Tech Briefs Magazine - November 2021 - PIT-21

Let's Get Small: New Argonne Method Greatly Improves X-Ray
Nanotomography Resolution
Argonne National Laboratory, Lemont, IL
I
t's been a truth for a long time: if
you want to study the movement
and behavior of single atoms, electron
microscopy can give you what
X-rays can't. X-rays are good at
penetrating into samples - they
allow you to see what happens
inside batteries as they charge and
discharge, for example - but historically
they have not been able
to spatially image with the same
precision that electrons can.
But scientists are working to
improve the image resolution of
X-ray techniques. One such
method is X-ray tomography,
which enables non-invasive imaging
of the inside of materials. If
you want to map the intricacies of
a microcircuit, for example, or
trace the neurons in a brain without
destroying the material you
are looking at, you need X-ray
tomography, and the better the resolution,
the smaller the phenomena you
can trace with the X-ray beam.
To that end, a group of scientists led
by the U.S. Department of Energy's
(DOE) Argonne National Laboratory
has created a new method for improving
the resolution of hard X-ray nanotomography.
(Nanotomography is Xray
imaging on the scale of nanometers.
For comparison, an average human
hair is 100,000 nanometers wide.) The
team constructed a high-resolution Xray
microscope using the powerful Xray
beams of the Advanced Photon
Source (APS) and created new computer
algorithms to compensate for issues
encountered at tiny scales. Using this
method, the team achieved a resolution
below 10 nanometers. According to the
researchers, these optics and algorithms
are applicable to other x-ray
techniques as well.
Using the in-house Transmission Xray
Microscope (TXM) at beamline 32ID
of the APS - including special lenses
fashioned at the Center for
Nanoscale Materials (CNM) - the
team was able to use the unique characThis
image of a plate with 16-nanometer-wide features was captured in resolutions of less than 10 nanometers,
allowing scientists to see the tiny defects in its shape. (Image by Vincent De Andrade.)
teristics of X-rays and achieve high-resolution
3D images in about an hour.
But even those images were not quite at
the desired resolution, so the team
devised a new computer-driven technique
to improve them further.
The main issues the team sought to
correct were sample drift and deformation.
At these small scales, if the sample
moves within the beam, even by a couple
nanometers, or if the X-ray beam
causes even the slightest change in the
sample itself, the result will be motion
artifacts on the 3D image of the sample.
This can make subsequent analysis
much more difficult.
A sample drift can be caused by all
kinds of things at that small a scale,
including changes in temperature. To
perform tomography, the samples also
must be rotated very precisely within the
beam, and that can lead to motion errors
that look like sample drifts in the data.
The Argonne team's new algorithm
works to remove these issues, resulting in
a clearer and sharper 3D image.
The team tested their equipment and
technique in several ways. First, they
captured 2D and 3D images of a tiny
Photonics & Imaging Technology, November 2021
Cov
ToC
plate with 16-nanometer-wide features
fabricated by Kenan Li, then of
Northwestern University and now at
DOE's SLAC National Accelerator
Laboratory. They were able to image
tiny defects in the plate's structure.
They then tested it on an actual electrochemical
energy storage device, using
the X-rays to peer inside and capture
high-resolution images. However, they
feel there is still room for this technique
to improve.
The capabilities of this instrument
and technique will improve with a continuing
research and development effort
on optics and detectors and will benefit
from the in-progress upgrade of the
APS. When complete, the upgraded
facility will generate high-energy X-ray
beams that are up to 500 times brighter
than those currently possible, and further
advances in X-ray optics will enable
even narrower beams with higher resolution.
After the upgrade, they will push
for eight nanometers and below, hoping
this will be a powerful tool for research
at smaller and smaller scales.
For more information, contact Leslie
Krohn at lkrohn@anl.gov.
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Tech Briefs Magazine - November 2021

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