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

我们的目的是研究在特高压条件下，在良好控制的清洁表面上快速离子诱导的二次电子发射机制的细节。到目前为止，人们只很好地了解了薄片的二次电子产率的平均值。我们最近开发了一种新技术来测量它们在正向和反向发射的数量分布。我们利用来自东京大学MALT的22.5MeV离子束，并将光束引导到特高压室中。我们采用10-100mug/cm^2的碳箔作为样品，加热至700度，提前清洁表面。首先，我们观察了两个方向上发射的数量分布及其与箔厚度和入射离子电荷的相关性。结果表明：(1)该分布总是比泊松分布更宽；(2)平均产额反映了次级电子产生区域的停止功率。3)相关性呈正相关，且箔越薄相关性越强。此外，我们还尝试了一种金刚石薄片，据报道，这种薄片即使在空气中也能保持表面清洁，并表现出负电子亲和力。我们期望得到大量的二次电子，然而，与碳箔壳相比，我们只观察到反向发射电子的两倍，而正向发射电子的数量相同。我们认为，表面状况取决于生产工艺，负电子亲和性没有得到明确的证实。

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.