  The orientation of the lamellae formed by the phase separation of symmetric
diblock copolymer thin films is strongly affected by the wetting properties of
the polymer blocks with respect to the substrate. On bare silicon wafers the
lamellae of polystyrene-b-polymethylmethacrylate thin films tend to order
parallel to the wafer surface, with the polymethylmethacrylate block
preferentially wetting silicon. We have developed a methodology for inducing
the arrangement of lamellae perpendicular to the substrate by using chemically
modified substrates. This is done by chemisorbing a self-assembled monolayer of
thiol-terminated alkane chains on thin gold films deposited on silicon wafers.
We also show that it is possible to spatially control the perpendicular
orientation of the lamellae at sub-micron length scales by using simple
chemical patterns and etch them, in order to produce nanolithographic
templates. This method may be of great technological interest for the
preparation of well-defined templates using block copolymer thin films.
