Crystalline, Uniform‐Sized TiO₂ Nanosphere Films by a Novel Plasma CVD Process at Atmospheric Pressure and Room Temperature

Abstract

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

Facile and Fast Deposition of Amorphous TiO2 Film under Atmospheric Pressure and at Room Temperature, and its High Photocatalytic Activity under UV‐C Light

“…To achieve a low‐temperature CVD process, the CVD reaction should occur at such a temperature. With the assistance of plasma activation for gaseous reactants, plasma CVD is an effective method for preparing TiO 2 films at low temperatures . Another strategy is to select a suitable CVD reaction which can start spontaneously at low temperatures.…”

Uniformity, Structure, and Photocatalytic Activity of TiO2 Films Deposited by Atmospheric‐Pressure Linear Cold Plasma

“…Dielectric barrier discharge (DBD) is a simple and easily operated approach for generating AP cold plasma, and has recently been adopted for the preparation of TiO 2 nanopowder or film 10–17. In these studies, AP volume‐DBD plasma was commonly used, typically using inexpensive and volatile TiCl 4 and O 2 as precursors.…”

A review on the recent progress, challenges, and perspectives of atmospheric‐pressure cold plasma for preparation of supported metal catalysts

“…It should be noted that the dielectric constant, conductivity, and thickness have significant impacts on the cold plasma treatment. However, this may be avoided by using coplanar DBD and surface DBD, which had been developed and used for deposition of TiO 2 photocatalytic films.…”