Using Transmission Electron Microscopy (TEM) for Chemical Analysis of Semiconductors

The transmission electron microscope (TEM) is an invaluable tool for the characterization of crystals, polycrystalline materials, biological specimens, nanostructures etc. It provides a wide range of different imaging modes with the ability to provide information on elemental composition and electronic structure at the ultimate sensitivity, that of a single atom. Convergent beam electron diffraction provides information on crystal structure and crystallography. STEM provides the simultaneous acquisition of multiple different image and spectroscopy signals while scanning the electron probe across the specimen or pointing it directly onto different defect structures, such as, for instance, point defects, grain boundaries, or heterophase interfaces . The (S)TEM can be used to examine internal structure and composition of thin or sectioned specimens. STEM and high-angle annular dark field gives information on microstructure, atomic structure and atomic number. Energy dispersive x-ray spectroscopy permits sub-micrometer elemental identification and compositional analysis. The addition of electron energy loss spectroscopy and energy-filtered imaging allows for the detection of elements at higher spatial resolution, phase identification and bonding information. In summary, the (S)TEM with X-ray and EELS spectroscopy permits further characterization of both organic and inorganic materials. The brightness of the STEM probe substantially exceeds that of third-generation synchrotron sources, making the STEM a powerful means for analyzing electronic structure and identifying impurity species or dopants within nanostructures. Spectroscopic imaging can be achieved in the TEM through use of an energy filter. Electrons scattered at low angles are not used in this detection scheme, and are thus available for simultaneous electron energy-loss spectroscopy; in principle, this combination of techniques should allow the direct chemical analysis of single atomic columns in crystalline materials. A lot of information is present in an electron energy loss spectrum. The energy resolution (below 1 eV) is much better than in X-ray spectroscopy, and as a result more structural information can be obtained from the fine structure in EELS. For many questions, it is important to get this information with a high local resolution. Such mappings can be done with two different methods: