Introduction to Electron Probe Microanalysis (EPMA): Theory and Application

1. UofO- Geology 619 Electron Beam MicroAnalysis- Theory and ApplicationElectron Probe MicroAnalysis -(EPMA) Introduction: Merging discoveries in physics, chemistry, statistics and microscopy (Modified from Fournelle, 2006)

2. Scanning Electron Microscopy (SEM) & Electron Probe Micro Analysis (EPMA) Electron Gun and Column WDS Spectrometer Coaxial Zoom Optical System Airlock Specimen Stage

3. Related Analytical Techniques • Beam instruments: • Laser ablation ICP-MS (inductively coupled plasma mass spectrometry), LIMS • 10 to 50 um spot size • destructive • Ion microprobe, SIMS (secondary ion mass spectrometry), SHRIMP (high resolution) • low detection limits for many but not all elements • calibration curve type quantitation • isotopic sensitivity • Micro XRF (x-ray fluorescence) • low detection limits for many but not all elements • Auger- • not very quantitative • very surface sensitive • especially for lights elements • PIXE (particle induced x-ray excitation) uses protons (alpha particles) • order of magnitude lower detection limits • Non beam instruments: • XRF (x-ray fluorescence) • lower backgrounds, larger samples (bulk technique)

4. CAMCORCenter for Advanced Materials Characterization in ORegon • MicroAnalytical Facility- EPMA, VP-SEM, EBSD • John Donovan, donovan@uoregon.edu • Nano Fabrication Facility- SEM lithography, TEM, FIB • Kurt Langworthy, klangwor@uoregon.edu • Surface Analytical Laboratory- XPS, Auger, SIMS (TOF), AFM • Steve Golledge, golledge@uoregon.edu • X-ray Diffraction- XRD (powder, grazing incidence, single crystal) • Lev Zakharov, lev@uoregon.edu

5. EPMA: What is it good for? • Precise x-ray intensities • High spectral resolution • Sub-micron spatial resolution • Matrix/standard independent • Accurate quantitative chemistry

6. Applications of Electron Probe Microanalysis (EPMA) • Geology • Material Sciences • Chemistry • Physics • Biology • Civil Engineering • Paleontology • Soil Sciences • Archeology • Anthropology • Art History

7. Overview of Course Work (Lectures and Labs) • 1. Introduction to the EPMA/SEM laboratory: • Discussion of lecture notes, suggested reading materials. Grading methods, exams and current research projects. • Short history of the instrument and related techniques. • 2. Electron beam instrumentation and electron solid interactions: • Brief description of the major system components for both the electron microprobe and scanning electron microscope. • An introduction to elastic and inelastic scattering of electrons and associated principles. (chapters 1 and2). • 3. X-ray productions: • Generation and emission of characteristic and continuum x-rays. Absorption and fluorescence within the sample. (chapter 3). • 4. Electron Beam Columns: • Formation of electron beam, alignment. • Instrumental choices for parameterization with regards to application and specimen interaction. (chapter 4). • 5. Lab: Demonstration of electron beam parameters and sample interactions. • 6. WDS (wavelength dispersive spectrometer): • A description of the Bragg spectrometer and associated principles. (chapter 5) • 7. Lab: Demonstration of wavelength dispersive spectrometry technique and analysis. • 8. EDS (energy dispersive spectrometer): • Spectral analysis using the EDS detector. (chapter 6) • 9. Lab: Demonstration of energy dispersive spectrometry technique and analysis. • 10. Statistics: The essential key to scientific analysis. (chapter 7) • 11. Lab: Examples of the application of statistical calculations to quantitative analysis. • 12. Quantitative matrix corrections: • Introduction to the corrections being applied to the intensity data in order to obtain elemental concentrations. • Take home mid-term exam given out at the end of the lecture and due next class meeting. (chapter 9) • 13. Discussion: A demonstration of various compositionally dependent data corrections (peak shape, interferences, carbon contamination, volatile element loss, etc.) or a discussion of the questions from the take home mid-term test. • 14. Imaging and mapping: • An overview of electron and x-ray imaging and mapping techniques and the principles involved. (chapter 8) • 15. Lab: a demonstration of the analog and digital mapping capabilities on the electron microprobe and SEM.

8. Reference Books Reed (1996) 201 pages Paper: New:$36 Hard:New: $95 Used $80 Goldstein et al, 3rd Edition. 2003 New:$75

9. History of Electrons • 1650, Otto von Guericke built the first air pump; 1654 he demonstrated power of vacuum to German emperor (horses couldn’t pull 2 hemispheres apart) • Guericke built first frictional electric machine, producing sparks from a charged sulfur globe, which he reported to Leibniz in 1672 • 1745 at University of Leiden, the “Leyden jar” (primitive condensor) was built, a metal-lined glass jar with rod stuck in middle thru cork; it stored large quantities of static electricity produced thru friction • 1752, B. Franklin flew kite in thunderstorm and charged a Leyden jar (and was luckily not killed)

10. History of Electrons - cont’d • 18th Century: Benjamin Franklin described electricity as an elastic fluid made of extremely small particles. Electrical conductivity was observed in air near hot poker (= thermoionic emission of electrons) • Cathode ray effects (glow) noticed by Faraday (1821); named “fluorescence” in 1852 by Stokes • 1855 Geissler devised a pump to improve the vacuum in evacuated electric tubes (=Geissler tubes) • 1858 Plücker forced electric current thru a Geissler tube, observed fluorescence, and saw it was deflected by a magnet. Some credit him with discovery of cathode rays

11. History of Electrons - cont’d • 1875 Wm. Crookes devised a better vacuum tube • 1880 Crookes found that cathode rays travel in straight lines and could turn a wheel if it was struck on one side, and by their direction of curvature in magnetic field, that they were negatively charged particles • 1887 Photoelectric effect discovered by Heinrich Hertz: light (photon of l < critical for a metal) falling on metal surface ejects electrons from the metal • 1894, Philipp von Lenard (student of Hertz) put a thin metal window in vacuum tube and directed cathode rays into the outside air

12. History of Electrons - cont’d • Cathode rays confirmed by J.J. Thomson in 1897 to be electrons, and that they travel slower than light, they transport negative electricity and are deflected by electric field • 1900 Lenard, studying electric charges from illuminated metal surfaces (photoelectric effect), concluded they are identical to electrons of cathode ray tube • 1905 Einstein explained the theoretical basis of the photoelectric effect using Planck’s quantum theory (of 1900); for this, Einstein received Nobel Prize in physics in 1921

13. Electro-magnetic Spectrum

14. History of X-rays • 1885-1895 Wm. Crookes sought unsuccessfully the cause of repeated fogging of photographic plates stored near his cathode ray tubes. • X-rays discovered in 1895 by Roentgen, using ~40 keV electrons (1st Nobel Prize in Physics 1901) • 1909 Barkla and Sadler discovered characteristic X-rays, in studying fluorescence spectra (though Barkla incorrectly understood origin) (Barkla got 1917 Nobel Prize) • 1909 Kaye excited pure element spectra by electron bombardment

15. n l = 2d sin q History of X-rays - cont’d • 1912 von Laue, Friedrich and Knipping observe X-ray diffraction (Nobel Prize to von Laue in 1914) • 1912-13 Beatty demonstrated that electrons directly produced two radiations: (a) independent radiation, Bremsstrahlung, and (b) characteristic radiation only when the electrons had high enough energy to ionize inner electron shells. • 1913 WH + WL Bragg build X-ray spectrometer, using NaCl to resolve Pt X-rays. Braggs’ Law. (Nobel Prize 1915)

16. History of X-rays - cont’d • 1913 Moseley constructed an x-ray spectrometer covering Zn to Ca (later to Al), using an x-ray tube with changeable targets, a potassium ferrocyanide crystal, slits and photographic plates • 1914, figure at right is the first electron probe analysis of a man-made alloy T. Mulvey Fig 1.5 (in Scott & Love, 1983). Note impurity lines in Co and Ni spectra

17. l Z History of X-rays - cont’d • Moseley found that wavelength of characteristic X-rays varied systematically (inversely) with atomic number • Using wavelengths, Moseley developed the concept of atomic number and how elements were arranged in the periodic table. • The next year, he was killed in Turkey in WWI. “In view of what he might still have accomplished (he was only 27 when he died), his death might well have been the most costly single death of the war to mankind generally,” says Isaac Asimov (Biographical Encyclopedia of Science &Technology).

18. Historical Summary of X-rays • 1859 Kirchhoff and Bunsen showed patterns of lines given off by incandescent solid or liquid are characteristic of that substance • 1904 Barkla showed each element could emit ≥1 characteristic groups (K,L,M) of X-rays when a specimen was bombarded with beam of x-rays • 1909 Kaye showed same happened with bombardment of cathode rays (electrons) • 1913 Moseley found systematic variation of wavelength of characteristic X-rays of different elements • 1922 Mineral analysis using X-ray spectra (Hadding) • 1923 Hf discovered by von Hevesy (gap in Moseley plot at Z=72). Proposed XRF (secondary X-ray fluorescence) • 1923 Manne Siegbahn published The Spectroscopy of X-rays in which he shows that the Bragg equation must be revised to take refraction into account, and he lays out the “Siegbahn notation” for X-rays • 1931 Johann developed bent crystal spectrometer (higher efficiency)

19. Summary of X-ray Properties • X-rays are considered both particles and waves, i.e., consisting of small packets of electromagnetic waves, or photons. • X-rays produced by accelerating HV electrons in a vacuum and colliding them with a target. • The resulting spectrum contains (1) continuous background (Bremsstrahlung;“white X-rays”), (2) occurrence of sharp lines (characteristic X-rays), and (3) a cutoff of continuum at a short wavelength. • X-rays have no mass, no charge (vs. electrons)

20. History of the Electron Microscope • 1937 grad students J. Hillier and A. Prebus at Univ. of Toronto built an electron microscope that magnified 7000x • 1940 Hillier hired (pre PhD) by Zworykin of RCA to immediately build an electron microscope to sell (and pay back his salary) (Electron microscope, U.S. Patent No. 2,354,263; 1944)

21. History of the Electron Microscope - cont’d Cambridge Instrument Co Stereoscan MK-1

22. History of the Electron Microprobe • Hillier also developed the idea of adding an “x-ray spectroscope” strongly reminiscent of Moseley’s design, with a flat diffracting crystal and a photographic plate as a detector. • Electron probe analysis employing x-ray spectography (No. 2, 418, 029; 1947) • Unfortunately RCA had no interest in pursuing EPMA! From Hillier’s 1947 patent

23. History of the Electron Microprobe - cont’d • Castaing, while not the inventor under Patent Law, may be rightly regarded as the father of EPMA • In his Ph.D. (Castaing, 1951), he laid down the fundamental principles of the method and its use as a tool for microanalysis. • He established the theoretical framework for the matrix corrections for absorption and fluorescence effects • 1956, commercial electron microprobe production begins with Cameca MS85* *MicroSonde=microprobe

24. History of the Electron Microprobe - cont’d • 1960, Cambridge Instrument Co produced a rastered beam instrument (SEM) to make X-ray maps. • 1968, solid state EDS detectors developed. These are add-ons to SEMs and EMPs. • 1970, Microspec develops “add-on” crystal (WDS) spectrometer for SEMs. • By 1970-80s: Scanning coils included on EMPs for SE and BSE imaging. • 1984, development of synthetic multilayer diffractors (large 2d), for WDS of light elements. • 1990s experimental development of micro-calorimeter EDS detectors, large area crystals, development of sophisticated software.

25. General References Scanning Electron Microscopy and X-Ray Microanalysis, Third Edition by J. Goldstein, D.E. Newbury, D.C. Joy, C. E. Lyman, P. Echlin, E. Lifshin, L. C. Sawyer, and J.R. Michael. Plenum Press. 2003. Scanning Electron Microscopy and X-Ray Microanalysis, Second Edition by Goldstein, Newbury, Echlin, Joy, Fiori and Lifshin. Plenum Press. 1992. Scanning Electron Microscopy and X-Ray Microanalysis, First Edition, by Goldstein, Newbury, Echlin, Joy, Fiori and Lifshin. Plenum Press. 1981. Electron Microprobe Analysis by S. J. B. Reed. Cambridge Univ Press. Second edition, 1993. Electron Microprobe Analysis by S. J. B. Reed. Cambridge Univ Press. First edition, 1975. Electron Microprobe Analysis and Scanning Electron Microscopy in Geology by S. J. B. Reed. Cambridge Univ Press. 1996. Contact Information John J. Donovan donovan@uoregon.edu University of Oregon (541) 346-4632 (office) 1443 E. 13th Ave (541) 346-4655 (lab) Eugene, OR 97403-1241 Lab Web: http://epmalab.uoregon.edu/ EPMA (SX100)Schedule: http://sweetwater.uoregon.edu/sx100 EPMA (SX50) Schedule: http://sweetwater.uoregon.edu/epma SEM (Quanta) Schedule: http://sweetwater.uoregon.edu/sem Remote Access: http://epmalab.uoregon.edu/howto.htm Personal: http://www.uoregon.edu/~donovan/