Abstract
The nanostructure and photocatalytic properties of TiO2 thin films deposited by PECVD on silicon substrates were investigated. The films were grown at low temperature (<120 °C) in an rf inductively coupled oxygen/titanium tetraisopropoxide plasma, in continuous and pulsed modes with different plasma-on time (via variation of the duty cycle, DC). All the films exhibit nano-columnar structures, but the reduction of plasma-on time by decreasing the duty cycle for pulsed mode leads to a more homogenous morphology with a diminished column size, and a decrease in the surface roughness. TiO2 layers containing a high amount of anatase were grown at substrate temperatures less than 100 °C corresponding to DC ≥ 40%, then the crystallization was hindered with the decrease of DC, even inducing amorphous films for DC ≤ 10%. Moreover, the films deposited below 100 °C with deposition conditions where 50% ≤ DC ≤ 75% were shown to present a high photocatalytic activity, likely due to the presence of anatase crystalline nanocolumns at the surface.
Highlights
TiO2 thin films have attracted intensive research as photocatalysts for their advantages in chemical stability, non-toxicity, commercial availability at a low cost and high photocatalytic activity [1,2,3]
We investigate the influence of the duty cycle (DC), defined as the discharge time to the period ratio, on the structural and photocatalytic properties of the TiO2 films deposited on silicon substrates in pulsed plasma enhanced chemical vapor deposition (PECVD) mode
The evolution of cross-sectional morphology is reflected in the surface topography, for the films deposited at DC > 40%, the top surfaces are quite rough because of the disordered columns leading to some clustering of grains till the surface
Summary
TiO2 thin films have attracted intensive research as photocatalysts for their advantages in chemical stability, non-toxicity, commercial availability at a low cost and high photocatalytic activity [1,2,3]. PECVD processes were used to yield some nanocolumnar structures with different phases including amorphous, anatase and rutile [35,36] These processes exhibit favorable features such as low deposition temperature, good film adhesion, high purity, good step coverage and easy control of reaction parameters [28, 37]. We investigate the influence of the duty cycle (DC), defined as the discharge time to the period ratio, on the structural and photocatalytic properties of the TiO2 films deposited on silicon substrates in pulsed PECVD mode. The latter are compared to the film deposited in continuous mode. This allows us to calculate an UV light activity RSA defined as the number of molecules cm-2 of SA degraded per second
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