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SIMS AND SCANNING ION MICROSCOPYG. Allen, I. Brown

To cite this version:G. Allen, I. Brown. SIMS AND SCANNING ION MICROSCOPY. Journal de Physique Colloques,1989, 50 (C2), pp.C2-121-C2-125. �10.1051/jphyscol:1989221�. �jpa-00229419�

JOURNAL DE PHYSIQUE Colloque C2, supplhment au n02, Tome 50, f6vrier 1989

SIMS AND SCANNING ION MICROSCOPY

G.C. ALLEN and I.T. BROWN

Central Electricity Generating Board, Berkeley Nuclear Laboratories, Berkeley, GB-Gloucestershire GL13 9PB, Great-Britain

Resume - Un microscope a b a l l a y a g e i o n i q u e developpe aux "Berke ley -- Nuclear L a b o r a t o r i e s " du C . E . G . B . , e s t d e c r i t .

Par bombardement i o n i a u e a p a r t i r d 'une s o u r c e de g a l l i u m metal 1 i q u i d e e t a n a l y s e s c o n s e c u t i v e s des i o n s s e c o n d a i r e s e t des

e l e c t r o n s emi s , s e l on des t e c h n i q u e s c o n v e n t i o n n e l l e de s p e c t r o s c o p i e de masse e t de mic roscop ie e l e c t r o n i q u e , c e t a p p a r e i l permet d ' o b t e n i r l e s p e c t r e de masse des i o n s s e c o n d a i r e s e t de v i s u a l i s e r 1 a s u r f ace exami nee.

Des r e s u l t a t s de mic roscop ie a b a l l a y a g e a p p l i q u e e s a des e t u d e s de ma te r i aux m e t a l l i q u e s , i n o r q a n i q u e s e t o rgan ique s e r o n t p r e s e n t e s .

A b s t r a c t - A scann ing ion microscope developed a t t h e C E G B ' s

Berkeley Nuclear L a b o r a t o r i e s i s d e s c r i b e d .

By ion bombardment from a l i q u i d metal ga l l ium s o u r c e , and subsequen t a n a l y s i s of both t h e r e s u l t a n t secondary i o n s and

secondary e l e c t r o n s us ing c o n v e n t i o n a l t e c h n i q u e s of mass s p e c t r o m e t r y and e l e c t r o n microscopy, t h i s i n s t r u m e n t o f f e r s both

secondary ion mass a n a l y s i s (SIMS) and t h e f a c i l i t y f o r imaging t h e

s u r f a c e under i n v e s t i g a t i o n .

R e s u l t s from t h e a p p l i c a t i o n of t h e scann ing ion microscope t o t h e s tudy of meta l1 i c y i n o r q a n i c and o r q a n i c m a t e r i a l s a r e p r e s e n t e d .

The t e c h n i q u e s used f o r t h e examina t ion and a n a l y s i s of s o l i d s a r e many and v a r i e d b u t t h e i r development may be t r a c e d us i n q s c a n n i n g e l e c t r o n microscopy as a s t a r t i n g p o i n t . Fol lowing t h e i n t r o d u c t i o n of t h i s method came t h e d e s i r e t o de te rmine t h e chemical compos i t ion of t h e f e a t u r e s r e v e a l e d . A t f i r s t t h i s was p o s s i b l e th rough t h e a n a l y s i s of X - r a d i a t i o n produced dur ing t h e p r o c e s s of bombardment of t h e specimen w i t h t h e high energy e l e c t r o n beam, b u t two decades ago t e c h n i q u e s o f f e r i n g i n f o r m a t i o n

more r e p r e s e n t a t i v e of t h e s u r f a c e such as X-ray p h o t o e l e c t r o n s p e c t r o s c o p y ,

Auger e l e c t r o n s p e c t r o s c o p y (AES) and secondary ion mass s p e c t r o m e t r y (SIMS)

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1989221

C2-122 JOURNAL DE PHYSIQUE

were developed. Of t h e s e methods a c c e p t a n c e was gained most s lowly by t h e l a t t e r b u t mic roscop ic a n a l y s i s by SIMS has been made p o s s i b l e by t h e use of l i q u i d metal s o u r c e s t o produce t h e pr imary ion beaml. These hiqh

b r i g h t n e s s s o u r c e s pe rmi t t h e fo rma t ion of high i n t e n s i t y submicron i o n p robes and modern i n s t r u m e n t a t i o n a l l o w s t h e c o l l e c t i o n of secondary e l e c t r o n and secondary ion images which p r o v i d e s u r f a c e topography of one monolayer 2 . The Berkeley i n s t r u m e n t , shown s c h e m a t i c a l l y i n F i g u r e 1 , i s

t h e r e f o r e , a combinat ion of a microscope and a submicron a n a l y t i c a l p robe 3 .

DETECTOR r - - - *

MASS LIQUID METAL I O N GUN

VACUUM SYSTEM 25 DISPLAY D l SPLAY

COPIER / PRINTER i--i

F i g u r e 1: Schemat ic diagram of Berke ley Scanning Ion Microscope (SIM)

Typ ica l images from a number of specimens d i f f i c u l t t o examine w i t h o u t p r i o r c o a t i n g t e c h n i q u e s which mask o r modify i m p o r t a n t s u r f a c e chemical p r o p e r t i e s i n conven t iona l e l e c t r o n microscopy a r e shown i n F i g u r e s 2 and 3 .

F i g u r e 2 : Ion induced e l e c t r o n micrograph from f o o t of h o r s e f l y (Tabanus )

F i g u r e 3 : Scanning ion micrograph of ( a ) p u l v e r i s e d f u e l ash (PFA) p a r t i c l e ( b ) a r e a of p a r t i c l e a t h i g h e r m a g n i f i c a t i o n

Organic m a t e r i a l s a r e normal ly degraded i n an e l e c t r o n beam and i n s u l a t i n g samples such a s t h e PFA sample ( F i g u r e 3 ) which i s mainly

composed of s i l i c a , may be s u b j e c t t o c h a r g i n g '+. I n t h e ion microscope

however, good images w i t h a remarkable depth of f i e l d were o b t a i n e d a f t e r s e v e r a l minu tes ; presumably t h e i m p l a n t a t i o n of gal 1 ium i o n s a1 l e v i a t e s t h e

b u i l d up of s u r f a c e cha rge d u r i n g t h e bombardment p r o c e s s . Bombardment of t h e s u r f a c e w i t h i-ons n o t o n l y produces secondary

e l e c t r o n s b u t a l s o s t i m u l a t e s t h e emiss ion of secondary i o n s . I f t h e pr imary ion beam i s r a s t e r scanned ove r t h e s u r f a c e and s p e c i f i c secondary

i o n s moni tored a t each p o i n t , a chemical image can be gene ra ted : T h i s i s done by computer p r o c e s s i n q t h e d a t a t o y i e l d maps o r s p a t i a l images of t h e

secondary i o n s ana lysed which may then be r e l a t e d t o e l e c t r o n images from t h e same s u r f a c e ( F i g u r e 4 ) .

( a ) ( b )

F i g u r e 4 : ( a ) Ion induced e l e c t r o n image of wear s c a r s on t h e s u r f a c e of a

s t a i n 1 e s s s t e e l sampl e . ( b ) Map of t h e O H - ion t aken from t h e same sample.

C2-124 JOURNAL DE PHYSIQUE

To demons t ra t e t h e use of t h e i n s t r u m e n t i n secondary ion mass a n a l y s i s

(SIMS) t h supe rconduc t ing compound YBa2Cu307-x has been examined 5 . The

p o s i t i v e ion spect rum from a f r e s h l y p r e p a r e d sample i s shown i n F i g u r e 5 ( a )

and may be compared w i t h t h a t from t h e same m a t e r i a l f o l l o w i n g l e n g t h y

exposure t o t h e a tmosphere F i g u r e 5 ( b ) . The p r e s e n c e of a hydroxide l a y e r

a t t h e s u r f a c e of t h e sample exposed t o a i r i s r e a d i l y a p p a r e n t . Although

t h i s l a y e r i s r e a d i l y removed by s p u t t e r i n g t h e p r e s e n c e of y t t r i u m and

barium hydrox ides cou ld p lay a s - i g n i f i c a n t r o l e i n s u r f a c e conduc t ion

behav iour .

F i g u r e 5: P o s i t i v e SIMS S p e c t r a f o r YBa2Cu307-x ( a ) F r e s h l y S i n t e r e d

( b ) Exposed t o t h e Atmosphere

The i n t e n s i t i e s of t h e v a r i o u s c l u s t e r i o n s i n t h e s p e c t r a a r e n o t

r e l a t e d t o t h e composi t ion of t h e sample. They a r e a r e s u l t of t h e

thermodynamic/chemical equi 1 i b r i a i n v o l v e d i n t h e s p u t t e r i n g p r o c e s s 5 . The

bond d i s s o c i a t i o n e n e r g i e s f o r metal o x i d e i o n s a r e p l o t t e d a g a i n s t t h e

f u n c t i o n l o g ( M O + / M + ) i n F i g u r e 6 . T h i s r e l a t i o n s h i p s u g g e s t s t h a t a s t h e

d i s s o c i a t i o n energy of t h e meta l ox ide d e c r e a s e s , t h e obse rved meta l -oxi de

peak becomes l e s s prominent .

; 2 3 L S 6 7 8 3 I O

Dlssociat~on energy 0: (M-0 ) ' (eV)

F i g u r e 6: R e l a t i o n s h i p be tween m e t a l o x i d e SIMS i n t e n s i t i e s a.nd s t a b i l i t y o f m e t a l o x i d e i o n .

ACKNOWLEDGEMENT

The w o r k was c a r r i e d o u t a t t h e B e r k e l e y N u c l e a r L a b o r a t o r i e s o f t h e

R e s e a r c h D i v i s i o n and t h e p a p e r i s p u b l i s h e d w i t h t h e p e r m i s s i o n o f t h e

C e n t r a l E l e c t r i c i t y G e n e r a t i n g Board .

REFERENCES

1 P.D. P r e w e t t , D.K. J e f f r i e s . I n s t . Phys. Con f . Ser . V o l . 54 . L i q u i d m e t a l f i e l d e m i s s i o n i o n s o u r c e s and t h e i r a p p l i c a t i o n s . I n s t i t u t e o f P h y s i c s , B r i s t o l ( 1 9 8 0 ) p 316 .

2 R. L e v i - S e t t i , J.M. B h a b a l a , Y.L. Wang. U l t r a m i c r o s c o p y (19881 , 24, 97

G.C. A l l e n , I . T . Brown. CEGB R e s e a r c h ( 1 9 8 8 ) i n p r e s s .

4 G.C. A l l e n , A.R. J o n e s , A.G. Warner . P a r t . C h a r a c t . (19861 , 3, 89 .

5 G.C. A l l e n , I . T . Brown. P h i l . Mag. L e t t e r s ( 1 9 8 8 ) i n p r e s s .