Critical role of a buried interface in the Stranski-Krastanov growth of metallic nanocrystals: quantum size effects in Ag/Si(111)-(7×7).

: We show that the buried interface between a metallic nanocrystal and its supporting substrate is essential for understanding the stability of the ubiquitous class of nanomaterials that grow on a wetting layer in the Stranski-Krastanov growth mode. Importantly, these new results reveal the broad role played by quantum confinement effects in the growth of thin nanoscale metals. In situ x-ray scattering experiments on Ag/Si(111)-(7×7), where the apparent minimum stable thickness of the first two atomic layers on top of the wetting layer has posed a long-standing puzzle, show that the commensurate wetting layer is locally removed by the formation of incommensurate nanoislands, which is unanticipated for the conventional Stranski-Krastanov growth mode. The anomalous lattice expansion that had been previously proposed is not observed, and these new results for Ag are explained by electron confinement effects whose manifestation differs from other metals.