Crystalline bright-field contrast

The low degree of hard-segment crystallinity in the solvent-cast samples with the added problem of loss of crystallinity from electron-beam damage prevented visualization of either the hard- or soft-segment domains by dark-field microscopy. Therefore bright-field defocus electron microscopy was used to enhance contrast between the microphases (27, 28). Only for the 1/5/4 and 1/6/5 samples was a distinct domain... 

The contrast in the image is formed from the interactions between the incident electrons and the matter. The most common operating mode in TEM is the bright field imaging mode. In this mode and in the case of non crystalline materials such as polymers, the contrast is formed directly by absorption of electrons in the sample. Actually, the image is assumed to be a simple two dimensional projection... 

The most commonly employed imaging mode is bright field (BF), which uses only the central beam, usually called the transmitted beam. Image contrast is observed if, for whatever reason, the diffracted beams originating from different parts of the specimen vary in intensity. If a crystalline specimen is so oriented with respect to the incident beam that many strong diffracted beams are excited, then an extremely complex BF image... 

Moire contrast. We have calculated the distances between the Moire bands for the In, As, and InAs crystallites in Si matrix and compared the calculated quantities with the values measured from the bright-field TEM images. The experimental value of 1.8 nm is in a good agreement with the calculated one of 1.818 nm for the 220 planes of crystalline InAs. We have not found such a correlation for the crystalline In or As. 

If the sample is crystalline, the scattered intensity depends very strongly on the orientation of the crystals and on their thickness. In bright field, a thin crystal will appear dark when it is correctly oriented for diffraction. If the crystal is not perfectly flat, the contours of correct orientation will appear as dark lines, called bend contours. Variation of intensity such as this in crystalline specimens is called crystallographic or diffraction contrast. Many types of defects in crystals cause localized distortion of the crystal lattice. These defects change the crystal orientation locally and so cause variations in the crystallographic contrast. Detailed information... 

Different types of interactions with the sample define different contrast images, which can be controlled via the lens system. Basically, two types of contrast are of most interest in TEM amplitude contrast (or diffraction contrast) and phase contrast. In the first case, electrons are elastically scattered by the atoms of an amorphous or crystalline or diffracted material as the Bragg condition. In this type of contrast include the thickness contrast/mass Z and the diffraction. In phase contrast, occurs the elastic scattering of electrons atoms of a crystal [12, 21]. In contrast range, bright-field or dark-field images are the most common types in TEM analysis, especially bright field. 

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