High-resolution transmission electron microscopy HRTEM

2 High-resolution transmission electron microscopy (HRTEM) 

One of the most powerful methods of direct atomic structural analysis of solids is high-resolution TEM (HRTEM), where two or more Bragg reflections are used for imaging. Although Menter s first images of crystal lattice periodicity were 

The micrograph or the image obtained on the EM screen or photographic film is the result of two processes the interaction between the incident electron wavefiinction and the crystal potential followed by the interaction of this resulting wavefiinction with the EM parameters which incorporate lens aberrations. In the wave theory of electrons, during the propagation of electrons through the sample, the incident wavefiinction is modulated by its interaction with the sample and structural information about the sample is transferred to the wavefiinction, which is then further modified by the transfer function of the EM. 

The phase contrast is produced by the phase modulation of the incident electron wave when it is transmitted through the sample crystal potential V(x, y). The propagation of a plane electron wave traversing through a thin sample is thus treated as a weak (scattering) phase object. The wavefunction at the exit 

The image intensity /(x, y) at the image plane of the objective lens results from two-dimensional Fourier synthesis of the diffracted beams (the square of the FT of the waves at the exit face of the crystal), modified by a phase-contrast transfer function factor (CTF, sin /), given by Scherzer (1949), as 

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Regarding a historical perspective on carbon nanotubes, very small diameter (less than 10 nm) carbon filaments were observed in the 1970 s through synthesis of vapor grown carbon fibers prepared by the decomposition of benzene at 1100°C in the presence of Fe catalyst particles of 10 nm diameter [11, 12]. However, no detailed systematic studies of such very thin filaments were reported in these early years, and it was not until lijima s observation of carbon nanotubes by high resolution transmission electron microscopy (HRTEM) that the carbon nanotube field was seriously launched. A direct stimulus to the systematic study of carbon filaments of very small diameters came from the discovery of fullerenes by Kroto, Smalley, and coworkers [1], The realization that the terminations of the carbon nanotubes were fullerene-like caps or hemispheres explained why the smallest diameter carbon nanotube observed would be the same as the diameter of the Ceo molecule, though theoretical predictions suggest that nanotubes arc more stable than fullerenes of the same radius [13]. The lijima observation heralded the entry of many scientists into the field of carbon nanotubes, stimulated especially by the un-... 

The length and the diameter of MWCNT can be measured directly by TEM. From high-resolution transmission electron microscopy (HRTEM) images exhibiting oo.l fringes follows the number of coaxial tubes and possibly the microstructure of the caps in MWCNT, as viewed along the incident electron beam [24], Also anomalous intercylinder spacings and defects are revealed in this way [1,11]. 

Crystalline phases (truncated octahedra) of 5 nm silver particles, thiolate protected as well, have been detected by means of high-resolution transmission electron microscopy (HRTEM) [26-28]. Three-dimensional architectures of 5-6 nm thiolate-stabilized gold particles have also been described [29]. Several other reports on 3D superlattices of metal nanoparticles have become known during the last few years [30-33]. 

Ag-core/Au-shell bimetallic nanoparticles were prepared by NaBH4 reduction method [124]. UV-Vis spectra were recorded and compared with various ratios of AuAg alloy nanoparticles. The UV-Vis spectra of bimetallic nanoparticles suggested the formation of core/shell structure. Furthermore, the high-resolution transmission electron microscopy (HRTEM) image of the nanoparticles confirmed the core/shell type configuration directly. 

The synthesis of nanoparticles using plant biomass has been investigated by many [24,26]. Using high resolution transmission electron microscopy (HRTEM), it has been... 

High Resolution Transmission Electron Microscopy (HRTEM, Philips CM20, 200 kV) was applied to get structural and nanotextural information on the fibers, by imaging the profile of the aromatic carbon layers in the 002-lattice fringe mode. A carbon fiber coated with pyrolytic carbon was incorporated in epoxy resin and a transverse section obtained by ultramicrotomy was deposited on a holey carbon film. An in-house made image analysis procedure was used to get quantitative data on the composite. 

High resolution transmission electron microscopy (HRTEM) micrographies were performed with a JEOL JEM-3010 microscope operating at 300 kV (Cs= 0.6 mm, point resolution 1.7 A). Images were recorded with CCD camera (MultiScan model 794, Gatan, 1024 x 1024 pixels, pixel size 24 x 24 pm2). The powder samples were mixed in ethanol and then ultrasonicated for 10 min. A drop of the wet sample was placed on a copper grid and then allowed to dry for 10 min before TEM analysis. 

Microporous nanoparticles with ordered zeolitic structure such as Ti-Beta are used for incorporation into walls or deposition into pores of mesoporous materials to form the micro/mesoporous composite materials [1-3], Microporous particles need to be small enough to be successfully incorporated in the composite structure. This means that the zeolite synthesis has to be stopped as soon as the particles exhibit ordered zeolitic structure. To study the growth of Ti-Beta particles we used 29Si solid-state and liquid-state NMR spectroscopy combined with x-ray powder diffraction (XRPD) and high-resolution transmission electron microscopy (HRTEM). With these techniques we monitored zeolite formation from the initial precursor gel to the final Ti-Beta product. 

Fig. 4.4 Molecular model of (a) surface containing positive and negative curvature induced by a pentagon (red) and a heptagon (blue), respectively (b) molecular model of 5-7 defects (yellow) and a Thrower-Stone-Wales defect (green) [82] (c) high-resolution transmission electron microscopy (HRTEM) images of bond rotations V2 (555-777) divacancy, and (d) V2(5555-6-7777) divacancy within graphene scale bar is 1 nm [75].

Keywords Focal-Series Reconstruction, High-Resolution Transmission Electron Microscopy (HRTEM), Truelmage... 

Transition metal oxides attract great interests mainly due to their redox nature, which is thought to be related with their flexible stmcture modiflcation under reductive and oxidative conditions. Such stmcture modiflcation takes place by forming so called crystallographic shear (CS) stmctures to accommodate anion vacancies in speciflc crystallographic planes by simultaneous shear displacement and crystal stmctural collapse [30-32]. High-resolution transmission electron microscopy (HRTEM) is a... 

High-resolution transmission electron microscopy (HRTEM) images (Fig. 14) clearly show that dendrimer-encapsulated particles are nearly monodi-sperse and that their shape is roughly spherical. 

Fig. 26. High -resolution transmission electron microscopy (HRTEM) image of perfluoropoly-ether-modified G3 PPI dendrimers containing Pd metal nanoclusters prepared on aholey carbon copper grid by evaporation of a dilute solution of the dendrimer composite. Reprinted with permission from Ref. 100 Copyright 2000 WUey-VCH...

High-resolution transmission electron microscopy (HRTEM) has matured markedly in the preceding decade and has emerged as a powerful technique for investigation of nanostructured metal catalysts at the atomic level, even under working conditions. The ability to image the dynamic structure and morphology of supported metal nanocluster catalysts in such detail makes HRTEM an essential complement to the arsenal of spectroscopic techniques used for characterization of... 

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