Nanocrystalline anatase TiO2 has been successfully synthesized using TiCl4 and O2 as precursors by atmospheric cold plasmas generated by dielectric barrier discharges (DBD) without extra heating or thermal treatment. For the TiO2 powders synthesized by DBD plasma at an energy density of 5.9 kJ · L−1, XRD and TEM analyses revealed that the nanocrystallite size is about 10–15 nm. Only a single crystalline structure of anatase was observed performing XRD, HRTEM and SAED measurements. It was found that the particle size decreased with increasing the discharge power, and that the chlorine contamination dramatically decreased when using high discharge power levels.magnified image

TiO 2 films play an important role in extensive applications such as photocatalysis, photovoltaics, biocompatibility, and sanitary disinfection. [1,2] Low-temperature film fabrication processes are essential for all thermally sensitive or unstable substrate materials such as organic polymers and textiles. Plasma CVD is highly suitable for low-temperature fabrication, but it has mainly been low pressure incorporated with sophisticated discharge and vacuum systems that have been adopted. [3][4][5] Recently, a diffuse coplanar surface discharge (DCSD) for generating thin-layer plasma has brought new opportunities for plasma CVD under atmospheric pressure and at room temperature. [6][7][8] Here we report, for the first time, a DCSD-induced plasma CVD route for nanocrystal TiO 2 thin-film fabrication under atmospheric pressure and at room temperature. Using this simple, robust, low-cost, and fast deposition approach, the as-deposited TiO 2 films composed of uniform-size nanospheres with preferential anatase formation show quite smooth, uniform, and transparent characteristics, good adhesion onto the substrate, and photocatalytic activity. The TiO 2 thin films were successfully fabricated by the DCSD-induced plasma CVD using 28 kV peak-to-peak voltage and 5 min deposition time under atmospheric pressure and at room temperature (see Fig. 1a). The waveforms of applied voltage and current for TiO 2 film deposition are shown in Figure 1b. The electric discharge power, 1.4 W, was measured via the area of the voltage/charge Lissajous figures.[9] The temperature of the plasma layer, determined by a colored-alcohol thermometer, was very close to room temperature (see Fig. 1c).The as-deposited TiO 2 films show a rather smooth and uniform surface without cracks, particulates, or other defects (see the overview scanning electron microscopy (SEM) image at low magnification, Fig. 2a). From Figure 2b, it can be further observed that the as-deposited films were almost exclusively composed of closely packed nanospheres, about 20-25 nm in diameter, without the formation of larger agglomerations. Moreover, the higher magnification SEM image in Figure 2b shows that TiO 2 nanoparticles are quite uniform in size and shape, and well interconnected. Figure 2c reveals the 3-dimensional atomic force microscopy (AFM) images of the as-deposited TiO 2 film. The statistical root mean square (rms) roughness for the measured area (500 nm × 500 nm) was 0.42 nm, which indicates that the extremely flat surface of the TiO 2 film was obtained by the DCSD-induced plasma CVD process. Such high surface uniformity could only be observed in the films derived from O 2 cluster ion beam-assisted deposition, [10] plasma-enhanced atomic layer deposition (PEALD), [11] or sol-gel method using a titanium naphthenate precursor.[12] The fractured cross-section of the TiO 2