Transmission electron microscopy (TEM) has a number of applications including the analysis of components such as magnetic heads and media that are used in manufacturing disk drives. For example, the interaction of an electron beam with matter (e.g., a sample) generates a multitude of signals that can be acquired using transmission electron microscopy/microscope (TEM) with atomic spatial resolution, making it the most powerful spectroscopic and imaging tool currently available. Scanning TEM or STEM systems, where a probe forming beam with high spatial resolution scans over the sample to produce an image and to generate spectroscopic signals to be collected by the various detectors for spectroscopic studies of the fine chemical structure of magnetic materials, are of particular interest.
The STEM is the most commonly used tool to obtain directly interpretable, atomic resolution images from nano-structured materials. The most typical imaging mode in modern STEM systems is high angle annular dark field (HAADF), which is sensitive to atomic number and therefore reveals the so called atomic compositional contrast, or “Z-contrast”, over the scanned region of the TEM lamella. Bright field and dark field detectors, which are sensitive to comparatively lower angle scattering and thus form a diffraction contrast image, are also common. In terms of spectroscopic analysis, the most common techniques found in commercial STEM's are X-ray energy dispersive spectroscopy (XEDS) and electron energy loss spectroscopy (EELS).
In order to achieve a thorough understanding of the sample, a feature of interest and/or a related failure mechanism, it is often the case that a combination of different analytical signals must be acquired with the highest signal-to-noise ratio possible. Although many signals arise from the interaction of the electron beam with the sample, in practice due to substantially different signal yields amongst the different spectroscopic techniques, it is generally not possible to perform simultaneous spectroscopic acquisitions which are optimized to get the best signal from the respective techniques. As such, artifacts from over-saturated or under-saturated detectors and excessive beam exposure to the specimen are unavoidable in simultaneous spectroscopic experiments.
The most state-of-the-art transmission electron microscopes allow for simultaneous acquisition of EELS and XEDS signals, but there is no known technology for simultaneous acquisition of any of the other of the multitude of spectroscopic and imaging signals available from the STEM. Furthermore, while technology exists to collect both the zero-loss and core-loss regions of the EELS spectra simultaneously, the so-called dual-EELS, there is currently no known technology which allows for the combination or simultaneous acquisition of dual-EELS and XEDS or any other spectra. Thus, the various spectroscopic signals are acquired independently from separately optimized experiments. At this point, however, the spatial correlation between the different spectroscopic experiments becomes irreversibly lost. As such, a method for spatially resolving the alignment of independent spectroscopic data from scanning transmission electron microscopes is needed.