Surface modification of hexatriacontane by CF₄ plasmas studied by optical emission and threshold ionization mass spectrometries^*

¹ Unité Mixte de Recherche de Chimie et Physique des Matériaux Polymères (UMR CNRS 6515), Université du Maine, avenue O. Messiaen, 72017 Le Mans, France
² Laboratoire de Spectrométrie (UMR CNRS 5588), Université J. Fourier, BP 87, 38402 St Martin d'Hères, France

Corresponding author: epaillard@aviion.univ-lemans.fr

Received: 6 November 1998
Revised: 4 March 1998
Accepted: 7 July 1998
Published online: 15 November 1998

Abstract

The behavior of tetrafluoromethane microwave plasma (2% argon included) has been studied by emission spectroscopy during the treatment of hexatriacontane, a model for high density polyethylene. The evolution of the densities of F* atoms, and CF, CF^*₂, radicals has been followed by using the actinometric technique with 2% argon added to the gas. The surface properties, such as surface energy and surface roughness were correlated to the emission intensity of reactives species in the plasma gas phase. We found that the evolution of the fluorinated species emissions in the plasma gas phase can be a direct indication of the surface modifications by the plasma. A mild exposure to the plasma can result in a great decrease of surface energy corresponding to the fluorination. The surface roughness only changes under drastic plasma conditions. Threshold ionization mass spectroscopy is applied to detect the fluorine atoms and CF_x radicals. Time resolved measurements in pulsed plasma, give access to the decay rate of F atoms concentration in the afterglow, and to their sticking coefficient on different surfaces. The influences of the discharge parameters and of the surfaces (metal, silicon or hexatriacontane) in contact with the plasma are investigated. The results show that the plasma generated ions and/or UV radiations highly enhance the reactivity of the F atoms on polymer surface.