AUGER ELECTRON EMISSION ANALYSIS

The latter method of particle spectroscopy is closely related to the method discussed here, with the exception that X-ray excitation produces photoele...
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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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