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TiO2 thin films are used extensively for a broad range of applications including environmental remediation, self-cleaning technologies (windows, building exteriors, and textiles), water splitting, antibacterial, and biomedical surfaces. While a broad range of methods such as wet-chemical synthesis techniques, chemical vapor deposition (CVD), and physical vapor deposition (PVD) have been developed for preparation of TiO2 thin films, PVD techniques allow a good control of the homogeneity and thickness as well as provide a good film adhesion. On the other hand, the choice of the PVD technique enormously influences the photocatalytic performance of the TiO2 layer to be deposited. Three important parameters play an important role on the photocatalytic performance of TiO2 thin films: first, the different pathways in crystallization (nucleation and growth); second, anatase/rutile formation; and third, surface area at the interface to the reactants. This study aims to provide a review regarding some strategies developed by our research group in recent years to improve the photocatalytic performance of TiO2 thin films. An innovative approach, which uses thermally induced nanocrack networks as an effective tool to enhance the photocatalytic performance of sputter deposited TiO2 thin films, is presented. Plasmonic and non-plasmonic enhancement of photocatalytic performance by decorating TiO2 thin films with metallic nanostructures are also briefly discussed by case studies. In addition to remediation applications, a new approach, which utilizes highly active photocatalytic TiO2 thin film for micro- and nanostructuring, is also presented. [ABSTRACT FROM AUTHOR]

Highlights from the article: Ag Nanoparticles Decorated TiO2 Thin Films with Enhanced Photocatalytic Activity (Phys. In article number 1800898, Salih Veziroglu, Franz Faupel, Oral Cenk Aktas, and co-workers present a facile method to prepare Ag nanoparticles (NPs) decorated TiO SB 2 sb thin film by photocatalytic deposition. The presented method allows easy controlling size, morphology and distribution density of Ag NPs on TiO SB 2 sb to achieve a high photocatalytic activity.

Abstract: The RF magnetron sputtering of polytetrafluoroethylene target is studied with the aim to find out conditions leading to the deposition of super-hydrophobic thin films. It is shown that such coatings can be prepared at elevated pressures and a longer distance between the sputtered target and the substrate. This is explained by an increase in the density of longer CxFy molecules that reach the substrate and a lower flux of ions and CF2 radicals on the surface of growing film under such deposition conditions, as observed by optical emission spectroscopy and mass spectrometry. Such changes in plasma composition result in a deposition of rough films having F/C ratio close to 2 as observed by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. These findings clearly distinguish our results from the previous investigations of polytetrafluoroethylene sputtering performed at shorter distances from the target, where either low F/C ratio or low roughness of the deposited films did not allow reaching super-hydrophobic character of the coatings. [Copyright &y& Elsevier]

• Nanoclusters-Au/TiO 2 films for selective VOC detection (2-Propanol) at 250 °C. • Nanoclusters-Ag/TiO 2 films are more selective to n -Butanol at 250 °C. • Nanoclusters-Ag-Au/TiO 2 films for NH 3 detection by spray technology. • TiO 2 spray (40 nm) films with Ag nanoparticles showed two types of conductivity. • The synergetic effect of the nanoclusters Ag, Au, and Pt promotes H 2 selectivity for TiO 2 films. In this paper, the effect of the thickness of nano-structured TiO 2 thin films (12–40 nm) and successive deposition of different noble metal nanoparticles on the performances of propanol vapor and H 2 gas sensors was investigated. The obtained titania thin films were integrated into a device for UV, gas, and gas/vapor sensing studies at different operating temperatures. Qualitative analysis revealed that the sensor selectivity and its response could be altered by film thickness and type of noble metal nanoparticles. The results indicate that the sensor with 40 nm TiO 2 film has the highest response to H 2 gas (˜ 650%). The fastest response time and the most rapid recovery however were achieved by the sensors made of 12 nm sprayed TiO 2 ultra-thin films, which also offered the highest selectivity to H 2 gas. The best UV detection performances were demonstrated by films functionalized with Au nanoparticles (the I UV / I dark ≈ 80). The structural, chemical, electrical, UV, and gas sensing properties of such films were investigated using SEM, AFM, Raman spectroscopy, electrical characterization, and sensing experiments. It has been clearly demonstrated that films are nanostructured and have mixed phases that contain mostly anatase (annealed at 450 °C) and small amounts of rutile after thermal annealing at higher temperatures (more than 600 °C), as improved materials for sensor applications. Our combined study analyzes the relationship between thickness, electrical properties and the gas/vapor sensing performance of such thin film based TiO 2 gas sensors as well as the effect of different types of noble metal nanoparticles (Au, Ag, Ag-Au and Ag-Pt) deposited on the surface. The enhanced response was attributed to the involvement of noble nanoalloy or nanoparticle interface to titania forming nano-junctions in the gas sensing mechanism. Highly selective and sensitive sensors towards specific gas or vapor molecules are essential for environmental monitoring, and for health and safety issues. [ABSTRACT FROM AUTHOR]

Abstract The massive application requests for high-performance sensors indicate on the importance of precise controlling of the semiconducting oxide characteristics. The sensor longevity needed for the remote areas in harsh environments is mandatory and can benefit greatly from self-cleaning abilities. To serve this demand, we present in our work ultra-thin TiO 2 films deposited with different thicknesses down to 15 nm on glass substrates using atomic layer deposition (ALD). The morphological, chemical, topographic, electronic and chemical properties of the fabricated films were investigated in detail, showing the presence of the anatase phase. As it is known by the literature, the UV and gas sensing properties are highly dependent on the thickness of the films, however fully reversible and capable of long term detection. Thinner films (15 nm) showed higher UV and gas sensing performances than thicker films (45 nm), which was related to the film thickness comparable to the Debye length. Further improvement in the UV sensing properties was achieved by surface functionalization of TiO 2 films with Au nanoparticles. The UV response increased by about one order of magnitude after the surface functionalization with Au nanoclusters/nanoparticles. All TiO 2 ultra-thin films demonstrated good selectivity to hydrogen gas, independent of the thickness. The samples with 15 nm thickness showed a response of ~ 600% to 100 ppm of H 2 at 250 °C operating temperature. The presented study demonstrates the importance of the film thickness and surface functionalization with noble metals nanoclusters for sensing applications of ultra-thin TiO 2 layers. Such ultra-thin films could be used for the development of a series of integrated detectors and chemical field effect transistors (chemFETs) directly on highly complex chips. [ABSTRACT FROM AUTHOR]

While there is continuous progress in development of new photocatalytic thin films and coatings, the lack of a reliable and standard procedure for measuring the photocatalytic performance of such active surfaces makes it difficult to compare results between research groups and different measurement setups. Here, a comparative study was carried out to demonstrate the high photocatalytic activity of sputter-deposited TiO 2 film with self-organized nanocrack networks by using two different analytical approaches: (i) bleaching of a thin Methylene Blue (MB) solid layer on photocatalytic TiO 2 thin film (in-air) and (ii) the decolorization of a MB aqueous solution in the presence of TiO 2 thin film (in-solution). While the decolorization of aqueous MB solution provides an indirect observation of the photocatalytic effect imposed by the TiO 2 film, the use of a solid MB layer as an indicator allows monitoring of photocatalytic reactions at the solid-air interface directly. We showed the applicability of this approach as a complementary and a fast analysis method to reveal the photocatalytic efficiency of thin films by comparing it with the state of the art inks (based on MB and other similar organic dyes) used as photocatalysis indicator. [ABSTRACT FROM AUTHOR]

Abstract: Nanocomposite and nanostructured films have been studied for several decades mainly due to their unique physical, chemical or bioresponsive properties. The main attention has been paid to metal/plasma polymer nanocomposites prepared by simultaneous plasma polymerization and metal co-sputtering or evaporation. These nanocomposite films are concisely reviewed. More complex composites that are prepared by metal oxide incorporation into plasma polymer matrices using RF sputtering are discussed. Recently emerged utilization of beams of nanoclusters for the deposition of these nanocomposites and preparation of nanostructured surfaces of plasma polymers by various plasma based methods is described. [Copyright &y& Elsevier]

Abstract: A new method of deposition of nanocomposite gold/poly(ethylene oxide)-like thin films was investigated where gold was sputtered from an r. f. magnetron and poly(ethylene oxide)-like plasma polymer was simultaneously deposited via vacuum evaporation of conventional poly(ethylene oxide). Such method allows formation of the plasma polymer matrix with composition very close to that of precursor, a feature difficult to obtain in plasma polymerization processes. The films with different content of gold were prepared by varying the evaporation rate of poly(ethylene oxide) at constant power of the magnetron discharge. Chemical composition and cross-linking density of polymeric phase as well as the size distribution of gold nanoparticles were shown to be strongly dependent on the discharge power conditions. Stability of resultant nanocomposites in water was also studied. Such films are perspective for use in biomedical applications. [Copyright &y& Elsevier]