Ciystal truncation rods

Figure 16. Surface structure the (0001) surface of sapphire (a-A Os) from Eng et al. (2000) with permission of the editor of Science, (a) Structure of vacuum-equihbrated diy surface. Al metal atoms sit on the surface, (b) Ideal bulk terminated surface with no relaxation or reconstraction. (c) Model for the wet-equihbrated surface at one atmosphere from surface scattering (ciystal truncation rod) diffraction measurements. Al metal atoms have shifted, the surface is oxygen terminated, and an organized water monolayer is required to accurately describe the observations, (d) Structure of gibbsite or y-Al(OH)3. The relaxed wet-equilibrated sapphire surface is intermediate between this structure and that of the bulk terminated stracture (B).

Figure 5. (A) The ciystal truncation rod (CTR) structure factor, shown along with the N-layer structure factor for N = 1 and 32 (again plotted as F]2/fJ). (B) The CTR structure factor for an ideally terminated surface, with two surfaces where the outermost layer occupation fjfuc or position z is modified. These relatively small changes in have a substantial (-10-fold), highly Q-dependent effect on the reflected intensity that is measured.

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