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Modulation effect of continuous current oscillations in CdS
Volume 24A. number 3
PHYSICS LETTERS
A n o t h e r m e c h a n i s m c o n s i s t s in the t r a n s f e r of e n e r g y in the line t h r o u g h the wings of the s a t u r a b l e spin packet. E v a l u a t i o n of the t i m e p r o p a g a t i o n o f the s a t u r a t i o n into one spin p a c k e t that is a s s u m e d to be equal to T 2 g i v e s 10- ~ s e c f o r our s a m p l e s . The wings of the s a t u r a t e d p a c k e t w i l l c o v e r an e s s e n t i a l p a r t of the E P R line width and s a t u r a t e it h o m o g e n e o u s l y . On the background of the h o m o g e n e o u s s a t u r a t i o n the notches of the d i s c r e t e s a t u r a t i o n on the E P R line r e p r e s e n t the p o r t i o n s of " e a s y " s a t u r a t i o n , the f a c t which can be c a u s e d by the p r e d o m i n a n t t r a n s f e r of e n e r g y to those p a c k e t s on the E P R line which belong to the s u b s y s t e m s of the l e v e l s of the s a t u r a t e d spin packet. In conclusion it should be noted that the d i s c r e t e s a t u r a t i o n can be u s e d to study the s t r u c t u r e in E P R l i n e s in which s u p e r hfs is not r e solved.
MODULATION CURRENT
30 January 1967
The a u t h o r s e x p r e s s t h e i r g r a t i t u d e to a c a d e m i c i a n E. K, Z a v o i s k i , P r o f . G . R . K h u t s i s h v i l i and Dr. L. L. B u i s h v i l i f o r t h e i r i n t e r e s t in the w o r k and v a l u a b l e d i s c u s s i o n s and to P r o f . P. P . F e o f i l o v f o r single c r y s t a l s given for the e x p e r i m e n t s ,
References 1. A.M.Portis, Phys.Rev. 91 (1953) 1071. 2. G.Feher and E.A.Gere, Phys. Rev. 114 (1959) 1245. 3. B. Bleany, P.M. Llewellyn and D.A. Jones, Proc. Phys. Soc. B 69 (1956) 858. 4. 13. G. Berulava and T. I. Sanadze, Conference on Paramagnetic resonance 1959, Izd. Kazan. University (1960). 5. B.G. Berulava, T.I. Sanadzc and O. G. Khakhanashvili, Zh. Exp. i Teor. Fiz. 48 (1965) 437. 6. A.M. Clogston, J . P . Gordon, V. Jaccarino, M. Peter and LoR.Walker, Phys. Rev. 117 (1960) 1222.
EFFECT OF CONTINUOUS OSCILLATIONS IN C d S
H. H A R T N A G E L and R. G A Y Department of Electronic and Electrical Engineering, University of Sheffield, England
Received 20 December 1966 Electroacoustic oscillations in CdS with amplitude modulation have been measured, which depends on the position and background light of a thin masked area near the positive electrode.
Continuous o s c i l l a t i o n s of a c o u s t o e l e c t r i c c u r r e n t have been o b s e r v e d by many a u t h o r s in p h o t o - s e n s i t i v e CdS [1-5], CdSe [6, 7] and CdTe [8], when the s p e c i m e n s w e r e i l l u m i n a t e d with a light spot at an e x p e r i m e n t a l l y found position along its length. We have i l l u m i n a t e d a l a r g e a r e a , with the p o s i t i v e end of the c r y s t a l s l i g h t l y shaded, and obtained continuous o s c i l l a t i o n s with a f r e q u e n c y of 300 k c / s (see fig. 1). Then the total s p e c i m e n was i l l u m i n a t e d e x c e p t f o r a s m a l l d a r k band a c r o s s the c r y s t a l n e a r the p o s i t i v e end and the r e s u l t i n g o s c i l l a t i o n s w e r e found to be amplitude modulated with a modulation a m p l i t u d e dependent on the p o s i t i o n and s h a r p n e s s of the d a r k band (see fig. 2). The c r y s t a l s w e r e obtained f r o m E a g l e - P i c h e r Co. (Grade B), The s p e c i m e n had the d i m e n s i o n s 158
' llitil lll]lllllllllltlli!i!, "VVVVVVVVVVVVv!
20 mA
20,u se¢
Fig. 1. Continuous current oscillations positive half of crystal darkened.
Volume24A, number 3
PHYSICS LETTERS
30 January 1967
40mA
t
2Op~ ¢
t
Fig. 2. Amplitude modulation by a dark spot within the illuminated area. Illumination across entire crystal; dark spot of 1 mm width is a) 1.5 mm from the positive end; b) 1.2 mm from the positive end; c) in same position as b), however partly illuminated by background light. 3.5 × 4 × 6 m m 3. The o r i e n t a t i o n was such that the long edge was v e r t i c a l to the c - a x i s . D a r k and light r e s i s t a n c e s w e r e r e s p e c t i v e l y 10 m e g ohm and 30 kilohm. The i l l u m i n a t i o n was made with a 275W photo-flood bulb. The applied v o l t age of about 2000V was p u l s e d with a r e p e t i t i o n r a t i o of 10 c / s . E l e c t r o d e s w e r e p r e p a r e d by e v a p o r a t i n g indium on the two end s u r f a c e s in 10-5 T o r r vacuum. The d.c. field was applied p e r p e n d i c u l a r to the c - a x i s . D i r e c t c u r r e n t s a t u r a t i o n s t a r t e d at the t h r e s h o l d of o s c i l l a t i o n . The f r e q u e n c y of o s c i l l a t i o n is given by the t i m e r e q u i r e d f o r a single t r i p of the sound wave through the c r y s t a l of 6 m m length. A p o s s i b l e explanation for the modulation e f f e c t could be an e x t e n s i o n of Okada and M a t i n o ' s [2] t h e o r y . Owing to the d a r k spot n e a r the p o s i t i v e e l e c t r o d e , t h r e e r e s i s t i v i t y r e g i o n s a r e p r e s e n t . The additional r e g i o n c a u s e s the field in the o t h e r r e g i o n s
to a l t e r when the e l e c t r o a c o u e t i c flux t r a v e l s through it. The o p e r a t i n g point in the gain c h a r a c t e r i s t i c f o r the o t h e r two r e g i o n s w i l l change by an amount which depends on the p r e v i o u s cycle of the flux wave. T h i s can cause the a m p l i tude of the Current o s c i l l a t i o n s to v a r y p e r i o d i cally. We f e e l that a f u r t h e r i n v e s t i g a t i o n of this eff e c t m a y show that it will be useful f o r optical m e a s u r e m e n t t e c h n i q u e s o r f o r a p p l i c a t i o n s in connection with l a s e r - b e a m demodulation. 1. 2. 3. 4. 5. 6. 7. 8.
J. Okada and H. Matino, Jap. J.Appl. Phys. 2 (1963)736, J. Okada and H. Matino, Jap. J. Appl. Phys. 3 (1964) 698. S. Ibuki and K. Nojima, Jap. J.Appl. Phys. 4 (1965) 71. Wen-Chung Wang, Appl. Phys. Letters 6 (1965) 81. M.Miya and M.Terai, Jap. J.Appl.Phys. 5 (1966) 186. M. Kikuchi, Jap. J,Appl. Phys. 2 (1963) 812. M. Kikuchi, Jap. J.Appl. Phys. 3 (1964) 448. M. Kikuehi, Jap. J.Appl. Phys. 4 (1965) 233.
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159
PHYSICS LETTERS
A n o t h e r m e c h a n i s m c o n s i s t s in the t r a n s f e r of e n e r g y in the line t h r o u g h the wings of the s a t u r a b l e spin packet. E v a l u a t i o n of the t i m e p r o p a g a t i o n o f the s a t u r a t i o n into one spin p a c k e t that is a s s u m e d to be equal to T 2 g i v e s 10- ~ s e c f o r our s a m p l e s . The wings of the s a t u r a t e d p a c k e t w i l l c o v e r an e s s e n t i a l p a r t of the E P R line width and s a t u r a t e it h o m o g e n e o u s l y . On the background of the h o m o g e n e o u s s a t u r a t i o n the notches of the d i s c r e t e s a t u r a t i o n on the E P R line r e p r e s e n t the p o r t i o n s of " e a s y " s a t u r a t i o n , the f a c t which can be c a u s e d by the p r e d o m i n a n t t r a n s f e r of e n e r g y to those p a c k e t s on the E P R line which belong to the s u b s y s t e m s of the l e v e l s of the s a t u r a t e d spin packet. In conclusion it should be noted that the d i s c r e t e s a t u r a t i o n can be u s e d to study the s t r u c t u r e in E P R l i n e s in which s u p e r hfs is not r e solved.
MODULATION CURRENT
30 January 1967
The a u t h o r s e x p r e s s t h e i r g r a t i t u d e to a c a d e m i c i a n E. K, Z a v o i s k i , P r o f . G . R . K h u t s i s h v i l i and Dr. L. L. B u i s h v i l i f o r t h e i r i n t e r e s t in the w o r k and v a l u a b l e d i s c u s s i o n s and to P r o f . P. P . F e o f i l o v f o r single c r y s t a l s given for the e x p e r i m e n t s ,
References 1. A.M.Portis, Phys.Rev. 91 (1953) 1071. 2. G.Feher and E.A.Gere, Phys. Rev. 114 (1959) 1245. 3. B. Bleany, P.M. Llewellyn and D.A. Jones, Proc. Phys. Soc. B 69 (1956) 858. 4. 13. G. Berulava and T. I. Sanadze, Conference on Paramagnetic resonance 1959, Izd. Kazan. University (1960). 5. B.G. Berulava, T.I. Sanadzc and O. G. Khakhanashvili, Zh. Exp. i Teor. Fiz. 48 (1965) 437. 6. A.M. Clogston, J . P . Gordon, V. Jaccarino, M. Peter and LoR.Walker, Phys. Rev. 117 (1960) 1222.
EFFECT OF CONTINUOUS OSCILLATIONS IN C d S
H. H A R T N A G E L and R. G A Y Department of Electronic and Electrical Engineering, University of Sheffield, England
Received 20 December 1966 Electroacoustic oscillations in CdS with amplitude modulation have been measured, which depends on the position and background light of a thin masked area near the positive electrode.
Continuous o s c i l l a t i o n s of a c o u s t o e l e c t r i c c u r r e n t have been o b s e r v e d by many a u t h o r s in p h o t o - s e n s i t i v e CdS [1-5], CdSe [6, 7] and CdTe [8], when the s p e c i m e n s w e r e i l l u m i n a t e d with a light spot at an e x p e r i m e n t a l l y found position along its length. We have i l l u m i n a t e d a l a r g e a r e a , with the p o s i t i v e end of the c r y s t a l s l i g h t l y shaded, and obtained continuous o s c i l l a t i o n s with a f r e q u e n c y of 300 k c / s (see fig. 1). Then the total s p e c i m e n was i l l u m i n a t e d e x c e p t f o r a s m a l l d a r k band a c r o s s the c r y s t a l n e a r the p o s i t i v e end and the r e s u l t i n g o s c i l l a t i o n s w e r e found to be amplitude modulated with a modulation a m p l i t u d e dependent on the p o s i t i o n and s h a r p n e s s of the d a r k band (see fig. 2). The c r y s t a l s w e r e obtained f r o m E a g l e - P i c h e r Co. (Grade B), The s p e c i m e n had the d i m e n s i o n s 158
' llitil lll]lllllllllltlli!i!, "VVVVVVVVVVVVv!
20 mA
20,u se¢
Fig. 1. Continuous current oscillations positive half of crystal darkened.
Volume24A, number 3
PHYSICS LETTERS
30 January 1967
40mA
t
2Op~ ¢
t
Fig. 2. Amplitude modulation by a dark spot within the illuminated area. Illumination across entire crystal; dark spot of 1 mm width is a) 1.5 mm from the positive end; b) 1.2 mm from the positive end; c) in same position as b), however partly illuminated by background light. 3.5 × 4 × 6 m m 3. The o r i e n t a t i o n was such that the long edge was v e r t i c a l to the c - a x i s . D a r k and light r e s i s t a n c e s w e r e r e s p e c t i v e l y 10 m e g ohm and 30 kilohm. The i l l u m i n a t i o n was made with a 275W photo-flood bulb. The applied v o l t age of about 2000V was p u l s e d with a r e p e t i t i o n r a t i o of 10 c / s . E l e c t r o d e s w e r e p r e p a r e d by e v a p o r a t i n g indium on the two end s u r f a c e s in 10-5 T o r r vacuum. The d.c. field was applied p e r p e n d i c u l a r to the c - a x i s . D i r e c t c u r r e n t s a t u r a t i o n s t a r t e d at the t h r e s h o l d of o s c i l l a t i o n . The f r e q u e n c y of o s c i l l a t i o n is given by the t i m e r e q u i r e d f o r a single t r i p of the sound wave through the c r y s t a l of 6 m m length. A p o s s i b l e explanation for the modulation e f f e c t could be an e x t e n s i o n of Okada and M a t i n o ' s [2] t h e o r y . Owing to the d a r k spot n e a r the p o s i t i v e e l e c t r o d e , t h r e e r e s i s t i v i t y r e g i o n s a r e p r e s e n t . The additional r e g i o n c a u s e s the field in the o t h e r r e g i o n s
to a l t e r when the e l e c t r o a c o u e t i c flux t r a v e l s through it. The o p e r a t i n g point in the gain c h a r a c t e r i s t i c f o r the o t h e r two r e g i o n s w i l l change by an amount which depends on the p r e v i o u s cycle of the flux wave. T h i s can cause the a m p l i tude of the Current o s c i l l a t i o n s to v a r y p e r i o d i cally. We f e e l that a f u r t h e r i n v e s t i g a t i o n of this eff e c t m a y show that it will be useful f o r optical m e a s u r e m e n t t e c h n i q u e s o r f o r a p p l i c a t i o n s in connection with l a s e r - b e a m demodulation. 1. 2. 3. 4. 5. 6. 7. 8.
J. Okada and H. Matino, Jap. J.Appl. Phys. 2 (1963)736, J. Okada and H. Matino, Jap. J. Appl. Phys. 3 (1964) 698. S. Ibuki and K. Nojima, Jap. J.Appl. Phys. 4 (1965) 71. Wen-Chung Wang, Appl. Phys. Letters 6 (1965) 81. M.Miya and M.Terai, Jap. J.Appl.Phys. 5 (1966) 186. M. Kikuchi, Jap. J,Appl. Phys. 2 (1963) 812. M. Kikuchi, Jap. J.Appl. Phys. 3 (1964) 448. M. Kikuehi, Jap. J.Appl. Phys. 4 (1965) 233.
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159