Results of the treatment of poly(dimethylsiloxane) (PDMS) surfaces using novel atmospheric pressure pulsed dielectric barrier discharge plasmas are presented. Different gases (argon, helium, nitrogen) as well as their mixtures with water vapor were compared in terms of the improvement of adhesion between two PDMS samples after processing by plasma. The plasma was characterized by optical emission spectroscopy to identify the emitting species and determine the plasma temperatures. For all the gases studied, plasma processing resulted in increase of adhesion between PDMS samples if long exposure time (larger than 150 s) is applied. However, for very short treatment times (20 plasma pulses, total processing time about 3 s) the highest efficiency was found for helium plasmas. Water contact angles at PDMS surfaces as function of plasma processing time was analyzed. Atomic force microscopy analysis was performed to show reduction in the surface roughness after plasma treatment, which is likely to be the responsible for increase of the surface contact area and thus the adhesion between two PDMS surfaces. The role of the two mechanisms in the improvement of adhesion (enhanced wettability and changes in the surface morphology), for different time scales, is discussed. Interestingly, for the minimum processing time (20 plasma pulses), the improvement in adhesion and reduction of surface roughness are observed although the changes in the water contact angle are insignificant.
The structure of molecular oxygen discharge generated by a capacitively coupled reactor was experimentally investigated using a Langmuir probe and the results were compared to the Particle-inCell (PIC) simulation. The electron energy distribution functions (EEDF) were measured for a pressure range of 10 to 100 mTorr, keeping the power injected into the plasma at about 50 and 200W. The simulation calculated the EEDFs taking into account three main charged particle species presented in oxygen plasma: electron, O -and O 2 + . The PIC simulation gives the specie profiles; however is time-consuming for discharges with many species such as oxygen discharges. Despite that, the order of magnitude is the same as the experimental data. The simulation results show that the cold and hot electron temperatures are in a good agreement with the experimental data. Moreover, the results indicate that the EEDFs measured at lower pressures are bi-Maxwellian distributions.
A volume-averaged global model for inductively coupled carbon tetrafluoride (CF 4 ) plasma was used to study the role of the different processes of production and loss of atomic fluorine on the two different ways to vary the gas pressure: under variable or constant gas flow rate. The results obtained by plasma modeling confirm the behavior of atomic fluorine density with pressure observed in others studies (1-3) when the gas flow rate effect is considered. It's noticeable that the fluorine atoms are created mainly by dissociative processes and lost by recombination to the reactor walls for both gas flow conditions. The relative reaction rate for dissociative processes presents a similar behavior to the fluorine density with the variation of the gas pressure. We also note that the applied power has an important role in reducing the recombination of atomic fluorine to the walls, but does not affect the flow rate effect.
In this work an oxygen asymmetric capacitive radio frequency discharge was investigated with numerical global model and Langmuir Probe to evaluate the behavior of the electron density (ne) and the electron temperature (Te) as a function of input power and gas pressure. The experimental Langmuir probe measurements show that Te increases for pressures below 30 mTorr, which corresponds to low ne, as usual for Reactive Ion Etching type reactor. Moreover, the experimental and simulated electron temperature are in good agreement for gas pressure values above 25 mTorr, because in this case the electron energy distribution function (EEDF) is Maxwellian, according to assumption made in the global model, for the rate coefficient calculation. For electron density the discrepancy is higher for all pressure range, probably because the effect of secondary electron emission that is not considered in our global model simulations.
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