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A TECHNIQUE FOR THE GROWTH OF HIGH QUALITY SINGLE CRYSTALS OF ICE
M. Ohtomo, S. Ahmad, R. Whitworth
To cite this version:
M. Ohtomo, S. Ahmad, R. Whitworth. A TECHNIQUE FOR THE GROWTH OF HIGH QUALITY SINGLE CRYSTALS OF ICE. Journal de Physique Colloques, 1987, 48 (C1), pp.C1-595-C1-598.
�10.1051/jphyscol:1987181�. �jpa-00226446�
A TECHNIQUE FOR THE GROWTH OF HIGH QUALITY SINGLE CRYSTALS OF ICE
M. OHTOMO, S. AHMAD and R.W. WHITWORTH
Department
of
Physics, University of Birmingham, GB-Birmingham ~ 1 5 ZTT, Great-BritainRbsum6
-
Une n o u v e l l e t e c h n i q u e e s t d 6 c r i t e pour l a f a b r i c a t i o n de monocristaux de g l a c e a y a n t une f a i b l e d e n s i t 6 d e d i s l o c a t i o n s . Aucun germe c r i s t a l l i n n l e s t n 6 c e s s a i r e e t l ' e a u e s t g e l 6 e de b a s en h a u t de maniere o p 6 r e r sous v i d e ou sous atmosphere contr816e. Des c r i s t a u x de 45 mm de diamhtre e t de 80 mm de l o n g o n t a i n s i 6 t 6 f a b r i q u 6 s . La d e n s i t 6 de d i s l o c a t i o n s determinee p a r t o p o g r a p h i e X &l l a i d e du rayonnement synchrotron e s t i n f 6 r i e u r e & 100 c V 2 .
A b s t r a c t - A new t e c h n i q u e i s d e s c r i b e d f o r t h e growth of s i n g l e c r y s t a l s o f i c e of low d i s l o c a t i o n d e n s i t y . No seed c r y s t a l i s r e q u i r e d and t h e w a t e r i s f r o z e n f r o m t h e bottom upwards s o t h a t it i s p o s s i b l e t o work with a vacuum o r c o n t r o l l e d a t m o s p h e r e above i t . C r y s t a l s of 45 mm diameter and 80 mm l o n g have been grown and f o u n d b y s y n - c h r o t r o n r a d i a t i o n topography t o have d i s l o c a t i o n d e n s i t i e s l e s s t h a n about 100 ~ m - ~ .
INTRODUCTION
Many workers have developed t e c h n i q u e s f o r t h e growth o f s i n g l e c r y s t a l s of i c e by t h e p r o g r e s s i v e f r e e z i n g o f water. A modified Bridqman method s u i t a b l e f o r growing c r y s t a l s o f very low d i s l o c a t i o n d e n s i t y h a s been d e s c r i b e d by Oguro and Higashi [1,2]. We d e s c r i b e h e r e a t e c h n i q u e developed from t h e s e methods b u t i n c l u d i n g i n n o v a t i o n s which g i v e it major advantages.
I n c o n v e n t i o n a l methods f o r i c e t h e c r y s t a l u s u a l l y grows above t h e l i q u i d t o t a k e advantage o f t h e n a t u r a l c o n v e c t i o n a l s t a b i l i t y o f water. The d e s i g n h a s t h e n t o p e r m i t t h e expansion a s s o c i a t e d w i t h t h e formation o f t h e i c e ; t h i s normally means t h a t a f r e e l i q u i d s u r f a c e a t atmospheric p r e s s u r e h a s t o b e maintained
somewhere. I n o r d e r e a s i l y t o be a b l e t o grow i n vacuum o r a c o n t r o l l e d atmosphere, we have chosen t o grow t h e i c e from t h e bottom o f t h e c o n t a i n e r . The system
d e s c r i b e d i n [l] and [2] u s e s a s e e d c r y s t a l , b u t t h i s i s n o t p o s s i b l e i n o u r arrangement. We have e l i m i n a t e d t h e need f o r a s e e d , and t h i s i n f a c t makes t h e whole procedure s i m p l e r .
APPARATUS
The system used i s i l l u s t r a t e d i n f i g u r e 1. The main p a r t o f t h e c r y s t a l i s grown i n t h e 45 mm diameter s e c t i o n A of t h e s p e c i a l l y shaped Pyrex g l a s s c o n t a i n e r G. This c o n t a i n e r can b e opened a t t h e cone j o i n t C f o r t h e removal of t h e f i n a l c r y s t a l and i s c l o s e d a t b o t h ends by PTFE v a l v e s V1 and V2. I t i s suspended by a c o r d i n a l a r g e r g l a s s tube F, p a r t l y f i l l e d w i t h an a n t i f r e e z e s o l u t i o n AF which i s k e p t a t a c o n s t a n t l e v e l by t h e overflow OF. The t o p o f t h e a n t i f r e e z e i s
maintained a t a c o n s t a n t temperature n e a r t o -l°C by t h e s e n s o r T1 and h e a t e r HI.
The a i r i n t h e upper p a r t o f F i s maintained a t a uniform temperature o f +0.5OC by two independent s e n s o r s T2 and T3 w i t h a s s o c i a t e d h e a t e r s H2 and H3. The whole system i s i n a l a r g e r t e m p e r a t u r e - c o n t r o l l e d e n c l o s u r e i n s i d e a c o l d room.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987181
JOURNAL
DE
PHYSIQUE6 F A
Water
I Ice
Figure 1. Crystal growth system.
For c l a r i t y t h e diagram i s n o t drawn t o s c a l e .
I n operation the growth c o n t a i n e r G i s f i l l e d t o t h e l e v e l shown with p u r i f i e d and degassed water. I t i s cooled t o near o0C, and t h e bottom of t h e bulb B i s dipped i n t o a n t i f r e e z e a t below -lo°C u n t i l a mass of p o l y c r y s t a l l i n e i c e has formed i n t h e lower h a l f of t h e bulb. Once t h i s has happened t h e tube i s immediately suspended i n s i d e t h e tube F a s i n f i g u r e 1 b u t with the middle of B a t t h e l e v e l of t h e a n t i f r e e z e s o l u t i o n . After it has come i n t o thermal equilibrium t h e growth tube i s lowered i n t o t h e a n t i f r e e z e a t a steady r a t e of 12 mm p e r day, and a t t h e same time it i s r o t a t e d by r o t a t i n g t h e suspension cord a t a r a t e of 4 r e v o l u t i o n s p e r day.
A s t h e p o l y c r y s t a l l i n e i c e grows up t h e bulb B a few g r a i n s with t h e i r c-axes approximately h o r i z o n t a l become dominant, and e v e n t u a l l y only one of t h e s e e n t e r s t h e
c a p i l l a r y tube K which contains a kink ( a s suggested by M . Oguro, p r i v a t e communication).
Growth through t h i s c a p i l l a r y eliminates d i s l o c a t i o n s propagating from B and a c r y s t a l of low d i s l o c a t i o n d e n s i t y grows up the c o n i c a l p a r t of G i n t o t h e region A. When growing i n vacuum thorough degassing of the water i s important i f low p r e s s u r e bubbles a r e not t o form i n t h e c a p i l l a r y . The temperatures have t o be adjusted s o t h a t t h e growth i n t e r f a c e I i s s l i g h t l y convex to discourage t h e growth i n t o t h e c r y s t a l of d i s l o c a t i o n s formed a t t h e walls. Independent c o n t r o l of t h e
temperatures a t T2 and T3 i s needed t o prevent convection c u r r e n t s i n t h e water, which s p o i l t h e shape of the i n t e r f a c e and may l e a d t o t h e formation of i c e on t h e
top s u r f a c e of t h e water.
We have used t h i s technique t o grow a number o f c r y s t a l s w i t h a l e n g t h o f 80 mm i n t h e r e g i o n o f 45 mu diameter. Figure 2 i s an X-ray topograph taken with synchrotron r a d i a t i o n [3] o f a specimen 1 . 5 mm t h i c k c u t from t h e upper p a r t o f a grown c r y s t a l . The many d i s l o c a t i o n s a t t h e bottom o f t h e topograph a r i s e from h a n d l i n g and mounting damage. I n t h e remainder o f t h i s specimen t h e d i s l o c a t i o n d e n s i t y i s l e s s t h a n a b o u t 100 cm-'. Some o f t h e d i s l o c a t i o n s a r e i n t h e form o f s p i r a l s w i t h [0001] Burgers v e c t o r [4], which l i e i n a p l a n e t h a t i s p e r p e n d i c u l a r t o t h e o r i g i n a l growth i n t e r f a c e . They cannot t h e r e f o r e have been formed d u r i n g growth, and a r e thought t o have been g e n e r a t e d by climb d u r i n g t h e thermal h i s t o r y o f t h e c r y s t a l .
Fiqure 2. X-ray topograph o f specimen c u t from upper p a r t o f c r y s t a l . P l a n e of g r o je c t i o n approximately (0001)
.
D i f f r a c t i o n v e c t o r 1100
.
Growthd i r e c t i o n approximately h o r i z o n t a l i n p l a n e o f t h e f i g u r e .
Once developed t h i s t e c h n i q u e h a s proved simple t o o p e r a t e , and t h e d e n s i t y o f grown-in d i s l o c a t i o n s i s lower t h a n t h a t i n t r o d u c e d by o t h e r means. We have y e t t o a s s e s s t h e chemical p u r i t y o f t h e c r y s t a l s , b u t t h e method promises t o b e a s good a s a n y t h i n g t h a t can be a c h i e v e d i n g l a s s . Without a s e e d i t i s n o t p o s s i b l e t o choose t h e o r i e n t a t i o n o f t h e c r y s t a l , b u t t h i s i s n o t e s s e n t i a l f o r s u c c e s s f u l growth and specimens can s u b s e q u e n t l y b e c u t o u t i n whatever o r i e n t a t i o n i s d e s i r e d .
ACKNOWLEDGEMENTS
This work was s u p p o r t e d by t h e Science and Engineering Research Council by a r e s e a r c h g r a n t and by a V i s i t i n g Fellowship f o r D r Ohtomo.
REFERENCES
OGURO, M., and HIGASHI, A., P h i l . Mag., 24 (1971) 713-718.
HIGASHI, A . , J. C r y s t a l Growth,
24/25
(1974) 102-107.AHMAD, S., OHMMO, M., and WHITWORTH, R. W., t h i s conference.
OGURO, M., and HIGASHI, A . , J. C r y s t a l Growth,
2
(1981) 71-80.JOURNAL
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PHYSIQUECOMMENTS
Question of M.A. WHITE :
How important is it that you rotate the sample as it is cooled, with respect to the defect concentration ?
Answer :
We, have not performed experiments specifically to test this. Rotation tends to average out small inhomogenities in temperature and gives growth which is more axially symmetrical.
