical quenching technique. A summary of thermal and structural characterization is presented. Electrical conductivities of the samples have been determined by Impedance Spectroscopy. The compositions of low lithium content (below 20% mol) have presented low electronic conductivities close to 10⁻⁸ S/cm at room temperature. The compositions of medium lithium content (30–50% mol) have presented mixed ionic-electronic behavior with predominant on ionic conductivity with a maximum values around 10⁻⁶ S/cm for samples up to 50% Li₂S at room temperature. Arrhenius behavior is verified between 25°C and T_g for all glasses with activation energies about 0.55–0.64 eV. A comparative study of conductivities with glasses belonging to the other chalcogenide systems has been undertaken.     

Extruded thermoelectric materials based on Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> solid solutions

Extruded n-type materials based on Bi₂Te₃-Bi₂Se₃ alloys containing 6 to 40 mol % Bi₂Se₃ have been investigated using microstructural analysis and thermoelectric measurements at room temperature and in the range 100–400 K. Their electrical properties have been compared to those of single-crystal analogs. Compositions have been found at which the extruded materials offer the highest thermoelectric performance in different temperature ranges.     

Preparation of K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript>/TiO<Subscript>2</Subscript> bio-ceramic on titanium substrate by micro-arc oxidation

K₂Ti₆O₁₃/TiO₂ bio-ceramic coatings are prepared successfully by micro-arc oxidation on titanium substrate in pure KOH electrolyte solution. The coating is prepared at various applied current density (150–500 mA/cm²) and in KOH electrolyte with different concentrations (0.5–1.2 mol/L). The composition and surface morphologies of coatings are strongly dependent on the applied current density and the electrolyte concentration. On the condition of lower current density and electrolyte concentration, K₂Ti₆O₁₃ phase almost cannot be formed. The phase is mainly composed of rutile and K₂Ti₆O₁₃ with increasing current density and electrolyte concentration. The surface morphologies are composed of whiskers and porous structures. The ability of K₂Ti₆O₁₃/TiO₂ bio-ceramic films inducing apatite deposition is evaluated by soaking it in biological model fluids. The results show the K₂Ti₆O₁₃/TiO₂ bio-ceramic coatings possess excellent capability of inducing bone-like apatite to deposit.     

<Emphasis Type="Italic">In situ</Emphasis> fabrication of 2D SnS<Subscript>2</Subscript> nanosheets as a new electron transport layer for perovskite solar cells

To promote commercialization of perovskite solar cells (PSCs), low-temperature processed electron transport layer (ETL) with high carrier mobility still needs to be further developed. Here, we reported two-dimensional (2D) tin disulfide (SnS₂) nanosheets as ETL in PSCs for the first time. The morphologies of the 2D SnS₂ material can be easy controlled by the in situ synthesized method on the conductive fluorine-doped tin oxide (FTO) substrate. We achieved a champion power conversion efficiency (PCE) of 13.63%, with the short-circuit current density (J_SC) of 23.70 mA/cm², open-circuit voltage (V_OC) of 0.95 V, and fill factor (FF) of 0.61. The high J_SC of PSCs results from effective electron collection of the 2D SnS₂ nanosheets from perovskite layer and fast electron transport to the FTO. The low V_OC and FF are the results of the lower conduction band of 2D SnS₂ (4.23 eV) than that of TiO₂ (4.0 eV). These results demonstrate that 2D material is a promising candidate for ETL in PSCs.

Open image in new window

     

Catalase-imprinted Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Fe@fibrous SiO<Subscript>2</Subscript>/polydopamine nanoparticles: An integrated nanoplatform of magnetic targeting,magnetic resonance imaging,and dual-mode cancer therapy

Recent advances in the research on the molecular mechanism of cell death and methods for preparation of nanomaterials make the integration of various therapeutic approaches,targeting,and imaging modes into a single nanoscale complex a new trend for the development of future nanotherapeutics.Hence,a novel ellipsoidal composite nanoplatform composed of a magnetic Fe3O4/Fe nanorod core (～120 nm) enwrapped by a catalase (CAT)-imprinted fibrous SiO2/ polydopamine (F-SiO2/PDA) shell with thickness 70 nm was prepared in this work.In vitro experiments showed that the Fe3O4/Fe@F-SiO2/PDA nanoparticles can selectively inhibit the bioactivity of CAT in tumor cells by the molecular imprinting technique.As a result,the H2O2 level in tumor cells was elevated dramatically.At the same time,the Fe3O4/Fe core released Fe ions to catalyze the conversion of H2O2 to ·OH in tumor cells.Eventually,the concentration of ·OH in tumor cells rapidly rose to a lethal level thus triggering apoptosis.Combined with the remarkable near-infrared light (NIR) photothermal effect of the CATimprinted PDA layer,the Fe3O4/Fe@F-SiO2/PDA nanoparticles can effectively kill MCF-7,HeLa,and 293T tumor cells but are not toxic to nontumor cells.Furthermore,these nanoparticles show good capacity for magnetic targeting and suitability for magnetic resonance imaging (MRI).Therefore,the integrated multifunctional nanoplatform opens up new possibilities for high-efficiency visual targeted nonchemo therapy for cancer.