Here, the second layer balls consistently lie in corresponding empty slots between the balls. A close look to notice 'that each ball is surrounded by six other balls (hexagonal packing) Do you still remember the question posed at the end of the previous section: the motives why both figures do not match in the third layer? Obviously, the third layer of the balls can be placed in the gaps between the balls of the second layer in different ways. In the second layer there are empty slot located directly above the balls of the first layer; denote them by the letter A. But there are nests under which the balls are not available; denote them by the letter B. Through them, through both layers of the substrate can be seen.