Critical capture distances for highly charged ions above dielectric covered metal surfaces

We model the first stage of the electronic interaction between an ion and a metal surface covered with a thin dielectric layer. Specifically, we seek to answer two questions. (i) As an ion approaches the surface from far away, does the first electron that it captures originate from the exposed dielectric layer or the metal underneath it? (ii) What is the ion’s distance from the metal when the first electron is captured? To answer these questions, the classical potential that an electron is subject to during the interaction is calculated. The dielectric film is treated as a continuum with simple band structure. We input the parameters from recent experiments (Co with 1.5 nm thick Al₂O₃ film) and found that (i) the first capture proceeds from the metal, and (ii) the dielectric film extends the distance threshold for first capture compared to a metal with no film.     

Potential energy threshold of surface erosion on GaN by impact of slow highly charged heavy ions

In the present work the erosion behavior on the surface of GaN epi-layer by the impact of various slow highly charged heavy ions (SHCIs, including Ar^q+, Xe^q+ and Pb^q+, in two incidence geometries) was investigated. Atomic force microscopy reveals a well-defined threshold of potential energy carried by the incident heavy ions accounting for the surface erosion. This threshold also depends on the projected range of the SHCIs, the longer the projected range, the higher the potential energy required for the onset of surface erosion. And the etched depth is close to a linear function of potential energy deposited, increasing with the potential energy increases. Moreover, the etching rate for 60° off normal incidence is by more than a factor of 2 larger than etching rate for normal incidence, and the etch rate by Xe^q+ is larger than by Pb^q+ under the same potential energy and incident direction. And a mechanism is discussed.     

Surface nanostructuring of SrTiO3 single crystals by slow highly charged ions and swift heavy ions

Single crystals of strontium titanate have been irradiated with both slow highly charged Xe ions extracted from an Electron Beam Ion Trap and swift heavy Xe ions. After irradiation, the crystals were investigated by scanning force microscopy in air. In both cases nanohillocks due to impact of individual projectiles were observed. This similarity originates from the fact that both swift heavy ions and slow highly charged ions initially transfer their energy to the electronic system of the target, leading to a localized region of high electronic excitation. This electronic excitation is subsequently transferred to the lattice atoms by electron-phonon coupling, leading to pronounced lattice heating. The formation of surface hillocks can then be ascribed to a melting process. We also present first evidence for the existence of a potential energy threshold for nanohillock formation on strontium titanate surfaces by slow highly charged ions.     

低速高电荷态离子Xeq+在金属Al(111)面掠角散射的中性化过程研究

本文在经典过垒模型(COBM)下,通过计算机模拟研究了低速高电荷态离子Xeq 在金属Al(111)表面掠角散射过程中,高电荷态Xeq 离子的中性化过程、其电荷态与该高电荷态离子到Al(111)表面的距离R的关系.此外,还计算了不同电荷态的Xeq 离子在掠射过程中所获得的镜像能,并把该结果与实验值进行了比较.我们模拟的镜像能与实验值符合得非常好.