Accession Number : AD0013839

Title :   THERMIONIC EMISSION AND ELECTRON DIFFRACTION FROM THIN FILMS OF BARIUM OXIDE

Corporate Author : MISSOURI UNIV COLUMBIA

Personal Author(s) : RUSSELL,PAUL N. ; EISENSTEIN,A.S.

Report Date : 01 JUL 1953

Pagination or Media Count : 1

Abstract : A high-vacuum, glass, sealed-off electron diffraction tube was developed for observing the physical structure of evaporated BaO films on an Ni substrate. Simultaneous measurements of thermionic emission were made. The thermionic activity of the deposited film increased until about 20 monolayers were deposited; no further increase was detected up to 50 monolayers. The emission density of 0.4 amp/sq cm at 1000 deg K was comparable with that obtainable from sprayed oxide coatings. With the receiver at less than 450 deg K, the oxide film showed an amorphous structure. With the receiver at 800 deg K, the film appeared to be in crystalline aggregate form; the preferred orientation in the diffraction patterns of a few monolayers indicated that the (1,0,0) planes of the cyrstallites coincided with the surface of the underlying substrate. THe crystalline structure became amorphous when the films were heated to 1070 deg K; the form persisted as the oxide film was removed by evaporation and was accompanied by a decreasing thermionic emission. Continued reevaporation of BaO from the sample reduced the emission to a common minimum level which was 6 orders of magnitude above that obtainable from clean Ni at 1000 deg K. The same thermionic emission characteristics, work function, and characteristic emission at 1000 deg K were obtainable from samples in different physical states. The relationship of the thermionic emission from thin BaO films to that from sprayed oxide cathodes is discussed.

Descriptors :   AMORPHOUS MATERIALS, COATINGS, CRYSTAL STRUCTURE, CRYSTALS, DENSITY, DEPOSITION, DIFFRACTION, ELECTRON DIFFRACTION, ELECTRON TUBES, EMISSION, EVAPORATION, FILMS, MEASUREMENT, OXIDE CATHODES, OXIDES, PATTERNS, PHYSICAL PROPERTIES, SEALED SYSTEMS, SPRAYS, SUBSTRATES, SYNCHRONISM, THERMIONIC EMISSION, WORK FUNCTIONS.

Distribution Statement : APPROVED FOR PUBLIC RELEASE