Modifying Quantum Well States of Pb Thin Films via Interface Engineering

We demonstrate the importance of interface modification on improving electron confinement by preparing Pb quantum islands on Si(111) substrates with two different surface reconstructions, i.e., Si(111)-7× 7 and Si(111)-Root3×Root3-Pb (hereafter, 7× 7 and R3). Characterization with scanning tunneling microscopy/spectroscopy shows that growing Pb films directly on a 7×7 surface will generate many interface defects, which makes the lifetime of quantum well states (QWSs) strongly dependent on surface locations. On the other hand, QWSs in Pb films on an R3 surface are well defined with small variations in linewidth on different surface locations and are much sharper than those on the 7×7 surface. We show that the enhancement in quantum confinement is primarily due to the reduced electron-defect scattering at the interface.