Field electron microscopy

In dark-field electron microscopy it is not the transmitted beam which is used to construct an image but, rather, a beam diffracted from one facet of the object under investigation. One method for doing this is to shift the aperture of the microscope so that most of the beam is blocked and only those electrons... 

Physical metallurgy is concerned with the scientific study of materials. Phase transformations, recovery and recrystallization, precipitation hardening, structure-property correlations, characterization of microstructure by microscopy (optical, electron and field-ion), are some specific examples among the many topics covered under physical metallurgy. 

D. Evidence from Field Electron Emission Microscopy and from Low-... 

Figure 7.23 Ordering of adsorbates on a surface into islands gives rise to regions of different work function, which can be imaged because of the associated differences in photoelectron intensity. The principle forms the basis of photoemission electron microscopy (PEEM). The same principle underlies the imaging of single molecules in the field electron microscope (FEM) (see also Fig. 7.9).

Microscopic techniques, 70 428 Microscopists, role of, 76 467 Microscopy, 76 464-509, See also Atomic force microscopy (AFM) Electron microscopy Light microscopy Microscopes Scanning electron microscopy (SEM) Transmission electron microscopy (TEM) acronyms related to, 76 506-507 atomic force, 76 499-501 atom probe, 76 503 cathodoluminescence, 76 484 confocal, 76 483-484 electron, 76 487-495 in examining trace evidence, 72 99 field emission, 76 503 field ion, 76 503 fluorescence, 76 483 near-held scanning optical,... 

Dark-field electron microscopy (in which the image is formed from the scattered beam), when combined with improved techniques of sample handling and preparation and minimal radiation exposure, can lead to images of sufficiently undamaged DNA at a resolution of 10 A (116). Figure 45 shows such an image in which the two-dimensional projection of the helix is clearly visible on the undamaged part of the molecule. 

O.L. Krivanek, M.F. Chisholm, V. Nicolosi, T.J. Pennycook, G.). Corbin, N. Dellby, et al., Atom-by-atom structural and chemical analysis by annular dark-field electron microscopy, Nature, 464 (2010) 571-574. 

The art of making sharp tips using electrochemical etching was developed in the 1950s for preparing samples for field ion microscopy (FIM) and field electron spectroscopy (FES). A description of various tip-etching procedures can be found in Section 3.1.2 in the book of Tsong (1990). 

Figure 5-13 Electron micrograph of a DNA molecule (from a bacterial virus bacteriophage T7) undergoing replication. The viral DNA is a long ( 14 pm) duplex rod containing about 40,000 base pairs. In this view of a replicating molecule an internal "eye" in which DNA has been duplicated is present. The DNA synthesis was initiated at a special site (origin) about 17% of the total length from one end of the duplex. The DNA was stained with uranyl acetate and viewed by dark field electron microscopy. Micrograph courtesy J. Wolfson and D. Dressier.

Returning now to the observed effect of particle size on catalytic activity, van Hardeveld and Hartog 219) have calculated that the relative concentration of C7 sites on octahedral iron crystallites decreases with decreasing particle size and that, in general, the C7 site is not a small-particle surface site. The above correlation of increased catalytic activity with increased C7 site surface concentration thus also explains the observed structure sensitivity (particle size dependence) for this reaction. Finally, this correlation is consistent with results obtained from field electron microscopy of iron (220), single crystal reaction studies on tungsten (also a bee metal) (227), and symmetry considerations (222). 

The interaction of CO2 with group VIII metals was reviewed by Solymosi (29). At 80 K, the adsorption on a Rh field emitter exhibits an interesting crystal face dependency 30). In addition to molecular adsorption, dissociation occurs at an appreciable rate on the stepped surfaces around (111) and (100) at temperatures higher than 220 K. The field electron microscopy (FEM) patterns suggest that the surface structure of Rh has a striking influence on the ability of the metal to dissociate the CO2 molecule. From... 

The field emission microscope (FEM) and the field ion microscope (FIM) are in many respects complementary instruments. While the FIM can depict surface structure in atomic detail, study of field electron emission from the same specimen can yield information about the electronic structure of the surface layer. Field ion microscopy has been the subject of an earlier review and in this article more recent developments in field emission microscopy and its application to surface studies are reviewed. Earlier developments have been the subject of several reviews. 

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