  A tilting phase transition is predicted for systems comprising rod like
molecules which are irreversibly grafted to a flat surface, so that the non
interacting rods are perpendicularly oriented. The transition is controlled by
the grafting density $\rho$. It occurs as $\rho$ increases as a result of the
interplay between two energies. Tilt is favoured by the van-der-Waals
attraction between the rods. It is opposed by the bending elasticity of the
grafting functionality. The role of temperature is discussed, and the tilting
mechanism is compared to other tilting transitions reported in the literature.
