Long-range surface order, sensitivity

Understanding Sensitivity to Long-Range Surface Order... 

This chapter deals with the study of structural properties of catalysts and catalytic model surfaces by means of interference effects in scattered radiation. X-ray diffraction is one of the oldest and most frequently applied techniques in catalyst characterization. It is used to identify crystalline phases inside catalysts by means of lattice structural parameters, and to obtain an indication of particle size. Low energy electron diffraction is the surface sensitive analog of XRD, which, however, is only applicable to single crystal surfaces. LEED reveals the structure of surfaces and of ordered adsorbate layers. Both XRD and LEED depend on the constructive interference of radiation that is scattered by relatively large parts of the sample. As a consequence, these techniques require long-range order. 

In these electrooptic LC devices, the confining surfaces have to induce a pre-determined and well defined direction of the optical axis at the interface, that subsequently propagates into the bulk due to the long-range nature of the orientational order in liquid crystals. The solid-liquid crystal interface itself can therefore be considered as a discontinuity of the elastic and optical properties of the system. From this point of view, the interface is visible to those linear optical techniques that are enough sensitive to detect a discontinuity of the material properties across the interface. 

ESDIAD is obviously not a diffraction technique such as LEED, but it gives direct information about surface structure in real space. The sensitivity is to local bonding geometry, and long-range order is not necessary as in LEED. ESDIAD is especially sensitive to the orientation of hydrogen atoms in surface complexes, which is difficult to observe by any other technique. 

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