Fig. 1: Laser-induced material deposition.

a schematic illustrations of the principle of the LIMD method. (left) Schematic illustration of the material deposition process, i.e., under the optical field, the semiconductor nanoparticles are trapped towards the focus and on their surface photo-induced reduction reaction converts the metal ion into metal deposition. (middle) Ideal band structure of semiconductor particles. A photon excites an electron from the valence band into the conduction band to become the free electron which triggers the photo-induced reduction reaction. (right) Schematic illustration of the photo-induced chemical reduction process. Free electrons excited by photons in the semiconductor particle (black sphere) reduce metal ions into metal particles (yellow spheres) on the surface of the semiconductor. b schematic illustrations of the experimental procedure. (left) Drop-casting the thoroughly mixed reagents on the substrate surface, with one pipette containing metallate and the other containing semiconductor nanoparticles. (middle) a 532 nm laser beam, focused by a microscope objective, creates deposition in the focal spot. (right) After the deposition and washing with water, the deposited pattern is left on the substrate. c three samples of depositions on glass slides done with the LIMD method. The designs are shown in the upper row. The images in the lower row are the detail zoom-ins of the middle row. (left) A logo of CUHK written in platinum. (centre) A yin-yang symbol written with platinum and gold. (right) A Chinese traditional ink painting written with platinum and gold. The white scale bars represent 50 μm, the blue ones represent 25 μm.