XPS analyses of polystyrene thin films treated under DC pulsed discharges conditions in nitrogen, oxygen and oxygen-argon mixtures

Issue		Eur. Phys. J. Appl. Phys. Volume 18, Number 2, May 2002


Page(s)		135 - 151
Section		Plasmas, Discharges and Processes
DOI		10.1051/epjap:2002035

Eur. Phys. J. AP 18, 135-151 (2002)
DOI: 10.1051/epjap:2002035

XPS analyses of polystyrene thin films treated under DC pulsed discharges conditions in nitrogen, oxygen and oxygen-argon mixtures

F. Clément¹, B. Held¹, N. Soulem¹ and C. Guimon²

¹ Laboratoire d'Électronique, des Gaz et des Plasmas, Université de Pau, 64000 Pau, France
² Laboratoire de Chimie Théorique et Physicochimie Moléculaire (UMR CNRS 5624) , Université de Pau, 64000 Pau, France

bernard.held@univ-pau.fr

(Received: 17 October 2001 / Received in final form: 28 January 2002 / Accepted: 13 February 2002 )

Abstract
This paper is devoted to polystyrene thin film treatment under DC pulsed discharges in nitrogen, oxygen and oxygen-argon mixtures. XPS analysis is used in order to investigate the new chemical bonds generated by the reactive particles colliding the surface from the plasma. The experimental conditions are close to the best running conditions deduced from [16,75,86]. Correlations between microscopic analyses obtained by XPS through the knowledge of the surface chemical composition and macroscopic ones realized by studies of water drop deposited on the films (contact angle measurements) are presented. It is pointed out that the wettability is highly improved when the percentage of oxygen atoms incorporated in polystyrene surface reaches a high value. C - O, $\rm C = O$ and O - $\rm C = O$ are the main chemical bonds and it is found that the oxygen uptake happens during a very short time (about one second for the treatment duration time, i.e. about 10 ms on account of the duty factor value). A high oxygen rate is observed, correlated to the formation of a maximum $\Delta \theta/\theta_i$ plateau value (wettability). Reaction processes in the plasma bulk and on the polystyrene surface are proposed, taking into account the bond energies of polystyrene. As a consequence, the polystyrene treatment is interpreted assuming two steps for the reaction processes: in a first step, chemical bonds are broken by energy transfer from reactive particles to the surface and in a second step, new chemical bonds are generated. In this spirit, the main reactive plasma particles are described and surface reactions are proposed on the polystyrene surface.

PACS
52.75.-d - Plasma devices.
81.65.-b - Surface treatments.
82.80.Pv - Electron spectroscopy .

© EDP Sciences 2002

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