Analysis of inhomogeneous samples and trace element detection in alloys using QUANTAX Micro-XRF on SEM

Transcription

1 Analysis of inhomogeneous samples and trace element detection in alloys using QUANTAX Micro-XRF on SEM Bruker Nano Analytics, Berlin, Germany Webinar, June 02, 2016 Innovation with Integrity

2 Presenters Birgit Hansen Application Scientist EDS & Micro-XRF on SEM, Bruker Nano Analytics, Berlin, Germany Stephan Boehm Product Manager Micro-XRF on SEM, Bruker Nano Analytics, Berlin, Germany 2

3 Overview 1 st Part Why is Micro-XRF on SEM useful? (Comparison between Micro-XRF and EDS) Instrument design Working principle of Micro-XRF on SEM 2 nd Part Esprit 2 software Trace element detection in aluminum alloy Inhomogeneous sample analysis - copper alloy example Summary 3

4 Why is Micro-XRF on SEM useful? Comparison EDS Micro XRF SEM/EDS Is best suited for light elements with X- rays energies below 2 kev High spatial resolution 20 nm to 3 µm Sensitivity of EDS is limited due to the overlap of fluorescence lines with the bremsstrahlung background Can detect most elements that are present in amounts 0.1 wt% (1000 ppm) SEM/XRF Photon excitation produces spectra with little or no background better P/B- ratio For X rays above 2 kev XRF can detect elements below 100 ppm (depends on the matrix) The spatial resolution is lower µm range Higher information depth 4

5 Why is Micro-XRF on SEM useful? Comparison EDS Micro XRF Complementary advantages: Electron beam excitation is better suited to imaging and quantitative compositional analysis of particles and maps Photon beam excitation increases the detectability of peaks from elements at low concentrations that otherwise might lost in the background is better suited to quantify trace elements but over a much larger area Delivers information from deeper layers inside the sample 5

6 Comparison between EDS and XRF Improved Limits of Detection Detection limit in [wt%] 1,000 0,100 0,010 0,001 0,000 K Estimated detection limit K L Fe = 26 Rh = 45 Pb = Element [Z] L M X-ray exitation Electron exitation LOD for Micro-XRF are significantly better for elements with Z > 20 but depend strongly on analyzed element and matrix composition! Trace elements in a light matrix: LOD 100 ppm down to even 10 ppm Trace elements in a heavier matrix: LOD range 100 ppm to 200 ppm 6

7 Comparison between EDS and XRF XRF Information depth Advantages of X-ray excitation: X-rays penetrate deeper into the sample Examination of thicker layers / coatings and of multiple layer structures Information depth depends on the sample matrix Spectra of a multiple layer system: Au 3 µm, Ni 2 µm / Cu (EPMA: blue; µ-xrf: red) Differences in the spectra: Spectral background is different due to bremsstrahlung Upper layers are very well excited by electrons but deeper layers can excited by X-rays only Thicker layers or even multiple layer systems can analyzed with XRF only 7

8 Comparison between EDS and XRF XRF Information depth 8

9 Micro-XRF on SEM X-ray tube added to the SEM X- ray tube with housing Contains a micro - focus X-ray tube with a target spot size of 50 x 50 µm Target material according to analytical requirements: Rh, Mo preferred due to limited overlaps with lines of typical analyzing elements Source includes an integrated shutter allows an continuously X-ray beam even if the chamber is opened Tube radiation is captured by a polycapillary optics and concentrated on the sample surface down to spot sizes of either 10 or 35 µm X-ray detection will be done by a (existing) EDS (Bruker XFlash ) detector 9

10 Micro-XRF on SEM Instrument design Primary filter wheel Z adjustment Z adjustment EDS e- beam Filter wheel sample X - Y adjustment adjustment Warning lamps for HV and X-ray beam 10

11 Working principle of Micro-XRF for SEM X- ray tube (Physical principles) Rh-Ka Rh-L Rh-Kb Emission of electrons from the filament by electrical heating Acceleration of electrons to the anode by HV De-acceleration of electrons on the anode Emission of continuous bremsstrahlung and characteristic fluorescence radiation of the anode material 11

12 Working principle of Micro-XRF for SEM Polycapillary X-ray optics SEM image of a polycapillary structure. Inner diameter in the range of 2 µm Images courtesy of IfG GmbH, Berlin 12

13 XTrace Alignment Approach WD: 10 mm WD: 12 mm EDS e-beam sample EDS detector Polycapillary optics X-ray optics (the focused X-ray beam) has to be adjusted to match the location where the e-beam hits the sample (at the respective WD of the EDS detector) Thus, whenever the WD of the SEM is changed consequently the X-ray optic has to be realigned 13

14 XTrace Alignment Glass sample Glass makes the X-ray spot visible Misaligned Xray spot 14

15 ESPRIT 2 analytical software suite Integrated user interface Hardware Device Boxes All devices integrated under one user interface Use EDS and XRF alone or together In case of EDS measurement X-ray beam shutter is closed (HV on) In case of single XRF measurement e- beam is blanked 15

16 ESPRIT 2 - modes of operation Combining EDS + XRF analysis Integrated user interface for EDS and Micro-XRF including: Spot mode Object analysis Line scan Stage map Quantitative XRF analysis 16

17 Trace element detection Aluminum alloy - comparison EDS - XRF XRF (50 kv, 600 µa) 200 sec, ICR: 10.7 kcps EDS (20 kv) 200 sec, ICR: 9.5 kcps 17

18 Trace element detection Aluminum alloy - comparison EDS - XRF 600 ppm 100 ppm 100 ppm 300 ppm 18

19 Inhomogeneous sample analysis Copper alloy BSE image 19

20 Inhomogeneous sample analysis Copper alloy EDS analysis EDS (25 kv) 300 sec, ICR: 8.5 kcps 20

21 Inhomogeneous sample analysis Copper alloy XRF analysis BSE image 21

22 Inhomogeneous sample analysis Copper alloy XRF analysis 180 ppm 160 ppm XRF 50 kv, 600 µa 300 sec ICR: 5 kcps 22

23 Inhomogeneous sample analysis Copper alloy sample tilting XRF (50 kv, 600 µa) 300 sec, ICR: 44 kcps 23

24 Inhomogeneous sample analysis Copper alloy Ti filter XRF (50 kv, 600 µa) 300 sec, ICR: 5 kcps 24

25 Summary XTrace is attached to an inclined SEM port XTrace excitation radiation can be concentrated to spot sizes down to 35 µm Existing (Bruker) EDS detector for spectra acquisition 2 types of analysis on SEM (electron + photon excitation) One integrated user interface for EDS + Micro-XRF Improved limit of detection compared to EDS High sensibility of trace element detection Micro-XRF can be used for inhomogeneous sample analysis 25

26 Q&A Are There Any Questions? Please type in the questions you might have in the Q&A box and press Send. 26

27 More Information For more information, please contact us: 27

28 Copyright 2016 Bruker Corporation. All rights reserved. Innovation with Integrity