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

系统地了解中能离子大角度散射的电荷交换、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有关表面结构和晶格动力学的定量信息是必不可少的。然而，由于气体靶的密度和散射截面非常小，不可能直接测量上述物理量。本文利用具有良好能量分辨率（Δ E =9 × 10 ~（-3））的环形静电分析仪测量了He离子在单晶表面大角度散射的电荷态分布（CSD）、非弹性能量损失和谱形<-4>。所用单晶靶为MgO（001）、KI（001）、BbI（001）、B型NiSi_2（111）和Si（111）-<3>Al_2O_3-<3>Sb。 ...更多信息 d到一个大的角度从Ni，Sb和Hf原子。研究结果表明：（1）He离子与固体表面原子大角度散射时的CSD不是平衡的，靶原子的Z数越小，平均电荷越大; He离子从高Z原子（z [大于或类似]20）散射的平均电荷与Marion-Young [ii]提出的半经验公式在实验误差（±20%）内一致。(2)He离子在大角度碰撞后的平均电荷被标度为π ^∞_&lt;r_<min>&gt; P_e（r（t））dr/v（t），其中P_e（r（t））为r（t）处的靶电子密度，R_<min>为最近距离，v（t）为He速度。(3)从最顶部原子散射的He和Ne离子的平均电荷取决于出射角，并且出射角越小（从表面平面缩放），平均电荷越小（达到平衡值）。(4)用Si（111）-SixO 2-Sb直接测量了He离子与Sb原子散射的非弹性能量损失<3><3>，所得结果与Schiwietz用耦合沟道方法的理论计算结果一致. (5)在重离子（如Ne）与高Z原子大角度碰撞的情况下，由于碰撞过程中形成分子轨道，导致靶电子密度分布发生动态变化，从而使微分散射截面增大。

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