A study of collective electronic excitation by ion energy loss spectroscopy

应用于固体表面分析的高分辨率离子散射光谱已被改进为透射能量损失光谱。利用分辨率为20 ~ 60 eV的光谱，测量了能量为-100 KeV的H^+和He^+通过7 ~ 20 nm厚度的碳膜的能量损失分布。目前的结果总结如下。(1)未观察到单等离激元激发的峰值，即集体电子激发。在-7 nm碳膜上观察到200 eV左右的新能量损失峰，其原因正在调查中。(2)在100 KeV H^+和He^+条件下，从零能量损失峰强度得到的电子平均自由程分别为1.2 nm和1.4 nm。这些值与相同速度下电子的平均自由程相当。(3)观察到能量损失峰的增加，这是由于离子轰击引起的碳键的修饰。还发现这种效应是由电子激发引起的。(4)发现100 KeV H_2^+的能量损失峰与50 KeV H^+的能量损失峰几乎相等，说明分子对能量损失没有影响。100 KeV H_2^+对17 nm膜的存活率为6X10^<-3>。

High resolution ion scattering spectroscopy which was developed for solid surface analysis has been modified for transmission energy loss spectrosbopy. Using this spectroscopy with a resolution of 20-60 eV, the energy loss distribution of H^+ and He^+ with the energy of -100 KeV transmitted through carbon films with thickness of 7-20 nm were measured. The present results are summarized as follows.(1)No peak due to single plasmon excitation, viz, collective electronic excitation was observed. A new energy loss peak around 200 eV for -7 nm carbon films was observed and the origin is under investigation.(2)From the zero energy loss peak intensity, the electronic mean free path was obtained as 1.2 and 1.4 nm for 100 KeV H^+ and He^+, respectively. These values are comparable with the electronic mean free path of electrons at the same velocities.(3)The increase of the energy loss peak was observed and this effect is ascribed to the modification of carbon bond due to ion bombardment. It id also found that this effect is due to the electronic excitation.(4)The energy loss peak of 100 KeV H_2^+ was found to nearly equal to that of 50 KeV H^+ , indicating no molecular effect on the energy loss. The survival probability of 100 KeV H_2^+ for 17 nm film was 6X10^<-3>.