Hi, Licca,

Those cracks are probably due to the thermal stress generated during the
evaporation. A good paper for this issue is:

N. Bowden, S. Brittain, A. G. Evans, J. W. Hutchinson, G. M. Whitesides,
Spontaneous formation of ordered structures in thin films of metals supported on
an elastomeric polymer, Nature, Vol. 393, (1998) pp. 146-149.

I did not have any adhesion problems before when I e-beam evaported Al on top of
oxidized PDMS (Sylgard 184). If necessary, you can use Ti/Au instead.

Good luck,

Lydia