EELS.info

Search form

Why EELS?

EELS is a powerful technique that provides both compositional and chemical information from sub-nanometer areas in the sample. Due to the large interaction cross-sections and narrow angular distribution of the scattered electrons, EELS is very sensitive and highly localized technique. The benefit of core-level EELS is its sensitivity to all elements in the periodic table (with the exception of atomic hydrogen). The deexcitation processes are competitive, resulting in near zero x-ray yield for low Z elements and near zero Auger yield for high Z elements. The processes reaches parity (50/50 yield) around germanium (atomic number 32). In addition, EELS has the ability to probe the local density of states, which makes it uniquely suited to measure changes in local bonding at near atomic resolution.

High energy electrons interacting with the sample produce a myriad of signals. The elastic (including BSE) and inelastic interactions are the primary signals while the other signals are secondary events caused by the relaxation of the sample after the inelastic scattering event. The EELS signal is strongly peaked in the forward direction making near 100% collection efficiency possible.

ComparisonTable

Comparisons

  • Spatial resolution

    The spatial resolution of a technique is not easy to define precisely as there are a number of issues to consider. Given unlimited signal, the resolution is typically limited by the interaction volume of the probe with the material. However, the spatial resolution is often limited by the signal-to-noise ratio of the measurement.

  • Compositional sensitivity

    Common terms for compositional sensitivity are minimum detectable mass (MDM) and minimum detectable fraction (MDF). MDM measures the smallest amount of the material you can see in a very small volume. MDF looks at smallest fraction you can see in a given volume. Once a material is detected, the next question is how accurately you can quantify the measured value.

  • Chemical sensitivity

    Chemical sensitivity measures how well you can detect changes in the chemical bonding of a material. This is distinct from composition, which only addresses how many atoms of each type are under the beam. Here, we want to know how the atoms are bonded to one another.

  • Ease of use

    While not a quantitative value, ease of use is important. Here we look at how difficult it is to reach the desired result.