Visible absorbing TiO2 thin films by physical deposition methods

Titanium dioxide is one of the most widely used wide bandgap materials. However, the TiO2 deposited on a substrate is not always transparent leading to a loss in efficiency of the device, especially, the photo response. Herein, we show that atomic layer deposition (ALD) and sputtered TiO2 thin films can be highly absorbing in the visible region. While in ALD, the mechanism is purported to be due to oxygen deficiency, intriguingly, in sputtered films it has been observed that in fact oxygen rich atmosphere leads to visible absorption. We show that the oxygen content during deposition, the resistivity of the film could be controlled and also the photocatalysis response has been evaluated for both the ALD and sputtered films. High resolution TEM and STEM studies show that the origin of visible absorption could be due to the presence of nanoparticles with surface defects inside the amorphous film.