The critical nucleation temperature of stacking fault tetrahedra in gold
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g r e a t d e a l of w o r k h a s a p p e a r e d in the l i t e r a t u r e d e a l i n g with the f o r m a t i o n of s e c o n d a r y d e f e c t s in quenched gold ( e . g . Ref. 1). It is a w e l l d o c u m e n t e d f a c t that s t a c k i n g fault t e t r a h e d r a (SFT) f o r m r e a d i l y in l a r g e c o n c e n t r a t i o n s a f t e r quenching gold f o i l s o r w i r e s f r o m high t e m p e r a t u r e s , and t h e i r f o r m a t i o n i s v i a n u c l e a t i o n and growth. The c r i t i c a l s i z e n u c l e u s a p p e a r s to be a v e r y s m a l l v a c a n c y c l u s t e r , m o s t p r o b a b l y h e x a v a c a n c y which a f t e r l a t t i c e c o l l a p s e g r o w s to l a r g e r s i z e s by a b s o r b i n g v a c a n c i e s . Although c o n s i d e r a b l e work, both t h e o r e t i c a l and e x p e r i m e n t a l , was c a r r i e d out the n u c l e a t i o n p r o c e s s a p p e a r s c o n t r o v e r s i a l . F o r e x a m p l e , d e J o n g and K o e h l e r 2 had the view that t e t r a v a c a n c i e s f o r m the S F T n u c l e i while the s m a l l e s t t e t r a h e d r o n is a h e x a v a c a n c y . On the o t h e r hand Chik a s u p p o r t s the h e x a v a c a n c y a s the s t a b l e nucleus. In a d d i t i o n both h o m o g e n e o u s and h e t e r o g e n e o u s m o d e s of n u c l e a t i o n w e r e found p o s s i b l e . T h e p r o b l e m a p p e a r s to be in need of d i r e c t and q u a n t i t a t i v e e x p e r i m e n t a l a t t a c k of the n u c l e a t i o n p r o c e s s . One such study 4'5 r e v e a l s that a c h a r a c t e r i s t i c t e m p e r a t u r e T* d e f i n e s a c r i t i c a l s t a g e in the n u c l e a tion r e a c t i o n . F o r T < T* S F T f o r m in a n o r m a l m a n n e r i . e . the r a t e of n u c l e a t i o n i n c r e a s e s with t e m p e r a t u r e . F o r T > T* both r a t e and final c o n c e n t r a t i o n d e c r e a s e a s the t e m p e r a t u r e r i s e s . T h e a n a l y s i s of s u c h findings l e d to the concept of the n e g a t i v e r e a c t i o n , a r e f l e c t i o n of the i n s t a b i l i t y of a s m a l l c l u s t e r which is e s s e n t i a l to the n u c l e a t i o n p r o c e s s . T h i s c r i t i c a l n u c l e a t i o n t e m p e r a t u r e (60~ in Ref. 4) was o b t a i n e d v i a t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y and for a s i n g l e c o n c e n t r a t i o n of q u e n c h e d - i n v a c a n c i e s of 10 -4. It was thus d e c i d e d to c a r r y out the p r e s e n t i n v e s t i gation in o r d e r to study: 1) the e x i s t e n c e of t h i s c r i t i cal t e m p e r a t u r e u n d e r m a c r o s c o p i c c o n d i t i o n s by m e a n s of m e a s u r i n g the e l e c t r i c a l r e s i s t i v i t y ; and 2) the v a r i a t i o n of this t e m p e r a t u r e if any, with the t o t a l c o n c e n t r a t i o n of quenched in v a c a n c i e s . T h e o u t c o m e h e l p s putti
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