Transcript UW- Madison Geology 777 Electron probe microanalysis Electron microprobe analysis EPMA (EMPA) An Historical Introduction: Merging of discoveries in physics, chemistry and microscopy Revised 1/21/2012

UW- Madison Geology 777
Electron probe microanalysis Electron microprobe analysis
EPMA (EMPA)
An Historical Introduction:
Merging of discoveries in
physics, chemistry and
microscopy
Revised 1/21/2012
UW- Madison Geology 777
Overview
•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
• 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) 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
• 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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Electrons - 3
• 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
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Electrons - 4
• 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
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Electrons - 5
• 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
• 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 Xrays, 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
• 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)
n l = 2d sin q
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X-rays - 3
• 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
T. Mulvey Fig 1.5 (in Scott & Love, 1983). Note
impurity lines in Co and Ni spectra
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X-rays - 4
•Moseley found that wavelength of characteristic
X-rays varied systematically (inversely) with
atomic number
• Using wavelengths,
Moseley developed the
l
concept of atomic
number and how
elements were arranged
in the periodic table.
Z
• 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
• 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
•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)
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X-rays: 9 Features-1
(per Roentgen)
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)
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
•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)
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Electron Microscopy -1
• 1926 Busch developed theory of magnetic lens to
focus electrons, confirmed by Ernst Ruska in 1929 -- at
High Voltage Institute, Berlin, under Max Knoll-- all
related to need to find a way to study surges in HV
cables from lightning
• 1932 Ruska built the first electron microscope, with
prototype by Siemens & Halske Co. Ruska received,
belatedly, Nobel Prize for it in 1986.
• 1930’s, 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
• 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
• 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, Dennis
McMullan at Cambridge
(England) began working
on SEMs. Culminated in
1965 with first commercial
SEM, the Stereoscan by
Cambridge Instrument Co.
Stereoscan MK-1
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
(<10 mm), which would have critical implications for
development of microanalysis
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Electron Microprobe - 1
• 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
• 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
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Electron Microprobe - 3
• “It would appear that, because of postwar 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
• “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
• 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.*MicroSonde=microprobe
Electron Microprobe - 6
• In the early or mid-50s,
Buschmann at GE built an
electron microprobe (right)
modelled after Castaing’s 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
• 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 Castaing’s thesis
(with Army $).
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Developments for
SEM-Electron Microprobe
•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.
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Selected References
• Mulvey, T, 1983, The development of electron-probe microanalysis--An historical perspective, in Quantitative ElectronProbe Microanalysis (Eds V.D. Scott and G. Love), Wiley, p. 1535.
• Asimov, I, 1972, Asimov’s Biographical Encyclopedia of
Science and Technology, Doubleday, 805 pp.
• Asimov, I., 1994, Asimov’s 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 website