Laser Direct Writing of Crystallized TiO₂ by Photothermal Effect Induced by Gold Nanoparticles

Near-infrared (NIR) laser annealing is successfully used to crystallize TiO₂ thin films from a sol–gel solution deposited on gold nanoparticle arrays (AuNPs). The AuNPs are used as nano-heaters allowing a local temperature increase up to 500 °C in the film. The temperature reached under the laser is deduced from the presence of the anatase phase in the samples obtained by laser exposure, showing that crystallized TiO₂ can be obtained by the photothermal effect. Different analytical techniques supported this study, such as grazing X-ray diffraction (GIXRD), UV–vis, and Raman spectroscopy. The temperature increase is confirmed by a numerical model that emphasizes the role of NPs coupling in the photothermal effect. Direct laser patterning by NIR laser and in combination with Deep-UV photolithography (DUV) are demonstrated. This fabrication method opens new perspectives in applications such as photonics, photocatalysis, or biosensing.