Lucel Sirghi

Hydrophilicity of TiO2 thin films obtained by radio frequency magnetron sputtering deposition

This paper reports results of the macroscopic and microscopic studies of the UV-light-induced hydrophilicity of TiO2 thin films prepared by radio frequency magnetron sputtering of a pure TiO2 in an Ar–O2 mixture gas at different pressure values. The gas pressure affects the crystallographic structure as well as the surface topography and UV-light-induced hydrophilicity of the deposited films. The microscopic study of the film hydrophilicity is based on friction force microscopy measurements, which are used to microscopically distinguish regions of different hydrophilicity on the film surfaces. These measurements make use of the observation that for a hydrophilic tip, the more hydrophilic the sample surface is, the larger the tip–sample friction force is. The films deposited at a relatively high value of gas pressure (10 mtorr) had an amorphous structure, a good UV-light-induced hydrophilicity and a microscopically smooth and homogeneous surface. The films deposited at lower gas pressure values had mixed crystalline and amorphous structures and relatively rough and inhomogeneous surfaces. The effect of the gas pressure on the plasma particle bombardment of the growing films is discussed to account for the dependence of the structure and surface properties of the films on the gas pressure.

Role of terminal OH groups on the electrical and hydrophilic properties of hydro-oxygenated amorphous TiOx:OH thin films

Electrical and hydrophilic properties of TiOx films obtained by plasma enhanced chemical vapor deposition (PECVD) were investigated in connection with OH group content of the films. A microcrystalline TiOx film prepared by rf magnetron sputtering deposition (RFMSD) was used as a reference sample in this study. Compared to the RFMSD film, the PECVD TiOx films had good hydrophilicity after ultraviolet (UV) light irradiation, low dark, and high photoexcited currents in a vacuum and high sensitivity of their dark and photoexcited currents to surface adsorbates. Low dark and high photoexcited currents measured in vacuum for the PECVD TiOx films were explained by the effect of inactivation of the defect states such as dangling bonds by the termination of OH group. Due to this effect, the PECVD TiOx films are referred to as hydro-oxygenated TiOx:OH films in this article. The sensitivity of the photoexcited currents to surface adsorbates noticed for the TiOx:OH films suggests that the surface potential is modifie...

Formation mechanism for TiOx thin film obtained by remote plasma enhanced chemical vapor deposition in H2–O2 mixture gas plasma

TiOx thin film formation mechanism from titanium tetraisopropoxide [Ti-(O-i-C3H7)4, TTIP] by remote plasma enhanced chemical vapor deposition (RPE-CVD) was investigated. Plasma was generated by a microwave discharge in single H2, O2, or H2–O2 mixture gases. Emission spectra measurements suggested that H radical atoms dissociated TTIP molecules. By addition of O2 to H2 gas, the H radical density and film deposition rate drastically increased. Moreover, it was proved that the deposition rate was decreased by OH radical molecules formed in H2–O2 mixture gas plasma. OH radical molecules caused deactivation of precursors and hence suppressed TiOTi bond formation in the gas phase. The highest deposition rate of 11 nm/min, which was two orders higher than that for the case of single gas plasma, was obtained in the case of mixture gas ratio of 80% H2 and 20% O2. The substrate temperature had not affected the deposition rate, but significantly changed the film structure. It is concluded that the use of H2–O2 mixture gas is effective for obtaining a high deposition rate for the RPE-CVD process, and the deposition rate strongly depends on H radical density and ratio of H and OH radical densities.

Study on hydrophilic property of hydro-oxygenated amorphous TiOx:OH thin films

Abstract This paper is on hydrophilicity of amorphous TiOx thin films, which were prepared by plasma enhanced chemical vapor deposition, including a large amount of OH groups. The as-deposited film showed a good hydrophilicity (water contact angle below 5°) that deteriorated after long time storage in a dark ambient air (water contact angle of 59°). By UV light irradiation, the film surface recovered its initial hydrophilicity. Atomic force microscopic measurements of tip–sample adhesion force showed homogeneous distribution on the film surface before and after UV light irradiation. We suppose that the OH groups have a strong effect on the film hydrophilicity. Measurements of dark and photo-excited currents suggested that the deposited films have high photo-efficiency and very long lifetime of photo-excited carriers. Hence, we refer to them as hydro-oxygenated amorphous TiOx (a-TiOx:OH) films in analogy with a-Si:H. Furthermore, it was observed that the conductivity of a-TiOx:OH films was sensitive to the surrounding gases, especially to electron-withdrawing oxygen. In ambient air, it is deduced that the photo-excited electrons diffuse toward the film surface and react with oxygen to generate O 2 − . Considering the good hydrophilicity of the as-deposited a-TiOx:OH film and the strong oxidation power of O 2 − , it is concluded that the hydrophilicity of the a-TiOx:OH film was recovered by the photo-catalytic decomposition of hydrophobic adsorbates on the film surface.

Hydrophilic properties of hydro-oxygenated TiOx films prepared by plasma enhanced chemical vapor deposition

The hydrophilicity of the hydro-oxygenated amorphous TiO x (a-TiO x :OH) films, in which the dangling bonds at defects were inactivated by the termination with OH groups, was investigated. The a-TiO x :OH films were prepared by plasma enhanced chemical vapor deposition method. It was found that the a-TiO x :OH films, which showed good hydrophilicity at as-deposited state, recovered the initial hydrophilicity by UV light irradiation even if it deteriorated during long storage in dark. The recovery of hydrophilicity by UV light irradiation was recognized both in ambient air and in O 2 . Photo-response to the electrical conductivity of the a-TiO x :OH films was getting worse along with increase in O 2 pressure, suggesting the consumption of the photo-excited carriers by O 2 molecules during UV light irradiation. Considering the electron-withdrawing property of O 2 molecules, it is deduced that the photo-excited electrons easily reacted with O 2 to result in . O - 2 species, which have strong oxidation power. These imply that the recovery of the hydrophilicity for the a-TiO x :OH films was achieved by the decomposition of hydrophobic adsorbates on the film surface during UV light irradiation. Moreover, it is supposed that for the a-TiO x :OH films, O 2 molecules play an important role for recovering the hydrophilicity under UV light irradiation.

Control of plasma parameters and wall sheath voltage in radio frequency magnetron discharge by grid bias

The plasma of a radio frequency (rf) magnetron discharge used for deposition of TiOx thin films was separated by a mesh grid into source (negative glow) and diffusion (deposition) plasmas. Langmuir probes were used to measure the potential, electron density, and electron temperature of both plasmas. While the change of the grid bias affected the diffusion plasma parameters, it did not change the source plasma parameters (except the potential). The use of the biased grid resulted in a decrease of temperature and an increase of density of plasma electrons in the film deposition region. With an increase of the grid biasing potential, the plasma potential increased in order to maintain a negative bias voltage across the grid sheath, the electron temperature increased, and the electron density decreased. The biased-grid-induced change of the plasma potential and the bias voltage across the wall sheath is explained based on the model of the asymmetric double probe, which is formed by the discharge chamber wall ...

Reactive HIPIMS with auxiliary Al electrode for ZnO:Al thin film deposition

In this paper a new technique is proposed for precise doping control of ZnO:Al thin films deposited in reactive High Power Impulse Magnetron Sputtering (HIPIMS). An auxiliary aluminum electrode was added to a reactive Ar/O2 pulsed magnetron with planar Zn target in order to obtain a controlled doping of ZnO films. Al neutral density in gas phase has been controlled by the discharge current and the biasing voltage on the auxiliary electrode (which influence the ion bombardment of the electrode) and measured by laser resonant absorption spectroscopy. The fraction of Al dopant in the deposited films was estimated by X-ray Photoelectron Spectroscopy (XPS) measurements. The goal of this work was to correlate Al density measured in the gas phase with Al concentration in the deposited films. It was also investigated the effect of the aluminum concentration on the structural, electrical and optical properties of ZnO:Al thin films deposited by HIPIMS. The internal microstructure and chemical composition of the deposited films was examined by X-ray difractometry (XRD) and X-ray Photoelectron Spectroscopy (XPS). The optical properties of the deposited films were studied by UV/VIS and photoluminescence spectroscopy.

Charged Particles in the Reactor Chamber of a Remote Plasma Enhanced CVD System

A planar Langmuir probe installed at the center of the reactor chamber of a remote plasma enhanced chemical vapor deposition system and the conductive wall of the reactor chamber behave as a double probe. This probe system was used to measure the density and temperature of the electrons reaching the deposition region. In spite of the plasma source remoteness, the measurements revealed relatively large electron density values (106 cm−3) for argon plasma.