Figure 2.

(a) An optical micrograph of a highly regulated array of PMMA stripes on the SiO₂/Si substrate with a concentration of 0.125 mg mL⁻¹; the inset is the schematic drawing, in which the value of λ_c-c indicates the typical center-to-center distance between two adjacent stripes; X₁, X₂, X₃, and X₄ denote the distances of PMMA stripes away from the initial stage. (b) Optical micrographs of periodically patterned stripe arrays of PMMA with varied concentrations (C = 0.5 and 0.125 mg mL⁻¹); the images were measured at the different locations; scale bars are 20 μm for all images. (c,d) Atomic force microscopy (AFM) images of the PMMA stripes formed on the SiO₂/Si substrate, collected from the initial (left) to final (right) stages from concentration with 0.5 mg mL⁻¹ and 0.125 mg mL⁻¹, respectively. (e,f) The 3D topological AFM images from the concentration of 0.5 and 0.125 mg mL⁻¹, respectively; the scan position was in 2000 μm (X₄ region) with a size of 40 × 40 μm². (g–i) The measured gradient values of λ_c-c, w, and h at different locations, depending on the concentration of the PMMA solution, respectively.