Synthetic Metals

X-ray absorption in polymers

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We report on the results of a series of X-ray absorption experiments utilizing synchrotron radiation on the polymeric conductors, brominated (SN)x, and (CH)x doped with AsF5. These experiments employ the K-edges of bromine and arsenic at 13.47 keV and 11.89 keV, respectively, for the study of the short range order in the vicinity of the source atom. This information is supplied by the backscattering effect of the surrounding coordination shells on the ejected K-shell electron (EXAFS). In addition, the edge region fine structure is studied to deduce information on the molecular species present (Br2 orBr3- in (SN)x, AsF5 orAsF6- in (CH)x). Experiments were performed over a range of temperatures between 5 K and room temperature to check the relevant distance parameters and charge transfer for their temperature dependence. Nearest and second nearest neighbor distances are given for the bromine species in (SN)x, while an average AsF distance for the arsenic species in (CH)x is found to be somewhat larger than for AsF5 gas molecules. The advantages of X-ray absorption spectroscopy over other methods such as XPS and UPS for the resolution of chemical questions in partially disordered systems are stressed, particularly, the bulk sensitivity of X-ray absorption vis-à-vis the surface escape depth problems of the other techniques. © 1980.