AVS 56th International Symposium & Exhibition
    Applied Surface Science Friday Sessions
       Session AS-FrM

Paper AS-FrM7
Structure and Composition of Plasma Treated Polystyrene Surfaces Determined by Complementary Analytical Techniques

Friday, November 13, 2009, 10:20 am, Room C2

Session: Practical Surface Analysis
Presenter: P. Mack, Thermo Fisher Scientific, UK
Authors: P. Mack, Thermo Fisher Scientific, UK
R.G. White, Thermo Fisher Scientific, UK
T. Carney, Thermo Fisher Scientific, UK
E.H. Lock, Naval Research Laboratory
S.G. Walton, Naval Research Laboratory
D.Y. Petrovykh, Naval Research Laboratory and University of Maryland
Correspondent: Click to Email
Plasma-treatment of polymers produces materials that exhibit a wide range of surface compositions, properties, and structures. A new low-energy plasma treatment method aims to modify only the top few nanometres of polymer films, producing surfaces that pose challenges and offer opportunities for quantitative surface analysis. Using a variety of complementary analytical techniques maximizes the information available to the analyst.

High-quality polystyrene films were spin-coated onto silicon substrates and treated with low-energy plasmas generated by electron beams in different environments, including oxygen, nitrogen, and SF6. Atomic Force Microscopy was used to determine surface roughness and contact angle measurements were used to determine the hydrophobicity of the plasma-modified surfaces. The Thermo Scientific Theta Probe, an XPS system that provides a unique parallel-detection capability for angle-resolved XPS (PARXPS) and REELS measurements, was used to investigate the chemical and structural transformations produced by different plasmas.

The chemical changes produced by plasma treatments were examined by high energy resolution XPS, and PARXPS data were analyzed using maximum-entropy calculations to obtain non-destructive depth profiles of these chemical changes. Complementary REELS measurements were used to examine the level of carbon unsaturation at the uppermost surface of each of the plasma modified polystyrene films. The non-destructive PARXPS depth profiles were also compared with high-resolution low-energy ion sputter profiles measured in a Thermo Scientific K-Alpha system. The depth profiles obtained using several surface analysis methods confirmed that the chemical changes produced by the low-energy plasma modification are confined to the top 2–3 nm of the polymer surfaces. The observed depth distribution of unsaturated carbon species is also consistent with polystyrene surfaces undergoing “hydrophobic recovery” after treatments in oxygen and nitrogen plasmas.

This work was supported by the Office of Naval Research.

E. H. Lock is NRL/NRC Postdoctoral Research Associate.