Radiant energy – Inspection of solids or liquids by charged particles
Patent
1982-09-13
1984-12-04
Radiant energy
Inspection of solids or liquids by charged particles
G01N 2322, H01J 37285
Patent
active
044866593
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an emission-electron microscope.
There are various ways in which a specimen material can be stimulated so as to emit electrons. For example photo-electrons may be emitted from the surface of a specimen irradiated with photons of sufficient energy. Another method of stimulation is to irradiate the specimen with neutral atoms to produce emitted electrons. Also thermal electrons may be emitted when a specimen material is heated.
Throughout the description and claims of this specification, electrons which are emitted from the specimen itself, usually, though not always, as a result of being suitably stimulated, are referred to as "emission electrons".
The present invention is concerned with apparatus, referred to as a microscope, for imaging the surface of an electron emitting specimen usng these emission electrons. The image produced is indicative of the distribution over the imaged surface of the flux of emission electrons.
Considering particularly photo-electrons, the technique of photo-electron spectroscopy is well known and has been used for determining properties of specimens dependent on the ionization energy of atoms in the surface region of the specimen. Well known text books on the technique are "Principles of Ultra Violet Photoelectron Spectroscopy", by J. W. Rabalais, published by Wiley, and "Electron Spectroscopy, Theory Techniques and Applications" Vols. 1-3 Eds. C. R. Brundle and A. D. Baker, Academic Press 1977.
In photo-electron spectroscopy it is known to irradiate a specimen with ultra violet radiation, usually vacuum ultra violet, or alternatively with soft x-rays, to stimulate the specimen to emit photo-electrons. Various techniques are then employed to determine the energy spectrum of the emitted photo-electrons. One problem with photo-electron spectroscopy is that photo-electrons are normally emitted over a solid angle of a full 4.pi., or 2.pi. for the plain surface of a solid specimen, so only relatively few enter the aperture of the energy analyser.
One way of improving the flux of photo-electrons entering the electron analyser of the spectrometer involves carrying out the photo-electron experiment in a strong magnetic field. This is described in the journal, Phys. Scr. 61 186, in an article by Beamson, Pearce and Turner entitled "Photo-electron spectroscopy in a strong magnetic field". That article describes a technique of collimating the photo-electron flux using an axially symmetric homogeneous magnetic field. In such an arrangement, electrons emitted form the surface of the specimen at an angle to the direction of the magnetic field are constrained by the field to orbit about the lines of flux of the field and therefore travel with a helical path along the magnetic field direction.
It has also been proposed to carry out photo-electron spectroscopy in an axially symmetric inhomogeneous magnetic field, that is a field in which the flux lines converge or diverge along the axis of the field. It can then be shown that, if the specimen is located in a region of relatively high magnetic field so that photo-electrons emitted thereby travel along the axis of the field into a region of lower field strength, any kinetic energy of the electrons transverse to the direction of the magnetic field is progressively transferred to energy along the field direction as the electron moves into the region of weaker magnetic field. A discussion of this phenomenon is given in the article entitled "The collimating and magnifying properties of a superconducting field photoelectron spectrometer", by Beamson, Peter and Turner, published in the Journal of Physics, J. Phys. E:Sci. Instrum., Vol 13, 1980, page 64.
In that article it is explained that if the ratio between the magnetic field at the specimen and the field at the energy analyser is sufficiently large nearly all the transverse kinetic energy of the emitted electrons has been transferred to longitudinal energy by the time the electrons arrive at the analyser. This greatly facilitates the measurement of electron energy s
REFERENCES:
patent: 3822382 (1974-07-01), Koike
patent: 4096386 (1978-06-01), Rempfer et al.
Journal of Physics, E. Scientific Instuments, vol. 13, 1980 (London, GB), G. Beamson et al.: "The Collimating and Magnifying Properties of a Superconducting Field Photoelectron Spectrometer", pp. 64-66, see page 64, left-hand column, last paragraph, p. 65, left-hand column, last paragraph to p. 66, left-hand column, end of the first paragraph, figure 1, p. 66, pargraph 3 cited in the application.
Instruments and Experimental Techniques, vol. 21, No. 4, part 2, Jul./Aug. 1978 (New York, US), A. V. Gostev et al.: "Universal Instrument for the Investigation of Local and Integral Electron Emission", pp. 1053-1055, see whole document.
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