Amekura H, Toulemonde M, Narumi K, Li R, Chiba A, Hirano Y, Yamada K, Yamamoto S, Ishikawa N, Okubo N, Saitoh Y
National Institute for Materials Science (NIMS), Tsukuba, Japan.
CIMAP, Caen, France.
Sci Rep. 2021 Jan 8;11(1):185. doi: 10.1038/s41598-020-80360-8.
Damaged regions of cylindrical shapes called ion tracks, typically in nano-meters wide and tens micro-meters long, are formed along the ion trajectories in many insulators, when high energy ions in the electronic stopping regime are injected. In most cases, the ion tracks were assumed as consequences of dense electronic energy deposition from the high energy ions, except some cases where the synergy effect with the nuclear energy deposition plays an important role. In crystalline Si (c-Si), no tracks have been observed with any monomer ions up to GeV. Tracks are formed in c-Si under 40 MeV fullerene (C) cluster ion irradiation, which provides much higher energy deposition than monomer ions. The track diameter decreases with decreasing the ion energy until they disappear at an extrapolated value of ~ 17 MeV. However, here we report the track formation of 10 nm in diameter under C ion irradiation of 6 MeV, i.e., much lower than the extrapolated threshold. The diameters of 10 nm were comparable to those under 40 MeV C irradiation. Furthermore, the tracks formed by 6 MeV C irradiation consisted of damaged crystalline, while those formed by 40 MeV C irradiation were amorphous. The track formation was observed down to 1 MeV and probably lower with decreasing the track diameters. The track lengths were much shorter than those expected from the drop of S below the threshold. These track formations at such low energies cannot be explained by the conventional purely electronic energy deposition mechanism, indicating another origin, e.g., the synergy effect between the electronic and nuclear energy depositions, or dual transitions of transient melting and boiling.
当注入处于电子阻止 regime 的高能离子时，在许多绝缘体中会沿着离子轨迹形成称为离子径迹的圆柱形损伤区域，其宽度通常为纳米级，长度为几十微米。在大多数情况下，离子径迹被认为是高能离子密集电子能量沉积的结果，但也有一些情况，核能沉积的协同效应起着重要作用。在晶体硅（c-Si）中，直到 GeV 能量的任何单体离子都未观察到径迹。在 40 MeV 富勒烯（C）团簇离子辐照下，c-Si 中会形成径迹，其提供的能量沉积比单体离子高得多。径迹直径随着离子能量的降低而减小，直到在约 17 MeV 的外推值时消失。然而，在此我们报道在 6 MeV 的 C 离子辐照下形成了直径为 10 nm 的径迹，即远低于外推阈值。10 nm 的直径与 40 MeV C 辐照下的直径相当。此外，6 MeV C 辐照形成的径迹由受损晶体组成，而 40 MeV C 辐照形成的径迹是无定形的。观察到径迹形成的能量低至 1 MeV，并且随着径迹直径的减小可能更低。径迹长度比低于阈值时 S 的下降所预期的要短得多。这种低能量下的径迹形成不能用传统的纯电子能量沉积机制来解释，这表明存在另一种起源，例如电子和核能沉积之间的协同效应，或瞬态熔化和沸腾的双重转变。
