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Fast simultaneous access
to multiple analytical TEM data streams with GIF Tridiem
and STEMPack |
by
Mike Kundmann , Gatan Inc.
You
do analytical TEM to reveal important micro- and nano-scale
details of your samples. You need all the structural and compositional
information you can get and you need it in short order, preferably
within a single, easy-to-use data acquisition and analysis
environment.
So
what’s the best way to achieve such analytical TEM bliss?
The answer is a complete and fully integrated analytical TEM
data acquisition system from Gatan.
Gatan
has been developing spectrometers and energy filters, CCD
cameras, STEM detectors, and data acquisition and analysis
software for the past 25 years. We have deep expertise in
the electron optics of TEM energy filters, the physics of
electron energy loss spectroscopy (EELS), the engineering
challenges of high-performance electron detectors, and the
design of robust and highly capable software for instrument
control, data capture, and analysis.
Our GIF Tridiem and STEMPack products represent the culmination
of our many years experience in this field. They are Gatan’s
current state-of-the-art offerings for high-performance analytical
TEM work.
The
GIF Tridiem energy filter adds the full range of EELS analysis
techniques to your analytical TEM system, from high-resolution
EELS work to rapid elemental mapping via energy-filtered TEM
(EFTEM) imaging. STEMPack further enhances these capabilities
by providing rapid, simultaneous access to the entire gamut
of analytical STEM signals from STEM EELS and EDS to HAADF
Z-contrast STEM imaging and energy-filtered convergent-beam
electron diffraction (CBED). The Gatan Microscopy Suite (GMS)
software system ties it all together, providing integrated
access to all these techniques and a powerful data handling
and analysis environment. GMS helps you quickly distill these
various data streams down to the critical specimen information
you seek.
Read
on for further details about how GIF Tridiem and STEMPack
help you get the most out of your analytical TEM/STEM instrument.
GIF Tridiem
The
GIF Tridiem is Gatan’s 3rd-generation post-column energy
filter. It combines 3rd-order spectrometer aberration correction
with a multi-port, high-speed, high-resolution CCD sensor
to yield a system that defines the current state-of-the-art
in the capture of highly detailed EELS and EFTEM data sets
with maximum throughput. The GIF is particularly well suited
for generating the rich 3-dimensional data sets known as spectrum
images. The low residual aberrations of the GIF Tridiem enable
efficient acquisition of EFTEM image series from specimen
areas as large as 5-10 microns with energy-selecting slit
width as small as 3-5 eV. A scan through the EFTEM series
captured in the movie below illustrates the rich specimen
details that are revealed by such a data set.
Click to download movie
Note
the numerous contrast changes that occur as the selected electron
energy loss is varied. These are due to the characteristic
EELS signals of each component of this sample. The power of
an EFTEM spectrum image stack, like the one above, is that
it captures the actual EELS spectral details as well as the
image information. By extracting subsets of this data set
along the energy dimension, the nature of the EELS signals
can be clearly identified, extracted, and quantified. The
movie below illustrates the extraction of quantifiable EELS
spectra from the above EFTEM SI data cube using the spectrum
image exploration tools of the GMS software.
Click
to download movie
Multi-spectral
EELS analysis functions within GMS, both routine power-law
background subtraction as well as least-squares fitting to
reference spectra, allow you to transform the intensity variations
of these EELS signals into elemental and chemical maps such
as these:
Additional
GMS tools, such as Color Mix, help you combine these elemental
maps into revealing compositional displays of your samples,
like this:
GIF – The Post-Column
Advantage
The
GIF is designed to mount to the bottom of virtually any analytical
TEM/STEM column. This means you are free to choose your TEM
based on whatever characteristics are most important to you:
manufacturer and operation interface, type and resolution
of beam source, illumination system and STEM probe properties,
specimen stage, objective lens parameters, and aberration
corrector configuration.
The
GIF’s placement well after the key TEM imaging lenses
makes its operation highly independent of the particular operating
mode of the microscope. For example, you may freely optimize
the illumination focus and intensity without having to make
any compensating adjustments to the GIF optics. This is not
true for some in-column filter designs.
The
largely independent status of the GIF makes it easy for you
to deploy it in a broad range of analytical applications and
greatly simplifies its setup and operation compared to in-column
filters. In addition, the GIF comes with sophisticated performance
characterization and tuning software that ensures optimum
adjustment of the GIF on a routine basis. This patented software
(US patent 5,798,524) makes use of unique, integrated alignment
tools within the GIF and runs automatically with a single
mouse click. No other energy filter system can offer such
sophisticated diagnostics for trouble-free day-to-day operation.
The
diagram below highlights further key advantages of the GIF
post-column design. Note that any energy filter system, post-column
or in-column, consists of three primary sections: 1) pre-filter
optical configuration, 2) dispersion and focusing section,
and 3) projection section. The GIF design has clear advantages
in all three of these sections.
The
GIF allows for a very roomy and flexible pre-filter optical
configuration. The chief benefit of this is that multiple
pre-filter detectors can be deployed, each optimized for a
specific TEM task or modality. These include a fast electronic
camera to serve as a digital viewing screen, a high-resolution
CCD camera for scientific-grade capture of TEM images and
diffraction patterns, a high-angle annular dark-field (HAADF)
detector for Z-contrast STEM, a mid-angle ADF detector for
diffraction-contrast STEM, and a BF detector for phase-contrast
STEM. As discussed in the section on STEMPack, below, the
flexible STEM detector configuration is particularly important
for enabling multiple simultaneous STEM signal capture and
practical STEM EELS and EDS spectrum imaging with spatial
drift compensation. Note that the in-column design severely
limits the possibilities for deploying pre-filter CCD cameras
and STEM detectors.
In
the dispersion and focusing section, the GIF is again ahead
of the game because of its very simple beam path (a single
90-degree bend) and its ability to accommodate several multipole
lenses for compensating filter focusing aberrations (inherent
to any magnetic dispersing element, regardless of its mounting
position or effect on the beam path shape). The simplicity
of the GIF filter design is what makes its automated performance
evaluation and tuning software a practical reality. All other
commercially available energy filter systems either neglect
to compensate filter aberrations (thus making it necessary
to block out large fractions of the EELS signal with small
entrance apertures) or require you to trust and live with
a fixed compensation set up during initial installation of
the TEM column.
Finally,
the GIF’s projection section design is the only one
fully cognizant of the inherent loss of azimuthal symmetry
due to the filter’s dispersing element. From its inception,
the GIF has always deployed multipole lenses in this important
image-forming section of the energy-filter optics. This allows
precise compensation of both 1st and 2nd order image distortions
(again via our patented autotuning software) and yields optimized
coupling of the EELS spectral intensity distribution to the
rectangular geometry of the CCD detector. Virtually all in-column
filter systems still use round lenses for the projection section,
a serious limitation on their performance.
In
short, Gatan has been working on EELS spectrometer and TEM
energy filter technology for 25 years. Throughout that time
we have been learning the ins and outs of robust EELS and
EFTEM system design and we have been refining and improving
our GIF products with that hard-won knowledge. We know what
it takes to quickly and efficiently bring you critical information
about your TEM samples through high-quality EELS and EFTEM
data.
Gatan
gets it!
More
Information
For
further details about our GIF Tridiem line of energy filter
products, please follow the links below
:GIF
Tridiem
GIF Tridiem ER
If
you would like to learn more about the research and development
effort behind this product, please refer to the following
publications:H. A. Brink, M.M.G. Barfels, R.P. Burgner, B.N.
Edwards, Ultramicroscopy 96 (2003) 367.
G. Kothleitner and F. Hofer, Micron 34 (2003) 211.
STEMPack
STEMPack
is Gatan’s solution for high-quality digital STEM imaging
optimized for simultaneous EELS data capture. With the addition
of optional components for Z-contrast STEM detection and EDS
spectrum capture (from third-party systems), STEMPack provides
efficient access to all possible STEM-mode signals within
Gatan’s integrated GMS software environment. Furthermore,
STEMPack adds powerful line scan and spectrum imaging (SI)
capabilities, with automatic specimen drift correction, using
EELS and/or EDS signals, simultaneously, if desired. It includes
the advanced spectral analysis tools of GMS, allowing you
to extract compositional line profiles and maps (via EELS
and EDS elemental signals), as well as maps of electronic
structure variations (via linear least-squares fits to fine
structure in EELS reference spectra).
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One
of the key benefits of Gatan’s post-column spectrometer
and energy filter designs is the ability to accommodate
multiple detection systems within the pre-filter optical
configuration, as illustrated in the diagram at right.
This is particularly advantageous for multi-mode STEM
work.
Optimum
EELS signal capture with the 1 or 2 mm entrance aperture
of Gatan’s Enfina spectrometer or GIF Tridiem
energy filter requires STEM camera lengths in the 50
– 100 mm range (at the entrance aperture plane).
When such a camera length is selected, the space roughly
10 cm above the spectrometer/filter entrance aperture
allows for ideal placement of several cameras and detectors.
A
fast, retractable pre-filter CCD camera in this space
makes an excellent Ronchigram viewing system for STEM
alignment and aberration tuning.
Both
high-angle and medium-angle annular dark field STEM
detectors are best mounted just above the GIF entrance
aperture for simultaneous capture of Z-contrast and
diffraction-contrast STEM signals. By making sure the
STEM detectors are on-axis with the filter entrance
aperture, the bright-field portion of the STEM signal
can captured and harnessed in several different ways.
A
bright-field STEM detector can be inserted just below
the final ADF detector to yield simultaneous phase contrast
STEM images with the Z- and diffraction-contrast images.
Retracting the BF detector and activating the EELS mode
of the filter gives EELS spectra with the DF STEM images.
Finally, switching the filter to imaging mode yields
energy-filtered convergent-beam diffraction patterns
that can be captured with the CCD camera at the end
of the GIF (not shown). |
Note
that in any of the STEM data collection modes described above,
the EDS detector can always be activated to yield fluorescent
X-ray signals, simultaneously with any others, as the probe
is scanned across the sample.
For
example, to collect EELS and EDS spectrum image data, one
begins by taking a dark-field overview image (Z-contrast or
diffraction contrast or both simultaneously) of the specimen
area of interest, as shown below. This diffraction-contrast
ADF STEM image depicts the interface region between the dielectric
and metal contact components of a capacitor structure. Using
this survey image as a reference, one next defines the precise
region from which to acquire a systematic EELS and EDS spectrum
image data set, as indicated by the green box. Next, the number
of samples (within the x and y dimensions of the green box)
and the dwell time per sample are specified. Finally, a reference
area to be used for tracking spatial drift (if any) is identified,
as shown by the yellow box. From there, the data acquisition
proceeds automatically, yielding two 3-dimensional data sets
(covering the x, y, and E dimensions for both EELS and EDS
signals)
The resulting data sets are shown in
the movie below, which illustrates the use of GMS spectrum
imaging tools to explore EELS and EDS SI data sets, post-acquisition,
either on-line at the microscope or off-line in your office.
Further GMS tools enable you to extract both EELS and EDS
elemental maps from these complementary signals.
Click
to download movie
The
image pair below gives another example of simultaneous signal
capture with STEMPack. The detector configuration made possible
by the post-column filter geometry permits simultaneous capture
of Z-contrast and diffraction-contrast dark field STEM images
from a single scan
.
In brief, STEMPack is designed to work hand-in-hand with Gatan’s
Enfina and GIF products to bring you the maximum sample information
with every scan of the STEM probe.
Gatan
gets it!
More
Information
For further details about the STEMPack product and its components,
please follow the link below:
STEMPack
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