Fig. 3: Characterization by X-ray reflectivity and atomic force microscopy.

The X-ray reflectivity (XRR) data including a fit of the pristine and fully photopolymerized (28 s) film are shown for LT in a and HT in b. Density curves calculated from XRR curves for each polymerization time step of (0 s, 0.1 s, 0.3 s, 0.6 s, 1 s, 28 s) for LT in c and (0 s, 0.1 s, 0.2 s, 0.5 s, 1 s, 28 s) for HT in d. In e and f are the corresponding AFM topographical maps of the fully polymerized (28 s) films for LT and HT respectively. The surface rms-roughness of the fully polymerized sample is σ_LT = (0.74 ± 0.07) nm and σ_HT = (0.55 ± 0.07) nm, as extracted from the AFM images. The thicknesses of the thin films were fitted by the distances in the Kiessig fringes of their XRR profiles: d_{LT, 28s} = (143.2 ± 1.5) nm, d_{HT, 28s} = (160.1 ± 1.9) nm, which are confirmed by measuring the depth of a scratch in the fully polymerized film with AFM. The XRR patterns are divided in two regimes to study the evolution in peak-to-valley distance and therefore the correlated roughness at the air/polymer and polymer/substrate interface, see Supplementary Fig. 6.