硬X射线磁圆二色实验方法的建立

在北京同步辐射装置(BSRF)1W1B光束线和XAFS实验站上国内首次建立了硬X射线波段的磁圆二色实验(XMCD)方法. 以单晶金刚石作为相位延迟片, 在透射劳埃(Laue)模式下, 利用衍射双折射效应, 将入射的单色线偏振光转变为相应的左旋和右旋圆偏振光, 测量磁化样品对左旋和右旋圆偏振光吸收的差异, 获得了XMCD信号. 本实验使用透射方法测量了Pt-Fe合金Pt L_2,3边的XMCD, 获得了XMCD信号. XMCD实验方法的建立, 为研究磁性材料尤其是磁性薄膜材料的电子结构和磁结构提供了实验基础.     

Modification of the surface state of rough substrates by two different varnishes and influence on the reflected light

Modification of the visual appearance when a rough surface is covered by a varnish is mostly attributed to the levelling of the substrate surface, which depends on the molecular weight of the varnish. The topography of varnished surfaces, however, has never been measured directly. Surfaces of varnishes applied over glass substrates of varying roughness were studied, therefore, using mechanical profilometry. Two different varnishes made with a low and a high molecular weight resin were studied. Both varnishes lower the r.m.s. roughness of the substrates and filter the high spatial frequencies. These results are amplified for the varnish containing the low molecular weight resin. The light reflected by the varnished samples is modelled from these topographical data. Its angular distribution, calculated from the probability density of slopes is presented, taking into account separately the air/varnish and the varnish/substrate interfaces. These analyses are presented in a back-scattering configuration. They show that varnishing significantly reduces the angular width of the reflected light and that this effect is magnified for the low molecular weight resin. Modelling furthermore shows that the influence of the roughness of the varnish/substrate interface is negligible in the total reflected light.     

不完全信息群体决策专家权重的集结

本文对于属性权重信息和属性效用信息都不完全的群体多属性决策问题，通过构造属性值区间和运用系统聚类分析法，对群体决策中的专家进行分类，并确定每位专家的权重．     

a-C:F薄膜的热稳定性与光学带隙的关联

以CF4和C6H6的混合气体作为气源,在微波电子回旋共振化学气相沉积(ECRCVD)装置中制备了氟化非晶碳薄膜(aC:F),并在N2气氛中作了退火处理以考察其热稳定性.通过傅里叶变换红外吸收谱和紫外可见光谱获得了薄膜中CC双键的相对含量和光学带隙,发现膜中CC键含量与光学带隙之间存在着密切的关联,在高微波功率下沉积的氟化非晶碳膜具有低的光学带隙和较好的热稳定性. 关键词： 氟化非晶碳膜 光学带隙 退火温度 热稳定性     

Vanadium valency charge state in solid solutions ScNb2−2xTa2xVO9

Phase equilibria in the Sc₂O₃-V₂O₅-Nb₂O₅-Ta₂O₅ system and properties of ScNb_2−2xTa_2xVO₉ phases were studied by X-ray phase analysis, optical and radio spectroscopy. A continuous series of solid solutions was shown to exist at 0≤x≤1. V(IV) centers with different crystallographic surrounding were detected for all the considered compositions. A correlation between the number of V(IV) ions and the width of the forbidden gap in the solid solutions was found.     

Characterizations of Tb:Zn2SiO4 films on silicon wafer prepared by sol-gel dip-coating and solid-phase reaction

Terbium-doped Zn_2SiO_4 films were successfully prepared on Si wafers by a simple sol-gel dip-coating and solid-phase reaction method of ZnO and SiO_2. X-ray diffraction (XRD) and UV－Vis absorption results revealed that films processed below 850℃ were ZnO in wurzite structure, and films processed above 850℃ were Zn_2SiO_4 in wellimite structure. Photoluminescence measurements of the Tb-doped Zn_2SiO_4 films showed two strong emission bands at 490 and 545nm. The photoluminescence lifetime was 4.6ms.     

Nanostructure and conductivity of thin metal films

Amorphous silver, copper, gold, and iron films of a thickness between 6 and 350 nm are grown on polymeric substrates by vacuum evaporation. The nanostructure of the films is investigated. The dependence of the conductivity on the film thickness is obtained, and a correlation between the surface morphology and the conductivity is established.     

Synthesis and characterization of well‐defined diblock and triblock copolymers of poly(N‐isopropylacrylamide) and poly(ethylene oxide)

Well‐defined diblock and triblock copolymers composed of poly(N‐isopropylacrylamide) (PNIPAM) and poly(ethylene oxide) (PEO) were successfully synthesized through the reversible addition–fragmentation chain transfer polymerization of N‐isopropylacrylamide (NIPAM) with PEO capped with one or two dithiobenzoyl groups as a macrotransfer agent. ¹H NMR, Fourier transform infrared, and gel permeation chromatography instruments were used to characterize the block copolymers obtained. The results showed that the diblock and triblock copolymers had well‐defined structures and narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight < 1.2), and the molecular weight of the PNIPAM block in the diblock and triblock copolymers could be controlled by the initial molar ratio of NIPAM to dithiobenzoate‐terminated PEO and the NIPAM conversion. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4873–4881, 2004     

Extension of the chain‐end,free‐volume theory for predicting glass temperature as a function of conversion in hyperbranched polymers obtained through one‐pot approaches

Compared with linear polymers, more factors may affect the glass‐transition temperature (T_g) of a hyperbranched structure, for instance, the contents of end groups, the chemical properties of end groups, branching junctions, and the compactness of a hyperbranched structure. T_g's decrease with increasing content of end‐group free volumes, whereas they increase with increasing polarity of end groups, junction density, or compactness of a hyperbranched structure. However, end‐group free volumes are often a prevailing factor according to the literature. In this work, chain‐end, free‐volume theory was extended for predicting the relations of T_g to conversion (X) and molecular weight (M) in hyperbranched polymers obtained through one‐pot approaches of either polycondensation or self‐condensing vinyl polymerization. The theoretical relations of polymerization degrees to monomer conversions in developing processes of hyperbranched structures reported in the literature were applied in the extended model, and some interesting results were obtained. T_g's of hyperbranched polymers showed a nonlinear relation to reciprocal molecular weight, which differed from the linear relation observed in linear polymers. T_g values decreased with increasing molecular weight in the low‐molecular‐weight range; however, they increased with increasing molecular weight in the high‐molecular‐weight range. T_g values decreased with increasing log M and then turned to a constant value in the high‐molecular‐weight range. The plot of T_g versus 1/M or log M for hyperbranched polymers may exhibit intersecting straight‐line behaviors. The intersection or transition does not result from entanglements that account for such intersections in linear polymers but from a nonlinear feature in hyperbranched polymers according to chain‐end, free‐volume theory. However, the conclusions obtained in this work cannot be extended to dendrimers because after the third generation, the end‐group extents of a dendrimer decrease with molecular weight. Thus, it is very possible for a dendrimer that T_g increases with 1/M before the third generation; however, it decreases with 1/M after the third generation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1235–1242, 2004     

Fluorinated Copolymer-Oxide Hybrids

A fluorinated copolymer/metal oxide hybrid is fabricated by refluxing a high hydroxyl content fluorinated copolymer with tetraethoxysilane. The resulting organic-inorganic hybrids are transparent throughout the entire compositional range if processed with HCl as a catalyst. They exhibit a continuous variation in hardness, hydrophobicity, and abrasion resistance, intermediary between the properties of the pure polymer and that of a silica gel. The catalyst has a strong influence over the microstructure of the hybrid. ²⁹Si MAS-NMR indicates the presence of highly condensed silica clusters within the structure of the hybrid. If a Nd(III) alkoxide is used instead of TEOS, a Nd ³⁺-doped fluoropolymer is obtained. These results indicate that when a fluorinated copolymer contains groups amenable to hydrolysis and condensation, cross-linking with a metal alkoxide is possible, leading to an interesting families of hybrids.