Lawrence A. Harris Research and Development Center General Electric Company Schenectady, New York
AUGER ELECTRON
EMISSION ANALYSIS A NALYTICAL
SCIENTISTS
are
be-
~^*- coming increasingly aware of the advantages, usefulness, and potential applications of various forms of electron spectroscopy, especially in t h e area of surface analysis. Recent articles in this journal, for example, have noted the advantages of low energy electron diffraction ( L E E D ) (1) and electron spectroscopic chemical analysis (ESCA) (£). The latter method of particle spectroscopy is closely related to the method discussed here, with the exception t h a t X - r a y excitation produces photoelectric as well as Auger emission of electrons. Auger electrons, with energies characteristic of t h e emitting atom,
have been known for quite some time (3—6), b u t it has only been recently t h a t dramatic steps have been taken to move spectroscopic detection of t h e electrons, with a concomitant indication of t h e elements associated with various peak energies, toward a reliable analytical procedure. The Auger electron spectroscopic procedure described herein possesses several real advantages : • Light elements are more readily detected • Equipment required is of modest size and cost • The method is nondestructive • Extremely thin layers on t h e
surface of solids can be detected • T h e method is sensitive On t h e other side of the coin, the method requires a vacuum and freedom from organic material contamination, and detection of heavier elements becomes difficult. However, since X - r a y methods are available for the heavier elements, this last disadvantage does not detract from t h e overall usefulness of the method, and Auger electron emission should take its place among the sensitive methods for elemental detection (and quantitative determination, as improvements are made). The Method
VACUUM
SINGLE ATOM
SOLID
Figure 1 . Schematic of the Auger process
24 A
•
ANALYTICAL CHEMISTRY
Figure 1 shows, in a simplified schematic way, t h e essential nature of the Auger process with which we are concerned. W e postulate t h a t an atom has been ionized in one of its inner shells, either by electron or photon irradiation. T h e excited atom rearranges itself b y filling the ionized shell with an electron from a higher energy orbit and b y releasing t h e energy of t h e transition. This energy m a y be carried off either by a photon or by another electron, the Auger electron. I n either case the energy released is characteristic of the parent atom and m a y be used to identify it. X - r a y fluorescence has been a standard method of analysis for a long time, b u t t h e probability of
REPORT FOR ANALYTICAL CHEMISTS
Sample Wheel
Electron Emitter for Sample Heating
127° Sector Analyzer
Primary Power Supply
Electron Multiplier. J ^ Deflector Supply
Reference ac Signal
Multiplier Supply
Lock-In Amplifier
Figure 2 . Apparatus used for measuring Auger emission
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