Composition variation in the sub-surface layers. Sample cross-section (left) with the marked (turquoise) position of the composition profile that is shown on the right. The surface of the samples is to the left from the beginning of the turquoise line. The red dashed lines mark the boarders of the regions of partially amorphous layers, and the green dashed lines mark the boarders of the completely amorphous layers. The yellow arrows show an approximate region of chemical changes. Right: the black dashed lines in the graphs mark an approximate depth, d, under which the composition does not change significantly.