- Email: [email protected]
233. Anode surface effects in diodes containing oxide-coated cathodes
Abstracts 230--239
344
Coefficients of Evaporation and Condensation. N o . 216. 18.
17 : 16 See Abstract
G a s e o u s Electronics
18 230. Noise Propagation on Uniformly Accelerated Multivelocity Electron Beams. W. M. Mueller a n d M. R. Currie, J. Appl. Phys., 1876-1880, Dec. 1959. 18 231. Propagation Characteristics of Detonation-Generated Plasmas. Melvin A. C o o k , R o b e r t T. K e y e s a n d Lex L. Udy, J. Appl. Phys., 1881-1892, Dec. 1959.
232. Charge Cathodes.
Localization
18 on the Surfaces of Oxide-Coated
United Kingdom. A n o m a l o u s results o b t a i n e d while u s i n g the Kelvin m e t h o d o f d e t e r m i n i n g c o n t a c t potential differences between oxide-coated c a t h o d e s a n d a n e v a p o r a t e d gold film reference surface in an a t m o s p h e r e o f h y d r o g e n have been investigated. Very high c o n t a c t potential differences have been associated with a s e p a r a t i o n o f charge f r o m ionized gas o n the p a s s a g e o f a discharge current. This charge, either positive ions or electrons, r e m a i n s on the surface o f the oxide c a t h o d e for periods ( s o m e t i m e s as long as several days) d e p e n d e n t on the c o n d u c t i v i t y o f the oxide coating. This in turn d e p e n d s u p o n the n a t u r e o f the oxide material, its state of activation a n d its t e m p e r a t u r e . E x p e r i m e n t s are also described o n the b e h a v i o u r o f p r o b e c a t h o d e s in h y d r o g e n . B. J. H o p k i n s a n d F. A. Vick, Brit. J. Appl. Phys., 11, 223-227, J u n e 1960. 18:33 233. Anode Surface Effects in Diodes Containing Oxide-Coated Cathodes. United Kingdom. T w o types of e x p e r i m e n t a l t u b e h a v e been built to s t u d y the b e h a v i o u r o f thin films deposited on the a n o d e by e v a p o r a t i o n d u r i n g the b r e a k d o w n a n d activation o f calcium a n d b a r i u m oxide coated c a t h o d e s . First, with diodes of cylindrical s y m m e t r y , a contact-potential-difference m e t h o d h a s been used to follow t h e c h a n g e s in a n o d e w o r k f u n c t i o n d u r i n g activation o f t h e c a t h o d e at several a n o d e potentials. E m i s s i o n - p o i s o n i n g effects have been related to c h a n g e s in the a n o d e w o r k f u n c t i o n a n d it a p p e a r s that there are two separate c o n t a m i n a t i n g films on the a n o d e surface : a very tightly held electropositive layer a n d a loosely b o u n d electronegative layer. T h e e m i s s i o n decay process by the d e c o m p o s i t i o n of c o m p o u n d s on the a n o d e does n o t explain the results adequately. T h e second tube c o n t a i n e d a m o v a b l e glass electrode u p o n which a gold film could be deposited by e v a p o r a t i o n . T h e results f r o m these t u b e s confirmed t h o s e f r o m the cylindrical diodes a n d also the validity of the contact-potential-difference m e t h o d . B. J. H o p k i n s , Brit. J. Appl. Phys., 11, 124---128, M a r c h 1960. 18 234. Cathode Work Function, Sparking Potentials and Secondary Ionization Coefficients for Oxide-coated Cathodes in Hydrogen. U~dted Kingdom. T h e Kelvin v i b r a t i n g electrode t e c h n i q u e has been applied to m e a s u r e the c o n t a c t potential difference between oxide-coated c a t h o d e s a n d a gold reference surface in the presence of h y d r o g e n . Special high v a c u u m (Alpert) t e c h n i q u e s were used to e n s u r e high gas purity. By the use o f both calcium oxide a n d b a r i u m oxide cathodes, in v a r i o u s states o f activation, it was possible to o b t a i n a r a n g e of w o r k f u n c t i o n f r o m 1.4 to 3 , 6 e V . P a s c h e n curves were plotted for each o f these oxide c a t h o d e s at r o o m t e m p e r a t u r e , a n d m i n i m u m s p a r k i n g potentials a n d s e c o n d a r y ionization coefficients were determined. A
linear relation was f o u n d between the c a t h o d e work function a n d the m i n i m u m s p a r k i n g potential. T h e slope o f this line indicated that a 1 eV c h a n g e in work function c o r r e s p o n d e d to a c h a n g e of 55 V in the m i n i m u m s p a r k i n g potential. T h e slope of the line was confirmed by independent work f u n c t i o n m e a s u r e m e n t s using the g r a p h of the R i c h a r d s o n t h e r m i o n i c equation. The curves (~o/~) v (E/p) s h o w e d a rapid increase in ~o/a with decreasing values of E/p at E/p 100 V / c m m m H g . D, E. Davies a n d B. J. H o p k i n s , Brit. J. AppL Phys., 10, 498-501. Nov. 1959. 18 235. Influence of the Cathode Work Function on the Sparking Potential in Hydrogen. United Kingdom. T h e Kelvin or vibrating electrode m e t h o d o f m e a s u r i n g c o n t a c t potential differences has been used to follow c h a n g e s in work function of e v a p o r a t e d metallic films in a parallel plate electrode s y s t e m in h y d r o g e n at a b o u t 10 m m H g pressure. A reduction in c a t h o d e work function o f the order of 0.3 eV was effected by p a s s i n g a c u r r e n t of 10 7 A for t0 s. After a b o u t 30 vain the c a t h o d e work f u n c t i o n r e t u r n e d to its original value. Similar t r e a t m e n t caused a reduction in the s p a r k i n g potential of 30 V, which also returned to its original pre-discharge value in times of the order o f 30 min. This, together with o t h e r experimental data, is consistent with the fact that positive ions f r o m the discharge c u r r e n t r e m a i n e d on the c a t h o d e surface for periods tip to 30 rain after the current was switched off. It has been possible to d e m o n s t r a t e thai, while these positive ions are being neutralized, there is a relationship between the w o r k f u n c t i o n o f a c a t h o d e a n d its s p a r k i n g potential in h y d r o g e n . D. E. Davies a n d R. K. Fitch, Brit. J, Appl. Phys., 10, 502-505, Nov. 1959. 18 236. Glow Discharge Characteristics of Helium-Neon Mixtures. United Kingdom. T h e m a i n t a i n i n g a n d b r e a k d o w n potentials for a n u m b e r of h e l i u m - n e o n m i x t u r e s have been d e t e r m i n e d over a pressure * distance (pd) range of I to 75 cm m m H g . T h e n o r m a l c a t h o d e fall a n d the m i n i m u m b r e a k d o w n potential were higher for m i x t u r e s c o n t a i n i n g f r o m 1 to 5 per cent neon, t h a n for either o f the pure gases. At higher pd values the b r e a k d o w n potential was lower for mixtures of the o r d e r of 50 per cent helium-50 per cent neon, than for the pure gases. T h e s e results suggest reactions between the two gases affecting the ionization coefficients. C h a r g e e x c h a n g e processes, detected by O s k a m in the afterglow o f such mixtures, are consistent with the emission spectra of the glow discharge, a n d are the probable c a u s e of the variations. G. F. W e s t o n , Brit. J. Appl. Phys., 10, 523-526, Dec. 1959. 18 : 33 : 56 237. Deuterium-Filled Thyratrons. Note by K. G. C o o k a n d G. G. Isaacs, Brit. J. Appl. Phys., 9, 497-498, Dec. 1958. 18 : 33 : 56 238. Deuterium as a Filling for High-Voltage Thyratrons. N o t e by R. J. A r m s t r o n g a n d N. S. Nicholls, Brit. J. Appl. Phys., 9, 498-499, Dec. 1958. 18 239. The Grid Emitting Properties of Titanium. United Kingdom. E x p e r i m e n t s are described in which the e m i s s i o n f r o m thin films of b a r i u m a n d b a r i u m oxide deposited on t i t a n i u m is c o m p a r e d with t h a t f r o m sirnilar deposits on tungsten. With deposits o f b o t h b a r i u m a n d b a r i u m oxide the e m i s s i o n f r o m t i t a n i u m is very m u c h less t h a n t h a t f r o m t u n g s t e n t h r o u g h o u t the t e m p e r a t u r e r a n g e investigated (7001000'~C). A b o v e a b o u t 900"C the e v a p o r a t i o n o f t i t a n i u m will poison the emission o f an adjacent oxide cathode, but it is
344
Coefficients of Evaporation and Condensation. N o . 216. 18.
17 : 16 See Abstract
G a s e o u s Electronics
18 230. Noise Propagation on Uniformly Accelerated Multivelocity Electron Beams. W. M. Mueller a n d M. R. Currie, J. Appl. Phys., 1876-1880, Dec. 1959. 18 231. Propagation Characteristics of Detonation-Generated Plasmas. Melvin A. C o o k , R o b e r t T. K e y e s a n d Lex L. Udy, J. Appl. Phys., 1881-1892, Dec. 1959.
232. Charge Cathodes.
Localization
18 on the Surfaces of Oxide-Coated
United Kingdom. A n o m a l o u s results o b t a i n e d while u s i n g the Kelvin m e t h o d o f d e t e r m i n i n g c o n t a c t potential differences between oxide-coated c a t h o d e s a n d a n e v a p o r a t e d gold film reference surface in an a t m o s p h e r e o f h y d r o g e n have been investigated. Very high c o n t a c t potential differences have been associated with a s e p a r a t i o n o f charge f r o m ionized gas o n the p a s s a g e o f a discharge current. This charge, either positive ions or electrons, r e m a i n s on the surface o f the oxide c a t h o d e for periods ( s o m e t i m e s as long as several days) d e p e n d e n t on the c o n d u c t i v i t y o f the oxide coating. This in turn d e p e n d s u p o n the n a t u r e o f the oxide material, its state of activation a n d its t e m p e r a t u r e . E x p e r i m e n t s are also described o n the b e h a v i o u r o f p r o b e c a t h o d e s in h y d r o g e n . B. J. H o p k i n s a n d F. A. Vick, Brit. J. Appl. Phys., 11, 223-227, J u n e 1960. 18:33 233. Anode Surface Effects in Diodes Containing Oxide-Coated Cathodes. United Kingdom. T w o types of e x p e r i m e n t a l t u b e h a v e been built to s t u d y the b e h a v i o u r o f thin films deposited on the a n o d e by e v a p o r a t i o n d u r i n g the b r e a k d o w n a n d activation o f calcium a n d b a r i u m oxide coated c a t h o d e s . First, with diodes of cylindrical s y m m e t r y , a contact-potential-difference m e t h o d h a s been used to follow t h e c h a n g e s in a n o d e w o r k f u n c t i o n d u r i n g activation o f t h e c a t h o d e at several a n o d e potentials. E m i s s i o n - p o i s o n i n g effects have been related to c h a n g e s in the a n o d e w o r k f u n c t i o n a n d it a p p e a r s that there are two separate c o n t a m i n a t i n g films on the a n o d e surface : a very tightly held electropositive layer a n d a loosely b o u n d electronegative layer. T h e e m i s s i o n decay process by the d e c o m p o s i t i o n of c o m p o u n d s on the a n o d e does n o t explain the results adequately. T h e second tube c o n t a i n e d a m o v a b l e glass electrode u p o n which a gold film could be deposited by e v a p o r a t i o n . T h e results f r o m these t u b e s confirmed t h o s e f r o m the cylindrical diodes a n d also the validity of the contact-potential-difference m e t h o d . B. J. H o p k i n s , Brit. J. Appl. Phys., 11, 124---128, M a r c h 1960. 18 234. Cathode Work Function, Sparking Potentials and Secondary Ionization Coefficients for Oxide-coated Cathodes in Hydrogen. U~dted Kingdom. T h e Kelvin v i b r a t i n g electrode t e c h n i q u e has been applied to m e a s u r e the c o n t a c t potential difference between oxide-coated c a t h o d e s a n d a gold reference surface in the presence of h y d r o g e n . Special high v a c u u m (Alpert) t e c h n i q u e s were used to e n s u r e high gas purity. By the use o f both calcium oxide a n d b a r i u m oxide cathodes, in v a r i o u s states o f activation, it was possible to o b t a i n a r a n g e of w o r k f u n c t i o n f r o m 1.4 to 3 , 6 e V . P a s c h e n curves were plotted for each o f these oxide c a t h o d e s at r o o m t e m p e r a t u r e , a n d m i n i m u m s p a r k i n g potentials a n d s e c o n d a r y ionization coefficients were determined. A
linear relation was f o u n d between the c a t h o d e work function a n d the m i n i m u m s p a r k i n g potential. T h e slope o f this line indicated that a 1 eV c h a n g e in work function c o r r e s p o n d e d to a c h a n g e of 55 V in the m i n i m u m s p a r k i n g potential. T h e slope of the line was confirmed by independent work f u n c t i o n m e a s u r e m e n t s using the g r a p h of the R i c h a r d s o n t h e r m i o n i c equation. The curves (~o/~) v (E/p) s h o w e d a rapid increase in ~o/a with decreasing values of E/p at E/p 100 V / c m m m H g . D, E. Davies a n d B. J. H o p k i n s , Brit. J. AppL Phys., 10, 498-501. Nov. 1959. 18 235. Influence of the Cathode Work Function on the Sparking Potential in Hydrogen. United Kingdom. T h e Kelvin or vibrating electrode m e t h o d o f m e a s u r i n g c o n t a c t potential differences has been used to follow c h a n g e s in work function of e v a p o r a t e d metallic films in a parallel plate electrode s y s t e m in h y d r o g e n at a b o u t 10 m m H g pressure. A reduction in c a t h o d e work function o f the order of 0.3 eV was effected by p a s s i n g a c u r r e n t of 10 7 A for t0 s. After a b o u t 30 vain the c a t h o d e work f u n c t i o n r e t u r n e d to its original value. Similar t r e a t m e n t caused a reduction in the s p a r k i n g potential of 30 V, which also returned to its original pre-discharge value in times of the order o f 30 min. This, together with o t h e r experimental data, is consistent with the fact that positive ions f r o m the discharge c u r r e n t r e m a i n e d on the c a t h o d e surface for periods tip to 30 rain after the current was switched off. It has been possible to d e m o n s t r a t e thai, while these positive ions are being neutralized, there is a relationship between the w o r k f u n c t i o n o f a c a t h o d e a n d its s p a r k i n g potential in h y d r o g e n . D. E. Davies a n d R. K. Fitch, Brit. J, Appl. Phys., 10, 502-505, Nov. 1959. 18 236. Glow Discharge Characteristics of Helium-Neon Mixtures. United Kingdom. T h e m a i n t a i n i n g a n d b r e a k d o w n potentials for a n u m b e r of h e l i u m - n e o n m i x t u r e s have been d e t e r m i n e d over a pressure * distance (pd) range of I to 75 cm m m H g . T h e n o r m a l c a t h o d e fall a n d the m i n i m u m b r e a k d o w n potential were higher for m i x t u r e s c o n t a i n i n g f r o m 1 to 5 per cent neon, t h a n for either o f the pure gases. At higher pd values the b r e a k d o w n potential was lower for mixtures of the o r d e r of 50 per cent helium-50 per cent neon, than for the pure gases. T h e s e results suggest reactions between the two gases affecting the ionization coefficients. C h a r g e e x c h a n g e processes, detected by O s k a m in the afterglow o f such mixtures, are consistent with the emission spectra of the glow discharge, a n d are the probable c a u s e of the variations. G. F. W e s t o n , Brit. J. Appl. Phys., 10, 523-526, Dec. 1959. 18 : 33 : 56 237. Deuterium-Filled Thyratrons. Note by K. G. C o o k a n d G. G. Isaacs, Brit. J. Appl. Phys., 9, 497-498, Dec. 1958. 18 : 33 : 56 238. Deuterium as a Filling for High-Voltage Thyratrons. N o t e by R. J. A r m s t r o n g a n d N. S. Nicholls, Brit. J. Appl. Phys., 9, 498-499, Dec. 1958. 18 239. The Grid Emitting Properties of Titanium. United Kingdom. E x p e r i m e n t s are described in which the e m i s s i o n f r o m thin films of b a r i u m a n d b a r i u m oxide deposited on t i t a n i u m is c o m p a r e d with t h a t f r o m sirnilar deposits on tungsten. With deposits o f b o t h b a r i u m a n d b a r i u m oxide the e m i s s i o n f r o m t i t a n i u m is very m u c h less t h a n t h a t f r o m t u n g s t e n t h r o u g h o u t the t e m p e r a t u r e r a n g e investigated (7001000'~C). A b o v e a b o u t 900"C the e v a p o r a t i o n o f t i t a n i u m will poison the emission o f an adjacent oxide cathode, but it is