Change in the form of CTRs by varying the out-of-plane distance of the top atomic layer - “relaxation” 

This animation tracks the change in the CTR profile as one varies the distance of the top atomic layer of a simple-cubic crystal between +/- 5% from the bulk value. On the left is the CTR intensity as a function of out-of-plane scattering vector, given in normalized reciprocal lattice units (i.e., in units of 2π/c). The bulklike CTR is also plotted in light blue for comparison. On the right is a cartoon of the movement of the top layer, whereby the deviation from the bulk position is exaggerated by a factor of 5. 

The equation describing the CTR profile as a function of is given by