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Nuclear tracks created by 90 MeV carbon ions in ZnO crystal
Radiation Measurements, Vol. 25, Nos 1-4, pp. 117-118, 1995
Pergmon
Copyright O 1995 Elsevier Science Ltd Printed in Carat Britain. All rights reserved 1350-4487/95 $9.50 + .00
13.50-4487(95)0~49-6
NUCLEAR TRACKS CREATED BY 90 MeV CARBON IONS IN ZnO CRYSTAL
F. P. DENISOV, V. A. NIK1TENKO and I. P. KUZMINA Department of Physics, Moscow Sm~ Railway University, Moscow, 101475, Russia
ABSTRACT The d i s t r i b u t i o n of the lengths of the tracks, createed b y 90 M e v c o n s i s t s of three groops w i t h an average value about 52, 67 and group of the tracks m a y be t r e a t e d as ttnchannelling particles. The channeling particles and the third one represents superchannelling
C a r b o n ions in Zno crystal 102 micrometers. The first second group corresponds to particles.
E~YWORDS Nuclear tracks;
implantation;
channeling.
C H A N N E L I N G A N D S U P E R C H A N N E L I N G C A R B O N IONS IN ZnO CRYSTAL Implantation of the h i q h e n e r g y (90 Mev) He ions into the hydrothermal ZnO:Li single crystal a ~ channelling and s u p e r c h a n n e l i n g of the particles had b e e n investigated b y two laboratories (Nikitenko et al., 1994, Denisov et al., 1991). Experimental and theoretical m e t h o d s used in those works had b e e n u n i t e d and d e v e l o p e d in this work.
Experiment and its results. ZnO crystal had b e e n grown from h i g h - e n e r g y alkaline solutions (Kusmina et al., 1993). The characteristic feature of hydrothermal monocrystals is the increased content of l i t h i u m impurities (up to 0.001-0.01 ppm). For the implantation of 90 M e V c a r b o n ions the cyclotron U-200 had b e e n used. The d i r e c t i o n of the incident carbon ions b e a m was c o i n c i d e d w i t h the hexagonal axis of the ZnO crystal. The d e n s i t y of the implanted ions was 1.3"1014 c m 2. As the depth of the i m p l a n t a t i o n was more than 50 ~m, we h a d the p o s s i b i l i t y to r e s e a r c h the cleavage in the r e g i o n of the implantation. It is d i s p o s e d parallel to the h e x a g o n a l axis of the crystal. We used scanning electron microscope in the regimes of the r e f l e c t e d electrons and cathodoluminescence. The s p e c t r u m of the cathodoluminescence at 100 K h a d b e e n r e c o r d e d for the areas about l~m L. No specific features in the r e g i o n of the implantation h a d b e e n r e v e a l e d d u r i n g the investigation of the crystals in the regime of the reflected electrons. It means that there are no somewhat m a c r o d i s t r u c t i o n s in this region. But t h e y look almost black in the regime of cathodoluminescence. The exciton luminescence is absent and violet and yellow cathodoluminescence is v e r y weak. There are m a n y intrinsic defects of the crystal structure. It is confirmed b y the appearance of the typical yellow-brown color of i m p l a n t e d layers and discorder of the structure of it's exciton s p e c t r u m of the r e f l e c t i o n and luminescence (Regel et al.). For the v i s u a l i s a t i o n of the carbon ions tracks we used electron microscope in the regime of the cathodoluminescence. The d i s t r i b u t i o n of the length of the tracks consists of three groups w i t h an average value about 52, 67 and 102 ~ m (depth of the localization of i m p l a n t a t e d ions). The first a ~ second groups have a strong u n i f o r m background. The third one looks as a separated black islets.
Discussion. The experimental results had b e e n analysed f r o m the a point of v i e w of the c h a n ~ e l l i n g theory. A c c o r d i n g to this t h e o r y the first group of the tracks m a y be t r e a t e d as u n c h a n n e l l i n g particles. The second group corresponds to the channelling particles and the third one represents s u p e r c h a n n e l l i n g particles, w h i c h cause of the greatest interest. The specific characteristics of the superchannelling particles connect w i t h relativistic effects leading to
117
118
F.P. DENISOV et al.
existence of the q u a n t u m states w h i c h have a h i g h Because of this w e considered Klein-Gordon equation and having potential energy V(p)=-ZleZ2e/p (Zle and and channeling axis, and p is the distance f r o m the
stability conserning extenal disturbance. for the particle moving in axial potential Z2e are effective charges of the particle axis). This equation m a y be w r i t e n as
A T + [ (8-v) 2-~02] T=0,
(i)
where v, s, ~o are potential energy, energy and mass of the particle in the units hc. Let us introduce ~-(~o2+(pz/h)2)i/2; 8'-z-~; p,z,# are the polar co-ordinates; r=~K, K=(818'I~) I/2; Pz is the z - component impulse of the particle. The wave function of this equation as had b e e n revealed b y our calculation is Tnm(r, z, 4) =CnmeXp (i~-r/2+ipz/h) r2SF (-n, 2s+l, r),
(2)
where n=0, i,2,3...; m=0, I,2,3...; s=(m2-Vo2)i/2; Vo=ZIZ2/137; F(-n, 2s+l,r) is the confluent hypergeometrio function. As 8>0 we m a y use l~nml 2 and proper factor Cnm. E n e r g y spectrum of the particle moving in the plate w h i c h is perpendicular to axis z is 8' --Vo2m/[2 (n+s+i/2) 2] .
(3)
For the E=hcs>I, n, s>20 distance between the next levels is A E ~ 0 . 0 1 e V and characteristic time T=(h/AE)~I0-13s. Therefore w e m a y use the theory of the sudden disturbance for the tracks w h i c h length l
P== f l~12e~(-ikar)dV,
14)
V where ka=Pa/ (Kh) . Numerical calculations Pnm had b e e n carried out in the dipole approximation for the axis formed b y ions Zn- (direction (0001)) and for following values of the parameters: ZI=6 , Z2-0.6 , E-9OMev, r~10-10m. W e obtained two types of the solutions: w i t h m=0 and w i t h m>0. For these types of the solutions and m+n~10 probability Pnm~l, if PaC<105 eV (for m=0) and PaC<103eV (for m>0). To receive a qualitative estimate let us assume that on the distant d between the next atoms of the atomic r o w channeled particle gets an impulse as b y scattering on the single charge equal Z2e: Apac-Z2Zle2/@. For the above stated values of the parameters we obtain Apac~103 eV. As distribution of the scattering impulses has an accidental nature PaC~N'Apa c where N is the number of the atoms on the length l-Nd~10~m w h i c h corresponds to the quantum state w i t h a definite n. For n~10 we obtain length of the tracks about L=n.l~100~m. This result is not at varians w i t h experimental data. It is n e c e s s a r y to p e r f o r m quantitative calculations pa c befor definite conclusion has b e e n made.
REFERENCES
Denisov, F.P. and V.V. Cherdintsev (1991). Solutions of the Klein-Gordon equation for stable channeling particles. In: Prooeedigs of the 20th A l l - U n i o n Conference on Physics of the Interaction Charge Particles w i t h Crystals (A.F. Tulinov, ed., in Russian), pp. 12-13. M o s c o w State University, Moscow. Kuzmina, J.P., A.O. Lazarevskaya and V.A. Nikitenko (1993). The influence of the impurities on growth, kinetics and physical properties Zinc oxide. In: Proceeding of the 4-th International S y s ~ o s i u m on H~drothermal Reactions (M. Cuney, ed. ), pp. 121-122. Institut Lorrain Des Geosciences, Nancy. Landau, L.D. and E.M. Lifshitz (1977). Course of Theoretical Physics, Vol.3. Nikitenko, V.A., S.V. Mukhin, I.P. Kuzmina and N.G. Galastyan (1994) . Preparation and properties of ZnO:Li. In: Abstracts of the European Workshop on 11-V1 semiconductors (H. Sitter, ed.), p.76. Johannes Kepler University, Linz. Regel, W.R., V.A. Nikitenko, I.P. Kuzmlna, V.G. Galstyan, T.R. Doluhanyan, S.F. Nikulshin N.L.Sizova and V.A. Skuratov (1987). The influence of h i g h energy implantation on optical properties and defects in ZnO crystal. Journal of the Technical Physics, (in Russian) 5_/7, 306-310.
Pergmon
Copyright O 1995 Elsevier Science Ltd Printed in Carat Britain. All rights reserved 1350-4487/95 $9.50 + .00
13.50-4487(95)0~49-6
NUCLEAR TRACKS CREATED BY 90 MeV CARBON IONS IN ZnO CRYSTAL
F. P. DENISOV, V. A. NIK1TENKO and I. P. KUZMINA Department of Physics, Moscow Sm~ Railway University, Moscow, 101475, Russia
ABSTRACT The d i s t r i b u t i o n of the lengths of the tracks, createed b y 90 M e v c o n s i s t s of three groops w i t h an average value about 52, 67 and group of the tracks m a y be t r e a t e d as ttnchannelling particles. The channeling particles and the third one represents superchannelling
C a r b o n ions in Zno crystal 102 micrometers. The first second group corresponds to particles.
E~YWORDS Nuclear tracks;
implantation;
channeling.
C H A N N E L I N G A N D S U P E R C H A N N E L I N G C A R B O N IONS IN ZnO CRYSTAL Implantation of the h i q h e n e r g y (90 Mev) He ions into the hydrothermal ZnO:Li single crystal a ~ channelling and s u p e r c h a n n e l i n g of the particles had b e e n investigated b y two laboratories (Nikitenko et al., 1994, Denisov et al., 1991). Experimental and theoretical m e t h o d s used in those works had b e e n u n i t e d and d e v e l o p e d in this work.
Experiment and its results. ZnO crystal had b e e n grown from h i g h - e n e r g y alkaline solutions (Kusmina et al., 1993). The characteristic feature of hydrothermal monocrystals is the increased content of l i t h i u m impurities (up to 0.001-0.01 ppm). For the implantation of 90 M e V c a r b o n ions the cyclotron U-200 had b e e n used. The d i r e c t i o n of the incident carbon ions b e a m was c o i n c i d e d w i t h the hexagonal axis of the ZnO crystal. The d e n s i t y of the implanted ions was 1.3"1014 c m 2. As the depth of the i m p l a n t a t i o n was more than 50 ~m, we h a d the p o s s i b i l i t y to r e s e a r c h the cleavage in the r e g i o n of the implantation. It is d i s p o s e d parallel to the h e x a g o n a l axis of the crystal. We used scanning electron microscope in the regimes of the r e f l e c t e d electrons and cathodoluminescence. The s p e c t r u m of the cathodoluminescence at 100 K h a d b e e n r e c o r d e d for the areas about l~m L. No specific features in the r e g i o n of the implantation h a d b e e n r e v e a l e d d u r i n g the investigation of the crystals in the regime of the reflected electrons. It means that there are no somewhat m a c r o d i s t r u c t i o n s in this region. But t h e y look almost black in the regime of cathodoluminescence. The exciton luminescence is absent and violet and yellow cathodoluminescence is v e r y weak. There are m a n y intrinsic defects of the crystal structure. It is confirmed b y the appearance of the typical yellow-brown color of i m p l a n t e d layers and discorder of the structure of it's exciton s p e c t r u m of the r e f l e c t i o n and luminescence (Regel et al.). For the v i s u a l i s a t i o n of the carbon ions tracks we used electron microscope in the regime of the cathodoluminescence. The d i s t r i b u t i o n of the length of the tracks consists of three groups w i t h an average value about 52, 67 and 102 ~ m (depth of the localization of i m p l a n t a t e d ions). The first a ~ second groups have a strong u n i f o r m background. The third one looks as a separated black islets.
Discussion. The experimental results had b e e n analysed f r o m the a point of v i e w of the c h a n ~ e l l i n g theory. A c c o r d i n g to this t h e o r y the first group of the tracks m a y be t r e a t e d as u n c h a n n e l l i n g particles. The second group corresponds to the channelling particles and the third one represents s u p e r c h a n n e l l i n g particles, w h i c h cause of the greatest interest. The specific characteristics of the superchannelling particles connect w i t h relativistic effects leading to
117
118
F.P. DENISOV et al.
existence of the q u a n t u m states w h i c h have a h i g h Because of this w e considered Klein-Gordon equation and having potential energy V(p)=-ZleZ2e/p (Zle and and channeling axis, and p is the distance f r o m the
stability conserning extenal disturbance. for the particle moving in axial potential Z2e are effective charges of the particle axis). This equation m a y be w r i t e n as
A T + [ (8-v) 2-~02] T=0,
(i)
where v, s, ~o are potential energy, energy and mass of the particle in the units hc. Let us introduce ~-(~o2+(pz/h)2)i/2; 8'-z-~; p,z,# are the polar co-ordinates; r=~K, K=(818'I~) I/2; Pz is the z - component impulse of the particle. The wave function of this equation as had b e e n revealed b y our calculation is Tnm(r, z, 4) =CnmeXp (i~-r/2+ipz/h) r2SF (-n, 2s+l, r),
(2)
where n=0, i,2,3...; m=0, I,2,3...; s=(m2-Vo2)i/2; Vo=ZIZ2/137; F(-n, 2s+l,r) is the confluent hypergeometrio function. As 8>0 we m a y use l~nml 2 and proper factor Cnm. E n e r g y spectrum of the particle moving in the plate w h i c h is perpendicular to axis z is 8' --Vo2m/[2 (n+s+i/2) 2] .
(3)
For the E=hcs
P== f l~12e~(-ikar)dV,
14)
V where ka=Pa/ (Kh) . Numerical calculations Pnm had b e e n carried out in the dipole approximation for the axis formed b y ions Zn- (direction (0001)) and for following values of the parameters: ZI=6 , Z2-0.6 , E-9OMev, r~10-10m. W e obtained two types of the solutions: w i t h m=0 and w i t h m>0. For these types of the solutions and m+n~10 probability Pnm~l, if PaC<105 eV (for m=0) and PaC<103eV (for m>0). To receive a qualitative estimate let us assume that on the distant d between the next atoms of the atomic r o w channeled particle gets an impulse as b y scattering on the single charge equal Z2e: Apac-Z2Zle2/@. For the above stated values of the parameters we obtain Apac~103 eV. As distribution of the scattering impulses has an accidental nature PaC~N'Apa c where N is the number of the atoms on the length l-Nd~10~m w h i c h corresponds to the quantum state w i t h a definite n. For n~10 we obtain length of the tracks about L=n.l~100~m. This result is not at varians w i t h experimental data. It is n e c e s s a r y to p e r f o r m quantitative calculations pa c befor definite conclusion has b e e n made.
REFERENCES
Denisov, F.P. and V.V. Cherdintsev (1991). Solutions of the Klein-Gordon equation for stable channeling particles. In: Prooeedigs of the 20th A l l - U n i o n Conference on Physics of the Interaction Charge Particles w i t h Crystals (A.F. Tulinov, ed., in Russian), pp. 12-13. M o s c o w State University, Moscow. Kuzmina, J.P., A.O. Lazarevskaya and V.A. Nikitenko (1993). The influence of the impurities on growth, kinetics and physical properties Zinc oxide. In: Proceeding of the 4-th International S y s ~ o s i u m on H~drothermal Reactions (M. Cuney, ed. ), pp. 121-122. Institut Lorrain Des Geosciences, Nancy. Landau, L.D. and E.M. Lifshitz (1977). Course of Theoretical Physics, Vol.3. Nikitenko, V.A., S.V. Mukhin, I.P. Kuzmina and N.G. Galastyan (1994) . Preparation and properties of ZnO:Li. In: Abstracts of the European Workshop on 11-V1 semiconductors (H. Sitter, ed.), p.76. Johannes Kepler University, Linz. Regel, W.R., V.A. Nikitenko, I.P. Kuzmlna, V.G. Galstyan, T.R. Doluhanyan, S.F. Nikulshin N.L.Sizova and V.A. Skuratov (1987). The influence of h i g h energy implantation on optical properties and defects in ZnO crystal. Journal of the Technical Physics, (in Russian) 5_/7, 306-310.