HRTEM characterization

D. Miser, E. J. Shin, M. R. Hajaligol, and F. Rasouli, HRTEM characterization of phase changes and the occurrence of maghemite during catalysis by an iron oxide, Appl. Catal. A Gen. 258(1), 7-16 (2004). 

VI. Examples of HRTEM Characterization of Catalysts in Reactive Atmospheres... 

Detailed HRTEM characterization of the specimens showed that all metal-ceramic interfaces in the two different nanocomposites had thin ( 1 nm thick) amorphous films (see Fig. 11.5). In addition, occluded particles were found inside the alumina grains which also had thin amorphous films at their interfaces with alumina. Analytical microscopy showed the films to contain Ca, Si, and Al.41 Hamaker coefficients were calculated for metal-ceramic interfaces in the presence of a Si02-based film, which indicated that a stronger attractive force is expected for intergranular films at metal-alumina interfaces,... 

Fig. 4 shows an HRTEM overview of the fresh nanotube material. The comparative HRTEM characterization of the fresh and tested catalysts, shown in Fig. 5, indicates that some modifications of the carbon nanotube surface occurred during the reaction (Fig. 5, a and b). Fig. 5, a shows that the walls of the carbon nanotubes before the reaction consisted of two layers, an inner layer formed by conical graphene sheets and a thick outer layer of amorphous carbon parallel to the tube axis. After 20 hours time on stream in the ODH, the stacks of the inner, conical graphene layers can now be recognized well. The thick, outer... 

Eqiupment and techniques for NMR, FITR, Raman, EXAFS and HRTEM characterization are described in [5,6]. Equipment and XPS characterization technique and the methods for textural properties study are given in [7]. 

Armendariz, V., Jose-Yacaman, M., Duarte-Moller, A., Peralta-Videa, J.R., Troiani, H., Herrera, 1. and Gardea-Torresdey, J.L (2004) HRTEM characterization of gold nanoparticles... 

The different growth modes discussed above have been exemplified also from structural studies. Froment and Lincot [247] used structural characterization methods, such as TEM and HRTEM, to determine the formation mechanisms and habits of chemically deposited CdS, ZnS, and CdSe thin film at the atomic level. These authors formulated reaction schemes for the different deposition mechanisms and considered that these should be distinguished to (a) atom-by-atom process, providing autoregulation in normal systems (b) aggregation of colloids (precipitation) ... 

It is noteworthy that the HRTEM cannot distinguish core and shell even by combining X-ray or electron diffraction techniques for some small nanoparticles. If the shell epitaxially grows on the core in the case of two kinds of metals with same crystal type and little difference of lattice constant, the precise structure of the bimetallic nanoparticles cannot be well characterized by the present technique. Hodak et al. [153] investigated Au-core/Ag-shell or Ag-core/Au-shell bimetallic nanoparticles. They confirmed that Au shell forms on Ag core by the epitaxial growth. In the TEM observations, the core/shell structures of Ag/Au nanoparticles are not clear even in the HRTEM images in this case (Figure 7). 

With the combined methods of 29Si NMR spectroscopy, X-ray diffraction, HRTEM and SAED we were able to characterize the Ti-Beta particle growth. 29Si NMR spectroscopy gave us an opportunity to see the formation of nanoparticles even before they were detectable with other techniques such as XRD. The above mentioned techniques enabled us to obtain sufficient knowledge to prepare Ti-Beta nanoparticles which were than successfully incorporated in novel micro/mesoporous materials [1],... 

The electron crystallography method (21) has been used to characterize three-dimensional structures of siliceous mesoporous catalyst materials, and the three-dimensional structural solutions of MCM-48 (mentioned above) and of SBA-1, -6, and -16. The method gives a unique structural solution through the Fourier sum of the three-dimensional structure factors, both amplitude and phases, obtained from Fourier analysis of a set of HRTEM images. The topological nature of the siliceous walls that define the pore structure of MCM-48 is shown in Fig. 28. 

Conventional HRTEM operates at ambient temperature in high vacuum and directly images the local structure of a catalyst at the atomic level, in real space. In HRTEM, as-prepared catalyst powders can be used without additional sample preparation. The method does not normally require special treatment of thin catalyst samples. In HRTEM, very thin samples can be treated as WPOs, whereby the image intensity can be correlated with the projected electrostatic potential of the crystal, leading to the atomic structural information characterizing the sample. Furthermore, the detection of electron-stimulated XRE in the EM permits simultaneous determination of the chemical composition of the catalyst. Both the surface and sub-surface regions of catalysts can be investigated. 

Fig. 17.2 Structural and morphological characterization of W03/CNT sheets prepared at 300 °C and 400 °C (a), (d) SEM images showing the morphology of W03/CNT sheets (b), (e) TEM images showing the W03 wrapping on the CNT surface (c), (f) HRTEM images showing the lattice images of W03. Reprinted with permission from [20], Copyright 2012, The Royal Society of Chemistry.

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