Universitäre Service-Einrichtung für Transmissionselektronenmikroskopie
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Chemical characterisation

Qualitative and quantitative chemical characterisation can be performed in the scanning electron microscopes (SEM) by means of Energy Dispersive X-ray analysis (EDX). In addition to this, in the transmission electron microscopes (TEM) further analysis can be made using electron energy loss spectrometry (EELS).

EDX Elemental Mapping (Cr-C Ausscheidungen in einer Metalllegierung)

Energy dispersive x-ray spectroscopy (EDX)

By the electron beam of the SEM or TEM, x-rays are produced that are characteristic of the elements existing inside the sampled region. These x-rays are then analyzed with special detectors to identify the elements present in the sample.

With this investigation technology chemical elements can be determined starting from atomic number 5 (Boron).

Particularly in the TEM highest local resolutions are attainable.

In addition to this, line profiles and chemical distribution pictures are possible.

EELS spectrum of BN

Electron Energy Loss Spectrometry (EELS)

A proportion of the electrons within the electron beam lose energy when passing through a specimen because they excite inelastic scattering. These scattering events can be plasmon excitation, ionization, Auger-electron excitation, thermal excitations, etc. Depending on the specific excitation process a respective energy is transferred from the probe electron to the sample. A sector magnet disperses the electrons according to their energy losses so that an energy loss spectrum can be recorded. This analysis can be used for chemical characterisation and for the determination of other material parameters.

EELS is complementary to EDX because it is an excellent method for analysing light elements, which are not so easy accessible for EDX analysis.

Using a combination of STEM and EELS, chemical nano-analysis can be performed with a spatial resolution of a single nano-meter.

Another advantage of EELS is that the energy loss spectrum contains information about the optical, magnetic and electronic behaviour of the sample.

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EFTEM Image of an Al-Si interface

Energy filtered transmission electron microscopy (EFTEM)

EFTEM uses only electrons which have lost a certain energy for imaging. The energy range of electrons used for imaging is set by the operator. Elemental distribution images (maps) can be generated giving the elemental distribution with nano-meter accuracy.

The image shows an RGB-profile of an Al-Si interface, which is oxidized. From the elemental map it can be seen that the oxide is Alumina and not Silica. The thickness of the oxide layer is only 3 nm.

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