Resonant x-ray scattering techniques exploit the characteristic absorption spectra of molecular states (NEXAFS) to get access to element and bond specific information beyond the pure electron density distributions. In particular, the orientation of organic functional groups is encoded in the linear dichroism around the carbon K edge.

Using this scattering contrast molecular orientation in soft matter thin films can be probed by polarization-dependent resonant soft x-ray reflectivity in s- and p-incidence. In contrast to conventional spectroscopic techniques, the reflectivity data carries the full depth dependent information on the orientational profile between the free surface and the substrate.

Reflectivity data, collected on side-chain liquid crystalline polymer (LCP) thin films in which stiff elongated side-groups tend to align parallel to the surfaces, show pronounced linear dichroism that carries information on the side-group orientation. Measurements on films of amorphous polymers demonstrate the sensitivity of the technique to chain orientation in buried layers, which is inaccessible by other techniques.

Figure: Experimental (circles) and calculated (solid curves, Berreman formalism) reflectivity for a LCP thin film on silicon in s- (top) and p-incidence (bottom) at 284.8 eV. The Fresnel reflectivity of the substrate (dashed curve) is added for reference.