X-ray Reflectivity and Crystal Truncation Rods
X-ray reflectivity is the direct analogue of X-ray crystallography for interfacial
systems.
The X-ray scattering is in the form of “crystal-truncation rods” (CTRs) that
are
continuous rods of intensity connecting Bragg peaks along the surface normal
direction.
This shape derives from the loss of translational invariance along the surface
normal
direction and the crystalline order within the surface plane (resulting in ‘streaks’
of
intensity along the surface normal direction that are otherwise sharp within
the surface
plane). The variation of scattering intensity vs. Q along these CTRs is directly
sensitive
to the interfacial structure. The ability of X-rays to readily penetrate fluid
layers makes
it possible to directly define the interfacial structure through in-situ measurements.