Dark field diffraction

The conventional hand of a particular isochiral cluster of tubes can be deduced from dark field diffraction contrast tilting experiments [26]. 

AFM Atomic force microscopy BFDC Bright-field diffraction contrast DFDC Dark-field diffraction contrast ED Electron diffraction PTFE Poly(tetrafluoroethylene)... 

A) Bright-Held diffraction contrast mode B) Dark-field diffraction contrast mode C) High-resolution imaging mode a) Specimen b) Lens c) Aperture d) Screen... 

Several techniques can be used to determine the point group [169]. The method developed by Buxton et al. [170] is based on the use of zone axis patterns and of dark-field diffraction patterns obtained under exact two-beam conditions. By... 

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... 

Fig. 3 (left) TEM bright-field and (middle) dark-field images, and (right) selected area diffraction pattern from a 20 vol% Si3N4/5052 Al composite at 548 °C. (from Ref. [8,9])... 

Characterization methods. The 100 kV Vacuum Generator HB-5 STEM was used to mlcroanalyze samples. The HB-5 has a KEVEX SI(LI) energy dispersive X-ray spectrometer (EDS) and micro area electron diffraction (MAED) capabilities In conjunction with simultaneous bright and dark field Imaging capabilities. A more detailed explanation of the Instrumental operation can be obtained In a publication by C. Lyman(12). 

Figure 4. Electron diffraction pattern (bottom left) of a typical disordered wol-lastonite specimen. Evidence of the disorder comes from the streaked (Tc odd) diffraction spots. The fringes shown in the dark-field image (a) are 7 A apart. Dark-field image b, taken from the streaked diffraction spots, shows a one-dimensional image of the disordered wollastonite. Dark-field image c shows a two-dimensional image which shows the haphazard stacking of the triclinic and monoclinic...

Electrons are diffracted by particles if these are favorably oriented towards the beam, enabling one to obtain dark field images as well as crystallographic information. 

Figure 7.5 shows images of a Pd/AI2CF catalyst in bright and dark field mode. In the latter, the geometry was chosen such to selectively detect the (111) and (200) diffraction rings of Pd. Features indicated by arrows clearly demonstrate the better contrast and resolution of the dark field image [14],... 

Single-Particle Diffraction, Weak-Beam Dark-Field, and Topographic Images of Small Metallic Particles in Supported Catalysts... 

Dark field images can be used to determine the shape of a small particle as shown by Yacaman et al. (6-7). When an electron beam enters on a small particle the presence of wedges will produce a splitting on the diffracted spots as shown by Gomez et al (8). A... 

Transmission electron microscopy (TEM) resembles optical microscopy, except that electromagnetic instead of optical lenses are used to focus an electron beam on the sample. Two modes are available in TEM, a bright-freld mode where the intensity of the transmitted beam provides a two-dimensional image of the density or thickness of the sample, and a dark-field mode where the electron diffraction pattern is recorded. A combination of topographic and crystallographic information, including particle size distributions, can be obtained in this way [32],... 

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