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

Abstract

Titanium dioxide (TiO 2 ) is a remarkable metal-oxide semiconductor with unique optoelectronic properties ideal for photovoltaics and photocatalytic conversion. The principal crystalline phases for TiO 2 are anatase, rutile, and brookite. The combination of both anatase and rutile crystalline structures can positively impact the optoelectronic properties of TiO 2 films. With standard sol−gel processing, hightemperature conversion generally yields one dominant phase and limits the combined use of anatase and rutile TiO 2 for optoelectronic devices. We report on a singular route to controllably engineer hybrid nanocrystalline films of TiO 2 at room temperature to synergistically exploit both anatase and rutile TiO 2 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 TiO 2 crystalline phases within the same film. While achieving remarkable precision, reproducibility, and control, we also avoid costly high-temperature, ion-metalassisted, or specific atmospheric processing that currently prevents the integration of TiO 2 in several optoelectronic platforms. In the future, we believe this unprecedented level of control and the ability to engineer the TiO 2 crystalline structure at the microscopic scale will allow the design and fabrication of novel high-performance TiO 2 hybrids for energy conversion and environmental applications.

Structural‐Phase Catalytic Redox Reactions in Energy and Environmental Applications

“…The authors insist that both phases may be patterned using the system dimensions of 25 × 25 mm 2 for a usable device. However, they claimed that in the absence of any kind of dopant in the TiO 2 film prior to photoactivation, the phase conversion is still achievable, and the great accomplishments of this work suggest that easy integration with TiO 2 can be suitable for many photo‐electrocatalytic applications …”

“…The phase conversion from anatase to rutile to brookite is said to be challenging because of the poor understanding of the applied processes and technologies, even though a growing number of synthetic protocols are available . It is more believable that the coexistence of phases in TiO 2 photocatalysts could open opportunities to achieve higher photoactivity than that of the pure anatase or rutile phase because a synergistic phenomenon between them may need to be realized.…”

“…It is more believable that the coexistence of phases in TiO 2 photocatalysts could open opportunities to achieve higher photoactivity than that of the pure anatase or rutile phase because a synergistic phenomenon between them may need to be realized. Benavides et al have obtained various phases (anatase and/or rutile) of TiO 2 by varying the laser power density incident on a film of amorphous TiO 2 nanoparticles prepared by means of an incomplete nonhydrolytic sol–gel ester elimination reaction between titanium isopropoxide and oleic acid. The motivation was the low‐power‐assisted photoactivation of TiO 2 films at room temperature.…”

“…[195] The phase conversion from anatase to rutile to brookite is said to be challenging because of the poor understanding of the applied processes and technologies, even though a growing number of synthetic protocols are available. [196] It is more believable that the coexistence of phases in TiO 2 photocatalysts could open opportunities to achieve higher photoactivity than that of the pure anatase or rutile phase because a synergistic phenomenon between them may need to be realized. Benavides et al [196] have obtained various phases (anatase and/or rutile) of TiO 2 by varying the laser power density incident on a film of amorphous TiO 2 nanoparticles prepared by means of an incomplete nonhydrolytic sol-gel ester elimination reaction between titanium isopropoxide and oleic acid.…”

Laser‐Assisted, Large‐Area Selective Crystallization and Patterning of Titanium Dioxide Polymorphs

“…This setting reduces charge recombination boosting the degradation of organic contaminants. [28,33,34] However, previous results require the use of two types of independent nanoparticles working together, without the level of spatial control offered here. As demonstrated by our results, this is the first time that a TiO 2 large-area film can be produced on-demand where the ratio anatase:rutile is controlled directly by the geometry of each.…”