  A simple method based on UV/ozone treatment is proposed to control the
surface energy of dense grafted silane layers for orientating block copolymer
mesophases. Our method allows one to tune the surface energy down to a fraction
of a mN/m. We show that related to the surface, perpendicular orientation of a
lamellar phase of a PS-PMMA diblock copolymer (neutral surface) is obtained for
a critical surface energy of 23.9-25.7 mN/m. Perpendicular cylinders are
obtained for 24.6 mN/m and parallel cylinders for 26.8 mN/m.
