A method that combines thin film deposition and physical masking techniques has been used for the parallel synthesis of spatially addressable libraries of solid-state materials. Arrays containing different combinations, stoichiometries, and deposition sequences of BaCO(3), Bi(2)O(3), CaO, CuO, PbO, SrCO(3), and Y(2)O(3) were generated with a series of binary masks. The arrays were sintered and BiSrCaCuO and YBaCuO superconducting films were identified. Samples as small as 200 micrometers by 200 micrometers in size were generated, corresponding to library densities of 10,000 sites per square inch. The ability to generate and screen combinatorial libraries of solid-state compounds, when coupled with theory and empirical observations, may significantly increase the rate at which novel electronic, magnetic, and optical materials are discovered and theoretical predictions tested.

The irradiation of oxygen-free, face-centered-cubic C 60 films with visible or ultraviolet light phototransformed C 60 into a different solid phase. Results from laser desorption mass spectroscopy, scanning electron microscopy, Raman and infrared spectroscopy, optical absorption, and luminescence indicate that a photopolymerization of the fullerene molecules within the film occurred.

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We report the first ellipsometric measurement of the fundamental optical constants (n,k) of C60 films deposited on Si(100) and Au overcoated Si(100) substrates. We obtain a highest occupied molecular orbital-lowest unoccupied molecular orbit (HOMO-LUMO) gap value of 2.3 eV, slightly larger than the gap values obtained from the x-ray photoelectron spectroscopy and electron-energy-loss spectroscopy experiments. The structure observed in the UV is discussed in terms of single-electron excitations across the HOMO-LUMO gap.

Communications ADVANCED 2,5-DMNPAA (Table 1, Fig. 1b). However, the "improvement factor" varies with temperature due to the fact that the Tgs of the two composites are different (17 "C and 3 "C, respectively; Table 1). For a better comparison, we used the reduced temperature TR = T -Tg as a reference. In doing so, the improvement factor is constant at about 11-12, demonstrating the significant progress achieved here.A study of the temperature dependence of the shelf lifetime performed on the eutectic mixture and the composite using only 2,s-DMNPAA revealed the following regimes: i) Very long lifetimes are observed for TR < 30 K, which is attributed to the fact that, when the temperature is close to T,, the diffusional mobility of the small molecules within the polymer matrix is strongly reduced because the polymer backbone freezes and the internal free volume is reduced. ii) The shelf lifetime drops by more than one order of magnitude on going to temperatures TR > 40 K. In this regime, Arrhenius behavior i s observed in both cases, which is ascribed to thermally activated diffusion of the chromophore molecule^.^'^^ The activation energy Ea derived from our data is almost identical in both cases (Table 1). The value for pure 2,5-DMNPAA is a little higher than that for the eutectic mixture, which is probably due to its slightly higher Tg (Table 1). The most important result, however, is that the Arrhenius prefactor A is 25 times smaller for the eutectic composition than for pure 2,5-DMNPAA. As discussed above, we attribute this to the fact that for the eutectic composition the interactions between the dye molecules are the weakest for any binary mixture of the two DMNPAA isomers. The temperature-dependent studies, thus, unambiguously demonstrate the strongly reduced phase-separation tendency in the eutectic composite, yielding the best possible long-term device stability for the chromophores used.In conclusion, we obtained PR polymer devices with strongly improved shelf lifetimes by using a eutectic mixture of two isomeric EO chromophores, 2,S-DMNPAA and 3,S-DMNPAA. At this point, one can only speculate on the shelf lifetimes at room temperature, since a dramatic increase in the lifetime occurs for temperatures around Tg and below. As a matter of fact, PR devices using the eutectic composition remained clear for more than 18 months under arbitrary laboratory conditions, including peak temperatures of up to 45 "C, whereas all other devices showed at least some scattering or had even lost their transparency completely. Unlike other attempts to increase the lifetime of highly-doped organic PR devices,[82'0,"1 the PR performance of our improved devices was found to be the same as for the best materials previously known. This new concept may be extendible to mixtures of other chromophores as well.