Experimental and Theoretical Study of the Effect of the Inductive-to-Capacitive Transition in Propanethiol Plasma Polymer Chemistry

Abstract

The influence of the capacitive (E)-to-inductive transition (H) in inductively coupled plasma discharges is investigated for propanethiol plasma polymerization. In the E mode, at low plasma density, the sulfur content in the layers, measured by XPS, is quite high and strongly decreases after aging in the air. This phenomenon is attributed to the desorption of trapped sulfur-based molecules (e.g., H 2 S). In the H mode, presumably higher surface temperature prevents the trapping scenario during the layer growth and, as a consequence, yields a lower sulfur content which is stable after aging. Mass spectrometry measurements reveal important variations of the plasma chemistry depending on the discharge mode. The major change concerns the complete disappearance of the precursor in the H mode accompanied by the large production of CS 2 molecules. Furthermore, a linear correlation is found between the concentration of the CS 2 species and the atomic sulfur content in the Hmode synthesized layers. In addition, based on DFT calculations, different pathways of fragmentation are proposed as a function of the plasma parameters. The whole set of results highlight the importance of the E−H transition for the growth of thiol-based plasma polymers.

Dependence of E-H transition in argon ICP discharges for treatment of organic molecules

“…The most intense peaks detected result from fragments having from one to three carbons. THIRY et al [17] also found the same behavior on RGA analysis, with most carbonaceous compounds with 1-3 carbons. The higher molar mass fragments need more energetic sources to be produced, or more temperature to become volatile in the vacuum chamber.…”

“…THIRY et al [17] studied different treatment behaviours of propanethiol (in gas phase) to material deposition and growth, in both ICP discharges modes. The results showed that higher discharge temperatures and electron densities leaded to higher fragmentation of propanethiol.…”

A Detailed Description of the Chemistry of Thiol Supporting Plasma Polymer Films

“…However, the possible production of CS 2 molecules having the same mass than the precursor may lead to a wrong interpretation of the data. [19] Nevertheless, due to the relative abundance of the isotope 34 S ($4%), both molecules can be discriminated by examining their isotropic distribution through the evaluation of the I (m/z ¼ 78)/I (m/z ¼ 76) ratio. [38] Its evolution as a function of hPi is depicted in Figure S2, Supporting Information.…”

“…[3,17] In this context, we have recently published a detailed study on the influence of the experimental parameters on the chemical properties of propanethiol plasma polymer (Pr-PPF) synthesized in RF discharges. [18,19] One of the main conclusion of this work is that, depending on the growth conditions (capacitive or inductive coupling of the discharge, power, pressure,. .…”

“…), the chemical stability of the Pr-PPF can be strongly affected. [19] This conclusion has been drawn based on the evaluation of the overall amount of sulfur in the film including -SH functionalities but also other type of sufurbased chemical functions. Nevertheless, it is obvious that, in view of the potential applications, the main interest lies on the thiol functions.…”