Energy Dispersive Spectroscopy (EDS) is a popular microanalytical technique that is used to identify and quantify the elements present in a sample. When working alongside a scanning electron microscope (SEM) or scanning transmission electron microscope (STEM), EDS can be used to create elemental maps of samples.
Owing to its popularity EDS has many names - from the more conventional EDS to Energy Dispersive X-ray Spectroscopy (EDX or EDXS) or sometimes even Energy Dispersive Analysis of X-rays (EDAX). Elemental mapping allows researchers to see their samples in colour - regions of interest that were previously invisible can suddenly become clear, contamination can be spotted, or information can be retrieved that can help develop understanding of the sample's history, formation conditions and macroscopic properties. These are just a few of the applications of EDS. To find out more about this powerful technique, and what it can be used for, continue reading!
Owing to its popularity EDS has many names - from the more conventional EDS to Energy Dispersive X-ray Spectroscopy (EDX or EDXS) or sometimes even Energy Dispersive Analysis of X-rays (EDAX). Elemental mapping allows researchers to see their samples in colour - regions of interest that were previously invisible can suddenly become clear, contamination can be spotted, or information can be retrieved that can help develop understanding of the sample's history, formation conditions and macroscopic properties. These are just a few of the applications of EDS. To find out more about this powerful technique, and what it can be used for, continue reading!
How Does EDS Work?
EDS works by measuring the energy and intensity of the X-rays that are emitted by a sample when it is exposed to the electron beam of an electron microscope. Depending on if a SEM or TEM is used the technique is called either SEM EDS or TEM EDS.
During EDS anaylsis the microscope's high-energy electron beam interacts with the atoms of the sample. This interaction has many effects, one is the ejection of an atom's inner-shell electron creating an electron vacancy, which is quickly occupied by a higher-energy, outer-shell electron. As the outer-shell electron drops to a lower-level shell it loses energy and this excess energy is emitted as X-rays (figure 2).
The X-rays emitted during this process are called characteristic X-rays because their energies are unique for each element. Detecting and measuring these characteristic X-rays can be used to determine which elements are present in a sample and at what quantity.
The detection and measurement of the emitted X-rays is carried out by a SDD (short for silicon drift detector) and for each pixel of measurement the energies and intensities of the X-rays are recorded. Software and a spectral library are then used to to identify the elements present based on the measured characteristic X-ray energies and their amount based on the respective intensities.
EDS works by measuring the energy and intensity of the X-rays that are emitted by a sample when it is exposed to the electron beam of an electron microscope. Depending on if a SEM or TEM is used the technique is called either SEM EDS or TEM EDS.
During EDS anaylsis the microscope's high-energy electron beam interacts with the atoms of the sample. This interaction has many effects, one is the ejection of an atom's inner-shell electron creating an electron vacancy, which is quickly occupied by a higher-energy, outer-shell electron. As the outer-shell electron drops to a lower-level shell it loses energy and this excess energy is emitted as X-rays (figure 2).
The X-rays emitted during this process are called characteristic X-rays because their energies are unique for each element. Detecting and measuring these characteristic X-rays can be used to determine which elements are present in a sample and at what quantity.
The detection and measurement of the emitted X-rays is carried out by a SDD (short for silicon drift detector) and for each pixel of measurement the energies and intensities of the X-rays are recorded. Software and a spectral library are then used to to identify the elements present based on the measured characteristic X-ray energies and their amount based on the respective intensities.
Figure 2a - An incident electron from the SEM electron beam collides with an inner shell electron of an atom in the sample. This results in the emission of an inner core electron, leaving behind an inner shell vacancy.
Figure 2b - An outer shell electron relaxes to occupy the newly created inner shell vacancy. A characteristic X-ray, of energy hv, which is equal to the energy of the electronic transition, is emitted during the relaxation.
What is Elemental Mapping?
Elemental mapping is a technique used to visualize and characterize the spatial distribution of elements within a sample. It provides a detailed representation of how different elements are distributed across the sample's surface allowing users to develop a greater understanding of a samples structure.
Elemental maps are created by the combination of point-by-point elemental information collected during SEM EDS or STEM EDS. In the elemental map, the intensity or color scale represents the concentration of a particular element at each point. High intensities or brighter colors indicate regions with higher concentrations of the element, while low intensities or darker colors represent regions with lower concentrations.
The process behind the creation of an elemental map can be seen in figure 3. This example shows a HyperMap, also known as a spectral image, taken using hyperspectral imaging.
Elemental mapping is a technique used to visualize and characterize the spatial distribution of elements within a sample. It provides a detailed representation of how different elements are distributed across the sample's surface allowing users to develop a greater understanding of a samples structure.
Elemental maps are created by the combination of point-by-point elemental information collected during SEM EDS or STEM EDS. In the elemental map, the intensity or color scale represents the concentration of a particular element at each point. High intensities or brighter colors indicate regions with higher concentrations of the element, while low intensities or darker colors represent regions with lower concentrations.
The process behind the creation of an elemental map can be seen in figure 3. This example shows a HyperMap, also known as a spectral image, taken using hyperspectral imaging.
Figure 3: Elemental map taken by EDS SEM with associated spectra for three chosen points in the map. This data was processed using ESPRIT HyperMap software.
Figure 4: Elemental maps taken during EDS SEM, overlaid on a larger SEM image. This particular image is of the nanoscale features on a semiconductor-based FinFET device.
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