Electron Beam MicroAnalysis- Theory and Application Electron Probe MicroAnalysis - (EPMA)

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

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CAMCORCenter for Advanced Materials
Characterization in ORegon

• MicroAnalytical Facility- EPMA, VP-SEM, EBSD
• John Donovan, donovan_at_uoregon.edu
• Nano Fabrication Facility- SEM lithography, TEM,
  FIB
• Kurt Langworthy, klangwor_at_uoregon.edu
• Surface Analytical Laboratory- XPS, Auger, SIMS
  (TOF), AFM
• Steve Golledge, golledge_at_uoregon.edu
• X-ray Diffraction- XRD (powder, grazing
  incidence, single crystal)
• Lev Zakharov, lev_at_uoregon.edu

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EPMA What is it good for?

• Precise x-ray intensities
• High spectral resolution
• Sub-micron spatial resolution
• Matrix/standard independent
• Accurate quantitative chemistry

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Applications of Electron Probe Microanalysis
(EPMA)

• Geology
• Material Sciences
• Chemistry
• Physics

• Biology
• Civil Engineering
• Paleontology
• Soil Sciences

• Archeology
• Anthropology
• Art History

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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 and 2).
• 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)

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Reference Books
Reed (1996) 201 pages Paper New36 HardNew
95 Used 80
Goldstein et al, 3rd Edition. 2003
New75
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History of Electrons

• 1650, Otto von Guericke built the first air
  pump 1654 he demonstrated power of vacuum to
  German emperor (horses couldnt 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)

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History of Electrons - contd

• 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

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History of Electrons - contd

• 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 lt 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

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History of Electrons - contd

• 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 Plancks quantum
  theory (of 1900) for this, Einstein received
  Nobel Prize in physics in 1921

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Electro-magnetic Spectrum
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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

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History of X-rays - contd

• 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)

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History of X-rays - contd

• 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
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History of X-rays - contd

• 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).

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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 Z72). 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)

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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 (Bremsstrahlungwhite 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)

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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)

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History of the Electron Microscope - contd
Cambridge Instrument Co Stereoscan MK-1
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History of the Electron Microprobe

• Hillier also developed the idea of adding an
  x-ray spectroscope strongly reminiscent of
  Moseleys 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 Hilliers 1947 patent
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History of the Electron Microprobe - contd

• 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
  MicroSondemicroprobe

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History of the Electron Microprobe - contd

• 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.

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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_at_uoregon.edu University of Oregon
[phone] (office) 1443
E. 13th Ave [phone]
(lab) Eugene, OR
97403-1241 Lab Web http//epmala
b.uoregon.edu/ EPMA (SX100)Schedule http//sweetw
ater.uoregon.edu/sx100 EPMA (SX50)
Schedule http//sweetwater.uoregon.edu/epma SEM
(Quanta) Schedule http//sweetwater.uoregon.edu/s
em Remote Access http//epmalab.uoregon.edu/howto
.htm Personal http//www.uoregon.edu/donovan/