Scanning Electron Microscopy (SEM)

Typical SEM output is greyscale images with differences in contrast depending on the type of detector. A data bar is also found on the image and usually contains info on the accelerating voltage, SEM detector type, beam current, stage tilt, working distance, magnification, horizontal field width and a scale bar.

• SE greyscale contrast describes surface topography including brighter contrast at edges and high spots, and darker contrast for regions of shadow, valleys and holes. Good for highlighting different morphologies such as cracks, fibers and textures.
• BSE greyscale contrast describes composition contrast. Heavier elements with higher Z appear brighter, and lighter elements with lower Z appear darker. Can be used to determine compositional differences and locate different phases or materials.
• EDS output of data typically involves X-ray spectra, elemental maps or linescans.
• X-ray spectra are graphs that display X-ray energy on the X axis, and X-ray counts on the Y axis. The peaks in the spectra are matched to the specific X-ray energies of elements and used to determine the chemical composition of the area of interest (weight percent or atomic percent).
• Elemental maps visually display where in an area of interest specific elements are found. The brightness of the map in a specific area corresponds with how highly concentrated the element is in the AOI. The maps are color coded by element and can be overlaid on top of the SEM image.
• EDS linescans measure the X-ray EDS data along a single line. The data output is a line graph displaying X-ray count intensity vs position along the line. The different elements are color coded and can be overlaid with each other. The Y axis can be converted to weight percent or atomic percent.
• EBSD outputs include grain orientation maps, phase identification maps, grain size distribution charts, grain boundary maps.
• Grain orientation maps are color coded such that certain colors correspond to the crystallographic orientation of a sample grain for a specific crystal system.

If multiple material phases are being measured simultaneously, phase maps provide color coded display of the locations of the different phases in the field of view.

What we accept:

• Solid state samples required including thin films on substrates, powder samples, bulk samples.
• Must be vacuum compatible, no outgassing, volatile samples.
• Electrically conductive samples. Non-conductive samples will require additional preparation to apply a conductive coating.
• Samples should be thermally and mechanically stable under vacuum conditions and beam exposure. Need to be mounted to the stage or aluminum stubs with conductive tape or other adhesives.
• Samples need to be large enough to be easily manipulated with physical tools such as tweezers or powder scoops.
• Minimum detectable concentration with EDS is 0.1 atomic percent.
• Samples with significant variations in height may not be compatible especially for SEMs that have a short optimal working distance. This is especially true when FIB milling is also required.
• Samples requiring FIB milling should generally be flat and the area of interest on the top most surface of the sample. Some exceptions can be made depending on the geometry of the sample.
• Sample size, shape and weight are important considerations for sample mounting and orientation for SEM analysis and FIB milling. Samples need to be mechanically stable and not drift while the stage is tilted during FIB milling. Specialized sample holders and fixtures may be required for complex samples.