Near-field optical patterning on azo-hybrid sol-gel films

We report on the near-field optical patterning of photochromic sol-gel films with subwavelength resolution. The sample containing functionalized azobenzene species is locally illuminated in the visible absorption band of these photochromes through the aperture of a metallized tapered optical fiber. The surface topography imaged by in situ shear-force microscopy reveals that, due to repeated photoisomerization cycles of the azobenzene molecules, photoinduced matter migration occurs under the tip leading to the formation of a surface relief. The shape of this structure is characteristic of the electromagnetic field distribution and strongly depends on the tip-to-sample distance. In near-field illumination conditions, protrusions of lateral dimension as small as 60 nm (≈λ/10) are currently produced. When repeating this process, compact arrays of nanodots are optically inscribed.