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INVESTIGATIONS OF THE QUANTITY OF ELEMENTARY ACTS OF FIELD EMISSION WITH
TIME RESOLUTION OF 5 µs - 100 ps
V. Maslov, G. Fursey, A. Kocheryshenkov
To cite this version:
V. Maslov, G. Fursey, A. Kocheryshenkov. INVESTIGATIONS OF THE QUANTITY OF ELE-
MENTARY ACTS OF FIELD EMISSION WITH TIME RESOLUTION OF 5
µs - 100 ps. Journalde Physique Colloques, 1989, 50 (C8), pp.C8-113-C8-116. �10.1051/jphyscol:1989820�. �jpa-00229918�
COLLOQUE DE PHYSIQUE
Colloque C8, suppl6ment au n o 11, Tome 50, novembre 1989
INVESTIGATIONS OF THE QUANTITY OF ELEMENTARY ACTS OF FIELD EMISSION WITH TIME RESOLUTION OF 5 ps
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100 psV . I . MASLOV, G.N. FURSEY and A.V. KOCHERYSHENKOV
Research Scientific Centre for Electrophysical Problems of Surface (RSC EPS), Leningrad Institute of Telecommunication, 191065 Leningrad, Moika 61, USSR
A b s t r a c t
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The p r e s e n t s t u d y i s d e v o t e d t o i n v e s t i g a t i o n s of t h e number of e l e m e n t a r y e v e n t s and s t a t i s t i c s of f i e l d e m i s s i o n i n l a r g e c u r r e n t d e n s i . t i e s . New method of h i g h t i m e r e s o l u t i o n i s d e s c r i b e d .The s t u d y o f m u l t i p l e - p a r t i c l e phenomena i n f i e l d e l e c t r o n e m i s s i o n ( F E ) i s r e l a t e d t o a fundamental problem: t h e o b s e r v a t i o n p r o b a b i l i t y of s u c h phenomena may c r i t i c a l l y depend on t h e t r a n s p a r e n c y of t h e p o t e n t i a l b a r - r i e r , i n p a r t i c u l a r , t h e o b s e r v a t i o n p r o b a b i l i t y o f p a i r e d t u n n e l i n g i s p r o p o r t i o n a l t o t h e s q u a r e of t h e t o t a l c u r r e n t . T h i s was shown, f o r ex- ample, by Gadzuk and Plummer i n /I/, where t h e model i s p r e s e n t e d which i s based on t h e exchange i n t e r a c t i o n r e s u l t i n g i n t h e p a i r e d t u n n e l i n g of e l e c t r o n s t h r o u g h t h e p o t e n t i a l b a r r i e r i n FE from e l e m e n t a r y m e t a l s . The measurement of t h e number of e l e m e n t a r y e v e n t s of FE i s t h e d i r e c t me- t h o d of t h e o b s e r v a t i o n o f s u c h m u l t i p a r t i c l e phenomena. The most e x t e n s i - v e l y a p p l i e d m e t h o d o l o g i e s of s t a t i s t i c a l i n v e s t i g a t i o n use t h e method of
s e p a r a t e r e g i s t r a t i o n of g r o u p s of p a r t i c l e s w i t h v a r i o u s numbers / 2 / . The a p p l i c a t i o n of t h i s method e n t a i l s g r e a t d i f f i c u l t y : s u p e r p o s i t i o n o f
e l e c t r i c i m p u l s e s i n s p e c t r o m e t e r c a n a l c h a n n e l s l i m i t s t h e flow r a t e of t h e p a r t i c l e s r e g i s t e r e d t o t h e l e v e l o f 10 3 p a r t i c l e s / s w i t h t h e s e n s i t i v i t y t o p a i r e d a c t a t t h e l e v e l o f 0.1%. The measurement o f FE s t a t i s t i c s w i t h t h e h i g h p o t e n t i a l b a r r i e r t r a n s p a r e n c y and, a c c o r d i n g l y , w i t h l a r g e c u r - r e n t d e n s i t y t h u s e n c o u n t e r s some e s s e n t i a l t e c h n i c a l problems.
The d e c r e a s e of t h e a r e a o f probe diaphragm w i t h t h e purpose o f t h e p a r t - i c l e f l o w l i m i t a t i o n i s r e a s o n a b l e o n l y up t o a c e r t a i n e x t e n t : t h i s may l e a d t o t h e p a r t i a l l o s s o f i n f o r m a t i o n on t h e c o r r e l a t i o n e f f e c t s of d i - m e n s i o n a l c h a r a c t e r .
Approaches known, s u c h as a r e j e c t i o n of s u p e r p o s i t i o n s by means of e l e c - t r o n i c c i r c u i t s o r methods of machine p r o c e s s i n g o f d i s t o r t e d s p e c t r a do n o t a l l o w s i g n i f i c a n t i n c r e a s e i n t h e dynamic r a n g e of c u r r e n t d e n s i t y . We have developed t h e method of c h a r g e d p a r t i c l e r e g i s t r a t i o n which a l l o w s t o o b t a i n p i c o s e c o n d r e s o l u t i o n of two p a r t i c l e s s o t h a t t h e f l o w of p a r t - i c l e s r e c o r d e d c o u l d be i n c r e a s e d by 6-8 o r d e r s o f magnitude. The e s s e n c e
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1989820
o f t h e method i s i n t h e e x t r a c t i o n ( r e j e c t i o n ) of t h e e l e c t r o n s from thebeam o n t o t h e d e t e c t o r Tor a s h o r t p e r i o d of t i m e d u r i n g which t h e e l e c t r o n beam, w h i l e s c a n n i n g ( s w i n g i n g ) by t h e r e j e c t i o n p u l s e f r o n t , i n t e r s e c t s t h e a p e r - t u r e diaphragm.
The p r e s e n t s t u d y aims a t t h e i n v e s t i g a t i o n of FE s t a t i s t i c s o v e r a wide r a n g e of t h e c u r r e n t d e n s i t i e s and w i t h t h e t i m e r e s o l u t i o n of 5 f i s
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100psThe b l o c k diagram of t h e t e s t a p p a r a t u s t o g e t h e r w i t h t h e e x p e r i m e n t a l de- v i c e i s shown i n P i g . 1. The e x p e r i m e n t a l d e v i c e where t h e e x t r a c t i o n of e l e c t r o n s d i r e c t l y t a k e s p l a c e , c o n s i s t s of a f i e l d e m i s s i o n p r o j e c t o r with t h e probe h o l e i n t h e s c r e e n , a n e l e c t r o n f o c u s s i n g system, a semiconductor d e t e c t o r , a g e t t e r and an i o n i s a t i o n gauge. FE-cathode 1 h a v i n g t h e form o f a t i p o f t h e m e t a l s t u d i e d welded t o t h e t u n g s t e n l o o p . 2. FE-cathode i s p l a c e d a t t h e c e n t e r o f g i m b a l s u s p e n s i o n 3 , which p r e l i m i n a r i l y a l i g n e d by a d j u s t i n g s c r e w s 4 . B e l l o w s assembly 5 a l l o w s t o change t h e t i p s l o p e w i t h - i n any p l a n e a t an a n g l e up t o 40' m a i n t a i n i n g t h e p o s i t i o n o f t h e t i p v e r - t e x p r a c t i c a l l y a t t h e axis of t h e d e v i c e . This, i n i t s t u r n , a l l o w s t o ex- t r a c t t h e e l e c t r o n f l o w from t h e v a r i o u s c r y s t a l l o g r a p h i c d i r e c t i o n s of e m i t t i n g s u r f a c e i n t o t h e probe h o l e . Anode 6 p r e s e n t s t h e diaphragm w i t h t h e probe h o l e and l u m i n e s c e n t s c r e e n 7 , h a v i n g t h e h o l e a t t h e c e n t r e and a l l o w i n g t o viewing of t h e f i e l d e m i s s i o n image. Luminescent s c r e e n 7 i s cover- e d by t h e s p r a y e d c o n d u c t i n g l a y e r of SnO and h a s t h e e l e c t r i c a l c o n t a c t w i t h t h e anode.
5 s o u r c e
4
s o u r c e
mult i o h a n
I
a m p l i f i e rt
Fig.1. Scheme of t h e e x p e r i m e n t a l p l a n t
Behind t h e anode two p a i r s of a d j u s t i n g p l a t e s 8 a r e p l a c e d which change t h e t r a j e c t o r y of an e l e c t r o n beam, d i r e c t i n g it p a r a l l e l t o t h e o p t i c a l
a x i s of t h e d e v i c e . Focusing system 9, of a s i n g l e l e n s type, f o c u s e s t h e e l e c - t r o n beam w i t h i n t h e p l a n e o f c o l l e c t o r 12. D e f l e c t i n g yoke 10 i s designed f o r t h e sweeping o f t h e e l e c t r o n beam i n t h e p l a n e of t h e drawing. F o r t h e f i n a l c o r r e c t i o n of t h e e l e c t r o n beam t r a j e c t o r y and e x t r a c t i o n of it t o t h e middle of t h e l e n g t h of c o l l e c t o r a p e r t u r e diaphragm, t h e d e f l e c t i n g p l a t e s I 1 a r e u s e d .
C o l l e c t o r 12 i s made i n a form of a cup having t h e diameter of 20 mm, i n which t h e a p e r t u r e diaphragm i s i n s e r t e d , and above t h i s t h e luminescent s c r e e n 13 h a v i n g t h e h o l e i n t h e c e n t e r and t h e c o n d u c t i n g l a y e r SnO i s i n - s t a l l e d .
Behind t h e c o l l e c t o r , S i - d e t e c t o r of a s u r f a c e - b a r r i e r t y p e , 1 4 , i s p l a c e d . I n s t a t i s t i c s measurement FE d e t e c t o r was cooled down t o t h e temperature of l i q u i d n i t r o g e n .
The e s s e n c e of FE s t a t i s t i c s measurement method w i t h l a r g e c u r r e n t d e n s i t i e s i s i n t h e f o l l o w i n g . The e l e c t r o n beam coming through t h e probe h o l e i n t h e anode i s focused and t h e n by means of t h e d e f l e c t i n g system 10 i t ' s pulsed d e f l e c t i o n w i t h i n t h e p l a n e p e r p e n d i c u l a r t o t h e c o l l e c t o r p l a n e is produc- ed. During t h e s c a n n i n g of t h e beam a c r o s s t h e diaphragm t h e r e j e c t i o n (ex- t r a c t i o n ) of t h e e l e c t r o n s of a beam o n t o t h e d e t e c t o r f o r a s h o r t p e r i o d of t i m e , d e t e r m i n i n g t h e time r e s o l u t i o n , t a k e s p l a c e .
The p e r i o d of r e j e c t i o n p u l s e s s h o u l d n o t be l e s s t h a n t h e o p e r a t i n g time d u r a t i o n of t h e s p e c t r o m e t r i c c h a n n e l and, t h u s , t h e s u p e r p o s i t i o n of t h e p u l s e s i n s p e c t r o m e t e r i s t o t a l l y excluded. Then t h e r e s o l u t i o n time is de- termined by t h e approximated formula tree = Tf
-,
So whereTf -
t h e dura- t i o n of r e j e c t i o n p u l s e f r o n t , So-
width of t h e a p e r t u r e diaphragm, S-
f u l l d e f l e c t i o n o f t h e beam w i t h i n t h e p l a n e of c o l l e c t o r .
The measurements were t a k e n on t h e u n s o l d e r e d d e v i c e w i t h t h e r e s i d u a l g a s p r e s s u r e
- lom9 t o r r . A s an e m i t t e r t h e t i p of t u n g s t e n m o n o c r y s t a l , o r i e n t e d in t h e d i r e c t i o n (100) o r i n t h e d i r e c t i o n < I l O > . was used. Be- s i d e s t h e s t u d y o f b r i g h t a r e a s around t h e f a c e t (100) o f t h e o r d i n a r y smoothed t i p of W , a l s o t h e measurements of t h e t i p , s u b j e c t e d t o t h e t h e r - mof i e l d rearrangement were made.
With r e l a t i v e l y s m a l l c u r r e n t d e n s i t i e s (up t o 10-I A/cm 2 ) t h e r e j e c t i o n of e l e c t r o n beam by t h e p u l s e v e r t e x was a p p l i e d which corresponds t o t h e r e - s o l u t i o n time up t o 5 n s .
One of t h e t y p i c a l s p e c t r a of FE s t a t i s t i c s of t u n g s t e n from t h e b r i g h t en- vironment o f t h e f a c e t (100) w i t h time r e s o l u t i o n of tres = 5 n s i s shown i n F i g . 2a. Current d e n s i t y i n t h i s measurement was 0.2 ~ / c m 2
.
The measurement of FE s t a t i s t i c s i n t h e range o f t h e c u r r e n t d e n s i t i e s
2 2
(10"
-
10 ) A/cm were t a k e n i n t h e r e j e c t i o n c o n d i t i o n by t h e p u l s e f r o n t . Then t h e time r e s o l u t i o n of 1 . 1 0 ' ~ ~ s was achieved. The t y p i c a l spectrum o fFE s t a t i s t i c s of W w i t h t h e c u r r e n t d e n s i t y of 10 ~ / c m ~ i s shown i n Fig.2b.
F i g . 2. S t a t i s t i c s s p e c t r a of f i e l d emission from W-cathode
The p r o c e s s i n g of t h e s p e c t r a of FE W s t a t i s t i c s have shown t h e absence o f d o u b l e - p a r t i c l e e v e n t s w i t h t h e response o f t h e methodology t o e l e c t r o n p a i r s a t t h e l e v e l of 0.1%. With t h e d e n s i t y of l o 2 A/cm 2 due t o t h e i n - c r e a s e of t h e s u p e r p o s i t i o n r a t i o , m o n o e l e c t r o n n a t u r e of PE W s t a t i s t i c s was d e f i n e d t o t h e accuracy of 99%. These measurements, w i t h t h e i n c r e a s e d s u p e r p o s i t i o n r a t i o , were t a k e n w i t h t h e o b j e c t o f i d e n t i f i c a t i o n of m u l t i - p l e - p a r t i c l e phenomena t h e p r o b a b i l i t y of which would have more c r i t i c a l dependence on t h e t o t a l c u r r e n t t h a n t h e q u a d r a t i c one.
I n t h e p r e s e n t s t u d y a n a t t e m p t i s made of p r e l i m i n a r y i n v e s t i g a t i o n of FE s t a t i s t i c s of high-tempersture s u p e r c o n d u c t i n g (H?PSC)-emitters i n t h e i n - s t r u m e n t s w i t h t h e e l e c t r o n beam r e j e c t i o n . E m i t t e r was manufactured i n t h e same manner a s i n /3/ by means of t h e mechanical s h a r p e n i n g of a c e r a - mics sample ( Y Ba2Cu3O7) by a diamond f i l e . The i n s u f f i c i e n t f o c u s i n g o f . t h e e l e c t r o n beam caused by t h e s p e c i f i c f e a t u r e s of HTSC-emitter h a s li- m i t e d t h e time r e s o l u t i o n a t t h e l e v e l of 5 n s . AE s t a t i s t i c s was measured from t h e b r i g h t l y - e m i t t i n g p o r t i o n s o f Y Ba2Cu3O7. The t o t a l FE c u r r e n t was v a r i e d i n t h e range of (10"'
+
A . The r e s u l t s of t h e measure- ment have shown t h a t i n t h e i n t e r n a l of t h e r e s o l u t i o n time of ,s-
,5,FE from s t r o n g l y - e m i t t i n g r e g i o n s of Y Ba2Cu307 i s of monoelectron n a t u r e w i t h t h e s e n s i t i v i t y t o p a i r e d e v e n t s n o t l e s s t h a n 0.1%.
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