Composition profiling in a binary polymer blend thin film using polarized neutron reflectivity

The concentration profile in an ultra-thin film (film thickness d = 435 Ang strom) of a high molecular mass-poly(isoprene)/deuterated poly(butadiene) b lend is measured in the bulk system's miscible region with a new polarized neutron reflectivity method. By using a buried ferromagnetic layer inside t he wafer and a polarized neutron beam, it is possible to obtain the neutron specular reflection amplitude A including its phase angle phi. Conventiona l reflectivity measurements only determine the reflected intensity I = A(2) which does not contain information on the phase angle. Only the knowledge of the phase angle allows an unambiguous determination of the neutron scatt ering length density profile of the film. The scattering length density pro file thus obtained reveals poly(isoprene) segregating symmetrically to the polymer/air and polymer/Si interfaces. The adsorption profile at both inter faces can be approximately described using an exponential- or tanh-function with a decay constant smaller than the bulk correlation length.