Using polarized neutrons to determine the phase of reflection from thin film structures

It is now known that the phase of neutron specular reflection from a flat f ilm structure can be determined exactly using reference layers, even in the dynamical regime at small wavevector transfer where the Born approximation is not valid. By employing a single buried ferromagnetic layer and polariz ed beams, two complex reflection amplitudes for the unknown part of the fil m can be algebraically extracted, only one of which is physical. We describ e here a means of identifying the physical branch for actual polymer film d ata which fits the true reflection amplitude and produces the film's scatte ring length density profile directly and unambiguously. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.