Nanoindentation study of optically patterned surface relief grating of azobenzene polymers.

We present the light-controlled hierarchical mechanical properties of optically patterned azobenzene thin films through a nanoindentation study. In this study, we inscribed holographic surface relief grating (SRG) of azopolymers by two-beam coupling-based light interference lithography. The resultant morphological profile of azopolymers was monitored by atomic force microscope (AFM), followed by the nanoindentation study. From the load-displacement curve of the indentation procedure, photomechanical changes of the azopolymers along grating patterns were evaluated in terms of hardness and modulus at the crest and trough of the SRG, respectively. The results revealed that the surface height as well as the mechanical properties was modulated according to the light interference pattern.