Properties of thin antimultipactor TiN and Cr/sub 2/O/sub 3/ coatings for klystron windows

Journal Article · Mon Sep 01 00:00:00 EDT 1986 · J. Vac. Sci. Technol., A; (United States)

DOI:https://doi.org/10.1116/1.574076· OSTI ID:5062602

Nyaiesh, A R; Garwin, E L; King, F K; Kirby, R E

Low secondary electron emission yield (1--1.3), low radio-frequency (rf) loss films are of interest as coatings for alumina ceramic high power klystron windows. Very thin (15--50 A-circle) Ti and TiN layers have been previously used with success in klystron tubes operating at lower power levels (<35 MW peak power) and short (2.5 ..mu..s) pulses but are subject to property changes during air exposure, tube bakeout (550 /sup 0/C for up to 10 days) and i-italicn-italic s-italici-italict-italicu-italic electron bombardment. Higher power tubes (> or =50 MW) with longer (5 ..mu..s) pulse lengths require coatings that remain stable under these more rigorous conditions in order to avoid multipactoring and window failure due to overheating. Air-oxidized Cr films offer an alternative to TiN. This work shows that they have the required resistivity for low rf loss, combined with stability in the secondary electron emission (SEE) yield under bakeout and electron bombardment. SEE, AES, XPS, ELS, oxidation, bakeout, and electron bombardment results are presented for Cr and TiN layers deposited by sputtering onto high density alumina substrates. The surface of TiN oxidized to a 9 A-circle thick TiO/sub 2/ layer which, under bakeout to 550 /sup 0/C in vacuum, thinned to 6 A-circle. This extreme layer thinness resulted in a significant drop in the SEE yield which, unfortunately, was reversible upon reoxidation. The oxidized layer on Cr was 17 A-circle of Cr/sub 2/O/sub 3/ which thinned to 13 A-circle upon bakeout. This thicker oxide layer produced a stable SEE yield which, although not as low as oxidized TiN, is sufficient to prevent electron multipactor. Windows covered by air-oxidized Cr films are at least as good, under tube processing conditions, as the best TiN-coated windows.

• Research Organization: Stanford Linear Accelerator Center, Stanford University, Stanford, California 94305
• DOE Contract Number: AC03-76SF00515
• OSTI ID: 5062602
• Journal Information: J. Vac. Sci. Technol., A; (United States), Vol. 4:5
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
COATINGS
CHROMIUM OXIDES
SECONDARY EMISSION
SURFACE COATING
KLYSTRONS
OPERATION
WINDOWS
TITANIUM NITRIDES
CERAMICS
OXIDATION
STABILITY
THIN FILMS
ALUMINIUM COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
CHROMIUM COMPOUNDS
DEPOSITION
ELECTRON TUBES
ELECTRONIC EQUIPMENT
EMISSION
EQUIPMENT
FILMS
MICROWAVE EQUIPMENT
MICROWAVE TUBES
NITRIDES
NITROGEN COMPOUNDS
OPENINGS
OXIDES
OXYGEN COMPOUNDS
PNICTIDES
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
360204* - Ceramics
Cermets
&amp; Refractories- Physical Properties