Search

Incorporation of isolated metal centers into well-organized nanostructures is a promising route in the development of the next generation of chemical, magnetic and electronic devices. In this work, a layer-by-layer protocol to grow highly ordered thin films of metal-decorated organic-inorganic cage-like polyhedral oligomeric silsesquioxane (POSS) is introduced. The key strategy is to use metal ions (Cu2+ or Fe3+) as linker for the amino-functionalized cage-like POSS, which are self-assembled between arachidic acid layers during Langmuir–Schaefer deposition. The Langmuir–Schaefer films are examined by X-ray photoelectron spectroscopy, X-ray diffraction, grazing incidence wide-angle X-ray scattering and extended X-ray absorption fine structure in order to understand how the coordination of metal ions influences the structure in the course of the layer-by-layer formation of the films.

Two-dimensional (2D) perovskites incorporating hydrophobic organic spacer cations show improved film stability and morphology compared to their three-dimensional (3D) counterparts. However, 2D perovskites usually exhibit low photoluminescence quantum efficiency (PLQE) owing to strong exciton-phonon interaction at room temperature, which limits their efficiency in light-emitting diodes (LEDs). Here, we demonstrate that the device performance of 2D perovskite LEDs can be significantly enhanced by doping Mn(2+)in (benzimidazolium)(2)PbI4 2D perovskite films to suppress the exciton-phonon interaction. The distorted [PbI6](4-) octahedra by Mn-doping and the rigid benzimidazolium (BIZ) ring without branched chains in the 2D perovskite structure lead to improved crystallinity and rigidity of the perovskites, resulting in suppressed phonon-exciton interaction and enhanced PLQE. On the basis of this strategy, for the first time, we report yellow electroluminescence from free excitons in 2D (n = 1) perovskites with a maximum brightness of 225 cd m(-2) and a peak EQE of 0.045%. Funding Agencies|Major Research Plan of the National Natural Science Foundation of China [91733302]; European Union [2016YFE0112000]; National Basic Research Program of China-Fundamental Studies of Perovskite Solar Cells [2015CB932200]; National Natural Science Foundation of China [61634001, 51703094]; Natural Science Foundation of Jiangsu Province, China [BK20170991, BK20150043, BK20150064]; National Science Fund for Distinguished Young Scholars [61725502]; Natural Science Fund for Colleges and Universities in Jiangsu Province of China [17KJB150023]; Synergetic Innovation Center for Organic Electronics and Information Displays

Tuning the architecture of multilayer nanostructures by exploiting the properties of their constituents is a versatile way to develop multifunctional films. Herein, we report a bottom-up approach for the fabrication of highly ordered hybrid films consisting of dimethyldioctadecylammonium (DODA), iron decorated polyhedral oligomeric silsesquioxanes (POSS), and montmorillonite clay platelets. Clay platelets provided the template where Fe/POSS moieties were grafted by the use of the surfactant. Driven by the iron ions present, DODA adopted a staggered arrangement, which is essential to realize the controllable layer-by-layer growth of the film. The elemental composition of the film was studied by X-ray photoelectron spectroscopy and X-ray reflectivity confirmed the existence of smooth interfaces between the different layers.

GEO (Geostationary Earth Orbit) satellites are important components of BDS (BeiDou navigation satellite system), whose static characteristic ensures the long-term visibility and has special advantages in GNSS-R (global navigation satellite system reflectometry) sea surface height (SSH) measurement. In order to evaluate the ability of GEO satellite reflection in SSH estimation, we used DDMs (Delay Doppler Maps) and phase differences to perform the coastal experiment. On July 9, 2019 we conducted GNSS-R real-time ground-based sea level estimation experiment in Weihai, Shandong Province, China. By using DDMs and phase measurement of BDS B1I direct and reflected signal from GEO satellite we have got the offshore sea level height. Meanwhile we made the in-situ range measurements to verify the precision of the two kinds of SSH results. Finally, we found that the RMSE (Root Mean Square Error) of DDMs and phase altimetry is 0.82m and 0.039m respectively, which showed great potential of GEO satellite reflectometry in marine applications, especially in moving platforms.

Contains fulltext : 166243.pdf (Publisher’s version ) (Closed access) Fe7Se8 exists as a hexagonal NiAs-like crystal structure with a large number of ordered intrinsic vacancies. It is an ideal candidate for studying the effect of defects on properties such as magnetism and electrical transport. In this work, highly crystalline Fe7Se8 with the 3c crystal structure was synthesized by a solid-state reaction. Sharp changes in the magnetization at 100 K confirm a rotation of the spins from the ab plane to the c axis with decreasing temperature. We observe an interesting metal–insulator transition at the same temperature as the spin-direction changes. We propose that locked spins in the grain boundaries induce electron localization and result in the metal–insulator transition. Electron localization is confirmed by X-ray photoelectron spectroscopy of the Fe 2p peaks, which exhibit two characteristic satellite peaks. This mechanism is also verified by comparing it with the properties of the 4c-Fe7Se8 crystal structure.

Incorporation of isolated metal centers into well-organized nanostructures is a promising route in the development of the next generation of chemical, magnetic and electronic devices. In this work, a layer-by-layer protocol to grow highly ordered thin films of metal-decorated organic-inorganic cage-like polyhedral oligomeric silsesquioxane (POSS) is introduced. The key strategy is to use metal ions (Cu

Conductivity, carrier mobility, and a suitable Gibbs free energy are important criteria that determine the performance of catalysts for a hydrogen evolution reaction (HER). However, it is a challenge to combine these factors into a single compound. Herein, we discover a superior electrocatalyst for a HER in the recently identified Dirac nodal arc semimetal PtSn4. The determined turnover frequency (TOF) for each active site of PtSn4 is 1.54 H-2 s(-1) at 100 mV. This sets a benchmark for HER catalysis on Pt-based noble metals and earth-abundant metal catalysts. We make use of the robust surface states of PtSn4 as their electrons can be transferred to the adsorbed hydrogen atoms in the catalytic process more efficiently. In addition, PtSn4 displays excellent chemical and electrochemical stabilities after long-term exposure in air and long-time HER stability tests. Funding Agencies|European Research Council (ERC Advanced Grant) [291472]; ERC Advanced Grant [742068]

Conductivity, carrier mobility, and a suitable Gibbs free energy are important criteria that determine the performance of catalysts for a hydrogen evolution reaction (HER). However, it is a challenge to combine these factors into a single compound. Herein, we discover a superior electrocatalyst for a HER in the recently identified Dirac nodal arc semimetal PtSn4. The determined turnover frequency (TOF) for each active site of PtSn4 is 1.54 H2 s−1 at 100 mV. This sets a benchmark for HER catalysis on Pt‐based noble metals and earth‐abundant metal catalysts. We make use of the robust surface states of PtSn4 as their electrons can be transferred to the adsorbed hydrogen atoms in the catalytic process more efficiently. In addition, PtSn4 displays excellent chemical and electrochemical stabilities after long‐term exposure in air and long‐time HER stability tests.

The presence of elemental vacancies in materials are inevitable according to statistical thermodynamics, which will decide the chemical and physical properties of the investigated system. However, the controlled manipulation of vacancies for specific applications is a challenge. Here we report a facile method for creating large concentrations of S vacancies in the inert basal plane of MoS2 supported on semimetal CoMoP2. With a small applied potential, S atoms can be removed in the form of H2S due to the optimized free energy of formation. The existence of vacancies favors electron injection from the electrode to the active site by decreasing the contact resistance. As a consequence, the catalytic current is increased by 221% with the vacancy-rich MoS2 as electrocatalyst for hydrogen evolution reaction (HER). A small overpotential of 75 mV is needed to deliver a current density of 10 mA cm−2, which is considered among the best values achieved for MoS2. It is envisaged that this work may provide a new strategy for utilizing the semimetal phase for structuring MoS2 into a multi-functional material.

The electrolysis processes such as hydrogen evolution reaction (HER) require high efficient catalysts with robust surface stability. A high conductivity is also necessary to speed up the charge transport between the catalyst and the electrolyte. Recently, the observation of exceedingly high conductivity in the topological semimetal MoP, has provided a model catalyst to investigate the correlation between the electrical transport and the electrocatalytic activity for the HER. Thus, MoP is encapsulated in a Mo, P codoped carbon layer (MoP@C). This composite material exhibits outstanding HER performance, with an extremely low overpotential of 49 mV at a current density of 10 mA cm-2 and a Tafel slope of 54 mV dec-1 in an alkaline medium. In addition, electron transport analysis indicates that MoP exhibits high conductivity and mobility due to the existence of triple-point fermions and a complex Fermi surface. Furthermore, the presence of P−C and Mo−C bonds at the interface between the carbon layer and the MoP particles modulates the band structure of MoP@C and facilitates fast electron transfer, accumulation, and subsequent delocalization, which are in turn responsible for the excellent HER activity.

Organic-inorganic hybrids are a rapidly developing class of multifunctional materials, which can present properties different from those of either of their building blocks. Control over the structure during the assembly process is crucial to achieve the desired functions. Here we present the layer-by-layer deposition in ambient conditions of CoCl4-octahedra or MnCl4-octahedra and organic layers to tailor their magnetic properties. The Langmuir-Blodgett technique used to assemble these structures provides intrinsic control over the film structure down to the molecular level. Magnetic characterization reveals that MnCl4-based hybrid Langmuir-Blodgett films order antiferromagnetically like the bulk hybrid, while the CoCl4-based hybrid Langmuir-Blodgett films show ferromagnetic coupling in contrast to the bulk hybrid, which is a paramagnet.

Fe

The pyrolytic conversion of vinyl-terminated poly[hydridomethylsiloxane-co-vinylmethylsiloxane] (PSO) into SiOC ceramic at various heating rates has been investigated by thermogravimetry coupled with mass spectrometry. Kinetic analysis on pyrolysis process of PSO has been conducted by peak-fitting method. The results show that all the experimental derivative thermogravimetric curves recorded at five different heating rates can be best fitted by four Gaussian functions. The activation energy for each peak was determined by an isoconversional method, and kinetic models for Peaks 1 and 2 were investigated on the basis of Master plots. The results show that Peak 1 was governed by R2-type mechanisms, while Peak 2 followed diffusion-type transport mechanisms. Plausible chemical pathways for the evolved gases within these peaks are also discussed. The release of a large amount of carbon-containing species was identified in the temperature ranges corresponding to Peak 2 and 4, which are associated with the mineralization and ceramization steps, respectively. The transition from mineralization to ceramization process occurs in the region of Peak 3, and is accompanied by the evolution of H2.

Transition metal sulfides exhibit chemical and physical properties that are of much scientific and technological interest and can largely be attributed to their covalent bonding of 3d electrons. Hierarchical structures of these materials are suited for a broad range of applications in energy storage, as biological scaffold, and as sensors. In this work, hierarchical SnS2 structures have been synthesized and show excellent photocatalytic performance for the production of H-2 under blue light (450 nm) irradiation. A combination of high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy indicates the formation of layered SnS2/SnS superstructures with a lattice mismatch between the two alternating layers. This indicates the presence of S vacancies and results in a drastic decrease of the band gap by 0.3 eV compared to bulk SnS2. This strategy of self-narrowing of the bandgap demonstrates its great potential for the design of new materials with visible light reactivity. Finally, we have extended this strategy to the synthesis of other transition metal sulfides (Ni3S4, CuS, CuS@C, and FeS2) with similar hierarchical structures, which have potential applications such as supercapacitors and electrode materials for sodium/lithium ion batteries.

Micro/nano-porous SiOC foams with narrow pore size distribution were fabricated by pyrolysis of polymeric gels prepared from mixtures of crosslinkable polysiloxane PSO and methyl-terminated polydimethylsiloxane PDMS. By simply changing the viscosity of the PDMS or its mass ratio in the mixed polymers, the pore sizes and porosities of the porous SiOC materials could be adjusted in the range from 10 nm to 3 μm, and 20% to 90%, respectively.

Samples from the North American, Australasian, and Ivory Coast microtektite layers were examined for unmelted impact ejecta (>125 οm size). Coesite and shocked quartz, identified by X-ray diffraction, were found at all the sites where a well-defined North American microtektite layer had previously been documented. Coesite and shocked quartz were also foundin seven out of 33 cores from the Australasian strewn field; however, no coesite or shocked quartz was found associated with the Ivory Coast microtektite layer. Stishovite was also found at three of the Australasian sites. All of the Australasian cores containing coesite and shocked quartz were taken from within 2000 km of Indochina, which is believed by most to be the source area for the Australasian tektites and microtektites. Six of the seven cores have the highest concentrations of microtektites ever determined for Australasian microtektite- bearing cores. The seventh core did not contain any microtektites, which may be consistent with the hypothesis that the microtektites were deposited in a raylike pattern. The discovery of coesite and impact ejecta associated with both the North American and Australasian microtektite layers provides further support for the hypothesis of terrestrial impact origin of tektites.