Search

The plasma of a radio frequency (rf) magnetron discharge used for deposition of TiO[sub χ] 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 and the grid. The effect of the biased grid on the diffusion plasma parameters is discussed accounting for the particle transport phenomena in the system. [ABSTRACT FROM AUTHOR]

The effect of surface cleaning on the hydrophilicity of commercial atomic force microscopy (AFM) silicon probes and on the adhesive force measurements in water and air is investigated. The presence of water soluble contaminants at the tip-sample contact has lowered the capillary pressure in the water bridge formed by capillary condensation at the AFM tip-sample contact, which has consequently lowered the adhesive force.

Tantalum pentoxide thin films have been deposited at room temperature by (dual) ion beam sputtering for applications as waveguides in biosensors. The oxygen partial pressure and the energy of the substrate ion beam were the major parameters varied in ion beam sputtering and dual ion beam sputtering experiments, respectively. For sufficiently high oxygen partial pressures, the films were stoichiometric, free of contaminants, amorphous, and extremely smooth. Ion bombardment of the growing films with Ar+ ions up to 200 eV had no significant influence on these properties. The refractive index of stoichiometric films was 2.1±0.1 and the extinction coefficient well below the resolution limit of ellipsometry and UV/visible measurements. By coupling a laser beam via an optical grating into a 150 nm thick Ta2O5 layer, the optical losses could be estimated to be below 3 dB/cm. A series of experiments has been carried out to prove that this deposition process is compatible with the use of thermoplast substrates which are sensitive not only to high temperatures but also to ion bombardment and UV radiation. Finally, first experiments are presented to functionalize the surfaces of Ta2O5 films with amine and epoxy groups. [ABSTRACT FROM AUTHOR]

Tantalum pentoxide (Ta2O5) thin films have been deposited by reactive ion beam sputtering at room temperature. The films have been characterized by scanning electron microscopy, atomic force microscopy, x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), variable angle ellipsometry, and UV-VIS spectroscopy. The main parameter varied was the oxygen partial pressure. Stoichiometry is reached for pO>=3×10-2 Pa; within the limit of XPS (∼1%) the films are free of contaminations. They are extremely smooth with a surface roughness of 0.14 nm only. From FTIR, it can be concluded that they are amorphous. For stoichiometric Ta2O5 films, the refractive index at 532 nm is in the range from 2.05 to 2.2, while the extinction coefficient is below the detection limit of our ellipsometer. UV-VIS spectra show stoichiometric films to possess a high transmission in a wide wavelength range with an absorption edge below 300 nm. [ABSTRACT FROM AUTHOR]

Atomic force microscopy (AFM) measurements of the tip–sample friction and adhesive forces were used to study the chemical homogeneity of the surface of titanium dioxide thin films deposited by radio frequency magnetron sputtering deposition. As a result of the photocatalytic activity, the film surface turned superhydrophilic by UV light irradiation in air. However, the AFM measurements showed that the surface of titanium dioxide deposited at low gas pressure (1 mTorr) was chemically heterogeneous with grains of very low photocatalytic activity. In the ambient air, due to the capillary condensation of the water vapor at the AFM tip–sample contact, the superhydrophilic regions on the film surface show larger friction and adhesive forces compared to the regions of low hydrophilicity. [ABSTRACT FROM AUTHOR]

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. [Copyright &y& Elsevier]

Investigates nonlocal particle loss effects on the electron kinetics in a direct current helium diffusion-controlled positive column of low-pressure and discharge current. Factors that determine the electron energy diffusion function; Radial ambipolar diffusion due to the gradient of plasma density.

The present work proposes an extension of Oliver-Pharr analysis [J. Mater. Res. 7, 1564 (1992)] of unloading force-displacement data obtained in nanoscale indentation experiments to account for contact adhesion. The loading force is considered a sum of the contact elastic and adhesion forces. During the unloading, both forces suffer variations. For conical geometry, the unloading force-displacement curve is described by a sum of a quadratic term (accounting for the elastic force) and a linear term (accounting for adhesive force). Results of atomic force microscopy indentation experiments performed with sharpened silicon tips on poly(dimethylsiloxane) agreed well with the prediction of the proposed theoretical model. [ABSTRACT FROM AUTHOR]

A single nanoasperity contact in ambient air is usually wetted by capillary condensation of water vapor and is surrounded by a water meniscus. This phenomenon strongly affects the contact friction, not only by the effect of meniscus loading force (superficial tension and capillary forces), but also by a friction force that accounts for the energy loss in the meniscus movement along with the sliding contact. Occurrence of the water-meniscus-generated friction is experimentally proved by atomic force microscopy measurements of the tip-sample friction force at minimum possible external load (before pull-off). A qualitative explanation for the observed dependence of the friction force on air humidity and solid surface wettability is proposed. [ABSTRACT FROM AUTHOR]

The UV-light-induced hydrophilicity of amorphous titanium dioxide thin films obtained by radio frequency magnetron sputtering deposition was studied in relation with film thickness. The effect of UV light irradiation on the film hydrophilicity was fast, strong and did not depend on substrate or thickness for films thicker than a threshold value of about 12 nm, while for thinner films it was weak and dependent on substrate or thickness. The weak effect of UV light irradiation observed for the ultra-thin films (with thickness less than 12 nm) is explained based on results of measurements of surface topography, UV-light absorption and photocurrent decay in vacuum. Comparing to thicker films, the ultra-thin films have a smoother surface, which diminish their real surface area and density of defects, absorb partially the incident UV light radiation, and exhibit a longer decay time of the photocurrent in vacuum, which proves a spatial charge separation. All these effects may contribute to a low UV light irradiation effect on the ultra-thin film hydrophilicity. [Copyright &y& Elsevier]