Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 10 de 10
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
ChemSusChem ; 2020 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-32187860

RESUMO

Electrocatalytic water splitting, as one of the most promising methods to store renewable energy generated by intermittent sources, such as solar and wind energy, has attracted tremendous attention in recent years. Developing efficient, robust, and green catalysts for the hydrogen and oxygen evolution reactions (HER and OER) is of great interest. This study concerns a facile and green approach for producing RuNi/RuNi oxide nanoheterostructures by controllable partial oxidation of RuNi nanoalloy, which is characterized and confirmed by various techniques, including high-resolution transmission electron microscopy and synchrotron-based X-ray absorption spectroscopy. This nanoheterostructure demonstrates outstanding bifunctional activities for catalyzing the HER and OER with overpotentials that are both among the lowest reported values. In a practical alkali-water-splitting electrolyzer, it also achieves a record-low cell voltage of 1.42 V at 10 mA cm-2 , which is significantly superior to the commercial RuO2 //Pt/C couple and other reported bifunctional water-splitting electrocatalysts. Density functional theory calculations are employed to elaborate the effect of Ni incorporation. This simple catalyst preparation approach is expected to be transferrable to other electrocatalytic reactions.

2.
ACS Appl Mater Interfaces ; 11(44): 41304-41312, 2019 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-31603303

RESUMO

The ever-increasing demand for large-scale energy storage has driven the prosperous investigation of sodium-ion batteries (NIBs). As a promising cathode candidate for NIBs, P2-type Na2/3Ni1/3Mn2/3O2 (NaNMO), a prototype sodium-layered oxide, has attracted extensive attention because of its high operating voltage and high capacity density. Although its electrochemical properties have been extensively investigated, the fundamental charge compensation mechanism, that is, the cationic and anionic redox reactions, is still elusive. In this report, we have systematically investigated the transition metal and oxygen redox reactions of NaNMO nanoflakes using bulk-sensitive soft X-ray absorption spectroscopy and full-range mapping of resonant inelastic X-ray scattering from an atomic-level view. We show that the bulk Mn3+/Mn4+ redox couple emerges from the first discharge process with the increment of inactive Mn3+ upon cycling, which may have a negative effect on the cyclability. In contrast, the bulk Ni redox mainly stems from the Ni2+/Ni3+ redox couple, in contrast to the conventional wisdom of the Ni2+/Ni4+ redox couple. The quantitative analysis provides unambiguous evidence for the continuous reduction of the average valence state of Mn and Ni over extended cycles, leading to the voltage fading. In addition, we reveal that the oxygen anions also participate in the charge compensation process mainly through irreversible oxygen release rather than reversible lattice oxygen redox. Such understanding is vital for the precise design and optimization of NaNMO electrodes for rechargeable NIBs with outstanding performance.

3.
Nanoscale ; 11(13): 6182-6191, 2019 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-30874273

RESUMO

Inorganic lead halide perovskite CsPbX3 (X = Cl, Br, or I) nanocrystals are promising candidate materials for light-emitting devices and optoelectronics. Mn-Doped CsPbX3 is of particular interest, as the Mn-doping introduces an additional emission band, making this material a promising white-light emitter. In this study, Mn-doped CsPb(Br/Cl)3 nanocrystals are prepared at room-temperature and ambient pressure. The chemical environment of Mn, and the luminescence of these nanocrystals are analyzed in detail using X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES) and X-ray excited optical luminescence (XEOL). Although the introduction of Mn does not alter the long-range order of the CsPbX3 crystal, it leads to a local lattice contraction with the bond length of Mn-X much shorter than Pb-X. We also find excitation energy-dependence in both the intensity and wavelength of the perovskite excitonic emission band, while only in intensity of the Mn emission band. Detailed fitting of the XEOL reveals that the perovskite emission band is dual-channel, and it is the excitation energy-dependent intensity variation of these two channels that drives the observed red-shift of the combined emission band. Our findings also confirm that the Mn emission band is driven by exciton-Mn energy transfer and clarify the Mn chemical environment and the luminescence mechanism in Mn-doped CsPb(Br/Cl)3 nanocrystals.

4.
Langmuir ; 33(50): 14244-14251, 2017 12 19.
Artigo em Inglês | MEDLINE | ID: mdl-29148786

RESUMO

We observed the growth phase transition of n-alkanethiols (AT), CH3(CH2)n-1SH, n = 4-16, directly implanted on a bare Si(111) surface, forming an AT monolayer. These monolayers were characterized with static water-contact angle, high-resolution X-ray photoelectron spectroscopy, near-edge X-ray fine-structure spectroscopy, and grazing-angle reflection absorption Fourier-transform infrared spectroscopy. The integrated spectral results indicated that the implanted n-AT molecules formed a self-oriented and densely packed monolayer through formation of an S-Si bond. With the number of carbons in the alkyl chain at six or more, namely beginning at hexanethiol, the molecular monolayer began to develop an orientation-ordered structure, which is clearly shorter than that for AT monolayers on Au and Ag. This result implies that, with a stronger molecule-substrate interaction, an ordered molecular monolayer can form with a short chain.

5.
Nano Lett ; 17(10): 6469-6474, 2017 10 11.
Artigo em Inglês | MEDLINE | ID: mdl-28926715

RESUMO

Atomically thin materials, such as graphene, are the ultimate building blocks for nanoscale devices. But although their synthesis and handling today are routine, all efforts thus far have been restricted to flat natural geometries, since the means to control their three-dimensional (3D) morphology has remained elusive. Here we show that, just as a blacksmith uses a hammer to forge a metal sheet into 3D shapes, a pulsed laser beam can forge a graphene sheet into controlled 3D shapes in the nanoscale. The forging mechanism is based on laser-induced local expansion of graphene, as confirmed by computer simulations using thin sheet elasticity theory.

6.
Nanotechnology ; 28(39): 395704, 2017 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-28715345

RESUMO

Micrometer sized oxidation patterns were created in chemical vapor deposition grown graphene through scanning probe lithography (SPL) and then subsequently reduced by irradiation using a focused x-ray beam. Throughout the process, the films were characterized by lateral force microscopy, micro-Raman and micro-x-ray photoelectron spectroscopy. Firstly, the density of grain boundaries was found to be crucial in determining the maximum possible oxygen coverage with SPL. Secondly, the dominant factor in SPL oxidation was found to be the bias voltage. At low voltages, only structural defects are formed on grain boundaries. Above a distinct threshold voltage, oxygen coverage increased rapidly, with the duration of applied voltage affecting the final oxygen coverage. Finally, we found that, independent of initial conditions, types of defects or the amount of SPL oxidation, the same set of coupled rate equations describes the reduction dynamics with the limiting reduction step being C-C â†’ C=C.

7.
Adv Mater ; 28(37): 8240-8247, 2016 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-27384240

RESUMO

Carrier-type modulation is demonstrated in 2D transition metal dichalcogenides as n-type monolayer MoSe2 is converted to nondegenerate p-type monolayer Mo1-x Wx Se2 through isoelectronic doping. Although the alloys are mesoscopically uniform, the p-type conduction in monolayer Mo1-x Wx Se2 appears to originate from the upshift of the valenceband maximum toward the Fermi level at highly localized "W-rich" regions in the lattice.

8.
Sci Rep ; 6: 28326, 2016 06 21.
Artigo em Inglês | MEDLINE | ID: mdl-27325155

RESUMO

In the past few decades, gate insulators with a high dielectric constant (high-k dielectric) enabling a physically thick but dielectrically thin insulating layer, have been used to replace traditional SiOx insulator and to ensure continuous downscaling of Si-based transistor technology. However, due to the non-silicon derivative natures of the high-k metal oxides, transport properties in these dielectrics are still limited by various structural defects on the hetero-interfaces and inside the dielectrics. Here, we show that another insulating silicon compound, amorphous silicon nitride (a-Si3N4), is a promising candidate of effective electrical insulator for use as a high-k dielectric. We have examined a-Si3N4 deposited using the plasma-assisted atomic beam deposition (PA-ABD) technique in an ultra-high vacuum (UHV) environment and demonstrated the absence of defect-related luminescence; it was also found that the electronic structure across the a-Si3N4/Si heterojunction approaches the intrinsic limit, which exhibits large band gap energy and valence band offset. We demonstrate that charge transport properties in the metal/a-Si3N4/Si (MNS) structures approach defect-free limits with a large breakdown field and a low leakage current. Using PA-ABD, our results suggest a general strategy to markedly improve the performance of gate dielectric using a nearly defect-free insulator.

9.
Biosens Bioelectron ; 78: 213-220, 2016 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-26613511

RESUMO

We report a new mechanism for liquid crystal (LC)-based sensor system for trypsin detection. In this system, bovine serum albumin (BSA) was immobilized on gold grids as the enzymatic substrate. When the BSA-modified grid was filled with LC and immersed in the solution containing trypsin, the peptide bonds of BSA were hydrolyzed and peptide fragments were desorbed from the surface of gold grid, which disrupted the orientation of LC at the vicinity and resulted in a dark-to-bright transition of optical image of LCs. By using this mechanism, the limit of detection (LOD) of trypsin is 10 ng/mL, and it does not respond to thrombin and pepsin. Besides, the cleavage behavior on gold surfaces was directly visualized by the scanning photoelectron microscopy (SPEM), in particular for the chemical composition identification and element-resolved image. The loss of BSA fragments and the enhancement of Au photoelectron signal after trypsin cleavage were corresponding to the proposed mechanism of the LC-based sensor system. Because the signals reported by LC can be simply interpreted through the human naked-eye, it provides a simple method for fast-screening trypsin activity in aqueous solution.


Assuntos
Técnicas Biossensoriais , Soroalbumina Bovina/química , Tripsina/isolamento & purificação , Animais , Bovinos , Humanos , Cristais Líquidos/química , Soluções/química , Tripsina/química , Água/química
10.
Langmuir ; 27(7): 3436-41, 2011 Apr 05.
Artigo em Inglês | MEDLINE | ID: mdl-21401112

RESUMO

We have grown 1-dodecandthiol (DDT) monolayer on a bare Si(111) surface through ultraviolet-assisted photochemical reaction. The resulting monolayer was investigated by means of water contact angle measurement, synchrotron radiation-based high-resolution X-ray photoelectron spectroscopy, and polarization-dependent near-edge X-ray absorption fine structure spectroscopy. These combined probes for characterization reveal a hydrophobic ambient surface; the DDT was directly attached to Si through a Si-S bond, and the molecules formed an ordered monolayer with an average tilt angle of 57° of the alkyl chains relative to the substrate surface.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA