A. Mansour

The Form of the Enriched Surface Layer in Polymer Blends

The concentration profile at the surface in blends of deuterated and protonated polystyrene (d-PS and PS) is inferred from measurements of neutron reflectivity and secondary-ion mass spectrometry, using constraints provided by forward recoil spectrometry and X-ray reflectometry results on the same samples. The surface is enriched in d-PS, the volume fraction and the decay length of which are in good agreement with the predictions of mean-field theory but the form of the profile shows small, but statistically significant, deviations from that predicted by the theory.

Antiferromagnetic interlayer exchange coupling in sputtered Fe/Cr multilayers: Dependence on number of Fe layers

The antiferromagnetic arrangement of the magnetic moments of Fe layers in sputtered Fe/Cr multilayered structures is directly demonstrated from polarized neutron reflectometry studies. Such an antiferromagnetic interlayer exchange coupling is also consistent with magnetization studies on a series of [Fe/Cr]N structures. A remanent magnetization is observed for structures containing an odd number of bilayers but no remanent moment is found for an even number of bilayers. By examining the dependence of saturation field on the number of bilayers it is shown that the antiferromagnetic coupling strength is independent of the number of bilayers and is the same for superlattice and sandwich structures.

Surface enrichment in polymer blends — A neutron reflection test

Abstract In polymer melts of protonated and deuterated polystyrene (PS and d-PS) surface segregation of d-PS occurs at temperatures and compositions in the one phase region close to the coexistence curve for phase separation. Neutron reflection is capable of obtaining detailed information on surface segregation, as corroborated by a test on a polymer blend containing 10% volume fraction of d-PS where a thermal treatment caused a surface enrichment of d-PS up to 28%.

Magnetic field penetration into the high temperature superconductor YBa2Cu3O7−x

The penetration depth of a magnetic field into a superconducting YBa2Cu3O7−x film was measured by polarized neutron reflection. The sample comprised an epitaxial film with the c-axis of its orthorhombic structure perpendicular to the films surface. Measurements at 14 K showed that a magnetic field (parallel to the surface) penetrates into the surface over a depth of 1400 A.

On the Scale of Diffusion Lengths Observable by Neutron Reflection: Application to Polymers.

A systematic approach has been applied to neutron reflectivity data to study interdiffusion across an interface. It is shown that with this technique it is possible to probe interface broadening from {approximately}10 {angstrom} to upward of 200 {angstrom}, the upper limit being already within the range of observation of other techniques such as Rutherford backscattering spectrometry (RBS), forward recoil spectrometry (FRES) and secondary ions mass spectroscopy (SIMS). As example is analyzed the interdiffusion of a bilayered polymer system: a deuterated polystyrene (d-PS) layer on protonated polystyrene (h-PS). 7 refs., 2 figs.

Neutron Reflection Study of Surface Enrichment in an Isotopic Polymer Blend

We have measured neutron reflectivities from the surface of films of deuterated polystyrene (d-PS) and protonated polystyrene (PS) blends before and after annealing, and used the results to determine the concentration versus depth profile of the films. After annealing, the surface is enriched in d-PS, with a surface excess proportional to the bulk concentration of d-PS, in agreement with previous measurements using forward recoil spectrometry[l]. The decay of the enhanced concentration into the bulk occurs over a length approximately equal to the bulk correlation length (∼200 A), in closeagreement with that predicted by current mean-field theoryometry[2]. However, the agreement between the experimental reflectivity curves and the fitted curves is not completely adequate. Figure 1, a plot of k 4 R against k, demonstrates thi point for a 15% d-PS sample. The dashed line is the best fit assuming the mean field profile. The inset shows the corresponding concentration profile and a trial profile, solidline, which fits the data much better. The small deviation between the theoretical and trial profiles may be due to the assumption of the theory that surface interactions leading to enrichment is short ranged.