A study of collective electronic excitation by ion energy loss spectroscopy

对用于固体表面分析的高分辨离子散射谱进行了改进，使之适用于传输能量损失谱。利用这一分辨率为20-60 eV的光谱，测量了能量为-100keV的H和He通过厚度为7-20 nm的碳膜的能量损失分布。主要研究结果如下：(1)没有观察到单一等离子体激元激发峰，即集体电子激发峰。对于-7 nm碳膜，在200 eV附近观察到一个新的能量损失峰，并对其来源进行了探讨。(2)从零能量损失峰强度出发，得到100keVH^和He^的电子平均自由程分别为1.2和1.4 nm。这些值与相同速度下电子的平均自由程是相当的。(3)观察到能量损失峰的增加，这归因于离子轰击对碳键的修饰。(4)发现100keV H_2^的能量损失峰与50keV H_2^的能量损失峰几乎相等，表明分子效应对能量损失没有影响。100keV H_2对17 nm薄膜的存活概率为6×10~(-3)~(-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>.