Transmission electron microscopy 614 INDEX

One major problem of all these techniques is the sensitivity in the parameter selected to detect the presence of inhomogeneities. With visible light for example, inhomogeneous samples can appear transparent if the difference in the refractive index between the phases is less than 0.01. Staining (in the case of transmission electron microscopy, TEM), or chemical etching (in the case of scanning electron microscopy, SEM), can be helpful in revealing the structure. 

Since the number of atoms on the surface of a bulk metal or metal oxide is extremely small compared to the number of atoms in the interior, bulk materials are often too costly to use in a catalytic process. One way to increase the effective surface area of a valuable catalytic material like a transition metal is to disperse it on a support. Figure 5.1.5 illustrates how Rh metal appears when it is supported as nanometer size crystallites on a silica carrier. High-resolution transmission electron microscopy reveals that metal crystallites, even as small as 10 nm, often expose the common low-index faces commonly associated with single crystals. However, the surface to volume ratio of the supported particles is many orders of magnitude higher than an equivalent amount of bulk metal. In fact, it is not uncommon to use catalysts with 1 nm sized metal particles where nearly every atom can be exposed to the reaction environment. 

The composition of the as-deposited alloy films and anodized films was determined by Auger spectrometry (PHI-660 Perkin Elmer) after five seconds of ion milling of the films. The oxide films were also analyzed with scanning and transmission electron microscopy (TEM). The refractive index of the oxide was measured at A, = 633 nm by ellipsometer LEE - 3M. 

Obviously, aggregate size distribution characterization in the mix is very delicate. Some transmission electron microscopy observations have been conducted on microtome thin cuts, but such characterizations are restricted to a small number of aggregates and can only lead to qualitative conclusions [23]. Direct characterization of object distribution in tie mix has also been conducted using x-ray [105] or neutron diffraction, but such approaches are strongly limited by the high concentration of filler objects and their refraction index, which is relatively close to that of rubber. One other way to characterize object size distribution is to extract the filler from the mix by thermal or catalyzed polymer decomposition these procedures probably greatly affect object size, because of possible reagglomerations. 

Donald et al. [2] reported banded structures formed by several thermotropic polymers oriented by shear at temperatures above their softening points. Similar structures were also noted in fibers drawn from polymers with rigid backbones above the softening points. Viney et al. [3] point out that the banded structures observed in shear are due to the variation in the direction of the long molecular axis with respect to the direction of shear. Evidence obtained by both optical microscopy and electron diffraction measurements supports this view. Donald and Windle [4] studied the banded structure by electron microscopy and commented that The near sinusoidal variation in the direction of the principal axis of the refractive index ellipsoid is indeed reflecting the variations in the molecular orientation. Their transmission electron microscopy indicates that the transition from... 

The structure of crazes in bulk specimens was studied by Kambour [15], who used the critical angle for total reflection at the craze/polymer interface to determine the reliactive index of the craze, and showed that the craze was roughly 50 per cent polymer and 50 per cent void. Another investigation involved transmission electron microscopy of polystyrene crazes impregnated with an iodine-sulphur eutectic to maintain the craze in its extended state [33, 34]. The structure of the craze was clearly revealed as fibrils separated by the voids that are responsible for the overall low density. 

Cationic latex particles with surface amino groups were prepared by a multi-step batch emulsion polymerisation. Monodisperse cationic latex particles to be used as the seed were synthesised first. Then the amino-functionalised monomer, aminoethylmethacrylate hydrochloride, was used to synthesise the final functionalised latex particles. Three different azo initiators were used 2,2 -azobisisobutyramidine dihydrochloride, 2,2 -azobisdimethyleneisobutyramidine dihydrochloride, and 2,2 -azobisisobutyronitrile. Hexadecyltrimethylammonium bromide was used as the emulsifier. The latices were characterised by photon correlation spectroscopy to study the mean particle diameters, transmission electron microscopy to deteimine the particle size distributions, and hence the number- and weight-average diameters and the polydispersity index. The conversion was determined gravimetrically, the surface density of the amino groups was detemiined by conductimetric titrations, and the... 

All measurements are performed using the refractive index of CdS. In the case of cadmium sulfide nanoparticles produced in the w/o microemulsion the viscosity rj and the refractive index no of the continuous oil phase, namely the xylene-pentanol (1 1) mixture ( = 1.454 cP, D = 1165) are used. Consequently rj and no for water are used when the CdS nanoparticles are redispersed in the aqueous phase. Morphology and size of the redispersed CdS particles are also determined by transmission electron microscopy. Therefore, a small amount of the aqueous solutions is dropped on copper grids, dried and examined in the EM 902 transmission electron microscope (Zeiss) (acceleration voltage 90 kV). The high amount of surfactant brings also difficulties for the preparation of the samples for TEM measurements and consequently samples have to be washed with water to reduce the amount of surfactant. 

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