| AVS 59th Annual International Symposium and Exhibition | |
| Plasma Science and Technology | Thursday Sessions |
| Session PS-ThP |
| Session: | Plasma Science and Technology Poster Session |
| Presenter: | N. Vandencasteele, Université Libre de Bruxelles, Belgium |
| Authors: | N. Vandencasteele, Université Libre de Bruxelles, Belgium J. Hubert, Université Libre de Bruxelles, Belgium T. Dufour, Université Libre de Bruxelles, Belgium S. Collette, Université Libre de Bruxelles, Belgium C. De Vos, Université Libre de Bruxelles, Belgium F. Reniers, Université Libre de Bruxelles, Belgium |
| Correspondent: | Click to Email |
PTFE samples were treated by O2/He plasma at various pressures, from low (6.67 Pa) to atmospheric pressure. Treatments were carried out using different mixtures of He and O2. The first results highlight two completely different etching mechanisms depending on the gas mixture used and working pressure.
The etching was studied by mass loss measurements, weighing the sample before and after plasma exposure.
At low pressure the strongest etching occurs for pure oxygen plasma while no etching is detected for helium plasma. The opposite is observed at atmospheric pressure, the strongest etching takes place with pure helium.
X-ray photoelectron spectroscopy (XPS) analysis was used to study the chemistry of the PTFE surfaces as well as the etching products. High resolution F1s and C1s peak show different etching products as the pressure and/or the gas composition are changed. In all cases both carbon and fluorine are detected. Depending on the plasma parameters (pressure and gas composition) either CF2 fragments (BE C1s = 292 eV) or CC (BE C1s = 285 eV) are detected.
Optical emission spectroscopy (OES) measurements were used to study the plasma phase and the etching products. A change in the He plasma emission was observed above a certain pressure (around 13.3 Pa). The plasma color changes from greenish to pink. This change could be related to the increase of the He metastable emission line at 389 nm. OES measurements also allowed us to detect etching products in the gas phase during the plasma exposure of the PTFE samples. Fluorine, CO and CO2 lines were detected.
Those various results allow us to suggest two different mechanisms of PTFE etching.
In the case of low pressure O2 plasma, the surface composition after the treatment and the etching products (detected by XPS and OES) suggest an etching mechanism where the C-F bonds are broken by charged particles (probably e-). Oxygen then reacts with the carbon backbone to produce CO2. The role of the charged particles was evidenced using different sample positioning and magnets.
In the case of atmospheric pressure treatments the etching occurs via the removal of CF2 fragments. The main active specie responsible for the etching seems to be metastable He atoms.