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81.
Neil J. Everall John M. Chalmers Andrea Local Simon Allen 《Vibrational Spectroscopy》1996,10(2):253-259
Polarised Fourier transform infrared (FT-IR) external-reflection spectroscopy has been used to measure molecular orientation at the surface of uniaxially drawn poly(ethylene terephthalate) (PET) films as a function of draw ratio. The spectra, which were obtained using an FT-IR microscope operating in the reflectance mode, were of high signal-to-noise (S/N) ratio, and contained only the specular component of the reflected radiation. The dichroic ratio of the 1019 cm−1 ring stretching band was used to measure the PET orientation function, P200. Prior to quantifying band intensities, the reflectance spectra were either transformed using the Kramers-Kronig algorithm, or simply differentiated; it was found that the dichroic ratios obtained using either pretreatment were similar. It was shown that the P200 values obtained using the FT-IR method compared well with those obtained using surface refractive index measurements, provided that the intensity of the 1019 cm−1 band was normalised relative to a non-dichroic band in the spectrum prior to computing dichroic ratios. The use of a reflecting microscope to perform the analysis of surface orientation not only simplifies sample alignment compared with “macro” reflectance accessories, but also allows awkward-shaped or small samples to be examined with relative ease. Unfortunately, a significant current limitation is that samples must be sufficiently “optically thick” to prevent double-pass (“transflectance”) radiation reaching the detector and yielding non-specular features in the reflectance spectrum. For polyaromatics, this probably means thicknesses in excess of 50 μm to obtain good spectra in the fingerprint region. Polarised attenuated total reflectance microscopy may present an alternate approach for examining thinner films. 相似文献
82.
High Resolution Electron Microscopy Investigations of La2CeTaO6Cl3 and its Thermal Decomposition Product La2Ce Ce TaO6Cl3?x The thermal decomposition of the hexagonal La2CeTaO6Cl3 led to a mixed-valent product La2CeCe TaO6Cl3?x with a complicated monoclinic structure. The detailed inspection shows two subunits A and B, which form the monoclinic unit cell by a ABAB sequence. The subunit A is almost identical to the hexagonal cell of the starting material while subunit B has additional Ln- and Cl-positions. For this reason, the main structure features of the monoclinic compound and the starting material are related, which is clearly seen in the electron microscopy investigations. As might be expected from the relationship between the subunits A and B one can observe defects in the monoclinic compound arising from the various possibilities of combining these building elements. We also found structure defects in the hexagonal starting material, which are caused by the presence of the subunit B. 相似文献
83.
84.
In this review, some established concepts from Colloidal Science and their application to graphene and carbon nanotubes dispersions in organic or aqueous media are highlighted to rationalize alternatives for some issues in terms of colloidal properties. Recent applications for carbon-based dispersions are presented, as well as van der Waals interactions in carbon materials and strategies to overcome these interactions, such as increasing electrostatic repulsion between dispersed particles, surface functionalization, or adsorption of passivation agents such as macromolecules, which are the basis of many dispersion and exfoliation procedures. The demonstration of how knowledge and fine control of colloidal interactions have been used to overcome several limitations, such as the preparation of stable and concentrated dispersions of carbon materials and keeping appreciable electrical conductivity, is presented. It is also showed that the same knowledge can help the development of more environmentally friendly carbon-based colloids as well as the improvement of similar systems as dispersions of two-dimensional materials. 相似文献
85.
The interaction of carbon with the Ni(110) surface has been investigated by scanning tunneling microscopy (STM). Dissociation of ethylene at elevated temperatures resulted in the formation of two carbidic carbon structures, (4 × 3) and (4 × 5), both of which are formed by a significant reconstruction of the surface involving a long-range mass transport of 0.5 ML Ni. The density of C in the reconstructed phases was estimated based on Auger electron spectroscopy (AES). Atomic models, which are consistent with all existing experimental observations for carbidic carbon on Ni(110), are proposed for the (4 × 3) and (4 × 5) phases. 相似文献
86.
87.
Hassenkam T Jørgensen HL Pedersen MB Kourakis AH Simonsen L Lauritzen JB 《Micron (Oxford, England : 1993)》2005,36(7-8):681-687
AFM images were taken of the exterior surface of a single trabecula, extracted from a human femoral head removed during surgery for a hip fracture in an old women with former fractures. The images showed a dense structure of bundled collagen fibrils banded with 67 nm periodicity. Bundles were seen to run in parallel in layers confirming the collagen structure seen by other techniques. Single collagen fibrils were seen to cross the bundles, thus forming cross-links between neighboring bundles of collagen fibrils. Some of these crossing fibrils did not have the 67 nm band pattern and their dimensions were about half compared to the neighboring collagen fibrils. Very little mineral was found on the surface of the trabecula. An AFM image of a fracture plane was also displayed. The trabecula was extracted from a region close to the hip fracture. However, there were in this case no obvious features in the images that could be linked directly to osteoporosis, but altered collagen banding and collagen protrusions may alter mechanical competence. A path to extensive studies of the nanometer scale structure of bone was demonstrated. 相似文献
88.
Ultrafast magnetic processes are of great scientific interest but also form the basis of high density magnetic recording applications. We demonstrate the uniqueness of time resolved, high resolution magnetic X-ray microscopy, and show that the motion of a magnetic vortex core can be imaged. The vortex core direction is hidden to most experimental techniques, but has a decisive influence on the dynamics of the magnetic structure.We imaged the switching of a ferromagnetic nanostructure by a spin polarized current pulse using time resolved X-ray microscopy. As opposed to the common uniform switching process due to Néel and Stoner–Wohlfarth, the magnetization in spin injection devices does not switch uniformly, but involves the motion of a magnetic vortex. To cite this article: Y. Acremann, C. R. Physique 9 (2008). 相似文献
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90.
The undissolved fibre and gel residuals that had not completely reacted to form fully dissolved carboxymethyl cellulose (CMC) ID the production of CMC were studied to clarify the reactivity of wood components ID the pulp. The undissolved residuals, the pulp and the CMC were therefore analysed on the fibre level, the cell-wall level and the chemical composition level. The results may be interpreted as indicating that the presence of undissolved residuals ID the CMC was not due to any chemical difference. The undissolved residuals were shown to consist mainly of swollen cell wall parts and some whole wood cells, mainly thick-walled compression wood and summerwood cells. They react more slowly ID the mercerisation and etherification, probably because of a greater diffusion resistance due to their larger dimensions or to a more dense structure. These cells are assumed to be less accessible for chemical penetration, but they may also contain supramolecular structures that slow down the CMC reaction. 相似文献