Study of the number distribution of swift ion induced secondary electrons from a clean thin foil under UHV condition

点击翻译按钮获取中文摘要

We aimed to investigate the detail of swift ion induced secondary electron emission mechanism from a well cotrolled clean surface under UHV condition.So far only the average number of secondary electron yields from a thin foil has been well understood. We recently developed a new technique to measure their number distribution emitted in the forward and backward directions.We utilized 22.5MeV ion beams from MALT,the University of Tokyo, and guided the beam into a UHV chamber. We adopted 10-100mug/cm^2 carbon foils as samples and heated them up to 700 degree to clean the surface in advance. First, we observed the umber distributions emitted in the both directions and their correlation dependent of foil thickness and incident ion charge. As a result, we found that 1)The distribution is alway broader than the Poisson distribution 2) The average yield reflects the stopping power in the region where the secondary electrons are produced. 3) The correlation shows a positive character and the stronger correlation exists for the thinner foil.Furthermroe, we tried a diamond thin foil, which that been reported to keep a clean surface even in a air atomosphere, and to show negative electron affinity. We had expected to get a large yiled of secondary electrons, however, we observed only twice as many as backward emitted electrons compared with a carbon foil case, and the same number for forward emitted ones. We concluded the the surface condition depends on the production techique and the negative electron affinity was not clearly confirmed.