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DSi/A 1 = (2.02_o.06) • 10 -4 exp [- (136 + 3) kJ

mol-1/RT] mZ/s.

The K i r k e n d a l l m a r k e r was found to move toward the S i - r i e h side, indicating that the Si atom diffuses f a s t e r than the A1 atom in ANSi a l l o y s . F r o m the i n t e r d i f f u s i o n coefficient and the m a r k e r shift, the i n t r i n s i c diffusion coefficients were calculated. The d i f f e r e n c e in the a c t i v a t i o n e n e r g i e s (AQ) between the i m p u r i t y diffusion of Si in A1 and the s e l f - d i f f u s i o n of A1 was e s t i m a t e d by m e a n s of the a s y m p t o t i c o s c i l l a t i n g pot e n t i a l and the Le C l a i r e t h e o r y . The c a l c u l a t e d value of AQ is in f a i r a g r e e m e n t with the e x p e r i m e n t a l value. The v a c a n c y - s o l u t e b i n d i n g e n e r g y for Si in A1 was a l s o d i s c u s s e d b a s e d on the diffusion data.

1. INTRODUCTION T HERE a r e many i n v e s t i g a t i o n s of the i n t e r d i f f u s i o n in the A1-Si s y s t e m , but the r e s u l t s differ s i g n i f i c a n t l y a m o n g v a r i o u s w o r k e r . ~'e M o r e o v e r , v e r y little is known about the K i r k e n d a l l effect in the ANSi s y s t e m . T h u s , r e l i a b l e r e s u l t s of the i n t e r d i f f u s i o n in the A1Si s y s t e m a r e d e s i r e d f r o m the following r e a s o n s : 1) A n a p p r o p r i a t e r a d i o i s o t o p e for the i m p u r i t y diffusion e x p e r i m e n t i s not a v a i l a b l e for Si, 2) The r e a c t i o n between A1 thin f i l m s o r A[ w i r e s and Si l a y e r s has b e e n widely studied b e c a u s e of the i m p o r t a n c e in the i n t e g r a t e d c i r c u i t d e v i c e s . The diffusion r e s u l t s a r e u s e f u l to u n d e r s t a n d the i n t e r metallic reactions, 3) Silicon is one of the m o s t i m p o r t a n t a l l o y i n g e l e m e n t s in the c o m m e r c i a l A1 a l l o y s . Diffusion data a r e useful in a n a l y z i n g the f u n d a m e n t a l b e h a v i o r of Si in A1 a l l o y s , and 4) It is f u n d a m e n t a l to c o m p a r e the e x p e r i m e n t a l r e s u l t s with the t h e o r e t i c a l r e s u l t s on the i m p u r i t y diffusion of Si in A1, b e c a u s e Si has positive e x c e s s v a l e n c e in A1. In the p r e s e n t work, the i n t e r d i f f u s i o n was i n v e s t i gated in the t e m p e r a t u r e r a n g e f r o m 753 to 893 K, and the i m p u r i t y diffusion coefficients of Si in A1 were det e r m i n e d by applying D a r k e n ' s r e l a t i o n 7 on the i n t e r diffusion r e s u l t s . 2. E X P E R I M E N T A L PROCEDURES ANSi alloys containing 0.58, 0.87 and 1.15 at. pct Si were p r e p a r e d f r o m 99.999 wt pct Si and 99.999 wt pct A1. T h e y w e r e m e l t e d in an a l u m i n a c r u c i b l e u n d e r a NaC1-KCI flux and cast into an i r o n mold. T a b l e I shows the c h e m i c a I a n a l y s e s of the a l l o y s . The cast ingots were hot forged and armealed