Laser Selective Photoactivation of Amorphous TiO₂ Films to Anatase and/or Rutile Crystalline Phases

Titanium dioxide (TiO2) is a remarkable metal-oxide semiconductor with unique optoelectronic properties ideal for photovoltaics and photocatalytic conversion. The principal crystalline phases for TiO2 are anatase, rutile, and brookite. The combination of both anatase and rutile crystalline structures can positively impact the optoelectronic properties of TiO2 films. With standard sol–gel processing, high-temperature conversion generally yields one dominant phase and limits the combined use of anatase and rutile TiO2 for optoelectronic devices. We report on a singular route to controllably engineer hybrid nanocrystalline films of TiO2 at room temperature to synergistically exploit both anatase and rutile TiO2 phases. Relying on sol–gel chemistry, this approach starts from an amorphous film and uses photoinduced activation using a low-power laser to achieve specific spatially controlled pattern consisting of different TiO2 crystalline phases within the same film. While achieving remarkable precision, reproducibility, and control, we also avoid costly high-temperature, ion-metal-assisted, or specific atmospheric processing that currently prevents the integration of TiO2 in several optoelectronic platforms. In the future, we believe this unprecedented level of control and the ability to engineer the TiO2 crystalline structure at the microscopic scale will allow the design and fabrication of novel high-performance TiO2 hybrids for energy conversion and environmental applications.