Optical diagnostics and mass spectrometry on the afterglow of an atmospheric pressure Ar/O$_2$ radiofrequency plasma used for polymer surface treatment

TL;DR

This study characterizes the afterglow of an atmospheric pressure Ar/O$_2$ plasma used for polymer surface treatment, analyzing how gas flow and power affect plasma properties and interactions with substrates.

Contribution

It provides detailed optical and mass spectrometry analysis of plasma afterglow, highlighting the effects of operational parameters on plasma composition and substrate interaction.

Findings

Plasma creates a protective atmosphere at distances below 6 mm.

Ambient air influence increases at larger distances, affecting plasma composition.

Gradients in gas concentrations are measured as a function of position.

Abstract

In the context of polymer surface treatment, the afterglow of an atmospheric pressure Ar/O$_2$ radiofrequency plasma is characterized by optical emission spectroscopy, laser induced fluorescence and mass spectrometry. The influence of the O$_2$ gas flow rate and the source power on the plasma properties (gas temperature, Ar excitation temperature, relative concentrations of O atoms and OH radicals) are evaluated. We show that for plasma torch-to-substrate distances lower than 6 mm, the afterglow creates a protective atmosphere, thus the plasma gas composition interacting with the substrate is well controlled. For higher distances, the influence of ambient air can no longer be neglected and gradients in Ar, O$_2$ and N$_2$ concentrations are measured as a function of axial and vertical position.