High-resolution nanophotolithography in atomic force microscopy contact mode

According to near field theory, when irradiated in specific conditions, a metallic tip can give rise to a field enhancement (FE) at its apex and then be used as a nanosource to illuminate a photosensitive sample. In the case of polymers containing azobenzene groups, this exaltation process can lead to a displacement and rearrangement of chromophores in the vicinity of the tip. Contact mode atomic force microscopy (AFM) has been chosen to observe the photoinduced pattern. The use of semiconductor and dielectric probes as well as a normal incidence illumination mode, which minimizes the field enhancement (FE), still induces nanopatterns whatever the polarization state of the actinic light. In these conditions, the adhesion forces appear to be mainly responsible for the nanopattern process. The residual solvent contained in the bulk acts as a plasticizer. The height of the photoinduced nanoprotrusion can be modulated by adjusting the vertical deflection of the tip. Photoinduced nanopatterning obtained in AFM contact mode appears as a new and easy technique of high-resolution nanophotolithography.