The Tecnai TF30 ST, is a high-resolution analytical transmission electron microscope. The small electron wavelength, provided by the high accelerating voltage, 300 kV, the coherent electron source, provided by the Schottky field-emission electron gun (FEG), and the high mechanical and electrical stability of this instrument allow for high-resolution imaging with an information resolution limit of 0.14 nm. Equally important, the small spherical aberration of the "super twin" objective lens (Cs = 1.2 mm) and the high brightness FEG allow for microanalysis at both high spatial resolution and high probe current (>0.6 nA in a 1 nm spot), which is important for obtaining good signal-to-noise ratios. A scanning unit enables the instrument to acquire images and analytical data not only in the stationary mode, but also by scanning a fine electron probe with a diameter as small as 0.17 nm across the specimen. Owing to these basic features, this instrument is ideally suited for studying the structure and the local chemical composition of materials on the nanoscale. The synergy of various powerful methods of analytical and high-resolution TEM techniques in the same instrument greatly enhance the capability of SCSAM, particularly for nanotechnology research.
Under coherent imaging conditions, the Tecnai F30 in conjunction with digital image processing of images recorded at different focus settings of the objective lens, enables quantitative HRTEM with a resolution of 0.14 nm. The STEM unit also enables "Z-contrast" imaging by detection of the electrons scattered to a high-angle annular dark-field (HAADF) detector, which constitutes a powerful technique for high-resolution imaging under conditions that reduce the interpretation problems associated with conventional HRTEM imaging.
The Tecnai F30 is equipped with an EDAX XEDS system by EDAX. The heart of this system is a Li-drifted Si detector, with an energy resolution of 130 eV.
The basic capabilities of the Tecnai F30 are further enhanced by a post-column, imaging energy filter (GIF 2002 by Gatan). This component forces the electrons on an energy-dispersive path, enabling a powerful variety of advanced methods of microanalysis.
Among these advanced methods, electron energy-loss spectroscopy (EELS) is of particular importance. The energy-dispersive plane of the filter, when imaged onto the slow-scan CCD camera of the GIF, reveals an electron energy-loss spectrum of the illuminated area. Electron energy-loss spectra contain absorption edges that are specific to the elements in the specimen. By recording the electron intensity in the energy-dispersive plane with a CCD camera, the local chemical composition of the specimen can be analyzed. This method of high spatial resolution chemical microanalysis is particularly powerful for light elements.
Apart from this application, electron energy-loss spectra can provide information on the local electronic structure and atom coordination. Information on the electronic structure becomes available by analyzing the fine structure of energy-loss spectra near absorption edges, i.e. by analyzing the energy-loss near-edge structure (ELNES). Usually, this type of analysis is carried out on spectra obtained with a focused electron probe and an EELS spectrometer that allows for parallel data processing.
The second important application of the imaging energy filter is "zero-loss imaging." Given the energy-dispersive ray path and the energy-dispersive plane of the GIF, energy filtering of the transmitted electrons is achieved by placing a slit aperture in the energy-dispersive plane. In this way, it is possible to admit only electrons with a particular energy (or, equivalently, a particular energy-loss) to the image or diffraction pattern. One important mode of operation of the filter is known as "zero-loss filtering." In this case, the slit aperture is positioned such that only those electrons that suffered no energy loss in the specimen can pass. This means that only elastically scattered electrons arrive at the electron detector (viewing screen, photographic plate, or CCD camera). Zero-loss filtering has two major applications: imaging of thick specimens and quantitative electron diffraction (ED), particularly with a highly convergent primary electron beam (CBED).
Finally, the imaging energy filter (GIF) enables elemental mapping via "electron-spectroscopic imaging" (ESI). In this technique, the energy filter is employed for recording images with electrons that have lost a well-defined, element-specific amount of kinetic energy in the specimen. For elemental mapping, it often suffices to record ESI images with three different settings of the slit aperture in the energy-dispersive plane, which makes ESI a much more efficient technique than the competing technique of scanning the specimen with a focused electron beam and recording the entire EELS spectra at every scan point.