Mapping and Spectrum Matching for Phase Identification

The EDAX TEAM™ software package now offers the Spectrum Matching feature, the latest powerful and time-saving tool. Spectrum Matching is an automatic feature which enables users to explore a tailor-made spectrum library to locate matching spectra. Through this function, identification of unknowns is simplified by comparing them to a set of potential candidates and the difficulty of locating similarities and discrepancies between spectra is decreased.

Using the Spectrum Match Library

The matching of the active spectrum to those located in the library file is based on a chi squared goodness of fit test, directly matching either spectra or concentrations. The modifiable match sensitivity provides users with total control over the match outcomes, spanning from fully identical to approximately in the same ballpark. The probable matching spectra are superimposed on the unique spectrum with the match percentage providing a measure of how dissimilar or similar the spectra are together with a visual representation of the variations. Figure 1 illustrates an example spectrum with two superimposed spectra with a similar value of 62.64% and 81.53% for CaSO4 and SbS, respectively.

EDS spectrum with two matching spectra overlaid.

Figure 1. EDS spectrum with two matching spectra overlaid.

A visual examination can quickly inform users that the differences between the ideal matching spectrum and the sample are to be found in the Si, Ti, Ba and Zr content. Construction of a spectrum match library in the TEAM™ software is made simple and easy, thanks to the integrated spectrum search utility. The user is able to investigate the total spectral database stored on the system either via manual selection of particular project nodes or by including filters to detect spectra with the preferred characteristics.

The filters contain the presence of specified elements with range in atomic %, weight % or net intensity, acquisition date, kV used, and sample name. After the spectra are chosen, they are stored on a Spectrum Matching Library file, which can be circulated among systems and users. All of the data in the system database can be added to a Spectrum Matching Library file to respond to nagging questions.

Integrating Spectrum Matching and phase mapping highlights the advantages obtained from the two methods. In the present example, the spectrum library was built based on 15 varieties of mineral standards, and the library was applied to a high quality 512 x 400 pixel map of an automotive composite sample.

During the course of data acquisition, which took an hour, the phase mapping routine automatically divided and color coded the various sample phases, as illustrated in Figure 2. When the phases were identified, the TEAM™ software automatically produced a phase spectrum from the pixels in each separate phase. All of these phase spectra can be tracked easily in the software and compared to a match library.

SEM Image (left) and phase map (right) of the composite sample.

Figure 2. SEM Image (left) and phase map (right) of the composite sample.

Figure 3 shows the outcome of extracting the blue phase spectrum from the phase map and comparing it to the minerals library, leading to an 85.33% match to a barite standard. The Ba atomic % map in conjunction with the phase map, validates the existence of Ba in the blue phase (Figure 3).

By matching the other phase spectra, users can quickly spot the turquoise phase as strontium sulfate, steel blue as magnetite, red as almandine garnet, violet as lead sulfate, yellow as a blend of titanium dioxide and barite, and fuchsia as carbon resin.

Sum spectrum of the blue phase matched to the mineral library (top), Ba atomic % map (lower left) and phase map (lower right).

Figure 3. Sum spectrum of the blue phase matched to the mineral library (top), Ba atomic % map (lower left) and phase map (lower right).

Conclusion

This example illustrates how the matching routine is applied to a mineral sample. Spectrum Match is a versatile tool that can also be adapted for many other applications such as quality control and failure analysis, where defects can be matched to a library of potential contaminants.

It can also be used in process control where modifications in composition and distribution can rapidly be spotted with the integration of spectrum matching and phase mapping, or reverse engineering where material constituents can be compared against a library of traditional components present in the material. For any application, users can find their match with a simple push of a button.

This information has been sourced, reviewed and adapted from materials provided by EDAX Inc.

For more information on this source, please visit EDAX Inc.

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