Electron probe microanalysis - Scanning Electron Microscopy EPMA - SEM

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Electron probe microanalysis - Scanning Electron
MicroscopyEPMA - SEM
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• An Historical Introduction
• Merging of discoveries in physics, chemistry and
  microscopy

Revised 1/21/2019
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OverviewMany things come together to produce
the technology we have
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• Vacuum technology
• Discovery and understanding of electrons and
  x-rays
• Spectroscopy and chemical analysis
• Development of electron and x-ray instruments
• Essentials of an electron microprobe

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Electrons - 1
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• 1650, Otto von Guericke built the first air
  pump 1654 he demonstrated power of vacuum to
  German emperor (horses couldnt pull 2
  hemispheres apart) in Magdeburg
• Guericke built first frictional electric
  machine, producing sparks from a charged sulfur
  globe, which he reported to Leibniz in 1672
• 1705, Francis Hauksbee improved the frictional
  machine (evacuated glass sphere, turned by crank)
• 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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Electrons - 2
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• 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 ( electrons)

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Electrons - 3
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• 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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Electrons - 4
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• 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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Electrons - 5
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• 1922 Auger electrons discovered (internal
  photoelectric effect)
• 1927 electron diffraction discovered
  independently by Davisson (US) and Thomson (Gt.
  Britain)

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X-rays - 1
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• 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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X-rays - 2
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• 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 2 radiations (a) independent
  radiation, Bremsstrahlung, and (b) characteristic
  radiation only when the electrons had high enough
  energy
• 1913 WH WL Bragg build X-ray spectrometer,
  using NaCl to resolve Pt X-rays. Braggs Law.
  (Nobel Prize 1915)

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X-rays - 3
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• 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 manmade alloy (brass)

T. Mulvey Fig 1.5 (in Scott Love, 1983). Note
impurity lines in Co and Ni spectra
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X-rays - 4
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• 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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X-rays - 5
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• 1916 Manne Siegbahn and W. Stenstrom observe
  emission satellite lines (Nobel to first in 1924)
• 1923 Arthur Compton discovered effect relating
  direction taken by X-ray and electron after
  collision, with the energy of collision
• 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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X-rays - 6
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• X-rays are considered both particles and waves,
  i.e., consisting of small packets of
  electromagnetic photons or waves.
• 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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X-rays 9 Features-1 (per Roentgen)
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1. X-rays cause many materials to fluoresce
besides the original BaPbCN coating observed by
Roentgen. 2. X-rays affect photographic
emulsions. 3. When exposed to X-rays, electrified
objects lose charge. 4. Some materials
transparent to X-rays 5. X-rays collimated by
pinholes, showing they travel in straight
lines. 6. X-rays not deflected by magnetic
fields, and so are not streams of charged
particles.
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X-rays 9 Features-2(per Roentgen)
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7. X-rays produced by beams of high energy
cathode rays striking objects. 8. Heavy elements
more efficient producers of X-rays compared to
light elements. 9. Reflection and refraction of
X-rays (bending of rays at interface) not
observed (but later they were found to exist in
small degrees.)
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Chemical analysis
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• 1859 Kirchhoff and Bunsen showed patterns of
  lines (spectra, colors) 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 the 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)

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Electron Microscopy -1
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• 1926 Busch developed theory of magnetic lens to
  focus electrons, confirmed by Ernst Ruska in 1929
  -- at High Voltage Institute, Berlin, under Max
  Knoll -gt created first oscilliscope to study
  surges in HV cables from lightning in newly
  constructed streetcar lines
• 1932 Ruska built the first electron microscope,
  with prototype by Siemens Halske Co. Ruska
  received, belatedly, Nobel Prize for it in 1986.
• 1930s, electron microscopes also built in labs
  in England, Belgium, USA, Canada
• 1938-44, commercially Siemens delivered 38
  electron microscopes also models built by RCA
  and Japanese firms.

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Electron Microscopy -2
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• 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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Electron Microscopy - SEM
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• A scanning electron microscope was built in mid
  1930s by Manfred von Ardenne (his Berlin lab was
  bombed in 1944 and he never returned to SEM
  development)
• 1942 at RCA, Hillier built SEM and used it to
  examine surfaces of specimens

• Post WWII (1950s), Dennis McMullan at Cambridge
  (England) began working on SEMs under Oakley.
  Culminated in 1965 with first commercial SEM, the
  Stereoscan by Cambridge Instrument Co.

Stereoscan MK-1
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Electron Microprobe - Precursors

• 1898 in Berlin, Starke measured the
  backscattered fraction of electrons and plotted
  it against atomic weight. First electron probe
  (not micro).
• 1909, Kaye built apparatus to bombard moveable
  specimens with 28 keV electrons and observe gas
  discharge in ionization chamber using various
  elemental absorption screens to identify unknown
  by deduction
• 1912-13, Beatty built apparatus that showed that
  the effective depth of production of x-rays was
  very small (lt10 mm), which would have critical
  implications for development of microanalysis

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Electron Microprobe - 1
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• Hillier 1943 and Hillier and Baker (1944) at RCA
  Labs at Princeton NJ built an electron
  microprobe, by combining an electron projection
  microscope and an energy-loss spectrometer.
• They obtained spectra of C, N and O K radiation
  from a collodion film
• U.S. Patent 1945, Electron microanalyzer (No.
  2,372,422)

RCA electron-probe microanalyzer (Hillier and
Baker, 1944)
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Electron Microprobe - 2
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• 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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Electron Microprobe - 3
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• It would appear that, because of post-war
  difficulties in scientific communication, news of
  the Hillier Patent had not reached Castaing and
  Guinier in France in 1947.
• In January 1947 Raymond Castaing had joined
  the research staff of ONERA and became involved
  in the setting up of

an electron microscope laboratory for
metallurgical and materials research. In 1948
during an investigation into properties of Cu-Al
alloys, Professor Guinier asked Castaing about
the possibility of making a point by point
analysis of a metal sample by bombarding it with
electrons and measuring the characteristic x-ray
emission.
Quotes from T. Mulvey (1983) Development of
electron-probe microanalysis-an historical
perspective
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Electron Microprobe - 4
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• The idea was to analyze at least qualitatively
  areas of some hundreds of Å units in diameter
  although it was realized that the counting rates
  would be low, perhaps a few pulses a minute. It
  was a tall order but by early 1949 Castaing had
  succeeded in producing an electron probe of 1 mm
  in diameter with current 10 nA when everything
  worked OK.

• The first version of his probe used a Geiger
  counter which could not distinguish elements
  directly. In 1950 he fitted a quartz crystal
  prior to the Geiger counter to permit wavelength
  discrimination, and added an optical microscope
  to view the point of beam impact.

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Electron Microprobe - 5
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• 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 (above), followed in
  1958 by Hitachi.MicroSondemicroprobe

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Electron Microprobe - 6

• In the early or mid-50s, Buschmann at GE built
  an electron microprobe (right) modelled after
  Castaings that has been called the first
  operating microprobe in the U.S.
• However, the bean counters at GE said there was
  no market for such an instrument and persuaded
  management to abandon its commercial development.

Newberry, p. 57
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Electron Microprobe - 7
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• 1960 ARL EMX, and MAC EMPs. 1961, first JEOL
  EMP. Many researchers build homebrew electron
  microprobes
• Motivation space/arms race, semi-conductor and
  other materials research.

David Wittry built an EMP at Cal Tech, shown to
right (Thesis, 1957). He and his advisor Pol
Duwez also translated Castaings thesis (with
Army ).
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Developments forSEM-Electron Microprobe
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• 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 (He-cooled very
  problematic).

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Developments forSEM-Electron Microprobe
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• 1999, development of non-Rowland Circle X-ray
  detectors using polycapillary optics (Madison
  Thermo)
• 2003 JEOL introduces an electron microprobe with
  a field emission source (CAMECA joins club 8
  years later)
• 2011 Soft X-ray Emission Spectrometer (SXES)
  demonstrates ability to analyze Li and other
  light elements (Terauchi, Takahashi)
• 2018 Wuhrer Moran replace the traditional gas
  X-ray detector with a solid state (EDS-type)
  detector. Important advance, yet to come to the
  market.

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Selected References
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• Mulvey, T, 1983, The development of
  electron-probe micro-analysis--An historical
  perspective, in Quantitative Electron-Probe
  Microanalysis (Eds V.D. Scott and G. Love),
  Wiley, p. 15-35.
• Asimov, I, 1972, Asimovs Biographical
  Encyclopedia of Science and Technology,
  Doubleday, 805 pp.
• Asimov, I., 1994, Asimovs Chronology of Science
  and Discovery, Harper Collins, 791 pp.
• Newberry, S. P., 1992, EMSA and Its People The
  First Fifty Years, Electron Microscopy Society of
  America
• Clark, G. L., 1940, Applied X-rays, McGraw Hill
  (Ch.1 Before and after the discovery by
  Roentgen)
• David Wittry, Early history of Microbeam
  Analysis Society, on MAS (Microanalysis Society)
  website