Properties of pulsed reactive DC magnetron sputtered tantalum oxide (Ta2O5) thin films for photocatalysis

Tantalum oxide (Ta2O5) is a wide band gap semiconductor, known for a wide range of applications in many areas. The present investigation reports the effect of pulsing on the physical and photocatalytic properties of Ta2O5 thin films. The samples are prepared at room temperature on quartz and ITO substrates by pulsed reactive direct current (DC) magnetron sputtering. The pulsing frequency is varied between 5 kHz and 100 kHz. The photocatalytic activity is measured by the Rhodamine B dye. The thicknesses of all films were kept constant of ~ 500 nm. The microstructure obtained by X-ray diffraction is amorphous for all the samples. A lowest surface roughness of 4.62 nm for 50 kHz pulsing frequency is seen in atomic force microscopy measurements. The calculated relative density, optical band gap and the surface work function varies with the pulsing frequency. The sample prepared at 50 kHz pulsing frequency shows high photocatalytic activity: 2.59 × 1013 number of Rhodamine B molecules were oxidized per an incident photon flux of 1.78 × 1016 photons/s at 254 nm. The pulsed-Ta2O5 thin films were compared with continuous DC-Ta2O5 films and showed that pulsing (target power) gives the enhanced film properties, leading to better photocatalytic properties.