Analysis of Structural and Photocatalytical Properties of Anatase, Rutile and Mixed Phase TiO2 Films Deposited by Pulsed-Direct Current and Radio Frequency Magnetron Co-Sputtering

Authors: S. Varnagiris, M. Urbonavicius, S. Tuckute, M. Lelis, K. Bockute

Abstract:

Amongst many water purification techniques, TiO₂ photocatalysis is recognized as one of the most promising sustainable methods. It is known that for photocatalytical applications anatase is the most suitable TiO₂ phase, however heterojunction of anatase/rutile phases could improve the photocatalytical activity of TiO₂ even further. Despite the relative simplicity of TiO₂ different synthesis methods lead to the highly dispersed crystal phases and photocatalytic activity of the corresponding samples. Accordingly, suggestions and investigations of various innovative methods of TiO₂ synthesis are still needed. In this work structural and photocatalytical properties of TiO₂ films deposited by the unconventional method of simultaneous co-sputtering from two magnetrons powered by pulsed-Direct Current (pDC) and Radio Frequency (RF) power sources with negative bias voltage have been studied. More specifically, TiO₂ film thickness, microstructure, surface roughness, crystal structure, optical transmittance and photocatalytical properties were investigated by profilometer, scanning electron microscope, atomic force microscope, X-ray diffractometer and UV-Vis spectrophotometer respectively. The proposed unconventional two magnetron co-sputtering based TiO₂ film formation method showed very promising results for crystalline TiO₂ film formation while keeping process temperatures below 100 °C. XRD analysis revealed that by using proper combination of power source type and bias voltage various TiO₂ phases (amorphous, anatase, rutile or their mixture) can be synthesized selectively. Moreover, strong dependency between power source type and surface roughness, as well as between the bias voltage and band gap value of TiO₂ films was observed. Interestingly, TiO₂ films deposited by two magnetron co-sputtering without bias voltage had one of the highest band gap values between the investigated films but its photocatalytic activity was superior compared to all other samples. It is suggested that this is due to the dominating nanocrystalline anatase phase with various exposed surfaces including photocatalytically the most active {001}.

Keywords: Films, magnetron co-sputtering, photocatalysis, TiO2.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.3566285

References:

[1] S. Varnagiris, M. Urbonavicius, S. Tuckute, M. Lelis, and D. Milcius, “Development of photocatalytically active TiO2 thin films on expanded polystyrene foam using magnetron sputtering,” Vacuum, vol. 143, pp. 28–35, Sep. 2017.
[2] D. Wojcieszak, M. Mazur, D. Gibson, G. Zatryb, D. Kaczmarek, and J. Misiewicz, “Influence of europium on structure modification of TiO2 thin films prepared by high energy magnetron sputtering process,” Surf. Coatings Technol., vol. 320, pp. 132–137, 2017.
[3] A. R. G. Korpi, S. Rezaee, C. Luna, Ţălu, A. Arman, and A. Ahmadpourian, “Influence of the oxygen partial pressure on the growth and optical properties of RF-sputtered anatase TiO2 thin films,” Results Phys., vol. 7, pp. 3349–3352, 2017.
[4] C. Li, B. Wang, H. Cui, J. Zhai, and Q. Li, “Preparation and characterization of buoyant nitrogen-doped TiO2 composites supported by fly ash cenospheres for photocatalytic applications,” J. Mater. Sci. Technol., vol. 29, no. 9, pp. 835–840, 2013.
[5] M. M. Hasan, A. S. M. A. Haseeb, R. Saidur, H. H. Masjuki, and M. Hamdi, “Influence of substrate and annealing temperatures on optical properties of RF-sputtered TiO2 thin films,” Opt. Mater. (Amst)., vol. 32, no. 6, pp. 690–695, 2010.
[6] K. J. Singh, M. Sahni, and M. Rajoriya, “Study of Structural, Optical and Semiconducting Properties of TiO2 Thin Film deposited by RF Magnetron Sputtering,” Mater. Today Proc., vol. 12, pp. 565–572, Jan. 2019.
[7] B. Pongthawornsakun et al., “Deposition of Pt nanoparticles on TiO2 by pulsed direct current magnetron sputtering for selective hydrogenation of vanillin to vanillyl alcohol,” Catal. Today, Aug. 2019.
[8] M. Lelis, S. Tuckute, S. Varnagiris, M. Urbonavicius, G. Laukaitis, and K. Bockute, “Tailoring of TiO2 film microstructure by pulsed-DC and RF magnetron co-sputtering,” Surf. Coatings Technol., vol. 377, p. 124906, Nov. 2019.
[9] J. Zheng, S. Bao, Y. Guo, and P. Jin, “TiO2 films prepared by DC reactive magnetron sputtering at room temperature: Phase control and photocatalytic properties,” Surf. Coatings Technol., vol. 240, pp. 293–300, 2014.
[10] B. Wang et al., “Effect of deposition parameters on properties of TiO2 films deposited by reactive magnetron sputtering,” Ceram. Int., vol. 43, no. 14, pp. 10991–10998, 2017.
[11] M. Batzill, “Fundamental aspects of surface engineering of transition metal oxide photocatalysts,” Energy Environ. Sci., vol. 4, no. 9, pp. 3275–3286, 2011.
[12] C. K. Nguyen, H. G. Cha, and Y. S. Kang, “Axis-Oriented, Anatase TiO2 Single Crystals with Dominant {001} and {100} Facets,” Cryst. Growth Des., vol. 11, no. 9, pp. 3947–3953, 2011.
[13] K. Y. Jung, S. Bin Park, and S.-K. Ihm, “Linear relationship between the crystallite size and the photoactivity of non-porous titania ranging from nanometer to micrometer size,” Appl. Catal. A Gen., vol. 224, no. 1–2, pp. 229–237, Jan. 2002.
[14] T. Luttrell, S. Halpegamage, J. Tao, A. Kramer, E. Sutter, and M. Batzill, “Why is anatase a better photocatalyst than rutile? - Model studies on epitaxial TiO2 films,” Sci. Rep., vol. 4, pp. 1–8, 2015.