3D Fluorescence image of the dual-pattern obtained via the light direct-writing method. (a) Fluorescence image on the upside of the pattern; (b) fluorescence image on the downside of the pattern; (c-f) the fluorescence images and corresponding sectional fluorescence images of the dual-patterns at different depths of the film (5 μm, 10 μm, 15 μm, and 20 μm). The pattern was written with positive concentric square photomasks (size width/space: 50/50 μm). The thickness of the polymer blend film was ≈200 μm. The intensity and exposure time of 365 nm UV light were ≈50 mW/cm2 and 30 seconds, respectively.