M. Massi

Protective carbon layer for chemical corrosion of stainless steel

c ˜ EESC-USP-SC, Sao Carlos, SP, Brazil d ˜ Abstract Hydrogenated carbon (a-C:H) films were studied as an alternative material to be used as protective layer on steel, because of their chemical inertness, wear resistance, thermal stability, thermal conductivity. The films were deposited on stainless steel, plain steel and silicon wafers by a RF magnetron sputtering system at 0.6 Pa and RF power of 150 W, at room temperature. A methane plasma was used in these processes. Wet etching tests were carried out using acids (H SO , HNO , HCl, HF), alkaline solutions 24 3 (NH OH, KOH), organicsolvents (2-propanol, xylene and acetone). The samples were analysed by Fourier transformed infrared, 4 Raman spectroscopy, atomic force microscopy and cyclic voltammetry. The low degradation and corrosion levels of the samples show the high chemical resistance of the a-C:H films indicating that they are a promising material to be used as protective layer in many applications of the chemical industry. 2003 Elsevier Science B.V. All rights reserved.

Effects of the methane content on the characteristics of diamond like carbon films produced by sputtering

In this work, hydrogenated carbon films were sputter deposited at low temperatures using different Ar-CH 4 mixtures. The deposition rate of the films increases by up to a factor of 6 when comparing a CH 4 -rich mixture to a pure Ar plasma. At the same time, the sp 3 carbon content is much higher when CH 4 is added to the Ar, and as a consequence the resistivity increases by approximately six orders of magnitude, and the breakdown electric field increases by approximately a factor of three. Another attractive feature of the films deposited with a CH 4 -rich plasma is the low dielectric constant, down to 1.8 for a pure CH 4 plasma. The rms roughness of a 1-μm thick film is as low as 1.6 nm. All these features make this technique interesting for depositing intermetallic layers.

Micro-machine fabrication using diamond-like carbon films

Abstract In this work we use diamond-like carbon (DLC) films deposited by a RF magnetron sputtering system in micro-electro mechanical systems (MEMS) development. The principal applications of DLC films in MEMS application are micro-channels for microfluidric devices, mechanical micro-machines, micro-optical devices, and mechanical actuators. These films were produced by a reactive RF magnetron sputtering system from a target of carbon in a stable graphite allotropic form with purity of 99.9999% and methane plasma. The DLC films were deposited on silicon substrates. The deposition rate was 2.5 nm/min and the films showed low mechanical stress. The films were patterned by a lithography step and the structures were obtained by a reactive ion etching using oxygen plasma. The etching rate in this process was 1 μm/min. The film thickness was measured with a height step meter and a ellipsometer. Fourier transform infrared (FTIR) and Raman spectroscopy were used to identify the sp2 and sp3 hybridization of C, CH bonds and other possible bonds that can appear; atomic force microscopy (AFM), was used to measure film roughness.

Effect of multiple firing and silica deposition on the zirconia-porcelain interfacial bond strength

OBJECTIVES To test the hypothesis that multiple firing and silica deposition on the zirconia surface influence the bond strength to porcelain. MATERIALS AND METHODS Specimens were cut from yttria-stabilized zirconia blocks and sintered. Half of the specimens (group S) were silica coated (physical vapor deposition (PVD)) via reactive magnetron sputtering before porcelain veneering. The remaining specimens (group N) had no treatment before veneering. The contact angle before and after silica deposition was measured. Porcelain was applied on all specimens and submitted to two (N2 and S2) or three firing cycles (N3 and S3). The resulting porcelain-zirconia blocks were sectioned to obtain bar-shaped specimens with 1mm(2) of cross-sectional area. Specimens were attached to a universal testing machine and tested in tension until fracture. Fractured surfaces were examined using optical microscopy. Data were statistically analyzed using two-way ANOVA, Tukeys test (α=0.05) and Weibull analysis. RESULTS Specimens submitted to three firing cycles (N3 and S3) showed higher mean bond strength values than specimens fired twice (N2 and S2). Mean contact angle was lower for specimens with silica layer, but it had no effect on bond strength. Most fractures initiated at porcelain-zirconia interface and propagated through the porcelain. SIGNIFICANCE The molecular deposition of silica on the zirconia surface had no influence on bond strength to porcelain, while the number of porcelain firing cycles significantly affected the bond strength of the ceramic system, partially accepting the study hypothesis. Yet, the Weibull modulus values of S groups were significantly greater than the m values of N groups.

Longitudinal magnetic field effect on the electrical breakdown in low pressure gases

The electrical breakdown has been investigated for low-pressure argon and nitrogen discharges under the influence of an external longitudinal magnetic field. Plane-parallel aluminum electrodes (5 cm diameter) separated by a variable distance d (4.0 cm < d < 11.0 cm) were sustained with a dc voltage (0 < V < 1 kV). A Helmholtz coil was used to produce an uniform magnetic field(B) parallel to the discharge axis. Paschen curves were obtained and the secondary electron emission coefficient (g), the first Townsend ionization coefficient (a) and the ionization efficiency(h), were plotted with respect to the variation of the reduced field (E/P). To observe the effect of the magnetic field these curves were plotted for fixed values of B=0 and B=350 Gauss. As consequence of the longitudinal magnetic field, the free paths of the electrons in the Townsend discharge are lengthened and their lateral diffusion is reduced, thus reducing electron losses to the walls. The data presented in this paper give a quantitative description of the B-field effect on the Townsends coefficients and overall it is concluded that the DC electrical breakdown of the gases is facilitated if a longitudinal magnetic field is applied along the discharge axis.

Effects of plasma etching on DLC films

Abstract Magnetron sputtered diamond like carbon (DLC) films were etched in oxygen reactive ion etching (RIE) plasmas. The hydrogenated films etch 35% slower than the non-hydrogenated films. Etch rates increase with power. The anisotropy decreases with both pressure and power. Processes at 6.5 Pa yield anisotropies of over 0.9, with etch rates up to 185 nm/min for the hydrogenated films. Raman analysis indicates that these oxygen RIE processes etch preferentially non-crystalline carbon atoms in the hydrogenated films, the remaining film has more sp 3 -bound carbon atoms than the original DLC film. This phenomenon occurs in a much lesser degree for the non-hydrogenated films, and Raman analysis indicates that the sp 2 -bound carbon atoms etch at approximately the same rate as the non-crystalline bound atoms.

Electrochemical behavior of the Ti–6Al–4V alloy coated with a-C:H films

Abstract In this work diamond-like carbon films were deposited on the Ti–6Al–4V alloy, which has been used in aeronautics and biomedical fields, by electrical discharges using a magnetron cathode and a 99.999% graphite target in two different atmospheres, the first one constituted by argon and hydrogen and the second one by argon and methane. Films deposited using the argon/hydrogen mixture were called a-C:H, while films deposited using the argon/methane mixture were called DLC. Raman spectroscopy was used to study the structure of the films. The Raman spectra profile of the a-C:H films is quite different from that of the DLC films. The disorder degree of the graphite crystalline phase in a-C:H films is higher than in DLC films (a-C:H films present small values for the the I D / I G ratio). Potentiodynamic corrosion tests in 0.5 mol l −1 NaCl aqueous solution, pH 5.8, at room temperature (≈25 °C) were carried out as for the a-C:H as for the DLC coated surfaces. Comparison between the corrosion parameters of a-C:H and DLC coated surfaces under similar deposition time, showed that DLC coated surfaces present bigger corrosion potential ( E corr ) and polarization resistance than those coated with a-C:H films. Electrochemical impedance spectroscopy (EIS) was also used to study the electrochemical behavior of a-C:H and DLC coated surfaces exposed to 0.5 mol l −1 aqueous solution. The EIS results were simulated with equivalent electrical circuit models for porous films. The results of these simulations showed similar tendency to the one observed in the potentiodynamic corrosion tests. The DLC film resistance and the charge transfer resistance ( R ct ) for the DLC coated surface/electrolyte interface were bigger than the ones determined for the a-C:H coated surfaces.

Dielectric characteristics of AlN films grown by d.c.-magnetron sputtering discharge

Abstract Aluminium nitride(AlN) films have attracted much interest as a promising opto-electronic material. In this work, AlN films were deposited on p-type silicon by d.c.-magnetron sputtering using different nitrogen concentrations in a mixture with argon and at different substrate temperatures. Structural analysis of the AlN films was performed by X-ray diffraction. The AlN capacitors (MIS structures) were obtained by evaporating aluminium on the back of the silicon wafer, and on circular areas on the film. These capacitors were used to obtain quasi-static current–voltage characteristics at room temperature. The effect of substrate heating on produced AlN films and MIS capacitors is shown. Capacitance–voltage measurements were obtained and indicated that the substrate heating plays an important hole on the MIS capacitor dielectric properties.

Friction coefficient measurements By LFM on DLC films as function of sputtering deposition parameters

Diamond-like carbon (DLC) coatings are widely used as protective overcoats on space junctions, magnetic media and magnetic head sliders in hard disk-drive systems, etc. In the present work, the friction coefficient of DLC films was investigated by lateral force microscopy (LFM) as a function of sputtering deposition parameters. The lateral force acts on the pyramidal tip attached to the end of the cantilever, due to friction or viscous forces, resulting in cantilever measurable torsion and deflection, related to the frictions magnitude. The relationship among data from friction coefficient distribution on DLC films surface with flow of precursor gases, surface composition, morphology structure, hardness and elastic module parameters was evaluated. Characterization techniques such as Raman scattering spectroscopy (RSS), X-ray photoelectron spectroscopy (XPS) and nanoindentation were used. The results have showed good agreement with the literature for DLC tribological parameters.

End-point detection of polymer etching using Langmuir probes

The adequate determination of the end point of a plasma-etching process is very important for integrated circuit fabrication. In this paper, the authors propose a new method, making use of the floating potential, as determined by a single Langmuir probe with a radio frequency (RF) choke. For the etching of a polymer film with an oxygen plasma using a reactive ion-etching system, this method yields a reproducible and reliable signal, which was successfully used to detect the end point for several wafers, it is better than the method using the DC self-bias voltage as the end-point detection signal, and approximately as good as when using emission spectrometry-at least when the resist area is larger than 4.4 cm/sup 2/-whereas it uses a much cheaper equipment set. Langmuir probe measurements indicate that the floating potential changes are caused by several mechanisms: the average mass change, the plasma density, the average electron temperature, and the electron energy distribution all change after the end point of the etching.