SummarySince the early years of X-ray spectrometry in electron microscopes, mapping the locations of chemical elements has been important. The X-rays needed in large numbers for this are rare, owing to poor production efficiency compared with electron signals, and at risk of loss by many mechanisms such as missing the limited solid angle of the detector, absorption before reaching the detector and pulse pile-up conventional digital mapping hardware reduces the information contained in the X-ray spectrum at each pixel to the itegrated counts from a few regions of interest.The acquisition technique of position-tagged spectrometry eliminates the conflict between the desire to see full frame X-ray images quickly versus the analytical advantages of having complete spectra for each pixel. As the beam is scanned rapidly relative to traditional X-ray mapping, photons are counted in a virtual 3-D multichannel analyser on disk, preserving both spatial and spectral information. Along with the sophisticated post-processing allowed by storing an entire spectrum per pixel, a unique degree of dynamic interaction with the developing data is made possible by integrating many short scans instead of using a single long dwell time at each pixel.

No abstract

Graphical display of the spatial distribution of elements in a specimen has been recognized as a powerful technique since the earliest days of electron-beam x-ray microanalysis. With recent advances in computing power and mass storage, it has become practical to save complete spectra at each pixel rather than simple window counts, providing great flexibility for analytical post-processing. The term "spectrum imaging" has been coined to describe such a data structure.Hunt and Williams give a concise summary of the advantages of spectrum imaging, including the ability to map an element which was not known to be present when the data were acquired, and the ability to integrate spectra from image regions of arbitrary shape to improve statistical precision. Quantitative analysis may also be applied at each pixel to produce a concentration map, which is more informative than the raw or perhaps background-subtracted window counts usually displayed. Sensitive discrimination of phases is possible using various fitting techniques on the pixel spectra, matching them against each other or against standards.

No abstract

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.