Decay mechanisms of excited electrons in quantum-well states of ultrathin Pb islands grown on Si(111): Scanning tunneling spectroscopy and theory

Abstract

Using low-temperature scanning tunneling spectroscopy at 5 and 50 K, we studied the linewidth of unoccupied quantum-well states in ultrathin Pb islands, grown on Si(111) on two different Pb/Si interfaces. A quantitative analysis of the differential conductance spectra allowed us to determine the electron-electron $(e\text{\ensuremath{-}}e)$, electron-phonon $(e\text{-ph})$ and the interface and defect contributions to the lifetime. Layer-dependent ab initio calculations of the $e\text{-ph}$ linewidth contribution are in excellent agreement with the data. Importantly, the sum of the calculated $e\text{\ensuremath{-}}e$ and $e\text{-ph}$ lifetime broadening follows the experimentally observed quadratic energy dependence.