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Thermal annealing of low-temperature X-irradiated KCl
Volume24A. number 7
THERMAL
ANNEALING
PHYSICS LETTERS
OF
27 March 1967
LOW-TEMPERATURE
X-IRRADIATED
KC1
A. BEHR, H. PEISL and W.WAIDELICH I. Physikalisches lnstitut der Technischen Hochschule, Darmstadt, Germany
Received 27 February 1967
Thermal annealing of latticedefects in KCI X-irradiated at liquidhelium temperature was studied by optical absorption measurements. The annealing behaviour of the ot and 195 n m bands, and of the F and H bands, respectively, can be interpreted as recombination of vacancies and interstitials.
I n f o r m a t i o n about the defects c r e a t e d by Xr a y s at liquid h e l i u m t e m p e r a t u r e can be obt a i n e d f r o m t h e r m a l a n n e a l i n g s t u d i e s [1-4]. The p u r p o s e of this p a p e r i s to r e p o r t about t h e r m a l a n n e a l i n g of a l l defects c r e a t e d in KC1 by X - i r r a d i a t i o n at liquid h e l i u m t e m p e r a t u r e . F o r this p u r p o s e the o p t i c a l a b s o r p t i o n of F , and H cer~ters and an a b s o r p t i o n band at 195 nm w e r e studied d u r i n g a n n e , Hug. The s p e c i m e n s u s e d w e r e cleaved f r o m a s i n g l e block of "pure" Harshaw KC1. They w e r e X - i r r a d t a t e d i n a liquid h e l i u m c r y o s t a t by a tutlgsten anode tube (150 kV, 12 mA). F i l t r a t i o n of the X - r a y s through the tube and cryostat wind o w and 0.1 s a m copper foil assured uniform coloratlon. Optical absorption m e a s u r e m e n t s w e r e m a d e , using a S e y a - N a m i o k a type u.v. e p e c t r o p h o t o m e t e r , i n t h e s a m e c r y o s t a t at l i q u i d h e l i u m t e m p e r a t u r e . Fig. 1 shows the r e -
s u l t s of the a n n e a l i n g of the a , 195 n m , F and H band. M e a s u r e m e n t s w e r e m a d e at the band m a x i m u m d u r i n g w a r m i n g up of t h e c r y s t a l s at about 1 d e g / m i n . The r e s u l t s c o m e f r o m four c r y s t a l s , in each c a s e d i f f e r e n t i r r a d i a t i o n t i m e s were u s e d to obtain o p t i m u m coloration. The a n n e a l i n g c~ the a and 195 n m band show an equivalent b s h a v i o u r i n f o r m of t h r e e d i s t i n c t a n n e a l i n g s t a g e s . In both c a s e s a n n e a l i n g in stage II i s a f i r s t o r d e r p r o c e s s with an a c t i v a tion e n e r g y of (25 ~ 3) meV and i n stage HI a s e c ond o r d e r p r o c e s s with a n a c t i v a t i o n e n e r g y of (30 ± 3) meV. F o r the s m a l l stage HII it was not p o s s i b l e to obtain both q u a n t i t i e s with sufficient a c c u r a c y . F r o m the equlv~len_t behaviour of ot and 195 n m band a n n ~ H - g we conclude that the 195 a m band i s v e r y p r o b a b l y r e l a t e d to i n t e r s t i t i a l c h l o r i n e i o n s , and so a n n e a l i n g t a k e s place by recombirattion of v a c a n c i e s and i n t e r s t i t i a l
Q5
(
I
o
ill
t.o
5
10
20
,4_I
30
40
temperoture
50 "K 60 ~--
Fig. 1. Thermal annealing of lattice defects in low-
temperature X-irradiated KC1. X-irradiation time: 0~: 1.5 hr; 195 nm:8 hr; F :2.5 hr;H :5.5 h~. Initial concentration ~6centers no (ct) = 6 × 1016cm-3; no (F) = 6 X 19 6cm -3. Max. temperature error ~- 1 deg. ions. (A further hint for the 195 n m band being related to the interstitialion m a y be the constant
r a t i o of optical a b s o r p t i o n of a and 195 nm band d u r i n g i r r a d i a t i o n , d e t e r m i n e d to be 8:1. ) The s u r p r i s i n g low activation e n e r g i e s for i n t e r s t i tial ion m i g r a t i o n can be explained by a n i n t e r s t i t i a l c y m e c h a n i s m [2, 5] in both c a s e s , a c e n t e r s a r e s e p a r a t e d not m o r e than about six l a t tice s i t e s f r o m an i n t e r s t i t i a l ion, otherwise a l l a c e n t e r s would become F c e n t e r s [6]. In stage II such close p a i r s r e c o m b i n e by the i n t e r s t i t i a l c y m e c h a n i s m . F o r c e r t a i n configurations of the v a c a n c y i n t e r s t i t i a l ion p a i r it i s not p o s 3'79
Volume24.A, number 7
PHYSICS LETTERS
s i b l e for the i n t e r s t i t i a l ion to r e a c h "his" v a c a n cy by this m e c h a n i s m . T h e r e f o r e it m u s t m i g r a t e q u a s i - f r e e to an other v a c a n c y in stage HI . In stage HII i n t e r s t i t i a l ions p r o b a b l y m i g r a t e r e a l ly f r e e . The a n n e a l i n g of F c e n t e r s t a k e s p l a c e in two stages with an a c t i v a t i o n e n e r g y of (40 ± 4) meV in a f i r s t o r d e r p r o c e s s and with (88 ±4) meV in a second o r d e r p r o c e s s . The a n n e a l i n g of the H band shows a v e r y s i m i l a r bebaviour. So the F and H band a n n e a l i n g could be a t t r i b u t e d to the r e c o m b i n a t i o n of F and H c e n t e r s , i. e. v a c a n cies plus e l e c t r o n s and i n t e r s t i t i a l atoms. Stage IA can be a t t r i b u t e d to the r e c o m b i n a t i o n of F and H c e n t e r s which a r e s e p a r a t e d m o r e than about six lattice s i t e s [6], but s t i l l sufficiently close to give close p a i r r e c o m b i n a t i o n in a f i r s t o r d e r p r o c e s s . Stage HA could be explained to be f r e e m i g r a t i o n of the i n t e r s t i t i a l atom. The i n c r e a s i n g of the H band a b s o r p t i o n above 37°K takes p l a c e at the s a m e t e m p e r a t u r e like stage KI I i n which the i n t e r s t i t i a l ions m i g r a t e f r e e . T h e r e b y the i n t e r s t i t i a l ion e i t h e r can r e c o m b i n e with a v a c a n c y o r f r o m together with a V K cent e r a H c e n t e r . It i s p o s s i b l e too that i n t e r s t i t i a l c l u s t e r s a r e f o r m e d which give an optical a b -
27 March 1967
sorption in the H band region. In s u m m a r y , the m o s t i m p o r t a n t c o n c m s i o n f r o m this work is that d u r i n g X - i r r a d i a t i o n at liquid helium t e m p e r a t u r e v a c a n c i e s and i n t e r s t i t i a l s a r e f o r m e d which r e c o m b i n e in d i s t i n c t a n n e a l i n g stages. The a u t h o r s wish to thank P r o f e s s o r Dr. H. F i s c h e r for the p o s s i b i l i t y to p e r f o r m these i n v e s t i g a t i o n s by a u.v. s p e c t r o m e t e r f r o m AFCRL.
References 1. H. RIlehardt, Z. Physik 140 (1955) 574; Phys. Rev. 103 (1956) 673. 2. W. Gebhart, Phys. Chem. Solids 23 (1962) 1123. 3. N.Itoh, B.S.H. Royce and R.Smoluchowski, Phys. Rev. 137 (1965) A1010. 4. G. Giuliani, A. Perinati, E. Regazzoni and G. Chiarotti, Solid State Comm. 3 (1965) 161. 5. K. Tharmalingam, Phys. Chem. Solids 25 (1964) 255. 6. F. Ltlty, Z.Physik 153 (1958) 247.
* * * * *
PERSISTENT SUPERFLUID FLOW FILLED WITH JEWELLER'S
IN A C I R C U I T ROUGE
W. M. VAN ALPHEN, R. DE BRUYN OUBOTER and K. W. TACONIS
The Kamerlingh Onnes Laboratory, Leiden, The Netherlands Received 20 February 1967 A persistent superfluid flow in a twofold connected circuit of compressed jeweller's rouge has been created and observed. The angular momentum and circulation have been investigated as a function of temperature.
In this l e t t e r we r e p o r t the g e n e r a t i o n and obs e r v a t i o n of a p e r s i s t e n t s u p e r f l u i d helium flow in a twofold connected c i r c u i t of c o m p r e s s e d j e w e l l e r ' s rouge. The device is in many a s p e c t s analogous to the s u p e r c o n d u c t i n g p e r s i s t a t r o n [1], and p r e s e n t s a r e a l i z a t i o n of some ideas, which have also been d e s c r i b e d by H a m m e l [2] for film flow. The apparatus c o n s i s t s m a i n l y of two s u p e r l e a k s , L 1 and L2, 6 and 40 cm long r e s p e c t i v e l y and 0.1 cm in diameter. These form two p a r a l l e l connections, as shown in the figure, 380
between a r e s e r v o i r R in which the level can be continuously m e a s u r e d and the helium bath. The c i r c u i t f o r m e d by the s u p e r l e a k s is mounted in a vacuum can. A sudden r a i s i n g or lowering of the a p p a r a t u s will produce a c r i t i c a l flow [3] through both of the s u p e r l e a k s L 1 and L2 and a c i r c u l a tion is imposed in the c i r c u i t which is equal to the product of the difference in length of the s u p e r l e a k s and the c r i t i c a l velocity vo , ; (J~ VsdS = (L2 - L1) Vs, C)" When t h e ~ n p e r a t u r e is not too low, the damping of the flow in the r e -
THERMAL
ANNEALING
PHYSICS LETTERS
OF
27 March 1967
LOW-TEMPERATURE
X-IRRADIATED
KC1
A. BEHR, H. PEISL and W.WAIDELICH I. Physikalisches lnstitut der Technischen Hochschule, Darmstadt, Germany
Received 27 February 1967
Thermal annealing of latticedefects in KCI X-irradiated at liquidhelium temperature was studied by optical absorption measurements. The annealing behaviour of the ot and 195 n m bands, and of the F and H bands, respectively, can be interpreted as recombination of vacancies and interstitials.
I n f o r m a t i o n about the defects c r e a t e d by Xr a y s at liquid h e l i u m t e m p e r a t u r e can be obt a i n e d f r o m t h e r m a l a n n e a l i n g s t u d i e s [1-4]. The p u r p o s e of this p a p e r i s to r e p o r t about t h e r m a l a n n e a l i n g of a l l defects c r e a t e d in KC1 by X - i r r a d i a t i o n at liquid h e l i u m t e m p e r a t u r e . F o r this p u r p o s e the o p t i c a l a b s o r p t i o n of F , and H cer~ters and an a b s o r p t i o n band at 195 nm w e r e studied d u r i n g a n n e , Hug. The s p e c i m e n s u s e d w e r e cleaved f r o m a s i n g l e block of "pure" Harshaw KC1. They w e r e X - i r r a d t a t e d i n a liquid h e l i u m c r y o s t a t by a tutlgsten anode tube (150 kV, 12 mA). F i l t r a t i o n of the X - r a y s through the tube and cryostat wind o w and 0.1 s a m copper foil assured uniform coloratlon. Optical absorption m e a s u r e m e n t s w e r e m a d e , using a S e y a - N a m i o k a type u.v. e p e c t r o p h o t o m e t e r , i n t h e s a m e c r y o s t a t at l i q u i d h e l i u m t e m p e r a t u r e . Fig. 1 shows the r e -
s u l t s of the a n n e a l i n g of the a , 195 n m , F and H band. M e a s u r e m e n t s w e r e m a d e at the band m a x i m u m d u r i n g w a r m i n g up of t h e c r y s t a l s at about 1 d e g / m i n . The r e s u l t s c o m e f r o m four c r y s t a l s , in each c a s e d i f f e r e n t i r r a d i a t i o n t i m e s were u s e d to obtain o p t i m u m coloration. The a n n e a l i n g c~ the a and 195 n m band show an equivalent b s h a v i o u r i n f o r m of t h r e e d i s t i n c t a n n e a l i n g s t a g e s . In both c a s e s a n n e a l i n g in stage II i s a f i r s t o r d e r p r o c e s s with an a c t i v a tion e n e r g y of (25 ~ 3) meV and i n stage HI a s e c ond o r d e r p r o c e s s with a n a c t i v a t i o n e n e r g y of (30 ± 3) meV. F o r the s m a l l stage HII it was not p o s s i b l e to obtain both q u a n t i t i e s with sufficient a c c u r a c y . F r o m the equlv~len_t behaviour of ot and 195 n m band a n n ~ H - g we conclude that the 195 a m band i s v e r y p r o b a b l y r e l a t e d to i n t e r s t i t i a l c h l o r i n e i o n s , and so a n n e a l i n g t a k e s place by recombirattion of v a c a n c i e s and i n t e r s t i t i a l
Q5
(
I
o
ill
t.o
5
10
20
,4_I
30
40
temperoture
50 "K 60 ~--
Fig. 1. Thermal annealing of lattice defects in low-
temperature X-irradiated KC1. X-irradiation time: 0~: 1.5 hr; 195 nm:8 hr; F :2.5 hr;H :5.5 h~. Initial concentration ~6centers no (ct) = 6 × 1016cm-3; no (F) = 6 X 19 6cm -3. Max. temperature error ~- 1 deg. ions. (A further hint for the 195 n m band being related to the interstitialion m a y be the constant
r a t i o of optical a b s o r p t i o n of a and 195 nm band d u r i n g i r r a d i a t i o n , d e t e r m i n e d to be 8:1. ) The s u r p r i s i n g low activation e n e r g i e s for i n t e r s t i tial ion m i g r a t i o n can be explained by a n i n t e r s t i t i a l c y m e c h a n i s m [2, 5] in both c a s e s , a c e n t e r s a r e s e p a r a t e d not m o r e than about six l a t tice s i t e s f r o m an i n t e r s t i t i a l ion, otherwise a l l a c e n t e r s would become F c e n t e r s [6]. In stage II such close p a i r s r e c o m b i n e by the i n t e r s t i t i a l c y m e c h a n i s m . F o r c e r t a i n configurations of the v a c a n c y i n t e r s t i t i a l ion p a i r it i s not p o s 3'79
Volume24.A, number 7
PHYSICS LETTERS
s i b l e for the i n t e r s t i t i a l ion to r e a c h "his" v a c a n cy by this m e c h a n i s m . T h e r e f o r e it m u s t m i g r a t e q u a s i - f r e e to an other v a c a n c y in stage HI . In stage HII i n t e r s t i t i a l ions p r o b a b l y m i g r a t e r e a l ly f r e e . The a n n e a l i n g of F c e n t e r s t a k e s p l a c e in two stages with an a c t i v a t i o n e n e r g y of (40 ± 4) meV in a f i r s t o r d e r p r o c e s s and with (88 ±4) meV in a second o r d e r p r o c e s s . The a n n e a l i n g of the H band shows a v e r y s i m i l a r bebaviour. So the F and H band a n n e a l i n g could be a t t r i b u t e d to the r e c o m b i n a t i o n of F and H c e n t e r s , i. e. v a c a n cies plus e l e c t r o n s and i n t e r s t i t i a l atoms. Stage IA can be a t t r i b u t e d to the r e c o m b i n a t i o n of F and H c e n t e r s which a r e s e p a r a t e d m o r e than about six lattice s i t e s [6], but s t i l l sufficiently close to give close p a i r r e c o m b i n a t i o n in a f i r s t o r d e r p r o c e s s . Stage HA could be explained to be f r e e m i g r a t i o n of the i n t e r s t i t i a l atom. The i n c r e a s i n g of the H band a b s o r p t i o n above 37°K takes p l a c e at the s a m e t e m p e r a t u r e like stage KI I i n which the i n t e r s t i t i a l ions m i g r a t e f r e e . T h e r e b y the i n t e r s t i t i a l ion e i t h e r can r e c o m b i n e with a v a c a n c y o r f r o m together with a V K cent e r a H c e n t e r . It i s p o s s i b l e too that i n t e r s t i t i a l c l u s t e r s a r e f o r m e d which give an optical a b -
27 March 1967
sorption in the H band region. In s u m m a r y , the m o s t i m p o r t a n t c o n c m s i o n f r o m this work is that d u r i n g X - i r r a d i a t i o n at liquid helium t e m p e r a t u r e v a c a n c i e s and i n t e r s t i t i a l s a r e f o r m e d which r e c o m b i n e in d i s t i n c t a n n e a l i n g stages. The a u t h o r s wish to thank P r o f e s s o r Dr. H. F i s c h e r for the p o s s i b i l i t y to p e r f o r m these i n v e s t i g a t i o n s by a u.v. s p e c t r o m e t e r f r o m AFCRL.
References 1. H. RIlehardt, Z. Physik 140 (1955) 574; Phys. Rev. 103 (1956) 673. 2. W. Gebhart, Phys. Chem. Solids 23 (1962) 1123. 3. N.Itoh, B.S.H. Royce and R.Smoluchowski, Phys. Rev. 137 (1965) A1010. 4. G. Giuliani, A. Perinati, E. Regazzoni and G. Chiarotti, Solid State Comm. 3 (1965) 161. 5. K. Tharmalingam, Phys. Chem. Solids 25 (1964) 255. 6. F. Ltlty, Z.Physik 153 (1958) 247.
* * * * *
PERSISTENT SUPERFLUID FLOW FILLED WITH JEWELLER'S
IN A C I R C U I T ROUGE
W. M. VAN ALPHEN, R. DE BRUYN OUBOTER and K. W. TACONIS
The Kamerlingh Onnes Laboratory, Leiden, The Netherlands Received 20 February 1967 A persistent superfluid flow in a twofold connected circuit of compressed jeweller's rouge has been created and observed. The angular momentum and circulation have been investigated as a function of temperature.
In this l e t t e r we r e p o r t the g e n e r a t i o n and obs e r v a t i o n of a p e r s i s t e n t s u p e r f l u i d helium flow in a twofold connected c i r c u i t of c o m p r e s s e d j e w e l l e r ' s rouge. The device is in many a s p e c t s analogous to the s u p e r c o n d u c t i n g p e r s i s t a t r o n [1], and p r e s e n t s a r e a l i z a t i o n of some ideas, which have also been d e s c r i b e d by H a m m e l [2] for film flow. The apparatus c o n s i s t s m a i n l y of two s u p e r l e a k s , L 1 and L2, 6 and 40 cm long r e s p e c t i v e l y and 0.1 cm in diameter. These form two p a r a l l e l connections, as shown in the figure, 380
between a r e s e r v o i r R in which the level can be continuously m e a s u r e d and the helium bath. The c i r c u i t f o r m e d by the s u p e r l e a k s is mounted in a vacuum can. A sudden r a i s i n g or lowering of the a p p a r a t u s will produce a c r i t i c a l flow [3] through both of the s u p e r l e a k s L 1 and L2 and a c i r c u l a tion is imposed in the c i r c u i t which is equal to the product of the difference in length of the s u p e r l e a k s and the c r i t i c a l velocity vo , ; (J~ VsdS = (L2 - L1) Vs, C)" When t h e ~ n p e r a t u r e is not too low, the damping of the flow in the r e -