Modification of the optical properties and nano-crystallinity of anatase TiO2nanoparticles thin film using low pressure O2 plasma treatment

Abstract

TiO2 nanoparticles (NPs) thin films with a thickness of 50 nm and a coreshell nanostructure were prepared using the spin coating technique and were treated using an inductively coupled O2 plasma at low pressure. While no significant features were observed during pumping, two kinetics can be identified during plasma processing using in situ spectroscopic ellipsometry. For very short plasma treatment times, the removal of solvent-based organic moieties surrounding TiO2 nanoparticles produces a densification of the inorganic TiO2 films. Such mineralization effect by the O2 plasma treatment was confirmed by X-ray photoelectron microscopy. For larger time scales, the average size of TiO2 NPs rises and significant changes of the optical properties occur. While no significant changes in the film nanostructure were observed by Scanning Electron Microscopy, a rise in the crystallite size and an increase in the agglomeration of TiO2 nanoparticles were confirmed by Transmission Electron Microscopy and Atomic Force Microscopy, respectively. The mechanisms involved in such plasma-induced modification of nanostructured TiO2 thin films are discussed in line with the energy fluxes of plasma-generated species.

TiO2–SiO2 nanocomposite thin films deposited by direct liquid injection of colloidal solution in an O2/HMDSO low-pressure plasma

“…The detailed results can be found in a very recent publication of the group. [25] The fit of the NC film using the second model (Model B), resulted in an improved error (MSE=4).…”

“…The fraction between HMDSO and O2 was chosen in a way to produce a silica-like matrix with a very low carbon content [29]. O2 was also used to ensure the removal of solvent-based organic moieties surrounding TiO2 NPs [30]. for a total of 20 s) and the second part without liquid injection (for a total off time TOFF = 40s).…”

“…Such feature suggests the well-known coffee-ring effect, happening when the solute migrate in the edge of the evaporating droplet due to the formation of preferential flow and faster evaporation at this area. [47][48][49] Based on such large-scale SEM and EDX observations, it seems that TiO2 species are provided to the substrate during growth as droplet and that evaporation and removal of organic species from the solvent [30] occur, at least partially, on the substrate surface rather than in the gas phase. A quantitative EDX analysis was conducted on the large region (2552 µm 2 ) avoiding an area exhibiting droplet traces such as the ones shown in Figure 7.…”

Nanoscale dielectric properties of TiO2 in SiO2 nanocomposite deposited by hybrid PECVD method

“…In order to produce a totally inorganic amorphous silica matrix [27], a high-density inductively coupled plasma (ICP) created at 13.56 MHz was ignited by applying a power discharge of 400 W to a gaseous mixture including O 2 95%-Ar 5%: 24 sccm and HMDSO: 0.11 sccm. No intentional heating of the substrate is required to remove the ligands and mineralize the NPs surface by interaction between the droplets of solution drying at the substrate surface and the plasma [28]. As reported, the volume fraction of TiO 2 NPs can be tuned by the TiO 2 precursor injection N within a sequence of 1 min.…”

Handling Nanoparticle Content in Nanocomposite Thin Films Deposited by Misty Plasma Processes through Controlled Flash Boiling Atomization

“…The SiO 2 matrix model was based on a Cauchy law fitted to data obtained from a plasma-deposited SiO 2 layer in the same reactor, while the TiO 2 nanoparticles model was a custom Tauc− Lorentz dispersion law. 22 Nanocomposite coatings were then modeled as a Bruggeman effective medium approximation (BEMA) of both materials, where the volume fraction of TiO 2 and SiO 2 was adjusted to fit the experimental data. 17 After each deposition, the samples were imaged using an OMAX optical microscope.…”