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Neutron reflection (NR) has been utilized to study the physical structure of the light-emitting polymer poly[2-(2'-ethylhexyloxy)-5-methoxy-l,4-phenylenevinylene) (MEHPPV). Films of soluble MEHPPV (S-MEHPPV) and insoluble MEHPPV (I-MEHPPV) prepared via a chloro precursor polymer were investigated. For S-MEHPPV spin-coated films were found to contain two layers, one of low-density and thickness of ≈ 1360 Å with the second layer being thinner, ≈240 Å, but denser. The thicker layer only covered about 30% of the substrate surface. In contrast, I-MEHPPV formed uniform films across the substrate. We found that during the thermal conversion of the chloro precursor polymer the film thickness was maintained and it was only on cooling that the films contracted. Importantly, the thermal expansion and contraction of I-MEHPPV was reversible. NR showed that thermal annealing of I-MEHPPV had little affect on the films physical structure while for S-MEHPPV only the thinner layer was changed and became more dense. Photoluminescence spectra of S-MEHPPV before and after annealing showed that the densification observed in the neutron reflection measurements was mirrored in the emission properties of the polymer film. [ABSTRACT FROM AUTHOR]

The article presents a theoretical study of the various properties of the [pi]-conjugated phenyl-cored thiophene dendrimers. These dendrimers are found to be the most commonly used for optoelectronic devices for photovoltaic applications.

We have investigated, using temperature-programed desorption, high-resolution electron energy loss spectroscopy and low-energy electron diffraction, the formation and decomposition of the suboxides of Ru which form after exposure of NO2 to the Ru(001) surface. The NO2 (radical) molecule is not limited by any significant kinetic barrier to its decomposition even at the high oxygen coverages considered. It is this barrier which restricts measurable rates of dissociative chemisorption of O2 to surface coverages below 0.5 under ultrahigh vacuum conditions. We have identified a subsurface state which is occupied after saturation of the surface overlayer. Utilizing isotopically labeled molecular oxygen and a detailed mixing/segregation model, we have been able to elucidate and quantify the nature of mixing between the surface and subsurface oxygen as a function of total oxygen uptake. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have investigated, using electron energy loss spectroscopy, the phonons on the Ru(001) surface that are rendered dipolar active in the specular direction by virtue of ordered p(2×2) and p(1×2) oxygen adatom overlayers. We show that two surface phonons are present in the specular EEL spectra, and we verify, using group-theoretical arguments that only two surface modes can be dipolar active. This analysis also allows polarizations to be assigned to these modes. Implications for the reconstruction of the Ru(001) surface induced by the oxygen adatom overlayers are discussed. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]