H. Bruining

Secondary electron emission: Part I. Secondary electron emission of metals

Summary In general metals are able to emit a small number of secondary electrons. The electropositive elements have a smaller secondary emission with a primary electron energy of 100 volts or more than metals with a high work function. The opposite contention is often encountered in literature; it is pointed out that this is due to experimental errors (insufficient vacuum), consisting in the fact that the measurements are carried out on the compounds which have a much higher secondary electron emission. Several short statements of the facts observed are given, and these facts will be interpreted in further articles.

Secondary electron emission: Part II. Absorption of secondary electrons

Summary It is demonstrated that the absorption of secondary electrons may be the cause of the fact that, with perpendicularly incident primary electrons, the secondary emission of metals with a large atomic volume is lower than that of metals with a small atomic volume. The absorption can be measured indirectly by allowing the primary electrons to strike the target at an angle of incidence greater than 0°; the results of the experiments show that this hypothesis is probably correct.

Secondary electron emission Part IV. Compounds with a high capacity for secondary electron emission

Abstract It is shown that a pure compound of an alkali metal has a high capacity for secondary electron emission. It is pointed out that the electrons fixed to the atoms of the electro-negative element (the electrons in the highest occupied energy band) have the greatest chance of being emitted as secondary electrons. It is proved experimentally that it is impossible that all secondary electrons have their source in metal atoms within or on the surface of the compound. These metal atoms serve only as sources of conduction electrons.

Secondary electron emission Part V. The mechanism of secondary electron emission

Abstract With the aid of a simple energy scheme (fig. 1) it can be understood, that the compounds of metals with a low ionisation energy, consisting of ions with closed electron shells, (table I) have a high capacity for secondary electron emission, whereas the compounds of metals with a high ionisation energy (table II) have a relatively low secondary emission.

Secondary electron emission: Part III. Secondary electron emission caused by bombardment with slow primary electrons

Summary Upon bombardment with very slow electrons (Vp = circa 10 volts) the electropositive elements (barium) have a higher secondary electron emission than metals such as silver. The coefficient of elastic reflection of barium is less than that of silver. Compounds of the electropositive elements have a high capacity for secondary emission and for reflection.

Secondary electron emission of soot in valves with oxidecathode

Summary When a carbon surface is covered with baryum atoms, the capability for secondary emission rises in the first instance. However, soot directly precipitated from the atmosphere round a burning flame is composed of very small particles and was found to behave exceptionally. It is apparent from the change of the secondary emission with time that the baryum atoms, precipitated on this carbon modification, fade away by a moderately strong electron bombardment. Owing to local heatings the baryum migrates then to soot particles at greater depth. Soot, sprayed on a metal surface, shows this migration in less degree. In this modification the small particles are conglomerated to larger ones. This is confirmed by electron diffraction experiments.

Secondary electron emission Part VI. The influence of externally adsorbedions and atoms on the secondary electron emission of metals

Abstract When a metal surface is gradually covered with atoms of an electropositive metal (Ba on Mo), the secondary and photoelectric emission both pass through a maximum at the same degree of covering (σ = σ m ). From this it may be concluded that the rise of the secondary emission is caused by the decrease of the workfunction. The secondary emission is a linear function ofσ, with small degree of covering (σ ≪ σ m ) the photoelectric emission is an exponential function ofσ (irradiation with white visible light). This difference is caused by the fact that the energy of the escaping secondary electrons is much greater than that of the photoelectrons. It is shown, that a selective secondary emission from the adsorbed atoms might be observable with slowly moving primary electrons.

Secondary electron emission from metals with a low work function

Zusammenfassung Die Sekundarelektronenemission von Aluminium- und Berylliumplatte, deren Oxydhaut mittels Kathodenzerstaubung entfernt worden ist, wird bestimmt.