ABSTRACT This work aimed to analyze the influence of treatment pressure on the interaction between stearic acid and an Argon-Oxygen plasma. The fixed variables were the applied RF plasma power (50 W), treatment time (30 min), and treatment starting temperature (273 K). The pressure was varied as follows: 0.2, 0.6, and 1.0 Torr. For all treatment conditions, the etching of the samples was observed, as evidenced by the mass loss of the specimens and by following the gaseous by-products of reactions employing a mass spectrometer coupled to the reaction chamber. Optical emission spectroscopy followed the emission lines of oxygen active species. Functionalization of the specimens was also observed, as shown by the results obtained by Fourier-transform infrared spectroscopy (FTIR) and through XRD analysis. A liquid phase was formed for samples treated at 0.6 and 1.0 Torr, which favored the functionalization process and broadened the band present in the region from 1750 to 1700 cm–1, resulting in amorphous phases. An increase in the intensity of the characteristic peaks of esters was also observed. It can be concluded that the higher pressure favors the formation of a liquid phase and reaction kinetics, resulting in higher functionalization and lower etching.

ABSTRACT Surface treatments such as heat treatments, paints, plasma treatments and galvanizing are important in metal working industry. In those treatments, the required adhesion characteristics can be limited if contaminants are present, so there is a need to clean these surfaces. Conventional processes can be costly, some generated waste may be environmentally hazardous and, in some cases, due to part geometry, they are not effective. Alternatively, plasma treatments which are considered to be environmentally clean, more efficient and with lower operating costs can overcome those difficulties. Due to the reactional complexity of these treatments, there are many fields to be researched, such as which reactions are due to impacts of (neutral) chemical species and which are due to excited species and radiation. The present work aims to verify the interactions between Ar-10%O2 plasma using amino acid L-proline in an inductively coupled radiofrequency plasma. This study showed that oxidative plasma promotes high degradation of the sample. A gas analyzer (quadrupole mass spectrometer) coupled to the gas outlet was used and many gaseous products are detected during treatment, such: H2, H2O, CO, NO (Nitric Oxide) and CO2 while L-proline undergoes intense degradation. The conclusions allow to state that the interaction between the Ar/O2 plasma and L-proline promotes intense degradation through the breakdown of the heterocyclic ring of the molecule.

The reactions that can occur on organic materials treated in plasma enviorement are strongly affected by surface temperature, thus the sharp determination of this variable is extremely important to process control. In situ temperature measurements are often employed; however, the measured point is generally under the treated surface. If in metallic materials the high thermal conductivity minimizes this problem, in non-metallic materials processing it becomes important, because its thermal resistivity besides a high sensibility to small temperature variations. The present work uses a simulation tool to extract thermal data on Ar+O2 RF plasma processing of Stearic Acid. Experimental data were obtained by thermocouples placed inside the samples. The extrapolation of surface temperature was performed by numerical simulation with Autodesk CFD software v.15.1. Results show that the temperature of the surface reaches values higher than the ones measured inside the sample holder. This difference of temperature is in good agreement with the visual observation of the phase transformations in the treated material, showing a simple and valuable tool to better control of plasma treatments.

ABSTRACT Plasma surface cleaning is an alternative process that aims at the fully removal of organic contaminants on several kinds of materials. Despite its advantages, there are still lacks on the comprehension of the complex relations between plasma-generated species and organic molecules during plasma cleaning. In the present work, a linear alkane (hexatriacontane - C36H74), used as a contaminant model, was exposed to an Argon radiofrequency (RF) inductively coupled plasma (ICP). The by-products from degradation were monitored by optical emission spectroscopy (OES) and residual gas analysis (RGA), to identify the influence of sample positioning on E and H discharge modes regions. The exposition to H-mode discharge resulted in more intense and profuse emissions of C-H and C2 systems. RGA results show similar byproducts from degradation in both modes; however, the intensity from treatment in H-mode is largely greater. It was also observed that plasma etching in H-mode is enough to melt the sample, while E-type discharge leaves the surface of the sample apparently unchanged.

Plasma cleaning is a promising technology in surface treatments, despite technological interest its use is limited because its mechanisms still are not entirely understood. This work aims to evaluate how the applied power of an inductively coupled RF discharge at 13,56 MHz, with Ar and Ar+10%O2 atmospheres, affects its capabilities to etch an organic molecule. Mass variation rate was used as direct characterization of degradation process and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) was performed to search for residual molecular modifications. Additionally, optical emission spectroscopy (OES) measurements were performed to monitor the offer of active species in the gaseous volume. In experimental conditions was possible attain mass reduction from sample, with higher mass loss rate when applied power is increased. Material characterization shows the possibility of attain a high etch rate, while no structural modifications were detected, if the temperature is controlled.