Lianghu Gu

Tin Nanoparticles Encapsulated in Porous Multichannel Carbon Microtubes: Preparation by Single-Nozzle Electrospinning and Application as Anode Material for High-Performance Li-Based Batteries

Tin nanoparticles encapsulated in porous multichannel carbon microtubes (denoted as SPMCTs) were prepared by carbonization of electrospun PAN-PMMA-tin octoate nanofibers fabricated using a single-nozzle electrospinning technique. This material exhibited excellent characteristics for lithium ion battery anode applications in terms of reversible capacities, cycling performance, and rate capability. Undertaking such a production configuration allows the long-existing problem of obtaining a high packing density of tin particles while retaining sufficient spare space to buffer the volume variation during lithium alloying and dealloying processes to be properly addressed. Furthermore, the porous carbon shell preserves both the mechanical and chemical stability of the function-active Sn metal, which also serves as a highly conductive medium allowing Li(+) to access.

Polycationic Ligands in Gold Catalysis: Synthesis and Applications of Extremely π-Acidic Catalysts

Very often ligands are anionic or neutral species. Cationic ones are rare, and, when used, the positively charged groups are normally appended to the periphery of the ligand. Here, we describe a dicationic phosphine with no spacer between the phosphorus atom and the two positively charged groups. This structural feature makes its donor ability poorer than that of phosphites and only comparable to extremely toxic or pyrophoric compounds such as PF3 or P(CF3)3. By exploiting these properties, a new Au catalyst has been developed displaying a dramatically enhanced capacity to activate π-systems. This has been used to synthesize very sterically hindered and naturally occurring 4,5-disubstituted phenanthrenes. The present approach is expected to be applicable to the development and improvement of many other transition metal catalyzed transformations that benefit from extremely strong π-acceptor ligands. The mechanism of selected catalytic transformations has been explored by density functional calculations.

Direct imaging of surface plasmon resonances on single triangular silver nanoprisms at optical wavelength using low-loss EFTEM imaging.

Using low-loss energy-filtering transmission electron microscopy (EFTEM) imaging, we map surface plasmon resonances (SPRs) at optical wavelengths on single triangular silver nanoprisms. We show that EFTEM imaging combining high spatial sampling and high energy resolution enables the detection and for the first time, to the best of our knowledge, mapping at the nanoscale of an extra multipolar SPR on these nanoparticles. As illustrated on a 276.5 nm long nanoprism, this eigenmode is found to be enhanced on the three edges where it exhibits a two-lobe distribution.

Experimental realization of graded L10-FePt/Fe composite media with perpendicular magnetization

A concept is suggested and experimentally realized to fabricate graded media for ultrahigh density magnetic recording where the material parameters vary gradually in the interfacial region between the hard magnetic part and the soft magnetic part of epitaxial L10-FePt/Fe exchange spring nanocomposites with perpendicular magnetization. A graded interface between the L10-FePt phase and the Fe phase is formed by depositing part of the Fe layer at elevated temperatures. The existence of the graded interface is verified by electron energy-loss spectroscopy. The influence of the character of the graded interface on the magnetic properties is studied. With increasing thickness of the graded interface the coercivity continuously decreases, which can be used for a fine tuning of the coercivity of exchange spring composite media.

Correlating the structural, chemical, and optical properties at nanometer resolution

Valence electron spectroscopic imaging (VESI) techniques, taking advantages of the energy-losses suffered by inelastic scattering of the fast electrons in the transmission electron microscope, offer an inherently high spatial resolution to characterize the electronic structure of materials close to the Fermi level. Here we demonstrate that the combination of an electron monochromator and a highly dispersive imaging energy filter, which has become available only recently, allows reliable measurements of local bandgaps on the nanometer scale. In addition, the correlations of structural, chemical, and optical properties can be revealed via VESI using monochromated electrons with a high spatial resolution.

α-Dicationic Chelating Phosphines: Synthesis and Application to the Hydroarylation of Dienes

A series of new P^P-chelating ligands constituted by a dicationic -[P(H2Im)2]+2 unit (H2Im = 1,3-dimethyl-4,5-dihydroimidazol-2-ylidene) and a -PPh2 group connected through structurally different backbones have been synthesized. Evaluation of their reactivity toward different metal centers provides evidence that the dicationic fragment, otherwise reluctant to coordinate metals, readily participates in the formation of chelates when embedded into such a scaffold. Moreover, it significantly enhances the Lewis acidity of the metals to which it coordinates. This property has been used to develop a Rh catalyst that efficiently triggers the hydroarylation of dienes with electron-rich aromatic molecules. Kinetic studies and deuterium-labeling experiments, as well as density functional theory calculations, were performed in order to rationalize these findings.

α-Radical Phosphines: Synthesis, Structure, and Reactivity

A series of phosphines featuring a persistent radical were synthesized in two steps by condensation of dialkyl-/diarylchlorophosphines with stable cyclic (alkyl)(amino)carbenes (cAACs) followed by one-electron reduction of the corresponding cationic intermediates. Structural, spectroscopic, and computational data indicate that the spin density in these phosphines is mainly localized on the original carbene carbon from the cAAC fragment; thus, it remains in the α-position with respect to the central phosphorus atom. The potential of these α-radical phosphines to serve as spin-labeled ligands is demonstrated through the preparation of several AuI derivatives, which were also structurally characterized by single-crystal X-ray diffraction.

Bis- and Tris(pyrazolyl)borate/Methane-Stabilized PIII-Centered Cations

We report the synthesis of [H2 B(pz)2 PR](+) , [H2 C(pz)2 PR](+2) , [HB(pz)3 P](+2) , and [HC(pz)3 P](+3) (H2 B(pz)2 =bis(pyrazolyl)borate; H2 C(pz)2 =bis(pyrazolyl)methane; HB(pz)3 =tris(pyrazolyl)borate; HC(pz)3 =tris(pyrazolyl) methane; R=Ph, Cy or Et2 N) by reaction of the corresponding neutral or anionic ligands with chlorophosphines in the presence of TMSOTf. The structures of these compounds were determined by X-ray crystallographic analysis and the nature of their bonding was examined using density functional theory.

VEELS band gap measurements using monochromated electrons

With the development of monochromators for transmission electron microscopes, valence electron energy-loss spectroscopy (VEELS) has become a powerful technique to study the band structure of materials with high spatial resolution. However, artefacts such as Cerenkov radiation and surface effects pose a limit for interpretation of the low-loss spectra; also the inelastic delocalisation restricts the spatial resolution on band gap mapping. For direct semiconductors, spectra acquired at thin regions can efficiently minimize the Cerenkov effects. Examples of h-GaN spectra acquired at different thickness showed that a correct band gap onset value can be obtained for sample thicknesses up to about 60 nm. For indirect semiconductors, the correct band gap onset can be obtained in the dark-field mode when the required momentum transfer for indirect transition is satisfied. At low energy-loss range the spatial resolution of this technique, which is mainly limited by the inelastic delocalisation, can be improved by dark-field VEELS at high collection angles.

Low-loss EFTEM Imaging of Surface Plasmon Resonances in Ag Nanostructures

Understanding how light interacts with matter at the nanometer scale is a fundamental issue in optoelectronics, nanophotonics and nanoplasmonics. The optical properties of metallic nanoparticles are entirely dependent on collective excitations of their valence electrons, known as surface plasmon resonances (SPR), under electromagnetic illumination. Measuring these properties locally at the level of the individual nanoobject in combination with spectral information over the entire visible range constitutes a challenging issue for linking of the global response of the nanoparticles and the underlying structure and morphology. The visualization of localized SPRs on the nanometer scale in combination with spectral information over the entire visible range is of prime importance in the field of biosensors, surface-enhanced Raman spectroscopy, and for the design of metamaterials. But also the explanation of abnormal transmission of light through sub-wavelength holes relies on such information.