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
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An Historical Introduction:
Merging of discoveries in physics, chemistry and microscopy
Electrons and x-rays
Spectroscopy and chemical analysis
Development of electron and x-ray instruments
Essentials of an electron microprobe
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)
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
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
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
1922 Auger electrons discovered (“internal photoelectric effect”)
1927 electron diffraction discovered independently by Davisson (US) and Thomson (Gt. Britain)
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
n l = 2d sin q
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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)
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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Moseley found that wavelength of characteristic X-rays varied systematically (inversely) with atomic number
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)
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)
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.
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.)
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)
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.
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)
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
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
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)
From Hillier’s 1947 patent
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”
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
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
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 $).
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.
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, 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