Fractal TiO2 nanostructures by nonthermal laser ablation at ambient pressure

Fractal TiO2 nanostructures in crystalline form are obtained at ambient pressure and temperature by pulsed laser deposition with femtosecond pulses. The synthesized structures have been studied by scanning electron microscopy, Raman spectroscopy, and X-ray photoemission spectroscopy. We show that the dendritic aggregations deposited on silicon wafers at room temperature are fractals. They are composed by nanoparticles with an average diameter in a range below 20 nm, with the presence of larger nanoparticles with a diameter above 50 nm. We demonstrate that the fractal dimension and area can be tuned by varying laser fluence and sample/target distance. X-ray photoemission spectroscopy shows that the as-deposited nanostructures are TiO2 while Raman spectroscopy reveals that the crystalline structure of fractals and nanoparticles are composed either by rutile or anatase phase, with a dominant relative concentration of anatase. We discuss possible mechanism of fractals and nanoparticles formation in comparison with the literature results.