Atomic force microscopy inspection of the early state of formation of polymer surface relief gratings

The process of surface relief grating formation was inspected by atomic force microscopy after short-pulse exposure with counter-rotating circularly polarized laser light of 488 nm on a polymer film containing an azobenzene side-chain homopolymer (pDR1M, TG=129 °C). During light inscription, the grating formation was probed by time-resolved visible scattering with red laser light. The efficiency of grating formation depends on the pulse length of blue light exposure. The shortest pulse length of 2 s did not create a permanent surface relief. After 5 s, a speckled surface modification starts rising and the surface relief becomes more and more uniform with a sinusoidal shape for longer exposure. The experimental findings reveal the individual addressing of azobenzene side groups by the actinic light providing a local lateral force via molecular trans-cis and cis-trans isomerization which subsequently causes grating formation.