Dear Hongjun

we use the "air plasma "  to activate the PDMS for bonding. We just
evapoarate the
reaction chamber of an ordinary plasma cleaner (Harrick) to the
appropriate pressure and expose the
PDMS surface to the plasma obtained in the residual air atmosphere . We
apply the plasma
only about 2 minutes  to obtain a thin sio2 layer on the pdms surface.
You should not  produce a too thick
layer which actually embrittles the pdms at the surface and does not
seal anymore.
You should apply some slight pressure to contact the pdms  and seal it
but thats of course very dependent on your structure
that should be distroted to much by the pressure.

Hans-Georg Braun