Surface-initiated mechanism for the formation of relief gratings on azo-polymer films

We report here a detailed experimental study, establishing the surface-initiated mechanism for the photoinduced relief grating formation on azobenzene functionalized polymer films. The grating formation process is found to be strongly dependent on the nature of the surface (20-200 Angstrom), while the birefringent grating appears to be a purely bulk process. Restriction of the surface of the azobenzene polymer film through the deposition of ultrathin top layers of transparent polyelectrolytes by electrostatic self-assembly dramatically decreases the relief grating formation. Thicker polyelectrolyte multilayer film (250 Angstrom) on the surface resulted in the formation of purely birefringent grating, without any surface features.