Fig. 4: Light-directed crack propagation obtained by dip-coating with a colloidal plasmonic solution.

a Scheme of the experimental dip-coating set-up of the formation of self-ordered cracks, light-deviated by a 852 nm laser. The localized heating of the colloidal plasmonic solution is obtained by irradiating the surface through a mask, placed in between the laser and the dip-coater. The grey spheres represent PS particles, whereas the yellow bipyramids represent the AuBP. b Optical microscopy image of non-deviated cracks. c Optical microscopy image of deviated cracks. The red circle represents the spot of light. Each crack starting from the normal is deviated with an angle equal to α and a distance equal to Delta A. Top-view SEM micrographs of a d deviated section of a cracked AuBP/PS film, with e, f high magnification images of the AuBPs and PS particles distribution. g SEM micrograph displaying a cross-section view of a deviated cracked zone. Hyperspectral analysis of a single crack formation during the drying of a colloidal plasmonic droplet results in an image where each pixel provides a scattering spectrum, enabling spatial mapping of the plasmonic scattering. h Dark-field optical microscopy image of a drying droplet of colloidal plasmonic solution with the formation of cracks and the corresponding scheme representing the concentration in nanoparticles from the solution to the formation of a wet colloidal gel. i Graphical plot of the distance of the spot, from A to J, as function of the maximum of the plasmon resonance peak. j Scattering spectra of the evaporating colloidal plasmonic solution depending on the distance. Source data of Figure i, j are provided as a Source Data file.