Pol. J. Chem. Tech., Vol. 17, No. 2, 2015 103 Polish Journal of Chemical Technology, 17, 2, 103 — 111, 10.1515/pjct-2015-0037 Influence of the structural and surface properties on photocatalytic activity of TiO 2 :Nd thin films Damian Wojcieszak 1 , Michał Mazur 1* , Danuta Kaczmarek 1 , Jerzy Morgiel 2 , Agata Poniedziałek 1 , Jarosław Domaradzki 1 , Aleksandra Czeczot 1 1 Wroclaw University of Technology, Faculty of Microsystem Electronics and Photonics, Janiszewskiego 11/17, 50-372 Wroclaw, Poland 2 Polish Academy of Sciences, Institute of Metallurgy and Materials Science, Reymonta 25, 30-059 Cracov, Poland *Corresponding author: e-mail: michal.mazur@pwr.edu.pl Titanium dioxide thin films doped with the same amount of neodymium were prepared using two different magnetron sputtering methods. Thin films of anatase structure were deposited with the aid of Low Pressure Hot Target Magnetron Sputtering, while rutile coatings were manufactured using High Energy Reactive Magnetron Sputtering process. The thin films composition was determined by energy dispersive spectroscopy and the amount of the dopant was equal to 1 at. %. Structural properties were evaluated using transmission electron microscopy and revealed that anatase films had fibrous structure, while rutile had densely packed columnar structure. Atomic force microscopy investigations showed that the surface of both films was homogenous and consisted of nanocrystal- line grains. Photocatalytic activity was assessed based on the phenol decomposition. Results showed that both thin films were photocatalytically active, however coating with anatase phase decomposed higher amount of phenol. The transparency of both thin films was high and equal to ca. 80% in the visible wavelength range. The photolu- minescence intensity was much higher in case of the coating with rutile structure. Keywords: TiO 2 , neodymium, thin films, magnetron sputtering, photocatalysis, phenol decomposition. INTRODUCTION One of the materials that has lately attracted much attention is titanium dioxide (TiO 2 ) 1–4 . Such interest is related to the unique properties of this material, e.g. nontoxicity, thermal, mechanical and chemical stability, transparency for the light in the wide spectral range, high dielectric constant and photocatalytic activity 5–9 . According to the application it is desired to obtain tita- nium dioxide with different crystal structure – anatase, rutile as well as a mixture of these two phases. Thin films with the rutile structure can be used as films with high refractive index in case of antireflective coatings, optical filters, protective coatings for solar cells or touch panels 10–13 . In turn, TiO 2 thin films with anatase struc- ture are widely applied as coatings with hydrophilic and self-cleaning properties due to their high photocatalytic properties 14–16 . Titania is well known and widely used effective photocatalyst for the photodegradation of organic pollutants in water and air 17 . The efficiency of the photocatalytic process of TiO 2 in aqueous solution depends on the electron-hole pairs generated under the light illumination, separation and transfer of electrons and holes to harmful compounds adsorbed on the catalyst surface 18 . The photogenerated holes in the titania are highly oxidizing and play key role in the photocatalysis process. However, recombination of electron/hole pairs significantly decreases its efficiency 19 . Therefore, various efforts are made to avoid the recombination process. Doping the titania catalyst with proper metal ions could be advantageous and increase its photocatalytic proper- ties by introducing or increasing the number of trapping sites. Trapping electrons and holes can lead to increased lifetimes and therefore the probability of reaching the surface without further recombination, allowing them to take part in the photocatalysis reaction 20 . Lanthanides as dopants for thin films based on TiO 2 can modify their surface properties that favourably influ- ence on e.g. increase of photocatalytic activity 21–23 . Most of the rare earths (Ce, Sm, Er, La, Eu, Pr, Gd and Nd) have been found to improve photocatalytic properties of TiO 2 . Among samples doped with Sm, Ce, Er, Pr, La the Gd- and Nd-doped TiO 2 showed highest photocatalytic activity 18 . Depending on the experimental setup, time of the decomposition and decomposed material the pho- tocatalytic activity of pure titania in the form of nano- powders reported in the literature may be high 17, 18, 23, 24 . However, the photocatalytic activity of TiO 2 may be further enhanced by doping with e.g. neodymium. Jiang et al. 25 reported that only precisely selected amount of Nd dopant can significantly increase the photocatalytic properties of TiO 2 . For example, Khalid et al. 26 stated that the optimum value of the neodymium dopant incor- porated into titania nanoparticles is ca. 1 at. % and then the efficiency of the photocatalytic reaction is enhanced by 20%. Also Bokare et al. 27 showed that incorporation of 1 at. % of neodymium increased the decomposition efficiency of 30% as-compared to undoped TiO 2 . The effectiveness of the dopant is related to its ionic radius and oxygen affinity of the dopant ion. Therefore, the large Nd 3+ ion can produce a localized charge perturbation when it is present substitutionally in titania and, in such way, enhances its photocatalytic activity 28 . Up to date there are a lot of reports regarding the preparation of the oxide composites based on titanium and neodymium by various techniques. Most of them concern preparation of nanopowders and the commonly used sol-gel method 27, 29 . However, the reports about preparation of TiO 2 :Nd thin film coatings are rare e.g. 30, 31 and among others one can also distinguish such fabrication methods as e.g.: pyrolysis 32 , spin-coating 33 or laser ablation 34 . Also magnetron sputtering is a popular method for the deposition of thin film coatings in various fields of industry, e.g. optical coatings or thin-film gas sensors 35, 36 . One advantage of this technique includes the