Surface deformation on azobenzene polymer film induced by optical near-field around polystyrene microspheres

The surface deformations of a urethane-urea copolymer containing azobenzene derivatives under the influence of the electric fields around polystyrene microspheres irradiated with polarized light were investigated. Monolayers of 500 and 100 nm diameter microspheres were formed on the copolymer surface and were irradiated with linearly polarized laser beam. After removing the microspheres, the copolymer surfaces were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The dents were formed on the copolymer surface where the microsphere had been located. The 500 mn microsphere caused the dent with sides heaped up along the polarization of the incident light; the dent was similar to the one induced by Gaussian beam, indicating that the surface deformation had relation to the electric field around the microsphere. On the contrary, the dent induced by the 100 nm microsphere showed weak dependence on the polarization in shape. This is ascribed to the interaction between the optical near-field of the microsphere and the substrate surface. (C) 2001 Elsevier Science B.V. All rights reserved.