Magnetics Business & Technology - November/December 2024 - 18

RESEARCH & DEVELOPMENT
Magnetic Field Cancelling System Actively Eliminates Image Interference in Ferroelectric
Material Research in China
Unfortunately, the laboratory is just 70 meters away from a
sandwich-structure road network containing a busy metro line (underneath),
a high street and an overpass, which generates a large
magnetic field with a strong gradient, causing intolerable levels of
image distortion. Prof. Guo highlighted the scale of this problem:
" To put this issue into perspective, our Thermo Scientific Spectra
300 TEM is rated to withstand external fields of up to 20 nanoTesla
(nT), but the field generated by the subway is almost 4,000
nT - orders of magnitude higher than the acceptable limits. Such
intense and non-uniform magnetic field interference was, therefore,
severely compromising image quality, making our research
activities extremely difficult. While passive shielding provided us
with some protection against AC fields, we were still in need of a
solution for our DC field problems. "
Magnetic field interference can be a vexing problem for an
electron microscope operating at high levels of magnification,
limiting the quality and resolution of the images generated. One
mitigation, of course, can be to place the instrument in a " quiet "
location but that may not be practical nor best serve the workflow.
Fortunately, dedicated magnetic field cancelling systems can be
employed to actively eliminate external fields, allowing microscopes
to perform to their specifications, producing high resolution
images even in challenging locations.
A recent case study from Spicer Consulting Ltd. in the UK illustrates
how its dual (2x) magnetic cancelling system is assisting in
the atomic level study of ferroelectric materials at Hubei University
in China. In the report, Jinming Guo, Professor of Materials Science
& Engineering, describes the application of the dual SC24
system.
Ferroelectric materials are dielectric substances that remain
permanently polarized after the removal of an applied electric
field; they are routinely used in applications ranging from energy
conversion to data storage. The School of Materials Science
and Engineering at Hubei University has an active ferroelectric
research program, largely focused on understanding the relationship
between the microstructures and macroscopic properties of
these valuable substances.
Prof. Guo explained: " We
employ transmission electron
microscopy (TEM) to study
ferroelectric materials at the
atomic scale, allowing us to
gain valuable insights into the
key mechanisms responsible
for their unique characteristics.
For example, we can use TEM
to determine the polarization
vectors in perovskite unit cells.
The relative displacement of
ions that occur in these structures
is in the order of tens of
picometers, so such minute
changes are only detectable
at an instrument's highest
magnification and resolution
settings. "
SC24 Magnetic Field Cancelling System stabilizes the magnetic field by
dynamically creating nearly equal and opposite field changes, so that
microscope performance is improved. It automatically responds to
field changes within 100 µs.
Spicer's magnetic field cancelling systems protect electron beam
instruments including SEMs, transmission electron microscopes,
electron beam lithography tools and SEM-based metrology and
inspection tools. They are located in some of the world's leading
laboratories, universities, semiconductor manufacturing plants
and test facilities of electron and ion beam equipment manufacturers.
Professor Jinming Guo with the
newly installed Spherical Aberration-Corrected
TEM Spectra 300
Each system is comprised of a magnetic field control unit, one or
more magnetic field sensors and three multicore cables, which
are installed around the microscope for which the field is to be
cancelled. Three power amplifiers in the control unit drive currents
through the cables to create a field of the opposite sign to the
change in ambient field. The sensor measures the resulting field
and real time negative feedback reduces the ambient field by the
loop gain of the system. The systems can be added to or replace
passive magnetic field shielding. Dual sensors can be mixed to
create a virtual sensor " inside " the EM column, useful for large
TEMs or where there is a high field gradient.
For more info and to see the complete case study, visit www.
spicerconsulting.com.
18 Magnetics Business & Technology * November/December 2024
www.MagneticsMag.com
After installing the system, the external interference dropped to
well within the manufacturer specified range, and all values at X,
Y, Z directions ranging from height of 3 meters to 0.5 meters are
below 20 nanoTesla obtained by 4 detectors, allowing it to operate
at its highest magnification and resolution levels with no issues
from magnetic interference, reports Prof. Guo. " The SC24 system
is also incredibly easy to use, and it is remarkable to see the realtime
difference in image quality when switching the unit on and
off. "
http://www.spicerconsulting.com http://www.spicerconsulting.com http://www.MagneticsMag.com
Magnetics Business & Technology - November/December 2024

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