Transmission electron microscopy support films

Khmenkov M, Nepijko S, Kuhlenbeck H, Baiimer M, Schldgl R, Ereund H-J. 1997. The structure of Pt-aggregates on a supported thin aluminum oxide film in comparison with unsupported alumina a transmission electron microscopy study. Surf Sci 391 27-36. 

Extremely thin, self-supporting film electrodes have been successfully produced. For example, polypyrrole films of 120 nm thickness have been used successfully to grow microcrystallites, followed by removal of the film plus crystallites from the substrate for characterization of the crystallographic structure and orientation of the microcrystallites by transmission electron microscopy with selected area electron diffraction [23]. Thin-film electrodes have been applied to allow transmission of high-energy beams, including x-rays, for in situ... 

For free-clusters, the cluster size distribution can be measured by the time-of-flight mass spectrometer for cluster films deposited on substrate by the cluster beam, the measurement of size distribution and observation of nanostructure are mostly done using transmission electron microscopy (TEM). In this section we will focus on the latter and pay special attention to FePt, CoPt clusters which have high anisotropy Tl0 phase after annealing [43-45]. For the TEM observations, FePt, CoPt nanoclusters, produced in a gas-aggregation chamber, in which high pressure Ar gas ( 0.5-lTorr) was applied and cooled by LN2, were directly deposited onto carbon-coated films supported by Cu grids. 

Figure 4. Inhomogeneity of silica-aluminas prepared by various methods. A series of 17 commercial samples of silica-aluminas from seven different producers was submitted to microanalysis. All of them showed considerable fluctuations of composition at the scale of several tens of nanometers to several micrometers. These samples were prepared by coprecipitation or by the sol-gel method. It is not known whether some of these samples were prepared from alkoxides. Smaller but significant fluctuations at the micrometer scale were also observed for two laboratory samples prepared from alkoxides. The samples were dispersed in water with an ultrasonic vibrator. A drop of the resulting suspension was deposited on a thin carbon film supported on a standard copper grid. After drying, the samples were observed and analyzed by transmission electron microscopy (TEM) on a JEOL-JEM 100C TEMSCAN equiped with a KEVEX energy dispersive spectrometer for electron probe microanalysis (EPM A). The accelerating potential used was 100 kV.

The support generally used for observation of catalysts in transmission electron microscopy comprises a thin film of amorphous carbon with holes, itself supported by a metallic grid. These carriers allow the observation of several zones of a preparation, of a few hundred square micrometres, without interference. We have pointed out the need to work in transmission electron microscopy on samples with a thickness not much above a hundred nanometres. In certain cases, which include that of reforming catalysts, this criteria is naturally satisfied due to the nature of the support. Transition aluminas are effectively made up of very fine platelets that can be separated by simple grinding. The preparation is then dispersed in a liquid and a drop is collected and placed on the carrier. 

PPO repeating units self-assemble into a supramolecular honeycomb-like layered structure, in which perforations are filled by coil segments. When cast from dilute CHCR solution onto a carbon support film, honeycomb-like supramolecular structure was observed, as revealed by transmission electron microscopy (TEM), in which coil perforations are packed on a hexagonal symmetry with distances between perforations of approximately 10 nm (Figure 14a). 

Scanning transmission electron microscopy (STEM), coupled with EDX, has been used to determine metal particle sizes. The specimens for STEM are prepared by dispersing the sample ultrasonicaUy in methanol and placing one drop of the suspension onto a Formvar film supported on a copper grid. 

The adherence of small particles of precious metals to the surface of the support can be assessed by transmission electron microscopy. It has been observed that mild ultrasonic treatment of the catalyst in a liquid, such as ethanol, can remove precious metal particles from the surface of the support. After applying a drop of the suspension resulting from the ultrasonic treatment on the carbon films used as specimen support the precious metal particles released from the support show up on the carbon support film. Especially dark-field techniques are useful to indicate the presence of precious metal particles on the carbon support film. 

The removal of direct carbon replicas is dependent upon the polymer. Boiling xylene vapor was used to remove drawn PE from replicas [436] in work on drawn polymer morphology. A direct carbon replica method for a PBT impact fracture surface was described by evaporation of platinum at 20° and PBT removal in hexafluoroisopropanol (HFIP) [437], Latex film coalescence in poly(vinyl acrylate) homopolymer and vinyl acrylic copolymer latexes was studied using direct replicas [438]. As the latex films have a low glass transition temperature, they were cooled by liquid nitrogen to about -150°C in the vacuum evaporator and shadowed with Pt/Pd at 45° followed by deposition of a carbon support film at 90° to the specimen surface. The latex films were dissolved in methyl acetate/methanol. Transmission electron microscopy micrographs of the latex films show the difference between films aged for various times (see Section 5.5.2). 

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