Catalystlike Behavior of Si Adatoms in the Growth of Monolayer Al Film on Si(111)

The formation mechanism of monolayer Al(111)1×1 film on the Si(111)√3×√3-Al substrate was studied by scanning tunneling microscopy and first-principles calculations. We found that the Si adatoms on the √3×√3-Al substrate play important roles in the growth process. The growth of Al-1×1 islands is mediated by the formation and decomposition of SiAl2 clusters. Based on experiments and theoretical simulations we propose a model where free Si atoms exhibit a catalystlike behavior by capturing and releasing Al atoms during the Al film growth.