硅表面纳米银团簇的氧助迁移行为

Oxygen-Induced Migration of Ag Nano-clusters on Si(111)-7×7 Surface

采用原位扫描隧道显微镜研究了Si(111) 7× 7表面蒸镀纳米银团簇的迁移行为以及氧气氛的促进作用 .在覆盖度较低的情况下 ,蒸镀的银原子在Si(111) 7× 7表面形成具有规整三角形结构单元的有序银团簇 ,它们主要占据在Si(111) 7× 7表面有位错的半单胞内 .在氧的存在下 ,形成的结构单元在硅表面发生迁移 ,并逐渐团聚成无明显结构特征的大粒子 .原位观察结果表明 ,在连续扫描过程中 ,团聚后的大粒子在氧覆盖的硅表面也会发生迁移 ,最后稳定在硅表面原子氧吸附位周围 .进一步的观察发现 ,硅表面银团簇的存在对随后氧的吸附状态具有明显的影响 .这些结果为解释纳米银团簇在SiO2

The oxygen induced migration of Ag clusters on Si (111) 7×7 surface was observed by in situ STM. All experiments were carried out in UHV system. The Si (111) 7×7 surface was obtained by directly heating to 1?200 ℃ for several times. At the beginning of Ag clusters growth on the Si (111) 7×7 surface, Ag clusters formed the uniform and well ordered arrays on the surface. The monomers, dimers and clusters of Ag were observed. After exposure to oxygen, some Ag clusters vanished and conglomerated into bigger clusters. As known, there are two kinds of adsorbed oxygen species on the Si surface, ad ins and ins ins. The Ag clusters appear to move easily on the surface until being trapped by adsorbed atomic oxygen and pinned around the adsorbed oxygen. It was confirmed that the migration of Ag clusters is caused by oxygen decoration. The statistical results show that the Ag clusters diffuse much easily on partly oxidized Si (111) 7×7 surface than on Si (111) 7×7 surface. It was also found that the strong interaction between Ag cluster and adsorbed oxygen species causes a distinct change of the property of adsorbed oxygen, i e a change of surface ins ins oxygen into ad ins oxygen species, reflecting the role of substrate at room temperature.