Energy Loss and charge exchange for medium energy ions in a large-angle collision

系统地了解介质能离子大角度散射时的电荷交换、非弹性能量损失和谱形，对于从固体表面散射离子的能谱中提取表面结构和晶格动力学的定量信息是必不可少的。然而，不幸的是，由于靶材密度和散射截面极小，用气体靶材直接测量上述物理量是不可能的。在这项研究中，我们使用具有优异能量分辨率的环形静电分析仪（Δ E =9 x 10^<-4>）测量了He离子在单晶表面大角度散射的电荷态分布（CSDs）、非弹性能量损失和光谱形状。本文使用的单晶靶有MgO（001）、KI（001）、BbI（001）、b型NiSi_2（111）和Si(111)-√<3> ×√<3>- sb。我们还用固体探测器测量了He和Ne离子从Ni、Sb和Hf原子向大角度散射的弹性散射截面。本研究揭示了以下几点：(1)He离子从固体表面上的原子向大角度散射时的CSDs不平衡，靶原子的z数越小，平均电荷越大。从高z原子（z【大于或相似】20）散射的He离子的平均电荷在实验范围内（±20%）与Marion-Young [ii]提出的半经验公式一致。(2)观察到的He离子大角度碰撞后的平均电荷被标为∫^∞_<r_<min>> P_e(r(t))dr/v(t)的函数，其中P_e（r(t)）为r(t)处的目标电子密度，r_<min>为最近距离，v(t)为He速度。(3) He和Ne离子的平均电荷依赖于出口角，出口角越小（从表面缩放），平均电荷越小（达到平衡值）。(4)用Si(111)-√<3> x√<3>-Sb直接测量了Sb原子散射离子的非弹性能量损失。所得结果与Schiwietz用耦合通道法的理论计算一致。(5)重离子（如Ne）与高z原子发生大角度碰撞时，靶电子密度分布的动态变化导致了靶电子密度分布的增强

Systematic understanding the charge exchange, inelastic energy loss and spectrum shape for medium energy ions scattered to a large-angle is indispensable to extract the quantitative information about the suiface structure and lattice dynamics from the energy spectra obseived for the ions scattered from solid surfaces. Unfortunately, however, it is impossible to measure directly the above physical quantities using gas targets, because of the extamely smali target densi and scattering cross sections. In this study, we measured the charge state distributions (CSDs), inelastic energy loss and spectrum shapes for He ions scattered to a large-angle at single ciystal surfaces using a toroidal electrostatic analyzer with an excellent energy resolution (Δ E =9 x 10^<-4>). The single ciystal targets used here are MgO(001), KI(001), BbI(001), B-type NiSi_2(111) and Si(111)-√<3> x√<3>-Sb. We also measured the elastic scattering cross sections with a solid state detector for He and Ne ions scattere … More d to a large-angle from Ni, Sb and Hf atoms. The present study has revealed the following points :(1) The CSDs for He ions scattered to a large-angle from the atoms on top of solid surfaces are not equilibrated and the smaller the Z-number of target atoms, the larger the average charge. The average charges for He ions scattered from high-Z atoms (z 【greater than or similar】20) observed agree with the semi-empirical formula proposed by Marion-Young [ii within experimental enors (±20%).(2) The observed avemge charges of He ions after a large-angle collision are scaled as a frmnction of ∫^∞_<r_<min>> P_e(r(t))dr/v(t), where P_e (r(t)) is the target electron density at r(t), R_<min> is the closest distance and v(t) is the He velocity.(3) The average charges of the He and Ne ions scattered from top most atoms are dependent on exit angle and the smaller the the exit angle (scaled from the surface plane), the smaller the average charges (reaching an equilibrium value).(4) The inelastic energy loss for he ions scattered from the Sb atoms were measured directly using the Si(111)-√<3> x√<3>-Sb. The result obtained agrees the theoretical calculation by Schiwietz using the coupled channel method.(5) In the case of a large-angle collision between a heavy ion such as Ne and a high-Z atom, the differential scattering cross sections are enhanced due to dynamical change of the target electron density distributions induced by formation of a molecular oitital during the collision Less