Here, Sx is the selectivity after x number of ALD cycles and R is the atomic composition of the deposited material on GS and NGS, respectively. Hence, the value ranges between 0 (no selectivity) to 1 (perfect selectivity). Comparison to computational data is possible, e.g., through the theoretical determination of relative reaction rates. Similar to the ALD window discussed above, a "selective ALD window" has been proposed. The typical reason behind selectivity in AS-ALD is nucleation delay on the NGS due to the mechanisms discussed below in more detail. However, selectivity can also be achieved via substrate-dependent diffusion (section 4.8). 1.