Interface between Quantum-Size-Effect Pb Nanocrystals and the Si(111)7 × 7 Substrate: an X-Ray Diffraction Study

In-situ X-ray diffraction is used to study the structure of Pb nanocrystalline islands grown on Si(111)7 × 7. The coverage dependence of the (0,8/7) surface reflection demonstrates that when the Pb nanocrystals nucleate, they consume the wetting layer. Concomitantly, the nanocrystals move away from the Si substrate and exhibit two-dimensional mosaicity in the substrate plane, while maintaining nearly perfect orientation in the direction perpendicular to the plane. These results, along with the fact that the nanocrystal interface is very smooth despite the highly corrugated substrate, indicate that the nanocrystals decouple from the Si substrate and provide an excellent interface to support electron standing waves that are needed for quantum-size effects (QSEs).