AMORPHOUS AuBi ALLOYS PRODUCED BY LASER QUENCHING AND ION IRRADIATION

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AMORPHOUS AuBi ALLOYS PRODUCED BY LASER QUENCHING AND ION IRRADIATION

A. Wolthuis, B. Stritzker

To cite this version:

A. Wolthuis, B. Stritzker. AMORPHOUS AuBi ALLOYS PRODUCED BY LASER QUENCH- ING AND ION IRRADIATION. Journal de Physique Colloques, 1983, 44 (C5), pp.C5-489-C5-493.

�10.1051/jphyscol:1983571�. �jpa-00223156�

JOURNAL

DE PHYSIQUE

Colloque C5, supplkrnent au nO1O, Tome 44, octobre 1983 page C5-489

AMORPHOUS AuBi ALLOYS PRODUCED BY LASER QUENCHING AND ION IRRADIATION

A. Wolthuis and B. Stritzker

I n s t i t u t fur Feestkijrperforschung, Kernforschungsanlagq J u l i c h , 0-5170 J u l i c h , F. R. G.

R6sum& - Nous avons pr6par& des alliages amorphes A u 1 0 0 - ~ B i ~ ( v x

6

90) par bombardement ionique ou par irradiation

laser intense d l a l l i a g e s cristallins maintenus

2

la temp&- rature de 1 1 h 6 1 i u m liquide. Nous avons identifi6 aprcs recuit plusieurs phases mPtastables qui diffPrent par leurs proprigt6s glectriques, supraconductrices et structurales.

Abstract - Amorphous A u 1 0 0 - ~ B i ~ alloys (20

4

x 4 90) could be prepared by ion o r laser bombardment o f crystalline alloys kept at liquid helium temperatures. Different metastable phases could be identified by their different electrical, superconducting and structural properties after annealing of the amorphous alloys.

Introduction:

The investigation o f metastable alloys arose rapidly growing interest during the last decade because of the remarkable electrical, mechani- cal and superconducting properties of these alloys

/ 1 - 3 / ,

A large va- riety of non-equilibrium preparation methods wich different quenching rates have been used for the production of metastable phases. In this paper we want t o compare the rather new methods o f ion and laser born- bardment o f targets at low temperatures with the more common method of vaporquenching. It has been demonstrated before that low temperature

ion irradiation and vapor quenching yield similar results, i.e. that the quenching rates of both processes are comparably high (1010-1014 K/s)

/ 4 , 5 / .

On the other hand it is known that quenching with 2 0 ns laser pulses is several orders of magnitude slower

/ 6 / .

Therefore it was interesting to study laser quenching in comparison with v a p o r - quenching and ion irradiation. Au100-xBix alloys w e r e chosen f o r this investigation because these alloys have been thoroughly studied by means of vaporquenching onto substrates at 4.2 K

/ 7 / .

In addition, the different metastable phases can be easily distinguished due to their different electrical and superconducting properties.

Experimental

:

Both Au and Bi

( 9 9 . 9 9 3 %

purity) were evaporated at pressures

L ~ o - ~

Torr onto quartz substrates at room temperature. After annealing at 4 8 0 K in Ar atmosphere f o r at least 25 h homogeneous AulOO-xBix films of about 5 0 nm were obtained. The concentration x could be determined within 5 at%.

The samples were mounted onto a substrate holder of a cryostat. A standard four-point-probe technique was used to measure the resis- tance, R(T), and the superconducting transition temperature, T of the AulOO-xBix films. Changes o f R(T) and Tc were used to deteFhine phase changes below 3 0 0 K. At room temperature the structure of the sample was determined by x-ray diffraction.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983571

CS-490 JOURNAL DE PHYSIQUE

The a s - e v a p o r a t e d a n d h o m o g e n i z e d f i l m s c o n s i s t o f t h e e q u i l i b r i u m p h a s e s , i . e . a p h a s e m i x t u r e o f A u 2 B i and Bi o r A u d e p e n d i n g on x ( A u p B i , C15 s t r u c t u r e , T c = 1 . 8 4 K ; c r y s t a l l i n e A u o r R i n o t s u p e r - c o n d u c t i n g ) .

The i r r a d i a t i o n o f t h e s e s a m p l e s was p e r f o r m e d w i t h ~ r ' i o n s . The em- p l o y e d e n e r g y o f 350 KeV e n s u r e s t h a t n e a r l y a l l Ar+ i o n s

( > 9 5 % )

come t o r e s t i n t h e q u a r t z s u b s t r a t e . T h u s i m p l a n t a t i o n e f f e c t s o f Ar i n t o t h e t h i n A u 1 0 0 - ~ B i x s a m p l e s c a n be n e g l e c t e d and o n l y i r r a d i a t i o n e f f e c t s h a v e t o be t a k e n i n t o a c c o u n t . I n a d d i t i o n some i m p l a n t e d

i n e r t a t o m s , l i k e Ar, would n o t c h a n g e t h e e l e c t r o n i c p r o p e r t i e s o f t h e e v a p o r a t e d f i l m s . The s a m p l e s r e m a i n b e l o w 1 0 K d u r i n g i r r a d i a t i o n . A n E x c i m e r l a s e r w i t h 249 n m w a v e l e n g t h ( K r F ) and 20 n s p u l s e d u r a t i o n was u s e d f o r t h e l a s e r q u e n c h i n g o f t h e A u l O O - x B i x s a m p l e s m o u n t e d o n t o

t h e s u b s t r a t e h o l d e r a t 4 . 2 K . A m o v a b l e c y l i n d r i c a l f o c u s l e n g t h i n f r o n t o f t h e c r y o s t a t was u s e d t o i n c r e a s e s t e p w i s e t h e e n e r g y d e n s i t y o f t h e l a s e r p u l s e by d e c r e a s i n g t h e c r o s s s e c t i o n o f t h e l a s e r beam a t t h e s a m p l e . Thus e n e r g y d e n s i t i e s i n t h e r a n g e o f 3 0 - 4 0 0 mJ/cm2 c o u l d be o b t a i n e d .

R e s u l t s :

The f i g u r e s l a and l b show Tc o f A u 1 0 0 - x B i x a s a f u n c t i o n o f i r r a d i - a t i o n w i t h an Arf beam f o r x = 6 0 pnd w i t h a l a s e r beam f o r x = 6 5 . The s t a r t i n g Tc a m o u n t s t o 1 . 9 K due t o p a r t i a l c o n t e n t o f A u 2 B i .

F i g . l a : TC o f a Au40Bi60 f i l m F i g . l b : T c o f a Au35Bitj5 f i l m v e r s u s d o s e of i r r a d i a t i n g Ar i o n s v e r s u s e n e r g y d e n s i t y o f t h e

l a s e r p u l s e

As c a n b e s e e n i n F i g . l a f i r s t Tc i n c r e a s e s s t e e p l y a s a f u n c t i o n o f Ar d o s e a n d t h e n T c s a t u r a t e s a t 5 . 1 K f o r d o s e s

3

1 0 1 6 a t o m s / c m Z . R e g a r d i n g low t e m p e r a t u r e i o n i r r a d i a t i o n a s a r a p i d q u e n c h i n g t e c h - n i q u e t h i s i n c r e a s e o f T c c a n b e u n d e r s t o o d i n t h e f o l l o w i n g way.

I n i t i a l l y e a c h inco'ming a t o m d e p o s i t s i t s e n e r g y w i t h i n a c a s c a d e r e g i o n o f t h e o r d e r o f 1 0 nm d i a m e t e r t h r o u g h o u t t h e f i l m t h i c k n e s s .

I I I I I -

- Lj-l--i-j -

- i"

/i

^Au35Bi65

* - a

-

I I I I I

,

^L

6 I I

4 -

4 -

yf-i--

A"40 Bi60

0 - ^{I I I ,}

Then t h i s " h o t " r e g i o n i s r a p i d l y q u e n c h e d d u e t o t h e s u r r o u n d i n g l a t t i c e a t 4 K . T h u s a n a r r o w r e g i o n o f m a t e r i a l w i t h a T c = 5 . 1 K i s p r o d u c e d . T h i s Tc c a n n o t be m e a s u r e d b e c a u s e t h e s u r r o u n d i n g m a t e r i a l s u p p r e s s e s t h i s h i g h e r Tc v i a p r o x i m i t y e f f e c t . F u r t h e r

i r r a d i a t i o n p r o d u c e s more and more " h i g h " Tc m a t e r i a l u n t i l t h e w h o l e s a m p l e i s t r a n s f o r m e d i n t o t h e I t h i g h " Tc p h a s e .

10 15 0

0 5 _{0 40 80 120 160}

Ar-Dose / loT5 ^{a t} cm-2

E l mJ ern-;!

6

4

K 4

2

F i g . l b shows t h e c o r r e s p o n d i n g r e s u l t f o r l a s e r q u e n c h i n g . W i t h i n c r e a s i n g e n e r g y d e n s i t y o f t h e l a s e r 2 p u l s e t h r e e d i f f e r e n t r e g i o n s can b e d i s t i n g u i s h e d . Up t o - 4 0 mJ/cm t h e r e i s no c h a n g e o f Tc ( T c = 1 . 9 K , A u 2 B i ) . T h e n Tc i n c r e a s e s s t e e p l y a n d s a t u r a t e s a t a h i g h v a l u e o f 5 . 4 K f o r e n e r g y d e n s i t i e s 2 8 0 m ~ / c m 2 . T h i s r e s u l t c a n b e e x p l a i n e d u n a m b i g u o u s l y i n t h e f o l l o w i n g way. I n t h e f i r s t r e g i o n t h e e n e r g y d e n s i t y o f t h e l a s e r beam i s 2 n o t h i g h e n o u g h t o m e l t t h e s u r f a c e o f t h e s a m p l e . Above 4 0 mJ/cm t h e m e l t i n g t h r e s - h o l d i s e x c e e d e d a n d t h e s u r f a c e s t a r t s t o m e l t . The m o l t e n s u r f a c e l a y e r s o l i d i f i e s v e r y r a p i d l y a f t e r t h e l a s e r p u l s e due t o t h e c o l d s u b s t r a t e . T h i s r a p i d s o l i d i f i c a t i o n y i e l d s a " h i g h N T c m a t e r i a l a t t h e s u r f a c e . W i t h i n c r e a s i n g e n e r g y d e n s i t y t h e m o l t e n s u r f a c e l a y e r a n d t h u s t h e r e s u l t i n g l a y e r o f " h i g h " Tc m a t e r i a l becomes t h i c k e r u n t i l t h e p r o x i m i t y e f f e c t f r o m t h e u n d e r l y i n g m a t e r i a l c a n b e n e g - l e c t e d a n d Tc s a t u r a t e s a t t h e h i g h v a l u e .

The r e s u l t i n g " h i g h " Tc m a t e r i a l h a s a c o n s i d e r a b l y h i g h e r r e s i s t i v i t y i n c o m p a r i s o n t o t h e s t a r t i n g m a t e r a i a l . Thus n o t o n l y t h e m e l t i n g t h r e s h o l d b u t a l s o t h e t h i c k n e s s o f t h e m o l t e n and r e s o l i d i f i e d l a y e r c a n b e s i m p l y d e t e r m i n e d b y m e a s u r i n g t h e r e s i s t i v i t y o f t h e s a m p l e . F r o m t h i s m e a s u r e m e n t i t c o u l d b e shown t h a t t h e w h o l e A u 3 5 B i 6 5 f i l m ( 4 6 nm t h i c k ) has b e e n m o l t e n f o r e n e r g y d e n s i t i e s - 1 8 0 mJ/cm

.

B e s i d e s d e t e r m i n a t i o n o f t h e m e l t i n g t h r e s h o l d a n d l a y e r t h i c k n e s s t h e m e a s u r e m e n t o f r e s i s t a n c e ,

R ( T ) ,

c a n b e u s e d f o r t h e d e t e r m i n a t i o n o f p h a s e t r a n s i t i o n s d u r i n g a n n e a l i n g o f t h e " h i g h " Tc p h a s e . A t r a n s - f o r m a t i o n i n t o a n o t h e r p h a s e c a n b e d e t e r m i n e d b y t h e f o l l o w i n g o b s e r - v a t i o n s d u r i n g a n n e a l i n g :

1 ) A s u d d e n , i r r e v e r s i b l e c h a n g e o f t h e r e s i s t a n c e 2 ) A d i f f e r e n t r e v e r s i b l e R ( T ) b e h a v i o r o f t h e new p h a s e 3 ) A d i f f e r e n t Tc v a l u e o f t h e new p h a s e .

The a n n e a l i n g e x p e r i m e n t s show 3 o r 4 d i f f e r e n t p h a s e s f o r x 4 33 o r x

>

3 3 .

D i s c u s s i o n :

The r e s u l t s o f t h e d i f f e r e n t q u e n c h i n g m e t h o d s a r e p l o t t e d i n F i g . 2, s h o w i n g t h e r e s u l t i n g Tc as a f u n c t i o n o f t h e a l l o y c o m p o s i t i o n . The u p p e r c u r v e was o b t a i n e d e i t h e r a f t e r i o n i r r a d i a t i o n a t l o w t e m p e r a t u r e s o r l a s e r q u e n c h i n g a t 4 K o r v a p o r q u e n c h i n g o n t o c o l d s u b s t r a t e s / 7 / . T h u s i t i s r e a s o n a b l e t o assume t h a t i n a l l c a s e s t h e same p h a s e was p r o d u c e d . I t was shown f o r t h e v a p o r q u e n c h e d s a m p l e s b y e l e c t r o n d i f f r a c t i o n , t h a t t h e s e a l l o y s a r e a m o r p h o u s / 7 / . I n a d d i t i o n t h e T c v a l u e s a i m t o t h e Tc o f a m o r p h o u s B i / 8 / . F r o m t h e s e o b s e r v a t i o n s we c o n c l u d e t h a t t h e " h i g h " TC p h a s e o b t a i n e d a f t e r i o n i r r a d i a t i o n o r l a s e r q u e n c h i n g i s a m o r p h o u s .

A n n e a l i n g o f t h e a m o r p h o u s p h a s e w i t h x b 33 t o 1 5 0

-

2 5 0 K y i e l d s a m e t a s t a b l e p h a s e w i t h a l o w e r T c ( p a r a b o l i c c u r v e i n F i g . 2 ) . T h i s p h a s e h a s a c u b i c s t r u c t u r e and i s m o s t p r o b a b l y v e r y s i m i l a r t o t h e p r e s s u r e p h a s e B i

I 1

( T - 3 . 9 K ) / 9 , 1 0 / . A t a h i g h e r a n n e a l i n g t e m p e r a - t u r e o f 280 K t h i s m e t a E t a b l e p h a s e t r a n s f o r m s i n a n o t h e r m e t a s t a b l e p h a s e . X - r a y d i f f r a c t i o n e x p e r i m e n t s show o n l y t h e p r e s e n c e o f t h e e l e m e n t s Au and B i . Tc o f t h i s p h a s e i s 2 . 6 K i n d e p e n d e n t o f t h e c o n - c e n t r a t i o n . A f e w a n n e a l i n g e x p e r i m e n t s a t t e m p e r a t u r e s a b o v e 3 0 0 . K h a v e a l r e a d y shown t h a t t h e t r a n s f o r m a t i o n i n t o t h e s t a b l e s t a t e o c c u r s f o r x < 33 a t 4 0 0 - 5 0 0 K and f o r x > 33 a t 3 0 0 - 3 5 0 K .

JOURNAL DE PHYSIQUE

Fig. 2: Tc versus Bi con- centration f o r the different

phases obtained by different 6 quenching methods

e

Ionirradiation, T~ -

o Vaporquenching /7/ K

Laserquenching.

Upper curve: amorphous alloys 4 Lower line: equilibrium alloys

(crystalline, con- taining Au2Bi) Intermediate curves

:

metastable alloys 2

Conclusion:

Amorphous A u 1 0 0 - ~ B i ~ alloys (20

-L

x " 90) could be produced not only by ion irradiation and vaporquenching but also by laserquenching.

Both, the superconducting transition temperatures and the transition temperatures into the different phases a r e identical indpendent o f the applied quenching method.

The result confirms again the similarity of ion irradiation and vaporquenching which has been observed before, f o r instance in AuTe alloys

/ 4 / .

However, the result is different t o AuTe alloys with respect to the slowest quenching method, i.e. laserquenching, which could not produce amorphous AuTe /11/. In contrast, for AuBi alloys the lower quenching rates o f laserquenching are sufficient t o produce amorphous AuBi alloys.

By means of annealing experiments different metastable phase w e r e

identified and a detailed metastable phase diagram was obtained.

R e f e r e n c e s :

/1/ G u n t h e r o d t H.J., O e l h a f e n P . , e t a l . , J . P h y s i q u e 41 ( 1 9 7 8 ) C8-381

/ 2 / Gilman J . J . , J . P h y s i q u e - 4 1 ( 1 9 8 0 ) C8-811 / 3 / Bergmann G., P h y s i c s Rep. 27C ( 1 9 7 6 ) 1 6 0

/ 4 / Meyer J . D . , S t r i t z k e r B . , Z . P h y s i k B 36 ( 1 9 7 9 ) 47 and N u c l . I n s t r . M e t h . 1 8 2 / 1 8 3 ( 1 9 8 1 ) 965

/ 5 / S t r i t z k e r B . , N A T O - I n s t i t u t e - B o o k : " S u r f a c e ~ d d i f i c a t i o n s and A l l o y i n g u ( 1 9 8 2 ) C h a p t e r 6 : M e t a s t a b l e A l l o y s

/ 6 /

v .

A l l m e n M . , L a s e r - g e n e r a t e d g l a s s y p h a s e s , t o be p u b l i s h e d i n P r o c . MRS-Meeting, B o s t o n 1 9 8 2

/ 7 / S c h n e i d e r M . , Diploma-work a t t h e U n i v e r s i t y K a r l s r u h e ( 1 9 7 9 ) / 8 / B u c k e l W . , H i l s c h R . , Z . P h y s i k 138 ( 1 9 5 4 ) 1 0 9 - 1 2 0

/ 9 / P a u l R . , " H a l b l e i t e r p h y ~ i k ~ ~ , V E B V e r l a g , B e r l i n ( 1 9 7 4 ) / l o / B r a n d t N . B . , G i n z b u r g N . I . , S o v . P h y s . JETP l2, ( 1 9 6 1 ) 1 0 8 2 /11/ S t r i t z k e r B . , W h i t e C . W . , A p p l e t o n B . R . , and S e k u l a S . T . ( 1 9 8 0 ) ,

t o be pub1 i s h e d .