Optoelectronic and photocatalytic properties of in situ platinum-doped TiO2 films deposited by means of pulsed laser ablation technique

We report on the effect of Pt incorporation on the microstructural, optoelectronic and catalytic properties of TiO2 thin films deposited by means of the pulsed-laser deposition (PLD) method. The structural, morphological, optoelectronic and catalytic properties of the deposited TiO2:Pt films were systematically investigated, as a function of their Pt content, by means of various techniques including X-ray diffraction, X-ray photoelectron spectroscopy (XPS), atomic force microscopy, Fourier-transform infra-red spectroscopy and ellipsometry. The in situ doping of the PLD-TiO2 films, at different Pt contents, was achieved by the concomitant laser ablation of a TiO2 target uniformly covered with Pt wires. We show that by increasing the number of Pt wires positioned on the TiO2 target from 1 to 4, the Pt concentration of the TiO2:Pt films increases from 0.05 to 0.35 at.%. While the bandgap of room-temperature (RT) deposited films was found to be insensitive to their Pt content (remaining around the 3.2 eV anatase value), the TiO2:Pt films deposited at high temperature (T-d = 500 A degrees C) were found to exhibit a significant narrowing of their bandgap (from 3.3 to 2.45 eV), when their Pt content is increased (from 3.3 to 2.45 eV). From a structural point of view, while the RT-deposited TiO2:Pt films deposited are mainly amorphous with the presence of some TiO2 nanocrystallites whose density increases as Pt content increases, while those deposited at 500 A degrees C were found to crystallize in the anatase phase with their crystallinity improving with increasing Pt contents. XPS analyses have revealed that the incorporated Pt mainly exists in a metallic state, likely as nano-inclusions in an otherwise TiO2 matrix. By being able to monitor the optoelectronic properties of the annealed TiO2:Pt films through their Pt content, their photocatalytic activity was significantly improved with respect to that of their undoped TiO2 counterpart. The enhancement of the photocatalytic activity is believed to be due to an enhanced photoabsorption of photons because of bandgap narrowing along with a better harvesting of the separated photogenerated charges.