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META'L ATOM ROUTES TO METAL-BASED CLUSTERS IN POLYMERS

MARK P. ANDREWS, MARY E. GALVIN, AND SHARON A. HEFFNER AT&T Bell Laboratories, 600 Mountain Avenue, Murray Hill, NJ 07074

ABSTRACT Past syntheses of polymer composites have largely evolved from chemical reduction or thermal decomposition of organometallic or inorganic precursor molecules in polymers, or plasma and thermal co-deposition of metal vapors and carbonaceous free radicals. Our approach involves the site-specific capture of metal atoms deposited in vacuum to give isolated, high energy mononuclear organometallic centers within a polymer film. These centers can be converted at ambient or sub-ambient temperatures (ie, below the polymer glass transition temperature) to, for example, metal oxide microclusters. We describe the results of our studies of a prototypical system involving chromium atoms and their conversion to corundum-type oxide microclusters in arene-functionalized polymer films. Thus Cr was deposited into 150 K liquid tetrahydrofuran solutions of polystyrene or poly(styrene-isoprene-styrene) triblock, spun in vacuo as thin films on the surface of a rotating glass cryostat. Evidence from epr spectrscopy shows that the resulting polymer-anchored (inter/intra-chain) bis(arene)Cr sandwich complex is locally mobile in the macroscopically rigid film at room temperature. The Cr atom is discharged from the rings by subsequent reaction with oxygen diffused into the film. Although ce-Cr 2 0 3 is a classic twosublevel antiferromagnet that is not epr active above 308 K, we observe an intense signal even at 77 K in these films. Cr 2 03 microclusters are indicated, and these are confirmed by in situ measurements of the oxidation and aggregation process. The metal atom methodology has also been used to synthesize silver microsphere/polymer composites. With quadratic electrooptic phase modulation, these composites were found to show a third order susceptibility enhanced by coupling the dipolar surface plasmon mode of the particles with incident light.

INTRODUCTION Other lectures in this Symposium have provided some elegant demonstrations of the reactivity and unusual electronic structure of gas phase cluster molecules. For materials applications, these studies also raise questions as to whether or not cluster science will mature into its own (quantum) technology, be subsumed under the developing cluster ion beam processing technologies, or contribute in more subtle ways by mediating our understanding of the role that size quantization plays in electron transport, magnetic, and optical processes. Although cluster science is an emerging discipline, such questions are only premature if we

Mat. Res. Soc. Syrup. Proc. Vol. 131.

1989 Materials Research Society

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insist on extrapolating directly from the gas phase to current trends in technology, or linking too literally, technology's material manifestations in processing and devices. Cluster science may ultimately drive new discoveries, conceptual and material, in areas like structural composites (fibers,