Titanium impurity effects in thin film oxide cathodes

R. S. Schmid, C. G. Pantano

Research output: Contribution to journalArticle

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Abstract

This investigation concerns a relatively new form of oxide cathode which is fabricated on a sapphire wafer utilizing electron beam evaporated metallurgy and an alkaline-earth carbonate/photoresist mixture. The heater (Ti/Mo/Ti sandwich), cathode (Ba, Sr, Ca-oxide on W) and grid (Ti on W) structures are delineated using photolithography and wet-etching. During the initial thermal activation of the cathode, the photoresist and carbonates decompose to leave the electron emissive alkaline-earth oxides in well defined areas. The behavior of some prototype thin-film cathodes was found to depend upon the concentration of Ti impurities in the W base-metal film. Secondary ion mass spectroscopy (SIMS) was used to quantitatively determine the concentration of Ti in the W films. High temperature Auger electron spectroscopy (AES) showed rapid surface segregation of these Ti impurities upon heating to 850°C in ultra-high vacuum. The emission lifetime of cathodes fabricated with these W films was inversely proportional to the Ti impurity concentration. Moreover, AES analyses of the emitting oxide surfaces showed a correlation between the Ba/O ratio and the emission current density. It is proposed that the Ti impurities segregate to the oxide/W interface at 850°C where they can reduce the BaO and thereby effectively activate the cathode. However, segregation to the interface, and/or the subsequent BaO reduction, occurs rapidly in the case of Ti in W and leads to a shortened emission lifetime. It is likely that the Ti-oxide reaction products left behind at the interface increase the cathode resistance, and perhaps more importantly, create a chemico-physical barrier which limits any subsequent reaction of Ti, W or other activating agents with the BaO species.

Original languageEnglish (US)
Pages (from-to)37-49
Number of pages13
JournalApplications of Surface Science
Volume21
Issue number1-4
DOIs
StatePublished - Apr 1985

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Titanium
Oxides
Cathodes
Impurities
Thin films
Carbonates
Auger electron spectroscopy
Photoresists
Earth (planet)
Surface segregation
Wet etching
Aluminum Oxide
Ultrahigh vacuum
Photolithography
Metallurgy
Reaction products
Sapphire
Electron beams
Current density
Metals

All Science Journal Classification (ASJC) codes

  • Engineering(all)

Cite this

Schmid, R. S. ; Pantano, C. G. / Titanium impurity effects in thin film oxide cathodes. In: Applications of Surface Science. 1985 ; Vol. 21, No. 1-4. pp. 37-49.
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Titanium impurity effects in thin film oxide cathodes. / Schmid, R. S.; Pantano, C. G.

In: Applications of Surface Science, Vol. 21, No. 1-4, 04.1985, p. 37-49.

Research output: Contribution to journalArticle

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