a leading global supplier of photoelastic modulators (PEMs), today announced
it was awarded a 2008 R+D 100 award from R&D Magazine for its Two Modulator
Generalized Ellipsometry Microscope (2-MGEM) Optical Anisotropy Factor Measurement
System. Dubbed the "Oscars of Invention" by the Chicago Tribune, the
R+D 100 awards recognize the 100 most technologically significant products introduced
over the past year.
The 2-MGEM solves a long-standing problem with the characterization of TRISO
(tristructural isotropic) nuclear fuel: how to best measure the optical anisotropy
of the pyrocarbon layers. Next-generation nuclear reactors require a fuel that
encapsulates the radioactive materials and can operate at much higher temperatures.
TRISO fuel solves this problem by encapsulating the radioactive kernel with
four layers of porous graphite, pyrocarbon, silicon carbide and pyrocarbon.
The quality of the pyrocarbon layers is related to the preferential orientation
of the graphite nanocrystals in the pyrocarbon layers. Since graphite is highly
optically anisotropic, its reflectivity will depend significantly on the polarization
state of the incident light. Thus, measuring this difference in reflectivity,
called the diattenuation or N, is a measure of this preferential orientation.
Additionally, it is important to measure the direction of the highest reflectivity,
called the principal axis angle or g. The 2-MGEM is a generalized ellipsometer
configured at near-normal incidence as a microscope, and can measure these two
parameters, as well as other parameters, over a 5 µm spot. Images of all
parameters are obtained by scanning the sample under the 2-MGEM.
The 2-MGEM represents a generational improvement over older Optical Anisotropy
Factor (OPTAF) systems. Not only does the 2-MGEM measure many more parameters
than OPTAF (8 versus 1), but also the accuracy in N is much greater (0.001 versus
0.01). By scanning, the 2-MGEM obtains images in N while OPTAF systems typically
measured a single point.
The 2-MGEM is a joint effort between Oak Ridge National Laboratory (ORNL) and
Hinds Instruments; ORNL created the design using Hinds Instruments' core PEM
technology. The instrument has been installed by the Institute for Transuranium
Elements (ITU), in Karlsruhe, Germany, part of the European Commission's Joint
"The 2-MGEM is a vast improvement over previous optical anisotropy measurement
techniques,” said Dr. Gerald E. Jellison, a senior scientist in the Materials
Science and Technology Division at ORNL. "For the first time, there's an
exceptionally repeatable, sensitive and accurate way to characterize the linear
diattenuation of pyrocarbon layers.”
“We are honored to have received such a prestigious award for the 2-MGEM,”
said Doug Mark, technical sales engineer with Hinds Instruments. “It’s
a nice testament to one of Hinds Instruments’ key capabilities: providing
custom instrumentation based on our core PEM technology. Our engineers worked
closely with ORNL and the ITU for well over a year, developing a practical,
commercialized solution that met the ITU’s exacting needs. The 2-MGEM
is a compact, turnkey instrument, complete with an intuitive interface, which
is optimized for nuclear fuel applications where the sample is completely enclosed
in a glove box.”
The Hinds Instruments 2-MGEM is easily adapted to a wide range of demanding
measurement applications including characterization of thin films, carbon compounds
and all 16 Mueller Matrix elements, from which diattenuation, retardation, direction
of principal axis, circular diattenuation and depolarization can be determined.
PEMs can be used at ultraviolet, visible and near infrared wavelengths. The
company also offers a complete selection of detectors, demodulators, polarizers
and PEM options to detect the small levels of ellipsometric polarization change
that can occur. The 2-MGEM is patented by ORNL (U.S. Patent No. 5956147) and
licensed by Hinds Instruments from UT-Battelle, LLC, management and operating
contractor of ORNL, under Patent License Agreement No. 972.