"Resonant X-Ray Scattering from Antiferroelectric and Ferrielectric
Liquid Crystal Films and Devices"
Ron Pindak
Bell Labs, Lucent Technologies
Abstract
The chiral smectic-C (SmC*) phases are comprised of fluid-like layers of
tilted molecules exhibiting a spontaneous in-plane polarization oriented
perpendicular to the molecular tilt direction. Since this polarization
is coupled to the tilt direction, variations in the interlayer ordering
of the tilt direction changes the electro-optic response of the
different SmC* phases from ferro to ferri to antiferroelectric. The
interlayer tilt variations have a periodicity short compared to optical
wavelengths so cannot be directly measured using optical techniques.
Moreover, because these phases lack three-dimensional positional order,
the interlayer tilt ordering cannot be observed using conventional x-ray
scattering. Nonetheless, if the energy of the incident x-rays matches an
absorption edge of one of the atoms in the core of the molecule, then
the atomic scattering factor is a tensor and orientational periodicities
will diffract x-rays with a polarization state that can differ from that
of the incident x-rays. We used such resonant x-ray measurements to
determine the structure of the various SmC* phases. These measurements
were applied to liquid crystals both as free-standing films as well as
confined between conducting glass plates as utilized in display devices.
Elizabeth K. Mann