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Molecular dynamics study of crater formation by core-shell structured cluster impact
Nuclear Instruments and Methods in Physics Research B 282 (2012) 29–32
Contents lists available at SciVerse ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Molecular dynamics study of crater formation by core-shell structured cluster impact Takaaki Aoki a,⇑, Toshio Seki b, Jiro Matsuo c a
Department of Electronic Science and Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan Department of Nuclear Engineering, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan c Quantum Science and Engineering Center, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan b
a r t i c l e
i n f o
Article history: Available online 16 September 2011 Keywords: Cluster impact Molecular dynamics simulation Crater formation
a b s t r a c t Crater formation processes by the impacts of large clusters with binary atomic species were studied using molecular dynamics (MD) simulations. Argon and xenon atoms are artificially organized in core-shell cluster structures with various component ratios and irradiated on a Si(1 0 0) target surface. When the cluster has Xe1000 core covered with 1000 Ar atoms, and impacts at a total of 20 keV, the core Xe cluster penetrates into the deep area, and a crater with a conical shape is left on the target. On the other hand, in the case of a cluster with the opposite structure, Ar1000 core covered with 1000 Xe atoms, the cluster stops at a shallow area of the target. The incident cluster atoms are mixed and tend to spread in a lateral direction, which results in a square shaped crater with a shallower hole and wider opening. The MD simulations suggest that large cluster impacts cause different irradiation effects by changing the structure, even if the component ratio is the same. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction Cluster is an aggregation of several hundred to several hundred thousand atoms or molecules. The impact of an accelerated cluster shows interesting phenomena when compared with a conventional single ion impact [1]. The characteristics of a cluster impact are due to the multiple collision mechanism, in that many cluster and target atoms interact with each other simultaneously at a narrow region of impact point. Various experiments have demonstrated that large gas cluster impacts cause dynamic motion of surface target atoms which results in crater formation [2–4], high-yield physical sputtering [5–7], and surface smoothing [8–10]. In addition, it has also been suggested that a cluster impact enhances the chemical reactivity at the cluster–target interface due to high-density particle and energy deposition, and it can be applied to high-yield etching [11–13] and thin film deposition [14–16]. On the other hand, fundamentals of collision processes have been studied in detail using molecular dynamics (MD) simulations [17–20]. The MD simulation revealed the dynamics of crater formation, sputtering, and the evolution of surface morphology. These irradiation effects were well-parameterized by incident energy, cluster size, and incident angle, which are also controlled in experimental conditions. In addition to these practical parameters, MD simulations with ideal and extraordinary conditions provide useful ⇑ Corresponding author. Tel.: +81 75 383 7136; fax: +81 75 383 7366. E-mail address: [email protected] (T. Aoki). 0168-583X/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2011.08.061
information for further analysis. It has been reported that a chain-like cluster with more than four atoms stacked in a vertical direction enhances the penetration depth when compared with spherical or lateral chain clusters [21]. The other MD simulations suggest the effects of element mass [22] and spatial density where the proximity effect works [23]. In this paper, MD simulations of cluster impacts with binary composite atoms coordinated in core-shell structure are studied. The dynamics of each part inside the cluster and crater formation process are investigated for various components ratio.
2. Simulation method Molecular dynamics (MD) simulations of clusters consist of Ar and Xe atoms impacting on an Si(1 0 0) target were performed using a simulation code that has been developed by our group [24]. The interaction among Si atoms is described by the Stillinger–Weber model potential [25]. The other interactions are governed by the Coulomb screening potential model by Ziegler, Biersack, and Littmark (ZBL) [26]. For the ZBL model potential, the cutoff length is simply given as the interatomic distance in the solid phase for each element. So it is noted that only repulsive force are applied on Ar–Ar, Xe–Xe, Ar–Xe, Ar–Si, and Xe–Si interactions. A Si2048000 slab with dimensions of 22 nm in depth and 43.4 nm 43.4 nm of surface area was prepared as the target. The atoms within 1 unit cell from the bottom are fixed to keep a diamond structure. The region within 5 nm from the bottom was
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T. Aoki et al. / Nuclear Instruments and Methods in Physics Research B 282 (2012) 29–32
Fig. 1. Snapshots of Xe1000 cluster covered with 1000 Ar shell atoms (Xe1000@Ar1000) impacting on Si(1 0 0) surface at 20 keV of total incident energy.
set as a thermal bath governed by Langevin dynamics to keep the target temperature at 300 K. Periodic boundary conditions were applied on lateral sides. Various clusters with the same total size of 2000, but different Ar/Xe component ratio, were prepared as projectiles. The atoms in these composite clusters were coordinated to have core-shell structures. For example, 1000 Xe atoms constructs a spherical core and 1000 Ar atoms are positioned to surround the Xe1000 core spherically. The atoms in the cluster were aligned in a h.c.p. lattice structure which corresponds to the solid phase of each element. These clusters were accelerated with a total of 20 keV and irradiated on the Si(1 0 0) target. One impact simulation was performed for each structure and ratio condition. The simulation time was up to about 32 ps, which is a long enough time for the incident cluster atoms to penetrate and leave the target.
3. Results and discussion Figs. 1 and 2 show the snapshots of an Ar1000Xe1000 cluster impact on a Si(1 0 0) target. The incident energy was a total of 20 keV. Each snapshot represents a cross-section of 2 nm thick including the impact point. In Figs. 1 and 2, both projectiles consist of 1000 Ar and 1000 Xe atoms, but each has a different core-shell structure. The projectile in Fig. 1 consists of a Xe1000 core surrounded by 1000
Ar atoms (termed as Xe1000@Ar1000), and the one in Fig. 2 has the opposite structure (Ar1000@Xe1000). The diameters of Xe1000@Ar1000 and Ar1000@Xe1000 are almost the same, 5.98 nm and 6.07 nm, respectively. Both incident clusters lose the same amount of kinetic energy, about 17.5 keV during the collision, but they form craters with different shapes. The crater caused by the Xe1000@Ar1000 in Fig. 1 has a conical shape with a deep hole and narrow opening. On the other hand, the crater by the Ar1000@Xe1000 in Fig. 2 shows a shallow and square shape. Motions of the center of mass (CM) for Ar1000Xe1000 clusters are shown in Fig. 3 describes three trajectories, CM for the total cluster, the Ar components, and the Xe components. In the case of the Ar1000@Xe1000 impact shown as Fig. 3(b), CMs of the Ar and Xe atoms show almost the same trajectories during the implantation process, whereas the CMs in Fig. 3(a) shows a completely different trajectory. The difference of trajectories is due to the motion of the upper-half section of the cluster. In the case of the impact of Xe1000@Ar1000, the Ar atoms of the upper-half section collides with the Xe atoms at the core region. These Ar atoms are preferentially reflected because of a mass ratio of Ar to Xe, which contributes acceleration of the Xe core part and the spread of the Ar atoms in an upper direction to the normal surface. Thus, the Xe core section reaches deeper into the target and leaves a deep and conical crater shape. In the case of the Ar1000@Xe1000 cluster impact, the
Fig. 2. Snapshots of Ar1000 cluster covered with 1000 Xe shell atoms (Ar1000@Xe1000) impacting on Si(1 0 0) surface at 20 keV of total incident energy.
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T. Aoki et al. / Nuclear Instruments and Methods in Physics Research B 282 (2012) 29–32
6
(Xe core cluster)
4
4
Ar Xe Total
2
Center of Mass [nm]
Center of Mass [nm]
6
(a) Xe1000@Ar1000
0 -2 -4 -6
2 0 (b) Ar1000@Xe1000
-2
(Ar core cluster) Ar Xe Total
-4
0
2
4
6
-6
8
0
2
time [ps]
4
6
8
time [ps]
Fig. 3. Time evolution of the center of mass of incident atoms.
9
6
8
Opening Diameter [nm]
Crater Depth [nm]
5
4
3
2
7
6
5
1
0
4 0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
Xe Contents Ratio
0.4
0.6
0.8
1.0
Xe Contents Ratio
Fig. 4. Crater depths and opening diameters caused by various Ar2000 xXex cluster impacts at 20 keV.
Xe atoms in the upper section keep their shell shape and compress the core Ar atoms. All the Ar and Xe atoms are mixed through multiple collisions and leave the surface. The penetration depth by cluster can be affected by two factors. One is an effect from the momentum of the projectile which means that heavy Xe projectiles can penetrate deeper than Ar when these have the same kinetic energy [22]. The other is a particle proximity effect which is characteristic of a cluster impact. In the case of a cluster impact, the cluster atom which collides with the target atoms first can be accelerated by the cluster atoms following it, and so can penetrate deeper. This effect becomes significant as the density of the cluster increases [23]. Xe2000 has the highest momentum but lowest atomic density among all conditions, whereas Ar2000 has the lowest momentum and highest density. Therefore, enhancement of the crater depth is realized by mixing Ar and Xe cluster structures. Fig. 4 shows the depths and opening radii caused by clusters with various Ar/Xe component ratios. The curves are different depending on the component ratio and the structure. When the ratio of Xe atoms increases from outside to inside, which is described as Ar2000 x@Xex, the depth and diameter of the crater varies almost monotonically. On the other hand, when the Xe contents ratio increases from inside to outside (Xex@Ar2000 x), the crater depth is enhanced when only 10% of Xe atoms are introduced as the core of the cluster and is deeper than that by a pure Xe2000 impact. The opening diameter of the cra-
ter decreases as the contents ratio of Xe increases. As a result, Xe1000@Ar1000 forms the deepest and narrowest crater. 4. Summary The MD simulations of cluster impacts with binary composite atoms and core-shell structures were performed. The crater formation effect by cluster is discussed as the combination of two effects, the large momentum effect and a high-density particle irradiation effect. The MD simulations demonstrated that the penetration and crater formation processes are different depending on cluster structures, even when the component ratio of the clusters is the same. The crater depth is enhanced when a cluster consists of a heavy atom core surrounded with light atoms, and where a high momentum is concentrated. The MD results suggest that the contents and structure of incident clusters are important parameters for crater formation, along with cluster size, energy, and species, and could be applied for novel surface modification processes. References [1] I. Yamada, Materials Science and Engineering: R: Reports 34 (2001) 231–295. [2] T. Seki, T. Kaneko, D. Takeuchi, T. Aoki, J. Matsuo, Z. Insepov, I. Yamada, Nuclear Instruments and Methods B 121 (1997) 498–502. [3] D. Takeuchi, T. Seki, T. Aoki, J. Matsuo, I. Yamada, Materials Chemistry and Physics 54 (1998) 76–79.
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T. Aoki et al. / Nuclear Instruments and Methods in Physics Research B 282 (2012) 29–32
[4] S. Houzumi, K. Mochiji, N. Toyoda, I. Yamada, Japanese Journal of Applied Physics 44 (2005) 6252–6254. [5] J. Matsuo, N. Toyoda, M. Akizuki, I. Yamada, Nuclear Instruments and Methods B 121 (1997) 459–463. [6] N. Toyoda, H. Kitani, N. Hagiwara, T. Aoki, J. Matsuo, I. Yamada, Materials Chemistry and Physics 54 (1998) 262–265. [7] N. Toyoda, H. Kitani, N. Hagiwara, J. Matsuo, I. Yamada, Materials Chemistry and Physics 54 (1998) 106–110. [8] N. Toyoda, N. Hagiwara, J. Matsuo, I. Yamada, Nuclear Instruments and Methods B 161–163 (2000) 980–985. [9] S. Kakuta, S. Sasaki, K. Furusawa, T. Seki, T. Aoki, J. Matsuo, Surface & Coatings Technology 201 (2007) 8632–8636. [10] S. Kakuta, S. Sakaki, T. Hirano, K. Ueda, T. Seki, S. Ninomiya, M. Hada, J. Matsuo, Nuclear Instruments and Methods B 257 (2007) 677–682. [11] T. Seki, J. Matsuo, Nuclear Instruments and Methods B 257 (2007) 666–669. [12] T. Seki, T. Aoki, J. Matsuo, Nuclear Instruments and Methods B 267 (2009) 1444–1446. [13] T. Seki, Y. Yoshino, T. Senoo, K. Koike, S. Ninomiya, T. Aoki, J. Matsuo, AIP Conference Proceedings 1321 (2011) 317–320. [14] M. Akizuki, J. Matsuo, W. Qin, T. Aoki, M. Harada, S. Ogasawara, K. Yodoshi, I. Yamada, Materials Chemistry and Physics 54 (1998) 255–257.
[15] W. Qin, R.P. Howson, M. Akizuki, J. Matsuo, G. Takaoka, I. Yamada, Materials Chemistry and Physics 54 (1998) 258–261. [16] H. Saito, M. Taguchi, M. Ohishi, M. Yoneta, K. Imai, Physica Status Solidi C 1 (2004) 2478–2482. [17] C. Anders, H. Urbassek, Nulclear Instruments and Methods B 228 (2005) 57. [18] Y. Yamaguchi, J. Gspann, Nulclear Instruments and Methods B 228 (2005) 309. [19] L. Rzeznik, B. Czerwinski, B. Garrison, N. Winograd, Z. Postawa, Applied Surface Science 255 (2008) 841–843. [20] T. Aoki, T. Seki, J. Matsuo, Vacuum 84 (2010) 994–998. [21] T. Aoki, J. Matsuo, Z. Insepov, I. Yamada, in: Proceedings of 1998 International Conference on Ion Implantation Technology (1999) pp. 1254–1257. [22] T. Aoki, J. Matsuo, G. Takaoka, I. Yamada, Nuclear Instruments and Methods B 206 (2003) 861–865. [23] T. Aoki, T. Seki, J. Matsuo, Nuclear Instruments and Methods B 267 (2009) 2999–3001. [24] T. Aoki, Molecular Dynamics Simulation of Cluster Ion Impact on Solid Surface [Doctoral Dissertion], Kyoto University, 2000 http://hdl.handle.net/2433/8942. [25] F. Stillinger, T. Weber, Physical Review B 31 (1985) 5262–5271. [26] J. F. Ziegler, http://www.srim.org/.
Contents lists available at SciVerse ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Molecular dynamics study of crater formation by core-shell structured cluster impact Takaaki Aoki a,⇑, Toshio Seki b, Jiro Matsuo c a
Department of Electronic Science and Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan Department of Nuclear Engineering, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan c Quantum Science and Engineering Center, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan b
a r t i c l e
i n f o
Article history: Available online 16 September 2011 Keywords: Cluster impact Molecular dynamics simulation Crater formation
a b s t r a c t Crater formation processes by the impacts of large clusters with binary atomic species were studied using molecular dynamics (MD) simulations. Argon and xenon atoms are artificially organized in core-shell cluster structures with various component ratios and irradiated on a Si(1 0 0) target surface. When the cluster has Xe1000 core covered with 1000 Ar atoms, and impacts at a total of 20 keV, the core Xe cluster penetrates into the deep area, and a crater with a conical shape is left on the target. On the other hand, in the case of a cluster with the opposite structure, Ar1000 core covered with 1000 Xe atoms, the cluster stops at a shallow area of the target. The incident cluster atoms are mixed and tend to spread in a lateral direction, which results in a square shaped crater with a shallower hole and wider opening. The MD simulations suggest that large cluster impacts cause different irradiation effects by changing the structure, even if the component ratio is the same. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction Cluster is an aggregation of several hundred to several hundred thousand atoms or molecules. The impact of an accelerated cluster shows interesting phenomena when compared with a conventional single ion impact [1]. The characteristics of a cluster impact are due to the multiple collision mechanism, in that many cluster and target atoms interact with each other simultaneously at a narrow region of impact point. Various experiments have demonstrated that large gas cluster impacts cause dynamic motion of surface target atoms which results in crater formation [2–4], high-yield physical sputtering [5–7], and surface smoothing [8–10]. In addition, it has also been suggested that a cluster impact enhances the chemical reactivity at the cluster–target interface due to high-density particle and energy deposition, and it can be applied to high-yield etching [11–13] and thin film deposition [14–16]. On the other hand, fundamentals of collision processes have been studied in detail using molecular dynamics (MD) simulations [17–20]. The MD simulation revealed the dynamics of crater formation, sputtering, and the evolution of surface morphology. These irradiation effects were well-parameterized by incident energy, cluster size, and incident angle, which are also controlled in experimental conditions. In addition to these practical parameters, MD simulations with ideal and extraordinary conditions provide useful ⇑ Corresponding author. Tel.: +81 75 383 7136; fax: +81 75 383 7366. E-mail address: [email protected] (T. Aoki). 0168-583X/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2011.08.061
information for further analysis. It has been reported that a chain-like cluster with more than four atoms stacked in a vertical direction enhances the penetration depth when compared with spherical or lateral chain clusters [21]. The other MD simulations suggest the effects of element mass [22] and spatial density where the proximity effect works [23]. In this paper, MD simulations of cluster impacts with binary composite atoms coordinated in core-shell structure are studied. The dynamics of each part inside the cluster and crater formation process are investigated for various components ratio.
2. Simulation method Molecular dynamics (MD) simulations of clusters consist of Ar and Xe atoms impacting on an Si(1 0 0) target were performed using a simulation code that has been developed by our group [24]. The interaction among Si atoms is described by the Stillinger–Weber model potential [25]. The other interactions are governed by the Coulomb screening potential model by Ziegler, Biersack, and Littmark (ZBL) [26]. For the ZBL model potential, the cutoff length is simply given as the interatomic distance in the solid phase for each element. So it is noted that only repulsive force are applied on Ar–Ar, Xe–Xe, Ar–Xe, Ar–Si, and Xe–Si interactions. A Si2048000 slab with dimensions of 22 nm in depth and 43.4 nm 43.4 nm of surface area was prepared as the target. The atoms within 1 unit cell from the bottom are fixed to keep a diamond structure. The region within 5 nm from the bottom was
30
T. Aoki et al. / Nuclear Instruments and Methods in Physics Research B 282 (2012) 29–32
Fig. 1. Snapshots of Xe1000 cluster covered with 1000 Ar shell atoms (Xe1000@Ar1000) impacting on Si(1 0 0) surface at 20 keV of total incident energy.
set as a thermal bath governed by Langevin dynamics to keep the target temperature at 300 K. Periodic boundary conditions were applied on lateral sides. Various clusters with the same total size of 2000, but different Ar/Xe component ratio, were prepared as projectiles. The atoms in these composite clusters were coordinated to have core-shell structures. For example, 1000 Xe atoms constructs a spherical core and 1000 Ar atoms are positioned to surround the Xe1000 core spherically. The atoms in the cluster were aligned in a h.c.p. lattice structure which corresponds to the solid phase of each element. These clusters were accelerated with a total of 20 keV and irradiated on the Si(1 0 0) target. One impact simulation was performed for each structure and ratio condition. The simulation time was up to about 32 ps, which is a long enough time for the incident cluster atoms to penetrate and leave the target.
3. Results and discussion Figs. 1 and 2 show the snapshots of an Ar1000Xe1000 cluster impact on a Si(1 0 0) target. The incident energy was a total of 20 keV. Each snapshot represents a cross-section of 2 nm thick including the impact point. In Figs. 1 and 2, both projectiles consist of 1000 Ar and 1000 Xe atoms, but each has a different core-shell structure. The projectile in Fig. 1 consists of a Xe1000 core surrounded by 1000
Ar atoms (termed as Xe1000@Ar1000), and the one in Fig. 2 has the opposite structure (Ar1000@Xe1000). The diameters of Xe1000@Ar1000 and Ar1000@Xe1000 are almost the same, 5.98 nm and 6.07 nm, respectively. Both incident clusters lose the same amount of kinetic energy, about 17.5 keV during the collision, but they form craters with different shapes. The crater caused by the Xe1000@Ar1000 in Fig. 1 has a conical shape with a deep hole and narrow opening. On the other hand, the crater by the Ar1000@Xe1000 in Fig. 2 shows a shallow and square shape. Motions of the center of mass (CM) for Ar1000Xe1000 clusters are shown in Fig. 3 describes three trajectories, CM for the total cluster, the Ar components, and the Xe components. In the case of the Ar1000@Xe1000 impact shown as Fig. 3(b), CMs of the Ar and Xe atoms show almost the same trajectories during the implantation process, whereas the CMs in Fig. 3(a) shows a completely different trajectory. The difference of trajectories is due to the motion of the upper-half section of the cluster. In the case of the impact of Xe1000@Ar1000, the Ar atoms of the upper-half section collides with the Xe atoms at the core region. These Ar atoms are preferentially reflected because of a mass ratio of Ar to Xe, which contributes acceleration of the Xe core part and the spread of the Ar atoms in an upper direction to the normal surface. Thus, the Xe core section reaches deeper into the target and leaves a deep and conical crater shape. In the case of the Ar1000@Xe1000 cluster impact, the
Fig. 2. Snapshots of Ar1000 cluster covered with 1000 Xe shell atoms (Ar1000@Xe1000) impacting on Si(1 0 0) surface at 20 keV of total incident energy.
31
T. Aoki et al. / Nuclear Instruments and Methods in Physics Research B 282 (2012) 29–32
6
(Xe core cluster)
4
4
Ar Xe Total
2
Center of Mass [nm]
Center of Mass [nm]
6
(a) Xe1000@Ar1000
0 -2 -4 -6
2 0 (b) Ar1000@Xe1000
-2
(Ar core cluster) Ar Xe Total
-4
0
2
4
6
-6
8
0
2
time [ps]
4
6
8
time [ps]
Fig. 3. Time evolution of the center of mass of incident atoms.
9
6
8
Opening Diameter [nm]
Crater Depth [nm]
5
4
3
2
7
6
5
1
0
4 0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
Xe Contents Ratio
0.4
0.6
0.8
1.0
Xe Contents Ratio
Fig. 4. Crater depths and opening diameters caused by various Ar2000 xXex cluster impacts at 20 keV.
Xe atoms in the upper section keep their shell shape and compress the core Ar atoms. All the Ar and Xe atoms are mixed through multiple collisions and leave the surface. The penetration depth by cluster can be affected by two factors. One is an effect from the momentum of the projectile which means that heavy Xe projectiles can penetrate deeper than Ar when these have the same kinetic energy [22]. The other is a particle proximity effect which is characteristic of a cluster impact. In the case of a cluster impact, the cluster atom which collides with the target atoms first can be accelerated by the cluster atoms following it, and so can penetrate deeper. This effect becomes significant as the density of the cluster increases [23]. Xe2000 has the highest momentum but lowest atomic density among all conditions, whereas Ar2000 has the lowest momentum and highest density. Therefore, enhancement of the crater depth is realized by mixing Ar and Xe cluster structures. Fig. 4 shows the depths and opening radii caused by clusters with various Ar/Xe component ratios. The curves are different depending on the component ratio and the structure. When the ratio of Xe atoms increases from outside to inside, which is described as Ar2000 x@Xex, the depth and diameter of the crater varies almost monotonically. On the other hand, when the Xe contents ratio increases from inside to outside (Xex@Ar2000 x), the crater depth is enhanced when only 10% of Xe atoms are introduced as the core of the cluster and is deeper than that by a pure Xe2000 impact. The opening diameter of the cra-
ter decreases as the contents ratio of Xe increases. As a result, Xe1000@Ar1000 forms the deepest and narrowest crater. 4. Summary The MD simulations of cluster impacts with binary composite atoms and core-shell structures were performed. The crater formation effect by cluster is discussed as the combination of two effects, the large momentum effect and a high-density particle irradiation effect. The MD simulations demonstrated that the penetration and crater formation processes are different depending on cluster structures, even when the component ratio of the clusters is the same. The crater depth is enhanced when a cluster consists of a heavy atom core surrounded with light atoms, and where a high momentum is concentrated. The MD results suggest that the contents and structure of incident clusters are important parameters for crater formation, along with cluster size, energy, and species, and could be applied for novel surface modification processes. References [1] I. Yamada, Materials Science and Engineering: R: Reports 34 (2001) 231–295. [2] T. Seki, T. Kaneko, D. Takeuchi, T. Aoki, J. Matsuo, Z. Insepov, I. Yamada, Nuclear Instruments and Methods B 121 (1997) 498–502. [3] D. Takeuchi, T. Seki, T. Aoki, J. Matsuo, I. Yamada, Materials Chemistry and Physics 54 (1998) 76–79.
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T. Aoki et al. / Nuclear Instruments and Methods in Physics Research B 282 (2012) 29–32
[4] S. Houzumi, K. Mochiji, N. Toyoda, I. Yamada, Japanese Journal of Applied Physics 44 (2005) 6252–6254. [5] J. Matsuo, N. Toyoda, M. Akizuki, I. Yamada, Nuclear Instruments and Methods B 121 (1997) 459–463. [6] N. Toyoda, H. Kitani, N. Hagiwara, T. Aoki, J. Matsuo, I. Yamada, Materials Chemistry and Physics 54 (1998) 262–265. [7] N. Toyoda, H. Kitani, N. Hagiwara, J. Matsuo, I. Yamada, Materials Chemistry and Physics 54 (1998) 106–110. [8] N. Toyoda, N. Hagiwara, J. Matsuo, I. Yamada, Nuclear Instruments and Methods B 161–163 (2000) 980–985. [9] S. Kakuta, S. Sasaki, K. Furusawa, T. Seki, T. Aoki, J. Matsuo, Surface & Coatings Technology 201 (2007) 8632–8636. [10] S. Kakuta, S. Sakaki, T. Hirano, K. Ueda, T. Seki, S. Ninomiya, M. Hada, J. Matsuo, Nuclear Instruments and Methods B 257 (2007) 677–682. [11] T. Seki, J. Matsuo, Nuclear Instruments and Methods B 257 (2007) 666–669. [12] T. Seki, T. Aoki, J. Matsuo, Nuclear Instruments and Methods B 267 (2009) 1444–1446. [13] T. Seki, Y. Yoshino, T. Senoo, K. Koike, S. Ninomiya, T. Aoki, J. Matsuo, AIP Conference Proceedings 1321 (2011) 317–320. [14] M. Akizuki, J. Matsuo, W. Qin, T. Aoki, M. Harada, S. Ogasawara, K. Yodoshi, I. Yamada, Materials Chemistry and Physics 54 (1998) 255–257.
[15] W. Qin, R.P. Howson, M. Akizuki, J. Matsuo, G. Takaoka, I. Yamada, Materials Chemistry and Physics 54 (1998) 258–261. [16] H. Saito, M. Taguchi, M. Ohishi, M. Yoneta, K. Imai, Physica Status Solidi C 1 (2004) 2478–2482. [17] C. Anders, H. Urbassek, Nulclear Instruments and Methods B 228 (2005) 57. [18] Y. Yamaguchi, J. Gspann, Nulclear Instruments and Methods B 228 (2005) 309. [19] L. Rzeznik, B. Czerwinski, B. Garrison, N. Winograd, Z. Postawa, Applied Surface Science 255 (2008) 841–843. [20] T. Aoki, T. Seki, J. Matsuo, Vacuum 84 (2010) 994–998. [21] T. Aoki, J. Matsuo, Z. Insepov, I. Yamada, in: Proceedings of 1998 International Conference on Ion Implantation Technology (1999) pp. 1254–1257. [22] T. Aoki, J. Matsuo, G. Takaoka, I. Yamada, Nuclear Instruments and Methods B 206 (2003) 861–865. [23] T. Aoki, T. Seki, J. Matsuo, Nuclear Instruments and Methods B 267 (2009) 2999–3001. [24] T. Aoki, Molecular Dynamics Simulation of Cluster Ion Impact on Solid Surface [Doctoral Dissertion], Kyoto University, 2000 http://hdl.handle.net/2433/8942. [25] F. Stillinger, T. Weber, Physical Review B 31 (1985) 5262–5271. [26] J. F. Ziegler, http://www.srim.org/.