HREM

Flueli M, Buffat P A and Borel J P 1988 Real time observation by high resolution electron microscopy (HREM) of the coalescence of small gold particles in the electron beam Surf. Sc/. 202 343... 

A special mention is in order of high-resolution electron microscopy (HREM), a variant that permits columns of atoms normal to the specimen surface to be imaged the resolution is better than an atomic diameter, but the nature of the image is not safely interpretable without the use of computer simulation of images to check whether the assumed interpretation matches what is actually seen. Solid-state chemists studying complex, non-stoichiometric oxides found this image simulation approach essential for their work. The technique has proved immensely powerful, especially with respect to the many types of defect that are found in microstructures. 

The samples were examined before and after catalysis by SEM (Phihps XL 20) and HREM by both a JEOL 200 CX operating at 200 kV and a JEOL 4000 EX operating at 400 kV. The specimens for TEM were either directly glued on copper grids or dispersed in acetone by ultrasound, then dropped on the holey carbon grids. 

Fig. 4. Catalytic particles encapsulated in tubules on Co-Si02 (a) low magnification (b) HREM.

Fig. 9. Carbon nanotubules on Co-Si02 (a) HREM image showing defects in tubules (b) helical tubules of various pitches between the straight tubules.

Fig. 11. Tips of carbon naiiotubules grown on Co-SiOj (acetylene reaction at 97.1 K, 30 minutes after oxidation in air for 30 minutes at 873 K (a) low magnification (b) HREM.

Fig, 1, (a) A cross-sectional TEM image of a bundle of buckytubes (b) an HREM image of a single bundle of bucky-lubes with their axes parallel to the bundle axis. 

Buckytubes were observed for the first time by HREM[1,2] and their structural properties were subsequently characterized. In this section, we will briefly describe observations of the structure of a bundle of buckytubes, evidence for a helical growth of buckytubes and their derivatives, and the single-shell structures. 

Fig. 2. Two HREM images of frozen growth of buckytubes seen end-on.

Fig. II. (a) and (b) are HREM images of the deposited rods produced by the glow discharge and by the...

Key Words—Graphite, fullerenes, HREM, nanostructures, electron irradiation. 

High-resolution transmission electron microscopy (HREM) is the technique best suited for the structural characterization of nanometer-sized graphitic particles. In-situ processing of fullerene-related structures may be performed, and it has been shown that carbonaceous materials transform themselves into quasi-spherical onion-like graphitic particles under the effect of intense electron irradiation[l 1],... 

Fig. 2. HREM image of a quasi-spherical onion-like graphitic particles generated by electron irradiation (dark lines represent graphitic shells, and distance between layers is 0.34 nm).

Fig. 3. High-resolution electron micrograph (HREM) of oxidised CNT tips. Note the amorphous carbon residue inside the lower nanotube (marked with an arrow).

Fig. 5. HREM of enclosed silver particles in CNTs. The metallic particles were obtained by electron irradiation-induced decomposition of introduced silver nitrate. Note that the gases produced by the nitrate decomposition have eroded the innermost layer of the tube.

Fig. 6. HREM picture of a CNT enclosing a silver nanorod generated by thermal treatment of silver nitrate filled CNTs.

D. Van Dyck and W. Coene, The real space method for dynamical electron diffraction calculations in HREM... 

D. Schryvers and L.E. Tanner, On the interpretation of HREM images of premartensitic microstructures in... 

D. Scbryvers, D.E. Lahjouji, B. Slootmaekers and P.L. Potapov, HREM investigation of martensite... 

The core structure of the 1/2 [112] dislocation is shown in Fig. 4. This core is spread into two adjacent (111) plames amd the superlattice extrinsic stacking fault (SESF) is formed within the core. Such faults have, indeed, been observed earlier by electron microscopy (Hug, et al. 1986) and the recent HREM observation by Inkson amd Humphreys (1995) can be interpreted as the dissociation shown in Fig. 4. This fault represents a microtwin, two atomic layers wide, amd it may serve as a nucleus for twinning. Application of the corresponding external shear stress, indeed, led at high enough stresses to the growth of the twin in the [111] direction. 

Fig. 6. HREM image of the ordered twin with APB type displacement, (a) Experiment, (b) Simulation based on the structure obtained using the fuU-potenOal LMTO method.

In the present study, we synthesized in zeolite cavities Co-Mo binary sulfide clusters by using Co and Mo carbonyls and characterized the clusters by extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and high resolution electron microscopy (HREM). The mechanism of catalytic synergy generation in HDS is discussed. 

The location or distribution of the Mo sulfide species, that is, inside or outside the zeolite cavities, was examined by HREM, XRD [17], and pore volume measurements by using benzene as adsorbate [18]. HREM observations for MoSx/NaY possessing 2Mo/SC obviously demonstrated that no Mo sulfide spiecies were formed on the outside of the zeolite and that the framework structure of the zeolite was not destroyed at all on the accommodation of Mo sulfide species. The XRD and pore volume measurements confirmed the HREM observations. It is concluded that highly dispiersed intrazeolite Mo sulfide species are produced by using Mo(CO),. 

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