Thin-film specialists seek to hone self-cleaning surfaces

A team at University College London (UCL) has devised a method to find the best combination of dopants to achieve certain desired properties.

Thin films of titanium dioxide (TiO₂) are already used in so-called self-cleaning windows. As wide-band semiconductors, these films are excited by sunlight leading to charge separation and the generation of radicals, which kill bacteria and degrade of organic molecules. Furthermore, this photocatalytic process also makes the glass hydroxylated and therefore superhydrophilic, so water spreads evenly on the surfaces to wash away dirt.

Some 10 million square metres of glass is coated with TiO₂ each year, with a worldwide market worth around £50bn. However, there are further inroads to be made as Prof Ivan Parkin of UCL explained to The Engineer.

‘The key issue in the area is that because it’s a wide band-gap semiconductor, titanium dioxide really only functions with the UV portion of sunlight and so the big challenge and where people are trying to move now is to get these films to work efficiently with room lighting conditions, where there is little UV.’