AVS 51st International Symposium
    Surface Science Thursday Sessions
       Session SS3-ThM

Paper SS3-ThM8
Atomic Oxygen Etching of Phosphorous-containing Polymer Surfaces

Thursday, November 18, 2004, 10:40 am, Room 213B

Session: Halogen and Oxygen Surface Reactions and Etching
Presenter: H. Fairbrother, Johns Hopkins University
Authors: H. Fairbrother, Johns Hopkins University
G. Wolfe, Johns Hopkins University
J. Torres, Johns Hopkins University
Correspondent: Click to Email
The aerospace industry has recently developed phosphorous-containing polymers that can resist the severely oxidizing environment encountered by vehicles traveling in Low Earth Orbit (LEO). Post-flight analysis shows that upon exposure to atomic oxygen (AO) present in LEO, these polymers form a self-passivating phopshate like (P@sub x@O@sub y@)overlayer that hinders etching of the underlying bulk. The protective capabilities of these phosphorous-containing polymers, whose synthesis is complex and expensive, derive solely from the chemical characteristics of the near surface region rather than the bulk. In an attempt to develop a more cost-effective and generally applicable method of creating polymer surfaces with the ability to resist etching by AO, we have initiated studies on polyethylene (PE) ion-implanted with trimethylphosphine. X-ray photoelectron spectroscopy reveals that under ambient conditions the P-implanted PE readily oxidizes to form phosphate-containing bonds at the surface. The thickness of the phosphate layer increases with a logarithmic dependence on air exposure, indicating that the growing phosphate structure limits diffusion of oxygen species through the near-surface region. Subsequent exposure of these films to AO leads to carbon etching from the surface, leaving behind a phosphorous-rich overlayer. Related studies of thin films used to simulate the P-implanted PE surface show that these phosphate structures remain thermally stable under vacuum conditions up until ~650 K. Results from atomic force microscopy studies will also be presented to illustrate the morphological changes in the polymer surface that accompany air oxidation and AO exposure.