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EELS and EDS Analysis


Figure 8 : Colorized representation of the elemental maps in Figure 7 using Ti L in green, La M in purple, and Mn L in blue obtained using EELS, and Sr L in red obtained using EDS. The numbers 1–7 correspond to the selected region where the EELS spectra in Figures 9a–c were extracted.


Discussion T e EELS and EDS data presented here can be regarded as highly complementary. T e main diff erence is that for the EDS case, each pixel carries little information because of the low signal-to-noise ratio of the data, even at relatively long acquisition times and with elements of high fl uorescence yield. T e high signal-to- background ratio of the EDS technique, however, allows summation of adjacent data almost indefi - nitely, which improves detection limits at the


expense of spatial resolution. T e EELS system, on the other hand, exhibits a high signal-to-noise ratio for each pixel because of the high collection effi ciently of the EELS. Summing adjacent pixels improves the detection limits here also but will show diminishing returns once the shot noise in the signal integral becomes irrelevant. T e techniques further complement each other when identifying artifacts in the data. For example, secondary fl uorescence and preferential absorption in the EDS data can be determined from the EELS data, while possible missing elements in the EELS data range acquired can be identifi ed in the summed EDS signal. A system for fast and effi cient acquisition of both EELS and EDS spectra allows the routine collection of both of these complementary signals. T ere is no longer a need to choose between analytical techniques; both EELS and EDS can be acquired easily with every data run. T e data presented here show the complementary nature of having both high signal-to- noise and high signal-to-background data acquired at the same location at the same time. Further, the ability of combining composition measurements from EELS and EDS with physical and electronic information also available only from EELS (for exmaple, plasmonic, bandgap, and density of states information) [ 19 ] promises to open whole new avenues of materials analysis.


Conclusion


EELS and EDS are complementary analysis techniques that can, in the best environmental settings, provide elemental analysis at the level of atomic columns. Large-area EELS spectrum images can display atomic-level details of element locations from areas up to 2,500 nm 2 . Simultaneous collection of detailed EELS and EDS elemental maps provides information about TEM thin specimens that is diffi cult or impossible to obtain by other means. Chemical bonding eff ects at the atomic column level can be detected when EELS setup parameters are adjusted for acquisition at the highest energy resolution.


Figure 9 : a) Ti L 2,3 , b) O K, and c) Mn L 2,3 EELS data extracted from the selected region in Figure 8 . All the spectra were normalized to same maximum in intensity and vertically offset for better visualization.


true chemical shift can be observed as shown in Figure 9c where the Mn L2,3-edges for the spectra in position 1 and 2 are slightly shifted at lower energy.


52


References [1] OL Krivaneck et al ., Ultramicroscopy 96 ( 2003 ) 229 – 37 . [2] S Pennycook , Microsc Anal 26 ( 6 ) ( 2012 ) 59 – 64 . [3] P Longo et al ., Microsccopy Today 20 ( 4 ) ( 2012 ) 30 – 36 . [4] P Longo et al ., Microscopy Today 21 ( 4 ) 2013 ) 36 – 40 . [5] P Schlossmacher et al ., Microscopy Today 18 ( 2010 ) 14 – 20 . [6] PJ Phillips et al ., Microsc Microanal 20 ( 2014 ) 1046 – 52 . [7] IOP Publishing . Nanotechweb.org , “EDX detects single atoms,” http://nanotechweb.org/cws/article/tech/50459 .


[8] P Longo et al ., Microscopy Today 21 ( 1 ) ( 2013 ) 28 – 33 . [9] AJ Gubbens et al ., Ultramicroscopy 110 ( 2010 ) 962 – 70 .


www.microscopy-today.com • 2015 July


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