Local photo-assisted poling of azo copolymer films by scanning probe microscopy

Azo copolymers are nonlinear-optical materials, in which polar orientation can be induced by optical poling or electrical poling. We report a new efficient approach to performing photo-assisted poling (PAP) by atomic force microscopy (AFM) for azo copolymer films containing disperse-red-1 chromophores, and to characterize the polar orientation by electrostatic force microscopy (EFM) at the submicrometre scale. Both PAP and contact electrification effects can be generated by the physical interaction between the probes and the films. We demonstrated that these two effects can be distinguished by the relationship between the signs of the charges (bound charges and transferred charges) and the probe bias. Finally, we achieve local PAP far below the glass transition temperature by AFM operated in the tapping mode, and the response of the polar chromophores to local PAP can be studied by EFM.