SIMS analysis of doped tungsten
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a n n e a l e d for 1 h at t e m p e r a t u r e s r a n g i n g f r o m 2200 to 2800~ Short p i e c e s f r o m each stock w e r e s n u g fitted into c y l i n d r i c a l s l o t s in s p e c i a l l y f a b r i c a t e d s t a i n l e s s s t e e l s a m p l e h o l d e r s . The t u n g s t e n s p e c i m e n s w e r e p o l i s h e d in t h e i r s a m p l e h o l d e r s to a 0.25 /lm d i a m o n d f i n i s h and then u l t r a s o n i c a l l y c l e a n e d . E x c e l l e n t ion i m a g e s could be a c h i e v e d on a c c o u n t of m i n i m u m d i s t o r t i o n of the e l e c t r i c a l field b e t w e e n the s a m p l e s u r f a c e and the e l e c t r o s t a t i c i m m e r s i o n l e n s . T u n g s t e n f i l a m e n t s 54t~m i n d i a m e t e r w e r e t a k e n f r o m p r o d u c t i o n l a m p s . The c o i l s w e r e s u p p o r t e d by a t u n g s t e n m a n d r e l , p r e c o a t e d with a t h i n Ni l a y e r , and t h e n a l m o s t t o t a l l y e m b e d d e d i n a Cu m a t r i x by e l e c t r o p l a t i n g . The s p e c i m e n s w e r e t h e n m o u n t e d in the s a m p l e h o l d e r with a low m e l t i n g S n - B i e u t e c t i c alloy and p o l i s h e d . Fig. 1 shows o p t i cal m i c r o g r a p h s of a c r o s s s e c t i o n t h r o u g h the s e c o n d a r y coil of a t u n g s t e n f i l a m e n t . 1.2 I n s t r u m e n t a t i o n The i n s t r u m e n t e m p l o y e d was a CAMECA IMS 300 S e c o n d a r y Ion Mass S p e c t r o m e t e r . In this s p e c t r o m e t e r , a c i r c u l a r s a m p l e a r e a of a p p r o x i m a t e l y 300 ~ m i n d i a m e t e r i s b o m b a r d e d with a high e n e r g y p r i m a r y ion b e a m (O~ o r Ar § and s e c o n d a r y ( s p u t t e r e d ) ions f r o m the s u r f a c e a r e m a s s a n a l y z e d . The unique ion optics of the s p e c t r o m e t e r allow ion i m a g e s with a s p a t i a l r e s o l u t i o n of ~ 1 ~tm to be f o r m e d f r o m a s e l e c t e d ion s p e c i e s . T h e s e i m a g e s give a r e p r e s e n t a tion of the d i s t r i b u t i o n in the s a m p l e of a n y s e l e c t e d e l e m e n t and m a y be viewed o p t i c a l l y o r r e c o r d e d pho~ t o g r a p h i c a l l y . A l t e r n a t i v e l y , the i n - d e p t h p r o f i l e of any e l e m e n t m a y be o b t a i n e d by e l e c t r i c a l l y r e c o r d ing its ion c u r r e n t d u r i n g c o n t i n u o u s s p u t t e r i n g . A p e r t u r e s of v a r i o u s s i z e s a r e u s e d to r e d u c e the r e g i o n f r o m which the s i g n a l is r e c o r d e d to a m i n i m u m s e l e c t e d c i r c u l a r a r e a of 10 ~ m i n d i a m e t e r . Oxygen was u s e d as the p r i m a r y ion b e a m , c o n s i s t i n g m a i n l y of O~ and about 10 pct O § The a c c e l e r a t i o n p o t e n t i a l was 5.5 keV. Depending on the d e s i r e d s p u t t e r i n g r a t e , the p r i m a r y b e a m c u r r e n t was v a r i e d b e t w e e n 0.1 and 10 ~tA. By c
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