Effect of Plasma Excitation Power on the SiOxCyHz/TiOx Nanocomposite

Abstract

Titanium dioxide has attracted a great deal of attention in the field of environmental purification due to its photocatalytic activity under ultraviolet light. Photocatalytic efficiency and the energy required to initiate the process remain the drawbacks that hinder the widespread adoption of the process. Consistently with this, it is proposed here the polymerization of hexamethyldisiloxane fragments simultaneously to TiO₂ sputtering for the production of thin films in low-pressure plasma. The effect of plasma excitation power on the molecular structure and chemical composition of the films was evaluated by infrared spectroscopy. Wettability and surface energy were assessed by a sessile drop technique, using deionized water and diiodomethane. The morphology and elemental composition of the films were determined using scanning electron microscopy and energy dispersive spectroscopy, respectively. The thickness and roughness of the resulting films were measured using profilometry. Organosilicon-to-silica films, with different properties, were deposited by combining both deposition processes. Titanium was detected from the structures fabricated by the hybrid method. It has been observed that the proportion of titanium and particles incorporated into silicon-based matrices depends on the plasma excitation power. In general, a decrease in film thickness with increasing power has been observed. The presence of Ti in the plasma atmosphere alters the plasma deposition mechanism, affecting film deposition rate, roughness, and wettability. An interpretation of the excitation power dependence on the plasma activation level and sputtering yield is proposed. The methodology developed here will encourage researchers to create TiO₂ films on a range of substrates for their prospective use as sensor electrodes, water and air purification systems, and biocompatible materials.

Keywords: HMDSO; PECVD; TiO2 nanoparticle; plasma.

Figure 1

Schematic representation of the experimental setup used for film deposition.

Figure 2

Thickness and deposition rate of (a) HMDSO and (b) HMDSO with TiO₂ films, as a function of plasma excitation power.

Figure 3

Infrared spectra of films deposited at different powers of, (a) HMDSO, (b) HMDSO with TiO₂ sputtering, and (c) the same as (b), highlighting the low wavenumber 500–1500 cm⁻¹ region.

Figure 4

The relative density of Si-OH, Si₂O, siloxane ring, and SiOx groups in the film deposition, as a function of plasma excitation of power, of (a) HMDSO and (b), HMDSO with TiO₂ sputtering.

Figure 5

The roughness as a function of the applied power of films deposited in discharges composed of HMDSO and argon, with and without TiO₂. The dotted line represents the roughness of the clean glass substrate.

Figure 6

Scanning electron micrographs of aluminum substrates as-received and coated in HMDSO and TiO₂ containing discharges at different power.

Figure 7

The atomic proportion of carbon, titanium, silicon, and oxygen in the films as a function of the plasma excitation power, (a) without TiO₂ sputtering, (b) with TiO₂ sputtering.

Figure 8

The contact angle and surface energy of the films derived from, (a) HMDSO and (b) HMDSO, with TiO₂ plasmas as a function of plasma excitation power.