Effect of Film Morphology and Thickness on Charge Transport in Ta 3 N 5 /Ta Photoanodes for Solar Water Splitting

Pinaud, Blaise A.; Vesborg, Peter C.; Jaramillo, Thomas F.

doi:10.1021/jp3041742

Optical coatings formed from amorphous oxide thin films have many applications in precision measurements. The Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo use coatings of

S i O_{2}

(silica) and

T i O_{2} : T a_{2} O_{5}

(titania-doped tantala) and post-deposition annealing to 500°C to achieve low thermal noise and low optical absorption. Optical scattering by these coatings is a key limit to the sensitivity of the detectors. This paper describes optical scattering measurements for single-layer, ion-beam-sputtered thin films on fused silica substrates: two samples of

T a_{2} O_{5}

and two of

T i O_{2} : T a_{2} O_{5}

. Using an imaging scatterometer at a fixed scattering angle of 12.8°, in-situ changes in the optical scatter of each sample were assessed during post-deposition annealing to 500°C in vacuum. The scatter of three of the four coated optics was observed to decrease during the annealing process, by 25–30% for tantala and up to 74% for titania-doped tantala, while the scatter from the fourth sample held constant. Angle-resolved scatter measurements performed before and after vacuum annealing suggest some improvement in three of the four samples. These results demonstrate that post-deposition, high-temperature annealing of single-layer tantala and titania-doped tantala thin films in vacuum does not lead to an increase in scatter, and may actually improve their scatter.

More Like this