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Observation and study of latent tracks on the surface of HOPG induced by H+ ions
Radiation Measurements. Vol.28. Nos i-6. pp. 97-100. 1997 C 1997 Elsevier Science Ltd Printed in Great Britain.All rights reserved
Pergamon
PII: S 1350-4487(97)00047-4
1350-4487/97 $17.00÷ 0.00
OBSERVATION AND STUDY OF LATENT TRACKS ON THE SURFACE OF HOPG INDUCED BY H ÷ IONS
P. J. ZHAI, Y. X. XING, Y. ZHANG, S. L. FENG, Y. X. KANG AND X. W. TANG Institute of High Energy Physics, Academia Sinica, P.O.Box 2732, Beijing,.China Y. G. WANG, W. J. ZHAO AND S. YAN Institute of Heavy Ion Physics Peking University, Beijing,.China ABSTRACT The topography and size of damage on the surface of HOPG (Highly Oriented Pyrolitic Graphite) bombarded by high fluence (lxl016 ions/cm2) of H" ions were observed and studied. In this work, 457 STM images of each one with 9x9 nm2 area were obtained. From 163 of these pictures visible damage was found. In these 163 STM images the diameter of most damage is from 0.2 to 0.8 nm. In this study the number density of visible damage is much less than the ion fluence. The probability of damage is only about 1.8x 10-4. The possible mechanism of damage formation is also analyzed and discussed. KEYWORDS Scanning tunneling microscope; HOPG (Highly Oriented Pyrolitic Graphite); H÷ ions implantation; surface damage. INTRODUCTION The bombardment of charged particles on materials could induce the damage both on the surface and in the internal crystal structure of the materials. The degree of the damage influences directly the effect of ion beam modification of materials. Therefore the study of irradiation damage and changes of materials caused by ion implantation, especially on atomic scale, is of strong interest for the scientists in the fields of material science and nuclear physics. Scanning electron microscope, transmission electronic microscope and field-ion microscope have been used to study the damages and tracks bombarded by ions, but the results are far from satisfaction. The invention of scanning tunneling microscope (STM) and atomic force microscope (AFM) makes it possibe to observe directly the radiation damage on atomic scale. In recent years, by using STM, the surfaces of HOPG, PbS, SiO2 and MoS2, etc., bombarded by ions of different kinds and different energies were investigated and many typies of damage were found (Wilson el al., 1988, 1989; Fcenstra and Oehrlein, 1985; Porte, 1991; Coratger et al., 1990; Neumann el al., 1991; Zhai et al., 1993; Junjue et al., 1994). Some of the damaged zones are craters (Wilson et al., 1988, 1989; Zhai et al., 1993) and the others are hillocks (Fcenstra and Oehrlein, 1985; Porte et al., 1991; Coratger et al., 1990; Neumann et al., 1991; Junjue et al., 1994). The direct observation of the damage on the target surface with STM is helpful for deeply understanding the interaction of energetic ions with materials. Proton is a kind of light ion and the stopping power in solids is small so that the probability of causing an observable defect is also small. In this work, large fluenc¢ of H* ions was implanted into HOPG, and the topography of HOPG surface and the defect density were studied and the results were analysed and discussed.
97
98
PROCEEDINGS OF THE 18TH INTERNATIONAL CONFERENCE EXPERIMENT
The HOPG samples were bombarded by H ÷ ions at Peking University with 5SDH-2 tandem accelerator. The newly cleaved HOPG sample was placed into the target chamber of the accelerator and then was bombarded uniformly with H ÷ ions of 3.0 MeV. The vacuum of the system is 4×10 .7 Tort and the fluence of H ÷ is ( l x l 0 ~6+ 10%) / cm 2 to ensure that there is about one proton impact on every area of0.01nm z. STM experiment was done in the STM Lab. of the High Energy Physics Institute. The STM was operated in air and at room temperature and constant current mode was used. The tunnel current and tip bias voltage are 0.80 nA and 150 mV, respectively. The pictures, given in this paper, are all grey-scale ones. The HOPG samples without ion bombardment were also observed in the same conditions but no visible damage could be found. In our experiment, 457 pictures of area 9 nm x 9 nm were got from different zones on the HOPG surface. From 163 of these pictures, damage could be found clearly. In addition, some large scale (12 nm x 12 n m - 150 nm x 150 nm) pictures were also obtained. RESULT AND DISCUSSION Figure I shows the high resolution STM image of atomic structure on the undamaged area of HOPG bombarded by H + ions of 3.0 MeV. The Figs. 2 to 7 show the surface of HOPG implanted by H + ions of 3.0 MeV. The scanning area of STM images is from 9 nm x 9 nm to 150 nm x 150 run. In these pictures, the damage region is obvious. The diameter for 80% of the damaged zones is from 0.2 to 0.8 nm. The mimimum defect is only several atomic scales and the maximum one is above 1.8 nm. Figure 8 shows the diameter histogram of the damaged zones. Carefully analysing the STM images of Fig.2 - Fig.7, we could find that the damage zones are the combination of some smaller defects. In Figs. 4 to 7, with the increase of the amplification, the combined damage region could be observed more clearly. From about 500 atomic resolution STM images on the surface of HOPG, we find that the number density of visible damage is much less than the fluence of H ÷ ions. The density of damage is 1.8 x 10~2/cm 2 and the fluence of implantation is 1 x 10~6/cm 2. Therefore the probability of damage is only about 1.8 x 10~. From these pictures we find that the damage caused by H ÷ ions is not uniform and appears approximately in the form of groups. Single damage is rare and the density of those kinds of damage combined with three or more smaller defects is about 2.9 x 10 ~z / cm 2. Two
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Fig. I. STM image of the undamaged area on the surface of HOPG (4.5x4.5 nm2).
Fig. 2. STM image on the surface of HOPG bombarded by H÷ ions of 3.0 MeV (150x150 nm2).
PROCEEDINGS OF THE 18TH I N T E R N A T I O N A L CONFERENCE
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Fig. 3. STM image on the surface of HOPG bombarded by H* ions of 3.0 MeV (100xl00 nm2).
Fig. 4. STM image on the surface of HOPG bombarded by H ÷ ions of 3.0 MeV (60x60 nm2).
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Fig. 5. STM image on the surface of HOPG bombarded by It + ions of 3.0 MeV (24x24 nm").
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Fig. 6. STM image on the surface of HOPG bombarded by H" ions of 3.0 MeV (9x9 nm~').
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Fig. 7. STM image on the surface of HOPG bombarded by 1t+ ions of 3.0 MeV (9x9 nm2).
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Diameter (nm) Fig. 8. Histogram of the number of damaged zones with the damage diameter on the surface of HOPG induced by H ÷ ions of 3.0 MeV.
100
PROCEEDINGS OF THE 18TH INTERNATIONAL CONFERENCE
defects with separations less than 2.0 nm is about 85%. The reason of this phenomena is complicated, probably some early formed defects from H+ bombardment have some influence on the defects induced by the following H÷ ion bombardment, or it is the result of the cascade collisions. Mazzei et al. (1984) have observed tracks in Makrofol E irradiated with 55 MeV alpha particles with a detection efficiency of 10"s and they explained their result from point of view of compound nucleus formation probability of the ions with the C atoms of the samples. But their experimental conditions were different from this experiment, therefore further experimental and theoretical studies are needed. REFERENCES Coratger R., Claverie A., Ajus~'on F. and Beauvillain J. (1990) Scanning tunneling microscopy of defects induced by carbon bombardment on graphite surface. Surf. Sci. 227, 7-14. Fcenstra R. M. and Oehrlein G. S. (1985) Surface mophology of oxidized and ion-etched silicon by scanning tunneling microscopy. Appl. Phys. Lett. 47, 97-99. Junjue Yah, Zhigang Li, Chuanyong Bai, W.S.Yang, Yugang Wang, Weijiang Zhao, Yixiu Kang, F.C.Yu, Pengii Zhai and Xiaowei Tang. (1994) Scanning tunneling microscopy investigation of graphite surface damage induced by gold-ion bombardment. J. Appl. Phys. 75, 1390-1395. Mazzei R., Bernaola O. A. and Molinari de Rey B. (1984) Compound nucleus cross section in Makrofol E irradiated with 55 MeV alpha particles. Nucl. Tracks 9, 189-197. Neumann R., Trautmam C., Vetter J., Angert N., Ackermann J., Kemmer H., Grattrom S., Neitzert M. and Wortge M. (1991) Scanning tunneling microscopy of surface modifications induced by UNILAC heavy-ion irradiation. GSI-Nachrichten 08-91, GSI Darmstadt. Porte L. de Villeneuve C. H. and Phaner M. (1991) Scanning tunneling microscopy observation of local damage on graphite surface by ion implantation. J Vac. Sci. Technol. B9, 1064-1067. Wilson T. H., Zheng N. J., Knipping U. and Tsong I. S. T. (1988) Effects of isolated atomic collision cascades on SiO2/Si interfaces studied by scanning tunneling microscopy. Phys. Rev. B38, 84448450. Wilson T. H., Zheng N. J., Knipping U. and Tsong I. S. T. (1989) Scanning tunneling microscopy of ion impacts on semiconductor surfaces. J. Vac. Sci Technol. A7, 2840-2844. Zhai Pengji, Lu Feng, Tang Xiaowei, Wei Jun, He Jie, Shang Guangyi and Yao Junen. (1993) Observation of radiation damage of energetic heavy ions impacts on MoS2 surface by scanning tunneling microscopy. Science in China (series A) 36, 715-719.
Pergamon
PII: S 1350-4487(97)00047-4
1350-4487/97 $17.00÷ 0.00
OBSERVATION AND STUDY OF LATENT TRACKS ON THE SURFACE OF HOPG INDUCED BY H ÷ IONS
P. J. ZHAI, Y. X. XING, Y. ZHANG, S. L. FENG, Y. X. KANG AND X. W. TANG Institute of High Energy Physics, Academia Sinica, P.O.Box 2732, Beijing,.China Y. G. WANG, W. J. ZHAO AND S. YAN Institute of Heavy Ion Physics Peking University, Beijing,.China ABSTRACT The topography and size of damage on the surface of HOPG (Highly Oriented Pyrolitic Graphite) bombarded by high fluence (lxl016 ions/cm2) of H" ions were observed and studied. In this work, 457 STM images of each one with 9x9 nm2 area were obtained. From 163 of these pictures visible damage was found. In these 163 STM images the diameter of most damage is from 0.2 to 0.8 nm. In this study the number density of visible damage is much less than the ion fluence. The probability of damage is only about 1.8x 10-4. The possible mechanism of damage formation is also analyzed and discussed. KEYWORDS Scanning tunneling microscope; HOPG (Highly Oriented Pyrolitic Graphite); H÷ ions implantation; surface damage. INTRODUCTION The bombardment of charged particles on materials could induce the damage both on the surface and in the internal crystal structure of the materials. The degree of the damage influences directly the effect of ion beam modification of materials. Therefore the study of irradiation damage and changes of materials caused by ion implantation, especially on atomic scale, is of strong interest for the scientists in the fields of material science and nuclear physics. Scanning electron microscope, transmission electronic microscope and field-ion microscope have been used to study the damages and tracks bombarded by ions, but the results are far from satisfaction. The invention of scanning tunneling microscope (STM) and atomic force microscope (AFM) makes it possibe to observe directly the radiation damage on atomic scale. In recent years, by using STM, the surfaces of HOPG, PbS, SiO2 and MoS2, etc., bombarded by ions of different kinds and different energies were investigated and many typies of damage were found (Wilson el al., 1988, 1989; Fcenstra and Oehrlein, 1985; Porte, 1991; Coratger et al., 1990; Neumann el al., 1991; Zhai et al., 1993; Junjue et al., 1994). Some of the damaged zones are craters (Wilson et al., 1988, 1989; Zhai et al., 1993) and the others are hillocks (Fcenstra and Oehrlein, 1985; Porte et al., 1991; Coratger et al., 1990; Neumann et al., 1991; Junjue et al., 1994). The direct observation of the damage on the target surface with STM is helpful for deeply understanding the interaction of energetic ions with materials. Proton is a kind of light ion and the stopping power in solids is small so that the probability of causing an observable defect is also small. In this work, large fluenc¢ of H* ions was implanted into HOPG, and the topography of HOPG surface and the defect density were studied and the results were analysed and discussed.
97
98
PROCEEDINGS OF THE 18TH INTERNATIONAL CONFERENCE EXPERIMENT
The HOPG samples were bombarded by H ÷ ions at Peking University with 5SDH-2 tandem accelerator. The newly cleaved HOPG sample was placed into the target chamber of the accelerator and then was bombarded uniformly with H ÷ ions of 3.0 MeV. The vacuum of the system is 4×10 .7 Tort and the fluence of H ÷ is ( l x l 0 ~6+ 10%) / cm 2 to ensure that there is about one proton impact on every area of0.01nm z. STM experiment was done in the STM Lab. of the High Energy Physics Institute. The STM was operated in air and at room temperature and constant current mode was used. The tunnel current and tip bias voltage are 0.80 nA and 150 mV, respectively. The pictures, given in this paper, are all grey-scale ones. The HOPG samples without ion bombardment were also observed in the same conditions but no visible damage could be found. In our experiment, 457 pictures of area 9 nm x 9 nm were got from different zones on the HOPG surface. From 163 of these pictures, damage could be found clearly. In addition, some large scale (12 nm x 12 n m - 150 nm x 150 nm) pictures were also obtained. RESULT AND DISCUSSION Figure I shows the high resolution STM image of atomic structure on the undamaged area of HOPG bombarded by H + ions of 3.0 MeV. The Figs. 2 to 7 show the surface of HOPG implanted by H + ions of 3.0 MeV. The scanning area of STM images is from 9 nm x 9 nm to 150 nm x 150 run. In these pictures, the damage region is obvious. The diameter for 80% of the damaged zones is from 0.2 to 0.8 nm. The mimimum defect is only several atomic scales and the maximum one is above 1.8 nm. Figure 8 shows the diameter histogram of the damaged zones. Carefully analysing the STM images of Fig.2 - Fig.7, we could find that the damage zones are the combination of some smaller defects. In Figs. 4 to 7, with the increase of the amplification, the combined damage region could be observed more clearly. From about 500 atomic resolution STM images on the surface of HOPG, we find that the number density of visible damage is much less than the fluence of H ÷ ions. The density of damage is 1.8 x 10~2/cm 2 and the fluence of implantation is 1 x 10~6/cm 2. Therefore the probability of damage is only about 1.8 x 10~. From these pictures we find that the damage caused by H ÷ ions is not uniform and appears approximately in the form of groups. Single damage is rare and the density of those kinds of damage combined with three or more smaller defects is about 2.9 x 10 ~z / cm 2. Two
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Fig. I. STM image of the undamaged area on the surface of HOPG (4.5x4.5 nm2).
Fig. 2. STM image on the surface of HOPG bombarded by H÷ ions of 3.0 MeV (150x150 nm2).
PROCEEDINGS OF THE 18TH I N T E R N A T I O N A L CONFERENCE
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Fig. 3. STM image on the surface of HOPG bombarded by H* ions of 3.0 MeV (100xl00 nm2).
Fig. 4. STM image on the surface of HOPG bombarded by H ÷ ions of 3.0 MeV (60x60 nm2).
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Fig. 5. STM image on the surface of HOPG bombarded by It + ions of 3.0 MeV (24x24 nm").
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Fig. 6. STM image on the surface of HOPG bombarded by H" ions of 3.0 MeV (9x9 nm~').
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Fig. 7. STM image on the surface of HOPG bombarded by 1t+ ions of 3.0 MeV (9x9 nm2).
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1.2
1.6
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Diameter (nm) Fig. 8. Histogram of the number of damaged zones with the damage diameter on the surface of HOPG induced by H ÷ ions of 3.0 MeV.
100
PROCEEDINGS OF THE 18TH INTERNATIONAL CONFERENCE
defects with separations less than 2.0 nm is about 85%. The reason of this phenomena is complicated, probably some early formed defects from H+ bombardment have some influence on the defects induced by the following H÷ ion bombardment, or it is the result of the cascade collisions. Mazzei et al. (1984) have observed tracks in Makrofol E irradiated with 55 MeV alpha particles with a detection efficiency of 10"s and they explained their result from point of view of compound nucleus formation probability of the ions with the C atoms of the samples. But their experimental conditions were different from this experiment, therefore further experimental and theoretical studies are needed. REFERENCES Coratger R., Claverie A., Ajus~'on F. and Beauvillain J. (1990) Scanning tunneling microscopy of defects induced by carbon bombardment on graphite surface. Surf. Sci. 227, 7-14. Fcenstra R. M. and Oehrlein G. S. (1985) Surface mophology of oxidized and ion-etched silicon by scanning tunneling microscopy. Appl. Phys. Lett. 47, 97-99. Junjue Yah, Zhigang Li, Chuanyong Bai, W.S.Yang, Yugang Wang, Weijiang Zhao, Yixiu Kang, F.C.Yu, Pengii Zhai and Xiaowei Tang. (1994) Scanning tunneling microscopy investigation of graphite surface damage induced by gold-ion bombardment. J. Appl. Phys. 75, 1390-1395. Mazzei R., Bernaola O. A. and Molinari de Rey B. (1984) Compound nucleus cross section in Makrofol E irradiated with 55 MeV alpha particles. Nucl. Tracks 9, 189-197. Neumann R., Trautmam C., Vetter J., Angert N., Ackermann J., Kemmer H., Grattrom S., Neitzert M. and Wortge M. (1991) Scanning tunneling microscopy of surface modifications induced by UNILAC heavy-ion irradiation. GSI-Nachrichten 08-91, GSI Darmstadt. Porte L. de Villeneuve C. H. and Phaner M. (1991) Scanning tunneling microscopy observation of local damage on graphite surface by ion implantation. J Vac. Sci. Technol. B9, 1064-1067. Wilson T. H., Zheng N. J., Knipping U. and Tsong I. S. T. (1988) Effects of isolated atomic collision cascades on SiO2/Si interfaces studied by scanning tunneling microscopy. Phys. Rev. B38, 84448450. Wilson T. H., Zheng N. J., Knipping U. and Tsong I. S. T. (1989) Scanning tunneling microscopy of ion impacts on semiconductor surfaces. J. Vac. Sci Technol. A7, 2840-2844. Zhai Pengji, Lu Feng, Tang Xiaowei, Wei Jun, He Jie, Shang Guangyi and Yao Junen. (1993) Observation of radiation damage of energetic heavy ions impacts on MoS2 surface by scanning tunneling microscopy. Science in China (series A) 36, 715-719.