Analytical Transmission Electron Microscopy (AEM)
Analytical Transmission Electron Microscopy (AEM) is an analytic technique that measures characteristic signals originating from the interaction between the electron beam and the sample atoms. These signals are complimentary and arise from measuring the energy dispersive X-ray spectrum (EDXS) and the electron energy loss spectrum (EELS). The EDXS signal is particularly good for higher Z materials, and the EELS signal compliments it well in having higher sensitivity to lower-Z materials.
Spot mode EDXS and EELS spectra can be acquired individually or simultaneously from small or large areas depending on operating conditions of the microscope. Through the STEM mode of the electron microscope a series of EDXS and/or EELS spectra can be acquired across lines or boxes giving line profiles and spectral images. From these scans, one can extract elemental linescans, elemental maps, and even phase maps.
Beyond spot mode and STEM acquisitions of EDXS and EELS spectra, Cerium Labs has the capability to use an EELS energy filter to acquire images based on electrons that undergo a specific range of energy losses. For example, one may acquire an image based on electrons that interacted inelastically with the sample and lost energy in the range of 75eV-80eV. Through this energy filtered TEM (EFTEM) imaging technique one may calculate elemental maps from three images, or stack a sequence of EFTEM images to create an EFTEM spectral image from which EELS spectra, EELS linescans, and elemental maps may be extracted.
In order to achieve the highest quality analytical information, the sample must be thinned to electron transparency as required for TEM, which is ideally less than 100nm. Consequently, this requires an intensive and exacting process of sample preparation. Cerium Labs has a world-class TEM sample preparation facility comprised of three dual-beam FIBs to prepare site-specific TEM samples, and traditional sample preparation tools for mechanical polishing and ion milling for bulk and blanket-wafer samples.
Today, we use the advantages of AEM to help our clients with challenges in process evaluation and development, process quantification, failure analysis, and various R&D tasks.
• JEOL JEM2010 (S)TEM operated with a thermionic emission gun at accelerating voltages of 100kV-200kV, equipped with the Thermo-Noran Vantage EDXS system.
• PHILIPS CM300 (S)TEM operated with a field emission gun at accelerating voltages of 80kV-300kV, equipped with the Noran System Six EDXS system and the GATAN Imaging Filter (GIF) model 2002.