Improvements in SDD Effi ciency
or collection solid angle and consider the entire processing chain. T e input count rate under a given set of conditions is dependent on geometry, collection solid angle, window material, window support structure, and specifi c SDD construction. Once the X-rays are detected, they also need to be processed properly to be of any use. With new develop- ments in amplifi er circuits and pulse processors, the quality and speed of spectrum acquisition are constantly improving. With improved energy- resolution stability and light-element detection at fast processing times, higher throughput can be achieved at modest count rates by using a short pulse processing time with only a slight impact on spectral quality. Fast processing speeds can confi dently be used for elemental mapping and for challenging applications with elemental overlaps.
Acknowledgements T e authors thank Russ Smith of EDAX for his continued focus on the importance of the quality of quanti- tative results even at high collection speeds. We also thank Kylie Simpson and Robert Rosenthal, our summer interns, who carried out the carbon measurements at high count rates.
References [1] R Fitzgerald et al ., Science 159 ( 3814 ) (1968 ) 528 – 30 .
Figure 9 : Quantitative results for trace carbon in a steel standard at 20 kV and 30% dead time. (a) Carbon peak acquired at 15,000 input cps with 7.86 µs processing time (red) and 200,000 input cps with 0.96 µs processing time (blue line). (b) Carbon concentration versus input count rate.
components of the detector. T e low carbon concentration of 0.50 wt% creates a further challenge to detection and quanti- fi cation. In this example, spectra were collected for 30 seconds at count rates ranging from 15,000 ICPS through to 200,000 ICPS, and the amplifi er processing time was adjusted to keep the dead time below 30%. Figure 9a shows an overlay of the zoomed carbon peak region of the spectrum, comparing the two extreme collection rates. Figure 9b shows the stability of the results as the count rate was increased, with a C concentration ranging from 0.46 wt% to 0.52 wt% compared with the given known value of 0.50 wt%.
Summary and Conclusions In order to really assess the effi ciency of an EDS system, one needs to look beyond the simple numbers of detector area
52
[2] L Strüder et al ., Mikrochim Acta (Suppl. 15 ) (1998 ) 11 – 19 .
[3] NJ Zaluzec , Microsc Microanal (2014 ) 1318 – 26 .
[4] NJ Zaluzec , XEDS Tools Solid
Angle Calculator V-2014091607 (October 2016) http://
tpm.amc.anl.gov/NJZTools/XEDSSolidAngle.html .
[5] JI Goldstein et al ., Scanning Electron Microscopy and X-Ray Microanalysis, Second edition . Plenum Press , New York , 1992 .
[6] P Lechner et al ., Adv X Ray Anal 47 ( 2004 ) 53 – 58 . [7] L Bombelli et al ., IEEE Nuclear Science Symposium Conference Record (2011) 1972–75.
[8] T Nylese and R Anderhalt , Microscopy Today 22 ( 2 ) (2014 ) 18 – 22 .
[9] F Eggert and W Scholz , Phys Status Solidi A 97 ( 1986 ) K9 .
[10] PT Törmä et al ., IEEE T Nucl Sci 61 ( 2014 ) 695 – 9 .
www.microscopy-today.com • 2017 March
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76