Acquiring EDS Images (X-ray Maps)

Before configuring and performing an acquisition that could take hours, one should test that the basic system is configured and operational. The user should verify beforehand that there is no problem either with acquiring an image or a calibrated spectrum. This page will assume knowledge on the part of the user about both of these procedures. For the purposes of the example, a Copper grid sample with an Aluminum background and Carbon traces was used.

First Run - Configuring the X-ray Maps

The first step is to select the Cu, Al, and C ROIs. The default pixel dwell of 10ms is retained. From the X-ray image prefs panel, activate the Color ROI Maps checkbox (shown already selected) and hit the Edit ROIs button (blue cursor):

The ROI dialog is opened: Elements Al and Cu are turned on by default. To add Carbon to the ROI list, single-click on the C button (blue cursor).

To assign a color to each element, shift-click on each (one at a time), opening the ROI dialog. The ROI dialog for Copper is shown (default color is always white): Optionally, add the L (M) lines to the ROI by clicking on the L (M) checkbox (blue cursor). The ROI definitions can also be edited in this dialog box.

Open the computer's color services by clicking on Set Color. Choose a color (green in this case) and dismiss the color services dialog. Close the ROI dialog and repeat the process for each element. We selected green for Cu, magenta for Al, and yellow for C.

First Run - Configuring the Color Phase Map

To turn on the Color Phase Map, enable the checkbox (blue cursor) in the X-ray Image Prefs panel: The SEM Blend control and name field will be highlighted [note that SEM Blend is set to zero (the default) for this example].

First Run - Configuring the SEM Image

To turn on the SEM Image, enable the Channel 1 checkbox (blue cursor) in the SEM Image Prefs panel (this is normally already on by default):

This step is optional with respect to the Color Phase Map in this example because the SEM Blend setting is zero (see above); however, the SEM image is always good as a reference, and adds negligible overhead to the acquisition because the the typical x-ray map dwell time is substantially more than that required for a good electron image.

Revolution 1.5.6 does not have an EDX Image toolbar. X-ray mapping can only be accomplished by selecting the multi-toolbar. Switch to multi-toolbar mode by selecting Multi-toolbar from the Mode menu. The default orientation of the toolbar is vertical. The orientation can be set with a menu in the General Prefs.

Select the edx map toolbar button (blue cursor):

Click the view button to start a repeating preview scan during which parameters can be changed in the various preference panels. Depending on which controls are modified, the image and maps may or may not automagically restart. When the settings are complete to the user's satisfaction, click on the acq button to start an acquisition. The final result for the given configuration is:

In this example, Carbon is quite faint, but it does contribute to the phase map (the phase map is slightly brighter green than the Copper map alone). Note that the Copper map includes the L line ROI because it was checked (see above). Also note again that the acquisition of the electron image is entirely optional; in this example, the electron image does not contribute at all to the final color phase map because the SEM Blend control was left at its default value of zero. To make the SEM image influence the color phase map to a greater extent, the SEM Blend should be increased.

The most common complaint about acquired x-ray maps is "nothing was acquired; the map is black." This is invariably because the physics of the acquisition process has not been considered. As an example, consider an output count rate of 2000/sec. This is counts into the entire spectrum. If the spectrum consists of 2000 channels, this is an average of one count per second per channel. A typical spectrum might have most of the counts concentrated in 5 ROIs, so there are perhaps 400 counts/sec going into each ROI. A dwell time of 10 millisec per pixel then yields, on average, 4 counts per ROI per pixel when the map is finished. When autoscaling, this is enough to create a visible map; however, if the map is not autoscaled, or if the count rate or dwell is not large enough, the maps will be black. Always do a back-of-the-envelope calculation to see if your acquisition conditions make sense!!