Quantum growth of a metal/insulator system: Lead on sapphire

We report the observation of quantum growth behavior in a metal-on-insulator system. Using insulating substrates, with their large band gaps, should maximize quantum confinement effects. In a study of Pb film growth and thermal processing on sapphire, we have observed robust preferred island height selection over a wide thickness range—a hallmark of quantum confinement effects—up to 250 °C. By contrast, room temperature is the limit for Pb films prepared on Si(111). These results provide the evidence connecting the quantum growth behavior of overlayers with the substrate band gap.