Racemates, resolution of. See Optical resolution


Diffraction contrast is often observed in tbe vicinity of defects in the lattice. The origins of this contrast are illustrated in Figure 3. Figure 3a shows a thin sample with atomic planes that are close to a Bragg diffraction orientation, but are actually unaligned with respect to an electron beam propagating down the optic axis of the microscope. On the lefihand side of the diagram, the atomic planes are undistorted, as they would be in a perfect crystal. On the righthand side of the dis tam, the sample contains an edge dislocation in the middle of the sample thickness. The dislocation lies normal to the page so that it appears in this diagram in cross section. Near the core of the dislocation, the atomic planes are distorted or bent to accommodate tbe strains associated with the atomic displacements at the dislocation core. See Figure 3a. The result of these local distortions is that some planes near the core adopt a Bragg orientation with respect to the incident beam. This is shown schematicaUy in Figure 3b, where the incident and transmitted electron ray paths are shown for the same sample region. The undistorted crystal on the lefrhand side, which is not in  [c.110]

The magneto-optic Kerr effect (MOKE), or Kerr rotation, provides a simple and straightforward optical method for magnetically characterizing the near-surface region of magnetic materials. Visible, linearly polarized light is reflected from a sample s surface and small rotations in the polarization and small changes in the ellipticity of the light are observed as schematically shown in Figure 1. Elliptical polarization of light results when the two orthogonal components of a light wave s electric field vector have a phase difference. These optical effects result from the interaction of the incident light with the conduction electrons in the magnetic solid. The magnitude of the rotation of the polarization is directly proponional to the net mj netization Moi the material reflecting the light. Additionally, MOKE measurements can be used to determine the direction of magnetization in the domains of the material, i.e., for magnetic domain imaging, since the magnitude and sign of the rotation in polarization depends on the relative orientation of the plane of incidence, the incident angle of the light, and the orientation of M. While the amount of rotation is small, typically < 0.5°, it is well within the detection limits of simple optical hardware.  [c.723]


See pages that mention the term Racemates, resolution of. See Optical resolution : [c.343]   
Organic synthesis (0) -- [ c.0 ]