THE INVESTIGATION OF FIELD IONIZATION PROCESS OF He GAS ABOVE THE SEPARATE SURFACE ATOMS OF TUNGSTEN EMITTERS

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THE INVESTIGATION OF FIELD IONIZATION PROCESS OF He GAS ABOVE THE SEPARATE

SURFACE ATOMS OF TUNGSTEN EMITTERS

W. Lenkow, M. Glowacki

To cite this version:

W. Lenkow, M. Glowacki. THE INVESTIGATION OF FIELD IONIZATION PROCESS OF He GAS ABOVE THE SEPARATE SURFACE ATOMS OF TUNGSTEN EMITTERS. Journal de Physique Colloques, 1986, 47 (C7), pp.C7-47-C7-51. �10.1051/jphyscol:1986709�. �jpa-00225898�

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Colloque C7, supplement au n o 11, Tome 47, Novembre 1986

THE INVESTIGATION OF FIELD IONIZATION PROCESS OF He GAS ABOVE THE SEPARATE SURFACE ATOMS OF TUNGSTEN EMITTERS

W.E. LENKOW and M.S. GLOWACKI

Institute of Physics, Surface Physics Laboratory, Pedagogical University of Czestochowa, Zawadzkiego 13/15,

PL-42-200 Czestochowa, Poland

~ 6 s u m 6 . A l ' a i d e du microscope i o n i q u e ;quip6 de l a magn6tique son- d e atomique, t r a v a i l l a n t s o u s l a p r e s s i o n b a i s s k e du gaz d e t r a v a i l /h;liwn/, on a mesur; l e c o u r a n t i o n i q u e p r o d u i t au-dessus d e s atomes i s o l 6 s l a s u r f a c e de l t 6 m e t e u r d e t u n g s t b n e , d e s e s p a c e s a u d i a m b t r e d e 6 14 2.

On a mesur; l e s c o u r b e s d e s dGpendances d e l t i n t e n s i t 6 du c o u r a n t i o n i q u e d e 1 9 i n t e n s i t 6 du champ 6 l e c t r i q u e d e l t i o n i s a t i o n pour d e s atomes l e s p o s i t i o n s m e ' t a s t a b l e s s u r l e s &ages du p l a n (110) , pour l e s atomes d e bord de c e s 6 t a g e s d a n s l e s p o s i t i o n s normales e t pour lpatorne de 1 9 a d s o r b a t e /probablement l a mol6cule CO/ s u r un 6 t a g e du p l a n (1 10)

.

On a c o n s t a t 6 l ' a p p a r i t i o n du maximum du courbe pour l e s atomes m 6 t a s t a b l e s quand l a v a l e u r du champ 6tait ^;gale a u champ du raeil- l e u r e image.

Summary. F i e l d i o n i s a t i o n c u r r e n t , g e n e r a t e d above t h e s i n g l e atom s i t e s of (110) t u n g s t e n p l a n e , i n FIhi working w i t h low p r e a s s u r e He g a s , as a f u n c t i o n of f i e l d s t r e n g t h h a s been measured, by magnetic s e c t o r a l atom-probe FD4 using.The f i e l d i o n i s a t i o n c u r r e n t from 6-14 2

s i z e a r e a , h a s beon r e g i s t r a t e d by channel p l a t e d e t e c t o r , t h e f i e l d s t r e n g t h was c a l i b r a t e d on t h e base of b e s t image conditions.The meas- urements h a s been done f o r m e t a s t a b l e atoms s i t e s on t h e s t e p s of (110) p l a n e , a s w e l l as f o r l e d g e atoms of t o p and n e x t d i s k s f o r 1 4 o r i - e n t e d e m i t t e r . The c u r v e s measured f o r m e t a s t a b l e p o s i t i o n e d atoms, d i s p l a y s a d i s t i n c t maxima correspondence t h e B I P v a l u e , whereas t h e r e m a i n i n g c u r v e s showe a q u i t e d i f f e r e n t c h a r a c t e r .

1 n t r o d u c t i o n . T h e p r e s e n t paper i s a s h o r t i n f o r m a t i o n a b o u t pos- s i b i l i t i e s of i n v e s t i g a t i o n s of p a r e x c e l l e n c e l o c a l s u r f a c e phenomena as f i e l d i o n i s a t i o n p r o c e s s e s above t h e s e p a r a t e atoms s i t e s by mag- n e t i c s e c t o r a l atom probe FIM using.!Phis c o n t r i b u t i o n should be a mod- e s t completion t o t h e l o c a l s u r f a c e phenomena i n v e s t i g a t i o n s d e s c r i b e d by o t h e r a u t h o r s ,2,3]

.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986709

C7-48 JOURNAL DE PHYSIQUE

A ~ p a r a t u s . The 60' m a g n e t i c s e c t o r atom probe FIN, b u i l t by a u t h o r s and d e s c r i b e d p r e v i o u s l y [4,g h a s been used t o i n v e s t i g a t i n g o f t h e f i e l d i o n i s a t i o n o f t h e helium g a s , above s e p a r a t e atom s i t e s of (110) t u n g s t e n micromonocrystal p l a n e . T h i s a p p a r a t u s h a s probe h o l e a p e r - t u r e a n g l e amounts 16 mrad. A t t h i s a n g l e o f view t h e a n a l y s e d s u r f a c e a r e a s i z e i s a b o u t 6

a

E x p e r i m e n t a l p r o c e d u r e and r e s u l t s . F i e l d i o n i s a t i o n c u r r e n t , o r i - g i n a t e d above t h e s i n g l e atom m e t a s t a b l e s i t e s o f t h e l e d g e o f (110) p l a n e [7], f o r t h e f i r s t and second n e t p l a n e s t e p s , as a f m c t i o n o f a p p l i e d f i e l d was measured. The measurements were made on t h e [110]

o r i e n t e d , w e l l e v a p o r a t e d e m i t t e r s w i t h t i p r a d i i 360 2, 470 8 and 870 8, a t t h e f i e l d r a n g e 3 , 5 t o 5 , 5 f / 8 and t e m p e r a t u r e 80 K. Compar- a t i v e l y t h e s i m i l a r measurements were made f o r norma1,ledge p o s i t i o n e d atom s i t e s on t h e f i r s t and second (110) p l a n e n e t s t e p s , as well as f o r a d s o r b a t e o b j e c t / p r o b a b l y CO molecule/ s i t u a t e d s i m i l a r l y . The l a s t m e a s u r e x e n t s were made on t h e e m i t t e r w i t h t i p r a d i u s 420 2.0n t h e Fig. I a, b, c , d t h e photographs a l l t h e i n v e s t i z a t e d o b j e c t s a r e p r e s e n t i n s .

Piy.1. The p h o t o z r a p h s o f i n v e s t i q a t e d o b j c t : a/ t h e m e t a s t a b l e atom on t h e second n e t s t e p of t h e 360

fi

b;

a/

The r e s u l t s of t h e f i e l d i o n i s a t i o n c u r r e n t measurements above t h e a l l m e t a s t a b l e s i t e s and a d d i t i o n a l l y f o r a d s o r b a t e showes Pig.2. The f i e l d s t r e n g t h was e s t i a a t e d on t h e base of c r i t e r i o n , t h a t t h e b e s t image f i e l d amount t o 4,4

~ / a

1 x10-'5-

L,s s

Fig.2. The f i e l d i o n c u r r e n t as a

'M

f u n c t i o n o f f i e l d s t r e n g t h f o r m e t a s t a b l e atom s i t e s f o r d i f f e r e n t t i p r a d i i

Fig.3. The f i e l d i o n c u r r e n t as a f u n c t i o n of f i e l d f o r l e d g e atoms s i t e s

D i s c u s s i o n . T h i s experiment was c a r r y e d o u t on t h e e m i t t e r s w i t h t i p r a d i i a few hundred 8, t h e g r e a t e s t one was a b o u t 900 8. F o r t h e a n g l e a p e r t u r e o f probe h o l e system 1 6 m a d t h e l i m i t i n g a n a l y s e d a r e a s a r e p r e s e n t i n g on F i a / t h e g r e a t e s t a r e a w i t h d i a m e t e r -14

a/

a/,

F i g u r e s 4 and 5 a , b s u g 3 e s t a n observed m e t a s t a b l e s i t e s on t h e b o t h e m i t t e r s and two p o s s i b l e normal l e d g e s i t e s . I t i s confirmed by a u t h o r * s o b s e r v a t i o n s , t h a t o n l y advanced p o q i t i o n / l e f t on t h e ~ i g .5b/

i s v i s i b l e i n t h e F M working w i t h pure He g a s . I t i s worthy of b e i n g mentioned t h a t a c c o r d i n g t o a u t h o r ' s e v a l u a t i o n s , o n l y one t o a b o u t

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25 and one t o about 15 atoms

f

The r e s u l t s of f i e l d i o n i - s a t i o n c u r r e n t measurements, from so small a r e a s , were de- s c r i b e d i n physical l i t e r a t u r e very scanty. The photometrical measurements by Mtlller and a l l [9J were made f o r t h e g r e a t e r r e g i o n of (1 1 1) plane, Plummer

- - -

t h e I - s t s t e p ^{~ O I} 1) p l a n e s t e p s of (100) , (I 1 2) and (1 10) on t h e e m i t t e r w i t h t i p ra-

d i u s 870 g. The probe h o l e tungsten e m i t t e r planes, how- covers a r e a about 14 8 d i - ever without t h e BLV marked m e t e r and e v a l u a t i o n of t h e i n v e s t i - g a t i n g a r e a . ^The most compara- b l e r e s u l t s c o n t a i n s t h e paper of Chen and Seidman [ll] ,but t h e meas- urements a r e p r e s e n t i n g only t o t h e BIV value,being i n agreement with a u t h o r * s r e s u l t s .

TO (1001 PLANE 360

8-NO

f

Pig.5.a/ The metastable p o s i t i o n on t h e s u r f a c e of t h e second s t e p , R = 360 2, analysed a r e a h a s 6 8 diameter;

b/ normal ledge p o s i t i o n s of i n v e s t i g a t i n g atoms. Only l e f t s i t e i s v i s i b l e i n experiment.

Authors a r e s t i l l i n c a p a b l e t o i n t e r p r e t t h e o b t a i n e d r e s u l t s , par- t i c u l s r l y t h e d i f f e r e n c e i n t h e c h a r a c t e r o f c u r v e s p r e s e n t on t h e F i g . 2 and Fig.3. Although t h e p o s s i b i l i t y of e x i s t e n c e o f t h e i n d i s - t i n c t maxima of f i e l d i o n i s a t i o n c u r r e n t , o r i g i n a t i n g above b r i g h t s p o t o f a b o u t 22 2 d i a m e t e r , a t e l e c t r i c a l f i e l d 3 t o 5 ~ / 8 was p r e d i c t e d by van Eekelen w i t h t h e a i d o f a s i m p l e g a s dynamical c a l c u l a t i o n h2], t h e p r e s e n t i n g r e s u l t s a r e r a t h e r d i f f e r e n t , e s p e c i a l l y i n t h e c a s e of t h e m e t a s t a b l e atom s i t e s . It i s p o s s i b l e t h a t observed e f f e c t i s caused by e x t e r n a l f i e l d i n t e r a c t i o n w i t h t h e l o c a l i z e d t u n g s t e n or- b i t a l s of d-type, e s p e c i a l l y w i t h t h e one c o m p l e t l y f r e e and one par- t i a l l y occupated o r b i t a l from t h e m e t a s t a b l e s i t u a t e d atom, which i s i n t e r a c t i n g w i t h t h r e e n e a r s t n e i g h b o u r s o n l y [I 3J

.

Acknowled~ement. The a u t h o r s a p p r e c i a t e lvlr. J. Krasowski M. Sc. f o r h i s c o l l a b o r a t i o n i n e x p e r i m e n t a l works.

R e f e r e n c e s

[I] ^G. E h r l i c h , S u r f . S c i . , &5, 422-447 /1977/ and r e f e r e n c e s t h e r e i n [2] G.L. Kellogg and T.T. Tsong, S u r f . S c i . , 3, 343 /1977/

[3] ^N. E r n s t and G. E h r l i c h , J. d e Physique, 41 / ~ 2 / , 47 /1986/

141 Iv1.S. Gkowacki and W.E. Lenkow, 27-th IFES Rep. Tokyo, Japan p.p. 21-26. ed. Y. Yashiro and N. I g a t a

[5J M.S. Gkowacki and W.E. Lenkow, Journ. Techn. Phys., 2, 203-21 2 / I 9821

[6] W.E. Lenkow and b1.S. GZowacki, Acta Univ. Wrat., B, 75 /1977/

17) E.W. bIBller, S u r f . S c i . , 2, 484 /1964/

[8] E.W. K t i l l e r and T.T. Tsong, " F i e l d Ion I~Iicroscopy P r i n c i p l e s and A p p l i c a t i o n s " . New York 1969 p. 154

[g] E.W. Mtiller, S , Nakamura, 0. Nishikawa and S.B. Mc.Lane, J. Appl.

Phys.,

z,

Md E.W. Plummer and T.N. Rhodin, J. Chem. Phys.,

a,

(1 11 Y.C. Chkn and D.N. Seidnan, S u r f . S c i . ,

.a,

1 'i8 H.A.M. van Eekelen, S u r f . S c i . , 21, 21 /1970/

M.S. Gzowacki, Doct. T h e s s i s , Czg stochowa

-

z,

T h i s work was supported by C e n t r a l P r o j e c t of t h e B a s i c Research 01.08.AS.