Energy Dispersive Spectroscopy (EDS) in Scanning Electron Microscopes (SEM) was primarily designed for acquiring spectral data and quantifying important sample features. For decades however it has also been used to map elemental distributions within samples.
EDS uses a scanning electron beam which is concentrated on a specific sample area, and the subsequent excitation produces a distinct X-ray spectra. The elements with high corresponding X-ray intensities, or those which the user chooses for a map image, are extracted. Using the latest analysis techniques, it is possible for analysts to study the X-ray data for distinct elemental phases and/or mixtures and determine the phase distributions.
A focused ion beam (FIB) can be used to cross-section a defect in a sample and provide an in-depth image through the feature. Another analysis method involves eliminating a thin slice of material over a large area so that a new surface is exposed. In this way, several image slices together can offer an insight into the three-dimensional nature of the sample.
It is possible to perform EDS analyses on each slice to provide several elemental image maps. The number of slices may be small (less than five), although the latest automatic collection techniques can offer a high number of slices (greater than 50).
Interpretation becomes tough and time-consuming with a large amount of EDS data and ascertaining the real 3D morphology of the material from several two-dimensional slices can be challenging.
One of the most practical methods of interpreting the elemental data is to visualize the data as a 3D volumetric display. The ability to zoom, rotate and isolate key features helps in interpreting the structure. Older 3D visualization software usually takes an image slice stack in order to generate a 3D volume. Elemental maps can be concurrently displayed using color coding based on intensity. The normal rotate/tilt/zoom functions developed for simple images are also used for elemental maps, but offer minimal interpretive data.
This article describes the 3D analysis of EDS data using imaging and analysis operations, in order to counter some of these traditional issues.
EDAX 3D Solution
EDAX has partnered with a sister company within AMETEK to create a 3D model for EDS data, which performs both analysis and imaging in the same package. The partner created the 3D software, which serves as a visual and analytical tool for interpreting atom probe tomography (APT) data.
Furthermore, with its extensive 3D imaging experience, EDAX has developed the best 3D tool for EDS data. The developers created the tool using typical 3D EDS data sets from simple elemental maps to full spectral imaging data sets for each FIB slice.
While extracting the sub-sets of the data for interpretation, a complete spectrum is also extracted for performing quantification. In this way, the comprehensive visual and analytical interpretation of 3D EDS data is carried out.
Illustration of 3D EDS System Capabilities
The first example illustrates the functions of the 3D EDS system that includes a CdTe multilayer structure. The display as shown in the Figure 1 is a hybrid revealing Cd-L as magenta dots, O-K as a blue transparent volume and S-K as an orange volume.
Using this data, a cumulative linear composition profile is formed, which is shown in Figure 2. The profile shows the elemental distributions normal to the O-K interface. The sharp interface is observed in the plot as shown in the visual display.
Figure 1. A hybrid showing Cd-L X-rays as magenta dots, S-K X-rays as an orange volume, and O-K X-rays as a blue transparent volume
Figure 2. A proxigram showing the elemental distributions normal to the O-K interface
Another example includes the distribution of all of the X-rays using a rare-earth modified steel sample. Figure 3 shows the typical 2D elemental maps of the primary elemental lines. Interpretation with the help of individual slices is extremely difficult owing to the spatial overlap of all of the elemental contributions and difficulty in combining the areas.
Figure 4 shows the 3D distribution of all the x-rays as dots. Interpretation is complex as various information are displayed at once.
Figure 3. The typical 2D elemental maps of the primary elemental lines of a rare-earth modified steel sample
Figure 4. The 3D distribution of all of the X-rays as dots
However, placing the iso-concentration surfaces through the volume and selecting the limited number of elements is the preferred method. The Nd-L enriched regions are shown in the Figure 5, where each isolate particle has a distinct shape.
Figure 6 shows the cumulative spectrum automatically provided for the whole data set. The interpretation of the structure is based on the knowledge of the spectrum of individual particles. These capabilities are illustrated in Figure 7.
It is evident from the graph that the particle contains a significant enhancement of Pr-L and Nd-L when compared to the average material.
Figure 5. A 3D distribution showing only the Nd-L enriched regions
Figure 6. A cumulative spectrum automatically provided for the whole data set.
Figure 7. Graph showing that the particle contains a significant enhancement of Nd-L and Pr-L compared with the average material
As shown in the Figure 8, a cumulative linear composition profile was generated around particle 2, showing elemental distributions that are normal to the Nd-L interface. The Fe-K contribution was observed to decrease while the Nd-L and Pr-L contributions were found to increase within the particle.
By contrast, it is also possible to define a sub-volume within the data set. Figure 9 shows the selection and orientation of a cylindrical volume. A 1D composition profile as shown in the Figure 10 is derived from the slices within this shape to create a profile across the major particle in the analysis. The same elements are segregated as before, and sharpness of the interface between the matrix and the particle was observed.
Figure 8. Cumulative proxigram created around particle 2
Figure 9. Cylindrical volume of a defined sub-volume within the data set
Figure 10. 1D composition profile derived from slices
Recent advancements in the quality and speed of EDS hardware has paved the way for 3D analysis of material, providing insights on microstructures and material properties. TEAM™ 3D IQ enables complete quantification of 3D renderings adding another dimension to the existing knowledge on material properties.
About EDAX Inc.
EDAX is the global leader in Energy Dispersive X-ray Microanalysis, Electron Backscatter Diffraction and Micro X-ray Fluorescence systems. EDAX manufactures, markets and services high-quality products and systems for leading companies in semiconductors, metals, and geological, biological, material and ceramics markets.
Since its founding in 1962, EDAX has utilized its knowledge and expertise to develop ultra-sensitive silicon radiation sensors, digital electronics and specialized application software that facilitate solutions to research, development and industrial requirements.
EDAX is a unit of AMETEK Materials Analysis Division. AMETEK, Inc. is a leading global manufacturer of electronic instruments and electric motors with annualized sales of more than $1.8 billion.
This information has been sourced, reviewed and adapted from materials provided by EDAX Inc.
For more information on this source, please visit EDAX Inc.