2. 680 11. Stduble-PSmpin et al. 'PDv.vica C 235 240 (1994) 679 657)
0
.£ 7 p = 5. ] It-:" m b a r
5
% 1
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-1
~9(i 731} 77(~ ~ lU ,~,,5~~
Figmre 3. Volume ratio of c/I to c 2 m a t e r i a l as ~
fhnction Tsu b. The line is a gmide to t h e eye.
b)
X-ray dill?action frocking curves) was a p p l i e d
to d e t e r m i n e t h e volume r a t i o of c//to c± m a t e r l a /
as a function of s u b s t r a t e t e m p e r a t u r e Tsu b and
c h a m b e r p r e s s u r e p (Fig° 3). The full dots
r e p r e s e n t a series of films grown at a c h a m b e r
p r e s s u r e of 5.10 .6 mbar, which c o r r e s p o n d s i.,~
an ozone incidence r a t e at t h e s a m p l e ,,f
a p p r o x i m a t e l y 1016 molecules/cm2sec. The open
dot refers to a film grown a t a s o m e w h a t higher
p r e s s u r e of 3.10 .5 m b a r . The e r r o r b a r s for t h e s e
m e a s u r e m e n t s a r e of the size of t h e dots or
F i g u r e 2. (a) T E M cross-sectional view of t h e smaller. Fig. 3 clearly shows t h a t t h e r e l a t i v e
Sm123 film whose surface is shown in Fig. 1. (b) a m o u n t of c// m a t e r i a l p r e s e n t in a film r a p i d l y
E n l a r g e d view of (a). The d a r k lines c o r r e s p o n d i n c r e a s e s fbr d e c r e a s i n g Tsu b and for i n c r e a s i n g
to p l a n e s p e r p e n d i c u l a r to t h e c-axis of Sm123. p, i.e. far i n c r e a s i n g s u p e r s a t u r a t i o n . B a s e d on
t h e s e r e s u l t s , it s e e m s likely t h a t t h e reduced
should k e e p in m i n d t h a t with this t e c h n i q u e mobility of a d s o r b e d species on t h e surface of' t h e
only a thin slice of a 3D s a m p l e is i n v e s t i g a t e d . fihn d u r i n g deposition is r e s p o n s i b l e fbr the
D u e to an a n i s o t r o p y in t h e growth speeds nucleation of c// g r a i n s . In addition, due to the
p a r a l l e l a n d p e r p e n d i c u l a r to t h e c-axis, c//grams a n i s o t r o p y of growth s p e e d s p a r a l l e l and
a r e not only thin a n d long, b u t also r a t h e r tall, as p e r p e n d i c u l a r to t h e c-axis, once a c//-nucleus is
c o m p a r e d to t h e a v e r a g e t h i c k n e s s of t h e film fbrmed, conditions of large s u p e r s a t u r a t i o n will
(i.e. 150 nm). This o b s e r v a t i o n is e m p h a s i s e d by a fhvour the r a p i d growth of" such grains, at tile
"shadow-effect" t a k i n g place d u r i n g film growth e x p e n s e of t h e f u r t h e r growth of c ± - g r a l n s
a n d r e s u l t i n g in a film t h i c k n e s s of less t h a n 150 p r e s e n t on t h e film.
nm in b e t w e e n n a r r o w l y s p a c e d c// g r a i n s (see In conclusion, t h e r e s u l t s p r e s e n t e d here
Fig. 2a). W h i l e t h e STM i m a g e s e e m s to i n d i c a t e indicate that kinetic factors, such as
a full coverage of t h e film s u r f a c e by c// grains, s u p e r s a t u r a t i o n , play an i m p o r t a n t role in the
the TEM r e s u l t s clearly show t h a t c± regnons nucleation and g r o w t h of" c// g r a i n s in Sm123
exist in b e t w e e n t h e slabs. This d i s c r e p a n c y can films. No evidence for a cross-over from c± to c//
be e x p l a i n e d by t h e fact t h a t due to its l a t e r a l growth was fbund.
d i m e n s i o n s , a S T M - t i p will u s u a l l y not be able to
scan t h e regions in b e t w e e n two c// slabs. The REFERENCES:
s a m e g r a i n s of c// material will most probably be 1. H.M. A p p e l b o o m et al., P h y s i c a (] 2 1 4 (1993) :423.
i m a g e d by v a r i o u s l a t e r a l l y and v e r t i c a l l y shifted 2. M.E. H a w l e y et al., U ] t r a m i c r o s c o p y 42 (1992) 71}5.
mini-tips. 3. S.J. P e n n y c o o k et al., P h y s i c a C 202 ( 1 9 9 2 ) 1.