Controlling the effective mass of quantum well states in Pb/Si(111) by interface engineering

The in-plane effective mass of quantum well states in thin Pb films on a Bi reconstructed Si(111) surface is studied by angle-resolved photoemission spectroscopy. It is found that this effective mass is a factor of 3 lower than the unusually high values reported for Pb films grown on a Pb reconstructed Si(111) surface. Through a quantitative low-energy electron diffraction analysis the change in effective mass as a function of coverage and for the different interfaces is linked to a change of about 2% in the in-plane lattice constant. To corroborate this correlation, density functional theory calculations are performed on freestanding Pb slabs with different in-plane lattice constants. These calculations show an anomalous dependence of the effective mass on the lattice constant including a change of sign for values close to the lattice constant of Si(111). This unexpected relation is due to a combination of reduced orbital overlap of the 6pz states and altered hybridization between the 6pz and the 6pxy derived quantum well states. Furthermore, it is shown by core-level spectroscopy that the Pb films are structurally and temporally stable at temperatures below 100 K. © 2011 American Physical Society DOI: https://doi.org/10.1103/PhysRevB.83.035409 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-45379 Accepted Version Originally published at: Slomski, B; Meier, F; Osterwalder, J; Dil, J (2011). Controlling the effective mass of quantum well states in Pb/Si(111) by interface engineering. Physical Review. B, Condensed Matter and Materials Physics, 83(3):035409 . DOI: https://doi.org/10.1103/PhysRevB.83.035409 Controlling the effective mass of quantum well states in Pb/Si(111) by interface engineering Bartosz Slomski, Fabian Meier, Jürg Osterwalder, and J. Hugo Dil Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland 2 Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen, Switzerland (Dated: October 27, 2010) The in-plane effective mass of quantum well states in thin Pb films on a Bi reconstructed Si(111) surface is studied by angle-resolved photoemission spectroscopy. It is found that this effective mass is a factor of three lower than the unusually high values reported for Pb films grown on a Pb reconstructed Si(111) surface. Through a quantitative low-energy electron diffraction analysis the change in effective mass as a function of coverage and for the different interfaces is linked to a change of around 2 % in the in-plane lattice constant. To corroborate this correlation, density functional theory calculations were performed on freestanding Pb slabs with different in-plane lattice constants. These calculations show an anomalous dependence of the effective mass on the lattice constant including a change of sign for values close to the lattice constant of Si(111). This unexpected relation is due to a combination of reduced orbital overlap of the 6pz states and altered hybridization between the 6pz and 6pxy derived quantum well states. Furthermore it is shown by core level spectroscopy that the Pb films are structurally and temporally stable at temperatures below 100 K. PACS numbers: 73.20.At, 73.21.Fg, 79.70.Dp