Figure 6.
Effect of the measurement area on the DLOA δθ. For different sizes of the LIPSS-covered area chosen for analysis (a), different spectra (b) of orientations θ can be obtained with the module OrientationJ 23 of the open software ImageJ 59. The normalized spectra of orientation are shown for the case of Al. The orientation axis ranges from −90° to +90° (orientation is π-periodic: the orientation angle of +91° corresponds to the orientation of −89°). Note that on (b) the distribution is centered around 45°, in line with the LIPSS orientation on (a). Colors of lines in (b) correspond to areas in (a) highlighted by the same colors. (c) Good convergence of the DLOA measurements is achieved when the surface area selected for analysis is large enough. Side length a refers to the square area (of side a i, i = 1, 2, 3) in Fig. (a) The measurement performed on Ti is also reported for comparison.