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The most common electron spectrometers today, especially in STEM instruments, are based on magnetic sector prism, such as Gatan GIF (Gatan Imaging Filter) systems. The post-column Gatan Image Filter (GIF) is a development of Gatan magnetic-prism PEELS. The GIF is installed underneath a conventional TEM system and has similar functions to an in-column energy filters. An important reason for its popularity is that they are not designed to be in-column, but can be attached as a peripheral to an existing EM column. An advantage of GIF design is that it combines both spectral and imaging capabilities.
By using quadrupole lenses Gatan introduced the Model 666 spectrometer to obtain spectra onto a YAG transmission screen and photodiode array in 1986. After that, the company has developed many versions of EEL spectrometers and GIF cameras. On the other hand, with a two-dimensional CCD array as the detector, Gatan imaging filters (GIFs) use both quadrupole and sextupole lenses to correct spectrometer aberrations.
The GIF camera is a setup of electron energy imaging filter which can be used to acquire EFTEM (energy filtered TEM) images and EELS (electron energy loss spectrum, e.g. PEELS mainly), by collecting a dispersed electron spectra on a CCD camera. The electrons are chromatically dispersed by a magnetic prism. The imaged line spectra are converted into a two dimensional line plot of electron intensity as a function of electron energy loss. Figure 4618a presents the structure of general Gatan PEEL spectrometers and Figure 4618b shows an advanced GIF Tridiem [1].
| Figure 4618a. Top image: example of Gatan PEEL spectrometers; Bottom image: schematic of spectrometer.
The components labelled
Q1–Q4 are quadrupole electron lenses. TE coolar stands for thermoelectric cooler. |
Figure 4618b. Schematic of GIF (Gatan Imaging Filter) Tridiem camera.
Table 4618. Examples of Gatan GIF cameras
|
|
Entrance Aperture (Example) |
Pixel |
Frequency of appearance in literature |
Reference examples |
Note |
|
|
|
|
2 |
|
|
|
|
|
|
1 |
|
|
|
|
|
|
1 |
|
Energy filter/spectrometer
|
|
|
|
1024 x 1024 pixels/pixel-size of 24 µm x 24 µm
|
1 |
|
slow scan CCD camera |
GIF2002 |
|
|
|
1 |
[2] |
|
The Gatan energy-loss spectrometers have been improved with an ultrafast electrostatic shutter so that we are able to record the entire spectrum, including both the low-loss and core-loss regions almost simultaneously, in milliseconds. Such a system (e.g. GIF Quantum) has advanced characteristics, e.g. fifth-order aberration correction, faster CCD readout, and even a 1-μs electrostatic shutter.
[1] Fast simultaneous access to multiple analytical TEM data streams with GIF Tridiem and STEMPack, Mike Kundmann , Gatan Inc. (2011)
[2] Koji Kimoto, Kazuo Ishizuka, Toru Asaka, Takuro Nagai, Yoshio Matsui, 0.23 eV energy resolution obtained using a cold field-emission gun and a streak imaging technique, Micron 36 (2005) 465–469.
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