Local Structure Surrounding Implanted As + Ions in Polysulfone Films
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ABSTRACT Results from As K-edge XAFS studies on polysulfone films implanted with 50 KeV As' in the dose range of 1015 to 1016 ions/cm2 indicate that As reacts chemically with 0 atoms to form As-(3)O based molecular structures having As-O bond lengths equal to 1.81±0.02 A. In comparison to samples implanted in the dose range 1015 to 1016 ions/cm 2 , the molecular environment surrounding As in polysulfone implanted at 1017 ions/cm2 has additional structure beyond the nearest-neighbor 0 atoms.
INTRODUCTION Polymers constitute one of the most widely used class of materials in modern society, second only to metals: Past trends indicate an increase in demand in the future of polymer-based materials.' In particular, modification of polymers leading to their improved physical properties, such as mechanical strength and electrical conductivity, is certain to have a significant role in the future. One way in which modification of polymers is being accomplished is by ion implantation. In general, ion implantation in polymers causes cross-linking between chains and formation of carbonized structures as a result of weakening and breakage of chemical bonds. Results of studies on modifications of physical properties of polymers resulting from ion-implantation have been reviewed elsewhere."'3 An interesting consideration regarding ion implantation in polymers is the nature of chemical activity of implanted ions after coming to rest in the material. The molecular structure in the immediate vicinity of the implanted ionic species is a direct consequence of its chemical activity in the polymer. Because the structural environment surrounding the implanted ionic species in polymers is expected to be highly disordered and short-ranged, experimental techniques based on long-ranged atomic or molecular order are inappropriate for investigative use. One technique which is ideally suited for such studies is x-ray absorption fine structure (XAFS). To our knowledge, there have been no prior direct studies on structure surrounding implanted ions in polymers. We report here on first direct investigations of this kind showing that As' ions become chemically active upon implantation in polysulfone (Figure 1) as evidenced by bonding directly to oxygen.
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Figure 1. Polysulfone
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Mat. Res. Soc. Symp. Proc. Vol. 321. ©1994 Materials Research Society
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12000
12200
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Radial Distance (A)
Energy (eV)
Figure 2. As K edge x-ray absorption fine structure
Figure 3. Fourier transform of (XAFS).k 2, where k
spectra for 1015 (solid), 1016 (short-dash), 10"7
is the photoelectron wavenumber. The transform
(dot-dash) As÷/cm 2 implanted in polysulfone film samples, and
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