HRTEM

Thust A and Rosenfeid R 1998 State of the art of focai-series reconstruction in HRTEM Electron Microscopy 1998 14th Int. Cent, on Electron Microscopy (Cancun) voi 1 (Bristoi institute of Physics Pubiishing) pp 119-20... 

E. M. AHen, "Mineral Definition by HRTEM Problems and Opportunities," Minerals and Reactions at theMtomic Scale, Minerals Society ofMmerica Reviews in Mineralogy, Nov. 1992, Chap. 8. 

The HRTEM technique has become popular in recent years due to the more common availability of high-volti e TEMs with spatial resolutions in excess of... 

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-... 

Fig. 13. HRTEM image of an as-grown thick PCNT. 002 lattice image demonstrates the innermost hollow core (core diam. 2.13 nm) presumably corresponding to the as-formed nanotube. The straight and continuous innermost two fringes similar to Fig. 5 are seen (arrow).

The simulations were carried out on a Silicon Graphics Iris Indigo workstation using the CERIUS molecular modeling and the associated HRTEM module. The multislice simulation technique was applied using the following parameters electron energy 400 kV (lambda = 0.016 A) (aberration coefficient) = 2.7 mm focus value delta/ = 66 nm beam spread = 0.30 mrad. 

In Fig. 1 is shown a HRTEM image of part of the end of a PCNT. The initial material consisted of carbon nanotubes upon which bi-conical spindle-like secondary growth had deposited[21], apparently by inhomogeneous deposition of aromatic carbonaceous, presumably disordered, layers on the primary substrate nanotube. Prior to further heat treatment, the second-... 

The detailed analysis of the way in which the overall and internal structure of PCNTs apparently arise is discussed elsewhere[20j. Here, we draw attention to some particularly interesting and unusual structures which occur in the body of the nanotubes. An expansion of the section of the central core which lies ca. 5 below the tip of the nanotube in Fig. 1 is shown in Fig. 2. Loop structures occur at points a-d and a -d in the walls in directly opposing pairs. This parallel behaviour must, on the basis of statistical arguments, be related and we interpret the patterns as evidence for a hemi-toroidal connection between the inner and outer adjacent concentric graphene tubes (i.e., turnovers similar to a rolled-over sock). That the loops, seen in the HRTEM, are evidence for very narrow single-walled closed-ended tubes trapped within the walls can be discounted, also on statistical grounds. 

Similar results were found by Bacsa el al. [26] for cathode core material. Raman scattering spectra were reported by these authors for material shown in these figures, and these results are discussed below. Their HRTEM images showed that heating core material in air induces a clear reduction in the relative abundance of the carbon nanoparticles. The Raman spectrum of these nanoparticles would be expected to resemble an intermediate between a strongly disordered carbon black synthesized at 850°C (Fig. 2d) and that of carbon black graphitized in an inert atmosphere at 2820°C (Fig. 2c). As discussed above in section 2, the small particle size, as well as structural disorder in the small particles (dia. —200 A), activates the D-band Raman scattering near 1350 cm . ... 

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]. 

Using HRTEM the chiral angle can also be deduced from the moird or coincidence pattern formed in the central area of the tube image between "front" and "back" surfaces of the tube. 

Figure I HRTEM images of the (a) 14M and (b) Llo martensite in Ni-Al including the corresponding SAED patterns.

Figure 2 [001] HRTEM images of the austenite with static precursor distortions observed prior to the (a) 14M and (b) LIq transformation in Ni-Al. The position of the satellite for (a) is indicated in the inset.

Figure 3 (a) [001] HRTEM image of the distorted austenite of figure 4 after (a) 1 min. and (b) 5 min. irradiation with 400 keV electrons inside the microscope. The increase of the modulation amplitude is apparent. The line in (b) indicates an interface between two adjacent martensite variants. 

Figure 6 [001] HRTEM image of the distorted austenite of L2i Ni2MnGa Heusler alloy clearly revealing modulated ISO s. The modulation wavelength is appr. 6(110) planes (courtesy Zheludev et al. ).

Figure 8 HRTEM image of the ineommensurately modulated phase observed at room temperature in Ti5oPd43Cr7- The modulations can be described by a sinusoidal wave with wave-vector 0.31 [IlOJbcc (courtesy Schwartz et al. )...

For a long time the structural classification of the mineral todorokite was uncertain, until Turner and Buseck [4] could demonstrate by HRTEM investigations that the crystal structure of that mineral consists of triple chains of edge-sharing octahedra, which form [3 x 3] tunnels by further corner-sharing. These tunnels are partially filled by Mg2+, Ca2+, Na+, K+, and water (according to the chemical analysis of natural todorokites). In 1988 Post and Bish could perform a Rietveld structure determination from XRD data taken for a sample of natural todorokite [25], This diffraction study confirmed the results of Turner and Buseck. The cations... 

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