Given that pure Mo has BCC structure (density - 10.28g/cm3) and pure Si has diamond cubic structure (density = 2.33 g/cm3, see your book for more details on this structure), with the additional of small amount of energy it is possible to from MoSi2 with body-centered tetragonal structure (where a = 0.321nm and c = 0.452 nm), as shown below.
Questions-
1) What are the point coordinates for the Silicon atoms in the MoSi2 system?
2) On average, what volume of space is occupied by each Mo and Si atom in their elemental crystal forms (you should not use their atomic radii but rather work backwards from density and crystal structure); and how much space is occupied by a molecule of MoSi2?
3) What could explain the phenomenon of initial shrinking and apparent "mixing" of the layers?
4) What could explain the bubbles that form at high dose? Why do they not form initially at low dose?