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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.
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.
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:
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 MLLS 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 left. 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 be 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.
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:
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© Gatan, Inc. 2007. All rights reserved. |