Anisotropic surface properties

Ho R, Heng JYY (2013) A review of inverse gas chromatography and its development as a tool to characterize anisotropic surface properties of pharmaceutical solids. Kona Powder Part J 30 164-180... 

For optically uniaxial crystals we know that the refractive index values for extraordinary waves are variable, with that for ordinary waves fixed. We can link this observation with that concerning the vibration directions for the two waves travelling along a general wave normal direction the ordinary vibration direction is always perpendicular to the optic axis, while the extraordinary vibration is always in the plane containing the optic axis and wave normal direction. This suggests that we may connect the variation of the refractive index in the crystal with the vibration direction of the light. This concept allows a convenient representation of anisotropic optical properties in the form of a spatial plot of the variation of refractive index as a function of vibration direction. Such a surface is known as the optical indicatrix. 

Whether or not the Si—Si dimer a bond is cleaved, it seems to be the consensus that the majority of the surface product forms two Si—C bonds, an analog of the [2 + 2] product. This is useful, since the orientation of the individual molecules can be controlled, yielding anisotropic physical properties of a chemically modified silicon surface as discussed in recent accounts50. 

The machining process is used to separate the material, e.g., to generate a certain shape or geometry of the workpiece and to improve the surface quality. The machining of CFRP or composites is mostly difficult because of the inhomogeneous and anisotropic material properties. 

Correspondingly, the wear behavior (essentially a surface property) of processed polymer shows 3D anisotropic behavior [8]. 

D profiles do not, however, adequately describe 3-D properties, particularly in the ease of anisotropic surfaces. The next step in the application of the wavelength-depen-dent roughness concept will therefore be an extension to 3-D evaluation, as discussed in Section 3.5. Another frequent limitation in applications is related to the limits of lateral and/or vertical resolution and to instrumental artefacts. In comparison to the laser profilometry technique, interference microscopy, AFM and stereo-SEM are able to resolve finer structures and surface features, although — in the case of AFM — problems in ease of contacting envelope may be critical for strongly corrugated surfaces. A comparative study of different teehniques will be published separately. 

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