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ELECTRONIC STRUCTURE OF AMORPHOUS Co-P AND Ni-P METALLIC ALLOYS : EVIDENCE FOR
SHORT-RANGE ORDER
J. Rivory, B. Bouchet, Yves Bertrand
To cite this version:
J. Rivory, B. Bouchet, Yves Bertrand. ELECTRONIC STRUCTURE OF AMORPHOUS Co-P AND
Ni-P METALLIC ALLOYS : EVIDENCE FOR SHORT-RANGE ORDER. Journal de Physique Col-
loques, 1980, 41 (C8), pp.C8-430-C8-432. �10.1051/jphyscol:19808107�. �jpa-00220202�
JOURNAL DE PHYSIQUE
Co Zloque
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n08,Tome
4 1 ,aoct 1980, page
C8-430ELECTRONIC STRUCTURE OF ArlORPHOUS Co-P AND N i - P M E T A L L I C ALLOYS
:
EVIDENCE FOR SHORT-RANGE ORDER
J. R i v o r y , B. Bouchet and Y . B e r t r a n d
*
Laboratoire dlOptique des SoZides t , Uniuersit8 Pierre e t Marie Curie,
4place Jussieu 75230 Paris Cgdex 05, France.
* Laboratoire de
Spectroscopic 11, U. S. T .L., place EugDne Batail Zon, 34060 MontpeZ l i e r , France.
Rdsum6.
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Les p r o p r i d t 6 s o p t i q u e s de c o u c h e s s e m i - t r a n s q a r e n t e s d ' a l l i a g e s amorphes Co-P e t Ni-P p r d p a r e e s p a r 6 v a a o r a t i o n r a p i d e s o u s v i d e s o n t d d t e r m i n d e s d a n s un g r a n d domaine s p e c t r a l . E l l e s s o n t compardes d ' u n e p a r t A c e l l e s d e couches de Co e t N i p u r s , d ' a u t r e D a r t 2 c e l l e s de composds c r i s t a l l i n s Co P e t N i P. Les s i m i l i t u d e s o b s e r v d e s e n t r e l e s s p e c t r e s o p t i q u e s d e s a l l i a g e s a m r -2 3
p h e s e t d e s compos6s c r i s t a l l i n s s u p g h r e n t l a ~ r g s e n c e d ' a r r a n g e m e n t s a t o m i q u e s l o c a u x de t y p e Co P e t N i P d a n s l ' d t a t a m r p h e . Nos r d s u l t a t s m e t t e n t e n c a u s e l a v a l i d i t d d ' u n s i m ? l e modPle 2 3 d ' e l e c t r o n s l i b r e s e t s o n t e n f a v e u r d ' u n e h y b r i d a t i o n d e s & t a t s p du phosphore a v e c l e s 6 t a t s d du m6tal d e t r a n s i t i o n d a n s c e s a l l i a g e s m g t a l l i q u e s amorphes.
A b s t r a c t . - The o p t i c a l p r o p e r t i e s o f t h i n s e m i - t r a n s ~ a r e n t amorphous Co-P and Ni-P a l l o y f i l m s p r e p a r e d by f l a s h - e v a p o r a t i o n under vacuum a r e d e t e r m i n e d o v e r a l a r g e e n e r g y r a n g e . They a r e compared t o th0s.e o f p u r e Co and N i f i l m s on t h e one h a n d , o f c r y s t a l l i n e Co P and 2 N i 3 P f i l m s on t h e o t h e r hand. The s i m i l a r i t i e s o b s e r v e d between t h e o p t i c a l s p e c t r a o f t h e amorphous a l l o y s and of t h e c r y s t a l l i n e compounds s u g R e s t t h e o r e s e n c e o f l o c a l a t o m i c a r r a n g e m e n t s o f t h e Co 2 P and N i P t y p e i n t h e amorphous s t a t e . Our r e s u l t s t e n d t o q u e s t i o n t h e v a l i d i t y o f a s i m o l e n e a r l y - f r e e e l e c t r o n m d e l and i s i n f a v o u r o f a n h y b r i d i z a t i o n o f t h e P p - s t a t e s w i t h t h e t r a n s i t i o n m e t a l 3 d - s t a t e s i n t h e s e amorphous m e t a l l i c a l l o y s .
I . I n t r o d u c t i o n . - During t h e l a s t few y e a r s , Co-P and Ni-P have been t h e ~ s e x t ? n s i v e ! y s t u - c d i e d amorphous m e t a l l i c a l l o y s ; t h e i r s t r u c t u r e ( 1 ) t h e i r m a g n e t i c p r o p e r t i e s (2) and, i n t h e Co-P c a s e , t h e i r o p t i c a l p r o p e r t i e s (3) have a l r e a d y been i n - v e s t i g a t e d . U n t i l r e c e n t l y , a model p r o p o s e d i n o r d e r t o d e s c r i b e t h e e l e c t r o n i c s t r u c t u r e o f t h e s e m a t e r i a l s , i . e . a s i m p l e r i g i d band model i n which t h e m e t a l l o i d atoms add t h e i r v a l e n c e e l e c t r o n s t o t h e t r a n s i t i o n m e t a l c o n d u c t i o n band w i t h o u t any i n t e r a c t i o n was w i d e l y a c c e p t e d ( 4 ) . I t was a p p l i e d t o Au-Si a l l o y s by Tauc e t a l . ( 5 ) and t o Pd-Si a l l o y s by S c h l e g e l e t a l . (6) i n o r d e r t o i n t e r - p r e t e t h e i r o p t i c a l p r o p e r t i e s .
I n t h i s p a p e r , we i n t e n d t o show t h a t o u r o p t i - c a l r e s u l t s on b o t h Co-P and Ni-P a m r p h o u s a l l o y s a r e i n c o n t r a d i c t i o n w i t h a r i g i d band model b u t f a v o u r a model b a s e d on p-d h y b r i d i z a t i o n . They a l s o s u g g e s t t h e e x i s t e n c e i n t h e amorphous a l l o y s o f a l o c a l a t o m i c a r r a n g e m e n t c l o s e t o t h a t o f t h e c r y s t a l l i n e compounds Co P and N i P.
2 3
t h i c k n e s s r a n ~ e d from 200 t o 600 A and was de- t e r v i n e d h v a n X-ray i n t e r f e r e n c e method ( 1 "
a c c u r a c y ) .
R e f l e c t a n c e and t r a n s m i t t a n c e measurements were q e r f o r m e d o n t h e s e f i l m s i n a i r between 0 . 5 and 6.2 eV; t h e r e f l e c t a n c e o f t h i c k e r opaque s a m p l e s was moreover measured from 4 t o 10 eV under vacuum
.
The c o m ~ l e x d i e l e c t r i c c o n s t a n t was deduced f r o c t h e r e f l e c t a n c e and t r a n s m i t t a n c e d a t a i n t h e v i s i b l e and n e a r U.V. r a n g e ; a Kramers-Kronig a n a l y s i s o f t h e r e f l e c t a n c e d a t a o v e r t h e whole s p e c t r a l r a n g e was a l s o u s e d , w i t h t h e h e l p o f e l l i p s o m e t r i c m e a s u r e m n t s f o r t h e f i t t i n g p r o c e - d u r e .The P c o n c e n t r a t i o n was d e t e r m i n e d by m i c r o p r o b e a n a l y s i s w i t h r e l a t i v e l y h i p h u n c e r t a i n t i e s ; t h e room t e m o e r a t u r e v a l u e o f t h e r e s i s t i v i t y was t h e n u s e d t o comoare s a m p l e s . The s t r u c t u r e was c o n t r o l - l e d by e l e c t r o n microscopy and e l e c t r o n d i f f r a c t i o n . The c r y s t a l l i z a t i o n D r o c e s s e s f o r b o t h Co-P a n d . Ni-P have a l r e a d y been d e s c r i b e d ( 3 , 7 ) .
2. ~ x p e r i m e i t .
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Thin f i l m s were d e p o s i t e d under 3 . Co-P a l l o y s .-
F i g u r e 1 shows t h e o p t i c a l c l a s s i c a l vacuum o n t o amorphous s i l i c a s u b s t r a t e s a b s o r u t i o n E / A v e r s u s e n e r g y ( E ~ b e i n g t h e imagi-2
a t room t e m p e r a t u r e by f l a s h - e v a p o r a t i o n , from n a r y v a r t o f t h e d i e l e c t r i c c o n s t a n t ) f o r a n amor- a l l o y s e l e c t r o d e p o s i t e d o n t u n g s t e n w i r e s . The f i l m nhous Co-P a l l o y w i t h a r e s i s t i v i t y : p = 120 ~62cm
and f o r p u r e Co. E x c e p t a t low e n e r g i e s , b o t h
J .
' Equipe de Recherche A s s o c i 6 e au CURS n o 462 s p e c t r a p r e s e n t a rouph o v e r a l l s i m i l a r i t y . The
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19808107
F i g u r e 1.
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O p t i c a l a b s o r p t i o n v e r s u s e n e r x y f o r amorphous Co-P ( p = 120 pRcm) ( c o n t i n u o u s l i n e ) and f o r p u r e Co ( b r o k e n l i n e ).
d i f f e r e n t s t r u c t u r e s a r e i n d i c a t e d by a r r o w s . For t h e amorphous a l l o y , we f i n d maxima a t 2 , 5 . 4 , 7 ell and a l s o a f a i n t s t r u c t u r e around 4 . 3 eV. I n p u r e Co, a p r o m i n e n t s t r u c t u r e i s o b s e r v e d a t 0 . 8 eV, two s m a l l e r o n e s a t 2 and 5.4 eV. The o p t i c a l ab- s o r p t i o n f o r t h e amorphous a l l o y s d o e s n o t v a r y w i t h t h e P c o n c e n t r a t i o n . For a more c o n c e n t r a t e d sample ( p = 134 p&m) t h e s t r u c t u r e s a r e o n l y more pronounced, a s s e e n o n f i g u r e 2 . The s p e c t r u m o f t h e same sample a f t e r a n n e a l i n g a t 4 9 0 ' ~ i s a l s o g i v e n on f i e u r e 2 f o r compzrison; c o m o l e t e c r y s t a l - l i z a t i o n and.phase s e p a r a t i o n have b e e n a c h i e v e d , l e a d i n g t o a m i x t u r e o f Co and Co P .
2-
--
- -1 2 3 4 5
ENERGY ( e ~ 1
F i g u r e 2.
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O n t i c a l a b s o r p t i o n v e r s u s e n e r p y f o r a Co-P a l l o y i n amorphous s t a t e ( p = 134 vficm) ( c o n t i n u o u s l i n e ) and a f t e r a n n e a l i n g a t 490°C (broken l i n e ).
Between 0 . 6 and 2 eV, we n o t i c e a b r o a d a b s o r p t i o n band w i t h e s s e n t i a l l y two neaks a t 0.8-0.9 eV and 2 eV, l i k e i n p u r e Co.
4. Ni-P a l l o y s .
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The c o m p a r i s o n between t h e op- t i c a l a b s o r o t i o n o f a n amorphous Ni-P a l l o y( 0 = l lo pficm) a n d o f p u r e N i , shown i n f i g u r e 3 , r e v e a l s m r e i m ~ o r t a n t d i f f e r e n c e s t h a n between amorphous Co-P and n u r e Co.
F i g u r e 3 . - O p t i c a l a b s o r p t i o n v e r s u s e n e r g y f o r a m r o h o u s Vi-P (p = 1 10 ~ R c m ) ( c o n t i n u o u s l i n e ) and f o r p u r e N i ( b r o k e n l i n e 9
.
W e l l - d e f i n e d p e a k s a t 3.4 and 7 eV a r e s e e n f o r a m r p h o u s Ni-P, w h i l e p e a k s a t 1.4 and 4.5 eV a r e o b s e r v e d f o r p u r e Y i . L i k e f o r Co-P, t h e low-energy peak d i s a p ~ e a r s , b u t two i m ~ o r t a n t new s t r u c t u r e s a o p e a r a t 3.4 and 7 eV. The c r y s t a l l i z a t i o n o f t h e amorphous a l l o y s b r i n p f u r t h e r i n f o r m a t i o n . F i g u r e 4 shows t h e o p t i c a l a b s o r p t i o n f o r a Ni-P a l l o y i n
ENERGY (eV 1
F i g u r e 4 . - O p t i c a l a b s o r o t i o n v e r s u s e n e r g y f o r a Ni-p a l l o y i n amor9hous s t a t e ( p = 122 pRcm) ( c o n t i n u o u s l i n e ) and a f t e r a n n e a l i n g a t 3 7 5 O ~ ( b r o k e n l i n e ) .
t h e amorphous s t a t e ( 0 = 122 ~ Q c r n ) and a f t e r an- n e a l i n g a t 375OC, when i t c o n s i s t s i n a m i x t u r e o f N i and Ni P ( 7 ) . The a b s o r p t i o n peak a t 1.4 eV
3
c h a r a c t e r i s t i c o f n u r e N i a u p e a r s a g a i n , b u t t h e s t r o n g a b s o r o t i o n a t 3.4 eV i s s e e n b o t h i n t h e amoruhous and t h e c r y s t a l l i n e s t a t e ; i t must be c h a r a c t e r i s t i c o f 'TijP.
JOURNAL DE PHYSIQUE
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5 . D i s c u s s i o n .
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The d i s a p p e a r a n c e o f t h e low- BERRADA, A., LAPIERRE, M.F., LOEGEL, B., PANIS- e n e r u a b s o r p t i o n peak o b s e r v e d f o r b o t h p u r e Co SOD, P. and POBERT, C., J . P h y s . F: Y e t a lP h y s . 8 ( 1 9 7 8 ) 845.
a n d N i when t o t h e a m o r ~ h o u s a l l o l r s i s i n d i - ( 3 ) PTVC)!?Y, J. and BOUCHET, B., J . Phys. F: Metal c a t i v e o f a s h i f t o f t h e Fermi l e v e 1 , i n a p r e e m e n t P h y s . 9 (1979) 327.
( 4 ) N4GEL, S.R. and TAUC, J., P h y s . Rev. L e t t . 3 5 w i t h t h e d e c r e a s e o f t h e w i p n e t i z a t i o n a s t h e P (1975) 380.
c o n c e n t r a t i o n i n c r e a s e s ( 2 ) . One c a n i m a p i n e a ( 5 )
&USER,
E.,
ZIRKE, R. J . , TAUC, J . , HAUSER, J . J . and NAGEL, S.R., P h y s . Rev. B19 (1979) 6 3 3 1 . s h i f t t o h i g h e r e n e r p i e s i f o n e a s s u m e s a f i l l i n g ( 6 ) SCHLEGEL, A., UACHTER, P . , ACPERMANN, K.P., o f t h e d b a n d due t o t h e e l e c t r o n s t r a n s f e r r e d LIARD, M. a n d GUNTHERODT, H . J . , S o l i d S t a t eC o m u n . 31 (1979) 373.
f r o m P t o t h e m e t a l . A d i f f e r e n t model h a s however b e e n p r o p o s e d b y Amamou a n d K r i l l ( 8 1 , d e d u c e d f r o m
( 7 ) F.IVDR?, J . and BOUCHET, B., P r o c e e d i n g s o f t h e
? h o t o e m i s s i o n m e a s u r e m e n t s o n c r y s t a l l i n e Co R a n d
3 T h i r d I n t . C o n f . on R a p i d l y Quenched V e t a l s , amorphous C O ~ ~ P , ~ B ~ . An h y b r i d i z a t i o n b e t w e e n t h e C a n t o r , B., e d i t o r (The M e t a l s S o c i e t y , London)
1978, Vol. 2 , p . 5 6 .
P a n d B p - s t a t e s and t h e Co d - s t a t e s i s assumed (8) AF.(A"OU, A. and W I L L , G . , S o l i d S t a t e C o m u n . l e a d i n g t o t h e p r e s e n c e o f more a v a i l a b l e e l e c t r o - 31 ( 1 9 7 9 ) 9 7 1 .
( 9 )nRAKE, J . and SCHLESINGER, X., S o l i d S t a t e n i c s t a t e s i n t h e low p a r t o f t h e d-band, t h e u n o e r Coinmun. 1 1 (1972) 1597.
p a r t b e i n g s i m i l a r t o t h a t o f p u r e Co. The m a j o r i t y b a n d i s t h e n l e s s f i l l e d and t h i s l o w e r i n g o f t h e Fermi l e v e l a l s o r e d u c e s t h e m a g n e t i c moment. Our r e s u l t s t e n d t o s u p p o r t t h e l a t t e r m o d e l . F o r q u r e Co, t h e a b s o r p t i o n n e a k a t 5 . 4 eV i s r e l a t e d t o t r a n s i t i o n s from t h e b o t t o m o f t h e d band t o E
F ' T h i s p e a k i s a l s o o b s e r v e d f o r amorphous Co-P a t a b o u t t h e same l o c a t i o n . On t h e c o n t r a r y , t h e p e a k a t 7 eV (and p o s s i b l y t h e one a t 4 . 4 eV) w h i c h a p p e a l s f o r t h e a l l o y s i s r e l a t e d t o t r a n s i t i o n s i n v o l v i n g t h e h y b r i d i z e d p h o s p h o r u s p - s t a t e s ; s u c h i n f o r m a t i o n was o b t a i n e d by p h o t o e m i s s i o n o n Co78P14B8 by ( 8 ) . We may, i n t h e same way, c o n c l u d e t h a t i n Ni-P amorphous a l l o y s , t h e ~ h o s p h o r u s p s t a t e s a r e h y b r i d i z e d w i t h t h e N i d s t a t e s . r h e f a c t t h a t t h e peak a t 3.4 eV i s a l s o o b s e r v e d i n t h e c r y s t a l l i n e p h a s e t e n d s t o p r o v e t h e n r e s e n c e o f a l o c a l a t o m i c a r r a n g e m e n t i n t h e a m o r ~ h o u s s t a t e v e r y s i m i l a r t o t h a t i n Ni3P. An e a r l y b a n d s t r u c t u r e c a l c u l a t i o n f o r N i P ( 9 ) shows a p e a k i n
3
t h e d e n s i t y o f s t a t e s a b o v e EF, w h i c h c a n b e i n - v o l v e d i n t r a n s i t i o n s f r o m t h e d b a n d o c c u r r e d a t e n e r g i e s n e a r EF. S i m i l a r c a l c u l a t i o n s f o r Co2P (10) c o u l d a c c o u n t f o r t h e s m a l l p e a k a t 4 . 4 eV i n Co-P amorphous a l l o y .
Acknowledgement.
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T h i s work h a s b e e n s p o n s o r e d i n p a r t b y t h e " D i r e c t i o n d e s R e c h e r c h e s , E t u d e s e t~ e c h n i ~ u e s " u n d e r c o n t r a c t n o 791440.
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