Doped coupled frustrated spin-1/2 chains with four-spin exchange

The role of various magnetic interchain couplings is investigated by numerical methods in doped frustrated quantum spin chains. A nonmagnetic dopant introduced in a gapped spin chain releases a free spin-1/2 soliton. The formation of a local magnetic moment is analyzed in terms of soliton confinement. A four-spin coupling which might originate from cyclic exchange is shown to produce such a confinement. Dopants on different chains experience an effective space-extended nonfrustrating pairwise spin interaction.     

Optical near-field microscopy of light focusing through a photonic crystal flat lens

We report here the direct observation by using a scanning near-field microscopy technique of the light focusing through a photonic crystal flat lens designed and fabricated to operate at optical frequencies. The lens is fabricated using a III-V semiconductor slab, and we directly visualize the propagation of the electromagnetic waves by using a scanning near-field optical microscope. We directly evidence spatially, as well as spectrally, the focusing operating regime of the lens. At last, in light of the experimental scanning near-field optical microscope pictures, we discuss the lens ability to focus light at a subwavelength scale.     

Optical management in high‐efficiency thin‐film silicon micromorph solar cells with a silicon oxide based intermediate reflector

In the effort to increase the stable efficiency of thin film silicon micromorph solar cells, a silicon oxide based intermediate reflector (SOIR) layer is deposited in situ between the component cells of the tandem device. The effectiveness of the SOIR layer in increasing the photo‐carrier generation in the a‐Si:H top absorber is compared for p–i–n devices deposited on different rough, highly transparent, front ZnO layers. High haze and low doping level for the front ZnO strongly enhance the current density (J_sc) in the μc‐Si:H bottom cell whereas J_sc in the top cell is influenced by the angular distribution of the transmitted light and by the reflectivity of the SOIR related to different surface roughness. A total J_sc of 26.8 mA/cm² and an initial conversion efficiency of 12.6% are achieved for 1.2 cm² cells with top and bottom cell thicknesses of 300 nm and 3 μm, and without any anti‐reflective coating on the glass. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

From Si nanowire to SiC nanotube

Si nanowires (NWs), with diameters of about 800 nm and lengths of about 10 ??m, previously synthesized by the VLS method with gold catalyst, were carburized at 1,100 °C under methane for conversion into SiC nanostructures. These experiments have shown that Si NWs have been transformed into SiC nanotubes (NTs) with approximately the same sizes. Nanotubes?? sidewall thickness varies from 20 to 150 nm depending on the NTs?? height. These SiC nanotubes are hexagonal in shape and polycrystalline. A model of growth based on the out-diffusion of Si through the SiC layer was proposed to explain the transformation from Si nanowires to SiC nanotubes. This model was completed with thermodynamic calculations on the Si?CH₂?CCH₄?CO₂ system and with results from complementary experiment using propane precursor. Routes for obtaining crystalline SiC NTs using this reaction are proposed.     

Numerical Approaches to Compute Spectra of Non-Self Adjoint Operators and Quadratic Pencils

In this article we are interested in the numerical computation of spectra of non-self adjoint quadratic operators. This leads to solve nonlinear eigenvalue problems. We begin with a review of theoretical results for the spectra of quadratic operators, especially for the Schrödinger pencils. Then we present the numerical methods developed to compute the spectra: spectral methods and finite difference discretization, in infinite or in bounded domains. The numerical results obtained are analyzed and compared with the theoretical results. The main difficulty here is that we have to compute eigenvalues of strongly non-self-adjoint operators which are very unstable.     

广义基的多重散射理论

提出了任意函数基表象中的多重散射理论. 基于这个框架, 一组新基的多重散射计算表明其收敛性比传统的球谐函数基的要好, 从而可以实现更快和更节省物理内存的计算. 另外, 将多重散射矩阵分为传播矩阵和散射矩阵, 很好地描述了散射性质和减小了多重散射计算中块矩阵的尺寸.     

Phosphonated Polyethylenimine‐Coated Nanoparticles: Size‐ and Zeta‐Potential‐Adjustable Nanomaterials

Novel partially phosphonated polyethylenimine polymers are developed in order to control the modification of nanoparticle (NP) surfaces. This polymer is built by an accessible one‐step process. The numerous phosphonate functions assume both a strong covalent anchoring on metal oxide NPs and a modulation of electric charges, while amino groups are associated with dispersion preservation and subsequent biofunctionalization. The zwitterionic nanomaterials obtained display a good stability toward pH and ionic strength. According to the selected percentage of phosphonation and the polymer size, zeta potential, and diameter of the particles are controlled.     

Alternatively linking fullerene and conjugated polymers

The stereo‐electronic control over bisadditions of conjugated polymers to fullerene (C₆₀) is explored in the formation of alternating copolymers. The chemistry, resulting configuration, and properties of poly(3‐hexylthiophene)‐alt‐C₆₀ copolymers prepared by either classic pyrrolidine ring formation or an atom transfer radical addition are compared. Both routes result in controlled additions of polymers to C₆₀. Extensive macromolecular modeling through PM6 methods indicate that there is no conjugation between P3HT and C₆₀ in the systems studied. This along with 2D‐NMR, AFM, and photovoltaic characterizations of the materials indicate the importance of the structure of the modified C₆₀ and the nature of the linking group between C₆₀ and P3HT segments in determining the morphology of the copolymers in the solid state. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2304–2317, 2009