Bill-

  Thanks for your reply.

  I'm using a Harrick Expanded Plasma Cleaner which has an RF
inductively coupled plasma (http://www.harrickplasma.com/products.php).
I use the Plasma Cleaner on the "High" setting which corresponds to
29.6W. A manually controlled valve allows air to flow into the chamber,
but I don't know at what pressure.  A metal wire is wound around the
chamber to induce the RF field.

  The chamber is cylindrical with the cylinder lying on its side -- so
the bottom of the chamber is curved.  The plasma looks like a band that
has the same axis as the cylinderical chamber.  Radially, the plasma is
symmeteric; however, the plasma varies in intesity along the chamber.
Where the field is weaker (at the ends of the chamber) the plasma is
correspondingly weaker.

  I put my rectangular solid-ly shaped PDMS pieces along the bottom of
the chamber.  The pieces are all the same height.  Corresponding to your
advice, now I've tried not to vary them along the length of the chamber,
but only radially since the plasma is constant radially.

  So, what I understand from your email is that it's important that all
of the PDMS surfaces see the same plasma strength.  --do you have any
technical explanation for why this is? are there any papers you can
refer me to?  I've done research and found many papers using plasma
activation for PDMS surfaces, but I haven't found any sources that
clearly explain the actiavation and bonding phenomenon and the effects
of the different parameters (power, duration, pressure, etc...).  The
closest paper I've found to explaining what I'm after is
"Three-dimensional Micro-Channel Fabrication..." by Byung-Ho Jo et al.
from the David J. Beebe lab -- except this is more of a list of results
rather than a fundamental explanation of the effects that produce such
results.

  The other problem that I have is since I control the air flow manually
it's hard to keep the pressure constant during the whole exposure, hence
the plasma isn't constant either.  If the plasma changes over time, is
that a problem?

thanks again for the help.

best,
Michael

-----Mensaje original-----
De: Bill Moffat [mailto:[email protected]]

Michael,
        The plasma density/uniformity.  The system I use is a capacitive

system which means the plasma is uniform when parallel to the flat
electrode it sees last.  I can load samples on a shelf and because the
shelf is parallel to the lower electrode and the samples are the same
height he top surface of the sampes sees the same intensity plasma every

where.  Let me know what plasma system you are using and what the shape
of the samples are. It is possible I can run some samples for you.  Bill