University of Cambridge > Talks.cam > Electron Microscopy Group Seminars > Some ideas how to improve quantification of chemical signals in transmission electron microscopy studies of very thin layers

Some ideas how to improve quantification of chemical signals in transmission electron microscopy studies of very thin layers

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Thin layer structures can be produced by many different techniques and are important for a variety of different applications. Transmission electron microscopy (TEM) is a unique method to investigate such layers locally and to obtain information on crystallographic structure, defects, thickness, interface roughness, compositional grading and chemistry with spatial resolution on the (sub) nm scale, usually rather direct without the need of extensive modelling. This talk will give an overview of novel experimental methods to determine the chemistry of very thin layers using a number of different TEM methods: a) Spectroscopic transverse image profiling in energy-filtered TEM with a Gatan Imaging Filter allows to measure shifts of the energy- loss near edge structure (ELNES) across interfaces with a precision much better than both the energy-resolution or the typical long-term energy stability of the system, b) Linear least-squares fitting of series of spectra acquired with different electron beam sizes can be applied to either energy- dispersive X-ray (EDX) or electron energy-loss spectra (EELS) and, by making use of a rather simple geometrical approach, yields segregation levels of elements to a precision an order of magnitude better than standard analytical approaches, c) Energy-filtered annular dark-field imaging is shown to allow accurate interpretation of the image contrast in terms of pure Rutherford scattering if the image contrast is plotted as a function of the camera length and then extrapolated to zero (i.e. infinite scattering angle), d) Monochromatic aberration corrected scanning TEM (MacSTEM) will allow us in the future to form well-defined small electron probes intense enough for a local chemical analysis of single atomic columns in crystals.

This talk is part of the Electron Microscopy Group Seminars series.

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