Cf. Majkrzak et al., Experimental demonstration of phase determination in neutron reflectometryby variation of the surrounding media, PHYSICA B, 283(1-3), 2000, pp. 248-252
We have recently shown that it is possible to unambiguously determine the r
eal part of the complex reflection coefficient for a thin film structure by
measuring the neutron specular reflectivities for the him in contact with
two different backing or two different fronting media, thus simplifying the
reference methodology of phase determination and making it more practical.
Here we demonstrate the technique in two different experiments. In the fir
st, one backing medium is air, the other, heavy water. In the second, sapph
ire and silicon serve as two different fronting (incident) media. In additi
on, we show how the two possible branches of the imaginary part of the refl
ection coefficient inferred by the real part, while not required for invert
ing the data to find the film structure, can be a sensitive diagnostic for
indicating whether the him of interest is inhomogeneous on a transverse sca
le comparable to the neutron coherence length. This is especially important
in avoiding misinterpretation of data which result from the incoherent ave
rage of reflectivities from large-scale heterogeneities. (C) 2000 Elsevier
Science B.V. All rights reserved.